Preparation method for and use of iron phosphate material

Abstract

The present invention relates to the field of lithium-ion battery positive electrode materials. A preparation method for an iron phosphate material. The method comprises the following steps: mixing an organic phosphorus solution with humic acid, so as to obtain a mixed solution; adding a solution containing ferrate radicals into the mixed solution, so as to obtain a solution containing ferric iron; adjusting the pH of the solution containing ferric iron to generate a precipitate, and filtering same to obtain the precipitate; and drying the precipitate, and removing crystal water, so as to obtain an anhydrous FePO4 material. By using a ferrate to oxidize organic phosphorus, the ferrate itself is reduced into ferric iron, and provides an iron source and also serves as an oxidizing agent; by introducing humic acid during the oxidation process, a competitive oxidation relationship with the organic phosphorus is formed; the ferrate is activated into an iron-based intermediate having higher oxidizability; and after the humic acid is oxidized, the electronegativity is enhanced, such that iron ions can be adsorbed to play a dispersing role, thereby preventing the generated iron phosphate from being agglomerated, such that the particle size thereof is uniform, which is conductive to improving the electrical properties of the subsequently prepared lithium iron phosphate.

Description

Preparation method and application of iron phosphate material Technical Field

[0001] The present disclosure relates to the field of lithium-ion battery positive electrode materials, and in particular to a preparation method and application of an iron phosphate material. Background Art

[0002] With the vigorous development of new energy sources, the application scope of lithium batteries in various industries has gradually expanded. From small household electrical appliances and digital products to large-scale transportation and industrial manufacturing, lithium batteries can be found everywhere. Lithium iron phosphate batteries, in particular, benefit from the stability of the olivine structure, which has excellent cycle performance and safe use, and has broad commercial prospects in electric vehicles. Iron phosphate, an important raw material for lithium iron phosphate, is mainly prepared by using soluble iron salts and phosphates as raw materials, oxidizing divalent iron to trivalent iron, and adjusting the pH to produce battery-grade iron phosphate through co-precipitation. This method easily causes primary particles to agglomerate into secondary particles, affecting the quality of the synthesized lithium iron phosphate and causing it to have poor conductivity. In addition, the use of iron salts and phosphates as raw materials will introduce excessive impurities, increasing the cost of process impurity removal.

[0003] To this end, patent publication CN116409767A uses an organic phosphorus source and an organic iron source as raw materials. These are first oxidized at high temperature and then placed in a high-temperature, low-pressure reactor containing a carbon material. Adsorption occurs between the raw materials and the carbon material surface, increasing the reaction contact area and dispersibility. The resulting nano-iron phosphate is then calcined at high temperature to produce less agglomerated nano-iron phosphate. While this reduces the introduction of impurities, the reaction, using organic materials as raw materials, still requires the addition of an oxidant for oxidation, and adds the step of high-temperature adsorption of the oxidized raw materials and carbon material in the reactor.

[0004] Summary of the Invention

[0005] Based on this, the purpose of the present disclosure is to provide a method for preparing iron phosphate material, which uses ferrate to oxidize organic phosphorus. Ferrate not only provides an iron source but also acts as an oxidant. In the process of preparing iron phosphate material, the use of a large amount of oxidant is avoided, which causes waste.

[0006] Part 1:

[0007] A method for preparing an iron phosphate material comprises the following steps:

[0008] mixing the organophosphorus solution with humic acid to obtain a mixed solution;

[0009] adding a ferrate solution to the mixed solution to obtain a solution containing trivalent iron;

[0010] Adjusting the pH of the ferric iron-containing solution to generate precipitation, and filtering to obtain a precipitate;

[0011] The precipitate is dried and crystal water is removed to obtain anhydrous FePO4 material.

[0012] The present invention uses ferrate to oxidize organic phosphorus. The ferrate itself is reduced to trivalent iron, which not only provides an iron source but also serves as an oxidant. Humic acid is introduced into the oxidation process to form a competitive oxidation relationship with the organic phosphorus, and the ferrate is activated into a higher-order iron-based intermediate with higher oxidizability. After the humic acid is oxidized, the electronegativity is enhanced and it can adsorb iron ions to play a dispersing role, preventing the generated iron phosphate from agglomerating. The particle size is uniform, which is beneficial to improving the electrical properties of the subsequently prepared lithium iron phosphate.

