Method for preparing positive electrode material, positive electrode material, positive electrode sheet, battery and electric device

Abstract

A method for preparing a positive electrode material, a positive electrode material, a positive electrode sheet, a battery and an electric device. The method for preparing a positive electrode material comprises: mixing precursor lithium manganese iron phosphate, a carbon source and a source of a doping element in a solvent, drying and sintering the mixture, so as to obtain a positive electrode material. The positive electrode material comprises an inner core and a coating layer coating the inner core, wherein the inner core comprises LiMnxFe1-xPO4, where 0＜x＜1; and the coating layer comprises carbon and a doping element, with the doping element comprises one or more of an IIA-group element, an IIIA-group element, an IVA-group element and a transition metal element. The method reduces the powder resistivity and specific surface area of the positive electrode material, and improves the gram capacity and cycle performance of a battery.

Description

Method for preparing positive electrode material, positive electrode material, positive electrode sheet, battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202311644140.8 filed on December 1, 2023, entitled “Method for preparing positive electrode material, positive electrode material, positive electrode sheet, battery and electrical device,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the technical field of lithium batteries, and in particular to a method for preparing a positive electrode material, a positive electrode material, a positive electrode sheet, a battery, and an electrical device. Background Art

[0004] In recent years, the application of secondary batteries has become increasingly widespread. They are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As secondary batteries have achieved great development, higher requirements have been placed on the electrochemical performance of batteries.

[0005] Summary of the Invention

[0006] This application is made in view of the above-mentioned problems and aims to provide a method for preparing a positive electrode material, a positive electrode material, a positive electrode sheet, a battery, and an electrical device. The method of the application reduces the powder resistivity and specific surface area of ​​the positive electrode material, increases the gram capacity of the positive electrode material, and improves the cycle performance of the battery.

[0007] In order to achieve the above-mentioned object, the first aspect of the present application provides a method for preparing a positive electrode material, comprising:

[0008] Mixing precursor lithium manganese iron phosphate, a carbon source, and a source of a doping element in a solvent, drying, and sintering to obtain a positive electrode material;

[0009] The positive electrode material includes a core and a coating layer covering the core; the core includes LiMn x Fe 1-x PO4, wherein 0<x<1; the coating layer comprises carbon and doping elements; the doping elements comprise one or more of Group IIA elements, Group IIIA elements, Group IVA elements, and transition metal elements.

[0010] Therefore, the present application simultaneously adds a carbon source and a source of doping elements during the coating process, which is conducive to the formation of a tight structure between the coating layer and the core surface, and stabilizes the crystals of the positive electrode material, reduces the powder resistivity of the positive electrode material, reduces the specific surface area of ​​the positive electrode material within a reasonable range, and improves the battery's gram capacity and cycle performance.

[0011] In any embodiment, 0.1≤x≤0.9; and / or,

[0012] The doping elements include one or more elements selected from the group consisting of Mg, Ti, V, Si, Cr, Mn, Fe, Co, Ni, and B.

[0013] In any embodiment, the molar ratio of the precursor to the carbon element in the carbon source is 1:1.5-1:0.001, optionally 1:1.45-1:0.01; and / or,

[0014] The molar ratio of the precursor to the doping element in the source of the doping element is 1:0.25-1:0.00001, and can be optionally 1:0.2-1:0.0001.

[0015] The carbon element in the precursor and the carbon source being within the above-mentioned ratio range is conducive to forming a suitable coating layer thickness, which is beneficial to improving the battery's gram capacity and cycle performance.

[0016] The ratio of the precursor to the doping element within the above range is conducive to the presence of the doping element between the core and the carbon element and in the coating layer, thereby improving the specific capacity and cycle performance of the battery.

[0017] In any embodiment, the mixing is performed at 5°C-70°C, optionally, the mixing is performed at 10°C-60°C; and / or,

[0018] The mixing time is 0.5-12 hours; and / or,

[0019] The mixing is performed by grinding.

[0020] Therefore, the above-mentioned mixing temperature and time are conducive to the uniform distribution of doping elements in the coating layer and at the boundary between the core and the coating layer, and are also conducive to the uniform distribution of carbon elements in the coating layer, thereby improving the battery's gram capacity and cycle performance.

[0021] In any embodiment, the sintering temperature is 350° C.-950° C., optionally 400° C.-900° C.; and / or,

[0022] The sintering time is 2-20 hours; and / or,

[0023] The sintering is performed in an inert atmosphere.

[0024] Therefore, the use of the above-mentioned sintering temperature and sintering time when preparing the positive electrode material is conducive to a more complete reaction, forming a tight structure between the coating layer and the core surface, thereby improving the battery's gram capacity and cycle performance.

[0025] In any embodiment, the drying temperature is 150° C.-400° C.; and / or,

[0026] The drying is performed by spray drying or oven drying; and / or,

[0027] The method further comprises sieving the mixture before drying, collecting the sieved portion; and / or,

[0028] The method further comprises crushing after the sintering, optionally followed by screening; and / or,

[0029] The carbon source includes one or more of an organic carbon source and an inorganic carbon source, and can be selected from one or more of citric acid, glucose, sucrose, polyvinyl alcohol, polypyrrole, polyethylene glycol, asphalt, anthracene, and aniline; and / or,

[0030] The source of the doping element includes one or more of a hydroxide of the doping element, an oxide of the doping element, an acid of the doping element, and a salt of the doping element; and / or,

[0031] The solvent includes one or more of water and an organic solvent. Optionally, the solvent includes one or more of water, ethanol, methanol, acetone, ethylene glycol, and isopropanol.

[0032] In any embodiment, the precursor is prepared by the following steps:

[0033] reacting a lithium source, a manganese source, an iron source, and a phosphorus source in a solvent, performing solid-liquid separation, and collecting a solid phase;

[0034] The solid phase is dried and sintered to obtain a precursor.

[0035] In any embodiment, the precursor comprises LiMn x Fe 1-x PO4, wherein 0<x<1, optionally, 0.1≤x≤0.9;

[0036] Optionally, in the step of preparing the precursor, the molar ratio of the lithium element in the lithium source, the manganese element in the manganese source, the iron element in the iron source, and the phosphorus element in the phosphorus source is 1:x:(1-x):1.

