Positive electrode active materials and electrochemical devices

Abstract

The present application discloses a positive electrode active material and an electrochemical device. The positive electrode active material includes secondary particles having pores, and the pore size distribution of the secondary particles satisfies: 0.05≤D HW / D max ≤0.5; where D HW The half-peak width of the pore size distribution of the positive electrode active material, D max Represents the maximum pore size of the positive electrode active material. The positive electrode active material of this application has an appropriate pore size distribution and porosity, enabling sufficient wettability with the electrolyte. Combined with an appropriate particle size distribution, it can achieve higher power performance at lower temperatures, effectively reducing the problem of side reactions between the newly exposed material surface and the electrolyte, thereby improving the cycle life of the electrochemical device.

Description

[0001] This application is a divisional application of the invention patent application with application number 202211010347.5, application date August 23, 2022, and name “Positive Electrode Active Material and Electrochemical Device”. Technical Field

[0002] The present application relates to the technical field of secondary batteries, and in particular to a positive electrode active material and an electrochemical device. Background Art

[0003] Electrochemical devices, such as lithium-ion batteries, offer advantages such as high energy density, excellent cycle performance, and high charging efficiency. They are experiencing rapid growth, particularly in the electric vehicle sector. However, lithium-ion batteries also face challenges such as insufficient battery life, short battery life, and poor performance in cold weather. Therefore, there is a need to improve the battery's cycle stability and low-temperature performance.

[0004] The existing technology improves the performance of lithium-ion batteries to a certain extent by surface coating or doping the positive electrode active material. However, due to the close stacking of primary particles, the conductivity of the primary particles inside the secondary particles will decrease, and the coating effect of the internal primary particles is poor. The positive electrode active material with secondary particle morphology will inevitably shrink and expand during the cycle, thereby exposing new grain surfaces, causing side reactions with electrolysis, and reducing the cycle life of the battery. In addition, the existing prepared materials have a large particle size and a small specific surface area, resulting in poor kinetic performance of the battery at low temperatures, limiting the power performance and reducing the application range of the battery. Summary of the Invention

[0005] Purpose of the invention: The present application provides a positive electrode active material composed of secondary particles with a specific pore size distribution, which improves the coating effect of the primary particles inside the material, thereby achieving higher low-temperature power performance of the electrochemical device and ensuring that the electrochemical device has a better long-term life; another purpose of the present application is to provide an electrochemical device comprising the above-mentioned positive electrode active material.

[0006] Technical solution: A positive electrode active material of the present application includes secondary particles with pores, wherein the pore size distribution of the secondary particles satisfies: 0.05≤D HW / D max ≤0.5; where D HW The half-peak width of the pore size distribution of the positive electrode active material, D max Indicates the maximum pore size of the positive electrode active material.

[0007] In some embodiments, the D HW Satisfy: 100nm≤D HW ≤400nm; the D max Satisfy: 800nm≤D max≤2000 nm.

[0008] In some embodiments, the porosity P1 of the positive electrode active material satisfies: 30% ≤ P1 ≤ 80%.

[0009] In some embodiments, the secondary particles include lithium nickel cobalt manganese oxide particles, and the lithium nickel cobalt manganese oxide further includes an A element, and the A element includes one or more of Zr, Sr, W, Al, Ti, Mg, Ce, and Y.

[0010] In some embodiments, the positive electrode active material includes lithium nickel cobalt manganese oxide particles. Based on the molar amounts of the nickel element, the cobalt element, and the manganese element being 1, the molar ratio of the nickel element is greater than or equal to 0.4.

[0011] In some embodiments, the positive electrode active material includes Li x A y Ni <000001...​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​

[0016] In some embodiments, the a j The variance I satisfies: 0≤I≤1×10 -3 ; said a j The range D satisfies: 0≤D≤0.05.

[0017] In some embodiments, the variance E and the range C are calculated by taking a data set consisting of the content of element A measured in m areas randomly selected from the surface of the secondary particles; the variance I and the range D are calculated by taking a data set consisting of the content of element A measured in n areas randomly selected from the surface of the primary particles; wherein, m and n are at least 3, and the preferred values of m and n are 10.

[0018] In some embodiments, the positive electrode active material satisfies at least one of the following characteristics:

[0019] (a) the average pore size of the positive electrode active material is 100 nm to 2000 nm;

[0020] (b) The specific surface area of the positive electrode active material is 0.2 m 2 / g~1.5m 2 / g;

[0021] (c) The average particle size Dv50 of the positive electrode active material is 2 μm to 8 μm.

[0022] In some embodiments, an electrochemical device of the present application includes a positive electrode current collector and a positive electrode plate disposed on the positive electrode current collector, wherein the positive electrode plate includes a positive electrode active material.

[0023] In some embodiments, the porosity P2 of the positive electrode sheet satisfies: 20%≤P2≤50%.

[0024] In some embodiments, the low-temperature charging power P of the electrochemical storage device CC >20W, the low temperature discharge power P of the electrochemical energy storage device DC >60W.

[0025] Beneficial effects: Compared with the prior art, the positive electrode active material of the present application includes secondary particles with pores, and the secondary particles have an appropriate pore size distribution, which can improve the wetting performance between the positive electrode active material and the electrolyte. Since the tightness between the secondary particles is properly adjusted, the particle breakage during rolling and circulation is reduced. With the appropriate particle size distribution, higher power performance can still be exerted at lower temperatures. The secondary particles have pores, which significantly improves the coating effect, so that even if the secondary particles are broken during rolling and circulation, the side reaction problem between the newly exposed material surface and the electrolyte can be effectively improved, thereby improving the cycle life of the electrochemical device. The present application achieves the effect of improving the low-temperature power performance of the electrochemical device and ensuring a good long-term cycle life by limiting the pore size distribution and porosity. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The following detailed description of the specific embodiments of the present application in conjunction with the accompanying drawings will make the technical solutions and other beneficial effects of the present application apparent.

[0027] Figure 1 This is an electron microscope characterization test image of the positive electrode material provided in the embodiment of the present application;

[0028] Figure 2 This is an electron microscope characterization test image of the hollow structure of the secondary particles provided in the examples of this application;

[0029] Figure 3 The test parameters of the positive electrode active material provided in the embodiments of the present application;

[0030] Figure 4 These are the low-temperature charge and discharge power test and cycle number test results of the electrochemical device provided in the embodiments of this application. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of this application.

[0032] In the description of this application, "plurality" means two or more, unless otherwise specifically defined. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features being referred to. Thus, features defined as "first" or "second" may explicitly or implicitly include one or more features.

