Composite solid electrolyte synergistically modified lithium iron phosphate positive electrode material and preparation method thereof

Abstract

The invention relates to the field of lithium iron phosphate, in particular to a composite solid electrolyte synergistically modified lithium iron phosphate positive electrode material and a preparation method thereof. The preparation method is used for solving the problems that existing lithium iron phosphate is poor in electronic conductivity, high in interface impedance and poor and low in interface stability. The lithium iron phosphate positive electrode material synergistically modified by the composite solid electrolyte comprises COF / neodymium-doped lithium titanium aluminum phosphate modified lithium iron phosphate, acetylene carbon black, polyethylene glycol and N-methyl pyrrolidone, according to the preparation method, firstly, lithium iron phosphate is prepared, neodymium ions are doped in the process of preparing lithium titanium aluminum phosphate to serve as a first modification layer, cyanophenothiazine COF is synthesized to serve as a second modification layer, two layers of solid electrolyte are modified on the surface of the lithium iron phosphate to achieve a synergistic effect to form a protective film, and formation of lithium dendrites can be effectively reduced; the interface stability and the cycle performance of the material are remarkably improved, and the safety of the battery is enhanced.

Description

Composite solid electrolyte synergistic modification of lithium iron phosphate cathode material and its preparation method Technical Field

[0001] This invention relates to the field of lithium iron phosphate, specifically to lithium iron phosphate cathode materials synergistically modified with composite solid electrolytes and their preparation methods. Background Technology

[0002] Currently, lithium-ion batteries are widely used in many fields due to their high energy density and excellent cycle performance. Cathode materials are one of the core components of lithium-ion batteries. Lithium iron phosphate (LFP), as a traditional cathode material, has advantages such as abundant raw materials, environmental friendliness, and low cost. However, LFP materials suffer from poor conductivity, high interfacial impedance, and poor interfacial stability, limiting their performance in high-power applications. This invention provides a lithium iron phosphate cathode material synergistically modified with a composite solid electrolyte. By modifying the LFP cathode material with a composite solid electrolyte, the aforementioned problems can be effectively solved, potentially further improving the overall performance of lithium-ion batteries and possessing practical application value. Summary of the Invention

[0003] In order to overcome the above-mentioned technical problems, the present invention aims to provide: a composite solid electrolyte synergistic modification of lithium iron phosphate cathode material and its preparation method, which solves the problems of poor electronic conductivity, high interface impedance and poor interface stability of existing lithium iron phosphate materials.

[0004] The objective of this invention can be achieved through the following technical solution: Firstly, this application provides a composite solid electrolyte synergistic modification of lithium iron phosphate cathode material, comprising the following components by weight: 45-90 parts of COF / NdFeB-doped aluminum titanium phosphate modified lithium iron phosphate, 4-8 parts of acetylene black, and 1.5-3 parts of polyethylene glycol; wherein the COF / NdFeB-doped aluminum titanium phosphate modified lithium iron phosphate is prepared by the following steps: Step A1: Lithium carbonate, iron phosphate, and ethanol are added to a ball mill jar, the mass ratio of raw materials to milling beads is 1:20, ball milling is performed for 4 hours, and then vacuum dried in a drying oven to obtain lithium iron phosphate; Step A2: Lithium carbonate, alumina, titanium dioxide, ammonium dihydrogen phosphate, NdFeB, and isopropanol are added to a ball mill jar, the mass ratio of raw materials to milling beads is 1:2, ball milling is performed for 10 hours, lithium iron phosphate is added and ball milled for 2 hours, then dried in a drying oven at 70°C for 12 hours, and then... After sintering in a muffle furnace at 650℃ for 10 hours, the raw material is added to a ball mill jar at a mass ratio of 1:2. The mixture is ball-milled for 12 hours, dried in a drying oven at 70℃ for 12 hours, and then sintered in a muffle furnace at 950℃ for 12 hours. The mixture is then ground to obtain neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate. Step A3: 1-chloro-4-iodobenzene, phenothiazine, copper powder, and potassium carbonate are added to a two-necked flask equipped with a stirrer and thermometer. Under nitrogen protection, the mixture was evacuated and nitrogen was added three times at 100-200 r / min, with each evacuation lasting ten minutes and nitrogen addition lasting one minute. N,N-dimethylformamide was added, and the mixture was reacted at 145℃ for 48 h. The mixture was washed with dichloromethane and extracted 3-5 times with saturated brine. The organic layer was collected, dried with anhydrous sodium sulfate, and N,N-dimethylformamide was removed by vacuum distillation. The mixture was then purified by column chromatography with dichloromethane to obtain the first intermediate.

