Carbon-coated lithium iron phosphate material, preparation method thereof, positive plate and battery

Abstract

The invention relates to a carbon-coated lithium iron phosphate material and a preparation method thereof, a positive plate and a battery. The carbon-coated lithium iron phosphate material comprises a lithium iron phosphate matrix and a carbon coating layer at least partially coating the lithium iron phosphate matrix, and the carbon coating layer comprises a carbon material doped with a silicon element and a boron element. According to the carbon-coated lithium iron phosphate material, the surface of the lithium iron phosphate matrix is coated with the carbon coating layer, and the carbon material in the carbon coating layer is doped with the silicon element and the boron element, so that the electronic conductivity of the lithium iron phosphate material can be improved; in addition, doping sources of the silicon element and the boron element can react with magnetic substances such as iron phosphide in the coating process to be converted into non-magnetic inert substances, then the content of magnetic foreign matter impurities in the carbon-coated lithium iron phosphate material is reduced, the overcharge problem is solved, the carbon-coated lithium iron phosphate material has good overcharge prevention performance, and the safety performance is improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to carbon-coated lithium iron phosphate materials and their preparation methods, positive electrode sheets, and batteries. Background Technology

[0002] With the continuous expansion of battery applications, battery technology has developed rapidly. Lithium iron phosphate (LFP) is a lithium-ion battery cathode material with an olivine structure. Due to its advantages such as high safety, long cycle life, and controllable cost, it is widely used in new energy vehicles, energy storage systems, and consumer electronics.

[0003] With the widespread application of lithium-ion batteries in new energy vehicles, energy storage systems, and other fields, the requirements for battery safety performance are becoming increasingly stringent, leading to stricter control requirements for the magnetic impurity content of lithium iron phosphate materials. However, traditional preparation methods for lithium iron phosphate materials are prone to causing excessive magnetic impurities, which can result in safety issues such as overcharging. Summary of the Invention

[0004] Therefore, it is necessary to provide a carbon-coated lithium iron phosphate material, its preparation method, a positive electrode sheet, and a battery. This carbon-coated lithium iron phosphate material has good overcharge protection performance, which can improve the safety performance of the battery.

[0005] One embodiment of this application provides a carbon-coated lithium iron phosphate material, comprising a lithium iron phosphate matrix and a carbon coating layer at least partially coated on the lithium iron phosphate matrix, wherein the carbon coating layer comprises a carbon material doped with silicon and boron.

[0006] In some embodiments, the carbon coating layer has a mass content of 1.1% to 1.6% in the carbon-coated lithium iron phosphate material.

[0007] In some embodiments, one or more of the following conditions are met:

[0008] (1) The carbon content in the carbon-coated lithium iron phosphate material is 1.05%~1.35% by mass;

[0009] (2) The total mass content of silicon and boron in the carbon-coated lithium iron phosphate material is 0.05%~0.4%;

[0010] (3) The molar ratio of silicon to boron in the carbon-coated lithium iron phosphate material is (1~3):1.

[0011] In some embodiments, one or more of the following conditions are met:

[0012] (1) The iron content of the carbon-coated lithium iron phosphate material is less than 10 ppm;

[0013] (2) The mass content of magnetic foreign matter in the carbon-coated lithium iron phosphate material is less than 0.5 ppm.

[0014] In some embodiments, one or more of the following conditions are met:

[0015] (1) The Dv50 of the carbon-coated lithium iron phosphate material is 900nm~2000nm, and can be selected as 1200nm~1800nm;

[0016] (2) The specific surface area of ​​the carbon-coated lithium iron phosphate material is 9m². 2 / g~14m 2 / g, optional 10m 2 / g~12m 2 / g;

[0017] (3) The compaction density of the carbon-coated lithium iron phosphate material is 2.59 g / cm³. 3 ~2.68 g / cm 3 .

[0018] One embodiment of this application provides a method for preparing carbon-coated lithium iron phosphate material, comprising the following steps:

[0019] Under an inert atmosphere, the first material is subjected to a sintering process to obtain a primary sintered material; the first material includes an iron source, a phosphorus source, a lithium source, and a first carbon source;

[0020] Under an inert atmosphere, the second material is subjected to a secondary sintering process to obtain the carbon-coated lithium iron phosphate material; the second material includes the primary sintering material, the second carbon source, and the coating dopant, wherein the coating dopant contains silicon and boron.

[0021] In some embodiments, one or more of the following conditions are met:

[0022] (1) The coating dopant comprises a mixture of silicates and borates and one or more of silyl-containing borates; optionally, the silyl-containing borate comprises one or more of tris(trimethylsilyl)boronic acid, 1-trimethylsilylallylboronic acid, 1-trimethylsilylallylboronic acid, 4-(trimethylsilyl)naphthyl-2-boronic acid pinacol ester, 2-trimethylsilyl-1-ethylboronic acid pinacol ester and 4-(trimethylsilyl)-3-butyn-1-boronic acid pinacol ester; optionally, the mixture comprises a mixture of tetra(2-ethylbutyl) silicate and triethyl borate;

[0023] (2) The mass content of the coating dopant in the second material is 0.3% to 5%, and can be 0.8% to 3%.