[0013] Ferrate (FeO4) 2- By using its strong oxidizing property, it can weaken the P=O, P=S and other bonds in organic phosphorus and cause them to break, thereby degrading them into CO2, PO4 3- , H2O and other inorganic small molecule products, ferrate itself is reduced to trivalent iron, and the trivalent iron and oxidized inorganic phosphate co-precipitate to form ferric phosphate, avoiding the tedious oxidation steps of iron source and the introduction of too many impurities in the traditional process.

[0014] Furthermore, ferrate oxidation during the auto-redox process produces hydroxide ions, and organic phosphorus degradation produces water, which, to a certain extent, regulates pH and reduces the introduction of alkaline substances. The reaction time required for ferrate to oxidize organic phosphorus to inorganic phosphorus can reduce the crystallization and growth rate of ferric phosphate, thereby promoting the orderly growth of ferric phosphate crystals.

[0015] The organophosphorus solution contains a small amount of humic acid. During the oxidation of ferrate, humic acid and organophosphorus form an oxidative competition. Humic acid contains a large number of active functional groups, which can first react with ferrate to activate Fe(VI) to form higher-order iron-based intermediates Fe(V) / Fe(IV). This has a higher oxidizing power and enhances the efficiency of organophosphorus oxidation. The oxidized humic acid has increased hydrophilicity and electronegativity, which can adsorb the reduced trivalent iron ions and disperse them, preventing the resulting ferric phosphate from agglomerating. The humic acid and the resulting ferric phosphate precipitate form a mixture. During the dehydration of the ferric phosphate, the humic acid evaporates into gas, leaving pores within the ferric phosphate.

[0016] As a preferred embodiment, the organic phosphorus is at least one of phosphate, diethyl phosphate, and triethyl phosphate.

[0017] As a preferred solution, the concentration of the organic phosphorus is 0.01-0.06 mol / L, which is conducive to the full oxidation of the organic phosphorus by ferrate. Too high an organic phosphorus concentration will result in insufficient and incomplete oxidation.

[0018] As a preferred embodiment, the humic acid is at least one of fulvic acid and palmitic acid.

[0019] As a preferred solution, the concentration of humic acid in the mixed solution is 1-6 mg / L. Humic acid is a competitive oxidant. If the concentration is too high, it will affect the amount of organic phosphorus participating in the oxidation.

[0020] As a preferred embodiment, the ferrate-containing solution is at least one of sodium ferrate, potassium ferrate, and ferric acid.

[0021] As a preferred solution, the concentration of the ferrate is 0.1-0.3 mol / L. Under acidic conditions, the higher the ferrate concentration, the faster the decomposition, so the concentration cannot be too high.

[0022] As a preferred embodiment, the ferrate-containing solution is slowly and uniformly added to the mixed solution over 1 hour; in the ferric iron-containing solution, the molar ratio of Fe to P is 1-1.3:1; ferrate decomposes quickly and easily under acidic conditions, so it needs to be added slowly to prevent excessive decomposition; a slightly higher molar amount of Fe than that of P is conducive to the full oxidation of organic phosphorus.

[0023] As a preferred solution, when the ferrate-containing solution is added to the mixed solution, the pH of the mixed solution needs to be maintained at no more than 2.3. Since ferrate is converted into trivalent iron and hydroxide ions after reduction, lowering the pH value can avoid the generation of iron hydroxide and improve the utilization rate of iron ions.

[0024] As a preferred solution, the pH of the ferric iron solution is adjusted to 1.8-2.2 and heated to 65-95° C. for 2-6 hours. The pH is controlled to avoid the formation of ferric hydroxide precipitation. Heating the ferric iron solution can accelerate precipitation.

[0025] As a preferred solution, before drying the precipitate, it is also necessary to wash it with deionized water and ethanol until the pH of the supernatant is neutral. The drying temperature is 70-110°C, the dehydration temperature is 500-650°C, and the dehydration time is 3-5h.

[0026] Part II:

[0027] An anhydrous FePO4 material is prepared by the preparation method of the iron phosphate material described in the first part.

[0028] Part III:

[0029] A lithium iron phosphate positive electrode material is prepared from the anhydrous FePO4 material described in the second part.

[0030] Part 4:

[0031] A lithium-ion battery comprises the lithium iron phosphate positive electrode material described in the third part.

