Carbon-coated lithium manganese iron phosphate, preparation method thereof, positive pole piece comprising carbon-coated lithium manganese iron phosphate, battery and electric device

Abstract

The invention discloses carbon-coated lithium manganese iron phosphate, a preparation method thereof, a positive pole piece containing the carbon-coated lithium manganese iron phosphate, a battery and an electric device, and the preparation method of the carbon-coated lithium manganese iron phosphate comprises the following steps: carrying out dry mixing on a lithium source, a manganese source, an iron source and a phosphorus source to obtain first mixed powder; carrying out presintering treatment and crushing treatment on the obtained first mixed powder under the protection of protective gas to obtain a lithium manganese iron phosphate precursor; carrying out dry mixing on the obtained lithium manganese iron phosphate precursor and a solid organic carbon source to obtain second mixed powder; and carrying out step-by-step sintering treatment and crushing treatment on the obtained second mixed powder under the protection of protective gas to obtain the carbon-coated lithium manganese iron phosphate. The preparation method of the carbon-coated lithium manganese iron phosphate provided by the invention is simple in process, low in production cost and suitable for large-scale production, and the prepared carbon-coated lithium manganese iron phosphate also has relatively high powder compaction density and relatively high gram volume.

Description

Technical Field

[0001] The present application relates to a carbon-coated lithium manganese iron phosphate, a preparation method thereof, and a positive electrode sheet, a battery and an electrical device containing the same. Background Art

[0002] In recent years, batteries have been widely used in energy storage 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. With the application and promotion of batteries, their safety performance has received increasing attention. Lithium manganese iron phosphate has become one of the most popular positive electrode active materials due to its advantages such as high capacity, good safety performance, and abundant raw material sources. The preparation methods of lithium manganese iron phosphate can be roughly divided into solid-phase and liquid-phase methods. Liquid-phase methods mainly include co-precipitation and hydrothermal methods. The resulting products have good performance, but the process flow is long, the reaction conditions are strict, the equipment corrosion resistance is high, and the large amount of solution must be processed, resulting in high energy consumption and high production costs. Solid-phase methods mainly include high-temperature solid-phase methods. They have simple processes, easy-to-control preparation conditions, and are easy to scale up. However, the compacted density of the resulting products is generally not high. The above statements are only intended to provide background information related to this application and do not necessarily constitute prior art. Summary of the Invention

[0003] The present application provides a carbon-coated lithium manganese iron phosphate, a preparation method thereof, and a positive electrode plate, a battery and an electrical device containing the same. The preparation method has a simple process, low production cost, and is suitable for large-scale production. The carbon-coated lithium manganese iron phosphate prepared thereby also has a high powder compaction density and a high gram capacity.

[0004] In a first aspect, the present application provides a method for preparing carbon-coated lithium manganese iron phosphate, comprising the following steps: dry-mixing a lithium source, a manganese source, an iron source, and a phosphorus source to obtain a first mixed powder; pre-sintering and crushing the obtained first mixed powder under the protection of a protective gas to obtain a lithium manganese iron phosphate precursor; dry-mixing the obtained lithium manganese iron phosphate precursor with a solid organic carbon source to obtain a second mixed powder; sintering and crushing the obtained second mixed powder in steps under the protection of a protective gas to obtain a carbon-coated lithium manganese iron phosphate, wherein the steps The step sintering includes a first-stage sintering treatment, a second-stage sintering treatment and a third-stage sintering treatment. The insulation temperature of the first-stage sintering treatment is lower than the insulation temperature of the second-stage sintering treatment, and the insulation temperature of the second-stage sintering treatment is lower than the insulation temperature of the third-stage sintering treatment. The insulation temperature of the first-stage sintering treatment is between the softening temperature of the solid organic carbon source and the initial weight loss temperature of the solid organic carbon source, the insulation temperature of the second-stage sintering treatment is greater than or equal to the end weight loss temperature of the solid organic carbon source, and the insulation temperature of the third-stage sintering treatment is 600°C-800°C.

[0005] The preparation method of lithium iron manganese phosphate provided in the embodiment of the present application is a high-temperature solid-phase method, and the mixing process of lithium iron manganese phosphate and a carbon source is a solid-solid mixing process. No solvent or dispersant is used in the preparation process of the carbon-coated lithium iron manganese phosphate, and no waste liquid treatment is required. Therefore, the carbon-coated lithium iron manganese phosphate provided in the embodiment of the present application can save equipment investment, reduce energy consumption in the manufacturing process, and reduce raw material costs, thereby reducing production costs. In addition, the preparation method provided in the embodiment of the present application also has the advantages of simple process and easy large-scale production.

[0006] The preparation method provided in the embodiment of the present application first dry-mixes the crushed lithium manganese iron phosphate precursor with a solid organic carbon source, and then adopts a step-by-step sintering process, which can improve the coating effect of the carbon coating layer and can also prepare carbon-coated lithium manganese iron phosphate with high compaction density and gram capacity.

[0007] In some embodiments, the holding time of the first sintering process is shorter than the holding time of the second sintering process, and the holding time of the second sintering process is shorter than the holding time of the third sintering process.

[0008] The holding time of the first sintering treatment and the holding time of the second sintering treatment are shorter, which can reduce the growth of the primary particles of the lithium manganese iron phosphate, and thus make the prepared carbon-coated lithium manganese iron phosphate have a high gram capacity.

[0009] In some embodiments, the holding time of the sintering treatment is 1 hour to 3 hours.

[0010] In some embodiments, the holding time of the second-stage sintering process is 3h-5h.

[0011] In some embodiments, the holding time of the three-stage sintering process is 6 hours to 25 hours.

[0012] In some embodiments, the heating rate of the first stage sintering process is less than or equal to the heating rate of the second stage sintering process, and the heating rate of the second stage sintering process is less than or equal to the heating rate of the third stage sintering process.

[0013] The first-stage sintering treatment uses a smaller heating rate, which is conducive to better coating the softened solid organic carbon source on the surface of the lithium manganese iron phosphate precursor, thereby better improving the electronic conductivity and gram capacity of the lithium manganese iron phosphate.

[0014] The second-stage sintering treatment adopts a smaller heating rate, which is conducive to the full volatilization of the volatile matter in the solid organic carbon source, thereby reducing the amount of pores introduced into the carbon coating layer due to the failure to discharge the gas in time, thereby helping to increase the powder compaction density of the carbon-coated lithium manganese iron phosphate and reduce the specific surface area of ​​the carbon-coated lithium manganese iron phosphate; it can also promote the discharge of carbonized tar, thereby making the carbon coating layer have a better degree of graphitization.

[0015] In some embodiments, the heating rate of the first sintering treatment is 2°C / min-5°C / min. A heating rate of the first sintering treatment within the above range is conducive to better coating the softened solid organic carbon source on the surface of the lithium manganese iron phosphate precursor, thereby further improving the electronic conductivity and specific capacity of the lithium manganese iron phosphate.

[0016] In some embodiments, the heating rate of the second-stage sintering process is 2°C / min-5°C / min. A heating rate within the above range facilitates the full volatilization of volatiles in the solid organic carbon source, thereby reducing the amount of pores introduced into the carbon coating layer due to delayed gas discharge, thereby helping to increase the powder compaction density of the carbon-coated lithium manganese iron phosphate and reduce the specific surface area of ​​the carbon-coated lithium manganese iron phosphate. It also promotes the discharge of carbonized tar, thereby ensuring that the carbon coating layer has a better degree of graphitization.

[0017] In some embodiments, the three-stage sintering process has a heating rate of 2°C / min-5°C / min. The heating rate of the three-stage sintering process within the above range is conducive to a good degree of graphitization of the carbon coating layer, thereby further improving the electronic conductivity and specific capacity of the lithium manganese iron phosphate.

[0018] In some embodiments, the solid organic carbon source has a softening temperature of less than 300°C.

[0019] In some embodiments, the solid organic carbon source has an initial weight loss temperature of 300°C-500°C.

[0020] In some embodiments, the solid organic carbon source has an end weight loss temperature of 500°C-600°C.

[0021] In some embodiments, the solid organic carbon source comprises one or more of solid polyethylene glycol, polyvinyl alcohol, polyvinyl butyral, glucose, maltose, sucrose, tannic acid, citric acid, polyacrylonitrile, polytetrafluoroethylene, and polyvinylidene fluoride.

[0022] In some embodiments, the solid organic carbon source has a volume distribution particle size Dv50 of 5 μm or less. Using a solid organic carbon source with a small particle size facilitates better coating of the softened solid organic carbon source on the surface of the lithium manganese iron phosphate precursor, thereby further improving the electronic conductivity and specific capacity of the lithium manganese iron phosphate.

[0023] In some embodiments, the obtained first mixed powder is pre-sintered and crushed under protective gas to obtain a lithium manganese iron phosphate precursor, wherein the crushing includes grinding and / or air flow milling.

[0024] In some embodiments, the obtained first mixed powder is pre-sintered and crushed under protective gas protection to obtain a lithium manganese iron phosphate precursor, and the volume distribution particle size Dv50 of the obtained lithium manganese iron phosphate precursor is 0.5 μm-3 μm.

[0025] The volume distribution particle size Dv50 of the lithium manganese iron phosphate precursor is within the above range, which is conducive to the mixing of the lithium manganese iron phosphate precursor and the solid organic carbon source, and is conducive to the coating of the solid organic carbon source on the surface of the lithium manganese iron phosphate primary particles, thereby helping to further improve the electronic conductivity and gram capacity of the prepared carbon-coated lithium manganese iron phosphate.

[0026] In some embodiments, the obtained second mixed powder is subjected to step-by-step sintering and crushing treatment under the protection of protective gas to obtain carbon-coated lithium manganese iron phosphate. In the step, the volume distribution particle size Dv50 of the carbon-coated lithium manganese iron phosphate obtained by the step-by-step sintering treatment is 5μm-10μm.

[0027] In some embodiments, the step of performing a step-by-step sintering and crushing of the obtained second mixed powder under protective gas to obtain the carbon-coated lithium manganese iron phosphate is performed using a rotary kiln. The use of a rotary kiln facilitates uniform mixing of the lithium manganese iron phosphate precursor and the solid organic carbon source, improves the coating effect of the carbon coating layer, and can also produce carbon-coated lithium manganese iron phosphate with a high compacted density and gram capacity.

[0028] In some embodiments, the obtained second mixed powder is subjected to step-by-step sintering and crushing treatments under protective gas protection to obtain carbon-coated lithium manganese iron phosphate, wherein the crushing treatment includes grinding treatment and / or air flow milling treatment.

