Phosphate composite positive electrode active material, preparation method thereof, positive electrode sheet, battery cell, battery and electric device

Abstract

The application discloses a phosphate composite positive electrode active material and a preparation method thereof, a positive electrode sheet, a battery monomer, a battery and a power utilization device. The preparation method of the phosphate composite positive electrode active material comprises the following steps: providing a first mixed solution containing graphite oxide and a metal salt; performing a first peeling reaction on the first mixed solution at a first shearing speed of 6000 r / min or above to obtain a second mixed solution; maintaining the first shearing speed, adding a precipitant or an aqueous solution of the precipitant into the second mixed solution to perform a second precipitation reaction, and obtaining a third mixed solution; performing washing and drying on the third mixed solution to obtain a mixture of a phosphate positive electrode active material precursor and graphene oxide; performing grinding treatment on the mixture and a lithium source, a phosphorus source, a carbon source and a doping element source in the presence of a first solvent to obtain a slurry, and then performing spray drying granulation and sintering treatment to obtain the phosphate composite positive electrode active material.

Description

TECHNICAL FIELD

[0001] The present application relates to a phosphate composite cathode active material, a preparation method thereof, a cathode sheet, a battery cell, a battery and a power utilization device. BACKGROUND

[0002] In recent years, batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. The cathode active material is one of the key factors affecting the electrochemical performance of the battery. Phosphate cathode active materials have become one of the most concerned cathode active materials due to their advantages such as abundant raw material sources. However, the electronic conductivity of phosphate cathode active materials is poor. At present, the electronic conductivity of phosphate cathode active materials is mainly improved by coating phosphate cathode active materials with graphene. However, the raw material cost of graphene is high, and the interface bonding force between graphene and phosphate cathode active material particles is poor, making it difficult to achieve complete coating, thereby affecting the capacity development of the battery and the electrochemical performance of the battery. The above statements are only used to provide background technical information related to the present application, and do not necessarily constitute the prior art. SUMMARY

[0003] The present application provides a phosphate composite cathode active material, a preparation method thereof, a cathode sheet, a battery cell, a battery and a power utilization device, which can reduce the raw material cost, energy cost and time cost of the phosphate composite cathode active material, and also can improve the capacity and electrochemical performance of the phosphate composite cathode active material.

[0004] The first aspect of the present application provides a preparation method of a phosphate composite positive electrode active material, comprising the following steps: providing a first mixed solution containing graphite oxide and a metal salt used for preparing a phosphate positive electrode active material, wherein the solvent in the first mixed solution comprises water; performing a first exfoliation reaction on the first mixed solution at a first shear rate of 6000 r / min or higher, so that the graphite oxide is exfoliated into graphene oxide, to obtain a second mixed solution; maintaining the first shear rate, adding a precipitant or an aqueous solution of the precipitant into the second mixed solution to perform a second precipitation reaction, to obtain a third mixed solution, wherein the precipitant comprises one or more of oxalic acid and a water-soluble oxalate; performing washing and drying on the third mixed solution to obtain a mixture of a phosphate positive electrode active material precursor and graphene oxide; performing grinding treatment on the mixture of the phosphate positive electrode active material precursor and graphene oxide in the presence of a first solvent, to obtain a slurry, and then performing spray drying granulation and sintering treatment to obtain a phosphate composite positive electrode active material, wherein the phosphate composite positive electrode active material comprises a phosphate positive electrode active material, amorphous carbon coating the phosphate positive electrode active material, and reduced graphene oxide coating the amorphous carbon.

[0005] The preparation method of the phosphate composite positive electrode active material provided by the present application uses low-cost graphite oxide as a raw material, thereby reducing the raw material cost in production, and also reducing the energy consumption cost and time cost. The preparation method of the phosphate composite positive electrode active material provided by the present application also has the advantages of simple process and high production efficiency, thereby being easy to be industrialized for large-scale production.

[0006] The preparation method of the phosphate composite positive electrode active material provided by the present application can obtain a phosphate composite positive electrode active material with single crystal phase, high purity, small particle size, narrow particle size distribution, uniform element distribution and high batch consistency. In addition, the obtained phosphate composite positive electrode active material can form a continuous conductive network. Therefore, the phosphate composite positive electrode active material obtained by using the preparation method provided by the present application has high electronic conductivity and high ionic conductivity, which is beneficial to promoting efficient transmission of electrons, and also beneficial to shortening the transmission path of ions, thereby being beneficial to improving the capacity and electrochemical performance of the battery, such as the cycle performance and rate performance.

[0007] In any embodiment, the first exfoliation reaction is performed in a high-speed dispersion homogenizer.

[0008] In any embodiment, the first shear rate is 6000-15000 r / min, which can be 6000-10000 r / min.

[0009] In any embodiment, the first peeling reaction time is 30-150 min, optionally 60-120 min.

[0010] In any embodiment, the number of layers of the graphene oxide is 1-6, optionally 3-5.

[0011] Adjusting the first shearing speed and the first peeling reaction time can adjust the number of layers of the graphene oxide. The greater the first shearing speed and the longer the first peeling reaction time, the fewer the number of layers of the graphene oxide peeled from the graphene oxide. Therefore, the preparation method provided in the embodiments of the present application can also realize the regulation of the number of layers of the graphene oxide.

[0012] In any embodiment, the mass ratio of the graphene oxide to the metal salt for preparing the phosphate positive electrode active material is 0.03:1-0.08:1.

[0013] In any embodiment, the concentration of the metal salt for preparing the phosphate positive electrode active material in the first mixed solution is 0.5-2 mol / L.

[0014] In any embodiment, the metal salt for preparing the phosphate positive electrode active material comprises a water-soluble divalent metal salt, which optionally comprises one or more of a sulfate, a nitrate, a hydrochloride and an acetate.

[0015] In any embodiment, the divalent metal element comprises an Mn element and / or an Fe element and optionally an M element, the M element representing a doping element of an Mn site and / or an Fe site of the phosphate composite positive electrode active material, which optionally comprises one or more of Ni, Co, Mg, Zn, Ca, Ti, V and Cr.

[0016] In any embodiment, the second precipitation reaction time is 10-60 min.

[0017] In any embodiment, the molar ratio of the precipitant to the metal salt for preparing the phosphate positive electrode active material is 1:1-3:1. Adjusting the amount of the precipitant helps to improve the conversion efficiency of the metal ions, reduce the difference in precipitation rate of different metal ions in the reaction system, thereby helping the uniform co-precipitation of the metal ions, and further helping the proportion of each metal element in the prepared phosphate composite positive electrode active material to have a higher consistency with the proportion of each metal element in the raw material. Adjusting the amount of the precipitant also helps to make the co-precipitation reaction more complete, thereby reducing the metal ion content in the reaction waste liquid, and reducing the difficulty of waste liquid treatment process and reducing environmental pollution; in addition, it also helps to improve the purity of the obtained phosphate positive electrode active material precursor and reduce the content of impurities.

[0018] In any embodiment, the precipitant comprises one or more of oxalic acid, sodium oxalate, potassium oxalate, and ammonium oxalate.

[0019] In any embodiment, the concentration of the aqueous solution of the precipitant is 0.5-2 mol / L.

[0020] In any embodiment, the step of providing the first mixed solution comprising graphite oxide and a metal salt for preparing a phosphate cathode active material comprises the following steps: adding graphite oxide into water under a protective gas atmosphere, and then adding the metal salt for preparing a phosphate cathode active material, and obtaining the first mixed solution after uniform dispersion.

[0021] In any embodiment, the protective gas comprises nitrogen, an inert gas, or a combination thereof.

[0022] In any embodiment, the first solvent comprises one or more of an alcohol solvent, water, and optionally comprises one or more of ethanol and water.

[0023] In any embodiment, the grinding treatment comprises high-energy ball milling or sand milling.

[0024] In any embodiment, the rotation speed of the grinding treatment is 1000-2500 r / min.

[0025] In any embodiment, the time of the grinding treatment is 1-5 h.

[0026] In any embodiment, the sintering treatment comprises a pre-sintering treatment and a high-temperature sintering treatment.

[0027] In any embodiment, the temperature of the pre-sintering treatment is 350-550°C, and optionally 400-500°C.

[0028] In any embodiment, the time of the pre-sintering treatment is 2-12 h, and optionally 3-10 h.

[0029] In any embodiment, the temperature of the high-temperature sintering treatment is 600-800°C, and optionally 650-750°C.

[0030] In any embodiment, the time of the high-temperature sintering treatment is 5-24 h, and optionally 8-12 h.

[0031] In any embodiment, the pre-sintering treatment is performed under a protective gas atmosphere.

[0032] In any embodiment, the high-temperature sintering treatment is performed under a protective gas atmosphere.

