Positive electrode material and preparation method therefor, positive electrode sheet, battery and electric device

Abstract

Provided in the present application are a positive electrode material and a preparation method therefor, a positive electrode sheet, a battery and an electric device. The positive electrode material of the present application comprises an inner core and a coating layer that coats the inner core, wherein the inner core comprises lithium iron phosphate or M-element-containing lithium iron phosphate, and the coating layer comprises carbon and an optional M element. The positive electrode material satisfies: the powder resistivity at 8 MPa is less than or equal to 20 Ω.cm; and the BET specific surface area at a liquid nitrogen temperature is 6-15.2 m2 / g. The positive electrode material of the present application has few side reactions, and improves the cycle performance of a battery.

Description

Positive electrode material and preparation method thereof, positive electrode sheet, battery and electrical device

[0001] This application is based on and claims priority to the Chinese patent application with application number 202410043846.7 and application date January 11, 2024. All contents of the application are hereby introduced as a whole into this application. Technical Field

[0002] The present application relates to the technical field of lithium batteries, and in particular to a positive electrode material, a method for preparing the positive electrode material, a positive electrode sheet, a battery, and an electrical device. Background Art

[0003] In recent years, the application scope of secondary batteries has become increasingly broad. 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 their cycle performance. Summary of the Invention

[0004] The present application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode material, a preparation method of the positive electrode material, a positive electrode sheet, a battery and an electrical device. The positive electrode material of the present application has fewer side reactions and less loss of active lithium, thereby improving the cycle performance of the battery.

[0005] In order to achieve the above-mentioned object, the first aspect of the present application provides a positive electrode material, comprising a core and a coating layer covering the core, wherein the core comprises lithium iron phosphate or lithium iron phosphate containing an M element, and the coating layer comprises carbon or comprises carbon and an M element; wherein the M element in the core and the coating layer independently comprises one or more elements of Group IIA, Group IIIA, Group IVA, Group IVB, and Group VB, and may optionally comprise one or more elements of Si, Al, B, Mg, Zr, Ti, Nb, and V;

[0006] Furthermore, the positive electrode material satisfies:

[0007] Powder resistivity at 8 MPa ≤ 20 Ω·cm; and

[0008] The BET specific surface area at liquid nitrogen temperature is 6-15.2 m 2 / g.

[0009] The positive electrode material of the present application has both a low water absorption rate and a low water absorption contact area, which reduces the water absorption of the positive electrode material and reduces the occurrence of side reactions between water in the positive electrode material and the electrolyte, thereby improving the cycle performance of the battery.

[0010] In any embodiment, the powder resistivity of the positive electrode material at 8 MPa is ≤10Ω·cm; and / or,

[0011] The BET specific surface area of ​​the positive electrode material at liquid nitrogen temperature is 8-11m 2 / g.

[0012] In any embodiment, the amount of iron dissolved per gram of the positive electrode material in 100 mL of hydrochloric acid solution is ≤60 ppm; and / or,

[0013] The primary particle size distribution consistency index (PDI) of the positive electrode material is ≤0.87.

[0014] In any embodiment, the amount of iron dissolved per gram of the positive electrode material in 100 mL of hydrochloric acid solution is ≤55 ppm; and / or,

[0015] The primary particle size distribution consistency index (PDI) of the positive electrode material is ≤0.4.

[0016] The iron dissolution amount of the positive electrode material of the present application meets the above range, which can improve the situation where iron settles at the negative electrode and destroys the formation of the SEI film, thereby improving the cycle performance of the battery.

[0017] The consistency index PDI of the primary particle size distribution of the positive electrode material of the present application meets the above range, which is conducive to controlling the concentration and uniformity of the primary particle size of the positive electrode material, reducing the precipitation of small particle metal ions and / or reducing the occurrence of side reactions with the electrolyte after large particles are crushed, thereby improving the cycle performance of the battery.

[0018] In any embodiment, the weight content of the carbon in the positive electrode material is 1.2%-2.0%; and / or,

[0019] The weight content of the M element in the positive electrode material is 297ppm-10 4 ppm.

[0020] In any embodiment, the weight content of the M element in the positive electrode material is 10 3 ppm-10 4 ppm.

[0021] This is conducive to obtaining a coating layer with thin thickness, good integrity, high density, high uniformity, and high degree of graphitization, thereby improving the cycle performance of the battery.

[0022] In any embodiment, the Dv50 particle size of the positive electrode material is 0.6-1.5 μm; and / or,

[0023] The compaction density of the positive electrode material at 221.55 MPa is ≥ 2.3 g / cm3 .

[0024] This is conducive to obtaining a positive electrode sheet with high compaction and high compaction density.

[0025] The second aspect of the present application also provides a method for preparing a positive electrode material, comprising:

[0026] Ball-milling and sand-milling the iron source, lithium source, phosphorus source, organic carbon source and inorganic carbon source in a solvent to obtain a mixture;

[0027] drying and sintering the mixture to obtain a positive electrode material;

[0028] The positive electrode material is the positive electrode material of the first aspect of this application.

[0029] Therefore, the present application adopts the above-mentioned raw materials and combines them with operations such as ball milling, sand milling, and sintering, and optionally adds doping elements to the coating layer so that the powder resistivity and BET specific surface area of ​​the positive electrode material meet the above-mentioned ranges, so that the prepared positive electrode material has both a lower water absorption rate and a lower water absorption contact area, thereby reducing the water absorption of the positive electrode material and reducing the occurrence of side reactions between water in the positive electrode material and the electrolyte, thereby improving the cycle performance of the battery.