[0024] In some embodiments, one or more of the following conditions are met:

[0025] (1) The molar ratio of lithium in the lithium source to iron in the iron source is (1.02~1.10):1;

[0026] (2) The lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium phosphate, lithium dihydrogen phosphate and lithium acetate;

[0027] (3) The molar ratio of iron in the iron source to phosphorus in the phosphorus source is (0.96~0.985):1;

[0028] (4) The iron source includes one or more of ferric oxide, iron(II) oxide, ferric hydroxide, ferric nitrate and ferric phosphate;

[0029] (5) The phosphorus source includes one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium phosphate, and lithium dihydrogen phosphate;

[0030] (6) The first carbon source accounts for 0.5% to 5% of the mass of the first material;

[0031] (7) The second carbon source accounts for 0.5% to 5% of the mass of the second material;

[0032] (8) The first carbon source and the second carbon source each independently include one or more of glucose, sucrose, fructose, starch, polyethylene glycol, polyvinylpyrrolidone and polyvinyl alcohol;

[0033] (9) The temperature of the first sintering treatment is 500℃~800℃ and the time is 3h~10h;

[0034] (10) The temperature of the secondary sintering treatment is 650℃~790℃, and the time is 5h~12h;

[0035] (11) The first material further includes additives, which include one or more compounds containing Ti, V, Nb, Mg, W and Y; optionally, the additives account for 0.1% to 2% of the mass content of the first material.

[0036] One embodiment of this application provides a positive electrode sheet, comprising the carbon-coated lithium iron phosphate material described above or the carbon-coated lithium iron phosphate material prepared according to the preparation method described above.

[0037] One embodiment of this application provides a battery including the above-described positive electrode.

[0038] The aforementioned carbon-coated lithium iron phosphate material has a carbon coating layer on the surface of its lithium iron phosphate substrate. The carbon material in the carbon coating layer is doped with silicon and boron, which can improve the electronic conductivity of the lithium iron phosphate material. In addition, the silicon and boron dopants can react with magnetic materials such as iron phosphide during the coating process to transform into non-magnetic inert materials, thereby reducing the content of magnetic foreign impurities in the carbon-coated lithium iron phosphate material, improving the overcharge problem, exhibiting good overcharge protection performance, and enhancing safety performance. Attached Figure Description

[0039] Figure 1 This is a SEM image of the carbon-coated lithium iron phosphate material prepared in Example 1 of this application.

[0040] Figure 2 The image shows the XRD pattern of the carbon-coated lithium iron phosphate material prepared in Example 1 of this application.

[0041] Figure 3 This is a particle size distribution diagram of the carbon-coated lithium iron phosphate material prepared in Example 1 of the present invention.

[0042] Figure 4 This is an EDS surface scan image of the carbon-coated lithium iron phosphate material prepared in Example 1 of the present invention. Detailed Implementation

[0043] To facilitate understanding of the present invention, a more comprehensive description is provided below, along with preferred embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. It should be understood that these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0045] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0046] The "range" disclosed in this application can be 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, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints. Any endpoint can be independently included or excluded, and they 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, it is expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0047] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0048] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0049] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0050] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0051] In this application, open-ended technical features or solutions described using terms such as "containing," "including," or "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may also include other members or exclude additional members unless otherwise specified. This can be considered as providing both the feature or solution that "A consists of a1, a2, and a3" and the feature or solution that "A includes not only a1, a2, and a3, but also other members." In this application, unless otherwise specified, A (e.g., B) indicates that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0052] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0053] As described in the background section, traditional methods for preparing lithium iron phosphate materials are prone to leading to excessive levels of magnetic foreign matter, which can cause safety issues such as overcharging. The content of magnetic foreign matter in lithium iron phosphate materials directly affects the battery's conductivity, safety, and lifespan. For example, magnetic foreign matter may penetrate the separator, forming a micro-short circuit, leading to an increased battery self-discharge rate, and even causing thermal runaway, resulting in fire or explosion accidents.

[0054] This application provides a carbon-coated lithium iron phosphate material and its preparation method. The carbon-coated lithium iron phosphate material prepared by the method has good overcharge performance, thereby improving the safety performance of the battery.

[0055] One embodiment of this application provides a carbon-coated lithium iron phosphate material, comprising a lithium iron phosphate matrix and a carbon coating layer at least partially coated on the lithium iron phosphate matrix, wherein the carbon coating layer comprises a carbon material doped with silicon and boron.

[0056] The aforementioned carbon-coated lithium iron phosphate material has a carbon coating layer on the surface of its lithium iron phosphate substrate. The carbon material in the carbon coating layer is doped with silicon and boron, which can improve the electronic conductivity of the lithium iron phosphate material. In addition, the silicon and boron dopants can react with magnetic materials such as iron phosphide during the coating process to transform into non-magnetic inert materials, thereby reducing the content of magnetic foreign impurities in the carbon-coated lithium iron phosphate material, improving the overcharge problem, exhibiting good overcharge protection performance, and enhancing safety performance.

[0057] Silicon can repair defects in the carbon coating layer, and the formed Si-C bonds effectively inhibit the dissolution of iron. Furthermore, it can react with magnetic foreign matter, eliminating magnetism and reducing the content of magnetic impurities in carbon-coated lithium iron phosphate materials. Boron can optimize the interaction between the carbon coating layer and the electrolyte, reducing polarization and improving discharge performance. It can also reduce side reactions between the electrolyte and magnetic foreign matter, lowering the risk of gas generation. The elemental ratios can be freely adjusted according to the lithium iron phosphate matrix.

[0058] In addition, the carbon material in the carbon coating layer is doped with silicon and boron, which can improve the electronic conductivity of lithium iron phosphate material, and thus also help improve the charge and discharge specific capacity of the battery using it.

[0059] In some embodiments, the carbon coating layer has a mass content of 1.1% to 1.6% in the carbon-coated lithium iron phosphate material. For example, it can be 1.1%, 1.15%, 1.2%, 1.3%, 1.4%, 1.5%, 1.55%, 1.6%, or any value within the range of any two of the aforementioned values; it can be selected as 1.15% to 1.55%.

