A positive electrode active material, a method for preparing the same, and an application thereof

Abstract

The application provides a positive electrode active material, a preparation method and application thereof. The positive electrode active material comprises ternary single crystal particles. The maximum size of the center of the ternary single crystal particles to the surface of the ternary single crystal particles is R. The ternary single crystal particles comprise a first part extending 10%R from the surface of the ternary single crystal particles to the center. The first part comprises a first site away from the center and a second site close to the center in the extending direction. The molar content W1 of Co elements in the first site is greater than the molar content W2 of Co elements in the second site based on the total amount of molar nickel-cobalt-manganese elements in each site, and W1-W2 is not less than 5%. The application realizes the synergistic improvement of the specific capacity and the cycle life of the positive electrode active material.

Description

Technical Field

[0001] This application relates to the field of batteries, and in particular to a positive electrode material, its preparation method, and its application. Background Technology

[0002] As the core of modern electrochemical energy storage systems, secondary batteries have been deeply integrated into various aspects of social production and daily life. From portable electronic devices to electric vehicles, and then to large-scale renewable energy storage systems, the technological development and popularization of secondary batteries are of strategic significance for promoting energy structure transformation and achieving sustainable development goals. With the market's increasing demands for device endurance and system operating efficiency, optimizing the energy density, cycle life, and overall performance of secondary batteries has become a key driving force for industrial technological iteration.

[0003] Among numerous cathode materials, ternary cathode active materials have become one of the mainstream technologies in the power battery field due to their high operating voltage and high energy density brought about by tunable composition. By increasing the nickel content and other methods, ternary cathode active materials can effectively improve the energy density of individual battery cells, providing an important technical path for extending the driving range of electric vehicles. However, current ternary cathode active materials, especially high-nickel systems, still face severe challenges in practical applications: their actual achievable specific capacity is still lower than theoretical expectations. At the same time, the interfacial side reactions between the material surface and the electrolyte are relatively severe, leading to continuous increase in impedance and failure of active materials, making it difficult for the battery's cycle life to meet consumers' high demands for durability. These defects in specific capacity and cycle stability restrict further breakthroughs in the overall performance of ternary cathode active materials.

[0004] Therefore, it is particularly urgent to conduct in-depth material structure design to address the core issues of insufficient specific capacity release and poor cycle performance in existing ternary cathode materials. Summary of the Invention

[0005] This application provides a positive electrode active material. By optimizing the morphology and interface characteristics of the material, the specific capacity and cycle life of the positive electrode active material are synergistically improved. This has important practical significance for promoting the technological progress and commercial application of high-performance lithium-ion batteries.

[0006] This application also provides a method for preparing the above-mentioned positive electrode active material, which is used to prepare the above-mentioned positive electrode active material.

[0007] This application also provides a positive electrode sheet, including the above-mentioned positive electrode active material, for improving the capacity and cycle performance of a secondary battery.

[0008] This application also provides a secondary battery, including the above-mentioned positive electrode, which has excellent discharge capacity and cycle performance.

[0009] This application provides a positive electrode active material comprising ternary single crystal particles. The maximum dimension from the center to the surface of the ternary single crystal particles is R. Each ternary single crystal particle includes a first portion extending 10%R from the surface of the ternary single crystal particle towards the center. The first portion includes a first site away from the center and a second site close to the center in the extension direction. Based on the total molar amount of nickel, cobalt, and manganese at each site, the molar content of Co at the first site, W1, is greater than the molar content of Co at the second site, W2, and W1-W2 is not less than 5%.

[0010] The positive electrode active material as described above, wherein 5% ≤ W1 - W2 ≤ 15%.

[0011] The positive electrode active material as described above, wherein the first part comprises the compound shown in Formula 1 and a cobalt-containing compound;

[0012] Li y Ni a Co b Mn c A x O2, Formula 1

[0013] Where 0.90≤y≤1.10, 0.80≤a≤0.98, 0.01≤b≤0.10, 0.01≤c≤0.10, 0≤x≤0.10, a+b+c+x=1, and element A includes at least one of Mn, Zr, Al, Sr, Ti, Mg, Ca, Ce, Y, and W.

[0014] The positive electrode active material as described above, wherein the first part further includes at least one of an oxide of element G and a lithium compound of element G; the element G includes at least one of Mn, Zr, Al, Sr, Ti, Mg, Ca, Ce, Y, F, P, and W.

[0015] The positive electrode active material as described above, wherein the ternary single crystal particle further includes a second portion surrounded by the first portion; in the extension direction, the absolute value E of the difference in the molar content of Co element at any two points of the second portion is less than 3%; and / or,

[0016] Based on the mass of the positive electrode active material, the Co content in the ternary single crystal particles is 15,000-35,000 ppm, and the A content is 300-2,000 ppm.

[0017] The positive electrode active material as described above, wherein the positive electrode active material comprises ternary single crystal particles and a coating layer disposed on at least a portion of the surface of the ternary single crystal particles, the coating layer comprising at least one of oxides and lithides of coating elements, the coating elements comprising boron and J, the J element comprising at least one of Mn, Zr, Al, Sr, Ti, Mg, Ca, Ce, Y, F, P, and W.

[0018] The positive electrode active material as described above, wherein the residual alkali content of the positive electrode active material is 800-2000 ppm; and / or,

[0019] The Dv50 of the positive electrode active material is 1.5-4 μm.

[0020] This application also provides a method for preparing the above-described positive electrode active material, comprising the following steps:

[0021] 1) A first raw material mixture including a ternary cathode active material precursor, a lithium source, and an A element source is subjected to a first sintering to obtain a first sintered product;

[0022] The element A in the source of element A includes at least one of Mn, Zr, Al, Sr, Ti, Mg, Ca, Ce, Y, and W.

[0023] 2) The second raw material mixture, including the first sintering product and the Co source, is subjected to a second sintering to obtain the positive electrode active material.

[0024] In the preparation method described above, in the first sintering treatment, the sintering temperature is 500℃-850℃, the holding time is 4h-15h, and the heating rate is 2℃ / min-5℃ / min.

[0025] In the second sintering process, the sintering temperature is 550℃-650℃, the holding time is 4h-10h, and the heating rate is 2℃ / min-5℃ / min; and / or,

[0026] After step 2), the process further includes: subjecting a third raw material mixture, comprising the product of the second sintering treatment, a boron source, and a J element source, to a third sintering to obtain the positive electrode active material; in the third sintering treatment, the sintering temperature is 250℃-450℃, the holding time is 4h-10h, and the heating rate is 2℃ / min-5℃ / min; the J element source includes at least one of Mn, Zr, Al, Sr, Ti, Mg, Ca, Ce, Y, F, P, and W.

[0027] This application also provides a positive electrode sheet, comprising the positive electrode active material described in any one of the above claims, or the positive electrode active material prepared by the preparation method described above.