[0030] In any embodiment, the organic carbon source includes a small molecule organic carbon source and a medium molecule organic carbon source, or includes a small molecule organic carbon source and a high molecule organic carbon source.

[0031] In any embodiment, the weight ratio of the small molecule organic carbon source to the medium molecule organic carbon source, or the weight ratio of the small molecule organic carbon source to the high molecule organic carbon source is 1:9-9:1; and / or,

[0032] The weight average molecular weight of the medium molecular organic carbon source is greater than 500 and less than or equal to 2000; and / or,

[0033] The weight average molecular weight of the polymer organic carbon source is greater than 2000 and less than or equal to 1000000; and / or,

[0034] The inorganic carbon source includes one or more of acetylene black, Ketjen black, graphite oxide, graphene, and carbon nanotubes.

[0035] This facilitates the formation of a dense and well-integrated coating, thereby reducing the amount of iron dissolution and powder resistivity of the cathode material. The inorganic carbon source acts as a supporting skeleton during the carbonization process of the organic carbon source, improving the uniformity and integrity of the carbon film.

[0036] In any embodiment, the organic carbon source comprises one or more of glucose, sucrose, fructose, citric acid, starch, polyvinyl alcohol, polyethylene glycol, and polyaniline.

[0037] In any embodiment, in the step of preparing the mixture, the iron source, lithium source, phosphorus source, organic carbon source, inorganic carbon source, and source of element M are ball-milled and sand-milled in a solvent to obtain the mixture.

[0038] In any embodiment, the weight ratio of the inorganic carbon source to the iron element in the iron source is 1:50-1:345.

[0039] In any embodiment, the Dv50 particle size of the insoluble particles in the mixture is 0.40-0.85 μm; and / or,

[0040] The sanding temperature is 25°C-35°C; and / or,

[0041] The sanding time is 0.5-4 hours; and / or,

[0042] Sand at 5000-10000 rpm.

[0043] This is beneficial to improving the consistency of the primary particle size distribution of the positive electrode material, improving the concentration and uniformity of the positive electrode material particles, reducing the precipitation of small particle metal ions and / or the side reaction of large particles with the electrolyte after crushing, and improving the cycle performance of the battery.

[0044] In any embodiment, the method further comprises: before sintering, granulating the dried mixture to obtain particles; wherein the average particle size of the particles is 2 mm to 10 mm; and / or,

[0045] The method further includes: crushing the sintered product after sintering to obtain the positive electrode material, thereby facilitating improving the consistency of the primary particle size distribution of the positive electrode material.

[0046] In any embodiment, after drying or granulation, the temperature is raised to the sintering temperature at a constant rate within 2.5-9 hours; and / or,

[0047] The sintering temperature is 600° C.-800° C.; and / or,

[0048] The sintering time is 5-10 hours; and / or,

[0049] Heating and sintering in a reducing atmosphere; and / or,

[0050] The volume content of the reducing gas in the reducing atmosphere is 2%-8%.

[0051] Therefore, on the one hand, it is beneficial to the full cracking and carbonization of the organic carbon source to obtain an ultra-thin coating layer with a high degree of graphitization; on the other hand, it is beneficial to improve the uniformity of the coating layer and reduce the problem of metal ion dissolution caused by uneven or incomplete coating.

[0052] In any embodiment, the molar ratio of the iron element in the iron source to the phosphorus element in the phosphorus source is 0.96-0.98; and / or,

[0053] The molar ratio of the lithium element in the lithium source to the iron element in the iron source is 1.015-1.045; and / or,

[0054] The molar ratio of the M element to the iron element in the iron source is 1:1000-3:100; and / or,

[0055] The Dv50 particle size of the insoluble particles in the ball-milled material is 2.0-5.0 μm.

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

[0057] The fourth aspect of the present application provides a battery, comprising the positive electrode material of the first aspect of the present application, the positive electrode material prepared by the method of the second aspect of the present application, or the positive electrode plate of the third aspect of the present application.

[0058] The fifth aspect of the present application provides an electrical device comprising the battery of the fourth aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0060] FIG. 2 is an exploded view of the battery cell according to the embodiment of the present application shown in FIG. 1 .

[0061] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0062] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0063] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application.

[0064] 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.

[0065] FIG7 is a SEM photograph of the positive electrode material of Example 1 of the present application.

[0066] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 battery cell; 51 housing; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0067] Below, with appropriate reference to the accompanying drawings, the embodiments of the positive electrode material and its preparation method, positive electrode sheet, negative electrode sheet, battery cell, battery module, battery pack and electric device of the present application are specifically disclosed in detail. 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 structure 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.

[0068] " 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.

[0069] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0070] 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.

[0071] 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.

[0072] Unless otherwise specified, the Dv50 particle size in this application refers to the particle size when the cumulative value of volume distribution is 50%.

[0073] [Battery Cell]

[0074] 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.

[0075] Typically, a battery cell consists of a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During the charge and discharge process of the battery, 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.

