WO2023093589A1 - 锂二次电池 - Google Patents

锂二次电池 Download PDF

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WO2023093589A1
WO2023093589A1 PCT/CN2022/132225 CN2022132225W WO2023093589A1 WO 2023093589 A1 WO2023093589 A1 WO 2023093589A1 CN 2022132225 W CN2022132225 W CN 2022132225W WO 2023093589 A1 WO2023093589 A1 WO 2023093589A1
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Prior art keywords
secondary battery
lithium secondary
battery
metal element
battery according
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PCT/CN2022/132225
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English (en)
French (fr)
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钱韫娴
刘中波
邓永红
王勇
黄雄
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深圳新宙邦科技股份有限公司
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Publication of WO2023093589A1 publication Critical patent/WO2023093589A1/zh

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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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • 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 invention belongs to the technical field of energy storage battery devices, and in particular relates to a lithium secondary battery.
  • lithium-ion batteries Due to the advantages of high working voltage, wide working temperature range, high energy density and power density, no memory effect and long cycle life, lithium-ion batteries have been widely used in the field of 3C digital products such as mobile phones and notebook computers, as well as in the field of new energy vehicles. Applications. In recent years, with the continuous development of thinner and thinner 3C digital products, the battery industry has higher and higher requirements for high energy density of lithium-ion batteries. Therefore, there is an urgent need to increase the energy density of lithium-ion batteries.
  • surface coating modification is an important means to improve the performance of cathode materials for lithium-ion batteries.
  • the surface coating material can effectively reduce the corrosion of the positive electrode by the electrolyte and reduce the dissolution of metal ions.
  • the surface coating material can also physically isolate the contact between the electrolyte and the positive surface active material.
  • positive electrode surface coating materials such as alumina
  • the invention provides a lithium secondary battery.
  • the invention provides a lithium secondary battery, comprising a positive pole, a negative pole and a non-aqueous electrolyte, the positive pole comprises a positive electrode material layer, the positive pole material layer comprises a positive pole active material, and the positive pole active material comprises LiCoO2 and doped or a coated compound containing a first metal element and a second metal element;
  • the first metal element includes at least one of Mg, Al and W;
  • the second metal element includes at least one of Ti, Cr, Zr, Mo, La, Ce and rare earth elements;
  • Described non-aqueous electrolytic solution comprises the compound shown in lithium salt, organic solvent and structural formula 1:
  • R 1 is selected from unsaturated hydrocarbon groups with 3-6 carbon atoms
  • the lithium secondary battery satisfies the following conditions:
  • a is the mass percentage of the compound shown in structural formula 1 in the non-aqueous electrolyte, and the unit is wt%;
  • b is the doping amount or coating amount of the first metal element relative to the quality of LiCoO2 , the unit is wt%
  • c is the doping amount or covering amount of the second metal element relative to the mass of LiCoO 2 , and the unit is wt%.
  • the lithium secondary battery satisfies the following conditions:
  • the compound represented by the structural formula 1 is selected from one or more of the following compounds:
  • the mass percentage a of the compound represented by the structural formula 1 in the non-aqueous electrolyte is 0.1 to 5 wt %; preferably, the mass percentage of the compound represented by the structural formula 1 in the non-aqueous electrolyte in the lithium secondary battery is The component content a is 0.1 to 2 wt%.
  • the doping amount or coating amount b of the first metal element relative to the mass of LiCoO2 is 0.1 to 1.2 wt %; preferably, the doping amount or coating amount of the first metal element relative to the mass of LiCoO2 b is 0.5 to 0.8 wt%.
  • the doping amount or coating amount c of the second metal element relative to the LiCoO2 mass is 0.001-0.1 wt %; preferably, the doping amount or coating amount c of the second metal element relative to the LiCoO2 mass c is 0.005 to 0.05 wt%.
  • the charging cut-off voltage of the lithium secondary battery is greater than or equal to 4.45V.
  • the compacted density of the positive electrode material layer is greater than or equal to 3.8g/cm 3 ; preferably, the compacted density of the positive electrode material layer is 3.9g/cm 3 -4.15g/cm 3 ;
  • the compacted density of the negative electrode material layer is greater than or equal to 1.6g/cm 3 ; preferably, the compacted density of the negative electrode material layer is 1.65g/cm 3 -1.8g/cm 3 ;
  • the lithium salt is selected from LiPF 6 , LiPO 2 F 2 , LiBF 4 , LiBOB, LiClO 4 , LiCF 3 SO 3 , LiDFOB, LiN(SO 2 CF 3 ) 2 and LiN(SO 2 F) 2 one or more;
  • the concentration of the lithium salt in the non-aqueous electrolytic solution is 0.5-3.5 mol/L.
  • the non-aqueous electrolyte also contains auxiliary additives, the auxiliary additives are cyclic sulfate compounds, sultone compounds, cyclic carbonate compounds, unsaturated phosphate compounds and nitriles at least one of the compounds;
  • the amount of the auxiliary additive added is 0.01%-30%.
  • cyclic sulfate ester compound is selected from at least one of vinyl sulfate, propylene sulfate or vinyl methyl sulfate;
  • the sultone compound is selected from at least one of 1,3-propane sultone, 1,4-butane sultone or 1,3-propene sultone;
  • the cyclic carbonate compound is selected from at least one of vinylene carbonate, ethylene carbonate, fluoroethylene carbonate or the compound shown in structural formula 2,
  • R 21 , R 22 , R 23 , R 24 , R 25 , and R 26 are each independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group;
  • the unsaturated phosphate compound is selected from at least one of the compounds shown in structural formula 3:
  • R 31 , R 32 , and R 33 are each independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halogenated hydrocarbon groups, -Si(C m H 2m+1 ) 3 , m is 1 to A natural number of 3, and at least one of R 31 , R 32 , and R 33 is an unsaturated hydrocarbon group;
  • nitrile compound comprises succinonitrile, glutaronitrile, ethylene glycol two (propionitrile) ether, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelanitrile, sebaconitrile one or more.
  • the doping amount or coating amount of the first metal and the second metal element doped or coated on the surface of the positive electrode active material is closely related to the content of the compound shown in structural formula 1 in the electrolyte.
  • 0.05 ⁇ a ⁇ (b+c) ⁇ 3 it can effectively inhibit the dissolution of cobalt ions and repair the damage to the SEI film of the negative electrode caused by the cobalt ions dissolved in the positive electrode.
  • the doping amount or coating of the first metal element and the second metal element While stabilizing the high-voltage characteristics of the LiCoO 2 positive electrode active material, it can also slow down the transmission problem of lithium ions during the battery charge and discharge cycle, reduce the battery impedance and battery polarization, so that the battery has a higher energy density. At the same time, it has good high temperature cycle performance.
  • An embodiment of the present invention provides a lithium secondary battery, including a positive electrode, a negative electrode, and a non-aqueous electrolyte, the positive electrode includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, and the positive electrode active material includes LiCoO2 and Doped or clad compounds containing a first metal element and a second metal element;
  • the first metal element includes at least one of Mg, Al, Zr, and W;
  • the second metal element includes at least one of Ti, Cr, Mo, and rare earth elements
  • the negative pole includes a negative electrode material layer;
  • the non-aqueous electrolytic solution includes a lithium salt, an organic solvent and a compound shown in structural formula 1:
  • R 1 is selected from unsaturated hydrocarbon groups with 3-6 carbon atoms
  • R 2 is selected from alkylene groups with 2-5 carbon atoms
  • n is 1 or 2;
  • the lithium secondary battery satisfies the following conditions:
  • a is the mass percentage of the compound shown in structural formula 1 in the non-aqueous electrolyte, and the unit is wt%;
  • b is the doping amount or coating amount of the first metal element relative to the quality of LiCoO2 , the unit is wt%
  • c is the doping amount or covering amount of the second metal element relative to the mass of LiCoO 2 , and the unit is wt%.