[0029] In some embodiments, the holding temperature of the pre-sintering process is 520°C-680°C.

[0030] In some embodiments, the holding time of the pre-sintering treatment is 6 hours to 25 hours.

[0031] The holding temperature and / or holding time of the pre-sintering treatment being within the above range is conducive to preparing a lithium manganese iron phosphate precursor with a smaller primary particle size, thereby enabling the carbon-coated lithium manganese iron phosphate to have a high gram capacity.

[0032] In some embodiments, the heating rate of the pre-sintering process is 2° C. / min-5° C. / min.

[0033] In some embodiments, the lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium acetate, and lithium oxide.

[0034] In some embodiments, the manganese source includes one or more of manganese nitrate, manganese acetate, manganese phosphate, manganese oxalate, manganese carbonate, and ammonium manganese phosphate.

[0035] In some embodiments, the iron source includes one or more of ferric nitrate, ferric phosphate, ferric acetate, ferrous oxalate, ferric manganese nitrate, ferric manganese oxalate, ferric manganese acetate, ferric manganese phosphate, ammonium ferric manganese phosphate, and ferrous carbonate.

[0036] In some embodiments, the phosphorus source includes one or more of lithium phosphate, lithium dihydrogen phosphate, dilithium hydrogen phosphate, manganese hydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and manganese iron hydrogen phosphate.

[0037] In some embodiments, the first mixed powder further includes one or more of a source of a doping element M, a source of a doping element N, a source of a doping element Q, and a source of a doping element R, where M represents a doping element at the manganese position and the iron position, N represents a doping element at the lithium position, Q represents a doping element at the phosphorus position, and R represents a doping element at the oxygen position.

[0038] In some embodiments, before dry mixing the lithium source, manganese source, iron source, and phosphorus source, the step of grinding the lithium source, manganese source, iron source, and phosphorus source separately is also included.

[0039] In some embodiments, the volume distribution particle size Dv50 of the obtained first mixed powder is 1 μm-5 μm.

[0040] In a second aspect, the present application provides a carbon-coated lithium manganese iron phosphate, which is prepared by the preparation method of the first aspect of the present application.

[0041] In some embodiments, the carbon-coated lithium manganese iron phosphate has a volume distribution particle size Dv50 of 0.5 μm to 2 μm.

[0042] In some embodiments, the carbon-coated lithium manganese iron phosphate powder has a compaction density of 2.38 g / cm 3 -2.45g / cm 3 .

[0043] In some embodiments, the carbon-coated lithium manganese iron phosphate has a gram capacity of 148 mAh / g to 152 mAh / g.

[0044] In a third aspect, the present application provides a positive electrode plate, comprising a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material, the positive electrode active material comprising a first carbon-coated lithium manganese iron phosphate, and the first carbon-coated lithium manganese iron phosphate is prepared by the preparation method of the first aspect of the present application.

[0045] In some embodiments, the volume distribution particle size Dv50 of the first carbon-coated lithium manganese iron phosphate is 0.5 μm-2 μm.

[0046] In some embodiments, the first carbon-coated lithium manganese iron phosphate powder compaction density is 2.38 g / cm 3 -2.45g / cm 3 .

[0047] In some embodiments, the first carbon-coated lithium manganese iron phosphate has a gram capacity of 148 mAh / g to 152 mAh / g.

[0048] In some embodiments, the positive electrode active material further includes a second carbon-coated lithium manganese iron phosphate, which is prepared by a liquid phase method, and has a volume distribution particle size Dv50 of 10 μm-15 μm.

[0049] In some embodiments, a mass ratio of the first carbon-coated lithium manganese iron phosphate to the second carbon-coated lithium manganese iron phosphate is 1:0.1 to 1:0.5.

[0050] In some embodiments, the powder compaction density of the positive electrode active material is greater than the powder compaction density of the first carbon-coated lithium manganese iron phosphate.

[0051] In some embodiments, the powder compaction density of the positive electrode active material is greater than the powder compaction density of the second carbon-coated lithium manganese iron phosphate.

[0052] In some embodiments, the powder compaction density of the positive electrode active material is 2.4 g / cm 3 -2.5g / cm 3 .

[0053] In a fourth aspect, the present application provides a battery comprising the positive electrode sheet according to the third aspect of the present application.

[0054] In a fifth aspect, the present application provides an electrical device comprising the battery according to the fourth aspect of the present application, wherein the battery is used to provide electrical energy.

[0055] The electric device of the present application includes the battery provided by the present application, and thus has at least the same advantages as the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] To more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive effort.

[0057] Figure 1 is a schematic diagram of a battery cell provided in some embodiments of the present application.

[0058] Figure 2 is a schematic diagram of a battery module provided in some embodiments of the present application.

[0059] Figure 3 is a schematic diagram of a battery pack provided in some embodiments of the present application.

[0060] Figure 4 yes Figure 3 Schematic diagram of the battery pack shown.

[0061] Figure 5 This is a schematic diagram of an exploded view of a battery cell provided in some embodiments of the present application.

[0062] Figure 6 This is a schematic diagram of an electrical device provided in some embodiments of the present application.

[0063] In the accompanying drawings, the drawings are not necessarily drawn to scale.

[0064] The description of the accompanying figures is as follows: 1. battery pack; 2. upper box; 3. lower box; 4. battery module; 5. battery cell; 51. shell; 52. electrode assembly; 53. cover plate. DETAILED DESCRIPTION

[0065] Hereinafter, the carbon-coated lithium manganese iron phosphate, its preparation method, and the embodiments of the positive electrode sheet, battery and electrical device containing the same of the present application will be described in detail with appropriate reference to the accompanying 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.

[0066] " 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.

[0067] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0068] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0069] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0070] In this application, the terms "plurality" and "multiple" refer to two or more.

[0071] Unless otherwise specified, the terms used in this application have the common meanings that are commonly understood by those skilled in the art.

[0072] Unless otherwise stated, the numerical values ​​of the various parameters mentioned in this application can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this application. Unless otherwise stated, the test temperature of each parameter is 25°C.

[0073] The battery mentioned in the embodiments of the present application may be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the present application may include a battery cell, a battery module, or a battery pack.

[0074] A battery cell is the smallest unit that makes up a battery and can independently realize the function of charging and discharging. A battery cell can be cylindrical, rectangular or other shapes, etc., which is not limited in the embodiments of the present application. Figure 1 As an example, a battery cell 5 having a rectangular parallelepiped structure is shown.

[0075] When there are multiple battery cells, the multiple battery cells are connected in series, in parallel, or in mixed series via a busbar. In some embodiments, the battery may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery may be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed in the housing. In some embodiments, the housing may serve as part of the vehicle's chassis structure. For example, a portion of the housing may form at least a portion of the vehicle's floor, or a portion of the housing may form at least a portion of the vehicle's crossbeam or longitudinal beam.

[0076] In some embodiments, the battery may be an energy storage device, including an energy storage container, an energy storage cabinet, and the like.

[0077] In some embodiments, battery cells may be assembled into a battery module. A battery module may contain multiple battery cells, and the specific number may be adjusted according to the application and capacity of the battery module. Figure 2 FIG. 4 is a schematic diagram of a battery module 4 as an example. Figure 2 As shown, in the battery module 4, the plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0078] 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.

[0079] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0080] Figure 3 and Figure 4 FIG. 1 is a schematic diagram of a battery pack 1 as an example. Figure 3 and Figure 4 As shown, a battery pack 1 may include a housing and multiple battery modules 4 disposed therein. The housing comprises an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 may be arranged in any manner within the housing.

[0081] The battery cells provided in the embodiments of the present application may include lithium-ion battery cells, lithium metal battery cells, negative electrode-free lithium metal battery cells, etc.

[0082] The battery cell includes an electrode assembly and an electrolyte. The electrode assembly can be a wound structure or a laminated structure, which is not limited in the present embodiment.

[0083] The battery cell may also include an outer packaging, which can be used to encapsulate the electrode assembly and electrolyte. The outer packaging can be a hard shell, such as a hard plastic shell, aluminum shell, steel shell, etc. The outer packaging can also be a soft package, such as a bag-type soft package. The soft package can be made of plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0084] In some embodiments, as Figure 5 As shown, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, which together form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening, thereby sealing the receiving cavity. The electrode assembly 52 is enclosed in the receiving cavity. The number of electrode assemblies 52 contained in a battery cell 5 can be one or more, and can be adjusted according to needs.

[0085] As the positive electrode active material for battery cells, the performance of lithium iron phosphate (LiMnP) itself affects the overall performance of the battery cells. The high-temperature solid-phase method offers a simple process, easily controlled preparation conditions, and ease of scalable production. However, the resulting powder compaction density is typically low. This low powder compaction density of LiMnP affects the volumetric energy density of battery modules and battery packs. Currently, complex processes are often employed to increase the powder compaction density of LiMnP prepared using the high-temperature solid-phase method, resulting in high costs and unsuitability for large-scale production.

[0086] The embodiment of the present application provides a method for preparing carbon-coated lithium manganese iron phosphate by a high-temperature solid-phase method. The preparation method has a simple process, low production cost, and is suitable for large-scale production. The carbon-coated lithium manganese iron phosphate prepared thereby also has a high powder compaction density and a high gram capacity.

[0087] The preparation method of carbon-coated lithium iron manganese phosphate provided in an embodiment of the present application includes the following steps: dry-mixing a lithium source, a manganese source, an iron source, and a phosphorus source to obtain a first mixed powder; pre-sintering and crushing the obtained first mixed powder under the protection of a protective gas to obtain a lithium iron manganese phosphate precursor; dry-mixing the obtained lithium iron manganese phosphate precursor with a solid organic carbon source to obtain a second mixed powder; and step-by-step sintering and crushing the obtained second mixed powder under the protection of a protective gas to obtain carbon-coated lithium iron manganese phosphate.

[0088] The step-by-step sintering process includes a first-stage sintering process, a second-stage sintering process, and a third-stage sintering process. The holding temperature of the first-stage sintering process is lower than the holding temperature of the second-stage sintering process, and the holding temperature of the second-stage sintering process is lower than the holding temperature of the third-stage sintering process. The holding temperature of the first-stage sintering process is between the softening temperature of the solid organic carbon source and the starting weight loss temperature of the solid organic carbon source. The holding temperature of the second-stage sintering process is greater than or equal to the ending weight loss temperature of the solid organic carbon source. The holding temperature of the third-stage sintering process is 600°C-800°C.

