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

Abstract

A positive electrode material and a preparation method therefor, and a lithium-ion battery. The positive electrode material has a general chemical formula of LiNiaCobMncMdO2, wherein 0.7<a<0.98, 0<b<0.3, 0<c<0.3, 0<d≤0.01, a+b+c=1, and M is a doping element. An acid-base potentiometric titration test is performed on the positive electrode material by using a potentiometric titrator, with hydrochloric acid having a concentration of 0.02 mol / L as a titration agent, and therefore a curve graph showing the relationship between the differential value dE / dV and the potential E is obtained by means of the differentiation of the potential E with respect to the consumed volume V of the hydrochloric acid. In the curve graph showing the relationship between the differential value dE / dV and the potential E, the positive electrode material has a first characteristic peak when the potential E is within the range of -200 mV to -50 mV, with the peak area of the first characteristic peak being A; the positive electrode material has a second characteristic peak when the potential E is within the range of 120 mV to 250 mV, with the peak area of the second characteristic peak being B; the positive electrode material has at least one characteristic peak when the potential E is within the range of -50 mV to 120 mV, with the sum of the peak areas of the at least one characteristic peak being C; and the residual alkali conversion coefficient of the positive electrode material is ξ, and 0.200≤ξ≤0.350. The positive electrode material is slightly influenced by water vapor, and the content of a residual alkali on the surface of the material is low; therefore, the stability of the surface structure of the positive electrode material can be improved, and side reactions on the surface of the positive electrode material can be effectively reduced, thereby improving the capacity and cycling stability of the positive electrode material.

Description

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

[0001] The present invention relates to the technical field of positive electrode materials, and in particular to positive electrode materials and preparation methods thereof, and lithium ion batteries. Background Art

[0002] At present, there are more and more types of lithium-ion battery positive electrode materials that have been put into practical use, the more representative of which include lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide and ternary materials. Among them, high-nickel positive electrode materials (Ni≥0.8) have become the focus of future research and development and industrialization in the field of power batteries due to their high theoretical reversible capacity. However, high-nickel positive electrode materials have the problem of high total residual lithium content, which seriously affects the battery processing performance. At present, in order to solve the problem of high total residual lithium content in high-nickel materials affecting processing performance, a mature water washing process has been developed to effectively remove residual alkali, and related products have been widely used in power batteries, power tools and other fields. However, the water washing process will also bring some defects in actual application, causing irreversible chemical changes on the surface of the positive electrode material particles, thereby reducing the electrochemical performance. Therefore, there is an urgent need for a positive electrode material that can reduce the surface residual alkali content and improve the surface structure stability.

[0003] Summary of the Invention

[0004] The purpose of this application is to provide a positive electrode material and a preparation method thereof, and a lithium-ion battery, which can effectively reduce the occurrence of side reactions on the surface of the positive electrode material, thereby improving the capacity and cycle stability of the positive electrode material.

[0005] In the first aspect, the present application provides a positive electrode material, the chemical formula of which is LiNi a Co b Mn c M d O2, wherein 0.7<a<0.98, 0<b<0.3, 0<c<0.3, 0<d≤0.01, a+b+c=1, M is a doping element;

[0006] 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 as a titrant, and a curve graph showing the relationship between the differential value dE / dV obtained by differentiating the potential E with respect to the consumed volume V of hydrochloric acid and the potential E is obtained. In the curve graph showing the relationship between the differential value dE / dV and the potential E, the positive electrode material has a first characteristic peak in the range of -200 mV to -50 mV of the potential E, and the peak area of ​​the first characteristic peak is A. The positive electrode material has a second characteristic peak in the range of 120 mV to 250 mV of the potential E, and the peak area of ​​the second characteristic peak is B. The positive electrode material has at least one characteristic peak in the range of -50 mV to 120 mV of the potential E, and the sum of the peak areas of the at least one characteristic peak is C. The residual alkali conversion coefficient of the positive electrode material is ξ, 0.2≤ξ≤0.35.

[0007] In some embodiments, the doping element M includes at least one of B, P, S, F, La, Sr, Ti, Al, Zr, Y, Ba, Mg, Nb, Mo, W, and V.

[0008] In some embodiments, 0.8≤a<0.98.

[0009] In some embodiments, the peak area of ​​the first characteristic peak is A, 2000≤A≤200000.

[0010] In some embodiments, the peak area of ​​the second characteristic peak is B, 2000≤B≤200000.

[0011] In some embodiments, the sum of the peak areas of the at least one characteristic peak is C, 2000≤C≤200000.

[0012] In some embodiments, the mass content of LiOH in the positive electrode material is α LH wt%, 0.1≤α LH ≤1.0.

[0013] In some embodiments, the mass content of Li2CO3 in the positive electrode material is α LC wt%, 0.1≤α LC ≤1.0.

[0014] In some embodiments, the molar ratio of Li to all metals Me except Li in the positive electrode material is γ Li / Me , 0.95<γ Li / Me <1.05.

[0015] In some embodiments, the specific surface area of ​​the positive electrode material is βm 2 / g, 0.2<β<1.5.

[0016] In some embodiments, the mass content of LiOH in the positive electrode material is α LH wt%, 0.1≤α LH ≤1.0.

[0017] In some embodiments, the mass content of Li2CO3 in the positive electrode material is α LC wt%, 0.1≤α LC ≤1.0.

[0018] In some embodiments, 0.25≤α LH +α LC ≤0.65.

[0019] In a second aspect, the present application provides a method for preparing a positive electrode material, comprising the following steps:

[0020] A mixture comprising a nickel-cobalt-manganese-based precursor, a lithium source, and a dopant containing a metal element is subjected to a primary sintering treatment in an oxygen-containing atmosphere to obtain a matrix material; the temperature of the primary sintering treatment is 200° C. to 900° C., and the pressure during the primary sintering treatment is in a gradient increasing state within a pressure range of 3 Pa to 13 Pa;

[0021] The base material and the coating agent are subjected to a secondary sintering process to obtain a positive electrode material.

[0022] In some embodiments, the chemical formula of the nickel-cobalt-manganese based precursor is Ni a Co b Mn c (OH)2, wherein 0.7<a<0.98, 0<b<0.3, 0<c<0.3, a+b+c=1.

[0023] In some embodiments, the mass content of the metal element in the nickel-cobalt-manganese-based precursor is 60.5 wt % to 63.5 wt %.

[0024] In some embodiments, the mass ratio of the nickel-cobalt-manganese-based precursor, the lithium source, and the dopant containing a metal element is 1:(1.0-1.05):(0-0.01).

[0025] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium acetate.

[0026] In some embodiments, the metal element-containing dopant includes at least one of Nb2O5, Nb2O3, MoO3, WO2, V2O5, V2O3, Sr(OH)2, SrO, TiO2, Al2O3, Al(OH)3, ZrO2, Zr(OH)4, Y2O3, BaO, MgO and Mg(OH)2.

[0027] In some embodiments, the mixing conditions for obtaining the mixture are: dry mixing at 10° C. to 50° C. for 0.3 h to 2 h.

[0028] In some embodiments, the mass content of oxygen in the oxygen-containing atmosphere is ≥95%.

[0029] In some embodiments, the primary sintering process includes a first stage, a second stage, and a third stage.

[0030] In some embodiments, the first stage comprises: heating the mixture from 200°C to 550°C within 2 hours to 5 hours, controlling the pressure P1 to be 7Pa to 11Pa, wherein the amount of oxygen-containing atmosphere introduced is controlled to be 10m 3 / h~30m 3 / h, and control the exhaust volume of the reaction system to 10% to 30%.

[0031] In some embodiments, the second stage comprises: heating the mixture from 550°C to 700°C within 2 hours to 5 hours, controlling the pressure P2 to be 8Pa to 12Pa, wherein the amount of oxygen-containing atmosphere introduced is controlled to be 20m 3 / h~30m 3 / h, and control the exhaust volume of the reaction system to 10% to 20%.

[0032] In some embodiments, the third stage comprises: sintering the mixture at 700°C to 900°C for 5h to 10h, controlling the pressure P3 to be 9Pa to 13Pa, wherein the amount of oxygen-containing atmosphere introduced is controlled to be 20m 3 / h~30m 3 / h.

[0033] In some embodiments, the median particle size D of the matrix material is 50 9μm~12μm.

[0034] In some embodiments, the coating agent includes La(NO3)3·6H2O, NH4F, NH4HF, (NH4)3PO4, (NH4)2HPO4, (NH4)2MoO4, (NH4)2SO4, NH4HSO4, (NH4)6W7O 24 6H2O, (NH4)3PW 12 O40 ·3H2O、Zr(SO4)2·4H2O、H 28 N6O 41 W 12 , at least one of WO3, Al2O3, and Al(OH)3.

[0035] In some embodiments, the mass ratio of the matrix material to the coating agent is 1:(0.001-0.05).

[0036] In some embodiments, the secondary sintering process is performed in an oxygen-containing atmosphere.

[0037] In some embodiments, the secondary sintering process is performed in an oxygen-containing atmosphere, and the mass content of oxygen in the oxygen-containing atmosphere is ≥95%.

[0038] In some embodiments, the temperature of the secondary sintering process is 200°C to 700°C.

[0039] In some embodiments, the secondary sintering treatment lasts for 10 hours to 20 hours.

[0040] In some embodiments, before the base material and coating agent are subjected to a secondary sintering process, the preparation method further comprises: dissolving the coating agent in water to form a coating solution; and coating the coating solution and the base material using an atomization method. In some embodiments, the atomization pressure is 0 MPa to 0.05 MPa.

[0041] In some embodiments, the coating process is performed under stirring, and the stirring frequency is controlled to be 20 Hz to 50 Hz.

[0042] In some embodiments, the coating treatment is performed at a temperature of 150°C to 250°C.