[0032] Part 5:

[0033] An application of an iron phosphate material comprises the following steps:

[0034] The anhydrous FePO4 material described in the second part, lithium carbonate, and glucose are uniformly dispersed and mixed in water according to the stoichiometric ratio of iron, lithium, and carbon elements of 1:1-1.05:0.04-0.15, ball milled at a speed of 500-850 r / min for 4-5 h until the mixture is uniform, and then spray dried to obtain a precursor powder;

[0035] The precursor powder was heated to 300° C. at a heating rate of 3° C. / min under a nitrogen atmosphere and kept at that temperature for 3 h, and then heated to 750° C. and calcined at a high temperature for 6.5 h to obtain a LiFePO 4 / C positive electrode material.

[0036] As a preferred solution, the LiFePO4 / C positive electrode material, acetylene black, and polyvinylidene fluoride are uniformly mixed in N-methylpyrrolidone at a mass ratio of 92:4:4 to obtain a mixed slurry;

[0037] The mixed slurry is coated on aluminum foil, and then placed in a vacuum drying oven for drying to obtain a positive electrode sheet;

[0038] The positive electrode sheet is placed in an argon glove box to assemble into a battery, the negative electrode is a metal lithium sheet, the separator is a polypropylene porous membrane, and the electrolyte consists of LiPF6, ethylene carbonate and dimethyl carbonate, wherein the LiPF6 concentration is 1 mol / L, and the volume ratio of ethylene carbonate and dimethyl carbonate is 1:1. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG1 is a SEM image of the iron phosphate prepared in Example 2;

[0040] FIG2 is a SEM image of the iron phosphate prepared in Comparative Example 2;

[0041] FIG3 is an XRD pattern of iron phosphate prepared in Example 2. DETAILED DESCRIPTION

[0042] A method for preparing an iron phosphate material comprises the following steps:

[0043] Mixing 0.01-0.06 mol / L of an organophosphorus solution and humic acid, stirring for 20-45 minutes to obtain a mixed solution, wherein the concentration of the humic acid in the mixed solution is 1-6 mg / L;

[0044] Slowly and uniformly adding a 0.1-0.3 mol / L ferrate solution to the mixed solution over 1 hour to adjust the molar ratio of ferrate to Fe and P in the organophosphorus to 1.2:1, continuing stirring for 0.5-1 hour after the addition is complete, and adding hydrochloric acid when the pH of the mixed solution is too high to ensure that the pH of the mixed solution is no greater than 2.3, thereby obtaining a solution containing trivalent iron;

[0045] The ferric iron solution is heated to 65-95° C. for 2-6 hours, the pH is adjusted to 1.8-2.2, and the FePO 4 ·xH 2 O precipitate is obtained after filtering;

[0046] The FePO4·xH2O precipitate is washed with deionized water and ethanol until the pH of the supernatant is neutral, then placed in a drying oven at 70-110°C for drying, and finally placed in a muffle furnace and heated to 500-650°C at a certain heating rate and kept for 3-5 hours to remove crystallization water, thereby obtaining anhydrous FePO4 material.

[0047] An application of an iron phosphate material comprises the following steps:

[0048] The anhydrous FePO4 material, lithium carbonate, and glucose are uniformly dispersed and mixed in water according to a stoichiometric ratio of iron, lithium, and carbon elements of 1:1-1.05:0.04-0.15, ball-milled at a speed of 500-850 r / min for 4-5 hours until the mixture is uniformly mixed, and then spray-dried to obtain a precursor powder;

[0049] The precursor powder was heated to 300°C at a heating rate of 3°C / min under a nitrogen atmosphere and kept at that temperature for 3 hours, and then heated to 750°C and calcined at a high temperature for 6.5 hours to obtain a LiFePO4 / C positive electrode material;

[0050] The LiFePO4 / C positive electrode material, acetylene black, and polyvinylidene fluoride are uniformly mixed in N-methylpyrrolidone at a mass ratio of 92:4:4 to obtain a mixed slurry;

[0051] The mixed slurry is coated on aluminum foil, and then placed in a vacuum drying oven for drying to obtain a positive electrode sheet;

[0052] The positive electrode sheet is placed in an argon glove box to assemble into a battery, the negative electrode is a metal lithium sheet, the separator is a polypropylene porous membrane, and the electrolyte consists of LiPF6, ethylene carbonate and dimethyl carbonate, wherein the LiPF6 concentration is 1 mol / L, and the volume ratio of ethylene carbonate and dimethyl carbonate is 1:1.

