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 iron manganese phosphate, a preparation method thereof, a positive pole piece containing the carbon-coated lithium iron manganese phosphate, a battery containing the carbon-coated lithium iron manganese phosphate, and an electric device containing the carbon-coated lithium iron manganese phosphate. Lithium iron manganese phosphate slurry with the volume distribution particle size Dv50 of 100-150 nm and lithium iron manganese phosphate slurry with the volume distribution particle size Dv50 of 400-800 nm are mixed, and then spray granulation treatment, sintering treatment and crushing treatment are performed to obtain the carbon-coated lithium iron manganese phosphate. And the carbon-coated lithium manganese iron phosphate is obtained. The carbon-coated lithium manganese iron phosphate prepared by the preparation method provided by the invention can have high gram volume, high powder compaction density, low specific surface area and high cycle stability, and when the carbon-coated lithium manganese iron phosphate is applied to a positive pole piece and a battery, the battery can have high energy density and good cycle performance.

Description

Technical Field

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

[0002] In recent years, batteries have been widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. With the application and popularization of batteries, their safety performance has received more and more attention. Lithium iron manganese phosphate has become one of the most concerned positive active materials at present due to its advantages such as high capacity, good safety performance and rich raw material sources, and there is a trend to replace lithium iron phosphate. Although lithium iron manganese phosphate has a higher specific capacity per gram than lithium iron phosphate, there is still a large gap in the tap density between lithium iron manganese phosphate and lithium iron phosphate. As a result, the improvement effect of the volume energy density of lithium iron manganese phosphate is not obvious compared with that of lithium iron phosphate. Therefore, how to improve the tap density of lithium iron manganese phosphate is an urgent problem to be solved at present. The above statements are only used to provide background technical information related to the present application, and do not necessarily constitute prior art. Summary of the Invention

[0003] The present application provides a carbon-coated lithium iron manganese phosphate, a preparation method thereof, a positive electrode sheet, a battery and an electrical device comprising the same. The carbon-coated lithium iron manganese phosphate has both high specific capacity, high powder tap density, low specific surface area and high cycle stability, and can also endow the battery with both high energy density and good cycle performance.

[0004] In a first aspect, the present application provides a method for preparing carbon-coated lithium iron manganese phosphate, comprising the following steps: uniformly stirring a lithium source, an iron source, a manganese source, a phosphorus source, and water to obtain a first slurry; subjecting the obtained first slurry to grinding treatment, spray granulation treatment, and pre-sintering treatment to obtain a first lithium iron manganese phosphate; uniformly stirring a lithium source, an iron source, a manganese source, a phosphorus source, and water to obtain a second slurry; subjecting the obtained second slurry to grinding treatment, spray granulation treatment, and pre-sintering treatment to obtain a second lithium iron manganese phosphate, wherein the molar ratio of Mn element to Fe element in the first slurry is equal to the molar ratio of Mn element to Fe element in the second slurry; uniformly stirring the obtained first lithium iron manganese phosphate with an organic carbon source and water, and grinding to obtain a third slurry, wherein the volume distribution particle size Dv50 of the third slurry is 100 nm - 150 nm; uniformly stirring the obtained second lithium iron manganese phosphate with an organic carbon source and water, and grinding to obtain a fourth slurry, wherein the volume distribution particle size Dv50 of the fourth slurry is 400 nm - 800 nm; mixing the third slurry and the fourth slurry in a predetermined ratio to obtain a fifth slurry; subjecting the obtained fifth slurry to spray granulation treatment, sintering treatment, and crushing treatment to obtain carbon-coated lithium iron manganese phosphate.

[0005] The carbon-coated lithium iron manganese phosphate prepared by the preparation method provided by the embodiments of the present application can have both high specific capacity, high powder tap density, low specific surface area, and high cycle stability. When applied to a positive electrode sheet and a battery, the battery can have both high energy density and good cycle performance.

[0006] In some embodiments, the volume distribution particle size Dv50 of the third slurry is 100 nm - 125 nm.

[0007] In some embodiments, the volume distribution particle size Dv50 of the fourth slurry is 500 nm - 650 nm.

[0008] In some embodiments, the ratio of the volume distribution particle size Dv50 of the third slurry to the volume distribution particle size Dv50 of the fourth slurry is 1:3.5 - 1:8.0, and can be optionally 1:4.2 - 1:6.5.

[0009] When the ratio of the volume distribution particle size Dv50 of the third slurry to the volume distribution particle size Dv50 of the fourth slurry is within the above range, the carbon-coated lithium iron manganese phosphate can have a higher powder tap density.

[0010] In some embodiments, in the obtained fifth slurry, the mass ratio of the first lithium iron manganese phosphate to the second lithium iron manganese phosphate is 90:10 - 50:50, and can be optionally 80:20 - 60:40.

[0011] By further adjusting the mass ratio of the first lithium iron manganese phosphate to the second lithium iron manganese phosphate within the above range, the carbon-coated lithium iron manganese phosphate can better have both high specific capacity, high powder tap density, and low specific surface area.

[0012] In some embodiments, the ratio of the molar amount of P element in the first slurry to the sum of the molar amounts of Mn element and Fe element is less than the ratio of the molar amount of P element in the second slurry to the sum of the molar amounts of Mn element and Fe element.

[0013] The preparation method provided by the embodiments of the present application creates certain vacancy defects by adjusting the ratio of the molar amount of P element in the slurry to the sum of the molar amounts of Mn element and Fe element, thereby changing the unit cell structure of lithium iron manganese phosphate, and further obtaining two kinds of lithium iron manganese phosphate particles with inconsistent primary particle sizes, that is, the sizes of the primary particles agglomerated to form the first lithium iron manganese phosphate and the second lithium iron manganese phosphate are inconsistent. This method has a simple preparation process, low energy consumption, and the sizes of the primary particles in the first lithium iron manganese phosphate and the second lithium iron manganese phosphate are easier to adjust.

[0014] In some embodiments, the ratio of the molar amount of P element in the first slurry to the sum of the molar amounts of Mn element and Fe element is (1 - 1.02):1, and can be optionally (1.012 - 1.018):1.

[0015] In some embodiments, the ratio of the molar amount of P element in the second slurry to the sum of the molar amounts of Mn element and Fe element is (1.04 - 1.06):1, and can be optionally (1.042 - 1.052):1.

[0016] In some embodiments, the ratio of the molar amount of Mn element to the molar amount of Fe element in the first slurry is 4:6 - 8:2, and can be optionally 5.5:4.5 - 6.5:3.5.

[0017] In some embodiments, the ratio of the molar amount of Mn element to the molar amount of Fe element in the second slurry is 4:6 - 8:2, and can be optionally 5.5:4.5 - 6.5:3.5.

[0018] In some embodiments, the volume - based median diameter Dv50 of the carbon - coated lithium iron manganese phosphate obtained after spray granulation treatment and sintering treatment of the obtained fifth slurry is 5 μm - 10 μm.

[0019] In some embodiments, the carbon-coated lithium iron manganese phosphate obtained after spray granulation treatment and sintering treatment of the obtained fifth slurry is a secondary particle formed by agglomeration of primary particles of small particles and primary particles of large particles, and the number of primary particles of small particles is greater than the number of primary particles of large particles. The volume distribution particle size Dv50 of the primary particles of small particles is 100 nm - 200 nm, and the volume distribution particle size Dv50 of the primary particles of large particles is 400 nm - 800 nm.

[0020] In some embodiments, after the obtained fifth slurry is subjected to spray granulation treatment, sintering treatment and crushing treatment, the volume distribution particle size Dv50 of the carbon-coated lithium iron manganese phosphate is 500 nm - 1000 nm, and may be 500 nm - 900 nm.

[0021] In some embodiments, after the obtained fifth slurry is subjected to spray granulation treatment, sintering treatment and crushing treatment, the powder tap density of the carbon-coated lithium iron manganese phosphate is 2.23 g / cm 3 - 2.41 g / cm 3 and may be 2.32 g / cm 3 - 2.41 g / cm 3 .

[0022] In some embodiments, in the steps of subjecting the obtained fifth slurry to spray granulation treatment, sintering treatment and crushing treatment, the inlet temperature of the spray granulation treatment is 100°C - 280°C, and the outlet temperature is 50°C - 180°C.

[0023] In some embodiments, in the steps of subjecting the obtained fifth slurry to spray granulation treatment, sintering treatment and crushing treatment, the holding temperature of the sintering treatment is 700°C - 800°C.

[0024] In some embodiments, in the steps of subjecting the obtained fifth slurry to spray granulation treatment, sintering treatment and crushing treatment, the holding time of the sintering treatment is 8 h - 16 h.

[0025] In some embodiments, in the steps of subjecting the obtained fifth slurry to spray granulation treatment, sintering treatment and crushing treatment, the atmosphere of the sintering treatment includes one or more of nitrogen, argon, and helium.

[0026] In some embodiments, in the steps of subjecting the obtained first slurry to grinding treatment, spray granulation treatment and pre-sintering treatment, the volume distribution particle size Dv50 of the first slurry after the grinding treatment is 300 nm - 1000 nm.

[0027] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained first slurry, the inlet temperature of the spray granulating is 100°C - 280°C, and the outlet temperature is 50°C - 180°C.

[0028] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained first slurry, the holding temperature of the pre-sintering is 600°C - 650°C.

[0029] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained first slurry, the holding time of the pre-sintering is 4h - 10h.

