CN115084505B

CN115084505B - Positive electrode active material and electrochemical device

Info

Publication number: CN115084505B
Application number: CN202211010347.5A
Authority: CN
Inventors: 朱泰洋; 陈巍; 胡燚
Original assignee: Sunwoda Electric Vehicle Battery Co Ltd
Current assignee: Xinwangda Power Technology Co ltd
Priority date: 2022-08-23
Filing date: 2022-08-23
Publication date: 2023-01-10
Anticipated expiration: 2042-08-23
Also published as: WO2024040830A1; CN115084505A; CN115548329A

Abstract

The application discloses a positive electrode active material and an electrochemical device. A positive electrode active material including secondary particles having pores, the pore size distribution of the secondary particles satisfying: d is more than or equal to 0.05 _HW /D _max Less than or equal to 0.5; wherein D is _HW Denotes a half-peak width, D, of a pore size distribution of the positive electrode active material _max Represents the maximum value of the pore diameter of the positive electrode active material. The positive active material has proper pore size distribution and porosity, can be fully infiltrated with electrolyte, can exert higher power performance at a lower temperature by matching with proper particle size distribution, and effectively improves the problem of side reaction between the surface of a newly exposed material and the electrolyte, thereby prolonging the cycle life of an electrochemical device.

Description

Positive electrode active material and electrochemical device

Technical Field

The application relates to the technical field of secondary batteries, in particular to a positive electrode active material and an electrochemical device.

Background

Electrochemical devices, such as lithium ion batteries, have the advantages of high energy density, good cycle performance, high charging efficiency, and the like, and particularly, the development in the field of electric vehicles is very rapid, but the lithium ion batteries are simultaneously subjected to severe tests such as insufficient endurance, short battery life, insufficient performance in cold weather, and the like. It is therefore required to improve the cycle stability and low-temperature performance of the battery.

The prior art carries out surface coating or doping on the positive electrode active material, the performance of the lithium ion battery is improved to a certain extent, but the electric conductivity of the primary particles in the secondary particles is reduced due to the close packing of the primary particles, the coating effect of the primary particles in the secondary particles is poor, the shrinkage and expansion of the grains can be inevitably generated in the positive electrode active material in the secondary particle shape in the circulating process, so that the new surface of the grains is exposed, side reaction is generated with electrolysis, the circulating life of the battery is shortened, the particle size of the currently prepared material is larger, the specific surface area is smaller, the low-temperature dynamic performance of the battery is poor, the power performance is limited, and the application range of the battery is reduced.

Disclosure of Invention

The purpose of the invention is as follows: the application provides a positive active material composed of secondary particles with specific pore size distribution, which improves the coating effect of primary particles in the positive active material, not only realizes higher low-temperature power performance of an electrochemical device, but also ensures that the electrochemical device has better long-term service life; another object of the present application is to provide an electrochemical device comprising the above-mentioned cathode active material.

The technical scheme is as follows: a positive electrode active material of the present application includes secondary particles having pores, the pore size distribution of the secondary particles satisfying: d is more than or equal to 0.05 _HW /D _max Less than or equal to 0.5; wherein D is _HW Denotes a half-peak width, D, of a pore size distribution of the positive electrode active material _max Represents the maximum value of the pore diameter of the positive electrode active material.

In some embodiments, the D _HW Satisfies the following conditions: 100nm is less than or equal to D _HW Less than or equal to 400 nm; said D _max Satisfies the following conditions: 800nm is less than or equal to D _max ≤2000 nm。

In some embodiments, the positive electrode active material has a porosity P ₁ Satisfies the following conditions: p is more than or equal to 30% ₁ ≤80%。

In some embodiments, the secondary particles comprise lithium nickel cobalt manganese oxide particles further comprising an a element comprising one or more of Zr, sr, W, al, ti, mg, ce, Y.

In some embodiments, the positive electrode active material includes lithium nickel cobalt manganese oxide particles, and a molar amount of the nickel element is greater than or equal to 0.4 based on a molar amount of the nickel element, the cobalt element, and the manganese element being 1.

In some embodiments, the positive electrode active material comprises Li _x A _y Ni _a Co _b Mn _c O _z Wherein x is more than or equal to 0.9 and less than or equal to 1.1, y is more than or equal to 0 and less than or equal to 0.2, z is more than or equal to 1 and less than or equal to 2, a is more than or equal to 0.4 and less than or equal to 2<1，0<b<0.3，0<c<1,a + bc= 1, said A contains one or more of Zr, sr, W, al, ti, mg, ce, Y.

In some embodiments, the secondary particle includes a hollow structure formed by stacking primary particles, and a surface of the secondary particle and a surface of the primary particle located in the hollow structure have an a element; the average content a of the element A on the surface of the secondary particles ₀₁ And the average content a of the element A on the surface of the primary particles in the hollow structure ₀₂ Satisfies the following conditions:

and is and

，

；

in the formula, a _i Representing the content of an element A obtained by testing an ith area selected on the surface of the secondary particles, wherein i is more than or equal to 1 and less than or equal to m, and m is an integer more than or equal to 3; a is a _j The content of the element A obtained by testing the jth area selected on the surface of the primary particles is shown, j is more than or equal to 1 and less than or equal to n, and n is an integer more than or equal to 3.

In some embodiments, the a _i The variance E of (c) satisfies: e is more than or equal to 0 and less than or equal to 1 multiplied by 10 ^-4 (ii) a A is a _i The extreme difference C satisfies: c is more than or equal to 0 and less than or equal to 0.05.

In some embodiments, the a _j The variance I of (1) satisfies: i is more than or equal to 0 and less than or equal to 1 multiplied by 10 ^-3 (ii) a A is a _j The range D of (A) satisfies: d is more than or equal to 0 and less than or equal to 0.05.

In some embodiments, the variance E and the range C are calculated by composing a data set from the content of the element a measured in m regions arbitrarily selected on the surface of the secondary particle; the variance I and the range D are obtained by calculating a data set formed by the content of the element A measured by randomly selecting n areas on the surface of the primary particles; wherein m and n are at least 3, and the preferable value of m and n is 10.

In some embodiments, the positive electrode active material satisfies at least one of the following characteristics:

(a) The average pore diameter of the positive active material is 100nm to 2000nm;

(b) The specific surface area of the positive electrode active material was 0.2m ² /g~1.5m ² /g；

(c) The average particle diameter Dv50 of the positive electrode active material is 2 μm to 8 μm.

In some embodiments, an electrochemical device of the present application includes a positive current collector and a positive electrode tab disposed on the positive current collector, the positive electrode tab including a positive active material.

