Positive electrode active material, method for preparing same, secondary

Abstract

The invention provides a positive electrode active material, a preparation method thereof, a secondary battery and an electric device. The positive electrode active material comprises a substrate and a coating layer at least partially covering the substrate, and the positive electrode active material satisfies: W1gt, the mass content of the Co element in the W1 coating layer is calculated based on the mass of the positive electrode active material, and the W2 is the mass content of the Co element in the matrix. The positive electrode active material has high discharge capacity per gram, and a material basis is provided for preparing a high-energy-density battery.

Description

Technical Field

[0001] 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

[0002] In recent years, as the application scope of secondary batteries becomes wider and wider, secondary batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. As secondary batteries have made great progress, higher requirements have been put forward for their energy density. The positive electrode active material is an important component of the secondary battery. It not only affects the safety and cost of the battery, but also is a key factor that directly determines the electrochemical performance of the battery. In order to obtain a secondary battery with high energy density, it is necessary to adopt certain strategies to optimize the positive electrode active material and improve the discharge capacity of the positive electrode active material. Summary of the invention

[0003] 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 a high energy density battery.

[0004] 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.

[0005] On the one hand, the coating layer on the surface of the substrate is a Co-enriched layer. The coating layer is rich in Co and doped, which can improve the conductivity of active ions, reduce the charge transfer impedance of 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-depleted 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.

[0006] 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.

[0007] 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%.

[0008] The mass content of the Co element in the coating layer is within a suitable range, so that the Co element is evenly and tightly wrapped on the positive electrode active material matrix, effectively improving the structural performance of the material, while reducing the possibility of island accumulation due to excessive coating, reducing the influence of island accumulation on material performance, and making the positive electrode active material have a high discharge gram 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.

[0009] 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 0%.

[0010] 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 gram capacity and the battery has excellent cycle performance.

[0011] 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 selected from one or more of Ba, Y, and Sb.

[0012] 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.

[0013] 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.

[0014] Controlling the mass content of the doping element M within a suitable range can achieve the purpose of reducing the tendency of lithium-nickel mixing in the positive electrode active material, while also reducing the negative impact of excessive 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.

[0015] In any embodiment, the matrix comprises lithium nickelate.

[0016] In any embodiment, 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.

[0017] Al and B can form LiAlO with the positive electrode active material matrix 2 or Li 3 BO 3 The glass-like material 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 glass-like material has excellent ion conductivity, which can increase the transmission rate of lithium ions on the surface of the material, reduce the DC internal resistance of the battery, and improve the kinetic performance of the battery.

[0018] In any embodiment, the coating layer has a thickness of 0.5 nm to 4 nm, and may be 1 nm to 2 nm.

[0019] When the thickness of the coating layer is within a suitable 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 coulomb efficiency, storage performance and cycle performance.

[0020] The second aspect of the present application provides a method for preparing a positive electrode active material, comprising:

[0021] Evenly mixing a first raw material including a lithium source and a precursor material, and performing a sintering operation to obtain a first product;

[0022] uniformly mixing a second raw material including the first product and a Co element additive, and performing secondary sintering to obtain a positive electrode active material;

[0023] 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.

[0024] By adopting the above preparation, a positive electrode active material with a coating layer being a Co-enriched 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 a high energy density battery.

[0025] In any embodiment, the Co element additive includes at least one of cobalt tetroxide, cobalt hydroxide, cobaltous oxide, cobalt oxyhydroxide, cobalt acetate, cobalt oxalate, and cobalt carbonate.

[0026] In any embodiment, 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.

[0027] Controlling the sintering temperature and / or sintering time of the secondary sintering within a suitable range can reduce the possibility of excessive Co element entering the matrix of the positive electrode active material during the secondary sintering process, reduce the possibility of generating a positive electrode active material with a Co-depleted layer as the coating layer and a Co-rich region as the matrix, and enable the generated positive electrode active material to have a coating layer with a Co-rich layer and a matrix with a Co-depleted region structure.

