CN115020695A - Positive electrode active material, electrochemical device, and electronic device - Google Patents
Positive electrode active material, electrochemical device, and electronic device Download PDFInfo
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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
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
- H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
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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
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
- H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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- 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
Abstract
The invention provides a positive active material, an electrochemical device and electronic equipment, wherein the positive active material comprises a positive active material inner core and a positive active material outer shell coated on the surface of the positive active material inner core; the positive active material core includes LiNi a Co b Mn 1‑a‑b‑c M c O 2 Wherein a is more than or equal to 0.56 and less than or equal to 0.60, b is more than or equal to 0.09 and less than or equal to 0.13, c is more than or equal to 0.001 and less than or equal to 0.01, M comprises W, Nb and Mo, or the combination of at least two of the two, and the positive active material shell comprises M compound. The invention improves the crystallinity and the interface stability of the anode active material, reduces the polarization of the battery, and improves the dynamic performance, the capacity and the cycle performance of the battery.
Description
Technical Field
The invention belongs to the technical field of batteries, and relates to a positive electrode active material, an electrochemical device and electronic equipment.
Background
In recent years, the low-nickel and low-cobalt ternary material is widely applied due to the reasons of lower preparation cost, higher safety performance, high nickel ternary material and the like; however, the small nickel content and cobalt content in the medium-low nickel and low cobalt ternary material affect the capacity exertion and the overall conductivity of the material, and bring about a serious kinetic retardation problem, thereby reducing the energy density of the battery.
The W element coating can well improve the dynamic performance of the medium-low nickel and low cobalt ternary material and reduce the interface electrochemical reaction impedance, but the tungsten source in the industry is mostly a micron-sized large-particle-size W source, the activity is low, and the W element is not easy to be well combined with a substrate after being sintered by a pyrogenic process, so that the coating effect is poor, and the improvement on the electrochemical performance of the material is limited. In addition, in the process of processing the battery cell, after the slurry is stirred, the coating layer with poor bonding can fall off, so that concave points appear on the coating surface, and the appearance of the pole piece and the performance of the battery cell are influenced.
Disclosure of Invention
In view of the disadvantages of the prior art, an object of the present invention is to provide a positive electrode active material, an electrochemical device, and an electronic apparatus. The anode active material is doped and coated by W, Nb and/or Mo element, so that the crystallinity and interface stability of the material are improved, the polarization of the battery is reduced, and the dynamic performance, capacity and cycle performance of the battery are improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a positive electrode active material, including a positive electrode active material core and a positive electrode active material shell coated on a surface of the positive electrode active material core; the positive active material core includes LiNi a Co b Mn 1-a-b-c M c O 2 Wherein a is more than or equal to 0.56 and less than or equal to 0.60, b is more than or equal to 0.09 and less than or equal to 0.13, c is more than or equal to 0.001 and less than or equal to 0.01, M comprises W, Nb and Mo, or the combination of at least two of the two, and the positive active material shell comprises M compound.
In the present invention, 0.56. ltoreq. a.ltoreq.0.60, for example, may be 0.56, 0.57, 0.58, 0.59, or 0.6, etc., 0.09. ltoreq. b.ltoreq.0.13, for example, may be 0.09, 0.1, 0.11, 0.12, or 0.13, etc., 0.001. ltoreq. c.ltoreq.0.01, for example, may be 0.001, 0.002, 0.004, 0.006, 0.008, or 0.01, etc., M includes any one or a combination of at least two of W, Nb and Mo, for example, may be a combination of W and Nb, a combination of Nb and Mo, a combination of W and Mo, or a combination of W, Nb and Mo.
The positive active material comprises a positive active material core and a positive active material shell coated on the surface of the positive active material core, wherein the core is a medium-low nickel and low cobalt ternary material doped with M element, so that the use of rare element Co is reduced, the safety performance of a finished battery is improved, and M compound is coated outside the core; the positive active material has high crystallinity, strong interface stability, excellent dynamic performance, and higher gram capacity, coulombic efficiency and circulation capacity retention rate in an electrochemical device.
