Positive electrode active material, and preparation method therefor and application thereof

Abstract

Provided are a positive electrode active material, and a preparation method therefor and an application thereof. The positive electrode active material comprises primary particles, and secondary particles formed by agglomeration of the primary particles. The primary particles comprise a ternary positive electrode material matrix, and a coating layer arranged on at least part of the surface of the ternary positive electrode material matrix. The coating layer comprises a lithium oxide including an element A. The element A comprises at least one of Co, W, Zr, Sb, Nb, Cr and Ta. The positive electrode active material satisfies L / TM≥1 and (BET1-BET0) / BET0≤20%, and the porosity is not higher than 3%. The positive electrode active material has good charging and discharging uniformity, and can effectively improve the cycle stability of a battery.

Description

A positive electrode active material and a preparation method and application thereof

[0001] The present application claims priority to the Chinese patent application No. 202411370716.0, filed on September 27, 2024, and titled "A positive electrode active material and a preparation method and application thereof", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application belongs to the technical field of lithium ion batteries, and relates to a positive electrode active material, in particular to a positive electrode active material and a preparation method and application thereof. BACKGROUND

[0003] Lithium ion batteries are one of the most widely used batteries today, and play an important role in the fields of electric vehicles, portable electronic devices, etc. Among them, the positive electrode active material, as one of the core components of lithium ion batteries, has a direct impact on the performance of the battery.

[0004] Currently, the electrochemical performance of the positive electrode material is generally improved by coating, but the coating effect directly affects whether the positive electrode active material can be uniformly charged and discharged during the cycle process. Moreover, the conductivity of the positive electrode material also has a great influence on the uniformity of charging and discharging, and whether the charging and discharging is uniform is one of the key factors to ensure the cycle performance and life of the battery.

[0005] Therefore, it is necessary to study a positive electrode material that can be uniformly charged and discharged to improve the cycle performance of the battery.

[0006] SUMMARY

[0007] In view of the above defects, the present application provides a positive electrode active material which can be uniformly charged and discharged, effectively improving the cycle performance of the battery.

[0008] The present application also provides a preparation method of the above positive electrode active material, and the positive electrode active material prepared by the preparation method has good charging and discharging uniformity, which can effectively improve the cycle performance of the battery.

[0009] The present application also provides a positive electrode sheet comprising the above positive electrode active material or the positive electrode active material prepared by the above preparation method. When the positive electrode sheet is used in a lithium ion battery, the charging and discharging uniformity of the battery can be effectively improved, thereby improving the cycle performance of the battery.

[0010] The present application also provides a lithium ion battery comprising the above positive electrode active material or the positive electrode active material prepared by the above preparation method or the above positive electrode sheet. The lithium ion battery has a longer cycle life.

[0011] The application provides a positive electrode active material, which comprises primary particles and secondary particles formed by agglomeration of the primary particles; the primary particles comprise a ternary positive electrode material matrix and a coating layer arranged on at least part of the surface of the ternary positive electrode material matrix; the coating layer comprises a lithium oxide containing an A element; the A element comprises at least one of Co, W, Zr, Sb, Nb, Cr and Ta.

[0012] The positive electrode active material satisfies formula 1 and formula 2, L / TM≥1 Formula 1 (BET1-BET0) / BET0≤20% Formula 2

[0013] In formula 1, L is the molar amount of lithium elements in the positive electrode active material after chemical conversion, and TM is the total molar amount of transition metal elements in the positive electrode active material after chemical conversion; the baking temperature is 600-700 ℃, and the time is 9-11 h.

[0014] In formula 2, BET0 is the initial specific surface area of the positive electrode active material, and BET1 is the specific surface area of the positive electrode active material after chemical conversion and baking.

[0015] The porosity of the positive electrode active material is not higher than 3%.

[0016] Further, the BET0 is 0.4-0.8 m 2 / g, and / or the BET1 is 0.5-1.0 m 2 / g.

[0017] Further, the D10 of the positive electrode active material is 5-8 μm, the D50 is 5-11 μm, and the D90 is 10-25 μm.

[0018] And / or, the maximum particle size D max of the positive electrode active material is 16-30 μm, and the minimum particle size D min is 2-6 μm.

[0019] Further, the porosity of the positive electrode active material is 1-3%.

[0020] Further, the powder conductivity of the positive electrode active material is not lower than 0.001 S / cm.

[0021] The application also provides a preparation method of the positive electrode active material.

[0022] 1) mixing a ternary positive electrode material precursor with a first lithium source to obtain a first product after first sintering;

[0023] The molar amount Q1 of lithium element in the first lithium source and the total molar amount M0 of transition metal elements in the ternary positive electrode material precursor satisfy: 1 < Q1 / M0 ≤ 1.03.

[0024] 2) mixing the first product with a second lithium source and a coating material, and performing second sintering to obtain a second product including a coating layer;

[0025] The molar amount Q2 of lithium element in the second lithium source, the molar amount W1 of the coating material, the molar amount Q1 of lithium element in the first lithium source, and the ratio K of the molar amount of lithium element to the molar amount of element A in the theoretical chemical composition of the coating layer satisfy: Q2 = K*W1, and Q1+Q2 ≤ 1.05M0.

[0026] 3) performing third sintering on the second product in an oxygen atmosphere, the pressure in the furnace during the third sintering being 1-2 MPa, to obtain the positive electrode active material.

[0027] Further, in step 1), the temperature in the first sintering is 300-800 ℃, and the holding time is 3-10 h.

[0028] Further, in step 2), the temperature in the second sintering is 300-800 ℃, and the holding time is 2-8 h.

[0029] Further, in step 3), the sintering temperature in the third sintering is 300-600 ℃, and the sintering time is 1-5 h.

[0030] The application also provides a positive electrode sheet including the positive electrode active material according to any one of the above or prepared by the preparation method.

[0031] Further, the compaction density of the positive electrode sheet is 3.0-3.8 g / cm 3 .

[0032] The application also provides a lithium ion battery including the positive electrode active material according to any one of the above or prepared by the preparation method, or the positive electrode sheet.

[0033] The positive electrode active material in the application includes primary particles and secondary particles formed by agglomeration of the primary particles, wherein the primary particles include a ternary positive electrode material matrix and a coating layer located on at least part of the surface of the matrix, and the coating layer includes a lithium oxide containing element A. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is an SEM image of the positive electrode active material in Example 1 of the present application at 10.0k;

[0035] Figure 2 is an SEM image of the positive electrode active material in Example 1 of the present application at 50.0k;

[0036] Figure 3 is an SEM image of the positive electrode active material in Comparative Example 2 of the present application at 10.0k;

[0037] Figure 4 is an SEM image of the positive electrode active material in Comparative Example 2 of the present application at 50.0k;

[0038] Figure 5 is an SEM image of the positive electrode active material in Example 1 of the present application after formation and baking at 10.0k;

[0039] Figure 6 is an SEM image of the positive electrode active material in Example 1 of the present application after formation and baking at 50.0k;

[0040] Figure 7 is an SEM image of the positive electrode active material in Comparative Example 2 of the present application after formation and baking at 10.0k;

[0041] Figure 8 is an SEM image of the positive electrode active material in Comparative Example 2 of the present application after formation and baking at 50.0k;

[0042] Figure 9 is a comparison chart of the cycle performance of the positive electrode active materials in Example 1 and Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without any creative effort fall within the scope of protection of the present application.

