Carbon-coated lithium iron phosphate anode material and preparation method thereof

Abstract

The application discloses a kind of carbon-coated lithium iron phosphate positive electrode materials and preparation method thereof, it is related to lithium ion battery positive electrode material field, the carbon-coated lithium iron phosphate positive electrode material is to product 5 ultrasonic dispersion liquid with lithium iron phosphate powder is stirred, dried, then sintered in protective gas atmosphere and obtained.The carbon-coated lithium iron phosphate positive electrode material prepared by the application has strong interface bonding force between carbon coating layer and lithium iron phosphate, and the carbon coating layer has high structural stability and conductivity, fast mass transfer rate, which can give lithium ion battery strong electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode materials, specifically to a carbon-coated lithium iron phosphate cathode material and its preparation method. Background Technology

[0002] Lithium-ion batteries are currently the mainstream energy storage devices in the new energy field. Lithium iron phosphate (LFP) is widely used in lithium-ion battery cathode materials due to its advantages such as high energy density, low cost, stable charge and discharge platform, environmental friendliness, and high safety. However, due to the limitations of LFP's crystal structure, its low electronic conductivity and poor ion mobility restrict its application in high-rate batteries. Therefore, the electrochemical performance of LFP cathode materials needs to be improved.

[0003] To improve the performance of lithium iron phosphate (LFP) cathode materials, coating the surface with conductive carbon materials is a common method. This can increase the conductivity of the LFP cathode material while preventing the growth and aggregation of LFP particles and maintaining a high specific surface area. However, at high charge / discharge rates, the uneven distribution of charge on the electrode surface will significantly reduce the efficiency of the active material. Carbon fiber is a highly conductive carbon material, but its surface is highly inert, resulting in weak interfacial bonding with the LFP surface, and there is a risk of peeling off after prolonged charge-discharge use.

[0004] Therefore, further exploration is needed to find ways to enhance the interfacial bonding between carbon fibers and lithium iron phosphate, improve the electrochemical activity of the carbon coating formed on the surface of lithium iron phosphate by carbon fibers, and provide new ideas for developing high electrochemical performance lithium iron phosphate cathode materials for lithium-ion batteries. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a carbon-coated lithium iron phosphate cathode material and its preparation method.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for preparing carbon-coated lithium iron phosphate cathode material includes the following steps:

[0008] Step (1): Mix and stir the nitro aromatic aldehyde and acetic anhydride, add potassium carbonate, heat and reflux and stir to obtain product 1;

[0009] Step (2): After mixing and stirring product 1, fatty alcohol containing heteroatoms and anhydrous ethanol, sulfuric acid is added, reflux is turned on, and the mixture is heated and stirred to obtain product 2;

[0010] Step (3): After mixing and stirring product 2 and methanol, add reducing agent, heat and stir to react and obtain product 3;

[0011] Step (4): Mix carbon fiber and oxidant, heat and ultrasonically soak, wash with water and dry to obtain product 4; mix product 4, product 3 and anhydrous DMF, add triethylamine and DCC, heat and stir in a protective gas to obtain product 5;

[0012] Step (5): Mix product 5 and DMF, disperse by ultrasonication, add lithium iron phosphate powder and PVP, stir, dry under vacuum, and sinter in a protective gas atmosphere to obtain carbon-coated lithium iron phosphate cathode material.

[0013] The preparation method of the carbon-coated lithium iron phosphate cathode material includes the following specific steps:

[0014] Step (1): Mix and stir the nitro aromatic aldehyde and acetic anhydride for 10-15 min, add potassium carbonate, heat to 120-140℃, reflux and stir for 3-4 h to obtain product 1;

[0015] Furthermore, the ratio of nitroaromatic aldehyde, acetic anhydride, and potassium carbonate used is 8-9g: 5.5-6.5g: 7-8g; the nitroaromatic aldehyde is m-nitrobenzaldehyde;

[0016] In step (1), the aldehyde group containing nitro aromatic aldehyde reacts with acetic anhydride to convert into olefinic acid, yielding product 1 containing nitro and phenyl olefinic acid;

[0017] Step (2): Mix product 1, fatty alcohol containing heteroatoms, and anhydrous ethanol and stir for 15-20 min. Add sulfuric acid, turn on reflux, heat to 100-110℃, and stir for 12-14 h to obtain product 2.