[0033] In any embodiment, the step of mixing the phosphate positive electrode active material precursor and graphene oxide mixture with a lithium source, a phosphorus source, a carbon source, optionally a Li-site doping element source, optionally a P-site doping element source, optionally an O-site doping element source in the presence of a first solvent to obtain a slurry, followed by spray drying granulation, sintering treatment to obtain the phosphate composite positive electrode active material comprises the following steps: first grinding treatment of the phosphate positive electrode active material precursor and graphene oxide mixture with a lithium source, a phosphorus source, optionally a Li-site doping element source, optionally a P-site doping element source, optionally an O-site doping element source in the presence of a first solvent to obtain a first slurry; spray drying granulation of the first slurry to obtain a powder, followed by pre-sintering treatment to obtain a pre-sintered powder; second grinding treatment of the pre-sintered powder with the carbon source in the presence of a first solvent to obtain a second slurry; spray drying granulation of the second slurry to obtain a powder, followed by high-temperature sintering treatment, optionally crushing treatment to obtain the phosphate composite positive electrode active material.

[0034] Thus, the obtained phosphate composite positive electrode active material can form a continuous conductive network, thereby facilitating the improvement of the capacity and electrochemical performance, such as cycle performance and rate performance, of the battery.

[0035] In any embodiment, the rotation speed of the first grinding treatment is 1500-2500 r / min.

[0036] In any embodiment, the time of the first grinding treatment is 1-5 h.

[0037] In any embodiment, the rotation speed of the second grinding treatment is 1000-2500 r / min.

[0038] In any embodiment, the time of the second grinding treatment is 1-3 h.

[0039] In any embodiment, the Li-site doping element comprises one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W.

[0040] In any embodiment, the P-site doping element comprises one or more elements selected from B, S, Si and N.

[0041] In any embodiment, the O-site doping element comprises one or more elements selected from S, F, Cl and Br.

[0042] In any embodiment, the lithium source comprises one or more selected from lithium hydroxide, lithium carbonate, lithium dihydrogen phosphate, lithium hydrogen phosphate, lithium nitrate and lithium acetate.

[0043] In any embodiment, the carbon source comprises one or more of sucrose, glucose, polyvinyl alcohol, polyethylene glycol, phenol formaldehyde resin, citric acid, and cyclodextrin.

[0044] In any embodiment, the carbon source comprises one or more of sucrose, glucose, polyvinyl alcohol, polyethylene glycol, phenol formaldehyde resin, citric acid, and cyclodextrin.

[0045] In any embodiment, the Li-site doping element source comprises one or more of a sulfate, a nitrate, a hydrochloride, and an acetate of the Li-site doping element.

[0046] In any embodiment, the P-site doping element source comprises one or more of a sulfate, a borate, a nitrate, and a silicate of the P-site doping element.

[0047] In any embodiment, the O-site doping element source comprises one or more of an elemental substance and an ammonium salt of the O-site doping element.

[0048] The second aspect of the present application provides a phosphate composite positive electrode active material prepared by the method of the first aspect of the present application, the phosphate composite positive electrode active material comprising a phosphate positive electrode active material, amorphous carbon coated on the phosphate positive electrode active material, and reduced graphene oxide coated on the amorphous carbon.

[0049] The phosphate composite positive electrode active material provided by the present application has the characteristics of single crystal phase, high purity, regular morphology, small particle size, narrow particle size distribution, uniform element distribution, and high batch consistency. In addition, the phosphate composite positive electrode active material also has a continuous conductive network and a shortened ion transport path, which is conducive to promoting the efficient transmission of electrons and ions, and thus is conducive to improving the capacity and electrochemical performance of the battery, such as the cycle performance and rate performance.

[0050] In any embodiment, the volume distribution particle size Dv50 of the phosphate composite positive electrode active material satisfies 0.5 pm≤Dv50≤3 pm.

[0051] In any embodiment, the volume distribution particle size Dv90 and Dv50 of the phosphate composite positive electrode active material satisfy 1

[0052] In any embodiment, the powder resistivity of the phosphate composite positive electrode active material is 1-100 W-cm.

[0053] In any embodiment, the molecular formula of the phosphate positive electrode active material is Li a N b Fe x Mn y M 1-x-y P 1-m Q mO 4- n R n M represents a doping element of Mn site and / or Fe site, optionally including one or more elements of Ni, Co, Mg, Zn, Ca, Ti, V and Cr; N represents a doping element of Li site, optionally including one or more elements of Zn, Al, Na, K, Mg, Nb, Mo and W; Q represents a doping element of P site, optionally including one or more elements of B, S, Si and N; R represents a doping element of O site, optionally including one or more elements of S, F, Cl and Br; 0.9≤a≤1.1; 0≤b≤0.1; 0≤x≤1; 0≤y≤1; 0≤1-x-y<1; 0≤m≤0.1; 0≤n≤0.1.

[0054] In any embodiment, 0.001≤x≤0.999, 0.001≤y≤0.999, 0≤1-x-y≤0.10.

[0055] In any embodiment, 0.199≤x≤0.500, 0.499≤y≤0.800, 0<1-x-y≤0.10.

[0056] The third aspect of the present application provides a positive electrode tab, comprising 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 comprises the phosphate composite positive electrode active material prepared by the method of the first aspect of the present application or the phosphate composite positive electrode active material of the second aspect of the present application.

[0057] The fourth aspect of the present application provides a battery monomer comprising the positive electrode tab of the third aspect of the present application.

[0058] The fifth aspect of the present application provides a battery comprising the battery monomer of the fourth aspect of the present application.

[0059] The sixth aspect of the present application provides an electric device comprising the battery of the fifth aspect of the present application.

[0060] The electric device of the present application comprises the battery provided by the present application, and thus has at least the same advantages as the battery. BRIEF DESCRIPTION OF DRAWINGS

[0061] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the drawings.

[0062] Figure 1is a structural schematic diagram of a battery cell provided by some embodiments of the present application.

[0063] Figure 2 is a structural schematic diagram of a battery cell provided by some embodiments of the present application.

[0064] Figure 3 is a structural schematic diagram of a battery module provided by some embodiments of the present application.

[0065] Figure 4 is a structural schematic diagram of a battery pack provided by some embodiments of the present application.

[0066] Figure 5 is Figure 4 is an exploded schematic diagram of the battery pack shown in

[0067] Figure 6 is a schematic diagram of an electrical device provided by some embodiments of the present application.

[0068] Figure 7 (a) shows a scanning electron microscope (SEM) image of the Mn 0.6 Fe 0.4 C2O4·2H2O and graphene oxide mixture, Figure 7 (b) shows a scanning electron microscope (SEM) image of the Mn 0.6 Fe 0.4 C2O4·2H2O prepared in Comparative Example 1.

[0069] Figure 8 (a) shows a scanning electron microscope (SEM) image of the phosphate composite cathode active material prepared in Example 1, Figure 8 (b) shows a scanning electron microscope (SEM) image of the phosphate composite cathode active material prepared in Comparative Example 1.

[0070] Figure 9 is a capacity-voltage curve of a button cell prepared from the phosphate composite cathode active material of Example 1 and Comparative Example 1.

[0071] Figure 10 is a rate curve of a button cell prepared from the phosphate composite cathode active material of Example 1 and Comparative Example 1.

[0072] In the drawings, the drawings are not necessarily drawn according to the actual proportions. The reference signs are explained as follows: 1, battery pack; 2, upper box body; 3, lower box body; 4, battery module; 5, battery cell; 51, shell; 52, electrode assembly; 53, cover plate. DETAILED DESCRIPTION

[0073] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the phosphate composite positive electrode active material, its preparation method, positive electrode sheet, battery cell, battery, and power device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for a full understanding of this application by those skilled in the art and are not intended to limit the subject matter of the claims.

[0074] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0075] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0076] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0077] Unless otherwise specified, all steps in this 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 it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0078] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0079] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: 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).

[0080] Unless otherwise specified, in this application, the terms "first," "second," "third," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0081] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0082] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0083] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in the embodiments of this application. Unless otherwise stated, the test temperature for each parameter is 25°C.

[0084] Poor electronic conductivity is a significant factor limiting the large-scale application of phosphate cathode active materials. Currently, the main approach is to directly mix phosphate cathode active materials with commercially available graphene and then prepare coated phosphate composite cathode active materials using complex hydrothermal or high-temperature solid-state methods to improve the electronic conductivity of the phosphate cathode active material core. However, the high price of commercially available graphene leads to high raw material costs for phosphate composite cathode active materials, hindering their widespread application. Furthermore, the interfacial bonding between graphene and the phosphate cathode active material core is weak, making it difficult to achieve complete coating and form a continuous conductive network. Consequently, the electronic conductivity of the phosphate composite cathode active material fails to meet expectations, thus affecting battery capacity and electrochemical performance.

[0085] Furthermore, graphene-coated phosphate composite cathode active materials are mainly prepared via high-temperature solid-state methods, such as physical grinding and mixing of lithium sources, manganese sources, iron sources, dopant sources, and graphene through high-energy ball milling. However, due to the limited particle size of the raw materials, it is difficult to achieve atomic-level mixing of manganese and iron, and the dopant elements also do not easily penetrate the phosphate crystals, affecting the electrochemical performance of the prepared phosphate composite cathode active material. Simultaneously, the content of each metal element in the prepared phosphate composite cathode active material deviates significantly from the metal ratio in the raw materials, resulting in poor batch-to-batch consistency.

