Positive electrode material and battery

Abstract

The embodiments of the present application relate to the technical field of lithium-ion batteries, and particularly relate to a positive electrode material and a lithium-ion battery. The positive electrode material comprises a matrix material and a coating layer on at least part of the surface of the matrix material. The positive electrode material is measured by means of an XRD ray, the resultant diffraction intensity of a (104) crystal plane of the positive electrode material is I104, the resultant diffraction intensity of a (003) crystal plane thereof is I003, and R = I003 / I104; in addition, the grain size corresponding to the (104) crystal plane obtained by means of calculation according to a Scherrer formula is D104 nm; the structural stability coefficient ε of the positive electrode material satisfies: ε = log(D104) / R, and 0.90＜ε＜1.03, wherein R=I003 / I104; and the pellet hardness GD50of the positive electrode material is greater than 80 MPa, and GD90＞50 MPa. The positive electrode material of the present application can reduce the gas production and impedance of the positive electrode material, and can also improve the structural orderliness and structural stability of the positive electrode material, such that the safety performance, capacity and cycle performance of the positive electrode material can be improved.

Description

Cathode materials and batteries

[0001] The present invention claims priority to the Chinese patent application filed with the State Intellectual Property Office on September 26, 2024, with application number 2024113546243 and application name “Positive Electrode Materials and Batteries”, parts of which are incorporated by reference into this application. Technical Field

[0002] The present invention relates to the technical field of lithium ion batteries, and in particular to positive electrode materials and lithium ion batteries. Background Art

[0003] Lithium-ion batteries have the advantages of high operating voltage, long cycle life, wide application range, low environmental pollution and no memory effect, so they are widely used in portable electronic devices. As the core component of lithium-ion batteries, the performance of positive electrode materials directly determines the overall performance of the battery. Therefore, the development of positive electrode materials with excellent performance has always been a research hotspot. Among a series of positive electrode materials, layered high nickel ternary materials LiNi x CO y MnO2 (NCM, x ≥ 0.8, x + y + z = 1) is considered the most promising cathode material in the power battery field due to its high specific capacity and high voltage platform. However, as nickel content continues to increase, high-nickel cathode materials have become increasingly problematic, with problems such as cation mixing, surface residual alkali, gas generation, increased impedance, poor rate performance, and poor cycling stability, limiting their further application in the power battery market.

[0004] At present, the conventional technical means to improve the above problems are mainly doping and coating. However, the existing modification methods such as doping and coating are complex and have high process costs, and the improvement effect on the above problems is limited. They cannot simultaneously meet the requirements for improving the electrochemical properties and safety performance of positive electrode materials.

[0005] Summary of the Invention

[0006] The present application provides a positive electrode material and a lithium-ion battery, wherein the positive electrode material can reduce the gas production and impedance of the positive electrode material, while improving the structural orderliness and structural stability of the positive electrode material, thereby improving the safety performance, capacity and cycle performance of the positive electrode material.

[0007] In the first aspect, the present application provides a positive electrode material, wherein the positive electrode material is a lithium nickel cobalt oxide composite oxide, and the positive electrode material is measured by XRD ray, and the diffraction intensity of the (104) crystal plane of the positive electrode material is obtained to be I 104 The diffraction intensity of the (003) crystal plane is I 003 , R=I 003 / I 104; According to the Scherrer formula, the grain size corresponding to the (104) crystal plane is D 104 nm; the structural stability coefficient of the positive electrode material is ε=log(D 104 ) / R, and satisfies 0.93<ε<1.03; and the particle hardness G of the positive electrode material D50 >80Mpa, G D90 >50Mpa.

[0008] In one embodiment, 45≤D 104 ≤65.

[0009] In one embodiment, R>1.6.

[0010] In one embodiment, 1≤G D50 / G D90 ≤1.5.

[0011] The present application also provides a positive electrode material, wherein the positive electrode material is a lithium nickel cobalt oxide composite oxide; 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;

[0012] The positive electrode material was subjected to an acid-base potentiometric titration test using a potentiometric titrator and hydrochloric acid with a concentration of 0.02 mol / L to obtain a curve graph showing the relationship between the differential value dpH / dV obtained by differentiating the pH value with respect to the consumed volume VmL of hydrochloric acid and the consumed volume V of the hydrochloric acid. In the curve graph showing the relationship between the differential value dpH / dV and the consumed volume V of the hydrochloric acid, the positive electrode material had a first characteristic peak when the consumed volume of the hydrochloric acid was V1 mL, and the positive electrode material had a last characteristic peak when the consumed volume of the hydrochloric acid was V2 mL, and V1 and V2 satisfied the relationship: 0.6<V2-V1<2.7.

[0013] In one embodiment, 4<V1<8.

[0014] In one embodiment, 5<V2<11.

[0015] In one embodiment, the positive electrode material has N characteristic peaks within the range of the consumed volume V of the hydrochloric acid being 4 to 11 (excluding 4 and 11), and 2<N≤4.

[0016] In one embodiment, 0<dpH / dV<10.

[0017] In one embodiment, the chemical formula of the positive electrode material is LiNi a Co b Mn c M d Q eO2, where 0.8<a<0.98, b<0.2, c<0.2, 0<d+e<0.2, a+b+c+d+e=1.

[0018] In one embodiment, the matrix material is a lithium nickel cobalt manganese oxide compound doped with an M element, where the M element is a metal element.

[0019] In one embodiment, the M includes at least one of Sr, Ti, Al, Zr, Y, Ba, Mg, Nb, Mo, W, and V.

[0020] In one embodiment, the Q includes at least one of S, W, F, P and Mo.

[0021] In one embodiment, the chemical formula of the coating layer is Li x Q e O y , where 0<x≤3, 0<y≤4.

[0022] In one embodiment, the coating layer includes at least one of Li2WO4, Li3BO3, LiMoO4, LiVO3, Li2SO4 and Li3PO4.

[0023] In one embodiment, 0.985≤Li / Me≤0.999, where Li / Me is a molar ratio of lithium metal to other metals except lithium in the positive electrode material.

[0024] In one embodiment, 1.001≤Li / Me≤1.015, where Li / Me is a molar ratio of lithium metal to other metals except lithium in the positive electrode material.

[0025] In one embodiment, in the XRD spectrum of the positive electrode material, the half-maximum width of the diffraction peak of the (104) crystal plane is 0.19° to 0.25°.

[0026] In one embodiment, the positive electrode material includes secondary particles, and the volume median particle size D50 of the secondary particles is 7 μm to 12 μm.

[0027] In one embodiment, the volume particle size distribution curve of the positive electrode material has a characteristic peak.

[0028] In one embodiment, the pH value of the positive electrode material is 10-13.

[0029] In one embodiment, the specific surface area of ​​the positive electrode material is 0.2 m 2 / g~0.8m 2 / g.

[0030] In one embodiment, the compaction density of the positive electrode material is greater than 3 g / cm3。

[0031] In one embodiment, the conductivity σ of the positive electrode material is greater than 0.03 S / cm.

[0032] In one embodiment, the mass content of Li2CO3 in the positive electrode material is α Li wt%, 0.1≤α Li ≤0.55.

[0033] In one embodiment, the mass content of LiOH in the positive electrode material is β Li wt%, 0.1≤β Li ≤0.7.

[0034] In one embodiment, the initial moisture content of the positive electrode material is less than 200 ppm, and the moisture content after being exposed to air for 24 hours is less than 1000 ppm.

[0035] In a second aspect, the present application further provides a lithium-ion battery, which includes the positive electrode material as described above.

[0036] Compared with the existing technology, this technical solution has at least the following technical effects:

[0037] The positive electrode material provided by the present application is a lithium nickel cobalt oxide composite oxide; 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; it satisfies the relationship: ε = log (D104) / R, the grain size of the positive electrode material of this product on the (104) crystal plane and the peak intensity ratio of the material I 003 / I 104 (i.e. R value) has a certain correlation, and the ratio of the two can reflect the grain size development and the stability of the layered structure of the positive electrode material, which can further reflect the excellent electrochemical performance of the positive electrode material. The inventors found through a large amount of experimental data analysis that the structural stability coefficient ε=log(D 104) / R, 0.93<ε<1.03. ε can reflect the deviation of grain growth from the stable layered structure. When ε is close to 1, it indicates that the grain and layered structure of the positive electrode material have grown to the best, and the electrochemical performance of the positive electrode material is optimal. When ε deviates from 1 by a large amount, it indicates that the grain growth of the material is not ideal or the layered structure is not maintained ideally, and doping or coating fails to effectively modify the positive electrode material, reflecting that the electrochemical performance of the positive electrode material is poor. The ε value is an indicator for evaluating the deviation of the layered structure and crystal growth order of the positive electrode material from a microscopic perspective. When the value of the structural stability coefficient ε is between 0.90 and 1.03 (excluding 0.90 and 1.03), the grain size and ordered layered structure of the positive electrode material reach an ideal state. At this time, the positive electrode material has a suitable grain size and an ordered layered structure, which can improve the structural stability of the positive electrode material and improve the capacity and cycle performance of the positive electrode material. At the same time, after further extensive research and analysis by the applicant, it was found that the ε value can also affect the mechanical properties of the positive electrode material from a macroscopic perspective, and is related to the particle hardness G of the positive electrode material. D50 and particle hardness G D90 The applicants speculate that the enhanced bonding strength between the positive electrode material matrix and the coating material is beneficial to improving the particle hardness of the material, wherein the particle hardness G D50 Represents the high hardness of most particles, achieving external resistance to extrusion force, internal dispersion of extrusion force and internal stress dispersion. Moreover, when the ε range is adjusted to 0.90~1.03 (excluding 0.90 and 1.03), G D90 This shows that large particles in the positive electrode material can also have high hardness, which can improve the overall uniformity and hardness of the positive electrode material particles. Therefore, ε, G D50 , G D90 The coordinated interaction between these parameters not only regulates the structural stability of the cathode material from a macroscopic perspective, but also achieves structural stability at the individual particle level. Furthermore, the interaction of these parameters also indicates that the uneven gaps between the primary particles of the cathode material are further adjusted and filled, thereby improving the mechanical stability of the material.