[0028] This application also provides a secondary battery, including the positive electrode sheet described above.

[0029] The cathode active material of this application, by controlling the morphology of the cathode active material and specifically controlling the cobalt content on its surface, achieves several advantages. Firstly, this ordered cobalt content not only improves the ionic conductivity of the cathode active material but also promotes the charge compensation effect of redox pairs and suppresses the formation of oxygen vacancies. Secondly, this near-surface high-steep cobalt content gradient distribution can alleviate lattice stress mismatch caused by lithium-ion extraction during charging and discharging, reduce the formation of microcracks in particles, and improve the cycle stability of single-crystal materials. Therefore, the cathode active material of this application helps to improve the discharge capacity and cycle performance of secondary batteries, promoting the development and application of high-performance secondary batteries. Attached Figure Description

[0030] Figure 1 This is a schematic cross-sectional view of the positive electrode active material of this application;

[0031] Figure 2 This is a SEM image of the ternary precursor of Embodiment 1 of this application;

[0032] Figure 3 This is an SEM image of the first sintered product of Example 1 of this application;

[0033] Figure 4 This is an SEM image of the second sintered product of Example 1 of this application;

[0034] Figure 5 This is a SEM image of the positive electrode active material of Example 1 of this application;

[0035] Figure 6 This is a cross-sectional view of the positive electrode active material of Example 1 of this application;

[0036] Figure 7 This is a schematic diagram comparing the contour lines of the cobalt concentration gradient distribution of the positive electrode active materials in Example 1 and Comparative Example 1 of this application;

[0037] Figure 8 This is a cycle curve of a secondary battery containing the positive electrode active material of Example 1 and Comparative Example 1. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0039] Currently, the discharge capacity and cycle performance of rechargeable batteries still fall short of application expectations. The inventors have investigated this issue and believe that the reason for this deficiency lies in the fact that, in the pursuit of high energy density, the positive electrode active material is more prone to cation mixing under high voltage, leading to obstruction of lithium-ion transport channels and thus limiting the battery's charge and discharge capacity. Simultaneously, the positive electrode active material is prone to volume expansion and crack propagation during cycling, which are also major reasons for reduced cycle life. Therefore, the key to overcoming this technological bottleneck is to maintain the structural stability of the positive electrode active material while ensuring high lithium-ion conductivity.

[0040] Based on this, this application provides a positive electrode active material, which includes ternary single crystal particles. The maximum dimension from the center to the surface of the ternary single crystal particles is R. The ternary single crystal particles include a first part extending 10%R from the surface of the ternary single crystal particles towards the center. The first part includes a first site away from the center and a second site close to the center in the extension direction. Based on the total molar amount of nickel, cobalt and manganese elements at each site, the molar content of Co element W1 at the first site is greater than the molar content of Co element W2 at the second site, and W1-W2 is not less than 5%.

[0041] The positive electrode active material in this application is a ternary positive electrode active material, namely a lithium-containing oxide including nickel-cobalt-manganese or nickel-cobalt-aluminum. This ternary positive electrode active material is a single-crystal particle. This application does not limit the shape of the single-crystal particle; for example, it can be spherical (the distance deviation from any point on the particle surface to the center is ≤5%) or near-spherical (such as ellipsoidal or oblate, the distance deviation from any point on the surface to the center is ≤15%). Its specific shape can be confirmed by observation using a scanning electron microscope.

[0042] The single-crystal particle includes a center V, and the maximum distance from center V to the outer surface of the particle is R. It should be noted that center V refers to the geometric center of the single-crystal particle. For example, by using image processing software to fit the contour of the SEM image of the single-crystal particle, the circumcircle (or quasi-circumcircle) of the particle's contour can be calculated, and the center V is the center of this circumcircle. Alternatively, for irregular, quasi-spherical particles in actual production, the center V can be obtained by measuring the longest and shortest diameters of the particle and taking the intersection of the lines connecting the midpoints of these two diameters. R refers to the maximum distance from center V to the particle surface, which is the radius of the aforementioned circumcircle (or half the longest diameter). The radius can be obtained by measuring with a particle size analyzer.

[0043] Taking the positive electrode active material as regular spherical particles as an example, Figure 1 This is a schematic cross-sectional view of the positive electrode active material of this application, as shown below. Figure 1 As shown, in this application, the shell formed when any point on the surface of the single crystal particle extends towards the center V, with the extension dimension being 10%R, constitutes the first part P1 of the positive electrode active material of this application. In the extension direction, the starting point of the first part is the first point, and the ending point is the second point. The molar content W1 of Co at the first point is the ratio of the amount of Co at the first point to the sum of the amounts of Ni, Co, and Mn at the first point. The molar content W2 of Co at the second point is the ratio of the amount of Co at the second point to the sum of the amounts of Ni, Co, and Mn at the second point. Since W1-W2 is not less than 5%, the difference in the molar ratio of cobalt at the first point and the second point is relatively large. It can be understood that the cobalt content has a steep distribution in the first part.

[0044] The inventors discovered that when the cobalt mass content exhibits a steep gradient distribution from the outside to the inside in the first part, cobalt ions in the high-cobalt region on the surface, through their strong electrostatic field effect and electronic orbital hybridization characteristics, can effectively suppress the mixing of lithium and nickel ions, reduce the disordered migration of transition metal ions to lithium sites, significantly reduce the degree of lattice distortion, and greatly improve the long-range order of the layered crystal structure of the ternary cathode active material. This provides a smooth and stable transport channel for lithium ion insertion / extraction, ensuring that the active sites fully participate in the electrochemical reaction and enabling efficient utilization of the specific capacity. Furthermore, the difference in cobalt content with high steepness in the first part not only makes it easier for cobalt ions to participate in electrochemical reactions, enhances the charge compensation effect, improves electron transfer efficiency, and ensures efficient output of specific capacity, but also suppresses the extraction of lattice oxygen during charge-discharge cycles by forming stronger Co-O bond energy, reducing the generation of oxygen vacancies and reducing the collapse of the lattice structure due to oxygen deficiency. At the same time, the surface crystal structure stabilized by the strong field effect of cobalt ions can reduce the side reactions between the cathode active material and the electrolyte at high-temperature interfaces, especially reducing the dissolution of transition metal ions and the resulting catalytic oxidative decomposition of the electrolyte, thereby stabilizing the cathode / electrolyte interface, reducing the irreversible consumption of active lithium and the increase in interface impedance. Therefore, this application can fundamentally and synergistically improve the cycle stability and storage stability of the material.