  • the LiCoO2 positive electrode of the lithium secondary battery is doped or coated with metal elements such as Mg, Al, W, Ti, Cr, Zr, Mo, La, Ce and rare earth elements, compared to those without Doped or coated LiCoO 2 positive electrode, Mg, Al, W and other elements improve the stability of LiCoO 2 positive electrode at high temperature and high pressure, Ti, Cr, Zr, Mo, La, Ce and rare earth elements due to the sintering process Slow diffusion kinetics form a unique layered distribution, which is mainly enriched on the top surface and can form strong ionic bonds with oxygen ions, thereby inhibiting the loss of surface oxygen and further improving the high-pressure structural stability of positive electrode active material particles containing cobalt and lithium compounds sex.
  • metal elements such as Mg, Al, W, Ti, Cr, Zr, Mo, La, Ce and rare earth elements
  • the coated metal elements that are not electrochemically active inhibit the transmission of lithium ions at the interface of the positive electrode, resulting in an increase in the impedance of the positive electrode, which is not conducive to the long-term cycle of the lithium secondary battery.
  • the non-aqueous electrolyte of the lithium secondary battery of the present invention contains the substance shown in structural formula 1, and its mechanism of action is not very clear, but the inventor speculates that it is because it can effectively complex on the surface of the positive electrode and inhibit the dissolution of cobalt ions At the same time, due to its special structure, it can effectively repair the damage to the SEI film of the negative electrode caused by the cobalt ions dissolved in the positive electrode, thereby effectively inhibiting the impedance growth of the battery during high temperature and high pressure cycling.
  • the amount of doping and coating of the positive electrode material can be appropriately reduced, thereby indirectly reducing the amount of non-electrochemically active metal elements, alleviating the problem of inhibiting lithium ion conduction caused by it, thereby improving the high-temperature and high-pressure cycle performance of the battery, but the structural formula 1 shows If the compound is used in too much amount, the battery performance will be deteriorated due to too high viscosity.
  • the doping amount or coating amount of the first metal and the second metal element doped or coated on the surface of the positive electrode active material and the content of the compound shown in the structural formula 1 in the electrolyte satisfy 0.05 ⁇ a
  • the compound represented by structural formula 1 in the electrolyte can effectively inhibit the dissolution of cobalt ions and repair the damage of the dissolved cobalt ions to the negative electrode SEI film, while the doping of the first and second metal elements While stabilizing the high-voltage characteristics of the positive electrode active material, the amount or coating amount can also slow down the transmission problem of lithium ions during the battery charge and discharge cycle, reduce the battery impedance and battery polarization, so that the battery can have a better performance. High temperature cycle performance.
  • the lithium secondary battery meets the following conditions:
  • the content of the compound shown in the non-aqueous electrolyte structural formula 1 is combined with the content of the first metal element and the second metal element on the surface of the positive electrode active material in the lithium secondary battery.
  • the doping amount or coating amount of the compound is related, and to a certain extent, the effects of the first metal element, the second metal element, and the compound shown in structural formula 1 on the battery performance can be integrated, that is, to weaken the battery polarization, reduce the battery impedance, and slow down the battery performance.
  • the battery decomposes lithium, so that the battery can have better high-temperature cycle performance.
  • the compound represented by the structural formula 1 is selected from one or more of the following compounds:
  • the doping amount or coating amount b of the first metal element relative to the mass of LiCoO 2 is 0.1-1.2 wt%.
  • the doping amount or coating amount b of the first metal element relative to the mass of LiCoO 2 is 0.5-0.8 wt%.
  • the doping amount or coating amount c of the second metal element relative to the mass of LiCoO 2 is 0.001-0.1 wt%.
  • the doping amount or coating amount c of the second metal element relative to the mass of LiCoO 2 is 0.005-0.05 wt%.
  • Doping or coating the compound containing the first metal element and the second metal element on the surface of the positive electrode active material LiCoO2 can effectively increase the battery voltage, but doping or coating excessive metal elements hinders the lithium in the positive electrode active material. Embedding or protruding, thereby reducing the battery capacity and increasing the impedance of the battery.
  • the inventor found that the doping amount or coating amount b of the first metal element relative to the LiCoO2 mass in the positive electrode material layer reaches 0.1-1.2 wt%, and the doping amount or coating amount b of the second metal element relative to the LiCoO2 mass When the coating amount c reaches 0.001-0.1wt%, the first metal element, the second metal element and the compound shown in the structural formula 1 in the electrolyte cooperate with each other, which can not only effectively increase the battery voltage, but also alleviate the inhibition of lithium ions in the positive electrode active material. transmission.
  • the mass percentage a of the compound represented by structural formula 1 in the non-aqueous electrolyte is 0.1-5 wt%.
  • the mass percentage a of the compound represented by structural formula 1 in the non-aqueous electrolyte is 0.1-2 wt%.
  • the positive electrode active material contains lithium cobaltate compound so that the lithium secondary battery has better rate performance, but when the mass percentage of Co element in the positive electrode material layer is too large, it is easy to cause the positive electrode active material to be separated from the non-aqueous material under high voltage conditions.
  • the reaction of the electrolyte leads to the dissolution of the Co element, and the addition of the compound shown in Structural Formula 1 can effectively inhibit the reaction between the non-aqueous electrolyte and the positive active material, thereby inhibiting the dissolution of the Co element in the positive active material, but as shown in Structural Formula 1
  • the addition amount of the compound should not be too large, the initial impedance of the SEI film formed on the negative electrode of the battery is relatively large, which will cause the battery impedance to increase, and excessive addition of the compound shown in structural formula 1 will increase the viscosity of the electrolyte and reduce the conductance, thereby It is not conducive to the cycle performance of the battery.
  • the above analysis is only based on the impact of each parameter or multiple parameters on the battery alone, but in the actual battery application process, the above three parameters are interrelated and inseparable.
  • the relational formula given by the present invention relates the three, and the three affect the electrochemical performance of the battery together, so the mass percentage content a of the compound shown in structural formula 1, the first metal element in the positive electrode material layer relative to the LiCoO quality ratio is adjusted.
  • the doping amount or coating amount b, the doping amount or coating amount c of the second metal element in the positive electrode material layer relative to the quality of LiCoO2 , so that 0.05 ⁇ a ⁇ (b+c) ⁇ 3, can guarantee lithium secondary While the battery has high stable voltage characteristics, it can also improve the high-temperature cycle performance of the battery; beyond the above-mentioned range, the battery will experience kinetic deterioration, which will shorten the cycle life of the battery under high-temperature conditions, and even fail.
  • the charging cut-off voltage of the lithium secondary battery is greater than or equal to 4.45V.
  • the positive electrode of the battery of the present invention is doped or coated with a metal element that isolates the contact between the electrolyte and the surface active material of the positive electrode, and the compound shown in structural formula 1 is added to the electrolyte, and the two cooperate to make the battery charge cut-off voltage Greater than or equal to 4.45V, meeting the demand for high energy density of lithium-ion batteries.
  • the compacted density of the positive electrode material layer is greater than or equal to 3.8g/cm 3 ; preferably, the compacted density of the positive electrode material layer is 3.9g/cm 3 -4.15g/cm 3 ;
  • the compacted density of the negative electrode material layer is greater than or equal to 1.6g/cm 3 ; preferably, the compacted density of the negative electrode material layer is 1.65g/cm 3 -1.8g/cm 3 ;
  • the porosity of the positive electrode material layer and the negative electrode material layer is less than or equal to 50%; preferably, the porosity of the positive electrode material layer and the negative electrode material layer is 10%-35%.