[0038] The positive electrode material provided in the present application is a lithium nickel cobalt oxide composite oxide; 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; the positive electrode material is subjected to an acid-base potentiometric titration test using a potentiometric titrator and hydrochloric acid with a concentration of 0.02 mol / L to obtain a curve diagram showing the relationship between the differential value dpH / dV obtained by differentiating the pH value with respect to the consumed volume VmL of hydrochloric acid and the consumed volume VmL of hydrochloric acid. In the curve diagram showing the relationship between the differential value dpH / dV and the consumed volume VmL of hydrochloric acid, the positive electrode material has a first characteristic peak when the consumed volume of hydrochloric acid is V1mL, and V1mL represents the consumed volume of hydrochloric acid when the residual alkali on the surface of the positive electrode material begins to be neutralized. The positive electrode material has a last characteristic peak when the consumed volume of hydrochloric acid is V2mL, and V2mL represents the consumed volume of hydrochloric acid when the residual alkali on the surface and inside of the positive electrode material is completely neutralized. In the present application, the value of V2-V1 can reflect the coating effect of the coating layer on the surface of the positive electrode material to a certain extent. When the value of V2-V1 is between 0.6 and 2.7 (excluding 0.6 and 2.7), the coating layer on the surface of the positive electrode material is evenly distributed and the coating effect is good, which can reduce the surface residual alkali and impedance of the positive electrode material, so that the positive electrode material has both low gas production and low impedance, thereby improving the safety performance of the positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG1 is a schematic diagram of a discharge state of a battery provided in an embodiment;

[0040] 2 is a graph showing the relationship between the differential value dpH / dV of the cathode material provided in Example 1 and the consumed volume V of hydrochloric acid;

[0041] 3 is a graph showing the relationship between the differential value dpH / dV of the positive electrode material provided in Example 7 and the consumed volume V of hydrochloric acid;

[0042] 4 is a graph showing the relationship between the differential value dpH / dV of the positive electrode material provided in Comparative Example 2 and the consumed volume V of hydrochloric acid;

[0043] 5 is a graph showing the relationship between the differential value dpH / dV of the positive electrode material provided in Comparative Example 3 and the consumed volume V of hydrochloric acid;

[0044] FIG6 is an XRD pattern of the positive electrode material prepared in Example 3;

[0045] FIG7 is a particle size distribution diagram of Example 7.

[0046] In Figure 1:

[0047] 1-positive electrode sheet; 11-positive electrode current collector; 12-positive electrode active material layer; 2-negative electrode sheet; 21-negative electrode current collector; 22-negative electrode active material layer; 3-isolation membrane. DETAILED DESCRIPTION

[0048] In order to better understand the technical solutions of this specification, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0049] It should be clear that the embodiments described are only part of the embodiments of this specification, not all of the embodiments. Based on the embodiments in this specification, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this specification.

[0050] The terms used in the examples of this application are for the purpose of describing specific embodiments only and are not intended to limit this specification. The singular forms "a," "an," "the," and "the" used in the examples of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0051] The electrochemical performance of lithium-ion batteries during the cycle is largely affected by the performance of the positive electrode material. The main reasons are as follows: 1. Residual alkali on the surface of the positive electrode material causes the decomposition of active substances inside the battery, insufficient hardness of the positive electrode particles, structural degradation, electrode stratification, etc., resulting in excessive initial impedance and affecting battery performance; 2. Due to the residual alkali, the pH value on the surface of the positive electrode material is too high, and even a brief contact with air is easy to absorb moisture, causing side reactions, thereby deteriorating the overall performance of the material; 3. The crystal growth of the positive electrode material is too fast during the manufacturing process, D 104 The increase leads to slow lithium ion diffusion kinetics and increasing impedance; 4. There is a lack of in-depth research on the uniformity of coating and doping of most particles and the physical properties of the particles, which makes it impossible to accurately and stably control the performance of the battery.

[0052] After conducting a lot of experiments, the inventors of this application found that the D 104 Value and I 003 / I 104 There is a certain correlation between the peak intensity ratio R and the positive electrode material. The ratio of the two can reflect the grain size development and the stability of the layered structure of the positive electrode material. Generally, the larger the peak intensity ratio R, the better the layered structure of the transition metal layer and the lithium metal layer is maintained, which can ensure better reaction kinetics. However, simply increasing the peak intensity ratio R may change the structural properties of the positive electrode material. A single parameter cannot directly reflect the excellent performance of the positive electrode material. 104 It can be measured by XRD. This parameter can reflect the capacity of the positive electrode material. 104 Too large or too small will affect the performance of the positive electrode material. In order to balance the structure of the positive electrode material, D 104Combining these two parameters, R and R, reveals that when they reach a balance, the capacity and cycling performance of the cathode material can be significantly improved. Furthermore, the inventors have discovered that these parameters are also correlated with the particle hardness of the cathode material within different particle size ranges. These parameters, acting in concert, significantly influence the gas production, impedance, capacity, and cycling performance of lithium-ion batteries assembled from the cathode material.

[0053] Based on this, in the first aspect, the embodiment of the present application provides a positive electrode material, which is a nickel cobalt lithium composite oxide; 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; the positive electrode material is tested using an XRD diffractometer, and the diffraction peak intensity of the (003) crystal plane of the positive electrode material is obtained to be I 003 , the diffraction peak intensity of (104) crystal plane is I 104 , and according to the Scherrer formula, the grain size corresponding to the (104) crystal plane is calculated to be D 104 ; Positive electrode material satisfies: ε=log(D 104 ) / R, 0.90<ε<1.03, where R=I 003 / I 104 ; and the particle hardness G of the positive electrode material D50 >80Mpa, G D90 >50Mpa. The grain size of the positive electrode material of this product on the (104) crystal plane and the peak intensity ratio of the material I 003 / I 104 (i.e. R value) has a certain correlation, and the ratio of the two can reflect the grain size development and the stability of the layered structure of the positive electrode material, which can further reflect the excellent electrochemical performance of the positive electrode material. The inventors found and speculated through a large amount of experimental data analysis that the coefficient ε=log(D 104) / R, 0.90<ε<1.03. ε can reflect the deviation of grain growth from the stable layered structure. When ε is close to 1, it indicates that the grain and layered structure of the positive electrode material have grown to the best, and the electrochemical performance of the positive electrode material is optimal. When ε deviates from 1 by a large amount, it indicates that the grain growth of the material is not ideal or the layered structure is not maintained ideally, and doping or coating fails to effectively modify the positive electrode material, reflecting that the electrochemical performance of the positive electrode material is poor. The ε value is an indicator for evaluating the deviation of the layered structure and crystal growth order of the positive electrode material from a microscopic perspective. When the value of the structural stability coefficient ε is between 0.90 and 1.03 (excluding 0.90 and 1.03), the grain size and ordered layered structure of the positive electrode material reach an ideal state. At this time, the positive electrode material has a suitable grain size and an ordered layered structure, which can improve the structural stability of the positive electrode material and improve the capacity and cycle performance of the positive electrode material. At the same time, after further extensive research and analysis by the applicant, it was found that the ε value can also affect the mechanical properties of the positive electrode material from a macroscopic perspective, and is related to the particle hardness G of the positive electrode material. D50 and particle hardness G D90 Can coordinate with each other. D50 >80Mpa, G D90 When the range is >50Mpa, the applicants speculate that the enhanced bonding strength between the cathode material matrix and the coating material is beneficial to improving the particle hardness of the material, wherein the particle hardness G D50 Represents the high hardness of most particles, achieving external resistance to extrusion force, internal dispersion of extrusion force and internal stress dispersion. Moreover, when the ε range is adjusted to 0.90~1.03 (excluding 0.90 and 1.03), G D90 This indicates that large particles in the positive electrode material can also have high hardness, thereby improving the overall uniformity and hardness of the positive electrode material particles. Therefore, ε, G D50 , G D90 The coordinated interaction between these parameters not only regulates the structural stability of the cathode material from a macroscopic perspective, but also achieves structural stability at the individual particle level. Furthermore, the interaction of these parameters also indicates that the uneven gaps between the primary particles of the cathode material are further adjusted and filled, thereby improving the mechanical stability of the material.

[0054] In some embodiments, 0.90 < ε < 1.03, and the value of ε can be specifically 0.91, 0.92, 0.93, 0.94, 0.95, 0.98, 1.0, 1.01, 1.02, or 1.03, etc., but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable. It can be understood that when the value of the structural stability coefficient ε is within the above range, the grain size and ordered layered structure of the positive electrode material reach an ideal state. At this time, the positive electrode material has a suitable grain size and ordered layered structure, which can improve the structural stability of the positive electrode material and improve the capacity and cycle performance of the positive electrode material.

[0055] In one embodiment, 45 < D 104 <65, specifically can be 45.1, 45.5, 46, 48, 50, 55, 57, 60, 61, 62, 63, 64 or 64.8, of course, it can also be other values ​​within the above range, which is not limited here. 104 When D is less than 45, the distance between atoms in the cathode material is relatively short, and the internal crystal structure of the cathode material is prone to form dislocations or stacking faults, which disrupts the orderliness of the layered structure of the cathode material and leads to a decrease in the capacity of the cathode material. 104 When the value is ≥65, the TM-O interlayer spacing of the positive electrode material (the interlayer spacing between the transition metal TM and oxygen O) will be enlarged, and lithium ions will easily cause structural collapse during repeated insertion and extraction, which will reduce the structural stability of the positive electrode material and thus lead to a decrease in the cycle performance of the positive electrode material.

