Positive electrode material and preparation method therefor, and lithium ion battery

Abstract

The present application relates to the technical field of lithium ion batteries, and particularly to a positive electrode material and a preparation method therefor, and a lithium ion battery. The positive electrode material is a lithium nickel cobaltate-based composite oxide, the particle size distribution curve of the positive electrode material has a first characteristic peak and a second characteristic peak, the peak area of the first characteristic peak is A1, the peak area of the second characteristic peak is A2, and P=A2 / A1; the free lithium stabilization coefficient of the positive electrode material is L, L=(L1-L2) / L1, and a measurement method for L1 and L2 comprises: dispersing 5 g of the positive electrode material in 100 mL of deionized water, magnetically stirring for t min, performing suction filtration to obtain a filtrate, and measuring the free lithium content, wherein when t=60, the measured mass content of free lithium in the positive electrode material is L1; when t=10, the measured mass content of free lithium in the positive electrode material is L2; and the positive electrode material satisfies the following relational expressions: 10≤G≤25 and G=P*L.

Description

Positive electrode material and preparation method thereof, and lithium ion battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the National Intellectual Property Administration of China on December 25, 2023, with application number "202311803462.2" and application name "Positive Electrode Materials and Preparation Methods, Lithium-ion Batteries", all of the contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the technical field of lithium-ion batteries, and in particular to a positive electrode material and a preparation method thereof, and a lithium-ion battery. Background Art

[0004] As the global energy crisis and environmental pollution become increasingly severe, countries around the world are calling for carbon emissions reduction and the development of sustainable, clean energy to replace traditional fossil fuels. Lithium-ion batteries, as a new type of high-energy, green battery, offer higher energy density, longer cycle life, and a wider range of applications compared to traditional energy batteries. In recent years, fueled by generous government subsidies and market demand for new energy, lithium-ion batteries have experienced rapid development. As the core component of lithium-ion batteries, cathode materials determine their overall performance, and the development of high-performance cathode materials has long been a research hotspot.

[0005] High-nickel cathode materials offer advantages such as a high voltage platform and high specific capacity, making them the most promising cathode materials for large-scale application in the power battery market. However, as the nickel content continues to increase, the residual alkalinity in the cathode material increases, thereby affecting the cycling stability of the cathode material.

[0006] Summary of the Invention

[0007] The present application provides a positive electrode material and a preparation method thereof, and a lithium-ion battery, which can improve the cycle performance of lithium nickel cobalt oxide-based positive electrode materials.

[0008] In a first aspect, the present application provides a positive electrode material, wherein the positive electrode material is a lithium nickel cobalt oxide composite oxide;

[0009] The particle size distribution curve of the positive electrode material has a first characteristic peak and a second characteristic peak, the peak area of ​​the first characteristic peak is A1, the peak area of ​​the second characteristic peak is A2, and P=A2 / A1;

[0010] The free lithium stability coefficient of the positive electrode material is L, L = (L1-L2) / L1, and the test method for L1 and L2 is as follows: 5 g of the positive electrode material is dispersed in 100 mL of deionized water, magnetically stirred for t min, and the filtrate is filtered to determine the free lithium content; when t = 60, the mass content of free lithium in the positive electrode material is measured to be L1, and when t = 10, the mass content of free lithium in the positive electrode material is measured to be L2;

[0011] The positive electrode material satisfies the following relationship: 10≤G≤25, wherein G=P*L.

[0012] In a second aspect, the present application also proposes a method for preparing a positive electrode material, comprising the following steps:

[0013] Adding a free lithium ion conversion agent to an aqueous solution of a base material for modification treatment, wherein the amount of the free lithium ion conversion agent added is 0.6 wt % to 1.2 wt % based on 100 wt % of the base material, and performing solid-liquid separation to obtain a precursor;

[0014] Sintering the precursor to obtain a positive electrode material, wherein a particle size distribution curve of the positive electrode material has a first characteristic peak and a second characteristic peak, the peak area of ​​the first characteristic peak is A1, the peak area of ​​the second characteristic peak is A2, and P=A2 / A1;

[0015] The free lithium stability coefficient of the positive electrode material is L, L = (L1-L2) / L1, and the test method for L1 and L2 is as follows: 5 g of the positive electrode material is dispersed in 100 mL of deionized water, magnetically stirred for t min, and the filtrate is filtered to determine the free lithium content; when t = 60, the mass content of free lithium in the positive electrode material is measured to be L1, and when t = 10, the mass content of free lithium in the positive electrode material is measured to be L2;

[0016] The positive electrode material satisfies the following relationship: 10≤P*L≤25.

[0017] In a third aspect, the present application further proposes a lithium-ion battery, comprising the positive electrode material as described above, or comprising the positive electrode material prepared by the preparation method as described above.

[0018] Compared with the existing technology, this technical solution has at least the following technical effects:

[0019] The positive electrode material of the present application includes a lithium nickel cobalt oxide positive electrode material, which satisfies the relationship: 10≤G≤25, has the characteristics of excellent cycle performance, and solves the problem in the prior art that the application of lithium nickel cobalt oxide positive electrode materials is limited due to poor cycle performance. During the research process, the applicant found through reasoning and verification that there is a certain correlation between the free lithium stability coefficient L and the peak area ratio P. The area of ​​the grain boundary can be changed by changing the peak area A1 of the first characteristic peak and the peak area ratio of the second characteristic peak A2. Specifically, the smaller the peak area ratio, the more grains in the small particle size range, which leads to an increase in the number of grain boundaries and an increase in the total grain boundary area, so that there are more grain boundary surfaces that can adsorb free lithium, and the free lithium in the grain boundary is difficult to react with carbon dioxide and water in the air to generate residual alkali, thereby reducing the conversion efficiency of free lithium; and the free lithium in the grain boundary is also easy to precipitate and react with the electrolyte during the charge and discharge process, affecting the cycle performance. The larger the peak area ratio, the fewer grains in the small particle size range, resulting in a decrease in the number of grain boundaries and a decrease in the total grain boundary area. As a result, less free lithium is absorbed by the grain boundary surface, and most of the free lithium in the positive electrode material can react with carbon dioxide and water in the air to form residual alkali, thereby improving the conversion efficiency of free lithium. Therefore, by controlling the P value, the free lithium content in the grain boundary can be reduced and the free lithium conversion efficiency can be improved. However, although the conversion efficiency of free lithium can be controlled to a certain extent by controlling the P value, the free lithium remaining at the grain boundary cannot be completely eliminated by controlling the P value. Therefore, on the basis of controlling the peak area ratio P, the inventors further introduced a free lithium stability coefficient L to control the precipitation stability of the free lithium remaining at the grain boundary. When the relationship between the free lithium coefficient L and the peak area ratio P satisfies: 10≤G≤25, the surface free lithium content of the positive electrode material is low and the stability of the residual lithium in the grain boundary is high, so that the positive electrode material has good structural stability and excellent cycle performance during the charge and discharge process.

[0020] In the preparation method of the present application, the peak area ratio P is limited to an appropriate range by regulating the particle size of the matrix material and the matching ratio of the particles, so that the matrix material has a good free lithium conversion efficiency, and then by adding a free lithium ion converter to the aqueous solution of the matrix material, the free lithium ion converter will react with the free lithium to form a lithium salt coating layer coated on the surface of the matrix material. The lithium salt coating layer can form a physical barrier on the surface of the matrix material, inhibiting the precipitation of residual lithium in the grain boundaries, thereby achieving control of the free lithium stability coefficient, so that the positive electrode material satisfies 10≤G≤25, and comprehensively improving the structural stability and cycle performance of the positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present application is further described below with reference to the accompanying drawings and examples.

[0022] FIG1 is a process flow chart of the preparation method of the positive electrode material of the present application;

[0023] Figures 2-25 are particle size distribution diagrams of Examples 1-14 and Comparative Examples 1-10, respectively;

[0024] FIG26 is an XRD diagram of Example 1 and Example 5. DETAILED DESCRIPTION

[0025] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0026] It should be clear that the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0027] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0028] It should be understood that the term "and / or" as used in this application is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this application generally indicates that the associated objects are in an "or" relationship.