[0043] In some embodiments, the coating treatment time is 3 hours to 8 hours.

[0044] In a third aspect, the present application provides a lithium-ion battery, comprising the positive electrode material described in the first aspect or the positive electrode material prepared by the preparation method described in the second aspect.

[0045] Compared with the prior art, the technical solution of this application has at least the following beneficial effects:

[0046] The positive electrode material provided in this application has a residual alkali conversion coefficient of ξ, 0.2≤ξ≤0.35, where the A value can reflect the mass content of LiOH participating in the reaction on the surface of the positive electrode material, the B value can reflect the mass content of Li2CO3 participating in the reaction on the surface of the positive electrode material, and the C value can be regarded as the result of the reaction between the titrant and the residual additives on the surface of the positive electrode material particles or the products on the particle surface during the residual lithium titration process, that is, the amount of titrant consumed by all functional surface substances. Therefore, the higher the C value, the higher the amount of functional surface substances. In the present application, the residual alkali conversion coefficient ξ of the positive electrode material is within the above range, and more residual alkali can be converted to form lithium composite metal oxides attached to the surface of the positive electrode material, reducing the residual alkali content on the surface of the positive electrode material, improving the surface structure stability of the positive electrode material, and thus reducing the occurrence of side reactions on the surface of the positive electrode material, generating an ideal microscopic material structure surface, the surface energy tends to be stable, and the probability of water vapor generation in the positive electrode material is reduced, preventing the lattice lithium on the surface of the positive electrode material from being corroded by water vapor to form residual alkali secondary; at the same time, it can also prevent part of the lithium from being carried away by water vapor, inhibiting the generation of surface structural defects of the positive electrode material, achieving the effect of removing more residual lithium without destroying the surface structure, and regulating the conversion of LiOH and Li2CO3 in the positive electrode material, thereby improving the capacity and cycle performance of the positive electrode material.

[0047] The present application provides a method for preparing a positive electrode material. First, a mixture comprising a nickel-cobalt-manganese-based precursor, a lithium salt, and a dopant containing a metal element is subjected to a single sintering treatment in an oxygen-containing atmosphere to obtain a base material. By controlling the temperature and pressure of the single sintering process, the pressure of the sintering system is simultaneously controlled to be in a gradient rising state during the single sintering heating process, so that water vapor can be discharged as much as possible in the low temperature section of the sintering process, thereby reducing the side reaction between the unreacted lithium and water vapor during the single sintering process and reducing the residual alkali content on the surface of the base material. At the same time, during the single sintering process, the metal element in the dopant can increase the thermal diffusion rate of lithium ions, accelerate the crystallization rate of lithium ions inside the base material, optimize the lattice structure of the positive electrode material, and improve the structural stability of the positive electrode material. In addition, the metal element in the dopant can form a Li-MO structure on the surface of the base material during the single sintering process, which can reduce the corrosion of the surface structure of the material by water vapor, thereby strengthening the surface structure of the positive electrode material. Secondly, by subjecting the base material and the coating agent to a secondary sintering treatment, during the secondary sintering process, the coating agent can form a coating layer on the surface of the positive electrode material, reducing the side reaction between the positive electrode material and the electrolyte, and further improving the surface structural stability of the positive electrode material; at the same time, the residual lithium on the surface of the base material can react with the coating agent to form a lithium composite metal oxide that adheres to the surface of the base material to form a coating layer, thereby improving the surface structural stability of the positive electrode material. The positive electrode material prepared by the above preparation method can effectively reduce the influence of water vapor on the positive electrode material and reduce the residual alkali content on the surface of the positive electrode material, thereby improving the surface structural stability of the positive electrode material and reducing the occurrence of side reactions on the surface of the positive electrode material, so that the positive electrode material has better capacity and cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The present invention will be further described below with reference to the accompanying drawings and examples.

[0049] FIG1 is a graph showing an E-dE / dV test curve of a cathode material provided in this application;

[0050] FIG2 is a graph showing the relationship between the surface structure stability coefficient ε and the capacity of the positive electrode material provided in this application;

[0051] FIG3 is a graph showing the relationship between the surface structure stability coefficient ε of the positive electrode material provided in this application and normal temperature cycling;

[0052] FIG4 is a graph showing the relationship between the surface structure stability coefficient ε and high temperature cycles of the positive electrode material provided in this application;

[0053] FIG5 is a diagram showing the relationship between the residual alkali conversion coefficient ξ and the capacity of the positive electrode material provided in this application;

[0054] FIG6 is a graph showing the relationship between the residual alkali conversion coefficient ξ of the cathode material provided in this application and normal temperature cycling;

[0055] FIG7 is a graph showing the relationship between the residual alkali conversion coefficient ξ of the positive electrode material provided in this application and high-temperature cycles. DETAILED DESCRIPTION

[0056] In order to better understand the technical solution of the present invention, the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0057] It should be understood that the embodiments described are only a portion of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative work are within the scope of protection of the present invention.

[0058] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The singular forms "a", "an", "the" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0059] It should be understood that the term "and / or" as used herein is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0060] In the existing technology, the research on reducing the total amount of residual lithium on the surface of positive electrode materials mainly focuses on the post-treatment process to reduce the residual lithium in a targeted manner, but there are fewer studies on the control of the source of residual lithium, and less attention is paid to the morphology of residual lithium. The current technical means of reducing the total amount of residual lithium on the surface of positive electrode materials face the following limitations: 1) Low tolerance to the amount of residual lithium in the matrix, and it is not suitable to process products with too high residual lithium; 2) Most non-water washing post-treatment processes use residual lithium conversion as the main means, and are highly dependent on the amount of residual lithium on the surface and type-specific treatment; 3) It is necessary to convert and remove more residual lithium without destroying the surface structure, and the process is relatively difficult. Therefore, how to regulate residual lithium and reduce the generation of residual lithium while maintaining the structural stability of the positive electrode material is a problem that still needs to be solved.

[0061] The inventors of the present application have found in the preparation of positive electrode materials that the degree to which the material is affected by water vapor during the primary sintering process will directly determine the performance of the finished positive electrode material. When the material is greatly affected by water vapor, water vapor will corrode the surface of the particles during the high-temperature sintering process, causing the surface lattice lithium to be reconverted into residual lithium, the residual alkali significantly increases, and the material capacity and cycle decrease; when the material is not affected by water vapor, the surface residual alkali is low, and a stable particle structure can be formed, which makes the material performance better. Materials affected by water vapor are difficult to modify during post-processing, and their electrical properties (especially cycle performance) are difficult to reach the same level as positive electrode materials that are not affected by water vapor. Therefore, it is very important to ensure that the material is not affected by water vapor during the primary sintering process. At the same time, it is necessary to construct a certain judgment mechanism to judge the degree to which the material is affected by water vapor in advance, so as to facilitate the evaluation of the material.

[0062] In addition, the inventors of this application also focused on the degree of conversion of residual alkali in the post-treatment process. Studies have found that by converting residual alkali into a surface functional layer (electron transport layer, ion transport layer or passivation layer), the capacity and cycle life of the positive electrode material will be significantly increased. Therefore, the performance of the positive electrode material can be effectively predicted by the degree of conversion of residual alkali. In summary, under the condition that the matrix material is not affected by water vapor during the primary sintering process, the residual alkali can be efficiently converted through an effective post-treatment process, which can greatly improve the performance of the positive electrode material and ensure that the positive electrode material has the advantages of high capacity and long cycle.

[0063] In the first aspect, the present application provides a positive electrode material, the chemical formula of the positive electrode material is LiNi a Co b Mn c M d O2, wherein 0.7<a<0.98, 0<b<0.3, 0<c<0.3, 0<d≤0.01, a+b+c=1, M is a doping element;

[0064] The mass content of LiOH in the positive electrode material is α LH wt%, the mass content of Li2CO3 in the positive electrode material is α LC wt%, the molar ratio of Li to all metals Me except Li in the positive electrode material is γ Li / Me , the specific surface area of ​​the positive electrode material is βm 2 / g; the surface structure stability coefficient of the positive electrode material is ε, 0.5≤ε≤1.5.

[0065] The positive electrode material provided in this application has a mass content of LiOH of α LH wt%, the mass content of Li2CO3 in the positive electrode material is α LC wt%, the molar ratio of Li to all metals Me except Li in the positive electrode material is γ Li / Me, the specific surface area of ​​the positive electrode material is βm 2 / g; the surface structure stability coefficient of the positive electrode material is ε, 0.5≤ε≤1.5. The surface structure stability coefficient ε of the positive electrode material can reflect the degree to which the positive electrode material is affected by water vapor. In the present application, when the surface structure stability coefficient ε of the positive electrode material is within the above range, the degree to which the positive electrode material is affected by water vapor is small, which can reduce the side reaction between the positive electrode material and water vapor, thereby reducing the residual alkali content on the surface of the positive electrode material and improving the surface structure stability of the positive electrode material, thereby effectively reducing the occurrence of side reactions on the surface of the positive electrode material and improving the capacity and cycle stability of the positive electrode material.

