Positive electrode active material and preparation method therefor, positive electrode sheet, battery, and electric device

Abstract

A positive electrode active material and a preparation method therefor, a positive electrode sheet, a battery, and an electrical device. The positive electrode active material comprises secondary particles, wherein the secondary particles are formed by the aggregation of primary particles; the secondary particles comprise open pores and closed pores; and the open pore porosity P0 of the positive electrode active material accounts for 25%-85% of the total porosity Pt of the positive electrode active material.

Description

Cathode active material, preparation method thereof, cathode sheet, battery and electric device TECHNICAL FIELD

[0001] The present application belongs to the field of batteries, and in particular relates to a cathode active material, a preparation method thereof, a cathode sheet, a battery and an electric device. BACKGROUND

[0002] Lithium ion batteries are widely used in various electronic products and vehicles such as electric vehicles due to their light weight, low pollution, high energy density and high single cell voltage. In order to meet the increasing demand for endurance and life of electronic products and vehicles such as electric vehicles, lithium ion batteries with high energy density and long cycle life are continuously iterated and upgraded in research and application. As the component with the greatest impact on performance in lithium ion batteries, the main development direction of the cathode active material is to increase the Ni content in the ternary cathode material to improve the energy density, but the exacerbation of the cycle performance and safety problems cannot be ignored.

[0003] SUMMARY

[0004] The present application aims to at least partially solve one of the technical problems in the related art. To this end, one object of the present application is to propose a cathode active material, a preparation method thereof, a cathode sheet, a battery and an electric device, so that the cathode active material has high electrochemical reactivity, lithium ion migration ability, energy density and particle strength, and thus can have excellent performance of high energy density, good rate performance and long cycle life.

[0005] The present application is mainly based on the following problems and findings:

[0006] The polycrystalline or single-crystal-like ternary cathode material is usually formed by agglomeration of a plurality of primary particles to form secondary particles, and a plurality of pores are formed on the surface or inside of the material. Currently, there are studies on designing the structure and arrangement of the cathode active material particles to intrinsically control the cycle and safety performance of the material, for example, limiting the total pore volume of the surface to be below 200 nm to be 0.008 cm 3 / g-0.012 cm 3a ternary positive electrode material with a pore volume of 15 nm or less accounting for no more than 50% of the total pore volume of the ternary positive electrode material; also limited is a positive electrode material with a large porosity in the center of the cross section of the secondary particles and a small porosity on the surface, and the ratio of the short axis length to the long axis length of the secondary particles in the cross section and the ratio of the total pore area to the total area of the particles in the cross section both meet preset requirements; in addition, there is also a positive electrode material with a ratio of the cross-sectional area of the secondary particles to the area of the pore part meeting preset requirements, and so on. In fact, controlling the appropriate pore volume or porosity is crucial to the design of the positive electrode active material and the electrode sheet, which not only affects the electrochemical performance of the positive electrode active material, but also affects the particle strength and the compaction density of the material, as well as the cycle life and other performances. In this application, by adjusting the relationship between the open pores and the closed pores of the positive electrode active material and / or the structure (which can be achieved by adjusting the agglomeration effect between the primary particles and the like), the balance between the particle strength, energy density and cycle stability of the material is solved to a certain extent, so as to realize the purpose of making the material have high electrochemical activity and high rate performance, avoiding excessive side reactions between the material surface and the electrolyte, ensuring the particle strength and the compaction density, and finally obtaining a positive electrode active material with high energy density, high particle strength and long cycle life.

[0007] Therefore, in the first aspect of the present application, a positive electrode active material is provided, comprising: secondary particles formed by the accumulation of primary particles, the secondary particles comprising open pores and closed pores, the open pore porosity P o accounts for 25%-85% of the total porosity P t of the positive electrode active material.

[0008] Among them, for agglomerated positive electrode active materials such as ternary positive electrode active materials, the porosity can reflect the degree of fusion and aggregation between the primary particles. A small part of the pores is exposed on the surface as open pores, which is related to the surface activity and electrolyte infiltration area of the material. Most of the pores are closed pores, which are in the interior of the secondary particles of the material that cannot be infiltrated by the electrolyte, which is related to the particle strength of the material, the contact effect between the primary particles, and the expansion and contraction space of the material during the cycle. The lower the ratio of the open pore porosity to the total porosity of the material, that is, the higher the ratio of the closed pore porosity, the worse the mass transfer and conductivity between the primary particles in the secondary particles, and the lower the particle strength. However, a suitable closed pore porosity can provide the expansion and contraction space of the material during charging and discharging, release the extrusion stress between the primary particles, and correspondingly improve the cycle performance. In this application, by controlling the ratio of the open pore porosity to the total porosity of the positive electrode active material to be 25%-85%, the material can have high particle strength, high rate performance and good cycle stability against expansion and contraction during the charging and discharging process.

[0009] In addition, the positive electrode active material according to the above-mentioned embodiments of the present application can further have the following additional technical features.

[0010] In some embodiments of the present application, the open porosity P of the positive electrode active material is 0.5% to 3%. o

[0011] In some embodiments of the present application, the average open pore diameter D of the positive electrode active material is 10 nm to 50 nm. o

[0012] In some embodiments of the present application, the open pore volume Vo of the positive electrode active material is 0.002 cm3 / g to 0.01 cm3 / g. 3 3

[0013] In some embodiments of the present application, the skeleton volume Vt of the positive electrode active material is 0.2 cm3 / g to 0.25 cm3 / g. 3 3

[0014] In some embodiments of the present application, the total porosity P of the positive electrode active material is 1% to 10%. t

[0015] In some embodiments of the present application, the average closed pore diameter D of the secondary particles is 40 nm to 200 nm. C

[0016] In some embodiments of the present application, the specific surface area of the positive electrode active material is S, the specific surface area of the positive electrode active material after being fractured by a pressure of 3.5 tons is S, and the specific surface area change rate ΔSSA of the positive electrode active material is 0 to 50%, wherein ΔSSA = (S-S) / S×100%. 0 3.5 3.5 0 0

[0017] In some embodiments of the present application, the particle diameter corresponding to the cumulative volume distribution of 10% of the positive electrode active material is D, the particle diameter corresponding to the cumulative volume distribution of 10% of the positive electrode active material after being fractured by a pressure of 3.5 tons is D, and the particle diameter change rate ΔD of the positive electrode active material is 0 to 20%, wherein ΔD = (D-D) / D×100%. 10 0 10 3.5 10 10 10 0 10 3.5 ​​​​​​​​​​​​​​​​​​) / D 10 0 ×100%.

[0018] In some embodiments of the present application, the positive electrode active material comprises Li 1+a Ni x Co y Mn z M m O2, -0.05≤a≤0.3, 0.8≤x≤1, 0≤y≤0.2, 0≤z≤0.2, 0≤m≤0.01, M comprises at least one of Mg, La, Al, Sr, Ba, Y, Zr, Ca, Fe, Zn, Sn, W, V, Mo, Sb, Ta, Ti, Nb, S, P and B.