[0037] The elements in the precursor of the present application are evenly distributed and have good batch consistency. The elements in the positive electrode material made using the precursor material of the present application are evenly distributed and have good batch consistency, thereby improving the electrical properties of the battery such as gram capacity and cycle performance.

[0038] In any embodiment, in the step of preparing the precursor, the reaction is carried out at 5°C-60°C, optionally, the reaction is carried out at 10°C-50°C; and / or,

[0039] The reaction time is 10 minutes to 8 hours, optionally 10 minutes to 6 hours; and / or,

[0040] The drying temperature is 50°C-250°C; and / or,

[0041] The drying time is 10 minutes to 12 hours; and / or,

[0042] The sintering temperature is 150°C-800°C, optionally 200°C-700°C; and / or,

[0043] The sintering time is 1-12 hours; and / or,

[0044] The sintering is performed in an inert atmosphere.

[0045] Using the above reaction temperature and time when preparing the precursor is beneficial to reducing side reactions, so as to obtain a precursor material with uniform composition and good batch consistency, thereby improving the battery's gram capacity and cycle performance.

[0046] The above-mentioned sintering temperature and time are used in the preparation of the precursor, which is conducive to the growth of crystals to reduce the proportion of amorphous particles, thereby obtaining a precursor with better crystallinity, thereby improving the battery's gram capacity and cycle performance.

[0047] In any embodiment, in the step of preparing the precursor, the solid-liquid separation is performed by filtration or centrifugation; and / or,

[0048] Before the drying, the solid phase is ball-milled; optionally, the rotation speed of the ball mill is 100-600 rpm, optionally 200-500 rpm, and the ball milling time is 1-12 hours, optionally 2-10 hours; and / or,

[0049] Before the drying, the solid phase is washed; and / or,

[0050] Between the drying and the sintering, the solid phase is crushed; and / or,

[0051] The lithium source includes one or more of lithium hydroxide, oxide, inorganic acid salt, and organic acid salt, and can be selected from one or more of lithium hydroxide, lithium oxide, lithium carbonate, lithium acetate, lithium oxalate, lithium phosphate, and lithium chloride; and / or,

[0052] The manganese source includes one or more of organic acid salts, inorganic acid salts, oxides, and hydroxides of manganese; and / or,

[0053] The iron source includes one or more of organic acid salts, inorganic acid salts, oxides, and hydroxides of iron; and / or,

[0054] The phosphorus source includes one or more of phosphoric acid, phosphates, hydrogen phosphates, and dihydrogen phosphates, and can be selected from one or more of phosphoric acid, ferric phosphate, ferrous phosphate, ferrous ammonium phosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, ammonium phosphate, lithium monohydrogen phosphate, lithium dihydrogen phosphate, and lithium phosphate; and / or,

[0055] A carbon source is added during the reaction.

[0056] The use of the above-mentioned ball milling speed and time when preparing the precursor is beneficial to improving the degree of solid-solid reaction, making the reaction more efficient, thereby improving the battery's gram capacity and cycle performance.

[0057] The second aspect of the present application also provides a positive electrode material, comprising a core and a coating layer covering the core, wherein the core comprises LiMn x Fe 1-x PO4, wherein 0<x<1, optionally, 0.1≤x≤0.9; the coating layer comprises carbon and a doping element; the doping element comprises one or more of Group IIA elements, Group IIIA elements, Group IVA elements, and transition metal elements, and may optionally comprise one or more of Mg, Ti, V, Si, Cr, Mn, Fe, Co, Ni, and B;

[0058] Optionally, the molar ratio of manganese element to iron element in the core is 1:9-9:1.

[0059] Therefore, the present application simultaneously adds a carbon source and a source of doping elements during the coating process, which is conducive to the formation of a tight structure between the coating layer and the core surface, and stabilizes the crystals of the positive electrode material, reduces the powder resistivity of the positive electrode material, reduces the specific surface area of ​​the positive electrode material within a reasonable range, and improves the battery's gram capacity and cycle performance.

[0060] In any embodiment, the LiMn in the core x Fe 1-x The molar ratio of PO4 to the carbon element in the coating layer is 1:1.5-1:0.001, optionally 1:1.45-1:0.01; and / or,

[0061] The LiMn in the core x Fe 1-x The molar ratio of PO4 to the doping element in the coating layer is 1:0.25-1:0.00001, and can be optionally 1:0.2-1:0.0001.

[0062] In any embodiment, the Dv50 particle size of the positive electrode material is 0.1-13 μm; and / or,

[0063] The BET specific surface area of ​​the positive electrode material is 10-27 m2 / g, and can be 10-25 m2 / g; and / or,

[0064] The powder resistivity of the positive electrode material is ≤1200Ω·cm. Optionally, the powder resistivity of the positive electrode material is ≤300Ω·cm; and / or,

[0065] The positive electrode material is prepared by the method of the first aspect of the present application.

[0066] The third aspect of the present application further provides a positive electrode plate, comprising the positive electrode material prepared by the method of the first aspect of the present application or the positive electrode material of the second aspect of the present application.

[0067] The fourth aspect of the present application further provides a battery, comprising the positive electrode material prepared by the method of the first aspect of the present application, the positive electrode material of the second aspect of the present application, or the positive electrode plate of the third aspect of the present application.

[0068] The fifth aspect of the present application further provides an electrical device comprising the battery of the fourth aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0070] FIG. 2 is an exploded view of the battery cell according to the embodiment of the present application shown in FIG. 1 .

[0071] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0072] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0073] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application.

[0074] FIG6 is a schematic diagram of an electrical device using a battery cell as a power source according to an embodiment of the present application.

[0075] FIG7 is a TEM photograph of the positive electrode material of Example 1 of the present application.

[0076] FIG8 is a TEM photograph of the positive electrode material of Comparative Example 3 of the present application.

[0077] Description of reference numerals:

[0078] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0079] Below, the embodiments of the negative electrode active material and its manufacturing method, positive electrode sheet, negative electrode sheet, battery cell, battery module, battery pack and electric device of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0080] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0081] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0082] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0083] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may further include step (c), which 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 may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0084] Unless otherwise specified, the Dv50 particle size in this application refers to the particle size when the cumulative value of volume distribution is 50%.