[0076] [Cathode material]

[0077] One embodiment of the present application provides a positive electrode material, comprising a core and a coating layer coating the core, wherein the core comprises lithium iron phosphate or lithium iron phosphate containing an M element, and the coating layer comprises carbon or comprises carbon and an M element; wherein the M element in the core and the coating layer independently comprises one or more elements of Group IIA, Group IIIA, Group IVA, Group IVB, and Group VB, and may optionally comprise one or more elements of Si, Al, B, Mg, Zr, Ti, Nb, and V;

[0078] Furthermore, the positive electrode material satisfies:

[0079] The powder resistivity at 8 MPa is ≤20 Ω·cm, and may be ≤19 Ω·cm or ≤18 Ω·cm, for example, 0.01 Ω·cm, 0.05 Ω·cm, 0.1 Ω·cm, 0.5 Ω·cm, 1 Ω·cm, 2 Ω·cm, 4 Ω·cm, 5 Ω·cm, 7 Ω·cm, 8 Ω·cm, 9 Ω·cm, 10 Ω·cm, 12 Ω·cm, 14 Ω·cm, 15 Ω·cm, 16 Ω·cm, 18 Ω·cm, 20 Ω·cm, or a range formed by using any of the above values ​​as the upper limit, or a range consisting of any of the above values; and

[0080] The BET specific surface area at liquid nitrogen temperature is 6-15.2 m 2 / g, for example 6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g、10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g、15m 2 / g, 15.2m 2 / g or any range consisting of the above values.

[0081] The inventors of this application have discovered through research that the main mechanisms of battery cycle performance degradation using iron-based polyanion phosphate positive electrode materials include: after the surface of the positive electrode material absorbs water, water reacts with the electrolyte to produce hydrofluoric acid, and the hydrogen ions will destroy the SEI film on the surface of the negative electrode, or react with the lithium on the surface of the negative electrode, causing cycle performance degradation.

[0082] Although the mechanism is not clear, the applicant unexpectedly found that:

[0083] The positive electrode material of the present application whose powder resistivity meets the above range has a dense and highly graphitized coating layer, which is beneficial to reducing the water absorption rate of the positive electrode material; the BET specific surface area of ​​the positive electrode material of the present application is within the above range, which is beneficial to reducing the water absorption contact area of ​​the positive electrode material; therefore, the positive electrode material of the present application has both a low water absorption rate and a low water absorption contact area, which reduces the water absorption of the positive electrode material and reduces the occurrence of side reactions between water in the positive electrode material and the electrolyte, thereby improving the cycle performance of the battery.

[0084] In some embodiments, the core comprises Li 1+e M f Fe aPO4, wherein 0≤e<0.1 (e.g., 0, 0.001, 0.003, 0.005, 0.007, 0.008, 0.009, 0.01, 0.02, 0.04, 0.05, 0.07, 0.08, 0.09, 0.095 or any range thereof), 0≤f≤0.05 (e.g., 0, 0.001, 0.003, 0.005, 0.007, 0.008, 0.009 , 0.01, 0.02, 0.04, 0.05 or a range consisting of any of the above values), 0.95≤a≤1 (for example, 0.95, 0.96, 0.97, 0.98, 0.99, 1 or a range consisting of any of the above values); the M element includes one or more elements of Group IIA, Group IIIA, Group IVA, Group IVB, and Group VB, and can be optionally one or more elements of Si, Al, B, Mg, Zr, Ti, Nb, and V.

[0085] In some embodiments, the powder resistivity of the cathode material at 8 MPa is ≤10Ω·cm; and

[0086] The BET specific surface area of ​​the positive electrode material at liquid nitrogen temperature is 8-11m 2 / g.

[0087] In some embodiments, the amount of iron dissolved per gram of the positive electrode material in 100 mL of hydrochloric acid solution is ≤60 ppm, optionally ≤55 ppm, and more optionally ≤15 ppm, for example, 5 ppm, 10 ppm, 15 ppm, 17 ppm, 20 ppm, 22 ppm, 25 ppm, 27 ppm, 30 ppm, 33 ppm, 36 ppm, 39 ppm, 40 ppm, 42 ppm, 45 ppm, 47 ppm, 50 ppm, 53 ppm, 55 ppm, 57 ppm, 58 ppm, 59 ppm, 60 ppm, or any of the above values ​​as the upper limit of the range, or the range composed of any of the above values; and / or,

[0088] The consistency index PDI value of the primary particle size distribution of the positive electrode material is ≤0.87, which can be optionally ≤0.4, for example, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.75, 0.8, 0.85, 0.87 or any of the above values ​​as the upper limit of the range, or the range consisting of any of the above values.

[0089] The iron dissolution amount of the positive electrode material of the present application meets the above range, which can improve the situation where iron settles at the negative electrode and destroys the formation of the SEI film, thereby improving the cycle performance of the battery.

[0090] The consistency index PDI of the primary particle size distribution of the positive electrode material of the present application meets the above range, which is conducive to controlling the concentration and uniformity of the primary particle size of the positive electrode material, reducing the precipitation of small particle metal ions and / or reducing the side reaction of large particles with the electrolyte after crushing.

[0091] In some embodiments, the weight content of the carbon in the positive electrode material is 1.2%-2.0%, for example, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0% or a range consisting of any of the above values; and / or,

[0092] The weight content of the M element in the positive electrode material is 297ppm-10 4 ppm, optional 10 3 ppm-10 4 ppm or 297ppm-2.5×10 3 ppm, or 2×10 3 ppm-6×10 3 ppm, such as 297ppm, 350ppm, 400ppm, 500ppm, 600ppm, 700ppm, 800ppm, 1000ppm, 1100ppm, 1200ppm, 1 500ppm, 1700ppm, 2000ppm, 2200ppm, 2500ppm, 3000ppm, 4000ppm, 5000ppm, 7000ppm, 9000ppm, 10 4 ppm or any range consisting of the above values.

[0093] This is conducive to obtaining a coating layer with thin thickness, good integrity, high density, high uniformity, and high degree of graphitization, thereby improving the cycle performance of the battery.

