Positive electrode active material, method for manufacturing the same, positive electrode sheet, battery, and electric device

Abstract

The application discloses a positive electrode active material and a preparation method thereof, a positive electrode sheet, a battery and a power utilization device. The positive electrode active material comprises secondary particles, the secondary particles are formed by accumulation of primary particles, the secondary particles comprise open pores and closed pores, and the open porosity P o of the positive electrode active material accounts for 25% to 85% of the total porosity P t of the positive electrode active material. By controlling the proportion of the open porosity of the positive electrode active material in the total porosity to be 25% to 85%, the material can have high particle strength, high rate performance and good cycle stability against expansion and shrinkage in the charging and discharging process.

Description

Technical Field

[0001] This invention belongs to the field of batteries, specifically relating to positive electrode active materials and their preparation methods, positive electrode sheets, batteries, and electrical devices. Background Technology

[0002] Lithium-ion batteries are widely used in various electronic products and transportation vehicles, such as electric vehicles, due to their advantages of light weight, low pollution, high energy density, and high single-cell voltage. To meet consumers' growing demands for longer driving range and lifespan in electronic products and electric vehicles, the research and development and application of lithium-ion batteries with high energy density and long cycle life are continuously evolving. As the component with the greatest impact on the performance of lithium-ion batteries, the current main development direction for cathode active materials is to increase the Ni content in ternary cathode materials to improve energy density. However, the resulting intensification of cycle performance and safety issues cannot be ignored. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one object of this invention is to provide a positive electrode active material and its preparation method, a positive electrode sheet, a battery, and an electrical device, so that the positive electrode active material possesses high electrochemical reactivity, lithium-ion migration capability, energy density, and particle strength, thereby simultaneously exhibiting excellent properties such as high energy density, good rate performance, and long cycle life.

[0004] This invention is primarily based on the following problems and findings:

[0005] Polycrystalline or near-monocrystalline ternary cathode materials are typically formed by the agglomeration of multiple primary particles into secondary particles, creating numerous pores on the material's surface or within. Currently, research is underway to design the structure and arrangement of cathode active material particles to intrinsically control the material's cycle life and safety performance. For example, there are studies limiting the total pore volume to 0.008 cm³ on surfaces with a diameter below 200 nm. 3 / g-0.012cm 3Ternary cathode materials with a porosity of / g, where the proportion of pores smaller than 15nm to the total pore volume does not exceed 50%; there are also cathode materials with a defined requirement that the central part of the secondary particle cross-section has high porosity and the surface part has low porosity, while the ratio of the minor axis to the major axis of the secondary particles in the cross-section and the ratio of the total pore area to the total particle area in the cross-section meet preset requirements; in addition, there are cathode materials with a defined requirement that the ratio of the cross-sectional area of ​​the secondary particles to the area of ​​the pore portion meets preset requirements, and so on. In fact, controlling the appropriate pore volume or porosity is crucial for the design of cathode active materials and electrode sheets, which not only affects the electrochemical performance of the cathode active material, but also the particle strength, compaction density, and cycle life of the material. In this invention, it is hoped that by controlling the relationship and / or structure between open and closed pores in the positive electrode active material (such as by controlling the agglomeration effect between primary particles), the balance between particle strength, energy density, and cycle stability of the material can be solved to a certain extent. This will enable the material to have high electrochemical activity and high rate performance, avoid excessive side reactions between the material surface and the electrolyte, and ensure particle strength and compaction density, ultimately obtaining a positive electrode active material with high energy density, high particle strength, and long cycle life.

[0006] In view of this, in a first aspect of the present invention, a positive electrode active material is provided, comprising: secondary particles, said secondary particles being formed by the accumulation of primary particles, said secondary particles including open pores and closed pores, wherein the open pore porosity P of said positive electrode active material is... o The percentage of the total porosity P of the positive electrode active material t 25%-85%.

[0007] For agglomerated positive electrode active materials, such as ternary positive electrode 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 of the material 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, a suitable 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 invention, by controlling the ratio of open pores to total porosity of the positive electrode active material to 25%-85%, the material can have higher particle strength, higher rate performance, and better cycle stability with resistance to expansion and contraction during charging and discharging.

[0008] In addition, the positive electrode active material according to the above embodiments of the present invention may also have the following additional technical features:

[0009] In some embodiments of the present invention, the open porosity P of the positive electrode active material o It ranges from 0.5% to 3%.

[0010] In some embodiments of the present invention, the average pore size D of the positive electrode active material is... o The range is 10nm-50nm.

[0011] In some embodiments of the present invention, the pore volume Vo of the positive electrode active material is 0.002 cm³. 3 / g-0.01cm 3 / g.

[0012] In some embodiments of the present invention, the framework volume Vt of the positive electrode active material is 0.2 cm³. 3 / g-0.25cm 3 / g.

[0013] In some embodiments of the present invention, the total porosity P of the positive electrode active material t It ranges from 1% to 10%.

[0014] In some embodiments of the present invention, the average pore size D of the closed pores in the secondary particles is... C The range is 40nm-200nm.

[0015] In some embodiments of the present invention, 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 subjected to 3.5 tons of pressure fracturing is S. 3.5 The specific surface area change rate ΔSSA of the positive electrode active material is 0-50%, where ΔSSA=(S 3.5 -S 0 ) / S 0 ×100%.

[0016] In some embodiments of the present invention, 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 is 0-20%, where ΔD 10 =(D 10 0 -D 10 3.5) / D 10 0 ×100%.

[0017] In some embodiments of the present invention, the positive electrode 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.

[0018] In some embodiments of the present invention, M includes at least one of Sn, W, V, La, Mo, Sb, Ta, Ti, and Nb, and the full width at half maximum (FWHM) of the diffraction peak corresponding to the 104 crystal plane in the XRD pattern of the primary particle is 0.245-0.270.