[0044] The first aspect of the present application provides a positive electrode active material, which comprises primary particles and secondary particles formed by agglomeration of the primary particles; the primary particles comprise a ternary positive electrode material matrix and a coating layer arranged on at least part of the surface of the ternary positive electrode material matrix; the coating layer comprises a lithium oxide containing an A element; the A element comprises at least one of Co, Al, W, Zr, Sb, Nb, Cr, Ta and B;

[0045] The positive electrode active material satisfies formula 1 and formula 2, L / TM≥1 Formula 1 (BET1-BET0) / BET0≤20% Formula 2

[0046] In formula 1, L is the molar amount of lithium element in the positive electrode active material after formation and baking, TM is the total molar amount of transition metal elements in the positive electrode active material after formation and baking; the baking temperature is 600-700°C, and the time is 9-11h;

[0047] In formula 2, BET0 is the initial specific surface area of the positive electrode active material, and BET1 is the specific surface area of the positive electrode active material after formation and baking.

[0048] The porosity of the positive electrode active material is not higher than 3%.

[0049] The positive electrode active material in the present application includes primary particles and secondary particles formed by agglomeration of the primary particles, wherein the primary particles include a ternary positive electrode material matrix and a coating layer located on at least part of the surface of the matrix, and the coating layer includes a lithium oxide containing A elements. By making the positive electrode active material satisfy formula 1 and formula 2, the charge-discharge uniformity of the positive electrode active material can be effectively improved. The applicant analyzes the phenomenon and considers that the reason may be as follows: generally, the positive electrode active material with a coating layer, in the process of forming the coating layer, most of the coating material will react with lithium on the surface layer of the matrix, causing the surface layer of the matrix material particles to be in a lithium-deficient state and the inside to be rich in lithium. Due to the non-uniformity of the surface coating, the charge-discharge of individual primary particles or multiple particles is non-uniform, that is, at high voltage or deep discharge, the lithium-deficient region in the high-nickel material is more likely to cause a transition from a layered structure to a spinel structure or even a rock salt structure, thereby causing structural collapse. In the discharge process, lithium ions separated from the negative electrode cannot return to the positive electrode active material smoothly, causing irreversible loss of lithium, thereby causing the L / TM in the positive electrode active material after formation to decrease; at the same time, after high-temperature baking of the positive electrode active material after formation, the spinel structure is converted into a rock salt phase structure. Due to the difference in unit cell volume between the rock salt phase and the spinel, the volume of the lithium-deficient part of the particle changes, forming multiple small pores on the surface of the particle, causing the specific surface area of the positive electrode active material to increase. By making the positive electrode active material L / TM≥1 and (BET1-BET0) / BET0≤20%, the present application ensures that the content of lithium elements in the positive electrode active material remains at a high level after formation, and the change rate of the specific surface area is low; at the same time, by controlling the porosity of the positive electrode active material to be not higher than 3%, the close arrangement between primary particles can be improved, the conductivity of the positive electrode active material can be effectively improved, and the charge-discharge uniformity of the positive electrode active material can be comprehensively improved. The transition of the material from a layered phase to a spinel or even a rock salt phase is avoided, the loss of the positive electrode active material is reduced, the crushing of the positive electrode active material in the charge-discharge process due to lattice mismatch between different phases is also avoided, thereby reducing the side reaction of the new interface with the electrolyte, and improving the cycle performance of the battery.

[0050] Exemplarily, the temperature of the baking is 600℃, 620℃, 640℃, 660℃, 680℃ or 700℃, and the time is 9h, 9.5h, 10h, 10.5h or 11h.

[0051] The method of formation in the present application is not specifically limited, for example, the formation can be carried out by the following method:

[0052] The positive electrode active material, the conductive agent and the binder are prepared into a positive electrode slurry with a mass ratio of 95:2.5:2.5, the positive electrode slurry is coated on the surface of an aluminum foil, and after drying, rolling, and slitting, a positive electrode sheet with a compacted density of 3.0-3.8 g / cm 3 The negative electrode active material graphite, Super P, butadiene styrene rubber (SBR) and sodium carboxymethyl cellulose (CMC) are prepared into a negative electrode slurry with a mass ratio of 95.5:1:2:1.5, the negative electrode slurry is coated on the surface of a copper foil, and after drying, rolling, and slitting, a negative electrode sheet with a compacted density of 1.55 g / cm 3 The foregoing positive electrode sheet and the negative electrode sheet are assembled into a full cell, and after formation, the full cell is disassembled in an empty state to obtain a positive electrode sheet after formation; the formation mechanism is as follows: charging at 0.05C or 0.1C for 1h, then charging at 0.2C constant current and constant voltage to 4.25V, with a cutoff current of 0.05C, and then discharging at 0.5C to 2.8V; then charging and discharging at 1C between 2.8-4.25V for 2 cycles.

[0053] The molar amount of lithium element and the total molar amount of Ni, Co and Mn elements in the positive electrode active material after formation and baking in the present application can be obtained by ICP testing, for example, the testing can be carried out by the following method:

[0054] 0.2g of the positive electrode active material after formation and baking is taken into a beaker, then 10mL of aqua regia (7.5mL of concentrated hydrochloric acid + 2.5mL of concentrated nitric acid) is added, and the solution is digested at 190℃ for 15min, finally the remaining liquid is transferred to a volumetric flask, and diluted with deionized water, shaken well, and diluted to 100mL. The solution after shaking is taken for testing of main elements Li, Ni, Co and Mn, the mass ratio of each element obtained is converted into molar ratio, and finally L / TM is obtained.

[0055] The heating rate in the baking process is not specifically limited in the present application, for example, the heating rate is 2-5℃ / min.

[0056] The chemical composition of the ternary positive electrode material substrate is not specifically limited in the present application, only the positive electrode active material after formation and baking needs to satisfy formula 1 and formula 2.

[0057] The source of the ternary cathode material substrate is not specifically limited in the present application. For example, commercially available products or products prepared by conventional preparation methods known to those skilled in the art can be used.

[0058] In one specific embodiment, BET0 is 0.4-0.8 m 2 / g, and / or, BET1 is 0.5-1.0 m 2 / g. When BET0 and / or BET1 are in the aforementioned ranges, the cathode active material can be more uniform in charging and discharging in the electrochemical process, reducing the consumption of irreversible active lithium, the phase change degree is more uniform, and the cycle performance of the battery is further improved.

[0059] BET in the present application can be tested by a specific surface area tester.

[0060] Illustratively, BET0 is 0.4 m 2 / g, 0.5 m 2 / g, 0.6 m 2 / g, 0.7 m 2 / g, or 0.8 m 2 / g; and BET1 is 0.5 m 2 / g, 0.6 m 2 / g, 0.7 m 2 / g, 0.8 m 2 / g, 0.9 m 2 / g, or 1.0 m 2 / g.

[0061] In one specific embodiment, the D10 of the cathode active material is 5-8 μm, the D50 is 5-11 μm, and the D90 is 10-25 μm.

[0062] and / or the maximum particle size D max of the cathode active material is 16-30 μm, and the minimum particle size D min is 2-6 μm.

[0063] Illustratively, the D10 is 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, or 8 μm, the D50 is 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or 11 μm, and the D90 is 10 μm, 13 μm, 16 μm, 19 μm, 22 μm, or 25 μm.

[0064] Illustratively, the maximum particle size D max is 16 μm, 18 μm, 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, or 30 μm, and the minimum particle size D min is 2 μm, 3 μm, 4 μm, 5 μm, or 6 μm.