[0030] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained first slurry, the atmosphere of the pre-sintering includes one or more of nitrogen, argon, and helium.

[0031] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained first slurry, the volume distribution particle size Dv50 of the obtained first lithium iron manganese phosphate is 3μm - 8μm.

[0032] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained second slurry, the volume distribution particle size Dv50 of the second slurry after grinding is 300nm - 1000nm.

[0033] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained second slurry, the inlet temperature of the spray granulating is 100°C - 280°C, and the outlet temperature is 50°C - 180°C.

[0034] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained second slurry, the holding temperature of the pre-sintering is 600°C - 650°C.

[0035] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained second slurry, the holding time of the pre-sintering is 4h - 10h.

[0036] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained second slurry, the atmosphere of the pre-sintering includes one or more of nitrogen, argon, and helium.

[0037] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained second slurry, the volume-based median diameter Dv50 of the second lithium iron manganese phosphate obtained after the pre-sintering is 3 μm - 8 μm.

[0038] In some embodiments, the lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium acetate, lithium oxalate, lithium citrate, lithium dihydrogen phosphate, and lithium phosphate.

[0039] In some embodiments, the iron source includes one or more of ferrous oxalate, ferrous acetate, ferrous carbonate, iron phosphate, and iron hydrogen phosphate.

[0040] 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.

[0041] In some embodiments, the phosphorus source is one or more of lithium phosphate, lithium dihydrogen phosphate, disodium hydrogen phosphate, manganese hydrogen phosphate, diammonium phosphate, dibasic ammonium phosphate, and iron manganese hydrogen phosphate.

[0042] In some embodiments, the organic carbon source includes one or more of glucose, sucrose, maltose, citric acid, hydroxypropyl-β-cyclodextrin, ethylene glycol, polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polyvinylidene fluoride, polytetrafluoroethylene, polystyrene, and polypropylene.

[0043] In some embodiments, the first slurry further includes one or more of a source of metal doping element M and a source of non-metal doping element N.

[0044] In some embodiments, the second slurry further includes one or more of a source of metal doping element M and a source of non-metal doping element N.

[0045] In a second aspect, the present application provides a carbon-coated lithium iron manganese phosphate, which is prepared by the preparation method of the first aspect of the present application.

[0046] In a third aspect, the present application provides a positive electrode sheet, including a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector, where the positive electrode film layer includes the carbon-coated lithium iron manganese phosphate prepared by the preparation method of the first aspect of the present application or the carbon-coated lithium iron manganese phosphate of the second aspect of the present application.

[0047] In a fourth aspect, the present application provides a battery, including the positive electrode sheet of the third aspect of the present application.

[0048] In a fifth aspect, the present application provides an electrical device, including the battery of the fourth aspect of the present application, where the battery is used to provide electrical energy.

[0049] The electrical device of the present application includes the battery provided by the present application, and thus has at least the same advantages as the battery. Description of the Drawings

[0050] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the drawings.

[0051] Figure 1 It is a schematic diagram of a battery cell provided by some embodiments of the present application.

[0052] Figure 2 It is a schematic diagram of a battery module provided by some embodiments of the present application.

[0053] Figure 3 It is a schematic diagram of a battery pack provided by some embodiments of the present application.

[0054] Figure 4 is Figure 3 An exploded schematic diagram of the battery pack shown.

[0055] Figure 5 It is an exploded schematic diagram of a battery cell provided by some embodiments of the present application.

[0056] Figure 6 It is a schematic diagram of an electrical device provided by some embodiments of the present application.

[0057] Figure 7 Shows a scanning electron microscope (SEM) image of the first lithium iron manganese phosphate prepared in Example 1.

[0058] Figure 8 Shows a scanning electron microscope (SEM) image of the second lithium iron manganese phosphate prepared in Example 1.

[0059] In the drawings, the drawings are not necessarily drawn to actual scale.

[0060] The description of the reference numerals is as follows: 1. Battery pack; 2. Upper box body; 3. Lower box body; 4. Battery module; 5. Battery cell; 51. Shell; 52. Electrode assembly; 53. Cover plate. Detailed Embodiments

[0061] Hereinafter, embodiments of the lithium iron manganese phosphate coated with carbon, a method for preparing the same, a positive electrode sheet, a battery, and an electrical device including the same, which specifically disclose the present application, will be described in detail with reference to the accompanying drawings as appropriate. However, there may be cases where unnecessary details are omitted. For example, there may be cases where details of well-known matters are omitted and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying 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 recited in the claims.

[0062] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The range defined in this way may or may not include the end values and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present application, unless otherwise stated, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" represents that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when it is stated that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0063] If there is no special instruction, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution, and such a technical solution should be considered to be included in the disclosure of the present application.

[0064] If there is no special instruction, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution, and such a technical solution should be considered to be included in the disclosure of the present application.

[0065] Unless otherwise specified, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method can include steps (a) and (b) carried out sequentially, or steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0066] In this application, the terms "a plurality of" and "multiple types" refer to two or more than two.

[0067] Unless otherwise specified, the terms used in this application have the well-known meanings commonly understood by those skilled in the art.

[0068] Unless otherwise specified, the numerical values of the various parameters mentioned in this application can be measured by various commonly used testing methods in the art. For example, they can be measured according to the testing methods given in the embodiments of this application. Unless otherwise specified, the test temperature for each parameter is 25 °C.

[0069] The battery mentioned in the embodiments of this application can be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application can include battery cells, battery modules, battery packs, etc.

[0070] A battery cell is the smallest unit that makes up a battery and can independently perform the functions of charging and discharging. The battery cell can be in the shape of a cylinder, a cuboid or other shapes, etc., and the embodiments of this application do not limit this. For example, Figure 1 is a battery cell 5 in the shape of a cuboid as an example.

[0071] When there are multiple battery cells, the multiple battery cells are connected in series, parallel or in a hybrid connection through a busbar component. In some embodiments, the battery can 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 can be a battery pack, and the battery pack includes a box body and battery cells, and the battery cells or battery modules are accommodated in the box body. In some embodiments, the box body can be part of the chassis structure of a vehicle. For example, part of the box body can become at least part of the vehicle floor, or part of the box body can become at least part of the cross beams and longitudinal beams of the vehicle.

[0072] In some embodiments, the battery can be an energy storage device. The energy storage device includes an energy storage container, an energy storage cabinet, etc.

[0073] In some embodiments, battery cells can be assembled into a battery module. The number of battery cells included in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. Figure 2 is a schematic diagram of a battery module 4 as an example. As Figure 2 shown, in the battery module 4, a 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.

[0074] Optionally, the battery module 4 can further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0075] In some embodiments, the above battery module can be further assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0076] Figure 3 and Figure 4 are schematic diagrams of a battery pack 1 as an example. As Figure 3 and Figure 4 shown, the battery pack 1 can include a box body and a plurality of battery modules 4 arranged in the box body. The box body includes an upper box body 2 and a lower box body 3. The upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the box body in any manner.

[0077] The battery cells provided in the embodiments of the present application can include lithium-ion battery cells, lithium metal battery cells, lithium metal battery cells without a negative electrode, etc.

[0078] The battery cell includes an electrode assembly and an electrolyte. The electrode assembly can be a wound structure or a stacked structure, and the embodiments of the present application do not limit this.

[0079] The battery cell can further include an outer package, and the outer package can be used to encapsulate the electrode assembly and the electrolyte. The outer package can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0080] In some embodiments, as Figure 5As shown, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to 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 to close the receiving cavity. The electrode assembly 52 is encapsulated in the receiving cavity. The number of electrode assemblies 52 included in the battery cell 5 may be one or more, which can be adjusted according to requirements.

[0081] In view of the technical problems mentioned in the background art, the embodiments of the present application provide a method for preparing carbon-coated lithium iron manganese phosphate. The carbon-coated lithium iron manganese phosphate prepared by this method can have both high specific capacity, high powder tap density, low specific surface area and high cycle stability. When applied to the positive electrode sheet and the battery, the battery can have both high energy density and good cycle performance.

[0082] The method for preparing carbon-coated lithium iron manganese phosphate provided by the embodiments of the present application includes the following steps: uniformly stirring a lithium source, an iron source, a manganese source, a phosphorus source and water to obtain a first slurry, and performing grinding treatment, spray granulation treatment and pre-sintering treatment on the obtained first slurry to obtain a first lithium iron manganese phosphate; uniformly stirring a lithium source, an iron source, a manganese source, a phosphorus source and water to obtain a second slurry, and performing grinding treatment, spray granulation treatment and pre-sintering treatment on the obtained second slurry to obtain a second lithium iron manganese phosphate, wherein the molar ratio of the Mn element to the Fe element in the first slurry is equal to the molar ratio of the Mn element to the Fe element in the second slurry; uniformly stirring the obtained first lithium iron manganese phosphate with an organic carbon source and water, and grinding to obtain a third slurry, wherein the volume distribution particle size Dv50 of the third slurry is 100 nm - 150 nm; uniformly stirring the obtained second lithium iron manganese phosphate with an organic carbon source and water, and grinding to obtain a fourth slurry, wherein the volume distribution particle size Dv50 of the fourth slurry is 400 nm - 800 nm; mixing the third slurry and the fourth slurry according to a predetermined ratio to obtain a fifth slurry, and performing spray granulation treatment, sintering treatment and crushing treatment on the obtained fifth slurry to obtain carbon-coated lithium iron manganese phosphate.