[0018] Furthermore, the ratio of product 1, heteroatom-containing fatty alcohol, anhydrous ethanol, and sulfuric acid is 10-11g: 12-15g: 20-25mL: 0.7-0.9g;

[0019] Furthermore, the heteroatom-containing fatty alcohol is obtained by mixing 2,2,2-trifluoroethanol and 3-methylthiopropanol in a molar ratio of 1:2-3;

[0020] In step (2), the carboxyl group of the olefinic acid in product 1 can react with a fatty alcohol containing heteroatoms to obtain a phenyl olefinic acid esterified product containing nitro and heteroatoms, namely product 2;

[0021] Step (3): Mix product 2 and methanol and stir for 30-35 min, add reducing agent, heat to 45-55℃, stir and react for 1-2 h to obtain product 3;

[0022] Furthermore, the ratio of product 2, methanol, and reducing agent is 23-25g: 50-55mL: 20-25mL;

[0023] Furthermore, the reducing agent is a sodium dithionite solution with a mass fraction of 35-45%;

[0024] In step (3), the nitro group in product 2 is reduced to an amino group to obtain product 3;

[0025] Step (4): Mix carbon fiber and oxidant, and ultrasonically soak at 65-75℃ and 150-200W for 45-50 min, wash with water, and dry to obtain product 4; mix product 4, product 3, and anhydrous DMF and stir for 20-30 min, add triethylamine and DCC, and stir and react in a protective gas at 50-60℃ for 24-25 h to obtain product 5;

[0026] Furthermore, the ratio of carbon fiber to oxidant is 1-2g: 5-10mL; the oxidant is a nitric acid solution with a mass fraction of 10-12%.

[0027] Furthermore, the ratio of product 4, product 3, anhydrous DMF, triethylamine, and DCC is 0.5-1g: 0.1-0.2g: 50-55mL: 0.15-0.25g: 0.25-0.35g;

[0028] In step (4), the carbon fiber is treated with an oxidant to obtain carboxylated carbon fiber, i.e., product 4; some of the carboxyl groups in product 4 condense with the amino groups in product 3 to obtain product 5.

[0029] Step (5): Mix product 5 and DMF, ultrasonically disperse at 50-100W power for 20-25min, add lithium iron phosphate powder and PVP, stir for 3-4h, place in vacuum drying at 60-70℃ for 6-7h, and in a protective gas atmosphere, heat to 350-450℃ at a rate of 1.5-2℃ / min and hold for 2-3h to obtain carbon-coated lithium iron phosphate cathode material;

[0030] Furthermore, the ratio of product 5, DMF, lithium iron phosphate powder, and PVP is 0.5-1g: 100-120mL: 10g: 0.1-0.2g;

[0031] In step (5), a carbon layer is coated on the surface of lithium iron phosphate powder through sintering to obtain carbon-coated lithium iron phosphate cathode material.

[0032] The beneficial effects of this invention are:

[0033] This invention provides a carbon-coated lithium iron phosphate cathode material and its preparation method. The carbon-coated lithium iron phosphate cathode material is obtained by adding lithium iron phosphate powder to an ultrasonically dispersed liquid of product 5, stirring, drying, and then sintering in a protective gas atmosphere. In this invention, the aldehyde group in a nitro aromatic aldehyde is first converted to an olefinic acid to obtain product 1. Then, the carboxyl group in product 1 reacts with a heteroatom-containing fatty alcohol to obtain product 2. Next, the nitro group in product 2 is reduced to an amino group to obtain product 3. Finally, product 4 (carboxylated carbon fiber) undergoes a condensation reaction with the amino group in product 3 to obtain product 5. The amide groups and unreacted carboxyl groups introduced on the surface of the carbon fiber in product 5 can form hydrogen bonds and other chemical interactions with the hydroxyl groups on the surface of the lithium iron phosphate powder, enhancing the interfacial bonding force between the sintered carbon coating layer and the lithium iron phosphate, preventing the coating layer from peeling off, and ensuring the integrity and stability of the cathode material.

