Positive electrode active material and preparation method therefor, secondary battery, and electric device

Abstract

Provided are a positive electrode active material and a preparation method therefor, a secondary battery, and an electric device. The positive electrode active material comprises a matrix and a coating layer, which at least partially coats the matrix. The positive electrode active material satisfies: W1＞W2, wherein based on the mass of the positive electrode active material, W1 is the mass content of Co in the coating layer, and W2 is the mass content of Co in the matrix. The positive electrode active material has a high discharge gram capacity, and provides a material basis for preparing a high-energy density battery.

Description

Positive electrode active material, preparation method thereof, secondary battery and electric device

[0001] Cross-references

[0002] This application claims priority to Chinese Patent Application No. 202311548622.3, filed on November 20, 2023, entitled “Positive Electrode Active Material, Preparation Method Thereof, Secondary Battery and Electrical Device,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to a positive electrode active material, a preparation method thereof, a secondary battery, and an electrical device. Background Art

[0004] In recent years, the application of secondary batteries has become increasingly widespread. They are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As secondary batteries have achieved tremendous development, higher requirements have been placed on their energy density. The positive electrode active material is a key component of secondary batteries, not only affecting the safety and cost of the battery, but also directly determining the battery's electrochemical performance. To achieve high-energy-density secondary batteries, it is necessary to adopt certain strategies to optimize the positive electrode active material and increase its discharge capacity.

[0005] Summary of the Invention

[0006] The present application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode active material, which has a high discharge gram capacity and provides a material basis for preparing high energy density batteries.

[0007] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a positive electrode active material, including a substrate and a coating layer at least partially covering the substrate, and the positive electrode active material satisfies: W1>W2, wherein W1 is the mass content of the Co element in the coating layer, and W2 is the mass content of the Co element in the substrate, based on the mass of the positive electrode active material.

[0008] On the one hand, the coating layer on the surface of the substrate is a Co-rich layer. The coating layer is rich in Co doping, which can improve the conductivity of active ions, reduce the charge transfer impedance at the material interface, improve the capacity platform of the positive electrode active material in the low voltage range, and improve the discharge capacity of the positive electrode active material. At the same time, the coating layer on the surface of the substrate is rich in Co, which can also reduce the residual lithium impurities on the surface of the material and improve its cycle stability. On the other hand, the substrate is a Co-poor area, and the mass content of the Co element in the matrix is ​​small. Its mass content in the matrix is ​​small, which provides a larger mass content for the Ni element in the matrix that provides the electrons required for electrochemistry, making it possible for the positive electrode active material to be a high-nickel material, which can effectively improve the discharge capacity and cycle performance of the positive electrode active material.

[0009] In summary, controlling the coating layer to be a Co-rich layer and the matrix to be a Co-poor area can increase the discharge capacity of the positive electrode active material, provide a material basis for the preparation of high energy density batteries, and effectively improve the battery's cycle performance and extend the battery's service life.

[0010] In any embodiment, based on the mass of the positive electrode active material, the mass content W1 of the Co element in the coating layer is 0.4%-1.6%, and optionally 0.9%-1.4%.

[0011] The mass content of the Co element in the coating layer is within an appropriate range, so that the Co element is evenly and tightly wrapped on the positive electrode active material matrix, effectively improving the structural properties of the material. At the same time, it can also reduce the possibility of island accumulation due to excessive coating, reduce the influence of island accumulation on material properties, and make the positive electrode active material have a high discharge capacity. At the same time, the material has high cycle stability, the battery has a high number of cycles, and the battery performance is comprehensively improved.

[0012] In any embodiment, based on the mass of the positive electrode active material, the mass content W2 of the Co element in the matrix is ​​less than or equal to 0.02%, and can be optionally 0%.

[0013] The Co element in the matrix is ​​within a suitable range and can provide a larger mass content for the Ni element in the matrix that provides the electrons required for electrochemistry, so that the positive electrode active material has a high discharge capacity and the battery has excellent cycle performance.

[0014] In any embodiment, the matrix further includes a doping element M, and the M element includes one or more of Ba, W, Nb, Bi, Mg, Na, Sn, Y, and Sb, and can be optionally one or more of Ba, Y, and Sb.

[0015] The matrix contains doping elements such as Ba, W, Nb, Bi, Mg, Na, Sn, Y or Sb, which can weaken the tendency of lithium-nickel mixing in the positive electrode active material, improve the cycle stability of the material, and increase the cycle life of the battery.

[0016] In any embodiment, the mass content of the M element is 200 ppm to 800 ppm based on the mass of the positive electrode active material.

[0017] By controlling the mass content of the doping element M within an appropriate range, the purpose of reducing the tendency of lithium-nickel mixing in the positive electrode active material can be achieved. At the same time, it also reduces the negative impact of excessive content of the doping element M on the high mass content of the Ni element in the matrix, thereby affecting the discharge capacity of the positive electrode active material.

[0018] In any embodiment, the matrix comprises lithium nickelate.

[0019] In any embodiment, the coating layer further includes a doping element N, and the N element includes one or both of B and Al; optionally, based on the mass of the positive electrode active material, the mass content of the N element is 200 ppm-700 ppm.