[0019] In some embodiments of the present invention, M includes at least one of S, P, and B, and the full width at half maximum (FWHM) of the diffraction peak corresponding to the 104 crystal plane in the XRD pattern of the primary particle is 0.250-0.275.

[0020] In some embodiments of the present invention, M includes at least one of Mg, Al, Sr, Ba, Y, Zr, Ca, Fe, and Zn, and the full width at half maximum (FWHM) of the diffraction peak corresponding to the 104 crystal plane in the XRD pattern of the primary particle is 0.255-0.280.

[0021] In some embodiments of the present invention, the secondary particles include a matrix and a coating layer, wherein the matrix includes the Li 1+a Ni x Co y Mn z M m O2, at least a portion of the surface of the substrate is provided with the coating layer.

[0022] In some embodiments of the present invention, the coating layer includes an element J, which includes at least one of Al, Zr, Ti, F, B, Cl, Br, I, S, W, Co, Sn, and Mo.

[0023] In some embodiments of the present invention, the coating layer includes element J, and the ratio of the total number of moles of Ni, Co, Mn and M in the matrix to the number of moles of element J in the coating layer is 1:(0-0.05).

[0024] In a second aspect of the present invention, a method for preparing the above-mentioned positive electrode active material is provided, comprising:

[0025] (1) A co-precipitation reaction was carried out on aqueous solutions of nickel, cobalt and manganese sources under alkaline conditions to obtain precursor particles;

[0026] (2) The precursor particles are mixed with lithium source and M source and sintered to obtain positive electrode active material.

[0027] According to the method for preparing positive electrode active materials of the second aspect of the present invention, the sintering temperature and time, as well as the grain size and arrangement of the primary particles, can be controlled by combining the composition of nickel, cobalt, and manganese, the porosity control of the precursor, and the doping amount of element M, thereby controlling the agglomeration effect between the primary particles in the secondary particles. This is beneficial for obtaining positive electrode active materials with an open porosity ratio of 25%-85% of the total porosity, resulting in materials with high particle strength, high rate performance, and good cycle stability during charge and discharge processes to resist expansion and contraction.

[0028] In some embodiments of the present invention, in step (1), the coprecipitation reaction is carried out under alkaline conditions with a pH of 10-11.5.

[0029] In some embodiments of the present invention, step (2) includes sintering treatment including holding at 650℃-900℃ for 4h-15h.

[0030] In some embodiments of the present invention, step (2) further includes: mixing the sintered product with a coating material containing J source and holding it at 300℃-700℃ for 5h to 10h.

[0031] In a third aspect of the invention, a positive electrode sheet is provided, comprising the above-described positive electrode active material, or a positive electrode active material prepared by the above-described method. The features and effects described for the above-described positive electrode active material and the above-described method for preparing the positive electrode active material also apply to this positive electrode sheet, and will not be repeated here. In general, this positive electrode sheet exhibits good cycle stability and a long cycle life.

[0032] In a fourth aspect of the invention, a battery is provided, comprising the aforementioned positive electrode.

[0033] In a fifth aspect of the invention, an electrical device is provided, comprising the battery described above. Attached Figure Description

[0034] Figure 1 This is a cross-sectional view of the precursor obtained according to Embodiment 1 of the present invention.

[0035] Figure 2 The distribution and pore size of closed pores in the cross-section of the positive electrode active material prepared according to Example 1 of the present invention are described. Detailed Implementation

[0036] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0037] In a first aspect of the invention, a positive electrode active material is provided, comprising: secondary particles formed by the accumulation of primary particles, the secondary particles including open pores and closed pores (see reference). Figure 1 (Understanding), the open porosity P of the positive electrode active material o P, the total porosity of the positive electrode active material t 25%-85%.

[0038] For example, 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 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or 85%, etc. Among these, the open porosity P... o V is the pore volume V of the positive electrode active material that can be filled with nitrogen gas. o The ratio of the positive electrode active material's volume to its total volume can be obtained by testing and analyzing the N2 adsorption-desorption isotherm of the positive electrode active material, such as using a surface analyzer like the Micromeritics Tristar 3020. (Reference) Figure 2 Understand, total porosity P t The total pore area S of the positive electrode active material under an electron microscope can be represented by the cross-section of the material. t With the total cross-sectional area S of the material m The ratio raised to the power of 3 / 2, i.e. S t / S m The 3 / 2 power, where the total porosity P t The porosity can be obtained by averaging the total porosity of multiple secondary particles in the test sample. Specific procedures may include: ion-cutting the positive electrode active material sample using an ion mill (such as a Hitachi IM4000Ⅱ ion mill) to obtain cross-sections of multiple secondary particles; sampling the material cross-sections using a scanning electron microscope; and then performing image contrast analysis using the LIBMAS intelligent microscopic image analysis system. The number of secondary particles selected for testing in the sample should be ≥6, for example, ≥8, ≥10, ≥15, ≥20, ≥30, ≥40, or ≥50, etc. Those skilled in the art can flexibly choose according to actual needs. Additionally, when taking sample images using a scanning electron microscope, the cross-section diameter can be selected within the material particle size D. 50 -D 80Samples were taken between these points to ensure that the photographed samples were at or near the center of the secondary particle spheres, thereby improving the accuracy of the total porosity test. Among these, D... 50 The 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).

[0039] 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 invention, 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 during charge and discharge processes with resistance to expansion and contraction.

[0040] The following is for reference. Figures 1-2 The positive electrode active material of the above embodiments of the present invention will be described in detail.

[0041] In some specific embodiments of the present invention, 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 according to actual needs. For example, the agglomeration 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.

[0042] In some specific embodiments of the present invention, the open porosity P of the positive electrode active material is... o It can account for P of the total porosity of the positive electrode active material tThe 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.