[0086] In view of this, the inventors improved the preparation process of phosphate composite positive electrode active materials.

[0087] This application provides a method for preparing a phosphate composite positive electrode active material, comprising the following steps: providing a first mixture containing graphite oxide and a metal salt for preparing the phosphate positive electrode active material, wherein the solvent in the first mixture includes water; subjecting the first mixture to a first exfoliation reaction at a first shear rate of 6000 r / min or higher to exfoliate the graphite oxide into graphene oxide, thereby obtaining a second mixture; maintaining the first shear rate, adding a precipitant or an aqueous solution of the precipitant to the second mixture to carry out a second precipitation reaction, thereby obtaining a third mixture, wherein the precipitant includes one or more of oxalic acid and water-soluble oxalate; and further... The third mixture is washed and dried to obtain a mixture of phosphate cathode active material precursor and graphene oxide. The mixture of phosphate cathode active material precursor and graphene oxide is then ground with a lithium source, a phosphorus source, a carbon source, an optional Li site doping element source, an optional P site doping element source, and an optional O site doping element source in the presence of the first solvent to obtain a slurry. After spray drying, granulation, and sintering, a phosphate composite cathode active material is obtained. The phosphate composite cathode active material includes a phosphate cathode active material, amorphous carbon coating the phosphate cathode active material, and reduced graphene oxide coating the amorphous carbon.

[0088] The first stripping reaction was carried out in a high-speed dispersing homogenizer.

[0089] The high-speed dispersion homogenizer has a unique stator and rotor structure that can generate super shear force and can also circulate materials to complete online dispersion, emulsification, homogenization and mixing processes.

[0090] In the preparation of phosphate composite cathode active materials, a high-speed high-speed disperser homogenizer can be used to draw the first mixture into its working chamber. The powerful centrifugal force propels the material radially into the narrow, precise gap between the rotor and stator. Here, the material is thoroughly dispersed and broken down under intense liquid-phase shearing, liquid-layer friction, and tearing collisions. Simultaneously, it is ejected at high speed through the stator slots, and its flow direction changes due to the resistance of the material itself and the container wall. At the same time, the axial suction force generated in the rotor region creates two strong turbulent flows. After multiple cycles, graphene oxide (usually in block form) can be exfoliated into graphene oxide, and metal ions in the first mixture can be tightly adsorbed onto the graphene oxide. Conventional stirrers, even at high stirring speeds, can only achieve simple dispersion and cannot exfoliate graphene oxide into graphene oxide.

[0091] The surface of graphene oxide exfoliated from graphene oxide possesses oxygen-containing functional groups (such as hydroxyl and carboxyl groups), which can electrostatically adsorb positively charged metal ions, thereby tightly adsorbing metal salts onto the graphene oxide surface. With the addition of a precipitant, crystal nuclei can grow and adhere in situ on the graphene oxide surface. Furthermore, under the strong dispersion and fragmentation action of a high-speed dispersion homogenizer, graphene oxide-encapsulated phosphate cathode active material precursors are formed. Additionally, the high-speed shearing action of the high-speed dispersion homogenizer instantly increases the initial concentration of the reaction system upon the addition of the precipitant, allowing the metal salt and precipitant to co-precipitate directly. This promotes faster nucleation rather than particle growth, thus facilitating the preparation of small-particle-size phosphate cathode active material precursors. Moreover, it promotes uniform co-precipitation of various metal elements, resulting in phosphate cathode active material precursors with regular morphology, narrow particle size distribution, uniform elemental distribution, and high batch-to-batch consistency.

[0092] When the obtained phosphate cathode active material precursor and graphene oxide mixture are further ground with a lithium source, a phosphorus source, a carbon source, an optional Li-site dopant source, an optional P-site dopant source, and an optional O-site dopant source in the presence of a first solvent, the carbon source can fill the spaces between the phosphate cathode active material particles, forming an in-situ grown amorphous carbon coating layer on the surface of the phosphate cathode active material. This amorphous carbon coating layer can enhance the interfacial interaction between the graphene coating layer and the phosphate cathode active material, and can also form a continuous conductive network with the outer graphene coating layer. This continuous conductive network can connect the phosphate cathode active material particles in the cathode film layer and reduce particle aggregation, resulting in a phosphate composite cathode active material with high electronic conductivity, which is beneficial for efficient electron transport and also helps improve the cycle performance and rate performance of the battery.

[0093] The phosphate cathode active material precursor obtained by the preparation method provided in this application has the advantages of regular morphology, small particle size, narrow particle size distribution, uniform element distribution and high batch consistency. When using it as a raw material to continue preparing phosphate composite cathode active materials, the grinding time (e.g., high-energy ball milling or sand milling) can be reduced, thereby reducing energy and time costs in production. It is also easy to achieve uniform mixing of multiple elements (e.g., Mn, Fe, doping elements, etc.), and the proportion of each metal element in the prepared phosphate composite cathode active material has a high consistency with the proportion of each metal element in the raw material. This also enables the prepared phosphate composite cathode active material to have high batch consistency and good electrochemical performance.

[0094] Therefore, the preparation method of the phosphate composite positive electrode active material provided in this application uses low-cost graphite oxide as a raw material, thereby reducing raw material costs, energy costs, and time costs in production. The preparation method of the phosphate composite positive electrode active material provided in this application also has the advantages of simple process and high production efficiency, thus facilitating large-scale industrial production.

[0095] The preparation method of phosphate composite positive electrode active material provided in this application can obtain phosphate composite positive electrode active material with single crystal phase, high purity, small particle size, narrow particle size distribution, uniform elemental distribution, and high batch consistency. Furthermore, it can enable the obtained phosphate composite positive electrode active material to form a continuous conductive network. Therefore, the phosphate composite positive electrode active material obtained by the preparation method provided in this application has high electronic conductivity and high ionic conductivity, which is beneficial for promoting efficient electron transport and shortening ion transport paths, thereby improving battery capacity and electrochemical performance, such as cycle performance and rate performance.

[0096] The first shearing rate can be 6000 r / min, 7000 r / min, 8000 r / min, 9000 r / min, 10000 r / min, 11000 r / min, 12000 r / min, 13000 r / min, 14000 r / min, 15000 r / min, or any range of the above values. Optionally, in some embodiments, the first shearing rate is 6000-15000 r / min, optionally 6000-10000 r / min.

[0097] In some embodiments, the time for the first stripping reaction can be 30-150 min, optionally 60-120 min.

[0098] In some embodiments, the number of graphene oxide layers can be 1-6, and optionally 3-5.

[0099] The number of graphene oxide layers can be adjusted by regulating the first shear rate and the duration of the first exfoliation reaction. A higher first shear rate and a longer first exfoliation reaction time result in fewer graphene oxide layers obtained from the graphene oxide. Therefore, the preparation method provided in this application can also control the number of graphene oxide layers.

[0100] In some embodiments, the mass ratio of graphite oxide to the metal salt used to prepare the phosphate cathode active material can be 0.03:1-0.08:1.

[0101] In some embodiments, the concentration of the metal salt used for preparing the phosphate cathode active material in the first mixture can be 0.5-2 mol / L. The concentration of the metal salt refers to the total concentration of all metal salts used for preparing the phosphate cathode active material in the first mixture. For example, the metal salts include ferrous sulfate and manganese sulfate, and the concentration of the metal salt refers to the total concentration of ferrous sulfate and manganese sulfate.

[0102] In some embodiments, the metal salt used to prepare the phosphate cathode active material includes a water-soluble divalent metal salt. Optionally, the water-soluble divalent metal salt may include one or more of the following: sulfate, nitrate, hydrochloride, and acetate of a divalent metal.

[0103] In some embodiments, the divalent metal element may include Mn and / or Fe, and optionally M, where M represents the doping element at the Mn site and / or Fe site of the phosphate composite cathode active material, and optionally includes one or more elements selected from Ni, Co, Mg, Zn, Ca, Ti, V, and Cr.

[0104] Phosphate cathode active material precursors refer to the products resulting from the precipitation reaction of metal salts used in the preparation of phosphate cathode active materials with a precipitant. In some embodiments, phosphate cathode active material precursors may include manganese ferric oxalate, etc.

[0105] In some embodiments, the step of providing a first mixture comprising graphite oxide and a metal salt for preparing a phosphate cathode active material includes the following steps: adding graphite oxide to water under a protective gas atmosphere, then adding the metal salt for preparing a phosphate cathode active material, and dispersing it evenly to obtain the first mixture.

[0106] In some embodiments, the protective gas may include nitrogen, an inert gas, or a combination thereof.

[0107] In some embodiments, the second precipitation reaction can take 10-60 minutes.

