Positive electrode active material and preparation method and application thereof

Abstract

The invention provides a positive electrode active material and a preparation method and application thereof, the positive electrode active material satisfies formula 1: formula 1, in the formula 1, theta is an edge angle (degree) of a primary particle of the positive electrode active material; % of the porosity of the positive electrode active material; s is the specific surface area of the positive electrode active material, m < 2 > / g. The positive electrode active material provided by the invention can improve the energy density, the rate capability and the cycle performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and particularly relates to a positive electrode active material, its preparation method and application. Background Technology

[0002] Despite the potential for high energy density and excellent cost-effectiveness, the application of high-nickel ternary cathode active materials in secondary batteries still faces many challenges in practical applications.

[0003] First, high-nickel ternary cathode active materials are prone to structural phase transitions during battery cycling. These phase transitions are typically accompanied by lithium-ion deintercalation and reintercalation, leading to irreversible changes in the crystal lattice and volume expansion. This structural instability causes mechanical stress concentration in the material, resulting in particle cracking and degradation of the cathode active material, severely impacting battery cycle performance. Furthermore, high-nickel ternary cathode active materials are susceptible to environmental influences, leading to side reactions at the interface. These side reactions not only generate an electrochemically inert layer, hindering efficient lithium-ion migration, but may also produce unstable byproducts, further exacerbating interface degradation and thus affecting the battery's energy density, rate performance, and cycle performance. Therefore, developing a cathode active material that can improve the energy density, rate performance, and cycle performance of batteries is a pressing technical problem that needs to be solved at present. Summary of the Invention

[0004] The main objective of this invention is to provide a positive electrode active material that, when applied to a battery, can improve the battery's energy density, rate performance, and cycle performance.

[0005] The present invention also provides a method for preparing a positive electrode active material, which can prepare the above-mentioned positive electrode active material, and the process is simple and low in cost.

[0006] The present invention also provides a positive electrode sheet comprising the above-mentioned positive electrode active material. Therefore, when this positive electrode sheet is applied to a battery, it can improve the battery's energy density, rate performance, and cycle performance.

[0007] The present invention also provides a battery comprising the above-described positive electrode, thereby the battery having excellent energy density, rate performance and cycle performance.

[0008] In a first aspect, the present invention provides a positive electrode active material, wherein the positive electrode active material satisfies Formula 1:

[0009] Formula 1,

[0010] Wherein, θ is the edge angle of the primary particles of the positive electrode active material, in °; The porosity of the positive electrode active material is %; S is the specific surface area of ​​the positive electrode active material, m².2 / g.

[0011] As described above, the edge angle θ of the primary particles of the positive electrode active material satisfies: 115°≤θ≤145°;

[0012] And / or, the porosity of the positive electrode active material Satisfy: 1.0% ≤ ≤5.0%;

[0013] And / or, the specific surface area S of the positive electrode active material satisfies: 0.75 m² / s. 2 / g≤S≤3.0m 2 / g.

[0014] As described above, in the X-ray diffraction pattern of the positive electrode active material, the ratio of the intensity of the diffraction peak corresponding to the (003) crystal plane to that corresponding to the (104) crystal plane is I. 003 / I 104 <1.3.

[0015] The positive electrode active material as described above includes a positive electrode active material matrix, a transition layer covering at least a portion of the surface of the positive electrode active material matrix, and a coating layer covering at least a portion of the surface of the transition layer;

[0016] The content of +2 valent nickel in the transition layer is greater than the content of +2 valent nickel in the positive electrode active material matrix.

[0017] The positive electrode active material as described above, wherein the coating layer comprises a piezoelectric material;

[0018] And / or, the thickness of the coating layer is 1nm-18nm;

[0019] And / or, the coating layer accounts for 0.3-5% of the mass percentage of the positive electrode active material.

[0020] The positive electrode active material described above has a piezoelectric material with a chemical composition of Li. a X b Y c Z d O3, wherein a+b=1, c+d=1, 0≤b≤0.1, 0≤d≤0.5, X is selected from at least one of Mg, Zn, Fe, Cu, Na, K, Y is selected from Nb and / or Ta, and Z is selected from at least one of Ta, Ti, Zr, Sb, Hf, In, Nd, Sc, Er, Tb;

[0021] And / or, the chemical composition of the positive electrode active material matrix is ​​Li e Ni f Cog M h Q i O2, wherein 0.95≤e≤1.05, 0<i≤0.05, 0.60≤f<1, 0.01≤g<0.40, f+g<1, h=1-fg; M includes Mn and / or Al, and Q is selected from at least one of Al, Zr, Ti, Na, K, Cs, Ca, Sr, Y, Ba, La, Ce, Nb, Ta, W, Mo, and Sb.

[0022] The positive electrode active material as described above has a particle size distribution SPAN ≤ 2.

[0023] Secondly, the present invention provides a method for preparing the positive electrode active material as described above, comprising the following steps:

[0024] 1) The first system, including the positive electrode active material precursor, lithium source, and Q source, is sintered to obtain the sintered product;

[0025] The chemical composition of the positive electrode active material precursor is Ni. x Co y M 1-x-y (OH)2, where 0.60≤x<1, 0.01≤y<0.40, z=1-xy, and M includes Mn and / or Al;

[0026] 2) The sintered product is subjected to air quenching treatment to obtain an intermediate;

[0027] 3) The second system, including the intermediate and the coating material, is coated to obtain the positive electrode active material.

[0028] In the above-described method for preparing the positive electrode active material, the sintering temperature is 650-950℃, the time is 15-24h, and the heating rate is 2-10℃ / min.

[0029] And / or, the coating treatment is performed at a temperature of 250-500℃ for 8-20 hours, with a heating rate of 1-5℃ / min;

[0030] And / or, the coating material includes a piezoelectric material;

[0031] And / or, the mass ratio of the intermediate to the coating material is 100:(0.5-5).

[0032] The air quenching process in the above-described method for preparing the positive electrode active material includes: cooling the sintered product to 10-30°C at a rate of 100-200°C / min in an air atmosphere.

[0033] Thirdly, the present invention provides a positive electrode sheet, comprising the positive electrode active material as described above or the positive electrode active material prepared according to the preparation method of the positive electrode active material as described above.

[0034] Fourthly, the present invention provides a battery comprising the positive electrode sheet as described above.

[0035] The positive electrode active material provided by this invention satisfies Equation 1 in terms of the edge angle of the primary particles, the porosity of the positive electrode active material, and the specific surface area of ​​the positive electrode active material. This can balance the problems of ion diffusion and interfacial side reactions. When applied to batteries, it can improve the energy density, rate performance, and cycle performance of the batteries. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments of the present invention or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 A schematic diagram illustrating a method for calculating particle edge angle provided by the present invention;

[0038] Figure 2 SEM image of the positive electrode active material of Example 1 provided by the present invention;

[0039] Figure 3 SEM image of the positive electrode active material of Comparative Example 3 provided by the present invention;

[0040] Figure 4 XRD patterns of the positive electrode active materials of Examples 1, 2, and 1 of this invention;

[0041] Figure 5 TEM image of the positive electrode active material of Example 5 provided by the present invention;

[0042] Figure 6 XPS images of the positive electrode active materials of Example 1 and Comparative Example 1 provided by the present invention. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0044] Lithium-ion batteries are the core power source for modern portable electronic devices and electric vehicles, and their performance and safety have always been a key research focus. Traditional lithium-ion batteries typically use organic liquids as electrolytes. While this design offers advantages in energy density and cost, it also introduces safety hazards such as flammability, explosion risks, and solvent leakage. To overcome these problems, all-solid-state lithium batteries have emerged. All-solid-state batteries use solid electrolytes, which improves battery safety.

