Modified Lithium Iron Manganese Phosphate Material, Its Preparation Method, Cathode, and Lithium-Ion Battery

Abstract

The present invention provides a modified lithium iron manganese phosphate material, a preparation method thereof, a positive electrode, and a lithium ion battery. The modified lithium iron manganese phosphate material includes an iron-based triphenylphosphine boride and a lithium iron manganese phosphate material, and the iron-based triphenylphosphine boride is located on the surface of the lithium iron manganese phosphate material. The chemical formula of the iron-based triphenylphosphine boride is FeCl 2‑x (BH4) x (PPh3)2, where the value range of x is 0 < x < 2. The provided modified lithium iron manganese phosphate material uses an iron-based triphenylphosphine boride to modify the lithium iron manganese phosphate material, which can effectively improve the electrochemical stability and electrical properties of the positive electrode material, and further improve the cycle performance and electrochemical performance of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and specifically relates to the modification of lithium iron manganese phosphate cathode materials. Background Art

[0002] As an important upgraded version of lithium iron phosphate batteries, lithium iron manganese phosphate batteries have always been highly anticipated by the market due to their advantages such as high voltage, high safety, and low cost. Lithium iron manganese phosphate has a higher voltage platform than lithium iron phosphate, and its theoretical energy density is 20% higher than that of lithium iron phosphate, which can to a certain extent break through the energy density bottleneck faced by lithium iron phosphate. Compared with ternary materials, lithium iron manganese phosphate batteries also have higher safety.

[0003] The introduction of manganese elements can improve the energy density of the original lithium iron phosphate battery, but after the introduction of manganese, the lithium ion diffusion rate and electronic conductivity of the material will both decrease. In addition, due to the dual voltage platform characteristics of lithium iron manganese phosphate batteries, there are challenges in management and control, which may affect the stability and reliability of the battery. Summary of the Invention

[0004] Aiming at the above technical problems, the purpose of the present invention is to provide a modified lithium iron manganese phosphate material, its preparation method, cathode, and lithium ion battery.

[0005] To achieve the above purpose, the present invention proposes the following solutions:

[0006] In the first aspect, a modified lithium iron manganese phosphate material is provided. The modified lithium iron manganese phosphate material includes iron-based triphenylphosphine boride and lithium iron manganese phosphate material, and the iron-based triphenylphosphine boride is located on the surface of the lithium iron manganese phosphate material. The chemical formula of the iron-based triphenylphosphine boride is FeCl 2-x (BH4) x (PPh3)2, where the value range of x is 0 < x < 2.

[0007] The present invention uses iron-based triphenylphosphine boride to modify lithium iron manganese phosphate material. The iron-based triphenylphosphine boride exhibits excellent redox activity and can adsorb irreversible decomposition products in the organic electrolyte to the greatest extent, so that the main material itself is not corroded by the electrolyte, thereby effectively improving the structural stability of the cathode material.

[0008] Further, the mass ratio of the iron-based triphenylphosphine boride to lithium iron manganese phosphate is 0.01~0.05:1.

[0009] Further, the chemical formula of the lithium iron manganese phosphate is LiMn y Fe 1-y PO4 / C, where the value range of y is 0.1 ≤ y ≤ 0.6.

[0010] Second aspect, a preparation method of a modified lithium iron manganese phosphate material is provided, including:

[0011] Dissolve ferrous chloride in an organic solvent, add an organic phosphorus ligand, and carry out a first reaction to obtain an intermediate product;

[0012] Add a borohydride to the intermediate product, dropwise add an organic amine solvent, carry out a second reaction, and after the reaction ends, carry out solid-liquid separation and drying to obtain an iron-based triphenylphosphine boride material;

[0013] Mix and ball-mill lithium iron manganese phosphate and the iron-based triphenylphosphine boride material, and carry out low-temperature sintering to obtain a modified lithium iron manganese phosphate material.