[0020] Al and B can form glassy substances such as LiAlO2 or Li3BO3 with the positive electrode active material matrix. The above-mentioned glassy substances can be wrapped at the grain boundaries of the particles, which can inhibit the generation of oxygen defects, improve the cycle performance of the battery, and reduce the gas production of the battery. At the same time, the glassy substances have excellent ion conductivity, which can increase the transmission rate of lithium ions on the material surface, reduce the DC internal resistance of the battery, and improve the battery's dynamic performance.

[0021] In any embodiment, the thickness of the coating layer is 0.5 nm to 4 nm, and optionally 1 nm to 2 nm.

[0022] When the thickness of the coating layer is within an appropriate range, it can form an effective protective layer on the positive electrode active material matrix, while also facilitating the rapid transmission of lithium ions on the surface of the material, improving the ion conductivity of the material, and making the battery have a low DC internal resistance, so that the battery has excellent discharge capacity, first coulombic efficiency, storage performance and cycle performance.

[0023] A second aspect of the present application provides a method for preparing a positive electrode active material, comprising:

[0024] Evenly mixing a first raw material including a lithium source and a precursor material, and performing a primary sintering to obtain a first product;

[0025] uniformly mixing a second raw material comprising the first product and a Co element additive, and performing secondary sintering to obtain a positive electrode active material;

[0026] The positive electrode active material includes: a substrate and a coating layer located on the surface of the substrate. The positive electrode active material satisfies the following: W1>W2, wherein W1 is the mass content of the Co element in the coating layer, and W2 is the mass content of the Co element in the substrate, based on the mass of the positive electrode active material.

[0027] By adopting the above preparation, a positive electrode active material with a coating layer being a Co-rich layer and a matrix being a Co-poor region can be obtained. The positive electrode active material has a high discharge gram capacity, providing a material basis for preparing high energy density batteries.

[0028] In any embodiment, the Co element additive includes at least one of cobaltous oxide, cobalt hydroxide, cobaltous oxide, cobalt oxyhydroxide, cobalt acetate, cobalt oxalate, and cobalt carbonate.

[0029] In any embodiment, the sintering temperature of the secondary sintering is 250° C.-350° C., optionally 250° C.-300° C.; and / or the sintering time of the secondary sintering is 5 h-10 h, optionally 5 h-6 h.

[0030] Controlling the sintering temperature and / or sintering time of the secondary sintering within an appropriate range can reduce the possibility of excessive Co element entering the matrix of the positive electrode active material during the secondary sintering process, and reduce the possibility of generating a positive electrode active material in which the coating layer is a Co-poor layer and the matrix is ​​a Co-rich region, so that the generated positive electrode active material has a structure of a coating layer of a Co-rich layer and a matrix of a Co-poor region.

[0031] In any embodiment, the first raw material further includes an M source. Optionally, the M source includes one or more of a Ba source, a W source, a Nb source, a Bi source, a Mg source, a Na source, a Sn source, a Y source, and a Sb source. Optionally, the M source is one or more of a Ba source, a Y source, and a Sb source.

[0032] In any embodiment, the second raw material further includes a N source. Optionally, the N source includes one or both of a B source and an Al source.

[0033] A third aspect of the present application provides a secondary battery, comprising a positive electrode plate, wherein the positive electrode plate comprises the positive electrode active material of the first aspect or the positive electrode active material prepared by the preparation method of the second aspect.

[0034] A fourth aspect of the present application provides an electrical device comprising the secondary battery according to the third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0036] FIG2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG1 ;

[0037] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0038] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0039] FIG5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG4 ;

[0040] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0041] Description of reference numerals:

[0042] 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0043] Below, the embodiments of the positive electrode active material, its manufacturing method, secondary battery and electric device of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0044] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0045] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0046] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0047] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0048] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0049] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0050] Secondary batteries, with their advantages of high voltage, light weight, long cycle life, no memory effect, and excellent safety, have become widely used. Secondary batteries consist of a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The positive active material in the positive electrode sheet is crucial to the overall performance of a secondary battery. With the continuous advancement of secondary battery technology, the energy density requirements for secondary batteries are constantly increasing, and this in turn places increasing demands on the discharge capacity of the positive active material.

[0051] [Positive electrode active material]

[0052] The present application provides a positive electrode active material, comprising a substrate and a coating layer at least partially covering the substrate, wherein the positive electrode active material satisfies: W1>W2, wherein W1 is the mass content of the Co element in the coating layer, and W2 is the mass content of the Co element in the substrate, based on the mass of the positive electrode active material.

[0053] The mass content of Co in the coating layer and the matrix can be measured using methods and equipment known in the art, such as using EDS to measure the mass content of Co in the coating layer and the matrix. Specifically, the following steps are used: a sample preparation glue is mixed evenly with the positive electrode active material powder (the weight of the powder is 5 times that of the sample preparation glue), and then coated on a copper foil to obtain a sample, which is then dried at 60°C for 30 minutes. The prepared sample is cut into 6mm×6mm pieces using scissors, fixed on a sample stage, and placed in an ion polisher (model: IB-19500CP). The sample edge is adjusted parallel to the centerline X-axis and the Y-axis position is 40-60μm for cutting. After cutting, an X-Max energy dispersive spectrometer (EDS) from the Oxford Instruments Group in the UK is combined with a Sigma-02-33 scanning electron microscope (SEM) from ZEISS in Germany. An appropriate particle section is selected on the cut sample, and a linear scan of the characteristic element Co of the coating layer and the characteristic element Co of the matrix is ​​performed along the particle diameter direction to obtain the mass content of Co in the matrix and the coating layer.