[0094] In some embodiments, the Dv50 particle size of the positive electrode material is 0.6-1.5 μm, for example, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm or a range consisting of any of the above values; and / or,

[0095] The compaction density of the positive electrode material at 221.55 MPa is ≥ 2.3 g / cm 3 , optional 2.3-2.6g / cm 3 , for example 2.3g / cm 3 , 2.4g / cm 3 , 2.5g / cm 3 , 2.6g / cm 3 Or any range consisting of the above values.

[0096] This is conducive to obtaining a positive electrode sheet with high compaction and high compaction density.

[0097] In the present application, the powder resistivity can be measured by conventional methods in the art, for example, with reference to the national standard GB / T 33822-2017. Specifically, the sample can be tested using a powder resistivity meter, a pressure of 8 MPa is applied, and the forward resistivity and reverse resistivity of the sample are tested respectively, and the average value of the two is taken as the powder resistivity of the sample.

[0098] In the present application, the BET specific surface area can be measured by conventional methods in the art, for example, with reference to the national standard GB / T 19587-2017. Specifically, the test can be performed using a specific surface area analyzer, with the sample placed in a dedicated sample tube, heated and vacuumed for degassing; the sample tube containing the sample is placed in a workstation, the adsorption gas is nitrogen, the test atmosphere is high-purity liquid nitrogen, and the adsorption amount of the gas on the solid surface under different relative adsorption pressures is measured. The analyzer automatically calculates the BET specific surface area based on the BET multilayer adsorption theory and formula.

[0099] In this application, the consistency index PDI value of the primary particle size distribution can be determined by conventional methods in the art; for example, an argon ion beam is used to cut the surface of the positive electrode perpendicularly, and the cross section is photographed using a scanning electron microscope. The particle size of primary particles with a particle size greater than 50 nm is counted, and the PDI is calculated according to the following formula; wherein, the average particle size It is the sum of the particle sizes of primary particles divided by the number of primary particles;

[0100] Where σ is the standard deviation of particle size, is the average particle size, x i is the particle size of the primary particles, and n is the total number of primary particles counted.

[0101] In the present application, the amount of iron dissolved per gram of the positive electrode material in 100 mL of hydrochloric acid solution (0.01 mol / L) can be determined by conventional methods in the art, for example, a dilute hydrochloric acid solution (0.01 mol / L) is added to the positive electrode material, sealed and stirred, sealed and allowed to stand at room temperature, the supernatant is filtered, and the concentration of Fe element in the filtrate is tested by ICP-OES. The amount of iron dissolved per gram of positive electrode material in 100 mL of hydrochloric acid solution is calculated.

[0102] In this application, the Dv50 particle size can be measured using conventional methods in the art, such as adding deionized water to completely disperse the sample, and ensuring that the sample concentration has an occlusion of 8-12%. The Dv50 particle size of the material can be measured using a laser particle size analyzer.

[0103] In the present application, the compaction density can be measured by conventional methods in the art, for example, the sample powder is placed in a compaction density mold, placed in a compaction density machine, and compacted with a certain pressure before testing the compaction density.

[0104] [Method for preparing positive electrode material]

[0105] One embodiment of the present application provides a method for preparing a positive electrode material, comprising:

[0106] Ball-milling and sand-milling the iron source, lithium source, phosphorus source, organic carbon source and inorganic carbon source in a solvent to obtain a mixture;

[0107] drying and sintering the mixture to obtain a positive electrode material;

[0108] The positive electrode material is the positive electrode material mentioned above.

[0109] Therefore, the present application adopts the above-mentioned raw materials and combines them with operations such as ball milling, sand milling, and sintering, and optionally adds doping elements to the coating layer so that the powder resistivity and BET specific surface area of ​​the positive electrode material meet the above-mentioned ranges, so that the prepared positive electrode material has both a lower water absorption rate and a lower water absorption contact area, thereby reducing the water absorption of the positive electrode material and reducing the occurrence of side reactions between water in the positive electrode material and the electrolyte, thereby improving the cycle performance of the battery.

[0110] In some embodiments, the organic carbon source includes a small molecule organic carbon source and a medium molecule organic carbon source, or includes a small molecule organic carbon source and a high molecule organic carbon source.

[0111] In some embodiments, the weight ratio of the small molecule organic carbon source to the medium molecule organic carbon source or the weight ratio of the small molecule organic carbon source to the high molecule organic carbon source is 1:9-9:1, and more preferably 1:8-2:1, for example, 1:9, 1:8, 1:7, 1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or a range consisting of any of the above values; and / or,

[0112] The molar mass of the small molecule organic carbon source is less than or equal to 500 g / mol; and / or,

[0113] The weight average molecular weight of the medium molecular organic carbon source is greater than 500 and less than or equal to 2000; and / or,

[0114] The weight average molecular weight of the polymer organic carbon source is greater than 2000 and less than or equal to 1000000; and / or,

[0115] The inorganic carbon source includes one or more of acetylene black, Ketjen black, graphite oxide, graphene, and carbon nanotubes.

[0116] This is conducive to forming a coating layer with good density and integrity, thereby reducing the iron dissolution amount and powder resistivity of the positive electrode material.

[0117] In some embodiments, the organic carbon source includes one or more of glucose, sucrose, fructose, citric acid, starch, polyvinyl alcohol, polyethylene glycol, and polyaniline.

[0118] In some embodiments, in the step of preparing the mixture, the iron source, lithium source, phosphorus source, organic carbon source, inorganic carbon source, and source of element M are ball-milled and sand-milled in a solvent to obtain the mixture.

