Positive electrode active material, method for producing the same, and battery

Abstract

This application discloses a positive electrode active material, its preparation method, and a battery. The positive electrode active material includes: a substrate comprising lithium cobalt oxide; and a coating layer at least partially covering the surface of the substrate, comprising a composite phosphate and including multiple spaced island structures. After ball milling and agitation treatment, the mass fraction retention rate of phosphorus (P) in the positive electrode active material is not less than 70%, and / or the mass fraction retention rate of titanium (Ti) in the positive electrode active material is not less than 70%. The ball milling and agitation treatment is performed using a planetary ball mill with a main disk rotation speed of 200 rpm for 20 minutes, using ball stones with a diameter of 3 mm. This improves the surface structure stability of the positive electrode active material, reduces interfacial side reactions, and enhances impedance and thermal stability under high SOC conditions. Simultaneously, the coating layer exhibits good interfacial bonding stability with the substrate.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, specifically to positive electrode active materials and their preparation methods, and batteries. Background Technology

[0002] Lithium-ion batteries are widely used in consumer electronics, power tools, and energy storage systems due to their advantages such as high energy density, long cycle life, and environmental friendliness. As a crucial component of lithium-ion batteries, the cathode material significantly impacts the battery's capacity, cycle stability, and safety performance. Among them, layered LiCoO2 (Lithium Cobalt Oxide, LCO) maintains a significant position in high-end consumer electronics batteries due to its high compaction density, good structural stability, and mature industrialization system.

[0003] As electronic products increasingly demand higher battery energy density, the charging cutoff voltage of LCO cathode active materials has gradually increased from the traditional 4.2V to 4.45V or even above 4.55V. Under high voltage conditions, the capacity of LCO cathode active materials can be further released, but this also brings a series of new problems.

[0004] It should be noted that the above statements are only used to provide background information related to this application and do not necessarily constitute prior art. Summary of the Invention

[0005] In a first aspect, this application proposes a positive electrode active material, comprising: a matrix comprising lithium cobalt oxide; and a coating layer at least partially covering the surface of the matrix, the coating layer comprising a composite phosphate and comprising a plurality of spaced-apart island structures; after ball milling perturbation treatment, the mass fraction retention rate of phosphorus (P) in the positive electrode active material is not less than 70%, and / or the mass fraction retention rate of titanium (Ti) in the positive electrode active material is not less than 70%; wherein the ball milling perturbation treatment is performed using a planetary ball mill, the main disk rotation speed of the planetary ball mill is 200 rpm, the time is 20 min, and the diameter of the ball used is 3 mm. This is beneficial for improving the surface structure stability of the positive electrode active material, reducing interfacial side reactions, improving impedance stability and thermal stability under high SOC conditions, and simultaneously providing good interfacial bonding stability between the coating layer and the matrix.

[0006] In some embodiments of this application, after ball milling and disturbance treatment, the mass fraction retention rate of P element in the positive electrode active material is not less than 80%, and / or the mass fraction retention rate of Ti element in the positive electrode active material is not less than 80%. Therefore, the coating layer is less likely to detach from the surface of the matrix particles under mechanical disturbance conditions, exhibits better interfacial bonding stability between the coating layer and the matrix, and has stronger resistance to detachment.

[0007] In some embodiments of this application, the average size of a single island structure is 120 nm to 260 nm; optionally, 150 nm to 220 nm; and / or, the minimum spacing between adjacent island structures is 200 nm to 600 nm; optionally, 300 nm to 500 nm. Therefore, under high SOC conditions, local surface structure reconstruction of the positive electrode active material can be limited, and surface stress can be dispersed, thereby improving the surface structure stability of the positive electrode active material. Simultaneously, since the coating layer is not a continuous and dense cover, a portion of the matrix region remains on the surface of the positive electrode active material particles as a lithium-ion migration channel, thereby reducing the obstruction of lithium-ion diffusion caused by the coating layer.

[0008] In some embodiments of this application, the coating layer covers 2% to 20% of the substrate surface; optionally, 5% to 15%. Thus, a portion of the substrate area remains on the surface of the positive electrode active material particles as a lithium-ion migration channel, which helps to reduce the adverse effects of excessive coating on lithium-ion transport.

[0009] In some embodiments of this application, the composite phosphate includes Al, Ti, P, and Q elements, wherein the Q element includes at least one of Ge, In, Y, Sc, Mg, Zr, Nb, Mn, Co, Ni, Mo, and W. This is beneficial for improving the lattice stability of the positive electrode active material surface and suppressing oxygen release behavior under high-temperature conditions.

[0010] In some embodiments of this application, the Q element includes at least one of Nb, Zr, Mg, and Y; optionally, the Q element includes Nb and / or Zr; more optionally, the Q element includes Nb. The aforementioned Q element can form stable QO bonds with oxygen and, together with the phosphate structural units, construct a stable composite phosphate coating structure. Nb and Zr elements have strong metal-oxygen bonding characteristics, which can improve the thermal and chemical stability of the coating layer and enhance the confinement effect of the coating layer on the oxygen structure of the lithium cobalt oxide surface, thereby reducing the tendency for surface structure reconstruction and oxygen release of the cathode active material under high SOC conditions. Mg element helps to regulate the local ion transport environment of the coating layer and reduce interfacial polarization; Y element helps to enhance the structural stability and interfacial tolerance of the coating layer. Therefore, the composite phosphate coating layer containing the aforementioned Q element can further improve the impedance stability and thermal stability of the cathode active material under high SOC conditions.

[0011] In some embodiments of this application, the molar ratio of Al, Ti, P, and Q elements in the coating layer is (0.2~0.4):(1.4~2.0):(1.8~3.1):(0~0.1). This is beneficial for improving the surface lattice stability of the positive electrode active material and suppressing oxygen release behavior under high-temperature conditions.

[0012] In some embodiments of this application, the chemical formula of the matrix satisfies: Li x Co y M z O2, wherein 0.95≤x≤1.05, 0.9≤y≤1, 0≤z≤0.1; M includes at least one of Mg, Al, Ti, Zr, Y, La, and Nb. This is beneficial for improving the structural stability of the positive electrode active material and reducing the occurrence of side reactions.

[0013] In some embodiments of this application, the median particle size of the positive electrode active material is 2 μm to 20 μm; and / or, the compaction density of the positive electrode active material is 3.9 g / cm³. 3 ~4.4g / cm 3 This helps to shorten the lithium-ion diffusion path and increase the specific capacity of the positive electrode active material.

[0014] In some embodiments of this application, ΔW = W0 - W1 is 300 J / g to 1000 J / g; optionally, 400 J / g to 1000 J / g; wherein W0 is the unit heat release of the matrix as measured by DSC, and W1 is the unit heat release of the positive electrode active material as measured by DSC. This helps to reduce the heat release of the positive electrode active material and improve its thermal stability.