[0089] The softening temperature of the solid organic carbon source refers to the temperature at which the physical state of the solid organic carbon source begins to change. Below this temperature, the solid organic carbon source remains solid. Above this temperature, the physical state of the solid organic carbon source changes, for example, to liquid, or gradually to liquid or molten.

[0090] The initial weight loss temperature of the solid organic carbon source is the extrapolated starting temperature, which can be obtained by the intersection of the tangent line drawn from the temperature at which the mass change step begins and the temperature at the point with the maximum slope on the thermogravimetric curve.

[0091] The end weight loss temperature of the solid organic carbon source is the extrapolated termination temperature, which can be obtained by the intersection of the tangent line of the temperature where the mass change step ends and the temperature of the point with the maximum slope on the thermogravimetric curve.

[0092] In this application, the thermogravimetric test conditions of the solid organic carbon source are as follows: scanning temperature is from room temperature to 800° C., nitrogen atmosphere, and heating rate is 10° C. / min.

[0093] The preparation method of lithium iron manganese phosphate provided in the embodiment of the present application is a high-temperature solid-phase method, and the mixing process of lithium iron manganese phosphate and a carbon source is also a solid-solid mixing process. No solvent or dispersant is used in the preparation process of the carbon-coated lithium iron manganese phosphate, and no waste liquid treatment is required. Therefore, the carbon-coated lithium iron manganese phosphate provided in the embodiment of the present application can save equipment investment, reduce energy consumption in the manufacturing process, and reduce raw material costs, thereby reducing production costs. In addition, the preparation method provided in the embodiment of the present application also has the advantages of simple process and easy large-scale production.

[0094] The mixing process of lithium iron manganese phosphate and a solid organic carbon source is a solid-solid mixing process. When a solid organic carbon source is used, the mixing of lithium iron manganese phosphate and the solid organic carbon source is difficult, which can easily affect the uniformity of the carbon coating layer and also affect the powder compaction density and capacity of the prepared carbon-coated lithium iron manganese phosphate. The preparation method provided in the embodiment of the present application first dry-mixes the crushed lithium iron manganese phosphate precursor with the solid organic carbon source, and then uses a step-by-step sintering process. This can improve the coating effect of the carbon coating layer and can also prepare carbon-coated lithium iron manganese phosphate with a high compaction density and gram capacity.

[0095] The holding temperature of the first sintering treatment is between the softening temperature of the solid organic carbon source and the initial weight loss temperature of the solid organic carbon source, thereby allowing the solid organic carbon source to soften first and better coat the surface of the lithium manganese iron phosphate precursor, thereby better improving the electronic conductivity and gram capacity of the lithium manganese iron phosphate.

[0096] The holding temperature of the second-stage sintering treatment is greater than or equal to the final weight loss temperature of the solid organic carbon source, thereby allowing the volatile matter in the solid organic carbon source to fully volatilize during the second-stage sintering treatment, reducing the amount of pores introduced into the carbon coating layer due to the failure to discharge the gas in time, thereby helping to increase the powder compaction density of the carbon-coated lithium manganese iron phosphate and reduce the specific surface area of ​​the carbon-coated lithium manganese iron phosphate.

[0097] The holding temperature of the three-stage sintering treatment is 600℃-800℃. At this temperature, the electronic conductivity and gram capacity of the carbon coating layer can be improved, and the presence of impurities in lithium manganese iron phosphate can be avoided.

[0098] Therefore, the high-temperature solid-phase method provided in the embodiments of the present application can prepare carbon-coated lithium manganese iron phosphate with high compaction density and gram capacity.

[0099] Optionally, the holding temperature of the second-stage sintering process is greater than or equal to the end weight loss temperature of the solid organic carbon source and less than or equal to 650° C. The holding temperature of the second-stage sintering process is within the above range, which can also reduce the growth of primary particles of the lithium manganese iron phosphate, thereby enabling the prepared carbon-coated lithium manganese iron phosphate to have a high gram capacity.

[0100] In some embodiments, the holding time of the first sintering process may be shorter than that of the second sintering process, and the holding time of the second sintering process may be shorter than that of the third sintering process.

[0101] The holding time of the first sintering treatment and the holding time of the second sintering treatment are shorter, which can reduce the growth of the primary particles of the lithium manganese iron phosphate, and thus make the prepared carbon-coated lithium manganese iron phosphate have a high gram capacity.

[0102] Optionally, the holding time of one sintering treatment can be 1 hour to 3 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, or a range consisting of any of the above values. More optionally, the holding time of one sintering treatment can be 1.5 hours to 2.5 hours.

[0103] Optionally, the holding time of the second stage sintering process can be 3 hours to 5 hours, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, or a range consisting of any of the above values. More optionally, the holding time of the second stage sintering process can be 3.5 hours to 4.5 hours.

[0104] Optionally, the holding time of the three-stage sintering process can be 6 hours to 25 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 25 hours, or a range consisting of any of the above values. More optionally, the holding time of the three-stage sintering process can be 8 hours to 20 hours, or 10 hours to 16 hours. In some embodiments, the heating rate of the first stage sintering process can be less than or equal to the heating rate of the second stage sintering process, and the heating rate of the second stage sintering process can be less than or equal to the heating rate of the third stage sintering process.

[0105] The first-stage sintering treatment uses a smaller heating rate, which is conducive to better coating the softened solid organic carbon source on the surface of the lithium manganese iron phosphate precursor, thereby better improving the electronic conductivity and gram capacity of the lithium manganese iron phosphate.

[0106] The second-stage sintering treatment adopts a smaller heating rate, which is conducive to the full volatilization of the volatile matter in the solid organic carbon source, thereby reducing the amount of pores introduced into the carbon coating layer due to the failure to discharge the gas in time, thereby helping to increase the powder compaction density of the carbon-coated lithium manganese iron phosphate and reduce the specific surface area of ​​the carbon-coated lithium manganese iron phosphate; it can also promote the discharge of carbonized tar, thereby making the carbon coating layer have a better degree of graphitization.

[0107] In some embodiments, the heating rate of the first sintering process, the heating rate of the second sintering process, and the heating rate of the third sintering process can be the same.

[0108] In some embodiments, the heating rate of the first sintering process can be 2°C / min-8°C / min, for example, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, or a range thereof. Alternatively, the heating rate of the first sintering process can be 2°C / min-5°C / min, or 2°C / min-4°C / min.

[0109] The heating rate of the first stage sintering treatment is within the above range, which is conducive to better coating of the softened solid organic carbon source on the surface of the lithium manganese iron phosphate precursor, thereby better improving the electronic conductivity and gram capacity of the lithium manganese iron phosphate.

[0110] In some embodiments, the heating rate of the second-stage sintering process may be 2°C / min-8°C / min, for example, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, or any range thereof. Alternatively, the heating rate of the second-stage sintering process may be 2°C / min-5°C / min, or 2°C / min-4°C / min.

[0111] The heating rate of the second-stage sintering treatment is within the above range, which is conducive to the full volatilization of the volatile matter in the solid organic carbon source, thereby reducing the amount of pores introduced into the carbon coating layer due to the failure to discharge the gas in time, thereby helping to increase the powder compaction density of the carbon-coated lithium manganese iron phosphate and reduce the specific surface area of ​​the carbon-coated lithium manganese iron phosphate; it can also promote the discharge of carbonized tar, thereby making the carbon coating layer have a better degree of graphitization.

[0112] In some embodiments, the heating rate of the three-stage sintering process may be 2°C / min-8°C / min, for example, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, or any range thereof. Alternatively, the heating rate of the three-stage sintering process may be 2°C / min-5°C / min, or 2°C / min-4°C / min.

[0113] The heating rate of the three-stage sintering treatment is within the above range, which is conducive to the carbon coating layer having a better degree of graphitization, thereby better improving the electronic conductivity and gram capacity of lithium manganese iron phosphate.

[0114] In some embodiments, the softening temperature of the solid organic carbon source may be less than 300°C.

[0115] In some embodiments, the initial weight loss temperature of the solid organic carbon source can be 300°C-500°C, for example, 300°C, 320°C, 340°C, 360°C, 380°C, 400°C, 420°C, 440°C, 460°C, 480°C, 500°C, or a range consisting of any of the above values.

[0116] In some embodiments, the end weight loss temperature of the solid organic carbon source can be 500°C-600°C, for example, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, 600°C, or a range consisting of any of the above values.

[0117] In some embodiments, the solid organic carbon source may include one or more of a polymer, an organic small molecule compound, optionally, the solid organic carbon source may include one or more of solid polyethylene glycol, polyvinyl alcohol, polyvinyl butyral, glucose, maltose, sucrose, tannic acid, citric acid, polyacrylonitrile, polytetrafluoroethylene, and polyvinylidene fluoride.

[0118] By selecting parameters such as the molecular weight, molecular weight distribution, crystallinity, and particle size of the polymer, a solid organic carbon source that meets the above-mentioned softening temperature, initial weight loss temperature, and final weight loss temperature can be obtained.

[0119] In some embodiments, the added mass of the solid organic carbon source can be 1%-10% of the mass of the lithium manganese iron phosphate precursor, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any of the above values.

[0120] Optionally, the added mass of the solid organic carbon source may be 5%-10% of the mass of the lithium manganese iron phosphate precursor.

[0121] In some embodiments, the volume distribution particle size Dv50 of the solid organic carbon source can be less than or equal to 5 μm, optionally less than or equal to 4 μm, and more optionally less than or equal to 3 μm. Using a solid organic carbon source with a small particle size facilitates better coating of the softened solid organic carbon source on the surface of the lithium manganese iron phosphate precursor, thereby further improving the electronic conductivity and gram capacity of the lithium manganese iron phosphate.

[0122] In some embodiments, the device for dry mixing the lithium source, manganese source, iron source, and phosphorus source can be any one of a high-speed mixer, a V-type mixer, and a ribbon mixer.

[0123] Optionally, before dry-mixing the lithium source, manganese source, iron source, and phosphorus source, the lithium source, manganese source, iron source, and phosphorus source may be ground separately. This can produce a lithium manganese iron phosphate precursor with a smaller primary particle size, thereby enabling the carbon-coated lithium manganese iron phosphate to have a high gram capacity.

[0124] Optionally, the volume distribution particle size Dv50 of the obtained first mixed powder may be 1 μm-5 μm.

[0125] In some embodiments, the equipment for the pre-sintering process can be any one of a rotary kiln, a roller kiln, and a box furnace.

[0126] In some embodiments, the holding temperature of the pre-sintering process may be 450° C.-700° C., for example, 450° C., 460° C., 480° C., 500° C., 520° C., 540° C., 560° C., 580° C., 600° C., 620° C., 640° C., 650° C., 660° C., 680° C., 700° C., or a range thereof. Alternatively, the holding temperature of the pre-sintering process may be 520° C.-680° C.