[0043] In some specific embodiments of the present invention, the open porosity P of the positive electrode active material is... o The porosity can range from 0.5% to 3%, for example, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, or 3%, etc. The porosity of the positive electrode active material is related to the surface activity of the material and the electrolyte wetting area. A larger porosity results in more interfacial reaction channels for lithium ion insertion and extraction, higher reactivity, and better charge / discharge capacity, initial efficiency, and rate performance. Appropriately reducing the porosity of the positive electrode active material helps reduce side reactions between the surface of the positive electrode active material and the electrolyte. In this invention, the porosity P of the positive electrode active material... o Meeting the given range is beneficial for the positive electrode active material to possess high electrochemical reactivity and rate performance. It also reduces the risk that excessive open-pore porosity can lead to excessive side reactions between the material surface and the electrolyte, resulting in a decline in the material's storage, gas generation, and cycling performance. This, in turn, allows the positive electrode active material to achieve both high capacity and long service life. Furthermore, the open-pore porosity P of the positive electrode active material... o It can be 1.0%-2.5%.

[0044] In some specific embodiments of the present invention, the average pore size D of the positive electrode active material is... oThe pore size can range from 10nm to 50nm, for example, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, or 50nm, etc. The average pore size of the positive electrode active material can be measured using a surface analyzer based on the BJH (Barrett Joyner Halenda) model. For example, it can be measured using a Tristar 3020 surface analyzer from Micromeritics. The BJH model and pore size test are as follows: the pore shape is assumed to be cylindrical, and the Kelvin relationship between the pore size that produces capillary condensation and the relative pressure of N2 is established. The pore size distribution of the material is characterized by testing the N2 adsorption amount of different partial pressures and corresponding pore sizes. The average pore size is obtained by multiplying the pore size of each size by a proportion factor. The pore size distribution obtained from the adsorption isotherm is largely derived from the internal diameter of the pore; the pore size distribution obtained from the desorption isotherm is largely derived from the diameter of the pore inlet. In this invention, the pore inlet diameter can be obtained using the desorption isotherm. In this invention, the pore size of the positive electrode active material meets the given range, which is beneficial for the relatively uniform distribution of pores on the surface of the secondary particles, and further improves the uniformity of lithium-ion diffusion and reaction rate. Furthermore, the average pore size D of the positive electrode active material... o It can be 15nm-45nm.

[0045] In some specific embodiments of the present invention, the pore volume Vo of the positive electrode active material can be 0.002 cm³. 3 / g-0.01cm 3 / g, for example, can be 0.003cm 3 / g, 0.004cm 3 / g, 0.005cm 3 / g, 0.006cm 3 / g, 0.007cm 3 / g, 0.008cm 3 / g, 0.009cm 3 / g or 0.01cm 3 / g, etc. The pore volume of the positive electrode active material can be measured and analyzed using a surface analyzer based on the N2 adsorption-desorption isotherm. For example, it can be measured using a Micromeritics Tristar 3020 surface analyzer. Specifically, the N2 adsorption-desorption isotherm test can include: using a conventional measuring device (Tristar 3020, etc.), gradually adding N2 to the sample of the test material (after removing physically adsorbed components) under vacuum, 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 N2 adsorption isotherm from 0 atm to 0.995 atm at liquid nitrogen temperature. After reaching 0.995 atm, the N2 pressure is gradually reduced to 0 atm to obtain the N2 desorption isotherm from 0.995 atm to 0 atm, and the N2 adsorption-desorption isotherms are then obtained. The N2 adsorption-desorption isotherm analysis is performed by calculating the pore volume from the N2 adsorption amount when the relative pressure (p / p0) of the N2 adsorption isotherm is 0.995. The pores of the positive electrode active material are mostly distributed on the surface of the secondary particles. In this invention, the pore volume of the positive electrode active material meets the given range. This provides more lithium-ion reaction channels and reduces the risk of excessive electrolyte erosion into the material's interior, ensuring that the electrolyte forms a suitable CEI layer only on the material surface and at the surface pores. Therefore, the positive electrode active material can possess both high initial charge-discharge efficiency and good storage and cycle performance. Furthermore, the pore volume Vo of the positive electrode active material can be 0.002 cm³. 3 / g-0.008cm 3 / g.

[0046] In some specific embodiments of the present invention, the framework volume Vt of the positive electrode active material can be 0.2 cm³. 3 / g-0.25cm 3 / g, for example, can be 0.2cm 3 / g, 0.21cm 3 / g, 0.22cm 3 / g, 0.23cm 3 / g, 0.24cm 3 / g or 0.25cm 3 / g, etc. The framework volume of the positive electrode active material can be measured using the gas displacement method combined with a true density analyzer, such as the Micromeritics Accupy II 1345 true density analyzer. Specifically, the gas displacement method can include: using inert gas N2 as the displacement medium, sealing the sample in an N2-filled sample chamber, opening the expansion chamber to allow gas diffusion, and calculating the sample volume by measuring the pressure change before and after stabilization. It is understood that because N2 can rapidly fill pores with diameters down to the angstrom level, the measured volume is only the framework volume of the material. In this invention, the framework volume of the positive electrode active material meets the given range, which is beneficial for balancing the particle size and intrinsic density of the material, resulting in a high charge / discharge specific capacity. Furthermore, the framework volume Vt of the positive electrode active material can be 0.2 cm³. 3 / g-0.24cm 3 / g.

[0047] In some specific embodiments of the present invention, the total porosity P of the positive electrode active material t It can range from 1% to 10%, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, etc. The total porosity P of the positive electrode active material... t This includes both open-pore porosity and closed-pore porosity, with closed-pore porosity typically being greater than open-pore porosity. Ensuring the total porosity of the positive electrode active material meets the given range facilitates further expansion and contraction during charge and discharge, improving the cycle stability and overall cycle performance of the material. Furthermore, the total porosity P of the positive electrode active material... t It can range from 1.5% to 8.5%.