[0014] Furthermore, the organic phosphorus ligand is triphenylphosphine; the borohydride is at least one of sodium borohydride and lithium borohydride; the organic amine solvent is one or more of triethanolamine, ethanolamine, and ethylenediamine; the organic solvent is at least one of ethanol and tetrahydrofuran.

[0015] Furthermore, the molar ratio of ferrous chloride to the organic phosphorus ligand is 1:2 to 3.

[0016] Furthermore, the molar ratio of ferrous chloride to the borohydride is 1:1 to 2.

[0017] Furthermore, the molar ratio of the borohydride to the organic amine solvent is 1 to 2:0.01 to 0.05.

[0018] Furthermore, the temperature of the first reaction is 30 to 50 °C; the duration of the first reaction is 6 to 10 h; the first reaction is carried out in a protective atmosphere.

[0019] Furthermore, the temperature of the second reaction is 40 to 60 °C; the duration of the second reaction is 10 to 20 h; the second reaction is carried out in a protective atmosphere.

[0020] Furthermore, the mixing and ball-milling are carried out in a protective atmosphere.

[0021] Furthermore, the temperature of the low-temperature sintering is 200 to 300 °C; the duration of the low-temperature sintering is 2 to 6 h; the atmosphere of the low-temperature sintering is a nitrogen or argon atmosphere.

[0022] Third aspect, a positive electrode is provided, including the aforementioned modified lithium iron manganese phosphate material.

[0023] Fourth aspect, a lithium-ion battery is provided, including the aforementioned positive electrode.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The provided modified lithium iron manganese phosphate material is modified with iron-based triphenylphosphine boride for the lithium iron manganese phosphate material, which can effectively improve the electrochemical stability and electrical properties of the cathode material, and further improve the cycle performance and electrochemical performance of the battery.

[0026] The preparation method of the provided modified lithium iron manganese phosphate material has a simple process and is easy to operate. Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0028] Figure 1 It is the HRTEM image of the iron-based triphenylphosphine boride material prepared in step (2) of Example 1.

[0029] Figure 2 It is the EDS Mapping image of the iron-based triphenylphosphine boride material prepared in step (2) of Example 1, where (a), (b), (c), (d), (e), and (f) are the EDS Mapping images of Fe, Cl, C, P, O, and B elements respectively.

[0030] Figure 3 It is the TGA image of the iron-based triphenylphosphine boride material prepared in step (2) of Example 1.

[0031] Figure 4 It is the cycle performance image of the battery assembled with the cathode materials prepared in each example and Comparative Example 1.

[0032] Figure 5 It is the TEM images of the cathode material prepared in Example 1 before (a) and after (b) cycling.

[0033] Figure 6 It is the SEM image of the cathode material prepared in Example 1 after cycling.

[0034] Figure 7 It is the TEM images of the cathode material prepared in Comparative Example 1 before (a) and after (b) cycling.

[0035] Figure 8 It is the SEM image of the cathode material prepared in Comparative Example 1 after cycling. Detailed Embodiments

[0036] The applicant has found through research that by using iron-based triphenylphosphine boride FeCl 2-x (BH4) x(PPh3)2 is used to modify lithium iron manganese phosphate material, which can significantly improve the electrochemical stability and electrical properties of lithium iron manganese phosphate material, and then improve the cycle performance and electrochemical performance of the battery. Based on this, the present invention is completed.

[0037] Some embodiments provide a modified lithium iron manganese phosphate material, which includes iron-based triphenylphosphine boride and lithium iron manganese phosphate material, and the iron-based triphenylphosphine boride is located on the surface of the lithium iron manganese phosphate material. The chemical formula of the iron-based triphenylphosphine boride is FeCl 2-x (BH4) x (PPh3)2, where the value range of x is 0 < x < 2.