[0015] In some embodiments of this application, ΔJ = J0 - J1 is 50 ppm to 300 ppm; where J1 is the residual alkali content of the positive electrode active material and J0 is the residual alkali content of the matrix. This indicates that the coating material has an interfacial trapping effect on residual lithium on the matrix surface during sintering, which helps to reduce the accumulation of free lithium salts on the surface of the positive electrode active material particles and reduces the resulting interfacial side reactions.

[0016] In some embodiments of this application, J1 is 100ppm to 500ppm. Therefore, the residual alkali content on the surface of the positive electrode active material is relatively low, which helps to reduce the occurrence of interfacial side reactions.

[0017] In some embodiments of this application, the positive electrode active material comprises a single crystal. This helps to improve the interface stability and impedance stability of the single-crystal positive electrode active material under high SOC conditions.

[0018] In a second aspect, this application proposes a method for preparing the aforementioned positive electrode active material, comprising: mixing an aluminum source, a titanium source, an optional Q source, and a phosphorus source; adjusting the pH to 4.5-9.0; performing a co-precipitation reaction; and aging the mixture to obtain a coating material; and then sintering the coating material with lithium cobalt oxide under an oxygen-containing atmosphere to obtain the positive electrode active material; wherein the sintering temperature is 700℃-900℃. Thus, this application prepares a coating material through a co-precipitation process, and allows the coating material to undergo an interfacial reaction with residual lithium compounds on the surface of the matrix material during sintering, thereby constructing a discretely distributed composite phosphate island-like coating layer on the surface of the lithium cobalt oxide matrix. This reduces the accumulation of free lithium salts on the surface of the positive electrode active material particles. Furthermore, this preparation method is simple, feasible, easy to operate, and suitable for large-scale promotion.

[0019] In some embodiments of this application, the temperature of the coprecipitation reaction is 30℃~90℃, and the rotation speed is 400rpm~1200rpm; and / or, the temperature of the aging treatment is 25℃~70℃, and the time is 0.2h~2h. This facilitates the reaction and yields a coating material with a suitable particle size.

[0020] In some embodiments of this application, the median particle size D of the coating material is... 50 Satisfies: 0.25μm < D 50 <5μm; optionally, 0.25μm <D 50 <3μm; and / or, the specific surface area of ​​the coating material is 20m². 2 / g~90m 2 / g; optional, 30m 2 / g~60m 2 / g. This facilitates the formation of a coating layer with moderate coverage.

[0021] In some embodiments of this application, the aluminum source includes at least one of aluminum sulfate, aluminum nitrate, and aluminum chloride; and / or, the titanium source includes at least one of titanium tetrachloride and titanium oxysulfate; and / or, the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium monohydrogen phosphate, sodium monohydrogen phosphate, potassium monohydrogen phosphate, ammonium phosphate, sodium phosphate, and potassium phosphate. Therefore, the raw materials are widely available, the cost is low, and large-scale promotion is convenient.

[0022] In some embodiments of this application, the sintering process is a single sintering, wherein the heating rate of the single sintering is 1℃ / min to 5℃ / min, the temperature is 700℃ to 900℃, and the time is 5h to 20h. This is beneficial for improving sintering efficiency and shortening the reaction time.

[0023] In some embodiments of this application, the sintering process includes: sequentially performing a first sintering process, a second sintering process, and a third sintering process; wherein the heating rate of the first sintering process is 1℃ / min~5℃ / min, the temperature is 200℃~450℃, and the time is 0.5h~5h; and / or, the heating rate of the second sintering process is 1℃ / min~5℃ / min, the temperature is 450℃~700℃, and the time is 1h~8h; and / or, the heating rate of the third sintering process is 1℃ / min~3℃ / min, the temperature is 700℃~900℃, and the time is 3h~15h. This facilitates the formation of a composite phosphate coating layer characterized by an island-like distribution, while avoiding premature agglomeration or continuous densification of the coating material.

[0024] In some embodiments of this application, the amount of coating material added is 0.01wt% to 5wt% based on the total mass of the lithium cobalt oxide; optionally, 0.01wt% to 2wt%. This ensures the stability of the cathode active material interface while reducing the adverse effects of excessive coating on lithium-ion transport.

[0025] In a third aspect of this application, a battery is provided, including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive active material layer located on at least one side of the positive current collector, the positive active material layer including the positive active material described in the first aspect of this application or a positive active material prepared by the method described in the second aspect of this application.

[0026] In some embodiments of this application, ΔDCR(10%-90%) / DCR(10%-90%)avg is 14%~22%; optionally, 14%~20%; wherein, DCR(10%-90%)avg is the average value of the battery's DC resistance during the process of charging the battery from 10% SOC to 90% SOC, and ΔDCR(10%-90%) is the difference between the maximum and minimum values ​​of the battery's DC resistance during the process of charging the battery from 10% SOC to 90% SOC. Therefore, the impedance fluctuation of the positive electrode active material is small within a wide SOC range, resulting in better power output stability.

[0027] In some embodiments of this application, DCR(90%) / DCR(50%) is 1.05~1.4; optionally, 1.05~1.3; wherein, DCR(90%) is the DC resistance corresponding to the battery at 90% SOC, and DCR(50%) is the DC resistance corresponding to the battery at 50% SOC. Therefore, the impedance rise of the positive electrode active material is relatively small in the high SOC range, and the impedance stability is good. Attached Figure Description

[0028] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, wherein, Figure 1 This is a schematic diagram of the structure of a positive electrode active material according to an embodiment of this application; Figure 2 These are SEM and EDS images of the positive electrode active material of Example 1 of this application; Figure 3 This is a comparison chart of DSC tests between Example 1 and Comparative Example 1 of this application; Figure 4 This is a comparison chart of HPPC test DCR between Example 1 and Comparative Example 1 of this application.

[0029] Explanation of reference numerals in the attached figures: 1-Matrix, 2-Covering layer. Detailed Implementation

[0030] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0031] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0032] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0033] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0034] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] In the description of this application, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. "First feature" and "second feature" may include one or more of that feature.

[0036] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0037] In this application, the order in which the steps are written does not imply a strict execution order and does not limit the implementation process. The specific execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps in this application can be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0038] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0039] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0040] Under high charge, the surface of LCO cathode active material is prone to structural reconstruction, forming a surface phase different from the host layered structure, accompanied by lattice oxygen release. This leads to decreased thermal stability and increased interfacial side reactions. Furthermore, during high-voltage cycling, the enhanced interfacial reaction between the material and the electrolyte may cause a gradual increase in electrode interfacial impedance, thereby affecting the battery's rate performance and cycle stability.

[0041] To improve the structural stability of LCO cathode active materials under high-voltage conditions, single-crystal LCO materials are employed in related technologies. Compared with traditional polycrystalline secondary particle materials, single-crystal LCO particles lack obvious grain boundary structures, which reduces grain boundary stress concentration during charge and discharge processes, thereby lowering the risk of particle cracking and pulverization, and improving the material's structural stability and cycle life. However, due to the lack of grain boundary structures within single-crystal particles, the material surface becomes the primary location for electrochemical reactions and structural evolution; therefore, the interfacial structural stability has a more significant impact on the performance of single-crystal LCO materials.