[0033] In the description of this application, the term "process" includes not only independent processes, but also processes that cannot be clearly distinguished from other processes as long as the purpose of the process can be achieved. In addition, in this specification, the numerical range indicated by "to" indicates a range that includes the numerical values recorded before and after "to" as the minimum and maximum values, respectively. In addition, in this specification, the term "layer" includes not only the configuration of a shape formed on the entire surface when observed in a plan view, but also the configuration of a shape formed on a portion.

[0034] The disclosure below provides many different embodiments or examples to realize the different structures of the present application. In order to simplify the disclosure of the present application, the components and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present application.

[0035] positive electrode active material

[0036] The present application provides a positive electrode active material, which includes secondary particles with a pore structure. The secondary particles are composed of stacked primary particles. The secondary particles have an appropriate pore size on their surface, and the pore size distribution satisfies: 0.05≤D HW / D max ≤0.5; where D HW The half-peak width of the pore size distribution of the positive electrode active material is the peak width corresponding to half of the maximum value of the pore size distribution peak; D max In some embodiments, D HW / D max Satisfies: 0.15≤D HW / D max ≤0.3. When the pore size distribution satisfies the above relationship, it can alleviate the particle breakage of the positive electrode active material during roller pressing and / or cycling. At the same time, the appropriate pore distribution can ensure sufficient wetting between the positive electrode active material and the electrolyte, so that the electrochemical device can still exert high power performance at a lower temperature.

[0037] In some implementations, D HW Satisfy: 100nm≤D HW ≤400nm; for example, it can be 100nm, 120nm, 150nm, 180nm, 200nm, 230nm, 250nm, 280nm, 290nm, 310nm, 350nm, 400nm or a range consisting of any two of them. HW Within the above range, the electrochemical device has a more optimal pore size distribution, so that the electrochemical device has better low-temperature power performance and better long-term cycle life performance.

[0038] In some implementations, 150 nm ≤ D HW≤300nm. When D HW Within the above range, the low-temperature power performance and cycle life of the electrochemical device can be further improved.

[0039] In some implementations, D max Satisfy: 800nm≤D max ≤2000nm; for example, it can be 800nm, 850nm, 900nm, 950nm, 1000nm, 1050nm, 1100nm, 1150nm, 1200nm, 1250nm, 1300nm, 1400nm, 1500nm, 1700nm, 1800nm, 2000nm or a range consisting of any two numbers therein. When D max Within the above range, the electrochemical device has a better pore size distribution, so that the electrochemical device has better comprehensive performance.

[0040] In some embodiments, 1050 nm ≤ D max ≤1500nm. When D max Within the above range, the electrochemical device has a better pore size distribution, and the compactness between the secondary particles is better adjusted, so that the electrochemical device has better overall performance.

[0041] In some embodiments, the porosity P1 of the positive electrode active material satisfies: 30%≤P1≤80%. When the pore size distribution of the positive electrode active material satisfies 0.05≤D HW / D max When the porosity is within the above range, the positive electrode active material can have better contact with the electrolyte, thereby improving the overall performance of the electrochemical device.

[0042] In some embodiments, the porosity P1 of the positive electrode active material satisfies: 35%≤P1≤72%.

[0043] In some embodiments, the porosity P1 of the positive electrode active material satisfies: 40%≤P1≤60%. When the porosity of the positive electrode active material is within this range, the electrochemical device can have better overall performance.

[0044] In some embodiments, the positive electrode active material comprises lithium nickel cobalt manganese oxide particles, and the molar amount of the nickel element accounts for greater than or equal to 0.4, based on the molar amount of the nickel element, the cobalt element, and the manganese element being 1.

[0045] In some embodiments, the molar ratio 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 within this range, the side reactions of the electrochemical device are reduced and the overall performance is better.

[0046] In some embodiments, the secondary particles include lithium nickel cobalt manganese oxide secondary particles, the lithium nickel cobalt manganese oxide further includes an A element, and the positive electrode active material includes Li x A y Ni a Co b Mn c O z , where 0.9≤x≤1.1, 0≤y≤0.2, 1≤z≤2, 0.4≤a<1, 0 <b<0.3,0<c<1,a+b+c=1。

[0047] In some embodiments, A may be a coating element, and A includes one or more of Zr, Sr, W, Al, Ti, Mg, Ce, and Y. The coating material can reduce side reactions between the electrolyte and the positive electrode active material. Element A on the surface of the positive electrode active material can more effectively isolate the positive electrode active material from direct contact with the electrolyte, thereby reducing electrolyte corrosion on the surface of the positive electrode material, avoiding thickening of the negative electrode SEI film, consumption of active lithium, and capacity degradation of the electrochemical device.

[0048] In some embodiments, A comprises Al, and one or more of Zr, Sr, W, Al, Ti, Mg, Ce, and Y.

[0049] In some embodiments, selecting a suitable A element can put the coating layer in a better state and achieve a better coating effect; by selecting a suitable A element, the positive electrode active material can react with the electrolyte in a suitable state, reducing side reactions, slowing down electrolyte consumption, avoiding obstruction of lithium ion migration, and increasing battery polarization, thereby reducing its power performance.

[0050] In some embodiments, the appropriate content of element A in the positive electrode active material can form a better protective layer on the surface of the positive electrode active material particles, so that the composition and thickness of the protective layer are in a better state, and the electrochemical device can have better overall performance.

[0051] 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.

[0052] In some embodiments, the pore structure on the secondary particles includes a hollow structure composed of stacked primary particles, and the surface of the secondary particles and the surface of the primary particles located in the hollow structure have A elements. The primary particles in the hollow structure refer to the primary particles on the surface of the hollow structure formed after the secondary particles are cut, specifically Figure 2 The average content of element A on the surface of secondary particles is shown as follows: 01 The average content of element A on the surface of primary particles in the hollow structure is a 02 satisfy:

[0053] and

[0054] Where a i represents the A element content measured in the i-th area selected on the surface of the secondary particle, 1≤i≤m and m is an integer greater than or equal to 3; a j It represents the content of element A obtained by testing the j-th area selected on the surface of the primary particle, 1≤j≤n and n is an integer greater than or equal to 3.

[0055] a 01 The test results may be for the content of element A in different regions of the same secondary particle, or for the content of element A in one region of each particle of different secondary particles.

[0056] a 02 The test results may be for the content of element A in different regions of the same secondary particle, or for the content of element A in one region of each particle of different secondary particles.

[0057] a 01 and a 02 The particles may be different, as long as they can reflect the A element content on the surface of the secondary particles and the surface of the primary particles in the hollow structure.