[0029] In the first aspect, the present application proposes a positive electrode material, which includes a lithium nickel cobalt oxide composite oxide. The particle size distribution curve of the positive electrode material includes a first characteristic peak and a second characteristic peak, the peak area of ​​the first characteristic peak is A1, the peak area of ​​the second characteristic peak is A2, and P = A2 / A1; the free lithium stability coefficient of the positive electrode material is L, L = (L1-L2) / L1, and the test method for L1 and L2 is as follows: take 5g of the positive electrode material and disperse it in 100mL of deionized water, magnetically stir for tmin, filter and obtain the filtrate for free lithium content determination; when t = 60, the mass content percentage of free lithium in the positive electrode material is measured to be L1%, and when t = 10, the mass content percentage of free lithium in the positive electrode material is measured to be L2%; the positive electrode material satisfies the following relationship: 10≤G≤25, where G = P*L. It should be noted that in the present application, the lithium nickel cobalt oxide composite oxide refers to lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide.

[0030] The positive electrode material of the present application includes a lithium nickel cobalt oxide positive electrode material, which satisfies the relationship: 10≤G≤25, has the characteristics of excellent cycle performance, and solves the problem in the prior art that the application of lithium nickel cobalt oxide positive electrode materials is limited due to poor cycle performance. During the research process, the applicant found through reasoning and verification that there is a certain correlation between the free lithium stability coefficient L and the peak area ratio P. The area of ​​the grain boundary can be changed by changing the peak area A1 of the first characteristic peak and the peak area ratio of the second characteristic peak A2. Specifically, the smaller the peak area ratio, the more grains in the small particle size range, which leads to an increase in the number of grain boundaries and an increase in the total grain boundary area, so that there are more grain boundary surfaces that can adsorb free lithium, and the free lithium in the grain boundary is difficult to react with carbon dioxide and water in the air to generate residual alkali, thereby reducing the conversion efficiency of free lithium; and the free lithium in the grain boundary is also easy to precipitate and react with the electrolyte during the charge and discharge process, affecting the cycle performance. The larger the peak area ratio, the fewer grains in the small particle size range, resulting in a decrease in the number of grain boundaries and a decrease in the total grain boundary area. As a result, less free lithium is absorbed by the grain boundary surface, and most of the free lithium in the positive electrode material can react with carbon dioxide and water in the air to form residual alkali, thereby improving the conversion efficiency of free lithium. Therefore, by controlling the P value, the free lithium content in the grain boundary can be reduced and the free lithium conversion efficiency can be improved. However, although the conversion efficiency of free lithium can be controlled to a certain extent by controlling the P value, the free lithium remaining at the grain boundary cannot be completely eliminated by controlling the P value. Therefore, on the basis of controlling the peak area ratio P, the inventors further introduced a free lithium stability coefficient L to control the precipitation stability of the free lithium remaining at the grain boundary. When the relationship between the free lithium coefficient L and the peak area ratio P satisfies: 10≤G≤25, the free lithium content on the surface of the positive electrode material is low and the stability of the free lithium in the grain boundary is high, so that the positive electrode material has good structural stability and excellent cycle performance during the charge and discharge process.

[0031] In some embodiments, the chemical formula of the positive electrode material is: LifNi a Co b Mn c M d N eO₂, where 0.8 < a < 0.98, b < 0.2, c < 0.2, 0.02 < d < 0.1, 0.02 < e < 0.1, a + b + c + d + e = 1, 0.95 ≤ f ≤ 1.05, and M includes at least one of Sr, Ti, Al, Zr, W, Ba, Mg, Nb, and the N includes at least one of W, B, Mo, F, S, V, P, and Cl. Specifically, a can be 0.81, 0.83, 0.88, 0.92, 0.96, b can be 0.1, 0.12, 0.15, 0.18, c can be 0.05, 0.1, 0.15, 0.18, d can be 0.02, 0.04, 0.05, 0.08, e can be 0.02, 0.04, 0.05, 0.08. f can be 0.95, 0.98, 1.01, 1.03, 1.04, or 1.05. In some embodiments, the positive electrode material includes a matrix material and a coating layer located on at least a part of the surface of the matrix material. The matrix material is a composite oxide including Ni, Co, Mn, and M element, and M includes at least one of Sr, Ti, Al, Zr, W, Ba, Mg, Nb; wherein, at least the M element is at least partially doped into the lattice of the matrix material, and the doping of the M element can construct an ionic conductor transport layer in the matrix material, which is beneficial to improving the conductivity of the positive electrode material.

[0032] In some embodiments, the coating layer includes lithium salt, and the chemical formula of the lithium salt is Li x N y O z , where x, y, z are each independently greater than 0, and N includes at least one of W, B, Mo, F, S, V, P, and Cl elements; Li x N y O z The structure of the coating layer is stable, which can effectively improve the cycle performance and safety performance of the positive electrode material. Specifically, Li x N y O z includes any one of LiWO₄, Li₂PO₄, Li₂SO₄, or LiClO₄.

[0033] In some embodiments, 0.25 ≤ L ≤ 0.85; in the present application, L is the free lithium stability coefficient of the positive electrode material, which is used to measure the stability of free lithium in the positive electrode material. If L is too high, it indicates that there are more lithium ions in unstable states inside the positive electrode material, and free lithium is easily dissolved out, resulting in poor stability of the structural functional layer on the surface of the positive electrode material; if L is too low, it means that the lattice lithium in the positive electrode material has suffered a certain loss, causing some stable Li to dissolve out. By limiting L within the above range, it is beneficial to control the stability of free lithium in the positive electrode material, thereby being beneficial to improving the structural stability of the positive electrode material and being beneficial to enhancing the cycle performance of the positive electrode material.

[0034] In some embodiments, L1 is 0.15% to 0.45%, specifically 0.15%, 0.25%, 0.35%, 0.45% or any value therebetween.

[0035] In some embodiments, L2 is 0.02% to 0.16%, specifically 0.02%, 0.08%, 0.12%, 0.16% or any value therebetween.

[0036] In some embodiments, L is 0.25 to 0.85, specifically 0.250, 0.278, 0.318, 0.506, 0.538, 0.57, 0.640, 0.682, 0.728, 0.737, 0.742, 0.831, 0.850 or a range consisting of any two values.

[0037] In some embodiments, A1 is 4 to 25, specifically 4, 8, 12, 16, 20, 25 or any value therebetween.

[0038] In some embodiments, A2 is 150-250, specifically 150, 200, 250 or any value therebetween.

[0039] In some embodiments, G is 10-25, specifically 10.57, 12.05, 12.63, 12.81, 12.94, 13.44, 13.47, 16.51, 16.8, 17.12, 19.19, 21.183, 24.02, or a range consisting of any two values.

[0040] In some embodiments, 8≤P≤50; ​​specifically, P can be 16.23, 18.27, 18.72, 20.21, 20.88, 21.36, 23.52, 27.36, 30.23, 39.34, 40.27, 45.48, or a range of any two values. In the present application, P is essentially the ratio of the peak area of ​​the volume density occupied by large particles to the peak area of ​​the volume density occupied by small particles in the positive electrode material. The area of ​​the grain boundary can be changed by changing the peak area ratio of the peak area A1 of the first characteristic peak and the peak area ratio of the second characteristic peak A2. Specifically, the smaller the peak area ratio, the more grains in the small particle size range, which leads to an increase in the number of grain boundaries and an increase in the total grain boundary area, thereby having more grain boundary surfaces for adsorbing free lithium. The free lithium in the grain boundary is difficult to react with carbon dioxide and water in the air to form residual alkali, thereby reducing the conversion efficiency of free lithium. The larger the peak area ratio, the smaller the number of grains in the small particle size range, which leads to a decrease in the number of grain boundaries and a decrease in the total grain boundary area. As a result, less free lithium is absorbed by the grain boundary surface. Most of the free lithium in the positive electrode material can react with carbon dioxide and water in the air to generate residual alkali, thereby improving the conversion efficiency of free lithium. By controlling the P value within the range of 8≤P≤50, the content of free lithium in the grain boundary can be controlled, and the conversion efficiency of free lithium can be improved to improve the structural stability and cycle performance of the positive electrode material.

[0041] In some embodiments, the conductivity of the positive electrode material is 0.025 S / cm to 0.080 S / cm, specifically 0.025 S / cm, 0.040 S / cm, 0.060 S / cm, 0.080 S / cm or any value therebetween.

[0042] In some embodiments, the compacted density of the positive electrode material is 3.10 g / cm 3 ~3.65g / cm 3 , specifically 3.10 g / cm 3 、3.20g / cm 3 、3.30g / cm 3 、3.40g / cm 3 、3.50g / cm 3 、3.65g / cm 3 or any value in between.