[0085] [Battery Cell]

[0086] A battery cell, also known as a rechargeable battery or storage battery, refers to a battery that can be recharged to activate the active material after discharge and continue to be used.

[0087] Typically, a battery cell consists of a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During the battery's charge and discharge process, active ions (such as lithium ions) are embedded and released back and forth between the positive and negative electrode sheets. The separator is set between the positive and negative electrode sheets, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing active ions to pass through. The electrolyte between the positive and negative electrode sheets mainly plays the role of conducting active ions.

[0088] [Method for preparing positive electrode material]

[0089] One embodiment of the present application provides a method for preparing a positive electrode material, comprising:

[0090] Mixing precursor lithium manganese iron phosphate, a carbon source, and a source of a doping element in a solvent, drying, and sintering to obtain a positive electrode material;

[0091] The positive electrode material includes a core and a coating layer covering the core; the core includes LiMn x Fe 1-x PO4, wherein 0<x<1, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a range consisting of any of the above values; the coating layer includes carbon and doping elements; the doping elements include one or more of Group IIA elements, Group IIIA elements, Group IVA elements, and transition metal elements.

[0092] Lithium manganese iron phosphate (LMP) has poor conductivity, with its structure consisting of an insulator with a spin exchange band gap of 0.2 eV and a semiconductor with a crystal field band gap of 0.3 eV. While conventional carbon coating can address the high resistance of LMP powders, it still fails to improve the electrochemical performance of batteries made with the material.

[0093] Although the mechanism is still unclear, the applicant unexpectedly discovered that the simultaneous addition of a carbon source and a source of doping elements during the coating process is beneficial to the formation of a tight structure between the coating layer and the core surface, and stabilizes the crystals of the positive electrode material, thereby reducing the powder resistivity of the positive electrode material, reducing the specific surface area of ​​the positive electrode material within a reasonable range, and improving the battery's gram capacity and cycle performance.

[0094] In some embodiments, 0.1≤x≤0.9; and / or,

[0095] The doping elements include one or more elements selected from the group consisting of Mg, Ti, V, Si, Cr, Mn, Fe, Co, Ni, and B.

[0096] In some embodiments, the molar ratio of the precursor to the carbon element in the carbon source is 1:1.5-1:0.001, optionally 1:1.45-1:0.01, for example, 1:1.5, 1:1.45, 1:1.4, 1:1.35, 1:1.3, 1:1.25, 1:1.2, 1:1.15, 1:1.1, 1:1.05, 1:1, 1:0.95, 1:0.9, 1:0.8, 1:0.7, 1:0.6, 1:0.5, 1:0.4, 1:0.3, 1:0.2, 1:0.1, 1:0.09, 1:0.07, 1:0.06, 1:0.05, 1:0.04, 1:0.03, 1:0.02, 1:0.01, 1:0.009, 1:0.007, 1:0.005, 1:0.003, 1:0.002, 1:0.001 or a range consisting of any of the above values; and / or,

[0097] The molar ratio of the precursor to the doping element in the source of the doping element is 1:0.25-1:0.00001, optionally 1:0.2-1:0.0001, for example, 1:0.25, 1:0.2, 1:0.15, 1:0.1, 1:0.05, 1:0.01, 1:0.009, 1:0.007, 1:0.005, 1:0.003, 1:0.001, 1:0.0009, 1:0.0007, 1:0.0005, 1:0.0003, 1:0.0002, 1:0.0001, 1:0.00009, 1:0.00007, 1:0.00005, 1:0.00003, 1:0.00002, 1:0.00001 or a range consisting of any of these values.

[0098] The carbon element in the precursor and the carbon source being within the above-mentioned ratio range is conducive to forming a suitable coating layer thickness, which is beneficial to improving the battery's gram capacity and cycle performance.

[0099] The ratio of the precursor to the doping element within the above range is conducive to the presence of the doping element between the core and the carbon element and in the coating layer, thereby improving the specific capacity and cycle performance of the battery.

[0100] In some embodiments, the mixing is performed at 5°C-70°C, optionally, the mixing is performed at 10°C-60°C, for example, the mixing is performed at 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C or any range of the above values; and / or,

[0101] The mixing time is 0.5-12 hours, for example, 0.5 hours, 1 hour, 2.5 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours or any range thereof; and / or,

[0102] The mixing is performed by grinding.

[0103] Therefore, the above-mentioned mixing temperature and time are conducive to the uniform distribution of doping elements in the coating layer and at the boundary between the core and the coating layer, and are also conducive to the uniform distribution of carbon elements in the coating layer, thereby improving the battery's gram capacity and cycle performance.

[0104] In some embodiments, the sintering temperature is 350°C-950°C, optionally 400°C-900°C, for example, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C or a range consisting of any of the above values; and / or,

[0105] The sintering time is 2-20 hours, for example, 2 hours, 3 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours or any range thereof; and / or,

[0106] The sintering is performed in an inert atmosphere.

[0107] Therefore, the use of the above-mentioned sintering temperature and sintering time when preparing the positive electrode material is conducive to a more complete reaction, forming a tight structure between the coating layer and the core surface, thereby improving the battery's gram capacity and cycle performance.

[0108] In some embodiments, the drying temperature is 150°C-400°C, for example, 150°C, 180°C, 200°C, 220°C, 250°C, 270°C, 300°C, 330°C, 350°C, 380°C, 400°C or any range thereof; and / or,

[0109] The drying is performed by spray drying or oven drying; and / or,

[0110] The method further comprises sieving the mixture before drying, collecting the sieved portion; and / or,

[0111] The method further comprises crushing after the sintering, optionally followed by screening; and / or,

[0112] The carbon source includes one or more of an organic carbon source and an inorganic carbon source, and can be selected from one or more of citric acid, glucose, sucrose, polyvinyl alcohol, polypyrrole, polyethylene glycol, asphalt, anthracene, and aniline; and / or,

[0113] The source of the doping element includes one or more of a hydroxide of the doping element, an oxide of the doping element, an acid of the doping element, and a salt of the doping element; and / or,

[0114] The solvent includes one or more of water and an organic solvent. Optionally, the solvent includes one or more of water, ethanol, methanol, acetone, ethylene glycol, and isopropanol.