[0058] When the average content of element A on the surface of secondary particles is 01 The average content of element A on the surface of primary particles in the hollow structure is a 02 When the above relationship is satisfied, the secondary particles can be in a better coating state, the side reaction between the positive electrode active material particles and the electrolyte can be further reduced, and the electrochemical device can be in a better state.

[0059] In some embodiments, a i The number of is determined by the number of test areas selected on the surface of the secondary particles. The A element content obtained in each test area constitutes a data set. The variance E of the data set satisfies: 0≤E≤1×10 -4 , the range C satisfies: 0≤C≤0.05.

[0060] In some embodiments, a j The number of is determined by the number of test areas selected on the primary particle surface. The A element content obtained from each test area constitutes a data set. The variance I of the data set satisfies: 0≤I≤1×10 -3 , the range D satisfies: 0≤D≤0.05.

[0061] In some embodiments, the variance E satisfies: 0≤E≤1×10 -4, the range C satisfies: 0≤C≤0.05. When the E and I values meet this range, the secondary particle surface has A element. The variance I satisfies: 0≤I≤1×10 -3 , the range D satisfies: 0≤D≤0.05, indicating that the distribution of element A on the surface of secondary particles and the surface of primary particles in the hollow structure is uniform, with better coating effect.

[0062] In some embodiments, a positive electrode active material particle sample including secondary particles is taken, and then the outer surface of the sample is inspected by SEM (Scanning Electron Microscope) to obtain a SEM image, such as Figure 1 Then, the secondary particles are dissected by ion milling (CP), focused ion beam (FIB), etc., and the hollow structure of the secondary particles is detected by TEM (Transmission Electron Microscope) to obtain a TEM image, as shown in FIG. Figure 2 As shown. Figure 1 and Figure 2 It can be seen that: from Figure 1 It can be seen that the secondary particles are formed by the accumulation of primary particles. Figure 2 It can be seen that the secondary particles have a hollow structure inside. Moderately sized through-holes are distributed between the primary particles. These holes allow the surface of the primary particles inside the hollow structure to be coated, improving the interface stability of the positive electrode material, the battery's cycling performance, and low-temperature power performance.

[0063] In some embodiments, the A element content a1 on the surface of the secondary particles and the A element content a2 on the surface of the primary particles refer to the mass concentration of element A in all elements, which can be obtained by EDS (Energy Dispersive Spectroscopy) or EDX (Energy Dispersive X Ray Spectroscopy) elemental analysis combined with SEM (Scanning Electron Microscope) or TEM (Transmission Electron Microscope) single-point scanning test element concentration distribution or other similar methods.

[0064] In some embodiments, when EDX or EDS elemental analysis is combined with TEM or SEM single point scanning testing, see Figure 1 , select ten randomly evenly distributed areas on the surface of the secondary particles for testing, and obtain the test values of the A element content in the ten areas. The test values of the A element content in the ten areas are combined into a data set to calculate the variance E and range C respectively; see Figure 2, ten randomly evenly distributed areas are selected on the surface of the primary particle for testing, and the test values of the A element content in the ten areas are obtained. The test values of the A element content in the ten areas are combined into a data set to calculate the variance I and the range D respectively.

[0065] In some embodiments, the secondary particle surface area is selected as Figure 1 As shown in the box in , you can select different positions on the surface of the same secondary particle, or you can select the surfaces of different secondary particles in the field of view; the internal area of the secondary particle cross section is selected as follows Figure 2 As shown in the boxes in , you can select primary particles inside the same secondary particle, or you can select primary particles inside different secondary particles. The principle is that it is more representative to include at least three secondary particles in the same field of view.

[0066] In some embodiments, the inventors found that when the difference in the average content of element A on the surface of the secondary particles and the surface of the primary particles inside the secondary particles is less than 40%, it indicates that the coating effect of the primary particle surface inside the positive electrode active material is consistent with the coating effect of the secondary particle surface, which can effectively improve the structural stability of the internal primary particles, reduce the side reactions with the electrolyte and improve the kinetic properties of the material. When the polycrystalline material is damaged by the secondary particles due to stress during rolling and cycling, the relative area of the exposed new surface is small, thereby reducing the electrolyte side reactions caused by the fresh surface exposed by the particle damage. In addition, due to the improved coating effect of the internal particles, the difference in internal and external kinetic properties is small, reducing electrode polarization, which is conducive to improving the capacity of the positive electrode active material, improving the stability of the material, and improving the cycle life of the battery.

[0067] In some embodiments, the distribution and size of the pore size are mainly affected by the preparation process. By adjusting the ammonia concentration and pH value to adjust the structure of the precursor, precursors with different degrees of looseness are formed, and then the sintering temperature and time are adjusted to obtain products with different pore sizes and pore size distributions.

[0068] In some embodiments, the internal pore structure of the secondary particles is closely related to the compressive strength, power, cycle and storage performance of the particles. A large porosity is beneficial to the low-temperature power of the material, but the long-term performance will be deteriorated. Therefore, the D of the pore size distribution can be controlled by adjusting the pore size distribution and porosity. HW / D max This is conducive to forming a good coating effect on the surface of the primary particles inside the secondary particles, so as to achieve a small difference in the coating effect between the inside and outside of the secondary particles.

[0069] In some embodiments, the pore size is between 10 nm and 2000 nm, which is conducive to the dispersion of the coating material and its entry into the inner surface through the pore channel, and 0.05≤D HW / D max When D HW / D max If the ratio is too large, it means that the contact between the material particles is poor, the structural stability is also affected, resulting in poor kinetics and cycle stability, which will increase the process difficulty and manufacturing cost as well as the occurrence of side reactions; when D HW / D max If the ratio is too small, it will be unfavorable for material coating and electrolyte infiltration, resulting in poor material stability and kinetic performance. Therefore, the pore size distribution of secondary particles should be adjusted. HW / D max When the ratio is within an appropriate range, it is beneficial to the low-temperature power performance, which can not only achieve higher low-temperature power performance of the positive electrode active material, but also ensure a better long-term life of the positive electrode active material.

[0070] In some embodiments, the average pore size of the positive electrode active material is 100 nm to 2000 nm; preferably, the average pore size of the positive electrode active material is 300 nm to 1500 nm, and more preferably 400 nm to 1000 nm. For example, the average pore size of the positive electrode active material is 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1100 nm, 1200 nm, 1300 nm, 1400 nm, 1500 nm, 1600 nm, 1700 nm, 1800 nm, or 1900 nm. The average pore size of the positive electrode active material reflects the state of primary particle accumulation. An appropriate pore size can provide a transmission channel for the coating material while ensuring the density of the secondary particles, so that the mechanical strength of the material can meet the requirements of cyclic stability.