[0028] 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 an Sb source, and may be one or more of a Ba source, a Y source, and an Sb source.

[0029] In any embodiment, the second raw material further includes an N source. Optionally, the N source includes one or two of a B source and an Al source.

[0030] The third aspect of the present application provides a secondary battery, including a positive electrode plate, and the positive electrode plate includes the positive electrode active material described in the first aspect or the positive electrode active material prepared by the preparation method described in the second aspect.

[0031] The fourth aspect of the present application provides an electrical device, including the secondary battery of the third aspect of the present application. Description of the Drawings

[0032] Figure 1 It is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0033] Figure 2 is Figure 1 The exploded view of the secondary battery according to an embodiment of the present application shown in

[0034] Figure 3 It is a schematic diagram of a battery module according to an embodiment of the present application.

[0035] Figure 4 It is a schematic diagram of a battery pack according to an embodiment of the present application.

[0036] Figure 5 is Figure 4 The exploded view of the battery pack according to an embodiment of the present application shown in

[0037] Figure 6 It is a schematic diagram of an electrical device using the secondary battery according to an embodiment of the present application as a power source.

[0038] Description of the Reference Numerals:

[0039] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0040] Hereinafter, the embodiments of the positive electrode active material, the method for manufacturing the same, the secondary battery and the electric device of the present application will be specifically disclosed with appropriate reference to the drawings. However, there will 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 descriptions 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.

[0041] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a 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 a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present 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 real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it 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.

[0042] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0043] 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.

[0044] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means 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), which means 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.

[0045] If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0046] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": 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).

[0047] Secondary batteries have the advantages of high voltage, light weight, long cycle life, no memory effect, good safety, etc., and have been widely used. Secondary batteries include positive electrode sheets, negative electrode sheets, separators, electrolytes, etc. Among them, the positive active material in the positive electrode sheet is the key to restricting the overall performance of secondary batteries. With the continuous development of technology in the application field of secondary batteries, the requirements for the energy density of secondary batteries are constantly increasing, and the requirements for the discharge capacity of positive active materials are also constantly increasing.

[0048] [Positive electrode active material]

[0049] The present application provides a positive electrode active material, including 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.

[0050] The mass content of Co in the coating layer and the matrix can be tested by methods and equipment known in the art, such as using EDS to test the mass content of Co in the coating layer and the matrix, 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 applied to the 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 the sample stage, and placed in an ion polisher (model: IB-19500CP), and the sample edge is adjusted to be parallel to the center line X axis, and the Y axis position is 40-60μm for cutting. After cutting, the X-Max energy spectrometer (EDS) of the Oxford Instruments Group of the United Kingdom is combined with the Sigma-02-33 scanning electron microscope (SEM) of the ZEISS of Germany, and a suitable particle section is selected on the cut sample, and the characteristic element Co element of the coating layer and the characteristic element Co element of the matrix are linearly scanned along the particle diameter direction to obtain the mass content of Co in the matrix and the coating layer.

[0051] On the one hand, the coating layer on the surface of the substrate is a Co-enriched layer. The coating layer is rich in Co and doped, which can improve the conductivity of active ions, reduce the charge transfer impedance of the material interface, and improve the capacity platform of the positive electrode active material in the low voltage range (voltage range below 3.7V). The discharge gram capacity of the positive electrode active material can be improved. 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-depleted 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 gram capacity of the positive electrode active material.

[0052] 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.

[0053] In some embodiments, 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%. In some embodiments, based on the mass of the positive electrode active material, the mass content W1 of the Co element in the coating layer can be 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6% or a value in the range of any two of the above points.

[0054] The mass content of the Co element in the coating layer is within a suitable range, so that the Co element is evenly and tightly wrapped on the positive electrode active material matrix, effectively improving the structural performance of the material, while reducing the possibility of island accumulation due to excessive coating, reducing the influence of island accumulation on material performance, and making the positive electrode active material have a high discharge gram 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.