[0056] In one embodiment, R=I 003 / I 104 , and R>1.6, specifically 1.61, 1.65, 1.68, 1.70, 1.72, 1.74, 1.77, 1.78 or 1.79, etc., but not limited to the listed values, other values ​​not listed in the numerical range are also applicable. When R≤1.6, I 003 The strength is weakened, I 104 The strength is enhanced, and the disorder of the (104) crystal plane Ni layer and Li layer increases, resulting in the deterioration of the structural stability of the positive electrode material.

[0057] In some embodiments, the particle hardness of the positive electrode material satisfies the relationship: 80 MPa < G D50 <110Mpa,50Mpa<G D90 <95Mpa,G D50 Specifically, it can be 80.1Mpa, 85.8Mpa, 90.9Mpa, 94.4Mpa, 99.8Mpa, 103.5Mpa, 105.7Mpa or 109.9Mpa, etc. D90Specifically, it can be 50.1Mpa, 60.2Mpa, 65.5Mpa, 77.7Mpa, 82.8Mpa, 85.9Mpa, 88.8Mpa, 90.2Mpa, 93.5Mpa or 94.9Mpa, etc. Of course, it can also be other values ​​within the above range, which is not limited here. Theoretically, the hardness G of the positive electrode material is D50 and G D90 The bigger the better, but too high particle hardness may affect the processing performance of the positive electrode material. D50 and G D90 When the content is controlled within the above range, the electrical properties of the positive electrode material particles can be further optimized.

[0058] In some embodiments, 1≤G D50 / G D90 ≤1.5, specifically 1.10, 1.16, 1.19, 1.22, 1.25, 1.28, 1.31, 1.36, 1.40, 1.44, 1.47 or 1.50, etc., but not limited to the listed values, other values ​​not listed in the numerical range are also applicable. D50 / G D90 When the positive electrode material particles are within the above range, not only the overall coating is uniform and the structure is stable, but also the gap between the positive electrode material particles and the positive electrode material particles is further reduced. 90 The hardness of large particles at the level of D 50 The gap between the hardness of large particles of the same level maintains the overall system energy of the positive electrode material at a low level, further improves the mechanical properties, and is also more conducive to uniform dispersion of particles. The embodiment of the present application also provides a positive electrode material, which is a nickel cobalt lithium composite oxide; 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; the positive electrode material is subjected to an acid-base potentiometric titration test using a potentiometer and hydrochloric acid with a concentration of 0.02 mol / L, and a curve diagram showing the relationship between the differential value dpH / dV obtained by differentiating the consumption volume VmL of hydrochloric acid and the consumption volume VmL of the hydrochloric acid is obtained. In the curve diagram showing the relationship between the differential value dpH / dV and the consumption volume VmL of the hydrochloric acid, the positive electrode material has a first characteristic peak when the consumption volume of the hydrochloric acid is V1mL, and the positive electrode material has a last characteristic peak when the consumption volume of the hydrochloric acid is V2mL, and V1 and V2 satisfy the relationship: 0.6<V2-V1<2.7. In the potentiometric titration curve of a cathode material, the effect of doping or coating on the cathode material can be determined by the amount of hydrochloric acid consumed between the first and last peaks (V2-V1). Appropriate coating is an effective means of improving the structural stability of the cathode material, reducing residual alkalinity, and increasing ionic conductivity. Within the above range, the greater the V2-V1, the less gassing the cathode material produces and the lower the impedance growth rate.

[0059] It should be noted that the lithium nickel cobalt oxide composite oxide, i.e., the lithium nickel cobalt oxide positive electrode material in the present application, can be a lithium nickel cobalt manganese oxide (NCM) positive electrode material or a lithium nickel cobalt aluminum oxide (NCA) positive electrode material.

[0060] In some embodiments, V1 and V2 satisfy the relationship: 0.6<V2-V1<2.7, which can be specifically 0.61, 0.65, 0.7, 1.0, 1.2, 1.5, 1.8, 2.0, 2.1, 2.3, 2.5 or 2.68, etc. Of course, it can also be other values ​​within the above range, which are not limited here. In the present application, V1mL represents the volume of hydrochloric acid consumed when the residual alkali on the surface of the positive electrode material begins to be neutralized, and V2mL represents the volume of hydrochloric acid consumed when the residual alkali on the surface and inside of the positive electrode material is completely neutralized. The value of V2-V1 can reflect the coating effect of the coating layer on the surface of the positive electrode material to a certain extent. When the value of V2-V1 is less than or equal to 0.6, the coating effect of the coating layer on the surface of the positive electrode material is poor, and the coating layer is difficult to completely coat the surface of the positive electrode material or is unevenly distributed on the surface of the positive electrode material, resulting in an increase in the residual alkali content on the surface of the positive electrode material, thereby increasing the gas production of the positive electrode material. When the value of V2-V1 is greater than or equal to 2.7, it indicates that a large volume of hydrochloric acid is consumed from the initial neutralization to the complete neutralization of the residual alkali in the positive electrode material during the titration process. This also indirectly indicates that the positive electrode material surface is over-coated. At this time, due to the excessive distribution of coating material or coating product on the surface of the positive electrode material, more hydrochloric acid is required to completely neutralize the residual alkali on the surface and inside the positive electrode material. Excessive coating can lead to a decrease in the lithium ion transport performance of the positive electrode material, and can also cause a decrease in the capacity of the positive electrode material and an increase in impedance. Preferably, 1<V2-V1<2.7.

[0061] In some embodiments, 4<V1<8, specifically 4.1, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 7.6, 7.7, 7.8, or 7.9, etc., but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable. When V1 is within this range, the surface byproducts of the positive electrode material (i.e., residual alkali on the surface, lithium hydroxide, lithium carbonate, etc.) are reduced, which is beneficial for the preparation and coating of the battery slurry.

[0062] In some embodiments, 5<V2<11, specifically 5.1, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or 10.9, but is not limited to the listed values, and other values ​​not listed in this numerical range are also applicable. When V2 ≥ 11, it indicates that the surface of the positive electrode material is excessively coated, resulting in an increase in the polarization rate of the positive electrode material, which is likely to accelerate the decrease in energy density in the later stage of the lithium-ion battery.

[0063] In some embodiments, in a graph plotting the differential value dpH / dV versus the volume V of hydrochloric acid consumed, the cathode material exhibits N characteristic peaks within a range of 4 to 11 (excluding 4 and 11) of hydrochloric acid consumption volume VmL, and 2<N≤4. This N value within this range indicates that the cathode material will not experience excessive ion reaction during the titration process, leading to interference with the titration results, a significant deviation between the V2-V1 value and the actual measured value, and a distorted assessment of the cathode material's performance by the experimenter.

[0064] In some embodiments, 0 < dpH / dV < 10. Specifically, it can be 1.1, 2.5, 2.2, 3.4, 3.8, 4.0, 4.6, 5.1, 5.7, 6.9, 6.3, 7.2, 7.5, 8.8, 9.5 or 9.9. However, it is not limited to the listed values, and other values ​​not listed in this numerical range are also applicable. The range of 0 < dE / dV < 10 indicates that the neutralization reaction of the positive electrode material is stable during the titration process, and there are no extra impurity ions in the positive electrode material that interfere with the titration reaction, reflecting that the elements of the positive electrode material are evenly distributed and the structural stability is good.

[0065] In some embodiments, the chemical formula of the positive electrode material is LiNi a Co b Mn c M d Q e O2, wherein 0.8<a<0.98, b<0.2, c<0.2, 0<d+e<0.2, a+b+c+d+e=1, M is a doping element, and Q is a coating element. In this embodiment, by controlling the content of the doping element in the positive electrode material within an appropriate range, the degree of Li / Ni cation mixing can be reduced, thereby preventing excessive residual lithium on the surface of the positive electrode material. At the same time, by controlling the content of the coating element in the positive electrode material within an appropriate range, the residual lithium content on the surface of the positive electrode material can also be reduced.

[0066] Specifically, the positive electrode material includes a base material and a coating layer located on the surface of the base material. The base material is a lithium nickel cobalt manganese oxide compound doped with an M element, where the M element is a metal element. Doping the base material with the metal element helps improve the base material's electrical conductivity, while providing the coating layer on the base material's surface helps enhance the base material's structural stability, thereby improving the impedance performance of the positive electrode material (corresponding to the impedance performance of a lithium-ion battery assembled from the positive electrode material, the same below).

[0067] In some embodiments, the matrix material is a lithium nickel cobalt manganese oxide compound doped with an M element, where the M element is a metal element.

[0068] In some embodiments, M includes at least one of Sr, Ti, Al, Zr, Y, Ba, Mg, Nb, Mo, W, and V;

[0069] In some embodiments, Q includes at least one of S, W, F, P, and Mo.

[0070] In some embodiments, the chemical formula of the coating layer is Li x Q e O y , where 0<x≤3, 0<y≤4.

[0071] In some embodiments, the coating layer includes at least one of Li2WO4, Li3BO3, LiMoO4, LiVO3, Li2SO4, and Li3PO4.

[0072] Li x Q e O y It is a functional structure with fast ion conductor / fast charge channel, which can reduce the initial impedance of the positive electrode material; for example, Li x Q e O y At least one of Li2WO4, Li3BO3, LiMoO4, LiVO3, Li2SO4 and Li3PO4 can be selected. Of course, Li x Q e O y It may also be other functional structures having fast ion conductors / fast charge channels, which are not listed here one by one.

[0073] In some embodiments, 0.985≤Li / Me≤0.999, where Li / Me is the molar ratio of lithium metal to other metals other than lithium in the positive electrode material;

[0074] In some embodiments, 1.001≤Li / Me≤1.015, where Li / Me is a molar ratio of lithium metal to other metals except lithium in the positive electrode material.