[0071] In some embodiments, the specific surface area of the positive electrode active material is 0.2 m 2 / g~1.5m 2 / g; the preferred specific surface area of the positive electrode active material is 0.5m 2 / g~1.3m 2 / g, more preferably 0.8m 2 / g~1.2m 2 / 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, 1.1m2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g. The specific surface area of the positive electrode active material is within an appropriate range, and the contact area between the positive electrode active material and the electrolyte is within an optimal range, so that the positive electrode sheet has a better wetting effect, the ohmic impedance is small, and the battery has better overall performance.

[0072] In some embodiments, the average particle size Dv50 of the positive electrode active material is 2 μm to 8 μm. Preferably, the average particle size Dv50 of the positive electrode active material is 2.5 μm to 6 μm, and more preferably, 3 μm to 5 μm. For example, the average particle size Dv50 of the positive electrode active material is 3 μm, 4 μm, 5 μm, 6 μm, or 7 μm. When the average particle size Dv50 of the positive electrode active material is within an appropriate range, the lithium ion migration path and the electrolyte reaction area are both within a suitable range, resulting in excellent battery cycle performance.

[0073] In some embodiments, the average particle size Dv50 of the positive electrode active material is generally known in the art and is also referred to as the median particle size, indicating the particle size corresponding to 50% of the volume distribution of the positive electrode active material particles. The average particle size Dv50 of the positive electrode active material can be measured using instruments and methods known in the art, such as a laser particle size analyzer.

[0074] In some embodiments, the specific surface area of the positive electrode active material has a meaning well known in the art and can be measured using instruments and methods well known in the art, for example, it can be tested using a nitrogen adsorption specific surface area analysis test method and calculated using the BET (Brunauer Emmett Teller) method.

[0075] In some embodiments, a method for preparing a positive electrode active material is also disclosed, the preparation method comprising:

[0076] Precursor preparation: A nickel source, a cobalt source, and a manganese source are dispersed in deionized water to obtain a mixed solution; the mixed solution, a strong base solution, and a complexing agent solution are simultaneously pumped into a stirred reactor using a continuous parallel flow reaction method, the pH value of the reaction solution is controlled to be 10-13, the temperature in the reactor is 25°C-90°C, and an inert gas is passed during the reaction process; after the reaction is completed, the nickel-cobalt-manganese hydroxide precursor is obtained through washing, filtration, vacuum drying, sieving, and other processes to remove iron.

[0077] Preparation of positive electrode active materials: The loose and porous nickel-cobalt-manganese hydroxide precursor prepared by the co-precipitation method is subjected to the first high-temperature sintering with a lithium source. The sintering temperature is between 600°C and 1100°C, and the sintering time is 8 to 24 hours. The structure of the precursor is adjusted by regulating the ammonia concentration and pH value to form precursors with different degrees of looseness. After that, the temperature and time of the first sintering can be adjusted to obtain intermediate products with different pore sizes and pore size distributions; the intermediate product is then subjected to a coating process, that is, the intermediate product and the coating material containing element A are subjected to a second high-temperature sintering at a sintering temperature of 400°C to 700°C and a sintering time of 6 to 12 hours to obtain different positive electrode active materials.

[0078] In some embodiments, the nickel source, the cobalt source, and the manganese source are one or more oxides, hydroxides, or carbonates containing Ni, Co, and Mn selected in a stoichiometric ratio.

[0079] In some embodiments, the structure of the nickel-cobalt-manganese hydroxide precursor can be controlled by selecting the reaction raw materials, pH value of the reaction solution, concentration of the mixed solution, concentration of the complexing agent, reaction temperature, and reaction time during the preparation of the precursor.

[0080] 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.

[0081] 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.

[0082] In some embodiments, the manganese source may include one or more of manganese sulfate, manganese chloride, manganese nitrate, or manganese hydroxide.

[0083] In some embodiments, the strong alkaline solution may include one or more of LiOH, NaOH, and KOH; the complexing agent may be one or more of ammonia water, ammonium sulfate, ammonium nitrate, and ammonium chloride.

[0084] In some embodiments, there is no particular limitation on the solvents of the mixed solution, the strong base solution, and the complexing agent solution. For example, the solvents of the mixed solution, the strong base solution, and the complexing agent solution are each independently one or more of deionized water, methanol, ethanol, acetone, isopropanol, and n-hexanol.

[0085] In some embodiments, the inert gas is one or more of nitrogen, argon, and helium.

[0086] In some embodiments, the lithium source may include one or more of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate, or lithium chloride.

[0087] In some embodiments, the precursor of the coating material containing element A may be one or more of A's oxides, chlorides, sulfates, nitrates, hydroxides, fluorides, carbonates, bicarbonates, acetates, phosphates, dihydrogen phosphates, and organic compounds.

[0088] In some embodiments, by reasonably controlling the primary sintering temperature and the secondary sintering temperature, the pore size distribution of the secondary particles is made wider so that suitable pores can be formed to ensure that 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 form on the surface of the primary particles.

[0089] In some embodiments, before the intermediate product and the coating containing element A are subjected to a second high-temperature sintering, the intermediate product may be crushed and sieved to obtain a positive electrode active material with an optimized particle size distribution and specific surface area. The crushing method is not particularly limited and can be selected according to actual needs, such as using a particle crusher.

[0090] The preparation method of the positive electrode active material of the present application is not limited to the above preparation method, as long as the formed positive electrode active material has the characteristics shown in the present application.

[0091] electrochemical devices

[0092] The electrochemical device of the present application includes a positive electrode current collector and a positive electrode plate disposed on the positive electrode current collector, wherein the positive electrode plate includes a positive electrode active material. Because the positive electrode plate includes the positive electrode active material, a battery using the positive electrode plate can achieve both high low-temperature power performance and good long-term life.

[0093] In some embodiments, the positive electrode current collector may be made of a metal foil or 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 alloys thereof, preferably aluminum foil.

[0094] In some embodiments, the positive electrode plate further includes a conductive agent and a binder, wherein the conductive agent may include conductive carbon black, carbon nanotubes, graphene, etc., and the binder may include polyvinylidene fluoride.

[0095] In some embodiments, the preparation of the positive electrode sheet includes: dispersing the above-mentioned positive electrode active material, conductive agent, and binder in N-methylpyrrolidone (NMP) in a mass ratio of (91-94): (1-7): (1-3), coating the resulting slurry on a 12μm-16μm aluminum foil, drying it in an oven at 100°C-130°C, and then cold pressing and slitting to obtain a positive electrode sheet.