[0060] In some embodiments, the mass content of carbon in the carbon-coated lithium iron phosphate material is 1.05% to 1.35%. For example, it can be 1.05%, 1.1%, 1.15%, 1.2%, 1.3%, 1.35%, or any value within the range of any two of the aforementioned values; it can be 1.08% to 1.3%.

[0061] In some embodiments, the total mass content of silicon and boron in the carbon-coated lithium iron phosphate material is 0.05% to 0.4%. Examples include 0.05%, 0.07%, 0.1%, 0.15%, 0.2%, 0.2%, 0.25%, 0.3%, 0.35%, and 0.4%, or any value within the range of any two of the aforementioned values; a range of 0.1% to 0.3% is also possible. Within this range, good overcharge protection performance can be improved while maintaining excellent discharge capacity.

[0062] In some embodiments, the molar ratio of silicon to boron in the carbon-coated lithium iron phosphate material is (1~3):1, and examples include 1:1, 2:1, 3:1, or any value within the range formed by any two of the aforementioned points. The molar ratio of silicon to boron is controlled within the above range.

[0063] The molar ratio of silicon to boron in carbon-coated lithium iron phosphate materials can be controlled by controlling the molar ratio of silicon to boron in the coating dopant during the preparation process.

[0064] In some embodiments, the dissolved iron content of the carbon-coated lithium iron phosphate material is less than 10 ppm. A low dissolved iron content indicates good structural stability in the carbon-coated lithium iron phosphate material, which improves battery safety and cycle performance. In some examples, the dissolved iron content of the carbon-coated lithium iron phosphate material is ≤9 ppm, optionally ranging from 1 ppm to 9 ppm. For example, the dissolved iron content of the carbon-coated lithium iron phosphate material is ≤5 ppm, ≤4 ppm, ≤3 ppm, or ≤2 ppm.

[0065] In this application, the test method for the leached iron content of carbon-coated lithium iron phosphate material is as follows: 5g of the sample to be tested is soaked in 50mL of tertiary water for 6 hours, then filtered through a 0.45μm inert filter membrane, and finally tested at a constant volume using ICP-OES. The specific test method can be found in standard GC / T 30835-2014.

[0066] In some embodiments, the mass content of magnetic foreign matter in the carbon-coated lithium iron phosphate material is less than 0.5 ppm. The low content of magnetic foreign matter impurities in the carbon-coated lithium iron phosphate material reduces the risk of overcharging caused by these impurities, improves overcharge performance, and enhances battery safety. In some examples, the mass content of magnetic foreign matter in the carbon-coated lithium iron phosphate material is ≤0.48 ppm, optionally ranging from 0.1 ppm to 0.48 ppm. As examples, the dissolved iron content of the carbon-coated lithium iron phosphate material is ≤0.4 ppm, ≤0.3 ppm, ≤0.2 ppm, and ≤0.1 ppm.

[0067] In some embodiments, the Dv50 of the carbon-coated lithium iron phosphate material is 900nm~2000nm. As an example, it can be 900nm, 1000nm, 1100nm, 1200nm, 1300nm, 1400nm, 1500nm, 1600nm, 1700nm, 1800nm, 1900nm, 2000nm, or any value within the range formed by any two of the aforementioned values, and can be selected as 1200nm~1800nm.

[0068] In this application, Dv50 refers to the median particle size, specifically the particle size corresponding to 50% of the cumulative volume, representing the average particle size of the system. It can be measured using a laser diffraction scattering particle size analyzer (Malvin 3000).

[0069] In some embodiments, the carbon-coated lithium iron phosphate material comprises large particles and small particles, wherein the large particles have a Dv50 of 1.8 μm to 2.3 μm, and the small particles have a Dv50 of 0.6 μm to 0.85 μm. Further, the volume ratio of large particles to small particles is 1.5 to 2.5:1, with examples being 1.5:1, 2:1, 2.5:1, or any value within the range of any two of the aforementioned values. Further, in the total amount of large and small particles, the mass percentage of large particles is 65% to 75%, with examples being 65%, 70%, 80%, or any value within the range of any two of the aforementioned values.

[0070] In some embodiments, the compaction density of the carbon-coated lithium iron phosphate material is 2.59 g / cm³. 3 ~2.68 g / cm 3 For example, it could be 2.59 g / cm³. 3 2.6g / cm 3 2.61 g / cm 3 2.63 g / cm 3 2.65g / cm 3 2.67 g / cm 3 2.68 g / cm 3 It can be any value within the range formed by any two of the aforementioned point values. This carbon-coated lithium iron phosphate material has a high compaction density, which in turn can improve the energy density of the battery.

[0071] In some embodiments, the specific surface area of ​​the carbon-coated lithium iron phosphate material is 9 m². 2 / g~14m 2 / g, as an example, could be 9m 2 / g, 10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g can be any value within the range formed by any two of the aforementioned point values, and can be 10m. 2 / g~12m 2 / g.

[0072] In some embodiments, the lithium iron phosphate matrix in the carbon-coated lithium iron phosphate material is also doped with one or more metal ions selected from Ti, V, Nb, Mg, W, and Y. For example, titanium dioxide can be used as a dopant to incorporate titanium into the lithium iron phosphate matrix, thereby improving the conductivity of the resulting lithium iron phosphate material.

[0073] One embodiment of this application provides a method for preparing carbon-coated lithium iron phosphate material, comprising the following steps:

[0074] S10. Under an inert atmosphere, the first material is subjected to a first sintering treatment to obtain a first sintered material; the first material includes an iron source, a phosphorus source, a lithium source, and a first carbon source.