In some embodiments, the porosity P of the positive electrode sheet ₂ Satisfies the following conditions: p is more than or equal to 20% ₂ ≤50%。

In some embodiments, the low temperature charging power P of the electrochemical storage device _CC More than 20W, and the low-temperature discharge power P of the electrochemical energy storage device _DC ＞60W。

Has the beneficial effects that: compared with the prior art, the positive active material comprises the secondary particles with holes, the secondary particles have proper pore size distribution, the infiltration performance between the positive active material and electrolyte can be improved, and the particle breakage in the rolling and circulating processes is reduced due to proper adjustment of the tightness degree between the secondary particles. By matching with proper particle size distribution, the composite material still can exert higher power performance at lower temperature. The secondary particles have holes, so that the coating effect is obviously improved, and the problem of side reaction between the surface of the newly exposed material and the electrolyte can be effectively improved even if the secondary particles are broken in the rolling and circulating processes, so that the cycle life of the electrochemical device is prolonged. The application achieves the effects of improving the low-temperature power performance of the electrochemical device and ensuring better long-term cycle life by limiting the pore size distribution and the porosity.

Drawings

The technical solutions and other advantages of the present application will become apparent from the following detailed description of specific embodiments of the present application when taken in conjunction with the accompanying drawings.

Fig. 1 is an electron microscope characterization test chart of a positive electrode material provided in an embodiment of the present application;

FIG. 2 is an electron microscope characterization test chart of a hollow structure of a secondary particle provided in the embodiments of the present application;

FIG. 3 shows the parameters of the positive electrode active material test provided in the examples of the present application;

fig. 4 shows the low-temperature charge/discharge power test and cycle number test results of the electrochemical device provided in the embodiment of the present application.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. It is to be understood that the embodiments described are only a few embodiments of the present application and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

In the description of the present application, "a plurality" means two or more unless specifically limited otherwise. Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more features.

In the description of the present application, the term "step" includes not only an independent step but also a step that is not clearly distinguished from other steps as long as the purpose of the step is achieved. In the present specification, the numerical range indicated by the term "to" means a range including the numerical values described before and after the term "to" as the minimum value and the maximum value, respectively. In the present specification, the term "layer" includes, in addition to a structure having a shape formed over the entire surface, a structure having a shape formed in a part thereof when viewed in a plan view.

The following disclosure provides many different embodiments or examples for implementing different features of the application. In order to simplify the disclosure of the present application, specific example components and arrangements are described below. Of course, they are merely examples and are not intended to limit the present application.

Positive electrode active material

The application provides a positive active material, positive active material is including the secondary particle that has pore structure, and the secondary particle is piled up by primary particle and is constituteed, and the secondary particle surface has suitable aperture, and the pore size distribution satisfies: d is more than or equal to 0.05 _HW /D _max Less than or equal to 0.5; wherein D is _HW The half-peak width of the pore size distribution of the positive active material is represented, namely the peak width corresponding to half of the highest value of the pore size distribution peak is represented; d _max Represents the maximum value of the pore diameter of the positive electrode active material. In some implementations, D _HW /D _max Satisfies the following conditions: d is more than or equal to 0.15 _HW /D _max Less than or equal to 0.3. When the pore size distribution meets the relationship, the breakage of particles of the positive active material in the rolling and/or circulating process can be relieved, and meanwhile, the positive active material and the electrolyte can be fully infiltrated through the proper pore size distribution, so that the electrochemical device can still exert higher power performance at lower temperature.

In some implementations, D _HW Satisfies the following conditions: 100nm is less than or equal to D _HW Less than or equal to 400 nm; for example, the average particle diameter may be 100nm, 120nm, 150nm, 180nm, 200nm, 230nm, 250nm, 280nm, 290nm, 310nm, 350nm, 400nm, or a range consisting of any two of these. When D is present _HW Within the above range, the electrochemical device has a better pore size distribution, so that the electrochemical device has a better low-temperature power performance and a better long-term cycle life performance.

In some implementations, 150nm ≦ D _HW Less than or equal to 300nm. When D is present _HW Within the above range, the low-temperature power performance and cycle life of the electrochemical device can be further improved.

In some implementations, D _max Satisfies the following conditions:800 nm≤D _max less than or equal to 2000nm; for example, the average molecular weight of the light-emitting element may be 800nm, 850nm, 900nm, 950nm, 1000nm, 1050nm, 1100nm, 1150nm, 1200nm, 1250nm, 1300nm, 1400nm, 1500nm, 1700nm, 1800nm, 2000nm, or a range consisting of any two of them. When D is _max Within the above range, the electrochemical device has a more excellent pore size distribution, resulting in a more excellent overall performance of the electrochemical device.

In some embodiments, 1050nm ≦ D _max Less than or equal to 1500 nm. When D is present _max Within the range, the electrochemical device has better pore size distribution, and the tightness degree between secondary particles is better adjusted, so that the electrochemical device has better comprehensive performance.

In some embodiments, the porosity P of the positive electrode active material ₁ Satisfies the following conditions: p is more than or equal to 30% ₁ Less than or equal to 80 percent. When the pore size distribution of the positive electrode active material satisfies D of 0.05. Ltoreq _HW /D _max Less than or equal to 0.5, and when the porosity satisfies the above range, the positive active material can be better contacted with the electrolyte, and the comprehensive performance of the electrochemical device is improved.

In some embodiments, the porosity P of the positive electrode active material ₁ Satisfies the following conditions: p is more than or equal to 35 percent ₁ ≤72%。

In some embodiments, the porosity P of the positive electrode active material ₁ Satisfies the following conditions: p is more than or equal to 40% ₁ Less than or equal to 60 percent. When the porosity of the positive electrode active material is within this range, the electrochemical device can have more excellent overall performance.

In some embodiments, the positive electrode active material includes lithium nickel cobalt manganese oxide particles, and a molar amount of the nickel element, the cobalt element, and the manganese element is 1, and a ratio of the molar amount of the nickel element is greater than or equal to 0.4.

In some embodiments, the molar amount of the nickel element is less than or equal to 0.7. When the pore size distribution meets the above conditions and the nickel element is in the range, the side reaction of the electrochemical device is reduced, and the comprehensive performance is better.

In some embodiments, the secondary particles comprise lithium nickel cobalt manganese oxide secondary particles further comprising element a, plusThe electrode active material contains Li _x A _y Ni _a Co _b Mn _c O _z Wherein x is more than or equal to 0.9 and less than or equal to 1.1, y is more than or equal to 0 and less than or equal to 0.2, z is more than or equal to 1 and less than or equal to 2, a is more than or equal to 0.4 and less than or equal to 2<1，0<b<0.3，0<c<1，a+b+c=1。

In some embodiments, a may be a cladding element, a comprising one or more of Zr, sr, W, al, ti, mg, ce, Y. The coating material can reduce the side reaction of the electrolyte and the anode active material, and the element A on the surface of the anode active material can more effectively isolate the direct contact of the anode active material and the electrolyte so as to reduce the erosion of the electrolyte to the surface of the anode material and avoid the thickening of a negative electrode SEI film and the consumption of active lithium, so that the capacity of the electrochemical device is attenuated.

In some embodiments, a comprises Al, and one or more of Zr, sr, W, al, ti, mg, ce, Y.