[0048] In some specific embodiments of the present invention, the average pore size D of the closed pores in the secondary particles is... C It can range from 40nm to 200nm, for example, 40nm, 50nm, 60nm, 80nm, 100nm, 120nm, 150nm, 180nm, or 200nm, etc. (Reference) Figure 2To determine the average pore size of closed pores in secondary particles, the LIBMAS intelligent image analysis system can be used to perform contrast analysis on the cross-sectional electron microscope (TEM) images of the secondary particles to obtain the cross-sectional area of ​​each pore. Assuming the pore shape in the TEM image is circular, the average cross-sectional pore size can be obtained. This can be achieved either by ensuring the average pore size of closed pores in a single secondary particle meets the given range, or by ensuring the average pore size of closed pores in the secondary particles as a whole in the positive electrode active material meets the given range. In this case, when testing the positive electrode active material sample, the method described above for testing the total porosity of the positive electrode active material can be referenced. Multiple secondary particles can be sampled from the test sample, and the average pore size of closed pores for each of the multiple secondary particles can be obtained, and then the average value can be calculated. Ensuring the average closed-pore diameter of the secondary particles meets the given range not only allows vacancies in the material to exist as small pores, which can be relatively uniformly distributed within the particles, thus improving the structural stability and particle strength of the positive electrode active material, but also allows the small gaps between primary particles to provide greater expansion and contraction space for charge-discharge cycles, improving the cycle performance of the positive electrode active material. Simultaneously, it avoids excessive loss of good electrical and mass transfer properties between materials, which is beneficial for the positive electrode active material to achieve good rate performance. Furthermore, in the secondary particles, the average closed-pore diameter D... C It can be 60nm-180nm.

[0049] In some specific embodiments of the present invention, 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 subjected to 3.5 tons of pressure fracturing is S. 3.5 The specific surface area change rate ΔSSA of the positive electrode active material can be 0-50%, where 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.

[0050] In some specific embodiments of the present invention, 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.

[0051] In some specific embodiments of the present invention, 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 may 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, the value of a can be -0.05, -0.02, 0, 0.05, 0.1, 0.1, 0.2, 0.25, or 0.3, etc.; the value of x can be 0.8, 0.85, 0.9, 0.95, or 1, etc.; the value of y can be 0, 0.05, 0.1, 0.15, or 0.2, etc.; the value of z can be 0, 0.05, 0.1, 0.15, or 0.2, etc.; the value of 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 even more optionally, 0.002 ≤ m ≤ 0.01. The given range of positive electrode active materials have high energy density and operating voltage, and relatively good cycle performance, which can further improve the cycle life of the battery.

[0052] In some specific embodiments of the present invention, when m > 0, M in the positive electrode active material may include at least one of Sn, W, V, La, Mo, Sb, Ta, Ti, and Nb. The full width at half maximum (FWHM) of the diffraction peak corresponding to the 104 crystal plane in the XRD pattern of the primary particles may be 0.245-0.270, for example, 0.245, 0.250, 0.255, 0.260, 0.265, or 0.270, etc. The FWHM of the diffraction peak corresponding to the 104 crystal plane in the XRD pattern of the primary particles can be obtained by characterization using an X-ray diffractometer, such as the Smart Lab9 KW from Rigaku Corporation, Japan. By using high-valence elements of the given type as doping elements, the particle size of the primary particles of the cathode active material can be refined or the arrangement of the primary particles can be affected, thereby affecting the aggregation state when the primary particles form secondary particles and the overall pore structure of the cathode active material. By ensuring that the half-width at half-maximum (WHM) of the 104 crystal plane of the primary particles of the cathode active material with the given high-valence doping elements meets the given range, even if the WHM of the 104 crystal plane of the primary particles is at a small value, primary particles with a relatively large average size can be obtained. Therefore, when the primary particles are stacked to form secondary particles, it is still beneficial to obtain a better pore structure.

[0053] In some specific embodiments of the present invention, when m > 0, M may include at least one of S, P, and B. The full width at half maximum (FWHM) of the diffraction peak corresponding to the 104 crystal plane in the XRD pattern of the primary particles may be 0.250-0.275, for example, 0.250, 0.255, 0.260, 0.265, 0.270, or 0.275, etc. Using the given type of element as a dopant element can also have the effect of creating pores. The dopant element is mostly enriched between the primary particles. After washing with water, gaps can be left between the primary particles. At this time, the FWHM of the 104 crystal plane of the primary particles meets the particle size corresponding to the given range. When the particles are stacked to form secondary particles, it is also beneficial to obtain a better pore structure.

[0054] In some specific embodiments of the present invention, when m > 0, M may include at least one of Mg, Al, Sr, Ba, Y, Zr, Ca, Fe, and Zn. The full width at half maximum (FWHM) of the diffraction peak corresponding to the 104 crystal plane in the XRD pattern of the primary particles may be 0.255-0.280, for example, 0.255, 0.260, 0.265, 0.270, 0.275, or 0.280, etc. When using the given type of element as the dopant element, controlling the FWHM of the diffraction peak corresponding to the 104 crystal plane within the given range, so that the FWHM of the 104 crystal plane of the primary particles is at a larger value, can obtain primary particles with a relatively small average size. This helps to reduce the risk of loss of porosity due to excessive fusion and excessively dense growth of primary particles, thereby also helping to obtain a better pore structure.

[0055] In some specific embodiments of the present invention, the secondary particles in the positive electrode active material may include a matrix and a coating layer, and the matrix may include Li 1+a Ni x Co y Mn z M m O2, at least part of the surface of the substrate may be coated. The coating can, to a certain extent, regulate the pore structure of the positive electrode active material, thereby reducing the open porosity and minimizing side reactions between the positive electrode active material particles and the electrolyte; in addition, the coating can also, to some extent, improve the cycle stability of the positive electrode active material.

[0056] In some specific embodiments of the present invention, the coating layer may include element J, which may include at least one of Al, Zr, Ti, F, B, Cl, Br, I, S, W, Co, Sn, and Mo. Doping the coating layer with the given elements can protect the positive electrode active material, reduce side reactions between the surface of the positive electrode active material and the electrolyte, form a high-quality CEI film, suppress gas generation, and improve the storage life and electrochemical cycle performance of the positive electrode active material.