[0075] S20. Under an inert atmosphere, the second material is subjected to a secondary sintering treatment to obtain carbon-coated lithium iron phosphate material; the second material includes a primary sintering material, a second carbon source, and a coating dopant, the coating dopant containing silicon and boron elements.

[0076] The above preparation method employs a two-stage sintering process. In the first sintering process, a carbon coating layer is first formed on the surface of the lithium iron phosphate substrate. In the second sintering process, a second carbon source and coating dopant are added. Silicon and boron elements are doped simultaneously with the formation of the carbon coating layer. The carbon material in the carbon coating layer is doped with silicon and boron elements, which can improve the electronic conductivity of the lithium iron phosphate material. In addition, the silicon and boron dopant sources can react with magnetic materials such as iron phosphide during the coating process to transform into non-magnetic inert materials, thereby reducing the content of magnetic foreign impurities in the carbon-coated lithium iron phosphate material, improving the overcharge problem, exhibiting good overcharge protection performance, and enhancing safety performance.

[0077] In some embodiments, the coating dopant includes one or more of a mixture of silicates and borates, and silyl-containing borates. In the mixture of silicates and borates, the former is a silicon source and the latter is a boron source. The silyl-containing borate serves as both a silicon and a boron source.

[0078] Optionally, the silane-containing borate ester includes one or more of tris(trimethylsilyl)boronic acid ester, 1-trimethylsilylallylboronic acid ester, 4-(trimethylsilyl)naphthyl-2-boronic acid pinacol ester, 2-trimethylsilyl-1-ethylboronic acid pinacol ester, and 4-(trimethylsilyl)-3-butynedi-1-boronic acid pinacol ester. Optionally, the mixture includes a mixture of tetra(2-ethylbutyl)silicate and triethyl borate.

[0079] The molar ratio of silicon to boron in the coating dopant affects the molar ratio of silicon to boron in the carbon-coated lithium iron phosphate material. For example, a silicon-to-boron molar ratio of 3:1 in tris(trimethylsilyl)borate results in a 3:1 molar ratio of silicon to boron in the prepared carbon-coated lithium iron phosphate material. The coating dopant includes a mixture of silicate and borate esters, and the mixing ratio of the silicate and borate esters can be adjusted to obtain the desired silicon-to-boron molar ratio. For example, a mixture of tetra(2-ethylbutyl) silicate and triethyl borate with a 1:1 molar ratio as the coating dopant results in a 1:1 molar ratio of silicon to boron in the prepared carbon-coated lithium iron phosphate material.

[0080] In some embodiments, the mass content of the coating dopant in the second material is 0.3% to 5%, optionally 0.8% to 3%.

[0081] In some embodiments, the molar ratio of lithium in the lithium source to iron in the iron source is (1.02~1.10):1.

[0082] In some embodiments, the lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium phosphate, lithium dihydrogen phosphate, and lithium acetate.

[0083] In some embodiments, the molar ratio of iron in the iron source to phosphorus in the phosphorus source is (0.96~0.985):1.

[0084] In some embodiments, the iron source includes one or more of ferric oxide, magnetite, ferric hydroxide, ferric nitrate, and ferric phosphate. When ferric phosphate is used as the iron source, it can also serve as the phosphorus source.

[0085] In some embodiments, the phosphorus source includes one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium phosphate, and lithium dihydrogen phosphate.

[0086] In some embodiments, the first carbon source accounts for 0.5% to 5% of the mass content of the first material; as examples, it may be 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, or any value within the range of any two of the aforementioned values.

[0087] In some embodiments, the second carbon source accounts for 0.5% to 5% of the mass content of the second material; as examples, it can be 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, or any value within the range formed by any two of the aforementioned points.

[0088] In some embodiments, the first carbon source and the second carbon source each independently include one or more of glucose, sucrose, fructose, starch, polyethylene glycol, polyvinylpyrrolidone, and polyvinyl alcohol;

[0089] In some embodiments, the temperature of a single sintering process is 500°C to 800°C, and the time is 3 hours to 10 hours. As an example, the sintering temperature of a single sintering process is 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, or any value within the range of any two of the aforementioned values, and the sintering time is 3 hours, 4 hours, 6 hours, 8 hours, 10 hours, or any value within the range of any two of the aforementioned values.

[0090] In some embodiments, the secondary sintering treatment is carried out at a temperature of 650°C to 790°C for a time of 5 hours to 12 hours. As an example, the sintering temperature for the secondary sintering treatment is 650°C, 700°C, 750°C, 790°C, or any value within the range of any two of the aforementioned values, and the sintering time is 5 hours, 6 hours, 8 hours, 10 hours, 12 hours, or any value within the range of any two of the aforementioned values.

[0091] In some embodiments, the first material further includes additives, which include one or more compounds containing Ti, V, Nb, Mg, W, and Y. These compounds include, but are not limited to, oxides. Each additive independently includes one or more of titanium dioxide, ammonium metavanadate, tungsten trioxide, vanadium pentoxide, niobium pentoxide, magnesium oxide, and ytterbium trioxide.

[0092] In some embodiments, the first material further includes an additive, which accounts for 0.1% to 2% of the mass of the first material; for example, it may be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 2%, or any value within the range of any two of the aforementioned values.

[0093] One embodiment of this application provides a positive electrode sheet, comprising the carbon-coated lithium iron phosphate material described above or the carbon-coated lithium iron phosphate material prepared according to the preparation method described above.

[0094] The aforementioned positive electrode uses carbon-coated lithium iron phosphate material, which has a low content of magnetic foreign matter impurities, which helps to improve overcharging problems and enhance safety performance.

[0095] In some embodiments, the positive electrode includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, the positive active layer comprising a positive active material. The positive active material contains the aforementioned carbon-coated lithium iron phosphate material.