[0066] In this application, LiNi a Co b Mn c M d O2, where 0.7<a<0.98, 0<b<0.3, 0<c<0.3, 0<d≤0.01, a+b+c=1, the value of a can be 0.71, 0.75, 0.78, 0.8, 0.83, 0.86, 0.89, 0.9, 0.91, 0.95 or 0.97, and the value of b can be 0.001, 0.01, 0.05, The value of c can be 0.001, 0.01, 0.05, 0.1, 0.15, 0.2, 0.25 or 0.29, etc. The value of d can be 0.001, 0.002, 0.005, 0.006, 0.008 or 0.01, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0067] In the present application, the surface structure stability coefficient ε of the positive electrode material can specifically be 0.5, 0.55, 0.6, 0.65, 0.7, 0.8, 0.9, 0.97, 1.0, 1.15, 1.2, 1.3, 1.4 or 1.5, which is not limited here. It can be understood that the surface structure stability coefficient ε of the positive electrode material can reflect the degree to which the positive electrode material is affected by water vapor. If ε is too large, it means that the positive electrode material is greatly affected by water vapor, which in turn causes the surface structure of the positive electrode material to be corroded and destroyed by water vapor, and the capacity and cycle performance of the positive electrode material are reduced. When the surface structure stability coefficient ε of the positive electrode material is within the above range, it means that the surface of the positive electrode material has an ideal microscopic material structure, the surface energy tends to be stable, the probability of water vapor occurring in the positive electrode material is reduced, and the lattice lithium on the surface of the positive electrode material is prevented from being corroded by water vapor to form residual alkali for a second time, maintaining α LH and α LC At the same time, it can also prevent some lithium from being taken away by water vapor, resulting in γ Li / MeThe abnormality is reduced, further suppressing the generation of surface structural defects of the positive electrode material, achieving the effect of removing more residual lithium without destroying the surface structure.

[0068] In some embodiments, the mass content of LiOH in the positive electrode material is α LH wt%, 0.1≤α LH ≤1.0, specifically can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95 or 1.0, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0069] In some embodiments, the mass content of Li2CO3 in the positive electrode material is α LC wt%, 0.1≤α LC ≤1.0, specifically can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95 or 1.0, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0070] It can be understood that the residual alkali in the positive electrode material mainly exists in the form of LiOH and Li2CO3. The mass content of LiOH and the mass content of Li2CO3 in the positive electrode material of the present application are within the above range. The surface of the positive electrode material can maintain a low residual alkali content, and the positive electrode material is not easy to react with water vapor. That is, the influence of water vapor on the positive electrode material is small, and the surface structure of the positive electrode material is not easily corroded and destroyed by water vapor, thereby enabling the positive electrode material to maintain good surface structure stability and improve the capacity and cycle performance of the positive electrode material.

[0071] In some embodiments, the molar ratio of Li to all metals Me except Li in the positive electrode material is γ Li / Me , 0.95<γ Li / Me <1.05, specifically it can be 0.951, 0.96, 0.965, 0.97, 0.98, 0.99, 1.0, 1.01, 1.02, 1.03 or 1.04, etc., of course, it can also be other values ​​within the above range, which is not limited here. It can be understood that once the water vapor affects the positive electrode material, the lithium ions in the positive electrode material are likely to react with the water vapor, resulting in an increase in the residual alkali content on the surface of the positive electrode material and a decrease in the surface structural stability of the positive electrode material. At the same time, the lithium ions that can be embedded and extracted from the positive electrode material are reduced, resulting in a decrease in the capacity and cycle performance of the positive electrode material. In this application, the molar ratio of Li to all metals Me except Li in the positive electrode material is controlled to be γ Li / MeWithin the above range, it is beneficial to improve the surface structure stability of the positive electrode material, and can also ensure that there are sufficient lithium ions in the positive electrode material, realize the stable insertion and extraction of lithium ions in the positive electrode material during the cycle, and ensure the normal performance of lithium ion capacity and cycle performance.

[0072] In some embodiments, the specific surface area of ​​the positive electrode material is βm 2 / g, 0.2<β<1.5, specifically it can be 0.21, 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 1.0, 1.1, 1.2, 1.35 or 1.48, etc. Of course, it can also be other values ​​within the above range, which is not limited here. Here, the specific surface area can reflect the degree of conversion of residual alkali on the surface of the material during the post-treatment process. Usually, when the specific surface area is higher, it means that the residual alkali of the material is better converted into the functional layer and the performance is better. Usually, post-treatment coating can restore the influence of water vapor on the material to a certain extent, but if the coating quality is not good, this recovery ability is very limited. Therefore, β (specific surface area) can evaluate the effect of post-treatment coating of the material to a certain extent. Usually, when the specific surface area is low, the coating effect is poor, the degree of residual alkali conversion is low, the coating microstructure is not formed, and the material performance is poor; when the specific surface area is high, the performance is better, and a large amount of residual alkali can be converted into the surface functional layer, which effectively inhibits the influence of water vapor on the material. Therefore, when the material is greatly affected by water vapor, α LH +α LC Higher, γ Li / Me If the material is less affected by water vapor and has better surface coating, then ε is lower and performance is poor. Therefore, controlling the material's exposure to water vapor while efficiently coating the surface can be effective. It can be understood that controlling the specific surface area of ​​the positive electrode material within the above range in this application is beneficial for improving the surface structural stability of the negative electrode material, and is beneficial for improving the capacity and cycle performance of the positive electrode material.

[0073] The present application also provides a positive electrode material, the chemical formula of which is LiNi a Co b Mn c M d O2, wherein 0.7<a<0.98, 0<b<0.3, 0<c<0.3, 0<d≤0.01, a+b+c=1, M is a doping element;

[0074] 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 as a titrant, and a curve diagram showing the relationship between the differential value dE / dV obtained by differentiating the potential E with respect to the consumed volume V of hydrochloric acid and the potential E is obtained. As shown in FIG1 , in the curve diagram showing the relationship between the differential value dE / dV and the potential E, the positive electrode material has a first characteristic peak in the range of -200 mV to -50 mV in the potential E interval, and the peak area of ​​the first characteristic peak is A. The positive electrode material has a second characteristic peak in the range of 120 mV to 250 mV in the potential E interval, and the peak area of ​​the second characteristic peak is B. The positive electrode material has at least one characteristic peak in the range of -50 mV to 120 mV in the potential E interval, and the sum of the peak areas of the at least one characteristic peak is C. The residual alkali conversion coefficient of the positive electrode material is ξ. 0.2≤ξ≤0.35.

[0075] The positive electrode material provided in this application has a residual alkali conversion coefficient of ξ, 0.2≤ξ≤0.35, wherein the A value can reflect the mass content of LiOH participating in the reaction on the surface of the positive electrode material, the B value can reflect the mass content of Li2CO3 participating in the reaction on the surface of the positive electrode material, and the C value can be regarded as the result of the reaction between the titrant and the coating additive or coating product contained in the positive electrode material during the residual lithium titration process, that is, the amount of titrant consumed by all functional coating layers. Therefore, the higher the C value, the higher the amount of the functional coating layer. In the present application, the residual alkali conversion coefficient ξ of the positive electrode material is within the above range, and more residual alkali can be converted to form lithium composite metal oxides attached to the surface of the positive electrode material, reducing the residual alkali content on the surface of the positive electrode material, improving the surface structure stability of the positive electrode material, and thus reducing the occurrence of side reactions on the surface of the positive electrode material, generating an ideal microscopic material structure surface, the surface energy tends to be stable, and the probability of water vapor generation in the positive electrode material is reduced, preventing the lattice lithium on the surface of the positive electrode material from being corroded by water vapor to form residual alkali secondary; at the same time, it can also prevent part of the lithium from being carried away by water vapor, inhibiting the generation of surface structural defects of the positive electrode material, achieving the effect of removing more residual lithium without destroying the surface structure, and regulating the conversion of LiOH and Li2CO3 in the positive electrode material, thereby improving the capacity and cycle performance of the positive electrode material.

[0076] The specific value of ξ in this application can be 0.2, 0.22, 0.25, 0.26, 0.27, 0.28, 0.3, 0.31, 0.32, 0.33, 0.34 or 0.35, etc., and is not limited here. When ξ>0.35, the coating layer is too thick, and there are some inert parts on the outer surface, which reduces the material capacity. At the same time, the impedance and gas production performance deteriorate, which is not conducive to the stability of the electrode material performance. When ξ<0.2, the surface functional layer is thin and the content is low, the degree of residual alkali conversion is low, the ionic conductivity and surface structure stability are not good, which greatly reduces the capacity and cycle. In addition, the excessively high residual alkali leads to an excessively high pH and poor electrode processing performance.

[0077] In some embodiments, the doping element M includes at least one of B, P, S, F, La, Sr, Ti, Al, Zr, Y, Ba, Mg, Nb, Mo, W, and V. The doping element M includes the metal elements in the dopant added in the primary sintering described below and the metal elements in the coating agent added in the secondary sintering.

[0078] In some embodiments, the peak area of ​​the first characteristic peak is A, 2000≤A≤200000, and specifically can be 2000, 5000, 10000, 30000, 50000, 80000, 100000, 120000, 150000, 180000, or 200000, etc., and of course other values ​​within the above range are also possible, and are not limited here. When A is within this range, it indicates that there are fewer byproducts on the surface of the positive electrode material, which is beneficial to the material capacity and the preparation and coating of the battery slurry.

[0079] In some embodiments, the peak area of ​​the second characteristic peak is B, and 2000≤B≤200,000, specifically 2000, 5000, 10,000, 30,000, 50,000, 80,000, 100,000, 120,000, 150,000, 180,000, or 200,000, etc., but is not limited to these values, and other values ​​not listed in this numerical range are also applicable. When B is within this range, the initial gas production and long-cycle gas production on the material surface can be effectively controlled, thereby improving the material's safety and stability.

[0080] In some embodiments, the sum of the peak areas of at least one characteristic peak is C, 2000≤C≤200000, and specifically can be 2000, 5000, 10000, 30000, 50000, 80000, 100000, 120000, 150000, 180000, or 200000, etc., but is not limited to the listed values, and other values ​​not listed in this numerical range are also applicable. When C is within this range, it indicates that the amount of the surface functional layer is appropriate, and the appropriate amount of coating agent and coated product is an effective means to improve material stability and electrochemical activity, and significantly improves capacity, impedance, gas production, and circulation.