[0127] In some embodiments, the holding time of the pre-sintering treatment can be 6 hours to 25 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 25 hours, or a range consisting of any of the above values. Optionally, the holding time of the pre-sintering treatment can be 6 hours to 16 hours.

[0128] The holding temperature and / or holding time of the pre-sintering treatment being within the above range is conducive to preparing a lithium manganese iron phosphate precursor with a smaller primary particle size, thereby enabling the carbon-coated lithium manganese iron phosphate to have a high gram capacity.

[0129] In some embodiments, the heating rate of the pre-sintering process can be 2°C / min-8°C / min, for example, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, or a range consisting of any of the above values.

[0130] In some embodiments, in the step of pre-sintering and crushing the obtained first mixed powder under protective gas to obtain a lithium iron manganese phosphate precursor, the volume distribution particle size Dv50 of the lithium iron manganese phosphate precursor obtained by the pre-sintering treatment can be 20 μm to 30 μm. The lithium iron manganese phosphate precursor obtained by the pre-sintering treatment refers to the lithium iron manganese phosphate precursor that has not been crushed and has a secondary particle morphology, which is formed by the agglomeration of multiple primary particles.

[0131] In some embodiments, the obtained first mixed powder is pre-sintered and crushed under protective gas protection to obtain a lithium iron manganese phosphate precursor, and the volume distribution particle size Dv50 of the obtained lithium iron manganese phosphate precursor can be 0.5μm-3μm.

[0132] The obtained lithium manganese iron phosphate precursor may include one or more of primary particle morphology and agglomerates formed by a small number (eg, several) of primary particles.

[0133] The volume distribution particle size Dv50 of the obtained lithium manganese iron phosphate precursor is within the above range, which is conducive to the mixing of the lithium manganese iron phosphate precursor and the solid organic carbon source, and is conducive to the coating of the solid organic carbon source on the surface of the lithium manganese iron phosphate primary particles, thereby helping to further improve the electronic conductivity and gram capacity of the prepared carbon-coated lithium manganese iron phosphate.

[0134] In some embodiments, the obtained first mixed powder is pre-sintered and crushed under protective gas to obtain a lithium manganese iron phosphate precursor. The crushing process may include grinding and / or air flow milling.

[0135] In some embodiments, the device for dry mixing the lithium manganese iron phosphate precursor and the solid organic carbon source can be any one of a high-speed mixer, a V-type mixer, a ribbon mixer, and a honeycomb mill.

[0136] In some embodiments, the temperature for dry mixing the lithium manganese iron phosphate precursor and the solid organic carbon source can be 25°C-150°C.

[0137] In some embodiments, the stirring speed for dry mixing the lithium manganese iron phosphate precursor and the solid organic carbon source can be 500 rpm-2000 rpm.

[0138] In some embodiments, the dry mixing time of the lithium manganese iron phosphate precursor and the solid organic carbon source may be 0.1 h-1 h, optionally 0.25 h-1 h.

[0139] By adjusting one or more of the temperature, stirring speed, and mixing time of the dry mixing, the lithium manganese iron phosphate precursor and the solid organic carbon source are mixed evenly, which in turn helps to improve the coating effect of the carbon coating layer and improve the electronic conductivity and gram capacity of the prepared carbon-coated lithium manganese iron phosphate.

[0140] In some embodiments, the step of performing a step-by-step sintering and crushing process on the obtained second mixed powder under protective gas to obtain the carbon-coated lithium manganese iron phosphate can be performed using a rotary kiln. The use of a rotary kiln facilitates uniform mixing of the lithium manganese iron phosphate precursor and the solid organic carbon source, improves the coating effect of the carbon coating layer, and can also produce carbon-coated lithium manganese iron phosphate with a high compacted density and gram capacity.

[0141] In some embodiments, in the step of performing step-by-step sintering and crushing of the obtained second mixed powder under protective gas to obtain carbon-coated lithium manganese iron phosphate, the carbon-coated lithium manganese iron phosphate obtained by the step-by-step sintering may have a volume distribution particle size Dv50 of 5 μm to 10 μm. The carbon-coated lithium manganese iron phosphate obtained by the step-by-step sintering refers to the carbon-coated lithium manganese iron phosphate before crushing.

[0142] In some embodiments, the obtained second mixed powder is subjected to step-by-step sintering and crushing treatments under protective gas protection to obtain carbon-coated lithium manganese iron phosphate. In the step, the crushing treatment may include grinding treatment and / or air flow crushing treatment.

[0143] In some embodiments, the obtained second mixed powder is subjected to step-by-step sintering and crushing treatments under the protection of a protective gas to obtain carbon-coated lithium manganese iron phosphate. The crushing treatment may also include screening treatment.

[0144] In some embodiments, the obtained second mixed powder is subjected to step-by-step sintering and crushing treatments under protective gas protection to obtain carbon-coated lithium manganese iron phosphate. The volume distribution particle size Dv50 of the obtained carbon-coated lithium manganese iron phosphate can be 0.5 μm-2 μm.

[0145] In some embodiments, the obtained second mixed powder is subjected to step-by-step sintering and crushing under protective gas protection to obtain carbon-coated lithium manganese iron phosphate. The compacted density of the obtained carbon-coated lithium manganese iron phosphate powder can be 2.38 g / cm 3 -2.45g / cm 3 , optional 2.40g / cm 3 -2.45g / cm 3 .

[0146] In some embodiments, the obtained second mixed powder is subjected to step-by-step sintering and crushing treatments under protective gas protection to obtain carbon-coated lithium manganese iron phosphate. The gram capacity of the obtained carbon-coated lithium manganese iron phosphate can be 148mAh / g-152mAh / g.

[0147] The lithium source may be a lithium-containing compound known in the art that can be used to prepare lithium iron manganese phosphate. In some embodiments, the lithium source may include one or more of lithium carbonate, lithium hydroxide, lithium acetate, and lithium oxide.

[0148] The manganese source may be a manganese-containing compound known in the art that can be used to prepare lithium manganese iron phosphate. In some embodiments, the manganese source may include one or more of manganese nitrate, manganese acetate, manganese phosphate, manganese oxalate, manganese carbonate, and ammonium manganese phosphate.

[0149] The iron source may be an iron-containing compound known in the art that can be used to prepare lithium manganese iron phosphate. In some embodiments, the iron source may include one or more of ferric nitrate, ferric phosphate, ferric acetate, ferrous oxalate, ferric manganese nitrate, ferric manganese oxalate, ferric manganese acetate, ferric manganese phosphate, ammonium ferric manganese phosphate, and ferrous carbonate.

[0150] The phosphorus source may be a phosphorus-containing compound known in the art that can be used to prepare lithium manganese iron phosphate. In some embodiments, the phosphorus source may include one or more of lithium phosphate, lithium dihydrogen phosphate, dilithium hydrogen phosphate, manganese hydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and manganese iron hydrogen phosphate.

[0151] In some embodiments, the first mixed powder also includes one or more of a source of a doping element M, a source of a doping element N, a source of a doping element Q, and a source of a doping element R, where M represents a doping element at the manganese position and the iron position, N represents a doping element at the lithium position, Q represents a doping element at the phosphorus position, and R represents a doping element at the oxygen position.

[0152] M represents a doping element for manganese and iron, and may be selected from one or more of Co, Mg, Zn, Ca, Ti, V, Ni, and Cr. The source of the doping element M may include one or more of hydrochloride, nitrate, sulfate, and acetate of the doping element M.

[0153] N represents a doping element for lithium sites, which may be one or more of Zn, Al, Na, K, Mg, Nb, Mo, and W. The source of the doping element N may include one or more of hydrochloride, nitrate, sulfate, and acetate of the doping element N.

[0154] Q represents a doping element for the phosphorus site, and may be selected from one or more of B, S, Si, and N. The source of the doping element Q may include one or more of sulfates, borates, nitrates, and silicates of the doping element Q.

[0155] R represents an oxygen-site doping element, which may be one or more of S, F, Cl, and Br. The source of the doping element R may include one or more of a simple substance of the doping element R and an ammonium salt.

[0156] In some embodiments, the shielding gas may include one or more of nitrogen, argon, and helium.

[0157] In the above preparation method, unless otherwise specified, all raw materials can be purchased directly.

[0158] The present application also provides a carbon-coated lithium manganese iron phosphate prepared by the above-mentioned preparation method.

[0159] The volume distribution particle size Dv50 of the carbon-coated lithium manganese iron phosphate can be 0.5 μm-2 μm.

[0160] The powder compaction density of carbon-coated lithium manganese iron phosphate can be 2.38g / cm 3 -2.45g / cm 3 , optional 2.40g / cm 3 -2.45g / cm 3 .

[0161] The gram capacity of carbon-coated lithium manganese iron phosphate can be 148 mAh / g-152 mAh / g.

[0162] Lithium manganese iron phosphate may have the chemical formula Li a N b Fe x Mn y M 1-x-y P 1-m Q m O 4-n R n , M represents the doping element for manganese and iron positions, which may be selected from one or more of Co, Mg, Zn, Ca, Ti, V, Ni, and Cr; N represents the doping element for lithium position, which may be selected from one or more of Zn, Al, Na, K, Mg, Nb, Mo, and W; Q represents the doping element for phosphorus position, which may be selected from one or more of B, S, Si, and N; R represents the doping element for oxygen position, which may be selected from one or more of S, F, Cl, and Br; 0.9≤a≤1.1, 0≤b≤0.1, 0<x<1, 0<y<1, 0≤1-xy≤0.1, 0≤m≤0.1, 0≤n≤0.1, and lithium manganese iron phosphate is electrically neutral.

[0163] The lithium manganese iron phosphate provided in the embodiments of the present application can be used in battery cells.

[0164] The battery cell includes an electrode assembly and an electrolyte, and the electrode assembly includes a positive electrode sheet and a negative electrode sheet.

[0165] [Positive electrode]

[0166] In some embodiments, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector, the positive electrode film layer includes a positive electrode active material, the positive electrode active material includes a first carbon-coated lithium manganese iron phosphate, and the first carbon-coated lithium manganese iron phosphate is prepared by the preparation method provided in the embodiments of the present application.

[0167] The volume distribution particle size Dv50 of the first carbon-coated lithium manganese iron phosphate may be 0.5 μm-2 μm.

[0168] The first carbon-coated lithium manganese iron phosphate powder compaction density can be 2.38 g / cm 3 -2.45g / cm 3 , optional 2.40g / cm 3 -2.45g / cm 3 .