[0045] In the research of all-solid-state batteries, high-nickel ternary cathode active materials have become one of the most promising cathode active materials due to their excellent cost-effectiveness and high discharge specific capacity. However, the application of high-nickel ternary cathode active materials in all-solid-state batteries still faces many challenges. First, high-nickel ternary cathode active materials are prone to phase transitions and delithiation at high cutoff voltages, leading to severe structural distortions and affecting the cycle stability of the battery. In addition, high-nickel ternary cathode active materials are extremely sensitive to ambient air and easily form an electrochemically inert layer on their surface. This not only hinders the effective migration of charge but also increases interfacial impedance. More complicatedly, these surface defects may react chemically with the solid electrolyte, generating byproducts that are detrimental to battery performance and exacerbating interfacial degradation, thereby affecting the battery's energy density, rate performance, and cycle performance.

[0046] The inventors of this application have discovered through research that a specific relationship exists between the edge angle, porosity, and specific surface area of ​​the positive electrode active material, which can significantly improve the energy density, rate performance, and cycle performance of the battery.

[0047] Based on this, in a first aspect, the present invention provides a positive electrode active material, the positive electrode active material satisfying formula 1:

[0048] Formula 1,

[0049] Where θ is the edge angle of the primary particles of the positive electrode active material, in °; Porosity of the positive electrode active material (%); Specific surface area of ​​the positive electrode active material (m²) 2 / g.

[0050] For example, α can be a range consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or any two of them.

[0051] The edge angle, porosity, and specific surface area of ​​the primary particles in the positive electrode active material provided by this invention satisfy Equation 1. When applied to batteries, this improves the energy density, rate performance, and cycle performance of the positive electrode active material. This is because satisfying Equation 1 balances ion diffusion and interfacial side reactions, thus maintaining good capacity utilization, rate performance, and cycle life. Specifically, the edge angle θ of the primary particles describes the shape of the primary particles. A small edge angle indicates that the primary particles are too sharp, and sharp edges are prone to breakage during cycling, affecting the structural stability of the material. A large edge angle indicates that the primary particles are too rounded, leading to a longer diffusion path for lithium ions within the material and reducing the rate performance. The porosity of the positive electrode active material... If the porosity is too low, it will restrict the permeation of electrolyte, leading to a decrease in the conductivity of the material, an increase in the internal resistance of the battery, and a reduction in the rate performance of the battery; Increasing the surface area increases the electrochemical active area of ​​the material, but it also leads to increased interfacial side reactions and exacerbates electrolyte corrosion, thus affecting the material's stability. The specific surface area (S) of the cathode active material affects two aspects: firstly, it influences the effective reaction sites for lithium-ion insertion / extraction; a larger specific surface area results in a larger active reaction area and easier capacity utilization; secondly, it affects the interfacial side reactions of the cathode active material; a larger specific surface area leads to more interfacial side reactions and poorer structural stability. Therefore, a synergistic effect of these three factors is needed to satisfy Equation 1, balancing ion diffusion and interfacial side reactions, thereby improving the battery's energy density, rate performance, and cycle performance.

[0052] In this invention, the edge angle of the primary particles of the positive electrode active material can be determined by measuring the edge angle of the uncovered portion of the primary particles in the SEM image of the positive electrode active material and taking the average value. This process is repeated for 50 sets of data, and the average value is then taken to obtain the edge angle of the primary particles of the positive electrode active material. Specifically, as shown... Figure 1 As shown, along the length of the primary particle, one end of the primary particle is not covered. The angles of the two edge angles at the end are measured respectively. The angle of the first edge angle is θ1, and the angle of the second edge angle is θ2. The average value θ = (θ1 + θ2) / 2 is taken. The above average value θ is the average edge angle of a single primary particle. In this way, the average edge angle data of 50 sets of primary particles are measured and the average value is taken to obtain the edge angle of the primary particle of the positive electrode active material.

[0053] Therefore, the edge angle, porosity, and specific surface area of ​​the primary particles of the positive electrode active material provided by the present invention satisfy Equation 1. When applied to batteries, it can improve the energy density, rate performance, and cycle performance of the positive electrode active material.

[0054] In some embodiments of the present invention, the edge angle θ of the primary particles of the positive electrode active material satisfies: 115°≤θ≤145°, for example, it can be a range of 115°, 120°, 125°, 130°, 135°, 140°, 145° or any two of them.

[0055] The edge angle of the primary particles in the positive electrode active material is within an appropriate range, avoiding particles that are too sharp or too rounded. An appropriate edge angle can reduce the risk of particle breakage during cycling, while ensuring that the diffusion path of ions within the material is not too long, thereby improving the rate performance of the battery.

[0056] In some embodiments, the porosity of the positive electrode active material Satisfy: 1.0% ≤ ≤5.0%, for example, can be a range of 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, or any two of these.

[0057] When the porosity of the positive electrode active material is within a suitable range, conductivity and side reactions can be balanced. Appropriate porosity ensures good electrolyte permeability and conductivity, while limiting interfacial side reactions, thereby improving battery cycle life and stability.

[0058] In some embodiments, the specific surface area S of the positive electrode active material satisfies: 0.75 m² / s². 2 / g≤S≤3.0m 2 / g, for example, can be 0.75m 2 / g, 1.0m 2 / g, 1.5m 2 / g, 2.0m 2 / g, 2.5m 2 / g, 3.0m 2 / g or a range consisting of any two of them.

[0059] A suitable specific surface area for the positive electrode active material can balance reactivity and stability. An appropriate specific surface area provides sufficient reaction sites to enhance capacity utilization while reducing the possibility of interfacial side reactions and maintaining the material's structural stability.

[0060] In some embodiments of the present invention, in the X-ray diffraction pattern, the intensity ratio I of the diffraction peak corresponding to the (003) crystal plane of the positive electrode active material to the diffraction peak corresponding to the (104) crystal plane is... 003 / I 104 <1.3, for example, can be a range consisting of 0.1, 0.3, 0.5, 0.7, 0.9, 1.0, 1.1, 1.2, 1.29 or any two of them.

[0061] In this invention, the ratio of the intensity of the diffraction peak corresponding to the (003) crystal plane to the intensity of the diffraction peak corresponding to the (104) crystal plane of the positive electrode active material is within the above range, indicating that the material has a high degree of disorder and a high degree of lithium-nickel mixing, which can enhance the structural rigidity of the material, resist the volume strain and thermal stress during the cycle process, thereby improving the cycle stability of the battery and extending the battery's service life.

[0062] In some embodiments of the present invention, the positive electrode active material includes a positive electrode active material matrix, a transition layer covering at least a portion of the surface of the positive electrode active material matrix, and a coating layer covering at least a portion of the surface of the transition layer; the content of +2 valent nickel in the transition layer is greater than the content of +2 valent nickel in the positive electrode active material matrix. Li vacancies are replaced by Ni. 2+ Occupation leads to an increase in the content of +2 valent nickel in the transition layer. The increase in +2 valent nickel can form more strong Ni-O bonds, inhibit oxygen release and structural collapse, and further enhance the structural rigidity of the material, thereby improving the cycle stability of the battery.

