Interface-modified high-rate lithium iron phosphate positive electrode material and preparation method thereof

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a preparation method of an interface-modified high-rate lithium iron phosphate positive electrode material, which is used for solving the problems of low interface impedance, low rate capability and low energy density of the existing lithium iron phosphate. According to the preparation method, zirconium-niobium co-doped iron phosphate is used as a precursor of the lithium iron phosphate positive electrode material, a lithium ion diffusion channel is widened, the lithium ion diffusion coefficient is improved, meanwhile, an olivine structure framework is provided, a wider tunnel space is provided for lithium ion migration, zirconium-niobium provides additional electrons, and the electron conductivity is improved through cooperation of the zirconium-niobium co-doped iron phosphate and the olivine structure framework; li2ZrCl6-LiCl interface modification can isolate sulfide electrolyte from being in direct contact with a positive electrode material, and interface side reaction is inhibited; carbon nanotube coating can enhance the conductivity, reduce erosion, improve the diffusion coefficient of Li < + > and the stability of the material structure, and improve the charge-discharge rate.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to an interface-modified high-rate lithium iron phosphate cathode material and its preparation method. Background Technology

[0002] With the rapid development of electric vehicles and portable electronic devices, the demand for lithium-ion batteries is also increasing. In particular, high-rate performance cathode materials have become the key to improving battery performance. Lithium iron phosphate has become one of the preferred cathode materials due to its advantages such as good safety, low cost and long cycle life.

[0003] However, lithium iron phosphate cathode materials exhibit poor energy density and cycle stability at high-rate charge and discharge, which limits their application in high-performance batteries. Therefore, modifying lithium iron phosphate through various methods to improve its rate performance has become one of the current research hotspots and has important research and application value.

[0004] Therefore, developing an interface-modified high-rate lithium iron phosphate cathode material and its preparation method is of great significance to the field of lithium-ion batteries. Summary of the Invention

[0005] To overcome the aforementioned technical problems, the present invention aims to provide an interface-modified high-rate lithium iron phosphate cathode material and its preparation method. By doping zirconium-niobium during the synthesis of lithium iron phosphate to obtain double-doped lithium iron phosphate powder, and then mixing and stirring it with Li2ZrCl6-LiCl and carbon nanotubes respectively, followed by sintering, the interface-modified high-rate lithium iron phosphate cathode material is obtained, which solves the problems of low interface impedance, low rate performance, and low energy density of existing lithium iron phosphate.