In some embodiments, the proper element A is selected to enable the coating layer to be in a better state, so that the coating effect is better; by selecting the proper element A, the anode active material can be in a proper state with the reaction of the electrolyte, so that the side reaction is reduced, the consumption of the electrolyte is reduced, the blockage of lithium ion migration is avoided, the polarization of the battery is increased, and the power performance of the battery is reduced.

In some embodiments, the content of the element a in the positive electrode active material is appropriate, so that a better protective layer can be formed on the surface of the positive electrode active material particles, the components and the thickness of the protective layer are in a better state, and the electrochemical device has better comprehensive performance.

In some embodiments, the surface of the positive electrode active material particles may further include at least one of phosphorus, boron, fluorine, silicon, and sulfur.

In some embodiments, the pore structure on the secondary particle includes a hollow structure composed of a packing of the primary particles, and the surface of the secondary particle and the surface of the primary particle located in the hollow structure have the a element. The primary particles in the hollow structure are primary particles that are cut into secondary particles to form the surface of the hollow structure, as shown in fig. 2. Average content a of A element on the surface of secondary particle ₀₁ Average content a of A element on the surface of primary particles in hollow structure ₀₂ Satisfies the following conditions:

and is and

，

；

in the formula, a _i The content of the element A obtained by testing the ith area selected on the surface of the secondary particles is expressed, i is more than or equal to 1 and less than or equal to m, and m is an integer more than or equal to 3; a is a _j Represents the content of the A element obtained by the test of the jth area selected on the surface of the primary particles, j is more than or equal to 1 and less than or equal to n, and n is an integer more than or equal to 3.

a ₀₁ The test result of the content of the element a in different regions of the same secondary particle may be obtained, or the test result of the content of the element a in one region may be obtained for different secondary particles, each of which is obtained by testing.

a ₀₂ The test result of the content of the element a in different regions of the same secondary particle may be obtained, or the test result of the content of the element a in one region may be obtained for different secondary particles, each of which is obtained by testing.

a ₀₁ And a ₀₂ Different particles may be used as long as the content of the a element on the surface of the secondary particle and the surface of the primary particle in the hollow structure can be reflected.

When the average content a of the element A on the surface of the secondary particles ₀₁ Average content a of A element on the surface of primary particles in hollow structure ₀₂ When the above relationship is satisfied, the secondary particles can be in a preferable coating state, and the secondary reaction between the positive electrode active material particles and the electrolyte can be further reduced, so that the electrochemical device can be in a preferable state.

In some embodiments, a _i The number of the A element is determined by the number of the test areas selected on the surface of the secondary particles, and the component number of the A element content obtained by testing each test areaThe variance E of the data set satisfies: e is more than or equal to 0 and less than or equal to 1 multiplied by 10 ^-4 The range C satisfies: c is more than or equal to 0 and less than or equal to 0.05.

In some embodiments, a _j The number of the A elements is determined by the number of the test areas selected on the surface of the primary particles, the A element content obtained by testing under each test area forms a data set, and the variance I of the data set satisfies the following conditions: i is more than or equal to 0 and less than or equal to 1 multiplied by 10 ^-3 And the range D satisfies: d is more than or equal to 0 and less than or equal to 0.05.

In some embodiments, the variance E satisfies: e is more than or equal to 0 and less than or equal to 1 multiplied by 10 ^-4 The range C satisfies: c is more than or equal to 0 and less than or equal to 0.05, and when the values of E and I meet the range, the surface of the secondary particle is provided with the element A. The variance I satisfies: i is more than or equal to 0 and less than or equal to 1 multiplied by 10 ^-3 And the range D satisfies: d is more than or equal to 0 and less than or equal to 0.05, which shows that the element A is uniformly distributed on the surfaces of the secondary particles and the surfaces of the primary particles in the hollow structure, and has better coating effect.

In some embodiments, a sample of the positive electrode active material particles including the secondary particles is taken, and then SEM (Scanning Electron Microscope) detection is performed on the outer surface of the sample to obtain an SEM image, as shown in fig. 1; then, the secondary particles are cut by ion milling (CP), focused Ion Beam (FIB), or the like, and the hollow structure of the secondary particles is detected by a Transmission Electron Microscope (TEM), thereby obtaining a TEM image as shown in fig. 2. As can be seen from fig. 1 and 2: it can be seen from fig. 1 that the secondary particles are stacked from the primary particles, and from fig. 2 that the secondary particles have a hollow structure inside. Through holes with proper sizes are distributed among the primary particles, the surface of the primary particles in the hollow structure can be coated through the pore channels, and the interface stability of the anode material, the cycle performance of the battery and the low-temperature power performance are improved.

In some embodiments, the a element content a of the secondary particle surface ₁ And the A element content a of the primary particle surface ₂ Refers to the mass concentration of the A element in all the elements, and can be analyzed by EDS (Energy Dispersive Spectroscopy) or EDX (Energy Dispersive X-Ray Spectroscopy) in combination with SEM (Scanning Electron Microscope)Micromirror) or TEM (Transmission Electron Microscope) single point scanning to measure the elemental concentration distribution or the like.

In some embodiments, when EDX or EDS elemental analysis is combined with TEM or SEM single-point scan testing, referring to fig. 1, ten regions optionally and uniformly distributed on the surface of the secondary particles are selected for testing, to obtain test values of a content of the element a in the ten regions, and the test values of the a content in the ten regions are combined into a data set, so that a variance E and a range C can be calculated respectively; referring to fig. 2, ten regions which are optionally and uniformly distributed are selected on the surface of the primary particles for testing, test values of the content of the element a of the ten regions are obtained, and the test values of the content of the element a of the ten regions are combined into a data set, so that a variance I and a range D can be respectively calculated.

In some embodiments, the secondary particle surface area is selected as shown in the box of fig. 1, and different locations on the surface of the same secondary particle may be selected, or the surfaces of different secondary particles within the field of view may be selected; the selection of the cross-section internal area of the secondary particles is shown as a box in fig. 2, and primary particles in the same secondary particles can be selected, or primary particles in different secondary particles can be selected; it is more typical that the primary particles contain at least three or more secondary particles within the same field of view.

In some embodiments, the inventors found that when the average content difference between the a element on the surface of the secondary particles and the surface of the primary particles inside the secondary particles is 40% or less, it indicates that the coating effect on the surface of the primary particles inside the positive electrode active material is consistent with the coating effect on the surface of the secondary particles, which can effectively improve the structural stability of the primary particles inside the positive electrode active material, reduce the side reaction with the electrolyte, and improve the dynamic performance of the material. In addition, because the coating effect of the internal particles is improved, the difference of the internal and external dynamic properties is small, the electrode polarization is reduced, the capacity exertion of the positive active material is favorably improved, the stability of the material is improved, and the cycle life of the battery is favorably prolonged.

In some embodiments, the distribution and size of the pore size are mainly influenced by the preparation process, precursors with different porosity degrees are formed by regulating the structure of the precursor through regulating the concentration of ammonia water and the pH value, and then products with different pore sizes and pore size distributions can be obtained by regulating the sintering temperature and time.