[0065] Within this range, the contact between the positive active material particles is better, the lithium ion transmission path is shortened, the lithium ion conduction efficiency in the electrode is improved, the ion transmission internal resistance is reduced, and the cycle performance of the battery is further improved.

[0066] D10 in the present application refers to the particle size value corresponding to the cumulative distribution percentage of 10% of the particles, D50 refers to the particle size value corresponding to the cumulative distribution percentage of 50% of the particles, and D90 refers to the particle size value corresponding to the cumulative distribution percentage of 90% of the particles.

[0067] D10, D50, D90, D max , D min The powder conductivity in the present application can be tested by a MCP-PD51 powder impedance tester.

[0068] In one specific embodiment, the porosity of the positive active material is 1-3%. Within this range, not only can the primary particles be arranged more closely to improve the conductivity of the positive active material, but also the porosity can be avoided to be too small to cause insufficient impregnation of the electrolyte, thereby causing the capacity to be limited, so that the battery has higher cycle performance.

[0069] Illustratively, the porosity of the positive active material is 1%, 0.3%, 0.4%, 0.6%, 0.8% or 3%.

[0070] The porosity in the present application can be automatically identified by Metis software, and the specific testing method comprises: planar grinding of the positive active material in an ion grinder to expose the cross section, and then taking SEM, and then automatically identifying the porosity by Metis software.

[0071] In one specific embodiment, the powder conductivity of the positive active material is not less than 0.001 S / cm. The conductivity of the positive active material will affect the charge and discharge uniformity, and the applicant analyzes the reason that the extraction / insertion of lithium ions in a single primary particle is driven by an external effective potential, and the effective potential is determined by the potential drop caused by the potential applied on each particle and the material resistance. If the conductivity of the material itself is not good, the effective potential will be reduced, affecting the lithium ion migration efficiency, and then negatively affecting the charge and discharge uniformity of the positive active material. Within this range, the positive active material has good conductivity, which can ensure that the positive material has good lithium extraction / insertion capacity, avoid the problem of uneven extraction / insertion of active material in different regions caused by the thickness of the electrode sheet, and further improve the cycle performance of the battery.

[0072] The powder conductivity in the present application can be tested by a MCP-PD51 powder impedance tester.

[0073] The second aspect of the application provides a preparation method of the positive electrode active material of the first aspect, comprising the following steps:

[0074] 1) mixing the ternary positive electrode material precursor with the first lithium source, and obtaining a first product after first sintering;

[0075] wherein the molar amount Q1 of lithium element in the first lithium source and the total molar amount M0 of transition metal elements in the ternary positive electrode material precursor satisfy: 1 < Q1 / M0 ≤ 1.03;

[0076] 2) mixing the first product with the second lithium source and the coating material, and obtaining a second product comprising a coating layer after second sintering;

[0077] wherein the molar amount Q2 of lithium element in the second lithium source, the molar amount W1 of the coating material, the molar amount Q1 of lithium element in the first lithium source, and the ratio K of the molar amount of lithium element to the molar amount of element A in the theoretical chemical composition of the coating layer satisfy: Q2=K*W1, and Q1+Q2≤1.05M0;

[0078] 3) performing third sintering on the second product in an oxygen atmosphere, and obtaining the positive electrode active material, wherein the furnace pressure during the third sintering process is 1-2 MPa.

[0079] Specifically, in step 1), the ternary positive electrode material precursor and the first lithium source are uniformly mixed, and the ratio of the molar amount Q1 of lithium element in the first lithium source to the total molar amount M0 of transition metal elements in the ternary positive electrode material precursor is controlled to be 1-1.03, to obtain a mixture, and the mixture is subjected to first sintering in an air atmosphere to obtain a first product, i.e., a ternary positive electrode material matrix.

[0080] It can be understood that after the first sintering is completed, the sintered product needs to be cooled to obtain the first product.

[0081] The cooling method is not specifically limited in the application, for example, natural cooling can be used for cooling, or the cooling rate can be controlled to achieve the purpose of cooling; the cooling rate is not specifically limited in the application, for example, the cooling rate is 2-5 ℃ / min.

[0082] The "ternary positive electrode material precursor" in the application refers to a hydroxide comprising transition metal elements (such as Ni, Co, and Mn).

[0083] The "lithium source" in the application refers to a raw material providing lithium element, as long as it contains the target element, it belongs to the definition of the application; for example, the lithium source can be selected from at least one of lithium hydroxide monohydrate, lithium carbonate, lithium chloride, lithium nitrate, lithium phosphate, lithium formate, lithium acetate, and lithium ethoxide.

[0084] The application does not make specific limitation on the source of the ternary positive electrode material precursor and the lithium source. For example, commercially available products or products prepared by conventional preparation methods known to those skilled in the art can be used.

[0085] The application does not make specific limitation on the sintering temperature and holding time of the first sintering, and the heating rate during the first sintering.

[0086] The application does not make specific limitation on the mixing method, as long as the ternary positive electrode material precursor and the first lithium source are uniformly mixed. For example, the mixing can be performed by a high-speed mixer. Preferably, the rotation speed of the high-speed mixer is 600-1000 r / min, and the mixing time is 20-80 min.

[0087] In step 2), the first product prepared above is uniformly mixed with the second lithium source and the coating material. The molar amount Q2 of lithium element in the second lithium source, the molar amount W1 of the coating material, the molar amount Q1 of lithium element in the first lithium source, and the ratio K of the molar amount of lithium element to the molar amount of element A in the theoretical chemical composition of the coating layer satisfy Q2 = K*W1, and Q1 + Q2 ≤ 1.05M0, to obtain a mixture. The mixture is subjected to second sintering to obtain a second product.

[0088] It can be understood that after the second sintering is completed, the sintered product needs to be cooled to obtain the second product.

[0089] The application does not make specific limitation on the cooling method after the second sintering, which is consistent with the limitation in step 1) and will not be repeated here.

[0090] The application does not make specific limitation on the second lithium source, which can be consistent with the first lithium source in step 1) and will not be repeated here.

[0091] The application does not make specific limitation on the type of the coating material, as long as it contains element A. For example, the coating material can be selected from at least one of cobalt oxide, cobalt boride, zirconium oxide, zirconium fluoride, aluminum oxide, cobalt oxide, tungsten oxide, molybdenum oxide, cobalt hydroxide, titanium oxide, aluminum hydroxide, and aluminum fluoride.

[0092] The application does not make specific limitation on the source of the coating material. For example, commercially available products or products prepared by conventional preparation methods known to those skilled in the art can be used.

[0093] It should be noted that the "theoretical chemical composition of the coating layer" in the present application is obtained according to the chemical composition of the coating material. For example, when the coating material is cobalt boride, the cobalt boride reacts with the lithium source to form LiCoO2, and K is 1. Similarly, when the coating material is zirconium oxide, the coating layer is Li2ZrO3, and K is 2. When the coating material is tungsten oxide, the coating layer is Li2WO4, and K is 2. When the coating material is a mixture of the aforementioned substances, the value of K is calculated according to the theoretical chemical composition of the coating layer corresponding to each coating material, i.e., the K values of each coating layer are added together. For example, when the coating material is a mixture of tungsten oxide and zirconium oxide, the coating layer is Li2WO4and Li2ZrO3, and K is 2 / 1+2 / 1=4. When the coating material is a mixture of cobalt oxide, tungsten oxide, and zirconium oxide, the coating layer is LiCoO2, Li2WO4, and Li2ZrO3, and K is 1 / 1+2 / 1+2 / 1=5.