[0006] The objective of this invention can be achieved through the following technical solutions: In a first aspect, this application provides a method for preparing an interface-modified high-rate lithium iron phosphate cathode material, comprising the following steps: Step a1: Add FeCl3·H2O, NH4H2PO4 and deionized water to a three-necked flask equipped with a stirrer and thermometer, mix and stir for 15-20 min to obtain the first solution; separately add ZrOCl2·8H2O, C2H5NNbO4 and hydrochloric acid solution to a beaker and mix and stir for 20-30 min to obtain the second solution; add hexadecyltrimethylammonium bromide solution to the first solution, purge with nitrogen for protection, heat the first solution to 85℃, stir at a constant speed of 1200 r / min for 1-2 h, add the second solution, and simultaneously add NaOH solution to maintain pH at 1.8-2, react for 12 h, then centrifuge, place the precipitate in a vacuum drying oven, and dry at 50-55℃ for 2-3 h to obtain zirconium-niobium co-doped FePO4; Step a2: Zirconium-niobium co-doped FePO4, Li2CO3, and sucrose were mixed and added to a planetary ball mill. Anhydrous ethanol was added as a dispersion solvent. The ball-to-material ratio was 5:1 (the ball-to-material ratio refers to the mass ratio of grinding media to material in the mill). The mixture was ball-milled at 350 r / min for 4 h. After ball milling, it was placed in an 80℃ forced-air drying oven for 12 h to dry. After crushing and grinding, it was pre-calcined at 350℃ for 4 h in a vacuum tube furnace under a nitrogen atmosphere, and then sintered at 750℃ for 12 h to obtain modified lithium iron phosphate. Step a3: LiCl, ZrCl4, and NbCl5 in a molar ratio of 10 / 13 were vacuum dried at 120℃ for 24 h, and then placed in a ball mill jar with a ball-to-material ratio of 10:1. The mixture was ball-milled at 500 r / min for 10 h under argon protection. The remaining LiCl in a molar ratio of 3 / 13 was dissolved in anhydrous ethanol, sprayed onto liquid nitrogen for freezing, and then vacuum dried to obtain nano-LiCl. This nano-LiCl was added to the ball mill jar and ball-milled at 200 r / min for 1 h to obtain niobium-doped LiCl composite modified Li2ZrCl6. Step a4: Modified lithium iron phosphate and modified Li2ZrCl6 are loaded into a high-speed mixer at a speed of 2000 r / min, protected by nitrogen, and mixed for 15-30 min. Then, the mixture is processed through a hot roller press at a roller temperature of 150℃ and a pressure of 5MPa to obtain Li2ZrCl6-LiCl coated lithium iron phosphate. Step a5: Lithium iron phosphate and C6H coated with Li2ZrCl6-LiCl are then added. 12O6·H2O and carbon nanotubes were added to a ball mill jar with a ball-to-material ratio of 10:1. The grinding balls were nano-zirconium balls, and anhydrous ethanol was added as a dispersion solvent. The mixture was ball-milled at 600 r / min for 10-12 h. The ball mill jar was removed, the balls were separated, dried and ground, and then spread evenly on a ceramic boat. The material was then placed in a tube furnace for sintering at 25°C for 4 h. The temperature was then raised to 680°C and sintered at a constant temperature for 10 h. Finally, the material was naturally cooled to 25°C. After sintering, a high-rate lithium iron phosphate cathode material with interface modification was obtained.

[0007] As a further aspect of the present invention: the ratio of FeCl3·H2O, NH4H2PO4, deionized water, ZrOCl2·8H2O, C2H5NNbO4, hydrochloric acid solution and hexadecyltrimethylammonium bromide solution used in step a1 is 0.985mol:1mol:600mL:0.01mol:0.005mol:400mL:200mL.

[0008] As a further aspect of the present invention: the molar concentration of the hydrochloric acid solution in step a1 is 0.5 mol / L; the molar concentration of the hexadecyltrimethylammonium bromide solution is 0.1 mol / L; and the molar concentration of the NaOH solution is 4 mol / L.

[0009] As a further aspect of the present invention: the ratio of zirconium-niobium co-doped FePO4, Li2CO3, sucrose and anhydrous ethanol used in step a2 is 158.3g:1.03mol:0.1mol:200-300mL.

[0010] As a further aspect of the present invention: the ratio of LiCl, ZrCl4, NbCl5 and anhydrous ethanol used in step a3 is 2.34 mol: 0.8 mol: 0.2 mol: 540 mL.

[0011] As a further aspect of the present invention: the ratio of modified lithium iron phosphate and modified Li2ZrCl6 in step a4 is 90g:10g.

[0012] As a further aspect of the present invention: the lithium iron phosphate and C6H coated with Li2ZrCl6-LiCl described in step a5 12 The ratio of O6·H2O, carbon nanotubes, and anhydrous ethanol is 175.9g:1.23g:5.28g:200-300mL.

[0013] Secondly, this application provides an interface-modified high-rate lithium iron phosphate cathode material, which is prepared according to the above-described method for preparing interface-modified high-rate lithium iron phosphate cathode materials.