[0083] The ionic conductivity of lithium iron manganese phosphate is poor. In order to improve the ionic conductivity of lithium iron manganese phosphate, the commonly used means is to make the particles nano-sized. Particle nano-sizing can improve the specific capacity of lithium iron manganese phosphate. However, after nano-sizing, the size of the primary particles of lithium iron manganese phosphate becomes smaller, the powder tap density of lithium iron manganese phosphate becomes smaller, and the specific surface area becomes larger. As a result, the processing performance of lithium iron manganese phosphate becomes poor, and the slurry mixing and coating processes cannot be carried out normally, and the tap density of the prepared positive electrode sheet is also small. When the size of the primary particles of lithium iron manganese phosphate is large, the specific surface area of lithium iron manganese phosphate is small, the powder tap density is high, but the specific capacity is low.

[0084] The preparation method provided by the embodiments of the present application prepares the finished product of carbon-coated lithium iron manganese phosphate by sintering two kinds of primary particles of lithium iron manganese phosphate with different sizes together through a carbon coating process and then through a crushing treatment. Thus, the carbon-coated lithium iron manganese phosphate can have a high specific capacity, and at the same time, the carbon-coated lithium iron manganese phosphate can have a high powder tap density and a low specific surface area.

[0085] In the preparation method provided by the embodiments of the present application, both the first lithium iron manganese phosphate and the second lithium iron manganese phosphate obtained by the pre-sintering treatment are secondary particles formed by the aggregation of primary particles. Grinding the first lithium iron manganese phosphate obtained by the pre-sintering treatment together with the organic carbon source and water can de-aggregate the first lithium iron manganese phosphate to form primary particles of lithium iron manganese phosphate, and can also uniformly coat the organic carbon source on the surface of the primary particles of lithium iron manganese phosphate. Thus, the obtained carbon-coated lithium iron manganese phosphate can have good electronic conductivity and a lower specific surface area. Grinding the second lithium iron manganese phosphate obtained by the pre-sintering treatment together with the organic carbon source and water can de-aggregate the second lithium iron manganese phosphate to form primary particles of lithium iron manganese phosphate, and can also uniformly coat the organic carbon source on the surface of the primary particles of lithium iron manganese phosphate. Thus, the obtained carbon-coated lithium iron manganese phosphate can have good electronic conductivity and a lower specific surface area. In addition, after grinding, the organic carbon source is dispersed on the surface of the primary particles of lithium iron manganese phosphate with a volume distribution particle size Dv50 of 100 nm - 150 nm in the third slurry and on the surface of the primary particles of lithium iron manganese phosphate with a volume distribution particle size Dv50 of 400 nm - 800 nm in the fourth slurry. During the mixing, spray granulation and sintering of the third slurry and the fourth slurry, the above-mentioned primary particles of lithium iron manganese phosphate with different sizes can be better adsorbed together through electrostatic adsorption, so that the primary particles of lithium iron manganese phosphate with smaller particle sizes can better fill between the primary particles of lithium iron manganese phosphate with larger particle sizes during the sintering process, which further helps to improve the powder tap density of the finally prepared carbon-coated lithium iron manganese phosphate.

[0086] The third slurry after grinding includes primary particles of lithium iron manganese phosphate with a volume distribution particle size Dv50 of 100 nm - 150 nm, and the fourth slurry after grinding includes primary particles of lithium iron manganese phosphate with a volume distribution particle size Dv50 of 400 nm - 800 nm. The primary particles of lithium iron manganese phosphate with a volume distribution particle size Dv50 of 100 nm - 150 nm can make the prepared carbon-coated lithium iron manganese phosphate have a high specific capacity, and it can also fill between the primary particles of lithium iron manganese phosphate with a volume distribution particle size Dv50 of 400 nm - 800 nm during the sintering process. Thus, the gap between the primary particles can also be reduced, so that the carbon-coated lithium iron manganese phosphate can have both a high specific capacity, a high powder tap density and a low specific surface area.

[0087] In the preparation method provided by the embodiments of the present application, the ratio of the molar amount of Mn element to the molar amount of Fe element in the first slurry is equal to the ratio of the molar amount of Mn element to the molar amount of Fe element in the second slurry. Thus, the ratio of the molar amount of Mn element to the molar amount of Fe element in the first lithium iron manganese phosphate and the second lithium iron manganese phosphate is equal. At this time, the voltage platforms of the first lithium iron manganese phosphate and the second lithium iron manganese phosphate are close, and further, the carbon-coated lithium iron manganese phosphate and the battery can have more stable cycling performance.

[0088] Therefore, the carbon-coated lithium iron manganese phosphate prepared by the preparation method provided by the embodiments of the present application can have both high specific capacity, high powder tap density, low specific surface area and high cycling stability. When applied to the positive electrode sheet and the battery, the battery can have both high energy density and good cycling performance.

[0089] The volume distribution particle size Dv50 of the third slurry is 100 nm - 150 nm. For example, it can be 100 nm, 105 nm, 110 nm, 115 nm, 120 nm, 125 nm, 130 nm, 135 nm, 140 nm, 145 nm, 150 nm, or a range composed of any of the above values. Optionally, the volume distribution particle size Dv50 of the third slurry can be 100 nm - 125 nm.

[0090] The volume distribution particle size Dv50 of the fourth slurry is 400 nm - 800 nm. For example, it can be 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, or a range composed of any of the above values. Optionally, the volume distribution particle size Dv50 of the fourth slurry can be 500 nm - 650 nm.

[0091] Optionally, the ratio of the volume distribution particle size Dv50 of the third slurry to the volume distribution particle size Dv50 of the fourth slurry can be 1:3.5 - 1:8.0. It can be 1:3.5, 1:3.8, 1:4.0, 1:4.2, 1:4.4, 1:4.6, 1:4.8, 1:5.0, 1:5.2, 1:5.4, 1:5.6, 1:5.8, 1:6.0, 1:6.2, 1:6.5, 1:7.0, 1:7.5, 1:8.0, or a range composed of any of the above values.

[0092] When the ratio of the volume distribution particle size Dv50 of the third slurry to the volume distribution particle size Dv50 of the fourth slurry is within the above range, the carbon-coated lithium iron manganese phosphate can have a higher powder tap density.

[0093] More optionally, the ratio of the volume distribution particle size Dv50 of the third slurry to the volume distribution particle size Dv50 of the fourth slurry can be 1:4.2 - 1:6.5.

[0094] In some embodiments, the solid content of the third slurry may be 40%-50%, and the solid content of the fourth slurry may be 40%-50%.

[0095] In some embodiments, in the obtained fifth slurry, the mass ratio of the first lithium iron manganese phosphate to the second lithium iron manganese phosphate may be 90:10-50:50, and may be optionally 80:20-60:40. That is, the mass ratio of the primary particles of lithium iron manganese phosphate with a volume distribution diameter Dv50 of 100 nm-150 nm to the primary particles of lithium iron manganese phosphate with a volume distribution diameter Dv50 of 400 nm-800 nm may be 90:10-50:50, and may be optionally 80:20-60:40.

[0096] A high content of the first lithium iron manganese phosphate (primary particles of lithium iron manganese phosphate with a volume distribution diameter Dv50 of 100 nm-150 nm) can make the carbon-coated lithium iron manganese phosphate have a higher specific capacity per gram.

[0097] A high content of the second lithium iron manganese phosphate (primary particles of lithium iron manganese phosphate with a volume distribution diameter Dv50 of 400 nm-800 nm) can make the carbon-coated lithium iron manganese phosphate have a higher powder compaction density and a lower specific surface area.

[0098] By further adjusting the mass ratio of the first lithium iron manganese phosphate to the second lithium iron manganese phosphate within the above range, the carbon-coated lithium iron manganese phosphate can better have both a high specific capacity per gram, a high powder compaction density and a low specific surface area.

[0099] In some embodiments, in the steps of subjecting the obtained fifth slurry to spray granulation treatment, sintering treatment and crushing treatment, the inlet temperature of the spray granulation treatment may be 100°C-280°C, and the outlet temperature may be 50°C-180°C.

[0100] In some embodiments, in the steps of subjecting the obtained fifth slurry to spray granulation treatment, sintering treatment and crushing treatment, the holding temperature of the sintering treatment may be 700°C-800°C. Optionally, the heating rate of the sintering treatment may be 1°C / min-8°C / min.

[0101] In some embodiments, in the steps of subjecting the obtained fifth slurry to spray granulation treatment, sintering treatment and crushing treatment, the holding time of the sintering treatment may be 8 h-16 h.

[0102] In some embodiments, in the steps of subjecting the obtained fifth slurry to spray granulation treatment, sintering treatment and crushing treatment, the atmosphere of the sintering treatment may include one or more of nitrogen, argon, and helium.

[0103] In some embodiments, in the steps of subjecting the obtained fifth slurry to spray granulation, sintering, and crushing, the crushing may be air flow milling.

[0104] In some embodiments, the volume distribution particle size Dv50 of the carbon-coated lithium manganese iron phosphate obtained after the obtained fifth slurry is subjected to spray granulation treatment and sintering treatment is 5μm-10μm. That is, the volume distribution particle size Dv50 of the carbon-coated lithium manganese iron phosphate that has not been crushed is 5μm-10μm. The carbon-coated lithium manganese iron phosphate that has not been crushed is a secondary particle formed by the agglomeration of small primary particles and large primary particles. The volume distribution particle size Dv50 of the small primary particles is 100nm-200nm, and the volume distribution particle size Dv50 of the large primary particles is 400nm-800nm. The lithium manganese iron phosphate primary particles with a volume distribution particle size Dv50 of 100nm-150nm have a large specific surface area, and their particle size may increase during the sintering process.