In some embodiments, the internal pore structure of the secondary particles is closely related to the compressive resistance, power, cycling and storage properties of the particles, and the high porosity favors the low temperature power of the material but degrades long term performance, so that the D of the pore size distribution profile can be adjusted by adjusting the pore size distribution and porosity _HW /D _max The range is favorable for forming a good coating effect on the surface of the primary particles in the secondary particles so as to achieve the purpose that the difference between the coating effect of the inner part and the coating effect of the outer part of the secondary particles is small.

In some embodiments, the pore size is between 10nm and 2000nm, so that the dispersion of the coating material is facilitated, the coating material enters the inner surface through a pore-size channel, and D is more than or equal to 0.05 _HW /D _max When the temperature is less than or equal to 0.5, the coating effect of the inner surface is obviously improved, and the low-temperature power of the prepared battery is obviously improved; the reason is that when D _HW /D _max The ratio is too large, which indicates that the contact between material particles is poor, the structural stability is also affected, the dynamics and the cycling stability are poor, the process difficulty and the manufacturing cost are increased, and side reactions occur; when D is present _HW /D _max The ratio is too small, which is not beneficial to material coating and electrolyte infiltration, and causes poor material stability and dynamic performance, thereby regulating and controlling the D of the pore size distribution of the secondary particles _HW /D _max The ratio is in a proper range, which is beneficial to low-temperature power performance, not only can realize higher low-temperature power performance of the positive active material, but also can ensure better long-term service life of the positive active material.

In some embodiments, the average pore size of the positive electrode active material is from 100nm to 2000nm; preferably, the average pore diameter of the positive electrode active material is 300nm to 1500nm, and more preferably 400nm to 1000nm. For example, the average pore diameter of the positive electrode active material is 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1100nm, 1200nm, 1300nm, 1400nm, 1500nm, 1600nm, 1700nm, 1800nm, 1900nm. The average pore diameter of the anode active material reflects the state of primary particle accumulation, and the proper pore diameter can not only provide a transmission channel of a coating substance, but also ensure the density of secondary particles, so that the mechanical strength of the material can meet the requirement of circulation stability.

In some embodiments, the specific surface area of the positive electrode active material is 0.2m ² /g~1.5m ² (ii)/g; the specific surface area of the preferred positive electrode active material is 0.5m ² /g~1.3m ² A specific ratio of 0.8 m/g ² /g~1.2m ² (ii) in terms of/g. For example, the specific surface area of the positive electrode active material is 0.3m ² /g、0.4m ² /g、0.5m ² /g、0.6m ² /g、0.7m ² /g、0.8m ² /g、0.9m ² /g、1.0m ² /g、1.1m ² /g、1.2m ² /g、1.3m ² /g、1.4m ² (ii) in terms of/g. The specific surface of the positive active material is in a proper range, and the contact area of the positive active material and the electrolyte is in a better range, so that the positive pole piece has a better infiltration effect, simultaneously, the ohmic impedance is smaller, and the battery has better comprehensive performance.

In some embodiments, the cathode active material has an average particle diameter Dv50 of 2 μm to 8 μm; the average particle diameter Dv50 of the positive electrode active material is preferably 2.5 to 6 μm, and more preferably 3 to 5 μm. For example, the average particle diameter Dv50 of the positive electrode active material is 3 μm, 4 μm, 5 μm, 6 μm, 7 μm. The average particle diameter Dv50 of the positive electrode active material is within a proper range, so that the migration path of lithium ions and the reaction area of the electrolyte are both within a proper range, and the battery has excellent cycle performance.

In some embodiments, the average particle diameter Dv50 of the positive electrode active material is a value well known in the art, also referred to as a median particle diameter, which represents a particle diameter corresponding to 50% of the volume distribution of the positive electrode active material particles. The average particle diameter Dv50 of the positive electrode active material may be measured by an apparatus and a method known in the art, for example, by a laser particle size analyzer.

In some embodiments, the specific surface area of the cathode active material is well known in the art and can be determined using instruments and methods well known in the art, such as by nitrogen adsorption specific surface area analysis (BET) and calculated using the Brunauer Emmett Teller method.

In some embodiments, a method of preparing a positive active material is also disclosed, the method comprising:

preparing a precursor: dispersing a nickel source, a cobalt source and a manganese source in deionized water to obtain a mixed solution; simultaneously pumping the mixed solution, the strong base solution and the complexing agent solution into a reaction kettle with a stirrer by adopting a continuous parallel flow reaction mode, controlling the pH value of the reaction solution to be 10 to 13, controlling the temperature in the reaction kettle to be 25 to 90 ℃, and introducing inert gas for protection in the reaction process; after the reaction is finished, the precursor of the nickel-cobalt-manganese hydroxide is obtained through the procedures of washing, filtering, vacuum drying, sieving, iron removal and the like.

Preparing a positive electrode active material: carrying out first high-temperature sintering on a looser and porous nickel-cobalt-manganese hydroxide precursor prepared by a coprecipitation method and a lithium source, wherein the sintering temperature is 600-1100 ℃, the sintering time is 8-24h, adjusting the structure of the precursor by regulating the concentration of ammonia water and the pH value to form precursors with different loosening degrees, and then regulating the temperature and time of the first sintering to obtain intermediate products with different pore sizes and pore size distributions; and then, carrying out a coating process on the intermediate product, namely carrying out high-temperature sintering on the intermediate product and a coating material containing the element A for the second time, wherein the sintering temperature is 400-700 ℃, and the sintering time is 6-12 h, so as to obtain different anode active materials.

In some embodiments, the nickel source, cobalt source, manganese source are one or more of oxides, hydroxides, or carbonates containing Ni, co, and Mn, selected in stoichiometric ratios.

In some embodiments, the structure of the precursor can be controlled by selecting reaction raw materials, the pH value of the reaction solution, the concentration of the mixed solution, the concentration of the complexing agent, the reaction temperature, the reaction time, and the like in the preparation of the nickel-cobalt-manganese hydroxide precursor.

In some embodiments, the nickel source may include one or more of nickel acetate, nickel nitrate, nickel sulfate, nickel hydroxide, nickel chloride, or nickel carbonate.

In some embodiments, the cobalt source may include one or more of cobalt sulfate, cobalt hydroxide, cobalt nitrate, cobalt fluoride, cobalt chloride, or cobalt carbonate.

In some embodiments, the manganese source may include one or more of manganese sulfate, manganese chloride, manganese nitrate, or manganese hydroxide.

In some embodiments, the strong alkaline solution may include one or more of LiOH, naOH, and KOH; the complexing agent can be one or more of ammonia water, ammonium sulfate, ammonium nitrate and ammonium chloride.

In some embodiments, the solvent of each of the mixed solution, the alkali solution, and the complexing agent solution is not particularly limited, for example, the solvent of each of the mixed solution, the alkali solution, and the complexing agent solution is independently one or more of deionized water, methanol, ethanol, acetone, isopropanol, and n-hexanol.