[0014] The beneficial effects of this invention are: This invention discloses an interface-modified high-rate lithium iron phosphate cathode material and its preparation method. The method involves mixing FeCl3·H2O, NH4H2PO4, and deionized water to obtain a first solution; adding ZrOCl2·8H2O, C2H5NNbO4, and hydrochloric acid solution to a beaker and mixing to obtain a second solution; adding hexadecyltrimethylammonium bromide solution to the first solution and stirring, then adding the second solution and reacting, followed by centrifugation and drying to obtain zirconium-niobium co-doped FePO4; mixing and ball-milling the zirconium-niobium co-doped FePO4, Li2CO3, and sucrose, drying, crushing and grinding, and then sintering to obtain modified lithium iron phosphate; using zirconium-niobium co-doped iron phosphate as a precursor for the lithium iron phosphate cathode material, wherein Zr... 4+ Replace Li + Site, Nb 5+ Fe replacement 2+ The presence of sites in the olivine lattice creates cation vacancies and lattice distortion, effectively widening the lithium-ion diffusion channels and increasing the lithium-ion diffusion coefficient. Simultaneously, it maintains a stable olivine structural framework, providing a more spacious tunnel space for lithium-ion migration. Zirconium-niobium provides additional electrons, and the two work synergistically to improve electronic conductivity. LiCl, ZrCl4, and NbCl5 are dried and ball-milled. The remaining LiCl is dissolved in anhydrous ethanol, sprayed onto liquid nitrogen for freezing, and then vacuum-dried to obtain nano-LiCl. This nano-LiCl is then ball-milled in a ball mill jar to obtain niobium-doped Li2ZrCl6. Modified lithium iron phosphate and modified Li2ZrCl6 are mixed and rolled to obtain Li2ZrCl6-LiCl-coated lithium iron phosphate. Li2ZrCl6 provides three-dimensional lithium-ion channels, and niobium doping promotes cation mixing and induces lattice distortion, thereby enabling Li... + It is easier to transport in the crystal lattice, improving ionic conductivity. LiCl acts as an interfacial wetting agent, filling grain boundary voids. The interfacial lubrication effect of LiCl reduces the Li + The energy barrier of breaking free from lattice constraints lowers the activation energy, while simultaneously isolating the sulfide electrolyte from direct contact with the cathode material, suppressing interfacial side reactions, and providing a highly conductive lithium interface. The LiCl nano-processing, employing a low-temperature recrystallization method, significantly improves interfacial wettability and reduces interfacial impedance. Li2ZrCl6-LiCl-coated lithium iron phosphate and C6H... 12 O6·H2O and carbon nanotubes were mixed, ball-milled, and sintered to obtain a high-rate lithium iron phosphate cathode material with interface modification; carbon nanotubes were coated on the surface of lithium iron phosphate to enhance conductivity, which is beneficial to Li + The insertion and extraction of lithium iron phosphate particles during sintering inhibits their growth and shortens the Li-P2P sintering time. + Migration pathway; carbon nanotube coating reduces the erosion of lithium iron phosphate cathode material by the electrolyte, and lowers Li... + Migration barriers, improving Li +Improve the diffusion coefficient and material structure stability to increase the charge / discharge rate. Detailed Implementation