[0038] After analysis, the iron-based triphenylphosphine boride can significantly improve the electrochemical stability and electrical properties of the lithium iron manganese phosphate material. This may be because the iron-based triphenylphosphine boride can effectively combine with the organic groups in the lithium-based organic electrolyte through molecular bond action and can achieve preferential adsorption, so that the organic groups in the electrolyte are adsorbed in the structure of the iron-based triphenylphosphine boride, thus enabling the lithium ions in the electrolyte to achieve rapid lithium ion deintercalation and intercalation; and the iron-based triphenylphosphine boride can effectively adsorb the by-products of irreversible analysis of the electrolyte in the later stage of the electrochemical reaction, such as organic and inorganic fluoride by-products such as PF5 and HF, and form P-F and B-F molecular bonds with the iron-based triphenylphosphine boride, ultimately effectively improving the irreversible corrosion of the electrolyte to the host material and showing excellent structural stability.

[0039] In some preferred embodiments, the mass ratio of the iron-based triphenylphosphine boride to lithium iron manganese phosphate is 0.01~0.05:1, such as 0.01:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1, etc.

[0040] In some preferred embodiments, the chemical formula of the lithium iron manganese phosphate is LiMn y Fe 1-y PO4 / C, and the value range of y is 0.1 ≤ y ≤ 0.6.

[0041] It should be noted that the carbon content in the lithium iron manganese phosphate material can be the conventional carbon content in the art.

[0042] Some embodiments provide a preparation method of the modified lithium iron manganese phosphate material, including:

[0043] Dissolve ferrous chloride in an organic solvent, add an organic phosphorus ligand, and carry out a first reaction to obtain an intermediate product;

[0044] Add a borohydride to the intermediate product, dropwise add an organic amine solvent, carry out a second reaction, and after the reaction is completed, carry out solid-liquid separation and drying to obtain the iron-based triphenylphosphine boride material;

[0045] The lithium iron manganese phosphate and iron-based triphenylphosphine boride materials are mixed and ball-milled, and then sintered at a low temperature to obtain the modified lithium iron manganese phosphate material.

[0046] In some preferred embodiments, the organic phosphorus ligand is triphenylphosphine.

[0047] In some preferred embodiments, the borohydride is at least one of sodium borohydride and lithium borohydride.

[0048] In some preferred embodiments, the organic amine solvent is one or more of triethanolamine, ethanolamine, and ethylenediamine.

[0049] In some preferred embodiments, the organic solvent is at least one of ethanol and tetrahydrofuran.

[0050] In some preferred embodiments, the molar ratio of ferrous chloride to the organic phosphorus ligand is 1:2 to 3, such as 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9, 1:3, etc.

[0051] In some preferred embodiments, the molar ratio of ferrous chloride to the borohydride is 1:1 to 2, such as 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, etc.

[0052] In some preferred embodiments, the molar ratio of the borohydride to the organic amine solvent is 1 to 2:0.01 to 0.05, such as 20:1, 40:1, 60:1, 80:1, 100:1, 120:1, 140:1, 160:1, 180:1, 200:1, etc.

[0053] In some preferred embodiments, the temperature of the first reaction is 30 to 50 °C, such as 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, etc.; the duration of the first reaction is 6 to 10 h, such as 6 h, 7 h, 8 h, 9 h, 10 h, etc.; the first reaction is carried out in a protective atmosphere, such as a nitrogen atmosphere, an inert atmosphere (such as an argon atmosphere, etc.).

[0054] In some preferred embodiments, the temperature of the second reaction is 40 to 60 °C, such as 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, etc.; the duration of the second reaction is 10 to 20 h, such as 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, etc.; the second reaction is carried out in a protective atmosphere, such as a nitrogen atmosphere, an inert atmosphere (such as an argon atmosphere, etc.).

[0055] In some preferred embodiments, the hybrid ball milling is carried out in a protective atmosphere, such as a nitrogen atmosphere, an inert atmosphere (such as an argon atmosphere, etc.).