[0075] When the Li / Me value is within the above range, the lithium ion content in the positive electrode material is within an appropriate range, the distribution of lithium metal and other metal elements in the positive electrode material is relatively uniform, the structural stability of the positive electrode material is strong, and while taking safety into account, the positive electrode material also has a higher capacity.

[0076] In some embodiments, in the XRD spectrum of the positive electrode material, the half-maximum width of the diffraction peak of the (104) crystal plane is 0.19 to 0.25. When the half-maximum width of the (104) crystal plane is within the above range, the capacity and cycle performance of the positive electrode material are good.

[0077] In some embodiments, the positive electrode material includes secondary particles, and the median particle size D50 of the secondary particles is between 7 μm and 12 μm, specifically 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, or any value therebetween. The particle size of the secondary particles can improve the cracking of the positive electrode material. By controlling the median particle size of the secondary particles within the above range, the structural stability of the positive electrode material is improved, and the capacity of the positive electrode material can be ensured without affecting the volumetric energy density of the positive electrode material.

[0078] In some embodiments, the particle size distribution curve of the cathode material has a characteristic peak. The calculation formula for the structural stability coefficient ε proposed in this application has a strong correlation with the performance identification of cathode materials with a unimodal particle size distribution, and its identification accuracy is high, which can greatly reduce the testing cycle and reduce the testing cost.

[0079] In some embodiments, the pH value of the positive electrode material is 10-13, specifically 10, 11, 12, 13, or any value therebetween. Preferably, the pH value of the positive electrode material is 11-12, specifically 11, 12, or any value therebetween. By controlling the pH value of the positive electrode material within this range, electrode coating is facilitated and gas generation during battery manufacturing can be reduced.

[0080] In some embodiments, the specific surface area of ​​the positive electrode material is 0.2 m 2 / g~0.8m 2 / g, specifically 0.2m 2 / g, 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g or any value therebetween; preferably, the specific surface area of ​​the positive electrode material is 0.6m 2 / g~0.8m 2 / g, specifically 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g or any value therebetween. A high specific surface area facilitates contact between the positive electrode material and the electrolyte, thereby increasing the battery capacity. However, an excessively large specific surface area can lead to poor battery cycle performance. By controlling the specific surface area of ​​the positive electrode material within the above range, the cycle performance of the battery made with the positive electrode material can be improved while taking into account the capacity.

[0081] In some embodiments, the compacted density of the positive electrode material is greater than 3 g / cm 3When the compaction density of the positive electrode material is within the above range, it is beneficial to improve the energy density of the battery.

[0082] In some embodiments, the conductivity σ of the positive electrode material is greater than 0.03 S / cm. The positive electrode material has a relatively high conductivity because proper doping and coating modification improve the conductivity of the positive electrode material and reduce the initial impedance of the positive electrode material.

[0083] In some embodiments, 0.1≤α Li ≤0.55. The residual alkali on the surface of the positive electrode material will affect the coating of the positive electrode slurry, causing electrode stratification, thereby leading to increased interface side reactions and large initial impedance. In particular, compared with LiOH, Li2CO3 plays a more important role in the initial impedance of lithium-ion batteries. This is because Li2CO3 has lower electrochemical activity and worse conductivity than LiOH, so there are too many L in the residual alkali. i2 The CO3 content will ultimately affect the electrochemical performance of the positive electrode material; this embodiment helps to reduce the initial impedance of the positive electrode material (the initial impedance of the lithium-ion battery assembled from the corresponding positive electrode material, the same below) by controlling the Li2CO3 content within the above range.

[0084] Furthermore, 0.1≤β Li By controlling the content of LiOH within the above range, it is beneficial to further reduce the initial impedance of the positive electrode material.

[0085] In some embodiments, the initial moisture content of the positive electrode material is less than 200 ppm, and the moisture content after 24 hours of exposure to air is less than 1000 ppm. This means that the positive electrode material in these embodiments has strong resistance to moisture absorption, effectively controlling the increase in impedance of the positive electrode material during battery operation. This is primarily due to the fact that the dopant element M in the matrix material cooperates with other metal elements to stabilize the interface structure on the matrix material surface, and the coating element Q combines with residual lithium on the matrix material surface to form a protective layer covering the matrix material, thereby enhancing the structural stability of the positive electrode material and correspondingly improving its resistance to moisture absorption.

[0086] A method for preparing the above-mentioned positive electrode material is proposed below, and the preparation method comprises:

[0087] Step S100, uniformly mixing a hydroxide precursor, a lithium source, and a dopant containing an M element to form a mixture;

[0088] Step S200 , performing a first sintering treatment on the mixture at 600° C. to 800° C. in an oxygen-containing atmosphere to obtain a base material;

[0089] Step S300, spraying and dropping a coating solution containing Q element into the above-mentioned base material for coating treatment;

[0090] Step S400 , performing a second sintering treatment on the coated product in an oxygen-containing atmosphere to obtain a positive electrode material.

[0091] In the above scheme, a mixture containing a hydroxide precursor, a lithium source and a dopant containing an M element is first sintered in an oxygen-containing atmosphere to obtain a matrix material. By controlling the temperature of the first sintering process, the grain size D of the positive electrode material can be controlled. 104 , thereby reducing the formation of dislocations or stacking faults in the crystal structure of the positive electrode material, improving the orderliness of the layered structure of the positive electrode material, improving the structural stability of the positive electrode material, and thus improving the capacity and cycle performance of the positive electrode material. Secondly, the coating solution containing the Q element is sprayed and dripped into the above-mentioned base material for coating treatment. The coating uniformity can be improved by spraying and dripping, so that the coating solution containing the Q element is uniformly and completely coated on the surface of the base material; finally, the product after the coating treatment is subjected to a second sintering treatment. During the second sintering treatment, the coating solution containing the Q element forms a uniform and complete coating layer on the surface of the base material. At the same time, the residual lithium on the surface of the base material can react with the coating material to form a lithium composite metal oxide attached to the surface of the base material to form a coating layer, which can reduce the surface residual alkali and impedance of the positive electrode material, so that the positive electrode material has both low gas production and low impedance, thereby improving the safety performance of the positive electrode material. The following is a detailed introduction to the preparation method of the present application in combination with the above embodiments:

[0092] In step S100 , a hydroxide precursor, a lithium source, and a dopant containing an M element are uniformly mixed to form a mixture.

[0093] In some embodiments, the hydroxide precursor has the formula Ni a Co b Mn c (OH)2, wherein 0.8<a<0.98, 0<b<0.2, 0<c<0.2, a+b+c=1. The value of a can be 0.81, 0.83, 0.86, 0.89, 0.9, 0.91, 0.93, 0.95, 0.96 or 0.97, etc., the value of b can be 0.001, 0.01, 0.05, 0.1, 0.15, 0.16, 0.17 or 0.19, etc., and the value of c can be 0.001, 0.01, 0.05, 0.1, 0.15, 0.16, 0.18 or 0.19, etc., without limitation herein.

[0094] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium sulfate, lithium chloride, lithium nitrate, and lithium oxalate. Preferably, the lithium source is lithium hydroxide, specifically lithium hydroxide monohydrate or anhydrous lithium hydroxide, without limitation.

[0095] In some embodiments, the molar ratio of Li in the lithium source to the metal element in the hydroxide precursor is 0.9 to 1.1, specifically 0.9, 0.92, 0.95, 0.98, 1.0, 1.01, 1.02, 1.03, 1.05, 1.08 or 1.1, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0096] In some embodiments, the mass ratio of the dopant containing the M element to the hydroxide precursor is less than 0.1, and can be specifically 0.098, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02 or 0.01, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0097] In some embodiments, the dopant containing the M element includes at least one of Sr(OH)2, SrO, TiO2, Al2O3, Al(OH)3, ZrO2, Zr(OH)4, Y2O3, BaO, MgO, Mg(OH)2, Nb2O5, Nb2O3, MoO3, WO2, WO3, V2O5, and V2O3. Preferably, Al(OH)3, Sr(OH)2, and WO3 are used.

[0098] In some embodiments, the mixing time is 0.5 h to 1 h, specifically 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h or 1 h, etc., and other values ​​within the above range are also possible, and are not limited here. Preferably, the mixing time is 0.5 h.

[0099] Step S200 , performing a first sintering treatment on the mixture at 600° C. to 800° C. in an oxygen-containing atmosphere to obtain a base material.

[0100] In some embodiments, the temperature of the first sintering treatment is 600°C to 800°C, specifically 600°C, 620°C, 650°C, 700°C, 750°C, 780°C or 800°C, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0101] In some embodiments, the time for the first sintering treatment is 8 hours to 25 hours, specifically 8 hours, 10 hours, 12 hours, 15 hours, 18 hours, 20 hours, 22 hours, 24 hours or 25 hours, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0102] It can be understood that the present invention is beneficial to control the grain size D of the positive electrode material by controlling the temperature and time of the first sintering process within the above range. 104 , thereby reducing the formation of dislocations or stacking faults in the crystal structure of the positive electrode material, improving the orderliness of the layered structure of the positive electrode material, improving the structural stability of the positive electrode material, and thus improving the capacity and cycle performance of the positive electrode material.

[0103] In some embodiments, the oxygen inlet rate is controlled, and the bottom inlet rate is 10-50m 3 / h, the air intake rate on the left and right sides is 10-50m3 / h, and the air intake rate on the top is 10-50m 3 / h. Control the calcination chamber pressure to 10-100 Pa.

[0104] In some embodiments, the method further includes crushing and screening the sintered product to obtain a matrix material.