[0043] In some embodiments, the specific surface area of ​​the positive electrode material is 0.4 m 2 / g~0.8m 2 / g, specifically 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m2 / g or any value in between.

[0044] Secondly, the present application also proposes a method for preparing a positive electrode material.

[0045] Referring to FIG1 , in an embodiment of the present application, the method for preparing the positive electrode material includes the following steps:

[0046] S1. Adding a free lithium ion conversion agent to an aqueous solution of a base material for modification to obtain a modified mixture, and performing solid-liquid separation on the modified mixture to obtain a precursor; wherein the base material is a lithium nickel cobalt oxide composite oxide, and the particle size distribution curve of the base material has a first characteristic peak and a second characteristic peak, the peak area of ​​the first characteristic peak is A1, the peak area of ​​the second characteristic peak is A2, P = A2 / A1, 8≤P≤50;

[0047] S2. Sintering the precursor to obtain a positive electrode material.

[0048] In the preparation method of the present application, the peak area ratio P is limited to an appropriate range by regulating the particle size of the matrix material and the matching ratio of the particles, so that the matrix material has a good free lithium conversion efficiency, and then a free lithium ion converter is added to the aqueous solution of the matrix material, so that the free lithium ion converter can react with the free lithium in the matrix material to form a lithium salt coating layer coated on the surface of the matrix material. The lithium salt coating layer can form a physical barrier on the surface of the matrix material, inhibiting the precipitation of residual lithium in the grain boundaries, thereby achieving control of the free lithium stability coefficient, so that the positive electrode material satisfies 10≤P*L≤25, and comprehensively improving the structural stability and cycle performance of the positive electrode material.

[0049] The preparation method of the present application is described in detail below with reference to the examples:

[0050] In some embodiments, based on the mass of the matrix material as 100 wt%, the added amount of the free lithium ion converter is 0.6 wt%-1.2 wt%, specifically 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.1 wt%, 1.2 wt% or any value therebetween.

[0051] In some embodiments, the free lithium ion conversion agent contains N, and N includes at least one of W, B, Mo, F, S, V, P, and Cl elements.

[0052] In some embodiments, the free lithium ion conversion agent includes at least one of KAl(SO4)2, NH4HSO4, MgCl, NH4Cl, CaF, NH4HWO4, NH4MoO4, NH4HBO3, NH4HF2, NaVO3, NH4VO3, (NH4)3PO4, (NH4)2HPO4, and Ca(H2PO4)2. In this embodiment, after the free lithium ion conversion agent is added to the aqueous solution of the matrix material, it will be hydrolyzed into cations or cationic groups and anions or anionic groups, wherein the anions or anionic groups will combine with the lithium ions in the residual lithium (lithium hydroxide, lithium carbonate) on the surface of the matrix material to form lithium salts (Li2PO4) in situ on the surface of the matrix material. x N y O z ) molecular layer, such as Li2WO4, Li3BO3, LiMoO4, LiVO3, Li2SO4, Li3PO4 molecular layer, etc. x N y O z The compound is usually structurally stable and can form a physical barrier on the surface of the matrix material, inhibiting the precipitation of lithium in the grain boundary and improving the stability of the free lithium in the positive electrode material, thereby effectively improving the cycle performance of the positive electrode material. On the other hand, the cation or cationic group will react with the OH- and CO3 in the residual lithium. 2- A redox reaction occurs, generating H2O and CO2, which are then discharged. In this embodiment, the free lithium ion converter not only reduces the free lithium on the surface of the positive electrode material, but also inhibits the precipitation of lithium within the grain boundaries, thereby improving the free lithium stability of the positive electrode material and thus improving the cycle performance of the positive electrode material.

[0053] In some embodiments, the lithium salt molecular layer is Li3PO4, and the Li3PO4 protective layer can more effectively reduce the occurrence of structural damage and side reactions during the cycle process.

[0054] In some embodiments, during the sintering process of the precursor, the sintering temperature is 250°C to 500°C, specifically 250°C, 300°C, 350°C, 400°C, 450°C, 500°C or any value therebetween.

[0055] In some embodiments, during the sintering process of the precursor, the sintering time is 6 hours to 12 hours, specifically 6 hours, 8 hours, 10 hours, 12 hours, or any value therebetween.

[0056] In some embodiments, in the aqueous solution of the matrix material, the mass of deionized water is 15% to 30% of the mass of the matrix material, specifically 15%, 20%, 25%, 30% or any value therebetween.

[0057] In some embodiments, the step of preparing the aqueous solution of the matrix material includes mixing the matrix material with deionized water and stirring the mixture uniformly. During the preparation of the aqueous solution of the matrix material, the deionized water will elute some of the residual lithium on the surface of the matrix material, dispersing the residual lithium in the deionized water. By uniformly dispersing the matrix material in the deionized water, the activity of the residual lithium on the surface of the matrix material can be enhanced, facilitating subsequent modification of the matrix material by the free lithium ion conversion agent.

[0058] In some embodiments, the stirring speed is 20 Hz to 50 Hz, specifically 20 Hz, 30 Hz, 40 Hz, 50 Hz, or any value therebetween. Controlling the stirring speed within this range helps keep the P value within an appropriate range. Excessively high stirring speeds can easily lead to the loss of small particles, which can damage material stability and result in a high P value. Excessively low stirring speeds can cause uneven stirring and poor removal of residual alkali.

[0059] In some embodiments, the stirring time is 20 to 40 minutes, specifically 20 minutes, 30 minutes, 40 minutes, or any value therebetween. Controlling the stirring time within this range helps maintain the P value within an appropriate range. Excessive stirring time can easily lead to the loss of small particles, which can destabilize the material and result in a high P value. Excessively short stirring time can result in uneven stirring and poor removal of residual alkali.

[0060] In some embodiments, the matrix material is a composite oxide including Li, Ni, Co, and Mn elements. The composite oxide refers to an oxide containing at least two of the elements Li, Ni, Co, and Mn.

[0061] In some embodiments, the step of preparing the matrix material includes: preparing a mixture material including a ternary precursor and a lithium source, and sintering the mixture material under an oxygen atmosphere to obtain the matrix material.

[0062] In some embodiments, during the preparation step of the matrix material, the oxygen flow rate of the oxygen atmosphere is 200m 3 / h~450m 3 / h, specifically 200m 3 / h、250m 3 / h、300m 3 / h、350m 3 / h、400m 3 / h、450m 3 By controlling the oxygen flow rate of the oxygen atmosphere within the above range, it is advantageous to control the P value within the range of 8≤P≤50.

[0063] In some embodiments, during the preparation of the matrix material, the sintering furnace pressure is 3 Pa to 25 Pa, specifically 3 Pa, 6 Pa, 9 Pa, 12 Pa, 15 Pa, 18 Pa, 21 Pa, 23 Pa, 25 Pa, or any value therebetween. By controlling the sintering furnace pressure within the above range, it is advantageous to control the P value within 8 ≤ P ≤ 50.

[0064] In some embodiments, during the preparation of the matrix material, sintering includes a constant temperature stage. The sintering temperature during the constant temperature stage is 600°C-800°C, specifically 600°C, 700°C, 800°C, or any value therebetween. Controlling the sintering temperature during the constant temperature stage within the aforementioned range facilitates controlling the P value within the range of 8 ≤ P ≤ 50.

[0065] In some embodiments, the sintering time in the constant temperature stage is 8 hours to 15 hours, specifically 8 hours, 10 hours, 12 hours, 15 hours, or any value therebetween. By controlling the sintering time in the constant temperature stage within the above range, it is beneficial to control the P value within 8≤P≤50.

[0066] In some embodiments, in the preparation step of the matrix material, sintering also includes a heating stage, and the heating rate of the heating stage is 2°C / min to 5°C / min, specifically 2°C / min, 3°C / min, 4°C / min, 5°C / min or any value therebetween; during the sintering process, the sintering temperature is raised to 600°C-800°C at a heating rate of 2°C / min to 5°C, and then a constant temperature stage is performed for constant temperature sintering.

[0067] In some embodiments, the chemical formula of the ternary precursor is Ni a Co b Mn c (OH)2, 0.8≤a≤0.98, 0.01≤b≤0.2.0.01≤c≤0.2.