[0055] In some embodiments, based on the mass of the positive electrode active material, the mass content W1 of the Co element in the coating layer is 0.9%-1.4%. In some embodiments, based on the mass of the positive electrode active material, the mass content W1 of the Co element in the coating layer can be 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4% or a value in the range of any two of the above points.

[0056] By controlling the mass content of the Co element in the coating layer within a suitable range, the discharge gram capacity of the positive electrode active material and the cycle number of the battery can be further improved.

[0057] 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 ​​less than or equal to 0.02%. In some embodiments, based on the mass of the positive electrode active material, the mass content W2 of the Co element in the matrix can be selected as any one of less than or equal to 0.02% and less than or equal to 0.01%.

[0058] 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 gram capacity and the battery has excellent cycle performance.

[0059] 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%.

[0060] 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 number of cycles of the battery.

[0061] 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.

[0062] 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.

[0063] In some embodiments, the doping element M includes one or more of Ba, Y, and Sb.

[0064] 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.

[0065] In some embodiments, based on the mass of the positive electrode active material, the mass content of the M element is 200ppm-800ppm. In some embodiments, based on the mass of the positive electrode active material, the mass content of the M element can be 200ppm, 400ppm, 600ppm, 800ppm or a value in the range consisting of any two of the above points.

[0066] The mass content of the doping element M in the matrix can be tested by 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 applied to the 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 the sample stage, and placed in an ion polisher (model: IB-19500CP), and the edge of the sample is adjusted to be parallel to the centering line X axis, and the Y axis position is 40-60μm for cutting. After cutting, the X-Max energy spectrometer (EDS) of the Oxford Instruments Group of the United Kingdom is combined with the Sigma-02-33 scanning electron microscope (SEM) of the ZEISS of Germany, and a suitable particle section is selected on the cut sample, and the characteristic element doping element M of the matrix is ​​linearly scanned along the particle diameter direction to obtain the mass content of the doping element M in the matrix.

[0067] Controlling the mass content of the doping element M within a suitable range can achieve the purpose of reducing the tendency of lithium-nickel mixing in the positive electrode active material, while also reducing the negative impact of excessive 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.

[0068] In some embodiments, the matrix includes lithium nickelate.

[0069] Lithium nickel oxide has a high theoretical specific capacity. However, lithium nickel mixing is serious during the charge and discharge process of lithium nickel oxide materials, making it difficult to exert its high capacity characteristics.

[0070] 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 gram capacity of the positive electrode active material.

[0071] In some embodiments, the coating layer further includes a doping element N, and the N element includes one or both of B and Al.

[0072] Al and B can form LiAlO with the positive electrode active material matrix 2 or Li 3 BO 3 The glass-like material 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 glass-like material has excellent ion conductivity, which can increase the transmission rate of lithium ions on the surface of the material, reduce the DC internal resistance of the battery, and improve the kinetic performance of the battery.

[0073] In some embodiments, based on the mass of the positive electrode active material, the mass content of the N element is 200ppm-700ppm. In some embodiments, based on the mass of the positive electrode active material, the mass content of the N element can be 200ppm, 400ppm, 600ppm, 700ppm or a value in the range of any two of the above points.

[0074] 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.

[0075] In some embodiments, the coating layer has a thickness of 0.5 nm to 4 nm. In some embodiments, the coating layer has a thickness of 0.5 nm, 1 nm, 2 nm, 3 nm, 4 nm, or a value in a range consisting of any two of the above points.

[0076] 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 points.

[0077] The thickness of the coating layer can be tested by 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 put it into an ion polisher (model: IB-19500CP) for cutting. According to JBT9352-1999, put the cut sample into the American FEI Tecnai G2 transmission electron microscope equipment for thickness testing.

[0078] When the thickness of the coating layer is within a suitable 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 coulomb efficiency, storage performance and cycle performance.

[0079] Some embodiments of the present application also provide a method for preparing a positive electrode active material, comprising:

[0080] Evenly mixing a first raw material including a lithium source and a precursor material, and performing a sintering operation to obtain a first product;

[0081] uniformly mixing a second raw material including the first product and a Co element additive, and performing secondary sintering to obtain a positive electrode active material;

[0082] 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.

