Amorphous carbon-coated lithium iron manganese phosphate positive electrode material and preparation method and application thereof

Abstract

This invention provides an amorphous carbon-coated lithium manganese iron phosphate cathode material, its preparation method, and its applications. The preparation method includes the following steps: mixing a lithium source, an ferrous source, a manganese source, a phosphorus source, a carbon source, and a solvent to obtain a mixed slurry; spray-drying the mixed slurry, followed by plasma treatment of the dried material to obtain a precursor material; mixing the precursor material with a boron source, and then sintering to obtain the amorphous carbon-coated lithium manganese iron phosphate cathode material. This invention coats the surface of the lithium manganese iron phosphate cathode material with an amorphous carbon layer, resulting in high bonding strength between the amorphous carbon coating and the cathode material. It also solves the electronic conductivity problem of the lithium manganese iron phosphate cathode material, while boron doping improves the ionic conductivity of the material.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and relates to an amorphous carbon-coated lithium manganese iron phosphate cathode material, its preparation method, and its application. Background Technology

[0002] Against the backdrop of the rapid development of the global new energy industry, lithium-ion batteries, as core energy storage devices, have been widely used in electric vehicles, portable electronic devices, and large-scale energy storage systems. As the "energy core" of lithium-ion batteries, the performance of cathode materials directly determines the battery's energy density, power density, cycle life, and safety performance. Therefore, developing cathode materials that combine high energy, high stability, and low cost has become a key direction for promoting the upgrading of the lithium-ion battery industry.

[0003] Due to the excellent safety of lithium iron phosphate (LFP) due to its olivine-type crystal structure, introducing manganese into the LFP lattice yields lithium manganese iron phosphate (LFP) cathode material. The introduction of manganese can raise the material's voltage plateau to 3.8-4.1V and increase the theoretical energy density by 10%-20%, while retaining the excellent structural stability and low-cost advantages of LFP. This makes it a core transitional cathode material bridging LFP and high-nickel ternary materials, with broad application prospects in mid-to-high-end energy storage and long-range economical electric vehicles.

[0004] CN115810736A discloses a lithium manganese iron phosphate cathode material and its preparation method. The method involves uniformly coating the surface of the lithium manganese iron phosphate material with a metal salt and an organic carbon source using a liquid-phase method, followed by high-temperature carbonization to form a metal / carbon composite coating layer on the surface. Then, small organic molecules with Lewis acid / base groups are used to modify the surface of lithium manganese iron phosphate particles of different sizes via coordination bonds. After drying, surface-modified lithium manganese iron phosphate particles are obtained. Finally, lithium manganese iron phosphate particles of different sizes are mixed in a specific ratio to obtain a lithium manganese iron phosphate cathode material with suitable particle size and uniform distribution.

[0005] CN120398018A discloses a carbon-coated lithium manganese iron phosphate, which is obtained by mixing lithium manganese iron phosphate slurry with a volume distribution particle size D50 of 100nm-150nm and lithium manganese iron phosphate slurry with a volume distribution particle size D50 of 400nm-800nm, and then subjecting it to spray granulation, sintering and crushing treatments.

[0006] The above method prepares a carbon coating layer by high-temperature sintering carbon onto the surface of lithium manganese iron phosphate. However, the bonding strength between the coating layer and lithium manganese iron phosphate is low, it is easy to fall off, and the ionic conductivity is low. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide an amorphous carbon-coated lithium manganese iron phosphate cathode material, its preparation method, and its application. The present invention coats the surface of the lithium manganese iron phosphate cathode material with an amorphous carbon layer. The amorphous carbon coating layer has high bonding strength with the cathode material, and it solves the electronic conductivity problem of the lithium manganese iron phosphate cathode material. At the same time, boron doping improves the ionic conductivity of the material.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing an amorphous carbon-coated lithium manganese iron phosphate cathode material, the method comprising the following steps:

[0010] A mixed slurry is obtained by mixing lithium source, ferrous source, manganese source, phosphorus source, carbon source and solvent;

[0011] After spray drying the mixed slurry, the dried material is subjected to plasma treatment to obtain the precursor material;

[0012] The precursor material is mixed with a boron source and then sintered to obtain the amorphous carbon-coated lithium manganese iron phosphate cathode material.