[0119] In some embodiments, the core comprises Li 1+e M f Fe a PO4, wherein 0≤e<0.1 (e.g., 0, 0.001, 0.003, 0.005, 0.007, 0.008, 0.009, 0.01, 0.02, 0.04, 0.05, 0.07, 0.08, 0.09, 0.095 or any range thereof), 0≤f≤0.05 (e.g., 0, 0.001, 0.003, 0.005, 0.007, 0.008, 0.009 , 0.01, 0.02, 0.04, 0.05 or a range consisting of any of the above values), 0.95≤a≤1 (for example, 0.95, 0.96, 0.97, 0.98, 0.99, 1 or a range consisting of any of the above values); the M element includes one or more elements of Group IIA, Group IIIA, Group IVA, Group IVB, and Group VB, and can be optionally one or more elements of Si, Al, B, Mg, Zr, Ti, Nb, and V.

[0120] In some embodiments, the weight ratio of the inorganic carbon source to the iron in the iron source is 1:50-1:345, optionally 1:50-1:200, more optionally 1:50-1:172.5, for example 1:50, 1:60, 1:70, 1:80, 1:90, 1:100, 1:110, 1:119, 1:120, 1:130, 1:132.7, 1:140, 1:150, 1:172.5. 1:160, 1:170, 1:172.5, 1:180, 1:190, 1:200, 1:210, 1:215, 1:216, 1:220, 1:230, 1:240, 1:250, 1:260, 1:270, 1:280, 1:290, 1:300, 1:310, 1:320, 1:330, 1:340, 1:345 or a range consisting of any of the above values.

[0121] In some embodiments, the Dv50 particle size of the insoluble particles in the mixture is 0.40-0.85 μm, for example, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.85 μm or a range consisting of any of the above values; and / or,

[0122] The sanding temperature is 25°C-35°C, for example, 25°C, 27°C, 30°C, 32°C, 35°C or any range thereof; and / or,

[0123] The sanding time is 0.5-4 hours, for example 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4 hours or any range thereof; and / or,

[0124] The sanding is performed at a rotation speed of 5000-10000 rpm, for example, 5000 rpm, 6000 rpm, 7000 rpm, 8000 rpm, 9000 rpm, 10000 rpm or a rotation speed within a range composed of any of the above values.

[0125] This is beneficial to improving the consistency of the primary particle size distribution of the positive electrode material, improving the concentration and uniformity of the positive electrode material particles, reducing the precipitation of small particle metal ions and / or the side reaction of large particles with the electrolyte after crushing, and improving the cycle performance of the battery.

[0126] In some embodiments, before sintering, the dried mixture is granulated to obtain particles; wherein the average particle size of the particles is 2 mm to 10 mm, for example, 2 mm, 4 mm, 6 mm, 8 mm, 1 cm, or any range thereof; and / or,

[0127] After sintering, the sintered product is crushed to obtain the positive electrode material.

[0128] This is beneficial to improving the consistency of the primary particle size distribution of the positive electrode material.

[0129] In some embodiments, after drying or granulation, the temperature is uniformly raised to the sintering temperature within 2.5-9 hours, optionally within 3-9 hours, for example, within 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9 hours or any range thereof; and / or,

[0130] The sintering temperature is 600° C.-800° C., for example, 600° C., 620° C., 650° C., 670° C., 700° C., 720° C., 750° C., 770° C., 790° C., 800° C. or any range thereof; and / or,

[0131] The sintering time is 5-10 hours, for example, 5, 6, 7, 8, 9, 10 hours or any range thereof; and / or,

[0132] Heating and sintering in a reducing atmosphere; and / or,

[0133] The volume content of the reducing gas in the reducing atmosphere is 2%-8%, for example, 2%, 3%, 4%, 5%, 6%, 7%, 8% or any range thereof.

[0134] Therefore, on the one hand, it is beneficial to the full cracking and carbonization of the organic carbon source to obtain an ultra-thin coating layer with a high degree of graphitization; on the other hand, it is beneficial to improve the uniformity of the coating layer and reduce the problem of metal ion dissolution caused by uneven or incomplete coating.

[0135] In some embodiments, the molar ratio of the iron element in the iron source to the phosphorus element in the phosphorus source is 0.96-0.98, such as 0.95, 0.97, 0.98 or any range thereof; and / or,

[0136] The molar ratio of the lithium element in the lithium source to the iron element in the iron source is 1.015-1.045, for example, 1.015, 1.018, 1.02, 1.025, 1.03, 1.035, 1.04, 1.045 or any range thereof; and / or,

[0137] The molar ratio of the M element to the iron element in the iron source is 1:1000-3:100, optionally 2:1000-3:100, for example, 1:1000, 1:900, 1:800, 1:700, 1:600, 1:500, 1:400, 1:300, 1:200, 1:100, 2:100, 3:100 or any range thereof; and / or,

[0138] The Dv50 particle size of the insoluble particles in the ball-milled material is 2.0-5.0 μm, for example, 2.0 μm, 3.0 μm, 4.0 μm, 5.0 μm or a range consisting of any of the above values.

[0139] In some embodiments, the iron source includes one or more of an oxide, hydroxide, elemental substance, or salt of iron, and may be selected from one or more of ferric phosphate, ferric oxide, ferrous oxalate, iron powder, and ferric nitrate; and / or,

[0140] The lithium source includes one or more of lithium oxides, hydroxides, simple substances, and salts, and may be selected from one or more of lithium dihydrogen phosphate, lithium monohydrogen phosphate, lithium nitrate, lithium carbonate, lithium phosphate, lithium hydroxide, and lithium acetate; and / or

[0141] The phosphorus source includes one or more acids and salts of phosphorus, and may be selected from one or more of diammonium dihydrogen phosphate, ammonium phosphate, lithium phosphate, phosphoric acid, and iron phosphate; and / or

[0142] The source of the M element includes one or more of the oxide, hydroxide, simple substance, and salt of the M element; and / or,

[0143] The solvent is water.