[0096] In some embodiments, the mass ratio of the positive electrode active material, the conductive agent, and the binder may also include 96:3:1, 96:2:2, and the like.

[0097] In some embodiments, the porosity P2 of the positive electrode sheet satisfies: 20%≤P2≤50%.

[0098] In some embodiments, the porosity P2 of the positive electrode sheet satisfies: 25%≤P2≤46%. Within this range, the electrolyte and the positive electrode sheet have better wettability, resulting in better overall performance of the electrochemical device.

[0099] In some embodiments, the electrochemical device may further include a negative electrode sheet, a separator, and an electrolyte.

[0100] In some embodiments, the preparation of the negative electrode sheet includes: mixing the negative electrode active material, thickener, binder, and conductive agent in a mass ratio of (91 to 96): (0.5 to 1.5): (1.3 to 2.7): (1.3 to 2.7), adding deionized water, and obtaining a negative electrode slurry under the action of a vacuum mixer; uniformly coating the negative electrode slurry on a copper foil with a thickness of 5 μm to 12 μm, drying it in an oven at 100°C to 130°C, and then cold pressing and slitting to obtain a negative electrode sheet.

[0101] In some embodiments, the mass ratio of the negative electrode active material, the thickener, the binder, and the conductive agent may also include common ratios such as 97:1:1:1 and 96:1:2:1.

[0102] In some embodiments, the electrolyte comprises: an organic solvent, which may comprise a chain ester and a cyclic ester, wherein the mass percentage of the chain ester is greater than the mass percentage of the cyclic ester. The cyclic ester may comprise ethylene carbonate (EC) and / or propylene carbonate (PP), and the chain ester may comprise at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or diethyl carbonate (DEC). In some embodiments, the solvent of the electrolyte comprises EC, EMC, and DEC. In some embodiments, the mass ratio of EC, EMC, and DEC is (10-25):(10-25):(51-75). In some embodiments, the preparation of the electrolyte comprises: in an argon atmosphere glove box with a water content of <10 ppm, dissolving a fully dried lithium salt in an organic solvent, mixing uniformly, and obtaining an electrolyte. The concentration of the lithium salt is 0.8-1.3 mol / L.

[0103] In some embodiments, the lithium salt may be LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), or the like.

[0104] In some embodiments, the preparation of the isolation membrane includes: selecting a polypropylene film with a thickness of 9 μm to 18 μm as the isolation membrane. There is no particular limitation on the isolation membrane, and any known porous isolation membrane with electrochemical and mechanical stability can be selected.

[0105] In some embodiments, the preparation of the electrochemical device includes: stacking the positive electrode sheet, the isolation membrane, and the negative electrode sheet in order, so that the isolation membrane is located between the positive and negative electrode sheets to play an isolating role, and then winding them into a square bare battery cell, placing them in a battery shell, and then baking them at 65-95°C to remove water, injecting electrolyte, sealing, and after standing, hot and cold pressing, forming, clamping, volume separation and other processes, an electrochemical device is obtained.

[0106] In some embodiments, the electrochemical device includes a lithium-ion battery. The above only takes soft-pack lithium-ion batteries as an example. This application is not limited to the application of soft-pack batteries, but also includes the application of common lithium-ion battery forms such as aluminum shell batteries and cylindrical batteries.

[0107] In some embodiments, the electrochemical device of the present application can be used for, but is not limited to, backup power supplies, motors, electric vehicles, electric motorcycles, power-assisted bicycles, bicycles, power tools, large household batteries, and the like.

[0108] In some embodiments, the low temperature charging power P of the electrochemical device of the present application is CC >20W.

[0109] In some embodiments, the low temperature charging power P of the electrochemical device of the present application is CC >24W.

[0110] In some embodiments, the low temperature charging power P of the electrochemical device of the present application is CC >26W. Using its own electrochemical device, the low-temperature charging power of the electrochemical device can be within a relatively optimal range. The low temperature is a temperature below 0°C. The low temperature used in this application is -20°C.

[0111] In some embodiments, the low-temperature discharge power P of the electrochemical energy storage device of the present application is DC >60W.

[0112] In some embodiments, the low-temperature discharge power P of the electrochemical energy storage device of the present application is DC >68W. Using its own electrochemical device can make the low-temperature discharge power of the electrochemical device within a relatively optimal range. The low temperature is a temperature below 0°C. The low temperature used in this application is -20°C.

[0113] Example 1

[0114] 1) Preparation of precursor: nickel source, cobalt source and manganese source are dispersed in deionized water to obtain a mixed solution; the mixed solution, NaOH solution and ammonia complexing agent solution are simultaneously pumped into a stirred reactor in a continuous parallel flow reaction mode, the ammonia concentration is adjusted to 2.5 g / L, the pH value of the reaction solution is controlled to 12, the temperature in the reactor is 45° C., and an inert gas is passed during the reaction process; after the reaction is completed, the nickel cobalt manganese hydroxide precursor [Ni 0.5 Co 0.2 Mn 0.3 ](OH)2, the precursor is composed of tightly packed primary particles forming spherical secondary particles with an average particle size Dv50 of 4 μm. The primary particles have a length of 200 nm to 800 nm, a width of 100 nm to 400 nm, and an aspect ratio of 2 to 8; for example, the primary particle lengths are 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, and 800 nm; and the primary particle widths are 200 nm and 300 nm.

[0115] (2) Preparation of positive electrode active materials: lithium carbonate, precursor [Ni 0.5 Co 0.2 Mn 0.3 ](OH)2 was added to a high-speed mixer and mixed for 30 minutes, and then sintered once at a temperature of 850°C for 25 hours to obtain an intermediate product. After preliminary crushing, secondary mixing was performed. The oxides of Al and W and the intermediate product were added to a high-speed mixer according to a stoichiometric ratio and mixed for 20 minutes, and then sintered twice at a temperature of 500°C for 8 hours. After screening and demagnetization, the positive electrode active material Li 1.08 Al 0.002 W 0.0015 Ni 0.5 Co 0.2 Mn 0.3 O2, test the pore size distribution and coating element content of the positive electrode active material. For specific test parameters, see Figure 3 .

[0116] (3) Preparation of positive electrode sheets: The positive electrode active material, acetylene black, and polyvinylidene fluoride were dispersed in N-methylpyrrolidone (NMP) at a mass ratio of 92:6:2. The resulting slurry was coated on a 12 μm aluminum foil, dried in an oven at 120°C, and then cold pressed and slit to obtain positive electrode sheets.