[0105] In some embodiments, screening is performed using an ultrasonic vibration screener having a frequency of 20 kHz to 50 kHz, specifically 20 kHz, 25 kHz, 30 kHz, 35 kHz, 40 kHz, 45 kHz, or 50 kHz, etc., without limitation herein. It is understood that screening the sintered product using an ultrasonic vibration screener can ensure uniform dispersion of the matrix material particles, reduce agglomeration of the matrix material particles, and improve the coating uniformity between the matrix material and the coating material.

[0106] In some embodiments, the average particle size of the matrix material is 9 μm to 12 μm, specifically 9 μm, 9.2 μm, 9.5 μm, 10 μm, 11 μm, 11.5 μm, 11.8 μm, or 12 μm, etc., and other values ​​within the above range are also possible and are not limited herein. Preferably, the average particle size of the matrix material is 10.5 μm.

[0107] Step S300: spraying and dropping a coating solution containing Q element into the above-mentioned base material for coating treatment.

[0108] In some embodiments, before step S300 , the process further includes: dissolving a coating agent containing the Q element in water to form a coating solution containing the Q element.

[0109] In some embodiments, based on the mass of the positive electrode material as 100%, the amount of water added to the coating solution is 1% to 10%, specifically 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0110] In some embodiments, the mass ratio of the Q-containing coating agent to the base material is less than 0.1, and can specifically be 0.098, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, or 0.01, etc., and can also be other values ​​within the above range, which is not limited here. Preferably, the mass ratio of the Q-containing coating agent to the base material is 0.01 to 0.04.

[0111] In some embodiments, the coating treatment is carried out under stirring, and the stirring temperature is 100°C to 300°C, specifically 100°C, 120°C, 150°C, 180°C, 200°C, 240°C, 280°C or 300°C, etc., which is not limited here; the stirring time is 0.5h to 2h, specifically 0.5h, 0.8h, 1.0h, 1.1h, 1.2h, 1.5h, 1.8h or 2h, etc., which is not limited here.

[0112] The present application can improve the coating uniformity of the coating agent on the base material by controlling the stirring time and temperature during the coating process within the above range.

[0113] In some embodiments, the coating agent containing Q element includes (NH4)2SO4, NH4HSO4, (NH4)6W7O 24 6H2O, H 28 N6O 41 W 12 、H 18 N3O 43 PW 12 , at least one of NH4F, NH4HF, (NH4)3PO4, (NH4)2HPO4, and (NH4)2MoO4.

[0114] In some embodiments, the spray frequency is controlled, using a "spot spray" method. This involves setting a pulse current so that the solution is continuously sprayed for 1 to 20 seconds, paused for 1 to 20 seconds, and then cycled until the solution spraying is completed. The spray flow rate is set to 0.1 to 2 ml / min. The spray pressure is controlled by a frequency converter, with the spray starting at a pressure of 1 to 100 kPa and remaining at 1 to 100 kPa until the pulse spraying ends, with the pressure at the end of the spraying being greater than the pressure at the start of the spraying.

[0115] It can be understood that the present application sets a pulse "spot spraying" method during the control coating process, which reserves a certain reaction time for the positive electrode material and the coating material, and continues to spray after the reaction is completed. At the same time, the spray range is related to the spray pressure. In one cycle of "spot spraying", comprehensive coating from a small range to a large range can be achieved. Under such a cyclic spray injection, sufficient reaction area is reserved for the positive electrode material and the coating agent. During the continuous flipping of the material, the intermittent addition of the solution can improve the uniformity of the interface reaction, while further stabilizing the interface structure of the material and filling the micro gaps between the primary particles. Therefore, the mechanical properties of the positive electrode material, such as particle strength, are enhanced.

[0116] Step S400 , performing a second sintering treatment on the coated product in an oxygen-containing atmosphere to obtain a positive electrode material.

[0117] In some embodiments, the temperature of the second sintering treatment is 200°C to 600°C, and specifically can be 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, or 600°C, etc. Of course, other values ​​within the above range are also possible and are not limited here. Preferably, the temperature of the second sintering treatment is 300°C.

[0118] In some embodiments, the second sintering treatment time is 6 hours to 12 hours, specifically 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, etc., and of course other values ​​within the above range are also possible, and are not limited here. Preferably, the second sintering treatment time is 8 hours.

[0119] In a second aspect, the present application provides a battery, which includes the positive electrode material of the first aspect or the positive electrode material prepared according to the preparation method of the positive electrode material.

[0120] The battery provided herein may be a secondary battery (e.g., a lithium-ion battery, a sodium-ion battery, etc.), comprising a housing, an electrode assembly, and an electrolyte. The electrode assembly and the electrolyte are both located within the housing. The housing may be a packaging bag encapsulated with an encapsulating film (e.g., an aluminum-plastic film), such as a soft-pack secondary battery.

[0121] In other embodiments, the secondary battery may also be a steel-shell battery, an aluminum-shell battery, etc.

[0122] FIG1 is a schematic diagram of a battery in a discharge state according to an embodiment of the present application. As shown in FIG1 , the battery includes a housing and an electrode assembly. The electrode assembly includes a positive electrode sheet 1, a negative electrode sheet 2, and a separator 3. The separator 3 is disposed between the positive electrode sheet 1 and the negative electrode sheet 2. The electrode assembly may be a laminated structure, in which the positive electrode sheet 1, the separator 3, and the negative electrode sheet 2 are alternately stacked in sequence. In other embodiments, the electrode assembly may also be a wound structure, in which the positive electrode sheet, the separator, and the negative electrode sheet are stacked in sequence and then wound.

[0123] In some embodiments, the positive electrode sheet 1 includes a positive electrode current collector 11 and a positive electrode active material layer 12 disposed on at least one surface of the positive electrode current collector 11 .

[0124] In some embodiments, the positive electrode current collector 11 may be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, a current collector formed by combining the aforementioned conductive foil (aluminum foil or nickel foil, etc.) and a polymer substrate. The positive electrode active material layer 12 comprises a positive electrode active material, a conductive agent, and a binder, wherein the positive electrode active material is the positive electrode material of the first aspect described above or a positive electrode material prepared according to the above-described method for preparing the positive electrode material.

[0125] In some embodiments, the preparation method of the positive electrode sheet 1 is: the positive electrode active material, the conductive agent, the binder and the solvent are mixed uniformly in a certain proportion to form a slurry, and then the slurry is evenly coated on the positive electrode collector 11, and vacuum dried at a certain temperature to obtain the positive electrode sheet 1.

[0126] In some embodiments, the conductive agent includes at least one of conductive carbon black, Ketjen black, graphite, and acetylene black.

[0127] In some embodiments, the binder includes at least one of sodium carboxymethylcellulose, cyclodextrin, and polyvinylidene fluoride.

[0128] In some embodiments, the solvent is selected from at least one of deionized water, N-methylpyrrolidone, and N,N-dimethylformamide.

[0129] In some embodiments, the vacuum drying temperature is 60°C to 120°C, specifically 60°C, 70°C, 80°C, 90°C, 100°C, 110°C or 120°C, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0130] In some embodiments, the negative electrode sheet 2 includes a negative electrode current collector 21 and a negative electrode active material layer 22 disposed on at least one surface of the negative electrode current collector.

[0131] In some embodiments, the negative electrode current collector 21 can be made of at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or a carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, a current collector formed by combining the aforementioned conductive foil and a polymer substrate. The negative electrode active material layer 22 includes a negative electrode material, which includes, but is not limited to, at least one of natural graphite negative electrode material, natural graphite negative electrode material, or silicon-based negative electrode material.

[0132] The embodiments of the present application will be described in detail below in conjunction with specific examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, the conditions are carried out according to conventional conditions or manufacturer recommendations. The reagents or instruments used are not specified by the manufacturer and are conventional products that can be purchased commercially.

[0133] Example 1

[0134] (1) LiOH·H2O, hydroxide precursor Ni 0.9 Co 0.09 Mn 0.01 (OH)2 is uniformly mixed with Al(OH)3, 0.4wt% of Sr(OH)2 and 0.2wt% of WO3 in a molar ratio of 1.02 and a doping amount of 0.3wt% of the mass of the precursor to obtain a mixture;

[0135] (2) The mixture was placed in an oxygen atmosphere and sintered at 720°C for 12 hours. The oxygen inlet rate was controlled, and the bottom inlet rate was 40m 3 / h, the air intake rate on the left and right sides is 20m 3 / h, the top air intake rate is 30m 3 / h. The calcination chamber pressure is controlled at 30 Pa. The primary sintered product is cooled, crushed, and sieved to obtain the matrix material;

[0136] (3) 0.2g of ammonium tungstate (NH4)6W7O 24 6H2O was dissolved in 5g of deionized water to form a coating solution; 50g of the above-mentioned matrix material was added to the reactor, and the temperature of the reactor was raised to 200°C, and the coating solution was transferred to the spray system. The spray frequency was controlled, and a "point spray" method was adopted, that is, a pulse current was set, and the solution was continuously sprayed for 5 seconds, stopped for 10 seconds, and so on until the solution spraying was completed. The spray flow rate was set to 1ml / min. The spray pressure was controlled by a frequency converter, that is, the pressure at the start of the spray was 10kPa, and at the end of the pulse spraying, the pressure was 20kPa. After all the coating solution was dripped into the reactor, it was stirred for 2h to obtain a coated product.

[0137] (4) The coated product was placed in an oxygen-containing atmosphere and sintered at 450°C for 5 h, cooled, and sieved to obtain a positive electrode material.

[0138] The general chemical formula of the cathode material prepared in this embodiment is LiNi 0.8948 Co 0.0895 Mn 0.0099 Al 0.0012 Sr 0.0013 W 0.0033 O2.

[0139] Figure 2 is a curve diagram of the relationship between the differential value dpH / dV of the positive electrode material provided in Example 1 of the present application and the consumption volume VmL of hydrochloric acid; it can be seen from Figure 2 that the positive electrode material has four characteristic peaks in the range of the consumption volume VmL of hydrochloric acid of 4 to 11 (excluding 4 and 11), and the value of V2-V1 is 2.6.