[0096] In the positive electrode current collector, non-limiting examples of the metallic material may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The positive electrode active layer also includes a binder and a conductive agent.

[0097] One embodiment of this application provides a battery including the above-described positive electrode.

[0098] The battery contains the aforementioned positive electrode sheet, in which the carbon-coated lithium iron phosphate material has a low content of magnetic foreign matter impurities, which helps to improve overcharging issues and enhance safety performance.

[0099] Typically, a battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0100] To make the objectives, technical solutions, and advantages of this invention clearer and more concise, the invention is described using the following specific embodiments, but the invention is by no means limited to these embodiments. The embodiments described below are merely preferred embodiments of the invention and can be used to describe the invention, but should not be construed as limiting the scope of the invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the protection scope of this invention.

[0101] Unless otherwise specified, the reagents, materials, instruments, and analytical methods used in the following examples are all conventional reagents, materials, instruments, and analytical methods in the art, and are all commercially available. The reagents involved can also be synthesized using conventional methods in the art. Experimental methods in the following examples that do not specify specific conditions are all under standard operating conditions.

[0102] To better illustrate the present invention, the following embodiments are provided for further explanation. The specific embodiments are as follows.

[0103] Example 1

[0104] The preparation method of carbon-coated lithium iron phosphate material in this embodiment includes the following steps:

[0105] 1) Weigh out ferric phosphate, lithium carbonate, the first carbon source (glucose and PEG2000 in a mass ratio of 5:1), and the additive titanium dioxide sequentially, and add them to deionized water to form the first material. The iron-to-phosphorus ratio (i.e., the iron-to-phosphorus molar ratio) of ferric phosphate is 0.968, the molar ratio of lithium carbonate and ferric phosphate is 1.03:1 (Li:Fe), the additive titanium dioxide accounts for 1.2% of the first material (excluding water), and the first carbon source (glucose and PEG2000) accounts for 2.4% of the first material. Ball mill the first material for 50 minutes. Then, pass the slurry into a pin mill and mill for 70 minutes to obtain a slurry with a particle size Dv50 of 500 nm and a solid content of 40.79%.

[0106] 2) Spray dry the slurry obtained in step 1), and sinter the obtained spray material in a nitrogen atmosphere furnace. The temperature of the first sintering treatment is 750℃, and the reaction is kept at a constant temperature for 6 hours. After the temperature drops to room temperature, the sintered material is crushed and sieved to obtain the first sintered material.

[0107] 3) Weigh out the primary sintering material, the second carbon source (glucose and PEG2000 in a mass ratio of 2.5:1), and the coating dopant tris(trimethylsilyl)borate ester, and disperse them in N-methylpyrrolidone (NMP) to form the second material. The tris(trimethylsilyl)borate ester accounts for 3% of the mass percentage of the second material, and the second carbon source (glucose and PEG2000) accounts for 2.58% of the mass percentage of the second material. Mill the second material in a sand mill for 60 minutes until Dv50 = 1200 nm.

[0108] 4) The slurry obtained in step 3) is spray-dried, and then subjected to secondary sintering in a nitrogen atmosphere furnace at a temperature of 760℃ for 10 hours. After the temperature drops to room temperature, the secondary sintered material is subjected to air jet milling with the classifier wheel frequency adjusted to 115Hz to obtain carbon-coated lithium iron phosphate material. The carbon-coated lithium iron phosphate material includes a lithium iron phosphate matrix and a silicon-boron co-doped carbon coating layer on the surface of the lithium iron phosphate matrix.

[0109] SEM image of carbon-coated lithium iron phosphate material in Example 1, as shown. Figure 1 As shown. From Figure 1 It can be seen that the carbon-coated lithium iron phosphate particles have a relatively smooth surface and a relatively uniform coating, and the carbon coating layer contains particles of different sizes.

[0110] The XRD pattern of the carbon-coated lithium iron phosphate material in Example 1 is shown below. Figure 2 As shown. From Figure 2It can be seen that the XRD pattern of the carbon-coated lithium iron phosphate material in Example 1 is consistent with the standard lithium iron phosphate pattern (PDF#40-1499), with no impurity peaks, indicating that the lithium iron phosphate material prepared by this method is pure phase.

[0111] The particle size distribution diagram of the carbon-coated lithium iron phosphate material in Example 1 is as follows: Figure 3 As shown. From Figure 3 It can be seen that the particle size of the carbon-coated lithium iron phosphate material in Example 1 is between 300nm and 6.7μm, and the particle size distribution shows a bimodal distribution, corresponding to the peaks of small particles and large particles respectively. The volume ratio of large particles to small particles is 2:1, and Dv50=1572nm. The most frequent particle size of the left peak, Dmo1, is 0.75μm, and the most frequent particle size of the right peak, Dmo2, is 2.3μm.

[0112] EDS surface scan image of carbon-coated lithium iron phosphate material in Example 1, as shown below. Figure 4 As shown. From Figure 4 It can be seen that silicon and boron elements are uniformly distributed in the carbon coating layer on the surface of the lithium iron phosphate substrate, achieving the effect of silicon-boron co-doping carbon coating.

[0113] Example 2

[0114] The preparation method of carbon-coated lithium iron phosphate material in this embodiment includes the following steps:

[0115] 1) Weigh out ferric oxide, ammonium dihydrogen phosphate, lithium carbonate, a first carbon source (glucose and PEG2000 in a mass ratio of 5:1), and titanium dioxide as an additive in sequence, and add them to deionized water to form the first material. The molar ratio of Fe to P is 0.96:1, the molar ratio of lithium carbonate and ferric oxide is 1.10:1 (Li to Fe), the titanium dioxide additive accounts for 2% of the first material by mass, and the first carbon source (glucose and PEG2000) accounts for 4% of the first material by mass. Ball mill the first material for 50 minutes. Then, pass the slurry into a pin mill and mill for 70 minutes to obtain a slurry with a particle size Dv50 of 450 nm and a solid content of 43.79%.