[0115] In some embodiments, the precursor is prepared by the following steps:

[0116] reacting a lithium source, a manganese source, an iron source, and a phosphorus source in a solvent, performing solid-liquid separation, and collecting a solid phase;

[0117] The solid phase is dried and sintered to obtain a precursor.

[0118] In some embodiments, the precursor includes LiMn x Fe 1-x PO4, wherein 0<x<1, optionally, 0.1≤x≤0.9, for example, x is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a range consisting of any of the above values;

[0119] Optionally, in the step of preparing the precursor, the molar ratio of the lithium element in the lithium source, the manganese element in the manganese source, the iron element in the iron source, and the phosphorus element in the phosphorus source is 1:x:(1-x):1.

[0120] The elements in the precursor of the present application are evenly distributed and have good batch consistency. The elements in the positive electrode material made using the precursor material of the present application are evenly distributed and have good batch consistency, thereby improving the electrical properties of the battery such as gram capacity and cycle performance.

[0121] In some embodiments, in the step of preparing the precursor, the reaction is carried out at 5°C-60°C, optionally, the reaction is carried out at 10°C-50°C, for example, the reaction is carried out at 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C or any range of the above values; and / or,

[0122] The reaction time is 10 minutes to 8 hours, optionally 10 minutes to 6 hours, for example, 10 minutes, 20 minutes, 30 minutes, 50 minutes, 60 minutes, 1.5 hours, 2 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours or a range consisting of any of the above values; and / or,

[0123] The drying temperature is 50°C-250°C, for example, 60°C, 70°C, 80°C, 90°C, 100°C, 120°C, 140°C, 150°C, 160°C, 180°C, 200°C, 220°C, 230°C, 240°C, 250°C or any range thereof; and / or,

[0124] The drying time is 10 minutes to 12 hours, for example, 10 minutes, 20 minutes, 30 minutes, 50 minutes, 60 minutes, 1.5 hours, 2 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours or a range consisting of any of the above values; and / or,

[0125] The sintering temperature is 150°C-800°C, optionally 200°C-700°C, for example, 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C; and / or,

[0126] The sintering time is 1-12 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours or any range thereof; and / or,

[0127] The sintering is performed in an inert atmosphere.

[0128] Using the above reaction temperature and time when preparing the precursor is beneficial to reducing side reactions, so as to obtain a precursor material with uniform composition and good batch consistency, thereby improving the battery's gram capacity and cycle performance.

[0129] The above-mentioned sintering temperature and time are used in the preparation of the precursor, which is conducive to the growth of crystals to reduce the proportion of amorphous particles, thereby obtaining a precursor with better crystallinity, thereby improving the battery's gram capacity and cycle performance.

[0130] In some embodiments, in the step of preparing the precursor, the solid-liquid separation is performed by filtration or centrifugation; and / or,

[0131] Before the drying, the solid phase is ball-milled; optionally, the ball milling speed is 100-600 rpm, optionally 200-500 rpm, for example, 100 rpm, 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm or a range consisting of any of the above values, and the ball milling time is 1-12 hours, optionally 2-10 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours or a range consisting of any of the above values; and / or,

[0132] Before the drying, the solid phase is washed; and / or,

[0133] Between the drying and the sintering, the solid phase is crushed; and / or,

[0134] The lithium source includes one or more of lithium hydroxide, oxide, inorganic acid salt, and organic acid salt, and can be selected from one or more of lithium hydroxide, lithium oxide, lithium carbonate, lithium acetate, lithium oxalate, lithium phosphate, and lithium chloride; and / or,

[0135] The manganese source includes one or more of organic acid salts, inorganic acid salts, oxides, and hydroxides of manganese; and / or,

[0136] The iron source includes one or more of organic acid salts, inorganic acid salts, oxides, and hydroxides of iron; and / or,

[0137] The phosphorus source includes one or more of phosphoric acid, phosphates, hydrogen phosphates, and dihydrogen phosphates, and can be selected from one or more of phosphoric acid, ferric phosphate, ferrous phosphate, ferrous ammonium phosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, ammonium phosphate, lithium monohydrogen phosphate, lithium dihydrogen phosphate, and lithium phosphate; and / or,

[0138] A carbon source is added during the reaction.

[0139] The use of the above-mentioned ball milling speed and time when preparing the precursor is beneficial to improving the degree of solid-solid reaction, making the reaction more efficient, thereby improving the battery's gram capacity and cycle performance.

[0140] [Cathode material]

[0141] One embodiment of the present application provides a positive electrode material, comprising a core and a coating layer covering the core, wherein the core comprises LiMn x Fe 1-x PO4, wherein 0<x<1, optionally, 0.1≤x≤0.9, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a range consisting of any of the above values; the coating layer comprises carbon and a doping element; the doping element comprises one or more of Group IIA elements, Group IIIA elements, Group IVA elements, and transition metal elements, and may optionally comprise one or more of Mg, Ti, V, Si, Cr, Mn, Fe, Co, Ni, and B;

[0142] Optionally, the molar ratio of manganese to iron in the kernel is 1:9-9:1, for example, 1:8, 1:7.5, 1:7, 1:6.5, 1:6, 1:5.5, 1:5, 1:4.5, 1:4, 1:3.5, 1:3, 1:2.5, 1:2, 1:1.5, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1 or a range consisting of any of the above values.

[0143] Therefore, the present application simultaneously adds a carbon source and a source of doping elements during the coating process, which is conducive to the formation of a tight structure between the coating layer and the core surface, and stabilizes the crystals of the positive electrode material, reduces the powder resistivity of the positive electrode material, reduces the specific surface area of ​​the positive electrode material within a reasonable range, and improves the battery's gram capacity and cycle performance.