  • the compaction density of the positive electrode material layer and the compaction density of the negative electrode material layer have a certain influence on the electrical performance of the secondary battery.
  • the compaction density of the positive electrode material layer in general, the compaction density of the positive electrode material layer is too low, and the positive electrode material is easy to fall off during the preparation of the electrode sheet, which affects the consistency of the overall battery capacity; if the compaction density of the positive electrode material layer If the temperature is too high, the strip is easy to be broken during the preparation of the pole piece, and the process problems will occur, which will reduce the production efficiency.
  • it will be difficult for lithium ions to come out, which will increase the battery impedance, reduce the battery capacity, and decrease the battery cycle performance.
  • the compaction density of the negative electrode material layer in general, if the compaction density of the negative electrode material layer is too low, process abnormalities such as powder drop are more likely to occur during the preparation of the electrode sheet, which reduces production efficiency; if the compaction density of the negative electrode material layer is too large , not only affects the immersion of the electrolyte, but also affects the embedding of the electrolyte, reduces the battery capacity, increases the lithium precipitation of the battery, and reduces the safety performance of the battery.
  • the larger the porosity of the positive and negative electrode material layers the more conducive to the extraction or insertion of lithium ions, but if the porosity is too large, the volume of the battery will increase and the energy density of the battery will decrease.
  • the compacted density of the positive electrode material layer, the compacted density of the negative electrode material layer, the porosity of the positive electrode material layer and the negative electrode material layer are related to the compound of the electrolyte structural formula 1, after adding the compound shown in the structural formula 1 in the non-aqueous electrolyte, Changes in its ionic conductivity and viscosity will affect the permeability of the non-aqueous electrolyte to the positive and negative material layers, thereby affecting the intercalation and extraction efficiency of lithium ions; while the compaction density of the positive and negative material layers also affects The density of the SEI film formed by the decomposition of the compound represented by structural formula 1 on the surface of the negative electrode material layer affects the protective effect of the SEI film on free Co.
  • the lithium salt in the non-aqueous electrolyte is LiPF 6 , LiPO 2 F 2 , LiBF 4 , LiBOB, LiClO 4 , LiCF 3 SO 3 , LiDFOB, LiN(SO 2 CF 3 ) 2 and LiN One or more of (SO 2 F) 2 , in a preferred embodiment, the lithium salt is LiPF 6 .
  • the lithium salt contains lithium ions, which are beneficial to the electrochemical response of the battery during the charging and discharging process of the battery, supplementing the consumption of a small amount of lithium ions, and promoting the cycle performance of the battery.
  • the conductivity of the non-aqueous electrolyte solution at 25° C. is greater than or equal to 6 mS/cm.
  • the conductivity of the non-aqueous electrolyte has a certain influence on the cycle performance and storage performance of lithium secondary batteries. After a lot of research, the inventor found that when the conductivity of the non-aqueous electrolyte is low at room temperature, the conductivity in the electrolyte is low, the ion transmission rate is reduced, and the concentration polarization increases during the charging and discharging of the lithium secondary battery. Impedance also increases, reducing the cycle performance and storage performance of the battery.
  • the concentration of the lithium salt in the non-aqueous electrolyte is 0.5-3.5mol/L; in a preferred embodiment, the concentration of the lithium salt in the non-aqueous electrolyte is 0.8- 2.0mol/L.
  • the concentration of lithium salt is too low, and the concentration polarization increases in the electrochemical reaction of the battery, which is not conducive to the electrochemical reaction of the battery;
  • the ion transport efficiency of the compound affects the compound shown in structural formula 1 to repair the damage of the dissolved cobalt ion to the SEI film of the negative electrode, and inhibits the reduction of the dissolution efficiency of the cobalt ion.
  • the organic solvent in the non-aqueous electrolyte is one or more of cyclic carbonates, linear carbonates, carboxylates and ethers; preferably, the cyclic carbonates include One or more of vinylene carbonate, propylene carbonate and ethylene carbonate; preferably, the linear carbonate includes one or more of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate species; preferably, the carboxylic acid esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethyl acetate and trimethyl One or more of ethyl acetate; preferably, the ethers include ethylene glycol dimethyl ether, 1,3-dioxolane and 1,1,2,2-tetrafluoroethyl-2, One or more of 2,3,3-tetrafluoropropyl ether.
  • the non-aqueous electrolyte also contains auxiliary additives, and the auxiliary additives are cyclic sulfate compounds, sultone compounds, cyclic carbonate compounds, unsaturated phosphate compounds and at least one of nitrile compounds.
  • the cyclic sulfate ester compound is selected from at least one of vinyl sulfate, propylene sulfate or vinyl methyl sulfate;
  • the cyclic carbonate compounds include but are not limited to cyclic carbonate compounds with fluorine atoms, such as fluoroethylene carbonate and/or bisfluoroethylene carbonate; preferably, the cyclic carbonate compounds include But not limited to the cyclic carbonate compound of carbon-carbon unsaturated bond, for example, it can be vinylene carbonate, vinyl ethylene carbonate, vinyl ethylene carbonate, methyl vinylene carbonate or the compound shown in structural formula 2 one or more of
  • R 21 , R 22 , R 23 , R 24 , R 25 , and R 26 are each independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group.
  • the unsaturated phosphate compound is selected from at least one of the compounds shown in structural formula 3:
  • R 31 , R 32 , and R 33 are each independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halogenated hydrocarbon groups, -Si(C m H 2m+1 ) 3 , m is 1 to 3, and at least one of R 31 , R 32 , and R 33 is an unsaturated hydrocarbon group.
  • the unsaturated phosphoric acid ester compound may be tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, Dipropargyl trifluoromethyl phosphate, Dipropargyl-2,2,2-trifluoroethyl phosphate, Dipropargyl-3,3,3-trifluoropropyl phosphate, Dipropargyl Hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl Phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, diallyl hexafluoroisopropyl phosphate at least one of the
  • the sultone compounds include but are not limited to cyclic sulfonate compounds, such as 1,3-propane sultone, propylene sulfite, 1,4-butane sultone or at least one of 1,3-propene sultone;
  • the nitrile compound can be but not limited to succinonitrile, adiponitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azela One or more of nitrile and sebaconitrile.
  • the addition amount of any optional substance in the auxiliary additive in the non-aqueous electrolyte is 0.05-10%, preferably, the addition amount is 0.1-5%, More preferably, the added amount is 0.1% to 3%.
  • the addition amount of any optional substance in the auxiliary additive can be 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2% %, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5%, 10%.
  • the auxiliary additive is selected from fluoroethylene carbonate, based on 100% of the total mass of the non-aqueous electrolyte, the added amount of the fluoroethylene carbonate is 0.05%-30%.
  • the content of the auxiliary additive of the non-aqueous electrolyte is set in this range, which can avoid the decrease of the electrical conductivity due to the decrease of the dielectric constant of the non-aqueous electrolyte, and it is easy to make the high-current discharge characteristics of the non-aqueous electrolyte battery and the stability of the negative electrode ,
  • the cycle characteristics reach a good range; it can improve the oxidation/reduction resistance of the non-aqueous electrolyte, thereby helping to improve the stability of the battery during high-temperature cycle and high-temperature storage.
  • the compound shown in structural formula 1 when added together with the auxiliary additive, it shows obvious synergy in improving the high-temperature storage performance of the battery.
  • the promotion effect shows that the compound shown in structural formula 1 and the auxiliary additive can form a film together on the electrode surface to make up for the film-forming defect of a single addition, and obtain a more stable passivation film under high temperature conditions.