[0063] In some embodiments of the present invention, the coating layer comprises a piezoelectric material.

[0064] It is understandable that piezoelectric materials have a non-centrosymmetric crystal structure. When mechanical stress is applied to the crystal, the positions of ions in the unit cell change and deviate from the center, generating polarity and transforming the unit cell into an electric dipole. This, in turn, changes the polarization intensity of the crystal, producing the piezoelectric effect. The piezoelectric effect can convert the phase transition stress during long-cycle battery operation into an electric field, which can not only alleviate stress concentration during battery cycling and reduce mechanical damage to the material, but also enhance the electronic conductivity of the positive electrode active material, which is beneficial for capacity utilization and rate performance improvement. At the same time, the metallic elements in piezoelectric materials play a synergistic role. Structurally, they can adjust lattice parameters and enhance structural stability; performance-wise, they can change the polarization intensity and dielectric constant of the crystal and widen the stable operating temperature range of the material, thereby enhancing the high-temperature stability of the interface between the positive electrode active material and the electrolyte.

[0065] In some embodiments, the thickness of the coating layer is 1 nm to 18 nm, for example, it can be a range of 1 nm, 4 nm, 7 nm, 10 nm, 13 nm, 15 nm, 18 nm or any two of these.

[0066] A coating of suitable thickness can provide effective stress relief without significantly increasing battery weight, reducing mechanical damage during cycling. Furthermore, the appropriate thickness ensures that the electric field effect of the piezoelectric material effectively influences interfacial reaction kinetics, reducing side reactions. Simultaneously, the coating provides additional protection when the battery is subjected to external stress, reducing the risk of failure.

[0067] In some embodiments, the coating layer accounts for 0.3-5% of the mass percentage of the positive electrode active material, for example, it can be a range of 0.3%, 1%, 2%, 3%, 4%, 5% or any two of these.

[0068] An appropriate percentage of coating content can effectively provide stress relief and interfacial stability without significantly increasing the weight or cost of the material. Too high a content will affect the conductivity of the material, while too low a content will not provide effective protection.

[0069] In some embodiments of the present invention, the chemical composition of the piezoelectric material is Li. a X b Y c Z d O3, wherein a+b=1, c+d=1, 0≤b≤0.1, 0≤d≤0.5, X is selected from at least one of Mg, Zn, Fe, Cu, Na, K, Y is selected from Nb and / or Ta, and Z is selected from at least one of Ta, Ti, Zr, Sb, Hf, In, Nd, Sc, Er, Tb.

[0070] For example, b can be a range consisting of 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 or any two of them; d can be a range consisting of 0, 0.1, 0.2, 0.3, 0.4, 0.5 or any two of them.

[0071] The chemical composition of the aforementioned piezoelectric materials can effectively exert the piezoelectric effect, alleviate the stress generated during battery cycling, reduce mechanical damage to the materials, and reduce the occurrence of side reactions, thereby improving the rate performance, cycle life, and stability of the battery.

[0072] In some embodiments, the chemical composition of the positive electrode active material matrix is ​​Li e Ni f Co g M h Q i O2, wherein 0.95≤e≤1.05, 0<i≤0.05, 0.60≤f<1, 0.01≤g<0.40, f+g<1, h=1-fg; M includes Mn and / or Al, and Q is selected from at least one of Al, Zr, Ti, Na, K, Cs, Ca, Sr, Y, Ba, La, Ce, Nb, Ta, W, Mo, and Sb.

[0073] For example, e can be a range consisting of 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, 1.01, 1.02, 1.03, 1.04, 1.05, or any two of these; i can be a range consisting of 0.01, 0.02, 0.03, 0.04, 0.05, or any two of these; and f can be 0.60, 0.65, 0.70, 0.75, 0.80, 0.8 5. The range consisting of 0.90, 0.95, 0.99 or any two of them; g can be the range consisting of 0.01, 0.05, 0.15, 0.20, 0.25, 0.30, 0.34, 0.39 or any two of them; f+g can be the range consisting of 0.61, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 0.99 or any two of them.

[0074] The chemical composition of the aforementioned positive electrode active material matrix shows a high nickel content, which helps to improve the material's energy density. High-nickel materials typically have a higher voltage plateau, contributing to increased battery energy output. The presence of cobalt helps improve the material's structural stability and cycle life. Cobalt also improves the material's conductivity and thermal stability, reducing performance degradation at high temperatures. Among the M elements, manganese improves the material's thermal stability and safety while reducing cost. The introduction of aluminum helps improve the material's structural stability and cycle life, reducing phase transitions and volume expansion. The Q element improves the material's structural stability, conductivity, and interfacial properties through doping.

[0075] In some embodiments of the present invention, the particle size distribution SPAN of the positive electrode active material is ≤2, for example, it can be a range of 0.1, 0.3, 0.5, 0.7, 0.9, 1.0, 1.1, 1.2, 1.5, 1.7, 2 or any two of them.

[0076] In this invention, the particle size distribution SPAN can be calculated using the following formula: SPAN = (D90 – D10) / D50, where D50 represents the particle size of the positive electrode active material when the cumulative volume reaches 50% from the smallest particle size side in the volume-based particle size distribution; D10 represents the particle size of the positive electrode active material when the cumulative volume reaches 10% from the smallest particle size side in the volume-based particle size distribution; and D90 represents the particle size of the positive electrode active material when the cumulative volume reaches 90% from the smallest particle size side in the volume-based particle size distribution.

[0077] Smaller particle size distribution indicates uniform particle size, fewer irregular voids, and reduced electron transport resistance, which is conducive to the formation of a compact packing structure, thereby improving the energy density of the battery. Furthermore, uniform particle size reduces stress concentration and particle breakage caused by particle size differences during cycling, contributing to improved material structural stability and battery cycle life.

[0078] Secondly, the present invention provides a method for preparing the positive electrode active material as described above, comprising the following steps:

[0079] 1) The first system, including the positive electrode active material precursor, lithium source, and Q source, is sintered to obtain the sintered product; the chemical composition of the positive electrode active material precursor is Ni. x Co y M 1-x-y (OH)2, where 0.60≤x<1, 0.01≤y<0.40, z=1-xy, and M includes Mn and / or Al;

[0080] 2) The sintered product is subjected to air quenching to obtain an intermediate;

[0081] 3) The second system, including intermediates and coating materials, is coated to obtain the positive electrode active material.

[0082] In step 1), for example, x can be a range consisting of 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 0.99 or any two of them; y can be a range consisting of 0.01, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.39 or any two of them.

[0083] The lithium source can be selected from at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium sulfate, lithium chloride, and lithium fluoride; the Q source can be selected from at least one of the oxides corresponding to the Q element, the hydroxides corresponding to the Q element, the hydroxy oxides corresponding to the Q element, and the carbonates corresponding to the Q element.