[0094] The mixing method in the present application is not specifically limited, and only needs to uniformly mix the first product with the second lithium source and the coating material, which can be consistent with the mixing method in step 1), and will not be repeated here.

[0095] The sintering temperature and holding time of the second sintering, and the heating rate during the second sintering are not specifically limited in the present application; for example, the heating rate is 2-5℃ / min.

[0096] In step 3), the second product is subjected to third sintering in an oxygen atmosphere, and the furnace pressure during sintering is controlled to be 1-2MPa, to obtain a positive electrode active material.

[0097] It can be understood that the sintered product needs to be cooled after the third sintering is completed, and the cooling method is not specifically limited in the present application, which can be consistent with step 1), and will not be repeated here.

[0098] The sintering temperature and sintering time of the third sintering, and the heating rate during the third sintering are not specifically limited in the present application.

[0099] The preparation method of the positive electrode active material in the present application first performs first sintering on the mixture of the ternary positive electrode material precursor and the first lithium source, and controls the ratio of Q1 to M0 to be 1-1.03, to obtain a ternary positive electrode material matrix; then, the first product, the second lithium source and the coating material are mixed, and Q2=K*W1 is controlled, and Q1+Q2≤1.05M0, wherein the second lithium source plays a role of supplementing lithium elements, so that the coating material preferentially reacts with the second lithium source to form a coating layer in the second sintering process, avoids the coating material extracting lithium from the surface layer of the ternary positive electrode material matrix, makes the lithium distribution of the surface layer of the matrix material particles more uniform, avoids the uneven charging and discharging between single primary particles or multiple particles due to uneven lithium distribution, and further effectively avoids the phase change of the positive electrode active material in the charging and discharging process, reduces the irreversible lithium loss, and makes L / TM≥1; at the same time, the positive electrode active material after formation can not change significantly in volume due to phase change under high-temperature baking, effectively reduces the specific surface area change rate, and makes (BET1-BET0) / BET0≤20%; at this time, the lithium content in the positive electrode active material after formation is still at a high level, and the specific surface area change rate is low, so the loss of the positive electrode active material due to phase change can be effectively reduced, and the crushing of the positive electrode active material due to lattice mismatch can be improved, the side reaction between the new interface and the electrolyte is reduced, and the cycle performance of the battery is improved; finally, the second product is subjected to third sintering under a specific pressure, which helps to reduce the porosity of the positive electrode active material, make the primary particles in the secondary particles arrange more closely, and improve the conductivity of the secondary particles; when the porosity of the positive electrode active material is not higher than 3%, the lithium ion migration in the secondary particles during charging and discharging can be more rapid, the charging and discharging uniformity is further improved, and thus the charging and discharging uniformity of the positive electrode active material is comprehensively improved, and the cycle performance of the battery is improved.

[0100] In a specific embodiment, in step 1), the temperature in the first sintering is 300-800°C, and the holding time is 3-10h. Within this range, the size of the primary particles in the positive electrode active material is more appropriate, which helps the lithium ion to be smoothly deintercalated in the charging and discharging process; at the same time, the phase change caused by too high temperature can be avoided, the electrochemical performance is not affected, the crystallinity of the positive electrode active material can be improved, the internal defects and impurities of the material are reduced, and the electrochemical performance of the material is improved.

[0101] Illustratively, the temperature of the first sintering is 300°C, 400°C, 500°C, 600°C, 500°C, 700°C or 800°C; and the holding time is 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h.

[0102] In an embodiment, in step 2), the temperature in the second sintering is 300-800°C, and the holding time is 2-8h. Within this range, the over-diffusion or aggregation of the cladding layer material during sintering can be effectively prevented, a better cladding effect can be achieved, the surface resistance is reduced, the lithium ions can be smoothly deintercalated, and the cycle performance of the battery is improved.

[0103] Illustratively, the temperature of the second sintering is 300°C, 400°C, 500°C, 600°C, 500°C, 700°C or 800°C; and the holding time is 2h, 3h, 4h, 5h, 6h, 7h or 8h.

[0104] In an embodiment, in step 3), the sintering temperature in the third sintering is 300-600°C, and the sintering time is 1-5h. Within this range, the tightness between the primary particles in the positive electrode active material can be further improved, and the porosity of the active material is more appropriate, which is helpful to further enhance the particle conductivity.

[0105] Illustratively, the temperature of the third sintering is 300°C, 350°C, 400°C, 450°C, 500°C, 550°C or 600°C; and the holding time is 1h, 2h, 3h, 4h or 5h.

[0106] The third aspect of the present application provides a positive electrode sheet comprising the positive electrode active material of the first aspect or the positive electrode active material prepared by the preparation method of the second aspect. Since the porosity of the positive electrode active material therein is not higher than 3%, the positive electrode active material has high conductivity, and L / TM≥1 and (BET1-BET0) / BET0≤20%, so that the positive electrode active material after formation still has more lithium ions and has a low specific surface area change rate, and has high charge-discharge uniformity. Therefore, the positive electrode sheet comprising the positive electrode active material can effectively improve the cycle performance of the lithium ion battery when used in the lithium ion battery.

[0107] In an embodiment, the compaction density of the positive electrode sheet is 3.0-3.8g / cm 3 Within this range, the contact between the active material particles and between the active material and the conductive agent can be ensured to be close, the highest capacity can be achieved, and at the same time, the active particles can be prevented from being crushed during the rolling process, so that the interface is not exposed too much, thereby effectively reducing the occurrence of side reactions between the electrolyte and the active material, and the volume energy density and cycle performance of the battery can be further improved.

[0108] Illustratively, the compaction density of the positive electrode sheet is 3.0g / cm 3 , 3.1g / cm 3 , 3.2g / cm 3 , 3.3g / cm 3 , 3.4g / cm 33.5 g / cm 3 3.6 g / cm 3 3.7 g / cm 3 3.8 g / cm 3 .

[0109] The fourth aspect of the present application provides a lithium ion battery comprising the positive electrode active material of the first aspect, or the positive electrode active material prepared by the preparation method of the second aspect, or the positive electrode sheet of the third aspect. Therefore, the lithium ion battery has high cycle stability.

[0110] Hereinafter, the positive electrode active material comprising the present application is described in detail through specific examples.

[0111] Unless otherwise specified, the reagents, materials and instruments used in the following examples are conventional reagents, conventional materials and conventional instruments in the art, which can be obtained by commercial purchase, and the reagents involved can also be synthesized by conventional methods in the art.