Preferably, the particle diameter D of the positive electrode active material core v 50 is 3.4 to 4 μm, and may be, for example, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9 or 4 μm.
According to the invention, the size of the core of the positive active material is adjusted, and the core doped with specific ions is coated after growing to a certain size, so that the capacity and power performance of the positive active material can be further improved.
The particle diameter D of the precursor core v 50 is a term known in the art, also known as the mean or median particle diameter, and refers to the particle diameter corresponding to 50% of the volume distribution of the particles of the precursor core.
Preferably, the content of M in the positive electrode active material core is 2000ppm to 3000ppm, for example, 2000ppm, 2100ppm, 2200ppm, 2300ppm, 2400ppm, 2500ppm, 2600ppm, 2700ppm, 2800ppm, 2900ppm, 3000ppm, or the like, based on the mass of the positive electrode active material.
Preferably, the content of M in the positive electrode active material casing is 1000ppm to 2000ppm, for example, 1000ppm, 1100ppm, 1200ppm, 1300ppm, 1400ppm, 1500ppm, 1600ppm, 1700ppm, 1800ppm, 1900ppm, 2000ppm, or the like, based on the mass of the positive electrode active material.
According to the invention, W, Nb and/or Mo with appropriate content is adopted for doping and cladding, so that the crystallinity and stability of the material can be further improved, the diffusion rate of lithium ions is improved, the polarization is reduced, and the dynamic performance of the material is improved.
Preferably, the M is W, the compound of the M is lithium tungstate, and when the anode active material is prepared by adopting a coprecipitation mode, in a wet coprecipitation reaction stage, the W element can be uniformly doped in an inner core of the anode active material and uniformly coated on the surface of the inner core in the form of lithium tungstate in a subsequent reaction process, so that the effect of reducing interfacial polarization is fully exerted, the lithium ion diffusion rate is improved, and the electrochemical reaction impedance is reduced.
As a preferable technical scheme of the positive active material, the preparation method of the positive active material comprises the following steps:
(1) mixing nickel salt, cobalt salt, manganese salt, M salt, a complexing agent and a precipitator, and carrying out coprecipitation reaction to obtain a precursor core, wherein M comprises any one or combination of at least two of W, Nb and Mo;
(2) mixing the precursor core with M salt, a complexing agent and a precipitator, and carrying out coprecipitation reaction to obtain a precursor;
(3) and mixing the precursor with lithium salt, and sintering to obtain the positive active material.
In the invention, after the nickel, cobalt, manganese and M salt are coprecipitated to generate a precursor core, the M salt, the complexing agent and the precipitant are added again for coprecipitation to obtain a material with uniform particles, good sphericity and narrow particle size distribution, and the problem that the traditional tungsten source, niobium source and molybdenum source are large in particle size and are not easy to dope into the particles when the M salt is doped in the coprecipitation in the step (1) can be solved, so that the activity of the material is improved; coating M salt on the surface of the core of the precursor during coprecipitation in the step (2) can improve the problems of poor coating effect and easy substrate shedding of the traditional pyrogenic process; through two coprecipitation reactions, uniform doping and coating of the M element are achieved, the binding force of the doping element and a coating object is strong under the coprecipitation reaction, the crystallinity and the interface stability of the material can be improved under the synergistic effect, the prepared precursor is uniform in particle, good in sphericity and narrow in particle size distribution, and the anode active material with the optimal crystallinity and interface stability is obtained after the precursor and lithium salt are sintered, so that the dynamic performance of an electrochemical device obtained through subsequent preparation is improved, polarization is reduced, and products with excellent performance such as capacity, coulombic efficiency and circulation are obtained.