In some embodiments, the inert gas is one or more of nitrogen, argon, helium.

In some embodiments, the lithium source may include one or more of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate, or lithium chloride.

In some embodiments, the precursor of the coating material comprising the a element can be one or more of an oxide, chloride, sulfate, nitrate, hydroxide, fluoride, carbonate, bicarbonate, acetate, phosphate, dihydrogen phosphate, and an organic compound of a.

In some embodiments, by reasonably controlling the primary sintering temperature and the secondary sintering temperature, the pore size distribution of the secondary particles is wider, so that appropriate pores can be formed, and it is ensured that the element a can be formed on the surface of the secondary particles, and can enter the interior of the secondary particles through the pores and be formed on the surface of the primary particles.

In some embodiments, before the intermediate product and the coating containing the element a are subjected to the second high-temperature sintering, the intermediate product may be further subjected to a crushing treatment and a sieving treatment to obtain the cathode active material with optimized particle size distribution and specific surface area. The crushing mode is not particularly limited, and may be selected according to actual requirements, for example, a particle crusher is used.

The method for producing the positive electrode active material of the present application is not limited to the above-described production method as long as the formed positive electrode active material has the characteristics shown in the present application.

Electrochemical device

The electrochemical device comprises a positive current collector and a positive pole piece arranged on the positive current collector, wherein the positive pole piece comprises a positive active material. Because the positive pole piece adopts the positive active material, the battery adopting the positive pole piece can simultaneously give consideration to higher low-temperature power performance and better long-term service life.

In some embodiments, the positive electrode current collector may be made of a metal foil or a porous metal plate with good electrical conductivity and mechanical properties, and the material may be one or more of aluminum, copper, nickel, titanium, silver and their respective alloys. Preferably an aluminium foil.

In some embodiments, the positive electrode sheet further includes a conductive agent and a binder, wherein the conductive agent may include conductive carbon black, carbon nanotubes, graphene, and the like, and the binder may include polyvinylidene fluoride.

In some embodiments, the preparation of the positive electrode sheet comprises: dispersing the positive electrode active material, the conductive agent and the binder in N-methylpyrrolidone (NMP) according to the mass ratio of (91) - (94): (1) - (7): 1) - (3), coating the obtained slurry on an aluminum foil with the thickness of 12-16 mu m, drying the aluminum foil in an oven at the temperature of 100-130 ℃, and then carrying out cold pressing and splitting to obtain the positive electrode piece.

In some embodiments, the mass ratio of the positive electrode active material, the conductive agent, and the binder may further include 96.

In some embodiments, the porosity P of the positive electrode sheet ₂ Satisfies the following conditions: p is more than or equal to 25% ₂ Less than or equal to 46 percent. Within the range of (a) to (b),the electrolyte and the positive pole piece have better infiltration performance, so that the overall performance of the electrochemical device is better.

In some embodiments, the electrochemical device may further include a negative electrode tab, a separator, and an electrolyte.

In some embodiments, the preparation of the negative electrode sheet comprises: mixing a negative electrode active material, a thickening agent, an adhesive and a conductive agent according to a mass ratio of (91) - (96): (0.5) - (1.5): 1.3) - (2.7), adding deionized water, and obtaining a negative electrode slurry under the action of a vacuum stirrer; and uniformly coating the negative electrode slurry on copper foil with the thickness of 5-12 microns, drying by using an oven at 100-130 ℃, and then performing cold pressing and stripping to obtain the negative electrode piece.

In some embodiments, the mass ratio of the negative electrode active material, the thickener, the binder and the conductive agent may further include 97.

In some embodiments, the electrolyte comprises: the organic solvent can comprise chain ester and cyclic ester, and the mass percentage of the chain ester is larger than that of the cyclic ester. The cyclic ester may include Ethylene Carbonate (EC) and/or propylene carbonate (PP), and the chain ester may include at least one of dimethyl carbonate (DMC), ethyl Methyl Carbonate (EMC), or diethyl carbonate (DEC). In some embodiments, the solvent of the electrolyte includes EC, EMC, and DEC. In some embodiments the mass ratio of EC, EMC and DEC is (10 to 25): (51 to 75). In some embodiments, the preparing of the electrolyte comprises: and dissolving the fully dried lithium salt in an organic solvent in an argon atmosphere glove box with the water content of less than 10ppm, and uniformly mixing to obtain the electrolyte. Wherein the concentration of the lithium salt is 0.8 to 1.3mol/L.

In some embodiments, the lithium salt may be LiPF ₆ (lithium hexafluorophosphate), liBF ₄ (lithium tetrafluoroborate), and the like.

In some embodiments, the preparation of the separator comprises: selecting a polypropylene film with the thickness of 9-18 mu m as the isolating film. The separator is not particularly limited, and any known separator having a porous structure and electrochemical stability and mechanical stability may be used.

In some embodiments, the preparing of the electrochemical device comprises: the method comprises the steps of sequentially stacking a positive pole piece, an isolation film and a negative pole piece to enable the isolation film to be positioned between the positive pole piece and the negative pole piece to play a role of isolation, winding the positive pole piece and the negative pole piece into a square bare cell, then packaging the square bare cell into a cell shell, then baking the cell shell at 65-95 ℃ to remove water, injecting electrolyte into the cell shell, sealing the cell shell, and obtaining the electrochemical device after procedures of standing, hot cold pressing, formation, clamping, capacity grading and the like.

In some embodiments, the electrochemical device includes a lithium ion battery, and the above is only a soft package lithium ion battery, and the application is not limited to the application of soft package battery, but also includes the application of common lithium ion battery forms such as aluminum shell battery, cylindrical battery, etc.

In some embodiments, the electrochemical devices of the present application can be used in, but are not limited to, backup power sources, electric motors, electric automobiles, electric motorcycles, mopeds, bicycles, electric tools, large household batteries, and the like.

In some embodiments, the low temperature charging power P of the electrochemical devices of the present application _CC ＞20W。

In some embodiments, the low temperature charging power P of the electrochemical devices of the present application _CC ＞24W。

In some embodiments, the low temperature charging power P of the electrochemical devices of the present application _CC > 26W. The self electrochemical device is adopted, so that the low-temperature charging power of the electrochemical device is in a better range. The low temperature is a temperature below 0 ℃. The low temperature used in this application is-20 ℃.

In some embodiments, the low temperature discharge power P of the electrochemical energy storage devices of the present application _DC ＞60W。

In some embodiments, the low temperature discharge power P of the electrochemical energy storage devices of the present application _DC > 68W. By adopting the electrochemical device, the low-temperature discharge power of the electrochemical device can be in a better range. The low temperature is a temperature below 0 ℃. The low temperature used in this application is-20 ℃.