[0144] In some embodiments, the LiMn in the core x Fe 1-x The molar ratio of PO4 to the carbon element in the coating layer is 1:1.5-1:0.001, and can be optionally 1:1.45-1:0.01, such as 1:1.5, 1:1.45, 1:1.4, 1:1.35, 1:1.3, 1:1.25, 1:1.2, 1:1.15, 1:1.1, 1:1.05, 1:1, 1:0.95, 1:0.9, 1:0.8, 1:0.7, 1:0.6 , 1:0.5, 1:0.4, 1:0.3, 1:0.2, 1:0.1, 1:0.09, 1:0.07, 1:0.06, 1:0.05, 1:0.04, 1:0.03, 1:0.02, 1:0.01, 1:0.009, 1:0.007, 1:0.005, 1:0.003, 1:0.002, 1:0.001 or a range consisting of any of the above values; and / or,

[0145] The LiMn in the core x Fe 1-xThe molar ratio of PO4 to the doping element in the coating layer is 1:0.25-1:0.00001, and can be optionally 1:0.2-1:0.0001, for example, 1:0.25, 1:0.2, 1:0.15, 1:0.1, 1:0.05, 1:0.01, 1:0.009, 1:0.007, 1:0.005, 1:0.003, 1:0.001, 1:0.0009, 1:0.0007, 1:0.0005, 1:0.0003, 1:0.0002, 1:0.0001, 1:0.00009, 1:0.00007, 1:0.00005, 1:0.00003, 1:0.00002, 1:0.00001 or a range consisting of any of these values.

[0146] In some embodiments, the Dv50 particle size of the positive electrode material is 0.1-13 μm, for example, 0.1 μm, 1 μm, 2 μm, 3 μm, 5 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm or a range consisting of any of the above values; and / or,

[0147] The BET specific surface area of ​​the positive electrode material is 10-27 m2 / g, and can be 10-25 m2 / g, for example, 10 m2 / g, 11 m2 / g, 12 m2 / g, 13 m2 / g, 14 m2 / g, 15 m2 / g, 16 m2 / g, 17 m2 / g, 18 m2 / g, 19 m2 / g, 20 m2 / g, 21 m2 / g, 22 m2 / g, 23 m2 / g, 24 m2 / g, 25 m2 / g, 26 m2 / g, 27 m2 / g or a range consisting of any of the above values; and / or,

[0148] The powder resistivity of the positive electrode material is ≤1200Ω·cm. Optionally, the powder resistivity of the positive electrode material is ≤300Ω·cm, such as 10Ω·cm, 15Ω·cm, 20Ω·cm, 30Ω·cm, 40Ω·cm, 50Ω·cm, 60Ω·cm, 70Ω·cm, 80Ω·cm, 100Ω·cm, 120Ω·cm, 130Ω·cm, 150Ω·cm, 170Ω·cm, 1 80Ω·cm, 200Ω·cm, 220Ω·cm, 250Ω·cm, 280Ω·cm, 300Ω·cm, 350Ω·cm, 400Ω·cm, 500Ω·cm, 600Ω·cm, 700Ω·cm, 800Ω·cm, 850Ω·cm, 900Ω·cm, 1000Ω·cm, 1100Ω·cm, 1200Ω·cm, or a range consisting of any of the above values; and / or,

[0149] The positive electrode material is prepared by the method described above in this application.

[0150] In the present application, the Dv50 particle size is tested using conventional methods in the art; for example, a sample is added to water to completely disperse the sample, and the Dv50 particle size of the material is measured using a laser particle size analyzer.

[0151] In this application, the BET specific surface area refers to the BET specific surface area at -200°C and is measured using conventional methods in the art. For example, a sample is weighed and placed in a specific surface area test tube. A liquid nitrogen cup is filled with liquid nitrogen and placed in the specific surface area test tube. The sample is then exposed to a temperature of -200°C and tested using a specific surface area analyzer.

[0152] In this application, powder resistivity refers to the powder resistivity at 7.85 MPa, measured using conventional methods in the art. For example, a sample is placed in a mold, which is then placed in a four-probe resistivity tester with a pressure of 7.85 MPa. After the mold height and pressure stabilize, the forward and reverse resistivity of the sample are measured, and the average of the two values ​​is taken as the powder resistivity of the sample.

[0153] [Positive electrode]

[0154] The positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the aforementioned positive electrode material.

[0155] The battery's charge and discharge processes involve the intercalation and deintercalation of lithium, leading to different molar Li contents at different discharge states. The molar Li contents listed in this application for cathode materials refer to the initial state of the material, i.e., the state before addition of the materials. When the cathode material is used in a battery system, the molar Li content will change after charge and discharge cycles.

[0156] In the list of positive electrode materials in this application, the molar content of O is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0157] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0158] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0159] In some embodiments, it may further include positive electrode materials for batteries that are well known in the art. As an example, the positive electrode material may include at least one of the following materials: lithium transition metal oxides and modified compounds thereof. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and at least one of its modified compounds, etc.

[0160] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0161] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0162] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0163] [Negative electrode]

[0164] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0165] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0166] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0167] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0168] In some embodiments, the negative electrode film layer may further include a binder. For example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0169] In some embodiments, the negative electrode film layer may further include a conductive agent. For example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0170] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0171] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0172] [Electrolytes]

[0173] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0174] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0175] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0176] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0177] 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 properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0178] [Isolation film]

[0179] In some embodiments, the battery cell further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0180] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0181] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0182] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0183] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0184] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 5 with a square structure as an example.

[0185] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0186] In some embodiments, battery cells may be assembled into a battery module. The battery module may contain one or more battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0187] FIG3 shows an example battery module 4. Referring to FIG3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0188] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0189] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0190] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0191] In addition, the present application also provides an electrical device, which includes at least one of the battery cells, battery modules, or battery packs provided in the present application. The battery cells, battery modules, or battery packs can be used as power sources for the electrical device, or as energy storage units for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0192] As an electrical device, a battery cell, battery module or battery pack can be selected according to its usage requirements.

[0193] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the battery cells, a battery pack or battery module can be used.

[0194] [Example]

[0195] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0196] Example 1

[0197] (1) Preparation of precursor:

[0198] 1182g Li2CO3, 3325g NH4H2PO4, 2899g MnSO4, and 1945g FeSO4 were put into 14kg pure water, stirred and reacted at 25°C for 60 minutes, and the precipitate was collected by filtration; the precipitate was washed with pure water, filtered, ball milled at 350rpm for 120 minutes, dried at 100°C for 120 minutes, and crushed to obtain dry powder. The dry powder was then placed in a nitrogen atmosphere sintering furnace and sintered at a constant temperature of 500°C for 3 hours to obtain a precursor.