  • the positive electrode active material is lithium cobaltate as an example
  • the negative electrode active material is graphite as an example. The following steps are included:
  • the positive electrode active material is LiCoO 2
  • the positive electrode active material is doped or coated with the doping amount or coating amount of the first metal element is b
  • the positive electrode active material is doped or coated with the doping amount or coating amount of the second metal element is c
  • the values of b and c refer to each table, disperse the surface-doped or coated positive electrode active material LiCoO 2 , the conductive agent and the binder PVDF into the solvent NMP and mix them uniformly to obtain the positive electrode slurry
  • the positive electrode The slurry is uniformly coated on the aluminum foil of the positive electrode current collector, and after drying, rolling, and cutting, the positive electrode sheet is obtained.
  • the compacted density of the obtained positive electrode sheet is 4.1g/cm 3
  • the positive electrode active material, conductive carbon black And the mass ratio of binder PVDF is 96:2:2.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • the positive electrode sheet, separator and negative electrode sheet are laminated in sequence, and then the top and side sealing, injection of a certain amount of electrolyte and other processes are performed to make a soft pack battery.
  • High temperature cycle performance test At 45°C, charge the formed battery to the cut-off voltage with 1C constant current and constant voltage, then charge it at constant voltage until the current drops to 0.05C, and then discharge it at 1C constant current to 4.45V , so cycle 500 times, record the first discharge capacity and the last discharge capacity.
  • Capacity retention ratio last discharge capacity / first discharge capacity ⁇ 100%.
  • Battery internal resistance growth rate after 500 cycles of high-temperature cycle (battery internal resistance after the last full charge of the battery - internal resistance of the first fully charged battery) / internal resistance of the first full charge of the battery ⁇ 100%.
  • the improvement rate of high-temperature cycle performance and the suppression effect of internal resistance growth rate are far lower than the effect when the battery satisfies the preset relationship 0.05 ⁇ a ⁇ (b+c) ⁇ 3, This may be because the content of the compound shown in structural formula 1 in the electrolyte is relatively high, which easily increases the viscosity of the electrolyte and reduces the conductance, which is not conducive to the cycle performance of the battery.
  • the high content of the first metal element and the second metal element in the positive electrode hinder the insertion and extraction of lithium in the positive electrode active material, the battery impedance increases significantly, and the high temperature cycle performance of the battery is not good.
  • the above-mentioned additives PS (1,3-propane sultone), VC (ethylene carbonate), DTD (sulfuric acid) were added to the non-aqueous electrolyte Vinyl ester) or FEC (fluoroethylene carbonate), can further improve the high-temperature cycle performance of the battery, and reduce the growth of thermal internal resistance.

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Abstract