[0140] Example 2

[0141] The difference from Example 1 is that the doping amount of the dopant Al(OH) 3 in step (1) is 0.6 wt % of the mass of the precursor.

[0142] The general chemical formula of the cathode material prepared in this embodiment is LiNi 0.8940 Co 0.0894 Mn 0.0099 Al 0.0021 Sr 0.0013 W 0.0033 O2.

[0143] Example 3

[0144] The difference from Example 1 is that the doping amount of the dopant Sr(OH)2 in step (1) is 0.8 wt% of the mass of the precursor.

[0145] The general chemical formula of the cathode material prepared in this embodiment is LiNi 0.8936 Co 0.0894 Mn 0.0099 Al 0.0012 Sr 0.0026 W 0.0033 O2.

[0146] Example 4

[0147] The difference from Example 1 is that the doping amount of WO3 in step (1) is changed to 0.3wt% of the mass proportion of the precursor. The chemical formula of the positive electrode material prepared in this example is LiNi 0.8941 Co 0.0894 Mn 0.0099 Al 0.0010 Sr 0.0013 W 0.0043O2.

[0148] Example 5

[0149] The difference from Example 14 is that the sintering temperature in step (2) is 690°C.

[0150] The general chemical formula of the cathode material prepared in this embodiment is LiNi 0.8948 Co 0.0895 Mn 0.0099 Al 0.0012 Sr 0.0013 W 0.0033 O2.

[0151] Example 6

[0152] The difference from Example 1 is that the sintering temperature in step (2) is 750°C.

[0153] The general chemical formula of the cathode material prepared in this embodiment is LiNi 0.8948 Co 0.0895 Mn 0.0099 Al 0.0012 Sr 0.0013 W 0.0033 O2.

[0154] Example 7

[0155] The difference from Example 1 is that in step (3), the temperature of the reactor is adjusted to 50°C.

[0156] The general chemical formula of the cathode material prepared in this embodiment is LiNi 0.8948 Co 0.0895 Mn 0.0099 Al 0.0012 Sr 0.0013 W 0.0033 O2.

[0157] Figure 3 is a curve diagram of the relationship between the differential value dpH / dV of the positive electrode material provided in Example 7 of the present application and the consumption volume VmL of hydrochloric acid; it can be seen from Figure 3 that the positive electrode material has four characteristic peaks in the range of the consumption volume VmL of hydrochloric acid of 4 to 11 (excluding 4 and 11), and the value of V2-V1 is 1.82.

[0158] Example 8

[0159] The difference from Example 1 is that in step (3), the temperature of the reactor is adjusted to 250°C.

[0160] The general chemical formula of the cathode material prepared in this embodiment is LiNi 0.895 Co 0.089 Mn 0.010 Al 0.001 Sr0.001 W 0.003 O2.

[0161] Example 9

[0162] The difference from Example 1 is that the sintering temperature in step (4) is 200°C.

[0163] The general chemical formula of the cathode material prepared in this embodiment is LiNi 0.8948 Co 0.0895 Mn 0.0099 Al 0.0012 Sr 0.0013 W 0.0033 O2.

[0164] Example 10

[0165] The difference from Example 1 is that the sintering temperature in step (4) is 300°C.

[0166] The general chemical formula of the cathode material prepared in this embodiment is LiNi 0.8948 Co 0.0895 Mn 0.0099 Al 0.0012 Sr 0.0013 W 0.0033 O2.

[0167] Example 11

[0168] The difference from Example 1 is that the first sintering temperature in step (2) is 600°C.

[0169] The general chemical formula of the cathode material prepared in this embodiment is LiNi 0.8948 Co 0.0895 Mn 0.0099 Al 0.0012 Sr 0.0013 W 0.0033 O2.

[0170] Example 12

[0171] The difference from Example 1 is that the amount of deionized water in step (3) is reduced to 2 g.

[0172] The general chemical formula of the cathode material prepared in this embodiment is LiNi 0.8948 Co 0.0895 Mn 0.0099 Al 0.0012 Sr 0.0013 W 0.0033 O2.

[0173] Example 13

[0174] The difference from Example 4 is that in step (3), the injection time is 10 seconds and the dwell time is 15 seconds.

[0175] The general chemical formula of the cathode material prepared in this embodiment is LiNi 0.8948 Co 0.0895 Mn 0.0099 Al 0.0012 Sr 0.0013 W 0.0033 O2.

[0176] Example 14

[0177] The difference from Example 4 is that the injection flow rate in step (3) is 0.5 ml / min.

[0178] Example 15

[0179] The difference from Example 4 is that the injection flow rate in step (3) is 1.5 ml / min.

[0180] Example 16

[0181] The difference from Example 4 is that in step (3), the pulse start injection pressure is 20 kPa, and the pulse end injection pressure is 30 kPa.

[0182] Example 17

[0183] The difference between this embodiment and embodiment 1 is that in step (1), the hydroxide precursor is Ni 0.92 Co 0.07 Mn 0.01 (OH)2,

[0184] The general chemical formula of the positive electrode material prepared in this embodiment is LiNi0.9147Co0.0696Mn0.0099Al0.0012Sr0.0013W0.0033O2.

[0185] Example 18

[0186] The difference between this embodiment and embodiment 1 is that in step (1), the hydroxide precursor is Ni 0.83 Co 0.09 Mn 0.08 (OH)2,

[0187] The general chemical formula of the positive electrode material prepared in this embodiment is LiNi0.8252Co0.0895Mn0.0795Al0.0012Sr0.0013W0.0033O2.

[0188] Comparative Example 1

[0189] The difference from Example 1 is:

[0190] (2) sintering the mixture at 820° C. for 20 h in an oxygen-containing atmosphere, cooling, crushing, and screening the sintered product to obtain a matrix material;

[0191] (3) 0.2g of ammonium tungstate (NH4)6W7O 24 6H2O was dissolved in 5g of deionized water to form a coating solution; 50g of the above-mentioned substrate material was added to a reactor, and the reactor temperature was raised to 200°C. Then, a rubber-tipped dropper was used to continuously spray the coating solution into the reactor at a rate of 1ml / min. After the coating solution was completely added to the reactor, it was stirred for 2h to obtain a coated product.

[0192] Comparative Example 2

[0193] The difference from Example 1 is:

[0194] (3) 50g of the above matrix material was added to the reactor, and the reactor temperature was raised to 200°C, and then 0.2g of ammonium tungstate (NH4)6W7O was added thereto. 24 ·6H2O, stirred for 2h to obtain the coated product.

[0195] Figure 4 is a graph showing the relationship between the differential value dpH / dV of the positive electrode material provided in Comparative Example 2 of the present application and the consumed volume VmL of hydrochloric acid; as shown in Figure 4, the positive electrode material after dry coating has only two sudden peaks in its potentiometric titration, indicating that the dry coating method may not have successfully coated the coating agent on the surface of the base material, or the coating agent is less distributed on the surface of the base material. During the titration process, the titrant hydrochloric acid fails to react with the coating material or the coating product, and thus no sudden peak can be detected.

[0196] Comparative Example 3

[0197] The difference from Example 1 is:

[0198] (2) sintering the mixture at 580° C. for 12 h in an oxygen-containing atmosphere, cooling, crushing, and screening the sintered product to obtain a matrix material;

[0199] (3) 0.2g of ammonium tungstate (NH4)6W7O 24 6H2O was dissolved in 100g of deionized water to form a coating solution; 50g of the above-mentioned substrate material was added to a reactor, and the reactor temperature was raised to 200°C. Then, the coating solution was added dropwise to the reactor using a rubber-tipped dropper. After the coating solution was completely added to the reactor, the mixture was stirred for 2h to obtain a coated product.

[0200] Figure 5 is a graph showing the relationship between the differential value dpH / dV of the positive electrode material provided in Comparative Example 3 of the present application and the consumed volume V of hydrochloric acid; as shown in Figure 5, the potentiometric titration peak has more miscellaneous peaks. This is because during the wet coating process, water washing causes more lithium ions to be dissolved from the surface of the positive electrode material, resulting in more ions (such as metal ions dissolved during the hydrolysis process, etc.) interfering with the titration results.

[0201] The performance of the positive electrode materials prepared in the above embodiments and comparative examples was tested using the following method:

[0202] 1. Residual alkali test:

[0203] 5 g of the cathode material was dispersed in 100 mL of deionized water, and residual carbonate and hydroxide were dissolved by magnetic stirring. The filtrate was filtered and added with hydrochloric acid solution. The titration was performed using a Swiss Mettler G20S automatic potentiometric titrator using an equivalent drop method, and the carbonate and hydroxide contents of the cathode material were calculated.

[0204] 2. XRD test:

[0205] The samples were characterized by XRD using an XRD diffractometer with a scanning range of 10-90° and a scanning step of 0.05°. The incident angle (2θ), interplanar spacing (d), full width at half maximum (FWHM) and other parameters of the sample were read using Jade software to calculate the R value of the sample, and the D value of the sample was calculated using the Scherrer formula. 104 value.

[0206] 3. Particle size test:

[0207] The particle size distribution of the positive electrode material particles was obtained by using a British Malvern Mastersizer 3000 laser particle size analyzer and the light intensity distribution of the laser diffraction.

[0208] 4. Specific surface area test:

[0209] 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.

[0210] 5. Conductivity test:

[0211] 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.

[0212] 6. Moisture test:

[0213] The moisture content of the material was tested using a Mettler moisture meter. 5 g of powder sample was pre-dried and then placed in a glass vial. Coulometric titration with iodine was performed, and the moisture content of the material was calculated according to the Karl Fischer method.