[0084] Specifically, the cathode active material precursor, lithium source, and Q source can be mixed uniformly, and the resulting mixture can be placed in an atmosphere box furnace and sintered under an oxygen atmosphere to obtain the sintered product. The chemical composition of the cathode active material precursor affects the specific surface area of ​​the cathode active material. At the same sintering temperature, the higher the nickel content of the cathode active material precursor, the lower the ion diffusion activation energy during primary particle formation, and the easier it is for the primary particles to grow, thus leading to a decrease in the specific surface area of ​​the cathode active material. Conversely, when the nickel content of the precursor is low, due to the higher ion diffusion activation energy, primary particles are less likely to grow, resulting in a larger specific surface area of ​​the sintered cathode active material.

[0085] In step 2), the sintered product can be taken out from the atmosphere box furnace and placed in an air atmosphere at room temperature for rapid cooling. After the material is cooled to room temperature, it is crushed and sieved to obtain an intermediate with a nickel-rich disordered layer on the surface, i.e., a transition layer.

[0086] During air quenching, a transition layer is formed on the outside of the intermediate through surface reconstruction. The rapid cooling during air quenching causes some Li on the material surface to... + Diffusion from the lattice leaves behind Li vacancies, which are then absorbed by Ni. 2+ The presence of cations leads to increased cation disorder and exacerbated Li / Ni mixing, resulting in Ni-rich deposits on the material surface. 2+ The Li / Ni mixed transition layer has an increased number of Ni-O bonds.

[0087] Air quenching affects the porosity of cathode active materials. During air quenching, the cooling rate is much faster than the diffusion rate of gases inside the material. The gaseous products generated during sintering cannot escape in time, forming new pores and ultimately increasing the porosity of the cathode active material. Without air quenching, the diffusion rate of gases inside the material is faster than the cooling rate, and the gases generated during sintering escape before the material cools and solidifies, resulting in a dense cathode active material with extremely low porosity.

[0088] In step 3), the intermediate and coating material are mixed evenly and placed in an atmosphere-controlled furnace for coating treatment under an oxygen atmosphere. After cooling to room temperature, the mixture is crushed and sieved to obtain a positive electrode active material with a coating layer on its surface. The coating material's coating of the intermediate improves the edge angles of the primary particles of the positive electrode active material. That is, the coating treatment forms a protective coating layer on the surface of the positive electrode active material, enabling the primary particles to grow more rounded and increasing the edge angle number. Without coating treatment, the primary particles of the positive electrode active material lack a protective layer, resulting in sharp edges with low angles, making them prone to breakage during long-term cycling and affecting the structural stability of the positive electrode active material.

[0089] The method for preparing the positive electrode active material provided by the present invention can prepare the positive electrode active material provided by the first aspect of the present invention, and the positive electrode active material satisfies Formula 1. When applied to a battery, it can improve the energy density, rate performance and cycle performance of the positive electrode active material.

[0090] In some embodiments of the present invention, the sintering temperature is 650-950°C, for example, it can be a range of 650°C, 700°C, 750°C, 800°C, 850°C, 950°C or any two of these; the time is 15-24h, for example, it can be a range of 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, 24h or any two of these; the heating rate is 2-10°C / min, for example, it can be a range of 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min or any two of these.

[0091] Suitable sintering temperature and time can ensure good crystal structure formation in materials, reducing defects and inhomogeneities. Controlling the heating rate helps avoid thermal stress and uneven sintering, thereby improving the structural stability and electrochemical performance of materials.

[0092] In some embodiments, the coating treatment temperature is 250-500°C, for example, it can be a range of 250°C, 300°C, 350°C, 400°C, 450°C, 500°C or any two of these; the time is 8-20h, for example, it can be a range of 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h or any two of these; the heating rate is 1-5°C / min, for example, it can be a range of 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min or any two of these.

[0093] Appropriate coating temperature and time can ensure uniform distribution and good adhesion of the coating material on the surface of the positive electrode active material matrix. Controlling the heating rate helps to form a uniform coating layer, improves interfacial stability and the overall performance of the material.

[0094] In some embodiments, the coating material includes a piezoelectric material.

[0095] After coating treatment, the above-mentioned coating material can effectively coat piezoelectric materials on the surface of the positive electrode active material matrix, thereby further improving the rate performance and cycle performance of the battery.

[0096] In some embodiments, the mass ratio of the intermediate to the coating material is 100:(0.5-5), for example, it can be a range of 100:0.5, 100:1, 100:1.5, 100:2, 100:2.5, 100:3, 100:3.5, 100:4, 100:4.5, 100:5 or any two of these.

[0097] By maintaining the mass ratio of the intermediate to the coating material within the aforementioned range, the thickness and mass content of the coating layer can be controlled within a suitable range. This reduces mechanical damage during cycling, ensures that the electric field effect of the piezoelectric material effectively influences the interfacial reaction kinetics, and minimizes side reactions.

[0098] In some embodiments of the present invention, the air quenching process includes: cooling the sintered product to 10-30°C at a rate of 100-200°C / min in an air atmosphere, for example, a range of 10°C, 12°C, 15°C, 20°C, 25°C, 27°C, 30°C or any combination thereof.

[0099] For example, the cooling rate can be a range of 100°C / min, 110°C / min, 120°C / min, 130°C / min, 140°C / min, 150°C / min, 160°C / min, 170°C / min, 180°C / min, 190°C / min, 200°C / min or any combination thereof.

[0100] Rapid cooling can effectively cool some of the Li on the surface of the positive electrode active material matrix. + It diffuses out of the crystal lattice, forming residual alkali, and the left Li vacancies are occupied by Ni. 2+ The presence of cations leads to increased cation disorder and exacerbated Li / Ni mixing, resulting in Ni-rich deposits on the material surface. 2+ The Li / Ni mixed transition layer, with its increased nickel content, leads to an increase in Ni-O bonds. Stronger Ni-O bonds can suppress oxygen release and structural collapse, as well as enhance the structural rigidity of the material. This allows it to resist volumetric strain and thermal stress during cycling, reduce side reactions, and thus improve the cycle performance and stability of the battery.

[0101] Thirdly, the present invention provides a positive electrode sheet, comprising the positive electrode active material as described above or the positive electrode active material prepared according to the preparation method of the positive electrode active material as described above.

[0102] The positive electrode sheet of the present invention can be prepared using conventional techniques in the art. Specifically, the above-mentioned positive electrode active material, conductive agent and binder can be uniformly dispersed in a solvent to obtain a positive electrode active slurry. Then, the positive electrode active slurry is coated on at least one functional surface of the positive electrode current collector, and after drying, the positive electrode sheet of the present invention can be obtained.

[0103] This invention does not specifically limit the types of conductive agents and adhesives. The conductive agents, adhesives and other components can all be conventional substances in the field. For example, the conductive agent can be selected from one or more of conductive carbon black, carbon nanotubes, conductive graphite and graphene, and the adhesive can be selected from one or more of polyvinylidene fluoride (PVDF), acrylic modified PVDF, polyacrylate polymers, polyimide, styrene-butadiene rubber and styrene-acrylic rubber.

[0104] The present invention does not specifically limit the coating method, and any coating method such as gravure coating, extrusion coating, spraying, screen printing, etc. can be used to achieve the coating of the positive electrode active layer slurry.

[0105] The positive electrode sheet provided by the present invention includes the above-mentioned positive electrode active material. Therefore, when the positive electrode sheet is applied to a battery, it can improve the energy density, rate performance and cycle performance of the battery.

[0106] Fourthly, the present invention provides a battery comprising the positive electrode sheet as described above, which has advantages corresponding to the positive electrode sheet described above, and will not be elaborated further.