[0045] More notably, in the first part of the positive electrode active material, the high-steepness distribution of cobalt effectively constrains the abnormal expansion and contraction of the lithium interlayer spacing during charge-discharge cycles, alleviating the internal stress generated by the periodic expansion and contraction of the lattice, inhibiting the initiation, propagation, and particle breakage of microcracks. Simultaneously, in the storage state, this stable structure resists lattice distortion caused by temperature fluctuations or localized charge inhomogeneity, ensuring a stable state for lithium ions and reducing their spontaneous disordered migration or deactivation in the static state. By synergistically hindering lattice oxygen loss and side reactions at the positive electrode / electrolyte interface, material structural cracking and phase transition degradation are avoided, significantly improving cycle stability and high-temperature storage stability.

[0046] Meanwhile, since the positive electrode active material of this application is a single crystal particle, it can avoid the problems of stress concentration and ion transport bottleneck at the grain boundaries in polycrystalline particles, and reduce grain boundary cracking and capacity decay during cycling.

[0047] Therefore, the single-crystal structure of the positive electrode active material in this application, combined with the high steep gradient distribution of cobalt content near the surface, gives the positive electrode active material stronger chemical inertness, higher mechanical integrity, and interface stability. This enables the material to maintain structural integrity and capacity stability during long-term charge-discharge processes and high-temperature storage, achieving synergistic optimization of high specific capacity, long cycle performance, and excellent high-temperature storage performance.

[0048] In one specific embodiment, 5% ≤ W1-W2 ≤ 15%. Within this range, the stress in the lattice of the positive electrode active material can be further balanced, retaining the functions of suppressing ion mixing and stabilizing the interface, while further ensuring the continuity of the lattice structure, further maximizing the material's specific capacity, and reducing the number of microcracks induced during cycling.

[0049] Furthermore, the first part includes the compound of formula 1 and the cobalt-containing compound;

[0050] Li y Ni a Co b Mn c A x O2, Formula 1

[0051] Wherein, 0.90≤y≤1.10, 0.80≤a≤0.98, 0.01≤b≤0.10, 0.01≤c≤0.10, 0≤x≤0.10, a+b+c+x=1, and element A includes at least one or more elements selected from Mn, Zr, Al, Sr, Ti, Mg, Ca, Ce, Y, and W.

[0052] Specifically, element A is a bulk dopant element of the ternary cathode active material, making the first part include the composition of Formula 1. Element A can form a lattice pinning effect and improve the stability of the layered crystal structure of the ternary cathode material through strong metallic bonds between inactive A and B atoms.

[0053] The cobalt-containing compounds in the first part (such as LiCoO2 and Co3O4) have high stability, which can suppress the interfacial side reactions between the electrolyte and the active material during charge and discharge cycles, reduce the dissolution of transition metal ions, and improve the interfacial ionic conductivity.

[0054] Furthermore, the first part also includes at least one of oxides of element G and lithium compounds of element G; element G includes at least one of Mn, Zr, Al, Sr, Ti, Mg, Ca, Ce, Y, F, P, and W. These oxides and lithium compounds containing element G can buffer the stress generated by lattice expansion and contraction, suppress oxygen vacancy generation and lattice collapse, ensuring that active sites fully participate in the reaction to maintain high specific capacity, while also reducing cycle capacity decay, significantly improving the interfacial stability and cycle life of the cathode active material.

[0055] It should be noted that when the first part includes at least one of the oxides of element G and the lithium compounds of element G, the selection of element G and element A is independent of each other, that is, element G and element A can be the same or different.

[0056] Furthermore, the portion extending from the second point of the first part along the extension direction towards the center C constitutes the second part of the ternary single crystal particle. It can be understood that the second part is enclosed and contained within the first part. In the second part, the absolute value E of the difference in the molar content of Co element between any two points along the extension direction is less than 3%.

[0057] The molar content of Co mentioned above refers to the ratio of the amount of Co at any point in the second part to the amount of Ni, Co, and Mn at that point. Therefore, E is obtained by detecting the molar content of Co at any two points and performing difference and absolute value processing.

[0058] It should be noted that the second part includes the compound shown in Formula 1. In the extension direction, the absolute value E of the molar difference of cobalt content between any two points in the second part is less than 3%, meaning that the cobalt content in the second part exhibits a gentle gradient or near-uniform distribution. This near-uniform distribution further avoids internal lattice stress concentration caused by sudden changes in cobalt content, maintaining the high continuity and integrity of the crystal structure, providing a smoother lattice channel for long-range lithium-ion transport, ensuring stable ion diffusion efficiency, and helping to further optimize the specific capacity of the cathode active material. Simultaneously, it can also mitigate the non-uniformity of lattice expansion and contraction during cycling, reducing the probability of internal microcrack formation and further extending the lifespan of the secondary battery.

[0059] Furthermore, this application also controls the mass percentage content of cobalt and the mass percentage content of alumina in the cathode active material, as described in Part I. Specifically, based on the mass of the cathode active material, when the Co content in the ternary single-crystal particles is 15,000-35,000 ppm and the alumina content is 300-2,000 ppm, while maintaining the high capacity of the cathode active material, interfacial side reactions and structural degradation are further suppressed, thereby improving cycle stability.

[0060] Furthermore, the positive electrode active material of this application includes ternary single crystal particles and a coating layer disposed on at least a portion of the surface of the ternary single crystal particles. The coating layer includes at least one of oxides and lithides of coating elements, and the coating elements include boron and J. The J element includes at least one of Mn, Zr, Al, Sr, Ti, Mg, Ca, Ce, Y, F, P, and W.

[0061] On the one hand, this coating layer can directly block the contact between the positive electrode active material and the electrolyte, thereby effectively inhibiting the oxidative decomposition of the electrolyte under high voltage, the dissolution of transition metal ions, and the generation of gases caused by side reactions. On the other hand, the stable oxide layer can fix the surface oxygen of the positive electrode active material, further reducing the degree of irreversible phase transition of the positive electrode active material. Therefore, by setting this coating layer, the cycle life, thermal stability, and high-voltage stability of the positive electrode material can be further improved.

[0062] This application does not limit the specific distribution of the coating layer. It can be distributed in an island-like form on the surface of the ternary single crystal particles, or it can completely coat the surface of the ternary single crystal particles.

[0063] It should be noted that the selection of G elements and J elements is independent of each other; that is, G elements and J elements can be the same or different.

[0064] In one specific embodiment, the residual alkali content of the positive electrode active material is 800-2000 ppm. Exemplarily, this residual alkali can be an alkaline compound of lithium, such as lithium carbonate or lithium hydroxide. By controlling the aforementioned residual alkali content, this application ensures that the secondary battery reacts with the electrolyte during the first charge-discharge process, generating an interfacial film with lithium-ion conductivity in situ, which helps stabilize the interface and compensate for some of the loss of active lithium. Simultaneously, it avoids severe side reactions with the electrolyte caused by excessively high alkali content. Therefore, optimizing the residual alkali content within an appropriate range achieves a balance between optimizing interfacial chemistry and effectively suppressing side reactions.