[0214] 7. pH test:

[0215] The pH value of the material was measured using a Mettler pH meter. 5 g of powder sample was dissolved in 45 ml of pure water, stirred at a certain speed for 30 min, and then tested with a pH meter. The pH values ​​of the standard solutions were 4.01 / 7.0 / 9.21, respectively.

[0216] 8. Morphology test

[0217] The surface morphology of the material was characterized by a Hitachi Regulus 8100 field emission scanning electron microscope with an accelerating voltage of 1 kV.

[0218] 9. Compaction test:

[0219] 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, which met the compaction density requirement of >3g / cm 3 .

[0220] 10. Tap density test of positive electrode material:

[0221] Using a vibrator, weigh a certain amount of sample and vibrate 3000 times at 300 times / min to test the tap density.

[0222] 11. ICP test:

[0223] The metal content of the cathode material was measured using an Agilent 5110 ICP-OES. 0.2g of the cathode material was dissolved in a mixture of nitric acid and hydrochloric acid (3:1 by volume), heated for digestion, and then diluted to 100ml. The instrument then read the data and calculated the Li / Me ratio of the sample.

[0224] 12. Potentiometric titration:

[0225] 5g of cathode material is dispersed in 100ml of deionized water and magnetically stirred to dissolve residual carbonate and hydroxide. The filtrate is filtered and titrated with hydrochloric acid using an automatic potentiometric titrator using the equivalent drop method. The pH method is used for reading, and a "dpH / dV" differential fit is performed based on the pH change and the amount of hydrochloric acid solution consumed. The fitted differential curve is then calculated by calculating the distance between the first and last peaks of the curve, which can be used to assess the cathode material's gas production and other properties. Furthermore, the carbonate and hydroxide content in the cathode material can be calculated based on the break point and the amount of hydrochloric acid consumed.

[0226] 13. Particle hardness G of positive electrode material D50 and G D90 test:

[0227] Using a Shimadzu dynamic ultramicrohardness tester, three or more intact positive electrode material particles with a particle size in the range of 9um-13um and three or more intact positive electrode material particles with a particle size in the range of 16um-20um were randomly selected under the display of the instrument. A probe was used to apply a certain pressure to the positive electrode material particles, and the deformation displacement of the particles was recorded. When the particles broke, the pressure applied at this time was recorded and the average value was calculated. The particle hardness of the positive electrode material was obtained by calculation and recorded as G D50 and G D90 .

[0228] 14. Power-off performance test:

[0229] 0.8g of the positive electrode materials prepared in the above examples and exploratory examples, 0.1g of conductive carbon black, and 0.1g of polyvinylidene fluoride were placed in a ball mill. 15mL of N-methylpyrrolidone was added and ball milled to form a uniform slurry. The slurry was then evenly coated on aluminum foil and vacuum-dried at 110°C for 12 hours to obtain the positive electrode sheet. A lithium metal sheet was used as the negative electrode. In a glove box, the positive electrode shell, electrode sheet, 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 were assembled and sealed to produce a 2032 coin-shaped half-cell. The cells were allowed to stand for 24 hours. The resulting batteries were then placed in a constant temperature chamber for testing. 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.

[0230] 15. DC resistance test:

[0231] The DC resistance is tested using a full-cell battery. Unlike button-type half-cells, graphite is used as the negative electrode. After assembly, a 2032-type button-type full-cell battery is obtained. The battery is charged to 4.2V at a current density of 1C. After standing for 2 minutes, it is placed at 2.5V with a current of 1C to obtain the capacity C. Repeat the above steps to fully charge the battery and let it stand for 1 hour. The battery state of charge is adjusted to 50% SOC with a current of 1C. Discharge at a current of 1C for 30 seconds. The discharge DC resistance value at that SOC is the voltage difference before and after discharge divided by the current. Repeat the above steps for 500 cycles to obtain the discharge DC resistance value after 500 cycles.

[0232] 16. Soft pack battery volume expansion rate test:

[0233] The positive electrode materials and graphite negative electrodes prepared in Examples 1 to 16 and Comparative Examples 1 to 3 were fabricated into pole pieces, and soft-pack batteries were produced through lamination, tab welding, shell punching, packaging, liquid injection, pre-charging, formation, and degassing. The prepared soft-pack battery was immersed in a beaker filled with deionized water, and the scale mark V0 was recorded at this time. The soft-pack battery, which had been cycled at 60°C for 50, 100, and 200 cycles, was then immersed in the beaker, and the scale mark V3 was recorded at this time. The volume expansion rate of the soft-pack battery was calculated as (V3-V0) / V0*100.

[0234] The test results of the positive electrode material samples prepared in the above embodiments and comparative examples are shown in the following table:

[0235] Table 1: Test results of surface structure stability coefficient and other physical and chemical indicators

[0236] Table 2: Basic physical and chemical properties test results

[0237] Table 3: Titration curve test results

[0238] Table 4: Test results of power-off performance

[0239] Analyzing the above table, by comparing Examples 1-18 with Comparative Examples 1-3, it can be seen that when the positive electrode material satisfies the relationship: ε=log(D 104 ) / R, 0.90<ε<1.03, and in its potentiometric titration curve, 2<N≤4, 0.6<V2-V1<2.7, and 0<dE / dV<10, and it has the characteristics of reducing the gas generation and impedance of the positive electrode material, while improving the structural order and structural stability of the positive electrode material, thereby improving the safety performance, capacity and cycle performance of the positive electrode material.

[0240] Specific analysis:

[0241] According to the test data in Table 1, the positive electrode materials prepared in Examples 1 to 18 are obtained by controlling the grain size D corresponding to the (104) crystal plane. 104 , the diffraction peak intensity I of (003) crystal plane and (104) crystal plane 003 / I 104 The relationship between ε and the orderliness of the layered structure can be balanced by setting the value of ε between 0.90 and 1.03 (excluding 0.90 and 1.03), so that the grain size and ordered layered structure of the positive electrode material reach an ideal state, thereby making the positive electrode material have a suitable grain size and ordered layered structure, which can improve the structural stability of the positive electrode material and improve the capacity and cycle performance of the positive electrode material.

[0242] According to the test data of Example 1 and Example 2, the amount of Al(OH)3 was increased in Example 2, and the capacity of the positive electrode material decreased. It can be seen that excessive doping of inert elements will occupy the TM-O-Li layer, resulting in a decrease in the capacity and cycle performance of the positive electrode material.

[0243] According to the test data of Example 1 and Example 5, the positive electrode material of Example 5 has a lower grain size D due to the lower temperature of the first sintering treatment during the preparation process. 104 The atomic distance between small-sized particles is relatively short, which makes it easy to form dislocations or stacking faults. The order of the layered structure of the positive electrode material is disrupted, and lithium-nickel mixing is likely to occur, resulting in the diffraction peak intensity I of the (003) crystal plane and the (104) crystal plane of the positive electrode material. 003 / I 104 The ratio is reduced, resulting in a higher ε value, and the capacity and cycle performance of the positive electrode material are reduced compared to Example 1.

[0244] According to the test data of Example 1 and Example 11, the positive electrode material of Example 11 has a grain size D of 0.0477mm due to the low temperature of the first sintering process during the preparation process. 104 The atomic distance between the positive electrode material particles is smaller, the crystal structure of the positive electrode material is prone to dislocation or stacking fault, and the orderliness of the layered structure of the material is reduced, resulting in a decrease in the capacity and cycle performance of the positive electrode material compared to Example 1.

[0245] According to the test data of Example 1 and Comparative Example 1, the temperature of the first sintering of the positive electrode material in the preparation process of Comparative Example 1 is too high, resulting in a grain size D 104If the value of ε is too large, the ε value of the positive electrode material will be too large, and the grain size and ordered layered structure of the positive electrode material will be difficult to reach the ideal state. The structural stability of the positive electrode material will decrease, which will lead to a decrease in the capacity and cycle performance of the positive electrode material.

[0246] According to the test data of Example 1 and Comparative Example 2, the positive electrode material of Comparative Example 2 is prepared by dry coating. During the coating process, the coating material on the surface of the base material is unevenly distributed. Therefore, during the second sintering process, the coating material will form uneven penetration on the surface of the positive electrode material, thereby destroying the layered structure on the surface of the positive electrode material and reducing the grain size D of the positive electrode material. 104 Compared with Example 1, the diffraction peak intensity I of (003) crystal plane and (104) crystal plane is increased. 003 / I 104 The ratio decreases, resulting in an excessively large ε value of the prepared positive electrode material, making it difficult for the grain size and ordered layered structure of the positive electrode material to reach an ideal state, and reducing the capacity and cycle performance of the positive electrode material.

[0247] According to the test data of Example 1 and Comparative Example 3, the amount of deionized water added to the positive electrode material of Comparative Example 3 during the preparation of the coating solution is too much. During the coating process, the base material particles are very sensitive to water. When the particle surface is oxidized, the surface layered structure of the positive electrode material is easily transformed into a spinel structure or a rock salt phase. The Ni-O oxides of the 003 crystal face or the 104 crystal face with more exposed surfaces are easily converted into impurities such as NiO or NiOOH, resulting in I 003 / I 104 The ratio increases; at the same time, the first sintering temperature is too low, resulting in the grain size D of the positive electrode material 104 The ε value of the prepared positive electrode material is too small, and the grain size and ordered layered structure of the positive electrode material are difficult to reach the ideal state, and the capacity and cycle performance of the positive electrode material are reduced.

[0248] According to the test data in Table 3, the positive electrode materials prepared in Examples 1 to 16 have a V2-V1 value between 0.6 and 2.7 (excluding 0.6 and 2.7), and the coating material on the surface of the positive electrode material is evenly distributed and has a good coating effect, which can reduce the surface residual alkali and impedance of the positive electrode material, so that the positive electrode material has both low gas production and low impedance, thereby improving the safety performance of the positive electrode material.