[0054] On the one hand, the coating layer on the surface of the substrate is a Co-rich layer. The coating layer is rich in Co doping, which can improve the conductivity of active ions, reduce the charge transfer impedance at the material interface, and improve the capacity platform of the positive electrode active material in the low voltage range (voltage range below 3.7V). It can increase the discharge capacity of the positive electrode active material. At the same time, the coating layer on the surface of the substrate is rich in Co, which can also reduce the residual lithium impurities on the surface of the material and improve its cycle stability. On the other hand, the substrate is a Co-poor area, and the mass content of the Co element in the matrix is ​​small. Its mass content in the matrix is ​​small, which provides a larger mass content for the Ni element in the matrix that provides the electrons required for electrochemistry, making it possible for the positive electrode active material to be a high-nickel material, which can effectively improve the discharge capacity of the positive electrode active material.

[0055] In summary, controlling the coating layer to be a Co-rich layer and the matrix to be a Co-poor area can increase the discharge capacity of the positive electrode active material, provide a material basis for the preparation of high energy density batteries, and at the same time improve the cycle stability of the positive electrode active material and improve the cycle performance of the battery.

[0056] In some embodiments, the mass content W1 of the Co element in the coating layer is 0.4%-1.6% based on the mass of the positive electrode active material. In some embodiments, the mass content W1 of the Co element in the coating layer is 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, or a value in a range consisting of any two of the foregoing values, based on the mass of the positive electrode active material.

[0057] The mass content of the Co element in the coating layer is within an appropriate range, so that the Co element is evenly and tightly wrapped on the positive electrode active material matrix, effectively improving the structural properties of the material. At the same time, it can also reduce the possibility of island accumulation due to excessive coating, reduce the influence of island accumulation on material properties, and make the positive electrode active material have a high discharge capacity. At the same time, the material has high cycle stability, the battery has a high number of cycles, and the battery performance is comprehensively improved.

[0058] In some embodiments, the mass content W1 of the Co element in the coating layer is 0.9%-1.4% based on the mass of the positive electrode active material. In some embodiments, the mass content W1 of the Co element in the coating layer is 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, or a value in a range consisting of any two of the above values, based on the mass of the positive electrode active material.

[0059] By controlling the mass content of the Co element in the coating layer within an appropriate range, the discharge capacity of the positive electrode active material and the cycle number of the battery can be further improved.

[0060] In some embodiments, the mass content W2 of the Co element in the matrix is ​​less than or equal to 0.02% based on the mass of the positive electrode active material. In some embodiments, the mass content W2 of the Co element in the matrix is ​​less than or equal to 0.02% or less than or equal to 0.01% based on the mass of the positive electrode active material.

[0061] The Co element in the matrix is ​​within a suitable range and can provide a larger mass content for the Ni element in the matrix that provides the electrons required for electrochemistry, so that the positive electrode active material has a high discharge capacity and the battery has excellent cycle performance.

[0062] In some embodiments, based on the mass of the positive electrode active material, the mass content W2 of the Co element in the matrix is ​​0%.

[0063] The mass content of the Co element in the matrix is ​​0%, that is, the matrix does not contain the Co element, which can further increase the discharge gram capacity of the positive electrode active material and increase the cycle number of the battery.

[0064] In some embodiments, the matrix further includes a doping element M, and the M element includes one or more of Ba, W, Nb, Bi, Mg, Na, Sn, Y, and Sb.

[0065] The matrix contains doping elements such as Ba, W, Nb, Bi, Mg, Na, Sn, Y or Sb, which can weaken the tendency of lithium-nickel mixing in the positive electrode active material, improve the cycle stability of the material, and increase the cycle life of the battery.

[0066] In some embodiments, the doping element M includes one or more of Ba, Y, and Sb.

[0067] Ba, Y or Sb elements are doped into the matrix, and Ba, Y or Sb elements can form strong chemical bonds with oxygen atoms in the matrix, further inhibiting the trend of lithium-nickel mixing in the positive electrode active material, improving the structural stability of the material, and further improving the cycle performance of the battery.

[0068] In some embodiments, the mass content of the M element is 200 ppm to 800 ppm based on the mass of the positive electrode active material. In some embodiments, the mass content of the M element is 200 ppm, 400 ppm, 600 ppm, 800 ppm, or a value in a range consisting of any two of the above values, based on the mass of the positive electrode active material.