Example 1

1) Preparing a precursor: dispersing a nickel source, a cobalt source and a manganese source in deionized water to obtain a mixed solution; simultaneously pumping the mixed solution, a NaOH solution and an ammonia water complexing agent solution into a reaction kettle with a stirrer in a continuous parallel flow reaction mode, adjusting the concentration of ammonia water to 2.5g/L, controlling the pH value of the reaction solution to be 12, controlling the temperature in the reaction kettle to be 45 ℃, and introducing inert gas for protection in the reaction process; after the reaction is finished, the nickel-cobalt-manganese hydroxide precursor [ Ni ] is obtained through the procedures of washing, filtering, vacuum drying, sieving for removing iron and the like _0.5 Co _0.2 Mn _0.3 ](OH) ₂ The precursor is spherical secondary particles formed by closely packing primary particles, and the average particle diameter Dv50 of the precursor is 4 mu m. The length of the primary particles is 200nm to 800nm, the width of the primary particles is 100nm to 400nm, and the length-width ratio of the primary particles is 2 to 8; for example, the primary particle length is 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm; the primary particle width was 200nm and 300nm.

(2) Preparing a positive electrode active material: lithium carbonate and precursor [ Ni ] _0.5 Co _0.2 Mn _0.3 ](OH) ₂ Adding the mixture into a high-speed mixer, mixing for 30min, and performing primary sintering at 850 ℃ for 25h to obtain an intermediate product. Carrying out secondary mixing after primary crushing, adding oxides of Al and W and an intermediate product into a high-speed mixer according to a stoichiometric proportion, mixing for 20min, carrying out secondary sintering at the temperature of 500 ℃ for 8h, and carrying out screening and demagnetizing to obtain the anode active material Li _1.08 Al _0.002 W _0.0015 Ni _0.5 Co _0.2 Mn _0.3 O ₂ And testing the pore size distribution, the content of the coating elements and the like of the positive electrode active material, wherein the specific test parameters are shown in figure 3.

(3) Preparing a positive pole piece: dispersing a positive electrode active material, acetylene black and polyvinylidene fluoride in N-methylpyrrolidone (NMP) according to the mass ratio of 92.

(4) Preparing an electrolyte: mixing Ethylene Carbonate (EC), ethyl Methyl Carbonate (EMC) and diethyl carbonate (D)EC) is prepared into a mixed solution according to a volume ratio of 20. At water content<In a 10ppm argon atmosphere glove box, liPF with a concentration of 1mol/L was sufficiently dried ₆ Dissolving in organic solvent, and mixing to obtain electrolyte.

(5) The preparation of the negative pole piece comprises the following steps: mixing graphite, sodium carboxymethylcellulose, styrene butadiene rubber and acetylene black according to a mass ratio of 95; and uniformly coating the negative electrode slurry on a copper foil with the thickness of 8 mu m, drying by using a 120 ℃ oven, and then carrying out cold pressing and stripping to obtain the negative electrode piece.

(6) Preparation of electrochemical device: the method comprises the steps of sequentially stacking a positive pole piece, an isolating film and a negative pole piece to enable the isolating film to be positioned between the positive pole piece and the negative pole piece to play an isolating role, winding the positive pole piece and the negative pole piece into a square bare cell, filling an aluminum plastic film, baking at 80 ℃ to remove water, injecting electrolyte, sealing, standing, carrying out hot cold pressing, forming, clamping, capacity grading and the like to obtain the electrochemical device.

Example 2

The specific preparation process is the same as that in example 1, except that the positive electrode active materials having different pore size distributions are obtained by adjusting the concentration and pH of the ammonia water in step (1) and adjusting the primary sintering temperature and the primary sintering time in step (2), and specific test parameters are shown in fig. 3.

Wherein the ammonia water concentration in example 2 is 1.7g/L, the pH value of the reaction solution is 12.5, and the nickel-cobalt-manganese hydroxide precursor [ Ni ] is obtained _0.5 Co _0.2 Mn _0.3 ](OH) ₂ The primary sintering temperature is 840 ℃, the primary sintering time is 24 hours, and the prepared anode active material is Li _1.08 Al _0.002 W _0.0015 Ni _0.5 Co _0.2 Mn _0.3 O ₂ 。

Example 3

Wherein, in example 3, the ammonia water concentration is 1.8g/L, the pH value of the reaction solution is 12.4, and the precursor [ Ni, co-Mn hydroxide ] is obtained _0.5 Co _0.2 Mn _0.3 ](OH) ₂ The primary sintering temperature is 845 ℃, the primary sintering time is 24 hours, and the prepared anode active material is Li _1.08 Al _0.002 W _0.0015 Ni _0.5 Co _0.2 Mn _0.3 O ₂ 。

Example 4

The specific preparation process is the same as that in example 1, except that the proportions of Ni, co and Mn in the nickel-cobalt-manganese hydroxide precursors prepared at different primary sintering temperatures are different, and positive active materials with different main element contents are obtained, and specific test parameters are shown in fig. 3.

Among them, the positive active material prepared in example 4 was Li _1.08 Al _0.002 W _0.0015 Ni _0.46 Co _0.22 Mn _0.22 O ₂ 。

Example 5

Among them, the positive electrode active material prepared in example 5 was Li _1.08 Al _0.002 W _0.0015 Ni _1/3 Co _1/3 Mn _1/3 O ₂ 。

Example 6

The specific preparation process is the same as that in example 1, except that the proportions of Ni, co and Mn in the nickel-cobalt-manganese hydroxide precursors prepared at different primary sintering temperatures are different, and the positive electrode active materials with different main element contents are obtained, and specific test parameters are shown in fig. 3.

Among them, the positive electrode active material prepared in example 6 was Li _1.08 Al _0.002 W _0.0015 Ni _0.6 Co _0.1 Mn _0.3 O ₂ 。

Example 7

The specific preparation process is the same as that in example 1, except that the coating element is Ti, and positive active materials with different coating elements are obtained, and specific test parameters are shown in fig. 3.

Among them, the positive electrode active material prepared in example 7 was Li _1.08 Ti _0.002 Ni _0.5 Co _0.2 Mn _0.3 O ₂ 。

Example 8

The specific preparation process is the same as that in example 1, except that the coating elements are Al and Ce, and the positive active materials with different coating elements are obtained, and specific test parameters are shown in fig. 3.

Among them, the positive active material prepared in example 8 was Li _1.08 Al _0.002 Ce _0.0015 Ni _0.5 Co _0.2 Mn _0.3 O ₂ 。

Example 9

The specific preparation process is the same as that in example 1, except that the coating elements are Al, ti and W, and positive active materials with different coating elements are obtained, and specific test parameters are shown in fig. 3.

Among them, the positive electrode active material prepared in example 9 was Li _1.08 Al _0.002 Ti _0.002 W _0.0015 Ni _0.5 Co _0.2 Mn _0.3 O ₂ 。

Example 10

The specific preparation process is the same as that in example 1, except that the coating elements are Al, mg and Ti, and the positive electrode active materials with different coating elements are obtained, and specific test parameters are shown in fig. 3.

