WO2024073883A1 - Positive electrode active material and preparation therefor, positive electrode sheet, and secondary battery - Google Patents

Positive electrode active material and preparation therefor, positive electrode sheet, and secondary battery Download PDF

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WO2024073883A1
WO2024073883A1 PCT/CN2022/123777 CN2022123777W WO2024073883A1 WO 2024073883 A1 WO2024073883 A1 WO 2024073883A1 CN 2022123777 W CN2022123777 W CN 2022123777W WO 2024073883 A1 WO2024073883 A1 WO 2024073883A1
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positive electrode
active material
electrode active
lithium
coating layer
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PCT/CN2022/123777
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French (fr)
Chinese (zh)
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朱翠翠
张继君
王少飞
魏奕民
李杨
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宁德时代新能源科技股份有限公司
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Priority to PCT/CN2022/123777 priority Critical patent/WO2024073883A1/en
Publication of WO2024073883A1 publication Critical patent/WO2024073883A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to a positive electrode active material and also relates to a method for preparing the positive electrode active material, a positive electrode sheet prepared therefrom and a secondary battery.
  • lithium ion batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.
  • energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.
  • secondary ion batteries have made great progress, higher requirements are put forward for their positive electrode active materials.
  • Coating positive electrode active materials is currently a commonly used method to improve battery performance and has always been a research topic.
  • the present application is made in view of the above-mentioned problems, and its object is to provide a positive electrode active material with good stability and a secondary battery with low impedance and high capacity retention rate.
  • the first aspect of the present application provides a positive electrode active material, which includes a positive electrode body material and a coating layer coated on the surface of the positive electrode body material, wherein the coating layer is composed of a compound with a molecular formula of Li a MF x Cl (a+nx) , wherein
  • n is the valence state of M ion, n is in the range of 2-4,
  • M is selected from one or more of the elements In, Y, Sc, Er, Tb, Yb, Lu, Zr, Al, Ga, La, Ho, Ti, and Nb,
  • the content proportion of the F element in the compound with the molecular formula Li a MF x Cl (a+nx) gradually decreases, and the content proportion of the Cl element in the compound with the molecular formula Li a MF x Cl (a+nx) gradually increases.
  • the coating layer described in the present application can play the role of "blocking” and “isolating”, and can combine the advantages of the fluoride coating layer and the chloride coating layer while avoiding their disadvantages to a certain extent.
  • the present application is designed to use a compound containing more fluorine to coat the area where there are more transition metal ions inside the coating layer, and to use a compound containing less fluorine to coat the area where there are fewer transition metal ions than outside the coating layer, which can make the fluorine element and the transition metal ions more targeted and more effectively complexed, thereby more effectively preventing the transition metal ions from overflowing.
  • the present application adopts a method in which the fluorine element gradually decreases from the inside to the outside and the chlorine element content gradually increases from the inside to the outside, which is more conducive to the smooth migration and deintercalation of lithium ions, and is conducive to the improvement of lithium ion conductivity.
  • modified positive electrode active material of the present application has the above-mentioned beneficial effects, it is possible to improve the capacity retention rate of the battery and reduce the impedance of the positive electrode active material and the impedance of the battery accordingly.
  • the content ratio of the F element changes from large to small, that is, the gradient of x from a+n ⁇ 0 is (a+n)/(h/b), where h is the coating layer thickness and b is the minimum thickness at which the gradient changes; wherein h is in the range of 0-5nm; b is in the range of 0-0.5nm, optionally in the range of 0.1-0.5nm.
  • the content ratio of the Cl element changes from small to large, that is, the gradient of a+n-x from 0 ⁇ a+n, is (a+n)/(h/b).
  • the change of the content of fluorine and chlorine in the coating layer is carried out uniformly in a gradient manner, so that the change of the content of fluorine and chlorine in the coating layer is more uniform, which is more conducive to the accurate capture of transition metal ions produced by the positive electrode body material and more conducive to the smooth deintercalation of lithium elements.
  • the material of the coating layer is at least one selected from Li 3 InF x Cl (6-x) , Li 3 YF x Cl (6-x) , Li 3 ScF x Cl (6-x) , Li 3 MnF x Cl (6-x) , Li 3 ZrF x Cl (6-x) , wherein 0 ⁇ x ⁇ 6.
  • the electrochemical window of the positive electrode active material is 5.0 V or more, and/or the lithium ion conductivity of the positive electrode active material is 10 -8 -10 -3 S/cm.
  • the cathode bulk material is selected from at least one of ternary active materials, lithium iron phosphate, lithium manganese oxide, and lithium cobalt oxide.
  • a second aspect of the present application provides a method for preparing a positive electrode active material, the method comprising a coating step, the step comprising:
  • n is the valence state of M ion, n is in the range of 2-4,
  • M is selected from one or more of the elements In, Y, Sc, Er, Tb, Yb, Lu, Zr, Al, Ga, La, Ho, Ti, and Nb,
  • the content proportion of the F element in the compound with the molecular formula Li a MF x Cl (a+nx) gradually decreases, and the content proportion of the Cl element in the compound with the molecular formula Li a MF x Cl (a+nx) gradually increases.
  • the method for adsorbing and depositing the vaporized source on the surface of the positive electrode bulk material is an atomic deposition method.
  • the number of depositions is m, and m ranges from 1-100.
  • the source of Li a MF x Cl (a+nx) includes a lithium source, an M source, a fluorine source, and a chlorine source, wherein the boiling point of each source is between 70-300° C.;
  • the lithium source includes one or more of lithium halide, alkyl lithium, lithium carboxylate, lithium alkoxide, and lithium ester;
  • the M source includes one or more of an alkyl metal, a carboxylic acid metal, an alcohol metal, and an ester metal of the M element;
  • the fluorine source includes one or more of fluorinated alkanes, fluorinated carboxylic acids, fluorinated alcohols, and fluorinated esters;
  • the chlorine source comprises one or more of chlorinated alkanes, chlorinated carboxylic acids, chlorinated alcohols, and chlorinated esters.
  • the coating described in the present application can be achieved by atomic layer deposition (ALD), which is a method of chemical vapor deposition of thin films based on ordered surface self-saturation. It can form a deposition layer with a thickness of several atoms on the surface of the positive electrode body material to achieve uniform coating, and can achieve precise control of the gradient of fluorine and chlorine elements and the coating thickness of the coating layer.
  • ALD atomic layer deposition
  • the obtained coated positive electrode body material is calcined, and optionally, the calcination temperature is 150-300° C. and the calcination time is 4-20 h.
  • Calcination after coating can reduce the impedance of the positive electrode active material, improve the stability of the material and improve the rate performance, capacity retention and cycle stability of the corresponding battery cell.
  • the third aspect of the present application provides a secondary battery, which includes the positive electrode active material described in the first aspect of the present application or the positive electrode active material prepared according to the method described in the second aspect of the present application.
  • the secondary battery comprises an electrolyte comprising lithium hexafluorophosphate and/or lithium perchlorate.
  • FIG. 1 is a scanning electron microscope (SEM) image of the positive electrode active material particles prepared in Example 1 after surface coating.
  • FIG. 2 is a partial enlarged view of the SEM image ( FIG. 1 ) of the positive electrode active material particles prepared in Example 1 after surface coating.
  • range disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range.
  • the range defined in this way can be inclusive or exclusive of end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60-120 and 80-110 is listed for a specific parameter, it is understood that the range of 60-110 and 80-120 is also expected.
  • the numerical range "a-b" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers.
  • the numerical range "0-5" represents that all real numbers between "0-5" have been fully listed herein, and "0-5" is just the abbreviation of these numerical combinations.
  • a parameter is expressed as an integer ⁇ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially.
  • the method may further include step (c), which means that step (c) may be added to the method in any order.
  • the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.
  • the “include” and “comprising” mentioned in this application represent open-ended or closed-ended expressions.
  • the “include” and “comprising” may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.
  • the term "or” is inclusive.
  • the phrase “A or B” means “A, B, or both A and B”. More specifically, any of the following conditions satisfies the condition "A or B”: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).
  • the positive electrode active material is susceptible to corrosion by H2O and HF in the electrolyte, and the lattice may also undergo irreversible changes during the process of lithium insertion and extraction, resulting in the dissolution of the generated transition metal ions.
  • the dissolved transition metal ions easily migrate to the surface of the negative electrode and reduce themselves to metals. Such metals easily catalyze and decompose the SEI film, and consume active lithium, resulting in continuous deterioration of electrical performance.
  • transition metal or other metal halides can currently be used to coat the positive electrode bulk active material.
  • the coating layer fluoride when fluoride is used to coat the positive electrode active material, the coating layer fluoride is air-sensitive and easy to absorb water, so it is easy to undergo irreversible hydrolysis and then fail; and when chloride is used to coat the positive electrode active material, the electrochemical window of the coating layer chloride is low and the stability under high pressure is poor.
  • the positive electrode body material particles when using halides for coating, the positive electrode body material particles are usually first mechanically crushed and then coated. However, the particle size of the positive electrode body active material is about 2 ⁇ m, so the thickness of the material obtained after coating will generally exceed 2 ⁇ m. Such a thick coating will significantly increase the electron transfer resistance between the positive and negative electrode materials, increase the ohmic impedance, and cause the positive electrode material to have poor conductivity.
  • the inventors of the present application have proposed a scheme for coating the positive electrode material with a substance containing both fluorine and chlorine after a lot of research.
  • This scheme combines the advantages of the above-mentioned fluorides and chlorides while avoiding their disadvantages, and by gradually reducing or increasing the fluorine and chlorine elements in the coating layer, the lithium ions migrate or deintercalate more smoothly in the coating layer, thereby reducing the impedance of the positive electrode material.
  • the above scheme proposed in the present application can achieve an ultra-thin thickness, thereby further reducing the impedance of the positive electrode material.
  • the first aspect of the present application provides a positive electrode active material, which includes a positive electrode body material and a coating layer coated on the surface of the positive electrode body material, wherein the coating layer is composed of a compound with a molecular formula of Li a MF x Cl (a+nx) , wherein
  • n is the valence state of M ion, n is in the range of 2-4,
  • M is selected from one or more of the elements In, Y, Sc, Er, Tb, Yb, Lu, Zr, Al, Ga, La, Ho, Ti, and Nb,
  • the content proportion of the F element in the compound with the molecular formula Li a MF x Cl (a+nx) gradually decreases, and the content proportion of the Cl element in the compound with the molecular formula Li a MF x Cl (a+nx) gradually increases.
  • the material that plays a major role in the positive electrode is referred to as the "positive electrode bulk material” or "positive electrode bulk active material”.
  • the coating layer described in the present application can play the role of "blocking” and "isolating". Specifically, during the charge and discharge process of lithium-ion batteries, the active material of the positive electrode will inevitably produce transition metal ions; in addition, after several charge and discharge cycles, the electrolyte in the electrolyte will be decomposed, and water and highly corrosive substances (such as hydrofluoric acid) may be produced. At this time, if the positive electrode body material is in direct contact with the corrosive electrolyte, it will be directly corroded, thereby decomposing and producing more transition metal ions.
  • the presence of the coating layer described in the present application can effectively prevent the transition metal ions generated by the active material of the positive electrode body during the charge and discharge process of the battery from directly entering the electrolyte, thereby playing a "blocking" role, and can also prevent the positive electrode body material from being directly in contact with the electrolyte and being corroded by the electrolyte to produce more transition metal ions, thereby playing a "barrier” role, thereby reducing the number of transition metal ions present in the battery system and significantly slowing down the corrosion and decomposition of the positive electrode body material by corrosive substances, thereby improving battery performance.
  • the positive electrode body material is coated with a halide containing both fluorine and chlorine to form a coating layer composed of a substance with a molecular formula of Li a MF x Cl (a+nx) .
  • the amount of fluorine in the coating layer gradually decreases from the inside to the outside of the coating layer (x gradually decreases), while the amount of chlorine in the coating layer gradually increases from the inside to the outside, thereby combining the advantages of the fluoride coating layer and the chloride coating layer while avoiding their disadvantages to a certain extent.
  • fluoride coating layer when a fluoride coating layer is used, during the use of the battery, the fluorine element in the coating layer of the positive active material will migrate to the inside of the positive electrode body material to form a transition layer, thereby reducing the migration energy of Li ions and stabilizing lattice oxygen, thereby improving the lithium ion conductivity and structural stability of the positive electrode active material, and improving the capacity retention rate of the lithium ion battery.
  • fluoride ions can be complexed with transition metal ions, so that they can reduce the number of transition metal ions already produced inside the battery by chemical reaction or adsorption effect, thereby avoiding the overflow of transition metal ions.
  • the electrochemical window of fluoride is high (> 6.0V), and its coating of the positive electrode body material can improve the lithium ion stability of the positive electrode body active material, and can protect the positive electrode body active material from still maintaining good structural stability at a high voltage of 4.6V.
  • fluoride is air-sensitive and is easy to absorb water, thereby failing due to irreversible hydrolysis.
  • the chloride solid electrolyte has an ultra-high lithium ion conductivity (>10 -3 S/cm)
  • lithium ions can quickly pass through the chloride coating during the charge and discharge process, thereby increasing the speed of lithium ion extraction and embedding, and reducing the impedance of the positive electrode active material.
  • chloride has good air stability, and can be reversed by heating and drying again after absorbing water. It can protect the internal fluoride from contacting with the outside air and failing. Therefore, in the coating layer, in the place closer to the positive electrode body material, using a coating material containing less chlorine and more fluorine can well play the above-mentioned role of fluoride, improve the stability of the positive electrode active material and improve the capacity retention rate of the battery; in the place farther from the positive electrode body material and closer to the outside of the coating layer, using a coating material containing more chlorine and less fluorine, the air stability of chloride can be used to protect the internal fluoride from contacting with the outside air and failing, thereby stabilizing the coating material of the internal fluorine-containing part, achieving the stability of the coating layer, and the ultra-high conductivity of chloride also achieves the reduction of the impedance of the positive electrode active material.
  • the transition metal ions generated by the active material of the positive electrode body overflow, they will first enter the coating layer. Therefore, the number of transition metal ions is relatively large at the innermost part of the coating layer on the surface of the positive electrode body material, and the transition metal ions gradually decrease along the coating layer to the outside.
  • the present application is designed to use a compound containing more fluorine to coat the place where there are more transition metal ions inside the coating layer, and to use a compound containing less fluorine to coat the place where there are fewer transition metal ions outside the coating layer, that is, the fluorine content is the highest in the innermost part of the coating layer, and the fluorine content gradually decreases along the coating layer to the outside, thereby enabling the fluorine element and the transition metal ions to be more targeted and more effectively complexed, thereby more effectively preventing the transition metal ions from overflowing.
  • the present application adopts a method in which the fluorine element gradually decreases from the inside to the outside and the chlorine element content gradually increases from the inside to the outside, which is more conducive to the smooth migration and deintercalation of lithium ions and is conducive to the improvement of lithium ion conductivity.
  • the coating layer closest to the positive electrode main material contains only fluorine but no chlorine, and the coating layer closest to the outside contains only chlorine but no fluorine.
  • the modified positive electrode active material of the present application has the above-mentioned beneficial effects, it can slow down the generation of transition metals and their catalytic decomposition of the negative electrode SEI film (if any) during battery storage or use, thereby improving the battery capacity retention rate and reducing the battery impedance.
  • the changes in the fluorine and chlorine elements in the coating layer can be carried out by any means, as long as the trend of the fluorine content gradually decreasing from the inside to the outside and the chlorine content gradually increasing from the inside to the outside is satisfied.
  • the large particles are the cathode material NCM811, with a coating layer on the outside. From a wide field of view, the cathode particles are completely coated. By zooming in on the coating layer ( Figure 2), it can be found that the coating layer is uniform and dense, with no leaking areas. This proves that in the cathode active material of the present application, the coating layer is uniform, dense and relatively complete.
  • the content ratio of the F element changes from large to small, that is, the gradient of x from a+n ⁇ 0 is (a+n)/(h/b), where h is the coating thickness and b is the minimum thickness at which the gradient changes; wherein h is in the range of 0-5nm, optionally in the range of 0.5-5nm; b is in the range of 0-0.5nm, optionally in the range of 0.1-0.5nm.
  • the content ratio of the Cl element changes from small to large, that is, the gradient of a+n-x from 0 ⁇ a+n, is (a+n)/(h/b).