为克服现有高压电池高温循环性能差，本发明提供了一种锂二次电池，包括正极、负极以及非水电解液，其中正极活性材料表面掺杂或包覆有含第一金属元素和第二金属元素的化合物，非水电解液包括溶剂、电解质盐和结构式1所示的化合物：其中，R 1选自碳原子数为3-6的不饱和烃基，R 2选自碳原子数为2-5的亚烃基，n＝1或2；所述锂二次电池满足以下条件： 0.05≤a×(b+c)≤3；本发明提供的锂二次电池，电解液中结构式1所示的化合物可以有效抑制钴离子溶出并修复已溶出的钴离子对负极SEI膜的破坏，又能减缓掺杂金属元素带来的电池充放电循环过程中锂离子的传输问题，降低电池阻抗、电池极化，减缓电池析锂，从而使得电池能够有较好的高温循环性能。

Description

锂二次电池 技术领域
本发明属于储能电池器件技术领域，具体涉及一种锂二次电池。
背景技术
锂离子电池因具有工作电压高、工作温度范围广、能量密度和功率密度大、无记忆效应和循环寿命长等优点，在手机、笔记本电脑等3C数码产品领域以及新能源汽车领域都得到了广泛的应用。近年来，随着3C数码产品轻薄化的不断发展，电池行业对锂离子电池高能量密度化的要求也越来越高。因此亟需提升锂离子电池的能量密度。
目前提高电池能量密度的方法主要有两种，一是提高正极充电截止电压，二是对电极的活性物质层进行加压来实现高密度化。但是，提高正极充电截止电压以后，正极的活性会进一步提高，正极和电解液之间的副反应也会随之加剧，会导致正极过渡金属离子溶出，从而造成电池高温性能劣化。另外，采用高压实的电极时，由于高压实电极的孔隙率低，电池的保液量也会降低，使电解液在低孔隙率极片界面渗透困难，进而使电解液与电极之间的接触内阻增大，在长期循环过程中，充放电极化变大，造成因出现析锂而突然跳水的情况。因此，如何改善高电压、高压实锂离子电池的长期循环性能是一项行业难题，需要从电极材料、电解液等各个层面进行改进。
正极材料方面，表面包覆改性是改善锂离子电池正极材料性能的重要手段。表面包覆材料可以有效减少电解液对正极的腐蚀，降低金属离子的溶出。与此同时，表面包覆材料也可以从物理空间上隔绝电解液与正极表面活性材料的接触。然而在使用正极表面包覆材料例如氧化铝等的情况中，存在的问题在于，包覆的不具备电化学活性的金属氧化物抑制了锂离子在正极界面的传输，导致阻抗增大，不利于锂离子电池的长期循环。
电解液方面目前尚无良好的解决办法。所以，对于高电压高压实的高能量密度电池，从电解液角度保证电池长期循环性能，并且保证循环后期不析锂是高电压高压实锂离子电池的一大难题。
发明内容
针对现有技术中高电压高压实锂离子电池高温循环性能差、阻抗增长的问题，本发明提供一种锂二次电池。
本发明解决上述技术问题所采用的技术方案如下：
本发明提供了一种锂二次电池，包括正极、负极以及非水电解液，所述正极包括正极材料层，所述正极材料层包括正极活性材料，所述正极活性材料包括LiCoO 2以及掺杂或包覆的含第一金属元素和第二金属元素的化合物；
所述第一金属元素包括Mg、Al和W中的至少一种；
所述第二金属元素包括Ti、Cr、Zr、Mo、La、Ce及稀土元素中的至少一种；
所述非水电解液包括锂盐、有机溶剂和结构式1所示的化合物：
Figure PCTCN2022132225-appb-000001
其中，R 1选自碳原子数为3-6的不饱和烃基，R 2选自碳原子数为2-5的亚烃基，n＝1或2；
所述锂二次电池满足以下条件：
0.05≤a×(b+c)≤3；
其中，a为非水电解液中结构式1所示的化合物的质量百分含量，单位为wt％；
b为第一金属元素相对LiCoO 2质量的掺杂量或包覆量，单位为wt％，
c为第二金属元素相对LiCoO 2质量的掺杂量或包覆量，单位为wt％。
进一步的，所述锂二次电池满足以下条件：
0.08≤a×(b+c)≤2。
进一步的，所述结构式1所示的化合物选自以下化合物中的一种或多种：
Figure PCTCN2022132225-appb-000002
Figure PCTCN2022132225-appb-000003
进一步的，所述非水电解液中结构式1所示的化合物的质量百分含量a为0.1～5wt％；优选的，锂二次电池中非水电解液中结构式1所示的化合物的质量百分含量a为0.1～2wt％。
进一步的，所述第一金属元素相对LiCoO 2质量的掺杂量或包覆量b为0.1～1.2wt％；优选的，所述第一金属元素相对LiCoO 2质量的掺杂量或包覆量b为0.5～0.8wt％。
进一步的，所述第二金属元素相对LiCoO 2质量的掺杂量或包覆量c为0.001～0.1wt％；优选的，所述第二金属元素相对LiCoO 2质量的掺杂量或包覆量c为0.005～0.05wt％。
进一步的，所述锂二次电池充电截止电压大于等于4.45V。
进一步的，所述正极材料层的压实密度大于等于3.8g/cm 3；优选的，正极材料层的压实密度为3.9g/cm 3-4.15g/cm 3；
所述负极材料层的压实密度大于等于1.6g/cm 3；优选的，所述负极材料层的压实密度为1.65g/cm 3-1.8g/cm 3；
进一步的，所述锂盐选自LiPF 6、LiPO 2F 2、LiBF 4、LiBOB、LiClO 4、LiCF 3SO 3、LiDFOB、LiN(SO 2CF 3) 2和LiN(SO 2F) 2中的一种或多种；
所述锂盐在所述非水电解液中的浓度为0.5～3.5mol/L。
进一步的，所述非水电解液中还包含辅助添加剂，所述辅助添加剂为环状硫酸酯类化合物、磺酸内酯类化合物、环状碳酸酯类化合物、不饱和磷酸酯类化合物和腈类化合物中的至少一种；
进一步的，以所述非水电解液的总质量为100％计，所述辅助添加剂的添加量为0.01％～30％。
进一步的，所述环状硫酸酯类化合物选自硫酸乙烯酯、硫酸丙烯酯或甲基硫酸乙烯酯中的至少一种；
所述磺酸内酯类化合物选自1,3-丙烷磺酸内酯、1,4-丁烷磺酸内酯或1,3-丙烯磺酸内酯中的至少一种；
所述环状碳酸酯类化合物选自碳酸亚乙烯酯、碳酸乙烯亚乙酯、氟代碳酸乙烯酯或结构式2所示化合物中的至少一种，
Figure PCTCN2022132225-appb-000004
所述结构式2中，R 21、R 22、R 23、R 24、R 25、R 26各自独立地选自氢原子、卤素原子、C1-C5基团中的一种；
所述不饱和磷酸酯类化合物选自结构式3所示化合物中的至少一种：
Figure PCTCN2022132225-appb-000005
所述结构式3中，R 31、R 32、R 33各自独立的选自C1-C5的饱和烃基、不饱和烃基、卤代烃基、-Si(C mH 2m+1) 3，m为1～3的自然数，且R 31、R 32、R 33中至少有一个为不饱和烃基；
所述腈类化合物包括丁二腈、戊二腈、乙二醇双(丙腈)醚、己烷三腈、己二腈、庚二腈、辛二腈、壬二腈、癸二腈中的一种或多种。
本发明的有益效果：
本发明提供的锂二次电池，在LiCoO 2正极活性材料表面包覆或掺杂含第一金属元素和第二金属元素的化合物的同时，在非水电解液中加入结构式1所示的化合物，通过大量的研究发现，正极活性材料表面掺杂或包覆的第一金属和第二金属元素的掺杂量或包覆量与电解液中结构式1所示的化合物中的含量密切相关，当满足0.05≤a×(b+c)≤3时，可以有效抑制钴离子溶出并修复正极溶出的钴离子对负极SEI膜的破坏，同时第一金属元素、第二金属元素的掺杂量或包覆量在稳定LiCoO 2正极活性材料高压特性的同时，又能减缓其带来的电池 充放电循环过程中锂离子的传输问题，降低电池阻抗、电池极化，从而使得电池在具有较高的能量密度的同时，具有较好的高温循环性能。
具体实施方式
为了使本发明所解决的技术问题、技术方案及有益效果更加清楚明白，以下结合实施例，对本发明进行进一步详细说明。应当理解，此处所描述的具体实施例仅仅用以解释本发明，并不用于限定本发明。
本发明实施例提供了一种锂二次电池，包括正极、负极以及非水电解液，所述正极包括正极材料层，所述正极材料层包括正极活性材料，所述正极活性材料包括LiCoO 2及掺杂或包覆的含第一金属元素和第二金属元素的化合物；
所述第一金属元素包括Mg、Al、Zr、W中的至少一种；
所述第二金属元素包括Ti、Cr、Mo、及稀土元素中的至少一种；
所述负极包括负极材料层；所述非水电解液包括锂盐、有机溶剂和结构式1所示的化合物：