[0081] In a second aspect, the present application provides a method for preparing a positive electrode material, comprising the following steps:

[0082] Step S10, sintering a mixture comprising a nickel-cobalt-manganese-based precursor, a lithium source, and a dopant containing a metal element in an oxygen-containing atmosphere to obtain a matrix material; the temperature of the primary sintering treatment is 200° C. to 900° C., and the pressure during the primary sintering treatment is in a gradient increasing state, and the pressure range is 3 Pa to 13 Pa;

[0083] Step S20: performing a secondary sintering process on the base material and the coating agent to obtain a positive electrode material.

[0084] The present application provides a method for preparing a positive electrode material. First, a mixture comprising a nickel-cobalt-manganese-based precursor, a lithium salt, and a dopant containing a metal element is subjected to a single sintering treatment in an oxygen-containing atmosphere to obtain a base material. By controlling the temperature and pressure of the single sintering process, the pressure of the sintering system is simultaneously controlled to be in a gradient rising state during the single sintering heating process, so that water vapor can be discharged as much as possible in the low temperature section of the sintering process, thereby reducing the side reaction between the unreacted lithium and water vapor during the single sintering process and reducing the residual alkali content on the surface of the base material. At the same time, during the single sintering process, the metal element in the dopant can increase the thermal diffusion rate of lithium ions, accelerate the crystallization rate of lithium ions inside the base material, optimize the lattice structure of the positive electrode material, and improve the structural stability of the positive electrode material. In addition, the metal element in the dopant can form a Li-MO structure on the surface of the base material during the single sintering process, which can reduce the corrosion of the surface structure of the material by water vapor, thereby strengthening the surface structure of the positive electrode material. Secondly, by subjecting the base material and the coating agent to a secondary sintering treatment, during the secondary sintering process, the coating agent can form a coating layer on the surface of the positive electrode material, reducing the side reaction between the positive electrode material and the electrolyte, and further improving the surface structural stability of the positive electrode material; at the same time, the residual lithium on the surface of the base material can react with the coating agent to form a lithium composite metal oxide that adheres to the surface of the base material to form a coating layer, thereby improving the surface structural stability of the positive electrode material. The positive electrode material prepared by the above preparation method can effectively reduce the influence of water vapor on the positive electrode material and reduce the residual alkali content on the surface of the positive electrode material, thereby improving the surface structural stability of the positive electrode material and reducing the occurrence of side reactions on the surface of the positive electrode material, so that the positive electrode material has better capacity and cycle stability.

[0085] The preparation method of the present application is described in detail below with reference to the examples:

[0086] Before step S10, the method further includes:

[0087] A nickel-cobalt-manganese-based precursor is prepared by a coprecipitation method, and a metal salt solution, a complexing agent and a pH regulator are mixed to obtain the nickel-cobalt-manganese-based precursor.

[0088] In some embodiments, the mass ratio of the metal salt solution, the complexing agent and the pH adjuster is (2-5): (2-5): (1-4), specifically 2:2:1, 2:3:2, 2:4:3, 3:2:1, 4:4:4, 5:3:3 or 5:5:4, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0089] In some embodiments, the metal salt solution includes nickel ions, cobalt ions, and manganese ions.

[0090] In some embodiments, the concentration of nickel ions in the metal salt solution is a'mol / L, 0.7<a'<0.98, specifically 0.71, 0.75, 0.78, 0.8, 0.83, 0.86, 0.89, 0.9, 0.91, 0.95 or 0.97, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0091] In some embodiments, the concentration of cobalt ions in the metal salt solution is b'mol / L, 0<b'<0.3, specifically 0.001, 0.01, 0.05, 0.1, 0.15, 0.2, 0.25 or 0.29, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0092] In some embodiments, the concentration of manganese ions in the metal salt solution is c'mol / L, 0<c'<0.3, specifically 0.001, 0.01, 0.05, 0.1, 0.15, 0.2, 0.25 or 0.29, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0093] In some embodiments, the concentration of the pH regulator is 1 mol / L to 6 mol / L, specifically 1 mol / L, 1.5 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L or 6 mol / L, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0094] In some embodiments, the concentration of the complexing agent is 2 mol / L to 10 mol / L, specifically 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L or 10 mol / L, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0095] In some embodiments, the complexing agent comprises ammonia.

[0096] In some embodiments, the pH adjuster includes at least one of sodium hydroxide and potassium hydroxide.

[0097] In some embodiments, the mixing treatment temperature is 45°C to 85°C, specifically 45°C, 50°C, 60°C, 65°C, 70°C, 75°C, 80°C or 85°C, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0098] In some embodiments, the mixing treatment time is 5 h to 20 h, specifically 5 h, 8 h, 10 h, 12 h, 15 h, 16 h, 18 h or 20 h, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0099] In some embodiments, the mixing process is carried out under stirring, and the stirring rate is controlled to be 150 r / min to 850 r / min, specifically 150 r / min, 200 r / min, 300 r / min, 400 r / min, 500 r / min, 600 r / min, 750 r / min or 850 r / min, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0100] In some embodiments, the metal composite hydroxide precursor prepared by the mixing treatment is a slurry suspension, which is obtained through solid-liquid separation, washing, and drying.

[0101] In some embodiments, the solid-liquid separation method includes any one of centrifugation and filtration. The purpose of the solid-liquid separation is to separate the metal composite hydroxide from the solvent.

[0102] In some embodiments, the washing is performed with deionized water multiple times to remove impurities.

[0103] In some embodiments, the drying temperature is 100°C to 130°C. Specifically, the drying temperature may be 100°C, 110°C, 120°C, 130°C, etc. Of course, it may also be other values ​​within the above range, which is not limited here.

[0104] In some embodiments, the drying time is 12 hours to 24 hours. The drying time can specifically be 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours and 24 hours, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0105] Step S10, a mixture containing a nickel-cobalt-manganese-based precursor, a lithium source and a dopant containing a metal element is subjected to a single sintering treatment in an oxygen-containing atmosphere to obtain a matrix material; the temperature of the single sintering treatment is 200°C to 900°C, and the pressure during the single sintering treatment is in a gradient rising state, and the pressure range is 3Pa to 13Pa.

[0106] In some embodiments, the chemical formula of the nickel-cobalt-manganese based precursor is Ni a Co b Mn c(OH)2, wherein 0.7<a<0.98, 0<b<0.3, 0<c<0.3, a+b+c=1. The value of a can be 0.71, 0.75, 0.78, 0.8, 0.83, 0.86, 0.89, 0.9, 0.91, 0.95 or 0.97, etc., the value of b can be 0.001, 0.01, 0.05, 0.1, 0.15, 0.2, 0.25 or 0.29, etc., and the value of c can be 0.001, 0.01, 0.05, 0.1, 0.15, 0.2, 0.25 or 0.29, etc., without limitation herein.

[0107] In some embodiments, the mass content of metal elements in the nickel-cobalt-manganese-based precursor is 60.5wt% to 63.5%, specifically 60.5wt%, 60.8wt%, 61wt%, 61.3wt%, 61.5wt%, 62wt%, 62.1wt%, 60.5wt%, 62.8wt%, 63wt% or 63.5wt%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0108] In some embodiments, the mass ratio of the nickel-cobalt-manganese-based precursor, the lithium source and the metal element-containing dopant is 1:(1.0-1.05):(0-0.01), specifically 1:1.0:0, 1:1.01:0.001, 1:1.02:0.003, 1:1.03:0.005, 1:1.01:0.007, 1:1.05:0.009 or 1:1.05:0.01, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0109] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium acetate.

[0110] In some embodiments, the metal element-containing dopant includes at least one of Nb2O5, Nb2O3, MoO3, WO2, V2O5, V2O3, Sr(OH)2, SrO, TiO2, Al2O3, Al(OH)3, ZrO2, Zr(OH)4, Y2O3, BaO, MgO, and Mg(OH)2. Preferably, the dopant is Al(OH)3, Sr(OH)2, or TiO2.

[0111] In some embodiments, the mixing conditions for obtaining the mixture are: dry mixing at 10° C. to 50° C. for 0.3 to 2 hours. The dry mixing temperature can be 10° C., 20° C., 30° C., 40° C., and 50° C., and can also be other values ​​within the above range. The dry mixing time can be 0.3 h, 0.5 h, 0.8 h, 1 h, 1.5 h, or 2 h, and can also be other values ​​within the above range.

[0112] In some embodiments, the mass content of oxygen in the oxygen-containing atmosphere is ≥95%, specifically 95%, 95.5%, 96%, 97%, 97.5%, 98% or 99%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0113] It should be noted that since most of the water vapor during the primary sintering process comes from bound water and structural water formed by the release of the nickel-cobalt-manganese-based precursor and the lithium source, it is necessary to study the weight loss curve of the mixture containing the nickel-cobalt-manganese-based precursor, lithium salt, and metal-containing dopant to determine the temperature at which water vapor is generated. The inventors found that the mixture exhibits significant weight loss between 250°C and 300°C, and relatively slow weight loss between 300°C and 550°C. This water vapor loss is caused by the dehydration of structural water from the LiOH and precursor. At 550°C to 700°C, the structural water is slowly and completely removed. By the time the primary sintering temperature reaches 700°C, all structural water has been completely removed. Therefore, to prevent water vapor from entering the high-temperature zone and reacting with the material, it is necessary to expel as much water vapor as possible before 700°C. Currently, most primary sintering kilns on the market have exhaust ducts in the front heating zone, but not in the high-temperature or holding zones. However, even so, some water vapor will still enter the high-temperature zone or the insulation zone during the actual production process, so additional barriers to water vapor diffusion are needed. Therefore, the inventors designed a gradient furnace pressure of 200℃ to 900℃. By controlling the temperature of the primary sintering process to 200℃ to 900℃ and increasing the pressure during the primary sintering process in a gradient state, the pressure gradient is established to prevent water vapor from migrating to the high-pressure area in the latter section, ensuring that water vapor can be discharged in the front section. This can effectively prevent water vapor from diffusing into the high-temperature sintering zone and reduce the impact of water vapor on the positive electrode material. In addition, once water vapor enters the high-temperature zone (there is no corresponding exhaust duct in the high-temperature zone), it is difficult for the water vapor to escape in the high-temperature zone, and the damage to the material will be greater. Therefore, 700°C is the red line for water vapor diffusion. To ensure that water vapor does not enter the high-temperature zone, this application controls the furnace pressure during the primary sintering process to be in a gradient rising state, which can reduce the diffusion of high-temperature water vapor, reduce the damage of water vapor to the material, and regulate the conversion of surface residual alkali of the intermediate particles in the primary sintering, the molar ratio of all metals except Li, and the comprehensive performance of specific surface area.