[0013] This invention achieves atomic-level uniform mixing by pre-mixing various raw materials in liquid phase. Micron-sized spherical secondary particles are formed in a single step through spray drying. High-energy active particles in plasma treatment efficiently and at low temperatures break the chemical bonds of organic carbon source molecules, causing them to be uniformly deposited in an amorphous form on the surface of the LMFP precursor particles – this process produces amorphous carbon. This amorphous carbon has many defects, high activity, and a stronger bond with active materials, exhibiting superior conductivity compared to traditional pyrolytic carbon. Subsequently, it is mixed with boron and sintered. Boron's small atomic radius allows it to act as a lattice dopant, entering the lithium manganese iron phosphate lattice, creating lithium vacancies, and slightly expanding the one-dimensional lithium-ion diffusion channel, significantly improving lithium-ion conductivity and thus enhancing the material's rate performance. Furthermore, the introduction of the boron source after the plasma-formed amorphous carbon layer may allow some boron to not only be incorporated into the lattice but also exist within the carbon layer, forming BC bonds and further optimizing the carbon layer's conductivity.

[0014] Preferably, the lithium source includes any one or a combination of at least two of lithium hydroxide, lithium carbonate, or lithium dihydrogen phosphate.

[0015] Preferably, the ferrous source includes any one or a combination of at least two of ferrous oxalate, ferrous acetate, or ferrous phosphate.

[0016] Preferably, the manganese source includes any one or a combination of at least two of manganese carbonate, manganese oxalate, or manganese phosphate.

[0017] Preferably, the phosphorus source includes any one or a combination of at least two of phosphoric acid, ammonium dihydrogen phosphate, or diammonium hydrogen phosphate.

[0018] Preferably, the carbon source includes any one or a combination of at least two of glucose, sucrose, or starch.

[0019] Preferably, the solvent includes water.

[0020] Preferably, the molar ratio of iron, manganese, lithium, and phosphorus in the mixed slurry is (0.2~0.8):(0.8~0.2):(1~1.06):1, for example: 0.2:0.8:1:1, 0.3:0.7:1.05:1, 0.5:0.5:1.06:1, 0.6:0.4:1.05:1, or 0.8:0.2:1.06:1, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] Preferably, the total molar amount of iron and manganese in the mixed slurry is in a molar ratio of (0.95~1.05):1 with phosphorus, for example: 0.95:1, 0.98:1, 1:1, 1.02:1 or 1.05:1, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] Preferably, the solid content of the mixed slurry is 40% to 60%, for example: 40%, 45%, 50%, 55% or 60%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] Preferably, the mass percentage concentration of the carbon source in the mixed slurry is 10% to 20%, for example: 10%, 12%, 15%, 18% or 20%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] Preferably, the resulting slurry is ball-milled after mixing.

[0025] Preferably, the ball milling time is 5h to 15h, for example: 5h, 8h, 10h, 12h or 15h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] Preferably, the radio frequency of the plasma treatment is 12MHz~15MHz, for example: 12MHz, 12.5MHz, 13MHz, 14MHz or 15MHz, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] Preferably, the power of the plasma treatment is 120W to 500W, for example: 120W, 150W, 200W, 300W or 500W, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] Preferably, during the plasma treatment process, the gas flow rate is 50ccm to 500ccm, for example: 50ccm, 100ccm, 200ccm, 400ccm or 500ccm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] Preferably, the gas used in the plasma treatment process is a hydrogen-argon mixture.

[0030] Preferably, the volume percentage of hydrogen in the hydrogen-argon mixture is 20% to 50%, for example: 20%, 25%, 30%, 40% or 50%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] Preferably, the plasma treatment time is 100s to 180s, for example: 100s, 120s, 150s, 160s or 180s, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] Preferably, the boron source comprises hydrogen boride nanosheets.