[0005] Step A4: Add the first intermediate and tetrahydrofuran to a two-necked flask equipped with a stirrer, stir at 100-200 r / min in the dark, add N-chlorosuccinimide in four portions, each with the same amount, half an hour apart, react in the dark for 24 h, remove tetrahydrofuran by vacuum distillation, and purify by column chromatography with petroleum ether to obtain the second intermediate;

[0006] Step A5: Add the second intermediate, 4-formylphenylboronic acid, triphenylphosphine, and potassium carbonate to a two-necked flask equipped with a thermometer. Purge with nitrogen for protection, evacuate and replenish with nitrogen three times, each time for ten minutes and one minute for replenishing nitrogen. Add tetrahydrofuran and deoxygenated water and react at 95°C in the dark for 24 hours. Wash with dichloromethane and extract with saturated brine 3-5 times. Collect the organic layer, dry with anhydrous sodium sulfate, remove tetrahydrofuran and deoxygenated water by vacuum distillation, and purify by column chromatography with petroleum ether to obtain the third intermediate.

[0007] Step A6: 2,4,6-Tricyano-1,3,5-trimethylbenzene and the third intermediate were added to a Schlenk tube, transferred to an argon glove box, and dimethylamine, N,N-dimethylformamide and o-dichlorobenzene were added. After sealing and removal, the mixture was sonicated for 30-60 min, transferred to an oil bath and reacted at 180 °C and 400 r / min for 72 h. After filtration, the mixture was washed three times with o-dichlorobenzene and placed in a drying oven to be vacuum dried at 160 °C for 12 h to obtain cyanophithiazine COF.

[0008]

[0009] Step A7: Add neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate and deionized water to a ball mill jar, and ball mill at 400-500 r / min for 15-20 min. Add cyanophethiazine COF, mix at 900-1000 r / min for 4-5 h, transfer to an oven and dry at 80 °C to obtain COF / neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate.

[0010] As a further aspect of the present invention: the ratio of lithium carbonate, iron phosphate and ethanol used in step A1 is 0.0515-0.103 mol: 0.05-0.1 mol: 25-50 mL.

[0011] As a further aspect of the present invention: the volume fraction of ethanol in step A1 is 95%.

[0012] As a further embodiment of the present invention: the ratio of lithium carbonate, aluminum oxide, titanium dioxide, ammonium dihydrogen phosphate, neodymium oxide, isopropanol and lithium iron phosphate in step A2 is 0.08-0.16 mol: 0.0075-0.015 mol: 0.085-0.17 mol: 0.15-0.3 mol: 0.002-0.004 mol: 0.365-0.73 mol: 5-10 g.

[0013] As a further embodiment of the present invention: the ratio of 1-chloro-4-iodobenzene, phenothiazine, copper powder, potassium carbonate and N,N-dimethylformamide used in step A3 is 0.0265-0.053 mol: 0.0265-0.053 mol: 0.006-0.012 mol: 0.055-0.11 mol: 50-100 mL.

[0014] As a further embodiment of the present invention: in step A4, the ratio of the first intermediate, tetrahydrofuran and N-chlorosuccinimide is 0.007-0.014 mol: 25-50 mL: 0.042-0.084 mol.

[0015] As a further embodiment of the present invention: in step A5, the ratio of the second intermediate, 4-formylphenylboronic acid, triphenylphosphine, potassium carbonate, tetrahydrofuran, and deoxygenated water is 0.005-0.01 mol: 0.02-0.04 mol: 0.0001-0.0002 mol: 0.06-0.12 mol: 80-160 mL: 20-40 mL.

[0016] As a further embodiment of the present invention: the ratio of the amounts of 2,4,6-tricyano-1,3,5-trimethylbenzene, the third intermediate, dimethylamine, N,N-dimethylformamide and o-dichlorobenzene in step A6 is 1.2-1.6 mmol: 1.2-1.6 mmol: 6-8 mL: 30-40 mL: 30-40 mL.