[0068] In some embodiments, the ternary precursor includes first particles (large particles) and second particles (small particles) of different particle sizes. The chemical expressions of the first particles and the second particles can be the same or different. The particle size D50 of the first particles is 12μm-18μm, specifically 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, or any value therebetween. The particle size of the first particles will affect the specific surface area of ​​the positive electrode material. The smaller the particle size, the larger the specific surface area, and the positive electrode material is more likely to react with water and carbon dioxide in the air, resulting in an increase in residual lithium. By controlling the particle size D50 of the first particles within the above range, it is beneficial to reduce the amount of residual lithium on the surface of the positive electrode material.

[0069] In some embodiments, the particle size D50 of the second particles is 2 μm-5 μm, specifically 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or any value therebetween. Similarly, the particle size of the second particles affects the specific surface area of ​​the positive electrode material. The smaller the particle size, the larger the specific surface area, and the positive electrode material is more likely to react with water and carbon dioxide in the air, resulting in an increase in residual lithium. By controlling the particle size D50 of the second particles within the above range, the amount of residual lithium on the surface of the positive electrode material can be reduced.

[0070] In some embodiments, the particle size D50 of the first particles is 12 μm-18 μm, and the particle size D50 of the second particles is 2 μm-5 μm. By controlling the particle sizes of the first and second particles simultaneously within the above ranges, it is beneficial to improve the compatibility of the first and second particles, improve the compaction density and structural stability of the positive electrode material, and thus further improve the conductivity and cycle performance of the positive electrode material.

[0071] In some embodiments, the mass ratio of the first particles to the second particles is 1:(1-5), specifically 1:1, 1:2, 1:3, 1:4, 1:5, or any value therebetween. By controlling the mass ratio of the first particles to the second particles within the above range, the cycling performance of the positive electrode material can be further improved.

[0072] In some embodiments, the lithium source includes at least one of hydrated lithium hydroxide, lithium hydroxide, lithium carbonate, lithium acetate, lithium nitrate, and lithium oxalate.

[0073] In some embodiments, the molar ratio of the lithium element in the lithium source to the ternary precursor is 0.95 to 1.25, specifically 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, or any value therebetween. By controlling the molar ratio of the lithium element in the lithium source to the ternary precursor within the above range, it is beneficial to improve the binding force between the lithium element and the precursor, stabilize the crystal structure, release capacity, and improve cycle performance.

[0074] In some embodiments, the matrix material is doped with an M element, and the M element includes at least one of Sr, Ti, Al, Zr, W, Ba, Mg, and Nb.

[0075] In some embodiments, the mixed material also includes an M dopant; during the preparation of the matrix material, the M element in the M dopant will construct an ion conductor transport layer together with other metal elements in the ternary precursor, which is beneficial to improving the electrical conductivity of the positive electrode material.

[0076] In some embodiments, the M dopant includes at least one of Sr(OH)2, SrO, TiO2, Al2O3, Al(OH)3, ZrO2, Zr(OH)4, Ba(OH)2, BaO, MgO, Mg(OH)2, Nb2O5, Nb2O3, WO3 and CaWO4.

[0077] In some embodiments, the mass of the M dopant is 0.1% to 0.55% of the mass of the ternary precursor, specifically 0.1%, 0.2%, 0.3%, 0.4%, 0.55%, or any value therebetween. Preferably, the mass of the M dopant is 0.2% to 0.4% of the mass of the ternary precursor, specifically 0.2%, 0.3%, 0.4%, or any value therebetween. By controlling the amount of the M dopant added within an appropriate range, it is beneficial to improve the conductivity of the positive electrode material while taking into account the performance of the positive electrode material, such as capacity and cycle performance.

[0078] In some embodiments, the modification process is performed in an ultrasonic environment. Ultrasonic waves have good directionality and easily obtain concentrated acoustic energy. During the modification process, ultrasonic induction provides energy for the free lithium conversion agent to participate in the reaction, forming a highly reactive environment. At the same time, ultrasonic cavitation induces molecular aggregation, accelerates the diffusion of reactants and the formation of a coating layer, and achieves uniform mixing between the reactants. Under ultrasonic induction, the distribution uniformity of elements is significantly improved. The lithium salt compound generated by the reaction will form a structural protective layer on the surface of the positive electrode material in a directionally controlled manner, thereby protecting the main structure of the positive electrode material from loss and effectively improving the cycle performance of the positive electrode material.

[0079] In some embodiments, the frequency of the ultrasonic wave is 20kHz to 50kHz, specifically 20kHz, 30kHz, 40kHz, 50kHz, or any value therebetween. The frequency of the ultrasonic wave affects the conversion rate of residual lithium on the surface of the positive electrode material and the structural stability of the coating layer on the surface of the positive electrode material, thereby affecting the cycle performance of the positive electrode material. By controlling the frequency of the ultrasonic wave within the above range, it is beneficial to control the P value within 8≤P≤50 and reduce the content of free lithium in the positive electrode material, thereby improving the cycle performance of the positive electrode material.

[0080] In some embodiments, the ultrasonic time is 20 min-40 min, specifically 20 min, 30 min, 40 min or any value therebetween. Similarly, the ultrasonic time of the ultrasound wave will also affect the conversion rate of residual lithium on the surface of the positive electrode material and the structural stability of the coating layer on the surface of the positive electrode material, thereby affecting the cycle performance of the positive electrode material. By controlling the ultrasonic time of the ultrasound wave within 20-40 min, it is beneficial to adjust the P value to 8≤P≤50 and reduce the content of free lithium in the positive electrode material, thereby improving the cycle performance of the positive electrode material.

[0081] In some embodiments, the solid-liquid separation includes subjecting the modified mixture to a filter press treatment, wherein the extrusion pressure of the filter press is 0.2 MPa-0.5 MPa, specifically 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa or any value therebetween.

[0082] In some embodiments, the filtration time is 10 min-30 min, specifically 10 min, 20 min, 30 min or any value therebetween.

[0083] In some embodiments, after the filter press treatment, the solid-liquid separation further includes drying the modified mixture in succession, and the drying temperature is 80-170°C, specifically 80°C, 100°C, 120, 140°C, 160°C, 170°C or any value therebetween.

[0084] In some embodiments, the drying time is 1 h to 3 h, specifically 1 h, 2 h, 3 h or any value therebetween.

[0085] The positive electrode material prepared by the preparation method of the present application has a particle size distribution curve having a first characteristic peak and a second characteristic peak, the peak area of ​​the first characteristic peak is A1, the peak area of ​​the second characteristic peak is A2, P=A2 / A1, the free lithium stability coefficient is L, L=(L1-L2) / L1, and the testing method for L1 and L2 is: take 5g of the positive electrode material and disperse it in 100mL of deionized water, magnetically stir for t min, and filter to obtain the filtrate for free lithium content determination; when t=60, the mass content of free lithium in the positive electrode material is measured to be L1%, when t=10, the mass content of free lithium in the positive electrode material is measured to be L2%, and the positive electrode material satisfies the following relationship: 10≤G≤25, wherein G=P*L.

[0086] In a third aspect, the present application further proposes a lithium-ion battery, which includes the positive electrode material as described above, or includes the positive electrode material prepared by the above preparation method.

[0087] The above is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application.

[0088] The following further illustrates the embodiments of the present application in multiple embodiments. The embodiments of the present application are not limited to the following specific embodiments, and can be appropriately modified and implemented within the scope of the unchanged main rights.

[0089] Example 1

[0090] (1) Take large particle precursor Ni a Co b Mn c (OH)2 (i.e., the first particle), wherein the molar ratio of Ni, Co, and Mn is 88.5:9.0:2.5, and the particle size D50 is 16 μm; and, taking the small particle precursor NiaCobMnc(OH)2 (i.e., the second particle), wherein the molar ratio of Ni, Co, and Mn is 88.5:9.0:2.5, and the particle size D50 is 3 μm; the large particle precursor and the small particle precursor are mixed in a weight ratio of 1:4 to obtain the mixed precursor Ni 88.5 Co9Mn 2.5 (OH)2.

[0091] (2) The obtained precursor Ni 88.5 Co9Mn 2.5 (OH)2 and LiOH are mixed with dopants Al(OH)3, TiO2 and Sr(OH)2, and ground and pulverized. 88.5 Co9Mn 2.5 The molar ratio of (OH)2 to lithium source LiOH is 1.02, and the precursor Ni 88.5 Co9Mn 2.5 The mass of (OH)2 is 100wt%, the content of Al(OH)3 is 0.2wt%, the content of TiO2 is 0.1wt%, and the content of Sr(OH)2 is 0.2wt%; the mixed material is then heated to 750°C at a rate of 2°C / min under an oxygen atmosphere, and then sintered at a constant temperature for 10 hours, cooled, sieved and crushed to obtain a matrix material.