[0057] In some specific embodiments of the present invention, the coating layer may include element J. The ratio of the total molar number of Ni, Co, Mn, and M in the matrix to the molar number of element J in the coating layer may be 1:(0-0.05), for example, 1 / 0.01, 1 / 0.02, 1 / 0.03, 1 / 0.04, or 1 / 0.05, etc. Satisfying 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 that a high coating layer content will affect the specific capacity, electrochemical activity, and rate performance of the positive electrode active material. Therefore, it is further beneficial to enable the positive electrode active material to possess the advantages of high electrochemical activity, high energy density, high particle strength, and long cycle life.

[0058] In some specific embodiments of the present invention, 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 methods 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 precursor porosity, 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. Additionally, the porosity of the primary particle precursor can be controlled through methods such as precursor co-precipitation.

[0059] In a second aspect of the present invention, a method for preparing the above-mentioned positive electrode active material is proposed, comprising: (1) co-precipitating 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 a M source and performing sintering treatment to obtain the positive electrode active material. In this method, the temperature and time of sintering treatment, as well as the grain size and arrangement of the primary particles, can be controlled by combining the composition of nickel, cobalt, and manganese, the porosity control of the precursor, and the doping amount of the M element, thereby controlling the agglomeration effect between the primary particles in the secondary particles. This is beneficial to obtaining a positive electrode active material with an open porosity ratio of 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 charge and discharge. It should be noted that the characteristics and effects described for the above-mentioned positive electrode active material are also applicable to this method for preparing the positive electrode active material, and will not be repeated here.

[0060] In some specific embodiments of the present invention, in step (1), the co-precipitation reaction can be carried out under alkaline conditions with a pH of 10-11.5. For example, during the co-precipitation reaction, nickel, cobalt, and manganese sources can be dissolved in water, and the pH of the mixture can be controlled to 10-11.5 to allow crystal nucleation and growth until the median particle size D... 50 The micrometer size ranges from 9 μm to 20 μm. Controlling the pH of the mixture helps regulate the co-precipitation reaction rate and creates certain pores in the precursor, allowing the positive electrode active material to retain some porosity during subsequent sintering and fusion. Optionally, an ammonia solution can be added as a complexing agent in the co-precipitation reaction.

[0061] In some specific embodiments of the present invention, step (2) of the sintering process may include: holding at 650℃-900℃ for 4h-15h. For example, the sintering temperature may be 650℃, 700℃, 750℃, 800℃, 850℃, or 900℃, and the holding time may be 4h, 6h, 8h, 10h, 12h, or 15h. In actual operation, the sintering temperature and time can be flexibly controlled according to the type of dopant element M, the composition of nickel, cobalt, and manganese, etc., to obtain the expected primary particle size or 104 crystal plane half-peak width, which is beneficial to obtaining a suitable porosity effect of the positive electrode active material.

[0062] In some specific embodiments of the present invention, step (2) may include cooling, crushing, sieving and other operations after the sintering process is completed.

[0063] In some specific embodiments of the present invention, step (2) may further include: mixing the sintered product (i.e., a sintered material) with a coating material containing a J source and holding it at 300℃-700℃ for 5h-10h, thereby forming a coating layer containing J element on the surface of the sintered material, and obtaining a positive electrode active material with a matrix and a coating layer structure. The beneficial effects of forming the coating layer and the characteristics and effects of the types of J elements have been described in detail in the foregoing sections and will not be repeated here.

[0064] In a third aspect of the invention, a positive electrode sheet is provided, comprising the above-described positive electrode active material, or a positive electrode active material prepared by the above-described method. It should be noted that the features and effects described for the above-described positive electrode active material and the above-described method for preparing the positive electrode active material also apply to this positive electrode sheet, and will not be repeated here. In general, this positive electrode sheet exhibits good cycle stability and a long cycle life.

[0065] Typically, the positive electrode sheet may include a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer may include the aforementioned positive active material or a positive active material obtained using the aforementioned preparation method. The positive current collector may include, but is not limited to, metal foil (such as aluminum foil) or composite current collectors. The positive active material layer may also include binders and conductive agents. The specific types and sources of binders and conductive agents are not particularly limited, and those skilled in the art can flexibly select them according to actual needs. For example, binders may include, but are not limited to, polyvinylidene fluoride, and conductive agents may include, but are not limited to, one or more of conductive carbon black, carbon nanotubes, and graphene.

[0066] In a fourth aspect of the invention, a battery is provided, comprising the aforementioned positive electrode. It should be noted that the features and effects described for the positive electrode also apply to this battery, and will not be repeated here. Optionally, the battery can be a secondary battery.

[0067] Typically, in addition to the positive electrode, a battery may also include a negative electrode, an electrolyte, and a separator. The specific structure or composition of the negative electrode, electrolyte, and separator is not particularly limited, and those skilled in the art can choose flexibly according to actual needs. For example, the negative electrode may include a negative current collector and a negative active material layer disposed on at least one side of the negative current collector. The negative active material layer may include a negative active material, a binder, and a conductive agent. The negative current collector may include, but is not limited to, metal foil (such as copper foil) or composite current collectors. The specific types and sources of the active material, binder, and conductive agent in the negative electrode are not particularly limited, and those skilled in the art can choose flexibly according to actual needs. For example, the negative active material may include, but is not limited to, one or more of hard carbon, soft carbon, silicon-based materials, and silicon-carbon materials; the binder may include, but is not limited to, styrene-butadiene rubber; and the conductive agent may include, but is not limited to, one or more of conductive carbon black, carbon nanotubes, and graphene. Furthermore, conventional components such as thickeners may be selectively added to the negative active material layer. For example, the separator may include, but is not limited to, polyethylene (PE) membrane, polypropylene (PP) membrane, PP / PE / PP composite membrane, composite ceramic separator, and coated separator; for another example, the electrolyte may include organic solvents and electrolyte salts. Taking lithium batteries as an example, the organic solvent may include one or more of ester solvents such as dimethyl carbonate (DMC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC), and the electrolyte salt may include, but is not limited to, one or more of common lithium salts such as lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium bis(oxalateborate)borate (LiBOB), and lithium difluorophosphate (LiO2F2). Optionally, additives may also be added to the electrolyte, and the additives may include, but are not limited to, common additives such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0068] In a fifth aspect of the invention, an electrical device is provided, comprising the battery described above. It should be noted that the features and effects described for the battery also apply to this electrical device, and will not be repeated here. Furthermore, it should be noted that the specific type of the electrical device is not particularly limited, and those skilled in the art can flexibly choose according to actual needs, such as including but not limited to electronic devices, household appliances, vehicles, etc.