Figure PCTCN2022132225-appb-000006
其中，R 1选自碳原子数为3-6的不饱和烃基，R 2选自碳原子数为2-5的亚烃基，n为1或2；
所述锂二次电池满足以下条件：
0.05≤a×(b+c)≤3；
其中，a为非水电解液中结构式1所示的化合物的质量百分含量，单位为wt％；
b为第一金属元素相对LiCoO 2质量的掺杂量或包覆量，单位为wt％，
c为第二金属元素相对LiCoO 2质量的掺杂量或包覆量，单位为wt％。
在一些实施例中，所述锂二次电池的LiCoO 2正极掺杂或包覆有Mg、Al、W、Ti、Cr、Zr、Mo、La、Ce及稀土元素等金属元素，相比于不被掺杂或包覆的LiCoO 2正极，Mg、Al、W等元素提高了LiCoO 2正极在高温高压时的稳定性，Ti、Cr、Zr、Mo、La、Ce及稀土元素等由于烧结过程中缓慢扩散动力学形成独特的分层分布，主要富集于顶部表面可以与氧离子形成强离子键合，从而抑制表面氧的损失，能进一步改善含钴、锂化合物正极活性材料颗粒的高压结构稳 定性。但存在的问题在于，包覆的不具备电化学活性的金属元素抑制了锂离子在正极界面的传输，导致正极阻抗增大，不利于锂二次电池的长期循环。
基于上述不足，本发明的锂二次电池非水电解液中含有结构式1所示的物质，其作用机理不十分清楚，但发明人推测是因为其可有效络合在正极表面，抑制钴离子溶出，同时由于其特殊的结构，可有效修复正极溶出的钴离子对负极SEI膜的破坏，从而有效抑制高温高压循环过程中电池的阻抗增长。
发明人通过大量研究发现，电解液中结构式1所示的化合物的含量与掺杂包覆量存在一定关系，结构式1所示的化合物可有效抑制正极钴离子溶出，间接提升正极的稳定性，因此正极材料的掺杂包覆量可适当降低，从而间接降低非电化学活性金属元素的用量，减缓其带来的抑制锂离子传导的问题，从而提升电池高温高压循环性能，但结构式1所示的化合物用量过多又会因粘度太高造成电池性能变差。通过大量研究得出，当正极活性材料表面掺杂或包覆的第一金属和第二金属元素的掺杂量或包覆量与电解液中结构式1所示的化合物中的含量满足0.05≤a×(b+c)≤3时，电解液中结构式1所示的化合物可以有效抑制钴离子溶出并修复已溶出的钴离子对负极SEI膜的破坏，同时第一、第二金属元素的掺杂量或包覆量在稳定正极活性材料高压特性的同时，又能减缓其带来的电池充放电循环过程中锂离子的传输问题，降低电池阻抗、电池极化，从而使得电池能够有较好的高温循环性能。
在优选的实施例中，所述锂二次电池满足以下条件：
0.08≤a×(b+c)≤2；
在一些实施例中，本申请提供的锂二次电池，将非水电解液结构式1所示的化合物的含量与锂二次电池中正极活性材料表面的含第一金属元素和第二金属元素的化合物的掺杂量或包覆量相关联，能够一定程度上综合第一金属元素、第二金属元素和结构式1所示的化合物对电池性能的影响，即减弱电池极化、降低电池阻抗、减缓电池析锂，从而使得电池能够有较好的高温循环性能。
在一些实施例中，所述结构式1所示的化合物选自以下化合物中的一种或多种：
Figure PCTCN2022132225-appb-000007
在一些实施例中，所述第一金属元素相对LiCoO 2质量的掺杂量或包覆量b为0.1～1.2wt％。
在优选的实施例中，所述第一金属元素相对LiCoO 2质量的掺杂量或包覆量b为0.5～0.8wt％。
在一些实施例中，所述第二金属元素相对LiCoO 2质量的掺杂量或包覆量c为0.001～0.1wt％。
在优选的实施例中，所述第二金属元素相对LiCoO 2质量的掺杂量或包覆量c为0.005～0.05wt％。
在正极活性材料LiCoO 2表面掺杂或包覆含第一金属元素和第二金属元素的化合物，可以有效地提高电池电压，但是掺杂或包覆过量的金属元素，阻碍正极活性材料中锂的嵌入或脱出，从而降低电池容量，电池的阻抗增加。发明人经过大量的研究发现，正极材料层中第一金属元素相对LiCoO 2质量的掺杂量或包覆量b达到0.1～1.2wt％，第二金属元素相对LiCoO 2质量的掺杂量或包覆量c达到0.001～0.1wt％，第一金属元素、第二金属元素与电解液中的结构式1所示的化合物相互协同，不仅可以有效地提高电池电压，同时可以缓解抑制正极活性材料锂离子传输。
在一些实施例中，所述非水电解液中结构式1所示的化合物的质量百分含量a为0.1～5wt％。
在优选的实施例中，所述非水电解液中结构式1所示的化合物的质量百分含量a为0.1～2wt％。
正极活性材料包含钴酸锂化合物使得锂二次电池具有较好的倍率性能，但正极材料层中Co元素的质量百分含量过大时，容易在高电压的条件下导致正极活性材料与非水电解液发生反应导致Co元素的溶出，通过添加结构式1所示的化合物能够有效抑制非水电解液与正极活性物质之间的反应，进而抑制正极活性材料中Co元素的溶出，但结构式1所示的化合物添加量也不宜过大，其在电池负极所形成的SEI膜的初期阻抗较大，会造成电池阻抗增加，且过量添加结构式1所示的化合物会增大电解液粘度，降低电导，从而不利于电池的循环性能。
以上分析仅基于每个参数或多个参数单独存在时对电池的影响，但实际电池应用过程中，以上三个参数是相互关联，密不可分的。本发明给出的关系式将三者关联，三者共同影响电池的电化学性能，因此调节结构式1所示的化合物的质量百分含量a、正极材料层中第一金属元素相对LiCoO 2质量的掺杂量或包覆量b、正极材料层中第二金属元素相对LiCoO 2质量的掺杂量或包覆量c，使得0.05≤a×(b+c)≤3，能够在保证锂二次电池具有较高的稳定电压特性的同时，又能提高电池的高温循环性能；超过上述范围，电池将会出现动力学恶化，从而使得电池在高温条件下循环寿命缩短，甚至出现失效。
进一步的，所述锂二次电池充电截止电压大于等于4.45V。本发明电池正极中掺杂或包覆有隔绝电解液与正极表面活性材料接触的金属元素，加上电解液中添加有结构式1所示的化合物，二者协助配合，能够使电池的充电截止电压大于等于4.45V，满足对锂离子电池高能量密度的需求。
进一步的，所述正极材料层的压实密度大于等于3.8g/cm 3；优选的，正极材料层的压实密度为3.9g/cm 3-4.15g/cm 3；
所述负极材料层的压实密度大于等于1.6g/cm 3；优选的，所述负极材料层的压实密度为1.65g/cm 3-1.8g/cm 3；
所述正极材料层和所述负极材料层的孔隙率小于等于50％；优选的，所述正极材料层和所述负极材料层的孔隙率为10％-35％。
正极材料层的压实密度、负极材料层的压实密度对于二次电池的电性能具有一定的影响。对于正极材料层的压实密度，一般情况下，正极材料层的压实密度过低，在极片制备过程中正极材料容易脱落，影响整体电池容量的一致性；若正极材料层的压实密度过高，极片制备过程中容易断带，出现制程问题，降低生产效率，同时电池充放电过程中，锂离子脱出困难，增加电池阻抗，电池 容量降低，电池循环性能下降。对于负极材料层的压实密度，一般情况下，负极材料层的压实密度过低，极片制备过程中更容易出现掉粉等制程异常，降低生产效率；负极材料层的压实密度过大，不仅影响电解液的浸入，同时影响电解液的嵌入，降低电池容量，电池析锂情况增加，降低电池安全性能。正负极材料层的孔隙率越大，越有利于锂离子的脱出或者嵌入，但是孔隙率过大，电池的体积增加，降低电池的能量密度。
另外，正极材料层压实密度、负极材料层压实密度、正极材料层和负极材料层的空隙率与电解液结构式1的化合物相互关联，非水电解液中加入结构式1所示的化合物后，其离子导电率和粘度等发生改变，影响非水电解液对于正极、负极材料层的渗透性能，进而影响锂离子的嵌入脱出效率；而正极材料层、负极材料层的压实密度高低同时也影响着结构式1所示的化合物在负极材料层表面分解形成的SEI膜的致密程度，影响SEI膜对于游离Co的防护效果。
在一些实施例中，非水电解液中的所述锂盐为LiPF 6、LiPO 2F 2、LiBF 4、LiBOB、LiClO 4、LiCF 3SO 3、LiDFOB、LiN(SO 2CF 3) 2和LiN(SO 2F) 2中的一种或多种，优选实施例中，所述锂盐为LiPF 6。
非水电解液中，锂盐中含有锂离子，在电池充放电过程中，有利于电池电化学发应，补充少量锂离子的消耗，促进电池的循环性能。