[0015] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0016] Example 1: This embodiment describes a method for preparing a high-rate lithium iron phosphate cathode material with interface modification, including the following steps: Step S1: Add 0.985 mol FeCl3·H2O, 1 mol NH4H2PO4, and 600 mL deionized water to a three-necked flask equipped with a stirrer and thermometer, and mix and stir for 15 min to obtain the first solution; separately take 0.01 mol ZrOCl2·8H2O, 0.005 mol... C2H5NNbO4 and 400 mL of 0.5 mol / L hydrochloric acid solution were added to a beaker and stirred for 20 min to obtain a second solution. 200 mL of 0.1 mol / L hexadecyltrimethylammonium bromide solution was added to the first solution, and nitrogen gas was introduced for protection. The first solution was heated to 85 °C and stirred at a constant speed of 1200 r / min for 1 h. The second solution was added, and 4 mol / L NaOH solution was added simultaneously to maintain the pH at 1.8. The reaction was carried out for 12 h, and then centrifuged. The precipitate was placed in a vacuum drying oven and dried at 50 °C for 2 h to obtain zirconium-niobium co-doped FePO4. Step S2: 158.3g of zirconium-niobium co-doped FePO4, 1.03mol of Li2CO3 and 0.1mol of sucrose were mixed and added to a planetary ball mill. 200mL of anhydrous ethanol was added as a dispersion solvent. The ball-to-material ratio was 5:1. The mixture was ball-milled at 350r / min for 4h. After ball milling, it was placed in an 80℃ forced-air drying oven for 12h to dry. After crushing and grinding, it was pre-calcined at 350℃ for 4h in a vacuum tube furnace under a nitrogen atmosphere, and then sintered at 750℃ for 12h to obtain modified lithium iron phosphate. Step S3: 1.8 mol LiCl, 0.8 mol ZrCl4, and 0.2 mol NbCl5 were vacuum dried at 120 °C for 24 h, then placed in a ball mill jar with a ball-to-material ratio of 10:1 and ball-milled at 500 r / min for 10 h under argon protection. The remaining 0.54 mol LiCl was dissolved in 540 mL of anhydrous ethanol, sprayed onto liquid nitrogen for freezing, and then vacuum dried to obtain nano-LiCl. This nano-LiCl was then added to the ball mill jar and ball-milled at 200 r / min for 1 h to obtain niobium-doped LiCl composite modified Li2ZrCl6. Step S4: 90g of modified lithium iron phosphate and 10g of modified Li2ZrCl6 are loaded into a high-speed mixer at a speed of 2000r / min, nitrogen is introduced for protection, and the mixture is mixed for 15min. Then it is processed by a hot roller press at a roller temperature of 150℃ and a pressure of 5MPa to obtain Li2ZrCl6-LiCl coated lithium iron phosphate. Step S5: Add 175.9g of Li2ZrCl6-LiCl coated lithium iron phosphate and 1.23g of C6H 12 O6·H2O and 5.28g of carbon nanotubes were added to a ball mill jar with a ball-to-material ratio of 10:1. The grinding balls were nano-zirconium balls. 200mL of anhydrous ethanol was added as a dispersion solvent. The mixture was ball-milled at 600r / min for 10h. The ball mill jar was removed, the balls were separated, dried and ground, and then spread evenly on a ceramic boat. The material was placed in a tube furnace for sintering at 25℃ for 4h, then heated to 680℃ and sintered at a constant temperature for 10h. Finally, it was naturally cooled to 25℃. After sintering, a high-rate lithium iron phosphate cathode material with Li2ZrCl6-LiCl interface modification was obtained.