[0144] In some embodiments, the ratio of the total mass of the iron source, lithium source, and phosphorus source to the mass of the solvent is (1-3):(1-7), for example, 1:1, 1:2, 1:3, 1:4, 1:6, 1:7, 1.5:1, 2:1, 3:1 or a range consisting of any of the above values.

[0145] In some embodiments, the ball milling temperature is 25-35°C, such as 25°C, 30°C, 35°C or any range thereof; and / or,

[0146] The ball milling time is 0.5-4 h, for example, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4 h or any range thereof; and / or,

[0147] The ball milling is performed at a rotation speed of 800-2000 rpm, for example, at a rotation speed of 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm, 1400 rpm, 1500 rpm, 1700 rpm, 1800 rpm, 1900 rpm, 2000 rpm or a range of any of the above values.

[0148] In some embodiments, the drying is spray drying; optionally, the inlet air temperature of the spray drying is 200°C-300°C, and the outlet air temperature is 90°C-120°C.

[0149] In some embodiments, the reducing gas is carbon monoxide and / or hydrogen.

[0150] In some embodiments, the reducing atmosphere further comprises an inert gas; optionally, the inert gas is nitrogen and / or argon.

[0151] In some embodiments, the fragmentation is by gas fragmentation.

[0152] [Positive electrode]

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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.).

[0158] In some embodiments, the positive electrode material may further include positive electrode active materials for batteries that are well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium transition metal oxides and their respective modified compounds. 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 NCM211 ), 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.

[0159] 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.

[0160] 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.

[0161] 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 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.

[0162] [Negative electrode]

[0163] 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.

[0164] 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.

[0165] 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.).

[0166] 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.

[0167] 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).

[0168] 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.

[0169] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0170] 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.

[0171] [Electrolytes]

[0172] 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.

[0173] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0174] 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.

[0175] 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.

[0176] 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.

[0177] [Isolation film]

[0178] 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.

[0179] 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.

[0180] 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.

[0181] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0182] 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.

[0183] 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.

[0184] 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.

[0185] 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.

[0186] 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.

[0187] 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.

[0188] 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.

[0189] 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.

[0190] 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.

[0191] As an electrical device, a battery cell, battery module or battery pack can be selected according to its usage requirements.

[0192] 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.

[0193] [Example]

[0194] 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.

[0195] Example 1

[0196] (1) Preparation of positive electrode materials:

[0197] 15.081 kg of FePO4, 3.694 kg of Li2CO3, 0.425 kg of glucose, 0.200 kg of PEG 6000, 0.127 kg of Ketjen black, 0.280 kg of tetrabutyl titanate, and 10 L of water were added to a 50 L stainless steel stirred mill, and ball milled at 25°C and 1000 rpm for 1 h to obtain a ball-milled mixed solution, wherein the Dv50 particle size of the insoluble particles in the ball-milled mixed solution was 4±0.20 μm;

[0198] The ball-milled mixed solution was transferred into a sand mill and sand-milled at 8000 rpm for 1 h at 25° C. to obtain a sand-milled mixed solution, wherein the Dv50 particle size of the insoluble particles in the sand-milled mixed solution was 0.50±0.20 μm;

[0199] The mixed solution after sand milling is spray dried; during the spray drying process, the air inlet temperature is 300°C and the air outlet temperature is 200°C to obtain a dry powder;

[0200] The dried powder was placed in a tubular furnace and heated to 780°C at a uniform rate for 6 hours in a nitrogen atmosphere. The powder was then sintered at 780°C for 6 hours. The sintered material was crushed by gas crushing, and the Dv50 particle size of the crushed material was controlled to be 1 μm to obtain the positive electrode material.

[0201] (2) Preparation of positive electrode sheets: The positive electrode material, binder polyvinylidene fluoride (PVDF), and conductive agent carbon black are dissolved in solvent N-methylpyrrolidone (NMP) at a mass ratio of 90:5:5, and the mixture is thoroughly stirred and 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 positive electrode sheets.

[0202] (3) Negative electrode: metallic lithium sheet.

[0203] (4) Isolation membrane: Celgard 2400 microporous polyethylene membrane.

[0204] (5) Preparation of electrolyte: Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1, and then LiPF6 was uniformly dissolved in the above solution to obtain an electrolyte. The concentration of LiPF6 in the electrolyte was 1 mol / L.

[0205] (6) Preparation of button batteries:

[0206] In an argon-protected glove box, the positive electrode sheet, negative electrode sheet, separator and electrolyte are assembled into a button battery.

[0207] The secondary battery preparation methods of Examples 2-18 and Comparative Examples 1-4 are similar to those of Example 1, and the different preparation parameters are detailed in Table 1. The weight ratio of the organic carbon source to the inorganic carbon source is the same as that in Example 1.

[0208] Material testing and battery testing

[0209] (1) Test of core chemical formula and carbon content:

[0210] Weigh the positive electrode 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 h, and dilute to volume with a 100 mL volumetric flask; use a pipette to transfer 1 mL to a 100 mL volumetric flask and dilute to volume to obtain the test solution.

[0211] An inductively coupled plasma optical emission spectrometer (ICP-OES, instrument brand: Agilent 5800) was used to determine the contents of lithium, iron, phosphorus, oxygen, and doping elements in the test solution, calculate the element ratio in the material, and determine the chemical formula.