[0199] (2) Preparation of positive electrode materials:

[0200] 5000 g of the precursor was put into 14 kg of glucose aqueous solution (containing 1 kg of glucose), and 19 g of Mg(OH)2, 26 g of TiO2, 37 g of NH4VO3, 25 g of H2SiO3, 6 g of Cr2O3, 28 g of MnO2, 6 g of Fe2O3, 29 g of CoO2, 24 g of NiO and 20 g of H3BO3 were added. The mixture was ground at 25 °C by a sand mill for 3 hours to obtain a slurry; part of the slurry passing through a 400-mesh sieve was collected and spray-dried at 300 °C to obtain a dry powder; the dry powder was placed in a nitrogen atmosphere furnace at 800 °C and sintered for 6 hours, then cooled and taken out, and crushed until it could completely pass through an 800-mesh sieve to obtain a positive electrode material with a Dv50 particle size of 12 μm.

[0201] (3) Preparation of positive electrode sheet:

[0202] The positive electrode material, polyvinylidene fluoride, conductive carbon black and N-methylpyrrolidone are dissolved in the solvent N-methylpyrrolidone (NMP) in a weight ratio of 95:2.5:2.5:100, and the mixture is thoroughly stirred and evenly mixed to prepare a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and then dried, cold pressed and cut to obtain the positive electrode sheet.

[0203] (4) Preparation of negative electrode sheet:

[0204] The negative electrode active material artificial graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC-Na) are dissolved in deionized water in a weight ratio of 95.5:1.5:1.8:1.2, and the mixture is fully stirred and mixed to prepare a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector copper foil, and then dried, cold pressed, and cut to obtain the negative electrode sheet.

[0205] (5) Isolation film: Polypropylene film is used.

[0206] (6) Preparation of electrolyte:

[0207] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and then LiPF6 was uniformly dissolved in the above solution to obtain an electrolyte solution. The concentration of LiPF6 in the electrolyte solution was 1 mol / L.

[0208] (7) Preparation of button cells:

[0209] The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in order to obtain an electrode assembly; the electrode assembly is placed in an outer package, and the above-prepared electrolyte is added. After packaging, standing, formation, aging and other processes, a secondary battery is obtained.

[0210] The preparation methods of the secondary batteries of Examples 2-46 and Comparative Example 3 are similar to those of Example 1, but the parameters are adjusted, as shown in Table 1-2. The preparation method of Comparative Example 1-2 is as follows:

[0211] Comparative Example 1

[0212] Combine 1182g Li2CO3, 3325g NH4H2PO4, 2899g MnSO4, 1945g FeSO 4、 Add 14 kg of pure water and stir the reaction at 25 ° C for 60 minutes. Continue to add 19 g Mg (OH) 2, 26 g TiO2, 37 g NH4VO3, 25 g H2SiO3, 6 g Cr2O3, 28 g MnO2, 6 g Fe2O3, 29 g CoO2, 24 g NiO and 20 g H3BO3. After mixing, wash and collect the precipitate, microwave dry for 25 minutes, heating power 800 W, crush to obtain dry powder, and then place the dry powder in a nitrogen atmosphere sintering furnace and sinter at a constant temperature of 650 ° C for 6 hours to obtain a precursor.

[0213] 5000 g of the precursor and 1 kg of glucose were mixed, ground at 300 rpm for 1 hour, sintered in a nitrogen atmosphere furnace at 800°C for 5 hours, cooled, taken out, and crushed into pieces that could completely pass through an 800-mesh sieve to obtain the positive electrode material.

[0214] Comparative Example 2

[0215] Combine 1182g Li2CO3, 3325g NH4H2PO4, 2899g MnSO4, 1945g FeSO 4、 Add 14 kg of pure water and stir the reaction at 25 ° C for 60 minutes. Continue to add 28 g MnO2, 6 g Fe2O3, 6 g Cr2O3, and 29 g CoO2. After mixing, wash and collect the precipitate, microwave dry for 25 minutes, heating power 800 W, crush, and obtain dry powder. Then place the dry powder in a nitrogen atmosphere sintering furnace and sinter at a constant temperature of 650 ° C for 6 hours to obtain a precursor.

[0216] 5000 g of the precursor and 1 kg of glucose were mixed, ground at 300 rpm for 1 hour, sintered in a nitrogen atmosphere furnace at 800°C for 5 hours, cooled, taken out, and crushed into pieces that could completely pass through an 800-mesh sieve to obtain the positive electrode material.

[0217] Table 3: Parameters of positive electrode materials of Examples 1-46 and Comparative Examples 1-3

[0218] Materials and battery testing

[0219] (1) Testing of the chemical formula of the precursor, the coating composition of the cathode material, and the element ratio:

[0220] Weigh 0.2 g of the precursor or cathode material into a 100 mL beaker, add 10 mL of 10% w / w nitric acid solution, heat and digest at 120°C for 0.5 hours, and then dilute to volume with a 100 mL volumetric flask; then use a pipette to transfer 1 mL to a 100 mL volumetric flask and dilute to volume to obtain the test solution.

[0221] An inductively coupled plasma optical emission spectrometer (ICP-OES, instrument brand: Agilent 5800) is used to determine the mass fractions of lithium, manganese, iron, phosphorus, and doping elements in the test solution; the molar fraction of each element in the precursor is calculated based on the mass fraction of each element in the test solution of the precursor, thereby determining the chemical formula and element molar ratio of the precursor; the molar fraction of each element in the positive electrode material is calculated based on the mass fraction of each element in the test solution of the positive electrode material, and the molar fraction of each element in the precursor is deducted to obtain the elemental composition of the coating layer, thereby calculating the element molar ratio;

[0222] Weigh 0.1g of positive electrode material, add 1.5g of flux metal tungsten particles and mix, put it into a high-frequency infrared carbon-sulfur analyzer for sintering and test the mass ratio of carbon in the positive electrode material and convert it into a molar ratio.