[0033] Preferably, based on the mass of the precursor material as 100%, the amount of borohydride nanosheets added is 0.05% to 0.15%, for example: 0.05%, 0.08%, 0.1%, 0.12% or 0.15%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] Preferably, the atmosphere for the sintering process includes nitrogen and / or argon.

[0035] Preferably, the sintering process includes a first sintering and a second sintering.

[0036] Preferably, the temperature of the first sintering is 400℃~600℃, for example: 400℃, 450℃, 500℃, 550℃ or 600℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] Preferably, the first sintering time is 2h to 4h, for example: 2h, 2.5h, 3h, 3.5h or 4h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0038] Preferably, the second sintering temperature is 600℃~800℃, for example: 600℃, 650℃, 700℃, 750℃ or 800℃, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0039] Preferably, the second sintering time is 2h to 4h, for example: 2h, 2.5h, 3h, 3.5h or 4h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] In a second aspect, the present invention provides an amorphous carbon-coated lithium manganese iron phosphate cathode material, wherein the amorphous carbon-coated lithium manganese iron phosphate cathode material is prepared by the preparation method described in the first aspect.

[0041] Thirdly, the present invention provides a positive electrode sheet comprising the amorphous carbon-coated lithium manganese iron phosphate positive electrode material as described in the second aspect.

[0042] Fourthly, the present invention provides a lithium-ion battery comprising a positive electrode as described in the third aspect.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] (1) The present invention coats an amorphous carbon layer on the surface of lithium manganese iron phosphate cathode material. The amorphous carbon coating layer has a high bonding strength with the cathode material and solves the electronic conductivity problem of lithium manganese iron phosphate cathode material. At the same time, boron doping improves the ionic conductivity of the material.

[0045] (2) The battery made of the amorphous carbon-coated lithium manganese iron phosphate cathode material of the present invention can retain a capacity of more than 96.18% after 300 cycles of 2C and a specific capacity of more than 126.3 mAh / g after 5C discharge. Detailed Implementation

[0046] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0047] The "range" disclosed in this invention 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 the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning 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 specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​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 invention, 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.

[0048] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0049] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0050] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0051] In this invention, open-ended technical features or solutions described using terms such as "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, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0052] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0053] In this invention, the terms "first," "second," "third," "fourth," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0054] Example 1

[0055] This embodiment provides an amorphous carbon-coated lithium manganese iron phosphate cathode material, which is prepared by the following method:

[0056] Li₂CO₃, MnCO₃, ferrous oxalate, NH₄H₂PO₄, and water were mixed evenly, and glucose was added. The mixture was ball-milled for 10 hours to obtain a slurry. The molar ratio of iron, manganese, lithium, and phosphorus in the slurry was 0.5:0.5:1.05:1. The solid content of the slurry was 50%, and the mass concentration of glucose was 15%.

[0057] After spray drying the mixed slurry, the dried material is subjected to plasma treatment to obtain the precursor material. The radio frequency frequency of the plasma treatment is 13MHz, the power is 250W, a hydrogen-argon mixture with a volume ratio of 30:70 is introduced, the gas flow rate is 200sccm, and the plasma treatment time is 150s.

[0058] The precursor material was mixed with 0.1% borohydride nanosheets and sintered at 500°C for 3 hours under an argon atmosphere, followed by sintering at 700°C for 3 hours to obtain the amorphous carbon-coated lithium manganese iron phosphate cathode material.

[0059] Example 2

[0060] This embodiment provides an amorphous carbon-coated lithium manganese iron phosphate cathode material, which is prepared by the following method:

[0061] LiOH, manganese oxalate, ferrous acetate, phosphoric acid, and water were mixed evenly, and sucrose was added. The mixture was ball-milled for 5 hours to obtain a slurry. The molar ratio of iron, manganese, lithium, and phosphorus in the slurry was 0.2:0.8:1.05:1. The solid content of the slurry was 40%, and the mass concentration of sucrose was 10%.