[0053] Example 1

[0054] The present invention discloses a method for preparing an iron phosphate material, comprising the following steps:

[0055] A 0.02 mol / L phosphate aqueous solution and humic acid were mixed and stirred for 30 minutes to obtain a mixed solution, wherein the concentration of the humic acid in the mixed solution was 1 mg / L;

[0056] Slowly and uniformly adding a 0.2 mol / L potassium ferrate solution to the mixed solution over 1 hour to adjust the molar ratio of Fe to P in the potassium ferrate and phosphate to 1.2:1, stirring was continued for 0.5 hour after the addition was completed. When the pH was too high, hydrochloric acid was added to ensure that the pH of the mixed solution was not greater than 2, thereby obtaining a solution containing trivalent iron;

[0057] The ferric iron solution was heated to 85° C. for 5 h, 25% ammonia was added to adjust the pH to 2.0, and FePO 4 ·xH 2 O precipitate was obtained after filtration;

[0058] The FePO4·xH2O precipitate was washed with deionized water and ethanol until the pH of the supernatant was neutral, and then dried in a drying oven at 70°C. Finally, the precipitate was placed in a muffle furnace and heated to 600°C at a heating rate of 5°C / min and kept for 3 hours to remove the crystallization water, thereby obtaining anhydrous FePO4 material.

[0059] The application of the iron phosphate material disclosed in the present invention comprises the following steps:

[0060] The anhydrous FePO4 material, lithium carbonate, and glucose are uniformly dispersed and mixed in water according to a stoichiometric ratio of iron, lithium, and carbon elements of 1:1.03:0.06, ball-milled at a speed of 500 r / min for 4 h until the mixture is uniformly mixed, and then spray-dried to obtain a precursor powder;

[0061] The precursor powder was heated to 300°C at a heating rate of 3°C / min under a nitrogen atmosphere and kept at that temperature for 3 hours, and then heated to 750°C and calcined at a high temperature for 6.5 hours to obtain a LiFePO4 / C positive electrode material;

[0062] The LiFePO4 / C positive electrode material, acetylene black, and polyvinylidene fluoride are uniformly mixed in N-methylpyrrolidone at a mass ratio of 92:4:4 to obtain a mixed slurry;

[0063] The mixed slurry is coated on aluminum foil, and then placed in a vacuum drying oven for drying to obtain a positive electrode sheet;

[0064] The positive electrode sheet is placed in an argon glove box to assemble into a battery, the negative electrode is a metal lithium sheet, and the electrolyte consists of LiPF6, ethylene carbonate and dimethyl carbonate, wherein the LiPF6 concentration is 1 mol / L, and the volume ratio of ethylene carbonate and dimethyl carbonate is 1:1.

[0065] Example 2

[0066] The present invention discloses a method for preparing an iron phosphate material, comprising the following steps:

[0067] The concentration of the humic acid was 3 mg / L. Other conditions were exactly the same as those in Example 1.

[0068] Example 3

[0069] The present invention discloses a method for preparing an iron phosphate material, comprising the following steps:

[0070] The concentration of the humic acid was 5 mg / L. Other conditions were exactly the same as those in Example 1.

[0071] Example 4

[0072] The present invention discloses a method for preparing an iron phosphate material, comprising the following steps:

[0073] The concentration of the phosphate ester is 0.01 mol / L. Other conditions are exactly the same as those in Example 1.

[0074] Example 5

[0075] The present invention discloses a method for preparing an iron phosphate material, comprising the following steps:

[0076] The concentration of the phosphate ester is 0.05 mol / L. Other conditions are exactly the same as those in Example 1.

[0077] Comparative Example 1

[0078] A 0.02 mol / L aqueous phosphate solution was prepared, and a 0.2 mol / L potassium ferrate solution was slowly and uniformly added to the aqueous phosphate solution over 1 hour to adjust the molar ratio of Fe to P in the potassium ferrate and phosphate to 1.2:1. Stirring was continued for 0.5 hours after the addition was completed. If the pH was too high, hydrochloric acid was added to ensure that the pH of the mixture was no greater than 2, thereby obtaining a solution containing trivalent iron;

[0079] The ferric iron solution was heated to 85° C. for 5 h, 25% ammonia was added to adjust the pH to 2.0, and FePO 4 ·xH 2 O precipitate was obtained after filtration;

[0080] The FePO4·xH2O precipitate was washed with deionized water and ethanol until the pH of the supernatant was neutral, and then dried in a drying oven at 70°C. Finally, the precipitate was placed in a muffle furnace and heated to 600°C at a heating rate of 5°C / min and kept for 3 hours to remove the crystallization water, thereby obtaining anhydrous FePO4 material.