在一些实施例中，所述非水电解液25℃下的电导率大于等于6mS/cm。非水电解液的电导率对锂二次电池的循环性能和存储性能具有一定的影响。发明人经过大量研究发现，在非水电解液常温条件下电导率较低时，电解液中的电导率低，离子传输速率降低，在锂二次电池充放电过程中浓差极化增加，电池阻抗也随之增加，降低电池的循环性能和存储性能。研究发现，在非水电解液常温25℃条件下电导率大于6mS/cm时，在不影响锂离子的传输又能最大程度的减弱浓差极化，与结构式1所示的化合物共同作用，有效抑制钴离子溶出并修复已溶出的钴离子对负极SEI膜的破坏，提高电池的高温循环和高温存储性能。
在一些实施例中，所述锂盐在所述非水电解液中的浓度为0.5-3.5mol/L；优选实施例中，所述锂盐在所述非水电解液中的浓度为0.8-2.0mol/L。
非水电解液中，锂盐的浓度过低，电池电化学反应中浓差极化增加，不利于电池电化学反应；锂盐的浓度过高，非水电解液浓度增加，影响结构式1所示的化合物的离子传输效率，影响结构式1所示的化合物修复已溶出的钴离子对负极SEI膜的破坏，抑制钴离子的溶出效率降低。
在一些实施例中，所述非水电解液中有机溶剂为环状碳酸酯、线状碳酸酯、羧酸酯和醚类中的一种或多种；优选地，所述环状碳酸酯包括碳酸亚乙烯酯、碳酸丙烯酯和碳酸乙烯酯中的一种或多种；优选地，所述线状碳酸酯包括碳酸二甲酯、碳酸二乙酯和碳酸甲乙酯中的一种或多种；优选地，所述羧酸酯包括醋酸甲酯、醋酸乙酯、丙酸甲酯、丙酸乙酯、丁酸甲酯、异丁酸甲酯、三甲基乙酸甲酯和三甲基乙酸乙酯中的一种或多种；优选地，所述醚类包括乙二醇二甲醚、1,3-二氧戊环和1,1,2,2-四氟乙基-2,2,3,3-四氟丙基醚中的一种或多种。
在一些实施例中，所述非水电解液中还包含辅助添加剂，所述辅助添加剂为环状硫酸酯类化合物、磺酸内酯类化合物、环状碳酸酯类化合物、不饱和磷酸酯类化合物和腈类化合物中的至少一种。
在优选的实施例中，所述环状硫酸酯类化合物选自硫酸乙烯酯、硫酸丙烯酯或甲基硫酸乙烯酯中的至少一种；
所述环状碳酸酯类化合物包括但不限定氟原子的环状碳酸酯类化合物，例如氟代碳酸乙烯酯和/或双氟代碳酸乙烯酯；优选地，所述环状碳酸酯类化合物包括但不限定碳-碳不饱和键的环状碳酸酯类化合物，例如可以是碳酸亚乙烯酯、乙烯基碳酸亚乙酯、碳酸乙烯亚乙酯、甲基碳酸亚乙烯酯或结构式2所示化合物中的一种或多种；
Figure PCTCN2022132225-appb-000008
所述结构式2中，R 21、R 22、R 23、R 24、R 25、R 26各自独立地选自氢原子、卤素原子、C1-C5基团中的一种。
所述不饱和磷酸酯类化合物选自结构式3所示化合物中的至少一种：
Figure PCTCN2022132225-appb-000009
所述结构式3中，R 31、R 32、R 33各自独立的选自C1-C5的饱和烃基、不饱和烃基、卤代烃基、-Si(C mH 2m+1) 3，m为1～3的自然数，且R 31、R 32、R 33中至少有一个为不饱和烃基。
在优选的实施例中，所述不饱和磷酸酯类化合物可为磷酸三炔丙酯、二炔丙基甲基磷酸酯、二炔丙基乙基磷酸酯、二炔丙基丙基磷酸酯、二炔丙基三氟甲基磷酸酯、二炔丙基-2,2,2-三氟乙基磷酸酯、二炔丙基-3,3,3-三氟丙基磷酸酯、二炔丙基六氟异丙基磷酸酯、磷酸三烯丙酯、二烯丙基甲基磷酸酯、二烯丙基乙基磷酸酯、二烯丙基丙基磷酸酯、二烯丙基三氟甲基磷酸酯、二烯丙基-2,2,2-三氟乙基磷酸酯、二烯丙基-3,3,3-三氟丙基磷酸酯、二烯丙基六氟异丙基磷酸酯中的至少一种。
优选地，所述磺酸内酯类化合物包括但不限定环状磺酸酯类化合物，例如可以是1,3-丙烷磺内酯、亚硫酸丙烯酯、1,4-丁烷磺酸内酯或1,3-丙烯磺酸内酯中的至少一种；
优选地，所述腈类化合物可以但不限定是丁二腈、己二腈、乙二醇双(丙腈)醚、己烷三腈、己二腈、庚二腈、辛二腈、壬二腈和癸二腈中的一种或多种。
需要说明的是，除非特殊说明，一般情况下，所述辅助添加剂中任意一种可选物质在非水电解液中的添加量为0.05～10％，优选的，添加量为0.1-5％，更优选的，添加量为0.1％～3％。具体的，所述辅助添加剂中任意一种可选物质的添加量可以为0.05％、0.08％、0.1％、0.5％、0.8％、1％、1.2％、1.5％、1.8％、2％、2.2％、2.5％、2.8％、3％、3.2％、3.5％、3.8％、4％、4.5％、5％、5.5％、6％、6.5％、7％、7.5％、7.8％、8％、8.5％、9％、9.5％、10％。
在一些实施例中，当辅助添加剂选自氟代碳酸乙烯酯时，以所述非水电解液的总质量为100％计，所述氟代碳酸乙烯酯的添加量为0.05％～30％。
非水电解液的辅助添加剂的含量设定该范围，可避免由于非水电解液的介电常数降低而导致电导率降低，易于使非水电解质电池的大电流放电特性、相 对于负极的稳定性、循环特性达到良好的范围；可提高非水电解液的氧化/还原耐性，从而有助于提高电池高温循环、高温保存时的稳定性。
所述非水电解液中，相比于单一添加或是其他现有添加剂的组合，结构式1所示的化合物与所述辅助添加剂一同添加时，在提升电池的高温存储性能方面体现出明显的协同提升的作用，说明结构式1所示的化合物与所述辅助添加剂在电极表面共同成膜能够弥补单一添加的成膜缺陷，得到在高温条件下更加稳定的钝化膜。
以下通过实施例对本发明进行进一步的说明。
以下实施例和对比例中所采用的结构式1所示的化合物如下表：
Figure PCTCN2022132225-appb-000010
实施例1～30和对比例1-12
本实施例用于说明本发明公开的电池及其制备方法，正极活性材料以钴酸锂为例，负极活性材料以石墨为例，包括以下操作步骤：
(1)正极片的制备
正极活性材料为LiCoO 2，正极活性材料掺杂或包覆第一金属元素的掺杂量或包覆量为b、正极活性材料掺杂或包覆第二金属元素的掺杂量或包覆量为c，其中b、c取值参照各表格，将表面掺杂或包覆的正极活性材料LiCoO 2、导电剂及粘结剂PVDF分散至溶剂NMP中进行混合均匀，得到正极浆料；将正极浆料均匀涂布于正极集流体铝箔上，经烘干、辊压、裁片后，得到正极片，其中得到的正极片的压实密度为4.1g/cm 3，正极活性物质、导电炭黑及粘结剂PVDF的质量比为96:2:2。
(2)负极片的制备
将负极活性材料石墨、导电剂、粘结剂CMC及SBR按照质量比96:1:1:2分散于去离子水中进行搅拌，得到负极浆料；将负极浆料均匀涂布于负极集流体铜箔上，烘干、辊压、裁片后，得到压实密度为1.7g/cm 3的负极片。
(3)电解液的制备
将碳酸乙烯酯(EC)和碳酸二乙酯(DEC)以质量比3:7混合均匀，然后加入六 氟磷酸锂(LiPF 6)至摩尔浓度为1mol/L，以所述非水电解液的总重量为100％计，然后按照各表格加入添加剂。
(4)锂二次电池的制备
采用叠片工艺，将正极片、隔离膜及负极片依次层叠，再经顶侧封、注入一定量的电解液等工序后，制成软包电池。
性能测试
对上述制备得到的锂二次电池进行如下性能测试：
1、高温循环性能测试：在45℃下，将化成后的电池用1C恒流恒压充至截止电压，再恒压充电至电流下降至0.05C，然后以1C的电流恒流放电至4.45V，如此循环500圈，记录第1次的放电容量和最后1次的放电容量。
按下式计算高温循环的容量保持率：
容量保持率＝最后1次的放电容量/第1次的放电容量×100％。
2、高温循环500圈后的内阻增长率：在45℃下，将化成后的电池在常温下以1C的电流恒流充电至截止电压，再恒流恒压充电至电流下降至0.05C，测试电池的内阻，然后以1C的电流恒流放电至4.45V，之后如此循环500圈后，记录第1次充满电的电池内阻和最后1次电池充满电后的电池内阻。
电池高温循环500圈内阻增长率＝(最后1次电池充满电后的电池内阻-第1次充满电的电池内阻)/第1次充满电的电池内阻×100％。
1.1、实施例1～23和对比例1～8得到的测试结果填入表2。
表2
Figure PCTCN2022132225-appb-000011
Figure PCTCN2022132225-appb-000012