It should be noted that, in the step (1), nickel salt, cobalt salt, manganese salt, M salt, complexing agent and precipitant are mixed, and a precursor core is generated through a coprecipitation reaction, then, in the step (2), the precursor core, M salt, complexing agent and precipitant are mixed, and a coprecipitation reaction is performed again, and the two coprecipitation reactions can be performed in one container or two containers. For example, nickel salt, cobalt salt, manganese salt, M salt, complexing agent and precipitating agent can be continuously introduced into the reaction kettle, the reaction is carried out until the precursor core reaches a certain granularity, then the introduction of nickel salt, cobalt salt and manganese salt is stopped, and the introduction of M salt, complexing agent and precipitating agent is continued, so that the M salt is coprecipitated to the surface of the precursor core; or adding nickel salt, cobalt salt, manganese salt, M salt, complexing agent and precipitating agent into a reaction kettle, reacting until the precursor core reaches the required granularity, taking out the precursor core, placing the precursor core into another reaction kettle, adding the M salt, complexing agent and precipitating agent, and carrying out coprecipitation.
Preferably, the particle size D of the precursor core v 50 is 3.4 μm to 4 μm, and may be, for example, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm or 4 μm.
In the invention, preferably, when the precursor core grows to a certain particle size, the nickel, cobalt and manganese salts are stopped to be added, the M salt is continuously introduced, and the particle size D is v The surface of the precursor inner core with the thickness of 50 being 3.4-4 mu M is coated with M salt, so that the capacity and the power performance of the positive active material are further improved.
Preferably, the nickel salt of step (1) comprises nickel sulfate.
Preferably, the manganese salt of step (1) comprises manganese sulfate.
Preferably, the cobalt salt of step (1) comprises cobalt sulfate.
Preferably, the molar ratio of the nickel salt, the cobalt salt and the manganese salt in the step (1) is x: y (1-x-y), wherein 0.56 ≦ x ≦ 0.60, such as 0.56, 0.57, 0.58, 0.59 or 0.6, etc., and 0.09 ≦ y ≦ 0.13, such as 0.09, 0.1, 0.11, 0.12 or 0.13, etc.
Preferably, the M salt in step (1) and step (2) includes W, Nb and any one of or a combination of at least two of soluble salts of Mo, and may be, for example, a combination of soluble salts of W and Nb, a combination of soluble salts of Nb and Mo, a combination of soluble salts of W and Mo, or a combination of soluble salts of W, Nb and Mo.
Preferably, the complexing agent in step (1) and step (2) comprises ammonia water.
Preferably, the precipitant in step (1) and step (2) comprises sodium hydroxide.
Preferably, the complexing agent in step (1) and step (2) has a molar concentration independently of 0.2mol/L to 0.5mol/L, and may be, for example, 0.2mol/L, 0.25mol/L, 0.3mol/L, 0.35mol/L, 0.4mol/L, 0.45mol/L, 0.5mol/L, or the like.
Preferably, the molar concentration of the precipitant in step (1) and step (2) is independently 1.5mol/L to 2.5mol/L, and may be, for example, 1.5mol/L, 1.8mol/L, 2mol/L, 2.2mol/L, 2.5mol/L, or the like.
In the present invention, "independently" means that the selection of both is not interfered with each other, for example, the molar concentration of the complexing agent in the step (1) and the step (2) is independently 0.3mol/L, and when the molar concentration of the complexing agent in the step (1) is 0.2mol/L, the molar concentration of the complexing agent in the step (2) may be 0.2mol/L or 0.3mol/L, and the selection of both is not interfered with each other.
Preferably, the pH of the precipitating agent is 8 to 10, which may be, for example, 8, 8.5, 9, 9.5, or 10, etc.
Preferably, after the coprecipitation reaction in step (2) and before the sintering in step (3), the operations of washing, drying, mixing, sieving, demagnetizing and packaging the low-cobalt precursor are further included.
Preferably, the molar ratio of the precursor and the lithium salt in the step (3) is 1 (1.04 to 1.06), and may be, for example, 1:1.04, 1:1.045, 1:1.05, 1:1.055, 1:1.06, or the like.
Preferably, the sintering temperature in step (3) is 900 ℃ to 1000 ℃, and may be 900 ℃, 920 ℃, 940 ℃, 960 ℃, 980 ℃, or 1000 ℃, for example.