[0081] The anhydrous FePO4 material, lithium carbonate, and glucose are uniformly dispersed and mixed in water according to a stoichiometric ratio of iron, lithium, and carbon elements of 1:1.03:0.06, ball-milled at a speed of 500 r / min for 4 h until the mixture is uniformly mixed, and then spray-dried to obtain a precursor powder;

[0082] The precursor powder was heated to 300°C at a heating rate of 3°C / min under a nitrogen atmosphere and kept at that temperature for 3 hours, and then heated to 750°C and calcined at a high temperature for 6.5 hours to obtain a LiFePO4 / C positive electrode material;

[0083] The LiFePO4 / C positive electrode material, acetylene black, and polyvinylidene fluoride are uniformly mixed in N-methylpyrrolidone at a mass ratio of 92:4:4 to obtain a mixed slurry;

[0084] The mixed slurry is coated on aluminum foil, and then placed in a vacuum drying oven for drying to obtain a positive electrode sheet;

[0085] The positive electrode sheet is placed in an argon glove box to assemble into a battery, the negative electrode is a metal lithium sheet, and the electrolyte consists of LiPF6, ethylene carbonate and dimethyl carbonate, wherein the LiPF6 concentration is 1 mol / L, and the volume ratio of ethylene carbonate and dimethyl carbonate is 1:1.

[0086] Comparative Example 2

[0087] A 0.2 mol / L diammonium hydrogen phosphate aqueous solution and a 0.2 mol / L potassium ferrate solution were mixed to obtain a mixed solution, wherein the molar ratio of Fe to P in the mixed solution was 1:1;

[0088] The mixed solution was heated to 85° C. for 5 h, 25% ammonia water was added to adjust the pH to 2.0, and FePO 4 ·xH 2 O precipitate was obtained after filtration;

[0089] The FePO4·xH2O precipitate was washed with deionized water and ethanol until the pH of the supernatant was neutral, and then dried in a drying oven at 70°C. Finally, the precipitate was placed in a muffle furnace and heated to 600°C at a heating rate of 5°C / min and kept for 3 hours to remove the crystallization water, thereby obtaining anhydrous FePO4 material.

[0090] The steps of using anhydrous FePO4 material to prepare precursor, positive electrode material, positive electrode plate and battery assembly are the same as those in Comparative Example 1.

[0091] Comparative Example 3

[0092] A 0.2 mol / L aqueous diammonium hydrogen phosphate solution, a 0.2 mol / L potassium ferrate solution, and humic acid were mixed to obtain a mixed solution, wherein the molar ratio of Fe to P in the mixed solution was 1:1 and the concentration of humic acid was 3 mg / L;

[0093] The mixed solution was heated to 85° C. for 5 h, 25% ammonia water was added to adjust the pH to 2.0, and FePO 4 ·xH 2 O precipitate was obtained after filtration;

[0094] The FePO4·xH2O precipitate was washed with deionized water and ethanol until the pH of the supernatant was neutral, and then dried in a drying oven at 70°C. Finally, the precipitate was placed in a muffle furnace and heated to 600°C at a heating rate of 5°C / min and kept for 3 hours to remove the crystallization water, thereby obtaining anhydrous FePO4 material.

[0095] The steps of using anhydrous FePO4 material to prepare precursor, positive electrode material, positive electrode plate and battery assembly are the same as those in Comparative Example 1.

[0096] Table 1 Comparison of some data between the examples and the comparative examples

[0097] Comparison of anhydrous ferric phosphate

[0098] The Fe / P (%) in Table 1 is the iron-to-phosphorus ratio of the anhydrous ferric phosphate prepared in each example or comparative example. It can be seen that the lowest iron-to-phosphorus ratio in the anhydrous ferric phosphate material in the examples is 96.01%, which can be considered that the ferrate itself fully oxidizes the organic phosphorus, resulting in a high degree of oxidation. The iron-to-phosphorus ratio in the prepared anhydrous ferric phosphate is nearly equal to 1.

[0099] Electrochemical performance

[0100] The electrochemical workstation test was conducted at a temperature of 25°C and a voltage of 2.5-4.2V. The test results are shown in Table 1. It can be seen that the discharge capacity of the iron phosphate material prepared in the embodiment at 0.1C and 1C rates is greater than that of the iron phosphate material prepared in the comparative example.