[0092] (3) Weigh 200 g of the obtained matrix material and put it into a reactor, add deionized water, the content of deionized water is 25 wt% of the weight of the matrix material, set the stirring speed to 30 Hz, and stir for 30 minutes; after the stirring is completed, put the reactor into an ultrasonic vibrator, set the transducer frequency to 35 kHz, add a free lithium ion converter (NH4)2HPO4, the content of (NH4)2HPO4 is 0.8 wt% of the matrix material content, and ultrasonic vibration is carried out for 30 minutes.

[0093] (4) The material obtained in (3) was placed in a filter press for filtration at a pressure of 0.4 MPa for 20 min. After filtration, the material was placed in an oven for drying at a temperature of 150°C for 120 min. The obtained material was then further sintered at a temperature of 400°C for 8 h to obtain a positive electrode material. The general chemical formula of the positive electrode material is: LiNi 0.88 Co 0.089 Mn 0.023 Al 0.0025 Ti 0.001 Sr 0.0015 S 0.003 O2.

[0094] 2 , which shows the peak area A1 of the first characteristic peak and the peak area A2 of the second characteristic peak of the positive electrode material prepared in Example 1. The specific test results of the free lithium content L1 and the free lithium content L2, as well as the calculated values ​​of L, P, and G, are shown in Table 1.

[0095] Example 2

[0096] The difference from Example 1 is that:

[0097] The D50 of the large particle precursor was changed to 12 μm, and the D50 of the small particle precursor was changed to 2.5 μm.

[0098] 3 , the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1 and the free lithium content L2 of the positive electrode material prepared in Example 2, as well as the calculated values ​​of L, P and G are shown in Table 1.

[0099] Example 3

[0100] The difference from Example 1 is that:

[0101] The D50 of the large particle precursor was changed to 18 μm, and the D50 of the small particle precursor was changed to 2.5 μm.

[0102] 4 , the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1 and the free lithium content L2 of the positive electrode material prepared in Example 3, as well as the calculated values ​​of L, P and G are shown in Table 1.

[0103] Example 4

[0104] The difference from Example 3 is that:

[0105] The constant temperature sintering temperature in step (2) was adjusted to 700°C.

[0106] 5 , the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1, and the free lithium content L2 of the positive electrode material prepared in Example 4, as well as the calculated values ​​of L, P, and G are shown in Table 1.

[0107] Example 5

[0108] The difference from Example 3 is that:

[0109] The dopant is replaced by 0.4wt% Al(OH)3, 0.2wt% TiO2, 0.2wt% Sr(OH)2 and 0.3wt% Ba(OH)2. The chemical formula of the positive electrode material is: LiNi 0.0878 Co 0.088 Mn 0.021 Al 0.005 Ti 0.002 Sr 0.0015 Ba 0.0015 S 0.003 O2.

[0110] In conjunction with Figure 6 , the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1, and the free lithium content L2 of the positive electrode material prepared in Example 5, as well as the calculated values ​​of L, P, and G are shown in Table 1. In addition, Figure 26 shows the XRD spectra of the positive electrode materials provided in Example 5 and Example 1. As can be seen from Figure 26 , the peak intensity ratio of the 003 peak to the 104 peak is greater in Example 5, and the layered structure of the positive electrode material is more obvious.

[0111] Example 6

[0112] The difference from Example 5 is that:

[0113] In step (3), (NH4)3PO4 with a matrix material content of 1.2 wt% is added. The general chemical formula of the positive electrode material is: LiNi 0.0878 Co 0.088 Mn 0.020 Al 0.005 Ti 0.002Sr 0.0015 Ba 0.0015 S 0.004 O2.

[0114] 7 , the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1, and the free lithium content L2 of the positive electrode material prepared in Example 6, as well as the calculated values ​​of L, P, and G are shown in Table 1.

[0115] Example 7

[0116] The difference from Example 6 is that:

[0117] The free lithium ion converter is changed to NH4HSO4. The general chemical formula of the positive electrode material is: LiNi 0.0879 Co 0.088 Mn 0.021 Al 0.005 Ti 0.002 Sr 0.0015 Ba 0.0015 S 0.002 O2.

[0118] 8 , the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1, and the free lithium content L2 of the positive electrode material prepared in Example 7, as well as the calculated values ​​of L, P, and G are shown in Table 1.

[0119] Example 8

[0120] The difference from Example 5 is that:

[0121] The free lithium ion converter is changed to (NH4)2HPO4 and NH4HSO4, the content of (NH4)2HPO4 is 0.4wt% of the matrix material content, and the content of NH4HSO4 is 0.4wt% of the matrix material content. The chemical formula of the positive electrode material is: LiNi 0.0880 Co 0.088 Mn 0.021 Al 0.005 Ti 0.002 Sr 0.0015 Ba 0.0015 S 0.001 O2.

[0122] 9 , the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1, and the free lithium content L2 of the positive electrode material prepared in Example 8, as well as the calculated values ​​of L, P, and G are shown in Table 1.

[0123] Example 9

[0124] The difference from Example 1 is that:

[0125] The content of the free lithium ion converter (NH4)2HPO4 added in step (3) is 0.6wt% of the matrix material content. The general chemical formula of the positive electrode material is: LiNi 0.881 Co 0.089 Mn 0.023 Al 0.0025 Ti 0.001 Sr 0.0015 S 0.002 In conjunction with FIG10 , the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1, and the free lithium content L2 of the positive electrode material prepared in Example 9, as well as the calculated values ​​of L, P, and G are shown in Table 1.

[0126] Example 10

[0127] The difference from Example 6 is that:

[0128] In step (3), the frequency of the transducer is 50 kHz.

[0129] 11 , the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1, and the free lithium content L2 of the positive electrode material prepared in Example 10, as well as the calculated values ​​of L, P, and G are shown in Table 1.

[0130] Example 11

[0131] The difference from Example 6 is that:

[0132] The stirring time in step (3) is 40 min.

[0133] 12 , the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1, and the free lithium content L2 of the positive electrode material prepared in Example 11, as well as the calculated values ​​of L, P, and G are shown in Table 1.

[0134] Example 12

[0135] The difference from Example 1 is that:

[0136] In step (1), the mixing mass ratio of large particle precursor to small particle precursor is changed to 1:1. In step (2), the lithium source is replaced with hydrated lithium hydroxide, and the precursor Ni 88.5 Co9Mn 2.5 The molar ratio of (OH)2 to lithium source LiOH is 1.01. The general chemical formula of the positive electrode material is: Li 0.995 Ni 0.881 Co0.089 Mn 0.023 Al 0.0025 Ti 0.001 Sr 0.0015 S 0.002 O2.

[0137] 13 , the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1, and the free lithium content L2 of the positive electrode material prepared in Example 12, as well as the calculated values ​​of L, P, and G are shown in Table 1.

[0138] Example 13

[0139] The difference from Example 1 is that:

[0140] In step (1), the mass ratio of the large particle precursor to the small particle precursor is changed to 1:5. In step (2), the lithium source is replaced with lithium nitrate, and the precursor Ni 88.5 Co9Mn 2.5 The molar ratio of (OH)2 to lithium source LiOH is 1.01. The general chemical formula of the positive electrode material is: Li 0.995 Ni 0.881 Co 0.089 Mn 0.023 Al 0.0025 Ti 0.001 Sr 0.0015 S 0.002 O2.

[0141] 14 , the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1, and the free lithium content L2 of the positive electrode material prepared in Example 13, as well as the calculated values ​​of L, P, and G are shown in Table 1.

[0142] Example 14

[0143] The difference from Example 1 is that:

[0144] The D50 of the small particle precursor was changed to 4 μm. In conjunction with Figure 15 , the specific test results of the first characteristic peak area A1, the second characteristic peak area A2, the free lithium content L1, and the free lithium content L2 of the positive electrode material prepared in Example 14, as well as the calculated values ​​of L, P, and G are shown in Table 1.