[0019] In some embodiments of the present application, M comprises at least one of Sn, W, V, La, Mo, Sb, Ta, Ti, Nb, and the half-peak width of the diffraction peak corresponding to the 104 crystal face in the XRD pattern of the primary particle is 0.245-0.270.

[0020] In some embodiments of the present application, M comprises at least one of S, P, B, and the half-peak width of the diffraction peak corresponding to the 104 crystal face in the XRD pattern of the primary particle is 0.250-0.275.

[0021] In some embodiments of the present application, M comprises at least one of Mg, Al, Sr, Ba, Y, Zr, Ca, Fe, Zn, and the half-peak width of the diffraction peak corresponding to the 104 crystal face in the XRD pattern of the primary particle is 0.255-0.280.

[0022] In some embodiments of the present application, the secondary particle comprises a matrix and a coating layer, the matrix comprises the Li 1+a Ni x Co y Mn z M m O2, and at least part of the surface of the matrix is provided with the coating layer.

[0023] In some embodiments of the present application, the coating layer comprises J elements, and the J elements comprise at least one of Al, Zr, Ti, F, B, Cl, Br, I, S, W, Co, Sn, Mo.

[0024] In some embodiments of the present application, the coating layer comprises J elements, and the ratio of the total number of moles of Ni, Co, Mn and M in the matrix to the number of moles of J elements in the coating layer is 1:(0-0.05).

[0025] In a second aspect of the present application, a method for preparing the above positive electrode active material is provided, comprising:

[0026] (1) performing a co-precipitation reaction on an aqueous solution of a nickel source, a cobalt source and a manganese source under alkaline conditions to obtain precursor particles;

[0027] (2) mixing the precursor particles with a lithium source and an M source and performing a sintering treatment to obtain a positive electrode active material.

[0028] According to the method for preparing a positive electrode active material of the second aspect of the present application, the composition of nickel, cobalt and manganese, the porosity control of the precursor and the doping amount of the M element can be combined to regulate the temperature and time of the sintering treatment, and the grain size and arrangement of the primary particles, and further regulate the agglomeration effect between the primary particles in the secondary particles. Thus, it is beneficial to obtain a positive electrode active material with an open porosity ratio accounting for 25%-85% of the total porosity, so that the material has high particle strength, high rate performance and good cycle stability against expansion and contraction during charging and discharging.

[0029] In some embodiments of the present application, in step (1), the co-precipitation reaction is performed under alkaline conditions with a pH value of 10-11.5.

[0030] In some embodiments of the present application, in step (2), the sintering treatment includes: holding at 650℃-900℃ for 4h-15h.

[0031] In some embodiments of the present application, step (2) further includes: mixing the sintering product with a coating material containing a J source and holding at 300℃-700℃ for 5h-10h.

[0032] In the third aspect of the present application, a positive electrode tab is provided, which includes the above-mentioned positive electrode active material or the positive electrode active material prepared by the above-mentioned method. The features and effects described for the above-mentioned positive electrode active material and the above-mentioned method for preparing a positive electrode active material are equally applicable to the positive electrode tab, which will not be repeated here. In general, the positive electrode tab has good cycle stability and a long cycle life.

[0033] In the fourth aspect of the present application, a battery is provided, which includes the above-mentioned positive electrode tab.

[0034] In the fifth aspect of the present application, an electric device is provided, which includes the above-mentioned battery. BRIEF DESCRIPTION OF DRAWINGS

[0035] FIG. 1 is a cross-sectional view of a precursor prepared according to Embodiment 1 of the present application.

[0036] FIG. 2 is a distribution of closed pores and pore diameters in a cross-section of a positive electrode active material prepared according to Embodiment 1 of the present application. DETAILED DESCRIPTION

[0037] Embodiments of the present application are described in detail below. The embodiments described below are exemplary and are intended to be illustrative of the present application, and are not to be construed as limiting the present application.

[0038] In a first aspect of the present application, a positive electrode active material is provided, comprising: secondary particles, the secondary particles being formed by accumulation of primary particles, the secondary particles comprising open pores and closed pores (understood with reference to FIG. 1), an open porosity P o of the total porosity P t of the positive electrode active material.

[0039] Exemplarily, the open porosity P o of the total porosity P t of the positive electrode active material can be 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85%, etc. Among them, the open porosity P o is the ratio of the open pore volume V o that can be filled with nitrogen of the positive electrode active material to the total volume of the positive electrode active material, which can be obtained by N2 adsorption-desorption isotherm test and analysis of the positive electrode active material, such as can be tested by a surface instrument of Tristar 3020 model of Micromeritics company; understood with reference to FIG. 2, the total porosity P t can be the total pore area S t of the cross section of the positive electrode active material under the electron microscope, and the total area S m of the cross section of the material, i.e. the 3 / 2 power of S t / S m , wherein the total porosity P t can be obtained by testing the average value of the total porosity of a plurality of secondary particles in the sample, and the specific operation can include: ion cutting of the positive electrode active material sample by an ion milling instrument (such as an ion milling instrument of model Hitachi IM4000 II) to obtain a plurality of cross sections of the secondary particles, image sampling of the cross section of the material by a scanning electron microscope, and image contrast analysis by a LIBMAS microscopic intelligent image analysis system to obtain, the number of the secondary particles to be tested selected by sampling in the test sample should be ≥6, such as can be ≥8, ≥10, ≥15, ≥20, ≥30, ≥40 or ≥50, etc., which can be flexibly selected by the person skilled in the art according to the actual needs, in addition, when the sample is taken by the scanning electron microscope, the sample with a cross section diameter between the material particle size D 50 -D 80 can be selected to make the sample as much as possible to be the cross section of the secondary particle core or the cross section close to the secondary particle core, so as to improve the accuracy of the total porosity test. Among them, D 50The particle size corresponding to when the volume distribution of the positive electrode active material accumulates to 50% (i.e., the particle size is less than D). 50 The portion accounts for 50%), D 80 The particle size corresponding to when the volume distribution of the positive electrode active material accumulates to 80% (i.e., the particle size is smaller than D). 80 (80% of the total).

[0040] In this process, primary particles, when aggregated into secondary particles, form open pores that are open to the outside world and closed pores that are inaccessible to external gases or electrolytes. For agglomerated cathode active materials, such as ternary cathode active materials, porosity reflects the degree of fusion and aggregation between primary particles. A small portion of the pores are exposed on the surface as open pores, which are related to the surface activity of the material and the electrolyte wetting area. Most of the pores are closed pores, located inside the secondary particles that are not wetted by the electrolyte. This portion is related to the particle strength of the material, the contact effect between primary particles, and the expansion and contraction space of the material during cycling. The lower the ratio of open pores to total porosity, i.e., the higher the proportion of closed pores, the worse the mass transfer and conductivity between primary particles inside the secondary particles, and the lower the particle strength. However, an appropriate closed pore ratio can provide the expansion and contraction space of the material during charging and discharging, releasing the compressive stress between primary particles and correspondingly improving cycle performance. In this application, the ratio of open porosity to total porosity of the positive electrode active material is 25%-85%, which enables the material to have high particle strength, high rate performance, and good cycle stability to resist expansion and contraction during charge and discharge.