  • the change of the content of fluorine and chlorine in the coating layer is carried out uniformly in a gradient manner, so that the change of the content of fluorine and chlorine in the coating layer is more uniform, which is more conducive to the accurate capture of transition metal ions produced by the positive electrode body material and more conducive to the smooth deintercalation of lithium elements.
  • the content proportion of the F element changes gradient from large to small, that is, the change gradient of x from a+n ⁇ 0, is in the range of (a+n)/(h/0.1) to (a+n)/(h/0.5), h is the thickness of the coating layer, h is in the range of 0-5nm, optionally in the range of 0.5-5nm.
  • the F element content gradient is changed every 0.1nm-0.5nm thickness, and each gradient change amount is (a+n)/(h/0.1) to (a+n)/(h/0.5).
  • the gradient of the content proportion of the Cl element changes from small to large, that is, the gradient of a+n-x changes from 0 ⁇ a+n, is also in the range of (a+n)/(h/0.1) to (a+n)/(h/0.5).
  • the gradual change of the gradient of the fluorine element and the chlorine element reduces the grain boundary resistance inside the coating layer, thereby reducing the impedance of the positive electrode active material and the impedance of the battery accordingly, and further improving the cycle stability of the battery.
  • the coating layer has a thickness in the range of 0.5-5 nm.
  • the thickness of the coating layer will greatly affect the overall performance of the battery, such as impedance, cycle stability, and rate performance.
  • the coating thickness of the commonly used solid phase coating method is at the micron level, which causes the lithium ion conductivity and electronic conductivity to decrease significantly, resulting in a higher impedance of the positive electrode active material.
  • the coating layer described in the present application is an ultra-thin coating layer, between 0.5-5nm. The coating layer within this range can well cover the surface of the positive electrode bulk material and simultaneously ensure the theoretical energy density and impedance of the material.
  • the coating layer thickness is less than 0.5nm, the coating thickness is too thin, and the coating layer cannot completely cover the sample surface, which easily causes leakage, resulting in poor consistency of material performance.
  • the coating layer thickness is higher than 5nm, the coating layer is too thick, which will reduce the theoretical energy density of the material and increase the impedance of the material and the impedance of the battery accordingly.
  • the material of the coating layer is selected from at least one of Li 3 InF x Cl (6-x) , Li 3 YF x Cl (6-x) , Li 3 ScF x Cl (6-x) , Li 3 MnF x Cl (6-x) , and Li 3 ZrF x Cl (6-x) , wherein 0 ⁇ x ⁇ 6.
  • the electrochemical window of the positive electrode active material is above 5.0 V, and/or the lithium ion conductivity of the positive electrode active material is 10 -8 -10 -3 S/cm.
  • the electrochemical window test can be performed using the linear voltammetric test module of the electrochemical workstation. Specifically, the following method can be used: the positive electrode active material to be tested is mixed with the binder PVDF in a mass ratio of 95:5, dissolved in a solvent (such as N-methylpyrrolidone (NMP)), with no limit on concentration, and dripped on the surface of the glassy carbon electrode as a working electrode; then, a battery system (also called an electrolytic cell) is assembled with 1M LiPF6 as a solution and a lithium sheet as a counter electrode, and the battery system is tested for voltammetric curves, with a voltage range of 2.5 to 5V and a scan rate of 0.5mV/s, and the oxidation potential is recorded as the electrochemical window.
  • a solvent such as N-methylpyrrolidone (NMP)
  • the solid electrolyte is an ionic conductor and is not conductive to electrons.
  • the cathode bulk material is selected from at least one of ternary active materials, lithium iron phosphate, lithium manganese oxide, and lithium cobalt oxide.
  • the ternary active materials are those ternary materials used in the art, including, but not limited to, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, and the like.
  • a second aspect of the present application provides a method for preparing a positive electrode active material, the method comprising a coating step, the step comprising:
  • n is the valence state of M ion, n is in the range of 2-4,
  • M is selected from one or more of the elements In, Y, Sc, Er, Tb, Yb, Lu, Zr, Al, Ga, La, Ho, Ti, and Nb,
  • the content proportion of the F element in the compound with the molecular formula Li a MF x Cl (a+nx) gradually decreases, and the content proportion of the Cl element in the compound with the molecular formula Li a MF x Cl (a+nx) gradually increases.
  • the positive electrode body material can be prepared before preparing the coating layer, or can be purchased.
  • the method of adsorbing and depositing the gasified source on the surface of the positive electrode bulk material is an atomic deposition method.
  • the deposition number is m, and m ranges from 1-100.
  • step (2) deposition is performed using an atomic deposition method, each completed deposition is called a cycle, a total of m cycles are performed, m ranges from h/0.1 to h/0.5, h is defined as described above, and the deposition thickness of each cycle is 0.1-0.5 nm; wherein for the kth cycle, 1 ⁇ k ⁇ m, deposition is performed using a source of Li a MF x Cl (a+nx) , wherein x is (mk) ⁇ (a+n)/m, and a and n are defined as described above.
  • the source of Li a MF x Cl (a+nx) includes a lithium source, an M source, a fluorine source, and a chlorine source, wherein the boiling point of each source is between 70-300° C.;
  • the lithium source includes, but is not limited to, one or more of lithium halides, alkyl lithiums, lithium carboxylates, lithium alkoxides, and lithium esters, for example, lithium tert-butoxide,
  • the source of M includes, but is not limited to, one or more of alkyl metals, carboxylic acid metals, alcohol metals, and ester metals of the M element, with a boiling point between 70 and 300°C.
  • the fluorine source includes, but is not limited to, one or more of fluorinated alkanes, fluorinated carboxylic acids, fluorinated alcohols and fluorinated esters.
  • the fluorinated esters include fluorinated ethylene carbonate.
  • the chlorine source includes, but is not limited to, one or more of chlorinated alkanes, chlorinated carboxylic acids, chlorinated alcohols and chlorinated esters.
  • the chlorinated esters include chlorinated ethylene carbonate.
  • the source of Li a MF x Cl (a+nx) may also be referred to as a “precursor”.
  • the coating can be achieved by atomic layer deposition (ALD), which is a method of chemical vapor deposition thin film based on ordered surface self-saturation, and can form a deposition layer of several atoms thick on the surface of the positive electrode body material to achieve uniform coating.
  • ALD atomic layer deposition
  • the main steps of the method include: alternately passing the gas phase precursor pulse into the reactor, and then chemically adsorbing and reacting it on the deposition substrate to form a deposited film. When the precursor reaches the surface of the deposition substrate, they will chemically adsorb on its surface and react on the surface.
  • the atomic layer deposition reactor needs to be cleaned with an inert gas between the two pulses of the precursor.
  • the pulse time of the deposition gas phase precursor such as a chlorine source and a fluorine source
  • a suitable parameter program as needed to accurately adjust the deposition ratio of the two halide sources in the coating to form a gradient coating.
  • the deposition thickness of each layer is about 0.1nm, up to 0.5nm.
  • the coating thickness can be accurately controlled by adjusting the number of cycles of deposition.
  • the coating thickness and coating uniformity directly affect the performance of the positive electrode active material.
  • the coating thickness can be accurately controlled by atomic layer deposition. For example, an ultra-thin coating thickness of about 0.5 nm can be achieved.
  • the deposited material i.e., the above-mentioned sources
  • the pulse alternation program of the deposited gas phase precursor can be set in advance, thereby flexibly adjusting the amount of deposited material to form the desired halogen concentration gradient distribution. This method is simple and easy to optimize.
  • the obtained coated positive electrode body material is calcined.
  • the calcination temperature is 150-300° C. and the calcination time is 4-20 h.
  • the calcination may be performed under an inert atmosphere, such as argon or nitrogen.
  • the F element is helped to migrate into the interior of the cathode bulk material, forming a spinel-like transition layer as a connecting link, reducing the interfacial resistance at the interface between the coating layer and the cathode bulk material, reducing the migration energy of Li ions and stabilizing the lattice oxygen;
  • Calcination can improve the crystallinity of the coating material and form a cubic dense packing structure (CCP), which helps to form a 3D lithium ion transmission channel, thereby reducing the material impedance and battery impedance and improving the rate performance and cycle stability of the resulting battery cell;
  • CCP cubic dense packing structure
  • Calcination also helps to achieve better atomic fusion at the interface between the positive electrode and the inner fluoride layer and at the interface between the inner and outer coatings, forming a transition layer, reducing the grain boundary resistance caused by the coating interface, thereby reducing the impedance of the material and the impedance of the battery;
  • One aspect of the present application also provides a positive electrode plate, which includes a positive electrode collector and a positive electrode film layer arranged on at least one surface of the positive electrode collector, wherein the positive electrode film layer includes the positive electrode active material described in the first aspect of the present application or the positive electrode active material prepared by the method described in the second aspect of the present application.
  • the third aspect of the present application provides a secondary battery, which includes the positive electrode active material described in the first aspect of the present application or the positive electrode active material prepared by the method described in the second aspect of the present application.
  • the secondary battery can be in the form of a battery cell, a battery module, or a battery pack.
  • a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator.
  • active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet.
  • the electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet.
  • the separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared by the method described in the second aspect of the present application.
  • the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • the metal foil aluminum foil may be used.
  • the composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base.
  • the composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the positive electrode bulk material used for coating may be a positive electrode active material for a battery known in the art.
  • the positive electrode bulk material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds.
  • the present application is not limited to these materials, and other traditional materials that can be used as a positive electrode bulk material for a battery may also be used.
  • These positive electrode bulk materials may be used alone or in combination of two or more.
  • lithium transition metal oxides may include, but are not limited to , lithium cobalt oxide (such as LiCoO2 ), lithium nickel oxide (such as LiNiO2 ), lithium manganese oxide (such as LiMnO2 , LiMn2O4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi1 / 3Co1 / 3Mn1 / 3O2 (also referred to as NCM333 ), LiNi0.5Co0.2Mn0.3O2 (also referred to as NCM523 ) , LiNi0.5Co0.25Mn0.25O2 (also referred to as NCM211 ) , LiNi0.6Co0.2Mn0.2O2 (also referred to as NCM622 ), LiNi0.8Co0.1Mn0.1O2 (also referred to as NCM811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05
  • lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO 4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.
  • the cathode body material is selected from at least one of a ternary cathode active material system, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, and the like.
  • positive electrode active material of the first aspect of the present application in addition to the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared by the method described in the second aspect of the present application, other positive electrode active materials known in the art may also be used.
  • the positive electrode film layer may also optionally include a binder.
  • the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PTFE polytetrafluoroethylene
  • vinylidene fluoride-tetrafluoroethylene-propylene terpolymer vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer
  • the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • a conductive agent which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the mass ratio of the positive electrode active material described in the present application is in the range of 70 to 98 mass%, and can be optionally 90 mass%; the mass ratio of the binder is in the range of 1 to 15 mass%, and the mass ratio of the conductive agent is in the range of 1 to 15 mass%, all based on the total mass of the positive electrode film.
  • the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.
  • a solvent such as N-methylpyrrolidone
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.
  • the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • the metal foil copper foil may be used.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate.
  • the composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative electrode active material may adopt the negative electrode active material for the battery known in the art.
  • the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc.
  • the silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.
  • the tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys.
  • the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.
  • the negative electrode film layer may further include a binder.
  • the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • a conductive agent which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).
  • a thickener eg, sodium carboxymethyl cellulose (CMC-Na)
  • the mass ratio of the negative electrode material ranges from 70 to 98 mass%, and can be optionally 95 mass%; the mass ratio of the binder ranges from 1 to 15 mass%, and the mass ratio of the conductive agent ranges from 1 to 15 mass%, all based on the total mass of the positive electrode film.
  • the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.
  • a solvent such as deionized water
  • the electrolyte plays the role of conducting ions between the positive electrode and the negative electrode.
  • the present application has no specific restrictions on the type of electrolyte, which can be selected according to needs.
  • the electrolyte can be liquid, gel or all-solid.
  • the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.
  • the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.
  • the secondary battery includes an electrolyte
  • the electrolyte includes lithium hexafluorophosphate and/or lithium perchlorate.
  • the concentration of lithium hexafluorophosphate and/or lithium perchlorate in the electrolyte ranges from 0.5 to 3 mol/L.
  • the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.
  • the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.
  • additives such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.
  • the secondary battery further includes a separator.
  • the present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.
  • the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation.
  • the materials of each layer can be the same or different, without particular limitation.
  • the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.
  • the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.
  • the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package.
  • the material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.
  • FIG3 is a secondary battery 5 of a square structure as an example.
  • the outer package may include a shell 51 and a cover plate 53.
  • the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity.
  • the shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity.
  • the positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is encapsulated in the receiving cavity.
  • the electrolyte is infiltrated in the electrode assembly 52.
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • Secondary batteries include battery cells, battery modules, and battery packs.
  • battery cells can be assembled into a battery module, and the number of battery cells contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.
  • FIG5 is a battery module 4 as an example.
  • a plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.
  • the battery modules described above may also be assembled into a battery pack.
  • the battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.
  • FIG6 and FIG7 are battery packs 1 as an example.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be covered on the lower box body 3 to form a closed space for accommodating the battery modules 4.
  • the plurality of battery modules 4 can be arranged in the battery box in any manner.
  • the present application also provides an electric device, the electric device includes the secondary battery provided in the present application.
  • the secondary battery can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device.
  • the electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.
  • a secondary battery can be selected according to its usage requirements.
  • FIG8 is an example of an electric device.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.
  • a battery pack or a battery module may be used.
  • a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.
  • the coating material is Li 3 InF x Cl (6-x) .
  • Lithium source lithium tert-butoxide
  • fluorine source fluoroethylene carbonate
  • chlorine source chloroethylene carbonate
  • metal In source triethylindium
  • NCM 811 positive electrode bulk material Place the powder of NCM 811 positive electrode bulk material into a fluidized bed reactor, evacuate the reaction chamber and introduce Ar gas for purge, and control the gas flow rate so that the positive electrode bulk material can be dispersed.
  • lithium tert-butoxide Before each source is introduced into the fluidized bed reactor, lithium tert-butoxide is heated to 165°C, and fluoroethylene carbonate and chloroethylene carbonate are maintained at 200°C.
  • the duration of the injection pulse of lithium tert-butoxide and the purge between two injection pulses are set to 1s and 15s, respectively.
  • the duration of the injection pulse of chloroethylene carbonate and fluoroethylene carbonate and the purge between two injection pulses are set to 0.1s and 15s, respectively.
  • the deposition temperature is 200°C.
  • the injection pulse time of the fluorine source and the chlorine source is changed according to the ratio of the volume flow rate of the fluorine source: the chlorine source to x:(6-x) and Ar gas is used to purge for 15s between the two pulses.
  • Each completed pulse injection is called a cycle, and 20 cycles of co-deposition are performed, in which x changes evenly from 6 to 0, and the ratio decreases to 6/20 in each cycle, that is:
  • x is 6, and the pulse time of each source is set according to the ratio of Li 3 InF 6 .
  • x is 5.7
  • the pulse time of each source is set according to the ratio of Li 3 InF 5.7 Cl 0.3 , and so on.
  • x is 0, and the pulse time of each source is set according to the ratio of Li 3 InCl 6 .
  • Each circle deposits 0.1nm to complete the coating. Afterwards, continue to purge with Ar gas to clean the pipeline to obtain the coated positive electrode active material.
  • the positive electrode active material coated in step 1 is transferred to a tubular furnace and calcined with argon as the protective gas at a calcination temperature of 260° C. for 4 h to ensure that the outer coating has better crystallinity.
  • a positive electrode active material with a coating layer thickness of 2 nm was prepared.
  • Figure 1 is a surface image of the positive electrode active material obtained in Example 1, and Figure 2 is a partial enlarged image of the positive electrode active material in Figure 1.
  • the large particles are the positive electrode main material NCM811, which has a coating layer on the outside.
  • the positive electrode particles are completely coated in a wide field of view.
  • Figure 2 it can be found that the coating layer is uniform and dense, and there is no leaking area.
  • the positive electrode active material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) prepared in the previous step are stirred and mixed evenly with N-methylpyrrolidone (NMP) in a weight ratio of 90.0:5.0:5.0 to obtain a positive electrode slurry; then the positive electrode slurry is evenly coated on the positive electrode collector, and then dried, cold pressed, and cut to obtain a positive electrode sheet.
  • NMP N-methylpyrrolidone
  • the active material artificial graphite, the conductive agent carbon black, and the binder polyvinylidene fluoride (PVDF) are dissolved in the solvent deionized water in a weight ratio of 96.0:2.0:2.0, and the mixture is evenly mixed to prepare a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode collector copper foil once or multiple times, and the negative electrode sheet is obtained after drying, cold pressing, and slitting.