[0116] 2) Spray dry the slurry obtained in step 1), and sinter the obtained spray material in a nitrogen atmosphere furnace. The temperature of the first sintering treatment is 780℃, and the reaction is kept at a constant temperature for 10 hours. After the temperature drops to room temperature, the sintered material is crushed and sieved to obtain the first sintered material.

[0117] 3) Weigh out the primary sintering material, the second carbon source (glucose and PEG2000 in a mass ratio of 2.5:1), and the coating dopant 1-trimethylsilylallylboronic acid ester sequentially, and disperse them in NMP to form the second material. The 1-trimethylsilylallylboronic acid ester accounts for 1% of the mass percentage of the second material, and the second carbon source (glucose and PEG2000) accounts for 3.5% of the mass percentage of the second material. Mill the second material in a sand mill for 60 minutes until Dv50 = 1200 nm.

[0118] 4) The slurry obtained in step 3) is spray-dried, and then subjected to secondary sintering in a nitrogen atmosphere furnace at a temperature of 790℃ for 5 hours. After the temperature drops to room temperature, the secondary sintered material is subjected to air jet milling with the classifier wheel frequency adjusted to 110Hz to obtain carbon-coated lithium iron phosphate material. The carbon-coated lithium iron phosphate material includes a lithium iron phosphate matrix and a silicon-boron co-doped carbon coating layer on the surface of the lithium iron phosphate matrix.

[0119] Example 3

[0120] The preparation method of carbon-coated lithium iron phosphate material in this embodiment includes the following steps:

[0121] 1) Weigh out iron(III) oxide, phosphoric acid, lithium carbonate, a first carbon source (glucose and PEG2000 in a mass ratio of 5:1), and titanium dioxide (additive) sequentially, and add them to deionized water to form the first material. The molar ratio of Fe to P is 0.975:1, the molar ratio of Li to Fe in the first material is 1.06:1, the additive (titanium dioxide) accounts for 1.5% of the mass of the first material, and the first carbon source (glucose and PEG2000) accounts for 1.21% of the mass of the first material. Mill the first material in a basket mill for 45 minutes. Then, pump the slurry into a pin mill and mill it for 75 minutes to obtain a slurry with a particle size Dv50 of 350 nm and a solid content of 41.02%.

[0122] 2) Spray dry the slurry obtained in step 1), and sinter the obtained spray material in a nitrogen atmosphere furnace. The temperature of the first sintering treatment is 500℃, and the reaction is kept at a constant temperature for 10 hours. After the temperature drops to room temperature, the sintered material is crushed and sieved to obtain the first sintered material.

[0123] 3) Weigh out the primary sintering material, the second carbon source (glucose and PEG2000 in a mass ratio of 2.5:1), and the coating dopant sequentially. The coating dopant is a mixture of tetra(2-ethylbutyl) silicate and triethyl borate in a 1:1 molar ratio. Disperse the mixture in NMP to form the second material. The coating dopant accounts for 2% of the mass percentage of the second material, and the second carbon source (glucose and PEG2000) accounts for 1.5% of the mass percentage of the second material. Mill the second material in a sand mill for 55 minutes until Dv50 = 1200 nm.

[0124] 4) The slurry obtained in step 3) is spray-dried, and then subjected to secondary sintering in a nitrogen atmosphere furnace at a temperature of 730℃ for 10 hours. After the temperature drops to room temperature, the sintered material is subjected to air jet milling with the classifier wheel frequency adjusted to 95Hz to obtain carbon-coated lithium iron phosphate material. The carbon-coated lithium iron phosphate material includes a lithium iron phosphate matrix and a silicon-boron co-doped carbon coating layer on the surface of the lithium iron phosphate matrix.

[0125] Example 4

[0126] The preparation method of carbon-coated lithium iron phosphate material in this embodiment is basically the same as that in Example 1. The difference is that in step 3), the coating dopant (tris(trimethylsilyl)borate) accounts for 0.3% of the mass of the second material, and the second carbon source (glucose and PEG2000) accounts for 5% of the mass of the second material.

[0127] Example 5

[0128] The preparation method of carbon-coated lithium iron phosphate material in this embodiment is basically the same as that in Example 1. The difference is that the coating dopant (tris(trimethylsilyl)borate) accounts for 5% of the mass percentage of the second material, and the second carbon source (glucose and PEG2000) accounts for 0.5% of the mass percentage of the second material.

[0129] Example 6

[0130] The preparation methods of carbon-coated lithium iron phosphate material in Example 6 and Example 1 are basically the same, except that the additive in step 1) is vanadium pentoxide.

[0131] Example 7

[0132] The preparation methods of carbon-coated lithium iron phosphate material in Example 7 and Example 1 are basically the same, except that the additive in step 1) is tungsten trioxide.

[0133] Example 8

[0134] The preparation methods of carbon-coated lithium iron phosphate material in Example 8 and Example 1 are basically the same, except that the amount of additive added in step 1) is changed to 0.1% of the mass percentage of the first material.

[0135] Comparative Example 1

[0136] The preparation methods of carbon-coated lithium iron phosphate materials in Comparative Example 1 and Example 1 are basically the same, except that in step 3), the type of coating dopant is different, specifically tetrakis(2-ethylbutyl) silicate.