[0169] The gram capacity of carbon-coated lithium manganese iron phosphate can be 148 mAh / g-152 mAh / g.

[0170] In some embodiments, the positive electrode active material further includes a second carbon-coated lithium manganese iron phosphate, and the volume distribution particle size Dv50 of the second carbon-coated lithium manganese iron phosphate may be 10 μm-15 μm.

[0171] Optionally, the mass ratio of the first carbon-coated lithium manganese iron phosphate to the second carbon-coated lithium manganese iron phosphate may be 1:0.1 to 1:0.5.

[0172] Further adjusting the mass ratio of the first carbon-coated lithium manganese iron phosphate to the second carbon-coated lithium manganese iron phosphate can further increase the overall powder compaction density of the positive electrode active material, improve the electronic conduction efficiency and ion conduction efficiency of the positive electrode active material, and thus enable the battery to have both high energy density and good electrochemical performance.

[0173] The volume distribution particle size Dv50 of the second carbon-coated lithium manganese iron phosphate is larger than the volume distribution particle size Dv50 of the first carbon-coated lithium manganese iron phosphate. By mixing the large-particle size of the second carbon-coated lithium manganese iron phosphate with the first carbon-coated lithium manganese iron phosphate, the small particles of the first carbon-coated lithium manganese iron phosphate can be filled between the large particles of the second carbon-coated lithium manganese iron phosphate, thereby increasing the contact area between the particles in the positive electrode film layer and reducing the gaps between the particles. This can further increase the overall powder compaction density of the positive electrode active material, increase the compaction density of the positive electrode sheet, and improve the energy density of the battery.

[0174] Since the first carbon-coated lithium manganese iron phosphate and the second carbon-coated lithium manganese iron phosphate both have a carbon coating layer, the small particles of the first carbon-coated lithium manganese iron phosphate are filled between the large particles of the second carbon-coated lithium manganese iron phosphate, and the carbon coating layer in the positive electrode film layer can also form a spatial network structure with multiple cross-point connections, thereby increasing the electronic conduction efficiency and ion conduction efficiency of the positive electrode active material, and thus improving the electrochemical performance of the battery.

[0175] Optionally, the powder compaction density of the positive electrode active material is greater than the powder compaction density of the first carbon-coated lithium manganese iron phosphate.

[0176] Optionally, the powder compaction density of the positive electrode active material is greater than the powder compaction density of the second carbon-coated lithium manganese iron phosphate.

[0177] Alternatively, the powder compaction density of the positive electrode active material may be 2.4 g / cm 3 -2.5g / cm 3 .

[0178] In some embodiments, the second carbon-coated lithium manganese iron phosphate can be obtained by a liquid phase method.

[0179] Optionally, the preparation method of the second carbon-coated lithium manganese iron phosphate may include the following steps: adding a lithium source, a manganese source, an iron source, a phosphorus source, a carbon source and water into a stirring tank respectively, stirring and mixing to obtain a slurry; grinding the obtained slurry through a sand mill to obtain a ground slurry; passing the ground slurry into a spray dryer for spray granulation to obtain a powder; and sintering the obtained powder in an atmosphere furnace protected by a protective gas atmosphere to obtain a second carbon-coated lithium manganese iron phosphate.

[0180] Optionally, the obtained slurry may be ground by a sand mill for 2 hours to 8 hours.

[0181] Optionally, the sand mill can be a vertical sand mill or a horizontal sand mill.

[0182] Optionally, the particle size of the zirconium beads used in the sand mill may be 0.1 mm to 3 mm.

[0183] Optionally, the volume distribution particle size Dv50 of the ground slurry may be 0.1 μm-1 μm.

[0184] Optionally, the inlet temperature of the spray dryer may be 100°C-280°C, and the outlet temperature may be 50°C-180°C.

[0185] The temperature of the spray dryer is set within the above range, which can achieve high spray efficiency and high yield, and reduce the oxidation problem of ferrous ions and manganese ions.

[0186] Optionally, the sintering temperature of the atmosphere furnace may be 450°C-800°C.

[0187] Optionally, the sintering time in the atmosphere furnace can be 6h-25h.

[0188] Optionally, the atmosphere furnace can be any one of a rotary kiln, a roller kiln, and a box furnace.

[0189] Optionally, the added mass of the carbon source is 1%-10% of the mass of the second carbon-coated lithium manganese iron phosphate precursor, and optionally 5%-10%.

[0190] In some embodiments, the positive electrode film layer may further include other positive electrode active materials. For example, other positive electrode active materials may include, but are not limited to, one or more of lithium transition metal oxides and modified compounds thereof. As an example, lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. The modified compounds of the above-mentioned positive electrode active materials may be doping modification and / or surface coating modification of the positive electrode active materials.

[0191] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0192] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylic resin, styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and one or more of carboxymethyl chitosan (CMCS).

[0193] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include but is not limited to one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include but is not limited to one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0194] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and cold pressing it. The positive electrode slurry is typically formed by dispersing the positive electrode active material, positive electrode conductive agent, positive electrode binder, and any other components in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP).

[0195] [Negative electrode]

[0196] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector.

[0197] 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 (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0198] In some embodiments, the negative electrode active material may be a material known in the art. As an example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more 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 may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0199] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. As examples, the binder may include one or more 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).

[0200] In some embodiments, the negative electrode film layer may further include a negative electrode conductive agent. For example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0201] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC)).

[0202] The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, drying it, and cold pressing it. The negative electrode slurry is typically formed by dispersing the negative electrode active material, negative electrode conductive agent, negative electrode binder, and any other components in a solvent and stirring them uniformly. The solvent can be, but is not limited to, deionized water.

[0203] The negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate may further include a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode plate may further include a protective layer covering the surface of the negative electrode film layer.

[0204] [Electrolytes]

[0205] Battery cells also include an electrolyte. The electrolyte conducts ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte; it can be selected based on needs. For example, the electrolyte can include one or more of a solid electrolyte, a gel electrolyte, and a liquid electrolyte (i.e., an electrolyte solution).

[0206] In some embodiments, the electrolyte is an electrolyte solution including an electrolyte salt and a solvent.

[0207] In some embodiments, as examples, the electrolyte salt may include, but is not limited to, one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP).

[0208] In some embodiments, the solvent may include, but is not limited to, one or more of an ester solvent, a sulfone solvent, and an ether solvent. As an example, the solvent may include, but is not limited to, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and one or more of diethyl sulfone (ESE).

[0209] 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, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0210] [Isolation film]

[0211] Battery cells using electrolytes, as well as some battery cells using solid electrolytes, also include a separator. The separator is placed between the positive and negative electrode sheets to prevent internal short circuits.

[0212] The present application has no particular limitation on the type of isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0213] In some embodiments, the material of the isolation membrane may include, but is not limited to, one or more of fiberglass, non-woven fabric, polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different.

[0214] The preparation method of battery cells is well known. In some embodiments, the positive electrode sheet, separator, negative electrode sheet and electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, separator, and negative electrode sheet can be formed into an electrode assembly through a winding process and / or a lamination process, and the electrode assembly is placed in an outer package, dried and injected with the above-mentioned electrolyte, and then subjected to packaging, standing, formation and other processes to obtain a battery cell. Multiple battery cells can also be further connected in series, in parallel or in a mixed connection to form a battery module. Multiple battery modules can also be connected in series, in parallel or in a mixed connection to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.

[0215] The embodiments of the present application also provide an electrical device, which includes a battery provided in the embodiments of the present application, and the battery is used to provide electrical energy. The battery can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.

[0216] The electrical device can select a specific type of battery, such as a battery cell, a battery module, or a battery pack, according to its usage requirements.

[0217] Figure 6The diagram is a schematic diagram of an exemplary electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this device, a battery pack or battery module can be used.

[0218] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0219] Example

[0220] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing. The instruments used in the examples are commercially available.

[0221] Example 1-1

[0222] Lithium carbonate, ferrous oxalate, manganese oxalate and ammonium dihydrogen phosphate with a molar ratio of 1:0.6:1.4:2 were mixed evenly in a high-speed mixer and loaded into a rotary kiln. The mixture was heated to 650°C at a heating rate of 5°C / min under a nitrogen atmosphere and kept at a constant temperature for 8 hours. The mixture was then cooled to 50°C and taken out. After grinding, a lithium manganese iron phosphate precursor was obtained with a volume distribution particle size Dv50 of 0.5 μm.

[0223] The obtained lithium manganese iron phosphate precursor and solid organic carbon source glucose were mixed in a high-speed mixer at a mass ratio of 100:10 and then loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 200°C at a heating rate of 2°C / min and held at this temperature for 2 hours. Then, the mixture was heated to 600°C at a heating rate of 2°C / min and held at this temperature for 4 hours. Then, the mixture was heated to 750°C at a heating rate of 2°C / min and held at this temperature for 12 hours. The mixture was then cooled to 50°C and removed from the furnace. After grinding and airflow milling, carbon-coated lithium manganese iron phosphate with a volume distribution particle size Dv50 of 1.8 μm was obtained as the positive electrode active material. The softening temperature of glucose is 146°C-150°C, the initial weight loss temperature is 358°C-362°C, and the final weight loss temperature is 578°C-582°C. The volume distribution particle size Dv50 of glucose is 4.5 μm.

[0224] Comparative Example 1-1

[0225] Lithium carbonate, ferrous oxalate, manganese oxalate and ammonium dihydrogen phosphate with a molar ratio of 1:0.6:1.4:2 were mixed evenly in a high-speed mixer and loaded into a rotary kiln. The mixture was heated to 650°C at a heating rate of 5°C / min under a nitrogen atmosphere and kept at a constant temperature for 8 hours. The mixture was then cooled to 50°C and taken out. After grinding, a lithium manganese iron phosphate precursor was obtained with a volume distribution particle size Dv50 of 0.5 μm.

[0226] The obtained lithium manganese iron phosphate precursor and solid organic carbon source glucose were mixed in a high-speed mixer at a mass ratio of 100:10 and then loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 750°C at a heating rate of 2°C / min and held at this temperature for 12 hours. The mixture was then cooled to 50°C and removed from the furnace. After grinding and airflow milling, a carbon-coated lithium manganese iron phosphate with a volume distribution particle size Dv50 of 1.8μm was obtained as the positive electrode active material. The softening temperature of glucose is 146°C-150°C, the initial weight loss temperature is 358°C-362°C, and the final weight loss temperature is 578°C-582°C. The volume distribution particle size Dv50 of glucose is 4.5μm.