[0042] Under high voltage and high SOC conditions, local structural reconstruction easily occurs on the surface of single-crystal LCO materials, accompanied by oxygen release and enhanced interfacial side reactions, leading to decreased thermal stability and increased internal resistance of the battery. In terms of power performance, the variation of DC internal resistance of the battery in different SOC ranges directly affects its dynamic power output capability. The HPPC (Hybrid Pulse Power Characterization) method is commonly used to evaluate the DCR characteristics of the battery under different SOC conditions. If the material exhibits a significant increase in impedance or impedance fluctuations in the high SOC region, it may affect the power stability of the battery under high charge conditions.

[0043] Furthermore, during the sintering process of the positive electrode active material, a certain amount of excess lithium source is usually added to compensate for the volatilization of lithium under high-temperature conditions. After sintering, a certain amount of free lithium salt, such as LiOH or Li₂CO₃, may remain on the material surface. These substances are strongly alkaline and readily react with moisture or carbon dioxide in the air, potentially exacerbating interfacial side reactions between the electrode and the electrolyte during battery cycling, thereby affecting the interfacial stability and electrochemical performance of the positive electrode active material.

[0044] To improve the interfacial stability of LCO cathode active materials under high-voltage conditions, related technologies typically introduce oxide, phosphate, or other inorganic compound coating layers onto the particle surface to reduce direct contact between the electrolyte and the material surface. However, for single-crystal LCO materials, forming a continuous and dense coating layer may, to some extent, affect the migration process of lithium ions on the particle surface, thereby increasing interfacial polarization. Therefore, how to ensure interfacial stability while avoiding the adverse effects of excessive coating on ion transport, and further improve the impedance stability and thermal stability of LCO cathode active materials over a wide SOC range, remains an important technical problem to be solved in this field.

[0045] In the first aspect of this application, a positive electrode active material is proposed, with reference to Figure 1The positive electrode active material includes: a substrate 1 comprising lithium cobalt oxide; and a coating layer 2, which at least partially coats the surface of the substrate 1, comprising a composite phosphate and including multiple spaced island structures. After ball milling perturbation treatment, the mass fraction of phosphorus (P) in the positive electrode active material is retained at no less than 70%, and / or the mass fraction of titanium (Ti) in the positive electrode active material is retained at no less than 70%. The ball milling perturbation treatment is performed using a planetary ball mill with a main disk rotation speed of 200 rpm for 20 minutes, using ball stones with a diameter of 3 mm. This improves the surface structure stability of the positive electrode active material, reduces interfacial side reactions, and enhances impedance and thermal stability under high SOC conditions. Simultaneously, the coating layer exhibits good interfacial bonding stability with the substrate. The island-shaped coating layer improves the surface stability of the substrate while retaining a portion of the substrate surface as a lithium-ion migration channel, thus achieving a balance between interfacial protection and ion transport.

[0046] As an example, after ball milling and disturbance treatment, the mass fraction retention rate of P element in the positive electrode active material can be 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, or 90%, etc.

[0047] As an example, after ball milling disturbance treatment, the mass fraction retention rate of Ti element in the positive electrode active material can be 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, or 90%, etc.

[0048] In this application, the element retention rate was determined according to the following standard ball milling disturbance method. A Nanjing University Instruments QM-3SP2 planetary ball mill was used for testing. The specific steps of the ball milling disturbance treatment were as follows: 5.000g of the positive electrode active material sample was placed in a 100mL zirconia ball mill jar, and 40.0g of zirconia balls with a diameter of 3mm were added, resulting in a ball-to-material mass ratio of 8:1. Both the ball mill jar and the balls were made of zirconia. After sealing the ball mill jar, dry ball milling disturbance treatment was performed. The main disc speed of the ball mill was 200rpm, and the milling time was 20min. No alternating forward and reverse rotation was used during the milling process.

[0049] After ball milling, all samples were transferred to beakers, and 50 mL of anhydrous ethanol was added. The mixture was dispersed for 1 min under ultrasonic power of 100 W. The dispersion was then transferred to 50 mL centrifuge tubes and centrifuged for 3 min under a relative centrifugal force of 300 times the acceleration due to gravity (300 × g). The sediment was collected as the main particles of the positive electrode active material, and the supernatant was discarded as the detached fine powder. The obtained main particles of the positive electrode active material were dried in a 110℃ forced-air drying oven for 12 h.

[0050] In this application, the Ti and P element content of the positive electrode active material before and after ball milling disturbance treatment was determined by ICP testing. The mass retention rate of the elements was calculated according to the following formula: R i =C i,after / C i,before ×100%; Among them, R i The mass fraction retention rate of element i, expressed in % C i,before The mass fraction of element i in the positive electrode active material before ball milling disturbance treatment; C i,after The mass fraction of element i in the bulk particles of the positive electrode active material after ball milling disturbance treatment; element i includes at least one of Ti and P.

[0051] Each sample was tested in parallel three times, and the arithmetic mean was taken as the mass fraction retention rate of element i.

[0052] In some embodiments of this application, after ball milling and disturbance treatment, the mass fraction retention rate of P element in the positive electrode active material is not less than 80%, and / or the mass fraction retention rate of Ti element in the positive electrode active material is not less than 80%. Therefore, the coating layer is less likely to detach from the surface of the matrix particles under mechanical disturbance conditions, exhibits better interfacial bonding stability between the coating layer and the matrix, and has stronger resistance to detachment.

[0053] In some embodiments of this application, the average size of a single island structure is 120nm~260nm, for example, it can be 120nm, 140nm, 160nm, 180nm, 200nm, 220nm, 240nm or 260nm, etc.; optionally, 150nm~220nm. This island structure forms multiple interface control points on the substrate surface, which can limit the local surface structure reconstruction of the positive electrode active material under high SOC conditions and disperse surface stress, thereby improving the surface structure stability of the positive electrode active material. Simultaneously, since the coating layer is not a continuous and dense cover, a portion of the substrate area is still retained on the surface of the positive electrode active material particles as a lithium-ion migration channel, thereby reducing the obstruction of lithium-ion diffusion caused by the coating layer.

[0054] In SEM images, individual, independent, and clearly defined island-like regions are considered as a single island structure. The maximum and minimum Feret diameters of this island structure in the 2D projection image are measured, and their arithmetic mean is taken as the size of the individual island structure. The calculation formula is as follows: d i =(L max,i +L min,i ) / 2; d i Let i be the size of the i-th island structure; L max,i Let be the maximum Freette diameter of the i-th island structure; L min,i Let be the minimum Freette diameter of the i-th island structure.

[0055] The "average size of a single island structure" d refers to the size d of 50 island structures. i The arithmetic mean.

[0056] In some embodiments of this application, the minimum spacing between adjacent island structures is 200nm to 600nm, for example, it can be 200nm, 300nm, 400nm, 500nm, or 600nm; optionally, it is 300nm to 500nm. Therefore, under high SOC conditions, the local surface structure reconstruction of the positive electrode active material can be limited, and surface stress can be dispersed, thereby improving the surface structure stability of the positive electrode active material. Simultaneously, since the coating layer is not a continuous and dense cover, a portion of the matrix region remains on the surface of the positive electrode active material particles as a lithium-ion migration channel, thereby reducing the obstruction of lithium-ion diffusion caused by the coating layer.