[0065] In one specific embodiment, the Dv50 of the positive electrode active material is 1.5-4 μm. Dv50 represents the particle size of the positive electrode active material when the particles reach 50% of the total volume, measured from the smallest particle size, in a volume-based particle size distribution. This application controls Dv50 within the above range, balancing particle packing density and ion transport efficiency. This ensures both tight particle packing to improve the energy density of the electrode and shortens the diffusion distance of lithium ions within the particles, accelerating the electrochemical reaction rate and further maximizing the specific capacity.

[0066] A second aspect of this application provides a method for preparing a positive electrode active material, comprising the following steps:

[0067] 1) A first raw material mixture including a ternary cathode active material precursor, a lithium source, and an A element source is subjected to a first sintering to obtain a first sintered product;

[0068] 2) A second sintering is performed on a second raw material mixture including the first sintering product and the Co source to obtain the second sintering product;

[0069] The element A in the element A source includes at least one of Mn, Zr, Al, Sr, Ti, Mg, Ca, Ce, Y, and W.

[0070] In step 1), the ternary cathode active material precursor refers to nickel-cobalt-manganese or nickel-cobalt-aluminum hydroxides. During the first sintering process, in addition to the gradual formation of nickel-cobalt-manganese or nickel-cobalt-aluminum lithides from the ternary cathode active material precursor, element A from the A element source, as a dopant, also enters the lattice of the nickel-cobalt-manganese or nickel-cobalt-aluminum lithides through solid solution diffusion. Due to the larger ionic radius of element A, it forms a lattice pinning effect in the lattice and creates a local energy barrier, which blocks the Co source in the subsequent second sintering process.

[0071] In step 2), due to the blocking effect of element A, most of the Co elements in the Co source will accumulate on the outer surface of the lithium compound, and a small portion will enter the near surface of the lithium compound, thus forming the first part of the positive electrode active material of this application.

[0072] This application does not limit the basic composition of the lithium source, element A source, and Co source, as long as the corresponding elements are included. For example, the lithium source can be lithium carbonate, acetate, chloride, hydroxide, sulfate, etc.; the element A source can be element A (at least one of Mn, Zr, Al, Sr, Ti, Mg, Ca, Ce, Y, and W) carbonate, acetate, chloride, hydroxide, sulfate, etc.; and the Co source can be cobalt carbonate, acetate, chloride, hydroxide, sulfate, oxide, etc.

[0073] Furthermore, in the second sintering process, the second raw material mixture may also include a G element source, which may be at least one of the following: Mn source, Zr source, Al source, Sr source, Ti source, Mg source, Ca source, Ce source, Y source, F source, P source, and W source. In specific implementations, the G element source may be an oxide, hydroxide, or lithium compound of G. The addition of this G element source helps to ensure that the first part formed in the second sintering process includes at least one of an oxide or lithium compound of G.

[0074] In one specific embodiment, the particle size of the ternary cathode active material precursor satisfies Dv0≥0.3μm, 2.0μm≤Dv50≤4.0μm, and Dv100≤12.0μm.

[0075] In one specific embodiment, the element A in the element A source includes at least one of Zr (ionic radius 0.79 Å), Ti (ionic radius 0.605 Å), Y (ionic radius 0.90 Å), and Sr (ionic radius 1.18 Å). Taking Y and Sr as examples, after ions with larger radii are doped into the ternary cathode active material, their size is much larger than the original transition metal ions (such as Ni²⁺ 0.69 Å), which will generate a pillar effect to expand the space between adjacent lithium layers, expand the lithium ion diffusion channel, thereby reducing the resistance during lithium ion insertion and extraction, and significantly improving the cycle performance of the material. Meanwhile, the ionic radii of Zr and Ti are close to those of Ni or Mn, and after being doped into the crystal lattice, they can provide a more stable framework structure. This strong chemical bond can effectively suppress harmful phase transitions that occur during deep charge and discharge, thereby maintaining the integrity of the crystal structure and reducing microcracks caused by repeated contraction and expansion of the material. This not only helps to improve the structural stability of the material but also reduces the probability of side reactions, ultimately significantly improving the cycle performance of the battery.

[0076] Furthermore, the particle size Dv50 of element A source is 0.2-5 μm, which is beneficial to further improve the uniformity of the mixture and further reduce the segregation and enrichment of additives at some sites.

[0077] In one specific embodiment, a high-speed mixer is used to mix the precursor, lithium source and element A source. The high-speed mixer rotates at 800 rpm to 2000 rpm and the mixing time is 15 min to 30 min.

[0078] In one specific embodiment, in the first sintering process, the sintering temperature is 500℃-850℃, the holding time is 4h-15h, and the heating rate is 2℃ / min-5℃ / min.

[0079] In the second sintering process, the sintering temperature is 550℃-650℃, the holding time is 4h-10h, and the heating rate is 2℃ / min-5℃ / min.

[0080] The first sintering treatment can be carried out in an oxygen-containing atmosphere. Further, the sintering temperature is 700℃-850℃, and the holding time is 6h-12h. After obtaining the first sintered product, the process further includes a step of pulverizing the first sintered product. In one specific embodiment, the pulverization treatment can be carried out in an environment with a dew point temperature <-10℃, and the particle size is controlled to be 1.5μm ≤ Dv50 ≤ 4.0μm.

[0081] In the second sintering process, a high-speed mixer can be used to mix the pulverized product, Co source and G element source. The speed of the high-speed mixer is 800rpm-2000rpm and the mixing time is 15min-20min.

[0082] Furthermore, the second sintering process can be carried out in an oxygen atmosphere, with a sintering temperature of 580℃-630℃ and a holding time of 6h-10h.

[0083] Further, after step 2), the process includes: subjecting a third raw material mixture, comprising the product of the second sintering treatment, a boron source, and a J element source, to a third sintering to obtain a positive electrode active material; in the third sintering treatment, the sintering temperature is 250℃-450℃, the holding time is 4h-10h, the heating rate is 2℃ / min-5℃ / min, and the J element source includes at least one of Mn, Zr, Al, Sr, Ti, Mg, Ca, Ce, Y, F, P, and W. The third sintering facilitates the formation of the aforementioned coating layer on the surface of the single crystal particles.

[0084] In one specific embodiment, the J element source mainly includes oxides or boron-containing compounds of the aforementioned J element.

[0085] Furthermore, a high-speed mixer can be used to mix the product of the second sintering treatment, the boron source, and the J element source. The speed of the high-speed mixer is 800 rpm-1000 rpm, and the mixing time is 15 min-20 min.

[0086] Furthermore, the third sintering can be carried out in an oxygen-containing atmosphere, with a temperature of 250℃-350℃ and a holding time of 6h-10h.