[0069] The mass content of the doping element M in the matrix can be tested using methods and equipment known in the art, such as using EDS to test the mass content of the doping element in the matrix, specifically as follows: the sample preparation glue and the positive electrode active material powder are mixed evenly (the weight of the powder is 5 times that of the sample preparation glue), and then coated on a copper foil to obtain a sample, and dried at 60°C for 30 minutes. The prepared sample is cut into 6mm×6mm sizes with scissors, fixed on a sample stage, and placed in an ion polisher (model: IB-19500CP). The sample edge is adjusted parallel to the centerline X-axis and the Y-axis position is 40-60μm for cutting. After cutting, an X-Max energy dispersive spectrometer (EDS) of the Oxford Instruments Group in the UK is combined with a Sigma-02-33 scanning electron microscope (SEM) of the ZEISS in Germany. A suitable particle section is selected on the cut sample, and a linear scan of the matrix's characteristic element, the doping element M, is performed along the particle diameter direction to obtain the mass content of the doping element M in the matrix.

[0070] By controlling the mass content of the doping element M within an appropriate range, the purpose of reducing the tendency of lithium-nickel mixing in the positive electrode active material can be achieved. At the same time, it also reduces the negative impact of excessive content of the doping element M on the high mass content of the Ni element in the matrix, thereby affecting the discharge capacity of the positive electrode active material.

[0071] In some embodiments, the matrix comprises lithium nickelate.

[0072] Lithium nickelate has a high theoretical specific capacity. However, lithium nickelate materials have serious lithium-nickel mixing during the charge and discharge process, making it difficult to exert their high capacity characteristics.

[0073] To address this phenomenon, the present invention coats the surface of the lithium nickelate matrix with Co elements to reduce the material's impedance and ion diffusion impedance, improve the capacity platform in the low voltage range (voltage range below 3.7V), and increase the discharge capacity of the positive electrode active material.

[0074] In some embodiments, the coating layer further includes a doping element N, and the N element includes one or both of B and Al.

[0075] Al and B can form glassy substances such as LiAlO2 or Li3BO3 with the positive electrode active material matrix. The above-mentioned glassy substances can be wrapped at the grain boundaries of the particles, which can inhibit the generation of oxygen defects, improve the cycle performance of the battery, and reduce the gas production of the battery. At the same time, the glassy substances have excellent ion conductivity, which can increase the transmission rate of lithium ions on the material surface, reduce the DC internal resistance of the battery, and improve the battery's dynamic performance.

[0076] In some embodiments, the mass content of the N element is 200 ppm to 700 ppm based on the mass of the positive electrode active material. In some embodiments, the mass content of the N element is 200 ppm, 400 ppm, 600 ppm, 700 ppm, or a value in a range consisting of any two of the above values, based on the mass of the positive electrode active material.

[0077] The test method for the mass content of the doping element N in the coating layer can refer to the test method for the mass content of the doping element M in the matrix.

[0078] In some embodiments, the thickness of the coating layer is 0.5 nm to 4 nm. In some embodiments, the thickness of the coating layer can be selected from 0.5 nm, 1 nm, 2 nm, 3 nm, 4 nm, or a value in a range consisting of any two of the above values.

[0079] In some embodiments, the thickness of the coating layer is 1 nm to 2 nm. In some embodiments, the thickness of the coating layer can be 1 nm, 1.5 nm, 2 nm, or a value in a range consisting of any two of the above values.

[0080] The thickness of the coating layer can be tested using methods and equipment known in the art, such as using an IB-19500CP ion polisher and a transmission electron microscope. The specific process is as follows: clean the sample preparation tools, mix the sample preparation glue (a colloid formed by dispersing polyvinylidene fluoride in N-vinyl pyrrolidone, with a polyvinylidene fluoride mass content of 8%) with the sample powder (the weight of the powder is about 5 times that of the glue), evenly apply it on the copper foil, and dry it at 60°C for 30 minutes. Use scissors to cut the prepared sample into 6mm×6mm sizes, fix it on the sample table, and place it in an ion polisher (model: IB-19500CP) for cutting. According to JBT9352-1999, place the cut sample in the American FEI Tecnai G2 transmission electron microscope equipment for thickness testing.

[0081] When the thickness of the coating layer is within an appropriate range, it can form an effective protective layer on the positive electrode active material matrix, while also facilitating the rapid transmission of lithium ions on the surface of the material, improving the ion conductivity of the material, and making the battery have a low DC internal resistance, so that the battery has excellent discharge capacity, first coulombic efficiency, storage performance and cycle performance.

[0082] Some embodiments of the present application also provide a method for preparing a positive electrode active material, comprising:

[0083] Evenly mixing a first raw material including a lithium source and a precursor material, and performing a primary sintering to obtain a first product;

[0084] uniformly mixing a second raw material comprising the first product and a Co element additive, and performing secondary sintering to obtain a positive electrode active material;

[0085] The positive electrode active material includes: a substrate and a coating layer located on the surface of the substrate, and the positive electrode active material satisfies the following: W1>W2, wherein W1 is the mass content of the Co element in the coating layer, and W2 is the mass content of the Co element in the substrate, based on the mass of the positive electrode active material.

[0086] By adopting the above preparation, a positive electrode active material with a coating layer being a Co-rich layer and a matrix being a Co-poor region can be obtained. The positive electrode active material has a high discharge gram capacity, providing a material basis for preparing high energy density batteries.