[0041] The positive electrode active material of the above embodiments of this application will be described in detail below with reference to Figures 1-2.

[0042] In some specific embodiments of this application, the method for obtaining a positive electrode active material with the desired pore structure is not particularly limited. Those skilled in the art can flexibly choose the method according to actual needs. For example, the aggregation effect when primary particles are stacked into secondary particles can be controlled by adjusting one or more of the particle size, morphology, and arrangement of the primary particles, thereby controlling the pore structure of the positive electrode active material to obtain a positive electrode active material with the desired pore structure. Furthermore, the pore structure of the positive electrode active material can be further controlled by selecting whether to provide a coating layer, and by choosing one or more of the coating layer material and coating layer thickness.

[0043] In some specific embodiments of this application, the open porosity P of the positive electrode active material o It can account for P of the total porosity of the positive electrode active material t The percentage is 30%-60%, which helps to further improve the material's particle strength, rate performance, and cycle stability during charge and discharge processes, making it resistant to expansion and contraction.

[0044] In some embodiments of the present application, the open porosity P of the positive electrode active material o may be 0.5%-3%, for example, can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, or 3%, etc. The open porosity of the positive electrode active material is related to the surface activity and electrolyte infiltration area of the material, the greater the open porosity, the more the surface interface reaction channels of lithium ion intercalation and deintercalation, the higher the reaction activity, and the better the charge and discharge capacity, the initial efficiency and the rate performance of the material. However, appropriately reducing the open porosity of the positive electrode active material is beneficial to reducing the side reaction between the surface of the positive electrode active material and the electrolyte. In the present application, the open porosity P of the positive electrode active material o meets the given range, which is beneficial to making the positive electrode active material have higher electrochemical reaction activity and rate performance, and also can reduce the risk of excessive side reaction between the material surface and the electrolyte due to excessive open porosity, thereby leading to the decline of the storage, gas production and cycle performance of the material, and further beneficial to making the positive electrode active material have higher capacity and longer service life. Further, the open porosity P of the positive electrode active material o may be 1.0%-2.5%.

[0045] In some embodiments of the present application, the average open pore diameter D of the positive electrode active material o may be 10 nm-50 nm, for example, can be 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm or 50 nm, etc. The average open pore diameter of the positive electrode active material can be measured by a surface instrument according to the BJH (Barrett Joyner Halenda) model, for example, can be tested by a surface instrument of Tristar 3020 model of Micromeritics company. The BJH model and pore diameter test are as follows: the pore shape is assumed to be cylindrical, and the pore diameter and N2 relative pressure that produces capillary condensation satisfy the Kelvin relationship. By testing the N2 adsorption amount of each level of pore at different partial pressures, the distribution of material pore diameter is characterized, and the average pore diameter is obtained by multiplying the proportion coefficient of each level of pore diameter. The pore diameter distribution obtained from the adsorption isotherm is more derived from the internal diameter of the pore; the pore diameter distribution obtained from the desorption isotherm is more derived from the diameter of the pore entrance, and in the present application, the pore entrance diameter can be obtained from the desorption isotherm. In the present application, the open pore diameter of the positive electrode active material meets the given range, which is beneficial to making the open pores on the surface of the material relatively uniformly distributed on the surface of the secondary particles, and further beneficial to the uniformity of lithium ion diffusion and reaction rate. Further, the average open pore diameter D of the positive electrode active material o may be 15 nm-45 nm.

[0046] In some embodiments of the present application, the open pore volume Vo of the positive electrode active material can be 0.002 cm3 / g-0.01 cm3 / g 3 / g, for example, can be 0.003 cm3 / g 3 / g, for example, can be 0.003 cm3 / g 3 / g, 0.004 cm3 / g 3 / g, 0.005 cm3 / g 3 / g, 0.006 cm3 / g 3 / g, 0.007 cm3 / g 3 / g, 0.008 cm3 / g 3 / g, 0.009 cm3 / g 3 / g, or 0.01 cm3 / g 3 / g, etc. The open pore volume of the positive electrode active material can be tested and analyzed according to the N2 adsorption-desorption isotherm by a surface instrument. For example, it can be tested by a surface instrument of Tristar 3020 model of Micromeritics Company. The N2 adsorption-desorption isotherm test can specifically include: using a conventional measuring device (Tristar 3020, etc.), gradually adding N2 to the sample of the material to be tested from which the physical adsorption component is removed under vacuum, calculating the pressure change caused by N2 adsorption by constant volume method, and obtaining the N2 adsorption amount according to the gas equation. Thus, the N2 adsorption isotherm from 0 gas pressure to 0.995 atmosphere at liquid nitrogen temperature is obtained. After reaching 0.995 atmosphere, gradually reduce the N2 pressure to 0 atmosphere to obtain the N2 desorption isotherm from 0.995 atmosphere to 0 atmosphere, and the N2 adsorption-desorption isotherm is obtained. The N2 adsorption-desorption isotherm analysis is: the open pore volume obtained from the N2 adsorption amount at the relative pressure (p / p0) of 0.995 of the N2 adsorption isotherm. The open pores of the positive electrode active material are mainly distributed on the surface of the secondary particles. In the present application, the open pore volume of the positive electrode active material meets the given range, which can provide more lithium ion reaction channels on the one hand, and is also beneficial to reduce the risk of excessive erosion of the electrolyte into the material, so that the electrolyte forms a suitable CEI layer only at the surface layer and the surface open pores of the material. Thus, the positive electrode active material can have high first charge-discharge efficiency and good storage performance and cycle performance. Further, the open pore volume Vo of the positive electrode active material can be 0.002 cm3 / g-0.008 cm3 / g 3 / g. 3 / g.

[0047] In some embodiments of the present application, the skeleton volume Vt of the positive electrode active material can be 0.2 cm3 / g-0.25 cm3 / g 3 / g, for example, can be 0.2 cm3 / g 3 / g, for example, can be 0.2 cm3 / g 3 / g, 0.21 cm3 / g 3 / g, 0.22 cm3 / g3 / g, 0.23 cm 3 / g, 0.24 cm 3 / g or 0.25 cm 3 / g, etc. The skeleton volume of the positive active material can be measured according to the gas displacement method combined with a true density instrument, etc. device, such as can be tested by Micromeritics Accupy II 1345 true density instrument. Among them, the gas displacement method can specifically include: using inert gas N2 as displacement medium, sealing the sample in the N2 filled sample bin, opening the expansion bin to make the gas diffuse, and the volume of the sample can be calculated by the pressure change before and after the gas diffusion after stabilization. It can be understood that because N2 can quickly fill the pores with a diameter as small as angstrom level, therefore the measured volume is only the skeleton volume of the material. In this application, the skeleton volume of the positive active material meets the given range, which is beneficial to balance the particle size and intrinsic density of the material, so that the positive active material has a higher charge and discharge specific capacity. Further, the skeleton volume Vt of the positive active material can be 0.2 cm 3 / g-0.24 cm 3 / g.