[0145] Example 15

[0146] The difference between this embodiment and embodiment 1 is that:

[0147] Take the large particle precursor Ni a Co b Mn c(OH)2 (i.e., the first particle), wherein the molar ratio of Ni, Co, and Mn is 82.5:10.0:7.5, and the particle size D50 is 16 μm; and, taking the small particle precursor NiaCobMnc(OH)2 (i.e., the second particle), wherein the molar ratio of Ni, Co, and Mn is 82.5:10.0:7.5, and the particle size D50 is 3 μm; the large particle precursor and the small particle precursor are mixed in a weight ratio of 1:4 to obtain the mixed precursor Ni 82.5 Co 10 Mn 7.5 (OH)2.

[0148] (2) The obtained precursor Ni 82.5 Co 10 Mn 7.5 (OH)2 and LiNO3 are mixed with dopants Al(OH)3, TiO2 and Sr(OH)2, and ground and crushed. 82.5 Co 10 Mn 7.5 The molar ratio of (OH)2 to lithium source LiNO3 is 1.15, and the precursor Ni 82.5 Co 10 Mn 7.5 The mass of (OH)2 is 100wt%, the content of Al(OH)3 is 0.2wt%, the content of TiO2 is 0.1wt%, and the content of Sr(OH)2 is 0.2wt%; the mixed material is then heated to 750°C at a rate of 2°C / min under an oxygen atmosphere, and then sintered at a constant temperature for 10 hours, cooled, sieved and crushed to obtain a matrix material.

[0149] The general chemical formula of the positive electrode material is: Li 1.03 Ni 0.82 Co 0.09 Mn 0.082 Al 0.0025 Ti 0.001 Sr 0.0015 S 0,003 O2.

[0150] Example 16

[0151] The difference between this embodiment and embodiment 1 is that:

[0152] Take the large particle precursor Ni a Co b Mn c (OH)2 (i.e., the first particle), wherein the molar ratio of Ni, Co, and Mn is 92.5:5.0:2.5, and the particle size D50 is 16 μm; and the small particle precursor Ni a Co b Mnc (OH)2 (i.e., the second particle), wherein the molar ratio of Ni, Co, and Mn is 92.5:5.0:2.5, and the particle size D50 is 3 μm; the large particle precursor and the small particle precursor are mixed in a weight ratio of 1:4 to obtain the mixed precursor Ni 92.5 Co5Mn 2.5 (OH)2.

[0153] (2) The obtained precursor Ni 92.5 Co5Mn 2.5 (OH)2 and Li2CO3 are mixed with dopants Al(OH)3, TiO2 and Sr(OH)2, and ground and crushed. 92.5 Co5Mn 2.5 The molar ratio of (OH)2 to lithium source Li2CO3 is 0.95, and the precursor Ni 88.5 Co9Mn 2.5 The mass of (OH)2 is 100wt%, the content of Al(OH)3 is 0.2wt%, the content of TiO2 is 0.1wt%, and the content of Sr(OH)2 is 0.2wt%; the mixed material is then heated to 750°C at a rate of 2°C / min under an oxygen atmosphere, and then sintered at a constant temperature for 10 hours, cooled, sieved and crushed to obtain a matrix material.

[0154] The general chemical formula of the positive electrode material is: Li 0.99 Ni 0.92 Co 0.048 Mn 0.024 Al 0.0025 Ti 0.001 Sr 0.0015 S 0,003 O2.

[0155] Comparative Example 1

[0156] The difference from Example 5 is that:

[0157] The free lithium ion converter was changed to 0.4 wt% (NH4)2HPO4.

[0158] 16 , the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1 and the free lithium content L2 of the positive electrode material prepared in Comparative Example 1, as well as the calculated values ​​of L, P and G are shown in Table 1.

[0159] Comparative Example 2

[0160] The difference from Example 5 is that:

[0161] The free lithium ion converter was changed to 1.3 wt% (NH4)2HPO4.

[0162] In conjunction with Figure 17, the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1 and the free lithium content L2 of the positive electrode material prepared in Comparative Example 2, as well as the calculated values ​​of L, P and G are shown in Table 1.

[0163] Comparative Example 3

[0164] The difference from Example 1 is that:

[0165] The mixing mass ratio of large particle precursor to small particle precursor was changed to 3:2.

[0166] In conjunction with Figure 18, the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1 and the free lithium content L2 of the positive electrode material prepared in Comparative Example 3, as well as the calculated values ​​of L, P and G are shown in Table 1.

[0167] Comparative Example 4

[0168] The difference from Example 1 is that:

[0169] The mixing mass ratio of the large particle precursor to the small particle precursor was changed to 1:6.

[0170] In conjunction with Figure 19, the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1 and the free lithium content L2 of the positive electrode material prepared in Comparative Example 4, as well as the calculated values ​​of L, P and G are shown in Table 1.

[0171] Comparative Example 5

[0172] The difference from Example 1 is that:

[0173] The D50 of the large particle precursor was changed to 22 μm.

[0174] In conjunction with Figure 20, the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1 and the free lithium content L2 of the positive electrode material prepared in Comparative Example 5, as well as the calculated values ​​of L, P and G are shown in Table 1.

[0175] Comparative Example 6

[0176] The difference from Example 1 is that:

[0177] The D50 of the large particle precursor was changed to 8μm.

[0178] In conjunction with Figure 21, the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1 and the free lithium content L2 of the positive electrode material prepared in Comparative Example 6, as well as the calculated values ​​of L, P and G are shown in Table 1.

[0179] Comparative Example 7

[0180] The difference from Example 1 is that:

[0181] The D50 of the small particle precursor was changed to 8μm.

[0182] In conjunction with Figure 22, the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1 and the free lithium content L2 of the positive electrode material prepared in Comparative Example 7, as well as the calculated values ​​of L, P and G are shown in Table 1.

[0183] Comparative Example 8

[0184] The difference from Example 1 is that:

[0185] The D50 of the small particle precursor was changed to 1 μm.

[0186] In conjunction with Figure 23, the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1 and the free lithium content L2 of the positive electrode material prepared in Comparative Example 8, as well as the calculated values ​​of L, P and G are shown in Table 1.

[0187] Comparative Example 9

[0188] The difference from Example 1 is that:

[0189] 1.0 wt% (NH4)2HPO4 and 1.0 wt% NH4HSO4.

[0190] In conjunction with Figure 24, the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1 and the free lithium content L2 of the positive electrode material prepared in Comparative Example 9, as well as the calculated values ​​of L, P and G are shown in Table 1.

[0191] Comparative Example 10

[0192] The difference from Example 1 is that:

[0193] 0.1 wt% (NH4)2HPO4 and 0.1 wt% NH4HSO4.

[0194] In conjunction with Figure 25, the specific test results of the peak area A1 of the first characteristic peak, the peak area A2 of the second characteristic peak, the free lithium content L1 and the free lithium content L2 of the positive electrode material prepared in Comparative Example 10, as well as the calculated values ​​of L, P and G are shown in Table 1.

[0195] The performance tests of the samples prepared in the above Examples 1-14 and Comparative Examples 1-10 were carried out as follows:

[0196] 1. Free lithium content test:

[0197] 5 g of the positive electrode material was dispersed in 100 mL of deionized water, and the residual carbonate and hydroxide were dissolved by magnetic stirring for a certain period of time. The filtrate was obtained after filtration, and hydrochloric acid solution was added to an automatic potentiometric titrator for titration using an equivalent drop method. The carbonate and hydroxide contents of the positive electrode material were calculated based on the breakthrough point and the consumption of the hydrochloric acid solution. When the stirring time was 60 min, the mass content of free lithium in the sample was measured to be L1, and when the stirring time was 10 min, the mass content of free lithium in the sample was measured to be L2.

[0198] 2. Particle size test:

[0199] The volume particle size distribution of the positive electrode material particles was obtained by using a British Malvern Mastersizer 3000 laser particle size analyzer and utilizing the light intensity distribution of laser diffraction.

[0200] 3. Calculation of the peak area of ​​the first characteristic peak and the second characteristic peak:

[0201] Import the raw data obtained from the particle size distribution test into Origin to draw the particle size distribution curve image. Using the integrate command, select the starting point x1 (0-8μm) and the end point x2 (8-12μm) of the first characteristic peak to obtain the peak area A1 based on y=0. Use the same method to select the starting point x3 (8-12μm) and the end point x4 (20-40μm) of the second characteristic peak to obtain the peak area A2 of the second characteristic peak. Among them, the value range of the starting point x1 is between 0-8μm, the value range of the end point x2 is between 8-12μm, the value range of x3 is between 8-12μm, and the value range of x4 is between 20-40μm.