[0057] In this application, the minimum spacing between adjacent island structures refers to the shortest straight-line distance between the boundaries of two adjacent island-shaped covering regions located on the visible outer surface of the same matrix particle.

[0058] When multiple island-like structures exist on the surface of a single positive electrode active material particle, the shortest boundary distance between each adjacent island-like structure in the SEM image is measured, and the arithmetic mean of the obtained values ​​is defined as the island spacing on the particle surface; further, the arithmetic mean of the results measured for 30 particles is taken as the spacing between adjacent island-like structures.

[0059] In some embodiments of this application, the coverage of the coating layer on the substrate surface is 2% to 20%, for example, it can be 2%, 5%, 8%, 10%, 12%, 15%, 18%, or 20%; optionally, 5% to 15%. Thus, a portion of the substrate area is still retained on the surface of the positive electrode active material particles as a lithium-ion migration channel, which helps to reduce the adverse effects of over-coating on lithium-ion transport.

[0060] In this application, the coverage of the coating layer on the substrate surface refers to the ratio of the area occupied by the island-shaped coating layer within the visible outer surface projection area of ​​a single substrate particle to the total visible outer surface projection area of ​​that substrate particle, expressed as a percentage. The calculation formula is: η=A c / A t ×100%; Where η is the coverage of the coating layer on the substrate surface; A c The area occupied by the coating layer; A t This represents the total projected area of ​​the visible outer surface of the single matrix particle.

[0061] It is understandable that when multiple dispersed island-like coated regions exist on the same particle surface, A c This represents the sum of the areas of each island-shaped coating region. The coverage rate is the arithmetic mean of the results measured for no fewer than 30 positive electrode active material particles.

[0062] In some embodiments of this application, the composite phosphate includes Al, Ti, P, and Q elements, wherein the Q element includes at least one of Ge, In, Y, Sc, Mg, Zr, Nb, Mn, Co, Ni, Mo, and W. The QOP bond in the composite phosphate has a high bond energy, which can improve the lattice stability of the cathode active material surface and suppress oxygen release behavior under high-temperature conditions. Therefore, it is beneficial to improve the lattice stability of the cathode active material surface and suppress oxygen release behavior under high-temperature conditions.

[0063] In some embodiments of this application, the Q element includes at least one of Nb, Zr, Mg, and Y; optionally, the Q element includes Nb and / or Zr; more optionally, the Q element includes Nb. The aforementioned Q element can form stable QO bonds with oxygen and, together with the phosphate structural units, construct a stable composite phosphate coating structure. Nb and Zr elements have strong metal-oxygen bonding characteristics, which can improve the thermal and chemical stability of the coating layer and enhance the confinement effect of the coating layer on the oxygen structure of the lithium cobalt oxide surface, thereby reducing the tendency for surface structure reconstruction and oxygen release of the cathode active material under high SOC conditions. Mg element helps to regulate the local ion transport environment of the coating layer and reduce interfacial polarization; Y element helps to enhance the structural stability and interfacial tolerance of the coating layer. Therefore, the composite phosphate coating layer containing the aforementioned Q element can further improve the impedance stability and thermal stability of the cathode active material under high SOC conditions.

[0064] In some embodiments of this application, the molar ratio of Al, Ti, P, and Q elements in the coating layer is (0.2~0.4):(1.4~2.0):(1.8~3.1):(0~0.1), for example, 0.2:2.0:1.8:0.1, 0.4:1.4:3.1:0.05, 0.3:1.8:2.5:0, 0.2:1.5:3.1:0.1, or 0.4:2.0:2.0:0.06, etc. This is beneficial for improving the surface lattice stability of the positive electrode active material and suppressing oxygen release behavior under high-temperature conditions. It should be noted that the above ratios are used to characterize the composition range of each element in the coating layer, rather than limiting it to a single specific chemical formula.

[0065] In some embodiments of this application, the chemical formula of the matrix satisfies: Li x Co y M z O2, wherein 0.95≤x≤1.05, 0.9≤y≤1, 0≤z≤0.1; M includes at least one of Mg, Al, Ti, Zr, Y, La, and Nb. This is beneficial for improving the structural stability of the positive electrode active material and reducing the occurrence of side reactions.

[0066] As an example, x can be 0.95, 0.97, 0.99, 1.01, 1.03, or 1.05, etc.; y can be 0.9, 0.92, 0.94, 0.96, 0.98, or 1, etc.; z can be 0, 0.02, 0.04, 0.06, 0.08, or 0.1, etc.

[0067] In some embodiments of this application, the median particle size of the positive electrode active material is 2μm to 20μm, for example, it can be 2μm, 4μm, 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm, or 20μm. This is beneficial for shortening the lithium-ion diffusion path.

[0068] In this application, the median particle size of the positive electrode active material was obtained by measuring a Malvern 3000 particle size analyzer.

[0069] In some embodiments of this application, the compaction density of the positive electrode active material is 3.9 g / cm³. 3 ~4.4g / cm 3 For example, it can be 3.9 g / cm³. 3 4.0g / cm 3 4.1g / cm 3 4.2g / cm 3 4.3g / cm 3 Or 4.4g / cm 3 This is beneficial for improving the specific capacity of the positive electrode active material.

[0070] In this application, the test method for compaction density is GB / T 44330-2024 "Determination of compaction density of lithium-ion battery cathode material powder".

[0071] In some embodiments of this application, ΔW = W0 - W1 is 300 J / g to 1000 J / g, for example, it can be 300 J / g, 400 J / g, 500 J / g, 600 J / g, 700 J / g, 800 J / g, 900 J / g, or 1000 J / g, etc.; optionally, it is 400 J / g to 1000 J / g; wherein, W0 is the unit heat release of the matrix as tested by DSC, and W1 is the unit heat release of the positive electrode active material as tested by DSC. This helps to reduce the heat release of the positive electrode active material and improve its thermal stability.

[0072] In this application, the specific test method for DSC is as follows: the coin cell CC-CV is charged and discharged twice at 0.2C, charged to 4.6V at 0.2C, the battery is disassembled, the positive electrode is cleaned with DMC, the positive electrode is removed and dried, and a 4mm×4mm circular piece is cut from the electrode for testing. The DSC testing equipment is Mettler TGS / DSC3+, and the test conditions are: temperature: 35℃~350℃, reaction gas: N2, gas flow rate: 50mL / min, heating rate: 5℃ / min.

[0073] In some embodiments of this application, ΔJ = J0 - J1 is 50 ppm to 300 ppm, for example, it can be 50 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, or 300 ppm; where J1 is the residual alkali content of the positive electrode active material, and J0 is the residual alkali content of the matrix. This indicates that the coating material has an interfacial trapping effect on residual lithium on the matrix surface during sintering, which helps to reduce the accumulation of free lithium salts on the surface of the positive electrode active material particles and reduces the resulting interfacial side reactions.