由实施例1-23和对比例1-8的测试结果可知，当电解液中化合物1的质量百分含量a、正极活性材料中第一金属元素的掺杂量b、正极活性材料第二金属元素的掺杂量c满足预设关系0.05≤a×(b+c)≤3时，锂二次电池具有较高的高温循环性能。
由实施例1-23的测试结果可知，随着a×(b+c)值的增大，锂二次电池的高温循环性能先提升后降低，说明电解液中结构式1所示的化合物的含量、钴酸锂正极中第一金属元素的掺杂量和第二金属元素的掺杂量与锂二次电池的高温性能相关，尤其是，当0.08≤a×(b+c)≤2时，锂离子电池具有最佳的高温循环性能。
在对比例4的锂二次电池中，由于正极中第一金属元素含量很低，虽然内阻增长不是特别明显，但可能因为电解液中结构式1所示的化合物含量不高，不足以抑制正极钴离子溶出，正极稳定性较差，导致阻抗增长率大，电池高温循环性能不高。在对比例5-8的锂二次电池中，高温循环性能的提升幅度和内阻增长率的抑制效果远低于电池满足预设关系0.05≤a×(b+c)≤3时的效果，这可能是因为电解液中结构式1所示的化合物含量较高，容易增大电解液粘度，降低电导，不利于电池的循环性能，同时由于正极中第一金属元素和第二金属元素含量较高，阻碍正极活性材料中锂的嵌入与脱出，电池阻抗增长明显，电池高温循环性能不佳。
1.2、实施例12、24～26得到的测试结果填入表3。
表3
Figure PCTCN2022132225-appb-000013
由表3的测试结果可以看出，对于不同的结构式1所示的化合物，当正极材料层中第一金属元素含量、第二金属元素含量和结构式1所示化合物的含量 满足预设关系0.05≤a×(b+c)≤3时，其起到的作用相似，均对于电池的内阻增长和高温循环性能具有一定的改善作用，说明本发明提供的关系式适用于不同的结构式1所示的化合物。
1.3、实施例27～30、对比例9-12得到的测试结果填入表4。
表4
Figure PCTCN2022132225-appb-000014
由表4的测试结果可看出，在本发明提供的电池中，在非水电解液中加入上述的添加剂PS(1,3-丙烷磺内酯)、VC(碳酸乙烯酯)、DTD(硫酸乙烯酯)或FEC(氟代碳酸乙烯酯)，能够进一步提高电池的高温循环性能，以及降低热内阻增长，推测是由结构式1所示的化合物与上述的添加剂共同参与了电极表面钝化膜的成型，得到一种热稳定性能优异的钝化膜，抑制钴离子溶出，提高正极的稳定性，进而有效降低了电极表面电解液的反应，提高了电池的高温循环性能。
以上所述仅为本发明的较佳实施例而已，并不用以限制本发明，凡在本发明的精神和原则之内所作的任何修改、等同替换和改进等，均应包含在本发明的保护范围之内。

Claims (19)

  1. 一种锂二次电池，其特征在于，包括正极、负极以及非水电解液，所述正极包括正极材料层，所述正极材料层包括正极活性材料，所述正极活性材料包括LiCoO 2及掺杂或包覆的含第一金属元素和第二金属元素的化合物；
    所述第一金属元素包括Mg、Al和W中的至少一种；
    所述第二金属元素包括Ti、Cr、Zr、Mo、La、Ce及稀土元素中的至少一种；
    所述非水电解液包括锂盐、有机溶剂和结构式1所示的化合物：
    Figure PCTCN2022132225-appb-100001
    其中，R 1选自碳原子数为3-6的不饱和烃基，R 2选自碳原子数为2-5的亚烃基，n＝1或2；
    所述锂二次电池满足以下条件：
    0.05≤a×(b+c)≤3；
    其中，a为非水电解液中结构式1所示的化合物的质量百分含量，单位为wt％；
    b为第一金属元素相对LiCoO 2质量的掺杂量或包覆量，单位为wt％，
    c为第二金属元素相对LiCoO 2质量的掺杂量或包覆量，单位为wt％。
  2. 根据权利要求1所述的锂二次电池，其特征在于，所述锂二次电池满足以下条件：
    0.08≤a×(b+c)≤2。
  3. 根据权利要求1所述的锂二次电池，其特征在于，所述结构式1所示的化合物选自以下化合物中的一种或多种：
    Figure PCTCN2022132225-appb-100002
    Figure PCTCN2022132225-appb-100003
  4. 根据权利要求1所述的锂二次电池，其特征在于，所述锂二次电池中非水电解液中结构式1所示的化合物的质量百分含量a为0.1～5wt％。
  5. 根据权利要求4所述的锂二次电池，其特征在于，所述非水电解液中结构式1所示的化合物的质量百分含量a为0.1～2wt％。
  6. 根据权利要求1所述的锂二次电池，其特征在于，所述第一金属元素相对LiCoO 2质量的掺杂量或包覆量b为0.1～1.2wt％，所述第二金属元素相对LiCoO 2质量的掺杂量或包覆量c为0.001～0.1wt％。
  7. 根据权利要求6所述的锂二次电池，其特征在于，所述第一金属元素相对LiCoO 2质量的掺杂量或包覆量b为0.5～0.8wt％，第二金属元素相对LiCoO 2质量的掺杂量或包覆量c为0.005～0.05wt％。
  8. 根据权利要求1所述的锂二次电池，其特征在于，所述锂二次电池充电截止电压大于等于4.45V。
  9. 根据权利要求1所述的锂二次电池，其特征在于，所述正极材料层的压实密度大于等于3.8g/cm 3；所述负极材料层的压实密度大于等于1.6g/cm 3。
  10. 根据权利要求9所述的锂二次电池，其特征在于，所述正极材料层的压实密度为3.9g/cm 3-4.15g/cm 3；所述负极材料层的压实密度为1.65g/cm 3-1.8g/cm 3。
  11. 根据权利要求1所述的锂二次电池，其特征在于，所述锂盐选自LiPF 6、LiPO 2F 2、LiBF 4、LiBOB、LiClO 4、LiCF 3SO 3、LiDFOB、LiN(SO 2CF 3) 2和LiN(SO 2F) 2中的一种或多种。
  12. 根据权利要求11所述的锂二次电池，其特征在于，所述锂盐在所述非水电解液中的浓度为0.5-3.5mol/L。
  13. 根据权利要求1所述的锂二次电池，其特征在于，所述非水电解液还包含辅助添加剂，所述辅助添加剂包括环状硫酸酯类化合物、磺酸内酯类化合物、环状碳酸酯类化合物、不饱和磷酸酯类化合物和腈类化合物中的至少一种。
  14. 根据权利要求13所述的锂二次电池，其特征在于，以所述非水电解液的总质量为100％计，所述辅助添加剂的添加量为0.01％～30％。
  15. 根据权利要求14所述的锂二次电池，其特征在于，所述环状硫酸酯类 化合物选自硫酸乙烯酯、硫酸丙烯酯或甲基硫酸乙烯酯中的至少一种。
  16. 根据权利要求14所述的锂二次电池，其特征在于，所述磺酸内酯类化合物选自1,3-丙烷磺酸内酯、1,4-丁烷磺酸内酯或1,3-丙烯磺酸内酯中的至少一种。
  17. 根据权利要求14所述的锂二次电池，其特征在于，所述环状碳酸酯类化合物选自碳酸亚乙烯酯、碳酸乙烯亚乙酯、氟代碳酸乙烯酯或结构式2所示化合物中的至少一种，
    Figure PCTCN2022132225-appb-100004
    所述结构式2中，R 21、R 22、R 23、R 24、R 25、R 26各自独立地选自氢原子、卤素原子、C1-C5基团中的一种。
  18. 根据权利要求14所述的锂二次电池，其特征在于，所述不饱和磷酸酯类化合物选自结构式3所示化合物中的至少一种：
    Figure PCTCN2022132225-appb-100005
    所述结构式3中，R 31、R 32、R 33各自独立的选自C1-C5的饱和烃基、不饱和烃基、卤代烃基、-Si(C mH 2m+1) 3，m为1～3的自然数，且R 31、R 32、R 33中至少有一个为不饱和烃基。
  19. 根据权利要求14所述的锂二次电池，其特征在于，所述腈类化合物包括丁二腈、戊二腈、乙二醇双(丙腈)醚、己烷三腈、己二腈、庚二腈、辛二腈、 壬二腈、癸二腈中的一种或多种。
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