[0017] Example 2: This embodiment describes a method for preparing a high-rate lithium iron phosphate cathode material with interface modification, including the following steps: Step S1: Add 0.985 mol FeCl3·H2O, 1 mol NH4H2PO4, and 600 mL deionized water to a three-necked flask equipped with a stirrer and thermometer, and mix and stir for 18 min to obtain the first solution; separately take 0.01 mol ZrOCl2·8H2O, 0.005 mol... C2H5NNbO4 and 400 mL of 0.5 mol / L hydrochloric acid solution were added to a beaker and stirred for 25 min to obtain a second solution. 200 mL of 0.1 mol / L hexadecyltrimethylammonium bromide solution was added to the first solution, and nitrogen gas was introduced for protection. The first solution was heated to 85 °C and stirred at a constant speed of 1200 r / min for 1.5 h. The second solution was then added, and simultaneously, 4 mol / L NaOH solution was added to maintain the pH at 1.9. The reaction was carried out for 12 h, followed by centrifugation. The precipitate was placed in a vacuum drying oven and dried at 55 °C for 2.5 h to obtain zirconium-niobium co-doped FePO4. Step S2: 158.3g of zirconium-niobium co-doped FePO4, 1.03mol of Li2CO3 and 0.1mol of sucrose were mixed and added to a planetary ball mill. 250mL of anhydrous ethanol was added as a dispersion solvent. The ball-to-material ratio was 5:1. The mixture was ball-milled at 350r / min for 4h. After ball milling, it was placed in an 80℃ forced-air drying oven for 12h to dry. After crushing and grinding, it was pre-calcined at 350℃ for 4h in a vacuum tube furnace under a nitrogen atmosphere, and then sintered at 750℃ for 12h to obtain modified lithium iron phosphate. Step S3: 1.8 mol LiCl, 0.8 mol ZrCl4, and 0.2 mol NbCl5 were vacuum dried at 120 °C for 24 h, then placed in a ball mill jar with a ball-to-material ratio of 10:1 and ball-milled at 500 r / min for 10 h under argon protection. The remaining 0.54 mol LiCl was dissolved in 540 mL of anhydrous ethanol, sprayed onto liquid nitrogen for freezing, and then vacuum dried to obtain nano-LiCl. This nano-LiCl was then added to the ball mill jar and ball-milled at 200 r / min for 1 h to obtain niobium-doped LiCl composite modified Li2ZrCl6. Step a4: 90g of modified lithium iron phosphate and 10g of modified Li2ZrCl6 are loaded into a high-speed mixer at a speed of 2000r / min, nitrogen is introduced for protection, and the mixture is mixed for 25min. Then it is treated by a hot roller press at a roller temperature of 150℃ and a pressure of 5MPa to obtain Li2ZrCl6-LiCl coated lithium iron phosphate. Step S5: Add 175.9g of Li2ZrCl6-LiCl coated lithium iron phosphate and 1.23g of C6H 12O6·H2O and 5.28g of carbon nanotubes were added to a ball mill jar with a ball-to-material ratio of 10:1. The grinding balls were nano-zirconium balls. 250mL of anhydrous ethanol was added as a dispersion solvent. The mixture was ball-milled at 600r / min for 11h. The ball mill jar was removed, the balls were separated, dried and ground, and then spread evenly on a ceramic boat. The material was then placed in a tube furnace for sintering at 25℃ for 4h, then heated to 680℃ and sintered at a constant temperature for 10h. Finally, it was naturally cooled to 25℃. After sintering, a high-rate lithium iron phosphate cathode material with Li2ZrCl6-LiCl interface modification was obtained.

[0018] Example 3: This embodiment describes a method for preparing a high-rate lithium iron phosphate cathode material with interface modification, including the following steps: Step S1: Add 0.985 mol FeCl3·H2O, 1 mol NH4H2PO4, and 600 mL deionized water to a three-necked flask equipped with a stirrer and thermometer, and mix and stir for 20 min to obtain the first solution; separately take 0.01 mol ZrOCl2·8H2O, 0.005 mol... C2H5NNbO4 and 400 mL of 0.5 mol / L hydrochloric acid solution were added to a beaker and stirred for 30 min to obtain a second solution. 200 mL of 0.1 mol / L hexadecyltrimethylammonium bromide solution was added to the first solution, and nitrogen gas was introduced for protection. The first solution was heated to 85 °C and stirred at a constant speed of 1200 r / min for 2 h. The second solution was added, and 4 mol / L NaOH solution was added simultaneously to maintain the pH at 2. The reaction was carried out for 12 h, and then centrifuged. The precipitate was placed in a vacuum drying oven and dried at 55 °C for 3 h to obtain zirconium-niobium co-doped FePO4. Step S2: 158.3g of zirconium-niobium co-doped FePO4, 1.03mol of Li2CO3 and 0.1mol of sucrose were mixed and added to a planetary ball mill. 300mL of anhydrous ethanol was added as a dispersion solvent. The ball-to-material ratio was 5:1. The mixture was ball-milled at 350r / min for 4h. After ball milling, it was placed in an 80℃ forced-air drying oven for 12h to dry. After crushing and grinding, it was pre-calcined at 350℃ for 4h in a vacuum tube furnace under a nitrogen atmosphere, and then sintered at 750℃ for 12h to obtain modified lithium iron phosphate. Step S3: 1.8 mol LiCl, 0.8 mol ZrCl4, and 0.2 mol NbCl5 were vacuum dried at 120 °C for 24 h, then placed in a ball mill jar with a ball-to-material ratio of 10:1 and ball-milled at 500 r / min for 10 h under argon protection. The remaining 0.54 mol LiCl was dissolved in 540 mL of anhydrous ethanol, sprayed onto liquid nitrogen for freezing, and then vacuum dried to obtain nano-LiCl. This nano-LiCl was then added to the ball mill jar and ball-milled at 200 r / min for 1 h to obtain niobium-doped LiCl composite modified Li2ZrCl6. Step S4: 90g of modified lithium iron phosphate and 10g of modified Li2ZrCl6 are loaded into a high-speed mixer at a speed of 2000r / min, nitrogen is introduced for protection, and the mixture is mixed for 30min. Then, it is treated by a hot roller press at a roller temperature of 150℃ and a pressure of 5MPa to obtain Li2ZrCl6-LiCl coated lithium iron phosphate. Step S5: Add 175.9g of Li2ZrCl6-LiCl coated lithium iron phosphate and 1.23g of C6H 12 O6·H2O and 5.28g of carbon nanotubes were added to a ball mill jar with a ball-to-material ratio of 10:1. The grinding balls were nano-zirconium balls. 300mL of anhydrous ethanol was added as a dispersion solvent. The mixture was ball-milled at 600r / min for 12h. The ball mill jar was removed, the balls were separated, dried and ground, and then spread evenly on a ceramic boat. The material was placed in a tube furnace for sintering at 25℃ for 4h, then heated to 680℃ and sintered at a constant temperature for 10h. Finally, it was naturally cooled to 25℃. After sintering, a high-rate lithium iron phosphate cathode material with Li2ZrCl6-LiCl interface modification was obtained.