[0074] In some embodiments of this application, J1 is 100ppm to 500ppm, for example, it can be 100ppm, 200ppm, 300ppm, 400ppm, or 500ppm. Therefore, the residual alkali content on the surface of the positive electrode active material is relatively low, which helps to reduce the occurrence of interfacial side reactions.

[0075] In this application, the residual alkali content was determined according to GB / T 41704-2022 and expressed as Li2CO3 equivalent.

[0076] In some embodiments of this application, the positive electrode active material comprises a single crystal. Since there are no grain boundary structures within single crystal particles, the surface of the positive electrode active material becomes the primary region for structural evolution and interfacial reactions. Therefore, this application utilizes an island-like coating layer to modulate the surface of the positive electrode active material, which helps improve the interfacial stability and impedance stability of the single-crystal positive electrode active material under high SOC conditions.

[0077] In a second aspect, this application proposes a method for preparing the aforementioned positive electrode active material. This application prepares the coating material through a co-precipitation process, and during sintering, the coating material undergoes an interfacial reaction with residual lithium compounds on the surface of the matrix material, thereby constructing a discretely distributed composite phosphate island-like coating layer on the surface of the lithium cobalt oxide matrix. This reduces the accumulation of free lithium salts on the surface of the positive electrode active material particles. Furthermore, this preparation method is simple, feasible, easy to operate, and suitable for large-scale promotion. Specifically, the method includes: S1: Mix aluminum source, titanium source, optional Q source and phosphorus source, adjust pH to 4.5~9.0, carry out co-precipitation reaction, and age to obtain coating material.

[0078] It is understood that the coating material in the co-precipitation stage is a compound containing Al, Ti, Q, and PO4 structural units, and its molecular formula is not limited. Furthermore, the coating material in the co-precipitation stage does not contain lithium or contains virtually no lithium. During the subsequent sintering process, the coating material can undergo a solid-phase reaction with the residual lithium compounds on the substrate surface, allowing some lithium to enter the coating layer structure, thereby forming a composite phosphate structure coating layer on the particle surface. This composite phosphate structure coating layer may contain lithium-containing phosphate phases and / or lithium-free phosphate phases.

[0079] In some embodiments of this application, the aluminum source includes at least one of aluminum sulfate, aluminum nitrate, and aluminum chloride; and / or, the titanium source includes at least one of titanium tetrachloride and titanium oxysulfate; and / or, the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium monohydrogen phosphate, sodium monohydrogen phosphate, potassium monohydrogen phosphate, ammonium phosphate, sodium phosphate, and potassium phosphate. Therefore, the raw materials are widely available, the cost is low, and large-scale promotion is convenient.

[0080] In some embodiments of this application, the temperature of the coprecipitation reaction is 30℃~90℃ (e.g., 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, or 90℃), and the rotation speed is 400rpm~1200rpm (e.g., 400rpm, 600rpm, 800rpm, 1000rpm, or 1200rpm); and / or, the temperature of the aging treatment is 25℃~70℃ (e.g., 25℃, 30℃, 40℃, 50℃, 60℃, or 70℃), and the time is 0.2h~2h (e.g., 0.2h, 0.5h, 1h, 1.2h, 1.5h, or 2h). This facilitates the reaction and yields a coating material with a suitable particle size.

[0081] In some embodiments of this application, the median particle size D of the coating material is... 50 Satisfies: 0.25μm < D 50 <5μm, for example, it can be 0.26μm, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 4.9μm, etc.; optionally, 0.25μm <D 50 <3μm; and / or, the specific surface area of ​​the coating material is 20m². 2 / g~90m 2 / g, for example, can be 20m 2 / g、30m 2 / g、40m 2 / g, 50m 2 / g、60m 2 / g、70m 2 / g、80m 2 / g or 90m 2 / g etc.; optional, 30m 2 / g~60m 2 / g. This facilitates the formation of a coating layer with moderate coverage.

[0082] In some specific examples, the methods for synthesizing the coating material include: (1) Dissolve a soluble Al source, a Ti source, and an optional Q source in pure water to obtain a mixed metal salt solution A; (2) Dissolve the phosphorus source in pure water to obtain phosphorus source solution B; (3) Prepare pH adjustment solution C; (4) Add phosphorus source solution B to the reactor, turn on the stirrer, and raise the temperature to the required reaction temperature. Add pH value adjuster solution C to adjust the pH value of phosphorus source solution B. Add mixed metal salt solution A and pH value adjuster solution C in parallel to the reactor and react at a certain pH value to obtain slurry (the temperature for pH value testing is 25℃, which will not be described in detail later). (5) Stir and age the slurry at a temperature of 25℃~70℃ for 0.2h~2h to obtain aged slurry; (6) The aged slurry is filtered and washed to obtain filter cake; (7) The filter cake is dried to obtain dried material; (8) The dried material is crushed to obtain the coating material.

[0083] Furthermore, pH adjusters include sodium hydroxide, potassium hydroxide, ammonia, sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid, etc.

[0084] Furthermore, the concentration of the mixed metal salt solution A is 0.5 mol / L to 3 mol / L, preferably 0.8 mol / L to 2 mol / L.

[0085] Furthermore, the concentration of phosphorus source solution B is 0.5 mol / L to 4 mol / L, preferably 1 mol / L to 3 mol / L.

[0086] Furthermore, the concentration of pH adjuster solution C is 5 mol / L to 15 mol / L.

[0087] Furthermore, the water used for washing is pure water at 30℃~95℃, and the washing is continued until the filtrate is neutral. The preferred washing water temperature is 45℃~80℃.

[0088] Furthermore, the drying process can employ equipment such as blower ovens, vacuum ovens, and tray dryers. The drying temperature is 100℃~180℃, and the drying time is 3h~24h.

[0089] Furthermore, the crushing process can utilize crushing equipment such as soybean milk makers, roller mills, colloid mills, mechanical mills, and air jet mills.

[0090] S2: Under an oxygen-containing atmosphere, the coating material and lithium cobalt oxide are mixed and then sintered to obtain the positive electrode active material; wherein the sintering temperature is 700℃~900℃.

[0091] During the sintering process, the phosphate structure in the coating material can undergo an interfacial solid-phase reaction with the residual lithium compounds on the surface of the lithium cobalt oxide, allowing some lithium to enter the coating layer structure, thereby reducing the accumulation of free lithium salts on the surface of the lithium cobalt oxide. Due to the reduction in free lithium salts, the enrichment of alkaline substances on the surface of the positive electrode active material is suppressed, which helps to reduce the hygroscopicity of the positive electrode active material and decrease interfacial side reactions.

[0092] In this application, the coating layer is formed by the interfacial reaction between the coating material containing Al, Ti and PO4 structural units and the residual lithium on the surface of the lithium cobalt oxide during the sintering process. Therefore, the coating layer and the lithium cobalt oxide substrate are not simply physically attached, but form a more stable interfacial bonding state. The resulting coating layer is distributed in an island-like manner on the surface of the lithium cobalt oxide substrate.