[0062] After spray drying the mixed slurry, the dried material is subjected to plasma treatment to obtain the precursor material. The radio frequency frequency of the plasma treatment is 12MHz, the power is 120W, a hydrogen-argon mixture with a volume ratio of 20:80 is introduced, the gas flow rate is 50sccm, and the plasma treatment time is 180s.

[0063] The precursor material was mixed with 0.05% borohydride nanosheets and sintered at 400°C for 4 hours under an argon atmosphere, followed by sintering at 600°C for 4 hours to obtain the amorphous carbon-coated lithium manganese iron phosphate cathode material.

[0064] Example 3

[0065] This embodiment provides an amorphous carbon-coated lithium manganese iron phosphate cathode material, which is prepared by the following method:

[0066] LiOH, manganese oxalate, ferrous acetate, phosphoric acid, and water were mixed evenly, and then sucrose was added. The mixture was ball-milled for 15 hours to obtain a mixed slurry. The molar ratio of iron, manganese, lithium, and phosphorus in the mixed slurry was 0.8:0.2:1.02:1. The solid content of the mixed slurry was 60%, and the mass concentration of sucrose was 20%.

[0067] After spray drying the mixed slurry, the dried material is subjected to plasma treatment to obtain the precursor material. The radio frequency frequency of the plasma treatment is 15MHz, the power is 500W, a hydrogen-argon mixture with a volume ratio of 50:50 is introduced, the gas flow rate is 500sccm, and the plasma treatment time is 100s.

[0068] The precursor material was mixed with 0.15% borohydride nanosheets and sintered at 600°C for 2 hours under an argon atmosphere, followed by sintering at 800°C for 2 hours to obtain the amorphous carbon-coated lithium manganese iron phosphate cathode material.

[0069] Example 4

[0070] The only difference between this embodiment and Embodiment 1 is that the radio frequency of the plasma treatment is 10MHz, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0071] Example 5

[0072] The only difference between this embodiment and Embodiment 1 is that the radio frequency of the plasma treatment is 20MHz, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0073] Example 6

[0074] The only difference between this embodiment and Embodiment 1 is that the plasma treatment power is 100W, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0075] Example 7

[0076] The only difference between this embodiment and Embodiment 1 is that the plasma treatment power is 800W, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0077] Example 8

[0078] The only difference between this embodiment and Example 1 is that the amount of borohydride nanosheets added is 0.01%, while the other conditions and parameters are exactly the same as in Example 1.

[0079] Example 9

[0080] The only difference between this embodiment and Example 1 is that the amount of borohydride nanosheets added is 0.2%, while the other conditions and parameters are exactly the same as in Example 1.

[0081] Comparative Example 1

[0082] The only difference between this comparative example and Example 1 is that the plasma treatment is replaced with conventional 700°C heat treatment; all other conditions and parameters are exactly the same as in Example 1.

[0083] Comparative Example 2

[0084] The only difference between this comparative example and Example 1 is that borohydride nanosheets are not added; all other conditions and parameters are exactly the same as in Example 1.

[0085] Performance testing:

[0086] The prepared lithium manganese iron phosphate cathode material, conductive carbon black, and polyvinylidene fluoride were weighed out in a mass ratio of 8:1:1 and added to N-methylpyrrolidone to form a slurry. The slurry was then coated onto aluminum foil, dried, and sliced ​​to obtain the cathode sheet. A lithium metal sheet was used as the counter electrode, a polypropylene microporous membrane as the separator, and 1 mol / L LiPF6 as the electrolyte (wherein the solvent is a 1:1 volume ratio mixture of ethylene carbonate and dimethyl carbonate). The CR2025 button cell was assembled in an argon glove box. Cycle performance and rate performance tests were performed on the CR2025 button cell.

[0087] Cyclic performance test conditions: After the assembled battery is left to stand for 2 hours, it is subjected to 300 cycles at 25℃, voltage range of 2.5-4.35V, and 2C rate.