[0056] In some preferred embodiments, the temperature of the low-temperature sintering is 200-300 °C, such as 200 °C, 220 °C, 250 °C, 280 °C, 300 °C, etc.

[0057] In some preferred embodiments, the duration of the low-temperature sintering is 2-4 h, such as 2 h, 2.5 h, 3 h, 3.5 h, 4 h, etc.

[0058] In some preferred embodiments, the atmosphere of the low-temperature sintering is a nitrogen or argon atmosphere.

[0059] The lithium iron manganese phosphate material can be realized by a conventional preparation method.

[0060] Some embodiments provide a positive electrode, including the aforementioned modified lithium iron manganese phosphate material.

[0061] Some embodiments provide a lithium-ion battery, including the aforementioned positive electrode.

[0062] For the convenience of understanding the present invention, the present invention will be described more comprehensively and in detail below in conjunction with the accompanying drawings of the specification and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0063] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0064] Unless otherwise specifically stated, various raw materials, reagents, instruments and equipment used in the present invention can be obtained through the market or can be prepared by existing methods.

[0065] Example 1

[0066] (1) 0.2 mol of manganese sulfate and 0.2 mol of ferrous sulfate were dispersed in 400 ml of deionized water to form a metal salt solution. Another 0.412 mol of (NH4)2HPO4 was dissolved in 200 ml of deionized water to form a phosphate solution. The phosphate solution was added to the metal salt solution, and continuous stirring was carried out. After reacting for 16 h, a lithium iron manganese phosphate precursor was obtained after filtration, washing and drying. The lithium iron manganese phosphate precursor material was ball-milled and pulverized with 0.21 mol of lithium carbonate and 8 mmol of graphene, and then sintered at 900 °C for 22 h in a nitrogen atmosphere to prepare a lithium iron manganese phosphate positive electrode material.

[0067] (2) Dissolve 0.1 mol of FeCl2 in 800 ml of ethanol, add 0.25 mol of triphenylphosphine, and react at 40 °C for 8 h to obtain the intermediate product FeCl2(PPh3)2; further add 0.15 mol of sodium borohydride to the above solution, and drop 3 mmol of ethylenediamine to promote the dissolution of the boride, and continue the reaction. React for 16 h under heating conditions at 45 °C. After the reaction is completed, a multifunctional iron-based triphenylphosphine boride material can be prepared. The above reactions are all carried out under a nitrogen atmosphere.

[0068] The HRTEM image of the prepared iron-based triphenylphosphine boride complex material is as Figure 1 shown. It can be seen from the figure that the lattice fringes of the iron-based triphenylphosphine boride prepared in step (2) are a single-phase material phase, proving that the prepared iron-based triphenylphosphine boride is a pure phase rather than a composite. The EDS Mapping image of the iron-based triphenylphosphine boride is as Figure 2 shown. It can be seen from the figure that the elements in the iron-based triphenylphosphine boride material phase are evenly distributed, proving that the iron-based triphenylphosphine boride has been successfully synthesized. Combining its elements Fe, Cl, B, as well as P and C (elements such as H cannot be detected), the chemical formula of the product can be determined as FeCl 2-x (BH4) x (PPh3)2.

[0069] TGA test parameters: The test atmosphere is a nitrogen atmosphere, the test temperature range is from room temperature to 600 °C, the heating rate is 1 °C / min, and the sample weight is 1 g. The sample is ground into a powder.

[0070] The TGA image of the prepared complex material is as Figure 3 shown. From Figure 3 it can be seen that there is no obvious weight change in the complex material below 350 °C, indicating that the complex is stably present below 350 °C in an inert atmosphere.

[0071] (3) In a glove box filled with nitrogen, mix 10 g of lithium iron manganese phosphate prepared in step (1) with 0.3 g of the iron-based triphenylphosphine boride material prepared in step (2). After grinding and solid-phase mixing, seal the mixed material and transfer it to a tube furnace for low-temperature sintering at 240 °C for 3 h to prepare a lithium iron manganese phosphate material composite with iron-based triphenylphosphine boride.