[0108] In some embodiments, the molar ratio of the precipitant to the metal salt used to prepare the phosphate cathode active material can be 1:1 to 3:1. Adjusting the amount of precipitant helps to improve the conversion efficiency of metal ions and reduce the difference in precipitation rates of different metal ions in the reaction system, thereby facilitating the uniform co-precipitation of metal ions. This, in turn, helps to ensure that the proportions of each metal element in the prepared phosphate composite cathode active material are highly consistent with the proportions of each metal element in the raw materials. Adjusting the amount of precipitant also helps to make the co-precipitation reaction more complete, thereby reducing the metal ion content in the reaction waste liquid, reducing the difficulty of waste liquid treatment, and reducing environmental pollution. In addition, it also helps to improve the purity of the obtained phosphate cathode active material precursor and reduce the content of impurities.

[0109] In some embodiments, the precipitant may include one or more of oxalic acid, sodium oxalate, potassium oxalate, and ammonium oxalate.

[0110] The precipitant can be added to the second mixture in the form of an aqueous solution of the precipitant. In some embodiments, the concentration of the aqueous solution of the precipitant can be 0.5-2 mol / L.

[0111] In some embodiments, when washing the third mixture, the washing liquid may include ethanol, water, or a mixture of both, and the number of washing cycles may be one or more, which is not limited in this application.

[0112] The washed material can be dried using known drying processes. In some embodiments, a vacuum drying process can be used. Optionally, the drying temperature can be below 100°C.

[0113] The grinding process can employ suitable grinding methods known in the art. In some embodiments, the grinding process may include high-energy ball milling or sand milling, which is not limited in this application.

[0114] In some embodiments, the grinding speed can be 1000-2500 r / min.

[0115] In some embodiments, the grinding process can take 1-5 hours.

[0116] In some embodiments, the sintering process may include pre-sintering treatment and high-temperature sintering treatment.

[0117] In some embodiments, the temperature of the pre-sintering treatment can be 350°C-550°C, and optionally 400°C-500°C.

[0118] In some embodiments, the pre-sintering treatment time can be 2-12 hours, or optionally 3-10 hours.

[0119] In some embodiments, the pre-sintering process can be performed under a protective gas atmosphere.

[0120] In some embodiments, the temperature of the high-temperature sintering treatment can be 600℃-800℃, and optionally 650℃-750℃.

[0121] In some embodiments, the high-temperature sintering treatment time can be 5-24 hours, and optionally 8-12 hours.

[0122] In some embodiments, the high-temperature sintering process can be performed under a protective gas atmosphere.

[0123] In some embodiments, the pre-sintering treatment and high-temperature sintering treatment can be carried out in a tube furnace.

[0124] In some embodiments, the protective gas may include nitrogen, an inert gas, or a combination thereof.

[0125] In some embodiments, the step of grinding a mixture of phosphate cathode active material precursor and graphene oxide with a lithium source, a phosphorus source, a carbon source, an optional Li-site doping element source, an optional P-site doping element source, and an optional O-site doping element source in the presence of a first solvent to obtain a slurry, followed by spray drying, granulation, and sintering to obtain a phosphate composite cathode active material, includes the following steps: grinding the mixture of phosphate cathode active material precursor and graphene oxide with a lithium source, a phosphorus source, an optional Li-site doping element source, an optional P-site doping element source, and an optional O-site doping element source in the presence of a first solvent to obtain a first slurry; spray drying and granulating the first slurry to obtain a powder, and then pre-sintering to obtain a pre-sintered powder; grinding the pre-sintered powder with a carbon source in the presence of a first solvent to obtain a second slurry; spray drying and granulating the second slurry to obtain a powder, and then high-temperature sintering and optional crushing to obtain the phosphate composite cathode active material. Optionally, the crushing can be airflow crushing.

[0126] This allows the obtained phosphate composite cathode active material to form a continuous conductive network, which in turn helps to improve the battery's capacity and electrochemical performance, such as cycle performance and rate performance.

[0127] In some embodiments, the rotation speed of the first grinding process can be 1500-2500 r / min.

[0128] In some embodiments, the first grinding process can take 1-5 hours.

[0129] In some embodiments, the rotation speed of the second grinding process can be 1000-2500 r / min.

[0130] In some embodiments, the second grinding process can take 1-3 hours.

[0131] In some embodiments, the first solvent may include one or more of alcohol solvents and water, and may optionally include one or more of ethanol and water.

[0132] In some embodiments, the lithium source may be a lithium-containing compound known in the art that can be used to prepare phosphate cathode active materials. For example, the lithium source may include one or more of lithium hydroxide, lithium carbonate, lithium dihydrogen phosphate, lithium hydrogen phosphate, lithium nitrate, and lithium acetate.

[0133] In some embodiments, the phosphorus source may be a phosphorus-containing compound known in the art that can be used to prepare phosphate cathode active materials. For example, the phosphorus source may include one or more of phosphoric acid, ammonium monohydrogen phosphate, and ammonium dihydrogen phosphate.

[0134] In some embodiments, the carbon source may include one or more of organic and inorganic carbon sources. For example, the carbon source may include one or more of sucrose, glucose, polyvinyl alcohol, polyethylene glycol, phenolic resin, citric acid, and cyclodextrin.

[0135] In some embodiments, the Li-site doping element may include one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W.

[0136] In some embodiments, the Li-site dopant source may include one or more of the following: sulfate, nitrate, hydrochloride, and acetate of the Li-site dopant.

[0137] In some embodiments, the P-site doping element may include one or more elements selected from B, S, Si, and N.

[0138] In some embodiments, the P-site dopant source may include one or more of the following: sulfate, borate, nitrate, and silicate of the P-site dopant element.

[0139] In some embodiments, the O-site doping element may include one or more elements selected from S, F, Cl, and Br.

[0140] In some embodiments, the source of the O-site dopant element may include one or more of the elemental form of the O-site dopant element and an ammonium salt.

[0141] In the preparation method of the phosphate composite positive electrode active material provided in this application, the amount of each raw material added can conform to the stoichiometric ratio of the target phosphate composite positive electrode active material. In some embodiments, the amount of lithium source added can be slightly excessive, for example, it can be 100%-110% of the theoretical mass of the lithium source, where the theoretical mass of the lithium source refers to the mass of the lithium source calculated according to the stoichiometric ratio of the phosphate composite positive electrode active material.

[0142] In the preparation method of the phosphate composite positive electrode active material provided in this application, unless otherwise specified, all raw materials and instruments used can be purchased directly. The raw materials may or may not contain water of crystallization.

[0143] This application also provides a phosphate composite positive electrode active material obtained by the above preparation method. The phosphate composite positive electrode active material includes a phosphate positive electrode active material, amorphous carbon coated with the phosphate positive electrode active material, and reduced graphene oxide coated with amorphous carbon.

[0144] The phosphate composite cathode active material provided in this application has the characteristics of single crystal phase, high purity, regular morphology, small particle size, narrow particle size distribution, uniform element distribution and high batch consistency. In addition, the phosphate composite cathode active material also has a continuous conductive network and a shortened ion transport path, which is conducive to promoting the efficient transport of electrons and ions, and thus conducive to improving the battery capacity and electrochemical performance, such as cycle performance and rate performance.

[0145] In some embodiments, the volume distribution particle size Dv50 of the phosphate composite positive electrode active material satisfies 0.5μm≤Dv50≤3μm.

[0146] In some embodiments, the volume distribution particle sizes Dv90 and Dv50 of the phosphate composite positive electrode active material satisfy 1 < Dv90 / Dv50 ≤ 1.5.

[0147] In some embodiments, the resistivity of the phosphate composite positive electrode active material can be 1-100 Ω·cm.

[0148] In some embodiments, the molecular formula of the phosphate positive electrode active material is Li a N b Fe x Mn y M 1-x-y P 1-m Q m O 4-n R n M represents a doping element at the Mn site and / or Fe site, optionally including one or more elements selected from Ni, Co, Mg, Zn, Ca, Ti, V, and Cr; N represents a doping element at the Li site, optionally including one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; Q represents a doping element at the P site, optionally including one or more elements selected from B, S, Si, and N; R represents a doping element at the O site, optionally including one or more elements selected from S, F, Cl, and Br; 0.9≤a≤1.1; 0≤b≤0.1; 0≤x≤1; 0≤y≤1; 0≤1-xy<1; 0≤m≤0.1; 0≤n≤0.1.

[0149] In some embodiments, 0.001≤x≤0.999, 0.001≤y≤0.999, 0≤1-xy≤0.10. Optionally, 0.199≤x≤0.500, 0.499≤y≤0.800, 0<1-xy≤0.10.

[0150] This application also provides a positive electrode sheet.

[0151] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. For example, the positive current collector has two surfaces opposite 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 current collector.

[0152] The positive electrode film layer comprises the aforementioned phosphate composite positive electrode active material or the phosphate composite positive electrode active material obtained by the aforementioned preparation method. Of course, the positive electrode film layer may also include other positive electrode active materials, such as lithium transition metal oxides. Examples of lithium transition metal oxides may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. The modified compound may be a doping modification and / or surface coating modification of the positive electrode active material.

[0153] In some embodiments, the positive electrode film may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0154] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode binder. As an example, the positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0155] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. An example of a metal material may be one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. An example of a polymeric material substrate may be one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0156] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing positive electrode active materials, optional positive electrode conductive agents, optional positive electrode binders, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it.