Among them, the positive electrode active material prepared in example 10 was Li _1.08 Al _0.002 Mg _0.002 Ti _0.002 Ni _0.5 Co _0.2 Mn _0.3 O ₂ 。

Example 11

The specific preparation process is the same as that in example 1, except that the thickness of the primary crystal grains is adjusted and controlled by adjusting the pH value of the precursor prepared in the step (1), and the pore channel size of the generated pores is adjusted by the subsequent sintering processSmall sum distribution, half-peak width D of pore size distribution of the obtained positive active material _HW Is 420nm, the prepared anode active material is Li _1.08 Al _0.002 W _0.0015 Ni _0. ₅ Co _0.2 Mn _0.3 O ₂ See fig. 3 for specific test parameters.

Example 12

The specific preparation process is the same as that in example 1, except that the thickness of the primary crystal grains is adjusted by adjusting the pH of the precursor prepared in step (1), the size and distribution of pores generated are adjusted by the subsequent sintering process, and the half-peak width D of the pore size distribution of the obtained positive active material _HW Is 453nm, and the prepared positive active material is Li _1.08 Al _0.002 W _0.0015 Ni _0. ₅ Co _0.2 Mn _0.3 O ₂ See fig. 3 for specific test parameters.

Example 13

The specific preparation process is the same as that in example 1, except that the thickness of the primary crystal grains is adjusted by adjusting the pH of the precursor prepared in step (1), the size and distribution of pores generated are adjusted by the subsequent sintering process, and the half-peak width D of the pore size distribution of the obtained positive active material _HW Is 521nm, the prepared anode active material is Li _1.08 Al _0.002 W _0.0015 Ni _0. ₅ Co _0.2 Mn _0.3 O ₂ See fig. 3 for specific test parameters.

Example 14

The specific preparation process is the same as that in example 1, except that the thickness of the primary crystal grains is adjusted by adjusting the pH of the precursor prepared in step (1), the size and distribution of pores generated are adjusted by the subsequent sintering process, and the half-peak width D of the pore size distribution of the obtained positive active material _HW Is 561nm, and the prepared positive active material is Li _1.08 Al _0.002 W _0.0015 Ni _0. ₅ Co _0.2 Mn _0.3 O ₂ See fig. 3 for specific test parameters.

Example 15

The specific preparation process is the same as that in example 1, except that the thickness of the primary crystal grains is adjusted by adjusting the pH of the precursor prepared in step (1), the size and distribution of pores generated are adjusted by the subsequent sintering process, and at this time, the half-peak width D of the pore size distribution of the obtained positive electrode active material _HW Is 90nm, calculated

0.49, the positive electrode active material prepared was Li _1.08 Al _0.002 W _0.0015 Ni _0.5 Co _0.2 Mn _0.3 O ₂ See fig. 3 for specific test parameters.

Example 16

The specific preparation process is the same as that in example 1, except that the density of the precursor and the tap density of the material are controlled by adjusting the concentration of ammonia water for preparing the precursor so as to control the maximum aperture, and at this time, the maximum value D of the aperture of the obtained positive electrode active material is controlled _max 750nm, calculated

0.62, the positive electrode active material prepared was Li _1.0 ₈ Al _0.002 W _0.0015 Ni _0.5 Co _0.2 Mn _0.3 O ₂ See fig. 3 for specific test parameters.

Example 17

The specific preparation process is the same as that in example 1, except that the density of the precursor and the tap density of the material are controlled by adjusting the concentration of ammonia water for preparing the precursor, so as to control the size of the maximum aperture, and the maximum value D of the aperture of the obtained positive electrode active material is controlled _max 1517nm, the prepared positive active material is Li _1.08 Al _0.002 W _0.0015 Ni _0.5 Co _0.2 Mn _0.3 O ₂ See fig. 3 for specific test parameters.

Example 18

The specific preparation process is the same as that of example 1, except that the ammonia concentration of the prepared precursor is adjustedThe density of the precursor and the tap density of the material are controlled to control the maximum aperture and the maximum value D of the aperture of the obtained positive active material _max Is 1830nm, and the prepared positive active material is Li _1.08 Al _0.002 W _0.0015 Ni _0.5 Co _0.2 Mn _0.3 O ₂ See fig. 3 for specific test parameters.

Example 19

The specific preparation process is the same as that in example 1, except that the density of the precursor and the tap density of the material are controlled by adjusting the concentration of ammonia water for preparing the precursor, so as to control the size of the maximum aperture, and the maximum D of the aperture of the obtained positive active material is the same as that of the maximum aperture _max Is 2012nm, and the prepared anode active material is Li _1.08 Al _0.002 W _0.0015 Ni _0.5 Co _0.2 Mn _0.3 O ₂ See fig. 3 for specific test parameters.

Example 20

The specific preparation process is the same as that of example 1, except that the coating process and the secondary sintering are not performed, and the prepared positive electrode active material is Li _1.08 Ni _0.5 Co _0.2 Mn _0.3 O ₂ See fig. 3 for specific test parameters.

Comparative example 1

The specific preparation process is the same as that of example 1, except that the concentration and pH of ammonia water in step (1) and the primary sintering temperature and primary sintering time in step (2) are adjusted to obtain D of the pore size distribution of the positive electrode active material _HW /D _max More than 0.5, and the prepared anode active material is Li _1.08 Al _0.002 W _0.0015 Ni _0.5 Co _0.2 Mn _0.3 O ₂ See fig. 3 for specific test parameters.

Wherein, the ammonia water concentration in comparative example 1 was 3g/L, the pH of the reaction solution was 13, the primary sintering temperature was 900 ℃ and the primary sintering time was 30 hours.

Comparative example 2

The specific preparation process is the same as that of example 1, except that the step (A) is adjusted1) The ammonia water concentration and the pH value in the step (2) and the primary sintering temperature and the primary sintering time in the step (2) are adjusted so that D of the pore size distribution of the obtained positive electrode active material _HW /D _max Less than 0.05, and the prepared positive active material is Li _1.08 Al _0.002 W _0.0015 Ni _0.5 Co _0.2 Mn _0.3 O ₂ See fig. 3 for specific test parameters.

Wherein, the ammonia water concentration in comparative example 2 is 1.5 g/L, the pH value of the reaction solution is 13.5, the primary sintering temperature is 820 ℃, and the primary sintering time is 18h.

Electrochemical device testing

Low temperature charge and discharge power measurement

Charging the battery at a constant current and a constant voltage of 1C to 100% SOC, standing for 10 minutes, discharging at a constant current of 1C for 30 minutes to 50% SOC, standing at-20 ℃ for 180 minutes, discharging at 5C for 30 seconds, recording the voltage values before and after discharge, and calculating to obtain the discharge power.

Cycle testing

First, the battery voltage was calibrated, the voltage corresponding to 20% SOC and 90% SOC of the battery was confirmed, the battery was placed in a 25 ℃ incubator for cycling, charging and discharging were performed at a constant current of 4C, the cycling capacity and the number of cycles of the battery were recorded, and the number of cycles of the battery was recorded when the capacity retention rate was less than 80% of the capacity of the first cycle.