  • PVDF polyvinylidene fluoride
  • the preparation of the battery is the same as that of Example 1, except for the coating thickness, the gradient of the F and Cl elements, and the corresponding number of cycles, as detailed in the table below.
  • the preparation of the battery is the same as that of Example 1, except for the change gradient of F and Cl elements, the thickness of each deposition and the corresponding number of cycles, as detailed in the table below.
  • the preparation of the battery is the same as that of Example 1, except that the coating material is Li 3 YF x Cl (6-x) , wherein the source of metal Y is yttrium tris(2,2,6,6-tetramethyl-3,5-heptanedione), see the table below for details.
  • the preparation of the battery is the same as that of Example 1, except that the coating material is Li 3 ScF x Cl (6-x) , wherein the source of the metal Sc is scandium acetate, as shown in the table below.
  • the preparation of the battery is the same as that of Example 1, except that the coating material is Li 3 MnF x Cl (6-x) , wherein the source of the metal Mn is bis(cyclopentanediyl)manganese, as shown in the table below.
  • the preparation of the battery is the same as that of Example 1, except that the coating material is Li 3 ZrF x Cl (6-x) , wherein the source of the metal Zr is zirconium acetate, as shown in the table below.
  • the preparation of the battery is the same as that of Example 1, except that the ratio of F and Cl is changed and the gradient of the change. For details, see the table below.
  • the preparation of the battery is the same as in Example 1, except that in the calcination step, the calcination temperature and time are different. See the table below for details.
  • the preparation of the battery is the same as that of Example 1, except that the positive electrode bulk material NCM 811 is not coated and is directly used for the preparation of the positive electrode sheet. For details, see the table below.
  • the preparation of the battery is the same as that of Example 1, except that the coating material is Li 3 InF 6 , does not contain chlorine, and has no gradient change in the F element. See the table below for details.
  • the preparation of the battery is the same as that of Example 1, except that the coating material is Li 3 InCl 6 , does not contain fluorine, and the Cl element has no gradient change.
  • the coating material is Li 3 InCl 6 , does not contain fluorine, and the Cl element has no gradient change.
  • the preparation of the battery is the same as that of Example 1, except that the coating layer is two layers, the inner coating layer is 1 nm thick and the coating material is Li 3 InF 6 , the outer coating layer is 1 nm thick and the coating material is Li 3 InF 6 , and there is no gradient change in F and Cl elements. See the table below for details.
  • the preparation of the battery is the same as that of Example 1, except that the content of the F element and the Cl element changes in the same gradient as that in Example 1 but in the opposite direction, that is, the F element gradually increases but the Cl element gradually decreases. For details, see the table below.
  • the preparation of the battery was the same as in Example 1, except that the calcination step was not performed. See the table below for details.
  • the morphology parameter testing process of the positive electrode active materials of the present application examples and comparative examples is as follows:
  • the shape of the cathode material matrix used in the present application is not necessarily spherical, but may be irregular, and may be primary particles or secondary particles. It should also be noted that the shape of the coated cathode active material prepared in the present application is not necessarily spherical, but may be irregular.
  • the test process of the comparative example and other embodiments is the same as above.
  • Example 1 the fresh positive electrode sheet, polypropylene separator and 120 ⁇ L electrolyte obtained by coating Example 1 were assembled into a symmetrical battery with a positive electrode, and placed in a 25°C constant temperature box for 2 hours to ensure the infiltration of the electrolyte.
  • the AC impedance test was performed using the electrochemical workstation impedance test module, voltage perturbation mode PEIS, perturbation voltage 5mV, frequency range: 200kHZ ⁇ 30mHZ, voltage range: 0-5V, voltage protection: 0-5V.
  • the impedance test data was fitted, and the process was as follows:
  • Example 1 the data of Example 1 are fitted using Z-fit software, and the fitting circuit is selected as Rs + C1 / RSEI + C2 / Rct + W, where Rs is ohmic impedance, which is mainly related to the conductivity of the positive electrode material; Rct is charge transfer impedance, which mainly reflects the deintercalation rate of lithium ions in the positive electrode material; C1 is the double-layer capacitance of the SEI and electrolyte interface; RSEI is the SEI membrane resistance; C2 is the double-layer capacitance of the SEI and graphite interface; W is the Weber impedance.
  • Rs ohmic impedance, which is mainly related to the conductivity of the positive electrode material
  • Rct charge transfer impedance, which mainly reflects the deintercalation rate of lithium ions in the positive electrode material
  • C1 is the double-layer capacitance of the SEI and electrolyte interface
  • RSEI is the SEI membrane resistance
  • C2 is the
  • the judgment basis for fitting requires: the error is less than 5%, and the intersection with the real part should have a deviation of ⁇ 5% from the Rs obtained by fitting. Only the fitting results that meet the above requirements can be selected to be accepted, and Rct and Rs in the fitting results are extracted and recorded in the following table.
  • the process of processing data for the comparative example and other embodiments is the same as above.

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Abstract

The present application provides a positive electrode active material comprising a positive electrode body material and a coating layer coating the surface of the positive electrode body material. The coating layer is composed of a compound having a molecular formula LiaMFxCl(a+n-x), wherein M, a, n and x are defined in the description. In a direction extending from the surface of the positive electrode body material towards the outermost side of the coating layer, the content proportion of the element F in the compound is gradually reduced and the content proportion of the element Cl in the compound is gradually increased. The present application further provides a method for preparing the positive electrode active material, and a positive electrode sheet and lithium secondary battery comprising same. Using the positive electrode active material provided by the present application can reduce the resistance of batteries and improve the capacity retention rate of batteries.

Description

正极活性材料及其制备、正极极片及二次电池Positive electrode active material and preparation thereof, positive electrode sheet and secondary battery 技术领域Technical Field
本申请涉及一种正极活性材料。此外，本申请还涉及所述正极活性材料的制备方法、由其制备的正极极片和二次电池。The present application relates to a positive electrode active material and also relates to a method for preparing the positive electrode active material, a positive electrode sheet prepared therefrom and a secondary battery.
背景技术Background technique
近年来，随着二次离子电池的应用范围越来越广泛，锂离子电池广泛应用于水力、火力、风力和太阳能电站等储能电源***，以及电动工具、电动自行车、电动摩托车、电动汽车、军事装备、航空航天等多个领域。由于二次离子电池取得了极大的发展，因此对其正极活性材料提出了更高的要求。In recent years, as the application scope of secondary ion batteries becomes wider and wider, lithium ion batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. As secondary ion batteries have made great progress, higher requirements are put forward for their positive electrode active materials.
对正极活性材料进行包覆是目前常用改进电池性能的手段，也是一直以来的研究课题。Coating positive electrode active materials is currently a commonly used method to improve battery performance and has always been a research topic.
发明内容Summary of the invention
本申请是鉴于上述课题而进行的，其目的在于，提供一种稳定性好的正极活性材料以及一种阻抗低且容量保持率高的二次电池。The present application is made in view of the above-mentioned problems, and its object is to provide a positive electrode active material with good stability and a secondary battery with low impedance and high capacity retention rate.
为了实现上述目的，本申请的第一方面提供了一种正极活性材料，其包括正极本体材料和包覆在所述正极本体材料表面的包覆层，所述包覆层由分子式为Li aMF xCl (a+n-x)的化合物组成，其中 In order to achieve the above object, the first aspect of the present application provides a positive electrode active material, which includes a positive electrode body material and a coating layer coated on the surface of the positive electrode body material, wherein the coating layer is composed of a compound with a molecular formula of Li a MF x Cl (a+nx) , wherein
1≤a≤3，0≤x≤a+n；n为M离子的价态，n在2-4范围内，1≤a≤3, 0≤x≤a+n; n is the valence state of M ion, n is in the range of 2-4,
M选自元素In、Y、Sc、Er、Tb、Yb、Lu、Zr、Al、Ga、La、Ho、Ti、Nb中的一种或多种，M is selected from one or more of the elements In, Y, Sc, Er, Tb, Yb, Lu, Zr, Al, Ga, La, Ho, Ti, and Nb,
其中，以所述正极本体材料表面为起点，随着向外延伸至包覆层的最外侧的方向上，F元素在分子式为Li aMF xCl (a+n-x)的化合物中的含 量占比逐渐变小，Cl元素在分子式为Li aMF xCl (a+n-x)的化合物中的含量占比逐渐变大。 Wherein, starting from the surface of the positive electrode body material, as extending outward to the outermost direction of the coating layer, the content proportion of the F element in the compound with the molecular formula Li a MF x Cl (a+nx) gradually decreases, and the content proportion of the Cl element in the compound with the molecular formula Li a MF x Cl (a+nx) gradually increases.
本申请所述包覆层可起到“阻挡”、“阻隔”的作用，并且能够结合氟化物包覆层和氯化物包覆层的优势同时在一定程度上避开了它们的劣势。此外，本申请设计在包覆层内部过渡金属离子较多的地方使用含氟较多的化合物进行包覆，在包覆层较外部过渡金属离子较少的地方使用含氟较少的化合物进行包覆，能够使氟元素和过渡金属离子更有针对性且更效地络合，从而更有效地阻止过渡金属离子外溢。另外，本申请采用氟元素由内向外逐渐减少，氯元素含量由内向外逐渐增加的方式，更有利于锂离子的顺利迁移和脱嵌，有利于锂离子电导率的提高。The coating layer described in the present application can play the role of "blocking" and "isolating", and can combine the advantages of the fluoride coating layer and the chloride coating layer while avoiding their disadvantages to a certain extent. In addition, the present application is designed to use a compound containing more fluorine to coat the area where there are more transition metal ions inside the coating layer, and to use a compound containing less fluorine to coat the area where there are fewer transition metal ions than outside the coating layer, which can make the fluorine element and the transition metal ions more targeted and more effectively complexed, thereby more effectively preventing the transition metal ions from overflowing. In addition, the present application adopts a method in which the fluorine element gradually decreases from the inside to the outside and the chlorine element content gradually increases from the inside to the outside, which is more conducive to the smooth migration and deintercalation of lithium ions, and is conducive to the improvement of lithium ion conductivity.
由于本申请改性的正极活性材料具有上述有益效果，因而能够改善电池的容量保持率并降低正极活性材料的阻抗以及相应地电池的阻抗。Since the modified positive electrode active material of the present application has the above-mentioned beneficial effects, it is possible to improve the capacity retention rate of the battery and reduce the impedance of the positive electrode active material and the impedance of the battery accordingly.
在任意实施方式中，随着向外延伸至包覆层的最外侧的方向上，F元素的含量占比由大到小的变化梯度，即x从a+n→0的变化梯度，为(a+n)/(h/b)，其中h为包覆层厚度，b为发生梯度改变的最小厚度；其中，h在0-5nm范围内；b在0-0.5nm范围内，可选地在0.1-0.5nm范围内。相应地，随着向外延伸至包覆层的最外侧的方向上，Cl元素的含量占比由小到大的变化梯度，即a+n-x从0→a+n的变化梯度，为(a+n)/(h/b)。In any embodiment, as the outermost direction of the coating layer is extended outward, the content ratio of the F element changes from large to small, that is, the gradient of x from a+n→0 is (a+n)/(h/b), where h is the coating layer thickness and b is the minimum thickness at which the gradient changes; wherein h is in the range of 0-5nm; b is in the range of 0-0.5nm, optionally in the range of 0.1-0.5nm. Accordingly, as the outermost direction of the coating layer is extended outward, the content ratio of the Cl element changes from small to large, that is, the gradient of a+n-x from 0→a+n, is (a+n)/(h/b).
包覆层中氟元素和氯元素含量变化通过梯度方式均匀地进行，由此包覆层中氟元素和氯元素含量变化更为均匀，更有利于精准地捕获正极本体材料产生的过渡金属离子并且更有利于锂元素的脱嵌的顺利进行。The change of the content of fluorine and chlorine in the coating layer is carried out uniformly in a gradient manner, so that the change of the content of fluorine and chlorine in the coating layer is more uniform, which is more conducive to the accurate capture of transition metal ions produced by the positive electrode body material and more conducive to the smooth deintercalation of lithium elements.
在任意实施方式中，所述包覆层的材料选自Li 3InF xCl (6-x)、Li 3YF xCl (6-x)、Li 3ScF xCl (6-x)、Li 3MnF xCl (6-x)、Li 3ZrF xCl (6-x)中的至少一种，其中0≤x≤6。 In any embodiment, the material of the coating layer is at least one selected from Li 3 InF x Cl (6-x) , Li 3 YF x Cl (6-x) , Li 3 ScF x Cl (6-x) , Li 3 MnF x Cl (6-x) , Li 3 ZrF x Cl (6-x) , wherein 0≤x≤6.
在任意实施方式中，所述正极活性材料的电化学窗口为5.0V以上，和/或，所述正极活性材料的锂离子电导率为10 -8-10 -3S/cm。 In any embodiment, the electrochemical window of the positive electrode active material is 5.0 V or more, and/or the lithium ion conductivity of the positive electrode active material is 10 -8 -10 -3 S/cm.
在任意实施方式中，所述正极本体材料选自三元活性材料、磷酸铁锂、锰酸锂、钴酸锂中的至少一种。In any embodiment, the cathode bulk material is selected from at least one of ternary active materials, lithium iron phosphate, lithium manganese oxide, and lithium cobalt oxide.
本申请的第二方面提供一种正极活性材料的制备方法，所述方法包括包覆步骤，该步骤包括：A second aspect of the present application provides a method for preparing a positive electrode active material, the method comprising a coating step, the step comprising:
(1)制备或准备正极本体材料；(1) preparing or preparing positive electrode bulk material;
(2)在惰性气氛下将Li aMF xCl (a+n-x)的源进行气化，可选地，所述气化温度为200-300℃；使气化的所述源在正极本体材料表面吸附沉积，以包覆所述正极本体材料，得到所述正极活性材料； (2) vaporizing a source of Li a MF x Cl (a+nx) under an inert atmosphere, optionally at a vaporization temperature of 200-300° C.; allowing the vaporized source to be adsorbed and deposited on the surface of the positive electrode bulk material to coat the positive electrode bulk material, thereby obtaining the positive electrode active material;
其中，分子式Li aMF xCl (a+n-x)中， Among them, in the molecular formula Li a MF x Cl (a+nx) ,
1≤a≤3，0≤x≤a+n；n为M离子的价态，n在2-4范围内，1≤a≤3, 0≤x≤a+n; n is the valence state of M ion, n is in the range of 2-4,
M选自元素In、Y、Sc、Er、Tb、Yb、Lu、Zr、Al、Ga、La、Ho、Ti、Nb中的一种或多种，M is selected from one or more of the elements In, Y, Sc, Er, Tb, Yb, Lu, Zr, Al, Ga, La, Ho, Ti, and Nb,
其中，以所述正极本体材料表面为起点，随着向外延伸至包覆层的最外侧的方向上，F元素在分子式为Li aMF xCl (a+n-x)的化合物中的含量占比逐渐变小，Cl元素在分子式为Li aMF xCl (a+n-x)的化合物中的含量占比逐渐变大。 Wherein, starting from the surface of the positive electrode body material, as extending outward to the outermost direction of the coating layer, the content proportion of the F element in the compound with the molecular formula Li a MF x Cl (a+nx) gradually decreases, and the content proportion of the Cl element in the compound with the molecular formula Li a MF x Cl (a+nx) gradually increases.
在任意实施方式中所述使气化的所述源在正极本体材料表面吸附沉积的方法为原子沉积法，可选地，所述沉积次数为m，m范围为1-100。In any embodiment, the method for adsorbing and depositing the vaporized source on the surface of the positive electrode bulk material is an atomic deposition method. Optionally, the number of depositions is m, and m ranges from 1-100.