[0157] This application also provides a battery.

[0158] The battery mentioned in the embodiments of this application may be a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application may include battery cells, battery modules, or battery packs.

[0159] A battery cell is the smallest unit that makes up a battery, and it can independently perform the functions of charging and discharging. A battery cell can be cylindrical, cuboid, or other shapes, etc., and the embodiments of this application are not limited in this respect. Figure 1 The example shown is a rectangular battery cell 5.

[0160] When there are multiple battery cells, they are connected in series, parallel, or mixed via a busbar. In some embodiments, the battery can be a battery module; when there are multiple battery cells, they are arranged and fixed to form a battery module. In some embodiments, the battery can be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed within the housing. In some embodiments, the housing can be part of the vehicle's chassis structure. For example, a portion of the housing can be at least part of the vehicle's floor, or a portion of the housing can be at least part of the vehicle's crossbeams and longitudinal beams.

[0161] In some embodiments, the battery can be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0162] The battery cells mentioned in the embodiments of this application include lithium-ion primary battery cells, lithium-ion secondary battery cells, lithium metal battery cells, and negative electrode-free lithium metal battery cells, etc., but the embodiments of this application are not limited to these.

[0163] The battery cell includes an electrode assembly. The electrode assembly can be a wound structure or a stacked structure, and the embodiments of this application are not limited to this.

[0164] The battery cell also includes an outer packaging, which can be used to encapsulate the electrode components and electrolyte. The outer packaging can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging can also be a flexible package, such as a pouch-type flexible package. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0165] In some embodiments, such as Figure 2As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. Electrode assemblies 52 are encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, and can be adjusted according to requirements.

[0166] In some embodiments, individual battery cells can be assembled into a battery module, and the number of individual battery cells contained in the battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module. Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0167] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0168] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0169] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing includes an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the housing.

[0170] A single battery cell includes the aforementioned positive electrode and negative electrode. The structure and composition of the negative electrode can be selected according to the type of battery cell, and this application embodiment does not limit this.

[0171] In some embodiments, the negative electrode sheet may include a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite 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 current collector.

[0172] The negative electrode active material may be any material known in the art. As an example, the negative electrode active material may include, but is not limited to, one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide, and tin alloys. This application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials may also be used.

[0173] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0174] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include one or more of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0175] In some embodiments, the negative electrode film layer may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0176] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0177] The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional negative electrode conductive agent, optional negative electrode binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0178] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet may also include a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet may also include a protective layer covering the surface of the negative electrode film layer.

[0179] In some embodiments, the negative electrode sheet may include a negative current collector and a metal layer disposed on at least one surface of the negative current collector, the metal layer may include one or more of elemental lithium and lithium alloy.

[0180] Lithium alloys can be alloys formed from metallic lithium with other metallic or non-metallic elements. For example, other metallic elements in lithium alloys may include one or more of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, and platinum, while non-metallic elements may include one or more of boron, carbon, and silicon.

[0181] In some embodiments, the negative electrode may also include a negative current collector but not a metal layer, thereby enabling the assembly of a metal-free battery cell.

[0182] In some embodiments, the negative electrode sheet can also be made directly from lithium element or lithium alloy sheets (or foils).

[0183] [Electrolytes]

[0184] The electrolyte acts as a conductor of active ions between the positive and negative electrode plates. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte may include one or more of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0185] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0186] As an example, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0187] The type of solvent is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvent may include one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0188] In some embodiments, the electrolyte may optionally 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 performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, additives that improve battery low-temperature power performance, etc.

[0189] [Isolation membrane]

[0190] Battery cells using electrolytes, as well as some battery cells using solid electrolytes, also include a separator. The separator is positioned between the positive and negative electrodes, primarily serving to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0191] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0192] The methods for preparing battery cells are well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process and / or a stacking process. The electrode assembly is placed in an outer packaging, dried, and then injected with the electrolyte. After vacuum sealing, settling, formation, and shaping processes, a battery cell is obtained. Multiple battery cells can be further connected in series, parallel, or a combination thereof to form a battery module. Multiple battery modules can also be connected in series, parallel, or a combination thereof to form a battery pack. In some embodiments, multiple battery cells can also be directly assembled into a battery pack.

[0193] Electricity-using device

[0194] This application also provides an electrical device, which includes the battery described in this application. The battery can be used as a power source for the electrical device or as an energy storage unit of the electrical device. The electrical device can be, but is not limited to, mobile devices (such as mobile phones, tablets, 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.

[0195] Electrical devices can choose the specific type of battery according to their usage needs, such as individual battery cells, battery modules, or battery packs.

[0196] Figure 6 This is a schematic diagram illustrating an example of an electrical device. This device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used as the power source.

[0197] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0198] Embodiment

[0199] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0200] Example 1

[0201] Under nitrogen atmosphere, graphite oxide was added to an appropriate amount of deionized water, followed by the addition of ferrous sulfate and manganese sulfate, with a Mn:Fe molar ratio of 6:4, to prepare a first mixed solution with a metal salt concentration of 1 mol / L. The mass ratio of graphite oxide to metal salt was 0.05:1.

[0202] The first mixture was sheared and exfoliated using a high-speed homogenizer at a rotation speed (shear rate) of 8000 r / min for 120 min to prepare a second mixture, in which graphene oxide was exfoliated into graphene oxide. While maintaining the rotation speed at 8000 r / min, an aqueous solution of oxalic acid as a precipitant was added to the second mixture to form a transient supersaturated suspension. The molar ratio of oxalic acid to the metal salt was 1:2, and the precipitation reaction time was 20 min to obtain a third mixture. The third mixture was washed multiple times with deionized water and ethanol, and the slurry was collected by centrifugation. The slurry was then dried in an 80℃ vacuum oven to obtain Mn. 0.6 Fe 0.4 A mixture of C2O4·2H2O and graphene oxide, wherein the graphene oxide encapsulates Mn 0.6 Fe 0.4 C2O4·2H2O.

[0203] Mn 0.6 Fe 0.4 A mixture of C2O4·2H2O and graphene oxide, Li2CO3, and NH4H2PO4 in a molar ratio of Li:Mn:Fe:P = 1.02:0.6:0.4:1 was weighed, and then an appropriate amount of deionized water was added as a solvent. The mixture was milled at 2500 r / min for 2 h to obtain a slurry. The slurry was then transferred to a spray dryer for spray drying and granulation to obtain powder, with the drying temperature set at 210℃. The obtained powder was then sintered in a tube furnace at 400℃ under a nitrogen atmosphere for 5 h, and naturally cooled to room temperature to obtain pre-sintered powder. The pre-sintered powder was then placed in a sand mill, and an appropriate amount of deionized water was added as a solvent. 6 wt% sucrose (based on the total weight of the pre-sintered powder) was also weighed and added to the sand mill, and milled at 2500 r / min for 2 h to obtain a slurry. The slurry was then transferred to a spray dryer for spray drying and granulation to obtain powder, with the drying temperature set at 210℃. The obtained powder was sintered in a tube furnace at 700℃ under a nitrogen atmosphere for 10 hours, then naturally cooled to room temperature, and finally pulverized by air jet milling to obtain the phosphate composite positive electrode active material. The phosphate composite positive electrode active material includes the phosphate positive electrode active material LiMn. 0.6 Fe 0.4 PO4, LiMn coated phosphate positive electrode active material 0.6 Fe 0.4 Amorphous carbon in PO4 and reduced graphene oxide coated with amorphous carbon.

[0204] Example 2

[0205] Under nitrogen atmosphere, graphite oxide was added to an appropriate amount of deionized water, followed by the addition of ferrous sulfate and manganese sulfate, with a Mn:Fe molar ratio of 6:4, to prepare a first mixed solution with a metal salt concentration of 1 mol / L. The mass ratio of graphite oxide to metal salt was 0.05:1.

[0206] The first mixture was sheared and exfoliated using a high-speed homogenizer at a rotation speed (shear rate) of 10,000 r / min for 60 min to prepare a second mixture, in which graphene oxide was exfoliated into graphene oxide. While maintaining the rotation speed at 10,000 r / min, an aqueous solution of oxalic acid was added to the second mixture to form a transient supersaturated suspension. The molar ratio of oxalic acid to the metal salt was 1:2, and the precipitation reaction time was 20 min to obtain a third mixture. The third mixture was washed multiple times with deionized water and ethanol, and the slurry was collected by centrifugation. The slurry was then dried in an 80°C vacuum oven to obtain Mn. 0.6 Fe 0.4 A mixture of C2O4·2H2O and graphene oxide, wherein the graphene oxide encapsulates Mn 0.6 Fe 0.4 C2O4·2H2O.