[0019] Comparative Example 1: This comparative example illustrates a method for preparing a high-rate lithium iron phosphate cathode material with interface modification, comprising the following steps: Step S1: 1.8 mol LiCl, 0.8 mol ZrCl4, and 0.2 mol NbCl5 were vacuum dried at 120 °C for 24 h, then placed in a ball mill jar with a ball-to-material ratio of 10:1 and ball-milled at 500 r / min for 10 h under argon protection. The remaining 0.54 mol LiCl was dissolved in 540 mL of anhydrous ethanol, sprayed onto liquid nitrogen for freezing, and then vacuum dried to obtain nano-LiCl. This nano-LiCl was then added to the ball mill jar and ball-milled at 200 r / min for 1 h to obtain niobium-doped LiCl composite modified Li2ZrCl6. Step S2: 90g of lithium iron phosphate and 10g of modified Li2ZrCl6 are loaded into a high-speed mixer at a speed of 2000r / min, under nitrogen protection, and mixed for 25min. Then, the mixture is processed through a hot roller press at a roller temperature of 150℃ and a pressure of 5MPa to obtain a high-rate lithium iron phosphate cathode material with Li2ZrCl6-LiCl interface modification.

[0020] Comparative Example 2: This comparative example illustrates a method for preparing a high-rate lithium iron phosphate cathode material with interface modification, comprising the following steps: Step S1: Add 0.985 mol FeCl3·H2O, 1 mol NH4H2PO4, and 600 mL deionized water to a three-necked flask equipped with a stirrer and thermometer, and mix and stir for 18 min to obtain the first solution; separately take 0.01 mol ZrOCl2·8H2O, 0.005 mol... C2H5NNbO4 and 400 mL of 0.5 mol / L hydrochloric acid solution were added to a beaker and stirred for 25 min to obtain a second solution. 200 mL of 0.1 mol / L hexadecyltrimethylammonium bromide solution was added to the first solution, and nitrogen gas was introduced for protection. The first solution was heated to 85 °C and stirred at a constant speed of 1200 r / min for 1.5 h. The second solution was then added, and simultaneously, 4 mol / L NaOH solution was added to maintain the pH at 1.9. The reaction was carried out for 12 h, followed by centrifugation. The precipitate was placed in a vacuum drying oven and dried at 55 °C for 2.5 h to obtain zirconium-niobium co-doped FePO4. Step S2: 158.3g of zirconium-niobium co-doped FePO4, 1.03mol of Li2CO3 and 0.1mol of sucrose were mixed and added to a planetary ball mill. 250mL of anhydrous ethanol was added as a dispersion solvent. The ball-to-material ratio was 5:1. The mixture was ball-milled at 350r / min for 4h. After ball milling, it was placed in an 80℃ forced-air drying oven for 12h to dry. After crushing and grinding, it was pre-calcined at 350℃ for 4h in a vacuum tube furnace under a nitrogen atmosphere, and then sintered at 750℃ for 12h to obtain modified lithium iron phosphate. Step S3: 1.8 mol LiCl, 0.8 mol ZrCl4, and 0.2 mol NbCl5 were vacuum dried at 120 °C for 24 h, then placed in a ball mill jar with a ball-to-material ratio of 10:1 and ball-milled at 500 r / min for 10 h under argon protection. The remaining 0.54 mol LiCl was dissolved in 540 mL of anhydrous ethanol, sprayed onto liquid nitrogen for freezing, and then vacuum dried to obtain nano-LiCl. This nano-LiCl was then added to the ball mill jar and ball-milled at 200 r / min for 1 h to obtain niobium-doped LiCl composite modified Li2ZrCl6. Step S4: 90g of modified lithium iron phosphate and 10g of modified Li2ZrCl6 are loaded into a high-speed mixer at a speed of 2000r / min, under nitrogen protection, and mixed for 25min. Then, the mixture is processed through a hot roller press at a roller temperature of 150℃ and a pressure of 5MPa to obtain a high-rate lithium iron phosphate cathode material with Li2ZrCl6-LiCl interface modification.