在任意实施方式中，所述Li aMF xCl (a+n-x)的源包括锂源、M源、氟源、氯源，其中，所述各源的沸点介于70-300℃之间； In any embodiment, the source of Li a MF x Cl (a+nx) includes a lithium source, an M source, a fluorine source, and a chlorine source, wherein the boiling point of each source is between 70-300° C.;
可选地，锂源包括卤化锂，烷基锂、羧酸锂、醇锂、酯锂中的一种或多种；Optionally, the lithium source includes one or more of lithium halide, alkyl lithium, lithium carboxylate, lithium alkoxide, and lithium ester;
可选地，M源包括M元素的烷基金属、羧酸金属、醇金属、酯金属中的一种或多种；Optionally, the M source includes one or more of an alkyl metal, a carboxylic acid metal, an alcohol metal, and an ester metal of the M element;
可选地，氟源包括氟代烷烃、氟代羧酸、氟代醇和氟代酯中的一种或多种；Optionally, the fluorine source includes one or more of fluorinated alkanes, fluorinated carboxylic acids, fluorinated alcohols, and fluorinated esters;
可选地，氯源包括氯代烷烃、氯代羧酸、氯代醇和氯代酯中的一种或多种。Optionally, the chlorine source comprises one or more of chlorinated alkanes, chlorinated carboxylic acids, chlorinated alcohols, and chlorinated esters.
本申请所述包覆可以采用原子层沉积法(ALD)实现，原子层沉积法是基于有序的表面自饱和的化学气相沉积薄膜的方法，可以在正极本体材料表面形成几个原子厚度的沉积层以实现均匀包覆，并且能够实现对氟元素、氯元素变化梯度和包覆层包覆厚度的精准控制。The coating described in the present application can be achieved by atomic layer deposition (ALD), which is a method of chemical vapor deposition of thin films based on ordered surface self-saturation. It can form a deposition layer with a thickness of several atoms on the surface of the positive electrode body material to achieve uniform coating, and can achieve precise control of the gradient of fluorine and chlorine elements and the coating thickness of the coating layer.
在任意实施方式中，在所述包覆步骤之后，对所得包覆的正极本体材料进行煅烧，可选地，煅烧温度为150-300℃，煅烧时间为4-20h。In any embodiment, after the coating step, the obtained coated positive electrode body material is calcined, and optionally, the calcination temperature is 150-300° C. and the calcination time is 4-20 h.
在进行包覆后进行煅烧能够降低所述正极活性材料的阻抗、提高材料的稳定性并提高相应得到的电芯的倍率性能、容量保持率和循环稳定性。Calcination after coating can reduce the impedance of the positive electrode active material, improve the stability of the material and improve the rate performance, capacity retention and cycle stability of the corresponding battery cell.
本申请的第三方面提供一种二次电池，其包括本申请第一方面所述的正极活性材料或根据本申请第二方面所述的方法制备的正极活性材料。The third aspect of the present application provides a secondary battery, which includes the positive electrode active material described in the first aspect of the present application or the positive electrode active material prepared according to the method described in the second aspect of the present application.
在任意实施方式中，所述二次电池包括电解液，所述电解液包括六氟磷酸锂和/或高氯酸锂。In any embodiment, the secondary battery comprises an electrolyte comprising lithium hexafluorophosphate and/or lithium perchlorate.
附图说明BRIEF DESCRIPTION OF THE DRAWINGS
图1为实施例1中制备的正极活性材料颗粒表面包覆后的扫描电子显微镜(SEM)图。FIG. 1 is a scanning electron microscope (SEM) image of the positive electrode active material particles prepared in Example 1 after surface coating.
图2为实施例1中制备的正极活性材料颗粒表面包覆后的SEM图(图1)的局部放大图。FIG. 2 is a partial enlarged view of the SEM image ( FIG. 1 ) of the positive electrode active material particles prepared in Example 1 after surface coating.
具体实施方式Detailed ways
以下，适当地参照附图详细说明具体公开了本申请的正极活性材料及其制造方法、正极极片和二次电池的实施方式。但是会有省略不必要的详细说明的情况。例如，有省略对已众所周知的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说明 是为了本领域技术人员充分理解本申请而提供的，并不旨在限定权利要求书所记载的主题。Hereinafter, the embodiments of the positive electrode active material and its manufacturing method, the positive electrode sheet and the secondary battery of the present application are specifically disclosed with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60-120和80-110的范围，理解为60-110和80-120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1-3、1-4、1-5、2-3、2-4和2-6。在本申请中，除非有其他说明，数值范围“a-b”表示a到b之间的任意实数组合的缩略表示，其中a和b都是实数。例如数值范围“0-5”表示本文中已经全部列出了“0-5”之间的全部实数，“0-5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60-120 and 80-110 is listed for a specific parameter, it is understood that the range of 60-110 and 80-120 is also expected. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4 and 5 are listed, the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-6. In the present application, unless otherwise specified, the numerical range "a-b" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" represents that all real numbers between "0-5" have been fully listed herein, and "0-5" is just the abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成新的技术方案。Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.
如果没有特别的说明，本申请的所有技术特征以及可选技术特征可以相互组合形成新的技术方案。Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.
如果没有特别的说明，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，所述方法包括步骤(a)和(b)，表示所述方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，所述提到所述方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到所述方法，例如，所述方法可以包括步骤(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.
如果没有特别的说明，本申请所提到的“包括”和“包含”表示开放式，也可以是封闭式。例如，所述“包括”和“包含”可以表示还可以包括或包含没有列出的其他组分，也可以仅包括或包含列出的组分。If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).
在电池使用过程中，在高电压或高温条件下，正极活性材料易受到电解液中H 2O和HF腐蚀，并且在脱嵌锂的过程中晶格也可能发生不可逆变化，从而使得产生的过渡金属离子溶出。溶出的过渡金属离子容易迁移至负极表面，并自身还原成金属。这样的金属容易催化SEI膜并使其分解，而且消耗活性锂，从而导致电性能持续恶化。针对上述问题，目前可使用过渡金属或其他金属的卤化物来包覆正极本体活性材料。然而，采用氟化物包覆正极活性材料时，包覆层氟化物具有空气敏感性，易于吸水，因此易于发生不可逆的水解，之后失效；而采用氯化物包覆正极活性材料时，包覆层氯化物的电化学窗口较低，高压下的稳定性差。此外，采用卤化物进行包覆时，通常首先会将该正极本体材料颗粒机械破碎，然后进行包覆，但是，正极本体活性材料的颗粒尺寸约2μm，这样包覆后得到的材料的厚度一般会超过2μm，如此厚度的包覆将显著增加正负极材料间的电子传输阻力，增加欧姆阻抗，导致该正极材料导电性差。针对上述这些问题，本申请发明人经过大量研究，提出了采用同时含有氟和氯的物质来对正极材料进行包覆的方案，该方案在结合了上述氟化物和氯化物的优势的同时避开了它们的劣势，并且通过使氟元素、氯元素在包覆层中逐渐减小或逐渐增大的方式，使锂离子在包覆层中迁移或脱嵌时更加顺利，降低了正极材料的阻抗。另外，本申请提出的上述方案能够实现超薄的厚度，从而进一步降低了正极材料的阻抗。 During the use of the battery, under high voltage or high temperature conditions, the positive electrode active material is susceptible to corrosion by H2O and HF in the electrolyte, and the lattice may also undergo irreversible changes during the process of lithium insertion and extraction, resulting in the dissolution of the generated transition metal ions. The dissolved transition metal ions easily migrate to the surface of the negative electrode and reduce themselves to metals. Such metals easily catalyze and decompose the SEI film, and consume active lithium, resulting in continuous deterioration of electrical performance. In response to the above problems, transition metal or other metal halides can currently be used to coat the positive electrode bulk active material. However, when fluoride is used to coat the positive electrode active material, the coating layer fluoride is air-sensitive and easy to absorb water, so it is easy to undergo irreversible hydrolysis and then fail; and when chloride is used to coat the positive electrode active material, the electrochemical window of the coating layer chloride is low and the stability under high pressure is poor. In addition, when using halides for coating, the positive electrode body material particles are usually first mechanically crushed and then coated. However, the particle size of the positive electrode body active material is about 2μm, so the thickness of the material obtained after coating will generally exceed 2μm. Such a thick coating will significantly increase the electron transfer resistance between the positive and negative electrode materials, increase the ohmic impedance, and cause the positive electrode material to have poor conductivity. In response to the above problems, the inventors of the present application have proposed a scheme for coating the positive electrode material with a substance containing both fluorine and chlorine after a lot of research. This scheme combines the advantages of the above-mentioned fluorides and chlorides while avoiding their disadvantages, and by gradually reducing or increasing the fluorine and chlorine elements in the coating layer, the lithium ions migrate or deintercalate more smoothly in the coating layer, thereby reducing the impedance of the positive electrode material. In addition, the above scheme proposed in the present application can achieve an ultra-thin thickness, thereby further reducing the impedance of the positive electrode material.
为解决上述问题，本申请的第一方面提供了一种正极活性材料，其包括正极本体材料和包覆在所述正极本体材料表面的包覆层，所述包覆层由分子式为Li aMF xCl (a+n-x)的化合物组成，其中 To solve the above problems, the first aspect of the present application provides a positive electrode active material, which includes a positive electrode body material and a coating layer coated on the surface of the positive electrode body material, wherein the coating layer is composed of a compound with a molecular formula of Li a MF x Cl (a+nx) , wherein
1≤a≤3，0≤x≤a+n；n为M离子的价态，n在2-4范围内，1≤a≤3, 0≤x≤a+n; n is the valence state of M ion, n is in the range of 2-4,
M选自元素In、Y、Sc、Er、Tb、Yb、Lu、Zr、Al、Ga、La、Ho、Ti、Nb中的一种或多种，M is selected from one or more of the elements In, Y, Sc, Er, Tb, Yb, Lu, Zr, Al, Ga, La, Ho, Ti, and Nb,
其中，以所述正极本体材料表面为起点，随着向外延伸至包覆层的最外侧的方向上，F元素在分子式为Li aMF xCl (a+n-x)的化合物中的含量占比逐渐变小，Cl元素在分子式为Li aMF xCl (a+n-x)的化合物中的含量占比逐渐变大。 Wherein, starting from the surface of the positive electrode body material, as extending outward to the outermost direction of the coating layer, the content proportion of the F element in the compound with the molecular formula Li a MF x Cl (a+nx) gradually decreases, and the content proportion of the Cl element in the compound with the molecular formula Li a MF x Cl (a+nx) gradually increases.
本申请中，在正极中起主要作用的材料称为“正极本体材料”或“正极本体活性材料”。In the present application, the material that plays a major role in the positive electrode is referred to as the "positive electrode bulk material" or "positive electrode bulk active material".
本申请所述包覆层可起到“阻挡”、“阻隔”的作用。具体而言，在锂离子电池数次充放电过程中，正极本体活性材料会不可避免的产生过渡金属离子；此外，在数次充放电循环后，电解液中的电解质会被分解，可能产生水和强腐蚀性物质(例如氢氟酸)，此时，若正极本体材料与腐蚀性电解液直接接触，会被直接腐蚀，从而分解并产生更多过渡金属离子。本申请所述包覆层的存在既能够有效防止正极本体活性材料在电池充放电过程中产生的过渡金属离子直接进入电解液中，从而起到“阻挡”作用，也可以防止正极本体材料与电解液直接接触而被电解液腐蚀进而产生更多的过渡金属离子，从而起到“阻隔”作用，由此，降低了电池体系中存在的过渡金属离子的数量并显著减缓了腐蚀性物质对于正极本体材料的腐蚀分解，从而改善了电池性能。The coating layer described in the present application can play the role of "blocking" and "isolating". Specifically, during the charge and discharge process of lithium-ion batteries, the active material of the positive electrode will inevitably produce transition metal ions; in addition, after several charge and discharge cycles, the electrolyte in the electrolyte will be decomposed, and water and highly corrosive substances (such as hydrofluoric acid) may be produced. At this time, if the positive electrode body material is in direct contact with the corrosive electrolyte, it will be directly corroded, thereby decomposing and producing more transition metal ions. The presence of the coating layer described in the present application can effectively prevent the transition metal ions generated by the active material of the positive electrode body during the charge and discharge process of the battery from directly entering the electrolyte, thereby playing a "blocking" role, and can also prevent the positive electrode body material from being directly in contact with the electrolyte and being corroded by the electrolyte to produce more transition metal ions, thereby playing a "barrier" role, thereby reducing the number of transition metal ions present in the battery system and significantly slowing down the corrosion and decomposition of the positive electrode body material by corrosive substances, thereby improving battery performance.
根据本申请，采用同时含氟和氯的卤化物对正极本体材料进行包覆，形成由分子式为Li aMF xCl (a+n-x)的物质组成的包覆层。此外，根据本申请，所述包覆层中氟元素的量在包覆层由内向外的方向上逐渐减小(x逐渐减小)，而氯元素的量在包覆层由内向外的方向上逐渐增加，由此，结合氟化物包覆层和氯化物包覆层的优势同时在一定程度上避开了它们的劣势。 According to the present application, the positive electrode body material is coated with a halide containing both fluorine and chlorine to form a coating layer composed of a substance with a molecular formula of Li a MF x Cl (a+nx) . In addition, according to the present application, the amount of fluorine in the coating layer gradually decreases from the inside to the outside of the coating layer (x gradually decreases), while the amount of chlorine in the coating layer gradually increases from the inside to the outside, thereby combining the advantages of the fluoride coating layer and the chloride coating layer while avoiding their disadvantages to a certain extent.
具体而言，本申请中，当采用氟化物包覆层时，在电池使用过程中，正极活性材料的包覆层中的氟元素会迁移至正极本体材料内部形成过渡层，由此，能够降低Li离子的迁移能并稳定晶格氧，从而提 高正极活性材料的锂离子电导率与结构稳定性，并且提高了锂离子电池的容量保持率。此外，氟离子能够和过渡金属离子络合，因而其可以通过化学反应或吸附效应降低电池内部已经产生的过渡金属离子的数量，进而可避免过渡金属离子溢出。另外，氟化物的电化学窗口高(>6.0V)，其对正极本体材料的包覆可以提高正极本体活性材料的锂离子稳定性，并且可以保护正极本体活性材料在4.6V高电压下仍保持良好的结构稳定性。然而，氟化物具有空气敏感性，易于吸水从而发生不可逆水解而失效。在使用氯化物包覆层时，由于氯化物固态电解质具有超高的锂离子电导率(>10 -3S/cm)，因此在充放电过程中锂离子可迅速穿过氯化物包覆层，从而提高了锂离子的脱出嵌入的速度，降低了正极活性材料的阻抗。此外，氯化物具有良好的空气稳定性，吸水后再次加热干燥即可逆恢复。可以保护内部的氟化物与外界空气接触失效。因此，在包覆层中，在离正极本体材料更近的地方，使用含氯更少且含氟更多的包覆物质，能够很好地发挥氟化物的上述作用，提高正极活性材料的稳定性并提高电池的容量保持率；在离正极本体材料更远更靠近包覆层外侧的地方，使用含氯更多且含氟更少的包覆物质，可以利用氯化物的空气稳定性来保护内部的氟化物与外界空气接触失效，从而稳定了内部含氟部分的包覆层物质，实现了包覆层的稳定，并且氯化物的超高电导率也实现了正极活性材料的阻抗的降低。 Specifically, in the present application, when a fluoride coating layer is used, during the use of the battery, the fluorine element in the coating layer of the positive active material will migrate to the inside of the positive electrode body material to form a transition layer, thereby reducing the migration energy of Li ions and stabilizing lattice oxygen, thereby improving the lithium ion conductivity and structural stability of the positive electrode active material, and improving the capacity retention rate of the lithium ion battery. In addition, fluoride ions can be complexed with transition metal ions, so that they can reduce the number of transition metal ions already produced inside the battery by chemical reaction or adsorption effect, thereby avoiding the overflow of transition metal ions. In addition, the electrochemical window of fluoride is high (> 6.0V), and its coating of the positive electrode body material can improve the lithium ion stability of the positive electrode body active material, and can protect the positive electrode body active material from still maintaining good structural stability at a high voltage of 4.6V. However, fluoride is air-sensitive and is easy to absorb water, thereby failing due to irreversible hydrolysis. When using a chloride coating, since the chloride solid electrolyte has an ultra-high lithium ion conductivity (>10 -3 S/cm), lithium ions can quickly pass through the chloride coating during the charge and discharge process, thereby increasing the speed of lithium ion extraction and embedding, and reducing the impedance of the positive electrode active material. In addition, chloride has good air stability, and can be reversed by heating and drying again after absorbing water. It can protect the internal fluoride from contacting with the outside air and failing. Therefore, in the coating layer, in the place closer to the positive electrode body material, using a coating material containing less chlorine and more fluorine can well play the above-mentioned role of fluoride, improve the stability of the positive electrode active material and improve the capacity retention rate of the battery; in the place farther from the positive electrode body material and closer to the outside of the coating layer, using a coating material containing more chlorine and less fluorine, the air stability of chloride can be used to protect the internal fluoride from contacting with the outside air and failing, thereby stabilizing the coating material of the internal fluorine-containing part, achieving the stability of the coating layer, and the ultra-high conductivity of chloride also achieves the reduction of the impedance of the positive electrode active material.