[0207] Mn 0.6 Fe 0.4 A mixture of C2O4·2H2O and graphene oxide, Li2CO3, and NH4H2PO4 in a molar ratio of Li:Mn:Fe:P = 1.02:0.6:0.4:1 was weighed, and then an appropriate amount of deionized water was added as a solvent. The mixture was milled at 2500 r / min for 2 h to obtain a slurry. The slurry was then transferred to a spray dryer for spray drying and granulation to obtain powder, with the drying temperature set at 210℃. The obtained powder was then sintered in a tube furnace at 400℃ under a nitrogen atmosphere for 5 h, and naturally cooled to room temperature to obtain pre-sintered powder. The pre-sintered powder was then placed in a sand mill, and an appropriate amount of deionized water was added as a solvent. 6 wt% sucrose (based on the total weight of the pre-sintered powder) was also weighed and added to the sand mill, and milled at 2500 r / min for 2 h to obtain a slurry. The slurry was then transferred to a spray dryer for spray drying and granulation to obtain powder, with the drying temperature set at 210℃. The obtained powder was sintered in a tube furnace at 700℃ under a nitrogen atmosphere for 10 hours, then naturally cooled to room temperature, and finally pulverized by air jet milling to obtain the phosphate composite positive electrode active material. The phosphate composite positive electrode active material includes the phosphate positive electrode active material LiMn. 0.6 Fe 0.4 PO4, LiMn coated phosphate positive electrode active material 0.6 Fe 0.4Amorphous carbon in PO4 and reduced graphene oxide coated with amorphous carbon.

[0208] Example 3

[0209] Under nitrogen atmosphere, graphite oxide was added to an appropriate amount of deionized water, followed by the addition of ferrous sulfate and manganese sulfate, with a Mn:Fe molar ratio of 7:3, to prepare a first mixed solution with a metal salt concentration of 1 mol / L. The mass ratio of graphite oxide to metal salt was 0.05:1.

[0210] The first mixture was sheared and exfoliated using a high-speed homogenizer at a rotation speed (shear rate) of 6000 r / min for 120 min to prepare the second mixture, in which graphene oxide was exfoliated into graphene oxide. While maintaining the rotation speed at 6000 r / min, an aqueous solution of ammonium oxalate was added to the second mixture to form a transient supersaturated suspension. The molar ratio of ammonium oxalate to the metal salt was 1:2, and the precipitation reaction time was 20 min to obtain the third mixture. The third mixture was washed multiple times with deionized water and ethanol, and the slurry was collected by centrifugation. The slurry was then dried in an 80℃ vacuum oven to obtain Mn. 0.7 Fe 0.3 A mixture of C2O4·2H2O and graphene oxide, wherein the graphene oxide encapsulates Mn 0.7 Fe 0.3 C2O4·2H2O.

[0211] Mn 0.7 Fe 0.3 A mixture of C2O4·2H2O and graphene oxide, Li2CO3, and NH4H2PO4 in a molar ratio of Li:Mn:Fe:P = 1.02:0.7:0.3:1 was weighed, and then an appropriate amount of deionized water was added as a solvent. The mixture was milled at 2500 r / min for 2 h to obtain a slurry. The slurry was then transferred to a spray dryer for spray drying and granulation to obtain powder, with the drying temperature set at 210℃. The obtained powder was then sintered in a tube furnace at 400℃ under a nitrogen atmosphere for 5 h, and naturally cooled to room temperature to obtain pre-sintered powder. The pre-sintered powder was then placed in a sand mill, and an appropriate amount of deionized water was added as a solvent. 6 wt% PVA (based on the total weight of the pre-sintered powder) was also weighed and milled in the sand mill at 2500 r / min for 2 h to obtain a slurry. The slurry was then transferred to a spray dryer for spray drying and granulation to obtain powder, with the drying temperature set at 210℃. The obtained powder was sintered in a tube furnace at 700℃ under a nitrogen atmosphere for 10 hours, then naturally cooled to room temperature, and finally pulverized by air jet milling to obtain the phosphate composite positive electrode active material. The phosphate composite positive electrode active material includes the phosphate positive electrode active material LiMn. 0.7 Fe0.3 PO4, LiMn coated phosphate positive electrode active material 0.7 Fe 0.3 Amorphous carbon in PO4 and reduced graphene oxide coated with amorphous carbon.

[0212] Example 4

[0213] Under nitrogen atmosphere, graphite oxide was added to an appropriate amount of deionized water, followed by the addition of ferrous sulfate and manganese sulfate, with a Mn:Fe molar ratio of 6:4, to prepare a first mixed solution with a metal salt concentration of 1 mol / L. The mass ratio of graphite oxide to metal salt was 0.05:1.

[0214] The first mixture was sheared and exfoliated using a high-speed homogenizer at a rotation speed (shear rate) of 8000 r / min for 120 min to prepare a second mixture, in which graphene oxide was exfoliated into graphene oxide. While maintaining the rotation speed at 8000 r / min, an aqueous solution of ammonium oxalate was added to the second mixture to form a transient supersaturated suspension. The molar ratio of ammonium oxalate to the metal salt was 1:2, and the precipitation reaction time was 20 min to obtain a third mixture. The third mixture was washed multiple times with deionized water and ethanol, and the slurry was collected by centrifugation. The slurry was then dried in an 80℃ vacuum oven to obtain Mn. 0.6 Fe 0.4 A mixture of C2O4·2H2O and graphene oxide, wherein the graphene oxide encapsulates Mn 0.6 Fe 0.4 C2O4·2H2O.

[0215] Mn 0.6 Fe 0.4A mixture of C2O4·2H2O and graphene oxide, Li2CO3, and NH4H2PO4 in a molar ratio of Li:Mn:Fe:P = 1.02:0.6:0.4:1 was weighed, and then an appropriate amount of deionized water was added as a solvent. The mixture was milled at 2500 r / min for 2 h to obtain a slurry. The slurry was then transferred to a spray dryer for spray drying and granulation to obtain powder, with the drying temperature set at 210℃. The obtained powder was then sintered in a tube furnace at 400℃ under a nitrogen atmosphere for 5 h, and naturally cooled to room temperature to obtain pre-sintered powder. The pre-sintered powder was then placed in a sand mill, and an appropriate amount of deionized water was added as a solvent. 3 wt% PVA and 3% glucose (based on the total weight of the pre-sintered powder) were weighed into the sand mill and milled at 2500 r / min for 2 h to obtain a slurry. The slurry was then transferred to a spray dryer for spray drying and granulation to obtain powder, with the drying temperature set at 210℃. The obtained powder was sintered in a tube furnace at 720℃ under a nitrogen atmosphere for 10 hours, then naturally cooled to room temperature, and finally pulverized by air jet milling to obtain the phosphate composite positive electrode active material. The phosphate composite positive electrode active material includes the phosphate positive electrode active material LiMn. 0.6 Fe 0.4 PO4, LiMn coated phosphate positive electrode active material 0.6 Fe 0.4 Amorphous carbon in PO4 and reduced graphene oxide coated with amorphous carbon.

[0216] Comparative Example 1

[0217] Under nitrogen gas protection, ferrous sulfate and manganese sulfate were added to an appropriate amount of deionized water at a molar ratio of Mn:Fe of 6:4 to prepare a 1 mol / L mixed metal salt solution. The solution was then dispersed and dissolved using a stirrer at a speed of 600 r / min to obtain the mixed solution.

[0218] Under a stirring speed of 600 r / min, an aqueous solution of oxalic acid as a precipitant was added to the mixture to form a transient supersaturated suspension. The molar ratio of oxalic acid to the metal salt was 1:2, and the precipitation reaction time was 20 min until the reaction was complete. The resulting mixture was washed multiple times with deionized water and ethanol, and the slurry was collected by centrifugation. The slurry was then dried in an 80℃ vacuum oven to obtain Mn. 0.6 Fe 0.4 C2O4·2H2O.

[0219] Mn 0.6 Fe 0.4C2O4·2H2O, Li2CO3, and NH4H2PO4 were weighed in a molar ratio of Li:Mn:Fe:P = 1.02:0.6:0.4:1. Then, an appropriate amount of deionized water was added as a solvent, and the mixture was milled at 2500 r / min for 2 hours to obtain a slurry. The slurry was then transferred to a spray dryer for spray drying and granulation to obtain powder, with the drying temperature set at 210℃. The obtained powder was then sintered in a tube furnace at 400℃ under a nitrogen atmosphere for 5 hours, and naturally cooled to room temperature to obtain pre-sintered powder. The pre-sintered powder was then placed in a sand mill, and an appropriate amount of deionized water was added as a solvent. 11 wt% sucrose (based on the total weight of the pre-sintered powder) was also weighed and added to the sand mill, and milled at 2500 r / min for 2 hours to obtain a slurry. The slurry was then transferred to a spray dryer for spray drying and granulation to obtain powder, with the drying temperature set at 210℃. The obtained powder was sintered in a tube furnace at 700℃ under a nitrogen atmosphere for 10 hours, then naturally cooled to room temperature, and finally pulverized by air jet milling to obtain the phosphate composite positive electrode active material. The phosphate composite positive electrode active material includes the phosphate positive electrode active material LiMn. 0.6 Fe 0.4 PO4, LiMn coated phosphate positive electrode active material 0.6 Fe 0.4 Amorphous carbon in PO4.