[0227] Comparative Example 1-2

[0228] Lithium carbonate, ferrous oxalate, manganese oxalate and ammonium dihydrogen phosphate with a molar ratio of 1:0.6:1.4:2 were mixed evenly in a high-speed mixer and loaded into a rotary kiln. The mixture was heated to 650°C at a heating rate of 5°C / min under a nitrogen atmosphere and kept at a constant temperature for 8 hours. The mixture was then cooled to 50°C and taken out. After grinding, a lithium manganese iron phosphate precursor was obtained with a volume distribution particle size Dv50 of 0.5 μm.

[0229] The obtained lithium manganese iron phosphate precursor and solid organic carbon source glucose were mixed in a high-speed mixer at a mass ratio of 100:10 and then loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 600°C at a heating rate of 2°C / min and held at this temperature for 4 hours. The mixture was then heated to 750°C at a heating rate of 2°C / min and held at this temperature for 12 hours. The mixture was then cooled to 50°C and removed from the furnace. After grinding and airflow milling, a carbon-coated lithium manganese iron phosphate with a volume distribution particle size Dv50 of 1.8 μm was obtained as the positive electrode active material. The softening temperature of glucose is 146°C-150°C, the initial weight loss temperature is 358°C-362°C, and the final weight loss temperature is 578°C-582°C. The volume distribution particle size Dv50 of glucose is 4.5 μm.

[0230] Comparative Examples 1-3

[0231] Lithium carbonate, ferrous oxalate, manganese oxalate and ammonium dihydrogen phosphate with a molar ratio of 1:0.6:1.4:2 were mixed evenly in a high-speed mixer and loaded into a rotary kiln. The mixture was heated to 650°C at a heating rate of 5°C / min under a nitrogen atmosphere and kept at a constant temperature for 8 hours. The mixture was then cooled to 50°C and taken out. After grinding, a lithium manganese iron phosphate precursor was obtained with a volume distribution particle size Dv50 of 0.5 μm.

[0232] The obtained lithium manganese iron phosphate precursor and solid organic carbon source glucose were mixed in a high-speed mixer at a mass ratio of 100:10 and then loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 200°C at a heating rate of 2°C / min and held at this temperature for 2 hours. Then, the mixture was heated to 450°C at a heating rate of 2°C / min and held at this temperature for 4 hours. Then, the mixture was heated to 750°C at a heating rate of 2°C / min and held at this temperature for 12 hours. The mixture was then cooled to 50°C and removed from the furnace. After grinding and airflow milling, carbon-coated lithium manganese iron phosphate with a volume distribution particle size Dv50 of 1.8 μm was obtained as the positive electrode active material. The softening temperature of glucose is 146°C-150°C, the initial weight loss temperature is 358°C-362°C, and the final weight loss temperature is 578°C-582°C. The volume distribution particle size Dv50 of glucose is 4.5 μm.

[0233] Performance testing of positive electrode active materials

[0234] (1) Volume distribution particle size Dv50 test

[0235] Take an appropriate amount of sample, add 20 mL of deionized water, and ultrasonicate for 5 minutes (53 kHz, 120 W) to completely disperse the sample. Then, use a laser particle size analyzer (MasterSizer 2000) to measure the volume distribution particle size Dv50.

[0236] (2) Test of powder compaction density

[0237] Weigh 1g of sample powder and spread it flat in a compaction density mold with a cross-sectional area of ​​1.327cm 2 , then put it into the compaction density machine and test the powder compaction density after compacting with a pressure of 30000N.

[0238] (3) Discharge specific capacity test

[0239] The positive electrode active material, polyvinylidene fluoride (PVDF), and conductive carbon were added to a certain amount of N-methylpyrrolidone (NMP) in a weight ratio of 90:5:5. The mixture was stirred in a drying room to form a slurry. The slurry was coated on aluminum foil, dried, and cold-pressed to form a positive electrode sheet. A lithium sheet was used as the negative electrode and assembled with the prepared positive electrode sheet in a button box to form a button cell. The electrolyte concentration was 1 mol / L, the lithium salt was LiPF6, and the solvent was a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1. The separator was a polyethylene film.

[0240] At 25°C, button cells were cycled 50 times at a 0.1C charge / discharge rate, with a charge / discharge voltage range of 2.0V-4.3V. The discharge capacity at the final cycle was divided by the mass of the positive electrode active material to obtain the specific discharge capacity of the positive electrode active material at a 0.1C charge / discharge rate. The Shenzhen Xinweier battery testing system was used for cyclic charge and discharge testing.

[0241] Table 1

[0242]

[0243] It can be seen from the test results in Table 1 that the carbon-coated lithium manganese iron phosphate prepared by the preparation method provided in this application has a higher powder compaction density and a higher gram capacity.

[0244] Example 2-1

[0245] Lithium carbonate, ferrous oxalate, manganese oxalate and ammonium dihydrogen phosphate with a molar ratio of 1:0.6:1.4:2 were mixed evenly in a high-speed mixer and loaded into a rotary kiln. The mixture was heated to 650°C at a heating rate of 5°C / min under a nitrogen atmosphere and kept at a constant temperature for 8 hours. The mixture was then cooled to 50°C and taken out. After grinding, a lithium manganese iron phosphate precursor was obtained with a volume distribution particle size Dv50 of 0.5 μm.

[0246] The obtained lithium manganese iron phosphate precursor and solid organic carbon source glucose were mixed in a high-speed mixer at a mass ratio of 100:10 and then loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 200°C at a heating rate of 5°C / min and held at this temperature for 2 hours. Then, the mixture was heated to 600°C at a heating rate of 5°C / min and held at this temperature for 4 hours. Then, the mixture was heated to 750°C at a heating rate of 5°C / min and held at this temperature for 12 hours. The mixture was then cooled to 50°C and removed from the oven. After grinding and airflow milling, a carbon-coated lithium manganese iron phosphate with a volume distribution particle size Dv50 of 1.8 μm was obtained as the positive electrode active material. The softening temperature of glucose is 146°C-150°C, the initial weight loss temperature is 358°C-362°C, and the final weight loss temperature is 578°C-582°C. The volume distribution particle size Dv50 of glucose is 4.5 μm.

[0247] Example 2-2

[0248] Lithium carbonate, ferrous oxalate, manganese oxalate and ammonium dihydrogen phosphate with a molar ratio of 1:0.6:1.4:2 were mixed evenly in a high-speed mixer and loaded into a rotary kiln. The mixture was heated to 650°C at a heating rate of 5°C / min under a nitrogen atmosphere and kept at a constant temperature for 8 hours. The mixture was then cooled to 50°C and taken out. After grinding, a lithium manganese iron phosphate precursor was obtained with a volume distribution particle size Dv50 of 0.5 μm.

[0249] The obtained lithium manganese iron phosphate precursor and solid organic carbon source glucose were mixed in a high-speed mixer at a mass ratio of 100:10 and then loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 200°C at a heating rate of 8°C / min and held at this temperature for 2 hours. Then, the mixture was heated to 600°C at a heating rate of 8°C / min and held at this temperature for 4 hours. Then, the mixture was heated to 750°C at a heating rate of 8°C / min and held at this temperature for 12 hours. The mixture was then cooled to 50°C and removed from the furnace. After grinding and airflow milling, a carbon-coated lithium manganese iron phosphate with a volume distribution particle size Dv50 of 1.8 μm was obtained as the positive electrode active material. The softening temperature of glucose is 146°C-150°C, the initial weight loss temperature is 358°C-362°C, and the final weight loss temperature is 578°C-582°C. The volume distribution particle size Dv50 of glucose is 4.5 μm.

[0250] Table 2

[0251]

[0252] It can be seen from the test results in Table 2 that by further adjusting the heating rate of the distributed sintering treatment, the carbon-coated lithium manganese iron phosphate can have a higher powder compaction density and a higher gram capacity.

[0253] Example 3-1

[0254] Lithium carbonate, ferrous oxalate, manganese oxalate and ammonium dihydrogen phosphate with a molar ratio of 1:0.6:1.4:2 were mixed evenly in a high-speed mixer and loaded into a rotary kiln. The mixture was heated to 650°C at a heating rate of 5°C / min under a nitrogen atmosphere and kept at a constant temperature for 8 hours. The mixture was then cooled to 50°C and taken out. After grinding, a lithium manganese iron phosphate precursor was obtained with a volume distribution particle size Dv50 of 0.5 μm.

[0255] The obtained lithium manganese iron phosphate precursor and solid organic carbon source glucose were mixed in a high-speed mixer at a mass ratio of 100:10 and then loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 200°C at a heating rate of 2°C / min and held at this temperature for 3 hours. Then, the mixture was heated to 600°C at a heating rate of 2°C / min and held at this temperature for 5 hours. Then, the mixture was heated to 750°C at a heating rate of 2°C / min and held at this temperature for 12 hours. The mixture was then cooled to 50°C and removed from the furnace. After grinding and airflow milling, carbon-coated lithium manganese iron phosphate with a volume distribution particle size Dv50 of 1.8 μm was obtained as the positive electrode active material. The softening temperature of glucose is 146°C-150°C, the initial weight loss temperature is 358°C-362°C, and the final weight loss temperature is 578°C-582°C. The volume distribution particle size Dv50 of glucose is 4.5 μm.

[0256] Example 3-2

[0257] Lithium carbonate, ferrous oxalate, manganese oxalate and ammonium dihydrogen phosphate with a molar ratio of 1:0.6:1.4:2 were mixed evenly in a high-speed mixer and loaded into a rotary kiln. The mixture was heated to 650°C at a heating rate of 5°C / min under a nitrogen atmosphere and kept at a constant temperature for 8 hours. The mixture was then cooled to 50°C and taken out. After grinding, a lithium manganese iron phosphate precursor was obtained with a volume distribution particle size Dv50 of 0.5 μm.

[0258] The obtained lithium manganese iron phosphate precursor and solid organic carbon source glucose were mixed in a high-speed mixer at a mass ratio of 100:10 and then loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 200°C at a heating rate of 2°C / min and held at this temperature for 4 hours. Then, the mixture was heated to 600°C at a heating rate of 2°C / min and held at this temperature for 6 hours. Then, the mixture was heated to 750°C at a heating rate of 2°C / min and held at this temperature for 12 hours. The mixture was then cooled to 50°C and removed from the oven. After grinding and airflow milling, carbon-coated lithium manganese iron phosphate with a volume distribution particle size Dv50 of 1.8 μm was obtained as the positive electrode active material. The softening temperature of glucose is 146°C-150°C, the initial weight loss temperature is 358°C-362°C, and the final weight loss temperature is 578°C-582°C. The volume distribution particle size Dv50 of glucose is 4.5 μm.