[0069] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the invention in any way. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0070] In the following examples, all raw materials are commercially available unless otherwise specified.

[0071] In the following examples and comparative examples, the relevant parameters were obtained through testing using the following methods:

[0072] (1) Morphological test: obtained by scanning electron microscope of Hitachi S-4800 of Japan.

[0073] (2) Total porosity P t Testing: A cross-section of the positive electrode active material was obtained using a Hitachi IM4000Ⅱ ion mill. Images of the material cross-section were sampled using an S-4800 scanning electron microscope, and image contrast analysis was performed using the LIBMAS intelligent image analysis system. The test value for each sample is the average porosity measured using six spheres. When taking the sample images using the scanning electron microscope, the cross-section diameter was selected to be within the material particle size D. 50 -D 80 Samples between.

[0074] (3) Average pore diameter D of closed pore C Testing: The LIBMAS intelligent image analysis system was used to perform contrast analysis on the cross-sectional electron microscope images to obtain the cross-sectional area of ​​each hole. The hole shape in the cross-sectional electron microscope images was assumed to be circular to obtain the average cross-sectional hole diameter. For each sample, the test values ​​were obtained using 6 spheres, and the average value was taken.

[0075] (3) Specific surface area test of materials: Based on the principle of N2 static adsorption, the surface area was obtained by using the Tristar3020 surface analyzer from Micromeritics.

[0076] The static adsorption of N2 specifically involves gradually adding N2 to the test material (after pre-removing physically adsorbed components) under vacuum conditions in the testing apparatus. The pressure change caused by N2 adsorption is calculated using the constant volume method, and the amount of N2 adsorbed is determined according to the gas equation. This yields the amount of N2 adsorbed from 0 atm to 0.3 atm at liquid nitrogen temperature, which is then converted into specific surface area per unit weight.

[0077] (4) Opening pore volume Vo test: Based on the N2 adsorption-desorption isotherm test and analysis, the pore volume was obtained by the Tristar 3020 surface analyzer of Micromeritics.

[0078] The N2 adsorption-desorption isotherm test specifically involves the following steps: Using a conventional measuring apparatus (such as Tristar 3020), N2 is gradually added to the test material (after pre-removing physically adsorbed components) under vacuum. The pressure change caused by N2 adsorption is calculated using the constant volume method, and the amount of N2 adsorbed is determined according to the gas equation. This yields the N2 adsorption isotherm from 0 atm to 0.995 atm at liquid nitrogen temperature. After reaching 0.995 atm, the N2 pressure is gradually reduced to 0 atm, yielding the N2 desorption isotherm from 0.995 atm to 0 atm. These are then combined to obtain the N2 adsorption-desorption isotherm. The N2 adsorption-desorption isotherm analysis involves calculating the pore volume from the amount of N2 adsorbed when the relative pressure (p / p0) of the N2 adsorption isotherm is 0.995.

[0079] (5) Average aperture Do test: Based on the BJH (Barrett-Joyner-Halenda) model, it was obtained by testing with a Tristar 3020 surface analyzer from Micromeritics.

[0080] The BJH model and pore size testing specifically involve assuming a cylindrical pore shape and establishing a Kelvin relationship between the pore size at which capillary condensation occurs and the relative pressure of N2. The pore size distribution is characterized by testing the N2 adsorption capacity of different pore sizes and corresponding pore levels. The average pore size is obtained by multiplying each pore size by a percentage coefficient. This invention utilizes desorption isotherms to determine the pore inlet diameter.

[0081] (6) Test of the volume Vt of the positive electrode active material skeleton: The volume was obtained by using a Micromeritics Accupy II 1345 true density meter according to the gas displacement method.

[0082] The gas displacement method specifically involves using inert gas N2 as the displacement medium, sealing the sample in a sample chamber filled with N2, opening the expansion chamber to allow the gas to diffuse, and calculating the sample volume by measuring the pressure change before and after the gas diffusion once it has stabilized.

[0083] (7) Material XRD and finishing: obtained by Smart Lab9 KW test by Rigaku Corporation of Japan.

[0084] (8) Material particle size distribution test: obtained by Marvern Hydro 2000mu laser particle size analyzer.

[0085] (9) Particle strength test: The particle strength was obtained by testing the particles using the Shimadzu MCT-210 micro compression tester.

[0086] (10) Electrochemical performance testing:

[0087] In the following examples and comparative examples, the electrochemical performance of the multi-element cathode material was tested using a 2025 coin cell.

[0088] The specific manufacturing process of the 2025 coin cell is as follows:

[0089] Electrode preparation: A homogeneous slurry was formed by thoroughly mixing a multi-component positive electrode active material, acetylene black, and polyvinylidene fluoride (PVDF) at a mass ratio of 95:3:2 with an appropriate amount of N-methylpyrrolidone (NMP). The slurry was coated onto aluminum foil and dried at 120°C for 12 hours. Then, it was pressed into a positive electrode sheet with a diameter of 12 mm and a thickness of 120 μm using a pressure of 100 MPa. The loading of the multi-component positive electrode material was (15.5 ± 0.5) mg / cm³. 2 .