[0072] Comparative Example 1

[0073] Disperse 0.2 mol of manganese sulfate and 0.2 mol of ferrous sulfate in 400 ml of deionized water to form a metal salt solution. Separately, dissolve 0.412 mol of (NH4)2HPO4 in 200 ml of deionized water to form a phosphate solution. Add the phosphate solution to the metal salt solution and continuously stir. After fully reacting for 16 h, filter, wash, and dry to obtain the lithium iron manganese phosphate precursor. After ball-milling and pulverizing the lithium iron manganese phosphate precursor material with 0.21 mol of lithium carbonate and 8.4 mmol of graphene, sinter at 900 °C for 22 h under a nitrogen atmosphere to prepare the lithium iron manganese phosphate cathode material.

[0074] Example 2

[0075] (1) Disperse 0.24 mol of manganese sulfate and 0.16 mol of ferrous sulfate in 400 ml of deionized water to form a metal salt solution. Separately, dissolve 0.408 mol of (NH4)2HPO4 in 200 ml of deionized water to form a phosphate solution. Add the phosphate solution to the metal salt solution and continuously stir. After fully reacting for 10 h, filter, wash, and dry to obtain the lithium iron manganese phosphate precursor. After ball-milling and pulverizing the lithium iron manganese phosphate precursor material with 0.204 mol of lithium carbonate and 4 mmol of layered graphite, sinter at 800 °C for 30 h under a nitrogen atmosphere to prepare the lithium iron manganese phosphate cathode material.

[0076] (2) Dissolve 0.1 mol of FeCl2 in 800 ml of ethanol, add 0.2 mol of triphenylphosphine, and react at 30 °C for 10 h to obtain the FeCl2(PPh3)2 intermediate product; further add 0.1 mol of lithium borohydride to the above solution, drop in 1 mmol of triethanolamine to promote the dissolution of the boride, and continue the reaction. React at 40 °C under heating conditions for 20 h. After the reaction ends, a multifunctional iron-based triphenylphosphine boride material can be prepared. The above reactions are all carried out under a nitrogen atmosphere.

[0077] (3) In a glove box filled with nitrogen, mix 10 g of the lithium iron manganese phosphate prepared in step (1) with 0.1 g of the iron-based triphenylphosphine boride material prepared in step (2). After grinding and solid-phase mixing, seal the mixed material and transfer it to a tubular furnace for low-temperature sintering at 200 °C for 4 h to prepare the lithium iron manganese phosphate material composite with iron-based triphenylphosphine boride.

[0078] Example 3

[0079] (1) 0.04 mol of manganese nitrate and 0.36 mol of ferrous nitrate were dispersed in 400 ml of deionized water to form a metal salt solution. Separately, a certain amount of 0.42 mol of (NH4)2HPO4 was dissolved in 200 ml of deionized water to form a phosphate solution. The phosphate solution was added to the metal salt solution, and continuous stirring was carried out. After reacting fully for 24 h, the lithium iron manganese phosphate precursor was obtained through filtration, washing, and drying. The lithium iron manganese phosphate precursor material, 0.21 mol of lithium carbonate, and 0.012 mol of flaky graphite were ball-milled and pulverized, and then sintered at 900 °C for 22 h under a nitrogen atmosphere to prepare the lithium iron manganese phosphate cathode material.

[0080] (2) 0.1 mol of FeCl2 was dissolved in 800 ml of ethanol, 0.3 mol of triphenylphosphine was added, and the reaction was carried out at 50 °C for 6 h to obtain the intermediate product FeCl2(PPh3)2; further, 0.2 mol of sodium borohydride was added to the above solution, and 5 mmol of ethanolamine was dropped in to promote the dissolution of the boride. The reaction continued, and the reaction was carried out at 60 °C under heating conditions for 10 h. After the reaction ended, the multifunctional iron-based triphenylphosphine boride material was prepared. The above reactions were all carried out in a reaction chamber under a nitrogen atmosphere.