[0220] Comparative Example 2

[0221] Under nitrogen atmosphere, graphite oxide was added to an appropriate amount of deionized water, followed by the addition of ferrous sulfate and manganese sulfate, with a Mn:Fe molar ratio of 6:4, to prepare a first mixed solution with a metal salt concentration of 1 mol / L. The mass ratio of graphite oxide to metal salt was 0.05:1.

[0222] The first mixture was sheared and exfoliated using a high-speed homogenizer at a rotation speed (shear rate) of 8000 r / min for 120 min to prepare a second mixture, in which graphene oxide was exfoliated into graphene oxide. While maintaining the rotation speed at 8000 r / min, an aqueous solution of oxalic acid as a precipitant was added to the second mixture to form a transient supersaturated suspension. The molar ratio of oxalic acid to the metal salt was 1:2, and the precipitation reaction time was 20 min to obtain a third mixture. The third mixture was washed multiple times with deionized water and ethanol, and the slurry was collected by centrifugation. The slurry was then dried in an 80℃ vacuum oven to obtain Mn. 0.6 Fe 0.4 A mixture of C2O4·2H2O and graphene oxide, wherein the graphene oxide encapsulates Mn 0.6 Fe 0.4 C2O4·2H2O.

[0223] Mn 0.6 Fe 0.4 A mixture of C2O4·2H2O and graphene oxide, Li2CO3, and NH4H2PO4 were weighed at a molar ratio of Li:Mn:Fe:P = 1.02:0.6:0.4:1. Then, an appropriate amount of deionized water was added as a solvent, and the mixture was milled at 2500 rpm for 2 hours to obtain a slurry. The slurry was then transferred to a spray dryer for spray drying and granulation to obtain powder, with the drying temperature set at 210℃. The obtained powder was then sintered in a tube furnace at 400℃ under a nitrogen atmosphere for 5 hours, and naturally cooled to room temperature to obtain pre-sintered powder. The pre-sintered powder was then placed in a sand mill, and an appropriate amount of deionized water was added as a solvent. The mixture was milled at 2500 rpm for 2 hours to obtain a slurry. The slurry was then transferred to a spray dryer for spray drying and granulation to obtain powder, with the drying temperature set at 210℃. The obtained powder was sintered in a tube furnace at 700℃ under a nitrogen atmosphere for 10 hours, then naturally cooled to room temperature, and finally pulverized by air jet milling to obtain the phosphate composite positive electrode active material. The phosphate composite positive electrode active material includes the phosphate positive electrode active material LiMn. 0.6 Fe 0.4 PO4, LiMn coated phosphate positive electrode active material 0.6 Fe 0.4 Reduced graphene oxide with PO4.

[0224] Test section

[0225] (1) Powder resistivity test

[0226] The powder resistivity of phosphate composite cathode active materials is tested using a powder resistivity tester, such as the PRCD1100 from Yuaneng Technology. A certain amount of phosphate composite cathode active material powder is placed in a special mold, and then the mold is placed on a compaction density instrument. The pressure is set to 4 MPa, and the corresponding powder resistivity is read after the pressure is applied.

[0227] (2) Volume distribution particle size Dv50 test

[0228] The volumetric particle size distribution of phosphate composite cathode active materials was tested using a laser particle size analyzer, such as the Malvern Master Size 3000. Dv50 refers to the particle size corresponding to a cumulative volumetric distribution percentage of 50%. The testing standard can be found in GB / T 19077-2016.

[0229] (3) Metal element content test

[0230] The contents of manganese and iron in phosphate composite cathode active materials were determined and their molar ratios were calculated using an inductively coupled plasma atomic emission spectrometer, such as the Plasma 3000, by ICP-OES.

[0231] (4) Average number of graphene layers test

[0232] The number of graphene layers is determined using an atomic force microscope, such as the Multimode 8. The thickness of a single layer of graphene is typically between 0.4 nm and 0.7 nm. By observing the morphology of graphene using an atomic force microscope and analyzing the height profile, the number of graphene layers can be estimated.

[0233] (5) Fabrication and testing of button cells

[0234] The phosphate composite positive electrode active materials prepared in the above embodiments and comparative examples were added to a certain amount of N-methylpyrrolidone (NMP) along with polyvinylidene fluoride (PVDF) and conductive carbon in a weight ratio of 90:5:5. The mixture was stirred in a drying chamber to form a slurry. This slurry was then coated onto aluminum foil, dried, and cold-pressed to form a positive electrode sheet. A lithium sheet was used as the negative electrode, and the prepared positive electrode sheet was assembled into a coin cell in a coin cell box. The electrolyte concentration was 1 mol / L, the lithium salt was LiPF6, and the solvent was a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1.

[0235] At 25°C, the coin cell prepared above was charged at a constant current of 0.1C to 4.3V, and then charged at a constant voltage of 4.3V until the current ≤0.05C. After standing for 2 minutes, the charging capacity at this point was recorded as C0. Then, the coin cell was discharged at a constant current of 0.1C to 2.0V. The discharge capacity at this point was the initial discharge capacity, recorded as D0. The discharge specific capacity of the coin cell (mAh / g) = D0 / m, where m represents the mass of the phosphate composite positive electrode active material.

[0236] At 25°C, each coin cell prepared above was charged at a constant current of 1C to 4.3V, and then charged at a constant voltage of 4.3V until the current ≤0.05C. After standing for 2 minutes, the charging capacity at this point was recorded, which is the first charge capacity. Then, the coin cells were discharged at a constant current of 1C to 2.0V, and the discharge capacity at this point was recorded, which is the first discharge capacity. The coin cells were subjected to cyclic charge-discharge tests according to the above method, and the discharge capacity after each cycle was recorded. The capacity retention rate of the coin cell after 200 cycles = discharge capacity after 200 cycles / discharge capacity of the first cycle.

[0237] At 25°C, the coin cells prepared above were charged to 4.3V at constant currents of 0.1C, 0.5C, 1C, 2C, 5C and 10C, respectively. Then, they were charged at constant voltages of 4.3V until the current was ≤0.05C and left to stand for 2 minutes. The coin cells were then discharged to 2.0V at constant currents of 0.1C, 0.5C, 1C, 2C, 5C and 10C, respectively. The discharge capacity of the coin cells at different charge and discharge rates (0.1C, 0.5C, 1C, 2C, 5C and 10C) was recorded.

[0238] The test results are shown in Table 1.

[0239] Table 1

[0240]

[0241] Figure 7 (a) shows the Mn prepared in Example 1 0.6 Fe 0.4 Scanning electron microscope (SEM) image of a mixture of C2O4·2H2O and graphene oxide. Figure 7 (b) shows the Mn prepared in Comparative Example 1 0.6 Fe 0.4 Scanning electron microscope (SEM) image of C2O4·2H2O. From Figure 7 It can be seen that the phosphate positive electrode active material precursor obtained by the preparation method provided in the embodiments of this application has the characteristics of regular morphology, small particle size and narrow particle size distribution, and can also be well encapsulated by graphene oxide.

[0242] Figure 8 (a) shows a scanning electron microscope (SEM) image of the phosphate composite positive electrode active material prepared in Example 1. Figure 8 (b) shows a scanning electron microscope (SEM) image of the phosphate composite positive electrode active material prepared in Comparative Example 1. Figure 8 It can be seen that the phosphate composite positive electrode active material obtained by the preparation method provided in the embodiments of this application can form a continuous conductive network.

[0243] Figure 9 Capacity-voltage curves of coin cells prepared from the phosphate composite positive electrode active materials of Example 1 and Comparative Example 1. Figure 10 Rate curves for coin cells prepared from the phosphate composite positive electrode active materials of Example 1 and Comparative Example 1. (Summary) Figure 9 , Figure 10As shown in Table 1, the preparation method provided in this application can not only reduce the cost of raw materials, but also make the obtained phosphate composite positive electrode active material have the characteristics of regular morphology, small particle size, narrow particle size distribution, uniform element distribution and high batch consistency. In addition, it can form a continuous conductive network and shorten the ion transport path, which is conducive to promoting the efficient transport of electrons and ions. Thus, the battery can take into account high discharge specific capacity, good rate performance and good cycle stability.

[0244] In Comparative Example 2, no carbon source was added during the preparation of the phosphate composite positive electrode active material. As a result, a continuous conductive network could not be constructed in the phosphate composite positive electrode active material, leading to high powder resistivity and poor electron transport capability of the prepared phosphate composite positive electrode active material, which in turn affected the rate performance of the battery and also affected the cycle stability of the battery.