Preferably, the sintering time in step (3) is 7h to 9h, and may be 7h, 7.5h, 8h, 8.5h, 9h, or the like, for example.
In a second aspect, the present invention provides an electrochemical device comprising the positive electrode active material according to the first aspect in a positive electrode thereof.
The positive active material has high crystallinity, stable interface structure and good dynamic performance, and the electrochemical device prepared by the positive active material has higher gram capacity, coulombic efficiency and circulating capacity retention rate.
In an alternative embodiment, the present invention provides a method for detecting whether a positive active material according to the present invention is contained in an electrochemical device, comprising:
splitting the sample of the electrochemical device to obtain a positive electrode, washing the positive electrode by using a solvent, drying, blade-coating the surface of the positive electrode to obtain active substance powder, carrying out an Inductively Coupled Plasma (ICP) test on the active substance powder or cutting particles of the active substance powder by using a focused ion beam, and matching with SEM and EDS tests to obtain the distribution condition and content of each element;
when the test results show that the particles in the active material powder are divided into the core and the coating layer, the core contains Ni, Co, Mn and M (W, Nb and/or Mo), the coating layer contains M, the M is uniformly distributed in the coating layer and the core, the content of the M in the core is 2000ppm to 3000ppm, the content of the M in the coating layer is 1000ppm to 2000ppm, and the M element permeates the whole particle surface, the positive electrode of the electrochemical device sample can be confirmed to contain the positive electrode active material.
In an alternative embodiment, the present invention provides a method for preparing the positive electrode, including:
and mixing the positive active material, the conductive agent, the binder and the solvent to obtain positive slurry, coating the positive slurry on an aluminum foil, and rolling to obtain the positive electrode.
Preferably, the conductive agent comprises conductive carbon black (SP) and/or Carbon Nanotubes (CNT).
Preferably, the binder comprises polyvinylidene fluoride (PVDF).
Preferably, the mass ratio of the positive electrode active material, the SP, the CNT and the PVDF is (90 to 99):1:0.5:1, and may be, for example, 90:1:0.5:1, 92:1:0.5:1, 94:1:0.5:1, 96:1:0.5:1, 98:1:0.5:1 or 99:1:0.5:1, etc.
In an alternative embodiment, the electrochemical device is a lithium ion battery.
In an alternative embodiment, the negative electrode of the electrochemical device comprises graphite, SP, carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) in a mass ratio of (90 to 99):1:1.5:2, for example, 90:1:1.5:2, 92:1:1.5:2, 94:1:1.5:2, 96:1:1.5:2, 98:1:1.5:2 or 99:1:1.5:2, etc.
Preferably, the electrochemical device further includes an electrolyte and a separator.
Preferably, the electrolyte of the electrochemical device includes a lithium salt and a solvent.
Preferably, the lithium salt includes LiPF 6 。
Preferably, the lithium salt is contained in an amount of 4 wt% to 24 wt%, for example, 4 wt%, 8 wt%, 10 wt%, 15 wt%, 20 wt%, or 24 wt%, etc., based on 100 wt% of the mass of the electrolyte.
Preferably, the solvent comprises any one of or a combination of at least two of Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC), dimethyl carbonate (DMC) and Polycarbonate (PC), for example, a combination of EC and EMC, a combination of DMC and PC, a combination of EC, EMC and DMC, or a combination of EC, EMC, DMC and PC, etc.
Preferably, the mass ratio of EC, EMC, DMC and PC in the solvent is (2 to 4): (3 to 5): (2 to 4): (0 to 1), the selection range (2 to 4) of EC may be, for example, 2, 2.5, 3, 3.5, or 4, etc., the selection range (3 to 5) of EMC may be, for example, 3, 3.5, 4, 4.5, or 5, etc., the selection range (2 to 4) of DMC may be, for example, 2, 2.5, 3, 3.5, or 4, etc., the selection range (0 to 1) of PC may be, for example, 0, 0.1, 0.2, 0.3, 0.5, 0.7, or 1, etc., and when PC is 0, it means that PC is not contained in the solvent.