[0107] The battery of the present invention can be a liquid battery or a solid battery.

[0108] When it is a solid-state battery, such as a sulfide all-solid-state battery, it includes a solid electrolyte and a negative electrode in addition to the positive electrode. The solid electrolyte can be a conventional electrolyte in the art, such as at least one of oxide solid electrolytes LATP, LLZO, and LLTO, or halide solid electrolytes Li3InCl6, Li2ZrCl6, Li2YZrCl6, LiNbOCl4, LiTaOCl4, and Li3ZrCl4O. 1.5 At least one of the following materials: sulfide solid electrolytes Li2S-P2S5, Li3PS4, and Li7P3S 11 Li6PS5Cl, Li 5.5 PS 4.5 Cl 1.5 Li 7-x PS 6-x Cl x (0 < x < 1.7), Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 Li 10 GeP2S 12 At least one of the following materials. The negative electrode active material in the negative electrode sheet can be at least one of the commonly used negative electrode active materials, such as graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon suboxide and silicon-carbon negative electrodes), and tin-based negative electrode materials (mainly including tin and tin alloys).

[0109] The battery of the present invention can be a single cell, a battery pack, a battery stack, or a cylindrical cell formed by connecting single cells. These cells can be electrically connected by conventional methods in the art, such as series connection, parallel connection, or a hybrid connection including these connection methods, etc., without particular limitation.

[0110] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0111] Example 1

[0112] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0113] 1) Add 1 mol of the positive electrode active material precursor (nickel-cobalt-manganese hydroxide Ni) 0.9 Co 0.05 Mn 0.05 The mixture of 1.04 mol LiOH·H2O, 0.001 mol La(OH)3, and 0.003 mol SrO was homogeneously mixed to obtain a mixture. The mixture was placed in an atmosphere box furnace and heated to 850℃ at 2℃ / min under an oxygen atmosphere, and sintered at that temperature for 18 h. After the sintering process was completed, the sintered product was obtained.

[0114] 2) The sintered product is removed from the atmosphere box furnace and rapidly cooled at room temperature (25°C) in an air atmosphere, i.e., air quenching, at a cooling rate of 140°C / min. After the material powder is cooled to room temperature (25°C), it is crushed and sieved to obtain the intermediate.

[0115] 3) The intermediate was mixed with LiNbO3, MgO and Ta2O5 in a mass ratio of 100:1.78:0.024:0.53 and then placed in an atmosphere box furnace. The temperature was increased to 380℃ at 5℃ / min and held for 10h under an oxygen atmosphere, which is the coating treatment. After cooling to room temperature, the mixture was crushed and sieved to obtain the positive electrode active material.

[0116] The positive electrode active material includes a positive electrode active material matrix, a transition layer covering at least a portion of the surface of the positive electrode active material matrix, and a coating layer covering at least a portion of the surface of the transition layer. The content of +2 valent nickel in the transition layer is greater than the content of +2 valent nickel in the positive electrode active material matrix. The coating layer includes a piezoelectric material with a chemical composition of Li. 0.9 Mg 0.05 Nb 0.8 Ta 0.2 O3, the chemical composition of the positive electrode active material matrix is ​​Li 1.02 Ni 0.9 Co 0.05 Mn 0.05La 0.001 Sr 0.00 3O2.

[0117] Example 2

[0118] The preparation method of the positive electrode active material in Example 2 is basically the same as that in Example 1, except that in step 1), 1 mol of the positive electrode active material precursor (nickel-cobalt-manganese hydroxide Ni) is added. 0.9 Co 0.05 Mn 0.05 (OH)2), 1.04 mol LiOH·H2O, 0.001 mol Nb2O5, and 0.002 mol SrO are mixed evenly to obtain a mixture. In step 3), the intermediate is mixed with LiNbO3, K2CO3, and TiO2 in a mass ratio of 100:2.04:0.048:0.11 for coating treatment, resulting in a piezoelectric material with the chemical composition Li. 0.95 K 0.05 Nb 0.92 Ti 0.1 O3, the chemical composition of the positive electrode active material matrix is ​​Li 1.02 Ni 0.9 Co 0.05 Mn 0.05 Nb 0.002 Sr 0.002 O2.

[0119] Example 3

[0120] The preparation method of the positive electrode active material in Example 3 is basically the same as that in Example 1, except that in step 1), 1 mol of the positive electrode active material precursor (nickel-cobalt-manganese hydroxide Ni) is added. 0.9 Co 0.05 Mn 0.05 (OH)2), 1.04 mol LiOH·H2O, 0.0015 mol Nb2O5, and 0.001 mol WO3 were mixed evenly to obtain a mixture. In step 3), the intermediate was mixed with LiNbO3, Na2CO3, and Sb2O5 in a mass ratio of 100:1.941:0.07:0.21 and then coated to obtain a piezoelectric material with the chemical composition Li. 0.9 Na 0.1 Nb 0.9 Sb 0.1 O3, the chemical composition of the positive electrode active material matrix is ​​Li 1.02 Ni 0.9 Co 0.05 Mn 0.05 Nb 0.003 W 0.001 O2.

[0121] Example 4

[0122] The preparation method of the positive electrode active material in Example 4 is basically the same as that in Example 1, except that in step 1), 1 mol of the positive electrode active material precursor (nickel-cobalt-manganese hydroxide Ni) is added. 0.9 Co 0.05 Mn 0.05 (OH)2), 1.04 mol LiOH·H2O, 0.002 mol ZrO2, and 0.002 mol WO3 were mixed evenly to obtain a mixture. In step 3), the intermediate was mixed with LiNbO3, ZnO, and ZrO2 in a mass ratio of 100:1.99:0.022:0.33 for coating treatment, resulting in a piezoelectric material with the chemical composition Li. 0.96 Zn 0.02 Nb 0.84 Zr 0.2 O3, the chemical composition of the positive electrode active material matrix is ​​Li 1.02 Ni 0.9 Co 0.05 Mn 0.05 Zr 0.002 W 0.002 O2.

[0123] Example 5

[0124] The preparation method of the positive electrode active material in Example 5 is basically the same as that in Example 1, except that in step 1), 1 mol of the positive electrode active material precursor (nickel-cobalt-manganese hydroxide Ni) is added. 0.9 Co 0.05 Mn 0.05 (OH)2), 1.04 mol LiOH·H2O, 0.002 mol ZrO2, and 0.001 mol Al2O3 are mixed evenly to obtain a mixture. In step 3), the intermediate is mixed with LiTaO3, Fe2O3, In2O3, and Nd2O3 in a mass ratio of 100:1.96:0.013:0.16:0.14 and then coated to obtain a piezoelectric material with the chemical composition Li. 0.94 Fe 0.02 Ta 0.88 In 0.1 Nd 0.1 O3, the chemical composition of the positive electrode active material matrix is ​​Li 1.02 Ni 0.9 Co 0.05 Mn 0.05 Zr 0.002 Al 0.002 O2.