[0105] Optionally, the number of primary particles of the small particles is greater than the number of primary particles of the large particles.

[0106] In some embodiments, the volume distribution particle size Dv50 of the carbon-coated lithium manganese iron phosphate obtained after the obtained fifth slurry is subjected to spray granulation, sintering, and crushing can be 500 nm to 1000 nm. That is, after the crushing, the volume distribution particle size Dv50 of the carbon-coated lithium manganese iron phosphate is 500 nm to 1000 nm.

[0107] Optionally, the volume distribution particle size Dv50 of the carbon-coated lithium manganese iron phosphate obtained after the obtained fifth slurry is subjected to spray granulation treatment, sintering treatment and crushing treatment can be 500nm-900nm.

[0108] In some embodiments, the obtained fifth slurry is subjected to spray granulation, sintering and crushing to obtain a carbon-coated lithium manganese iron phosphate powder with a compaction density of 2.23 g / cm 3 -2.41g / cm 3 That is, after crushing, the compaction density of carbon-coated lithium manganese iron phosphate powder can be 2.23g / cm 3 -2.41g / cm 3 .

[0109] Optionally, the obtained fifth slurry is subjected to spray granulation, sintering and crushing to obtain a carbon-coated lithium manganese iron phosphate powder with a compaction density of 2.32 g / cm 3 -2.41g / cm 3 .

[0110] In some embodiments, the ratio of the molar amount of Mn element to the molar amount of Fe element in the first slurry may be 4:6 - 8:2. For example, it may be 4:6, 4.5:5.5, 5:5, 5.5:4.5, 6:4, 6.5:3.5, 7:3, 7.5:2.5, 8:2, or a range composed of any of the above values. Optionally, the ratio of the molar amount of Mn element to the molar amount of Fe element in the first slurry may be 5.5:4.5 - 6.5:3.5.

[0111] In some embodiments, the ratio of the molar amount of Mn element to the molar amount of Fe element in the second slurry may be 4:6 - 8:2. For example, it may be 4:6, 4.5:5.5, 5:5, 5.5:4.5, 6:4, 6.5:3.5, 7:3, 7.5:2.5, 8:2, or a range composed of any of the above values. Optionally, the ratio of the molar amount of Mn element to the molar amount of Fe element in the second slurry may be 5.5:4.5 - 6.5:3.5.

[0112] In some embodiments, the ratio of the molar amount of P element to the sum of the molar amounts of Mn element and Fe element in the first slurry is less than the ratio of the molar amount of P element to the sum of the molar amounts of Mn element and Fe element in the second slurry.

[0113] When the ratio of the molar amount of P element to the sum of the molar amounts of Mn element and Fe element in the slurry is small, the size of the primary particles in the prepared lithium iron manganese phosphate is small. When the ratio of the molar amount of P element to the sum of the molar amounts of Mn element and Fe element in the slurry is large, the size of the primary particles in the prepared lithium iron manganese phosphate is large.

[0114] The preparation method provided by the embodiments of the present application creates certain vacancy defects by adjusting the ratio of the molar amount of P element to the sum of the molar amounts of Mn element and Fe element in the slurry, thereby changing the crystal cell structure of lithium iron manganese phosphate, and then obtaining two kinds of lithium iron manganese phosphate particles with inconsistent primary particle sizes, that is, the sizes of the primary particles that agglomerate to form the first lithium iron manganese phosphate and the second lithium iron manganese phosphate are inconsistent. This method has a simple preparation process, low energy consumption, and the sizes of the primary particles in the first lithium iron manganese phosphate and the second lithium iron manganese phosphate are easier to adjust.

[0115] Optionally, the ratio of the molar amount of P element in the first slurry to the sum of the molar amounts of Mn element and Fe element can be (1 - 1.02):1. For example, it can be 1:1, 1.002:1, 1.004:1, 1.006:1, 1.008:1, 1.01:1, 1.012:1, 1.014:1, 1.016:1, 1.018:1, 1.02:1, or the range composed of any of the above values. Optionally, the ratio of the molar amount of P element in the first slurry to the sum of the molar amounts of Mn element and Fe element can be (1.012 - 1.018):1.

[0116] Optionally, the ratio of the molar amount of P element in the second slurry to the sum of the molar amounts of Mn element and Fe element can be (1.04 - 1.06):1. For example, it can be 1.04:1, 1.042:1, 1.044:1, 1.046:1, 1.048:1, 1.05:1, 1.052:1, 1.054:1, 1.056:1, 1.058:1, 1.06:1, or the range composed of any of the above values. Optionally, the ratio of the molar amount of P element in the second slurry to the sum of the molar amounts of Mn element and Fe element can be (1.042 - 1.052):1.

[0117] The lithium source can 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 can include, but is not limited to, one or more of lithium carbonate, lithium hydroxide, lithium acetate, lithium oxalate, lithium citrate, lithium dihydrogen phosphate, and lithium phosphate.

[0118] The iron source can be an iron-containing compound known in the art that can be used to prepare lithium iron manganese phosphate. In some embodiments, the iron source can include, but is not limited to, one or more of ferrous oxalate, ferrous acetate, ferrous carbonate, iron phosphate, and iron hydrogen phosphate. These substances can have crystal water or no crystal water.

[0119] The manganese source can be a manganese-containing compound known in the art that can be used to prepare lithium iron manganese phosphate. In some embodiments, the manganese source can include, but is not limited to, one or more of manganese nitrate, manganese acetate, manganese phosphate, manganese oxalate, manganese carbonate, and ammonium manganese phosphate. These substances can have crystal water or no crystal water.

[0120] The phosphorus source can be a phosphorus-containing compound known in the art that can be used to prepare lithium iron manganese phosphate. In some embodiments, the phosphorus source can include, but is not limited to, one or more of lithium phosphate, lithium dihydrogen phosphate, disodium hydrogen phosphate, manganese hydrogen phosphate, diammonium phosphate, diammonium hydrogen phosphate, and iron manganese hydrogen phosphate. These substances can have crystal water or no crystal water.

[0121] In some embodiments, the organic carbon source may include, but is not limited to, one or more of glucose, sucrose, maltose, citric acid, hydroxypropyl-β-cyclodextrin, ethylene glycol, polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polyvinylidene fluoride, polytetrafluoroethylene, polystyrene, and polypropylene.

[0122] In some embodiments, the first slurry may further include one or more of a source of metal doping element M and a source of non-metal doping element N.

[0123] In some embodiments, the second slurry may further include one or more of a source of metal doping element M and a source of non-metal doping element N.

[0124] The source of metal doping element M may include, but is not limited to, one or more of oxalates, acetates, carbonates, phosphates, hydrochlorides, nitrates, sulfates, oxides, and hydroxides of metal doping element M. These substances may or may not carry crystal water.

[0125] Optionally, the metal doping element M may include, but is not limited to, one or more of Ti, V, Cr, Cu, Mg, Al, Zn, Co, Ni, Sn, Nb, W, Zr, Ta, Ce, and Eu.

[0126] Optionally, the non-metal doping element N may include, but is not limited to, one or more of F, Cl, Br, B, S, Si, and N.

[0127] The metal doping element M and the non-metal doping element N may be doped at least at one of the lithium site, manganese site, iron site, phosphorus site, and oxygen site.

[0128] In some embodiments, the solid content of the first slurry may be 20%-45%. When providing the first slurry, there is no particular limitation on the addition order of each raw material, and they may be added simultaneously or in batches.

[0129] In some embodiments, in the steps of grinding, spray granulation, and pre-sintering the obtained first slurry, the volume distribution particle size Dv50 of the first slurry after grinding may be 300 nm - 1000 nm. Optionally, the grinding may be performed in a planetary ball mill.

[0130] In some embodiments, in the steps of grinding, spray granulation, and pre-sintering the obtained first slurry, the inlet temperature of the spray granulation may be 100°C - 280°C, and the outlet temperature may be 5°C - 180°C.

[0131] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained first slurry, the holding temperature of the pre-sintering treatment can be 600°C - 650°C. Optionally, the heating rate of the pre-sintering treatment can be 1°C / min - 8°C / min.

[0132] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained first slurry, the holding time of the pre-sintering treatment can be 4h - 10h.

[0133] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained first slurry, the atmosphere of the pre-sintering treatment can include one or more of nitrogen, argon, and helium.

[0134] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained first slurry, the volume distribution particle size Dv50 of the first lithium iron manganese phosphate obtained after the pre-sintering treatment is 3μm - 8μm. The first lithium iron manganese phosphate obtained by the pre-sintering treatment is secondary particles formed by the agglomeration of primary particles. The average particle size of the primary particles is 100nm - 150nm, and the volume distribution particle size Dv50 of the secondary particles is 3μm - 8μm.

[0135] In some embodiments, the solid content of the second slurry can be 20% - 45%. When providing the first slurry, there is no particular limitation on the addition order of each raw material. They can be added simultaneously or in batches.

[0136] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained second slurry, the volume distribution particle size Dv50 of the second slurry after the grinding treatment can be 300nm - 1000nm. Optionally, the grinding treatment can be carried out in a planetary ball mill.

[0137] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained second slurry, the inlet temperature of the spray granulating treatment can be 100°C - 280°C, and the outlet temperature can be 50°C - 180°C.