[0087] After the third sintering, the sintered material can be cooled, crushed, and sieved to obtain the positive electrode active material of this application.

[0088] A third aspect of this application provides a positive electrode sheet, comprising the positive electrode active material of the first aspect or the positive electrode active material prepared in the second aspect. Therefore, this positive electrode sheet has the advantage of effectively improving the specific capacity and cycle performance of a secondary battery.

[0089] In one specific embodiment, the positive electrode sheet of the present invention specifically includes a positive current collector and a positive active layer comprising a positive active material disposed on the surface of the positive current collector.

[0090] There are no particular limitations on the positive electrode current collector, as long as it is conductive and does not cause adverse chemical changes in the battery. Materials such as stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, or silver can be used. Furthermore, the positive electrode current collector typically has a thickness of 3μm-500μm, and fine irregularities can be formed on its surface to improve the adhesion of the positive electrode active material. The positive electrode current collector can be used in various shapes such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0091] In this case, the weight of the positive electrode active material can be 80wt%-99wt% relative to the total weight of the positive electrode active material layer, such as 85wt%-98.5wt% of the positive electrode active material, to obtain excellent capacity and energy characteristics.

[0092] In addition to the aforementioned positive electrode active material, the positive electrode active material layer may also optionally include conductive materials and adhesives.

[0093] Conductive agents are used to provide conductivity to the electrodes. Any conductive agent can be used without particular restriction, as long as it has suitable electronic conductivity and does not cause adverse chemical changes in the battery. Specific examples of conductive agents can be: graphite (such as natural or artificial graphite), carbonaceous materials (such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, and carbon fiber), metal powders or fibers (such as copper, nickel, aluminum, and silver); conductive whiskers (such as zinc oxide or potassium titanate), conductive metal oxides (such as titanium oxide), or conductive polymers (such as polyphenylene derivatives), and any one or a mixture of two or more of these can be used alone. The weight of the conductive material is typically 1–20 wt% relative to the total weight of the positive electrode active material layer.

[0094] Adhesives are used to improve the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples may include: polyvinylidene fluoride (PVDF), PVDF-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one or a mixture of two or more of them may be used. The weight of the adhesive relative to the total weight of the positive electrode active material layer is typically 1-20 wt%.

[0095] Besides using the aforementioned positive electrode active material, the positive electrode can be manufactured according to typical positive electrode manufacturing methods. Specifically, the positive electrode can be manufactured by coating a composition comprising the aforementioned positive electrode active material and optionally a binder and conductive material for forming a positive electrode active material layer onto a positive electrode current collector, followed by drying and calendering. Here, the type and content of the positive electrode active material, binder, and conductive material are the same as those described above. The composition is prepared by dissolving or dispersing the positive electrode active material, along with a selective binder and conductive agent, in a solvent.

[0096] The solvent can be one commonly used in the art, including dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, water, etc. One or a mixture of two or more of these solvents can be used. Considering the coating thickness and manufacturing yield of the slurry, the amount of solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to give the slurry a viscosity suitable for achieving excellent thickness uniformity when used in the preparation of the positive electrode.

[0097] In addition, a positive electrode can also be manufactured by casting the composition for forming the positive electrode active material layer onto a separate support, and then pressing the film layer obtained by peeling it off from the support onto the positive electrode current collector.

[0098] This application provides a fourth aspect of a secondary battery, which includes the positive electrode plate of the third aspect. Therefore, the secondary battery of this application has excellent capacity and cycle performance.

[0099] It is conceivable that, in addition to the aforementioned positive electrode, the secondary battery of this application also includes a negative electrode, an electrolyte, and a separator.

[0100] The secondary battery specifically includes: a positive electrode, a negative electrode arranged facing the positive electrode, a separator disposed between the positive and negative electrodes, and an electrolyte, wherein the positive electrode is the same as described above. Additionally, the secondary battery may optionally include a battery container housing the positive electrode, negative electrode, and separator electrode assembly, and a sealing member for sealing the battery container.

[0101] In a secondary battery, the negative electrode sheet includes a negative current collector and a layer of negative active material disposed on the negative current collector.

[0102] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and does not cause any chemical changes in the battery. For example, materials such as copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel with surface treatments of carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloys can be used. Furthermore, the negative electrode current collector can typically have a thickness of 3μm-500μm, and similar to the positive electrode current collector, fine irregularities can be formed on its surface to enhance the adhesion of the negative electrode active material. Various forms of negative electrode current collectors can be used, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0103] In addition to the negative electrode active material, the negative electrode active material layer selectively contains a binder and a conductive material. The negative electrode active material layer can be prepared by the following methods: coating a composition for forming a negative electrode, which contains a negative electrode active material and optionally a binder and a conductive material, on a negative electrode current collector and drying it; or alternatively, casting a composition for forming a negative electrode sheet on a separate support, and then laminating the film obtained by peeling from the support on the negative electrode current collector.

[0104] As the negative electrode active material, a compound capable of reversibly inserting and extracting lithium can be used. Specific examples thereof may include: carbonaceous materials (such as artificial graphite, natural graphite, graphitized carbon fiber or amorphous carbon); (semi) metallic materials capable of alloying with lithium (such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy or Al alloy); metal oxides capable of doping and undoping lithium (such as SiO x (0 < x < 2), SnO2, vanadium oxide or lithium vanadium oxide); or composites containing (semi) metallic materials and carbonaceous materials (such as Si-C composite or Sn-C composite), and any one of them alone or a mixture of two or more thereof can be used. A thin film of metallic lithium can also be used as the negative electrode active material. In addition, as the carbon material, low-crystalline carbon or high-crystalline carbon can also be used. Among them, soft carbon or hard carbon are typical examples of low-crystalline carbon. As representatives of high-crystalline carbon, amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, condensated graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase carbon microbead, mesophase pitch, or high-temperature sintered carbon (such as coke derived from petroleum or coal tar pitch) can be used.

[0105] Relative to the total weight of the negative electrode active material layer, the mass of the negative electrode active material can be 80 wt% - 99 wt%.

[0106] The selection of the binder and the conductive material can be the same as that in the positive electrode described above.

[0107] In secondary batteries, a separator is used to separate the negative and positive electrodes and provide a migration channel for lithium ions. Any separator can be used without particular limitation, as long as it is conventionally used in secondary batteries. In particular, separators with excellent electrolyte retention and low resistance to electrolyte ion migration are preferred. The separator can have a pore size of about 0.01 μm to 10 μm and a thickness of about 5 μm to 300 μm. Specifically, porous polymer membranes formed from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, or ethylene / methacrylate copolymers, or laminated structures having two or more layers, can be used. Alternatively, conventional porous nonwoven fabrics, such as nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and single-layer or multi-layer structures can be optionally used.