[0034] This invention combines the use of nitro aromatic aldehydes and heteroatom-containing fatty alcohols to introduce phenyl acrylate, N, S, and F onto the surface of carbon fibers. In the sintered carbon layer, the phenyl acrylate forms electron transfer channels between the carbon fibers and lithium iron phosphate, creating a continuous conductive network. The sintered carbon layer is doped with N, S, and F. N atoms increase the electron density of the carbon material and improve electronic conductivity; S atoms widen the interlayer spacing, promote lithium-ion transport, and provide additional lithium storage sites; F atoms enhance the chemical stability of the carbon coating layer and reduce side reactions. Through the synergistic effect of the phenyl acrylate and the doped N, S, and F in the carbon fibers, the conductivity and mass transfer rate of the carbon coating layer are significantly improved, battery polarization is reduced, and the electrochemical performance of the lithium-ion battery is enhanced.

[0035] This invention involves doping carbon fibers with N, S, and F, and then forming a carbon coating layer on the surface of lithium iron phosphate. This preparation method is simple, and the carbon coating layer has high uniformity and tightness of bonding. It can effectively improve the structural stability of lithium iron phosphate cathode materials for lithium-ion batteries, and enhance the electrochemical performance of lithium-ion batteries, such as conductivity and cycle stability, thus providing an effective solution for the development of high-performance lithium-ion batteries. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] Example 1

[0038] A carbon-coated lithium iron phosphate cathode material, the preparation method of which includes the following steps:

[0039] Step (1): Mix m-nitrobenzaldehyde and acetic anhydride and stir for 10 min, add potassium carbonate, heat to 120℃, reflux and stir for 3 h, cool, and rotary evaporate at 40℃. Adjust the pH to 3 with 0.1 mol / L hydrochloric acid solution, cool, filter, wash the filter cake three times with water, and recrystallize with an ethanol aqueous solution (95% ethanol and water in a volume ratio of 3:1). The volume ratio of ethanol aqueous solution to filter cake during recrystallization is 5 mL: 1 g. The dissolution temperature for recrystallization is 79℃, and the cooling temperature is room temperature, to obtain product 1. The volume ratio of m-nitrobenzaldehyde, acetic anhydride, and potassium carbonate is 8 g: 5.5 g: 7 g.

[0040] Step (2): Mix product 1, heteroatom-containing fatty alcohol, and anhydrous ethanol and stir for 15 min. Add sulfuric acid, turn on reflux, heat to 100℃, stir for 12 h, cool, add 25 mL of saturated sodium carbonate solution for extraction, extract three times, take the supernatant, wash three times with water, then wash three times with saturated brine, add 22 g of anhydrous sodium sulfate to dry, and filter to obtain product 2; the ratio of product 1, heteroatom-containing fatty alcohol, anhydrous ethanol, and sulfuric acid is 10 g: 12 g: 20 mL: 0.7 g; the heteroatom-containing fatty alcohol is obtained by mixing 2,2,2-trifluoroethanol and 3-methylthiopropanol in a molar ratio of 1:2;

[0041] Step (3): Mix product 2 and methanol and stir for 30 min, add 35% sodium dithionite solution, heat to 45℃, stir and react for 1 h, cool, wash three times with water, and vacuum dry at 60℃ for 1 h to obtain product 3; the ratio of product 2, methanol and 35% sodium dithionite solution is 23 g: 50 mL: 20 mL.

[0042] Step (4): Mix carbon fiber (supplier: Jiangxi Shuobang New Material Technology Co., Ltd., specification 1kg) with 10% nitric acid solution, ultrasonically soak at 65℃ and 150W for 45min, filter, wash three times with water, and dry at 100℃ for 4h to obtain product 4; mix product 4, product 3, and anhydrous DMF and stir for 20min, add triethylamine and DCC, stir and react in nitrogen at 50℃ for 24h, filter, wash three times with water, and dry at 100℃ for 5h to obtain product 5; the ratio of carbon fiber to 10% nitric acid solution is 1g:5mL; the ratio of product 4, product 3, anhydrous DMF, triethylamine, and DCC is 0.5g:0.1g:50mL:0.15g:0.25g;

[0043] Step (5): Mix product 5 and DMF, ultrasonically disperse at 50W power for 20min, add lithium iron phosphate powder (supplier: Aladdin, item number L302983) and PVP (supplier: Aladdin, item number P274371), stir for 3h, place at 60℃ for vacuum drying for 6h, in a nitrogen atmosphere, heat to 350℃ at a rate of 1.5℃ / min, hold for 2h, to obtain carbon-coated lithium iron phosphate cathode material; the ratio of product 5, DMF, lithium iron phosphate powder and PVP is 0.5g:100mL:10g:0.1g.