[0112] Example 1

[0113] 1) Mix the nickel-cobalt-manganese ternary precursor Ni 0.9 Co 0.05 Mn 0.05 (OH)2and the first lithium source lithium hydroxide monohydrate in a high-speed mixer, the mixing speed is 800 rpm, and the mixing time is 40 min, to obtain a mixture, wherein the ratio of the molar amount Q1 of lithium element in the first lithium source to the total molar amount M0 of Ni, Co and Mn elements in the ternary positive electrode material precursor is 1.02; perform first sintering on the mixture in oxygen, the heating rate is 5 ℃ / min, the sintering temperature is 600 ℃, and the holding time is 8 h, and after the sintering is completed, natural cooling is performed to obtain a first product;

[0114] 2) Mix the first product with the coating material cobalt oxide and the second lithium source lithium hydroxide monohydrate in a high-speed mixer, the mixing speed is 800 rpm, and the mixing time is 30 min, to obtain a mixture; wherein the molar amount Q2 of lithium element in the second lithium source is 0.02M0, the molar amount W1 of the coating material is 0.02M0, the molar amount Q1 of lithium element in the first lithium source is 1.02M0, the ratio K of the molar amount of lithium element to the molar amount of Co element in the coating layer (the theoretical chemical composition is LiCoO2) is 1 / 1=1, Q2=W1=0.02M0, Q1+Q2=1.02M0+0.02M0=1.04M0<1.05M0; perform second sintering on the mixture in oxygen, the heating rate is 5 ℃ / min, the sintering temperature is 500 ℃, and the holding time is 4 h, and after the sintering is completed, cooling is performed at a cooling rate of 2 ℃ / min to obtain a second product;

[0115] 3) the second product is subjected to a third sintering under an oxygen atmosphere, the temperature rising rate is 2°C / min, the sintering temperature is 550°C, the holding time is 3h, the pressure in the furnace is kept at 1.5MPa, and after the sintering is completed, the temperature is lowered at a rate of 2°C / min, to obtain the positive electrode active material A1 of the example.

[0116] Example 2

[0117] The preparation method of the positive electrode active material in the example is basically the same as that in example 1, the difference is that in step 2), the cobalt oxide is replaced by zirconium oxide, then the theoretical chemical composition of the coating layer is Li2ZrO3, K=2 / 1=2; the ratio of the molar amount Q2 of lithium element in the second lithium source to the total molar amount M0 of Ni, Co and Mn elements in the ternary positive electrode material precursor is 0.01, the molar amount W1 of the coating material is adjusted to 0.005M0, Q2=2W1=0.01M0, Q1+Q2=1.02M0+0.01M0=1.03M0<1.05M0.

[0118] Example 3

[0119] The preparation method of the positive electrode active material in the example is basically the same as that in example 1, the difference is that in step 1), the nickel-cobalt-manganese ternary precursor is replaced by Ni 0.85 Co 0.06 Mn 0.09 (OH)2, the first lithium source is replaced by lithium carbonate, the first sintering temperature is adjusted to 550°C, the holding time is 7h, and the others are unchanged;

[0120] In step 2), the second lithium source is replaced by lithium carbonate, the coating material is replaced by molybdenum oxide, the ratio of the molar amount of lithium element to the molar amount of Mo element in the coating layer (the theoretical chemical composition is Li2MoO4) is K=2 / 1=2; the molar amount W1 of the coating material is adjusted to 0.01M0, Q2=2W1=0.02M0, Q1+Q2=1.02M0+0.02M0=1.04M0<1.05M0;

[0121] In step 3), the third sintering temperature is adjusted to 520°C.

[0122] Example 4

[0123] The preparation method of the positive electrode active material in the example is basically the same as that in example 1, the difference is that in step 1), the temperature of the first sintering is adjusted to 800°C, and the holding time is adjusted to 6h;

[0124] In step 2), the coating material is replaced by tungsten oxide, the ratio K of the molar amount of lithium element to the molar amount of W element in the coating layer (the theoretical chemical composition is Li2WO4) is 2 / 1 = 2; the molar amount W1 of the coating material is adjusted to 0.01M0, Q2 = 2W1 = 0.02M0, Q1 + Q2 = 1.02M0 + 0.02M0 = 1.04M0 < 1.05M0, the second sintering temperature is adjusted to 400℃, and the sintering time is 8h;

[0125] In step 3), the third sintering temperature is adjusted to 400, and the holding time is adjusted to 5h.

[0126] Example 5

[0127] The preparation method of the positive electrode active material in the present embodiment is basically the same as that in Example 1, except that in step 1), the first lithium source is replaced by lithium carbonate, and the ratio of the molar amount Q1 of lithium element in the first lithium source to the total molar amount M0 of Ni, Co and Mn elements in the ternary positive electrode material precursor is adjusted to 1.03; the first sintering temperature is adjusted to 700℃, and the holding time is adjusted to 10h.

[0128] In step 2), the second lithium source is replaced by lithium carbonate, the coating material is replaced by titanium oxide, and the ratio K of the molar amount of lithium element to the molar amount of Ti element in the coating layer (the theoretical chemical composition is Li2TiO3) is 2 / 1 = 2; the molar amount W1 of the coating material is 0.005M0, Q2 = 2W1 = 0.01M0, Q1 + Q2 = 1.03M0 + 0.01M0 = 1.04M0 < 1.05M0; the second sintering temperature is adjusted to 800℃, and the sintering time is adjusted to 5h.

[0129] In step 3), the sintering temperature is replaced by 300℃, the sintering time is replaced by 5h, and the furnace pressure is replaced by 2Mpa.

[0130] Example 6

[0131] The preparation method of the positive electrode active material in the present embodiment is basically the same as that in Example 1, except that in step 1), the precursor is replaced by Ni 0.85 Co 0.06 Mn 0.09 (OH)2, the first sintering temperature is adjusted to 480℃, and the holding time is adjusted to 9h.

[0132] In step 2), the coating material is replaced by niobium oxide, the ratio K of the molar amount of lithium element to the molar amount of Nb element in the coating layer (the theoretical chemical composition is LiNbO3) is 1 / 1 = 1; the ratio of the molar amount Q2 of lithium element in the second lithium source to the total molar amount M0 of Ni, Co and Mn elements in the ternary positive electrode material precursor is adjusted to 0.01M0, the molar amount W1 of the coating material is 0.01M0, Q2 = W1 = 0.01M0, Q1 + Q2 = 1.02M0 + 0.01M0 = 1.03M0 < 1.05M0; the temperature of the second sintering is adjusted to 300°C, and the sintering time is adjusted to 6h;

[0133] In step 3), the temperature of the third sintering is adjusted to 400°C, and the holding time is adjusted to 2h.

[0134] Example 7

[0135] The preparation method of the positive electrode active material in the example is basically the same as that in example 1, except that in step 1), the precursor is replaced by Ni 0.71 Co 0.06 Mn 0.23 (OH)2, the ratio of the molar amount Q1 of lithium element in the first lithium source to the total molar amount M0 of Ni, Co and Mn elements in the ternary positive electrode material precursor is adjusted to 1.03, and the temperature of the first sintering is adjusted to 300°C, and the holding time is adjusted to 10h.

[0136] In step 2), the coating material is replaced by niobium oxide, the ratio K of the molar amount of lithium element to the molar amount of Nb element in the coating layer (the theoretical chemical composition is Li3NbO4) is 3 / 1 = 3; the molar amount W1 of the coating material is adjusted to 0.0033M0, Q2 = 3W1 = 0.01M0, Q1 + Q2 = 1.03M0 + 0.01M0 = 1.04M0 < 1.05M0; the temperature of the second sintering is adjusted to 700°C, and the holding time is adjusted to 2h.

[0137] In step 3), the temperature of the third sintering is adjusted to 600°C, the holding time is adjusted to 1h, and the pressure in the furnace is adjusted to 2Mpa.

[0138] Example 8

[0139] The preparation method of the positive electrode active material in the example is basically the same as that in example 1, except that in step 1), the ratio of the molar amount Q1 of lithium element in the first lithium source to the total molar amount M0 of Ni, Co and Mn elements in the ternary positive electrode material precursor is adjusted to 1.03, and the temperature of the first sintering is adjusted to 700°C.