[0087] In some embodiments, the Co element additive includes at least one of cobaltous oxide, cobalt hydroxide, cobaltous oxide, cobalt oxyhydroxide, cobalt acetate, cobalt oxalate, and cobalt carbonate.

[0088] In some embodiments, the precursor material comprises the element cobalt.

[0089] The precursor material contains cobalt element, and the cobalt element of the matrix in the positive electrode active material comes from the cobalt element in the precursor during the first sintering process, or the cobalt element in the matrix in the positive electrode active material comes from the cobalt element in the precursor during the first sintering process and the cobalt element in the cobalt element additive during the second sintering process.

[0090] In some embodiments, the precursor material does not contain the element cobalt.

[0091] The precursor material does not contain cobalt element, and the cobalt element of the matrix in the positive electrode active material comes from the cobalt element in the cobalt element additive during the secondary sintering process.

[0092] In some embodiments, the precursor material is Ni(OH)2.

[0093] In some embodiments, the first raw material further includes an M source.

[0094] In some embodiments, the first raw material further comprises one or more of a Ba source, a W source, a Nb source, a Bi source, a Mg source, a Na source, a Sn source, a Y source, and a Sb source. In some embodiments, the first raw material further comprises one or more of a Ba source, a Y source, and a Sb source.

[0095] In some embodiments, the B source includes one or more of barium sulfate, barium chloride, barium titanate, barium nitrate, and barium chloride.

[0096] In some embodiments, the W source includes one or more of tungsten trioxide, tungstic acid, ammonium tungstate, sodium tungstate, and lithium tungstate.

[0097] In some embodiments, the Nb source includes niobium oxide or lithium niobate.

[0098] In some embodiments, the Bi source includes one or more of bismuth subnitrate, bismuth subcarbonate, bismuth nitrate, bismuth sulfate, bismuth phosphate, bismuth vanadate, bismuth tungstate, bismuth germanate, bismuth citrate, bismuth acetate, and bismuth subsalicylate.

[0099] In some embodiments, the Mg source includes one or more of magnesium hydroxide, magnesium carbonate, magnesium oxide, magnesium chloride, and magnesium fluoride.

[0100] In some embodiments, the Na source includes one or more of sodium hydroxide, sodium carbonate, sodium chloride, sodium fluoride, and sodium oxide.

[0101] In some embodiments, the Sn source includes one or more of tin oxide, tin carbonate, tin chloride, tin nitrate, and tin sulfate.

[0102] In some embodiments, the Y source includes one or more of yttrium oxide, yttrium sulfate, yttrium nitrate, yttrium oxalate, yttrium acetate, and yttrium chloride.

[0103] In some embodiments, the Sb source includes antimony oxide or lithium antimonate.

[0104] In some embodiments, the second raw material further includes a N source. Optionally, the N source includes one or both of a B source and an Al source.

[0105] In some embodiments, the Al source includes one or more of aluminum oxide, aluminum hydroxide, aluminum sulfate, aluminum chloride, and aluminum nitrate.

[0106] In some embodiments, the B source includes one or more of boron chloride, boron sulfate, boron nitrate, boron nitride, boron oxide, boron fluoride, boron bromide, boron iodide, and boric acid.

[0107] In some embodiments, the secondary sintering temperature is 250°C-350°C.

[0108] In some embodiments, the sintering temperature of the secondary sintering may be selected from 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C or a value in a range consisting of any two of the above points.

[0109] In some embodiments, the sintering time of the secondary sintering can be selected as 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, or a value in a range consisting of any two of the above points.

[0110] Controlling the sintering temperature or sintering time of the secondary sintering within an appropriate range can reduce the possibility of excessive Co element entering the matrix of the positive electrode active material during the secondary sintering process, and reduce the possibility of generating a positive electrode active material in which the coating layer is a Co-poor layer and the matrix is ​​a Co-rich region, so that the generated positive electrode active material has a structure of a coating layer of a Co-rich layer and a matrix of a Co-poor region.

[0111] In some embodiments, the sintering temperature of the secondary sintering is 250° C.-300° C.; and / or the sintering time of the secondary sintering is 5 h-6 h.

[0112] In some embodiments, the sintering temperature of the secondary sintering may be 250° C., 260° C., 270° C., 280° C., 290° C., 300° C., or a value in a range consisting of any two of the above values.

[0113] In some embodiments, the sintering time of the secondary sintering may be 5 h, 5.5 h, 6 h, or a value within a range consisting of any two of the above points.

[0114] The sintering time or sintering temperature is controlled within an appropriate range so that the Co element additive does not basically enter the matrix during the secondary sintering, and the matrix is ​​basically free of cobalt elements as much as possible. It is also ensured that the matrix contains enough nickel elements as much as possible, so that the positive electrode active material has a high discharge capacity.

[0115] [Positive electrode]

[0116] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.

[0117] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0118] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0119] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0120] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0121] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0122] [Negative electrode]

[0123] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0124] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0125] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0126] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0127] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0128] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0129] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0130] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0131] [Electrolytes]

[0132] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0133] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0134] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0135] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0136] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0137] [Isolation film]

[0138] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0139] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0140] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0141] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0142] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0143] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 5 with a square structure as an example.