[0125] Example 6

[0126] The preparation method of the positive electrode active material in Example 6 is basically the same as that in Example 1, except that in step 1), 1 mol of the positive electrode active material precursor (nickel-cobalt-manganese hydroxide Ni) is added. 0.9 Co 0.05 Mn 0.05 (OH)2), 1.04 mol LiOH·H2O, 0.001 mol Y2O3, and 0.001 mol Al2O3 are mixed evenly to obtain a mixture. In step 3), the mass ratio of the intermediate to LiNbO3, MgO, and Ta2O5 is 100:2.23:0.03:0.66, resulting in a piezoelectric material with the chemical composition Li. 0.9 Mg 0.05 Nb 0.8 Ta 0.2 O3, the chemical composition of the positive electrode active material matrix is ​​Li 1.02 Ni 0.9 Co 0.05 Mn 0.05 Y 0.002 Al 0.002 O2.

[0127] Example 7

[0128] The preparation method of the positive electrode active material in Example 7 is basically the same as that in Example 1, except that in step 1), 1 mol of the positive electrode active material precursor (nickel-cobalt-manganese hydroxide Ni) is added. 0.9 Co 0.05 Mn 0.05 (OH)2), 1.04 mol LiOH·H2O, 0.001 mol Y2O3, and 0.002 mol MoO3 were mixed evenly to obtain a mixture. In step 3), the mass ratio of the intermediate to LiNbO3, MgO, and Ta2O5 was 100:3.12:0.042:0.93, resulting in a piezoelectric material with the chemical composition Li. 0.9 Mg 0.05 Nb 0.8 Ta 0.2 O3, the chemical composition of the positive electrode active material matrix is ​​Li 1.02 Ni 0.9 Co 0.05 Mn 0.05 Y 0.002 Mo 0.002 O2.

[0129] Example 8

[0130] The preparation method of the positive electrode active material in Example 8 is basically the same as that in Example 1, except that in step 1), 1 mol of the positive electrode active material precursor (nickel-cobalt-manganese hydroxide Ni) is added. 0.9Co 0.05 Mn 0.05 (OH)2), 1.04 mol LiOH·H2O, 0.001 mol Ta2O5, and 0.002 mol MoO3 are mixed evenly to obtain a mixture. In step 3), the mass ratio of the intermediate to LiNbO3, MgO, and Ta2O5 is 100:1.335:0.018:0.4, resulting in a piezoelectric material with the chemical composition Li. 0.9 Mg 0.05 Nb 0.8 Ta 0.2 O3, the chemical composition of the positive electrode active material matrix is ​​Li 1.02 Ni 0.9 Co 0.05 Mn 0.05 Ta 0.002 Mo 0.00 2O2.

[0131] Example 9

[0132] The preparation method of the positive electrode active material in Example 9 is basically the same as that in Example 1, except that in step 1), 1 mol of the positive electrode active material precursor (nickel-cobalt-manganese hydroxide Ni) is added. 0.93 Co 0.03 Mn 0.04 (OH)2), 1.04 mol LiOH·H2O, 0.002 mol SrO, and 0.002 mol TiO2 are mixed evenly to obtain a mixture. In step 3), the intermediate is mixed with LiNbO3 and MgO in a mass ratio of 100:1.988:0.027 for coating treatment, resulting in a piezoelectric material with the chemical composition Li. 0.9 Mg 0.05 NbO3, the chemical composition of the positive electrode active material matrix is ​​Li 1.02 Ni 0.93 Co 0.03 Mn 0.04 Sr 0.002 Ti 0.002 O2.

[0133] Example 10

[0134] The preparation method of the positive electrode active material in Example 10 is basically the same as that in Example 1, except that in step 1), 1 mol of the positive electrode active material precursor (nickel-cobalt-manganese hydroxide Ni) is added. 0.95 Co 0.03 Mn 0.02(OH)2), 1.04 mol LiOH·H2O, and 0.001 mol Na2CO3 were mixed evenly to obtain a mixture. In step 3), the intermediate was mixed with LiNbO3 and Ta2O5 in a mass ratio of 100:1.787:0.534 for coating treatment, resulting in a piezoelectric material with the chemical composition LiNb. 0.8 Ta 0.2 O3, the chemical composition of the positive electrode active material matrix is ​​Li 1.02 Ni 0.95 Co 0.03 Mn 0.02 Na 0.002 O2.

[0135] Example 11

[0136] The preparation method of the positive electrode active material in Example 11 is basically the same as that in Example 1, except that in step 1), 1 mol of the positive electrode active material precursor (nickel-cobalt-manganese hydroxide Ni) is added. 0.9 Co 0.05 Mn 0.05 (OH)2), 1.04 mol LiOH·H2O, and 0.002 mol BaSO4 are mixed evenly to obtain a mixture. In step 3), the intermediate is mixed with LiNbO3 at a mass ratio of 100:2 for coating treatment, resulting in a piezoelectric material with the chemical composition of LiNbO3 and a positive electrode active material matrix with the chemical composition of Li. 1.02 Ni 0.9 Co 0.05 Mn 0.05 Ba 0.002 O2.

[0137] Example 12

[0138] The preparation method of the positive electrode active material in Example 12 is basically the same as that in Example 1, except that in step 1), 1 mol of the positive electrode active material precursor (nickel-cobalt-manganese hydroxide Ni) is added. 0.9 Co 0.05 Mn 0.05 (OH)2), 1.04 mol LiOH·H2O, and 0.0015 mol Sb2O5 were mixed evenly to obtain a mixture. In step 3), LiNbO3, MgO, and Ta2O5 were mixed evenly in a mass ratio of 1.78:0.024:0.53 and placed in an atmosphere box furnace. The mixture was heated to 380℃ at a rate of 5℃ / min and held for 10 hours in an air atmosphere. After cooling to room temperature, the coating material of this embodiment was obtained, and its chemical composition is Li 0.9 Mg 0.05 Nb 0.8 Ta 0.2O3. The coating material prepared above was mixed with the intermediate at a mass ratio of 2:100 and placed in an atmosphere-controlled furnace. The mixture was heated to 300°C at a rate of 5°C / min under an oxygen atmosphere for 5 hours. After cooling, the mixture was crushed and sieved to obtain the positive electrode active material. The piezoelectric material has a chemical composition of Li. 0.9 Mg 0.05 Nb 0.8 Ta 0.2 O3, the chemical composition of the positive electrode active material matrix is ​​Li 1.02 Ni 0.9 Co 0.05 Mn 0.05 Sb 0.003 O2.

[0139] Example 13

[0140] The preparation method of the positive electrode active material in Example 13 is basically the same as that in Example 1, except that the mass ratio of the intermediate to LiNbO3, MgO and Ta2O5 is 100:7.12:0.096:2.12.

[0141] Example 14

[0142] The preparation method of the positive electrode active material in Example 14 is basically the same as that in Example 1, except that the intermediate is mixed with Nb₂O₅, MgO, and Ta₂O₅ in a mass ratio of 100:1.6:0.024:0.53 for coating treatment. Finally, the chemical composition of the coating layer of the positive electrode active material is Nb 0.8 Mg 0.05 Ta 0.5 O 3.3 Non-piezoelectric materials.

[0143] Comparative Example 1

[0144] The preparation methods of the positive electrode active material in Comparative Example 1 and Example 1 are basically the same, except that after the sintering process is completed, the sintering product is naturally cooled to room temperature (25°C) in an atmosphere box furnace without undergoing an air quenching process, and the cooling rate is 3°C / min.

[0145] Comparative Example 2

[0146] The preparation method of the positive electrode active material in Comparative Example 2 is basically the same as that in Example 1, except that step 3 is omitted, that is, the surface of the positive electrode active material substrate is not coated with a coating layer.