[0044] Example 2

[0045] A carbon-coated lithium iron phosphate cathode material, the preparation method of which includes the following steps:

[0046] Step (1): Mix m-nitrobenzaldehyde and acetic anhydride and stir for 13 min, add potassium carbonate, heat to 130℃, reflux and stir for 3.5 h, cool, rotary evaporate at 40℃, adjust pH to 3 with 0.1 mol / L hydrochloric acid solution, cool, filter, wash filter cake three times with water, recrystallize with ethanol aqueous solution (volume ratio of 95% ethanol to water is 3:1), the volume ratio of ethanol aqueous solution to filter cake during recrystallization is 5 mL: 1 g, the dissolution temperature for recrystallization is 79℃, and the cooling temperature is room temperature, to obtain product 1; the volume ratio of m-nitrobenzaldehyde, acetic anhydride and potassium carbonate is 8.5 g: 6.0 g: 7.5 g;

[0047] Step (2): Mix product 1, heteroatom-containing fatty alcohol, and anhydrous ethanol and stir for 18 min. Add sulfuric acid, turn on reflux, heat to 105℃, stir for 13 h, cool, add 30 mL of saturated sodium carbonate solution for extraction, extract three times, take the supernatant, wash three times with water, then wash three times with saturated brine, add 25 g of anhydrous sodium sulfate to dry, and filter to obtain product 2; the ratio of product 1, heteroatom-containing fatty alcohol, anhydrous ethanol, and sulfuric acid is 10.5 g: 13.5 g: 23 mL: 0.8 g; the heteroatom-containing fatty alcohol is obtained by mixing 2,2,2-trifluoroethanol and 3-methylthiopropanol in a molar ratio of 1:2.5;

[0048] Step (3): Mix product 2 and methanol and stir for 33 min, add 40% sodium dithionite solution, heat to 50℃, stir and react for 1.5 h, cool, wash with water three times, and vacuum dry at 60℃ for 1 h to obtain product 3; the ratio of product 2, methanol and 40% sodium dithionite solution is 24 g: 53 mL: 23 mL.

[0049] Step (4): Mix carbon fiber (supplier: Jiangxi Shuobang New Material Technology Co., Ltd., specification 1kg) with 11% nitric acid solution, ultrasonically soak at 70℃ and 180W for 47min, filter, wash three times with water, and dry at 100℃ for 4h to obtain product 4; mix product 4, product 3, and anhydrous DMF and stir for 25min, add triethylamine and DCC, stir and react in nitrogen at 55℃ for 24.5h, filter, wash three times with water, and dry at 100℃ for 5h to obtain product 5; the ratio of carbon fiber to 11% nitric acid solution is 1.5g:8mL; the ratio of product 4, product 3, anhydrous DMF, triethylamine, and DCC is 0.8g:0.15g:53mL:0.20g:0.30g;

[0050] Step (5): Mix product 5 and DMF, ultrasonically disperse at 80W power for 23min, add lithium iron phosphate powder (supplier: Aladdin, item number L302983) and PVP (supplier: Aladdin, item number P274371), stir for 3.5h, place at 65℃ for vacuum drying for 6.5h, in a nitrogen atmosphere, heat to 400℃ at a rate of 1.8℃ / min, and hold for 2.5h to obtain carbon-coated lithium iron phosphate cathode material; the ratio of product 5, DMF, lithium iron phosphate powder and PVP is 0.8g:110mL:10g:0.15g.

[0051] Example 3

[0052] A carbon-coated lithium iron phosphate cathode material, the preparation method of which includes the following steps:

[0053] Step (1): Mix m-nitrobenzaldehyde and acetic anhydride and stir for 15 min, add potassium carbonate, heat to 140℃, reflux and stir for 4 h, cool, rotary evaporate at 40℃, adjust pH to 3 with 0.1 mol / L hydrochloric acid solution, cool, filter, wash filter cake three times with water, recrystallize with ethanol aqueous solution (volume ratio of 95% ethanol to water is 3:1), the volume ratio of ethanol aqueous solution to filter cake during recrystallization is 5 mL: 1 g, the dissolution temperature for recrystallization is 79℃, and the cooling temperature is room temperature, to obtain product 1; the volume ratio of m-nitrobenzaldehyde, acetic anhydride, and potassium carbonate is 9 g: 6.5 g: 8 g;