[0144] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0145] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0146] Figure 3 shows an example battery module 4. Referring to Figure 3 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0147] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0148] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0149] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0150] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0151] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0152] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0153] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0154] Example

[0155] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0156] 1. Preparation method

[0157] Example 1

[0158] 1) Primary sintering: Lithium hydroxide and a precursor, Ni(OH)2, were mixed in a high-speed mixer to obtain a first mixed material, wherein the molar ratio of lithium hydroxide to Ni(OH)2 was 1.03:1. The first mixed material was placed in a kiln under a pure oxygen atmosphere and calcined for a first time at 685°C for 5 hours to obtain a first product.

[0159] 2) The first product and the coating additive Co(OH)2 are placed in a high-speed mixer for mixing to obtain a second mixture, wherein the mass content of the coating additive Co(OH)2 is 1.2%, based on the mass of Ni(OH)2 and Co(OH)2; the second mixture is placed in a kiln for calcination in a high-purity oxygen atmosphere at a temperature of 300°C for 6 hours, and the obtained material is subjected to mechanical pulverization and classification, demagnetization, sieving, and packaging to obtain the positive electrode active material.

[0160] 2) Preparation of positive electrode sheet

[0161] The positive electrode active material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97%:1%:2%, and N-methylpyrrolidone is added and mixed evenly to obtain a positive electrode slurry; then the slurry is coated on the positive electrode collector, dried, cold pressed, and cut to obtain a positive electrode sheet.

[0162] 3) Preparation of negative electrode sheet

[0163] The negative electrode active material, artificial graphite, hard carbon, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carbon methyl cellulose (CMC) were thoroughly mixed in a deionized water solvent system at a mass ratio of 90%:5%:2%:2%:1%. The mixture was then applied to copper foil, dried, and cold-pressed to obtain a negative electrode sheet.

[0164] 4) Electrolyte

[0165] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), lithium salt lithium hexafluorophosphate LiPF6 was dissolved in the organic solvent ethylene carbonate / ethyl methyl carbonate / dimethyl carbonate (the volume ratio of EC+EMC+DMC was 1:1:1) and stirred evenly to obtain an electrolyte with a LiPF6 concentration of 1 mol / L.

[0166] 5) Isolation film

[0167] A polyethylene porous polymer film is used as the separator.

[0168] 6) Preparation of button cells

[0169] The lithium sheet was used as the negative electrode and assembled with the positive electrode of Example 1 into a standard button cell.

[0170] 7) Preparation of secondary batteries

[0171] The positive electrode sheet, separator, and negative electrode sheet of Example 1 are stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation. The cells are then wound to obtain battery cells, the tabs are welded to the battery cells, and the battery cells are placed in an aluminum shell. The electrolyte is then injected and sealed. After standing, cold pressing, formation, shaping, capacity testing, and other processes, a lithium-ion secondary battery is obtained.

[0172] The preparation parameters in Examples 2-5 are basically the same as those in Example 1, but the mass content of the coating additives is adjusted, as follows:

[0173] Example 2: The mass content of the coating additive Co(OH)2 is 0.4%, based on the mass of Ni(OH)2 and Co(OH)2.

[0174] Example 3: The mass content of the coating additive Co(OH)2 is 0.9%, based on the mass of Ni(OH)2 and Co(OH)2.

[0175] Example 4: The mass content of the coating additive Co(OH)2 is 1.4%, based on the mass of Ni(OH)2 and Co(OH)2.

[0176] Example 5: The mass content of the coating additive Co(OH)2 is 1.6%, based on the mass of Ni(OH)2 and Co(OH)2.

[0177] The preparation parameters in Example 6 are basically the same as those in Example 1, but the secondary sintering temperature is adjusted to 350°C.

[0178] The preparation parameters of Example 7 are basically the same as those of Example 1, but the preparation method of the positive electrode active material is adjusted, as follows:

[0179] Primary sintering: Lithium hydroxide, precursor Ni(OH)2, and dopant barium titanate are mixed in a high-speed mixer to produce a first mixed material. The molar ratio of lithium hydroxide to precursor Ni(OH)2 is 1.03:1, and the weight content of dopant barium titanate is 0.05% (based on the weight of Ni(OH)2). Under a pure oxygen atmosphere, the first mixed material is placed in a kiln for a first calcination at 685°C for 5 hours to produce the first product.

[0180] 2) The first product and the coating additive Co(OH)2 are placed in a high-speed mixer for mixing to obtain a second mixture, wherein the mass content of the coating additive Co(OH)2 is 1.2%, based on the mass of Ni(OH)2 and Co(OH)2; the second mixture is placed in a kiln for calcination in a high-purity oxygen atmosphere at a temperature of 300°C for 6 hours, and the obtained material is subjected to mechanical pulverization and classification, demagnetization, sieving, and packaging to obtain the positive electrode active material.

[0181] Example 8

[0182] The preparation parameters of Example 8 are basically the same as those of Example 7, except that the dopant of barium titanate in the first sintering is replaced by tungsten trioxide.

[0183] Examples 9-12

[0184] The preparation parameters in Examples 9-12 are basically the same as those in Example 7, but the mass content of barium titanate is adjusted respectively, as follows:

[0185] Example 9: The mass content of the dopant barium titanate is 0.01%, based on the mass of Ni(OH)2.