[0223] (2) Dv50 particle size test:

[0224] Take an appropriate amount of sample, add 20 mL of deionized water, and ultrasonically treat for 5 minutes (53 KHz, 120 W) to completely disperse the sample. Use a laser particle size analyzer (MasterSizer 2000) to measure the Dv50 particle size of the material.

[0225] (3) BET specific surface area test:

[0226] Weigh 1 g of sample and place it in a specific surface area test tube. Fill a liquid nitrogen cup with liquid nitrogen and place it in the specific surface area test tube. Place the sample in a temperature environment of -200°C and use a specific surface area analyzer (Beijing Jingwei Gaobo, JWBK-112) for testing.

[0227] (4) Test of powder resistivity of positive electrode material:

[0228] Weigh 1g of sample and place it in a mold. Then place the mold in a four-probe resistivity tester and adjust the pressure to 7.85MPa. After the mold height and pressure are stable, test the forward resistivity and reverse resistivity of the sample respectively, and take the average of the two as the powder resistivity of the sample.

[0229] (5) TEM test of cathode materials:

[0230] The positive electrode materials of Example 1 and Comparative Example 3 were subjected to TEM testing, and the results are shown in Figures 7 and 8. The comparison shows that the coating layer of the positive electrode material of Example 1 of the present application is more complete, the structure is more compact, and the texture of the positive electrode material is more uniform and stable.

[0231] (6) Battery charge capacity and discharge capacity test:

[0232] Shenzhen Xinweier battery testing system was used to cycle the button batteries at a charge and discharge rate of 0.1C. The test temperature was 25.0℃, and the charge and discharge voltage was 2.0V-4.3V. The charge capacity in grams was obtained by dividing the charge capacity in the first cycle by the mass of the positive electrode material, and the discharge capacity in grams was obtained by dividing the discharge capacity in the first cycle by the mass of the positive electrode material.

[0233] (7) Test of battery capacity retention at 25°C:

[0234] Shenzhen Xinweier battery testing system was used to cycle the button batteries at a charge and discharge rate of 1C for 2000 times. The test temperature was 25.0℃, and the charge and discharge voltage was 2.0V~4.3V. The capacity retention rate was obtained by dividing the discharge capacity of the last cycle by the discharge capacity of the first cycle.

[0235] The above results are shown in Table 3-4.

[0236] Table 4: Performance test results of Examples 1-46 and Comparative Examples 1-3

[0237] According to the above results, we can know that:

[0238] Compared with Comparative Example 1 in which the doping element is added to the core, the cycle capacity retention rate of the batteries of Examples 1-13, 15-18, 20-29, 33-40, and 43-44 of the present application is significantly higher, and the charge gram capacity and discharge gram capacity of the batteries of Examples 1-13, 15-18, 20-29, 39-40, and 43-44 of the present application are significantly higher;

[0239] Compared with Comparative Example 2 in which the doping element is added to the core, the battery of Example 14 of the present application has significantly higher charge and discharge gram capacities and a significantly higher cycle capacity retention rate;

[0240] Compared with Comparative Example 3 in which no doping elements are added to the core and shell, the cycle capacity retention rates of the batteries of Examples 1, 14, 17-18, and 41-42 of the present application are significantly higher, and the charge and discharge gram capacities of Examples 1, 14, and 17-18 of the present application are significantly higher;

[0241] Compared with the lower reaction temperature and longer reaction time used in Example 33 when preparing the precursor, and the higher reaction temperature used in Example 34 when preparing the precursor, the charge and discharge gram capacities of the batteries of Examples 1-4 of the present application are significantly higher, and the cycle capacity retention rate is significantly higher;

[0242] Compared with the lower ball milling speed used in Example 35 and the higher ball milling speed used in Example 36, the charge and discharge gram capacities of the batteries in Examples 1 and 5-7 of the present application were significantly higher, and the cycle capacity retention rates were significantly higher.

[0243] Compared with the lower sintering temperature used in preparing the precursor in Example 37 and the higher sintering temperature used in preparing the precursor in Example 38, the charge and discharge gram capacities of the batteries in Examples 1 and 11-13 of the present application are significantly higher, and the cycle capacity retention rate is significantly higher;

[0244] Compared with the use of a lower molar ratio of precursor to carbon element when preparing the positive electrode material in Example 39, the charge and discharge gram capacity of the batteries in Examples 1 and 15-16 of the present application is significantly higher, and the cycle capacity retention rate is significantly higher; compared with the use of a higher molar ratio of precursor to carbon element when preparing the positive electrode material in Example 40, the charge and discharge gram capacity of the batteries in Examples 1 and 15-16 of the present application is significantly higher;

[0245] Compared with Example 41, which uses a lower molar ratio of precursor to doping element when preparing the positive electrode material, and Example 42, which uses a higher molar ratio of precursor to doping element when preparing the positive electrode material, the charge and discharge gram capacities of the batteries in Examples 1 and 17-18 of the present application are significantly higher, and the cycle capacity retention rate is significantly higher;

[0246] Compared with the lower grinding temperature used in Example 43 and the higher grinding temperature used in Example 44, the charge and discharge gram capacities of the batteries in Examples 1 and 20-22 of the present application are significantly higher, and the cycle capacity retention rate is significantly higher.

[0247] Compared with the use of a lower sintering temperature when preparing the positive electrode material in Example 45 and the use of a higher sintering temperature when preparing the positive electrode material in Example 46, the charge and discharge gram capacity of the batteries in Examples 1 and 26-28 of the present application is significantly higher, and the cycle capacity retention rate is significantly higher.

[0248] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing a positive electrode material, comprising: The precursor lithium manganese iron phosphate, the carbon source, and the source of the doping element are mixed in a solvent, dried, and sintered to obtain a positive electrode material; The positive electrode material comprises a core and a coating layer covering the core; the core comprises LiMn x Fe 1-x PO4, wherein 0<x<1; the coating layer comprises carbon and doping elements; the doping elements comprise one or more of group ⅡA elements, group ⅢA elements, group ⅣA elements, and transition metal elements.

2. The method according to claim 1, wherein: 0.1≤x≤0.9; and / or, The doping elements include one or more elements of Mg, Ti, V, Si, Cr, Mn, Fe, Co, Ni, and B.