[0259] Table 3

[0260]

[0261]

[0262] It can be seen from the test results in Table 3 that by further adjusting the holding time of the first sintering treatment and the holding time of the second sintering treatment, the carbon-coated lithium manganese iron phosphate can have a higher discharge specific capacity.

[0263] Example 4-1

[0264] Lithium carbonate, ferrous oxalate, manganese oxalate, and ammonium dihydrogen phosphate in a molar ratio of 1:0.6:1.4:2 were mixed evenly in a high-speed mixer and loaded into a rotary kiln. The mixture was heated to 500°C at a heating rate of 5°C / min under a nitrogen atmosphere and kept at a constant temperature for 8 hours. The mixture was then cooled to 50°C and taken out. After grinding, a lithium manganese iron phosphate precursor was obtained, and the volume distribution particle size Dv50 was 0.5 μm.

[0265] The obtained lithium manganese iron phosphate precursor and solid organic carbon source glucose were mixed in a high-speed mixer at a mass ratio of 100:10 and then loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 200°C at a heating rate of 2°C / min and held at this temperature for 2 hours. Then, the mixture was heated to 600°C at a heating rate of 2°C / min and held at this temperature for 4 hours. Then, the mixture was heated to 750°C at a heating rate of 2°C / min and held at this temperature for 12 hours. The mixture was then cooled to 50°C and removed from the furnace. After grinding and airflow milling, carbon-coated lithium manganese iron phosphate with a volume distribution particle size Dv50 of 1.8 μm was obtained as the positive electrode active material. The softening temperature of glucose is 146°C-150°C, the initial weight loss temperature is 358°C-362°C, and the final weight loss temperature is 578°C-582°C. The volume distribution particle size Dv50 of glucose is 4.5 μm.

[0266] Example 4-2

[0267] Lithium carbonate, ferrous oxalate, manganese oxalate and ammonium dihydrogen phosphate in a molar ratio of 1:0.6:1.4:2 were mixed evenly in a high-speed mixer and loaded into a rotary kiln. The mixture was heated to 700°C at a heating rate of 5°C / min under a nitrogen atmosphere and kept at a constant temperature for 8 hours. The mixture was then cooled to 50°C and taken out. After grinding, a lithium manganese iron phosphate precursor was obtained with a volume distribution particle size Dv50 of 0.5 μm.

[0268] The obtained lithium manganese iron phosphate precursor and solid organic carbon source glucose were mixed in a high-speed mixer at a mass ratio of 100:10 and then loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 200°C at a heating rate of 2°C / min and held at this temperature for 2 hours. Then, the mixture was heated to 600°C at a heating rate of 2°C / min and held at this temperature for 4 hours. Then, the mixture was heated to 750°C at a heating rate of 2°C / min and held at this temperature for 12 hours. The mixture was then cooled to 50°C and removed from the furnace. After grinding and airflow milling, carbon-coated lithium manganese iron phosphate with a volume distribution particle size Dv50 of 1.8 μm was obtained as the positive electrode active material. The softening temperature of glucose is 146°C-150°C, the initial weight loss temperature is 358°C-362°C, and the final weight loss temperature is 578°C-582°C. The volume distribution particle size Dv50 of glucose is 4.5 μm.

[0269] Table 4

[0270]

[0271] It can be seen from the test results in Table 4 that by further adjusting the holding time of the pre-sintering treatment, the carbon-coated lithium manganese iron phosphate can have a higher powder compaction density and a higher gram capacity.

[0272] Example 5-1

[0273] Lithium carbonate, ferrous oxalate, manganese oxalate and ammonium dihydrogen phosphate with a molar ratio of 1:0.6:1.4:2 were mixed evenly in a high-speed mixer and loaded into a rotary kiln. The mixture was heated to 650°C at a heating rate of 5°C / min under a nitrogen atmosphere and kept at a constant temperature for 8 hours. The mixture was then cooled to 50°C and taken out. After grinding, a lithium manganese iron phosphate precursor was obtained with a volume distribution particle size Dv50 of 0.5 μm.

[0274] The obtained lithium manganese iron phosphate precursor and solid organic carbon source polytetrafluoroethylene were mixed in a high-speed mixer at a mass ratio of 100:10 and then loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 350°C at a heating rate of 2°C / min and held at this temperature for 2 hours. Then, the mixture was heated to 650°C at a heating rate of 2°C / min and held at this temperature for 4 hours. Then, the mixture was heated to 750°C at a heating rate of 2°C / min and held at this temperature for 12 hours. The mixture was then cooled to 50°C and removed from the furnace. After grinding and airflow milling, carbon-coated lithium manganese iron phosphate with a volume distribution particle size Dv50 of 1.8 μm was obtained as the positive electrode active material. The softening temperature of polytetrafluoroethylene is 278°C-282°C, the initial weight loss temperature is 478°C-482°C, and the final weight loss temperature is 595°C-600°C. The volume distribution particle size Dv50 of polytetrafluoroethylene is 3 μm.

[0275] Comparative Example 2-1

[0276] Lithium carbonate, ferrous oxalate, manganese oxalate and ammonium dihydrogen phosphate with a molar ratio of 1:0.6:1.4:2 were mixed evenly in a high-speed mixer and loaded into a rotary kiln. The mixture was heated to 650°C at a heating rate of 5°C / min under a nitrogen atmosphere and kept at a constant temperature for 8 hours. The mixture was then cooled to 50°C and taken out. After grinding, a lithium manganese iron phosphate precursor was obtained with a volume distribution particle size Dv50 of 0.5 μm.

[0277] The obtained lithium manganese iron phosphate precursor and solid organic carbon source polytetrafluoroethylene were mixed in a high-speed mixer at a mass ratio of 100:10 and then loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 750°C at a heating rate of 2°C / min and held at this temperature for 12 hours. The mixture was then cooled to 50°C and removed from the furnace. After grinding and airflow milling, carbon-coated lithium manganese iron phosphate with a volume distribution particle size (Dv50) of 1.8 μm was obtained as the positive electrode active material. The softening temperature of polytetrafluoroethylene was 278°C-282°C, the initial weight loss temperature was 478°C-482°C, and the final weight loss temperature was 595°C-600°C. The volume distribution particle size (Dv50) of polytetrafluoroethylene was 3 μm.

[0278] Comparative Example 2-2

[0279] Lithium carbonate, ferrous oxalate, manganese oxalate and ammonium dihydrogen phosphate with a molar ratio of 1:0.6:1.4:2 were mixed evenly in a high-speed mixer and loaded into a rotary kiln. The mixture was heated to 650°C at a heating rate of 5°C / min under a nitrogen atmosphere and kept at a constant temperature for 8 hours. The mixture was then cooled to 50°C and taken out. After grinding, a lithium manganese iron phosphate precursor was obtained with a volume distribution particle size Dv50 of 0.5 μm.

[0280] The obtained lithium manganese iron phosphate precursor and the solid organic carbon source polytetrafluoroethylene were mixed in a high-speed mixer at a mass ratio of 100:10 and then loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 650°C at a heating rate of 2°C / min and held at this temperature for 4 hours. The mixture was then heated to 750°C at a heating rate of 2°C / min and held at this temperature for 12 hours. The mixture was then cooled to 50°C and removed from the furnace. After grinding and airflow milling, a carbon-coated lithium manganese iron phosphate with a volume distribution particle size Dv50 of 1.8 μm was obtained as the positive electrode active material. The softening temperature of polytetrafluoroethylene is 278°C-282°C, the initial weight loss temperature is 478°C-482°C, and the final weight loss temperature is 595°C-600°C. The volume distribution particle size Dv50 of polytetrafluoroethylene is 3 μm.

[0281] Comparative Examples 2-3

[0282] Lithium carbonate, ferrous oxalate, manganese oxalate and ammonium dihydrogen phosphate with a molar ratio of 1:0.6:1.4:2 were mixed evenly in a high-speed mixer and loaded into a rotary kiln. The mixture was heated to 650°C at a heating rate of 5°C / min under a nitrogen atmosphere and kept at a constant temperature for 8 hours. The mixture was then cooled to 50°C and taken out. After grinding, a lithium manganese iron phosphate precursor was obtained with a volume distribution particle size Dv50 of 0.5 μm.

[0283] The obtained lithium manganese iron phosphate precursor and the solid organic carbon source polytetrafluoroethylene were mixed in a high-speed mixer at a mass ratio of 100:10 and then loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 350°C at a heating rate of 2°C / min and held at this temperature for 2 hours. Then, the mixture was heated to 500°C at a heating rate of 2°C / min and held at this temperature for 4 hours. Then, the mixture was heated to 750°C at a heating rate of 2°C / min and held at this temperature for 12 hours. The mixture was then cooled to 50°C and removed from the furnace. After grinding and airflow milling, carbon-coated lithium manganese iron phosphate with a volume distribution particle size Dv50 of 1.8 μm was obtained as the positive electrode active material. The softening temperature of polytetrafluoroethylene is 278°C-282°C, the initial weight loss temperature is 478°C-482°C, and the final weight loss temperature is 595°C-600°C. The volume distribution particle size Dv50 of polytetrafluoroethylene is 3 μm.

[0284] Table 5

[0285]

[0286] It can be seen from the test results in Table 5 that the carbon-coated lithium manganese iron phosphate prepared by the preparation method provided in this application has a higher powder compaction density and a higher gram capacity.

[0287] Example 6-1

[0288] Preparation of the first carbon-coated lithium manganese iron phosphate

[0289] The carbon-coated lithium manganese iron phosphate prepared in Example 1-1 and having a volume distribution particle size Dv50 of 1.8 μm was used.

[0290] Preparation of the second carbon-coated lithium manganese iron phosphate

[0291] Lithium carbonate, ferrous carbonate, manganese carbonate, phosphoric acid and deionized water in a molar ratio of 1:0.6:1.4:2 are added to a reactor, stirred evenly, and then glucose is added to the reactor and stirred thoroughly. The stirring rate is controlled at 200 rpm for 2 hours to obtain a slurry; the slurry is passed into a sand mill for grinding and ground with 0.6 mm zirconium beads for 5 hours; the ground slurry is spray granulated by a spray dryer with an inlet temperature of 200°C and an outlet temperature of 120°C to obtain a powder; the powder is loaded into a sagger and placed in a box furnace, heated to 650°C at a heating rate of 5°C / min under a nitrogen atmosphere, kept constant at this temperature for 8 hours, taken out after cooling, and subjected to grinding and airflow crushing treatment to obtain a carbon-coated lithium manganese iron phosphate with a volume distribution particle size Dv50 of 12 μm, i.e., the second carbon-coated lithium manganese iron phosphate.