[0048] In some specific embodiments of the present application, the total porosity P t of the positive active material can be 1%-10%, for example, can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc. The total porosity P t of the positive active material includes open porosity and closed porosity, and the closed porosity is usually greater than the open porosity, so that the total porosity of the positive active material meets the given range, which is beneficial to further provide space for the expansion and contraction of the positive active material during the charge and discharge process, improve the cycle stability of the positive active material, and improve the cycle performance of the material. Further, the total porosity P t of the positive active material can be 1.5%-8.5%.

[0049] In some specific embodiments of the present application, in the secondary particle, the average pore size D Cmay be 40 nm-200 nm, for example, can be 40 nm, 50 nm, 60 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm or 200 nm, etc. Referring to FIG. 2, the average pore size of the closed pores in the secondary particles can be obtained by using the LIBMAS intelligent image analysis system to perform contrast analysis on the cross-sectional electron micrograph of the secondary particles to obtain the cross-sectional area of each pore, and assuming that the pore shape in the cross-sectional electron micrograph is circular to obtain the average cross-sectional pore size. At this time, either the average pore size of the closed pores of a single secondary particle can meet the given range, or the average pore size of the closed pores of the secondary particles in the positive electrode active material as a whole can meet the given range. At this time, when testing the positive electrode active material sample, the above-mentioned method for testing the total porosity of the positive electrode active material can also be referred to, and a plurality of secondary particles are selected for sampling in the test sample to obtain the average pore size of the closed pores corresponding to each of the plurality of secondary particles respectively and then take the average. Making the average pore size of the closed pores of the secondary particles meet the given range not only can make the vacancies in the material exist in the form of small pores, which can be relatively uniformly distributed in the particle interior, and is conducive to improving the structural stability and particle strength of the positive electrode active material, but also can make the small inter-particle gaps provide a larger expansion and contraction space for the charge and discharge cycles, thereby improving the cycle performance of the positive electrode active material. At the same time, it can also not excessively lose the good conductivity and mass transfer performance between the materials, which is conducive to making the positive electrode active material have good rate performance. Further, in the secondary particles, the average pore size D C may be 60 nm-180 nm.

[0050] In some embodiments of the present application, the specific surface area of the positive electrode active material is S 0 , the specific surface area of the positive electrode active material after being fractured under a pressure of 3.5 tons is S 3.5 , and the specific surface area change rate ΔSSA of the positive electrode active material can be 0-50%, wherein ΔSSA = (S 3.5 -S 0 ) / S 0×100%. For example, ΔSSA can be 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%, etc. The specific surface area of ​​the positive electrode active material can be measured using a surface analyzer based on the static adsorption principle of N2, such as the Tristar 3020 surface analyzer from Micromeritics. Specific operations may include: gradually adding N2 to the test material (after pre-removing physically adsorbed components) under vacuum conditions in the testing apparatus; calculating the pressure change caused by N2 adsorption using the constant volume method; and determining the amount of N2 adsorbed according to the gas equation. This yields the amount of N2 adsorbed from 0 atm to 0.3 atm at liquid nitrogen temperature, which can then be converted into a specific surface area per unit weight. The change rate of specific surface area before and after fracturing under 3.5 tons of pressure meets the given range, indicating that the positive electrode active material has good compressive strength. In the subsequent electrode manufacturing process, on the one hand, it helps to avoid the risk of material cracking during electrode compaction, improves battery stability, and reduces safety risks. On the other hand, it can also enable the positive electrode active material to withstand higher compressible density, and has the potential to further improve the energy density of the positive electrode and the battery.

[0051] In some specific embodiments of this application, the particle size corresponding to the cumulative volume distribution of the positive electrode active material reaching 10% is D. 10 0 The particle size corresponding to the accumulation of 10% in the volume distribution of the positive electrode active material after being subjected to 3.5 tons of pressure fracturing is D. 10 3.5 The particle size variation rate ΔD of the positive electrode active material 10 It can be 0-20%, where ΔD 10 =(D 10 0 -D 10 3.5 ) / D 10 0 ×100%. For example, ΔD 10 The percentages can be 0%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, or 20%, etc. The particle size of the positive electrode active material can be obtained using a laser particle size analyzer, such as the Marvern Hydro 2000mu model. Positive electrode active materials exhibiting particle size change rates within the given range after 3.5-ton pressure fracturing demonstrate good compressive strength, producing less fracturing fine powder under high pressure. This is beneficial for further improving the stability of the positive electrode active material during electrode fabrication and reducing safety risks.

[0052] In some specific embodiments of this application, the positive electrode active material may include Li 1+a Ni x Coy Mn z M m O2, wherein -0.05≤a≤0.3, 0.8≤x≤1, 0≤y≤0.2, 0≤z≤0.2, 0≤m≤0.01, and M can include at least one of Mg, La, Al, Sr, Ba, Y, Zr, Ca, Fe, Zn, Sn, W, V, Mo, Sb, Ta, Ti, Nb, S, P and B. For example, a can be -0.05, -0.02, 0, 0.05, 0.1, 0.1, 0.2, 0.25 or 0.3, etc.; x can be 0.8, 0.85, 0.9, 0.95 or 1, etc.; y can be 0, 0.05, 0.1, 0.15 or 0.2, etc.; z can be 0, 0.05, 0.1, 0.15 or 0.2, etc.; m can be 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009 or 0.01, etc.; optionally, m>0, and more optionally, 0.002≤m≤0.01. The positive active material with the given range has higher energy density and working voltage, and relatively better cycle performance, which can further improve the cycle life of the battery.

[0053] In some embodiments of the present application, when m>0, M in the positive active material can include at least one of Sn, W, V, La, Mo, Sb, Ta, Ti, Nb, and the half-peak width of the diffraction peak corresponding to the 104 crystal face in the XRD pattern of the primary particles can be 0.245-0.270, for example, 0.245, 0.250, 0.255, 0.260, 0.265 or 0.270, etc. The half-peak width of the diffraction peak corresponding to the 104 crystal face in the XRD pattern of the primary particles can be characterized by an X-ray diffractometer, for example, a Smart Lab9 KW of Rigaku Corporation, Japan. Using the given kind of high-valence element as a doping element can refine the particle size of the primary particles of the positive active material or affect the arrangement effect of the primary particles, thereby affecting the agglomeration state of the secondary particles formed by the primary particles and the overall pore structure of the positive active material. By making the half-peak width of the 104 crystal face of the primary particles of the positive active material with the given kind of high-valence doping element satisfy the given range, even if the half-peak width of the 104 crystal face of the primary particles is in a relatively small value, relatively large primary particles can be obtained, and when the primary particles are stacked to form secondary particles, it is still beneficial to obtain a better pore structure.