[0212] 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 weight percentage of carbon in the positive electrode material.

[0213] (2) Powder resistivity test:

[0214] Refer to the national standard GB / T 33822-2017. Using a powder resistivity meter (Suzhou Jingge, ST2722), weigh 1g of sample (within ±0.005g) and add it to the feeding chamber. Apply a pressure of 8MPa and measure the forward and reverse resistivity of the sample. The average of the two values ​​is taken as the powder resistivity of the sample.

[0215] (3) BET specific surface area test:

[0216] Refer to GB / T 19587-2017. Using a TRISTAR 302 surface area analyzer, test the sample using a dedicated sample tube. Heat, vacuum, and degas for 2 hours. After cooling to room temperature, weigh the total weight, subtracting the weight of the sample tube from the sample mass. Place the sample tube in a workstation. Adsorb nitrogen at relative pressures of 0.05, 0.10, 0.15, 0.20, 0.25, and 0.30, with an equilibrium time of 5 seconds. The test atmosphere is high-purity liquid nitrogen. The amount of gas adsorbed on the solid surface at different relative adsorption pressures is measured. The analyzer automatically calculates the BET surface area based on the BET multilayer adsorption theory and formula.

[0217] (4) Test of iron dissolution:

[0218] Weigh 5.00 g of positive electrode material powder into a 250 mL beaker, accurate to 0.01 g, add 100 mL of 0.01 mol / L hydrochloric acid solution with a measuring cylinder, add a stirring magnet, seal the beaker with a sealing film, and stir at 1200 r / min for 30 min; place the beaker in a 25°C constant temperature water bath, seal it and let it stand for 2 h, quickly draw about 10 mL of the upper clear liquid with a disposable syringe, and quickly filter it with a 0.22 μm needle-type microporous filter head; use ICP-OES to test the concentration of Fe element in the filtrate, calculate the total weight of iron element in the beaker solution, and then divide it by the weight of the positive electrode material to obtain the amount of iron dissolved per gram of positive electrode material in 100 mL of hydrochloric acid solution.

[0219] (5) Test of the consistency index PDI value of primary particle size distribution:

[0220] The surface of the positive electrode was cut vertically with an argon ion beam, and the cross section was photographed with a scanning electron microscope. The particle size of primary particles larger than 50 nm was counted, and the PDI was calculated according to the following formula; where the average particle size is It is the sum of the particle sizes of primary particles divided by the number of primary particles;

[0221] Where σ is the standard deviation of particle size, is the average particle size, x i is the particle size of the primary particles, and n is the total number of primary particles counted.

[0222] (6) Test of the Dv50 particle size of the positive electrode material, the Dv50 particle size of the insoluble particles in the mixture or the material after ball milling:

[0223] 0.1 g of the positive electrode material, mixture, or ball-milled material was added to 1% of a dedicated dispersant and 20 mL of deionized water. Ultrasonic treatment was performed for 5 minutes (53 kHz, 120 W) to completely disperse the sample. The sample concentration maintained an obscuration of 8-12%. The Dv50 particle size was measured using a laser particle size analyzer (MasterSizer 3000). Test parameters included a refractive index of 1.692, an absorptivity of 1.0, a test time of 6 seconds, 6000 test snaps, and 3 test cycles.

[0224] (7) The average particle size of the granulated particles was determined by the length diameter statistical method;

[0225] (8) Compaction density test:

[0226] Weigh 1g of sample powder and place it in a compaction density mold, put it into a compaction density machine, and test the compaction density after compaction at a pressure of 221.55MPa.

[0227] (9) SEM test: The positive electrode material was tested using SEM.

[0228] The SEM photograph of the positive electrode material of Example 1 is shown in FIG7 .

[0229] (10) Cyclic performance test method:

[0230] Place the battery in a 25℃ oven and let it stand for 2h, keeping the battery temperature at 25℃; charge to 3.65V at a constant current of 1C, and continue constant voltage charging until the charging current is less than 0.05C; let it stand for 5min, discharge to 2.5V at a constant current of 1C, and test the discharge capacity. This is one charge and discharge cycle; pause for 5min, repeat the above operations continuously, and measure the number of cycles when the battery capacity decays to 80% of the first discharge capacity.

[0231] The above results are shown in Table 2.

[0232] Table 2: Performance test results of Examples 1-18 and Comparative Examples 1-4

[0233] According to the above results, we can know that:

[0234] Compared with the powder resistivity of comparative examples 1 and 4 greater than 20Ω·cm, the cycle performance of the batteries of Examples 1-18 of the present application is better;

[0235] Compared with the powder of Comparative Example 2, the resistivity is greater than 20Ω·cm and the BET specific surface area is greater than 14m 2 / g, the cycle performance of the battery of Examples 1-18 of the present application is better;

[0236] The BET specific surface area of ​​comparative example 3 is less than 6m 2 / g, the cycle performance of the battery of Examples 1-18 of the present application is better;

[0237] Compared with the lower content of M element in the positive electrode material of Example 15, the cycle performance of the batteries of Examples 1, 4, and 14 of the present application is better;

[0238] Compared with Example 16 in which the weight ratio of the inorganic carbon source to the iron element in the iron source is relatively small when preparing the positive electrode material, the battery of Examples 1, 4, 6, 13, and 14 of the present application has better cycle performance;

[0239] Compared with the lower content of M element in the positive electrode material of Example 17, the cycle performance of the battery of Example 2 of the present application is better;

[0240] Compared with Example 18 in which no granulation is performed and the consistency index PDI value of the primary particle size distribution of the positive electrode material is larger, the cycle performance of the batteries in Examples 1, 4, and 7-8 of the present application is better.