[0245] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing a phosphate composite positive electrode active material, comprising the following steps: A first mixture comprising graphite oxide and a metal salt for preparing phosphate cathode active materials is provided, wherein the solvent in the first mixture includes water; The first mixture is subjected to a first exfoliation reaction at a first shear rate of 6000 r / min or higher to exfoliate the graphene oxide into graphene oxide, thereby obtaining a second mixture. While maintaining the first shear rate, a precipitant or an aqueous solution of the precipitant is added to the second mixture to carry out a second precipitation reaction, resulting in a third mixture. The precipitant includes one or more of oxalic acid and water-soluble oxalate. The third mixture is washed and dried to obtain a mixture of phosphate positive electrode active material precursor and graphene oxide. The phosphate cathode active material precursor and graphene oxide mixture are ground with a lithium source, a phosphorus source, a carbon source, an optional Li-site doping element source, an optional P-site doping element source, and an optional O-site doping element source in the presence of a first solvent to obtain a slurry. This slurry is then spray-dried, granulated, and sintered to obtain the phosphate composite cathode active material. in, The phosphate composite positive electrode active material includes a phosphate positive electrode active material, amorphous carbon coating the phosphate positive electrode active material, and reduced graphene oxide coating the amorphous carbon.

2. The method according to claim 1, wherein, The first stripping reaction is carried out in a high-speed dispersing homogenizer; and / or, The first shearing rate is 6000-15000 r / min; and / or, The first stripping reaction takes 30-150 min; and / or, The graphene oxide has 1-6 layers.

3. The method according to claim 2, wherein, The first shearing rate is 6000-10000 r / min; and / or, The first stripping reaction takes 60-120 min; and / or, The graphene oxide has 3-5 layers.

4. The method according to any one of claims 1-3, wherein, The mass ratio of the graphite oxide to the metal salt used to prepare the phosphate cathode active material is 0.03:1-0.08:1; and / or, The concentration of the metal salt used to prepare the phosphate positive electrode active material in the first mixture is 0.5-2 mol / L; and / or, The metal salts used to prepare phosphate cathode active materials include water-soluble divalent metal salts.

5. The method according to claim 4, wherein, The water-soluble divalent metal salts include one or more of sulfates, nitrates, hydrochlorides, and acetates.

6. The method according to claim 4 or 5, wherein, Divalent metal elements include Mn and / or Fe elements, and optionally M element, where M element represents the doping element at the Mn site and / or Fe site of the phosphate composite cathode active material.

7. The method according to claim 6, wherein, The M element includes one or more of the following: Ni, Co, Mg, Zn, Ca, Ti, V, and Cr.

8. The method according to any one of claims 1-7, wherein, The second precipitation reaction takes 10-60 min; and / or, The molar ratio of the precipitant to the metal salt used to prepare the phosphate positive electrode active material is 1:1-3:1; and / or, The precipitant includes one or more of oxalic acid, sodium oxalate, potassium oxalate, and ammonium oxalate; and / or, The concentration of the aqueous solution of the precipitant is 0.5-2 mol / L.

9. The method according to any one of claims 1-8, wherein, The step of providing a first mixture comprising graphite oxide and a metal salt for preparing phosphate cathode active materials includes the following steps: Under a protective gas atmosphere, graphite oxide is added to water, followed by the addition of a metal salt used to prepare phosphate cathode active materials. After being dispersed evenly, the first mixture is obtained.

10. The method according to claim 9, wherein, The protective gas includes nitrogen, an inert gas, or a combination thereof.

11. The method according to any one of claims 1-10, wherein, The first solvent includes one or more alcohol solvents and water; and / or, The grinding process includes high-energy ball milling or sand milling; and / or, The grinding speed is 1000-2500 r / min; and / or, The grinding process takes 1-5 hours.

12. The method according to claim 11, wherein, The first solvent includes one or more of ethanol and water.

13. The method according to any one of claims 1-12, wherein, The sintering process includes pre-sintering treatment and high-temperature sintering treatment.

14. The method according to claim 13, wherein, The pre-sintering treatment temperature is 350-550℃; and / or, The pre-sintering treatment time is 2-12 hours; and / or, The high-temperature sintering treatment is performed at a temperature of 600-800℃; and / or, The high-temperature sintering treatment time is 5-24 hours; and / or, The pre-sintering treatment is carried out under a protective gas atmosphere; and / or, The high-temperature sintering process is carried out under a protective gas atmosphere.

15. The method according to claim 14, wherein, The pre-sintering treatment temperature is 400-500℃; and / or, The pre-sintering treatment time is 3-10 hours; and / or, The high-temperature sintering treatment is performed at a temperature of 650-750℃; and / or, The high-temperature sintering treatment takes 8-12 hours.

16. The method according to any one of claims 13-15, wherein, The steps of grinding the phosphate cathode active material precursor and graphene oxide mixture with a lithium source, a phosphorus source, a carbon source, an optional Li-site doping element source, an optional P-site doping element source, and an optional O-site doping element source in the presence of a first solvent to obtain a slurry, followed by spray drying, granulation, and sintering to obtain the phosphate composite cathode active material include the following steps: The mixture of the phosphate positive electrode active material precursor and graphene oxide is subjected to a first grinding process in the presence of a lithium source, a phosphorus source, an optional Li site doping element source, an optional P site doping element source, and an optional O site doping element source to obtain a first slurry. The first slurry is spray-dried and granulated to obtain powder, and then pre-sintered to obtain pre-sintered powder. The pre-sintered powder and the carbon source are subjected to a second grinding process in the presence of the first solvent to obtain a second slurry; The second slurry is spray-dried and granulated to obtain powder, which is then subjected to high-temperature sintering and optionally crushing to obtain the phosphate composite positive electrode active material.

17. The method according to claim 16, wherein, The rotational speed of the first grinding process is 1500-2500 r / min; and / or, The first grinding process takes 1-5 hours; and / or, The rotational speed of the second grinding process is 1000-2500 r / min; and / or, The second grinding process takes 1-3 hours.

18. The method according to any one of claims 1-17, wherein, The Li-site doping element includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; and / or, The P-site doping element includes one or more elements selected from B, S, Si, and N; and / or, The O-site doping element includes one or more elements selected from S, F, Cl, and Br.

19. The method according to any one of claims 1-18, wherein, The lithium source includes one or more of lithium hydroxide, lithium carbonate, lithium dihydrogen phosphate, lithium dihydrogen phosphate, lithium nitrate, and lithium acetate; and / or, The phosphorus source includes one or more of phosphoric acid, ammonium monohydrogen phosphate, and ammonium dihydrogen phosphate; and / or, The carbon source includes one or more of sucrose, glucose, polyvinyl alcohol, polyethylene glycol, phenolic resin, citric acid, and cyclodextrin; and / or, The Li-site doping element source includes one or more of the following: sulfate, nitrate, hydrochloride, and acetate of the Li-site doping element; and / or, The P-site dopant source includes one or more of the following: sulfates, borates, nitrates, and silicates of the P-site dopant element; and / or, The source of the O-site doped element includes one or more of the elemental form of the O-site doped element and an ammonium salt.

20. A phosphate composite positive electrode active material prepared by the method according to any one of claims 1-19, wherein the phosphate composite positive electrode active material comprises a phosphate positive electrode active material, amorphous carbon coating the phosphate positive electrode active material, and reduced graphene oxide coating the amorphous carbon.

21. The phosphate composite positive electrode active material according to claim 20, wherein, The volume distribution particle size Dv50 of the phosphate composite positive electrode active material satisfies 0.5μm≤Dv50≤3μm; and / or, The volume distribution particle sizes Dv90 and Dv50 of the phosphate composite positive electrode active material satisfy 1 < Dv90 / Dv50 ≤ 1.5; and / or, The resistivity of the phosphate composite positive electrode active material is 1-100 Ω·cm.

22. The phosphate composite positive electrode active material according to claim 20 or 21, wherein, The molecular formula of the phosphate positive electrode active material is Li a N b Fe x Mn y M 1-x-y P 1-m Q m O 4-n R n , M represents the doping element at the Mn site and / or Fe site; N represents the Li-doped element; Q indicates a P-site doped element; R indicates an O-site doped element; 0.9≤a≤1.1; 0≤b≤0.1; 0≤x≤1; 0≤y≤1; 0≤1-xy<1; 0≤m≤0.1; 0≤n≤0.

1.

23. The phosphate composite positive electrode active material according to claim 22, wherein, M includes one or more elements selected from Ni, Co, Mg, Zn, Ca, Ti, V, and Cr.

24. The phosphate composite positive electrode active material according to claim 22, wherein, N includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W.

25. The phosphate composite positive electrode active material according to claim 22, wherein, Q includes one or more elements from B, S, Si, and N.

26. The phosphate composite positive electrode active material according to claim 22, wherein, R includes one or more elements selected from S, F, Cl, and Br.

27. The phosphate composite positive electrode active material according to any one of claims 22-26, wherein, 0.001≤x≤0.999, 0.001≤y≤0.999, 0≤1-xy≤0.

10.

28. The phosphate composite positive electrode active material according to claim 27, wherein, 0.199≤x≤0.500, 0.499≤y≤0.800, 0<1-xy≤0.

10.

29. A positive electrode sheet, comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, wherein, The positive electrode film layer comprises a phosphate composite positive electrode active material prepared by the method according to any one of claims 1-19 or the phosphate composite positive electrode active material according to any one of claims 20-28.

30. A battery cell comprising the positive electrode sheet as described in claim 29.

31. A battery comprising the battery cell of claim 30.

32. An electrical device comprising the battery of claim 31.

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