[0140] In step 2), the coating material is replaced by tantalum oxide, the ratio K of the molar amount of lithium element to the molar amount of Ta element in the coating layer (the theoretical chemical composition is LiTaO3) is 1 / 1 = 1; the ratio of the molar amount Q2 of lithium element in the second lithium source to the total molar amount M0 of Ni, Co and Mn elements in the ternary positive electrode material precursor is adjusted to 0.005, the molar amount W1 of the coating material is adjusted to 0.005M0, Q2 = W1 = 0.005M0, Q1 + Q2 = 1.03M0 + 0.005M0 = 1.035M0 < 1.05M0; the temperature of the second sintering is adjusted to 600℃, and the holding time is adjusted to 7h;

[0141] In step 3), the temperature of the third sintering is adjusted to 500℃, the sintering time is adjusted to 1.5h, and the pressure in the furnace is adjusted to 1.1Mpa.

[0142] Example 9

[0143] The preparation method of the positive electrode active material in the embodiment is basically the same as that in Example 1, except that in step 1), the ratio of the molar amount Q1 of lithium element in the first lithium source to the total molar amount M0 of Ni, Co and Mn elements in the ternary positive electrode material precursor is adjusted to 1.03, and the temperature of the first sintering is adjusted to 700℃.

[0144] In step 2), the coating material is replaced by a mixture of cobalt oxide and zirconium oxide (the molar ratio is 1:1), the ratio K of the molar amount of lithium element to the molar amount of Co and Zr elements in the coating layer (the theoretical chemical composition is LiCoO2 and Li2ZrO3) is 1 / 1+2 / 1 = 3; the molar amount W1 of the coating material is adjusted to 0.0067M0, Q2 = 3W1 = 0.02M0, Q1 + Q2 = 1.03M0 + 0.02M0 = 1.05M0 = 1.05M0;

[0145] In step 3), the sintering time is replaced by 3h, and the pressure in the furnace is replaced by 2Mpa.

[0146] Example 10

[0147] The preparation method of the positive electrode active material in the embodiment is basically the same as that in Example 1, except that in step 1), the ratio of the molar amount Q1 of lithium element in the first lithium source to the total molar amount M0 of Ni, Co and Mn elements in the ternary positive electrode material precursor is adjusted to 1.03, and the temperature of the first sintering is adjusted to 700℃.

[0148] In step 2), the coating material is replaced by a mixture of tungsten oxide and zirconium oxide (molar ratio of 1:1), the molar ratio of lithium element in the coating layer (theoretical chemical composition Li2WO4 and Li2ZrO3) to the molar amount of W and Zr elements is K = 2 / 1 + 2 / 1 = 4; the molar amount of the coating material W1 is adjusted to 0.005M0, Q2 = 4W1 = 0.02M0, Q1 + Q2 = 1.03M0 + 0.02M0 = 1.05M0 = 1.05M0, the temperature of the second sintering is adjusted to 480°C, and the holding time is adjusted to 2.5h;

[0149] In step 3), the temperature of the third sintering is adjusted to 480°C, the holding time is adjusted to 2.5h, and the furnace pressure is adjusted to 1.6Mpa.

[0150] Example 11

[0151] The preparation method of the positive electrode active material in this example is basically the same as that in Example 1, except that in step 1), the first lithium source is replaced by lithium carbonate, and the temperature of the first sintering is adjusted to 300°C, and the holding time is adjusted to 10h;

[0152] In step 2), the second lithium source is replaced by lithium carbonate, and the coating material is replaced by cobalt hydroxide oxide, the molar ratio of lithium element in the coating layer (theoretical chemical composition LiCoO2) to the molar amount of W and Zr elements is K = 1 / 1 = 1; the ratio of the molar amount of lithium element Q2 in the second lithium source to the total molar amount M0 of Ni, Co and Mn elements in the ternary positive electrode material precursor is adjusted to 0.01, and the molar amount of the coating material W1 is adjusted to 0.01M0, Q2 = W1 = 0.01M0, Q1 + Q2 = 1.02M0 + 0.01M0 = 1.03M0 < 1.05M0, the temperature of the second sintering is adjusted to 650°C, and the holding time is adjusted to 5h;

[0153] In step 3), the temperature of the third sintering is adjusted to 400°C, and the holding time is adjusted to 4h.

[0154] Example 12

[0155] The preparation method of the positive electrode active material in this example is basically the same as that in Example 1, except that in step 1), the precursor is replaced by Ni 0.85 Co 0.06 Mn 0.09 (OH)2, the temperature of the first sintering is adjusted to 500°C, and the holding time is adjusted to 6h.

[0156] Example 13

[0157] The preparation method of the positive electrode active material in this example is basically the same as that in Example 1, except that in step 1), the precursor is replaced by Ni 0.85Co 0.06 Mn 0.09 (OH)2;

[0158] In step 2), the second lithium source is replaced by lithium ethoxide, the coating material is replaced by zirconium oxide, the ratio K of the molar amount of lithium element to the molar amount of Zr element in the coating layer (theoretical chemical composition Li2ZrO3) is 2 / 1 = 2, the molar amount W1 of the coating material is adjusted to 0.01M0, Q2 = 2W1 = 0.02M0, Q1 + Q2 = 1.02M0 + 0.02M0 = 1.04M0 < 1.05M0, the temperature of the second sintering is adjusted to 800℃, and the holding time is adjusted to 3h.

[0159] In step 3), the temperature of the third sintering is adjusted to 300℃, and the holding time is adjusted to 1h.

[0160] Example 14

[0161] The preparation method of the positive electrode active material in the example is basically the same as that in example 1, except that in step 1), the temperature of the first sintering is adjusted to 800℃, and the holding time is adjusted to 7h.

[0162] Example 15

[0163] The preparation method of the positive electrode active material in the example is basically the same as that in example 1, except that in step 1), the ratio of the molar amount Q1 of lithium element in the first lithium source to the total molar amount M0 of Ni, Co and Mn elements in the ternary positive electrode material precursor is adjusted to 1.03, the temperature of the first sintering is adjusted to 700℃, and the holding time is adjusted to 10h.

[0164] Example 16

[0165] The preparation method of the positive electrode active material in the example is basically the same as that in example 1, except that in step 1), the temperature of the first sintering is adjusted to 600℃.

[0166] In step 2), the temperature of the second sintering is adjusted to 800℃, and the holding time is adjusted to 2h.

[0167] Example 17

[0168] The preparation method of the positive electrode active material in the example is basically the same as that in example 1, except that in step 3), the temperature of the third sintering is adjusted to 600℃, the holding time is adjusted to 5h, and the pressure in the furnace is adjusted to 2MPa.

[0169] Example 18

[0170] The preparation method of the positive electrode active material in the embodiment is basically the same as that in Embodiment 1, except that in step 1), the temperature of the first sintering is adjusted to 800 DEG C, and the holding time is adjusted to 10 h;

[0171] In step 2), the temperature of the second sintering is adjusted to 800 DEG C, and the holding time is adjusted to 3 h;

[0172] In step 3), the temperature of the third sintering is adjusted to 500 DEG C, the holding time is adjusted to 4 h, and the pressure in the furnace is adjusted to 1 MPa.

[0173] Embodiment 19

[0174] The preparation method of the positive electrode active material in the embodiment is basically the same as that in Embodiment 1, except that in step 1), the ratio of the molar amount Q1 of lithium element in the first lithium source to the total molar amount M0 of Ni, Co and Mn elements in the ternary positive electrode material precursor is adjusted to 1.03;

[0175] In step 2), the second lithium source is replaced by lithium carbonate, and the temperature of the second sintering is adjusted to 800 DEG C.