[0138] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained second slurry, the holding temperature of the pre-sintering treatment can be 600°C - 650°C. Optionally, the heating rate of the pre-sintering treatment can be 1°C / min - 8°C / min.

[0139] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained second slurry, the holding time of the pre-sintering treatment can be 4h - 10h.

[0140] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained second slurry, the atmosphere for the pre-sintering treatment may include one or more of nitrogen, argon, and helium.

[0141] In some embodiments, in the steps of grinding, spray granulating, and pre-sintering the obtained second slurry, the volume distribution particle size Dv50 of the obtained lithium iron manganese phosphate after the pre-sintering treatment is 3 μm - 8 μm. The lithium iron manganese phosphate obtained by the pre-sintering treatment is secondary particles formed by the aggregation of primary particles. The average particle size of the primary particles is 400 nm - 800 nm, and the volume distribution particle size Dv50 of the secondary particles is 3 μm - 8 μm.

[0142] In the above preparation method, if there is no special indication, each raw material can be directly purchased.

[0143] The embodiments of the present application also provide a carbon-coated lithium iron manganese phosphate prepared by the above preparation method, which can have both high specific capacity, high powder tap density, low specific surface area, and high cycle stability.

[0144] The carbon-coated lithium iron manganese phosphate provided by the embodiments of the present application can be used in the positive electrode sheet and the battery cell, and can endow the battery cell with both high energy density and good cycle performance.

[0145] The battery cell includes an electrode assembly and an electrolyte, and the electrode assembly includes a positive electrode sheet and a negative electrode sheet.

[0146] [Positive Electrode Sheet]

[0147] In some embodiments, the positive electrode sheet 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 the carbon-coated lithium iron manganese phosphate prepared by the preparation method provided by the embodiments of the present application or the carbon-coated lithium iron manganese phosphate provided by the embodiments of the present application.

[0148] In some embodiments, the mass content of the above carbon-coated lithium iron manganese phosphate in the positive electrode film layer can be 50% - 99.5%, optionally 90% - 99.5%, 95% - 99.5%, based on the total mass of the positive electrode film layer.

[0149] In some embodiments, the positive electrode film layer may further include other positive electrode active materials, for example, it may further include lithium transition metal oxides. Examples of lithium transition metal oxides may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. The modified compounds of the above positive electrode active materials may be doping modification and / or surface coating modification of the positive electrode active materials.

[0150] In some embodiments, the positive electrode film layer may further 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.

[0151] In some embodiments, the positive electrode film layer may further include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0152] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of the 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).

[0153] The positive electrode film layer is generally formed by coating a positive electrode paste on the positive electrode current collector and then drying and rolling. The positive electrode paste is generally formed by dispersing positive electrode active materials, a positive electrode binder, a positive electrode conductive agent, etc. in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0154] [Negative electrode tab]

[0155] In some embodiments, the negative electrode tab 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.

[0156] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of the metal foil, copper foil, copper alloy foil, aluminum foil, or aluminum alloy 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 one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0157] The negative electrode active material may be a material well-known in the art. In some embodiments, as an example, the negative electrode active material may include, but is not limited to, one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based materials may include, but are not limited to, one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based materials may include, but are not limited to, one or more of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as the negative electrode active material may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0158] In some embodiments, the negative electrode film layer may optionally further include a negative electrode binder. As an example, the negative electrode binder may include, but is not limited to, 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).

[0159] In some embodiments, the negative electrode film layer may optionally further include a negative electrode conductive agent. As an example, the negative electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0160] In some embodiments, the negative electrode film layer may optionally further include other additives. As an example, the other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0161] The negative electrode plate can be prepared by the following method: dispersing the negative electrode active material, negative electrode binder, negative electrode conductive agent, etc. in a solvent and stirring evenly to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, a negative electrode plate is formed. The solvent may be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0162] In some embodiments, the negative electrode sheet may not include a negative electrode active material capable of intercalating and deintercalating lithium ions. For example, the negative electrode sheet may include a lithium sheet or a lithium alloy sheet; or, the negative electrode sheet may include a reticular or foamed three-dimensional skeleton layer; or, the negative electrode sheet may include a negative electrode current collector and a lithium-containing layer provided on at least one surface of the negative electrode current collector.

[0163] [Electrolyte]

[0164] The battery cell further includes an electrolyte. The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The present application does not specifically limit the type of the electrolyte, and it can be selected according to requirements. For example, the electrolyte may include one or more of a solid electrolyte, a gel electrolyte, and a liquid electrolyte (i.e., an electrolyte solution).

[0165] In some embodiments, the electrolyte uses an electrolyte solution, and the electrolyte solution includes an electrolyte salt and a solvent.

[0166] In some embodiments, by way of example, 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 bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluoro(dioxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0167] In some embodiments, the solvent may include, but is not limited to, one or more of ester solvents, sulfone solvents, and ether solvents. By way of example, the solvent may include, but is not limited to, one or more of 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), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0168] In some embodiments, the electrolyte may further optionally include additives. For example, the additives may include negative electrode film-forming additives, may also include positive electrode film-forming additives, and may further include additives capable of improving certain battery performance, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature performance of the battery, additives for improving the low-temperature power performance of the battery, etc.

[0169] [Separator film]

[0170] Among battery cells using the electrolyte and some battery cells using solid electrolytes, a separator film is further included. The separator film is disposed between the positive electrode sheet and the negative electrode sheet, mainly functioning to prevent internal short circuits.

[0171] This application does not particularly limit the type of the separator film, and any well-known porous structure separator film with good chemical stability and mechanical stability can be selected.

[0172] In some embodiments, the material of the separator film may include, but is not limited to, one or more of glass fiber, non-woven fabric, polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride. The separator film can be a single-layer film or a multi-layer composite film. When the separator film is a multi-layer composite film, the materials of each layer can be the same or different.

[0173] The preparation method of the battery cell is well-known. In some embodiments, the positive electrode sheet, the separator film, the negative electrode sheet, and the electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, the separator film, and the negative electrode sheet can be formed into an electrode assembly through a winding process and / or a stacking process, the electrode assembly is placed in an outer package, dried, and then the above-mentioned electrolyte is injected, and after processes such as encapsulation, standing, and formation, a battery cell is obtained. Multiple battery cells can further be combined into a battery module via series connection or parallel connection or mixed connection. Multiple battery modules can further form a battery pack via series connection or parallel connection or mixed connection. In some embodiments, multiple battery cells can also directly form a battery pack.

[0174] The embodiments of this application further provide an electrical device. The electrical device includes the battery provided by the embodiments of this application, and the battery is used to provide electrical energy. The battery can be used as the power source of the electrical device or as the energy storage unit of 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, a satellite, an energy storage system, etc.

[0175] The electrical device can select the specific type of the battery according to its usage requirements, such as a battery cell, a battery module, or a battery pack.

[0176] Figure 6It is a schematic diagram of an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. To meet the requirements of the electrical device for high power and high energy density, a battery pack or a battery module can be adopted.

[0177] As another example, the electrical device can be a mobile phone, a tablet computer, a laptop computer, etc. The electrical device usually requires being thin and light, and a battery cell can be adopted as the power source.

[0178] Example

[0179] The following embodiments describe more specifically the content disclosed in the present application. These embodiments are only for illustrative purposes, because various modifications and changes within the scope of the present application disclosure are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the embodiments are all commercially available.

[0180] Example 1-1

[0181] Raw materials are configured according to the ratio of Li:Mn:Fe:P being 1.02:0.6:0.4:1.015. 437.5 g of pure water, 105.7 g of lithium dihydrogen phosphate (purity ≥ 99.8%), 0.19 g of lithium carbonate (purity ≥ 99.8%), 72.317 g of ferrous oxalate dihydrate (purity ≥ 99.5%), 107.93 g of manganese oxalate dihydrate (purity ≥ 99.5%), and 1.6 g of titanium dioxide are respectively added into a ball milling tank, stirred evenly to obtain a first slurry.

[0182] Raw materials are configured according to the ratio of Li:Mn:Fe:P being 1.05:0.6:0.4:1.045. 442.4 g of pure water, 108.8 g of lithium dihydrogen phosphate (purity ≥ 99.8%), 0.19 g of lithium carbonate (purity ≥ 99.8%), 73.42 g of ferrous oxalate dihydrate (purity ≥ 99.5%), 108.48 g of manganese oxalate dihydrate (purity ≥ 99.5%), and 1.6 g of titanium dioxide are respectively added into a ball milling tank, stirred evenly to obtain a second slurry.

[0183] The first slurry is ground by a planetary ball mill until the volume distribution particle size Dv50 is 300 nm - 1000 nm, and then spray-dried to obtain a powder. The inlet temperature of the spray drying is 240 °C and the outlet temperature is 150 °C; the obtained powder is placed in a graphite crucible, and then sintered in a box furnace under nitrogen protection at 650 °C for 6 hours to obtain a first lithium iron manganese phosphate, denoted as LFMP-A. Figure 7The scanning electron microscope (SEM) image of the first lithium iron manganese phosphate is shown.

[0184] The second slurry was ground with a planetary ball mill until the volume distribution particle size Dv50 was 300 nm - 1000 nm, and then spray-dried to obtain a powder. The inlet temperature of the spray drying was 240 °C and the outlet temperature was 150 °C; the obtained powder was placed in a graphite crucible and then sintered at 650 °C for 6 hours under nitrogen protection in a box furnace to obtain the second lithium iron manganese phosphate, denoted as LFMP-B. Figure 8 The scanning electron microscope (SEM) image of the second lithium iron manganese phosphate is shown.