[0114] In some embodiments, the primary sintering process includes a first stage, a second stage, and a third stage.

[0115] In some embodiments, the first stage comprises: heating the mixture from 200°C to 550°C within 2 hours to 5 hours, controlling the pressure P1 to be 7Pa to 11Pa, wherein the amount of oxygen-containing atmosphere introduced is controlled to be 10m 3 / h~30m 3 / h, and the exhaust volume of the reaction system is controlled to be 10% to 30%. Here, the exhaust volume of the reaction system refers to the opening and closing degree of the exhaust valve of the reaction system. It can be understood that by controlling the amount of oxygen-containing atmosphere introduced and the exhaust volume of the reaction system, the pressure in the first stage of the sintering process can be controlled within the above range.

[0116] Optionally, the first stage heating time can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, etc., which is not limited here.

[0117] Optionally, the pressure P1 in the first stage can be 7 Pa, 7.5 Pa, 8 Pa, 8.5 Pa, 9 Pa, 10 Pa, 10.5 Pa or 11 Pa, etc., which is not limited here.

[0118] Optionally, the amount of oxygen-containing atmosphere introduced in the first stage can be 10m 3 / h、12m 3 / h、15m 3 / h、18m 3 / h、20m 3 / h、25m 3 / h、28m 3 / h or 30m 3 / h, etc., which are not limited here; the exhaust volume of the reaction system can be 10%, 12%, 15%, 18%, 20%, 25%, or 30%, etc., which are not limited here. Specifically, the amount of oxygen-containing atmosphere introduced and the exhaust volume of the reaction system are controlled according to the required pressure during sintering, which are not specifically limited here.

[0119] In some embodiments, the second stage comprises: heating the mixture from 550°C to 700°C within 2 hours to 5 hours, controlling the pressure P2 to be 8Pa to 12Pa, wherein the amount of oxygen-containing atmosphere introduced is controlled to be 20m 3 / h~30m 3 / h, and control the exhaust volume of the reaction system to 10% to 20%.

[0120] Optionally, the second stage heating time can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, etc., which is not limited here.

[0121] Optionally, the pressure P2 in the second stage can be 8 Pa, 8.5 Pa, 9 Pa, 10 Pa, 10.5 Pa, 11 Pa, 11.5 Pa or 12 Pa, etc., which is not limited here.

[0122] Optionally, the amount of oxygen-containing atmosphere introduced in the first stage can be 20m 3 / h、22m 3 / h、25m 3 / h、26m 3 / h、27m 3 / h、28m 3 / h、29m 3 / h or 30m 3 / h, etc., which are not limited here; the exhaust volume of the reaction system can be 10%, 12%, 15%, 16%, 18%, 19%, or 20%, etc., which are not limited here. Specifically, the amount of oxygen-containing atmosphere introduced and the exhaust volume of the reaction system are controlled according to the required pressure during sintering, which are not specifically limited here.

[0123] In some embodiments, the third stage comprises: sintering the mixture at 700°C to 900°C for 5h to 10h, controlling the pressure P3 to be 9Pa to 13Pa, wherein the amount of oxygen-containing atmosphere introduced is controlled to be 20m 3 / h~30m 3 It is understandable that the third stage is a high-temperature sintering treatment stage, and the pressure during the sintering treatment is also higher. By controlling the amount of oxygen-containing atmosphere introduced, the pressure in the third stage can be controlled within the above range.

[0124] The sintering temperature in the third stage can specifically be 700°C, 720°C, 750°C, 800°C, 830°C, 850°C or 900°C, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0125] The sintering time of the third stage can be specifically 5 h, 5.5 h, 6 h, 7 h, 8 h, 9 h or 10 h, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0126] Optionally, the pressure P3 in the third stage can be 9Pa, 9.5Pa, 10Pa, 11Pa, 12Pa, 12.5Pa or 13Pa, etc., which is not limited here.

[0127] Optionally, the oxygen-containing atmosphere may be introduced in an amount of 20 m 3 / h、21m 3 / h、23m 3 / h、25m 3 / h、26m 3 / h、27m 3 / h、28m3 / h or 30m 3 / h, etc. The amount of oxygen-containing atmosphere introduced is regulated according to the pressure required during sintering and is not limited here.

[0128] In some embodiments, the sintered product is further shaped and screened, and the shaping includes at least one of crushing, mixing, ball milling or gas crushing.

[0129] In some embodiments, screening is performed using an ultrasonic vibration screener having a frequency of 10 kHz to 50 kHz, specifically 10 kHz, 15 kHz, 20 kHz, 30 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.

[0130] In some embodiments, the median particle size D of the matrix material is 50 It is 9μm to 12μm, specifically 9μm, 9.2μm, 9.5μm, 10μm, 11μm, 11.5μm, 11.8μm or 12μm, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0131] In some embodiments, the specific surface area of ​​the base 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 or 0.8m 2 / g, etc., but are not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0132] Step S20: performing a secondary sintering process on the base material and the coating agent to obtain a positive electrode material.

[0133] Before step S20, the method further includes: dissolving the coating agent in water to form a coating solution; and coating the coating solution and the base material by atomizing.

[0134] It can be understood that coating the base material and the coating agent in an atomization manner can improve the coating uniformity of the coating layer on the base material, which is beneficial to improving the electrochemical performance of the positive electrode material.

[0135] In some embodiments, the atomization pressure is 0 MPa to 0.05 MPa, specifically 0 MPa, 0.01 MPa, 0.015 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.045 MPa or 0.05 MPa, etc., and of course other values ​​within the above range can also be used, which are not limited here. It can be understood that the atomized coating solution can form a sheet-like water jet under the action of this pressure, which can maintain the tangential direction with the stirred base material and penetrate the stirred base material, thereby ensuring that the base material can contact and react with the coating agent evenly and accurately, further regulating the specific surface area of ​​the material, improving the doping coating effect, and more residual alkali can be converted to form lithium composite metal oxides that are stably attached to the surface of the positive electrode material, reducing the residual alkali content on the surface of the positive electrode material, improving the surface structural stability of the positive electrode material, and thus reducing the occurrence of side reactions on the surface of the positive electrode material.

[0136] In some embodiments, the coating treatment is carried out under stirring, and the stirring frequency is controlled to be 20 Hz to 50 Hz, specifically 20 Hz, 25 Hz, 30 Hz, 35 Hz, 40 Hz, 45 Hz or 50 Hz, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0137] In some embodiments, the coating treatment temperature is 150°C to 250°C, specifically 150°C, 180°C, 200°C, 220°C, 230°C or 250°C, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0138] In some embodiments, the coating treatment time is 3 hours to 8 hours, specifically 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 7.5 hours or 8 hours, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0139] The present application controls the stirring rate and temperature during the coating process within the above range, thereby improving the reaction activity of the coating agent and the base material, improving the coating uniformity of the coating agent on the base material, and improving the doping coating effect. More residual alkali can be converted into lithium composite metal oxides that stably adhere to the surface of the positive electrode material, reducing the residual alkali content on the surface of the positive electrode material, improving the surface structure stability of the positive electrode material, and thereby reducing the occurrence of side reactions on the surface of the positive electrode material, and adjusting the comprehensive performance of various parameters and microstructures of the positive electrode material.

[0140] In some embodiments, the capping agent includes La(NO3)3·6H2O, NH4F, NH4HF, (NH4)3PO4, (NH4)2HPO4, (NH4)2MoO4, (NH4)2SO4, NH4HSO4, (NH4)6W7O 246H2O, (NH4)3PW 12 O40·3H2O, Zr(SO4)2·4H2O, H 28 N6O 41 W 12 , at least one of WO3, Al2O3 and Al(OH)3.

[0141] It should be noted that the doping element M in the general formula of the positive electrode material in the first aspect of the present application includes the metal element in the dopant added in the first sintering and the metal element in the coating agent added in the second sintering.

[0142] In some embodiments, the mass ratio of the base material to the coating agent is 1:(0.001-0.05), and specifically can be 1:0.001, 1:0.005, 1:0.01, 1:0.015, 1:0.02, 1:0.03, 1:0.04, or 1:0.05, etc. Of course, other values ​​within the above range are also possible and are not limited here. Preferably, the mass ratio of the base material to the coating agent is 1:(0.01-0.04).

[0143] In some embodiments, the secondary sintering treatment is carried out in an oxygen-containing atmosphere, and the mass content of oxygen in the oxygen-containing atmosphere is ≥95%, which can be 95%, 95.5%, 96%, 96.5%, 97%, 98% or 99%, etc., but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable.

[0144] In some embodiments, the temperature of the secondary sintering treatment is 200°C to 700°C, specifically 200°C, 300°C, 300°C, 400°C, 450°C, 500°C, 600°C, 650°C or 700°C, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0145] In some embodiments, the secondary sintering treatment time is 10 h to 20 h, specifically 10 h, 11 h, 12 h, 15 h, 16 h, 18 h or 20 h, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0146] It can be understood that the secondary sintering process allows the coating layer to be more tightly coated on the surface of the base material, further improving the structural stability of the positive electrode material, which is beneficial to improving the cycle performance of the positive electrode material.