Preferably, the thickness of the separator is 9 μm to 18 μm, and may be, for example, 9 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, or the like.
Preferably, the air permeability of the membrane is 180s/100mL to 380s/100mL, and may be, for example, 180s/100mL, 200s/100mL, 240s/100mL, 250s/100mL, 280s/100mL, 300s/100mL, 250s/100mL, 380s/100mL, or the like.
Preferably, the porosity of the separator is 30% to 50%, for example, may be 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, or 50%, etc.
In the present invention, a method of assembling an electrochemical device using the cathode, the anode and the separator is the prior art, and those skilled in the art can assemble the electrochemical device by referring to the method disclosed in the prior art. Taking a lithium ion battery as an example, a positive electrode, a diaphragm and a negative electrode are sequentially wound or stacked to form a battery core, the battery core is placed in a battery case, electrolyte is injected, formation and packaging are performed, and the electrochemical device is obtained.
The diaphragm with appropriate parameters is selected to be matched with the anode and the cathode to prepare the electrochemical device, so that the capacity and the cycling stability of the electrochemical device are improved.
In a third aspect, the present invention provides an electronic device comprising an electrochemical device according to the second aspect.
The electronic device according to the present invention may be, for example, a mobile computer, a portable phone, a memory card, a liquid crystal television, an automobile, a motorcycle, a motor, a clock, a camera, or the like.
The system refers to an equipment system, or a production equipment.
Compared with the prior art, the invention has the beneficial effects that:
(1) the anode active material is doped and coated by W, Nb and/or Mo element, so that the crystallinity and interface stability of the material are improved, the polarization of the battery is reduced, and the dynamic performance, capacity and cycle performance of the battery are improved.
(2) The preferable preparation method can solve the problems that the traditional tungsten source, niobium source and molybdenum source have larger particle sizes and are not easy to be doped into particles, and the activity of the material is improved; the problems of poor cladding effect and easy falling of a matrix in the conventional fire sintering can be solved, and W, Nb and/or Mo element can be uniformly doped and clad through two coprecipitation reactions. The precursor prepared by the method has uniform particles, good sphericity and narrow particle size distribution, and can obtain the anode active material with optimal crystallinity and interface stability after being sintered with lithium salt, so that the dynamic performance of an electrochemical device obtained by subsequent preparation is improved, the polarization is reduced, and products with excellent performances such as capacity, coulombic efficiency, circulation and the like are obtained.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments.
Example 1
The present embodiment provides a positive electrode active material including a positive electrode active material core LiNi 0.58 Co 0.11 Mn 0.305 W 0.005 O 2 And lithium tungstate coated on the surface of the positive electrode active material core, wherein the content of W in the positive electrode active material core is 2500ppm and the content of W in the shell is 1563ppm based on the mass of the positive electrode active material.
The embodiment also provides a preparation method of the positive electrode active material, which comprises the following steps:
(1) introducing nickel sulfate, cobalt sulfate, manganese sulfate, sodium tungstate, ammonia water and sodium hydroxide into a reaction kettle, and carrying out coprecipitation reaction, wherein the molar concentration of the ammonia water is 0.3mol/L, and the molar concentration of the sodium hydroxide is 28%, so as to obtain a precursor core;
(2) particle size D of the precursor core v When the particle size of 50 is 3.6 mu m, stopping introducing nickel sulfate, cobalt sulfate and manganese sulfate, continuously introducing sodium tungstate, ammonia water and sodium hydroxide, and carrying out coprecipitation reaction to obtain a precursor;
(3) and mixing the precursor and lithium nitrate according to the molar ratio of 1:1.05, and sintering at 950 ℃ for 8 hours to obtain the positive active material.