[0021] Comparative Example 3: This comparative example illustrates a method for preparing a high-rate lithium iron phosphate cathode material with interface modification, comprising the following steps: Step S1: 1.8 mol LiCl, 0.8 mol ZrCl4, and 0.2 mol NbCl5 were vacuum dried at 120 °C for 24 h, then placed in a ball mill jar with a ball-to-material ratio of 10:1 and ball-milled at 500 r / min for 10 h under argon protection. The remaining 0.54 mol LiCl was dissolved in 540 mL of anhydrous ethanol, sprayed onto liquid nitrogen for freezing, and then vacuum dried to obtain nano-LiCl. This nano-LiCl was then added to the ball mill jar and ball-milled at 200 r / min for 1 h to obtain niobium-doped LiCl composite modified Li2ZrCl6. Step S2: 90g of lithium iron phosphate and 10g of modified Li2ZrCl6 are loaded into a high-speed mixer at a speed of 2000r / min, nitrogen is introduced for protection, and the mixture is mixed for 25min. Then it is treated by a hot roller press at a roller temperature of 150℃ and a pressure of 5MPa to obtain lithium iron phosphate coated with Li2ZrCl6-LiCl. Step S3: Add 175.9g of Li2ZrCl6-LiCl coated lithium iron phosphate and 1.23g of C6H 12 O6·H2O and 5.28g of carbon nanotubes were added to a ball mill jar with a ball-to-material ratio of 10:1. The grinding balls were nano-zirconium balls. 250mL of anhydrous ethanol was added as a dispersion solvent. The mixture was ball-milled at 600r / min for 11h. The ball mill jar was removed, the balls were separated, dried and ground, and then spread evenly on a ceramic boat. The material was then placed in a tube furnace for sintering at 25℃ for 4h, then heated to 680℃ and sintered at a constant temperature for 10h. Finally, it was naturally cooled to 25℃. After sintering, a high-rate lithium iron phosphate cathode material with Li2ZrCl6-LiCl interface modification was obtained.

[0022] Batteries were prepared using the interface-modified high-rate lithium iron phosphate cathode materials of Examples 1-3 and Comparative Examples 1-3, graphite, UTEC 4041 polyethylene produced by Yuetai, and lithium iodide, and their electrochemical performance was tested. The interfacial impedance was measured using EIS. The energy density and electrochemical performance were tested according to GB / T 31486-2024. The test results are shown in the table below.