[0202] 4. Power-off performance test:

[0203] 0.8g of positive electrode material, 0.1g of conductive carbon black, and 0.1g of polyvinylidene fluoride were placed in a ball mill, and 15mL of N-methylpyrrolidone was added. The mixture was ball-milled to form a uniform slurry, which was then evenly coated on aluminum foil and vacuum-dried at 110°C for 12 hours to obtain the positive electrode. The dried electrode was cut into 15mm discs and assembled and sealed in a glove box according to the following procedures: positive electrode shell, electrode, electrolyte (EC / DMC / EMC volume ratio of 1:1:1, LiPF6 concentration of 1 mol / L), separator (Celgard PP / PE / PP three-layer composite film), lithium sheet, electrolyte, nickel foam, and negative electrode shell to obtain a button battery, which was then left to stand for 24 hours. The resulting battery was then placed in a thermostat for testing. The battery was discharged to 2.0V at a current density of 1C, allowed to stand for 2 minutes, and then charged to 4.2V at a current density of 1C. The above steps were repeated for 50 cycles to obtain the cycle retention rate. The battery was fully charged to 4.2V and held for 1 hour. The battery was then adjusted to 100% SOC using a current density of 1C and allowed to stand for 30 minutes. The voltage V0 at this time was recorded. A discharge current ts of 1C was used, and the voltage V1 at ts was recorded. The DC resistance at the 50th cycle was calculated based on (V0-V1) / It.

[0204] The LAND battery testing system was used to conduct discharge capacity (0.1C / 0.5C / 1C) and first-cycle charge and discharge efficiency performance tests at 25°C and 3.0V to 4.3V. The reference capacity was set to 200mA / g, and 1C corresponded to a current density of 200mA / g.

[0205] 5. Conductivity test:

[0206] Using a resistivity tester (Suzhou Jingge Electronics ST-2255A), take a 5g powder sample and use an electronic press to press it to a constant pressure of 5000kg ± 2kg for 15-25s. Place the sample between the tester electrodes. The sample height is h (cm), the voltage across the two ends is U, the current is I, and the area of ​​the powder after pressing is S = 3.14cm. 2 The electronic conductivity of the powder is calculated according to the formula σ=h / (S*R) / 1000.

[0207] 6. Compaction test:

[0208] The compaction performance of the cathode material was tested using a compaction density tester model 4350 from the United States. 1g of the cathode material was processed and compacted under a pressure of 3t for 30s to obtain the compaction data of the material. The compaction density was > 3g / cm 3 .

[0209] 7. Specific surface area test:

[0210] The specific surface area of ​​the material was calculated using the American TriStar II specific surface and pore analyzer and nitrogen adsorption and the BET method.

[0211] 8. XRD test:

[0212] The crystal structure of the positive electrode active material can be determined by an X-ray powder diffractometer, for example, a Brucker D8A_A25 X-ray diffractometer from Brucker AxS, Germany, using CuKα radiation as the radiation source, scanning the 2θ angle range of the radiation wavelength from 10° to 90°, and a scanning rate of 4° / min.

[0213] The physicochemical parameter test results of the samples prepared in Examples 1-14 and Comparative Examples 1-10 are shown in Table 1 below:

[0214] The results of the buckling performance test of the samples prepared in Examples 1-14 and Comparative Examples 1-10 are shown in Table 2 below:

[0215] The test results of the electrical conductivity, compacted density and specific surface area obtained in Examples 1-14 and Comparative Examples 1-10 are shown in Table 3 below:

[0216] Analyze Table 1, Table 2 and Table 3 above:

[0217] By comparing Examples 1-16 with Comparative Examples 1-10, it can be concluded that when the positive electrode material satisfies the relationship: 10≤G=P*L≤25, it has relatively excellent cycle performance and conductivity; and when G is in the range of 10-20, the larger the θ value, the higher the cycle retention rate and conductivity of the positive electrode material, among which, when G is in the range of 18-20, the compaction density and specific surface area of ​​the positive electrode material have obvious advantages; when G is in the range of 20-25, the larger the G value, the smaller the cycle retention rate and conductivity of the positive electrode material; when G is not within the above range, the cycle performance and conductivity of the positive electrode material are relatively poor, and its application is greatly restricted.

[0218] Among them, by comparing Comparative Examples 1-2 with Example 5, it can be concluded that both too high and too low contents of free lithium ion converters are not conducive to forming a stable protective layer on the surface of the positive electrode material. Too high a content will lead to an uneven coating layer formed on the surface of the positive electrode material, and too low a content will not be able to effectively block the occurrence of side reactions. Both will lead to a decrease in material conductivity and a decrease in cycle performance.

[0219] By comparing Example 1 with Comparative Examples 3-8, it can be analyzed that: the role of large particles in the positive electrode material is mainly reflected in improving the capacity of the material, but cracks and pores are prone to appear during the cycle, affecting the cycle performance; small particles have better physical stability, can stabilize the material structure, and prevent the positive electrode material from breaking during the cycle, thereby improving the cycle stability and safety performance; the appropriate ratio of large and small particles in the positive electrode material is critical to improving its performance: appropriate particle size distribution and particle matching can increase the compaction density of the material, improve the mass of active substances per unit volume of the material, and facilitate the release of the electrochemical properties of the material.

[0220] By comparing Comparative Examples 3, 5, and 6 with Examples 1, 2, and 3, it can be concluded that in the positive electrode material, if the specific gravity of the large-particle precursor is too high or the D50 is too high, the stability and safety of the positive electrode material will decrease, and the compaction density and capacity of the positive electrode material will both decrease. At the same time, too many large particles will cause a significant decrease in the compaction density of the material; if the D50 of the large-particle precursor is too low, the lithium ion transmission rate will decrease, and the conductivity and capacity of the material will decrease.

[0221] By comparing Comparative Examples 4, 7, and 8 with Examples 1 and 14, it can be concluded that in the positive electrode material, the small particle precursor has a large specific gravity or D50 is large, and is prone to agglomeration, which causes the compaction density and specific surface area of ​​the material to decrease, resulting in a decrease in the capacity of the material, and affects the structural stability of the material, thereby reducing the cycle of the positive electrode material; if the specific gravity D50 of the small particle precursor is small, it will cause the finished positive electrode material to be prone to micropowder, affecting the electrochemical performance. At the same time, the micropowder will also affect the uniformity of the coating layer, resulting in a decrease in the electrical conductivity of the material.

[0222] In addition, through a detailed analysis of Examples 1-14, it can be concluded that: in the preparation process of the positive electrode material, the A1 value, A2 value, L1 value, and L2 value of the finished positive electrode material can be adjusted by regulating the particle size of the precursor and the matching ratio of the particles, the sintering temperature, the type of dopant, the type and content of the free lithium ion converter, the ultrasonic intensity, and the water washing and stirring time, so that the peak area ratio P value and the free lithium stability coefficient L of the prepared positive electrode material are within an appropriate range.

[0223] Specifically, compared to Example 1, Example 2 exhibits a smaller particle size (D50), smaller A1 peak area, and smaller A2 peak area for both the large and small particle precursors. This means that the smaller the particle size of both the large and small particle precursors, the higher the specific surface area, making the material more reactive with water and carbon dioxide in the air, and thus increasing the amount of free lithium in the cathode material. Consequently, the calculated θ value for the finished cathode material in Example 2 is 21.18, and its A1 is outside the specified range, resulting in reduced cycling performance compared to Example 1.

[0224] Compared with Example 1, A1 of Example 3 is reduced, A2 is increased, and the overall A2 / A1 is increased. The reason is that the particle size of small particles is reduced and the particle size of large particles is increased. Under this condition, the particle size adaptability of large and small particles is better: smaller particles reduce the volume expansion of the material during the charge and discharge process, making the structure of the material more stable, and the appropriate increase in the particle size of large particles also reduces the number of grain boundaries that hinder the diffusion of lithium ions, Li + The transmission is faster and the conductivity is increased. While maintaining a similar stability coefficient of free lithium, the θ value increases to 16.16, and the material's cycle performance is improved.