[0249] Compared to Example 1, Example 7 employed a low-temperature coating method during the coating reaction. However, according to the volume expansion results of the soft-pack battery in Table 3, it can be seen that the gas production in Example 7 was not improved. After the battery was cycled for 200 cycles, its volume expanded to 25.1%. This is because the decomposition temperature of ammonium tungstate is above 100°C. Therefore, during the low-temperature dropwise coating reaction, the ammonium tungstate is still distributed on the surface of the substrate material in the form of molecular groups and cannot react with the residual alkali in the form of ionic groups. As a result, the residual alkali content (carbonate, hydroxide, etc.) in the positive electrode material is increased compared to Example 1, resulting in increased gas production and increased impedance of the positive electrode material during the cycle.

[0250] According to the test data of Example 1 and Example 9, the temperature of the second sintering treatment of the positive electrode material in Example 9 is too low during the preparation process, the V2-V1 value of the obtained positive electrode material is lower than that of Example 1, the coating effect of the surface coating layer of the positive electrode material is deteriorated, the surface residual alkali and impedance of the positive electrode material are increased, and the gas production of the positive electrode material is increased, and the expansion rate is also increased.

[0251] According to the test data of Example 1 and Example 12, the amount of deionized water used in the preparation of the coating solution for the positive electrode material of Example 12 is relatively small, the coating effect of the coating layer on the surface of the positive electrode material is poor, the V2-V1 value of the obtained positive electrode material is lower than that of Example 1, and the expansion rate and impedance of the battery made of the positive electrode material are increased.

[0252] According to the test data of Example 1 and Comparative Example 1, it can be seen that in the process of continuous solution spraying in Comparative Example 1, the material easily absorbs water and agglomerates locally, resulting in poor coating effect of the positive electrode material coating layer. The V2-V1 value of the obtained positive electrode material is too low compared with that of Example 1, and the impedance and cycle expansion rate of the positive electrode material increase. In addition, due to the poor coating effect, the binding ability between the coating material and the positive electrode material is weak, and the inherent defects of the primary particles of the material are not significantly improved, resulting in the particle strength G of Comparative Example 1 being low. D50 Weaker than Example 1.

[0253] According to the test data of Example 1 and Comparative Example 2, the positive electrode material of Comparative Example 2 adopts dry coating during the preparation process, the coating effect of the coating layer on the surface of the positive electrode material is poor, the V2-V1 value of the prepared positive electrode material is too low compared with Example 1, the surface residual alkali and gas production of the positive electrode material increase, the impedance of the negative electrode material increases, the cycle expansion rate becomes larger, and the safety performance of the positive electrode material decreases.

[0254] According to the test data of Example 1 and Comparative Example 3, it can be seen that the amount of deionized water added to the positive electrode material of Comparative Example 3 during the preparation of the coating solution is too much. During the coating process, water washing significantly reduces the residual alkali on the surface of the material, but water washing also causes side reactions on the surface of the positive electrode material, making the layered structure on the surface of the positive electrode material easily transformed into a face-centered cubic structure, and finally transformed into an inactive rock salt phase, thereby causing the impedance of the positive electrode material to continue to increase during the cycle; in addition, the interface stability of the positive electrode material is poor, and it is easy to react with the electrolyte during the cycle, resulting in more gas production.

[0255] In addition, Figures 2 and 3 are titration curves of the positive electrode materials of Examples 1 and 7, respectively, and Figures 4 and 5 are titration curves of the positive electrode materials of Comparative Examples 2 and 3. Combining the analysis of Figures 2 to 5 and Table 3, compared with Comparative Examples 1-3: it can be concluded from the V2-V1 value that the positive electrode materials of Examples 1-16 have more reasonable doping and coating amounts, which are more conducive to improving the structural stability of the positive electrode materials and reducing the residual alkali in the positive electrode materials; it can be concluded from the dE / dV value that the elements in the positive electrode materials of Examples 1-16 are more uniformly distributed and have better structural stability; by controlling the N value within a reasonable range, the test accuracy of the V2-V1 values ​​of Examples 1-16 can be guaranteed, which also improves the persuasiveness of the above analysis of the V2-V1 values ​​in each of the Examples and Comparative Examples. In summary, when the potentiometric titration curve of the positive electrode material satisfies: 2<N≤4, 0.6<V2-V1<2.7, and 0<dE / dV<10, the positive electrode material has better processing performance, and better capacity performance and cycle performance.

[0256] It can be seen from Figure 6 that doping and coating have no effect on the crystal structure of the positive electrode material, and the two pairs of split peaks (006) / (012) and (018) / (110) are obvious. Combined with the peak intensity ratio of I003 / I104 in Table 1, they are all greater than 1.4, indicating that the positive electrode materials prepared in each embodiment have a good layered structure.

[0257] FIG7 is a particle size distribution diagram of the positive electrode material sample prepared in Example 7, which shows that the positive electrode product prepared in Example 7 has a unimodal particle size distribution.

[0258] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0259] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. Throughout the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

Claims

1. A positive electrode material, wherein the positive electrode material is a lithium nickel cobalt oxide composite oxide, 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; the positive electrode material is measured by XRD ray, and the diffraction intensity of the (104) crystal plane of the positive electrode material is obtained to be I 104 The diffraction intensity of the (003) crystal plane is I 003 , R=I 003 / I 104 ; According to the Scherrer formula, the grain size corresponding to the (104) crystal plane is calculated to be D 104 nm; the structural stability coefficient ε of the positive electrode material satisfies: ε=log(D 104 ) / R, 0.90<ε<1.03, where R=I 003 / I 104 ; and the particle hardness G of the positive electrode material D50 >80Mpa, G D90 >50Mpa.

2. The positive electrode material according to claim 1, wherein Also includes at least one of the following features: (1)45≤D 104 ≤65； (2)R＞1.6； (3)1≤G D50 / G D90 ≤1.5。 3. A positive electrode material, characterized in that The positive electrode material is a lithium nickel cobalt oxide composite oxide; 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; The positive electrode material was subjected to an acid-base potentiometric titration test using a potentiometric titrator and hydrochloric acid with a concentration of 0.02 mol / L to obtain a curve graph showing the relationship between the differential value dpH / dV obtained by differentiating the pH value with respect to the consumed volume VmL of hydrochloric acid and the consumed volume V of the hydrochloric acid. In the curve graph showing the relationship between the differential value dpH / dV and the consumed volume V of the hydrochloric acid, the positive electrode material has a first characteristic peak when the consumed volume of the hydrochloric acid is V1mL, and the positive electrode material has a last characteristic peak when the consumed volume of the hydrochloric acid is V2mL, and V1 and V2 satisfy the relationship: 0.6<V2-V1<2.

7.

4. The positive electrode material according to claim 3, wherein The relationship curve between the differential value dpH / dV of the positive electrode material and the consumed volume V of the hydrochloric acid satisfies at least one of the following characteristics: (1)4＜V1＜8； (2)5＜V2＜11； (3) The positive electrode material has N characteristic peaks within the range of the consumption volume V of the hydrochloric acid of 4 to 11 (excluding 4 and 11), and 2<N≤4; (4)0<dpH / dV<10.

5. The positive electrode material according to claim 1 or 3, characterized in that The chemical formula of the positive electrode material is LiNi a Co b Mn c M d Q e O2, where 0.8<a<0.98, b<0.2, c<0.2, 0<d+e<0.2, a+b+c+d+e=1.

6. The positive electrode material according to claim 5, characterized in that The M includes at least one of Sr, Ti, Al, Zr, Y, Ba, Mg, Nb, Mo, W and V.

7. The positive electrode material according to claim 6, wherein The chemical formula of the coating layer is Li x Q e O y , where 0<x≤3, 0<y≤4.

8. The positive electrode material according to claim 7, wherein The coating layer includes at least one of Li2WO4, Li3BO3, LiMoO4, LiVO3, Li2SO4 and Li3PO4.

9. The positive electrode material according to any one of claims 5 to 8, characterized in that The positive electrode material satisfies at least one of the following characteristics: (1) 0.985≤Li / Me≤0.999, where Li / Me is the molar ratio of lithium metal to other metals in the positive electrode material; (2) 1.001≤Li / Me≤1.015, where Li / Me is the molar ratio of lithium metal to other metals other than lithium in the positive electrode material.

10. The positive electrode material according to claim 1 or 3, characterized in that In the XRD spectrum of the positive electrode material, the half-maximum width of the diffraction peak of the (104) crystal plane is 0.19° to 0.25°.

11. The positive electrode material according to claim 1 or 3, characterized in that The positive electrode material includes secondary particles, and the volume median particle size D50 of the secondary particles is 7 μm to 12 μm.

12. The positive electrode material according to claim 1 or 3, characterized in that The volume particle size distribution curve of the positive electrode material has a characteristic peak.

13. The positive electrode material according to claim 1 or 3, characterized in that Have at least one of the following characteristics: (1) The pH value of the positive electrode material is 10-13; (2) The specific surface area of ​​the positive electrode material is 0.2 m 2 / g~0.8m 2 / g; (3) The compaction density of the positive electrode material is greater than 3g / cm 3 ; (4) The electrical conductivity of the positive electrode material is greater than 0.03 S / cm; (5) The mass content of Li2CO3 in the positive electrode material is α Li wt%, 0.1≤α Li ≤0.55; (6) The mass content of LiOH in the positive electrode material is β Li wt%, 0.1≤β Li ≤0.

7.

14. The positive electrode material according to claim 1 or 3, characterized in that The initial moisture content of the positive electrode material is less than 200 ppm, and the moisture content after being exposed to air for 24 hours is less than 1000 ppm.

15. A lithium ion battery, characterized in that: The positive electrode material comprises the positive electrode material according to any one of claims 1 to 14.

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