[0054] In some embodiments of the present application, when m > 0, M can include at least one of S, P, and B, and the half-peak width of the diffraction peak corresponding to the 104 crystal face in the XRD pattern of the primary particles can be 0.250-0.275, for example, can be 0.250, 0.255, 0.260, 0.265, 0.270, or 0.275, and the like. The use of the given types of elements as doping elements can also have a pore-forming effect. The doping elements are mostly doped and enriched between the primary particles. After water washing, voids can be left between the primary particles. At this time, the primary particle 104 crystal face half-peak width corresponding to the given range of particle size is beneficial to obtaining a better pore structure when the secondary particles are formed by stacking.

[0055] In some embodiments of the present application, when m > 0, M can include at least one of Mg, Al, Sr, Ba, Y, Zr, Ca, Fe, and Zn, and the half-peak width of the diffraction peak corresponding to the 104 crystal face in the XRD pattern of the primary particles can be 0.255-0.280, for example, can be 0.255, 0.260, 0.265, 0.270, 0.275, or 0.280, and the like. When the given types of elements are used as doping elements, controlling the half-peak width of the diffraction peak corresponding to the 104 crystal face in the given range and making the primary particle 104 crystal face half-peak width be in a larger value can obtain primary particles with a relatively small average size, which is beneficial to reducing the risk of losing pore effect due to excessive fusion growth of the primary particles, and thus is also beneficial to obtaining a better pore structure.

[0056] In some embodiments of the present application, in the positive electrode active material, the secondary particles can include a matrix and a coating layer, the matrix can include Li 1+a Ni x Co y Mn z M m O2, and at least part of the surface of the matrix can be provided with a coating layer. The setting of the coating layer can regulate the pore structure of the positive electrode active material to a certain extent to achieve the purpose of reducing the open porosity, reducing the side reaction of the positive electrode active material particles and the electrolyte, and the like; in addition, the setting of the coating layer is also beneficial to improving the cycle stability of the positive electrode active material to a certain extent.

[0057] In some embodiments of the present application, the coating layer can include J elements, and the J elements can include at least one of Al, Zr, Ti, F, B, Cl, Br, I, S, W, Co, Sn, and Mo. The doping of the given types of elements in the coating layer can protect the positive electrode active material, reduce the side reaction of the positive electrode active material surface and the electrolyte, form a high-quality CEI film, inhibit the gas production phenomenon, and improve the storage life and electrochemical cycle performance of the positive electrode active material.

[0058] In some embodiments of the present application, the coating layer can comprise J elements, and the ratio of the total moles of Ni, Co, Mn and M in the matrix to the moles of J elements in the coating layer can be 1:(0-0.05), for example, can be 1 / 0.01, 1 / 0.02, 1 / 0.03, 1 / 0.04 or 1 / 0.05, etc. Meeting the given range not only helps to improve the cycle performance of the positive electrode active material, but also takes into account the pore structure of the positive electrode active material, reducing the risk of affecting the specific capacity, electrochemical activity and rate performance of the positive electrode active material due to the high content of the coating layer. Thus, it is further beneficial to make the positive electrode active material have the advantages of high electrochemical activity, high energy density, high particle strength and long cycle life, etc.

[0059] In some embodiments of the present application, the method for obtaining the positive electrode active material with the desired pore structure is not particularly limited, and those skilled in the art can flexibly choose according to actual needs, for example, one or more of the porosity, particle size, morphology and arrangement of the precursor of the primary particles can be adjusted to control the agglomeration effect when the primary particles are accumulated into secondary particles, and then the pore structure of the positive electrode active material is adjusted to obtain the positive electrode active material with the desired pore structure. On this basis, one or more of whether to set the coating layer, the selection of the coating layer material, the thickness of the coating layer, etc. can be further adjusted to control the pore structure of the positive electrode active material. In addition, the porosity of the primary particle precursor can be adjusted by co-precipitation and other methods.

[0060] In the second aspect of the present application, a method for preparing the above-mentioned positive electrode active material is provided, comprising: (1) co-precipitation reaction of aqueous solution of nickel source, cobalt source and manganese source under alkaline conditions to obtain precursor particles; (2) mixing the precursor particles with lithium source and M source and performing sintering treatment to obtain the positive electrode active material. In this method, the composition of nickel, cobalt and manganese, the porosity control of the precursor and the doping amount of M elements can be combined to adjust the temperature and time of sintering treatment, as well as the grain size and arrangement of the primary particles, and then the agglomeration effect between the primary particles in the secondary particles is adjusted, thereby it is beneficial to obtain the positive electrode active material with the ratio of open porosity to total porosity being 25%-85%, so that the material has high particle strength, high rate performance and good cycle stability against swelling and shrinkage during charging and discharging process. It should be noted that the features and effects described for the above-mentioned positive electrode active material also apply to the method for preparing the positive electrode active material, which will not be repeated here.

[0061] In some embodiments of the present application, in step (1), the co-precipitation reaction can be carried out under alkaline conditions with a pH value of 10-11.5. For example, during the co-precipitation reaction, the nickel source, the cobalt source and the manganese source can be dissolved in water and the pH value of the mixed solution is controlled to be 10-11.5, so that the crystals are nucleated and grown, until the median particle size D 50 9-20 μm. By controlling the pH value of the mixed solution, the co-precipitation reaction rate can be controlled, and certain porosity can be created in the precursor, so that the positive active material still retains certain porosity effect during the subsequent sintering and fusion process. Optionally, ammonia solution can also be added as a complexing agent during the co-precipitation reaction.

[0062] In some embodiments of the present application, in step (2), the sintering treatment can include: holding at 650-900 °C for 4-15 h, for example, the sintering temperature can be 650 °C, 700 °C, 750 °C, 800 °C, 850 °C or 900 °C, and the holding time can be 4 h, 6 h, 8 h, 10 h, 12 h or 15 h. In actual operation, the sintering temperature and time can be flexibly controlled according to the type of the doping element M, the composition of nickel, cobalt and manganese, etc. to obtain the desired primary particle size or 104 crystal face half-peak width, thereby facilitating the obtaining of a suitable positive active material porosity effect.

[0063] In some embodiments of the present application, in step (2), after the sintering treatment is completed, cooling, crushing, sieving and other operations can also be included.

[0064] In some embodiments of the present application, step (2) can also include: mixing the sintered product (i.e., a sintered material) with a coating material containing a J source and holding at 300-700 °C for 5-10 h, so that a coating layer containing the element J can be formed on the surface of the sintered material, and a positive active material with a substrate and a coating layer structure is obtained. The beneficial effects of forming the coating layer and the type of the element J and other characteristics and effects have been described in detail in the foregoing part, and will not be repeated here.

[0065] In a third aspect of the present application, a positive electrode tab is provided, which includes the positive active material described above or the positive active material prepared by the method described above. It should be noted that the features and effects described for the positive active material and the method of preparing the positive active material are also applicable to the positive electrode tab, and will not be repeated here. In general, the positive electrode tab has good cycle stability and a long cycle life.