[0186] Example 10: The mass content of the dopant barium titanate is 0.02%, based on the mass of Ni(OH)2.

[0187] Example 11: The mass content of the dopant barium titanate is 0.08%, based on the mass of Ni(OH)2.

[0188] Example 12: The mass content of the dopant barium titanate is 1%, based on the mass of Ni(OH)2.

[0189] Comparative Example 1-2

[0190] The preparation parameters of Comparative Example 1 are basically the same as those of Example 1, but the preparation method of the positive electrode active material is adjusted. The specific preparation method is as follows:

[0191] Primary sintering: Lithium hydroxide and the precursor Ni(OH)2 are mixed in a high-speed mixer to produce a first mixed material. The molar ratio of lithium hydroxide to Ni(OH)2 is 1.03:1. Under a pure oxygen atmosphere, the first mixed material is placed in a kiln for a first calcination at 685°C for 5 hours to produce the positive electrode active material.

[0192] The preparation parameters of Comparative Example 2 are basically the same as those of Example 1, but the preparation method of the positive electrode active material is adjusted. The specific preparation method is as follows:

[0193] Primary sintering: Lithium hydroxide, precursor Ni(OH)2, and dopant Co(OH)2 are mixed in a high-speed mixer to obtain a first mixed material. The molar ratio of lithium hydroxide to precursor Ni(OH)2 is 1.03:1, and the mass content of the dopant additive Co(OH)2 is 1.2%, based on the mass of Ni(OH)2 and Co(OH)2. Under a pure oxygen atmosphere, the first mixed material is placed in a kiln for a first calcination at a temperature of 685°C for 5 hours to obtain the positive electrode active material.

[0194] 2. Performance Testing

[0195] 1. Cathode active material testing

[0196] 1) Determination of the mass content of characteristic elements in the matrix and coating layer of the positive electrode active material

[0197] The sample preparation glue and positive electrode active material powder were mixed evenly (the powder weight was 5 times that of the sample preparation glue) and then coated onto copper foil to produce the sample. The sample was then dried at 60°C for 30 min. The prepared sample was cut into 6 mm x 6 mm pieces using scissors, mounted on a sample stage, and placed in an ion polisher (Model: IB-19500CP). The sample edge was aligned parallel to the centerline (X-axis) and positioned 40-60 μm along the Y-axis for cutting. After cutting, an X-Max energy dispersive spectrometer (EDS) from Oxford Instruments (UK) combined with a Sigma-02-33 scanning electron microscope (SEM) from ZEISS (Germany) was used to select appropriate sections of the sample. Linear scans were performed along the particle diameter for the characteristic elements of the coating layer (Co or N) and the matrix (Co or M) to determine the mass content of the characteristic elements in the matrix and coating layer.

[0198] 2) Discharge capacity of positive electrode active material

[0199] At a voltage of 2.5V to 4.4V, the button batteries of the embodiment and comparative example were charged at a constant current of 0.1C to 4.4V, then charged at a constant voltage of 4.4V to a current of ≤0.05mA, and allowed to stand for 2 minutes. The charge capacity at this time was recorded as C0; then discharged at a constant current of 0.1C to 2.5V. The discharge capacity at this time was recorded as D0.

[0200] The ratio of the discharge capacity D0 to the mass of the positive electrode active material is the discharge gram capacity D1 of the positive electrode active material.

[0201] 2. Battery performance

[0202] 1) Cycle performance

[0203] The secondary batteries prepared in each example and comparative example were charged at a constant current rate of 0.5C to a charge cutoff voltage of 4.25V, then charged at a constant voltage rate to a current of ≤0.05C, allowed to rest for 5 minutes, and then discharged at a constant current rate of 0.33C to a discharge cutoff voltage of 2V, allowed to rest for 5 minutes. This constituted one charge-discharge cycle. The batteries were subjected to cyclic charge-discharge testing using this method until the battery capacity decayed to 80%. The number of cycles at this point is the battery's cycle life at 25°C.

[0204] 3. Analysis of test results of various embodiments and comparative examples

[0205] Batteries of various examples and comparative examples were prepared according to the above methods, and various performance parameters were measured. The results are shown in Table 1 below.

[0206] Table 1

[0207] From the above results, it can be seen that the positive electrode active materials in Examples 1-12 include a lithium nickelate substrate and a coating layer at least partially covering the substrate. Based on the mass of the positive electrode active material, the Co element content W1 in the coating layer is greater than the Co element content in the substrate. From the comparison of Examples 1-12 with Comparative Examples 1-2, it can be seen that compared to the absence of a coating layer or the Co element mass content in the substrate being higher than the Co element mass content in the coating layer, the Co element mass content in the substrate of the present application is lower than the Co element mass content in the coating layer, which can increase the discharge gram capacity of the positive electrode active material, provide a material basis for the preparation of high-energy batteries, and at the same time increase the number of battery cycles and extend the battery life.