[0054] Step (2): Mix product 1, heteroatom-containing fatty alcohol, and anhydrous ethanol and stir for 20 min. Add sulfuric acid, turn on reflux, heat to 110℃, stir for 14 h, cool, add 35 mL of saturated sodium carbonate solution for extraction, extract three times, take the supernatant, wash three times with water, then wash three times with saturated brine, add 27 g of anhydrous sodium sulfate to dry, and filter to obtain product 2; the ratio of product 1, heteroatom-containing fatty alcohol, anhydrous ethanol, and sulfuric acid is 11 g: 15 g: 25 mL: 0.9 g; the heteroatom-containing fatty alcohol is obtained by mixing 2,2,2-trifluoroethanol and 3-methylthiopropanol in a molar ratio of 1:3;

[0055] Step (3): Mix product 2 and methanol and stir for 35 min, add 45% sodium dithionite solution, heat to 55℃, stir and react for 2 h, cool, wash three times with water, and vacuum dry at 60℃ for 1 h to obtain product 3; the ratio of product 2, methanol and 45% sodium dithionite solution is 25 g: 55 mL: 25 mL.

[0056] Step (4): Mix carbon fiber (supplier: Jiangxi Shuobang New Material Technology Co., Ltd., specification 1kg) with 12% nitric acid solution, ultrasonically soak at 75℃ and 200W for 50min, filter, wash three times with water, and dry at 100℃ for 4h to obtain product 4; mix product 4, product 3, and anhydrous DMF and stir for 30min, add triethylamine and DCC, stir and react in nitrogen at 60℃ for 25h, filter, wash three times with water, and dry at 100℃ for 5h to obtain product 5; the ratio of carbon fiber to 12% nitric acid solution is 2g:10mL; the ratio of product 4, product 3, anhydrous DMF, triethylamine, and DCC is 1g:0.2g:55mL:0.25g:0.35g;

[0057] Step (5): Mix product 5 and DMF, ultrasonically disperse at 100W power for 25min, add lithium iron phosphate powder (supplier: Aladdin, item number L302983) and PVP (supplier: Aladdin, item number P274371), stir for 4h, place at 70℃ for vacuum drying for 7h, heat to 450℃ at a rate of 2℃ / min in a nitrogen atmosphere, and keep at the temperature for 3h to obtain carbon-coated lithium iron phosphate cathode material; the ratio of product 5, DMF, lithium iron phosphate powder and PVP is 1g:120mL:10g:0.2g.

[0058] Comparative Example 1

[0059] Compared with Example 3, product 1 was replaced with m-nitrobenzoic acid, and the rest was exactly the same as in Example 3, to obtain carbon-coated lithium iron phosphate cathode material.

[0060] Comparative Example 2

[0061] Compared with Example 3, the 3-methylthiopropanol in the heteroatom-containing fatty alcohol was replaced with 3-methylsulfonyl-1-propanol, and the rest was exactly the same as in Example 3, to obtain carbon-coated lithium iron phosphate cathode material.

[0062] Comparative Example 3

[0063] Compared with Example 3, the 2,2,2-trifluoroethanol in the heteroatom-containing fatty alcohol was replaced with 2-tert-butyldimethylsilaneoxyethanol, and the rest was exactly the same as in Example 3, to obtain carbon-coated lithium iron phosphate cathode material.

[0064] The following is a further performance test of the carbon-coated lithium iron phosphate cathode material prepared according to the present invention, and the test results are shown below.

[0065] Polyvinylidene fluoride (supplier: Aladdin, P741973), NMP, conductive carbon black (supplier: Aladdin, C742510), and carbon-coated lithium iron phosphate cathode materials obtained in Examples 1-3 and Comparative Examples 1-3 of this invention (where the mass ratio of polyvinylidene fluoride, conductive carbon black, and carbon-coated lithium iron phosphate cathode materials obtained in Examples 1-3 and Comparative Examples 1-3 of this invention is 1:1:8) were mixed and stirred evenly. The mixture was then coated onto aluminum foil and dried at 130°C for 3 hours. The resulting cathode discs were then rolled. Lithium foil was used as the anode, 1 mol / L LiPF6 (EC & DMC) as the electrolyte, and Celgard 2400 polypropylene membrane as the separator. The battery was assembled in a vacuum glove box. The capacity retention rate of the battery after 600 cycles at 10C and the discharge specific capacity at 5C were tested.