[0147] In a third aspect, the present application provides a lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator positioned between the positive and negative electrode sheets. The positive electrode sheet comprises a current collector and a positive electrode active material layer coated on the current collector. The current collector may be aluminum foil or nickel foil. The positive electrode active material layer comprises the positive electrode material described in the first aspect or a positive electrode material prepared by the method for preparing the positive electrode material described in the second aspect, as well as a conductive agent and a binder. The negative electrode sheet comprises a negative electrode active material layer and a negative electrode current collector. The negative electrode current collector may be copper foil or nickel foil.

[0148] In some embodiments, the conductive agent is one of conductive carbon black, Ketjen black, graphite, and acetylene black.

[0149] In some embodiments, the binder is one of sodium carboxymethyl cellulose, cyclodextrin, and polyvinylidene fluoride.

[0150] In some embodiments, the solvent in the positive electrode active material layer is selected from deionized water, N-methylpyrrolidone, and N,N-dimethylformamide.

[0151] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0152] Example 1

[0153] (1) According to n Ni :n Co :n Mn =0.9:0.06:0.04 Nickel sulfate, cobalt sulfate, and manganese sulfate were weighed and dissolved in deionized water to obtain 100 mL of a metal salt solution, wherein the molar concentration of nickel ions was 0.9 mol / L, the molar concentration of cobalt ions was 0.06 mol / L, and the molar concentration of manganese ions was 0.04 mol / L; NaOH solution (4 mol / L) and NH3·H2O (6 mol / L) were added to the metal salt solution, and the mixture was stirred at 65° C. for 15 h, with the stirring rate controlled at 450 r / min, and solid-liquid separation was performed to obtain a nickel-cobalt-manganese-based precursor Ni 0.9 Co 0.06 Mn 0.04 (OH)2.

[0154] (2) Ni-Co-Mn-based precursor Ni 0.9 Co 0.06 Mn 0.04 (OH)2, LiOH, Ba(OH)2 and ZrO2 were dry mixed at 40°C for 1 hour to obtain a mixture, wherein n(Ni+Co+Al): n Li=1:1.03, n(Ni+Co+Al):n (Ba) =1:0.003, n(Ni+Co+Al):n (Zr) =1:0.002.

[0155] (3) The mixture is placed in an oxygen atmosphere with an oxygen concentration of 95% for a sintering process. The process is divided into the first stage, the second stage and the third stage. The pressure during the sintering process is in a gradient rising state. The specific parameters are as follows: the first stage: the mixture is heated from 200°C to 550°C within 4 hours, and the pressure P1 is controlled to be 9Pa, wherein the amount of oxygen-containing atmosphere introduced is controlled to be 20m 3 / h, and control the exhaust volume of the reaction system to 20%; the second stage: within 5h, the mixture was heated from 550℃ to 700℃, and the pressure P2 was controlled to be 10Pa, wherein the amount of oxygen-containing atmosphere introduced was controlled to be 25m 3 / h, controlling the exhaust volume of the reaction system to 20%; the third stage includes: heating the mixture to 750℃ and sintering for 10h, controlling the pressure P3 to 11Pa, wherein the amount of oxygen-containing atmosphere introduced is controlled to be 20m 3 / h, the sintered product is crushed and screened to obtain the matrix material.

[0156] (4) Based on the mass of the base material as 100%, 6500ppm of tungsten oxide (WO3) was dissolved in deionized water to obtain a coating solution; the above-mentioned base material was added to a stirrable and heated reactor, the reactor temperature was set to 200°C, the stirring frequency was controlled to 40Hz, and the coating solution was atomized and sprayed into the reactor with an atomization pressure of 0.01Mpa. After the coating solution was completely sprayed into the reactor, stirring was continued for 5h to obtain a coated product.

[0157] (5) The coated product was sintered at 500° C. for 20 h in an oxygen atmosphere with an oxygen concentration of 95%, cooled, crushed and sieved to obtain a positive electrode material.

[0158] The chemical formula of the positive electrode material prepared in this embodiment is LiNi 0.9 Co 0.06 Mn 0.04 Ba 0.003 Zr 0.002 W 0.002 O2.

[0159] Example 2

[0160] The difference from Example 1 is that the dopant in step (2) is Al(OH)3, n(Ni+Co+Al): n (Al) =1:0.001, and other conditions are exactly the same as those in Example 1.

[0161] The chemical formula of the positive electrode material prepared in this embodiment is LiNi 0.9 Co 0.06 Mn 0.04 Al 0.001 W 0.002 O2.

[0162] Example 3

[0163] The difference from Example 1 is that the dopant in step (2) is Sr(OH)2, n(Ni+Co+Al): n (Sr) =1:0.01, and other conditions are exactly the same as those in Example 1.

[0164] The chemical formula of the positive electrode material prepared in this embodiment is LiNi 0.9 Co 0.06 Mn 0.04 Sr 0.01 W 0.002 O2.

[0165] Example 4

[0166] The difference from Example 1 is that no dopant is added in step (2), and other conditions are exactly the same as those in Example 1.

[0167] The chemical formula of the positive electrode material prepared in this embodiment is LiNi 0.9 Co 0.06 Mn 0.04 W 0.002 O2.

[0168] Example 5

[0169] The difference from Example 1 is that in step (2), n(Ni+Co+Al): n Li =1:1.01, and other conditions are exactly the same as those in Example 1.

[0170] The chemical formula of the positive electrode material prepared in this embodiment is LiNi 0.9 Co 0.06 Mn 0.04 Ba 0.003 Zr 0.002 W 0.002 O2.

[0171] Example 6

[0172] The difference from Example 1 is that in step (2), n(Ni+Co+Al): n Li =1:1.05, and other conditions are exactly the same as in Example 1.

[0173] The chemical formula of the positive electrode material prepared in this embodiment is LiNi 0.9 Co 0.06Mn 0.04 Ba 0.003 Zr 0.002 W 0.002 O2.

[0174] Example 7

[0175] The difference from Example 1 is that in step (2), n(Ni+Co+Al): n Li =1:1, and other conditions are exactly the same as in Example 1.

[0176] The positive electrode material prepared in this embodiment includes a base material and a coating layer located on at least a portion of the surface of the base material. The chemical formula of the base material is LiNi 0.9 Co 0.06 Mn 0.04 Ba 0.003 Zr 0.002 O2, the coating element is W, and the mass content of the coating layer is 0.5% based on the mass of the positive electrode material being 100%.

[0177] Example 8

[0178] The difference from Example 1 is that

[0179] (2) Ni-Co-Mn-based precursor Ni 0.9 Co 0.06 Mn 0.04 (OH)2 and LiOH were dry mixed at 40°C for 1 hour to obtain a mixture, wherein n(Ni+Co+Al): n Li =1:1.03.

[0180] (3) The mixture was heated to 750° C. and sintered for 20 h in an oxygen atmosphere with an oxygen concentration of 95%. The pressure during the sintering process was controlled to be 8 Pa to 12 Pa, and the pressure was increased in a gradient. After crushing and screening, the matrix material was obtained.

[0181] Other conditions are exactly the same as in Example 1.

[0182] The chemical formula of the positive electrode material prepared in this embodiment is LiNi 0.9 Co 0.06 Mn 0.04 Ba 0.003 Zr 0.002 W 0.002 O2.

[0183] Example 9

[0184] The difference from Example 1 is that

[0185] (2) Ni-Co-Mn-based precursor Ni 0.9 Co 0.06Mn 0.04 (OH)2, LiOH, Ba(OH)2 and ZrO2 were dry mixed at 40°C for 1 hour to obtain a mixture, wherein n(Ni+Co+Al): n Li =1:1.03, n(Ni+Co+Al):n (Ba) =1:0.0005, n(Ni+Co+Al):n (Zr) =1:0.0005.

[0186] (3) The mixture is placed in an oxygen atmosphere with an oxygen concentration of 95% for a sintering process. The process is divided into the first stage, the second stage and the third stage. The pressure during the sintering process is in a gradient rising state. The specific parameters are as follows: the first stage: the mixture is heated from 200°C to 550°C within 4 hours, and the pressure P1 is controlled to be 7Pa, wherein the amount of oxygen-containing atmosphere introduced is controlled to be 10m 3 / h, and control the exhaust volume of the reaction system to 15%; the second stage: within 5h, the mixture was heated from 550℃ to 700℃, and the pressure P2 was controlled to be 9Pa, wherein the amount of oxygen-containing atmosphere introduced was controlled to be 20m 3 / h, controlling the exhaust volume of the reaction system to 20%; the third stage includes: heating the mixture to 750℃ and sintering for 10h, controlling the pressure P3 to 13Pa, wherein the amount of oxygen-containing atmosphere introduced is controlled to be 25m 3 / h, the sintered product is crushed and screened to obtain the matrix material.

[0187] Other conditions are exactly the same as in Example 1.

[0188] The chemical formula of the positive electrode material prepared in this embodiment is LiNi 0.9 Co 0.06 Mn 0.04 Ba 0.00053 Zr 0.0005 W 0.002 O2.