[0090] Battery Assembly: In an argon-filled glove box with both water and oxygen content less than 5 ppm, the positive electrode, separator, negative electrode, and electrolyte were assembled into a 2025 coin cell and then left to stand for 6 hours. The negative electrode used a 17 mm diameter, 1 mm thick lithium metal sheet; the separator used a 25 μm thick polyethylene porous membrane (Celgard 2325); and the electrolyte used was a 1 mol / L mixture of equal parts LiPF6, ethylene carbonate (EC), and diethyl carbonate (DEC).

[0091] 2025 coin cell battery test:

[0092] In the following examples and comparative examples, the electrochemical performance of the 2025 coin cell was tested using the Shenzhen Xinwei Battery Testing System, with a charge / discharge current density of 200 mA / g at 0.1C.

[0093] The charge / discharge voltage range was controlled between 3.0 and 4.3V. At room temperature, the coin cell was charged and discharged at 0.1C to evaluate the electrochemical performance of the multi-element cathode material.

[0094] Cyclic performance test: The charge and discharge voltage range was controlled at 3.0-4.3V. At a constant temperature of 45℃, the coin cell was charged and discharged twice at 0.1C and then charged and discharged 80 times at 1C to evaluate the high-temperature capacity retention of the multi-element cathode material.

[0095] Rate performance testing: The charge / discharge voltage range was controlled at 3.0-4.3V. At room temperature, the coin cell was cycled twice at 0.1C, and then once each at 0.2C, 0.33C, 0.5C, and 1C. The rate performance of the multi-element cathode material was evaluated by the ratio of the initial discharge specific capacity at 0.1C to the discharge specific capacity at 1C. The initial discharge specific capacity at 0.1C is the discharge specific capacity of the coin cell in the first cycle, and the discharge specific capacity at 1C is the discharge specific capacity of the coin cell in the sixth cycle.

[0096] Example 1

[0097] (1) Nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in pure water at a molar ratio of nickel, cobalt, and manganese of 83.3:10:6 to obtain a mixed salt solution with a concentration of 2 mol / L. An 8 mol / L sodium hydroxide solution was prepared as a precipitant solution, and a 6 mol / L ammonia solution was prepared as a complexing agent solution. The mixed salt solution, sodium hydroxide solution, and ammonia solution were added to the reactor through the inlet pipe, and N2 protection was provided. The stirring speed was maintained at 600 rpm, the inlet flow rate of the mixed salt solution was controlled at 400 mL / h, and the flow rates of the sodium hydroxide solution and ammonia solution were adjusted to maintain the pH of the reaction system at 10.9 ± 0.05 and the temperature of the reaction system at 60℃. After the average particle size Dv50 of the particles in the reaction system grew to 14 μm, the mixture was aged for 1 h, separated, washed, and dried to obtain the precursor of the positive electrode active material.

[0098] (2) The above precursor, lithium hydroxide, aluminum oxide, and niobium pentoxide are mixed evenly with the sum of nickel, cobalt, and manganese elements in the precursor, and the molar ratio of lithium, aluminum, and niobium elements being 0.993:1.03:0.004:0.003. The mixture is heated in an oxygen furnace and then sintered at a constant temperature. The oxygen concentration in the oxygen furnace is greater than 95% by volume, the heating rate is 5℃ / min, the sintering temperature is 810℃, and the sintering time is 10h. After naturally cooling to room temperature, the mixture is crushed, sieved, and iron is removed to obtain the positive electrode active material sintered material.

[0099] (3) The positive electrode active material calcined material and boric acid were mixed evenly in a high-speed mixer at a molar ratio of 1:0.001 between the sum of Ni, Co, Mn, Al, and Nb in the positive electrode active material calcined material and boron. The mixture was then sintered at a constant temperature of 350°C in an oxygen furnace with an oxygen concentration greater than 90% by volume for 8 hours. After cooling, sieving, and iron removal, the positive electrode active material Li was obtained. 1.03 Ni 0.833 Co 0.100 Mn 0.060 Al 0.004 Nb 0.003 In the chemical formula of O2@B, the part before @ represents the matrix component, and the part after @ represents the main element in the coating layer.

[0100] Examples 2-10 and Comparative Examples 1-4

[0101] The differences between Examples 2-14 and Comparative Examples 1-6 and Example 1 are detailed in Tables 1 and 2. Wherein:

[0102] In Example 2, the dopant source M is zirconium dioxide and tungsten oxide, and the coating agent is boric acid.

[0103] In Example 3, the M source is magnesium oxide and tin dioxide, and the coating agent is tungsten trioxide.

[0104] In Example 4, the M source was strontium oxide and antimony trioxide, and the coating agent was tungsten trioxide.

[0105] In Example 5, the M source was aluminum oxide and lithium sulfate, and the coating agent was boric acid.

[0106] In Example 6, the M source was aluminum oxide and strontium hydroxide, and the coating agent was boric acid.

[0107] In Example 7, the M source is made of aluminum oxide and niobium pentoxide.

[0108] In Example 8, the M source was aluminum oxide and boric acid, and the coating agent was cobalt hydroxide.

[0109] In Example 9, the M source is titanium dioxide and niobium pentoxide, and the coating agent is tungsten trioxide.

[0110] In Example 10, the M source was aluminum oxide and lithium sulfate, and the coating agent was boric acid. In Comparative Example 1, the M source was aluminum oxide and niobium pentoxide, and the coating agent was boric acid. In Comparative Example 2, the M source was aluminum oxide and niobium pentoxide, and the coating agent was boric acid. In Comparative Example 3, the M source was aluminum oxide and niobium pentoxide, and the coating agent was boric acid. In Comparative Example 4, the M source was aluminum oxide and niobium pentoxide, and the coating agent was boric acid. The relevant test results for Examples 1-10 and Comparative Examples 1-2 are detailed in Table 2.