[0241] 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 cathode material, comprising a core and a coating layer coating the core, wherein the core comprises lithium iron phosphate or lithium iron phosphate containing M element, and the coating layer comprises carbon or comprises carbon and M element; Among them, the M element in the core and the coating layer independently comprises one or more elements selected from Group IIA, Group IIIA, Group IVA, Group IVB, and Group VB; moreover, the cathode material satisfies: the powder resistivity at 8 MPa ≤ 20 Ω·cm; and, The BET specific surface area at liquid nitrogen temperature is 6 - 15.2 m 2 / g.

2. The cathode material according to claim 1, wherein, the powder resistivity of the cathode material at 8 MPa ≤ 10 Ω·cm; and / or, The BET specific surface area of the positive electrode material at liquid nitrogen temperature is 8-11 m 2 / g; and / or, the M element in the core and the coating layer independently comprises one or more elements selected from Si, Al, B, Mg, Zr, Ti, Nb, and V.

3. The cathode material according to claim 1 or 2, wherein the iron dissolution amount per gram of the cathode material in 100 mL of hydrochloric acid solution ≤ 60 ppm; and / or, the consistency index PDI value of the primary particle size distribution of the cathode material ≤ 0.

87.

4. The cathode material according to any one of claims 1 to 3, wherein the iron dissolution amount per gram of the cathode material in 100 mL of hydrochloric acid solution ≤ 55 ppm; and / or, the consistency index PDI value of the primary particle size distribution of the cathode material ≤ 0.

4.

5. The cathode material according to any one of claims 1 to 4, wherein the weight content of carbon in the cathode material is 1.2% - 2.0%; and / or, The weight content of the M element in the positive electrode material is 297 ppm - 10 4 ppm.

6. The cathode material according to any one of claims 1 to 5, wherein, The weight content of the M element in the cathode material is 10 3 ppm - 10 4 ppm.

7. The positive electrode material according to any one of claims 1 to 6, wherein, the Dv50 particle size of the cathode material is 0.6 - 1.5 μm; and / or, The tap density of the positive electrode material under 221.55 MPa ≥ 2.3 g / cm 3 .

8. A method for preparing a cathode material, comprising: ball milling and sand milling an iron source, a lithium source, a phosphorus source, an organic carbon source, and an inorganic carbon source in a solvent to obtain a mixture; drying and sintering the mixture to obtain the cathode material; wherein the cathode material is the cathode material according to any one of claims 1 to 7.

9. The method according to claim 8, wherein the organic carbon source comprises a small molecule organic carbon source and a medium molecule organic carbon source, or comprises a small molecule organic carbon source and a high molecule organic carbon source.

10. The method according to claim 9, wherein, the weight ratio of the small molecule organic carbon source to the medium molecule organic carbon source or the weight ratio of the small molecule organic carbon source to the high molecule organic carbon source is 1:9 - 9:1; and / or, the weight average molecular weight of the medium molecule organic carbon source is greater than 500 and less than or equal to 2000; and / or, the weight average molecular weight of the high molecule organic carbon source is greater than 2000 and less than or equal to 1000000; and / or, the inorganic carbon source comprises one or more of acetylene black, Ketjen black, graphite oxide, graphene, and carbon nanotubes.

11. In the step of preparing the mixture according to the method of any one of claims 8 to 10, ball milling and sand milling an iron source, a lithium source, a phosphorus source, an organic carbon source, an inorganic carbon source, and a source of M element in a solvent to obtain a mixture.

12. The method according to any one of claims 8 to 11, wherein the weight ratio of the inorganic carbon source to the iron element in the iron source is 1:50 - 1:

345.

13. The method according to any one of claims 8 to 12, wherein, the Dv50 particle size of the insoluble particles in the mixture is 0.40 - 0.85 μm; and / or, the temperature of the sand milling is 25°C - 35°C; and / or, the time of the sand milling is 0.5 - 4 hours; and / or, Grind by sanding at a rotational speed of 5000 - 10000 rpm.

14. The method according to any one of claims 8 to 13, wherein, The method further includes: before sintering, granulating the dried mixture to obtain particles; wherein, the average particle size of the particles is 2 mm - 10 mm; and / or, The method further includes: after sintering, crushing the sintered product to obtain the cathode material.

15. The method according to any one of claims 8 to 14, wherein, After drying or granulating, the temperature is raised uniformly to the sintering temperature in 2.5 - 9 hours; and / or, The sintering temperature is 600°C - 800°C; and / or, The sintering time is 5 - 10 hours; and / or, Raise the temperature and sinter in a reducing atmosphere; and / or, The volume content of the reducing gas in the reducing atmosphere is 2% - 8%.

16. The method according to any one of claims 8 to 15, wherein, The molar ratio of the iron element in the iron source to the phosphorus element in the phosphorus source is 0.96 - 0.98; and / or, The molar ratio of the lithium element in the lithium source to the iron element in the iron source is 1.015 - 1.045; and / or, The molar ratio of the M element to the iron element in the iron source is 1:1000 - 3:100; and / or, The Dv50 particle size of the insoluble particles in the material after ball milling is 2.0 - 5.0 μm.

17. A cathode electrode sheet, comprising the cathode material according to any one of claims 1 - 7 or the cathode material prepared by the method according to any one of claims 8 - 16.

18. A battery, comprising the cathode material according to any one of claims 1 - 7, the cathode material prepared by the method according to any one of claims 8 - 16, or the cathode electrode sheet according to claim 17.

19. An electrical device, comprising the battery according to claim 18.

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