3. The method according to claim 1 or 2, wherein: The molar ratio of the precursor to the carbon element in the carbon source is 1:1.5-1:0.001, and can be optionally 1:1.45-1:0.01; and / or, The molar ratio of the precursor to the doping element in the source of the doping element is 1:0.25-1:0.00001, and can be optionally 1:0.2-1:0.0001.

4. The method according to any one of claims 1 to 3, wherein: The mixing is performed at 5°C-70°C, optionally, the mixing is performed at 10°C-60°C; and / or, The mixing time is 0.5-12 hours; and / or, The mixing is performed by grinding.

5. The method according to any one of claims 1 to 4, wherein: The sintering temperature is 350°C-950°C, and can be 400°C-900°C; and / or, The sintering time is 2-20 hours; and / or, The sintering is performed in an inert atmosphere.

6. The method according to any one of claims 1 to 5, wherein: The drying temperature is 150°C-400°C; and / or, The drying is performed by spray drying or oven drying; and / or, The method further comprises sieving the mixture before drying, collecting the sieved portion; and / or, The method further comprises crushing after the sintering, optionally followed by screening; and / or, The carbon source includes one or more of an organic carbon source and an inorganic carbon source, and can be selected from citric acid, glucose, sucrose, polyvinyl alcohol, polypyrrole, polyethylene glycol, asphalt, anthracene, aniline, etc. one or more; and / or, The source of the doping element includes one or more of a hydroxide of the doping element, an oxide of the doping element, an acid of the doping element, and a salt of the doping element; and / or, The solvent includes one or more of water and an organic solvent. Optionally, the solvent includes one or more of water, ethanol, methanol, acetone, ethylene glycol, and isopropanol.

7. The method according to any one of claims 1 to 6, wherein: The precursor is prepared by the following steps: reacting a lithium source, a manganese source, an iron source and a phosphorus source in a solvent, separating the solid from the liquid, and collecting a solid phase; The solid phase is dried and sintered to obtain a precursor.

8. The method according to claim 7, wherein: The precursor includes LiMn x Fe 1-x PO4, wherein 0<x<1, optionally, 0.1≤x≤0.9; Optionally, in the step of preparing the precursor, the molar ratio of the lithium element in the lithium source, the manganese element in the manganese source, the iron element in the iron source, and the phosphorus element in the phosphorus source is 1:x:(1-x):

1.

9. The method according to claim 7 or 8, wherein: In the step of preparing the precursor, the reaction is carried out at 5°C-60°C, optionally, the reaction is carried out at 10°C-50°C; and / or, The reaction time is 10 minutes to 8 hours, optionally 10 minutes to 6 hours; and / or, The drying temperature is 50°C-250°C; and / or, The drying time is 10 minutes to 12 hours; and / or, The sintering temperature is 150°C-800°C, and can be 200°C-700°C; and / or, The sintering time is 1-12 hours; and / or, The sintering is performed in an inert atmosphere.

10. The method according to any one of claims 7 to 9, wherein: In the step of preparing the precursor, the solid-liquid separation is performed by filtration or centrifugation; and / or, Before the drying, the solid phase is ball-milled; optionally, the rotation speed of the ball mill is 100-600 rpm, optionally 200-500 rpm, and the time of the ball milling is 1-12 hours, optionally 2-10 hours; and / or, Before the drying, the solid phase is washed; and / or, Between the drying and the sintering, the solid phase is crushed; and / or, The lithium source includes one or more of lithium hydroxide, oxide, inorganic acid salt, and organic acid salt, and may be selected from one or more of lithium hydroxide, lithium oxide, lithium carbonate, lithium acetate, lithium oxalate, lithium phosphate, and lithium chloride; and / or, The manganese source includes one or more of organic acid salts, inorganic acid salts, oxides and hydroxides of manganese; and / or, The iron source includes one or more of organic acid salts, inorganic acid salts, oxides and hydroxides of iron; and / or, The phosphorus source includes one or more of phosphoric acid, phosphate, hydrogen phosphate, and dihydrogen phosphate, and can be selected from one or more of phosphoric acid, ferric phosphate, ferrous phosphate, ammonium ferrous phosphate, diammonium phosphate, ammonium hydrogen phosphate, ammonium phosphate, lithium monohydrogen phosphate, lithium dihydrogen phosphate, and lithium phosphate; and / or, A carbon source is added during the reaction.

11. A positive electrode material, comprising a core and a coating layer coating the core, wherein the core comprises LiMn x Fe 1-x PO4, where 0<x<1, optionally, 0.1≤x≤0.9; the coating layer comprises carbon and doping elements; the doping elements comprise one or more of group ⅡA elements, group ⅢA elements, group ⅣA elements, and transition metal elements, and may be one or more of Mg, Ti, V, Si, Cr, Mn, Fe, Co, Ni, and B; Optionally, the molar ratio of manganese element to iron element in the inner core is 1:9-9:

1.

12. The positive electrode material according to claim 11, wherein The LiMn in the core x Fe 1- x The molar ratio of PO4 to the carbon element in the coating layer is 1:1.5-1:0.001, and can be optionally 1:1.45-1:0.01; and / or, The LiMn in the core x Fe 1-x The molar ratio of PO4 to the doping element in the coating layer is 1:0.25-1:0.00001, and can be optionally 1:0.2-1:0.0001.

13. The positive electrode material according to claim 11 or 12, wherein The Dv50 particle size of the positive electrode material is 0.1-13 μm; and / or, The BET specific surface area of ​​the positive electrode material is 10-27 m2 / g, and can be optionally 10-25 m2 / g; and / or, The powder resistivity of the positive electrode material is ≤1200Ω·cm. Optionally, the powder resistivity of the positive electrode material is ≤300Ω·cm; and / or, The positive electrode material is prepared by the method according to any one of claims 1 to 10. 14 . A positive electrode sheet, comprising the positive electrode material prepared by the method according to claim 1 or the positive electrode material according to claim 11 . 15 . A battery comprising a positive electrode material prepared by the method of claim 1 , a positive electrode material of claim 11 , or a positive electrode sheet of claim 14 .

16. An electrical device comprising the battery according to claim 15.

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