[0083] By adopting the above preparation, a positive electrode active material with a coating layer being a Co-enriched 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 a high energy density battery.

[0084] In some embodiments, the Co element additive includes at least one of cobalt tetroxide, cobalt hydroxide, cobaltous oxide, cobalt oxyhydroxide, cobalt acetate, cobalt oxalate, and cobalt carbonate.

[0085] In some embodiments, the precursor material comprises the element cobalt.

[0086] 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.

[0087] In some embodiments, the precursor material does not contain the element cobalt.

[0088] 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.

[0089] In some embodiments, the precursor material is Ni(OH) 2 .

[0090] In some embodiments, the first raw material further includes an M source.

[0091] 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.

[0092] In some embodiments, the B source includes one or more of barium sulfate, barium chloride, barium titanate, barium nitrate, and barium chloride.

[0093] In some embodiments, the W source includes one or more of tungsten trioxide, tungstic acid, ammonium tungstate, sodium tungstate, and lithium tungstate.

[0094] In some embodiments, the Nb source includes niobium oxide or lithium niobate.

[0095] 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.

[0096] In some embodiments, the Mg source includes one or more of magnesium hydroxide, magnesium carbonate, magnesium oxide, magnesium chloride, and magnesium fluoride.

[0097] In some embodiments, the Na source includes one or more of sodium hydroxide, sodium carbonate, sodium chloride, sodium fluoride, and sodium oxide.

[0098] In some embodiments, the Sn source includes one or more of tin oxide, tin carbonate, tin chloride, tin nitrate, and tin sulfate.

[0099] In some embodiments, the Y source includes one or more of yttrium oxide, yttrium sulfate, yttrium nitrate, yttrium oxalate, yttrium acetate, and yttrium chloride.

[0100] In some embodiments, the Sb source includes antimony oxide or lithium antimonate.

[0101] 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.

[0102] In some embodiments, the Al source includes one or more of aluminum oxide, aluminum hydroxide, aluminum sulfate, aluminum chloride, and aluminum nitrate.

[0103] 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.

[0104] In some embodiments, the sintering temperature of the secondary sintering is 250°C-350°C.

[0105] In some embodiments, the sintering temperature of the secondary sintering may be selected as 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.

[0106] In some embodiments, the sintering time of the secondary sintering may 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.

[0107] 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.

[0108] 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.

[0109] 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 points.

[0110] In some embodiments, the sintering time of the secondary sintering may be 5 h, 5.5 h, 6 h, or a value in a range consisting of any two of the above points.

[0111] The sintering time or sintering temperature is controlled within a suitable range so that the Co element additive does not substantially enter the matrix during the secondary sintering, the matrix is ​​substantially free of cobalt doping, and the matrix contains enough nickel elements so that the positive electrode active material has a high discharge capacity.

[0112] [Positive electrode]

[0113] The positive electrode plate 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.

[0114] 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 any one or both of the two opposite surfaces of the positive electrode current collector.

[0115] 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.).

[0116] 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), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0117] In some embodiments, the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0118] In some embodiments, the positive electrode sheet can be prepared in the following manner: 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 collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0119] [Negative electrode]

[0120] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0121] 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 any one or both of the two opposite surfaces of the negative electrode current collector.

[0122] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0123] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery 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 oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, 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.

[0124] 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).

[0125] 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.

[0126] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0127] In some embodiments, the negative electrode sheet can be prepared in the following manner: 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 collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0128] [Electrolytes]

[0129] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0130] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0131] In some embodiments, the electrolyte salt can 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.

[0132] 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, methyl propyl carbonate, ethyl propyl 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 sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0133] In some embodiments, the electrolyte may further include additives, such as 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, additives that improve battery high or low temperature performance, etc.

[0134] [Isolation film]

[0135] 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 stability and mechanical stability can be selected.

[0136] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0137] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0138] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0139] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0140] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 1 The secondary battery 5 is a square structure as an example.

[0141] In some embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a cover plate 53. Among them, 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 form 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.