[0176] Embodiment 20

[0177] The preparation method of the positive electrode active material in the embodiment is basically the same as that in Embodiment 1, except that in step 1), the first lithium source is replaced by lithium acetate, the ratio of the molar amount Q1 of lithium element in the first lithium source to the total molar amount M0 of Ni, Co and Mn elements in the ternary positive electrode material precursor is adjusted to 1.03, the temperature of the first sintering is adjusted to 800 DEG C, and the holding time is adjusted to 10 h;

[0178] In step 2), the temperature of the second sintering is adjusted to 800 DEG C, and the sintering time is adjusted to 5 h;

[0179] In step 3), the temperature of the third sintering is adjusted to 600 DEG C, and the sintering time is adjusted to 5 h.

[0180] Embodiment 21

[0181] The preparation method of the positive electrode active material in the embodiment is basically the same as that in Embodiment 1, except that in step 1), the first lithium source is replaced by lithium carbonate, the temperature of the first sintering is adjusted to 300 DEG C, and the sintering time is adjusted to 10 h;

[0182] In step 2), the second lithium source is replaced by lithium carbonate, the temperature of the second sintering is adjusted to 700 DEG C, and the holding time is adjusted to 8 h;

[0183] In step 3), the temperature of the third sintering is adjusted to 600 DEG C, and the holding time is adjusted to 5 h.

[0184] Embodiment 22

[0185] The preparation method of the positive electrode active material in the embodiment is basically the same as that in Embodiment 1, except that in step 3), the sintering temperature is replaced by 300 DEG C, and the sintering time is replaced by 1 h.

[0186] Comparative Example 1

[0187] The preparation method of the positive electrode active material in the embodiment is basically the same as that in Embodiment 1, except that in step 1), the ratio of the molar amount Q1 of lithium element in the first lithium source to the total molar amount M0 of Ni, Co and Mn elements in the ternary positive electrode material precursor is adjusted to 1.04.

[0188] In step 2), the second lithium source is not added, that is, only the mixture material including the coating material cobalt oxide and the first product is subjected to the second sintering, and the others remain unchanged.

[0189] Comparative Example 2

[0190] The preparation method of the positive electrode active material in the embodiment is basically the same as that in Comparative Example 1, except that in step 3), the furnace pressure during the third sintering is adjusted to 0.5 MPa.

[0191] Comparative Example 3

[0192] The preparation method of the positive electrode active material in the embodiment is basically the same as that in Embodiment 1, except that in step 1), the ratio of the molar amount Q1 of lithium element in the first lithium source to the total molar amount M0 of Ni, Co and Mn elements in the ternary positive electrode material precursor is adjusted to 0.95.

[0193] In step 2), the ratio of the molar amount Q2 of lithium element in the second lithium source to the total molar amount M0 of Ni, Co and Mn elements in the ternary positive electrode material precursor is adjusted to 0.09, and the others remain unchanged, so that Q2≠W1, Q1+Q2=0.95M0+0.09M0=1.04M0<1.05M0.

[0194] Comparative Example 4

[0195] The preparation method of the positive electrode active material in the embodiment is basically the same as that in Embodiment 1, except that in step 1), the ratio of the molar amount Q1 of lithium element in the first lithium source to the total molar amount M0 of Ni, Co and Mn elements in the ternary positive electrode material precursor is adjusted to 1.03.

[0196] In step 2), the ratio of the molar amount Q2 of lithium element in the second lithium source to the total molar amount M0 of Ni, Co and Mn elements in the ternary positive electrode material precursor is adjusted to 0.01, and the others remain unchanged, so that Q2≠W1, Q1+Q2=1.03M0+1.01M0=1.04M0≤1.05M0.

[0197] Comparative Example 5

[0198] The preparation method of the positive electrode active material in the present comparative example is basically the same as that in Example 1, except that in step 1), the ratio of the molar amount Q1 of lithium element in the first lithium source to the total molar amount M0 of Ni, Co and Mn elements in the ternary positive electrode material precursor is adjusted to 0.95;

[0199] In step 2), the ratio of the molar amount Q2 of lithium element in the second lithium source to the total molar amount M0 of Ni, Co and Mn elements in the ternary positive electrode material precursor is adjusted to 0.12, and the others remain unchanged, Q2≠W1, Q1+Q2=0.95M0+0.12M0=1.07M0>1.05M0;

[0200] In step 3), the pressure in the furnace is adjusted to 3.5 MPa.

[0201] Test Example

[0202] 1. The particle size distribution, porosity and powder conductivity of the above positive electrode active material were tested, including the following steps:

[0203] 1) Particle size distribution

[0204] The particle size distribution of Examples 1-22 and Comparative Examples 1-5 was tested. Specifically, the powder of the above positive electrode material was dissolved in ultrapure water, and then tested in an MS2000 instrument to obtain the particle size distribution data.

[0205] 2) Porosity

[0206] The porosity of Examples 1-22 and Comparative Examples 1-5 was tested. Specifically, the above positive electrode material was planarly ground, and then placed in a scanning electron microscope for picture taking. The obtained pictures were then placed in Metis software for automatic identification to obtain the porosity data.

[0207] 3) Powder conductivity

[0208] The conductivity of Examples 1-22 and Comparative Examples 1-5 was tested. Specifically, the above positive electrode material was placed in a MCP-PD51 powder impedance tester to obtain the conductivity data. The test results are shown in Table 1.

[0209] Table 1

[0210] 2. The positive electrode active materials prepared in the above examples and comparative examples, as well as the positive electrode active materials after formation and baking, were subjected to ICP test, BET test and SEM test, including the following steps:

[0211] 1) ICP test

[0212] The positive active material is prepared into a full battery, specifically including the following steps:

[0213] Preparation of the positive electrode sheet: the positive active material prepared in the above examples and comparative examples is mixed with conductive carbon black (SP) and polyvinylidene fluoride (PVDF) in a mass ratio of 95:2.5:2.5 to prepare a positive electrode slurry, the positive electrode slurry is coated on both surfaces of an aluminum foil, and after drying, rolling, and slitting, a positive electrode sheet with a compacted density of 3.5 g / cm 3 is obtained.

[0214] Preparation of the negative electrode sheet: the negative active material graphite, Super P, butadiene styrene rubber (SBR), and sodium carboxymethyl cellulose (CMC) are mixed in a mass ratio of 95.5:1:2:1.5 to prepare a negative electrode slurry, the negative electrode slurry is coated on the surface of a copper foil, and after drying, rolling, and slitting, a negative electrode sheet with a compacted density of 1.55 g / cm 3 is obtained.

[0215] Preparation of the full battery: the above positive electrode sheet, separator film (PP polypropylene / PE polyethylene / PP polypropylene), and negative electrode sheet are stacked and then wound to obtain an electric core, the electric core is placed in an outer packaging aluminum foil, and then electrolyte (Xinzhubang LBC-3021C48) is injected, and after vacuum packaging, standing, formation, shaping, sorting, and other processes, a lithium ion battery is obtained; the formation machine is configured as follows: charging at 0.05C or 0.1C for 1 h, then constant current and constant voltage charging to 4.25V at 0.2C, with a cutoff current of 0.05C, and then discharging to 2.8V at 0.5C; then charging and discharging at 1C between 2.8-4.25V for 2 cycles.

[0216] The positive electrode sheet after formation is peeled off to obtain an active layer including the positive active material, and the active layer is baked at a heating rate of 5℃ / min, a baking temperature of 650℃, and a holding time of 10h, and after natural cooling, the positive active material after formation and baking is obtained.