Assembling of lithium ion battery
(1) Preparation of the positive electrode: mixing the positive electrode active material, SP, CNT and PVDF which are prepared in the embodiment and the comparative example of the invention with N-methyl pyrrolidone (NMP) according to the mass ratio of 97.5:1:0.5:1 to prepare positive electrode slurry, then coating the positive electrode slurry on aluminum foil, and rolling to obtain a positive electrode;
(2) preparation of a negative electrode: mixing graphite, SP, CMC and SBR according to a mass ratio of 95.5:1:1.5:2 to prepare slurry, coating the slurry on a copper foil, and rolling to obtain a negative electrode;
(3) preparing a lithium ion battery: adhering an aluminum positive electrode tab to a positive electrode, adhering a copper negative electrode tab to a negative electrode, selecting a diaphragm with the thickness of 10 μm, the air permeability of 200s/100mL and the porosity of 40%, sequentially and tightly overlapping the positive electrode, the diaphragm and the negative electrode, and injecting 5 wt% LiPF solute into two sides of the diaphragm 6 And the solvent is an electrolyte of EC, EMC, DMC and PC with the mass ratio of 3:4:3:0.5 to obtain a battery cell, and the battery cell is stacked to the required number of layers to obtain the lithium ion battery.
Second, performance test
(1) Distribution and content of M element in positive electrode active material
And cutting the positive active material powder particles by using an inductively coupled plasma method and a focused ion beam method, and then testing the distribution condition of the M element by using a time-of-flight secondary ion mass spectrometer.
(2) Testing of the lithium ion battery:
adopting a battery performance test system (equipment model: BTS05/10C8D-HP) of the Shenghong electric appliance component electric company Limited to carry out a first discharge gram capacity test, a 800-week circulation capacity retention rate test and a power performance test;
the first discharge gram capacity test method comprises the following steps: under the condition of 25 ℃, charging and discharging for one week in a charging and discharging mode of 0.063A/g, wherein the voltage interval is 2.8V to 4.35V, and the obtained charging and discharging capacity is divided by the usage amount of a positive electrode, namely the first charging/discharging gram capacity; the first coulombic efficiency is obtained by dividing the first discharge capacity by the first charge capacity.
Cycle capacity retention test method: cycling is carried out under the condition of 25 ℃ in a charging and discharging mode of 0.19A/g (calculated by the mass of the anode material), and the voltage interval is 2.8V to 4.35V. After the cycle time reaches 800 weeks, the discharge capacity of the battery at the moment is divided by the discharge capacity of the first cycle, and the cycle capacity retention rate of the battery at 800 cycles is obtained.
Power performance: under the condition of 25 ℃, adjusting the SOC interval to be 50% SOC, carrying out HPPC pulse discharge according to a discharge standard of 0.53A/g (calculated by the mass of a positive electrode material), recording the voltage drop before and after pulse discharge, and calculating the resistance according to a formula: delta U/0.53.
Examples 2 to 9 and comparative examples 1 to 3 were modified based on the procedure of example 1, and the specific modified parameters and test results are shown in tables 1 to 4.
TABLE 1
TABLE 2
As can be seen from comparison between example 1 and examples 4 to 5 in table 2, in the present invention, when the precursor core is generated, the M element is coated by the second precipitation after the precursor core grows to a certain particle size, which can further improve the capacity and power performance of the material. In example 4, the lower size of the precursor core causes poor sphericity of the internal crystal nucleus, more pores, influences the tap density of the finished product, and deteriorates the cell cycle. In example 5, the precursor has a high size, which results in poor coating effect and uneven coating layer, thereby affecting capacity exertion and cell power performance. Therefore, the positive active material prepared from the precursor core with the proper particle size in example 1 has better discharging capacity and power performance.
TABLE 3
As can be seen from a comparison of example 1 with examples 6 to 9 in table 3, doping and coating with an appropriate content of the M element in the positive electrode active material of the present invention can further improve the electrochemical properties of the material. When the M element in the core is more or less, the capacity is seriously affected, and when the M element in the shell is more or less, the material polarization is increased and the cycle performance is deteriorated, so that the capacity and the cycle performance of example 1 are higher than those of examples 6 to 9.
TABLE 4
Comparative example 3
The process is the same as example 1 except that sodium tungstate is not added in the step (1), the step (2) is not performed, and tungstic acid is added after the step (3) is sintered at 650 ℃ for sintering for 6 hours.