[0292] Preparation of positive electrode active materials

[0293] The mass ratio of the first carbon-coated lithium manganese iron phosphate and the second carbon-coated lithium manganese iron phosphate is 1:0.1, and the first carbon-coated lithium manganese iron phosphate and the second carbon-coated lithium manganese iron phosphate are uniformly mixed using a V-type mixer to serve as a positive electrode active material.

[0294] Examples 6-2 to 6-3

[0295] The preparation of the positive electrode active material is the same as that of Example 6-1, except that the mass ratio of the first carbon-coated lithium manganese iron phosphate and the second carbon-coated lithium manganese iron phosphate is different. Specific parameters are shown in Table 3.

[0296] Comparative Example 3-1

[0297] Lithium carbonate, ferrous carbonate, manganese carbonate, phosphoric acid and deionized water in a molar ratio of 1:0.6:1.4:2 are added to a reactor, stirred evenly, and then glucose is added to the reactor and stirred thoroughly at a stirring rate of 200 rpm for 2 hours to obtain a slurry; the slurry is passed into a sand mill for grinding and ground with 0.6 mm zirconium beads for 5 hours; the ground slurry is spray granulated by a spray dryer with an inlet temperature of 200°C and an outlet temperature of 120°C to obtain a powder; the powder is loaded into a sagger and placed in a box furnace, heated to 650°C at a heating rate of 5°C / min under a nitrogen atmosphere, kept constant at this temperature for 8 hours, taken out after cooling, ground and airflow crushed to obtain carbon-coated lithium manganese iron phosphate with a volume distribution particle size Dv50 of 12 μm as a positive electrode active material.

[0298] Table 6

[0299]

[0300] The volume distribution particle size Dv50 of the second carbon-coated lithium manganese iron phosphate is larger than the volume distribution particle size Dv50 of the first carbon-coated lithium manganese iron phosphate. By mixing the second carbon-coated lithium manganese iron phosphate with large particles into the first carbon-coated lithium manganese iron phosphate, the positive electrode active material can have a high powder compaction density, thereby improving the energy density of the battery.

[0301] It can also be seen from the test results in Table 6 that by further adjusting the mixing ratio of the first carbon-coated lithium manganese iron phosphate and the second carbon-coated lithium manganese iron phosphate, the positive electrode active material can have a higher powder compaction density.

[0302] This is because the small particles of the first carbon-coated lithium manganese iron phosphate can be filled between the large particles of the second carbon-coated lithium manganese iron phosphate, thereby increasing the contact area between the particles in the positive electrode film layer, reducing the gaps between the particles, and thus improving the overall powder compaction density of the positive electrode active material.

[0303] 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 carbon-coated lithium manganese iron phosphate, characterized in that: The steps include: dry-mixing a lithium source, a manganese source, an iron source, and a phosphorus source to obtain a first mixed powder; The obtained first mixed powder is pre-sintered and crushed under protective gas protection to obtain a lithium manganese iron phosphate precursor; dry-mixing the obtained lithium manganese iron phosphate precursor with a solid organic carbon source to obtain a second mixed powder; The obtained second mixed powder is subjected to step-by-step sintering and crushing treatment under protective gas protection to obtain carbon-coated lithium manganese iron phosphate. The step-by-step sintering includes a first-stage sintering process, a second-stage sintering process and a third-stage sintering process, wherein the holding temperature of the first-stage sintering process is lower than the holding temperature of the second-stage sintering process, and the holding temperature of the second-stage sintering process is lower than the holding temperature of the third-stage sintering process; The holding temperature of the first stage sintering treatment is between the softening temperature of the solid organic carbon source and the starting weight loss temperature of the solid organic carbon source. The holding temperature of the second-stage sintering treatment is greater than or equal to the end weight loss temperature of the solid organic carbon source, The holding temperature of the three-stage sintering process is 600°C-800°C.

2. The preparation method according to claim 1, characterized in that The holding time of the first stage sintering treatment is shorter than the holding time of the second stage sintering treatment, and the holding time of the second stage sintering treatment is shorter than the holding time of the third stage sintering treatment.

3. The preparation method according to any one of claims 1 to 2, characterized in that The holding time of the sintering treatment is 1h-3h; and / or, The holding time of the second-stage sintering treatment is 3h-5h; and / or, The holding time of the three-stage sintering treatment is 6h-25h.

4. The preparation method according to any one of claims 1 to 3, characterized in that The heating rate of the first stage sintering process is less than or equal to the heating rate of the second stage sintering process, and the heating rate of the second stage sintering process is less than or equal to the heating rate of the third stage sintering process.

5. The preparation method according to any one of claims 1 to 4, characterized in that The heating rate of the first stage sintering treatment is 2°C / min-5°C / min; and / or, The heating rate of the second-stage sintering process is 2°C / min-5°C / min; and / or, The heating rate of the three-stage sintering process is 2°C / min-5°C / min.

6. The preparation method according to any one of claims 1 to 5, characterized in that The softening temperature of the solid organic carbon source is less than 300° C.; and / or, The solid organic carbon source has an initial weight loss temperature of 300° C. to 500° C.; and / or, The end weight loss temperature of the solid organic carbon source is 500°C-600°C.

7. The preparation method according to any one of claims 1 to 6, characterized in that The solid organic carbon source includes one or more of solid polyethylene glycol, polyvinyl alcohol, polyvinyl butyral, glucose, maltose, sucrose, tannic acid, citric acid, polyacrylonitrile, polytetrafluoroethylene, and polyvinylidene fluoride.

8. The preparation method according to any one of claims 1 to 7, characterized in that The volume distribution particle size Dv50 of the solid organic carbon source is less than or equal to 5 μm.

9. The preparation method according to any one of claims 1 to 8, characterized in that The obtained first mixed powder is pre-sintered and crushed under protective gas protection to obtain a lithium manganese iron phosphate precursor. The crushing process includes grinding and / or air flow crushing; and / or, The volume distribution particle size Dv50 of the obtained lithium manganese iron phosphate precursor is 0.5 μm-3 μm.

10. The preparation method according to any one of claims 1 to 9, characterized in that: The obtained second mixed powder is subjected to step-by-step sintering and crushing under protective gas protection to obtain carbon-coated lithium manganese iron phosphate. The volume distribution particle size Dv50 of the carbon-coated lithium manganese iron phosphate obtained by the step-by-step sintering treatment is 5 μm-10 μm; and / or, The equipment for the step-by-step sintering process is a rotary kiln; and / or, The crushing process includes grinding and / or air flow pulverization.

11. The preparation method according to any one of claims 1 to 10, characterized in that: The holding temperature of the pre-sintering treatment is 520° C.-680° C.; and / or, The holding time of the pre-sintering treatment is 6h-25h; and / or, The heating rate of the pre-sintering process is 2°C / min-5°C / min.

12. The preparation method according to any one of claims 1 to 11, characterized in that: The step of dry-mixing the lithium source, the manganese source, the iron source, and the phosphorus source to obtain a first mixed powder satisfies at least one of the following conditions (1) to (7): (1) The lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium acetate, and lithium oxide; (2) The manganese source includes one or more of manganese nitrate, manganese acetate, manganese phosphate, manganese oxalate, manganese carbonate, and ammonium manganese phosphate; (3) The iron source includes one or more of ferric nitrate, ferric phosphate, ferric acetate, ferrous oxalate, ferromanganese nitrate, ferromanganese oxalate, ferromanganese acetate, ferromanganese phosphate, ammonium ferromanganese phosphate, and ferrous carbonate; (4) The phosphorus source includes one or more of lithium phosphate, lithium dihydrogen phosphate, dilithium hydrogen phosphate, manganese hydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and manganese iron hydrogen phosphate; (5) The first mixed powder further includes one or more of a source of a doping element M, a source of a doping element N, a source of a doping element Q, and a source of a doping element R, where M represents a doping element for manganese and iron, N represents a doping element for lithium, Q represents a doping element for phosphorus, and R represents a doping element for oxygen; (6) Before dry mixing the lithium source, manganese source, iron source, and phosphorus source, the lithium source, manganese source, iron source, and phosphorus source are further ground; (7) The volume distribution particle size Dv50 of the obtained first mixed powder is 1 μm-5 μm.

13. A carbon-coated lithium manganese iron phosphate, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 12.

14. The carbon-coated lithium manganese iron phosphate according to claim 13, characterized in that The volume distribution particle size Dv50 of the carbon-coated lithium manganese iron phosphate is 0.5 μm-2 μm; and / or, The powder compaction density of the carbon-coated lithium manganese iron phosphate is 2.38 g / cm 3 -2.45g / cm 3 and / or, The carbon-coated lithium manganese iron phosphate has a gram capacity of 148 mAh / g to 152 mAh / g.

15. A positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector, characterized in that: The positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes a first carbon-coated lithium manganese iron phosphate, which is prepared by the preparation method according to any one of claims 1 to 12.

16. The positive electrode sheet according to claim 15, characterized in that: The volume distribution particle size Dv50 of the first carbon-coated lithium manganese iron phosphate is 0.5 μm-2 μm; and / or, The powder compaction density of the first carbon-coated lithium manganese iron phosphate is 2.38 g / cm 3 -2.45g / cm 3 and / or, The gram capacity of the first carbon-coated lithium manganese iron phosphate is 148 mAh / g-152 mAh / g.

17. The positive electrode sheet according to any one of claims 15 to 16, characterized in that: The positive electrode active material further includes a second carbon-coated lithium manganese iron phosphate, which is prepared by a liquid phase method. The volume distribution particle size Dv50 of the second carbon-coated lithium manganese iron phosphate is 10 μm-15 μm.

18. The positive electrode sheet according to claim 17, characterized in that: The mass ratio of the first carbon-coated lithium manganese iron phosphate to the second carbon-coated lithium manganese iron phosphate is 1:0.1 to 1:0.5; and / or, The powder compaction density of the positive electrode active material is greater than the powder compaction density of the first carbon-coated lithium manganese iron phosphate; and / or, The powder compaction density of the positive electrode active material is greater than the powder compaction density of the second carbon-coated lithium manganese iron phosphate; and / or, The powder compaction density of the positive electrode active material is 2.4 g / cm 3 -2.5g / cm 3 .

19. A battery, characterized in that: The positive electrode sheet comprises the positive electrode sheet according to any one of claims 15 to 18.

20. An electrical device, characterized in that: The battery according to claim 19 is used to provide electrical energy.

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