The low-temperature charge and discharge power test and the cycle number test of the electrochemical devices prepared in examples 1 to 20 and comparative examples 1 to 2, and the specific test results are shown in fig. 4.

As can be seen from fig. 3 and 4, in examples 2 to 3, compared to example 1, the porosity degree of the precursor is different, and the temperature and time of the primary sintering are different, so that intermediate products with different pore size distributions are obtained, and the coating effect of the inner surface of the secondary particles and the surface and internal structure of the finished secondary particles are controlled, thereby improving the low-temperature power performance and long-term cycle life of the electrochemical device.

From the results of examples 1 and 20, it is understood that in example 1, al and W element coatings are added, and the appropriate pore size distribution makes the content deviation of the inner and outer coating elements of the finished product 0.18, indicating that the inner and outer coating effects are good,with the proviso that D _HW /D _max Value in the appropriate range when D _HW /D _max The porosity of the pole piece is 0.25, when the porosity of the pole piece is 0.36, the pore size distribution of the secondary particles is wider, and the pole piece is provided with a proper pore channel so that the coating material can smoothly enter the inner surface of the secondary particles through the pores, and after secondary sintering, the coating material and the inner surface can form a stable coating layer so as to reduce the uncoated surface area; in addition, the internal and external coating effects are consistent, so that the structural damage of the positive active material in a long-term circulation process can be reduced, and the cycle life of the positive active material is prolonged.

In comparative examples 1 to 2, D is compared with example 1 and comparative examples 1 to 2 _HW /D _max The value is not within the range of 0.05 to 0.5, and the content deviation of the inner and outer coating elements is more than 40%, according to the test performance of fig. 4, the aperture part is not within the required range, the coating effect in the hollow structure of the anode material is poor, the content difference of the inner and outer coating elements is large, so that when an electrode is in contact with an electrolyte, a strong side reaction occurs, the electrolyte consumption and the surface of the anode material are corroded, the transition metal ions Ni, co and Mn are dissolved from the surface of the anode material to the electrolyte and then are deposited on the cathode, the surface structure of the anode material is damaged, the transition metal ions in a bulk phase are migrated to the surface, the structure of the anode material is damaged along with the release of lattice oxygen, and the active lithium is consumed by an SEI film generated by the cathode continuously, so that the cycle capacity and the stability are poor and the power performance is attenuated.

As can be seen from examples 4 to 6, when the contents of main elements are different, the dynamic influence on the material is large, and when the contents of Ni and Co are high, the dynamic performance is good, but the cost is increased, so that the main element proportion needs to be optimized, and although the main element proportions in examples 4 to 6 are large, the main element proportions in D are guaranteed to be different _HW /D _max From 0.05 to 0.Within the range of 5, when the content deviation of the inner and outer coating elements is less than 40%, the power performance is greatly improved compared with that of the embodiment 20 as well as the long-term cycle performance.

As can be seen from examples 7 to 9, the content variation of the different coating elements is less than 40% while ensuring the content variation of the inner and outer coating elements, D _HW /D _max When the ratio is in the range of 0.05 to 0.5, the power performance is greatly improved as compared with that of example 20 as well as the long-term cycle performance.

The positive electrode active material and the electrochemical device provided in the embodiments of the present application are described in detail above, and the principles and embodiments of the present application are described in the present application by applying specific examples, and the description of the above embodiments is only used to help understand the technical solutions and the core ideas of the present application; those of ordinary skill in the art will understand that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications or substitutions do not depart from the spirit and scope of the present disclosure as defined by the appended claims.

Claims

1. A positive electrode active material, comprising secondary particles having pores, the secondary particles having a pore size distribution satisfying: d is more than or equal to 0.05 _HW /D _max Less than or equal to 0.5; wherein D is _HW Denotes a half-peak width, D, of a pore size distribution of the positive electrode active material _max Represents the maximum value of the pore diameter of the positive electrode active material;

the secondary particles include a hollow structure formed by stacking primary particles, and the surface of the secondary particles and the surface of the primary particles located in the hollow structure have an element A; the average content a of the element A on the surface of the secondary particles ₀₁ And the average content a of the element A on the surface of the primary particles in the hollow structure ₀₂ Satisfies the following conditions:

and is made of

，

；

In the formula, a _i Representing the content of an element A obtained by testing an ith area selected on the surface of the secondary particles, wherein i is more than or equal to 1 and less than or equal to m, and m is an integer more than or equal to 3; a is _j The content of the element A obtained by testing the jth area selected on the surface of the primary particles is shown, j is more than or equal to 1 and less than or equal to n, and n is an integer more than or equal to 3.

2. The positive electrode active material according to claim 1, wherein D is _HW Satisfies the following conditions: 100nm is less than or equal to D _HW Less than or equal to 400 nm; said D _max Satisfies the following conditions: 800nm is less than or equal to D _max ≤2000 nm。

3. The positive electrode active material according to claim 1, wherein the positive electrode active material has a porosity P ₁ Satisfies the following conditions: p is more than or equal to 30% ₁ ≤80%。

4. The positive electrode active material according to claim 1, wherein the secondary particles comprise lithium nickel cobalt manganese oxide particles further comprising an A element comprising one or more of Zr, sr, W, al, ti, mg, ce, Y.

5. The positive electrode active material according to claim 1, wherein the positive electrode active material contains Li _x A _y Ni _a Co _b Mn _c O _z Wherein x is more than or equal to 0.9 and less than or equal to 1.1, y is more than or equal to 0 and less than or equal to 0.2, z is more than or equal to 1 and less than or equal to 2, a is more than or equal to 0.4 and less than or equal to 2<1，0<b<0.3，0<c<1,a + b + c =1, wherein A comprises one or more of Zr, sr, W, al, ti, mg, ce and Y.

6. The positive electrode active material according to claim 1, wherein a is _i Variance of E fullFoot: e is more than or equal to 0 and less than or equal to 1 multiplied by 10 ^-4 (ii) a A is a mentioned _i The extreme difference C satisfies: c is more than or equal to 0 and less than or equal to 0.05.

7. The positive electrode active material according to claim 1, wherein a is _j The variance I of (1) satisfies: i is more than or equal to 0 and less than or equal to 1 multiplied by 10 ^-3 (ii) a A is a _j The range D of (A) satisfies: d is more than or equal to 0 and less than or equal to 0.05.

8. The positive electrode active material according to claim 1, wherein the positive electrode active material satisfies at least one of the following characteristics:

9. An electrochemical device comprising a positive current collector and a positive electrode tab disposed on the positive current collector, the positive electrode tab comprising the positive active material of any one of claims 1-8.

10. The electrochemical device according to claim 9, wherein the porosity P of the positive electrode sheet ₂ Satisfies the following conditions: p is more than or equal to 20% ₂ ≤50%。

11. Electrochemical device according to claim 9, characterized in that the low temperature charging power P of the electrochemical device _CC > 20W, low temperature discharge power P of the electrochemical device _DC ＞60W。