As can be seen from comparison between example 1 and comparative examples 1 to 3 in table 4, in the present invention, doping and coating the M element on the surface of the positive active material by two coprecipitations can improve the first-time discharging capacity, coulombic efficiency, and capacity retention rate of the material. In comparative examples 1 and 2, the W element is not doped or coated, the inner core or the outer shell of the material does not contain W, the interfacial polarization cannot be effectively reduced, and the diffusion rate of lithium ions is improved, in comparative example 3, the tungstic acid is directly sintered on the surface of the ternary material for doping and coating by adopting a traditional fire sintering mode, although the doping and coating of W are realized, the fire sintering mode is not beneficial to the combination of the inner core and the outer shell, the outer shell is easy to fall off in the circulation process, the interface stability of the material is poor, the crystallinity is poor, the polarization is high, and the interface impedance is strong, so that the first discharge gram capacity, the first coulomb efficiency and the 800-week circulation capacity retention rate of the comparative examples 1 to 3 are all inferior to those of example 1.
In summary, in embodiments 1 to 9, W, Nb and/or Mo are doped and coated in the positive active material of the present invention, so that crystallinity and interface stability of the material are improved, polarization of the battery is reduced, and dynamic performance, capacity, and cycle performance of the battery are improved; furthermore, the method adopts twice coprecipitation reactions, overcomes the defects that the traditional large-particle tungsten source, niobium source and molybdenum source are not easy to dope into crystal lattices during pyrogenic sintering, are difficult to coat on the surface of a material crystal boundary, and have poor combination of a coating layer and a matrix, improves the crystallinity and interface stability of the material, reduces the polarization of the battery, and improves the dynamic performance, capacity and cycle performance of the battery.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The positive active material is characterized by comprising a positive active material inner core and a positive active material outer shell coated on the surface of the positive active material inner core; the positive active material core includes LiNi a Co b Mn 1-a-b-c M c O 2 Wherein a is more than or equal to 0.56 and less than or equal to 0.60, b is more than or equal to 0.09 and less than or equal to 0.13, c is more than or equal to 0.001 and less than or equal to 0.01, M comprises W, Nb and Mo, or the combination of at least two of the two, and the positive active material shell comprises M compound.
2. The positive electrode active material according to claim 1, wherein the particle diameter D of the positive electrode active material core v 50 is 3.4 μm to 4 μm.
3. The positive electrode active material according to claim 1, wherein the content of M in the positive electrode active material core is 2000ppm to 3000ppm based on the mass of the positive electrode active material.
4. The positive electrode active material according to claim 1, wherein the content of M in the positive electrode active material casing is 1000ppm to 2000ppm based on the mass of the positive electrode active material.
5. The positive electrode active material according to claim 1, wherein M is W, and the compound of M is lithium tungstate.
6. An electrochemical device, characterized in that a positive electrode of the electrochemical device comprises the positive electrode active material according to any one of claims 1 to 5.
7. The electrochemical device of claim 6, further comprising an electrolyte and a separator.
8. The electrochemical device according to claim 7, wherein the electrolyte includes a lithium salt and a solvent, and the lithium salt and the solvent satisfy any one of the following conditions (a) to (c):
(a) the lithium salt comprises LiPF 6 ；
(b) The content of the lithium salt is 4-24 wt% based on 100 wt% of the electrolyte;
(c) the solvent comprises any one of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and polycarbonate or the combination of at least two of the ethylene carbonate, the ethyl methyl carbonate, the dimethyl carbonate and the polycarbonate.
9. The electrochemical device according to claim 7, wherein the separator satisfies any one of the following conditions (d) to (f):
(d) the thickness of the diaphragm is 9 to 18 μm;
(e) the air permeability of the diaphragm is 180s/100mL to 380s/100 mL;
(f) the porosity of the separator is 30% to 50%.
10. An electronic device, characterized in that the electrochemical device according to any one of claims 6 to 9 is included in the electronic device.
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