[0088] Test conditions for rate performance: After the assembled battery is left to stand for 2 hours, it is subjected to 5 cycles at 0.2C, 0.5C, 1C, 2C and 5C respectively under the conditions of 25℃ and voltage range of 2.5-4.35V.

[0089] The test results are shown in Table 1:

[0090] Table 1

[0091]

[0092] As can be seen from Table 1, and from Examples 1-9, the battery made of the amorphous carbon-coated lithium manganese iron phosphate cathode material of the present invention can achieve a capacity retention rate of over 96.18% after 300 cycles at 2C, and a specific capacity of over 126.3 mAh / g at 5C discharge.

[0093] A comparison of Examples 1 and 4-5 shows that during the preparation of the amorphous carbon-coated lithium manganese iron phosphate cathode material of the present invention, the radio frequency frequency of plasma treatment affects the performance of the prepared amorphous carbon-coated lithium manganese iron phosphate cathode material. Controlling the radio frequency frequency of plasma treatment at 12MHz~15MHz results in better performance of the prepared amorphous carbon-coated lithium manganese iron phosphate cathode material. If the radio frequency frequency of plasma treatment is too high, the material performance is not significantly improved, but the requirements for power supply and matching network are higher, and the equipment cost and technical difficulty are also greatly increased. If the radio frequency frequency of plasma treatment is too low, low-frequency plasma is more likely to produce "filamentary discharge" rather than uniform "glow discharge", resulting in uneven coating of the amorphous carbon layer, with some areas being too thickly coated and some areas not coated at all.

[0094] A comparison of Examples 1 and 6-7 shows that during the preparation of the amorphous carbon-coated lithium manganese iron phosphate cathode material of the present invention, the radio frequency of the plasma treatment affects the performance of the amorphous carbon-coated lithium manganese iron phosphate cathode material. Controlling the plasma treatment power between 120W and 500W results in better performance of the amorphous carbon-coated lithium manganese iron phosphate cathode material. If the plasma treatment power is too high, the carbon source gas will decompose prematurely in the gas phase into particulate carbon black, resulting in a loose, uneven coating layer with poor bonding force. This layer is prone to detachment during subsequent sintering or electrode stirring, and may even lose its coating effect. If the plasma treatment power is too low, the carbon layer grows slowly and cannot form a complete and continuous protective layer within a reasonable time, resulting in poor coating effect and limited improvement in electronic conductivity.

[0095] A comparison of Examples 1 and 8-9 shows that the amount of boron source added during the preparation of the amorphous carbon-coated lithium manganese iron phosphate cathode material of the present invention affects the performance of the obtained amorphous carbon-coated lithium manganese iron phosphate cathode material. Controlling the amount of boron source added to 0.05%~0.15% of the precursor material mass results in better performance of the amorphous carbon-coated lithium manganese iron phosphate cathode material. If the amount of boron source added is too high, excess boron cannot enter the crystal lattice and will form an insulating borate glass phase or boron-phosphorus compound at the grain boundaries. This insulating impurity phase will block the transport path of lithium ions between particles and on the particle surface, significantly reducing ionic conductivity and causing a sharp decline in capacity and rate performance. If the amount of boron source added is too low, it cannot effectively widen the lithium ion migration channels, resulting in negligible improvement in ionic conductivity and limited improvement in the rate performance of the material, failing to fully exert its role in stabilizing the crystal structure and suppressing cycle decay.

[0096] As can be seen from the comparison between Example 1 and Comparative Example 1, the present invention can efficiently and at low temperature break the chemical bonds of organic carbon source molecules through high-energy active particles in plasma treatment, causing them to be uniformly deposited in an amorphous form on the surface of LMFP precursor particles. This process produces amorphous carbon with more defects, higher activity, stronger bonding with active substances, and better conductivity than traditional pyrolytic carbon.