[0185] LFMP-A, glucose, and pure water were made into a slurry with a solid content of 50% and ground. After grinding, the volume distribution particle size Dv50 was 110 nm to obtain the third slurry.

[0186] LFMP-B, glucose, and pure water were made into a slurry with a solid content of 50% and ground. After grinding, the volume distribution particle size Dv50 was 500 nm to obtain the fourth slurry.

[0187] The third slurry and the fourth slurry were stirred evenly according to the mass ratio of LFMP-A and LFMP-B of 90:10, and then spray-dried to obtain a powder. The inlet temperature of the spray drying was 240 °C and the outlet temperature was 150 °C; the obtained powder was placed in a graphite crucible and then sintered at 750 °C for 12 hours under nitrogen protection in a box furnace and pulverized by air flow to obtain carbon-coated lithium iron manganese phosphate.

[0188] Examples 1-2

[0189] The preparation method of the carbon-coated lithium iron manganese phosphate was the same as that of Example 1-1 except for the following differences.

[0190] The third slurry and the fourth slurry were stirred evenly according to the mass ratio of LFMP-A and LFMP-B of 80:20, and then spray-dried to obtain a powder. The inlet temperature of the spray drying was 240 °C and the outlet temperature was 150 °C; the obtained powder was placed in a graphite crucible and then sintered at 750 °C for 12 hours under nitrogen protection in a box furnace and pulverized by air flow to obtain carbon-coated lithium iron manganese phosphate.

[0191] Examples 1-3

[0192] The preparation method of the carbon-coated lithium iron manganese phosphate was the same as that of Example 1-1 except for the following differences.

[0193] The third slurry and the fourth slurry are stirred evenly according to the mass ratio of LFMP-A to LFMP-B of 70:30, and then spray-dried to obtain a powder. The inlet temperature of the spray drying is 240 °C and the outlet temperature is 150 °C; the obtained powder is placed in a graphite crucible, and then sintered at 750 °C for 12 hours under the protection of nitrogen in a box furnace, and after airflow pulverization, lithium iron manganese phosphate coated with carbon is obtained.

[0194] Examples 1-4

[0195] Except for the following differences, the preparation method of lithium iron manganese phosphate coated with carbon is the same as that of Examples 1-1.

[0196] The third slurry and the fourth slurry are stirred evenly according to the mass ratio of LFMP-A to LFMP-B of 60:40, and then spray-dried to obtain a powder. The inlet temperature of the spray drying is 240 °C and the outlet temperature is 150 °C; the obtained powder is placed in a graphite crucible, and then sintered at 750 °C for 12 hours under the protection of nitrogen in a box furnace, and after airflow pulverization, lithium iron manganese phosphate coated with carbon is obtained.

[0197] Examples 1-5

[0198] Except for the following differences, the preparation method of lithium iron manganese phosphate coated with carbon is the same as that of Examples 1-1.

[0199] The third slurry and the fourth slurry are stirred evenly according to the mass ratio of LFMP-A to LFMP-B of 50:50, and then spray-dried to obtain a powder. The inlet temperature of the spray drying is 240 °C and the outlet temperature is 150 °C; the obtained powder is placed in a graphite crucible, and then sintered at 750 °C for 12 hours under the protection of nitrogen in a box furnace, and after airflow pulverization, lithium iron manganese phosphate coated with carbon is obtained.

[0200] Comparative Example 1

[0201] Raw materials are configured according to the ratio of Li:Mn:Fe:P of 1.02:0.6:0.4:1.015. 437.5 g of pure water, 105.7 g of lithium dihydrogen phosphate (purity ≥ 99.8%), 0.19 g of lithium carbonate (purity ≥ 99.8%), 72.317 g of ferrous oxalate dihydrate (purity ≥ 99.5%), 107.93 g of manganese oxalate dihydrate (purity ≥ 99.5%), and 1.6 g of titanium dioxide are respectively added into a ball milling tank and stirred evenly to obtain a slurry.

[0202] The slurry is ground by a planetary ball mill until the volume distribution particle size Dv50 is 300 nm - 1000 nm, and then spray-dried to obtain a powder. The inlet temperature of the spray drying is 240 °C and the outlet temperature is 150 °C; the obtained powder is placed in a graphite crucible, and then sintered at 650 °C for 6 hours under the protection of nitrogen in a box furnace to obtain lithium iron manganese phosphate.

[0203] Mix lithium iron manganese phosphate, glucose and pure water to form a slurry with a solid content of 50%, grind it, and the volume distribution particle size Dv50 after grinding is 110 nm. Then spray-dry to obtain a powder. The inlet temperature of the spray drying is 240 °C and the outlet temperature is 150 °C. Place the obtained powder in a graphite crucible, and then sinter it at 750 °C for 12 hours under nitrogen protection in a box furnace. After airflow pulverization, carbon-coated lithium iron manganese phosphate is obtained.

[0204] Comparative Example 2

[0205] Prepare raw materials according to the ratio of Li:Mn:Fe:P being 1.05:0.6:0.4:1.045. Add 442.4 g of pure water, 108.8 g of lithium dihydrogen phosphate (purity ≥ 99.8%), 0.19 g of lithium carbonate (purity ≥ 99.8%), 73.42 g of ferrous oxalate dihydrate (purity ≥ 99.5%), 108.48 g of manganese oxalate dihydrate (purity ≥ 99.5%), and 1.6 g of titanium dioxide into a ball milling tank, stir evenly to obtain a slurry.

[0206] Grind the slurry with a planetary ball mill until the volume distribution particle size Dv50 is 300 nm - 1000 nm, then spray-dry to obtain a powder. The inlet temperature of the spray drying is 240 °C and the outlet temperature is 150 °C. Place the obtained powder in a graphite crucible, and then sinter it at 650 °C for 6 hours under nitrogen protection in a box furnace to obtain lithium iron manganese phosphate.

[0207] Mix lithium iron manganese phosphate, glucose and pure water to form a slurry with a solid content of 50%, grind it, and the volume distribution particle size Dv50 after grinding is 500 nm. Then spray-dry to obtain a powder. The inlet temperature of the spray drying is 240 °C and the outlet temperature is 150 °C. Place the obtained powder in a graphite crucible, and then sinter it at 750 °C for 12 hours under nitrogen protection in a box furnace. After airflow pulverization, carbon-coated lithium iron manganese phosphate is obtained.

[0208] Comparative Example 3

[0209] Prepare raw materials according to the ratio of Li:Mn:Fe:P being 1.02:0.8:0.2:1.015. Add 437.5 g of pure water, 105.7 g of lithium dihydrogen phosphate (purity ≥ 99.8%), 0.19 g of lithium carbonate (purity ≥ 99.8%), 36.16 g of ferrous oxalate dihydrate (purity ≥ 99.5%), 143.91 g of manganese oxalate dihydrate (purity ≥ 99.5%), and 1.6 g of titanium dioxide into a ball milling tank, stir evenly to obtain the first slurry.

[0210] Prepare raw materials in the ratio of Li:Mn:Fe:P being 1.05:0.2:0.8:1.045. Add 442.4 g of pure water, 108.8 g of lithium dihydrogen phosphate (purity ≥ 99.8%), 0.19 g of lithium carbonate (purity ≥ 99.8%), 144.64 g of ferrous oxalate dihydrate (purity ≥ 99.5%), 35.98 g of manganese oxalate dihydrate (purity ≥ 99.5%), and 1.6 g of titanium dioxide into the ball milling tank, and stir evenly to obtain the second slurry.

[0211] Grind the first slurry with a planetary ball mill until the volume distribution particle size Dv50 is 300 nm - 1000 nm, and then spray-dry to obtain a powder. The inlet temperature of spray drying is 240 °C and the outlet temperature is 150 °C; place the obtained powder in a graphite crucible, and then sinter at 650 °C for 6 hours under nitrogen protection in a box furnace to obtain the first lithium iron manganese phosphate, denoted as LFMP-A.

[0212] Grind the second slurry with a planetary ball mill until the volume distribution particle size Dv50 is 300 nm - 1000 nm, and then spray-dry to obtain a powder. The inlet temperature of spray drying is 240 °C and the outlet temperature is 150 °C; place the obtained powder in a graphite crucible, and then sinter at 650 °C for 6 hours under nitrogen protection in a box furnace to obtain the second lithium iron manganese phosphate, denoted as LFMP-B.

[0213] Prepare a slurry with a solid content of 50% by mixing LFMP-A, glucose, and pure water, and grind it. After grinding, the volume distribution particle size Dv50 is 100 nm to obtain the third slurry.

[0214] Prepare a slurry with a solid content of 50% by mixing LFMP-B, glucose, and pure water, and grind it. After grinding, the volume distribution particle size Dv50 is 550 nm to obtain the fourth slurry.

[0215] Stir the third slurry and the fourth slurry evenly according to the mass ratio of LFMP-A and LFMP-B being 50:50, and then spray-dry to obtain a powder. The inlet temperature of spray drying is 240 °C and the outlet temperature is 150 °C; place the obtained powder in a graphite crucible, and then sinter at 750 °C for 12 hours under nitrogen protection in a box furnace, and perform air flow pulverization to obtain carbon-coated lithium iron manganese phosphate.