[0066] Generally, the positive electrode sheet can include a positive electrode current collector and a positive electrode active material layer provided on at least one side of the positive electrode current collector, and the positive electrode active material layer can include the positive electrode active material described above or the positive electrode active material obtained by the preparation method described above. The positive electrode current collector can include, but is not limited to, a metal foil (such as an aluminum foil, etc.) or a composite current collector, etc. The positive electrode active material layer can further include a binder and a conductive agent, etc. The specific types and sources of the binder and the conductive agent are not particularly limited, and a person skilled in the art can flexibly select them according to actual needs. For example, the binder can include, but is not limited to, polyvinylidene fluoride, etc., and the conductive agent can include, but is not limited to, one or more of conductive carbon black, carbon nanotubes, graphene, etc.

[0067] In a fourth aspect of the present application, a battery is provided, which includes the positive electrode sheet described above. It should be noted that the features and effects described for the positive electrode sheet also apply to the battery, which will not be described here. Optionally, the battery can be a secondary battery.

[0068] Generally, in addition to the positive electrode sheet, the battery can also include a negative electrode sheet, an electrolyte, a separator, etc., wherein the specific structure or composition of the negative electrode sheet, the electrolyte, and the separator are not particularly limited, and a person skilled in the art can flexibly select according to actual needs. For example, the negative electrode sheet can include a negative electrode current collector and a negative electrode active material layer provided on at least one side of the negative electrode current collector, and the negative electrode active material layer can include a negative electrode active material, a binder, a conductive agent, etc. Among them, the negative electrode current collector can include but is not limited to a metal foil (such as a copper foil, etc.) or a composite current collector, etc., and the specific types and sources of the active material, the binder, and the conductive agent in the negative electrode sheet are not particularly limited, and a person skilled in the art can flexibly select according to actual needs. For example, the negative electrode active material can include but is not limited to one or more of hard carbon, soft carbon, silicon-based material, silicon-carbon material, etc., the binder can include but is not limited to butadiene styrene rubber, etc., and the conductive agent can include but is not limited to one or more of conductive carbon black, carbon nanotube, graphene, etc. In addition, whether to add a thickening agent and other conventional components in the negative electrode active material layer can also be selected. For another example, the separator can include but is not limited to a polyethylene (PE) film, a polypropylene (PP) film, a PP / PE / PP composite film, a composite ceramic separator, a rubber-coated separator, etc.; for yet another example, the electrolyte can include an organic solvent and an electrolyte salt. Taking a lithium battery as an example, the organic solvent can include one or more of dimethyl carbonate (DMC), ethylene carbonate (EC), methyl ethylene carbonate (EMC), etc. Ester solvents, and the electrolyte salt can include but is not limited to one or more of common lithium salts such as lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium bisoxalate borate (LiBOB), lithium difluorophosphate (LiO2F2), etc. Optionally, an additive can also be added to the electrolyte, and the additive can include but is not limited to common additives such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0069] In a fifth aspect of the present application, a power-using device is provided, which includes the above-mentioned battery. It should be noted that the features and effects described for the above-mentioned battery also apply to the power-using device, which will not be repeated here. In addition, it should be noted that the specific type of the power-using device is not particularly limited, and a person skilled in the art can flexibly select according to actual needs, which can include but is not limited to electronic devices, household appliances, vehicles, etc.

[0070] The present application will be described below with reference to specific examples, which should be noted that these examples are merely descriptive, and do not limit the present application in any way. The specific technology or conditions not mentioned in the examples are carried out according to the technology or conditions described in the literature in the art or according to the product instructions. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be obtained by purchase.

[0071] In the following examples, all raw materials are commercially available unless otherwise specified.

[0072] In the following examples and comparative examples, the relevant parameters are tested by the following methods:

[0073] (1) Morphology test: tested by S-4800 model scanning electron microscope of Japan Hitachi company.

[0074] (2) Total porosity P t Test: the cross section of the positive electrode active material is obtained by Hitachi IM4000 II ion grinder, the material cross section is imaged by S-4800 scanning electron microscope, and the image contrast analysis is obtained by LIBMAS intelligent image analysis system. Among them, the test value of each sample is the average value of the porosity measured by 6 particle balls. When taking the sample by scanning electron microscope, the sample with cross section diameter between D 50 -D 80 is selected.

[0075] (3) Average pore size of closed pores D C Test: the cross section area of each hole is obtained by LIBMAS intelligent image analysis system for contrast analysis of cross section electron microscope image, the hole shape in cross section electron microscope image is assumed to be circular, and the average cross section pore size is obtained. Among them, the test value of each sample is the average value of 6 particle balls.

[0076] (3) Material specific surface area test: according to the principle of N2 static adsorption, it is tested by Tristar 3020 model surface instrument of Micromeritics company.

[0077] Among them, N2 static adsorption is: in the test device, N2 is gradually added to the material to be tested which has been removed the physical adsorption component under vacuum state, the pressure change caused by N2 adsorption is calculated by constant volume method, and the N2 adsorption amount is obtained according to the gas equation. The N2 adsorption amount from 0 gas pressure to 0.3 atmospheric pressure at liquid nitrogen temperature is converted into unit gram weight specific surface area.

[0078] (4) Open pore volume Vo test: according to N2 adsorption and desorption isotherm test and analysis, it is tested by Tristar 3020 model surface instrument of Micromeritics company;

[0079] N2 adsorption-desorption isotherm test is as follows: using a conventional measuring device (Tristar 3020 or the like), N2 is gradually added to the material to be measured from which the physical adsorption component has been removed in advance under vacuum, the pressure change caused by N2 adsorption is calculated by constant volume method, and the N2 adsorption amount is obtained according to the gas equation. The N2 adsorption isotherm from 0 gas pressure to 0.995 atmospheric pressure at the temperature of liquid nitrogen is obtained. After reaching 0.995 atmospheric pressure, the N2 pressure is gradually reduced to 0 gas pressure, and the N2 desorption isotherm from 0.995 atmospheric pressure to 0 gas pressure is obtained, and the N2 adsorption-desorption isotherm is obtained. The open pore volume is obtained from the N2 adsorption amount at the relative pressure (p / p0) of 0.995 of the N2 adsorption isotherm.

[0080] (5) Open pore average pore diameter Do test: according to the BJH (Barrett-Joyner-Halenda) model, tested by the Tristar 3020 type surface instrument of Micromeritics company.

[0081] The BJH model and pore diameter test are as follows: the pore shape is assumed to be cylindrical, and the pore diameter and N2 relative pressure that causes capillary condensation satisfy the Kelvin relationship. The distribution of material pore diameter is characterized by testing the N2 adsorption amount of different partial pressures and corresponding pore levels, and the average pore diameter is obtained by multiplying the proportion coefficient of each pore level. The desorption isotherm of the present application focuses on obtaining the pore entrance pore diameter.