[0137] Comparative Example 2

[0138] The preparation methods of carbon-coated lithium iron phosphate materials in Comparative Example 2 and Example 1 are basically the same, except that in step 3), the type of coating dopant is different, specifically triethyl borate.

[0139] Comparative Example 3

[0140] The preparation method of carbon-coated lithium iron phosphate material in Comparative Example 3 is basically the same as that in Example 1, except that no coating dopant is added in step 3).

[0141] The specific steps are as follows: Weigh out the primary sintering material, glucose, and PEG2000 sequentially, and disperse them in NMP to form the second material. To ensure the same carbon content in the finished product, the amount of the second carbon source (glucose and PEG2000) added is increased to 5% of the mass percentage of the second material. The second material is then milled in a sand mill for 60 minutes until Dv50 = 1200 nm.

[0142] Battery fabrication:

[0143] The carbon-coated lithium iron phosphate material prepared in the examples and comparative examples was used as the positive electrode active material. It was mixed with the binder polyvinylidene fluoride and the conductive agent Super P at a mass ratio of 96.5:1.5:2. N-methylpyrrolidone was added and the mixture was stirred until a uniform and fluid positive electrode active slurry was formed. The positive electrode active slurry was uniformly coated on both sides of an aluminum foil with a thickness of 12 μm, and after baking, a positive electrode sheet was obtained. A 2032 coin cell was assembled using lithium metal as the negative electrode.

[0144] The following are the performance tests and testing methods.

[0145] 1. Dv50: The particle size of carbon-coated lithium iron phosphate material was obtained by particle size analysis using a Malvern 3000 laser particle size analyzer.

[0146] 2. Carbon content in carbon-coated lithium iron phosphate materials: The sample is heated and burned in an oxygen stream in a high-frequency induction furnace. The generated carbon dioxide and sulfur dioxide are carried by the oxygen to the measuring chamber of an infrared analyzer. Since carbon dioxide and sulfur dioxide absorb infrared energy of specific wavelengths, their absorption energy is proportional to their concentration. The carbon and sulfur content of the sample can be measured based on the change in energy received by the detector. For specific operation, please refer to the standard: GB / T 20123-2006.

[0147] Test of the total mass content of silicon and boron elements in carbon-coated lithium iron phosphate materials: The difference method is used for testing. The mass of the secondary sintering material m2 is subtracted from the mass of the primary sintering material m1 to obtain the mass M of the carbon coating layer after sintering. Then the mass percentage of the carbon coating layer is M / m2*100%. Subsequently, the carbon content is tested to obtain the carbon element content C%. Then the total mass content of silicon and boron elements is M / m2*100%-C.

[0148] 3. Compacted Density: A certain mass (m) of carbon-coated lithium iron phosphate powder is placed on a compaction mold of known diameter (e.g., a Sansi Zongheng UTM7305 mold). The mold has a metal sheet at the top and bottom, with the powder placed in the middle. A pressure of 3T is applied, and the corresponding powder thickness is measured. The volume (v) of the compacted powder is calculated based on the powder thickness and the cross-sectional area covered. The compacted density is then calculated using the formula ρ = m / v. Specific procedures can be performed according to standard GB / T24533-2009.

[0149] 4. Specific surface area: The powder sample to be tested is placed in a U-shaped sample tube, and a mixed gas containing a certain proportion of adsorbate molecules (N2) is passed through the sample. The amount of adsorbate molecules (N2) adsorbed by the sample is determined based on the change in gas concentration before and after adsorption. For specific operation, please refer to the standard: GB / T 13390-2008.

[0150] 5. Iron leaching: Immerse 5g of the sample in 50mL of grade III water for 6 hours, then filter it using a 0.45μm inert filter membrane, and perform a volume adjustment test using ICP-OES. For specific test methods, please refer to the standard: GC / T 30835-2014.

[0151] 6. Magnetic foreign matter: Disperse the sample to be tested in deionized water, use a magnetic rod to enrich magnetic foreign matter, then rinse the magnetic rod with deionized water, and after brief sonication several times, remove non-magnetic substances, then dissolve the magnetic foreign matter, and perform the test using ICP-OES. For specific operating procedures, please refer to GB / T 41704-2022.

[0152] 7. Battery performance test.

[0153] The test subject was the aforementioned 2032 coin cell assembled from carbon-coated lithium iron phosphate materials prepared in the examples and comparative examples.

[0154] Charge / discharge specific capacity: At 25℃, charge at a constant current of 1C to 3.75V, then charge at a constant voltage of 3.75V until the current is equal to 0.05C. The charging capacity at this time is recorded as the 1C charging specific capacity. After resting for 5 minutes, discharge at a constant current of 1C to a voltage of 2.0V. The discharge capacity at this time is recorded as the 1C discharging specific capacity.

[0155] Overcharge safety performance: The battery was charged to 3.8V at 0.1C rate at 25℃, and the charging capacity Q1 was recorded. Then it was charged to 5.45V at 0.1C rate at 60℃, and the overcharge capacity Q2 was recorded. The overcharge percentage Q2 / Q1*100% was used as a measure of overcharge safety. The lower the value, the better the overcharge performance.

[0156] The parameter results of the carbon-coated lithium iron phosphate materials prepared in each embodiment and comparative example are shown in Table 1 and Table 2.

[0157] Table 1

[0158]

[0159] It should be noted that in Comparative Example 1, the carbon coating layer is doped only with silicon and not with boron, and the total mass content of silicon and boron refers to the mass content of silicon. In Comparative Example 2, the carbon coating layer is doped only with boron and not with silicon, and the total mass content of silicon and boron refers to the mass content of boron.