[0142] In some embodiments, secondary batteries may be assembled into a battery module. The number of secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0143] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0144] 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.

[0145] 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 according to the application and capacity of the battery pack.

[0146] Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0147] In addition, the present application also provides an electrical 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 electrical device, and can also be used as an energy storage unit for the electrical device. The electrical 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 are not limited thereto.

[0148] As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

[0149] Figure 6 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0150] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be light and thin, and a secondary battery may be used as a power source.

[0151] Example

[0152] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0153] 1. Preparation method

[0154] Example 1

[0155] 1) Primary sintering: Lithium hydroxide and precursor Ni(OH) 2 Put it into a high-speed mixer for mixing to obtain a first mixed material, in which lithium hydroxide and precursor Ni(OH) 2 The molar ratio of is 1.03:1. In a pure oxygen atmosphere, the first mixed material is placed in a kiln for the first calcination at a temperature of 685°C for 5 hours to obtain a first product;

[0156] 2) The first product and the coating additive Co(OH) 2 Put it into a high-speed mixer for mixing to obtain a second mixture, wherein the coating additive Co(OH) 2 The mass content is 1.2%, based on Ni(OH) 2 and Co(OH) 2 The mass meter is used; in a high-purity oxygen atmosphere, the second mixture is placed in a kiln for calcination at a temperature of 300°C and a calcination time of 6 hours. The obtained material is subjected to mechanical pulverizing and grading, demagnetization, sieving, and packaging to obtain the positive electrode active material.

[0157] 2) Preparation of positive electrode

[0158] The positive electrode active material, the conductive agent carbon black, and the 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 it is coated on the positive electrode collector, and the positive electrode sheet is obtained after drying, cold pressing, and cutting.

[0159] 3) Preparation of negative electrode sheet

[0160] The negative electrode active material artificial graphite, hard carbon, conductive agent acetylene black, binder styrene butadiene rubber (SBR), thickener sodium carbon methyl cellulose (CMC) are fully stirred and mixed in a deionized water solvent system according to a mass ratio of 90%: 5%: 2%: 2%: 1%, and then coated on copper foil, dried, and cold pressed to obtain a negative electrode sheet.

[0161] 4) Electrolyte

[0162] In an argon atmosphere glove box (H2 O<0.1ppm, O 2 <0.1ppm), lithium salt lithium hexafluorophosphate LiPF 6 Dissolve in organic solvent ethylene carbonate / ethyl methyl carbonate / dimethyl carbonate (the volume ratio of EC+EMC+DMC is 1:1:1), stir evenly, and obtain LiPF 6 The concentration of the electrolyte is 1 mol / L.

[0163] 5) Isolation film

[0164] A polyethylene porous polymer film is used as the isolation membrane.

[0165] 6) Preparation of button cells

[0166] The lithium sheet was used as the negative electrode and assembled with the positive electrode of Example 1 into a standard button cell.

[0167] 7) Preparation of secondary batteries

[0168] The positive electrode sheet, isolation film, and negative electrode sheet of Example 1 are stacked in order, so that the isolation film is placed between the positive and negative electrode sheets to play an isolating role, and then wound to obtain a battery cell, the electrode ears are welded to the battery cell, and the battery cell is placed in an aluminum shell, and then the electrolyte is injected and sealed. After standing, cold pressing, formation, shaping, capacity testing and other processes, a lithium-ion secondary battery is obtained.

[0169] The preparation parameters in Examples 2-5 are substantially the same as those in Example 1, but the mass content of the coating additives is adjusted, as follows:

[0170] Example 2: Coating additive Co(OH) 2 The mass content is 0.4%, based on Ni(OH) 2 and Co(OH) 2 of the quality meter.

[0171] Example 3: Coating additive Co(OH) 2 The mass content is 0.9%, based on Ni(OH) 2 and Co(OH) 2 of the quality meter.

[0172] Example 4: Coating additive Co(OH) 2 The mass content is 1.4%, based on Ni(OH) 2 and Co(OH) 2 The quality meter.