[0082] (6) Positive electrode active material skeleton volume Vt test: according to the gas displacement method, tested by the Accupy II 1345 true density instrument of Micromeritics.

[0083] The gas displacement method is as follows: using inert gas N2 as displacement medium, the sample is sealed in the sample bin filled with N2, the expansion bin is opened to make the gas diffuse, and the volume of the sample can be calculated by the pressure change before and after the gas diffusion after stabilization.

[0084] (7) Material XRD and refinement: tested by Smart Lab9 KW of Rigaku Corporation.

[0085] (8) Material particle size distribution test: tested by the Hydro 2000mu type laser particle size instrument of Marven company.

[0086] (9) Particle strength test: tested by the micro compression tester MCT-210 of Shimadzu Instrument Corporation.

[0087] (10) Electrochemical performance test:

[0088] In the following examples and comparative examples, the electrochemical performance of the multi-element positive electrode material is tested using a 2025 button cell.

[0089] The preparation process of the 2025 button cell is as follows:

[0090] Preparation of the electrode sheet: the multi-element positive electrode active material, acetylene black and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 95:3:2 with an appropriate amount of N-methyl pyrrolidone (NMP) to form a uniform slurry. The slurry is coated on an aluminum foil and dried at 120°C for 12h, and then punched and formed into a positive electrode sheet with a diameter of 12mm and a thickness of 120μm using a pressure of 100MPa. The loading amount of the multi-element positive electrode material is (15.5±0.5)mg / cm 2 .

[0091] Battery assembly: in an argon-filled glove box with water content and oxygen content less than 5ppm, the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte are assembled into a 2025 button cell, and then left to stand for 6h. The negative electrode sheet uses a lithium metal sheet with a diameter of 17mm and a thickness of 1mm; the separator uses a polyethylene porous membrane (Celgard2325) with a thickness of 25μm; and the electrolyte uses an equal amount of mixture of 1mol / L LiPF6, ethylene carbonate (EC) and diethyl carbonate (DEC).

[0092] 2025 button cell test:

[0093] In the following examples and comparative examples, the electrochemical performance of the 2025 button cell is tested using a Shenzhen Xinhui battery test system, and the 0.1C charge-discharge current density is 200mA / g.

[0094] The charge-discharge voltage range is controlled to be 3.0-4.3V, and the button cell is charged and discharged at 0.1C at room temperature to evaluate the electrochemical performance of the multi-element positive electrode material.

[0095] Cycle performance test: the charge-discharge voltage range is controlled to be 3.0-4.3V, and the button cell is charged and discharged at 0.1C at a constant temperature of 45°C for 2 cycles, and then at 1C for 80 cycles to evaluate the high-temperature capacity retention rate of the multi-element positive electrode material.

[0096] Rate performance test: control the charge and discharge voltage interval to be 3.0-4.3V, at room temperature, cycle the button cell at 0.1C for 2 times, then cycle at 0.2C, 0.33C, 0.5C and 1C for 1 time respectively, and evaluate the rate performance of the multi-element positive electrode material by the ratio of the initial discharge specific capacity at 0.1C to the discharge specific capacity at 1C. Among them, the initial discharge specific capacity at 0.1C is the discharge specific capacity of the 1st week cycle of the button cell, and the discharge specific capacity at 1C is the discharge specific capacity of the 6th week cycle of the button cell.

[0097] Example 1

[0098] (1) Dissolve nickel sulfate, cobalt sulfate and manganese sulfate in pure water according to the molar ratio of nickel element, cobalt element and manganese element of 83.3:10:6 to obtain a mixed salt solution with a concentration of 2 mol / L. Prepare a sodium hydroxide solution with a concentration of 8 mol / L as a precipitant solution, and prepare an ammonia solution with a concentration of 6 mol / L as a complexing agent solution. Add the mixed salt solution, sodium hydroxide solution and ammonia solution from the liquid inlet pipeline into the reaction kettle respectively, protect with N2, keep the stirring speed at 600 rpm, control the liquid inlet amount of the mixed salt solution at 400 mL / h, adjust the flow rates of the sodium hydroxide solution and the ammonia solution to keep the pH of the reaction system stable at 10.9±0.05, and control the temperature of the reaction system at 60°C. After the average particle size Dv50 of the particles in the reaction system grows to 14 μm, age for 1 h, separate, wash and dry to obtain a positive electrode active material precursor;

[0099] (2) Mix the above-mentioned precursor, lithium hydroxide, aluminum oxide and niobium pentoxide in a molar ratio of the sum of nickel, cobalt and manganese elements in the precursor, lithium element, aluminum element and niobium element of 0.993:1.03:0.004:0.003, and sinter in an oxygen furnace by first heating and then constant temperature sintering. The oxygen concentration in the oxygen furnace is greater than 95% by volume, the heating rate is 5°C / min, the sintering temperature is 810°C, and the sintering time is 10 h. After natural cooling to room temperature, crush, sieve and remove iron to obtain a positive electrode active material one sintered material;

[0100] (3) Mix the positive electrode active material one sintered material with boric acid in a high-speed mixer at a molar ratio of the sum of Ni, Co, Mn, Al and Nb in the positive electrode active material one sintered material to boron element of 1:0.001, and sinter at 350°C in an oxygen furnace. The oxygen concentration in the oxygen furnace is greater than 90% by volume, and the sintering time is 8 h. After cooling, sieving and removing iron, a positive electrode active material Li 1.03 Ni 0.833 Co 0.100 Mn 0.060 Al 0.004 Nb 0.003 O2@B, in the chemical formula of the positive electrode active material, the front @ is the matrix component, and the rear @ is the main element in the coating layer.

[0101] Examples 2-10 and Comparative Examples 1-4

[0102] The differences between Examples 2-14 and Comparative Example 1-6 and Example 1 are shown in Table 1 and Table 2. Among them:

[0103] In Example 2, the M source is zirconium dioxide and tungsten oxide, and the coating agent is boric acid.

[0104] In Example 3, the M source is magnesium oxide and tin dioxide, and the coating agent is tungsten trioxide.

[0105] In Example 4, the M source is strontium oxide and antimony trioxide, and the coating agent is tungsten trioxide.

[0106] In Example 5, the M source is aluminum trioxide and lithium sulfate, and the coating agent is boric acid.

[0107] In Example 6, the M source is aluminum trioxide and strontium hydroxide, and the coating agent is boric acid.

[0108] In Example 7, the M source is aluminum trioxide and niobium pentoxide.

[0109] In Example 8, the M source is aluminum trioxide and boric acid, and the coating agent is cobalt hydroxide.

[0110] In Example 9, the M source is titanium dioxide and niobium pentoxide, and the coating agent is tungsten trioxide.

[0111] In Example 10, the M source is aluminum trioxide and lithium sulfate, and the coating agent is boric acid.

[0112] In Comparative Example 1, the M source is aluminum trioxide and niobium pentoxide, and the coating agent is boric acid.

[0113] In Comparative Example 2, the M source is aluminum trioxide and niobium pentoxide, and the coating agent is boric acid.