[0117] (4) Electrolyte Preparation: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were prepared in a volume ratio of 20:20:60 to form a mixed solution. In an argon atmosphere glove box with a water content of <10 ppm, fully dried LiPF6 at a concentration of 1 mol / L was dissolved in an organic solvent and mixed thoroughly to obtain an electrolyte.

[0118] (5) The preparation of the negative electrode sheet includes: mixing graphite, sodium carboxymethyl cellulose, styrene-butadiene rubber, and acetylene black in a mass ratio of 95:1:2:2, adding deionized water, and obtaining a negative electrode slurry under the action of a vacuum mixer; uniformly coating the negative electrode slurry on a copper foil with a thickness of 8 μm, drying it in an oven at 120°C, and then cold pressing and slitting it to obtain a negative electrode sheet.

[0119] (6) Preparation of electrochemical device: The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation. The cells are then wound into a square bare cell and filled with aluminum-plastic film. The cells are then baked at 80°C to remove water, and the electrolyte is injected and sealed. After standing, hot and cold pressing, forming, clamping, and volume separation, the electrochemical device is obtained.

[0120] Example 2

[0121] The specific preparation process is the same as that of Example 1, except that the positive electrode active materials with different pore size distributions are obtained by adjusting the ammonia concentration and pH value in step (1) and the primary sintering temperature and primary sintering time in step (2). For specific test parameters, see Figure 3 .

[0122] In Example 2, the concentration of ammonia water was 1.7 g / L, the pH value of the reaction solution was 12.5, and the obtained nickel cobalt manganese hydroxide precursor [Ni 0.5 Co 0.2 Mn 0.3 ](OH)2, the primary sintering temperature is 840℃, the primary sintering time is 24h, and the prepared positive electrode active material is Li 1.08 Al 0.002 W 0.0015 Ni 0.5 Co 0.2 Mn 0.3 O2.

[0123] Example 3

[0124] The specific preparation process is the same as that of Example 1, except that the positive electrode active materials with different pore size distributions are obtained by adjusting the ammonia concentration and pH value in step (1) and the primary sintering temperature and primary sintering time in step (2). For specific test parameters, see Figure 3 .

[0125] In Example 3, the concentration of ammonia water was 1.8 g / L, the pH value of the reaction solution was 12.4, and the obtained nickel cobalt manganese hydroxide precursor [Ni 0.5 Co 0.2 Mn 0.3 ](OH)2, the primary sintering temperature is 845℃, the primary sintering time is 24h, and the prepared positive electrode active material is Li 1.08 Al 0.002 W 0.0015 Ni 0.5 Co 0.2 Mn 0.3 O2.

[0126] Example 4

[0127] The specific preparation process is the same as that of Example 1, except that the ratios of Ni, Co and Mn in the nickel cobalt manganese hydroxide precursors prepared at different sintering temperatures are different, and the positive electrode active materials with different main element contents are obtained. For specific test parameters, see Figure 3 .

[0128] Among them, the positive electrode active material prepared in Example 4 is Li 1.08 Al 0.002 W 0.0015 Ni 0.46 Co 0.22 Mn 0.22 O2.

[0129] Example 5

[0130] The specific preparation process is the same as that of Example 1, except that the ratios of Ni, Co and Mn in the nickel cobalt manganese hydroxide precursors prepared at different sintering temperatures are different, and the positive electrode active materials with different main element contents are obtained. For specific test parameters, see Figure 3 .

[0131] Among them, the positive electrode active material prepared in Example 5 is Li 1.08 Al 0.002 W 0.0015 Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2.

[0132] Example 6

[0133] The specific preparation process is the same as that of Example 1, except that the ratios of Ni, Co and Mn in the nickel cobalt manganese hydroxide precursors prepared at different sintering temperatures are different, and the positive electrode active materials with different main element contents are obtained. For specific test parameters, see Figure 3 .

[0134] Among them, the positive electrode active material prepared in Example 6 is Li1.08 Al 0.002 W 0.0015 Ni 0.6 Co 0.1 Mn 0.3 O2.

[0135] Example 7

[0136] The specific preparation process is the same as that of Example 1, except that the coating element is Ti, and the positive electrode active materials with different coating elements are obtained. For specific test parameters, see Figure 3 .

[0137] Among them, the positive electrode active material prepared in Example 7 is Li 1.08 Ti 0.002 Ni 0.5 Co 0.2 Mn 0.3 O2.

[0138] Example 8

[0139] The specific preparation process is the same as that of Example 1, except that the coating elements are Al and Ce, and the positive electrode active materials with different coating elements are obtained. For specific test parameters, see Figure 3 .

[0140] Among them, the positive electrode active material prepared in Example 8 is Li 1.08 Al 0.002 Ce 0.0015 Ni 0.5 Co 0.2 Mn 0.3 O2.

[0141] Example 9

[0142] The specific preparation process is the same as that of Example 1, except that the coating elements are Al, Ti and W, and the positive electrode active materials with different coating elements are obtained. For specific test parameters, see Figure 3 .

[0143] Among them, the positive electrode active material prepared in Example 9 is Li 1.08 Al 0.002 Ti 0.002 W 0.0015 Ni 0.5 Co 0.2 Mn 0.3 O2.

[0144] Example 10

[0145] The specific preparation process is the same as that of Example 1, except that the coating elements are Al, Mg and Ti, and the positive electrode active materials with different coating elements are obtained. For specific test parameters, see Figure 3 .

[0146] Among them, the positive electrode active material prepared in Example 10 is Li 1.08 Al 0.002 Mg 0.002 Ti 0.002 Ni 0.5 Co 0.2 Mn 0.3 O2.

[0147] Example 11

[0148] The specific preparation process is the same as that of Example 1, except that the thickness of the primary grains is controlled by adjusting the pH value of the precursor prepared in step (1), and the pore size and distribution of the generated pores are adjusted by the subsequent sintering process. The half-peak width D of the pore size distribution of the obtained positive electrode active material is HW is 420nm, and the prepared positive electrode active material is Li 1.08 Al 0.002 W 0.0015 Ni 0. 5Co 0.2 Mn 0.3 O2, for specific test parameters, see Figure 3 .