[0147] Comparative Example 3

[0148] The preparation method of the positive electrode active material in Comparative Example 3 is basically the same as that in Example 1, except that 1 mol of the positive electrode active material precursor (nickel-cobalt-manganese hydroxide Ni) is used. 0.33 Co 0.01 Mn 0.66 The mixture of 1.04 mol LiOH·H2O and 0.05 mol La(OH)3 was homogeneously mixed to obtain a mixture. The chemical composition of the positive electrode active material matrix is ​​Li 1.02 Ni 0.33 Co 0.01 Mn 0.66 La 0.05 O2.

[0149] Experimental example:

[0150] 1. Morphology test: The positive electrode active materials of the examples and comparative examples were tested using a scanning electron microscope (SEM) of model SU 8010 from Hitachi, Japan.

[0151] 2. SPAN Test: The particle size of the positive electrode active materials prepared in the examples and comparative examples was tested using a laser particle size analyzer (MasterSizer 2000). The D10, D50, and D90 values ​​were read. SPAN = (D90 - D10) / D50. D50 represents the particle size of the positive electrode active material when the cumulative volume reaches 50% from the smallest particle size side in the volume-based particle size distribution; D10 represents the particle size of the positive electrode active material when the cumulative volume reaches 10% from the smallest particle size side in the volume-based particle size distribution; D90 represents the particle size of the positive electrode active material when the cumulative volume reaches 90% from the smallest particle size side in the volume-based particle size distribution.

[0152] 3. Specific Surface Area S Test: The specific surface area of ​​the positive electrode active materials prepared in the examples and comparative examples was tested. Specifically, the total weight of the empty small test tube and the stopper was weighed. The positive electrode active material powder sample to be tested was immersed in anhydrous ethanol for 4 hours. Then, the powder sample was taken out and dried in an oven at 105°C for half an hour. Next, the powder sample was placed in the sample tube, and the total weight of the powder sample, the small test tube, and the stopper was weighed to calculate the sample mass. The degassing station was turned on, and the small test tube containing the powder sample was placed in the degassing station at 105°C. Nitrogen (pure nitrogen) was purged for 30 minutes, cooled for 15 minutes, and then tested at 25°C and 60% humidity. P / P0, with points in the range of 0.05~0.25, was used as the x-axis, and P / V(P0-P) was used as the y-axis. A linear fit was performed by plotting the BET equation to obtain the slope and intercept of the straight line, thereby calculating the BET specific surface area of ​​the powder sample.

[0153] 4. Porosity Testing: The porosity of the material was tested using the N2 adsorption-desorption curve, and the value of the material porosity was determined based on the test results.

[0154] 5. Primary Particle Edge Angle θ Test: Observe the SEM images of the positive electrode active materials in the examples and comparative examples, and measure the uncovered edge angle of the primary particles. 50 sets of data were tested and the average value was taken. Figure 1 This is a schematic diagram illustrating the calculation method for the edge angle of a primary particle in this application, with reference to... Figure 1 Along the length of the primary particle, one end of the primary particle is not covered. The angles of the two edge angles at the end are measured and the average value is taken. The average value is the average edge angle of a single primary particle. The average value of 50 sets of data is recorded as θ.

[0155] 6. XRD Test: X-ray powder diffraction (XRD) tests were performed on the positive electrode active materials of the examples and comparative examples. After overall refinement by Topas software, the intensity ratio I of the diffraction peak corresponding to the (003) crystal plane and the diffraction peak corresponding to the (104) crystal plane of the positive electrode active material was obtained. 003 / I 104 .

[0156] 7. Coating thickness: Under 25℃ conditions, take positive electrode active material or scrape powder from the electrode sheet, cut it with focused ion beam (FIB) to obtain a cross-sectional sample, take the cross-sectional sample under a transmission electron microscope (TEM) to obtain the diffraction pattern, determine the crystal structure and measure the coating thickness.

[0157] 8. XPS Testing: The chemical properties of the elements in the positive electrode active material were tested using X-ray photoelectron spectroscopy (XPS). After analysis and refinement using the Avantage data processing software, the chemical state of nickel in the air-quenched positive electrode material was obtained. Using XPS sputtering at different depths, it was found that the content of +2 valent nickel in the transition layer was greater than that in the positive electrode active material matrix.

[0158] 9. Specific Capacity and Initial Coulombic Efficiency Tests: The positive electrode active materials from the examples and comparative examples, along with the sulfide solid electrolyte (Li6PS5Cl) and conductive agent (VGCF), were weighed into a mortar and manually mixed for at least 30 minutes at a mass ratio of 85:15:1 to obtain a mixture. Then, 1% (by mass) of polytetrafluoroethylene (PTFE) particles were added. The mixture was heated at 150°C for 5 minutes on a heating table and manually ground to form a film, pre-fiberizing the PTFE. The resulting film was then heated and rolled on a calender at 100°C. The film thickness was adjusted by controlling the gap width between the two hot rollers. Repeated rolling was performed to obtain a composite positive electrode active material film with a thickness of 40-60µm. This composite positive electrode active material film was calendered onto the surface of a 15µm thick Al foil current collector to obtain a positive electrode sheet. The positive electrode sheet was die-cut into 8mm diameter discs and then subjected to a glove box filled with Ar atmosphere with Li6P... S A fully solid-state battery can be obtained by stacking a 5Cl sulfide solid electrolyte membrane and a LiIn anode, followed by cold pressing and other steps.

[0159] At 25℃, the battery is charged at a constant current rate of 0.1C to 4.5V, and then charged at a constant voltage rate of 4.5V until the current equals 0.05C. The charging capacity at this point is recorded as the first charge specific capacity. After resting for 5 minutes, the battery is discharged at a constant current rate of 0.1C until the voltage reaches 2.5V. The discharge capacity at this point is recorded as the battery's first discharge specific capacity. The first coulombic efficiency is calculated by dividing the obtained discharge specific capacity by the charge specific capacity.

[0160] 10. Rate Performance Test: The all-solid-state battery is charged at 25℃ with a constant current of 0.1C to a voltage of 4.5V, then charged at 4.5V with a constant voltage until the current equals 0.05C. After resting for 5 minutes, it is discharged at a constant current of 0.1C to a voltage of 2.5V. The capacity at this point is recorded as the discharge capacity at 0.1C. After resting for 10 minutes, it is charged at a constant current of 1C to a voltage of 4.5V, then charged at 4.5V with a constant voltage until the current equals 0.05C. After resting for 5 minutes, it is discharged at a constant current of 1C to a voltage of 2.5V. The capacity at this point is recorded as the discharge capacity at 1C. The discharge capacity at 1C / the discharge capacity at 0.1C is the 1C rate performance.

[0161] 11. Cyclic performance test: The all-solid-state battery is charged at 25℃ with a constant current of 0.1C to a voltage of 4.5V, and then charged at a constant voltage of 4.5V to a current of 0.05C. After that, it is left to stand for 5 minutes, and then discharged at a constant current of 0.1C to a voltage of 2.5V. This cycle test is repeated until the capacity decays to 80%, and the number of cycles is recorded.