[0225] Compared with Example 3, the constant temperature sintering temperature of Example 4 is reduced, L1 increases, and the cycle performance deteriorates. This is because the temperature conditions required for grain growth of large particles and small particles are different, and it is necessary to determine the appropriate sintering temperature. Compared with Experimental Example 3, Example 4 reduces the sintering temperature, which slows the growth rate of the material grain size, makes the grain size smaller, and reduces the lithium ion transmission path. At the same time, there is also the problem of insufficient sintering temperature required for lithium to enter the lattice. Therefore, compared with Example 3, L1 of Example 4 increases, does not meet the range of 0.15% ≤ L1 ≤ 0.45%, and the cycle performance of the finished positive electrode material deteriorates.

[0226] Compared with Example 3, Example 5 uses co-doping of four metal ions of Al / Ti / Sr / Ba, which can effectively stabilize the crystal structure of the material, improve the chemical stability of TM-O-Li, and improve the Li / Ni mixing situation, thereby improving the conductivity and cycle stability of the finished positive electrode material.

[0227] Comparative Example 5, Example 6 and Example 9 adjusted the content of the free lithium ion converter, and the content of the free lithium ion converter was appropriately increased, which was beneficial to further improve the cycle stability of the positive electrode material; the reason is that: the increase in the content of the free lithium ion converter further improves the conversion efficiency of free lithium in the positive electrode material, and the excess residual alkali on the surface of the material fully reacts with the free lithium converter, so that the material obtains more effective coating layers, that is, the stability of the coating layer formed on the surface of the material is improved, which can reduce the generation of pores and cracks, and can more effectively reduce the side reactions of the active substance and the electrolyte.

[0228] Compared to Example 1, in Example 7, the free lithium ion conversion agent was replaced with NH4HSO4, resulting in a decrease in the cycling performance of the finished positive electrode material. The test results indicate that NH4HSO4 has a poorer conversion of residual alkali, making it more difficult to form a stable structural protective layer. The Li2SO4 coating has a lower conversion rate than the Li3PO4 coating, and the Li3PO4 coating is more effective in reducing structural damage and side reactions during cycling.

[0229] Comparing Example 5 and Example 8, which simultaneously used the free lithium ion converters (NH4)2HPO4 and NH4HSO4, and compared with Comparative Examples 9 and 10, the cycling performance of the finished positive electrode material decreased. This is due to the uneven formation of the Li2SO4 and Li3PO4 coating layers, which affects the structural stability of the coating layer on the surface of the finished positive electrode material. Using both free lithium ion converters simultaneously, with a low content, results in an uneven coating layer and structural instability, while excessive content can introduce impurities and reduce electrochemical performance.

[0230] Compared with Example 6, Example 10 increased the ultrasonic intensity to 50kHz, but the cycle performance of the finished positive electrode material decreased. The reason is that excessive ultrasonic energy causes the coating layer to be unstable and in a metastable state, which is not conducive to improving the structural stability of the coating layer.

[0231] Compared to Example 5, in Example 11, the pre-wash stirring time in the reactor was increased to 40 minutes, but the cycling performance of the finished cathode material decreased. This is because excessively high rotation speeds can easily lead to the loss of small particles, resulting in an excessively high A2 / A1 ratio, which compromises material stability and reduces the cycling performance of the finished cathode material.

Claims

1. A positive electrode material, characterized in that: The positive electrode material includes a nickel-cobalt-lithium oxide composite oxide; The particle size distribution curve of the positive electrode material has a first characteristic peak and a second characteristic peak, the peak area of ​​the first characteristic peak is A1, the peak area of ​​the second characteristic peak is A2, and P=A2 / A1; The free lithium stability coefficient of the positive electrode material is L, L = (L1-L2) / L1, and the test method of L1 and L2 is: take 5g of positive electrode material and disperse it in 100mL of deionized water, and the magnetic stirring time is t min. After filtration, the filtrate is obtained to measure the free lithium content; when t = 60, the mass content of free lithium in the positive electrode material is measured to be L1%, and when t = 10, the mass content of free lithium in the positive electrode material is measured to be L2%; The positive electrode material satisfies the following relationship: 10≤G≤25, wherein G=P*L.

2. The positive electrode material according to claim 1, characterized in that The general chemical formula of the positive electrode material is: Li f Ni a Co b Mn c M d N e O2, where 0.8<a<0.98, b<0.2, c<0.2, a+b+c+d+e=1, 0.95≤f≤1.05; And the M includes at least one of Sr, Ti, Al, Zr, W, Ba, Mg, Nb, Co, Mn, Nb, and Ca, and the N includes at least one of W, B, Mo, F, S, V, P, and Cl.

3. The positive electrode material according to claim 1, characterized in that The positive electrode material includes a base material and a coating layer located on at least a portion of the surface of the base material, wherein the base material is an oxide including Ni, Co, Mn and M elements, and the M element includes at least one of Sr, Ti, Al, Zr, W, Ba, Mg, Nb, Co, Mn, Nb and Mo.

4. The positive electrode material according to claim 1, characterized in that The positive electrode material comprises a base material and a coating layer located on at least a portion of the surface of the base material, wherein the coating layer comprises a lithium salt, and the chemical formula of the lithium salt is Li x N y O z , wherein x, y, z>0, and N includes at least one of W, B, Mo, F, S, V, P and Cl.

5. The positive electrode material according to claim 1, characterized in that Satisfy at least one of the following characteristics: (1)0.25≤L≤0.85； (2)0.15≤L1≤0.45； (3)0.02≤L2≤0.16。 6. The positive electrode material according to claim 1, characterized in that Satisfy at least one of the following characteristics: (1)8≤P≤50； (2)4≤A1≤25； (3)150≤A2≤250。 7. The positive electrode material according to claim 1, characterized in that Satisfy at least one of the following characteristics: (1) The conductivity of the positive electrode material is 0.025S / cm to 0.080S / cm; (2) The compaction density of the positive electrode material is 3.10 g / cm 3 ~3.65g / cm 3 ; (3) The specific surface area of ​​the positive electrode material is 0.4 m 2 / g~0.8m 2 / g.

8. A method for preparing a positive electrode material, characterized in that: The steps include: Adding a free lithium ion conversion agent to an aqueous solution of a base material for modification treatment, based on the mass of the base material being 100wt%, the addition amount of the free lithium ion conversion agent is 0.6wt%-1.2wt%, to obtain a modified mixture, and performing solid-liquid separation on the modified mixture to obtain a precursor; wherein the base material is a nickel cobalt acid lithium composite oxide, and the particle size distribution curve of the base material has a first characteristic peak and a second characteristic peak, the peak area of ​​the first characteristic peak is A1, the peak area of ​​the second characteristic peak is A2, P=A2 / A1, 8≤P≤50; ​​and The precursor is sintered to obtain a positive electrode material.

9. The preparation method according to claim 8, characterized in that: Also includes at least one of the following features: (1) The chemical formula of the ternary precursor is Ni a Co b Mn c (OH)2, 0.8≤a≤0.98, 0.01≤b≤0.2, 0.01≤c≤0.2; (2) The M dopant includes Sr(OH)2, SrO, TiO2, Al2O3, Al(OH)3, ZrO2, Zr(OH)4, Ba(OH)2, At least one of BaO, MgO, Mg(OH)2, Nb2O5, Nb2O3, WO3 and CaWO4; (3) The mass of the M dopant is 0.1% to 0.55% of the mass of the ternary precursor.

10. The preparation method according to claim 8, characterized in that: Also includes at least one of the following features: (1) The mass of the M dopant is 0.2% to 0.4% of the mass of the ternary precursor; (2) The ternary precursor comprises first particles and second particles of different particle sizes, and the mass ratio of the first particles to the second particles is 1:(1-5); (3) The molar ratio of the Li element in the lithium source to the ternary precursor is 0.95 to 1.

25.

11. The preparation method according to claim 8, characterized in that: Also includes at least one of the following features: (1) The mass of the free lithium ion conversion agent is 0.6%-1.2% of the mass of the matrix material; (2) The free lithium ion conversion agent contains N, and the N includes at least one of W, B, Mo, F, S, V, P and Cl; (3) The free lithium ion conversion agent includes at least one of KAl(SO4)2, NH4HSO4, MgCl, NH4Cl, CaF, NH4HWO4, NH4MoO4, NH4HBO3, NH4HF2, NaVO3, NH4VO3, (NH4)3PO4, (NH4)2HPO4, and Ca(H2PO4)2.

12. A lithium ion battery, characterized in that: The positive electrode material comprises the positive electrode material as described in any one of claims 1 to 7, or comprises the positive electrode material prepared by the preparation method as described in any one of claims 8 to 11.

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