[0149] Example 12

[0150] The specific preparation process is the same as that of Example 1, except that the thickness of the primary grains is controlled by adjusting the pH value of the precursor prepared in step (1), and the pore size and distribution of the generated pores are adjusted by the subsequent sintering process. The half-peak width D of the pore size distribution of the obtained positive electrode active material is HW is 453nm, and the prepared positive electrode active material is Li 1.08 Al 0.002 W 0.0015 Ni 0. 5Co 0.2 Mn 0.3 O2, for specific test parameters, see Figure 3 .

[0151] Example 13

[0152] The specific preparation process is the same as that of Example 1, except that the thickness of the primary grains is controlled by adjusting the pH value of the precursor prepared in step (1), and the pore size and distribution of the generated pores are adjusted by the subsequent sintering process. The half-peak width D of the pore size distribution of the obtained positive electrode active material is HW is 521nm, and the prepared positive electrode active material is Li 1.08 Al 0.002 W 0.0015 Ni 0. 5Co 0.2 Mn0.3 O2, for specific test parameters, see Figure 3 .

[0153] Example 14

[0154] The specific preparation process is the same as that of Example 1, except that the thickness of the primary grains is controlled by adjusting the pH value of the precursor prepared in step (1), and the pore size and distribution of the generated pores are adjusted by the subsequent sintering process. The half-peak width D of the pore size distribution of the obtained positive electrode active material is HW is 561nm, and the prepared positive electrode active material is Li 1.08 Al 0.002 W 0.0015 Ni 0. 5Co 0.2 Mn 0.3 O2, for specific test parameters, see Figure 3 .

[0155] Example 15

[0156] The specific preparation process is the same as that of Example 1, except that the thickness of the primary grains is regulated by adjusting the pH value of the precursor prepared in step (1), and the pore size and distribution of the generated pores are adjusted by the subsequent sintering process. At this time, the half-peak width D of the pore size distribution of the obtained positive electrode active material is HW is 90nm, the calculated is 0.49, and the prepared positive electrode active material is Li 1.08 Al 0.002 W 0.0015 Ni 0.5 Co 0.2 Mn 0.3 O2, for specific test parameters, see Figure 3 .

[0157] Example 16

[0158] The specific preparation process is the same as that of 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 in the precursor to achieve the control of the maximum pore size. At this time, the maximum pore size D of the obtained positive electrode active material is max is 750nm, the calculated is 0.62, and the prepared positive electrode active material is Li 1.08 Al 0.002 W 0.0015 Ni 0.5 Co 0.2 Mn 0.3 O2, for specific test parameters, see Figure 3 .

[0159] Example 17

[0160] The specific preparation process is the same as that of 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 in the preparation of the precursor to achieve the maximum pore size control. The maximum pore size D of the obtained positive electrode active material is max is 1517nm, and the prepared positive electrode active material is Li 1.08 Al 0.002 W 0.0015 Ni 0.5 Co 0.2 Mn 0.3 O2, for specific test parameters, see Figure 3 .

[0161] Example 18

[0162] The specific preparation process is the same as that of 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 in the preparation of the precursor to achieve the maximum pore size control. The maximum pore size D of the obtained positive electrode active material is max is 1830nm, and the prepared positive electrode active material is Li 1.08 Al 0.002 W 0.0015 Ni 0.5 Co 0.2 Mn 0.3 O2, for specific test parameters, see Figure 3 .

[0163] Example 19

[0164] The specific preparation process is the same as that of 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 in the preparation of the precursor to achieve the maximum pore size control. The maximum pore size D of the obtained positive electrode active material is max is 2012nm, and the prepared positive electrode active material is Li 1.08 Al 0.002 W 0.0015 Ni 0.5 Co 0.2 Mn 0.3 O2, for specific test parameters, see Figure 3 .

[0165] Example 20

[0166] The specific preparation process is the same as that of Example 1, except that the coating process and secondary sintering are not performed. The positive electrode active material prepared is Li 1.08 Ni 0.5 Co 0.2 Mn 0.3 O2, for specific test parameters, see Figure 3 .

[0167] Comparative Example 1

[0168] The specific preparation process is the same as that of Example 1, except that the pore size distribution of the obtained positive electrode active material is adjusted by adjusting the ammonia concentration and pH value in step (1) and the primary sintering temperature and primary sintering time in step (2). HW / D max >0.5, the prepared positive electrode active material is Li 1.08 Al 0.002 W 0.0015 Ni 0.5 Co 0.2 Mn 0.3 O2, for specific test parameters, see Figure 3 .

[0169] In Comparative Example 1, the concentration of aqueous ammonia is 3 g / L, the pH value of the reaction solution is 13, the primary sintering temperature is 900° C., and the primary sintering time is 30 h.

[0170] Comparative Example 2

[0171] The specific preparation process is the same as that of Example 1, except that the pore size distribution of the obtained positive electrode active material is adjusted by adjusting the ammonia concentration and pH value in step (1) and the primary sintering temperature and primary sintering time in step (2). HW / D max <0.05, the prepared positive electrode active material is Li 1.08 Al 0.002 W 0.0015 Ni 0.5 Co 0.2 Mn 0.3 O2, for specific test parameters, see Figure 3 .

[0172] In Comparative Example 2, the concentration of aqueous ammonia was 1.5 g / L, the pH value of the reaction solution was 13.5, the primary sintering temperature was 820° C., and the primary sintering time was 18 h.

[0173] Electrochemical device testing

[0174] Low temperature charge and discharge power measurement

[0175] The battery was charged to 100% SOC at 1C constant current and constant voltage, left to stand for 10 minutes, discharged at 1C constant current for 30 minutes to 50% SOC, placed in a -20°C environment and left to stand for 180 minutes, and discharged at 5C for 30 seconds. The voltage values before and after discharge were recorded, and the discharge power was obtained by calculation.

[0176] Cycle test

[0177] First, calibrate the battery voltage and confirm the voltage corresponding to 20% SOC and 90% SOC of the battery. Place it in a 25℃ constant temperature box for circulation, charge and discharge at a constant current of 4C, record the battery cycle capacity and number of cycles. When the capacity retention rate is lower than 80% of the capacity of the first cycle, record the number of battery cycles.

[0178] The low temperature charge and discharge power test and cycle number test of the electrochemical devices prepared in Examples 1-20 and Comparative Examples 1-2 are shown in FIG. Figure 4 .

[0179] Depend on Figure 3 and Figure 4 It can be seen that compared with Example 1, Examples 2 to 3 have different degrees of porosity of the precursors, and different temperatures and times for the first sintering, resulting in intermediate products with different pore size distributions, so as to regulate the coating effect on the inner surface of the secondary particles and the surface and internal structure of the secondary particles of the finished product, thereby improving the low-temperature power performance and long-term cycle life of the electrochemical device.