进一步地，经分析，当正极本体活性材料产生的过渡金属离子外溢时，会首先进入包覆层，因此，在正极本体材料表面包覆层最内部处过渡金属离子数量较多，沿着包覆层向外的方向上，过渡金属离子逐渐减少。根据这个规律，本申请设计在包覆层内部过渡金属离子较多的地方使用含氟较多的化合物进行包覆，在包覆层较外部过渡金属离子较少的地方使用含氟较少的化合物进行包覆，即，在包覆层最内部，氟元素含量最多，而在沿包覆层向外的方向上，氟元素含量相应地逐渐减少，由此，能够使氟元素和过渡金属离子更有针对性且更效地络合，从而更有效地阻止过渡金属离子外溢。另外，本申请采用氟 元素由内向外逐渐减少，氯元素含量由内向外逐渐增加的方式，更有利于锂离子的顺利迁移和脱嵌，有利于锂离子电导率的提高。Further, after analysis, when the transition metal ions generated by the active material of the positive electrode body overflow, they will first enter the coating layer. Therefore, the number of transition metal ions is relatively large at the innermost part of the coating layer on the surface of the positive electrode body material, and the transition metal ions gradually decrease along the coating layer to the outside. According to this rule, the present application is designed to use a compound containing more fluorine to coat the place where there are more transition metal ions inside the coating layer, and to use a compound containing less fluorine to coat the place where there are fewer transition metal ions outside the coating layer, that is, the fluorine content is the highest in the innermost part of the coating layer, and the fluorine content gradually decreases along the coating layer to the outside, thereby enabling the fluorine element and the transition metal ions to be more targeted and more effectively complexed, thereby more effectively preventing the transition metal ions from overflowing. In addition, the present application adopts a method in which the fluorine element gradually decreases from the inside to the outside and the chlorine element content gradually increases from the inside to the outside, which is more conducive to the smooth migration and deintercalation of lithium ions and is conducive to the improvement of lithium ion conductivity.
可选地，包覆层最靠近正极本体材料的地方仅含氟而不含氯，包覆层最靠外的地方仅含氯而不含氟。Optionally, the coating layer closest to the positive electrode main material contains only fluorine but no chlorine, and the coating layer closest to the outside contains only chlorine but no fluorine.
由于本申请改性的正极活性材料具有上述有益效果，因而能够减缓电池存储或使用过程中过渡金属的产生及其对负极SEI膜(如果有的话)的催化分解，从而改善电池的容量保持率并降低电池阻抗。Since the modified positive electrode active material of the present application has the above-mentioned beneficial effects, it can slow down the generation of transition metals and their catalytic decomposition of the negative electrode SEI film (if any) during battery storage or use, thereby improving the battery capacity retention rate and reducing the battery impedance.
应理解，本申请中，包覆层中的氟元素和氯元素的变化可以采用任意手段进行，只要满足氟元素由内向外含量逐渐降低，氯元素由内向外含量逐渐增加这个趋势即可。It should be understood that in the present application, the changes in the fluorine and chlorine elements in the coating layer can be carried out by any means, as long as the trend of the fluorine content gradually decreasing from the inside to the outside and the chlorine content gradually increasing from the inside to the outside is satisfied.
如图1所示，大颗粒为正极本体材料NCM811，外面有一层包覆层，大视野看到正极颗粒被完全包覆，对包覆层进行放大(图2)可以发现包覆层均匀且致密，无漏包区域。证明本申请的正极活性材料中，包覆层包覆的均匀致密且比较完全。As shown in Figure 1, the large particles are the cathode material NCM811, with a coating layer on the outside. From a wide field of view, the cathode particles are completely coated. By zooming in on the coating layer (Figure 2), it can be found that the coating layer is uniform and dense, with no leaking areas. This proves that in the cathode active material of the present application, the coating layer is uniform, dense and relatively complete.
在一些实施方式中，随着向外延伸至包覆层的最外侧的方向上，F元素的含量占比由大到小的变化梯度，即x从a+n→0的变化梯度，为(a+n)/(h/b)，其中h为包覆层厚度，b为发生梯度改变的最小厚度；其中，h在0-5nm范围内，可选地在0.5-5nm范围内；b在0-0.5nm范围内，可选地在0.1-0.5nm范围内。相应地，随着向外延伸至包覆层的最外侧的方向上，Cl元素的含量占比由小到大的变化梯度，即a+n-x从0→a+n的变化梯度，为(a+n)/(h/b)。In some embodiments, as the coating extends outward to the outermost direction, the content ratio of the F element changes from large to small, that is, the gradient of x from a+n→0 is (a+n)/(h/b), where h is the coating thickness and b is the minimum thickness at which the gradient changes; wherein h is in the range of 0-5nm, optionally in the range of 0.5-5nm; b is in the range of 0-0.5nm, optionally in the range of 0.1-0.5nm. Accordingly, as the coating extends outward to the outermost direction, the content ratio of the Cl element changes from small to large, that is, the gradient of a+n-x from 0→a+n, is (a+n)/(h/b).
包覆层中氟元素和氯元素含量变化通过梯度方式均匀地进行，由此包覆层中氟元素和氯元素含量变化更为均匀，更有利于精准地捕获正极本体材料产生的过渡金属离子并且更有利于锂元素的脱嵌的顺利进行。The change of the content of fluorine and chlorine in the coating layer is carried out uniformly in a gradient manner, so that the change of the content of fluorine and chlorine in the coating layer is more uniform, which is more conducive to the accurate capture of transition metal ions produced by the positive electrode body material and more conducive to the smooth deintercalation of lithium elements.
在一些可选实施方式中，随着向外延伸至包覆层的最外侧的方向上，F元素的含量占比由大到小的变化梯度，即x从a+n→0的变化梯度，在(a+n)/(h/0.1)～(a+n)/(h/0.5)范围内，h为包覆层厚度，h在0-5nm范围内，可选地在0.5-5nm范围内。In some optional embodiments, as extending outward to the outermost direction of the coating layer, the content proportion of the F element changes gradient from large to small, that is, the change gradient of x from a+n→0, is in the range of (a+n)/(h/0.1) to (a+n)/(h/0.5), h is the thickness of the coating layer, h is in the range of 0-5nm, optionally in the range of 0.5-5nm.
可选地，在制备上述渐变包覆层时，每0.1nm-0.5nm厚度改变一次F元素含量变化梯度，每次梯度变化量为(a+n)/(h/0.1)～(a+n)/(h/0.5)。Optionally, when preparing the above-mentioned gradient coating layer, the F element content gradient is changed every 0.1nm-0.5nm thickness, and each gradient change amount is (a+n)/(h/0.1) to (a+n)/(h/0.5).
相应地，随着向外延伸至包覆层的最外侧的方向上，Cl元素的含量占比由小到大的变化梯度，即a+n-x从0→a+n的变化梯度，也在(a+n)/(h/0.1)～(a+n)/(h/0.5)范围内。Correspondingly, as it extends outward to the outermost direction of the coating layer, the gradient of the content proportion of the Cl element changes from small to large, that is, the gradient of a+n-x changes from 0→a+n, is also in the range of (a+n)/(h/0.1) to (a+n)/(h/0.5).
氟元素和氯元素的梯度渐进变化降低了包覆层内部的晶界电阻，从而降低所述正极活性材料的阻抗以及相应地电池的阻抗，进一步提高了电池的循环稳定性。The gradual change of the gradient of the fluorine element and the chlorine element reduces the grain boundary resistance inside the coating layer, thereby reducing the impedance of the positive electrode active material and the impedance of the battery accordingly, and further improving the cycle stability of the battery.
在一些可选实施方式中，包覆层厚度在0.5-5nm范围内。In some optional embodiments, the coating layer has a thickness in the range of 0.5-5 nm.
包覆层的厚度会极大影响到电池整体性能，如阻抗，循环稳定性，倍率性能。通常应用的固相包覆法的包覆厚度都在微米级别，导致锂离子电导率和电子电导率均会明显下降，导致正极活性材料的阻抗更高。本申请所述的包覆层为超薄包覆层，在0.5-5nm之间。在该范围内的包覆层，能够很好地覆盖正极本体材料的表面并且同时保证了材料的理论能量密度和阻抗。而当包覆层厚度低于0.5nm时，包覆厚度太薄，包覆层无法完全覆盖样品表面，因而容易造成漏包，导致材料性能一致性变差。当包覆层厚度高于5nm时，包覆层太厚，会降低材料的理论能量密度并增加了材料的阻抗以及相应地电池的阻抗。The thickness of the coating layer will greatly affect the overall performance of the battery, such as impedance, cycle stability, and rate performance. The coating thickness of the commonly used solid phase coating method is at the micron level, which causes the lithium ion conductivity and electronic conductivity to decrease significantly, resulting in a higher impedance of the positive electrode active material. The coating layer described in the present application is an ultra-thin coating layer, between 0.5-5nm. The coating layer within this range can well cover the surface of the positive electrode bulk material and simultaneously ensure the theoretical energy density and impedance of the material. When the coating layer thickness is less than 0.5nm, the coating thickness is too thin, and the coating layer cannot completely cover the sample surface, which easily causes leakage, resulting in poor consistency of material performance. When the coating layer thickness is higher than 5nm, the coating layer is too thick, which will reduce the theoretical energy density of the material and increase the impedance of the material and the impedance of the battery accordingly.
在一些实施方式中，所述包覆层的材料选自Li 3InF xCl (6-x)、Li 3YF xCl (6-x)、Li 3ScF xCl (6-x)、Li 3MnF xCl (6-x)、Li 3ZrF xCl (6-x)中的至少一种，其中0≤x≤6。 In some embodiments, the material of the coating layer is selected from at least one of Li 3 InF x Cl (6-x) , Li 3 YF x Cl (6-x) , Li 3 ScF x Cl (6-x) , Li 3 MnF x Cl (6-x) , and Li 3 ZrF x Cl (6-x) , wherein 0≤x≤6.
在一些实施方式中，所述正极活性材料的电化学窗口为5.0V以上，和/或，所述正极活性材料的锂离子电导率为10 -8-10 -3S/cm。 In some embodiments, the electrochemical window of the positive electrode active material is above 5.0 V, and/or the lithium ion conductivity of the positive electrode active material is 10 -8 -10 -3 S/cm.
电化学窗口的测试可以采用电化学工作站线性伏安测试模块进行。具体而言，可以采用如下方法：将待测的正极活性材料与粘结剂PVDF采用95:5质量比混合，溶于溶剂(例如N-甲基吡咯烷酮(NMP))中，浓度不限，滴涂于玻碳电极表面作为工作电极；然后，以1M LiPF6为溶液，锂片作为对电极组装成一个电池***(也可称作电解池)， 对该电池***进行伏安曲线测试，设定电压范围2.5～5V，扫速0.5mV/s，记录氧化电位即为电化学窗口。The electrochemical window test can be performed using the linear voltammetric test module of the electrochemical workstation. Specifically, the following method can be used: the positive electrode active material to be tested is mixed with the binder PVDF in a mass ratio of 95:5, dissolved in a solvent (such as N-methylpyrrolidone (NMP)), with no limit on concentration, and dripped on the surface of the glassy carbon electrode as a working electrode; then, a battery system (also called an electrolytic cell) is assembled with 1M LiPF6 as a solution and a lithium sheet as a counter electrode, and the battery system is tested for voltammetric curves, with a voltage range of 2.5 to 5V and a scan rate of 0.5mV/s, and the oxidation potential is recorded as the electrochemical window.
离子电导率σ＝1/ρ，ρ可通过R＝h/(ρs)求解得出；其中R为交流阻抗，所述交流阻抗采用电化学工作站阻抗测试模块进行测试，设定电压扰动模式PEIS，扰动电压5mV，频率范围200kHZ～30mHZ，然后对正极活性材料片进行阻抗测试，得到R；其中h为固态电解质片的厚度，s为固态电解质片的面积。此外，固态电解质为离子导体，对电子不可导，因此进行阻抗测试之前，需要在电解质片两侧连接阻塞型Ag电极，如下：将固态电解质两面打磨光滑至一定厚度，于其上涂敷银浆引出Ag线，然后在马弗炉中进行烧Ag处理，使得Ag电极与电解质表面紧密接触。测定的电阻R＝h/(ρs)，根据该式子求解ρ，然后根据σ＝1/ρ得到离子电导率σ。Ionic conductivity σ＝1/ρ, ρ can be solved by R＝h/(ρs); where R is AC impedance, and the AC impedance is tested by the impedance test module of the electrochemical workstation, setting the voltage perturbation mode PEIS, the perturbation voltage 5mV, and the frequency range 200kHZ～30mHZ, and then the impedance test of the positive electrode active material sheet is performed to obtain R; where h is the thickness of the solid electrolyte sheet, and s is the area of the solid electrolyte sheet. In addition, the solid electrolyte is an ionic conductor and is not conductive to electrons. Therefore, before the impedance test, it is necessary to connect blocking Ag electrodes on both sides of the electrolyte sheet, as follows: polish both sides of the solid electrolyte to a certain thickness, apply silver paste on it to lead out the Ag wire, and then burn Ag in a muffle furnace to make the Ag electrode in close contact with the electrolyte surface. The measured resistance R＝h/(ρs), solve ρ according to this formula, and then obtain the ionic conductivity σ according to σ＝1/ρ.
在一些实施方式中，所述正极本体材料选自三元活性材料、磷酸铁锂、锰酸锂、钴酸锂中的至少一种。In some embodiments, the cathode bulk material is selected from at least one of ternary active materials, lithium iron phosphate, lithium manganese oxide, and lithium cobalt oxide.
所述三元活性材料为本领域中使用的那些三元材料，包括，但不限于，镍钴锰三元材料、镍钴铝三元材料等。The ternary active materials are those ternary materials used in the art, including, but not limited to, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, and the like.
本申请的第二方面提供一种正极活性材料的制备方法，所述方法包括包覆步骤，该步骤包括：A second aspect of the present application provides a method for preparing a positive electrode active material, the method comprising a coating step, the step comprising:
(1)制备或准备正极本体材料；(1) preparing or preparing positive electrode bulk material;
(2)在惰性气氛下将Li aMF xCl (a+n-x)的源进行气化，可选地，所述气化温度为200-300℃；使气化的所述源在正极本体材料表面吸附沉积，以包覆所述正极本体材料，得到所述正极活性材料； (2) vaporizing a source of Li a MF x Cl (a+nx) under an inert atmosphere, optionally at a vaporization temperature of 200-300° C.; allowing the vaporized source to be adsorbed and deposited on the surface of the positive electrode bulk material to coat the positive electrode bulk material, thereby obtaining the positive electrode active material;
其中，分子式Li aMF xCl (a+n-x)中， Among them, in the molecular formula Li a MF x Cl (a+nx) ,
1≤a≤3，0≤x≤a+n；n为M离子的价态，n在2-4范围内，1≤a≤3, 0≤x≤a+n; n is the valence state of M ion, n is in the range of 2-4,
M选自元素In、Y、Sc、Er、Tb、Yb、Lu、Zr、Al、Ga、La、Ho、Ti、Nb中的一种或多种，M is selected from one or more of the elements In, Y, Sc, Er, Tb, Yb, Lu, Zr, Al, Ga, La, Ho, Ti, and Nb,
其中，以所述正极本体材料表面为起点，随着向外延伸至包覆层的最外侧的方向上，F元素在分子式为Li aMF xCl (a+n-x)的化合物中的含 量占比逐渐变小，Cl元素在分子式为Li aMF xCl (a+n-x)的化合物中的含量占比逐渐变大。 Wherein, starting from the surface of the positive electrode body material, as extending outward to the outermost direction of the coating layer, the content proportion of the F element in the compound with the molecular formula Li a MF x Cl (a+nx) gradually decreases, and the content proportion of the Cl element in the compound with the molecular formula Li a MF x Cl (a+nx) gradually increases.
所述正极本体材料可在制备包覆层之前制备，也可购买获得。The positive electrode body material can be prepared before preparing the coating layer, or can be purchased.
在一些实施方式中，所述使气化的所述源在正极本体材料表面吸附沉积的方法为原子沉积法，可选地，所述沉积次数为m，m范围为1-100。In some embodiments, the method of adsorbing and depositing the gasified source on the surface of the positive electrode bulk material is an atomic deposition method. Optionally, the deposition number is m, and m ranges from 1-100.