[0216] Performance Test

[0217] (1) Test of volume distribution particle size Dv50

[0218] Take an appropriate amount of sample, add 20 mL of deionized water, and perform ultrasonic treatment for 5 minutes (53 KHz, 120 W) to completely disperse the sample. Then use a laser particle size analyzer to measure the volume distribution particle size Dv50 of the material. The tester is a MasterSizer2000 laser particle size analyzer.

[0219] (2) Microscopic morphology evaluation

[0220] The microscopic morphology of the material was observed using a scanning electron microscope. The test instrument was a ZEISS sigma 300 scanning electron microscope.

[0221] (3) Test of powder compaction density

[0222] Weigh 1 g of the sample powder and spread it evenly in the compaction density mold. The cross-sectional area of the mold is 1.327 cm 2 , and then put it into the compaction density machine. After compaction with a pressure of 30,000 N, the powder compaction density is obtained.

[0223] (4) Specific surface area test

[0224] Refer to GB / T 19587-2017, and use the nitrogen adsorption specific surface area analysis test method for testing, and calculate it by the BET (Brunauer Emmett Teller) method. The test instrument is a Tri-Star 3020 specific surface area and pore size analyzer produced by Micromeritics Company of the United States.

[0225] (5) Discharge specific capacity and cycle performance test

[0226] Take the prepared lithium iron phosphate manganese coated with carbon as the positive electrode active material, and add it to a certain amount of N-methylpyrrolidone (NMP) according to the mass ratio of 90:5:5 with polyvinylidene fluoride (PVDF) and carbon black, and stir to make a slurry in a drying room. Coat the above slurry on the aluminum foil, and after drying and cold pressing, make a positive electrode plate. Use a lithium sheet as the negative electrode, and assemble it with the above-prepared positive electrode plate into a button cell in a button cell assembly box. The concentration of the electrolyte is 1 mol / L, the lithium salt is LiPF6, and the solvent is a mixed system of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) with a volume ratio of 1:1:1. The separator is a polyethylene film.

[0227] At 25 °C, the button cell is cycled for charge and discharge at a charge and discharge rate of 0.1C, the number of cycles is 50 times, and the charge and discharge voltage is 2.0V - 4.3V.

[0228] Take the discharge capacity of the last cycle as the numerator and the mass of the positive electrode active material as the denominator to calculate the discharge specific capacity of the positive electrode active material at a charge and discharge rate of 0.1C.

[0229] Take the ratio of the discharge capacity of the last cycle to the discharge capacity of the first cycle as the capacity retention rate of the button cell after 50 cycles.

[0230] During the test, a Shenzhen Neware battery test system was used for cyclic charge and discharge.

[0231] Table 1

[0232]

[0233] As can be seen from the test results in Table 1, the carbon-coated lithium iron manganese phosphate prepared by the preparation method provided in the embodiments of the present application can have both high specific capacity, high powder tap density and low specific surface area.

[0234] In Comparative Example 1, only small-particle lithium iron manganese phosphate primary particles were used to prepare carbon-coated lithium iron manganese phosphate. The carbon-coated lithium iron manganese phosphate can have a high capacity, but has a small powder tap density and a large specific surface area, which easily leads to abnormal progress of the processes of preparing and coating the positive electrode paste.

[0235] In Comparative Example 2, only large-particle lithium iron manganese phosphate primary particles were used to prepare carbon-coated lithium iron manganese phosphate. The carbon-coated lithium iron manganese phosphate has a small specific surface area and a high powder tap density, but has a low specific capacity.

[0236] In Comparative Example 3, the molar ratio of Mn element to Fe element in the first slurry is greater than the molar ratio of Mn element to Fe element in the second slurry. Thus, the molar ratio of Mn element to Fe element in the first lithium iron manganese phosphate is greater than the molar ratio of Mn element to Fe element in the second lithium iron manganese phosphate. At this time, the voltage platforms of the first lithium iron manganese phosphate and the second lithium iron manganese phosphate have a large gap. Therefore, during the sintering process, it is difficult to mix the small-particle lithium iron manganese phosphate primary particles and the large-particle lithium iron manganese phosphate primary particles evenly, resulting in a low specific capacity and a small powder tap density of the prepared carbon-coated lithium iron manganese phosphate.

[0237] Table 2

[0238] Serial Number Capacity Retention Rate after 50 Cycles Example 1-1 99.6％ Example 1-2 99.6％ Example 1-3 99.5％ Example 1-4 99.4％ Example 1-5 99.4％ Comparative Example 3 90.0％

[0239] As can be seen from the test results in Table 2, the carbon-coated lithium iron manganese phosphate prepared by the preparation method provided in the embodiments of the present application can endow the battery with good cycle performance.

[0240] In Comparative Example 3, the molar ratio of Mn element to Fe element in the first slurry is greater than the molar ratio of Mn element to Fe element in the second slurry. Thus, the molar ratio of Mn element to Fe element in the first lithium iron manganese phosphate is greater than the molar ratio of Mn element to Fe element in the second lithium iron manganese phosphate. At this time, the voltage platforms of the first lithium iron manganese phosphate and the second lithium iron manganese phosphate have a large gap, which affects the cycle performance of the battery.

[0241] Example 2-1

[0242] The preparation method of carbon-coated lithium iron manganese phosphate is the same as that of Examples 1-3 except for the following differences.

[0243] Prepare the first slurry according to the ratio of Li:Mn:Fe:P being 1.023:0.6:0.4:1.018 and Ti:Mn:Fe being 0.02:0.6:0.4, and control the solid content to be about 40%.

[0244] Prepare the second slurry according to the ratio of Li:Mn:Fe:P being 1.045:0.6:0.4:1.04 and Ti:Mn:Fe being 0.02:0.6:0.4, and control the solid content to be about 40%.

[0245] The volume distribution diameter Dv50 of the third slurry after grinding is 125 nm.

[0246] The volume distribution diameter Dv50 of the fourth slurry after grinding is 400 nm.

[0247] Example 2-2

[0248] The preparation method of carbon-coated lithium iron manganese phosphate is the same as that of Examples 1-3 except for the following differences.

[0249] Prepare the first slurry according to the ratio of Li:Mn:Fe:P being 1.023:0.6:0.4:1.018 and Ti:Mn:Fe being 0.02:0.6:0.4, and control the solid content to be about 40%.

[0250] Prepare the second slurry according to the ratio of Li:Mn:Fe:P being 1.055:0.6:0.4:1.05 and Ti:Mn:Fe being 0.02:0.6:0.4, and control the solid content to be about 40%.

[0251] The volume distribution diameter Dv50 of the third slurry after grinding is 125 nm.

[0252] The volume distribution diameter Dv50 of the fourth slurry after grinding is 600 nm.

[0253] Example 2-3

[0254] The preparation method of carbon-coated lithium iron manganese phosphate is the same as that of Examples 1-3 except for the following differences.

[0255] Prepare the first slurry according to the ratio of Li:Mn:Fe:P being 1.02:0.6:0.4:1.015 and Ti:Mn:Fe being 0.02:0.6:0.4, and control the solid content to be about 40%.

[0256] Prepare the second slurry according to the ratio of Li:Mn:Fe:P being 1.055:0.6:0.4:1.05 and Ti:Mn:Fe being 0.02:0.6:0.4, and control the solid content to be about 40%.

[0257] The volume distribution particle size Dv50 of the third slurry after grinding is 110 nm.

[0258] The volume distribution particle size Dv50 of the fourth slurry after grinding is 600 nm.

[0259] Example 2-4

[0260] The preparation method of the carbon-coated lithium iron manganese phosphate is the same as that of Examples 1-3 except for the following differences.

[0261] Prepare the first slurry according to the ratio of Li:Mn:Fe:P being 1.025:0.6:0.4:1.02 and Ti:Mn:Fe being 0.02:0.6:0.4, and control the solid content to be about 40%.

[0262] Prepare the second slurry according to the ratio of Li:Mn:Fe:P being 1.045:0.6:0.4:1.04 and Ti:Mn:Fe being 0.02:0.6:0.4, and control the solid content to be about 40%.

[0263] The volume distribution particle size Dv50 of the third slurry after grinding is 150 nm.

[0264] The volume distribution particle size Dv50 of the fourth slurry after grinding is 400 nm.

[0265] Comparative Example 4

[0266] The preparation method of the carbon-coated lithium iron manganese phosphate is the same as that of Examples 1-3 except for the following differences.

[0267] Prepare the first slurry according to the ratio of Li:Mn:Fe:P being 1.033:0.6:0.4:1.028 and Ti:Mn:Fe being 0.02:0.6:0.4, and control the solid content to be about 40%.

[0268] Prepare the second slurry according to the ratio of Li:Mn:Fe:P being 1.055:0.6:0.4:1.05 and Ti:Mn:Fe being 0.02:0.6:0.4, and control the solid content to be about 40%.

[0269] The volume distribution particle size Dv50 of the third slurry after grinding is 250 nm.

[0270] The volume distribution particle size Dv50 of the fourth slurry after grinding is 600 nm.

[0271] Table 3

[0272]

[0273] As can be seen from the test results in Table 3, by adjusting the volume distribution particle size Dv50 of the third slurry, the volume distribution particle size Dv50 of the fourth slurry, and the ratio of the volume distribution particle size Dv50 of the third slurry to the volume distribution particle size Dv50 of the fourth slurry, the lithium iron manganese phosphate coated with carbon can have both a low specific surface area, a high powder tap density, a high capacity, and a high cycle stability.