[0189] Example 10

[0190] The difference from Example 1 is that

[0191] (3) The mixture is placed in an oxygen atmosphere with an oxygen concentration of 95% for a sintering process. The process is divided into the first stage, the second stage and the third stage. The pressure during the sintering process is in a gradient rising state. The specific parameters are as follows: the first stage: the mixture is heated from 200°C to 550°C within 4 hours, and the pressure P1 is controlled to be 9Pa, wherein the amount of oxygen-containing atmosphere introduced is controlled to be 20m 3 / h, and control the exhaust volume of the reaction system to 20%; the second stage: within 5h, the mixture was heated from 550℃ to 700℃, and the pressure P2 was controlled to be 8Pa, wherein the amount of oxygen-containing atmosphere introduced was controlled to be 12m 3 / h, controlling the exhaust volume of the reaction system to 15%; the third stage includes: heating the mixture to 750℃ and sintering for 10h, controlling the pressure P3 to 12Pa, wherein the amount of oxygen-containing atmosphere introduced is controlled to be 22m 3 / h, the sintered product is crushed and screened to obtain the matrix material.

[0192] Other conditions are exactly the same as in Example 1.

[0193] The chemical formula of the positive electrode material prepared in this embodiment is LiNi 0.9 Co 0.06 Mn 0.04 Ba 0.003 Zr 0.002 W 0.002 O2.

[0194] Example 11

[0195] The difference from Example 1 is that in step (2), n(Ni+Co+Al): n Li =1:1.07, and other conditions are exactly the same as those in Example 1.

[0196] The chemical formula of the positive electrode material prepared in this embodiment is LiNi 0.9 Co 0.06 Mn 0.04 Ba 0.003 Zr 0.002 W 0.002 O2.

[0197] Example 12

[0198] The difference from Example 1 is that in step (3), the exhaust volume of the reaction system in steps 1 and 2 is changed from 20% to 5%, and the other conditions are exactly the same as those in Example 1.

[0199] The chemical formula of the positive electrode material prepared in this embodiment is LiNi 0.9 Co 0.06 Mn 0.04 Ba 0.003 Zr 0.002 W 0.002 O2.

[0200] Example 13

[0201] The difference from Example 1 is that step (4) is changed to adding the above-mentioned base material and 6500ppm of tungsten oxide (WO3) dry powder into a high-speed mixer for dry coating at a speed of 500rpm and a mixing time of 30min to obtain a dry-coated product.

[0202] Other conditions are exactly the same as in Example 1.

[0203] The chemical formula of the positive electrode material prepared in this embodiment is LiNi 0.9 Co 0.06 Mn 0.04 Ba 0.003 Zr 0.002 W 0.002 O2.

[0204] Example 14

[0205] The difference from Example 1 is that in step (4), the reactor temperature is set to 150° C., and the other conditions are exactly the same as those in Example 1.

[0206] The chemical formula of the positive electrode material prepared in this embodiment is LiNi 0.9 Co 0.06 Mn 0.04 Ba 0.003 Zr 0.002 W 0.002 O2.

[0207] Example 15

[0208] The difference from Example 1 is that in step (1), according to n Ni :n Co :n Mn =0.75:0.05:0.2 to prepare the precursor, and other conditions are exactly the same as those in Example 1.

[0209] The chemical formula of the positive electrode material prepared in this embodiment is LiNi 0.75 Co 0.05 Mn 0.2 Ba 0.003 Zr 0.002 W 0.003 O2.

[0210] Example 16

[0211] The difference from Example 1 is that in step (1), according to n Ni :n Co :n Mn =0.85:0.05:0.1 to prepare the precursor, and other conditions are exactly the same as those in Example 1.

[0212] The chemical formula of the positive electrode material prepared in this embodiment is LiNi0.85 Co 0.05 Mn 0.1 Ba 0.003 Zr 0.002 W 0.003 O2.

[0213] Comparative Example 1

[0214] The difference from Example 1 is that

[0215] (2) Ni-Co-Mn-based precursor Ni 0.9 Co 0.06 Mn 0.04 (OH)2 and LiOH were dry mixed at 40°C for 1 hour to obtain a mixture, wherein n(Ni+Co+Al): n Li =1:1.03.

[0216] (3) The mixture is placed in an oxygen atmosphere with an oxygen concentration of 95% for a sintering process. The process is divided into the first stage, the second stage and the third stage. The pressure during the sintering process is in a gradient rising state. The specific parameters are as follows: the first stage: the mixture is heated from 200°C to 550°C within 4 hours, and the pressure P1 is controlled to be 11.5Pa, wherein the amount of oxygen-containing atmosphere introduced is controlled to be 25m 3 / h, and control the exhaust volume of the reaction system to 20%; the second stage: within 5h, the mixture was heated from 550℃ to 700℃, and the pressure P2 was controlled to be 10.5Pa, wherein the amount of oxygen-containing atmosphere introduced was controlled to be 22m 3 / h, controlling the exhaust volume of the reaction system to 20%; the third stage includes: heating the mixture to 750℃ and sintering for 10h, controlling the pressure P3 to 9.5Pa, wherein the amount of oxygen-containing atmosphere introduced is controlled to be 18m 3 / h, the sintered product is crushed and screened to obtain the matrix material.

[0217] Other conditions are exactly the same as in Example 1.

[0218] The chemical formula of the positive electrode material prepared in this comparative example is LiNi 0.9 Co 0.06 Mn 0.04 W 0.002 O2.

[0219] Comparative Example 2

[0220] The difference from Example 1 is that

[0221] (3) The mixture was heated to 750° C. and sintered for 20 h in an oxygen atmosphere with an oxygen concentration of 95%. The pressure during the sintering process was controlled to be constant at 10 Pa. After crushing and screening, the matrix material was obtained.

[0222] Other conditions are exactly the same as in Example 1.

[0223] The chemical formula of the positive electrode material prepared in this embodiment is LiNi 0.9 Co 0.06 Mn 0.04 Ba 0.003 Zr 0.002 W 0.002 O2.

[0224] Test Method

[0225] (1) dE / dV-E curve of positive electrode material and test method of residual alkali content:

[0226] 5g of cathode material was dispersed in 100ml of deionized water and magnetically stirred to dissolve residual carbonate and hydroxide ions. The filtrate was filtered and titrated with hydrochloric acid using an automatic potentiometric titrator using the equivalent drop method. A dE / dV-E curve was obtained after titration. The carbonate and hydroxide ion contents of the cathode material were calculated based on the breakpoint and the degree of hydrochloric acid consumption.

[0227] (2) Element content and test method in positive electrode materials:

[0228] General pretreatment method: Weigh 0.3-0.35g of cathode material, moisten with a small amount of ultrapure water, digest with 8mL of aqua regia at 200°C for 30 minutes, cool to room temperature, and dilute to 100mL. For example, pretreatment for W element testing: weigh 0.05±0.005g of sample, digest on a hotplate at 220°C for 30 minutes with 8mL of aqua regia, remove the sample, add 2mL of HF, dilute to 50mL, and inject the sample for testing. Pretreatment method for Zr element testing: weigh 0.3-0.35g of sample and add 0.5-0.6g of ammonium sulfate, heat at 250°C for 30 minutes, then at 120°C for 30 minutes, digest with 6mL of concentrated sulfuric acid and 8mL of aqua regia, dilute to 100mL, and inject the sample for testing. Impurity elements are analyzed using an ICP spectrometer (Agilent 5110 ICP-OES). Take 1mL of the mother solution, dilute to 100mL, and analyze the main elements using an ICP spectrometer. The inductively coupled plasma torch temperature can reach 6000-8000K. When a sample is introduced from the injector into the atomizer and carried into the torch by the argon carrier gas, the sample components are atomized, ionized, and excited, emitting energy in the form of light. Atoms of different elements emit characteristic spectra of different wavelengths when they return to their ground state after excitation or ionization. This characteristic light wavelength allows for qualitative analysis. Different elemental concentrations also produce different intensities of the emitted characteristic light, allowing for quantitative analysis to determine the corresponding elemental content.

[0229] (3) Testing method for specific surface area of ​​positive electrode material:

[0230] The specific surface area of ​​the positive electrode material was measured by the gas adsorption method. Specifically, Micromeritics TristarⅡ was used to perform N2 adsorption tests and calculate the adsorption values ​​at different equilibrium pressures. The isothermal adsorption line was obtained and the specific surface area of ​​the positive electrode material was calculated.

[0231] (4) Electrochemical performance test:

[0232] 0.8g of the positive electrode material, 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. The dried electrode was cut into 15mm diameter discs and assembled in a glove box, including the positive electrode casing, electrode, electrolyte (EC / DMC / EMC volume ratio of 1:1:1, LiPF6 concentration of 1 mol / L), separator (Celgard PP / PE / PP three-layer composite film), lithium sheet, electrolyte, nickel foam, and negative electrode casing. The battery was then left to stand for 24 hours. The resulting battery was then placed in a constant temperature chamber for testing.

[0233] 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.

[0234] The above test results are detailed in Table 1 and Table 2.

[0235] Table 1 Performance test results of positive electrode materials of Examples and Comparative Examples

[0236] Table 2 Electrochemical performance test results of positive electrode materials prepared in Examples and Comparative Examples

[0237] According to the test results in Tables 1 and 2, when ξ is controlled within the above range, the influence of water vapor on the positive electrode material can be reduced, the side reactions between the positive electrode material and water vapor can be reduced, and the surface structure stability of the positive electrode material can be improved. This can effectively reduce the occurrence of side reactions on the surface of the positive electrode material and improve the capacity and cycle stability of the positive electrode material.

[0238] According to the test results of Examples 1 to 16, the present application controls the temperature and pressure of the primary sintering process, and simultaneously controls the pressure of the sintering system to be in a gradient rising state during the primary sintering temperature rise process, so as to discharge water vapor as much as possible in the low-temperature section of the sintering process, thereby reducing the side reaction between the unreacted lithium and water vapor during the primary sintering process, reducing the residual alkali content on the surface of the matrix material, and thereby reducing the occurrence of side reactions on the surface of the positive electrode material, generating an ideal microscopic material structure surface, and the surface energy tends to be stable, preventing the lattice lithium on the surface of the positive electrode material from being corroded by water vapor to form residual alkali for a second time; inhibiting the generation of surface structural defects of the positive electrode material, achieving the effect of removing more residual lithium without destroying the surface structure, and improving the capacity and cycle performance of the positive electrode material.