[0101] Comparing Figures 1 and 2 shows that Example 2 used ferrate to oxidize the organophosphorus and added humic acid, while Comparative Example 2 did not add humic acid. Humic acid and organophosphorus form a competitive oxidation relationship, and the increased electronegativity of humic acid after oxidation can adsorb iron ions and disperse them, preventing the resulting iron phosphate from agglomerating and achieving a uniform particle size, which helps improve the electrical properties of the subsequently prepared lithium iron phosphate. Figure 3 demonstrates the successful synthesis of iron phosphate in Example 2.

Claims

1. A method for preparing an iron phosphate material, comprising the following steps: mixing the organophosphorus solution with humic acid to obtain a mixed solution; adding a ferrate-containing solution to the mixed solution to obtain a ferric iron-containing solution; Adjusting the pH of the ferric iron-containing solution to generate precipitation, and filtering to obtain the precipitate; The precipitate is dried and the crystal water is removed to obtain anhydrous FePO4 material.

2. The method for preparing an iron phosphate material according to claim 1, characterized in that: The organic phosphorus is at least one of phosphate ester, diethyl phosphate and triethyl phosphate.

3. The method for preparing an iron phosphate material according to claim 2, characterized in that: The concentration of the organic phosphorus is 0.01-0.06 mol / L.

4. The method for preparing an iron phosphate material according to claim 1, characterized in that: The humic acid is at least one of fulvic acid and palmitic acid.

5. The method for preparing an iron phosphate material according to claim 1, characterized in that: The concentration of the humic acid in the mixed solution is 1-6 mg / L.

6. The method for preparing an iron phosphate material according to claim 1, characterized in that: The ferrate-containing solution is at least one of sodium ferrate, potassium ferrate and ferric acid.

7. The method for preparing an iron phosphate material according to claim 6, characterized in that: The ferrate concentration is 0.1-0.3 mol / L.

8. The method for preparing an iron phosphate material according to claim 7, characterized in that: The ferrate-containing solution is slowly and uniformly added to the mixed solution within 1 hour; in the ferric iron-containing solution, the molar ratio of Fe to P is 1-1.3:

1.

9. The method for preparing an iron phosphate material according to claim 1, characterized in that: When the ferrate-containing solution is added to the mixed solution, the pH of the mixed solution needs to be maintained at no more than 2.

3.

10. The method for preparing an iron phosphate material according to claim 1, characterized in that: The pH of the ferric iron solution is adjusted to 1.8-2.2, and heated to 65-95° C. for 2-6 hours.

11. The method for preparing an iron phosphate material according to claim 1, characterized in that: Before drying the precipitate, it is also necessary to wash it with deionized water and ethanol until the pH of the supernatant is neutral. The drying temperature is 70-110° C., the dehydration temperature is 500-650° C., and the dehydration time is 3-5 hours.

12. An anhydrous FePO4 material prepared by the method for preparing an iron phosphate material according to any one of claims 1 to 11.

13. A lithium iron phosphate positive electrode material prepared from the anhydrous FePO4 material according to claim 12.

14. A lithium ion battery comprising the lithium iron phosphate positive electrode material according to claim 13.

15. An application of an iron phosphate material, comprising the following steps: The anhydrous FePO4 material of claim 12, lithium carbonate and glucose are uniformly dispersed and mixed in water according to a stoichiometric ratio of iron, lithium and carbon elements of 1:1-1.05:0.04-0.15, ball milled at a speed of 500-850 r / min for 4-5 hours to mix evenly, and then spray-dried to obtain a precursor powder; The precursor powder was heated to 300° C. at a heating rate of 3-5° C. / min under a nitrogen protective atmosphere and kept at that temperature for 3 h, and then heated to 750° C. and calcined at high temperature for 6.5 h to obtain a LiFePO4 / C positive electrode material.

16. The use of an iron phosphate material according to claim 15, further comprising the following steps: The LiFePO4 / C positive electrode material, acetylene black and polyvinylidene fluoride are uniformly mixed in N-methylpyrrolidone at a mass ratio of 92:4:4 to obtain a mixed slurry; The mixed slurry is coated on an aluminum foil, and then placed in a vacuum drying oven for drying to obtain a positive electrode sheet; The positive electrode sheet is placed in an argon glove box to assemble into a battery, the negative electrode is a metal lithium sheet, the diaphragm is a polypropylene porous membrane, and the electrolyte is composed of LiPF6, ethylene carbonate and dimethyl carbonate, wherein the LiPF6 concentration is 1 mol / L, and the volume ratio of ethylene carbonate and dimethyl carbonate is 1:1.

Images