[0111]

[0112]

[0113] Results and conclusions:

[0114] Combined with Examples 1-10 and Comparative Examples 1-4, and Tables 1-2 and Figures 1-2 ( Figure 1 The porosity structure of the precursor prepared in Example 1 is shown. Figure 2(The diagram showing the distribution of closed pores in the cross-section of the positive electrode active material prepared in Example 1) indicates that the preparation method of the above embodiments of the present invention can yield positive electrode active materials with an open porosity of 25%-85% of the total porosity. Furthermore, when the positive electrode active material is used in a battery, the positive electrode active material with an open porosity of 25%-85% of the total porosity exhibits a better improvement effect on the rate performance and cycle performance of the battery. The battery's energy density, first-time efficiency, rate performance, and cycle performance are all better, resulting in superior overall performance. Testing revealed that the elemental composition of the positive electrode active materials prepared in Examples 1-10 all satisfy 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. Furthermore, based on Examples 1 and 7, it can be seen that forming a coating layer on the positive electrode active material can further improve the electrochemical performance of the battery. Compared with Example 1, the proportion of open porosity in the total porosity of the positive electrode active materials prepared in Comparative Examples 1 and 3 is lower, while the proportion of open porosity in the total porosity of the positive electrode active materials prepared in Comparative Examples 2 and 4 is higher. The reasons for this may be that the calcination temperature in Comparative Example 1 is higher, and particle fusion during sintering reduces the volume of open and closed pores, thus affecting the proportion of open porosity in the total porosity; the calcination time in Comparative Example 2 is relatively long, and particle fusion during calcination leads to a significant reduction in the volume of closed pores and the total pore volume; the amount of coating agent used in Comparative Example 3 is relatively large, which reduces the open porosity of the material; and the pH value controlled during the co-precipitation reaction in Comparative Example 4 is relatively high, resulting in lower closed pore porosity and total porosity of the precursor.

[0115] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0116] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A positive electrode active material, characterized in that, include: Secondary particles, formed by the accumulation of primary particles, include open-pore and closed-pore structures, wherein the open-pore porosity P of the positive electrode active material is... o The percentage of the total porosity P of the positive electrode active material t 25%-85%; The average pore size D of the positive electrode active material o The range is 10nm-50nm; The positive electrode 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; Wherein, the porosity P o V is the pore volume V of the positive electrode active material filled with nitrogen gas. o The ratio of the volume of the positive electrode active material to the total volume of the positive electrode active material; The total porosity P of the positive electrode active material t The total pore area S of the cross-section of the positive electrode active material under an electron microscope. t With the total cross-sectional area S of the positive electrode active material m The ratio to the power of 3 / 2.

2. The positive electrode active material according to claim 1, characterized in that, At least one of the following conditions must be met: The porosity P of the positive electrode active material o It ranges from 0.5% to 3%; The pore volume Vo of the positive electrode active material is 0.002 cm³. 3 / g-0.01cm 3 / g; The framework volume Vt of the positive electrode active material is 0.2 cm³. 3 / g-0.25cm 3 / g.

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

4. The positive electrode active material according to claim 1 or 2, characterized in that, 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 subjected to 3.5 tons of pressure fracturing is S. 3.5 The specific surface area change rate ΔSSA of the positive electrode active material is 0-50%, where ΔSSA = (S 3.5 -S 0 ) / S 0 ×100%; and / or, When the volume distribution of the positive electrode active material accumulates to 10%, the corresponding particle size 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 is 0-20%, where ΔD 10 =(D 10 0 -D 10 3.5 ) / D 10 0 ×100%.

5. The positive electrode active material according to claim 1, characterized in that, M includes at least one of Sn, W, V, La, Mo, Sb, Ta, Ti, and Nb, and the full width at half maximum (FWHM) of the diffraction peak corresponding to the 104 crystal plane in the XRD pattern of the primary particle is 0.245-0.270; or, M includes at least one of S, P, and B, and the full width at half maximum (FWHM) of the diffraction peak corresponding to the 104 crystal plane in the XRD pattern of the primary particle is 0.250-0.275; or, M includes at least one of Mg, Al, Sr, Ba, Y, Zr, Ca, Fe, and Zn, and the full width at half maximum (FWHM) of the diffraction peak corresponding to the 104 crystal plane in the XRD pattern of the primary particle is 0.255-0.

280.

6. The positive electrode active material according to claim 1 or 2, characterized in that, The secondary particles comprise a matrix and a coating layer, the matrix comprising the Li 1+a Ni x Co y Mn z M m O2, at least a portion of the surface of the substrate is provided with the coating layer.

7. The positive electrode active material according to claim 6, characterized in that, The coating layer includes element J, which includes at least one of Al, Zr, Ti, F, B, Cl, Br, I, S, W, Co, Sn, and Mo; and / or, The ratio of the total number of moles of Ni, Co, Mn and M in the matrix to the number of moles of J in the coating layer is 1:(0-0.05).

8. A method for preparing the positive electrode active material according to any one of claims 1 to 7, characterized in that, include: (1) Co-precipitation reaction of aqueous solutions of nickel, cobalt and manganese sources under alkaline conditions to obtain precursor particles; (2) The precursor particles are mixed with lithium source and M source and sintered to obtain positive electrode active material.

9. The method according to claim 8, characterized in that, At least one of the following conditions must be met: In step (1), the coprecipitation reaction is carried out under alkaline conditions with a pH of 10-11.5; In step (2), the sintering treatment includes: holding at 650℃-900℃ for 4h-15h; Step (2) also includes: mixing the sintered product with a coating material containing J source and holding it at 300℃-700℃ for 5h~10h.

10. A positive electrode plate, characterized in that, It includes the positive electrode active material according to any one of claims 1 to 7, or the positive electrode active material prepared by the method according to any one of claims 8 to 9.

11. A battery, characterized in that, Includes the positive electrode sheet as described in claim 10.

12. An electrical appliance, characterized in that, Includes the battery as described in claim 11.

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