[0114] In Comparative Example 3, the M source is aluminum trioxide and niobium pentoxide, and the coating agent is boric acid.

[0115] In Comparative Example 4, the M source is aluminum trioxide and niobium pentoxide, and the coating agent is boric acid.

[0116] The test results of Examples 1-10 and Comparative Examples 1-4 are shown in Table 2.

[0117] Results and Conclusions:

[0118] It can be seen from Examples 1-10 and Comparative Examples 1-4, Tables 1-2 and Figures 1-2 (Figure 1 shows the pore structure of the precursor prepared in Example 1, and Figure 2 shows the distribution of closed pores in the cross section of the positive active material prepared in Example 1) that the preparation method of the above examples can obtain a positive active material with open porosity accounting for 25%-85% of the total porosity; and when the positive active material is used in a battery, the positive active material with open porosity accounting for 25%-85% of the total porosity has a relatively better improvement effect on the rate performance and cycle performance of the battery, and the energy density, initial efficiency, rate performance and cycle performance of the battery are all good, and the comprehensive performance is better. It has been tested that the element composition of the positive active material prepared in Examples 1-10 all meets the general formula Li 1+a Ni x Co y Mn z M m O2, -0.05≤a≤0.3, 0.8≤x≤1, 0≤y≤0.2, 0≤z≤0.2, 0≤m≤0.01. In addition, it can be seen from Example 1 and Example 7 that the formation of the coating layer on the positive active material can further improve the electrochemical performance of the battery; compared with Example 1, the positive active material prepared in Comparative Example 1 and Comparative Example 3 has a relatively low ratio of open porosity to total porosity, and the positive active material prepared in Comparative Example 2 and Comparative Example 4 has a relatively high ratio of open porosity to total porosity, and the reason may be that in Comparative Example 1, the calcination temperature is relatively high, and the particle fusion in the sintering process reduces the volume of open pores and closed pores, affecting the ratio of open porosity to total porosity; in Comparative Example 2, the calcination time is relatively long, and the particle fusion in the calcination process significantly reduces the volume of closed pores and total pores; in Comparative Example 3, the amount of coating agent is relatively large, which reduces the open porosity of the material; in Comparative Example 4, the pH value controlled in the coprecipitation process is relatively large, which results in relatively low closed porosity and total porosity of the precursor.

[0119] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples without contradiction.

[0120] Although the embodiments of the present application have been shown and described above, it is understood that the above embodiments are exemplary, and are not to be interpreted as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A positive electrode active material, wherein, Comprising: secondary particles formed by the accumulation of primary particles, the secondary particles including open pores and closed pores, the open porosity P of the positive electrode active material o 25% - 85% of the total porosity P of the positive electrode active material t .

2. The positive electrode active material according to claim 1, wherein At least one of the following conditions is met: The open porosity P of the positive electrode active material is 0.5-3%. o 0.5% - 3% The average pore size D of the positive electrode active material o The range is 10nm-50nm; The open pore volume Vo of the positive electrode active material is 0.002 cm3 / g 3 / g - 0.01 cm3 / g 3 / g; The skeleton volume Vt of the positive electrode active material is 0.2 cm 3 / g - 0.25 cm 3 / g.

3. The positive electrode active material according to claim 1 or 2, wherein The total porosity P of the positive electrode active material t For 1%-10%; and / or, In the secondary particles, the average pore diameter D of the closed pores is 40 nm to 200 nm. C 40 nm to 200 nm.

4. The positive electrode active material according to any one of claims 1 to 3, wherein The specific surface area of the positive electrode active material is S 0 , the specific surface area of the positive electrode active material after being fractured by a pressure of 3.5 tons is S 3.5 , the specific surface area change rate of the positive electrode active material is 0-50%, wherein, ΔSSA=(S 3.5 -S 0 ) / S 0 ×100%; and / or, The volume distribution of the positive electrode active material accumulates to 10% at a particle size of D 10 0 The volume distribution of the positive electrode active material accumulates to 10% at a particle size of D 10 3.5 The particle size variation rate ΔD 10 of the positive electrode active material is 0-20%, wherein ΔD 10 = (D 10 0 -D 10 3.5 ) / D 10 0 ×100%.

5. The positive electrode active material according to any one of claims 1 to 4, wherein The positive active material includes Li 1+a Ni x Co y Mn z M m O2, -0.05≤a≤0.3, 0.8≤x≤1, 0≤y≤0.2, 0≤z≤0.2, 0≤m≤0.01, M includes at least one of Mg, La, Al, Sr, Ba, Y, Zr, Ca, Fe, Zn, Sn, W, V, Mo, Sb, Ta, Ti, Nb, S, P, and B.

6. The positive electrode active material according to claim 5, wherein M comprises at least one of Sn, W, V, La, Mo, Sb, Ta, Ti, Nb, and the half-peak width of the diffraction peak corresponding to the 104 crystal face in the XRD pattern of the primary particles is 0.245-0.270; or, M comprises at least one of S, P, B, and the half-peak width of the diffraction peak corresponding to the 104 crystal face in the XRD pattern of the primary particles is 0.250-0.275; or, M comprises at least one of Mg, Al, Sr, Ba, Y, Zr, Ca, Fe, Zn, and the half-peak width of the diffraction peak corresponding to the 104 crystal face in the XRD pattern of the primary particles is 0.255-0.

280.

7. The positive electrode active material according to claim 5 or 6, wherein The secondary particles include a base and a coating layer, the base including the Li 1+a Ni x Co y Mn z M m O2, at least a part of a surface of the base being provided with the coating layer.

8. The positive electrode active material according to claim 7, wherein The coating layer comprises a J element, and the J element comprises at least one of Al, Zr, Ti, F, B, Cl, Br, I, S, W, Co, Sn, Mo; and / or, The ratio of the total number of moles of Ni, Co, Mn and M in the substrate to the number of moles of J elements in the coating layer is 1:(0-0.05).

9. A method for producing the positive electrode active material according to any one of claims 1 to 8, wherein, Comprising: (1) performing a co-precipitation reaction on an aqueous solution of a nickel source, a cobalt source and a manganese source under alkaline conditions to obtain precursor particles; (2) mixing the precursor particles with a lithium source and an M source and performing a sintering treatment to obtain a positive electrode active material.

10. The method of claim 9, wherein, At least one of the following conditions is met: In step (1), the co-precipitation reaction is performed under alkaline conditions with a pH value of 10-11.5; In step (2), the sintering treatment comprises: holding at 650-900°C for 4-15h; Step (2) further comprises: mixing the sintered product with a coating material containing a J source and holding at 300-700°C for 5-10h.

11. A positive electrode sheet, wherein, The positive electrode active material of any one of claims 1-8, or the positive electrode active material prepared by the method of any one of claims 9-10.

12. A battery, wherein, The positive electrode sheet of claim 11.

13. An electrical device, comprising: The battery of claim 12. The battery of claim 12.

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