[0160] Table 2

[0161]

[0162] As shown in Tables 1 and 2, Comparative Examples 1-3, which did not dope the carbon coating layer, or only doped with silicon or only doped with boron, produced carbon-coated lithium iron phosphate materials with a high content of magnetic foreign matter (≥1.2 ppm), a high content of dissolved iron (≥150 ppm), and a low compaction density. The resulting batteries exhibited lower charge / discharge specific capacity and a higher overcharge percentage, indicating poor safety performance. In contrast, the embodiments, by simultaneously doping the carbon coating layer with silicon and boron, produced carbon-coated lithium iron phosphate materials with very low contents of magnetic foreign matter (<0.5 ppm), very low contents of dissolved iron (<0.5 ppm), and high compaction density. The resulting batteries exhibited higher charge / discharge specific capacity and a lower overcharge percentage, indicating superior safety performance.

[0163] As can be seen from Examples 1-5, the total mass content of silicon and boron in carbon-coated lithium iron phosphate materials is 0.1% to 0.3%, which can improve the overcharge protection performance while also taking into account the excellent discharge capacity.

[0164] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0165] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A carbon-coated lithium iron phosphate material, characterized in that, It includes a lithium iron phosphate substrate and a carbon coating layer at least partially covering the lithium iron phosphate substrate, wherein the carbon coating layer comprises carbon material doped with silicon and boron.

2. The carbon-coated lithium iron phosphate material as described in claim 1, characterized in that, The carbon coating layer has a mass content of 1.1% to 1.6% in the carbon-coated lithium iron phosphate material.

3. The carbon-coated lithium iron phosphate material as described in claim 1, characterized in that, One or more of the following conditions must be met: (1) The carbon content in the carbon-coated lithium iron phosphate material is 1.05%~1.35% by mass; (2) The total mass content of silicon and boron in the carbon-coated lithium iron phosphate material is 0.05%~0.4%; (3) The molar ratio of silicon to boron in the carbon-coated lithium iron phosphate material is (1~3):

1.

4. The carbon-coated lithium iron phosphate material according to any one of claims 1 to 3, characterized in that, One or more of the following conditions must be met: (1) The iron content of the carbon-coated lithium iron phosphate material is less than 10 ppm; (2) The mass content of magnetic foreign matter in the carbon-coated lithium iron phosphate material is less than 0.5 ppm.

5. The carbon-coated lithium iron phosphate material according to any one of claims 1 to 3, characterized in that, One or more of the following conditions must be met: (1) The Dv50 of the carbon-coated lithium iron phosphate material is 900nm~2000nm, and can be selected as 1200nm~1800nm; (2) The specific surface area of ​​the carbon-coated lithium iron phosphate material is 9m². 2 / g~14m 2 / g, optional 10m 2 / g~12m 2 / g; (3) The compaction density of the carbon-coated lithium iron phosphate material is 2.59 g / cm³. 3 ~2.68 g / cm 3 .

6. A method for preparing carbon-coated lithium iron phosphate material, characterized in that, Includes the following steps: Under an inert atmosphere, the first material is subjected to a sintering process to obtain a primary sintered material; the first material includes an iron source, a phosphorus source, a lithium source, and a first carbon source; Under an inert atmosphere, the second material is subjected to a secondary sintering process to obtain the carbon-coated lithium iron phosphate material; the second material includes the primary sintering material, the second carbon source, and the coating dopant, wherein the coating dopant contains silicon and boron.

7. The preparation method according to claim 6, characterized in that, One or more of the following conditions must be met: (1) The coating dopant comprises a mixture of silicates and borates and one or more of silyl-containing borates; optionally, the silyl-containing borate comprises one or more of tris(trimethylsilyl)boronic acid, 1-trimethylsilylallylboronic acid, 4-(trimethylsilyl)naphthyl-2-boronic acid pinacol ester, 2-trimethylsilyl-1-ethylboronic acid pinacol ester and 4-(trimethylsilyl)-3-butyn-1-boronic acid pinacol ester; optionally, the mixture comprises a mixture of tetra(2-ethylbutyl) silicate and triethyl borate; (2) The mass content of the coating dopant in the second material is 0.3% to 5%, and can be 0.8% to 3%.

8. The preparation method according to claim 6 or 7, characterized in that, One or more of the following conditions must be met: (1) The molar ratio of lithium in the lithium source to iron in the iron source is (1.02~1.10):1; (2) The lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium phosphate, lithium dihydrogen phosphate and lithium acetate; (3) The molar ratio of iron in the iron source to phosphorus in the phosphorus source is (0.96~0.985):1; (4) The iron source includes one or more of ferric oxide, iron(II) oxide, ferric hydroxide, ferric nitrate and ferric phosphate; (5) The phosphorus source includes one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium phosphate, and lithium dihydrogen phosphate; (6) The first carbon source accounts for 0.5% to 5% of the mass of the first material; (7) The second carbon source accounts for 0.5% to 5% of the mass of the second material; (8) The first carbon source and the second carbon source each independently include one or more of glucose, sucrose, fructose, starch, polyethylene glycol, polyvinylpyrrolidone and polyvinyl alcohol; (9) The temperature of the first sintering treatment is 500℃~800℃ and the time is 3h~10h; (10) The temperature of the secondary sintering treatment is 650℃~790℃, and the time is 5h~12h; (11) The first material further includes additives, which include one or more compounds containing Ti, V, Nb, Mg, W and Y; optionally, the additives account for 0.1% to 2% of the mass content of the first material.

9. A positive electrode plate, characterized in that, This includes the carbon-coated lithium iron phosphate material according to any one of claims 1 to 5 or the carbon-coated lithium iron phosphate material prepared according to the preparation method according to any one of claims 6 to 8.

10. A battery, characterized in that, Includes the positive electrode sheet as described in claim 9.

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