[0162] 12. Energy Density Test: The all-solid-state battery was charged at 25℃ with a constant current of 0.1C to a voltage of 4.5V, then charged at 4.5V with a constant voltage until the current equals 0.05C. After resting for 5 minutes, it was discharged at a constant current of 0.1C to a voltage of 2.5V. The initial discharge capacity Q of the battery was recorded. 放 and the first discharge energy E 放 Weigh the battery and record the mass as W. Calculate the mass energy density ED = E. 放 / W.

[0163] Figure 2 SEM image of the positive electrode active material of Example 1 provided by the present invention.

[0164] from Figure 2 It can be seen that the edge angle, porosity, and specific surface area of ​​the positive electrode active material in Example 1 are more suitable. Through calculation, it can be found that the relationship between the three satisfies Equation 1, which can improve the energy density, rate performance and cycle performance of the battery.

[0165] Figure 3 The image shows the SEM image of the positive electrode active material of Comparative Example 3 provided by the present invention.

[0166] from Figure 3 It can be seen that the positive electrode active material of Comparative Example 3 has a low nickel content, which restricts the primary particle growth, resulting in excessive porosity and specific surface area. Calculations show that the relationship between the three does not satisfy Equation 1, which affects the energy density, rate performance and cycle performance of the battery.

[0167] Figure 4 XRD patterns of the positive electrode active materials of Examples 1, 2, and 1 of the present invention.

[0168] from Figure 4 From the XRD patterns, the Io of the positive electrode active materials in Examples 1, 2, and 1 (Comparative Example 1) can be calculated. 003 / I 104 The ratio of .

[0169] Figure 5 This is a TEM image of the positive electrode active material of Example 5 provided by the present invention.

[0170] from Figure 5 The TEM image can be used to measure the lattice fringes of the surface coating layer and the internal bulk phase of the positive electrode active material in Example 5, and the thickness of the coating layer can be measured.

[0171] Figure 6 XPS images of the positive electrode active materials of Example 1 and Comparative Example 1 provided by the present invention.

[0172] from Figure 6As can be seen, after removing the outermost coating layer, the surface of the positive electrode active material in Example 1 has a significantly higher content of +2 valent nickel due to the presence of the transition layer, which is greater than the content of +2 valent nickel in the positive electrode active material matrix. In contrast, the positive electrode active material in Comparative Example 1, having not undergone air quenching and thus not forming a transition layer, shows no change in the content of +2 valent nickel.

[0173] Table 1

[0174]

[0175] Table 2

[0176]

[0177] As shown in Tables 1-2, compared with the comparative examples, the edge angle, porosity, and specific surface area of ​​the primary particles of the positive electrode active material provided by the present invention satisfy Equation 1. When applied to batteries, it can improve the rate performance, energy density, and cycle performance of the batteries.

[0178] Compared to Comparative Example 1, the positive electrode active material of Example 1 underwent air quenching treatment, which made I 003 / I 104 A value of <1.3 can further improve the battery's specific capacity, initial coulombic efficiency, rate performance, energy density, and cycle performance.

[0179] Compared with Comparative Example 2, the positive electrode active material of Example 1 includes a coating layer, which can further improve the specific capacity, first coulombic efficiency, rate performance, energy density and cycle performance of the battery.

[0180] Compared with Comparative Example 3, the positive electrode active material matrix of Example 1 is a high-nickel material, which can further improve the specific capacity and energy density of the battery.

[0181] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material satisfies Equation 1: Formula 1, Wherein, θ is the edge angle of the primary particles of the positive electrode active material, in °; The porosity of the positive electrode active material is %; S is the specific surface area of ​​the positive electrode active material, m². 2 / g.

2. The positive electrode active material according to claim 1, characterized in that, The edge angle θ of the primary particles of the positive electrode active material satisfies: 115°≤θ≤145°; And / or, the porosity of the positive electrode active material Satisfy: 1.0% ≤ ≤5.0%; And / or, the specific surface area S of the positive electrode active material satisfies: 0.75 m² / s. 2 / g≤S≤3.0m 2 / g.

3. The positive electrode active material according to claim 1, characterized in that, The ratio of the intensity of the diffraction peak corresponding to the (003) crystal plane to the intensity of the diffraction peak corresponding to the (104) crystal plane of the positive electrode active material is I 003 / I 104 <1.

3.

4. The positive electrode active material according to claim 1, characterized in that, The positive electrode active material includes a positive electrode active material matrix, a transition layer covering at least a portion of the surface of the positive electrode active material matrix, and a coating layer covering at least a portion of the surface of the transition layer; The content of +2 valent nickel in the transition layer is greater than the content of +2 valent nickel in the positive electrode active material matrix.

5. The positive electrode active material according to claim 4, characterized in that, The coating layer includes a piezoelectric material; And / or, the thickness of the coating layer is 1nm-18nm; And / or, the coating layer accounts for 0.3-5% of the mass percentage of the positive electrode active material.

6. The positive electrode active material according to claim 5, characterized in that, The chemical composition of the piezoelectric material is Li. a X b Y c Z d O3, wherein a+b=1, c+d=1, 0≤b≤0.1, 0≤d≤0.5, X is selected from at least one of Mg, Zn, Fe, Cu, Na, K, Y is selected from Nb and / or Ta, and Z is selected from at least one of Ta, Ti, Zr, Sb, Hf, In, Nd, Sc, Er, Tb; And / or, the chemical composition of the positive electrode active material matrix is ​​Li e Ni f Co g M h Q i O2, wherein 0.95≤e≤1.05, 0<i≤0.05, 0.60≤f<1, 0.01≤g<0.40, f+g<1, h=1-fg; M includes Mn and / or Al, and Q is selected from at least one of Al, Zr, Ti, Na, K, Cs, Ca, Sr, Y, Ba, La, Ce, Nb, Ta, W, Mo, and Sb.

7. The positive electrode active material according to any one of claims 1-6, characterized in that, The particle size distribution of the positive electrode active material is SPAN≤2.

8. A method for preparing a positive electrode active material as described in any one of claims 1-7, characterized in that, Includes the following steps: 1) The first system, including the positive electrode active material precursor, lithium source, and Q source, is sintered to obtain the sintered product; The chemical composition of the positive electrode active material precursor is Ni. x Co y M 1-x-y (OH)2, where 0.60≤x<1, 0.01≤y<0.40, z=1-xy, and M includes Mn and / or Al; 2) The sintered product is subjected to air quenching treatment to obtain an intermediate; 3) The second system, including the intermediate and the coating material, is coated to obtain the positive electrode active material.

9. The method for preparing the positive electrode active material according to claim 8, characterized in that, The sintering treatment is performed at a temperature of 650-950℃ for 15-24 hours, with a heating rate of 2-10℃ / min. And / or, the coating treatment is performed at a temperature of 250-500℃ for 8-20 hours, with a heating rate of 1-5℃ / min; And / or, the coating material includes a piezoelectric material; And / or, the mass ratio of the intermediate to the coating material is 100:(0.5-5).

10. The method for preparing the positive electrode active material according to claim 8 or 9, characterized in that, The air quenching process includes: cooling the sintered product to 10-30°C at a rate of 100-200°C / min in an air atmosphere.

11. A positive electrode plate, characterized in that, The positive electrode active material includes the positive electrode active material according to any one of claims 1-7 or the positive electrode active material prepared according to the preparation method of the positive electrode active material according to any one of claims 8-10.

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

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