[0274] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same structure and the same function and effect as the technical idea within the technical solution scope of this application are all included in the technical scope of this application. In addition, within the scope not departing from the gist of this application, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways constructed by combining some of the constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A preparation method of carbon-coated lithium iron manganese phosphate, characterized in that, It includes the following steps: Mix a lithium source, an iron source, a manganese source, a phosphorus source, and water evenly to obtain a first slurry. Grind, spray granulate, and pre-sinter the obtained first slurry to obtain lithium iron manganese phosphate. Mix a lithium source, an iron source, a manganese source, a phosphorus source, and water evenly to obtain a second slurry. Grind, spray granulate, and pre-sinter the obtained second slurry to obtain a second lithium iron manganese phosphate. The ratio of the molar amount of Mn element to the molar amount of Fe element in the first slurry is equal to the ratio of the molar amount of Mn element to the molar amount of Fe element in the second slurry. Mix the obtained lithium iron manganese phosphate with an organic carbon source and water evenly, and grind to obtain a third slurry. The volume distribution particle size Dv50 of the third slurry is 100 nm - 150 nm. Mix the obtained second lithium iron manganese phosphate with an organic carbon source and water evenly, and grind to obtain a fourth slurry. The volume distribution particle size Dv50 of the fourth slurry is 400 nm - 800 nm. Mix the third slurry and the fourth slurry according to a predetermined ratio to obtain a fifth slurry. Spray granulate, sinter, and crush the obtained fifth slurry to obtain carbon-coated lithium iron manganese phosphate.

2. The preparation method according to claim 1, wherein the volume distribution particle size Dv50 of the third slurry is 100 nm - 125 nm; and / or the volume distribution particle size Dv50 of the fourth slurry is 500 nm - 650 nm.

3. The preparation method according to any one of claims 1-2, characterized in that, The ratio of the volume distribution particle size Dv50 of the third slurry to the volume distribution particle size Dv50 of the fourth slurry is 1:3.5 - 1:8.

0.

4. The preparation method according to claim 3, wherein, The ratio of the volume distribution particle size Dv50 of the third slurry to the volume distribution particle size Dv50 of the fourth slurry is 1:4.2 - 1:6.

5.

5. The preparation method according to any one of claims 1-4, characterized in that, In the obtained fifth slurry, the mass ratio of the first lithium iron manganese phosphate to the second lithium iron manganese phosphate is 90:10 - 50:

50.

6. The preparation method according to claim 5, wherein In the obtained fifth slurry, the mass ratio of the first lithium iron manganese phosphate to the second lithium iron manganese phosphate is 80:20 - 60:

40.

7. The preparation method according to any one of claims 1 - 6, wherein the ratio of the molar amount of P element in the first slurry to the sum of the molar amounts of Mn element and Fe element is less than the ratio of the molar amount of P element in the second slurry to the sum of the molar amounts of Mn element and Fe element; the ratio of the molar amount of P element in the first slurry to the sum of the molar amounts of Mn element and Fe element is (1 - 1.02):1; and / or the ratio of the molar amount of P element in the second slurry to the sum of the molar amounts of Mn element and Fe element is (1.04 - 1.06):

1.

8. The preparation method according to claim 7, wherein the ratio of the molar amount of P element in the first slurry to the sum of the molar amounts of Mn element and Fe element is (1.012 - 1.018):1; and / or the ratio of the molar amount of P element in the second slurry to the sum of the molar amounts of Mn element and Fe element is (1.042 - 1.052):

1.

9. The preparation method according to any one of claims 1-8, characterized in that, the molar ratio of Mn element to Fe element in the first slurry is 4:6 - 8:2; and / or, the molar ratio of Mn element to Fe element in the second slurry is 4:6 - 8:

2.

10. The preparation method according to claim 9, characterized in that, the molar ratio of Mn element to Fe element in the first slurry is 5.5:4.5 - 6.5:3.5; and / or, the molar ratio of Mn element to Fe element in the second slurry is 5.5:4.5 - 6.5:3.

5.

11. The preparation method according to any one of claims 1-10, characterized in that, The volume distribution particle size Dv50 of the lithium iron manganese phosphate coated with carbon obtained after spray granulation treatment and sintering treatment of the obtained fifth slurry is 5 μm - 10 μm.

12. The preparation method according to claim 11, wherein, The lithium iron manganese phosphate coated with carbon obtained after spray granulation treatment, sintering treatment of the obtained fifth slurry is a secondary particle formed by agglomeration of primary particles of small particles and primary particles of large particles, and the number of primary particles of small particles is greater than the number of primary particles of large particles. The volume distribution particle size Dv50 of the primary particles of small particles is 100 nm - 200 nm, and the volume distribution particle size Dv50 of the primary particles of large particles is 400 nm - 800 nm.

13. The preparation method according to any one of claims 1-12, characterized in that, the volume distribution particle size Dv50 of the lithium iron manganese phosphate coated with carbon obtained after spray granulation treatment, sintering treatment and crushing treatment of the obtained fifth slurry is 500 nm - 1000 nm; and / or, After subjecting the obtained fifth slurry to spray granulation treatment, sintering treatment, and crushing treatment, the tap density of the obtained lithium iron manganese phosphate coated with carbon powder is 2.23 g / cm 3 -2.41 g / cm 3 .

14. The preparation method according to claim 13, characterized in that, the volume distribution particle size Dv50 of the lithium iron manganese phosphate coated with carbon obtained after spray granulation treatment, sintering treatment and crushing treatment of the obtained fifth slurry is 500 nm - 900 nm; and / or, After subjecting the obtained fifth slurry to spray granulation treatment, sintering treatment, and crushing treatment, the tapped density of the obtained lithium iron manganese phosphate coated with carbon is 2.32 g / cm 3 -2.41 g / cm 3 .

15. The preparation method according to any one of claims 1-14, characterized in that, In the steps of spray granulation treatment, sintering treatment and crushing treatment of the obtained fifth slurry, the inlet temperature of the spray granulation treatment is 100°C - 280°C, and the outlet temperature is 50°C - 180°C; and / or, the holding temperature of the sintering treatment is 700°C - 800°C; and / or, the holding time of the sintering treatment is 8 h - 16 h; and / or, the atmosphere of the sintering treatment includes one or more of nitrogen, argon, and helium.

16. The preparation method according to any one of claims 1-15, characterized in that, In the steps of grinding treatment, spray granulation treatment and pre-sintering treatment of the obtained first slurry, the volume distribution particle size Dv50 of the first slurry after grinding treatment is 300 nm - 1000 nm; and / or, the inlet temperature of the spray granulation treatment is 100°C - 280°C, and the outlet temperature is 50°C - 180°C; and / or, the holding temperature of the pre-sintering treatment is 600°C - 650°C; and / or, the holding time of the pre-sintering treatment is 4 h - 10 h; and / or, the atmosphere of the pre-sintering treatment includes one or more of nitrogen, argon, and helium; and / or, The volume distribution particle size Dv50 of the first lithium iron manganese phosphate obtained after the pre-sintering treatment is 3 μm - 8 μm.

17. The preparation method according to any one of claims 1-16, characterized in that, In the steps of grinding, spray granulation and pre-sintering the obtained second slurry, the volume distribution particle size Dv50 of the second slurry after the grinding treatment is 300 nm - 1000 nm; and / or, the inlet temperature of the spray granulation treatment is 100°C - 280°C, and the outlet temperature is 50°C - 180°C; and / or, the heat preservation temperature of the pre-sintering treatment is 600°C - 650°C; and / or, the heat preservation time of the pre-sintering treatment is 4 h - 10 h; and / or, the atmosphere of the pre-sintering treatment includes one or more of nitrogen, argon, and helium; and / or, the volume distribution particle size Dv50 of the second lithium iron manganese phosphate obtained after the pre-sintering treatment is 3 μm - 8 μm.

18. The preparation method according to any one of claims 1 - 17, characterized in that the lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium acetate, lithium oxalate, lithium citrate, lithium dihydrogen phosphate, and lithium phosphate; and / or, the iron source includes one or more of ferrous oxalate, ferrous acetate, ferrous carbonate, iron phosphate, and ferric hydrogen phosphate; and / or, the manganese source includes one or more of manganese nitrate, manganese acetate, manganese phosphate, manganese oxalate, manganese carbonate, and ammonium manganese phosphate; and / or, the phosphorus source is one or more of lithium phosphate, lithium dihydrogen phosphate, disodium hydrogen phosphate, manganese hydrogen phosphate, diammonium phosphate, dipotassium hydrogen phosphate, and iron manganese hydrogen phosphate; and / or, the organic carbon source includes one or more of glucose, sucrose, maltose, citric acid, hydroxypropyl-β-cyclodextrin, ethylene glycol, polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polyvinylidene fluoride, polytetrafluoroethylene, polystyrene, and polypropylene; and / or, the first slurry further includes one or more of a source of metal doping element M and a source of non-metal doping element N; and / or, the second slurry further includes one or more of a source of metal doping element M and a source of non-metal doping element N.

19. A carbon-coated lithium iron manganese phosphate, characterized in that, Prepared by the preparation method according to any one of claims 1 - 18.

20. A positive electrode plate, comprising a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector, characterized in that, The positive electrode film layer includes carbon-coated lithium iron manganese phosphate prepared by the preparation method according to any one of claims 1 - 18 or the carbon-coated lithium iron manganese phosphate according to claim 19.

21. A battery, characterized in that, Including the positive electrode sheet according to claim 20.

22. An electrical device, characterized in that, Including the battery according to claim 21, and the battery is used to provide electrical energy.

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