[0208] As can be seen from Examples 1-12, controlling the mass content W1 of the Co element in the coating layer to 0.4%-1.6% can improve the positive electrode active material's discharge capacity per gram, while also providing high cycling stability and a high battery cycle number, thereby comprehensively improving battery performance. Comparing Examples 1, 3, 4, and 6 with Examples 2 and 5, it can be seen that controlling the mass content W1 of the Co element in the coating layer to 0.9%-1.4% can further improve the positive electrode active material's discharge capacity per gram and the battery cycle number.

[0209] As can be seen from Examples 1-12, when the Co content W2 of the matrix is ​​less than or equal to 0.02%, the positive electrode active material has a high discharge capacity per gram, and the material also has high cycling stability, resulting in a high number of battery cycles, thus comprehensively improving battery performance. A comparison of Example 1 with Example 6 shows that when the Co content W2 of the matrix is ​​0%, i.e., the matrix does not contain Co, the discharge capacity per gram of the positive electrode active material can be further increased, thereby improving the number of battery cycles.

[0210] Comparing Examples 7-12 with Example 1, it can be seen that the matrix of the positive electrode active material also contains Ba or W, which can increase the discharge capacity of the positive electrode active material and the number of battery cycles, thereby improving the battery's cycling performance. Comparing Example 7 with Example 8, it can be seen that the matrix of the positive electrode active material includes Ba, which can further increase the number of battery cycles and improve the battery's cycling performance.

[0211] From the comparison between Examples 7, 10-11 and Examples 9 and 12, it can be seen that controlling the mass content of the M element to 200ppm-800ppm can further increase the number of battery cycles, while the positive electrode active material has a high discharge capacity.

[0212] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode active material, characterized in that: include: A substrate and a coating layer at least partially covering the substrate, wherein the positive electrode active material satisfies: W1>W2, Wherein, W1 is the mass content of the Co element in the coating layer, and W2 is the mass content of the Co element in the matrix, based on the mass of the positive electrode active material.

2. The positive electrode active material according to claim 1, characterized in that: Based on the mass of the positive electrode active material, the mass content W1 of the Co element in the coating layer is 0.4%-1.6%, and can be optionally 0.9%-1.4%.

3. The positive electrode active material according to claim 1 or 2, characterized in that: Based on the mass of the positive electrode active material, the mass content W2 of the Co element in the matrix is ​​less than or equal to 0.02%, and can be optionally 0%.

4. The positive electrode active material according to any one of claims 1 to 3, characterized in that: The matrix also includes a doping element M, and the M element includes one or more of Ba, W, Nb, Bi, Mg, Na, Sn, Y, and Sb, and can be selected from one or more of Ba, Y, and Sb.

5. The positive electrode active material according to claim 4, characterized in that: The mass content of the M element is 200 ppm to 800 ppm based on the mass of the positive electrode active material.

6. The positive electrode active material according to any one of claims 1 to 5, characterized in that: The matrix includes lithium nickelate.

7. The positive electrode active material according to any one of claims 1 to 6, characterized in that: The coating layer further includes a doping element N, and the N element includes one or two of B and Al; optionally, based on the mass of the positive electrode active material, the mass content of the N element is 200ppm-700ppm.

8. The positive electrode active material according to any one of claims 1 to 7, characterized in that: The coating layer has a thickness of 0.5 nm to 4 nm, and can be optionally 1 nm to 2 nm.

9. A method for preparing a positive electrode active material, characterized in that: include: Evenly mixing a first raw material including a lithium source and a precursor material, and performing a sintering operation to obtain a first product; uniformly mixing a second raw material including the first product and a Co element additive, and performing secondary sintering to obtain the positive electrode active material; The positive electrode active material comprises: a substrate and a coating layer located on the surface of the substrate, and the positive electrode active material satisfies the following conditions: W1>W2, Wherein, W1 is the mass content of the Co element in the coating layer, and W2 is the mass content of the Co element in the matrix, based on the mass of the positive electrode active material.

10. The preparation method according to claim 9, characterized in that: The Co element additive includes at least one of cobalt tetroxide, cobalt hydroxide, cobaltous oxide, cobalt oxyhydroxide, cobalt acetate, cobalt oxalate, and cobalt carbonate.

11. The preparation method according to claim 9 or 10, characterized in that: The sintering temperature of the secondary sintering is 250° C.-350° C., and may be 250° C.-300° C.; and / or the sintering time of the secondary sintering is 5 h-10 h, and may be 5 h-6 h.

12. The preparation method according to any one of claims 9 to 11, characterized in that: The first raw material also includes an M source. Optionally, the M source includes one or more of a Ba source, a W source, a Nb source, a Bi source, a Mg source, a Na source, a Sn source, a Y source, and a Sb source. It can be selected from one or more of a Ba source, a Y source, and a Sb source.

13. The preparation method according to any one of claims 9 to 12, characterized in that: The second raw material further includes a N source. Optionally, the N source includes one or both of a B source and an Al source.

14. A secondary battery, comprising a positive electrode plate, characterized in that: The positive electrode sheet comprises the positive electrode active material according to any one of claims 1 to 8 or the positive electrode active material prepared by the preparation method according to any one of claims 9 to 13.

15. An electrical device, characterized in that: Includes the secondary battery as claimed in claim 14.

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