[0066] The results are recorded in Table 1;

[0067] Table 1: Test Results

[0068]

[0069] According to the data in Table 1, the lithium iron phosphate cathode material prepared by this invention has strong cycle performance and capacity retention capability at high discharge rates.

[0070] Comparing Example 3 with Comparative Example 1, it can be seen that replacing Product 1 with m-nitrobenzoic acid shows that the lithium iron phosphate cathode material prepared by using Product 1 in this invention has stronger cycle performance and capacity retention capability at high rate discharge.

[0071] Comparing Example 3 with Comparative Example 2, it can be seen that replacing 3-methylthiopropanol in the heteroatom-containing fatty alcohol with 3-methylsulfonyl-1-propanol indicates that the lithium iron phosphate cathode material prepared by using 3-methylthiopropanol in this invention has stronger cycle performance and capacity retention capability during high-rate discharge.

[0072] Comparing Example 3 with Comparative Example 3, it can be seen that replacing 2,2,2-trifluoroethanol in the heteroatom-containing fatty alcohol with 2-tert-butyldimethylsilaneoxyethanol demonstrates that the lithium iron phosphate cathode material prepared using 2,2,2-trifluoroethanol in this invention has stronger cycle performance and capacity retention capability during high-rate discharge.

[0073] The above description is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined in the claims, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing carbon-coated lithium iron phosphate cathode material, characterized in that: Includes the following steps: Step (1): Mix and stir the nitro aromatic aldehyde and acetic anhydride, add potassium carbonate, heat and reflux and stir to obtain product 1; Step (2): After mixing and stirring product 1, fatty alcohol containing heteroatoms and anhydrous ethanol, sulfuric acid is added, reflux is turned on, and the mixture is heated and stirred to obtain product 2; Step (3): After mixing and stirring product 2 and methanol, add reducing agent, heat and stir to react and obtain product 3; Step (4): Mix carbon fiber and oxidant, heat and ultrasonically soak, wash with water and dry to obtain product 4; mix product 4, product 3 and anhydrous DMF, add triethylamine and DCC, heat and stir in a protective gas to obtain product 5; Step (5): Mix product 5 and DMF, disperse by ultrasonication, add lithium iron phosphate powder and PVP, stir, dry under vacuum, and sinter in a protective gas atmosphere to obtain carbon-coated lithium iron phosphate cathode material.

2. The method for preparing a carbon-coated lithium iron phosphate cathode material according to claim 1, characterized in that: In step (1), the ratio of the amount of the nitroaromatic aldehyde, acetic anhydride and potassium carbonate is 8-9g: 5.5-6.5g: 7-8g; the nitroaromatic aldehyde is m-nitrobenzaldehyde.

3. The method for preparing a carbon-coated lithium iron phosphate cathode material according to claim 1, characterized in that: In step (2), the ratio of product 1, heteroatom-containing fatty alcohol, anhydrous ethanol, and sulfuric acid is 10-11g: 12-15g: 20-25mL: 0.7-0.9g.

4. The method for preparing a carbon-coated lithium iron phosphate cathode material according to claim 1, characterized in that: In step (2), the heteroatom-containing fatty alcohol is obtained by mixing 2,2,2-trifluoroethanol and 3-methylthiopropanol in a molar ratio of 1:2-3.

5. The method for preparing a carbon-coated lithium iron phosphate cathode material according to claim 1, characterized in that: In step (3), the ratio of product 2, methanol and reducing agent is 23-25g: 50-55mL: 20-25mL.

6. The method for preparing a carbon-coated lithium iron phosphate cathode material according to claim 1, characterized in that: In step (4), the ratio of carbon fiber to oxidant is 1-2g: 5-10mL.

7. The method for preparing a carbon-coated lithium iron phosphate cathode material according to claim 1, characterized in that: In step (4), the ratio of the amount of product 4, product 3, anhydrous DMF, triethylamine and DCC is 0.5-1g: 0.1-0.2g: 50-55mL: 0.15-0.25g: 0.25-0.35g.

8. The method for preparing a carbon-coated lithium iron phosphate cathode material according to claim 1, characterized in that: In step (5), the ratio of product 5, DMF, lithium iron phosphate powder, and PVP is 0.5-1g: 100-120mL: 10g: 0.1-0.2g.

9. A carbon-coated lithium iron phosphate cathode material is prepared by the preparation method of the carbon-coated lithium iron phosphate cathode material according to any one of claims 1-8.

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