[0081] (3) In a glove box filled with nitrogen, 10 g of the lithium iron manganese phosphate prepared in step (1) and 0.5 g of the iron-based triphenylphosphine boride material prepared in step (2) were ground and solid-phase mixed. After the mixed material was sealed, it was transferred to a tube furnace and sintered at a low temperature of 300 °C for 2 h to prepare the lithium iron manganese phosphate material composite with iron-based triphenylphosphine boride.

[0082] The materials prepared in Examples 1 - 3 and Comparative Example 1 were assembled into batteries by the following method:

[0083] The materials prepared in Examples 1 - 3 and Comparative Example 1 were used as the cathode materials respectively, and were mixed with the conductive agent acetylene black (AB) and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. Using N-methylpyrrolidone (NMP) as the solvent, the mixture was placed in a small beaker and stirred at a speed of 800 r / min for 2 h to obtain a slurry. The slurry was coated on the current collector aluminum foil using an automatic coater, placed flat on tempered glass and transferred to a vacuum drying oven at 85 °C for drying for 4 h. After punching into a pole piece with a diameter of 12 mm, it was dried in a vacuum drying oven at 105 °C for 4 h, and placed in a glove box with a water content and oxygen content both lower than 0.1 ppm and filled with an argon atmosphere for 4 h to reduce the moisture adsorbed by the pole piece during the transfer process. Then, a CR2032 type button battery was assembled in the glove box. This battery used a pure metal lithium sheet with a diameter of 16 mm and a thickness of 0.5 mm as the negative electrode, and a porous polyethylene film with a diameter of 18 mm and a model of Celgard 2300 as the separator.

[0084] After the battery is assembled, it is aged for 12 h, and then at a voltage of 2 - 4.3 V, it is activated for 3 cycles at a current density of 0.1 C and then cycled 100 times at a current density of 1 C.

[0085] Figure 4 It is the cyclic performance diagram of the batteries assembled with the cathode materials prepared in each example and Comparative Example 1. From Figure 4 It can be seen that the first discharge specific capacity of the batteries assembled with the cathode materials prepared in Examples 1 - 3 at 0.1 C and the cyclic performance at 1 C are significantly better than those of the batteries assembled with the cathode materials prepared in Comparative Example 1. After analysis, this may be because iron-based triphenylphosphine boride can effectively combine with the organic groups in the lithium-based organic electrolyte through molecular bond action and can achieve preferential adsorption, enabling the organic groups in the electrolyte to be adsorbed in the structure of iron-based triphenylphosphine boride, thereby enabling the lithium ions in the electrolyte to achieve rapid lithium ion deintercalation and intercalation; and iron-based triphenylphosphine boride can effectively adsorb the by-products of irreversible analysis of the electrolyte in the later stage of the electrochemical reaction, such as organic and inorganic fluoride by-products such as PF5 and HF, and form P-F and B-F molecular bonds with iron-based triphenylphosphine boride, ultimately effectively improving the irreversible corrosion of the electrolyte to the host material and showing excellent structural stability.

[0086] Figure 5 It is the TEM diagram of the cathode material prepared in Example 1 before cycling (a) and after 100 cycles at 1 C (b). By comparing the surfaces of the cathode materials before and after the electrochemical cycle, it can be seen that the lattice fringes of the cathode material of Example 1 are still obvious after cycling and there are fewer by-products. Figure 6 It is the SEM diagram of the cathode material prepared in Example 1 after cycling. From Figure 6 it can be seen that the cathode material after cycling is still intact.