[0108] The electrolyte in a secondary battery may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, or molten inorganic electrolytes that can be used to prepare a secondary battery, but this application is not limited to these.

[0109] Specifically, the electrolyte may contain organic solvents and lithium salts. Any organic solvent can be used without particular limitation, as long as it serves as the ion transport medium participating in the battery's electrochemical reactions. Specifically, the following substances can be used as organic solvents: ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic solvents such as benzene and fluorobenzene; or carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where R is a linear, branched, or cyclic C2-C20 hydrocarbon group and may contain double bonds, aromatic rings, or ether bonds); amides such as dimethylformamide; dioxolane such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate solvents can be used. For example, a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant, which can improve the charge / discharge performance of the battery, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) can be used. In this case, the electrolyte performance may be superior when the cyclic carbonate and the linear carbonate are mixed in a volume ratio of approximately 1:1 to 1:9.

[0110] There are no particular limitations on lithium salts, as long as they can provide lithium ions for use in secondary batteries. Specifically, lithium salts can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. The preferred lithium salt concentration is 0.1M to 2.0M. When the lithium salt concentration is within the above range, the electrolyte can have appropriate conductivity and viscosity, thus achieving excellent electrolyte performance and enabling efficient lithium ion movement.

[0111] To improve battery life characteristics, suppress battery capacity reduction, and increase battery discharge capacity, in addition to the electrolyte components, the electrolyte may contain one or more additives, such as alkylene carbonate halide compounds (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, etc. In this case, the content of the additive can be from 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

[0112] Because secondary batteries containing the positive electrode active material according to this application stably exhibit excellent discharge capacity and lifespan characteristics, they are suitable for use in: portable devices such as mobile phones, laptop computers and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs).

[0113] Secondary batteries can also serve as battery modules for unit cells and battery packs containing battery modules. Battery modules or battery packs can be used as a power source for at least one medium to large-sized device, including power tools, electric vehicles (EVs), hybrid electric vehicles and plug-in hybrid electric vehicles (HEVs), low-altitude aircraft, or energy storage systems.

[0114] The shape of the lithium secondary battery in this application is not particularly limited, and it can be used as a cylindrical, prismatic, pouch, or coin-shaped battery.

[0115] The secondary battery according to this application can be used not only as a battery cell for powering small devices, but also as a unit battery in medium and large battery modules containing multiple battery cells.

[0116] The positive electrode active material of this application will be described in more detail below through specific embodiments.

[0117] Example 1

[0118] The cathode active material of this example includes the following steps:

[0119] S1. Mix 5.00 kg of ternary precursor Ni 0.94 Co 0.04 Mn 0.02 (OH)2, 2.33 kg of lithium hydroxide, 0.14 wt% ZrO2 and 0.12 wt% SrO based on the mass of the precursor in a high - speed mixer. The mixing parameters are a rotation speed of 1000 rpm and a mixing time of 20 min. Among them, the molar ratio of lithium element in the lithium source to nickel - cobalt - manganese elements in the precursor is 1.04:1. Heat the above - mentioned mixed material in an oxygen atmosphere at a heating rate of 3℃ / min to 500℃ and keep it warm for 2 h. Then, heat it at a heating rate of 3℃ / min to 790℃ and keep it warm for 10 h. After the box - type furnace cools naturally to <60℃, the material is taken out of the furnace. After the material cools to room temperature, it is crushed by jaw crusher and roll crusher, and crushed under the environment with a dew - point temperature < - 10℃, and the particle size is controlled at 2.0 μm < D50 < 3.0 μm to obtain the first sintered product. Figure 2 is the SEM image of the ternary precursor of Example 1 of this application, Figure 3 is the SEM image of the first sintered product of Example 1 of this application. From Figure 2 and Figure 3 it can be seen that the precursor has a spherical structure and irregular whisker structures on the surface. After the first sintering treatment, the first sintered product is smooth - surfaced single - crystal particles.

[0120] S2. Mix 4.00 kg of the first sintered product obtained in step S1 with 1.42 wt% Co(OH)2 and 0.19 wt% Al2O3 in a high - speed mixer at a rotation speed of 1000 rpm and a mixing time of 20 min. Heat the above - mentioned mixed material in an oxygen atmosphere at a heating rate of 2.0℃ / min to 620℃ and keep it warm for 8 h. After the box - type furnace cools naturally to <60℃, the material can be taken out of the furnace and dispersed by mechanical grinding to obtain the second sintered product. Figure 4 is the SEM image of the second sintered product of Example 1 of this application. From Figure 4 it can be seen that after the second sintering, continuous first parts are formed on the single - crystal particles.

[0121] S3. Mix 3.50 kg of the second sintered product obtained in step S2 with 0.57 wt% B2O3, 0.19 wt% Al2O3 and 0.08 wt% TiO2 using a high-speed mixer at 800 rpm for 20 min. Then, heat the mixture to 300°C in an oxygen atmosphere at a heating rate of 2.0°C / min, hold for 10 h, and allow it to cool naturally in a box furnace to <60°C. The material can then be removed from the furnace, crushed, and passed through a 325-mesh sieve to obtain the positive electrode active material of this embodiment. Figure 5 This is a SEM image of the positive electrode active material of Example 1 of this application. From... Figure 5 It can be seen that after the third sintering, the surface of the final positive electrode active material forms a discontinuous dot-like or island-like coating layer.

[0122] Example 2

[0123] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in S1, 0.14wt% ZrO2 and 0.12wt% SrO, which account for 0.27wt% ZrO2 and 0.12wt% SrO by the mass of the precursor, are replaced with 0.27wt% ZrO2 and 0.12wt% SrO.

[0124] Example 3

[0125] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in S1, 0.14wt% ZrO2 and 0.12wt% SrO, which account for 0.14wt% of the precursor mass, are replaced with 0.14wt% ZrO2 and 0.06wt% SrO.

[0126] Example 4

[0127] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in S1, 0.14wt% ZrO2 and 0.12wt% SrO, which account for 0.14wt% of the precursor mass, are replaced with 0.14wt% ZrO2 and 0.18wt% SrO.

[0128] Example 5

[0129] The preparation method of this embodiment is basically the same as that of Example 1, except that in S2, 1.42wt% Co(OH)2 and 0.19wt% Al2O3 are replaced with 1.42wt% Co(OH)2, 0.19wt% Al2O3 and 0.14wt% LiF.

[0130] Example 6

[0131] The preparation method of this embodiment is basically the same as that of Example 1, except that in S2, 1.42wt% Co(OH)2 and 0.19wt% Al2O3 are replaced with 1.42wt% Co(OH)2, 0.19wt% Al2O3 and 0.37wt% Li3PO4.