[0239] FIG5 is a graph showing the relationship between the residual alkali conversion coefficient ξ and the capacity of the positive electrode material provided in an embodiment of the present application. As shown in FIG5 , the capacity of the positive electrode material increases with the increase of its residual alkali conversion coefficient ξ.

[0240] Figure 6 is a relationship diagram between the residual alkali conversion coefficient ξ of the positive electrode material provided in an embodiment of the present application and normal temperature cycling; Figure 7 is a relationship diagram between the residual alkali conversion coefficient ξ of the positive electrode material provided in an embodiment of the present application and high temperature cycling; as shown in Figures 6 and 7, the cycle capacity retention rate of the positive electrode material shows an upward trend with the increase of its residual alkali conversion coefficient ξ.

[0241] By comparing the test data of Example 1, Example 2, Example 3 and Example 4, it can be seen that during the reaction of the precursor, lithium source and dopant, under the condition that all conditions are the same, the residual alkali conversion coefficient changes with the change of the doping element, and the A, B and C values ​​of the positive electrode material without adding the dopant are greater than the A, B and C values ​​of the doped positive electrode material, indicating that the doping element can not only effectively stabilize the lattice structure inside the positive electrode material particles, but also further affect the composition of the surface of the positive electrode material particles, thereby affecting the residual alkali conversion coefficient ξ, thereby ensuring the normal performance of the lithium ion capacity and cycle performance.

[0242] Comparing the test data of Example 1 and Example 12, it can be seen that when the exhaust volume percentage is reduced, water vapor cannot be discharged, resulting in a significant increase in the residual alkali of the material, a significant increase in the A, B and C values ​​of the positive electrode material, and a significant decrease in the material cycle retention rate, indicating that the material is seriously affected by water vapor.

[0243] Comparing Example 1 and Example 13, it can be seen that when the wet coating method is changed to dry coating, the B value decreases, causing ξ to approach the lower limit, indicating that the residual alkali conversion rate is low and not fully converted into the functional layer. Comparing Example 1 and Example 14, it can be seen that by lowering the temperature of the wet coating reaction system, the presence time of water in the system can be effectively increased, the coating uniformity and reactivity can be improved, and the residual alkali conversion rate can be significantly increased (the ξ value is increased), which significantly improves the material capacity and cycle performance.

[0244] According to the test data of Example 1 and Comparative Example 1, in Comparative Example 1, no dopant was added during the first sintering, and the crystallization rate of lithium ions inside the matrix material was slow, resulting in an increase in the amount of unreacted lithium during the sintering process. At the same time, the pressure of the sintering system was in a gradient decline during the first sintering temperature rise process. Therefore, it was difficult for water vapor to be discharged in the low-temperature section of the sintering process, resulting in a large amount of water vapor entering the high-temperature section of the sintering process. These water vapors reacted with the unreacted lithium in the high-temperature section during the sintering process, resulting in a residual alkali content (α LH +α LC ) increases, the excessive residual alkali on the surface of the material is difficult to be converted, the value of the residual alkali conversion coefficient ξ of the material decreases, the surface structural stability of the positive electrode material decreases, and the side reactions on the surface of the material increase, which in turn leads to a decrease in the capacity and cycle performance of the material.

[0245] According to the test data of Example 1 and Comparative Example 2, the pressure of the sintering system of Comparative Example 2 is in a constant pressure state during the primary sintering temperature rise process. Therefore, it is difficult for water vapor to be discharged in the low temperature section of the sintering process, resulting in a large amount of water vapor entering the high temperature section of the sintering process. These water vapors react with the lithium that has not reacted completely in the high temperature section during the sintering process, resulting in a residual alkali content (α LH +α LC ) increases, the excessive residual alkali on the surface of the material is difficult to be converted, the value of the residual alkali conversion coefficient ξ of the material decreases, the surface structural stability of the positive electrode material decreases, and the side reactions on the surface of the material increase, which in turn leads to a decrease in the capacity and cycle performance of the material.

Claims

1. A cathode material, characterized in that, The chemical general formula of the positive electrode material is LiNi a Co b Mn c M d O2, where 0.7 < a < 0.98, 0 < b < 0.3, 0 < c < 0.3, 0 < d ≤ 0.01, a + b + c = 1, and M is a doping element; Using a potentiometric titrator and hydrochloric acid with a concentration of 0.02 mol / L as the titrant, an acid-base potentiometric titration test is performed on the positive electrode material to obtain a curve graph of the relationship between the differential value dE / dV obtained by differentiating the potential E with respect to the consumption volume V of hydrochloric acid and the potential E. In the curve graph of the relationship between the differential value dE / dV and the potential E, the positive electrode material has a first characteristic peak in the potential E range of -200 mV to -50 mV, the peak area of the first characteristic peak is A, the positive electrode material has a second characteristic peak between the potential E of 120 mV and 250 mV, and the peak area of the second characteristic peak is B; there is at least one characteristic peak in the potential E range of -50 mV to 120 mV, and the sum of the peak areas of the at least one characteristic peak is C, and the residual alkali conversion coefficient of the positive electrode material is ξ, 0.200 ≤ ξ ≤ 0.

350.

2. The cathode material according to claim 1, wherein The doping element M includes at least one of B, P, S, F, La, Sr, Ti, Al, Zr, Y, Ba, Mg, Nb, Mo, W, and V.

3. The cathode material according to claim 1, characterized in that, 0.8≤a＜0.98。 4. The cathode material according to claim 1, wherein The peak area of the first characteristic peak is A, and 2000 ≤ A ≤ 200000.

5. The cathode material according to claim 1, characterized in that, The peak area of the second characteristic peak is B, and 2000 ≤ B ≤ 200000.

6. The cathode material according to claim 1, characterized in that, The sum of the peak areas of the at least one characteristic peak is C, and 2000 ≤ C ≤ 200000.

7. The cathode material according to claim 1, characterized in that, The molar ratio of Li to all metals Me other than Li in the positive electrode material is γ Li / Me , 0.95 < γ Li / Me < 1.

05.

8. The cathode material according to claim 1, wherein The specific surface area of the positive electrode material is β m 2 / g, where 0.2 < β < 1.

5.

9. The cathode material according to claim 1, characterized in that, The positive electrode material includes at least one of the following characteristics: (1) The mass content of LiOH in the positive electrode material is α LH wt%, 0.1 ≤ α LH ≤ 1.0; (2) The mass content of Li2CO3 in the positive electrode material is α LC wt%, 0.1 ≤ α LC ≤ 1.0 10. The cathode material according to claim 9, characterized in that, 0.25≤α LH +α LC ≤0.65。 11. A method for preparing a cathode material, characterized in that, Including the following steps: Performing a primary sintering treatment on a mixture containing a nickel-cobalt-manganese-based precursor, a lithium source, and a dopant containing a metal element in an oxygen-containing atmosphere to obtain a matrix material; the temperature of the primary sintering treatment is 200°C to 900°C, and the pressure during the primary sintering treatment increases in a gradient manner, and the pressure range is 3 Pa to 13 Pa; Performing a secondary sintering treatment on the matrix material and a coating agent to obtain a positive electrode material.

12. The preparation method according to claim 11, characterized in that, The primary sintering treatment includes a first stage, a second stage, and a third stage, and the preparation method includes at least one of the following characteristics: (1) The first stage includes: heating the mixture from 200 °C to 550 °C within 2 h to 5 h, controlling the pressure P1 to be 7 Pa to 11 Pa, wherein the input amount of the oxygen-containing atmosphere is controlled to be 10 m 3 / h to 30 m 3 / h, and controlling the exhaust gas volume of the reaction system to be 10% to 30%; (2) The second stage includes: heating the mixture from 550 °C to 700 °C within 2 h to 5 h, controlling the pressure P2 to be 8 Pa to 12 Pa, wherein the introduced amount of the oxygen-containing atmosphere is controlled to be 20 m 3 / h to 30 m 3 / h, and controlling the exhaust gas volume of the reaction system to be 10％～20％； (3) The third stage includes: sintering the mixture at 700 °C to 900 °C for 5 h to 10 h, controlling the pressure P3 to be 9 Pa to 13 Pa, wherein the flow rate of the oxygen-containing atmosphere is controlled to be 20 m 3 / h to 30 m 3 / h.

13. The preparation method according to claim 11, wherein The preparation method includes at least one of the following characteristics: (1) The volume median diameter D of the matrix material 50 is 9 μm to 12 μm; (2) The coating agent includes at least one of La(NO3)3·6H2O, NH4F, NH4HF2, (NH4)3PO4, (NH4)2HPO4, (NH4)2MoO4, (NH4)2SO4, NH4HSO4, (NH4)6W7O 24 ·6H2O, (NH4)3PW 12 O 40 ·3H2O, Zr(SO4)2·4H2O, H 28 N6O 41 W 12 , WO3, Al2O3, and Al(OH)3; (3) The mass ratio of the matrix material to the coating agent is 1:(0.001 - 0.05).

14. The preparation method according to claim 11, wherein The preparation method includes at least one of the following characteristics: (1) The secondary sintering treatment is carried out in an oxygen-containing atmosphere; (2) The secondary sintering treatment is carried out in an oxygen-containing atmosphere, and the mass content of oxygen in the oxygen-containing atmosphere ≥ 95%; (3) The temperature of the secondary sintering treatment is 200°C to 700°C; (4) The time of the secondary sintering treatment is 10 h to 20 h.

15. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode material according to any one of claims 1 to 10 or the positive electrode material prepared by the preparation method according to any one of claims 11 to 14.

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