[0087] Figure 7 It is the TEM diagram of the cathode material prepared in Comparative Example 1 before cycling (a) and after 100 cycles at 1 C (b). By comparing the surfaces of the cathode materials before and after the electrochemical cycle, it can be seen that an obvious side reaction product layer is formed on the surface of the cathode material of Comparative Example 1 after cycling. Figure 8 It is the SEM diagram of the cathode material prepared in Comparative Example 1 after 100 cycles at 1 C. From Figure 8 it can be seen that obvious cracks occur in the particles of the cathode material of Comparative Example 1 after cycling, indicating that the structural stability of the cathode material prepared in Comparative Example 1 is poor during the electrochemical cycle.

[0088] The above comprehensive analysis further shows that the structural stability and interfacial stability of the cathode material prepared in Example 1 are significantly better than those of the cathode material prepared in Comparative Example 1, indicating that the coating modification has significantly improved the stability of the cathode material in the electrochemical cycle environment.

[0089] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. Modified lithium iron manganese phosphate material, characterized in that, The modified lithium iron manganese phosphate material includes an iron-based triphenylphosphine boride and a lithium iron manganese phosphate material, and the iron-based triphenylphosphine boride is located on the surface of the lithium iron manganese phosphate material. The chemical formula of the iron-based triphenylphosphine boride is FeCl 2-x (BH4) x (PPh3)2, where the value range of x is 0 < x < 2.

2. The modified lithium iron manganese phosphate material according to claim 1, characterized in that, The mass ratio of the iron-based triphenylphosphine boride to lithium iron manganese phosphate is 0.01~0.05:

1.

3. The modified lithium iron manganese phosphate material according to claim 1 or 2, wherein The chemical formula of the lithium iron manganese phosphate is LiMn y Fe 1-y PO4 / C, and the value range of y is 0.1 ≤ y ≤ 0.

6.

4. The preparation method of the modified lithium iron manganese phosphate material according to any one of claims 1 to 3, characterized in that, Comprising: Dissolve ferrous chloride in an organic solvent, add an organic phosphorus ligand, and carry out a first reaction to obtain an intermediate product; The organic phosphorus ligand is triphenylphosphine; Add a borohydride to the intermediate product, dropwise add an organic amine solvent, carry out a second reaction, and after the reaction is completed, carry out solid-liquid separation and drying to obtain an iron-based triphenylphosphine boride material; Mix and ball-mill lithium iron manganese phosphate and the iron-based triphenylphosphine boride material, and carry out low-temperature sintering to obtain a modified lithium iron manganese phosphate material; The temperature of the low-temperature sintering is 200~300 °C.

5. The preparation method of the modified lithium iron manganese phosphate material according to claim 4, wherein, The borohydride is at least one of sodium borohydride and lithium borohydride; the organic amine solvent is one or more of triethanolamine, ethanolamine, and ethylenediamine; the organic solvent is at least one of ethanol and tetrahydrofuran.

6. The preparation method of the modified lithium iron manganese phosphate material according to claim 4, characterized in that, The molar ratio of ferrous chloride to the organic phosphorus ligand is 1:2~3; The molar ratio of ferrous chloride to the borohydride is 1:1~2; The molar ratio of the borohydride to the organic amine solvent is 1~2:0.01~0.

05.

7. The preparation method of the modified lithium iron manganese phosphate material according to claim 4, characterized in that, The temperature of the first reaction is 30~50 °C; the duration of the first reaction is 6~10 h; the first reaction is carried out under a protective atmosphere; The temperature of the second reaction is 40~60 °C; the duration of the second reaction is 10~20 h; the second reaction is carried out under a protective atmosphere; The mixing and ball-milling are carried out under a protective atmosphere.

8. The preparation method of the modified lithium iron manganese phosphate material according to claim 4, characterized in that, The duration of the low-temperature sintering is 2~6 h; the atmosphere of the low-temperature sintering is a nitrogen or argon atmosphere.

9. The positive electrode, characterized in that, Comprising the modified lithium iron manganese phosphate material according to any one of claims 1~3.

10. A lithium-ion battery, characterized in that, Comprising the positive electrode according to claim 9.

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