[0180] From the results of Example 1 and Example 20, it can be seen that in Example 1, Al and W elements are added to the coating. The appropriate pore size distribution makes the deviation of the inner and outer coating element content of the finished product 0.18, indicating that the inner and outer coating effects are good. The premise is that D HW / D max When the value is in the appropriate range, HW / D max When the porosity is 0.25 and the electrode porosity is 0.36, it means that the pore size distribution of the secondary particles is wide and there are suitable pore channels so that the coating material can smoothly enter the inner surface of the secondary particles through the pores. At this time, after secondary sintering, the coating material can form a stable coating layer with the inner surface to reduce the uncoated surface area. Since the porosity of the material itself is moderate, the prepared electrode also has a suitable porosity. After the electrochemical device is prepared, the electrolyte can fully infiltrate the electrode and there will be no serious side reaction between the uncoated area and the electrolyte, thus forming a relatively stable interface state to facilitate internal charge transfer and transmission, and obtain good power performance even at lower temperatures. In addition, since the internal and external coating effects are consistent, the structural damage of the positive electrode active material in the long-term cycle process can be reduced, so its cycle life is improved.

[0181] Comparing Example 1 with Comparative Examples 1 and 2, in Comparative Examples 1 and 2, D HW / D max The value is not within the range of 0.05 to 0.5, and the deviation of the inner and outer coating element contents is greater than 40%. Figure 4From the test performance, it can be seen that the pore size is not within the required range, the internal coating effect of the hollow structure of the positive electrode material is poor, and the content of the inner and outer coating elements is very different, which leads to a strong side reaction when the electrode contacts the electrolyte, resulting in electrolyte consumption and corrosion of the positive electrode material surface. The transition metal ions Ni, Co, and Mn dissolve from the surface of the positive electrode material into the electrolyte and then deposit on the negative electrode, destroying the surface structure of the positive electrode material. The transition metal ions in the bulk phase migrate to the surface, accompanied by the release of lattice oxygen, which destroys the structure of the positive electrode material. In addition, the negative electrode continuously generates SEI film to consume active lithium, resulting in poor cycle capacity and stability and attenuation of power performance.

[0182] It can be seen from Examples 4 to 6 that different main element contents have a greater impact on the dynamics of the material itself. When the Ni and Co contents are higher, the dynamics performance is better, but the cost will also increase. Therefore, it is necessary to optimize the main element ratio. Although the main element ratios in Examples 4 to 6 are quite different, the D HW / D max In the range of 0.05 to 0.5, when the content deviation of the inner and outer coating elements is less than 40%, its power performance and long-term cycle performance are also greatly improved compared with Example 20.

[0183] From Examples 7 to 9, it can be seen that different coating elements can ensure that the content deviation of the inner and outer coating elements is less than 40%, D HW / D max When the value is in the range of 0.05 to 0.5, the power performance and long-term cycle performance are also greatly improved compared with Example 20.

[0184] The above is a detailed introduction to the positive electrode active materials and electrochemical devices provided in the embodiments of the present application. Specific examples are used in this application to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the technical solutions and core ideas of the present application. Ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some of the technical features therein with equivalents; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A positive electrode active material, characterized in that The secondary particles include pores, wherein the pore size distribution of the secondary particles satisfies: 0.05≤D HW / D max ≤0.5; where D HW The half-peak width of the pore size distribution of the positive electrode active material, D max Indicates the maximum pore size of the positive electrode active material; The positive electrode active material comprises lithium nickel cobalt manganese oxide particles, wherein the molar amount of the nickel element is less than or equal to 0.7, based on the molar amount of the nickel element, the cobalt element, and the manganese element being 1; The secondary particles include a hollow structure formed by stacking primary particles, and the surfaces of the secondary particles and the surfaces of the primary particles located in the hollow structure have element A; the average content of element A on the surface of the secondary particles is a 01 The average content of element A on the surface of the primary particles in the hollow structure is a 02 satisfy: ,and , ; Where a i represents the content of element A measured in the i-th area selected on the surface of the secondary particle, 1≤i≤m and m is an integer greater than or equal to 3; a j represents the content of element A measured in the j-th area selected on the surface of the primary particle, 1≤j≤n and n is an integer greater than or equal to 3.

2. The positive electrode active material according to claim 1, characterized in that The D HW Satisfies: 100 nm ≤ D HW ≤400nm; the D max Satisfies: 800 nm ≤ D max ≤2000 nm.

3. The positive electrode active material according to claim 1, characterized in that The porosity P1 of the positive electrode active material satisfies: 30%≤P1≤80%.

4. The positive electrode active material according to claim 1, characterized in that The secondary particles include lithium nickel cobalt manganese oxide particles, and the lithium nickel cobalt manganese oxide further includes element A, and the element A includes one or more of Zr, Sr, W, Al, Ti, Mg, Ce, and Y.

5. The positive electrode active material according to claim 1, characterized in that The positive electrode active material contains Li x A y Ni a Co b Mn c O z , where 0.9 ≤ x ≤ 1.1, 0 ≤ y ≤ 0.2, 1 ≤ z ≤ 2, 0.4 ≤ a < 1, 0 < b < 0.3, 0 < c < 1, a + b + c = 1, and the A contains one or more of Zr, Sr, W, Al, Ti, Mg, Ce, and Y.

6. The positive electrode active material according to claim 1, characterized in that The a i The variance E satisfies: 0≤E≤1×10 -4 ; said a i The range C satisfies: 0≤C≤0.

05.

7. The positive electrode active material according to claim 1, characterized in that The a j The variance I satisfies: 0≤I≤1×10 -3 ; said a j The range D satisfies: 0≤D≤0.

05.

8. The positive electrode active material according to claim 1, characterized in that The positive electrode active material satisfies at least one of the following characteristics: (a) The average pore size of the positive electrode active material is 100 nm to 2000 nm; (b) The specific surface area of the positive electrode active material is 0.2 m 2 / g~1.5m 2 / g; (c) The average particle size Dv50 of the positive electrode active material is 2 μm to 8 μm. 9 . An electrochemical device comprising a positive electrode current collector and a positive electrode plate disposed on the positive electrode current collector, wherein the positive electrode plate comprises the positive electrode active material according to claim 1 .

10. The electrochemical device according to claim 9, characterized in that The porosity P2 of the positive electrode sheet satisfies: 20%≤P2≤50%.

11. The electrochemical device according to claim 9, characterized in that The low-temperature charging power P of the electrochemical device CC >20W, the low temperature discharge power P of the electrochemical device DC >60W.

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