[0023] Referring to the table above, Comparative Example 1 is a blank control group that only underwent Li2ZrCl6-LiCl interface modification. Compared with Examples 1-3, it can be seen that the battery performance prepared by the interface-modified high-rate lithium iron phosphate cathode material of the present invention is significantly better than that of Comparative Example 1. According to the comparison between Examples 1-3 and Comparative Example 2, it can be seen that the synergistic Li2ZrCl6-LiCl interface modification by coating lithium iron phosphate with carbon nanotubes can significantly reduce the interface impedance and improve the rate performance and energy density of the material at 10C. According to the comparison between Examples 1-3 and Comparative Example 3, it can be seen that zirconium-niobium doping can significantly reduce the interface impedance, improve the rate performance of the battery at 0.2C, 5C, and 10C, improve the conductivity of the material, and increase the volumetric energy density.

[0024] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0025] The above description is merely an example and illustration 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 invention or exceed the scope defined in this application, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing an interface-modified high-rate lithium iron phosphate cathode material, characterized in that, Includes the following steps: Step a1: FeCl3·H2O, NH4H2PO4 and deionized water are mixed and stirred to obtain the first solution; ZrOCl2·8H2O, C2H5NNbO4 and hydrochloric acid solution are mixed and stirred to obtain the second solution; the first solution, hexadecyltrimethylammonium bromide solution and the second solution are mixed and stirred, NaOH solution is added to maintain the pH, centrifuged and dried to obtain zirconium-niobium co-doped FePO4; Step a2: Mix and ball-mill zirconium-niobium co-doped FePO4, Li2CO3, and sucrose, then sinter to obtain modified lithium iron phosphate; Step a3: Vacuum dry LiCl, ZrCl4, and NbCl5 in a molar ratio of 10 / 13, then ball mill them. Dissolve the remaining LiCl in anhydrous ethanol, then spray, dry, and ball mill it to obtain niobium-doped LiCl composite modified Li2ZrCl6. Step a4: Mix modified lithium iron phosphate and modified Li2ZrCl6 and roll them through a hot roller press to obtain Li2ZrCl6-LiCl coated lithium iron phosphate; Step a5: Lithium iron phosphate and C6H coated with Li2ZrCl6-LiCl are then added. 12 O6·H2O and carbon nanotubes were mixed, ball-milled, dried, ground, sintered, and naturally cooled to obtain a high-rate lithium iron phosphate cathode material with Li2ZrCl6-LiCl interface modification.

2. The method for preparing an interface-modified high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, The ratio of FeCl3·H2O, NH4H2PO4, deionized water, ZrOCl2·8H2O, C2H5NNbO4, hydrochloric acid solution, and hexadecyltrimethylammonium bromide solution used in step a1 is 0.985mol:1mol:600mL:0.01mol:0.005mol:400mL:200mL.

3. The method for preparing an interface-modified high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, The molar concentration of the hydrochloric acid solution in step a1 is 0.5 mol / L; the molar concentration of the hexadecyltrimethylammonium bromide solution is 0.1 mol / L; and the molar concentration of the NaOH solution is 4 mol / L.

4. The method for preparing an interface-modified high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, The ratio of zirconium-niobium co-doped FePO4, Li2CO3, sucrose, and anhydrous ethanol used in step a2 is 158.3g:1.03mol:0.1mol:200-300mL.

5. The method for preparing an interface-modified high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, The ratio of LiCl, ZrCl4, NbCl5 and anhydrous ethanol used in step a3 is 2.34 mol: 0.8 mol: 0.2 mol: 540 mL.

6. The method for preparing an interface-modified high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, The ratio of modified lithium iron phosphate to modified Li2ZrCl6 in step a4 is 90g:10g.

7. The method for preparing an interface-modified high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, The Li2ZrCl6-LiCl coated lithium iron phosphate and C6H mentioned in step a5 12 The ratio of O6·H2O, carbon nanotubes, and anhydrous ethanol is 175.9g:1.23g:5.28g:200-300mL.

8. A high-rate lithium iron phosphate cathode material with interface modification, characterized in that, The interface-modified high-rate lithium iron phosphate cathode material is prepared according to the preparation method of the interface-modified high-rate lithium iron phosphate cathode material according to any one of claims 1-7.

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