[0132] Example 7

[0133] The preparation method of this embodiment is basically the same as that of Example 1, except that in S2, 1.42wt% Co(OH)2 and 0.19wt% Al2O3 are replaced with 0.094wt% Co(OH)2 and 0.19wt% Al2O3.

[0134] Example 8

[0135] The preparation method of this embodiment is basically the same as that of Example 1, except that in S2, 1.42wt% Co(OH)2 and 0.19wt% Al2O3 are replaced with 1.89wt% Co(OH)2 and 0.19wt% Al2O3.

[0136] Example 9

[0137] The preparation method of this embodiment is basically the same as that of Example 1, except that in S3, 0.57wt% B2O3, 0.19wt% Al2O3 and 0.08wt% TiO2 are replaced with 0.57wt% B2O3, 0.19wt% Al2O3 and 0.07wt% WO3.

[0138] Example 10

[0139] The preparation method in this embodiment is basically the same as that in Example 1, except that in S1, the ternary precursor (Ni 0.94 Co 0.04 Mn 0.02 )OH replaced with (Ni 0.9 Co 0.05 Mn 0.05 )OH.

[0140] Example 11

[0141] The preparation method in this embodiment is basically the same as that in Example 1, except that in S1, the ternary precursor Ni is used. 0.94 Co 0.04 Mn 0.02 (OH)2 is replaced with Ni 0.96 Co 0.02 Mn 0.02 (OH)2.

[0142] Example 12

[0143] The preparation method of this comparative example is basically the same as that of Example 1, except that 0.57wt% B2O3, 0.19wt% Al2O3 and 0.08wt% TiO2 in S3 are omitted.

[0144] Example 13

[0145] The preparation method in this embodiment is basically the same as that in Example 1, except that step S3 is omitted. That is, the positive electrode active material in this embodiment is the second sintering product of Example 1.

[0146] Example 14

[0147] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in S1, the sintering temperature is increased from 790℃ to 820℃ and the heating rate is 5℃ / min; in S2, the sintering temperature is increased from 620℃ to 650℃ and the heating rate is 4℃ / min.

[0148] Example 15

[0149] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that the cobalt coating content is further increased in S2, and 1.42wt% Co(OH)2 and 0.19wt% Al2O3 are replaced with 3.79wt% Co(OH)2 and 0.19wt% Al2O3.

[0150] Comparative Example 1

[0151] The preparation method of this comparative example is basically the same as that of Example 1, except that 0.14wt% ZrO2 and 0.12wt% SrO in S1 are omitted.

[0152] Comparative Example 2

[0153] The preparation method of this comparative example is basically the same as that of Example 13, except that 0.14wt% ZrO2 and 0.12wt% SrO in S1 are omitted.

[0154] Experimental Example 1

[0155] The following tests were performed on the positive electrode active materials of the examples and comparative examples.

[0156] 1) W1 and W2

[0157] The single-crystal particles of the positive electrode active material are cut open using an argon ion polishing cutter (CP), with the cut surface passing through the geometric center of the single-crystal particle. Using 10% of the cut surface radius R as the boundary, the molar ratio W1 of the Co element at the first point outside the boundary (i.e., the first part) and the molar ratio W2 of the Co element at the second point extending 10%R from the first point to the center are measured by an energy dispersive spectrometer (EDS).

[0158] Figure 6 This is a cross-sectional view of the positive electrode active material of Embodiment 1 of this application, wherein point A is the first point of the first part, and point B is the second point in the first part corresponding to point A. Upon testing, the molar content of Co (W1) at point A is 15.7%, the molar content of Ni is 83.3%, and the molar content of Mn is 1.0%; the molar content of Co (W2) at point B is 6.3%, the molar content of Ni is 92.1%, and the molar content of Mn is 1.6%.

[0159] Figure 7 This is a schematic diagram comparing the contour lines of the cobalt concentration gradient distribution of the positive electrode active materials in Example 1 and Comparative Example 1 of this application. Figure 7 As shown, in Example 1, the cobalt concentration gradient of the positive electrode active material changes rapidly and has a large gradient difference at a distance of 90% from the surface to the center of the particle; this region corresponds to the first part. In Comparative Example 1, the cobalt concentration gradient is relatively uniformly distributed throughout the entire particle.

[0160] The results are shown in Tables 1A and 1B.

[0161] 2) The absolute value E of the maximum difference in the Co molar ratio in Part II max .

[0162] The interior of the boundary defined in 1) above is the second part.

[0163] In the direction of extension towards the geometric center, the boundary point B and the eight points in the second part are statistically analyzed using an energy dispersive spectroscopy (EDS) instrument. Figure 6 The molar content of Co at points C, D, E, F, G, H, I, and J in the diagram is calculated. The molar content of Co at each of these nine points is then subtracted pairwise. The absolute value of the largest difference is E. max See Tables 1A and 1B. For example... Figure 7 As shown, in the second part of the positive electrode active material of Example 1, the distribution of the cobalt concentration gradient is relatively more uniform than that in the first part.

[0164] 3): Composition of the first part and the covering layer

[0165] The substances in the coating layer of the positive electrode active material and the substances in the first part were analyzed by combining XPS and EDS tests.

[0166] The results are shown in Tables 1A and 1B.

[0167] 4): W co and W A

[0168] Based on the quality of the positive electrode active material, ICP was used to determine the Co element content (W) in the particles.co And the content of element A W A The tests were conducted. The results are shown in Tables 1A and 1B.

[0169] 5): Residual alkali content of the positive electrode active material

[0170] 30g of the prepared positive electrode active material powder was added to 100mL of water and stirred for 30min. The residual lithium in the sample was then titrated with a standard hydrochloric acid solution. The titration endpoint was determined by the abrupt change in potential using a composite pH electrode as the indicator electrode. The results are shown in Table 1C.

[0171] 6): Dv50 of positive electrode active material

[0172] The Dv50 of the positive electrode active material was measured using a particle size analyzer. The results are shown in Table 1C.

[0173] Table 1A

[0174]

[0175] Table 1B

[0176]

[0177] Table 1C

[0178]

[0179] Experimental Example 2

[0180] The positive electrode active materials, carbon black conductive materials, and PVDF binders prepared in the examples and comparative examples were mixed in N-methylpyrrolidone solvent at a weight ratio of 94.5:3:2.5 to prepare a positive electrode mixture (viscosity: 4500 mPa·s). The mixture was then coated on the surface of an aluminum current collector, dried at 130°C, and calendered to obtain a compacted density of 3.4 g / cm³. 3 The positive electrode sheet.

[0181] The negative electrode active material graphite, thickener sodium carboxymethyl cellulose, binder styrene-butadiene rubber, and conductive agent acetylene black were mixed in a mass ratio of 95.5:1.5:2:1. Deionized water was added, and the negative electrode slurry was obtained under the action of a vacuum mixer. The negative electrode slurry was uniformly coated on copper foil, dried at room temperature, and then transferred to an oven for drying. After cold pressing and slitting, the negative electrode sheet was obtained.