[0093] During the sintering process, the coating material can undergo an interfacial reaction with residual lithium compounds on the surface of lithium cobalt oxide, allowing lithium to enter the composite phosphate structure and forming a lithium-containing phosphate phase such as the Li-Al-Ti-PO4 phase, or LATP phase. Simultaneously, the coating layer may also contain other phosphate phases that do not contain lithium. Furthermore, due to variations in the content of residual lithium compounds, the degree of reaction, and diffusion conditions during the sintering process, the final chemical composition of the coating layer is not limited to a single chemical formula.

[0094] In some embodiments of this application, the sintering process is a single-stage sintering, wherein the heating rate of the single sintering is 1℃ / min to 5℃ / min (e.g., 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, or 5℃ / min, etc.), the temperature is 700℃ to 900℃ (e.g., 700℃, 750℃, 800℃, 850℃, or 900℃, etc.), and the time is 5h to 20h (e.g., 5h, 8h, 10h, 12h, 15h, 18h, or 20h, etc.). Therefore, the single-stage heating method is beneficial for improving sintering efficiency and shortening reaction time.

[0095] In some embodiments of this application, the sintering process is carried out in a segmented heating manner, including: sequentially performing a first sintering process, a second sintering process, and a third sintering process. This facilitates the formation of a composite phosphate coating layer characterized by an island-like distribution, while preventing premature agglomeration or continuous densification of the coating material.

[0096] Furthermore, the heating rate of the first sintering treatment is 1℃ / min to 5℃ / min (e.g., 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, or 5℃ / min), the temperature is 200℃ to 450℃ (e.g., 200℃, 250℃, 300℃, 350℃, 400℃, or 450℃), and the time is 0.5h to 5h (e.g., 0.5h, 1h, 2h, 3h, 4h, or 5h). This removes residual moisture, volatile components, and some weakly bound substances from the coating material and promotes stable adhesion of the coating material to the surface of the matrix particles.

[0097] Furthermore, the heating rate of the second sintering treatment is 1℃ / min to 5℃ / min (e.g., 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, or 5℃ / min), the temperature is 450℃ to 700℃ (e.g., 450℃, 500℃, 550℃, 600℃, 650℃, or 700℃), and the time is 1h to 8h (e.g., 1h, 2h, 3h, 4h, 5h, 6h, 7h, or 8h). This promotes a solid-phase reaction between the coating material and the residual lithium compounds on the substrate surface, allowing some lithium to enter the composite phosphate structure, thereby forming an initial composite phosphate coating layer on the surface of the substrate particles.

[0098] Furthermore, the heating rate of the third sintering treatment is 1℃ / min to 3℃ / min (e.g., 1℃ / min, 2℃ / min, or 3℃ / min), the temperature is 700℃ to 900℃ (e.g., 700℃, 750℃, 800℃, 850℃, or 900℃), and the time is 3h to 15h (e.g., 3h, 5h, 7h, 9h, 11h, 13h, or 15h). This promotes further densification, stabilization, and localized crystallization of the coating layers, thereby forming a composite phosphate coating layer.

[0099] In some embodiments of this application, after sintering, the furnace is cooled to room temperature; in some embodiments, controlled cooling can also be used, with a cooling rate of 1°C / min to 5°C / min.

[0100] In some embodiments of this application, the oxygen-containing atmosphere includes air, oxygen-enriched air, or an oxygen / air mixture atmosphere, preferably an atmosphere with an oxygen volume fraction of not less than 21%.

[0101] In some embodiments of this application, based on the total mass of the lithium cobalt oxide, the amount of coating material added is 0.01 wt% to 5 wt%, for example, 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%, etc.; optionally, 0.01 wt% to 2 wt%. This ensures the stability of the cathode active material interface while reducing the adverse effects of over-coating on lithium-ion transport. It is understood that since the coating material can react with residual lithium compounds on the substrate surface during sintering, the final composition of the coating layer may change. Therefore, in this application, the coating layer content is characterized by the amount of coating material added before sintering.

[0102] In a third aspect of this application, a battery is provided, including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive active material layer located on at least one side of the positive current collector, the positive active material layer including the positive active material described in the first aspect of this application or a positive active material prepared by the method described in the second aspect of this application.

[0103] In some embodiments of this application, ΔDCR(10%-90%) / DCR(10%-90%)avg is 14%~22%, for example, it can be 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, or 22%, etc.; optionally, it is 14%~20%; wherein, DCR(10%-90%)avg is the average value of the DC resistance of the battery during the process of charging the battery from 10% SOC to 90% SOC, and ΔDCR(10%-90%) is the difference between the maximum and minimum values ​​of the DC resistance of the battery during the process of charging the battery from 10% SOC to 90% SOC. Therefore, the impedance fluctuation of the positive electrode active material is small within a wide SOC range, and the impedance increase trend is effectively suppressed, which is beneficial to improving the power stability of the battery.

[0104] In some embodiments of this application, the DCR(90%) / DCR(50%) is 1.05~1.4, for example, it can be 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35 or 1.4, etc.; optionally, it is 1.05~1.3; wherein, DCR(90%) is the DC resistance corresponding to the battery at 90% SOC, and DCR(50%) is the DC resistance corresponding to the battery at 50% SOC. Therefore, the impedance rise of the positive electrode active material is small in the high SOC range, and the impedance stability is good.

[0105] In this application, the DCR test method is as follows: the test is conducted according to the HPPC (Hybrid Pulse Power Characterization) method shown in the FreedomCAR Power Assisted Hybrid Electric Vehicle Battery Test Manual.

[0106] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0107] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0108] Example 1 (1) Preparation of coating material According to the molar ratio of Al:Ti = 0.3:1.7, aluminum sulfate and titanium oxysulfate were weighed and dissolved in deionized water to prepare a 1 mol / L mixed salt solution A; Phosphoric acid was diluted to obtain phosphorus source solution B with a concentration of 1.5 mol / L; Prepare ammonia solution with a concentration of 10 mol / L as conditioning solution C; Add phosphorus source solution B to the reactor, turn on the stirrer at 700 rpm, heat to 50°C, add regulator solution C to adjust the pH value of phosphorus source solution B to 6.0, add mixed salt solution A and pH regulator solution C in parallel to the reactor, and react at pH 6.0 to obtain slurry; The slurry obtained from the reaction was stirred and aged at a temperature of 50°C for 1 hour to obtain aged slurry. The aged slurry was washed with 50°C pure water to obtain filter cake; The filter cake was placed in a forced-air drying oven at 120℃ and dried for 12 hours to obtain the dried material; The dried material was crushed using a colloid mill to obtain the coating material. SEM and EDS images of the coating material are shown below. Figure 2 .

[0109] (2) Preparation of positive electrode active material The coating material precursor obtained in step (1) was mixed evenly with the single-crystal LiCoO2 matrix and placed in a corundum sagger. It was then sintered in an oxygen-containing atmosphere (oxygen volume fraction of 30%) to obtain the coated positive electrode active material. Based on the total mass of the single-crystal LCO matrix, the amount of coating material added was 1.0 wt%.