[0173] Example 5: Coating additive Co(OH) 2 The mass content is 1.6%, based on Ni(OH) 2 and Co(OH)2 The quality meter.

[0174] The preparation parameters in Example 6 are substantially the same as those in Example 1, but the secondary sintering temperature is adjusted to 350°C.

[0175] 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:

[0176] Primary sintering: Lithium hydroxide and precursor Ni(OH) 2 and the dopant barium titanate are put into a high-speed mixer for mixing to obtain a first mixed material, wherein lithium hydroxide and the precursor Ni(OH) 2 The molar ratio of Ni(OH) is 1.03:1, and the mass content of the dopant barium titanate is 0.02%. 2 In a pure oxygen atmosphere, the first mixed material is placed in a kiln for the first calcination at a temperature of 685° C. for 5 hours to obtain a first product;

[0177] 2) The first product and the coating additive Co(OH) 2 Put it into a high-speed mixer for mixing to obtain a second mixture, wherein the coating additive Co(OH) 2 The mass content is 1.2%, based on Ni(OH) 2 and Co(OH) 2 The mass meter is used; in a high-purity oxygen atmosphere, the second mixture is placed in a kiln for calcination at a temperature of 300°C and a calcination time of 6 hours. The obtained material is subjected to mechanical pulverizing and grading, demagnetization, sieving, and packaging to obtain the positive electrode active material.

[0178] Example 8

[0179] The preparation parameters of Example 8 are basically the same as those of Example 7, but the dopant of barium titanate in the first sintering is replaced by tungsten trioxide.

[0180] Examples 9-12

[0181] The preparation parameters in Examples 9-12 are substantially the same as those in Example 7, but the mass content of barium titanate is adjusted respectively, as follows:

[0182] Example 9: The mass content of the dopant barium titanate is 0.01%, based on Ni(OH) 2 of the quality meter.

[0183] Example 10: The mass content of the dopant barium titanate is 0.02%, based on Ni(OH) 2 of the quality meter.

[0184] Example 11: The mass content of the dopant barium titanate is 0.08%, based on Ni(OH) 2 of the quality meter.

[0185] Example 12: The mass content of the dopant barium titanate is 1%, based on Ni(OH) 2 of the quality meter.

[0186] Comparative Example 1-2

[0187] 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:

[0188] Primary sintering: LiOH and precursor Ni(OH) 2 Put it into a high-speed mixer for mixing to obtain a first mixed material, in which lithium hydroxide and precursor Ni(OH) 2 The molar ratio of is 1.03: 1. In a pure oxygen atmosphere, the first mixed material is placed in a kiln for the first calcination at a temperature of 685° C. for 5 hours to obtain a positive electrode active material.

[0189] The preparation parameters of Comparative Example 2 are substantially 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:

[0190] Primary sintering: Lithium hydroxide and precursor Ni(OH) 2 and dopant Co(OH) 2 Put it into a high-speed mixer for mixing to obtain a first mixed material, in which lithium hydroxide and precursor Ni(OH) 2 The molar ratio is 1.03:1, and the doping additive Co(OH) 2 The mass content is 1.2%, based on Ni(OH) 2 and Co(OH) 2 In a pure oxygen atmosphere, the first mixed material was placed in a kiln for the first calcination at a temperature of 685° C. for 5 h to obtain a positive electrode active material.

[0191] 2. Performance Test

[0192] 1. Cathode active material testing

[0193] 1) Determination of the mass content of characteristic elements in the matrix and coating layer of the positive electrode active material

[0194] 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 the copper foil to obtain the sample, and dried at 60°C for 30 minutes. The prepared sample is cut into 6mm×6mm size with scissors, fixed on the sample stage, and placed in an ion polisher (model: IB-19500CP). The sample edge is adjusted to be parallel to the center line X axis and the Y axis position is 40-60μm for cutting. After cutting, the X-Max energy dispersive spectrometer (EDS) of the Oxford Instruments Group of the United Kingdom is combined with the Sigma-02-33 scanning electron microscope (SEM) of the German ZEISS. A suitable particle section is selected on the cut sample, and a linear scan of the characteristic elements (Co element or N element) of the coating layer and the characteristic elements (Co element or M element) of the matrix are performed along the particle diameter direction to obtain the mass content of the characteristic elements in the matrix and the coating layer.