[0217] The original positive active material and the positive active material after formation and baking are tested by ICP test: 0.2g of the positive active material after formation and baking is taken into a beaker, 10mL of aqua regia (7.5mL of concentrated hydrochloric acid + 2.5mL of concentrated nitric acid) is then added, and the solution is digested at 190℃ for 15min, finally the remaining liquid is transferred to a volumetric flask, and is diluted with deionized water, shaken well, and diluted to 100mL. The solution after shaking is taken for testing of the main elements Li, Ni, Co, and Mn, the mass ratio of each element measured is converted into molar ratio, and finally the initial L / TM and the L / TM after formation and baking are obtained, and the test results are shown in Table 2.

[0218] 2) BET test

[0219] The BET of the positive active material after formation and baking, and the positive active material before being made into a battery was tested by a specific surface area tester. Specifically, 4 g of a powder sample was dried and placed in a sample tube, the sample was subjected to a purging and degassing treatment, and BET0 and BET1 were obtained according to the principle of nitrogen adsorption and desorption. Thus, the BET change rate (BET1-BET0) / BET0 can be calculated. The calculation results are shown in Table 2.

[0220] 3) SEM test

[0221] The positive active material in Example 1 and Comparative Example 2, and the positive active material after formation and baking were tested by a scanning electron microscope. The results are shown in Figures 1-8.

[0222] Figure 1 is an SEM image of the positive active material in Example 1 at 10.0 k, Figure 2 is an SEM image of the positive active material in Example 1 at 50.0 k, Figure 3 is an SEM image of the positive active material in Comparative Example 2 at 10.0 k, Figure 4 is an SEM image of the positive active material in Comparative Example 2 at 50.0 k, Figure 5 is an SEM image of the positive active material in Example 1 after formation and baking at 10.0 k, Figure 6 is an SEM image of the positive active material in Example 1 after formation and baking at 50.0 k, Figure 7 is an SEM image of the positive active material in Comparative Example 2 after formation and baking at 10.0 k, and Figure 8 is an SEM image of the positive active material in Comparative Example 2 after formation and baking at 50.0 k. As can be seen from Figures 1-4, the surface of the positive active material in Example 1 does not have holes after formation and baking, and as can be seen from Figures 5-8, the surface of the positive active material in Comparative Example 2 has a large number of small holes after formation and baking, which causes the specific surface area of the particles to increase. Thus, the positive active material in the present application can effectively improve the non-uniformity of charging and discharging, and improve the cycle stability of the battery.

[0223] 3. The full battery prepared above was subjected to a cycle performance test, including the following steps:

[0224] The lithium ion battery after formation was subjected to a 1C constant current charging to 4.25 V at 45°C, a 4.25 V constant voltage charging, a cutoff current of 0.05C, and then a 1C constant current discharging to 2.8 V, and the discharge capacity was recorded as C0. The battery was cycled for 300 cycles according to the foregoing charging and discharging mechanism, and the discharge capacity after cycling was recorded as C1. The cycle capacity retention rate (%) = C1 / C0 x 100%, and the calculation results are shown in Table 2.

[0225] Figure 9 is a comparison chart of cycle performance of the positive electrode active materials in Example 1 and Comparative Example 2, from which it can be seen that the full battery comprising the positive electrode active material in Example 1 has a higher capacity retention rate than that of Comparative Example 2.

[0226] Table 2

[0227] From Table 1 and Table 2, it can be seen that:

[0228] Examples 1-22 have higher cycle performance than Comparative Examples 1-5, wherein the cycle capacity retention rate in Example 1 is as high as 90.1%, while the highest in the comparative examples is only 80.1%; thus, it can be seen that the positive electrode active material in the present application can be uniformly charged and discharged, thereby effectively improving the cycle performance of the battery.

[0229] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A positive electrode active material, wherein, The positive electrode active material comprises primary particles and secondary particles formed by agglomeration of the primary particles; the primary particles comprise a ternary positive electrode material matrix and a coating layer arranged on at least part of the surface of the ternary positive electrode material matrix; the coating layer comprises a lithium oxide containing an A element; the A element comprises at least one of Co, W, Zr, Sb, Nb, Cr and Ta; the positive electrode active material satisfies formula 1 and formula 2, L / TM≥1 Formula 1 (BET1-BET0) / BET0≤20% Formula 2 In formula 1, L is the molar amount of lithium elements in the positive electrode active material after chemical conversion and baking, and TM is the total molar amount of transition metal elements in the positive electrode active material after chemical conversion and baking; the baking temperature is 600-700 ℃, and the baking time is 9-11 h; In formula 2, BET0 is the initial specific surface area of the positive electrode active material, and BET1 is the specific surface area of the positive electrode active material after chemical conversion and baking; The porosity of the positive electrode active material is not higher than 3%.

2. The positive electrode active material according to claim 1, wherein said BET0 is 0.4-0.8 m 2 / g, and / or, said BET1 is 0.5-1.0 m 2 / g.

3. The positive electrode active material according to claim 1, wherein The D10 of the positive electrode active material is 5-8 μm, the D50 is 5-11 μm, and the D90 is 10-25 μm; and / or the maximum particle diameter D max is 16 to 30 pm, and the minimum particle diameter D min is 2 to 6 pm.

4. The positive electrode active material according to claim 1, wherein The porosity of the positive electrode active material is 1-3%.

5. The positive electrode active material according to claim 1, wherein The powder conductivity of the positive electrode active material is not lower than 0.001 S / cm.

6. A method for producing the positive electrode active material as claimed in any one of claims 1 to 5, wherein The method comprises the following steps: 1) mixing a ternary positive electrode material precursor with a first lithium source to obtain a first product after first sintering; wherein the molar amount Q1 of lithium elements in the first lithium source and the total molar amount M0 of transition metal elements in the ternary positive electrode material precursor satisfy: 1 2) mixing the first product with a second lithium source and a coating material to obtain a second product comprising a coating layer after second sintering; wherein the molar amount Q2 of lithium elements in the second lithium source, the molar amount W1 of the coating material, the molar amount Q1 of lithium elements in the first lithium source, and the ratio K of the molar amount of lithium elements to the molar amount of A elements in the theoretical chemical composition of the coating layer satisfy: Q2=K*W1, and Q1+Q2≤1.05M0; 3) performing third sintering on the second product in an oxygen atmosphere, wherein the furnace pressure in the third sintering process is 1-2 MPa, to obtain the positive electrode active material.

7. The method of producing a positive electrode active material according to claim 6, wherein In step 1), the temperature in the first sintering is 300-800 ℃, and the holding time is 3-10 h; and / or, in step 2), the temperature in the second sintering is 300-800 ℃, and the holding time is 2-8 h; and / or, in step 3), the sintering temperature in the third sintering is 300-600 ℃, and the sintering time is 1-5 h.

8. A positive electrode sheet, wherein The positive electrode sheet comprises the positive electrode active material according to any one of claims 1-5, or the positive electrode active material prepared by the preparation method according to claim 6 or 7.

9. The positive electrode sheet according to claim 8, wherein The compacted density of the positive electrode sheet is 3.0-3.8 g / cm 3 .

10. A lithium-ion battery, wherein, The lithium ion battery comprises the positive electrode active material according to any one of claims 1-5, or the positive electrode active material prepared by the preparation method according to claim 6 or 7, or the positive electrode sheet according to claim 9.

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