[0110] Specifically, the sintering process includes: performing a first sintering process, a second sintering process, and a third sintering process in sequence, followed by furnace cooling to room temperature; The heating rate of the first sintering treatment was 2℃ / min, the temperature was 300℃, and the time was 2h. The heating rate for the second sintering treatment was 2℃ / min, the temperature was 600℃, and the time was 3h. The heating rate for the third sintering treatment was 1℃ / min, the temperature was 800℃, and the time was 10h.

[0111] Comparative Example 2 Al2O3, TiO2, (NH4)2HPO4, and single-crystal LiCoO2 matrix were uniformly mixed and placed in a corundum sagger. Sintering was then performed under an oxygen-containing atmosphere (oxygen volume fraction of 30%) to obtain a coated positive electrode active material. Based on the total mass of the single-crystal LCO matrix, the sum of the added amounts of Al2O3, TiO2, and (NH4)2HPO4 was 1.0 wt%. Specifically, the sintering process included: sequentially performing a first sintering treatment, a second sintering treatment, and a third sintering treatment, followed by furnace cooling to room temperature. The heating rate of the first sintering treatment was 2℃ / min, the temperature was 300℃, and the time was 2h. The heating rate for the second sintering treatment was 2℃ / min, the temperature was 600℃, and the time was 3h. The heating rate for the third sintering treatment was 1℃ / min, the temperature was 800℃, and the time was 10h.

[0112] The differences between other embodiments and comparative examples and embodiment 1 are shown in Tables 1-1, 1-2 and 1-3.

[0113] Table 1-1

[0114] Table 1-2

[0115] Table 1-3

[0116] In this context, " / " indicates that the substance was not added or that the step was not performed.

[0117] The positive electrode active materials prepared in the above embodiments and comparative examples were subjected to the aforementioned tests, and the test results are shown in Table 2.

[0118] Table 2

[0119] Assembly of button cells: First, a mixture of non-aqueous electrolyte secondary battery positive electrode active material, acetylene black, and polyvinylidene fluoride (PVDF) in a mass ratio of 95:2.5:2.5 is coated onto aluminum foil and dried. The mixture is then stamped into a positive electrode sheet with a diameter of 12 mm and a thickness of 120 μm using a pressure of 100 MPa. Finally, the positive electrode sheet is placed in a vacuum drying oven and dried at 120 °C for 12 h.

[0120] The negative electrode uses a Li metal sheet with a diameter of 17 mm and a thickness of 1 mm; the separator uses a polyethylene porous membrane with a thickness of 25 μm; the electrolyte uses a mixture of equal amounts of 1 mol / L LiPF6, ethylene carbonate (EC), and diethyl carbonate (DEC).

[0121] The positive electrode, separator, negative electrode, and electrolyte were assembled into a 2025 coin cell in an Ar gas glove box with a water content and oxygen content of less than 5 ppm. The cell at this stage was considered an unactivated cell.

[0122] After fabricating the button cell, let it stand for 24 hours. Once the open-circuit voltage stabilizes, charge it at a current density of 20 mA / g to the cutoff voltage of 4.6V, and then charge it at a constant voltage of 4.6V until the cutoff current is 0.024 mA. Then discharge it at the same current density to the cutoff voltage of 2.0V, and repeat the above process once more. The resulting cell is considered the activated cell.

[0123] The batteries assembled above were subjected to the aforementioned tests, and the test results are shown in Table 3.

[0124] Table 3

[0125] This application prepares a coating material through a co-precipitation process, and allows the coating material to undergo an interfacial reaction with residual lithium compounds on the surface of single-crystal LiCoO2 during sintering. This results in the construction of a discretely distributed composite phosphate island coating layer on the surface of single-crystal LiCoO2, which is beneficial for improving the surface structural stability of the cathode active material, reducing interfacial side reactions, and improving impedance stability and thermal stability under high SOC conditions. At the same time, the coating layer and the substrate have good interfacial bonding stability. After ball milling and disturbance treatment, the mass fraction retention of P and Ti in the cathode active material is not less than 70%.

[0126] from Figure 3It can be seen that the unit heat release of the positive electrode active material prepared in Example 1 is less than that of the positive electrode active material prepared in Comparative Example 1, and it has higher thermal stability.

[0127] from Figure 4 It can be seen that, compared with Comparative Example 1, the positive electrode active material prepared in Example 1 has smaller impedance fluctuations in a wide SOC range and higher battery power stability.

[0128] As can be seen from Examples 5 and 6, lowering the sintering temperature reduces the bonding tightness between the substrate and the coating layer, which in turn leads to a slight decrease in the mass fraction retention of P and Ti in the positive electrode active material after ball milling disturbance treatment, thus affecting the impedance stability and thermal stability under high SOC conditions.

[0129] As can be seen from Examples 7 to 10, extending the sintering time will cause the island particles to grow and agglomerate, increasing the spacing between the island structures.

[0130] Comparative Example 1 did not coat the substrate, resulting in large impedance fluctuations in the wide SOC range of the prepared positive electrode active material, a large impedance increase in the high SOC range, and poor power output stability.

[0131] Comparative Example 2 did not prepare the coating material by co-precipitation. Instead, the raw materials and the matrix were directly mixed and sintered. This resulted in uneven element distribution in the coating layer on the surface of the obtained positive electrode active material. After ball milling and disturbance treatment, the mass fraction retention rate of P and Ti in the positive electrode active material was low, and the impedance stability and thermal stability under high SOC conditions were poor.

[0132] Comparative Example 3 did not undergo a third sintering treatment, resulting in a smaller average size of individual island structures in the coating layer and a smaller spacing between adjacent island structures. After ball milling disturbance treatment, the mass fraction retention rate of P and Ti in the positive electrode active material was low, and the impedance stability and thermal stability under high SOC conditions were poor.

[0133] In Comparative Example 4, the amount of coating material added during the preparation of the positive electrode active material was relatively small, resulting in a coating layer coverage of only 1% on the substrate surface. Although the coating layer still had a certain degree of bonding stability with the substrate, the island-like composite phosphate coating structure was not sufficiently distributed on the substrate surface, making it difficult to fully cover the highly active surface sites and capture the residual lithium compounds on the substrate surface. Therefore, the reduction in residual alkali, the improvement in thermal stability, and the high SOC impedance stability of the positive electrode active material were all limited.

[0134] In Comparative Example 5, a larger amount of coating material was added during the preparation of the positive electrode active material. This increased the coating layer's coverage on the substrate surface to 25%. While the coating layer's ability to capture residual lithium compounds and improve thermal stability remained relatively stable, the excessively large coverage area led to the formation of clusters or over-coverage of some island-like structures. This reduced the channels available for lithium-ion migration on the substrate surface, increased interfacial polarization, and consequently, increased DCR fluctuations across a wide SOC range, with a significant rise in impedance at high SOC. Therefore, controlling the coating layer coverage within the range of 2%–20%, especially 5%–15%, achieves a better balance between interfacial protection and lithium-ion transport.