[0097] As can be seen from the comparison between Example 1 and Comparative Example 2, the present invention introduces a boron source after the amorphous carbon layer is formed by plasma, which may allow some boron elements not only to be doped into the crystal lattice, but also to exist in the carbon layer, forming BC bonds, thereby further optimizing the conductivity of the carbon layer.

[0098] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing an amorphous carbon-coated lithium manganese iron phosphate cathode material, characterized in that, The preparation method includes the following steps: A mixed slurry is obtained by mixing lithium source, ferrous source, manganese source, phosphorus source, carbon source and solvent; After spray drying the mixed slurry, the dried material is subjected to plasma treatment to obtain the precursor material; The precursor material was mixed with a boron source and then sintered to obtain the amorphous carbon-coated lithium manganese iron phosphate cathode material. The phosphorus source includes any one or a combination of at least two of phosphoric acid, ammonium dihydrogen phosphate, or diammonium hydrogen phosphate. The radio frequency frequency of the plasma treatment is 12MHz~15MHz, the power of the plasma treatment is 120W~500W, the gas flow rate during the plasma treatment is 50ccm~500ccm, the gas used in the plasma treatment is a hydrogen-argon mixture, the volume percentage of hydrogen in the hydrogen-argon mixture is 20%~50%, and the plasma treatment time is 100s~180s.

2. The preparation method according to claim 1, characterized in that, The lithium source includes any one or a combination of at least two of lithium hydroxide, lithium carbonate, or lithium dihydrogen phosphate.

3. The preparation method according to claim 1, characterized in that, The ferrous source includes any one or a combination of at least two of ferrous oxalate, ferrous acetate, or ferrous phosphate.

4. The preparation method according to claim 1, characterized in that, The manganese source includes any one or a combination of at least two of manganese carbonate, manganese oxalate, or manganese phosphate.

5. The preparation method according to claim 1, characterized in that, The carbon source includes any one or a combination of at least two of glucose, sucrose, or starch.

6. The preparation method according to claim 1, characterized in that, The solvent includes water.

7. The preparation method according to claim 1, characterized in that, The molar ratio of iron, manganese, lithium and phosphorus in the mixed slurry is (0.2~0.8):(0.8~0.2):(1~1.06):

1.

8. The preparation method according to claim 1, characterized in that, The total molar amount of iron and manganese in the mixed slurry is 1:1 with the molar amount of phosphorus (0.95~1.05).

9. The preparation method according to claim 1, characterized in that, The solid content of the mixed slurry is 40% to 60%.

10. The preparation method according to claim 1, characterized in that, The mass percentage concentration of carbon source in the mixed slurry is 10%~20%.

11. The preparation method according to claim 1, characterized in that, The resulting slurry is then subjected to ball milling.

12. The preparation method according to claim 11, characterized in that, The ball milling process takes 5 to 15 hours.

13. The preparation method according to claim 1, characterized in that, The boron source includes boron nanosheets.

14. The preparation method according to claim 13, characterized in that, Based on the mass of the precursor material being 100%, the amount of borohydride nanosheets added is 0.05% to 0.15%.

15. The preparation method according to claim 1, characterized in that, The atmosphere for the sintering process includes nitrogen and / or argon.

16. The preparation method according to claim 1, characterized in that, The sintering process includes a first sintering and a second sintering.

17. The preparation method according to claim 16, characterized in that, The first sintering temperature is 400℃~600℃.

18. The preparation method according to claim 16, characterized in that, The first sintering time is 2h~4h.

19. The preparation method according to claim 16, characterized in that, The second sintering temperature is 600℃~800℃.

20. The preparation method according to claim 16, characterized in that, The second sintering time is 2h~4h.

21. An amorphous carbon-coated lithium manganese iron phosphate cathode material, characterized in that, The amorphous carbon-coated lithium manganese iron phosphate cathode material is prepared by the preparation method described in any one of claims 1-20.

22. A positive electrode plate, characterized in that, The positive electrode comprises the amorphous carbon-coated lithium manganese iron phosphate positive electrode material as described in claim 21.

23. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode as described in claim 22.

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