[0195] 2) Discharge capacity of positive electrode active material

[0196] At a voltage of 2.5V to 4.4V, the button cells of the embodiment and the comparative example were charged to 4.4V at a constant current of 0.1C, then charged to a current of ≤0.05mA at a constant voltage of 4.4V, and allowed to stand for 2min. The charging capacity at this time was recorded as C0; and then discharged to 2.5V at a constant current of 0.1C. The discharge capacity at this time was recorded as D0.

[0197] 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.

[0198] 2. Battery performance

[0199] 1) Cycle performance

[0200] The secondary battery prepared in each embodiment and comparative example is charged at a constant current of 0.5C to a charge cut-off voltage of 4.25V, then charged at a constant voltage to a current of ≤0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.33C to a discharge cut-off voltage of 2V, left to stand for 5 minutes. This is a charge and discharge cycle. The battery is tested for cyclic charge and discharge according to this method until the battery capacity decays to 80%. The number of cycles at this time is the cycle life of the battery at 25°C.

[0201] III. Analysis of test results of various embodiments and comparative examples

[0202] The batteries of the embodiments and comparative examples were prepared according to the above method, and various performance parameters were measured. The results are shown in Table 1 below.

[0203] Table 1

[0204]

[0205]

[0206]

[0207] From the above results, it can be seen that the positive electrode active material in Examples 1-12 includes a lithium nickelate substrate and a coating layer at least partially covering the substrate, and 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 between Examples 1-12 and Comparative Examples 1-2, it can be seen that compared with no coating layer or the Co element mass content in the substrate is 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 cycles of the battery and extend the service life of the battery.

[0208] As can be seen from Examples 1-12, by controlling the mass content W1 of the Co element in the coating layer to be 0.4%-1.6%, the positive electrode active material has a high discharge gram capacity, and the material has high cycle stability, the battery has a high number of cycles, and the battery performance is comprehensively improved. As can be seen from the comparison between Examples 1, 3, 4, and 6 and Examples 2 and 5, by controlling the mass content W1 of the Co element in the coating layer to be 0.9%-1.4%, the discharge gram capacity of the positive electrode active material and the number of cycles of the battery can be further improved.

[0209] From Examples 1-12, it can be seen that the mass content W2 of the Co element in the matrix is ​​less than or equal to 0.02%, the positive electrode active material has a high discharge gram capacity, and the material has high cycle stability, the battery has a high number of cycles, and the performance of the battery is comprehensively improved. From the comparison between Example 1 and Example 6, it can be seen that the mass content W2 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 number of cycles of the battery.

[0210] From the comparison between Examples 7-12 and Example 1, it can be seen that the matrix of the positive electrode active material also contains Ba or W elements, which can increase the discharge gram capacity of the positive electrode active material and the number of cycles of the battery, and improve the cycle performance of the battery. From the comparison between Example 7 and Example 8, it can be seen that the matrix of the positive electrode active material includes Ba elements, which can further increase the number of cycles of the battery and improve the cycle performance of the battery.

[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 cycles of the battery, and at the same time, the positive electrode active material has a high discharge gram capacity.

[0212] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining 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, It is 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, It is 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, It is 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, It is 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, It is 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, It is characterized in that The matrix includes lithium nickelate.

7. The positive electrode active material according to any one of claims 1 to 6, It is 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, It is characterized in that The thickness of the coating layer is 0.5nm-4nm, and can be optionally 1nm-2nm.

9. A method for preparing a positive electrode active material, It is characterized in that include: Mixing a first raw material including a lithium source and a precursor material uniformly, 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, It is 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, It is 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, It is 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, It is 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, It is 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, It is characterized in that Includes the secondary battery as claimed in claim 14.

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