[0135] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode active material, characterized by, include: The matrix comprises lithium cobalt oxide; A coating layer, the coating layer at least partially covering the surface of the substrate, the coating layer comprising a composite phosphate, the coating layer comprising a plurality of spaced-apart island structures; After ball milling disturbance treatment, the mass fraction retention rate of P element in the positive electrode active material is not less than 70%, and / or the mass fraction retention rate of Ti element in the positive electrode active material is not less than 70%; wherein, the ball milling disturbance treatment is carried out using a planetary ball mill, the main disk rotation speed of the planetary ball mill is 200 rpm, the time is 20 min, and the diameter of the ball used is 3 mm.

2. The positive electrode active material according to claim 1, characterized by After ball milling and disturbance treatment, the mass fraction of P element in the positive electrode active material is maintained at not less than 80%, and / or the mass fraction of Ti element in the positive electrode active material is maintained at not less than 80%.

3. The positive electrode active material according to claim 1 or 2, characterized by The average size of a single island structure is 120 nm to 260 nm; optionally, 150 nm to 220 nm.

4. The positive electrode active material according to claim 3, characterized by The minimum spacing between adjacent island structures is 200nm~600nm; optionally, 300nm~500nm.

5. The positive electrode active material according to claim 1 or 2, characterized by The coating layer has a coverage of 2% to 20% on the substrate surface; optionally, 5% to 15%.

6. The positive electrode active material according to claim 1 or 2, characterized by The composite phosphate includes Al, Ti, P and Q elements, wherein the Q element includes at least one of Ge, In, Y, Sc, Mg, Zr, Nb, Mn, Co, Ni, Mo and W.

7. The positive electrode active material according to claim 6, characterized by The Q element includes at least one of Nb, Zr, Mg, and Y; optionally, the Q element includes Nb and / or Zr; further optionally, the Q element includes Nb.

8. The positive electrode active material according to claim 6, characterized in that, In the coating layer, the molar ratio of Al, Ti, P and Q elements is (0.2~0.4):(1.4~2.0):(1.8~3.1):(0~0.1).

9. The positive electrode active material according to claim 1 or 2, characterized in that, The chemical formula of the matrix satisfies: Li x Co y M z O2, Wherein, 0.95≤x≤1.05, 0.9≤y≤1, 0≤z≤0.1; M includes at least one of Mg, Al, Ti, Zr, Y, La, and Nb.

10. The positive electrode active material according to claim 1 or 2, characterized in that, The median particle size of the positive electrode active material is 2 μm to 20 μm; and / or, The compacted density of the positive electrode active material is 3.9 g / cm 3 4.4 g / cm 3 .

11. The positive electrode active material according to claim 1 or 2, characterized in that, ΔW = W0 - W1 is 300 J / g ~ 1000 J / g; optionally, 400 J / g ~ 1000 J / g; where W0 is the unit heat release of the matrix as tested by DSC, and W1 is the unit heat release of the positive electrode active material as tested by DSC.

12. The positive electrode active material according to claim 1 or 2, characterized in that, ΔJ = J0 - J1 is 50ppm to 300ppm; where J1 is the residual alkali content of the positive electrode active material and J0 is the residual alkali content of the matrix. Optionally, J1 is 100ppm to 500ppm.

13. The positive electrode active material according to claim 1 or 2, characterized in that, The positive electrode active material includes single crystals.

14. A method for preparing the positive electrode active material according to any one of claims 1 to 13, characterized in that, include: Aluminum source, titanium source, optional Q source, and phosphorus source are mixed, pH is adjusted to 4.5~9.0, co-precipitation reaction is carried out, and aging treatment is performed to obtain coating material; The coating material and lithium cobalt oxide are mixed and sintered under an oxygen-containing atmosphere to obtain the positive electrode active material. The sintering temperature is 700℃~900℃.

15. The method according to claim 14, characterized in that, The coprecipitation reaction is carried out at a temperature of 30℃~90℃ and a rotation speed of 400rpm~1200rpm; and / or, The aging process is carried out at a temperature of 25℃ to 70℃ for a time of 0.2h to 2h.

16. The method according to claim 15, characterized in that, The median particle size D of the coating material 50 satisfies: 0.25 pm < D 50 < 5 pm; optionally, 0.25 pm < D 50 < 3 pm; and / or, The specific surface area of the coating material is 20 m 2 / g ~ 90 m 2 / g; optionally, 30 m 2 / g ~ 60 m 2 / g.

17. The method according to claim 14, characterized in that, The aluminum source includes at least one of aluminum sulfate, aluminum nitrate, and aluminum chloride; and / or, The titanium source includes at least one of titanium tetrachloride and titanium oxysulfate; and / or, The phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium monohydrogen phosphate, sodium monohydrogen phosphate, potassium monohydrogen phosphate, ammonium phosphate, sodium phosphate, and potassium phosphate.

18. The method according to any one of claims 14 to 17, characterized in that, The sintering process is a single sintering process, wherein the heating rate of the single sintering is 1℃ / min~5℃ / min, the temperature is 700℃~900℃, and the time is 5h~20h.

19. The method according to any one of claims 14 to 17, characterized in that, The sintering process includes: performing a first sintering process, a second sintering process, and a third sintering process in sequence; Wherein, the heating rate of the first sintering treatment is 1℃ / min~5℃ / min, the temperature is 200℃~450℃, and the time is 0.5h~5h; and / or, The second sintering treatment has a heating rate of 1℃ / min to 5℃ / min, a temperature of 450℃ to 700℃, and a time of 1h to 8h; and / or, The heating rate of the third sintering treatment is 1℃ / min to 3℃ / min, the temperature is 700℃ to 900℃, and the time is 3h to 15h.

20. The method according to claim 14, characterized in that, Based on the total mass of the lithium cobalt oxide, the amount of the coating material added is 0.01wt% to 5wt%; optionally, 0.01wt% to 2wt%.

21. A battery, characterized in that, The invention includes a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active material layer located on at least one side of the positive current collector, the positive active material layer comprising the positive active material according to any one of claims 1 to 13 or the positive active material prepared by the method according to any one of claims 14 to 20.

22. The battery according to claim 21, characterized in that, ΔDCR(10%-90%) / DCR(10%-90%)avg is 14%~22%; optionally, 14%~20%; Wherein, DCR(10%-90%)avg is the average value of the DC resistance of the battery during the process of charging the battery from 10% SOC to 90% SOC, and ΔDCR(10%-90%) is the difference between the maximum and minimum values ​​of the DC resistance of the battery during the process of charging the battery from 10% SOC to 90% SOC.

23. The battery according to claim 22, characterized in that, DCR(90%) / DCR(50%) is 1.05~1.4; optionally, 1.05~1.3; Wherein, DCR(90%) is the DC resistance corresponding to the battery at 90% SOC, and DCR(50%) is the DC resistance corresponding to the battery at 50% SOC.

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