在一些可选实施方式中，在步骤(2)中，使用原子沉积法进行沉积，每完成一次沉积称为一个循环，共进行m个循环，m范围为h/0.1～h/0.5，h定义如前文所述，每次循环沉积厚度为0.1-0.5nm；其中对于第k次循环，1≤k≤m，使用Li aMF xCl (a+n-x)的源进行沉积，其中x为(m-k)×(a+n)/m，a、n如前文所定义。 In some optional embodiments, in step (2), deposition is performed using an atomic deposition method, each completed deposition is called a cycle, a total of m cycles are performed, m ranges from h/0.1 to h/0.5, h is defined as described above, and the deposition thickness of each cycle is 0.1-0.5 nm; wherein for the kth cycle, 1≤k≤m, deposition is performed using a source of Li a MF x Cl (a+nx) , wherein x is (mk)×(a+n)/m, and a and n are defined as described above.
在一些实施方式中，所述Li aMF xCl (a+n-x)的源包括锂源、M源、氟源、氯源，其中，所述各源的沸点介于70-300℃之间； In some embodiments, the source of Li a MF x Cl (a+nx) includes a lithium source, an M source, a fluorine source, and a chlorine source, wherein the boiling point of each source is between 70-300° C.;
锂源包括，但不限于，卤化锂，烷基锂、羧酸锂、醇锂、酯锂中的一种或多种，例如，叔丁醇锂，The lithium source includes, but is not limited to, one or more of lithium halides, alkyl lithiums, lithium carboxylates, lithium alkoxides, and lithium esters, for example, lithium tert-butoxide,
M的源包括，但不限于，M元素的烷基金属、羧酸金属、醇金属、酯金属中的一种或多种，沸点介于70～300℃之间。The source of M includes, but is not limited to, one or more of alkyl metals, carboxylic acid metals, alcohol metals, and ester metals of the M element, with a boiling point between 70 and 300°C.
氟源包括，但不限于，氟代烷烃、氟代羧酸、氟代醇和氟代酯中的一种或多种。所述氟代酯包括氟代碳酸乙烯酯。The fluorine source includes, but is not limited to, one or more of fluorinated alkanes, fluorinated carboxylic acids, fluorinated alcohols and fluorinated esters. The fluorinated esters include fluorinated ethylene carbonate.
氯源包括，但不限于，氯代烷烃、氯代羧酸、氯代醇和氯代酯中的一种或多种。所述氯代酯包括氯代碳酸乙烯酯。The chlorine source includes, but is not limited to, one or more of chlorinated alkanes, chlorinated carboxylic acids, chlorinated alcohols and chlorinated esters. The chlorinated esters include chlorinated ethylene carbonate.
本申请中，所述Li aMF xCl (a+n-x)的源也可称为“前驱体”。 In the present application, the source of Li a MF x Cl (a+nx) may also be referred to as a “precursor”.
所述包覆可以采用原子层沉积法(ALD)实现，原子层沉积法是基于有序的表面自饱和的化学气相沉积薄膜的方法，可以在正极本体材料表面形成几个原子厚度的沉积层以实现均匀包覆。该方法的主要步骤包括：将气相前驱体脉冲交替地通入反应器，然后使其在沉积基体上化学吸附并反应，形成沉积膜。当前驱体达到沉积基体表面时，它们会在其表面化学吸附并在表面发生反应。在前驱体两次脉冲之间需要用惰性气体对原子层沉积反应器进行清洗。因此只需要调整沉积气 相前驱体(例如氯源和氟源)的脉冲时间并根据需要设置合适的参数程序，就可以精确地调节包覆物中两种卤化物源的沉积比例形成梯度包覆。每一层沉积厚度约0.1nm，最多可达0.5nm。由此，通过调整沉积的循环圈数能够精准调控包覆厚度。The coating can be achieved by atomic layer deposition (ALD), which is a method of chemical vapor deposition thin film based on ordered surface self-saturation, and can form a deposition layer of several atoms thick on the surface of the positive electrode body material to achieve uniform coating. The main steps of the method include: alternately passing the gas phase precursor pulse into the reactor, and then chemically adsorbing and reacting it on the deposition substrate to form a deposited film. When the precursor reaches the surface of the deposition substrate, they will chemically adsorb on its surface and react on the surface. The atomic layer deposition reactor needs to be cleaned with an inert gas between the two pulses of the precursor. Therefore, it is only necessary to adjust the pulse time of the deposition gas phase precursor (such as a chlorine source and a fluorine source) and set a suitable parameter program as needed to accurately adjust the deposition ratio of the two halide sources in the coating to form a gradient coating. The deposition thickness of each layer is about 0.1nm, up to 0.5nm. Thus, the coating thickness can be accurately controlled by adjusting the number of cycles of deposition.
此外，对于正极本体材料包覆而言，其包覆厚度、包覆均匀性直接影响了正极活性材料的性能。采用原子层沉积法进行包覆可精准控制包覆厚度，例如，可以做到0.5nm左右的超薄包覆厚度。另外，该方法中，将沉积物质(即上述各源)气化，气化后的沉积物质能够与正极本体材料表面接触完全，使得包覆更加均匀完全，避免了包覆缺陷。另外，可以提前设置沉积的气相前驱体脉冲交替程序，由此，能够灵活调节沉积的物质量，从而形成所需的卤素浓度梯度分布，该方法简单且易于优化。In addition, for the coating of the positive electrode bulk material, the coating thickness and coating uniformity directly affect the performance of the positive electrode active material. The coating thickness can be accurately controlled by atomic layer deposition. For example, an ultra-thin coating thickness of about 0.5 nm can be achieved. In addition, in this method, the deposited material (i.e., the above-mentioned sources) is vaporized, and the vaporized deposited material can be in complete contact with the surface of the positive electrode bulk material, making the coating more uniform and complete, avoiding coating defects. In addition, the pulse alternation program of the deposited gas phase precursor can be set in advance, thereby flexibly adjusting the amount of deposited material to form the desired halogen concentration gradient distribution. This method is simple and easy to optimize.
在一些实施方式中，在所述包覆步骤之后，对所得包覆的正极本体材料进行煅烧，可选地，煅烧温度为150-300℃，煅烧时间为4-20h。In some embodiments, after the coating step, the obtained coated positive electrode body material is calcined. Optionally, the calcination temperature is 150-300° C. and the calcination time is 4-20 h.
所述煅烧可在惰性气氛下进行，例如在氩气、氮气下进行。The calcination may be performed under an inert atmosphere, such as argon or nitrogen.
在包覆后对材料进行煅烧具有如下效果：Calcination of the material after coating has the following effects:
(1)煅烧过程中有助于F元素迁移至正极本体材料内部，形成尖晶石状的过渡层作为连接纽带，降低包覆层与正极本体材料界面处的界面电阻，并降低Li离子的迁移能并稳定晶格氧；(1) During the calcination process, the F element is helped to migrate into the interior of the cathode bulk material, forming a spinel-like transition layer as a connecting link, reducing the interfacial resistance at the interface between the coating layer and the cathode bulk material, reducing the migration energy of Li ions and stabilizing the lattice oxygen;
(2)煅烧能够提高包覆材料的结晶度，形成立方密实堆积结构(CCP)，有助于形成3D的锂离子传输通道，从而降低材料阻抗和电池阻抗并提高所得到的电芯的倍率性能和循环稳定性；(2) Calcination can improve the crystallinity of the coating material and form a cubic dense packing structure (CCP), which helps to form a 3D lithium ion transmission channel, thereby reducing the material impedance and battery impedance and improving the rate performance and cycle stability of the resulting battery cell;
(3)煅烧也有助于使正极与内层氟化物交界处、内外层包覆物交界处进行更好的原子融合，形成过渡层，降低由于包覆界面造成的晶界电阻，从而降低了材料的阻抗和电池的阻抗；(3) Calcination also helps to achieve better atomic fusion at the interface between the positive electrode and the inner fluoride layer and at the interface between the inner and outer coatings, forming a transition layer, reducing the grain boundary resistance caused by the coating interface, thereby reducing the impedance of the material and the impedance of the battery;
(4)高温煅烧也会进一步提高晶体材料的结晶度和包覆稳定性。(4) High temperature calcination will also further improve the crystallinity and coating stability of crystalline materials.
本申请的一个方面还提供一种正极极片，其包括正极集流体以及设置在正极集流体至少一个表面的正极膜层，所述正极膜层包括本申 请第一方面所述的正极活性材料或由本申请第二方面所述的方法制备的正极活性材料。One aspect of the present application also provides a positive electrode plate, which includes a positive electrode collector and a positive electrode film layer arranged on at least one surface of the positive electrode collector, wherein the positive electrode film layer includes the positive electrode active material described in the first aspect of the present application or the positive electrode active material prepared by the method described in the second aspect of the present application.
本申请的第三方面提供一种二次电池，其包括本申请第一方面所述的正极活性材料或由本申请第二方面所述的方法制备的正极活性材料。所述二次电池可以为电池单体的形式，可以为电池模块的形式，也可以为电池包的形式。The third aspect of the present application provides a secondary battery, which includes the positive electrode active material described in the first aspect of the present application or the positive electrode active material prepared by the method described in the second aspect of the present application. The secondary battery can be in the form of a battery cell, a battery module, or a battery pack.
通常情况下，二次电池包括正极极片、负极极片、电解质和隔离膜。在电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出。电解质在正极极片和负极极片之间起到传导离子的作用。隔离膜设置在正极极片和负极极片之间，主要起到防止正负极短路的作用，同时可以使离子通过。Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.
[正极极片][Positive electrode]
正极极片包括正极集流体以及设置在正极集流体至少一个表面的正极膜层，所述正极膜层包括本申请第一方面的正极活性材料或由本申请第二方面所述的方法制备的正极活性材料。The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared by the method described in the second aspect of the present application.
作为示例，正极集流体具有在其自身厚度方向相对的两个表面，正极膜层设置在正极集流体相对的两个表面的其中任意一者或两者上。As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.
在一些实施方式中，所述正极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可采用铝箔。复合集流体可包括高分子材料基层和形成于高分子材料基层至少一个表面上的金属层。复合集流体可通过将金属材料(铝、铝合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
在一些实施方式中，用于进行包覆的正极本体材料可采用本领域公知的用于电池的正极活性材料。作为示例，所述正极本体材料可包括以下材料中的至少一种：橄榄石结构的含锂磷酸盐、锂过渡金属氧化物及其各自的改性化合物。但本申请并不限定于这些材料，还可以 使用其他可被用作电池正极本体材料的传统材料。这些正极本体材料可以仅单独使用一种，也可以将两种以上组合使用。其中，锂过渡金属氧化物的示例可包括但不限于锂钴氧化物(如LiCoO 2)、锂镍氧化物(如LiNiO 2)、锂锰氧化物(如LiMnO 2、LiMn 2O 4)、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物(如LiNi 1/3Co 1/3Mn 1/3O 2(也可以简称为NCM 333)、LiNi 0.5Co 0.2Mn 0.3O 2(也可以简称为NCM 523)、LiNi 0.5Co 0.25Mn 0.25O 2(也可以简称为NCM 211)、LiNi 0.6Co 0.2Mn 0.2O 2(也可以简称为NCM 622)、LiNi 0.8Co 0.1Mn 0.1O 2(也可以简称为NCM 811)、锂镍钴铝氧化物(如LiNi 0.85Co 0.15Al 0.05O 2)及其改性化合物等中的至少一种。橄榄石结构的含锂磷酸盐的示例可包括但不限于磷酸铁锂(如LiFePO 4(也可以简称为LFP))、磷酸铁锂与碳的复合材料、磷酸锰锂(如LiMnPO 4)、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料中的至少一种。可选地，如上所述，所述正极本体材料选自三元正极活性材料体系、钴酸锂、锰酸锂、磷酸铁锂等中的至少一种。 In some embodiments, the positive electrode bulk material used for coating may be a positive electrode active material for a battery known in the art. As an example, the positive electrode bulk material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as a positive electrode bulk material for a battery may also be used. These positive electrode bulk materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to , lithium cobalt oxide (such as LiCoO2 ), lithium nickel oxide (such as LiNiO2 ), lithium manganese oxide (such as LiMnO2 , LiMn2O4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi1 / 3Co1 / 3Mn1 / 3O2 (also referred to as NCM333 ), LiNi0.5Co0.2Mn0.3O2 (also referred to as NCM523 ) , LiNi0.5Co0.25Mn0.25O2 (also referred to as NCM211 ) , LiNi0.6Co0.2Mn0.2O2 (also referred to as NCM622 ), LiNi0.8Co0.1Mn0.1O2 (also referred to as NCM811 ), lithium nickel cobalt aluminum oxide ( such as LiNi 0.85 Co 0.15 Al 0.05 O 2 ) and at least one of its modified compounds. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO 4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Optionally, as described above, the cathode body material is selected from at least one of a ternary cathode active material system, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, and the like.
应理解，在正极极片中，除了使用本申请第一方面的正极活性材料或由本申请第二方面所述的方法制备的正极活性材料之外，还可使用本领域公知的其他正极活性材料。It should be understood that in the positive electrode sheet, in addition to the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared by the method described in the second aspect of the present application, other positive electrode active materials known in the art may also be used.
在一些实施方式中，正极膜层还可选地包括粘结剂。作为示例，所述粘结剂可以包括聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物及含氟丙烯酸酯树脂中的至少一种。In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.
在一些实施方式中，正极膜层还可选地包括导电剂。作为示例，所述导电剂可以包括超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。In some embodiments, the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
在正极膜层中，本申请所述正极活性材料所占质量比范围为70～98质量％，可选为90质量％；粘结剂所占质量比范围为1～15质 量％，导电剂所占质量比范围为1～15质量％，全部基于正极膜片的总质量计。In the positive electrode film layer, the mass ratio of the positive electrode active material described in the present application is in the range of 70 to 98 mass%, and can be optionally 90 mass%; the mass ratio of the binder is in the range of 1 to 15 mass%, and the mass ratio of the conductive agent is in the range of 1 to 15 mass%, all based on the total mass of the positive electrode film.
在一些实施方式中，可以通过以下方式制备正极极片：将上述用于制备正极极片的组分，例如所述正极活性材料、导电剂、粘结剂和任意其他的组分分散于溶剂(例如N-甲基吡咯烷酮)中，形成正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，即可得到正极极片。In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.
[负极极片][Negative electrode]
负极极片包括负极集流体以及设置在负极集流体至少一个表面上的负极膜层，所述负极膜层包括负极活性材料。The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.
作为示例，负极集流体具有在其自身厚度方向相对的两个表面，负极膜层设置在负极集流体相对的两个表面中的任意一者或两者上。As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.
在一些实施方式中，所述负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体可通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
在一些实施方式中，负极活性材料可采用本领域公知的用于电池的负极活性材料。作为示例，负极活性材料可包括以下材料中的至少一种：人造石墨、天然石墨、软炭、硬炭、硅基材料、锡基材料和钛酸锂等。所述硅基材料可选自单质硅、硅氧化合物、硅碳复合物、硅氮复合物以及硅合金中的至少一种。所述锡基材料可选自单质锡、锡氧化合物以及锡合金中的至少一种。但本申请并不限定于这些材料，还可以使用其他可被用作电池负极活性材料的传统材料。这些负极活性材料可以仅单独使用一种，也可以将两种以上组合使用。In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.
在一些实施方式中，负极膜层还可选地包括粘结剂。所述粘结剂可选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、 聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的至少一种。In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
在一些实施方式中，负极膜层还可选地包括导电剂。导电剂可选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
在一些实施方式中，负极膜层还可选地包括其他助剂，例如增稠剂(如羧甲基纤维素钠(CMC-Na))等。In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).
在负极膜层中，负极材料所占质量比范围为70～98质量％，可选为95质量％；粘结剂所占质量比范围为1～15质量％，导电剂所占质量比范围为1～15质量％，全部基于正极膜片的总质量计。In the negative electrode film layer, the mass ratio of the negative electrode material ranges from 70 to 98 mass%, and can be optionally 95 mass%; the mass ratio of the binder ranges from 1 to 15 mass%, and the mass ratio of the conductive agent ranges from 1 to 15 mass%, all based on the total mass of the positive electrode film.
在一些实施方式中，可以通过以下方式制备负极极片：将上述用于制备负极极片的组分，例如负极活性材料、导电剂、粘结剂和任意其他组分分散于溶剂(例如去离子水)中，形成负极浆料；将负极浆料涂覆在负极集流体上，经烘干、冷压等工序后，即可得到负极极片。In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.