[0182] The positive electrode, porous polyethylene separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. After being wound into a square bare cell, it is placed in an aluminum-plastic film, baked at 80°C to remove water, injected with electrolyte (LBC3021C48), sealed, and then subjected to processes such as standing, hot and cold pressing, formation, clamping, and capacity testing to obtain a lithium secondary battery.

[0183] 1. Capacity testing of positive electrode active materials in lithium secondary batteries

[0184] The lithium secondary battery was left to stand at a constant temperature of 25 ℃ for 2 hours, then charged at 0.1C to 4.25V at a range of 2.8V to 4.25V, and then charged at a constant voltage of 4.25V until the current was ≤0.05mA. After standing for 5 minutes, it was discharged at 0.1C to 2.8V. The capacity of the lithium-ion battery was recorded. The specific capacity of the positive electrode active material in the lithium secondary battery was obtained by dividing the measured capacity value by the mass of the positive electrode active material in the battery.

[0185] 2. High-temperature cycle performance test of lithium secondary batteries

[0186] At 45°C, the lithium secondary battery was charged at a constant current of 1C until the voltage reached 4.25V, then charged at a constant voltage of 4.25V until the current reached 0.05C, followed by a constant current of 1C until the final voltage reached 2.8V. The discharge capacity Q1 of the first cycle was recorded. This charging and discharging cycle was then performed 300 times, and the discharge capacity Q at the 300th cycle was recorded. 300 The capacity retention rate Q after 300 cycles is calculated using the following formula. Figure 8 This is a cycle curve of a secondary battery containing the positive electrode active material of Example 1 and Comparative Example 1.

[0187] Capacity retention rate Q = Q 300 / Q1×100%.

[0188] 3. High-temperature storage performance test of lithium secondary batteries:

[0189] At 25°C, the lithium secondary battery was first charged to 4.25V with a constant current of 1C, and then further charged to 0.05C with a constant voltage of 4.25V. The volume of the lithium secondary battery was then measured by the water displacement method and recorded as the initial volume of the lithium secondary battery. The lithium secondary battery was then stored at 70°C for 21 days. After the storage period, the volume of the lithium secondary battery was measured again by the water displacement method and recorded as the volume of the lithium secondary battery after 21 days of storage at 70°C.

[0190] Volume expansion rate (%) of lithium secondary battery after 21 days of storage at 70℃ = [(volume of lithium-ion battery after 21 days of storage at 70℃ / initial volume of lithium-ion battery) - 1] × 100%

[0191] The results are shown in Table 2.

[0192] Table 2

[0193]

[0194] As shown in Table 2, the positive electrode active material of this application helps to improve the discharge capacity, cycle performance and storage performance of the battery.

[0195] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material includes ternary single crystal particles, the maximum dimension from the center to the surface of the ternary single crystal particles is R, and the ternary single crystal particles include a first portion extending 10%R from the surface of the ternary single crystal particles toward the center; the first portion includes a first site away from the center and a second site close to the center in the extension direction; based on the total molar amount of nickel, cobalt and manganese elements at each site, the molar content of Co element W1 at the first site is greater than the molar content of Co element W2 at the second site, and W1-W2 is not less than 5%.

2. The positive electrode active material according to claim 1, characterized in that, 5%≤W1-W2≤15%.

3. The positive electrode active material according to claim 2, characterized in that, The first part includes the compound shown in Formula 1 and the cobalt-containing compound; Li y Ni a Co b Mn c A x O2, Formula 1 Where 0.90≤y≤1.10, 0.80≤a≤0.98, 0.01≤b≤0.10, 0.01≤c≤0.10, 0≤x≤0.10, a+b+c+x=1, and element A includes at least one of Mn, Zr, Al, Sr, Ti, Mg, Ca, Ce, Y, and W.

4. The positive electrode active material according to claim 3, characterized in that, The first part further includes at least one of oxides of element G and lithium compounds of element G; the element G includes at least one of Mn, Zr, Al, Sr, Ti, Mg, Ca, Ce, Y, F, P, and W.

5. The positive electrode active material according to claim 3 or 4, characterized in that, The ternary single crystal particle further includes a second portion enclosed by the first portion; in the extension direction, the absolute value E of the difference in the molar content of Co element at any two points of the second portion is less than 3%; and / or, Based on the mass of the positive electrode active material, the Co content in the ternary single crystal particles is 15,000-35,000 ppm, and the A content is 300-2,000 ppm.

6. The positive electrode active material according to any one of claims 1-5, characterized in that, The positive electrode active material includes ternary single crystal particles and a coating layer disposed on at least a portion of the surface of the ternary single crystal particles. The coating layer includes at least one of oxides and lithides of coating elements. The coating elements include boron and J. The J element includes at least one of Mn, Zr, Al, Sr, Ti, Mg, Ca, Ce, Y, F, P, and W.

7. The positive electrode active material according to any one of claims 1-6, characterized in that, The residual alkali content of the positive electrode active material is 800-2000 ppm; and / or, The Dv50 of the positive electrode active material is 1.5-4 μm.

8. A method for preparing the positive electrode active material according to any one of claims 1-7, characterized in that, Includes the following steps: 1) A first raw material mixture including a ternary cathode active material precursor, a lithium source, and an A element source is subjected to a first sintering to obtain a first sintered product; The A element in the A element source includes at least one of Mn, Zr, Al, Sr, Ti, Mg, Ca, Ce, Y, and W; 2) A second sintering is performed on the mixture including the first sintering product and the second raw material of Co source to obtain the positive electrode active material.

9. The preparation method according to claim 8, characterized in that, In the first sintering process, the sintering temperature is 500℃-850℃, the holding time is 4h-15h, and the heating rate is 2℃ / min-5℃ / min; In the second sintering process, the sintering temperature is 550℃-650℃, the holding time is 4h-10h, and the heating rate is 2℃ / min-5℃ / min; and / or, After step 2), the process further includes: subjecting a third raw material mixture, comprising the product of the second sintering treatment, a boron source, and a J element source, to a third sintering to obtain the positive electrode active material; in the third sintering treatment, the sintering temperature is 250℃-450℃, the holding time is 4h-10h, and the heating rate is 2℃ / min-5℃ / min; the J element source includes at least one of Mn, Zr, Al, Sr, Ti, Mg, Ca, Ce, Y, F, P, and W.

10. A positive electrode plate, characterized in that, Includes the positive electrode active material according to any one of claims 1-7, or the positive electrode active material prepared by the preparation method according to claim 8 or 9.

11. A secondary battery, characterized in that, Includes the positive electrode sheet as described in claim 10.

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