[电解质][Electrolytes]
电解质在正极极片和负极极片之间起到传导离子的作用。本申请对电解质的种类没有具体的限制，可根据需求进行选择。例如，电解质可以是液态的、凝胶态的或全固态的。The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.
在一些实施方式中，所述电解质采用电解液。所述电解液包括电解质盐和溶剂。In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.
在一些实施方式中，电解质盐可选自六氟磷酸锂、四氟硼酸锂、高氯酸锂、六氟砷酸锂、双氟磺酰亚胺锂、双三氟甲磺酰亚胺锂、三氟甲磺酸锂、二氟磷酸锂、二氟草酸硼酸锂、二草酸硼酸锂、二氟二草酸磷酸锂及四氟草酸磷酸锂中的至少一种。In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.
在一些可选实施方式中，所述二次电池包括电解液，所述电解液包括六氟磷酸锂和/或高氯酸锂。可选地，所述六氟磷酸锂和/或高氯酸锂在电解液中的浓度范围为0.5～3mol/LIn some optional embodiments, the secondary battery includes an electrolyte, and the electrolyte includes lithium hexafluorophosphate and/or lithium perchlorate. Optionally, the concentration of lithium hexafluorophosphate and/or lithium perchlorate in the electrolyte ranges from 0.5 to 3 mol/L.
在一些实施方式中，溶剂可选自碳酸亚乙酯、碳酸亚丙酯、碳酸甲乙酯、碳酸二乙酯、碳酸二甲酯、碳酸二丙酯、碳酸甲丙酯、碳酸 乙丙酯、碳酸亚丁酯、氟代碳酸亚乙酯、甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、丁酸甲酯、丁酸乙酯、1,4-丁内酯、环丁砜、二甲砜、甲乙砜及二乙砜中的至少一种。In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.
在一些实施方式中，所述电解液还可选地包括添加剂。例如添加剂可以包括负极成膜添加剂、正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温或低温性能的添加剂等。In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.
[隔离膜][Isolation film]
在一些实施方式中，二次电池中还包括隔离膜。本申请对隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.
在一些实施方式中，隔离膜的材质可选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的至少一种。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.
在一些实施方式中，正极极片、负极极片和隔离膜可通过卷绕工艺或叠片工艺制成电极组件。In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.
在一些实施方式中，二次电池可包括外包装。该外包装可用于封装上述电极组件及电解质。In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.
在一些实施方式中，二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。二次电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，作为塑料，可列举出聚丙烯、聚对苯二甲酸丁二醇酯以及聚丁二酸丁二醇酯等。In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.
本申请对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。例如，图3是作为一个示例的方形结构的二次电池5。The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. For example, FIG3 is a secondary battery 5 of a square structure as an example.
在一些实施方式中，参照图4，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53能够盖设于 所述开口，以封闭所述容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔内。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。In some embodiments, referring to FIG. 4 , the outer package may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
二次电池包括电池单体形式、电池模块形式、电池包形式。在一些实施方式中，电池单体可以组装成电池模块，电池模块所含电池单体的数量可以为一个或多个，具体数量本领域技术人员可根据电池模块的应用和容量进行选择。Secondary batteries include battery cells, battery modules, and battery packs. In some embodiments, battery cells can be assembled into a battery module, and the number of battery cells contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.
图5是作为一个示例的电池模块4。参照图5，在电池模块4中，多个电池单体5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个电池单体5进行固定。FIG5 is a battery module 4 as an example. Referring to FIG5 , in the battery module 4, a plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.
可选地，电池模块4还可以包括具有容纳空间的外壳，多个电池单体5容纳于该容纳空间。Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.
在一些实施方式中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以为一个或多个，具体数量本领域技术人员可根据电池包的应用和容量进行选择。In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.
图6和图7是作为一个示例的电池包1。参照图6和图7，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。FIG6 and FIG7 are battery packs 1 as an example. Referring to FIG6 and FIG7 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be covered on the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.
另外，本申请还提供一种用电装置，所述用电装置包括本申请提供的二次电池。所述二次电池可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述用电装置可以包括移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能***等，但不限于此。In addition, the present application also provides an electric device, the electric device includes the secondary battery provided in the present application. The secondary battery can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.
作为所述用电装置，可以根据其使用需求来选择二次电池。As the electrical device, a secondary battery can be selected according to its usage requirements.
图8是作为一个示例的用电装置。该用电装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该用电装置对二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。FIG8 is an example of an electric device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module may be used.
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用二次电池作为电源。Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.
实施例Example
以下，说明本申请的实施例。下面描述的实施例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。实施例中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not indicate the manufacturer are all conventional products that can be obtained commercially.
实施例1Example 1
【正极活性材料的制备】【Preparation of positive electrode active materials】
步骤1：包覆Step 1: Wrapping
包覆层物质为Li 3InF xCl (6-x)。 The coating material is Li 3 InF x Cl (6-x) .
锂源：叔丁醇锂；氟源：氟代碳酸乙烯酯；氯源：氯代碳酸乙烯酯；金属In的源：三乙基铟Lithium source: lithium tert-butoxide; fluorine source: fluoroethylene carbonate; chlorine source: chloroethylene carbonate; metal In source: triethylindium
具体步骤如下：Specific steps are as follows:
将NCM 811正材本体材料的粉体放入流化床反应器中，对反应室抽真空并通入Ar气进行吹扫，控制气体流速使得正极本体材料能够分散。Place the powder of NCM 811 positive electrode bulk material into a fluidized bed reactor, evacuate the reaction chamber and introduce Ar gas for purge, and control the gas flow rate so that the positive electrode bulk material can be dispersed.
在将各源通入流化床反应器之前，将叔丁醇锂加热至165℃的温度，氟代碳酸乙烯酯和氯代碳酸乙烯酯保持在200℃的温度。设置叔丁醇锂的进样脉冲与两次进样脉冲之间的吹扫持续时间分别为1s和15s。设置氯代碳酸乙烯酯、氟代碳酸乙烯酯进样脉冲与两次进样脉冲之间的吹扫持续时间分别为0.1s和15s。沉积温度为200℃。按照氟源：氯源体积流量比为x:(6-x)比例改变氟源和氯源的进样脉冲时间 并在两次脉冲之间使用Ar气吹扫15s，每完成一次脉冲进样称为一个循环，共沉积20周，其中x从6均匀变成0，每一圈比例递减为6/20，即：Before each source is introduced into the fluidized bed reactor, lithium tert-butoxide is heated to 165°C, and fluoroethylene carbonate and chloroethylene carbonate are maintained at 200°C. The duration of the injection pulse of lithium tert-butoxide and the purge between two injection pulses are set to 1s and 15s, respectively. The duration of the injection pulse of chloroethylene carbonate and fluoroethylene carbonate and the purge between two injection pulses are set to 0.1s and 15s, respectively. The deposition temperature is 200°C. The injection pulse time of the fluorine source and the chlorine source is changed according to the ratio of the volume flow rate of the fluorine source: the chlorine source to x:(6-x) and Ar gas is used to purge for 15s between the two pulses. Each completed pulse injection is called a cycle, and 20 cycles of co-deposition are performed, in which x changes evenly from 6 to 0, and the ratio decreases to 6/20 in each cycle, that is:
沉积第一周时，x为6，按照Li 3InF 6的比例设置各源的脉冲时间， In the first cycle of deposition, x is 6, and the pulse time of each source is set according to the ratio of Li 3 InF 6 .
沉积第二周时，x为5.7，按照Li 3InF 5.7Cl 0.3的比例设置各源的脉冲时间，依次类推， In the second cycle of deposition, x is 5.7, and the pulse time of each source is set according to the ratio of Li 3 InF 5.7 Cl 0.3 , and so on.
沉积第20周时，x为0，按照Li 3InCl 6的比例设置各源的脉冲时间。 At the 20th deposition cycle, x is 0, and the pulse time of each source is set according to the ratio of Li 3 InCl 6 .
每一圈沉积0.1nm，完成包覆。之后，续继Ar气吹扫，清洗管路。得到包覆的正极活性材料。Each circle deposits 0.1nm to complete the coating. Afterwards, continue to purge with Ar gas to clean the pipeline to obtain the coated positive electrode active material.
步骤2：煅烧Step 2: Calcination
将步骤1中包覆好的正极活性材料转移至管式炉中，以氩气为保护气进行煅烧，煅烧温度260℃，煅烧时间4h，以确保外层包覆物具有更好的结晶度。The positive electrode active material coated in step 1 is transferred to a tubular furnace and calcined with argon as the protective gas at a calcination temperature of 260° C. for 4 h to ensure that the outer coating has better crystallinity.
制备得到包覆层厚度为2nm的正极活性材料。A positive electrode active material with a coating layer thickness of 2 nm was prepared.
图1为实施例1中所得正极活性材料的表面图，图2为图1中正极活性材料的局部放大图。图1中，大颗粒为正极本体材料NCM811，外面有一层包覆层，大视野看到正极颗粒被完全包覆，对包覆层进行放大(图2)可以发现包覆层均匀且致密，无漏包区域。Figure 1 is a surface image of the positive electrode active material obtained in Example 1, and Figure 2 is a partial enlarged image of the positive electrode active material in Figure 1. In Figure 1, the large particles are the positive electrode main material NCM811, which has a coating layer on the outside. The positive electrode particles are completely coated in a wide field of view. When the coating layer is enlarged (Figure 2), it can be found that the coating layer is uniform and dense, and there is no leaking area.
【正极极片的制备】【Preparation of positive electrode】
将前面步骤中制备的正极活性材料、导电剂碳黑、粘结剂聚偏二氟乙烯(PVDF)按重量比为90.0：5.0:5.0的量与N-甲基吡咯烷酮(NMP)搅拌混合均匀，得到正极浆料；之后将正极浆料均匀涂覆于正极集流体上，之后经过烘干、冷压、分切，得到正极极片。The positive electrode active material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) prepared in the previous step are stirred and mixed evenly with N-methylpyrrolidone (NMP) in a weight ratio of 90.0:5.0:5.0 to obtain a positive electrode slurry; then the positive electrode slurry is evenly coated on the positive electrode collector, and then dried, cold pressed, and cut to obtain a positive electrode sheet.
【负极极片的制备】【Preparation of negative electrode sheet】
将活性物质人造石墨、导电剂碳黑、粘结剂聚偏二氟乙烯(PVDF)按照重量比为96.0：2.0：2.0溶于溶剂去离子水中，混合均匀后制备成负极浆料；将负极浆料一次或多次均匀涂覆在负极集流体铜箔上，经过烘干、冷压、分切得到负极极片。The active material artificial graphite, the conductive agent carbon black, and the binder polyvinylidene fluoride (PVDF) are dissolved in the solvent deionized water in a weight ratio of 96.0:2.0:2.0, and the mixture is evenly mixed to prepare a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode collector copper foil once or multiple times, and the negative electrode sheet is obtained after drying, cold pressing, and slitting.
【电解液的制备】【Preparation of electrolyte】
在氩气气氛手套箱中(H 2O<0.1ppm，O 2<0.1ppm)，将有机溶剂碳酸乙烯酯(EC)/碳酸甲乙酯(EMC)按照体积比3/7混合均匀，加入12.5％LiPF6锂盐溶解于有机溶剂中，搅拌均匀，得到实施例1的电解液。 In an argon atmosphere glove box (H 2 O<0.1ppm, O 2 <0.1ppm), organic solvents ethylene carbonate (EC)/ethyl methyl carbonate (EMC) were mixed uniformly in a volume ratio of 3/7, 12.5% LiPF6 lithium salt was added and dissolved in the organic solvent, and stirred uniformly to obtain the electrolyte of Example 1.
【隔离膜】【Isolation film】
以商用聚丙烯膜作为隔离膜。Commercial polypropylene film was used as the isolation film.
【叠片锂离子电池的制备】【Preparation of laminated lithium-ion batteries】
将前面步骤中制备的负极极片51×43.5mm、隔膜53×46mm、正极极片49.5×42mm，按照顺序进行放置，叠片，采用铝塑膜进行封装，滴加电解液0.5g，抽真空后密封静置2h，上夹具，夹具力为0.4MPa,随后进行化成后，进行电池循环性能的测试。Place the negative electrode sheet of 51×43.5mm, the separator of 53×46mm, and the positive electrode sheet of 49.5×42mm prepared in the previous steps in order, stack them, and package them with aluminum-plastic film. Add 0.5g of electrolyte, evacuate and seal, let stand for 2h, clamp it with a clamp force of 0.4MPa, and then test the battery cycle performance after formation.
实施例2-5Embodiment 2-5
电池的制备与实施例1相同，不同之处在于包覆的厚度、F和Cl元素的变化梯度以及相应的循环圈数，详情参见下面的表格。The preparation of the battery is the same as that of Example 1, except for the coating thickness, the gradient of the F and Cl elements, and the corresponding number of cycles, as detailed in the table below.
实施例6Example 6
电池的制备与实施例1相同，不同之处在于F和Cl元素的变化梯度、每次沉积的厚度以及相应的循环圈数，详情参见下面的表格。The preparation of the battery is the same as that of Example 1, except for the change gradient of F and Cl elements, the thickness of each deposition and the corresponding number of cycles, as detailed in the table below.
实施例7Example 7
电池的制备与实施例1相同，不同之处在于包覆层物质为Li 3YF xCl (6-x)，其中金属Y的源为三(2,2,6,6-四甲基-3,5-庚二酮酸)钇，详情参见下面的表格。 The preparation of the battery is the same as that of Example 1, except that the coating material is Li 3 YF x Cl (6-x) , wherein the source of metal Y is yttrium tris(2,2,6,6-tetramethyl-3,5-heptanedione), see the table below for details.
实施例8Example 8
电池的制备与实施例1相同，不同之处在于包覆层物质为Li 3ScF xCl (6-x)，其中金属Sc的源为乙酸钪，详情参见下面的表格。 The preparation of the battery is the same as that of Example 1, except that the coating material is Li 3 ScF x Cl (6-x) , wherein the source of the metal Sc is scandium acetate, as shown in the table below.
实施例9Example 9
电池的制备与实施例1相同，不同之处在于包覆层物质为Li 3MnF xCl (6-x)，其中金属Mn的源为双(环戊二基)锰，详情参见下面的表格。 The preparation of the battery is the same as that of Example 1, except that the coating material is Li 3 MnF x Cl (6-x) , wherein the source of the metal Mn is bis(cyclopentanediyl)manganese, as shown in the table below.
实施例10Example 10
电池的制备与实施例1相同，不同之处在于包覆层物质为Li 3ZrF xCl (6-x)，其中金属Zr的源为乙酸锆，详情参见下面的表格。 The preparation of the battery is the same as that of Example 1, except that the coating material is Li 3 ZrF x Cl (6-x) , wherein the source of the metal Zr is zirconium acetate, as shown in the table below.
实施例11-13Examples 11-13
电池的制备与实施例1相同，不同之处在于F、Cl比例变化及变化梯度，详情参见下面的表格。The preparation of the battery is the same as that of Example 1, except that the ratio of F and Cl is changed and the gradient of the change. For details, see the table below.
实施例14-22Examples 14-22
电池的制备与实施例1相同，不同之处在于煅烧步骤中，煅烧温度和时间不同。详情参见下面的表格。The preparation of the battery is the same as in Example 1, except that in the calcination step, the calcination temperature and time are different. See the table below for details.
对比例1Comparative Example 1
电池的制备与实施例1相同，不同之处在于，不对正极本体材料NCM 811进行包覆，直接将其用于正极极片的制备。详情参见下面的表格。The preparation of the battery is the same as that of Example 1, except that the positive electrode bulk material NCM 811 is not coated and is directly used for the preparation of the positive electrode sheet. For details, see the table below.
对比例2Comparative Example 2
电池的制备与实施例1相同，不同之处在于，包覆层物质为Li 3InF 6，不含氯，且F元素无梯度变化。详情参见下面的表格。 The preparation of the battery is the same as that of Example 1, except that the coating material is Li 3 InF 6 , does not contain chlorine, and has no gradient change in the F element. See the table below for details.
对比例3Comparative Example 3
电池的制备与实施例1相同，不同之处在于，包覆层物质为Li 3InCl 6，不含氟，且Cl元素无梯度变化。详情参见下面的表格。 The preparation of the battery is the same as that of Example 1, except that the coating material is Li 3 InCl 6 , does not contain fluorine, and the Cl element has no gradient change. For details, see the table below.
对比例4Comparative Example 4
电池的制备与实施例1相同，不同之处在于，包覆层为两层，内层包覆层厚度为1nm，包覆物质为Li 3InF 6，外层包覆层厚度为1nm，包覆物质为Li 3InF 6，且F、Cl元素无梯度变化。详情参见下面的表格。 The preparation of the battery is the same as that of Example 1, except that the coating layer is two layers, the inner coating layer is 1 nm thick and the coating material is Li 3 InF 6 , the outer coating layer is 1 nm thick and the coating material is Li 3 InF 6 , and there is no gradient change in F and Cl elements. See the table below for details.
对比例5Comparative Example 5
电池的制备与实施例1相同，不同之处在于F元素、Cl元素含量变化与实施例1中的变化梯度相同但变化方向相反，即，F元素逐渐变大但氯元素逐渐变小。详情参见下面的表格。The preparation of the battery is the same as that of Example 1, except that the content of the F element and the Cl element changes in the same gradient as that in Example 1 but in the opposite direction, that is, the F element gradually increases but the Cl element gradually decreases. For details, see the table below.
对比例6Comparative Example 6
电池的制备与实施例1相同，不同之处在于不进行煅烧步骤。详情参见下面的表格。The preparation of the battery was the same as in Example 1, except that the calcination step was not performed. See the table below for details.
【正极活性材料的形貌测试】【Morphology test of positive electrode active materials】
本申请实施例和对比例的正极活性材料的形貌参数测试过程如下：The morphology parameter testing process of the positive electrode active materials of the present application examples and comparative examples is as follows:
使用ZEISS Gemini 360扫描电子显微镜，参照标准JY/T010-1996，对实施例1的正极活性材料的样品形貌进行观测，测试结果参见附图和2。The sample morphology of the positive electrode active material of Example 1 was observed using a ZEISS Gemini 360 scanning electron microscope in accordance with standard JY/T010-1996. The test results are shown in Figures 2 and 3.
这里需要指出的是，本申请中所使用的正极本体材料基体形状不一定是球形的，也有可能是无规则的，可以为一次颗粒也可以为二次颗粒。还需指出的是，本申请制得的经包覆的正极活性材料形状不一定是球形的，也有可能是无规则的。It should be noted that the shape of the cathode material matrix used in the present application is not necessarily spherical, but may be irregular, and may be primary particles or secondary particles. It should also be noted that the shape of the coated cathode active material prepared in the present application is not necessarily spherical, but may be irregular.
【电池性能测试】【Battery performance test】
1.电池容量保持率测试1. Battery capacity retention test
以实施例1为例，电池容量保持率测试过程如下：在25℃下，将实施例1对应的电池，以1/3C恒流充电至4.5V，再以4.5V恒定电压充电至电流为0.05C，搁置5min，再以1/3C放电至2.8V，所得容量记为初始容量C 0。对上述同一个电池重复以上步骤，并同时记录循环第n次后电池的放电容量C n，则每次循环后电池容量保持率P n＝C n/C 0×100％。表1中实施例1对应的电池容量保持率数据是在上述测试条件下循环100次之后测得的数据，即通过P 100＝C 100/C 0×100％得到的P 100的值。对比例以及其他实施例的测试过程同上。 Taking Example 1 as an example, the battery capacity retention rate test process is as follows: at 25°C, the battery corresponding to Example 1 is charged to 4.5V at a constant current of 1/3C, then charged to a current of 0.05C at a constant voltage of 4.5V, left for 5 minutes, and then discharged to 2.8V at 1/3C. The obtained capacity is recorded as the initial capacity C 0 . Repeat the above steps for the same battery, and record the discharge capacity C n of the battery after the nth cycle at the same time, then the battery capacity retention rate after each cycle is P n =C n /C 0 ×100%. The battery capacity retention rate data corresponding to Example 1 in Table 1 is the data measured after 100 cycles under the above test conditions, that is, the value of P 100 obtained by P 100 =C 100 /C 0 ×100%. The test process of the comparative example and other embodiments is the same as above.
2.电池交流阻抗测试2. Battery AC impedance test
以实施例1为例，将实施例1涂布得到的新鲜的正极极片、聚丙烯隔膜、电解液120μL，组装成正极的对称电池，在25℃恒温箱中静置2h保证电解液的浸润。采用电化学工作站阻抗测试模块进行交流阻抗测试，电压扰动模式PEIS，扰动电压5mV，频率范围：200kHZ～30mHZ，电压范围：0-5V，电压保护：0-5V。对阻抗测试数据进行拟合处理，过程如下：Taking Example 1 as an example, the fresh positive electrode sheet, polypropylene separator and 120 μL electrolyte obtained by coating Example 1 were assembled into a symmetrical battery with a positive electrode, and placed in a 25°C constant temperature box for 2 hours to ensure the infiltration of the electrolyte. The AC impedance test was performed using the electrochemical workstation impedance test module, voltage perturbation mode PEIS, perturbation voltage 5mV, frequency range: 200kHZ~30mHZ, voltage range: 0-5V, voltage protection: 0-5V. The impedance test data was fitted, and the process was as follows:
以实施例1为例，将实施例1的数据采用Z-fit软件进行数据拟合，选择拟合电路为R s+C 1/R SEI+C 2/R ct+W，其中R s是欧姆阻抗，主要与正极材质的导电性相关联；R ct是电荷转移阻抗，主要反映了正极材质中锂离子的脱嵌速率；C1为SEI与电解液界面双电层电容；R SEI为SEI膜电阻；C2为SEI与石墨界面双电层电容；W为韦伯阻抗。拟合的判断依据要求：误差小于5％，且与实部交点应与拟合得到R s的偏差<5％。满足以上要求的拟合结果才可选择被接纳，将拟合的结果中R ct与R s提取出，并记录在下面的表中。对比例以及其他实施例的处理数据的过程同上。 Taking Example 1 as an example, the data of Example 1 are fitted using Z-fit software, and the fitting circuit is selected as Rs + C1 / RSEI + C2 / Rct + W, where Rs is ohmic impedance, which is mainly related to the conductivity of the positive electrode material; Rct is charge transfer impedance, which mainly reflects the deintercalation rate of lithium ions in the positive electrode material; C1 is the double-layer capacitance of the SEI and electrolyte interface; RSEI is the SEI membrane resistance; C2 is the double-layer capacitance of the SEI and graphite interface; W is the Weber impedance. The judgment basis for fitting requires: the error is less than 5%, and the intersection with the real part should have a deviation of <5% from the Rs obtained by fitting. Only the fitting results that meet the above requirements can be selected to be accepted, and Rct and Rs in the fitting results are extracted and recorded in the following table. The process of processing data for the comparative example and other embodiments is the same as above.
Figure PCTCN2022123777-appb-000001
Figure PCTCN2022123777-appb-000001
Figure PCTCN2022123777-appb-000002
Figure PCTCN2022123777-appb-000002
需要说明的是，本申请不限定于上述实施方式。上述实施方式仅为示例，在本申请的技术方案范围内具有与技术思想实质相同的构成、发挥相同作用效果的实施方式均包含在本申请的技术范围内。此外，在不脱离本申请主旨的范围内，对实施方式施加本领域技术人员能够想到的各种变形、将实施方式中的一部分构成要素加以组合而构筑的其它方式也包含在本申请的范围内。It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims (12)

  1. 一种正极活性材料，其包括正极本体材料和包覆在所述正极本体材料表面的包覆层，其特征在于，所述包覆层由分子式为Li aMF xCl (a+n-x)的化合物组成，其中 A positive electrode active material, comprising a positive electrode main body material and a coating layer coated on the surface of the positive electrode main body material, characterized in that the coating layer is composed of a compound with a molecular formula of Li a MF x Cl (a+nx) , wherein
    1≤a≤3，0≤x≤a+n；n为M离子的价态，n在2-4范围内，1≤a≤3, 0≤x≤a+n; n is the valence state of M ion, n is in the range of 2-4,
    M选自元素In、Y、Sc、Er、Tb、Yb、Lu、Zr、Al、Ga、La、Ho、Ti、Nb中的一种或多种，M is selected from one or more of the elements In, Y, Sc, Er, Tb, Yb, Lu, Zr, Al, Ga, La, Ho, Ti, and Nb,
    其中，以所述正极本体材料表面为起点，随着向外延伸至包覆层的最外侧的方向上，F元素在分子式为Li aMF xCl (a+n-x)的化合物中的含量占比逐渐变小，Cl元素在分子式为Li aMF xCl (a+n-x)的化合物中的含量占比逐渐变大。 Wherein, starting from the surface of the positive electrode body material, as extending outward to the outermost direction of the coating layer, the content proportion of the F element in the compound with the molecular formula Li a MF x Cl (a+nx) gradually decreases, and the content proportion of the Cl element in the compound with the molecular formula Li a MF x Cl (a+nx) gradually increases.
  2. 根据权利要求1所述的正极活性材料，其特征在于，随着向外延伸至包覆层的最外侧的方向上，F元素的含量占比由大到小的变化梯度，即x从a+n→0的变化梯度，为(a+n)/(h/b)，其中h为包覆层厚度，b为发生梯度改变的最小厚度；其中，h在0-5nm范围内；b在0-0.5nm范围内。The positive electrode active material according to claim 1 is characterized in that, as it extends outward to the outermost direction of the coating layer, the content ratio of the F element changes from large to small, that is, the gradient of x from a+n→0 is (a+n)/(h/b), where h is the coating layer thickness and b is the minimum thickness for the gradient change; where h is in the range of 0-5nm; and b is in the range of 0-0.5nm.
  3. 根据权利要求1或2所述的正极活性材料，其特征在于，所述包覆层的材料选自Li 3InF xCl (6-x)、Li 3YF xCl (6-x)、Li 3ScF xCl (6-x)、Li 3MnF xCl (6-x)、Li 3ZrF xCl (6-x)中的至少一种，其中0≤x≤6。 The positive electrode active material according to claim 1 or 2, characterized in that the material of the coating layer is selected from at least one of Li3InFxCl (6-x) , Li3YFxCl ( 6-x) , Li3ScFxCl (6-x), Li3MnFxCl (6-x) , and Li3ZrFxCl ( 6-x) , wherein 0≤x≤6.
  4. 根据权利要求1-3中任一项所述的正极活性材料，其特征在于，所述正极活性材料的电化学窗口为5.0V以上，和/或，所述正极活性材料的锂离子电导率为10 -8-10 -3S/cm。 The positive electrode active material according to any one of claims 1 to 3, characterized in that the electrochemical window of the positive electrode active material is above 5.0 V, and/or the lithium ion conductivity of the positive electrode active material is 10 -8 -10 -3 S/cm.
  5. 根据权利要求1-4中任一项所述的正极活性材料，其特征在于，所述正极本体材料选自三元活性材料、磷酸铁锂、锰酸锂、钴酸锂中的至少一种。The positive electrode active material according to any one of claims 1 to 4, characterized in that the positive electrode body material is selected from at least one of a ternary active material, lithium iron phosphate, lithium manganese oxide, and lithium cobalt oxide.
  6. 一种正极活性材料的制备方法，其特征在于，所述方法包括包覆步骤，该步骤包括：A method for preparing a positive electrode active material, characterized in that the method includes a coating step, which includes:
    (1)制备或准备正极本体材料；(1) preparing or preparing positive electrode bulk material;
    (2)在惰性气氛下将Li aMF xCl (a+n-x)的源进行气化，可选地，所述气化温度为200-300℃；使气化的所述源在正极本体材料表面吸附沉积，以包覆所述正极本体材料，得到所述正极活性材料； (2) vaporizing a source of Li a MF x Cl (a+nx) under an inert atmosphere, optionally at a vaporization temperature of 200-300° C.; allowing the vaporized source to be adsorbed and deposited on the surface of the positive electrode bulk material to coat the positive electrode bulk material, thereby obtaining the positive electrode active material;
    其中，分子式Li aMF xCl (a+n-x)中， Among them, in the molecular formula Li a MF x Cl (a+nx) ,
    1≤a≤3，0≤x≤a+n；n为M离子的价态，n在2-4范围内，1≤a≤3, 0≤x≤a+n; n is the valence state of M ion, n is in the range of 2-4,
    M选自元素In、Y、Sc、Er、Tb、Yb、Lu、Zr、Al、Ga、La、Ho、Ti、Nb中的一种或多种，M is selected from one or more of the elements In, Y, Sc, Er, Tb, Yb, Lu, Zr, Al, Ga, La, Ho, Ti, and Nb,
    其中，以所述正极本体材料表面为起点，随着向外延伸至包覆层的最外侧的方向上，F元素在分子式为Li aMF xCl (a+n-x)的化合物中的含量占比逐渐变小，Cl元素在分子式为Li aMF xCl (a+n-x)的化合物中的含量占比逐渐变大。 Wherein, starting from the surface of the positive electrode body material, as extending outward to the outermost direction of the coating layer, the content proportion of the F element in the compound with the molecular formula Li a MF x Cl (a+nx) gradually decreases, and the content proportion of the Cl element in the compound with the molecular formula Li a MF x Cl (a+nx) gradually increases.
  7. 根据权利要求6所述的正极活性材料的制备方法，其特征在于，所述使气化的所述源在正极本体材料表面吸附沉积的方法为原子沉积法，可选地，所述沉积次数为m，m范围为1-100。The method for preparing a positive electrode active material according to claim 6 is characterized in that the method for adsorbing and depositing the vaporized source on the surface of the positive electrode body material is an atomic deposition method, and optionally, the number of depositions is m, and m ranges from 1 to 100.
  8. 根据权利要求6或7所述的正极活性材料的制备方法，其特征在于，所述Li aMF xCl (a+n-x)的源包括锂源、M源、氟源、氯源，其中，所述各源的沸点介于70-300℃之间； The method for preparing a positive electrode active material according to claim 6 or 7, characterized in that the source of Li a MF x Cl (a+nx) comprises a lithium source, an M source, a fluorine source, and a chlorine source, wherein the boiling point of each source is between 70-300° C.;
    可选地，锂源包括卤化锂，烷基锂、羧酸锂、醇锂、酯锂中的一种或多种；Optionally, the lithium source includes one or more of lithium halide, alkyl lithium, lithium carboxylate, lithium alkoxide, and lithium ester;
    可选地，M源包括M元素的烷基金属、羧酸金属、醇金属、酯金属中的一种或多种；Optionally, the M source includes one or more of an alkyl metal, a carboxylic acid metal, an alcohol metal, and an ester metal of the M element;
    可选地，氟源包括氟代烷烃、氟代羧酸、氟代醇和氟代酯中的一种或多种；Optionally, the fluorine source includes one or more of fluorinated alkanes, fluorinated carboxylic acids, fluorinated alcohols, and fluorinated esters;
    可选地，氯源包括氯代烷烃、氯代羧酸、氯代醇和氯代酯中的一种或多种。Optionally, the chlorine source comprises one or more of chlorinated alkanes, chlorinated carboxylic acids, chlorinated alcohols, and chlorinated esters.
  9. 根据权利要求6-8中任一项所述的正极活性材料的制备方法，其特征在于，在所述包覆步骤之后，对所得的已经包覆的正极活性材料进行煅烧，可选地，煅烧温度为150-300℃，煅烧时间为4-20h。The method for preparing a positive electrode active material according to any one of claims 6 to 8 is characterized in that, after the coating step, the obtained coated positive electrode active material is calcined, and optionally, the calcination temperature is 150-300° C. and the calcination time is 4-20 h.
  10. 一种二次电池，其包括权利要求1-5所述的正极活性材料或由权利要求6-9中任一项所述的方法制备的正极活性材料。A secondary battery comprising the positive electrode active material according to any one of claims 1 to 5 or the positive electrode active material prepared by the method according to any one of claims 6 to 9.
  11. 根据权利要求10所述的二次电池，其特征在于，所述二次电池包括电解液，所述电解液包括六氟磷酸锂和/或高氯酸锂。The secondary battery according to claim 10 is characterized in that the secondary battery comprises an electrolyte, and the electrolyte comprises lithium hexafluorophosphate and/or lithium perchlorate.
  12. 一种用电装置，其特征在于，包括权利要求10或11所述的二次电池。An electrical device, characterized by comprising the secondary battery according to claim 10 or 11.
PCT/CN2022/123777 2022-10-08 2022-10-08 Positive electrode active material and preparation therefor, positive electrode sheet, and secondary battery WO2024073883A1 (en)

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