[0017] As a further aspect of the present invention: the ratio of neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate, deionized water and cyanophithiazine COF in step A7 is 5-10g: 50-100mL: 1-2g.

[0018] Secondly, this invention provides a method for preparing a composite solid electrolyte synergistic modified lithium iron phosphate cathode material, comprising the following steps: Step 1: Weigh 45-90 parts by weight of COF / NdFeB-doped aluminum titanium phosphate modified lithium iron phosphate, 4-8 parts by weight of acetylene black, and 1.5-3 parts by weight of polyethylene glycol, and set aside; wherein the polyethylene glycol is polyethylene glycol PEG-300; Step 2: Grind the COF / NdFeB-doped aluminum titanium phosphate modified lithium iron phosphate, acetylene black, and polyethylene glycol PEG-300, then add N-methylpyrrolidone to adjust the solid content to 45%-55% and continue grinding, after grinding, coat it on an aluminum foil current collector and dry it in a constant temperature vacuum drying oven for 8-12 hours, place it in a roller press to compact it, and finally use a slicing machine to press it into a circular electrode to obtain the composite solid electrolyte synergistic modified lithium iron phosphate cathode material.

[0019] The beneficial effects of the present invention are as follows: The composite solid electrolyte of the present invention synergistically modifies the lithium iron phosphate cathode material. Neodymium-doped lithium aluminum titanium phosphate is used as the first modification layer, and cyanophethizine COF is synthesized as the second modification layer. The two work together to form a protective film on the surface of lithium iron phosphate, thereby reducing side reactions and the increase in impedance, and improving the long-term cycle life of the battery.

[0020] To prepare a composite solid-state electrolyte synergistically modified lithium iron phosphate cathode material, lithium iron phosphate was first prepared using lithium carbonate and iron phosphate. Then, neodymium-doped lithium aluminum titanium phosphate (LFP) was synthesized using lithium carbonate, aluminum oxide, titanium dioxide, ammonium dihydrogen phosphate, and neodymium oxide. LFP, as an oxide solid-state electrolyte material, possesses high ionic conductivity and chemical stability. The large ionic radius of neodymium, when doped into the LFP lattice, can induce lattice distortion, broadening the lithium-ion migration channels and thus improving conductivity. The cyano group in cyanophithiazine COF, as a strongly polar functional group, facilitates... The lone pair electrons of the nitrogen atom weakly coordinate with lithium ions to assist in dissociation, increasing the concentration of lithium ions in the electrolyte. The COF structure can provide transport channels for lithium ions, effectively suppressing the formation of lithium dendrites. The nitrogen and sulfur atoms in the phenthiazine group can guide the conduction of lithium ions. By modifying the lithium iron phosphate surface with neodymium-doped aluminum titanium phosphate and cyanophenthiazine COF as a composite solid electrolyte, a stable and dense interface layer is formed, which suppresses the instability between the electrolyte and the cathode material, reduces interface side reactions, improves interface stability, and thus enhances the overall performance and safety of the battery. Detailed Implementation

[0021] 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.

[0022] Example 1: This example describes a method for preparing a lithium iron phosphate cathode material synergistically modified with a composite solid electrolyte, comprising the following steps: Step A1: 0.0515 mol lithium carbonate, 0.05 mol iron phosphate, and 25 mL ethanol are added to a ball mill jar. The mass ratio of raw materials to milling beads is 1:20. The mixture is ball-milled for 4 hours and then vacuum-dried in a drying oven to obtain lithium iron phosphate. Step A2: 0.08 mol lithium carbonate, 0.0075 mol alumina, 0.085 mol titanium dioxide, 0.15 mol ammonium dihydrogen phosphate, and 0.002 mol oxygen are added to a ball mill jar. Neodymium and 0.365 mol of isopropanol were added to a ball mill jar, with a raw material to ball mill beads mass ratio of 1:2. The mixture was ball milled for 10 hours, then 5 g of lithium iron phosphate was added and ball milled for 2 hours. The mixture was then dried in a drying oven at 70°C for 12 hours, and sintered in a muffle furnace at 650°C for 10 hours. The mixture was then added back to the ball mill jar, with a raw material to ball mill beads mass ratio of 1:2, and ball milled for 12 hours. The mixture was then dried in a drying oven at 70°C for 12 hours, and sintered in a muffle furnace at 950°C for 12 hours. Finally, the mixture was ground to obtain neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate. Step A3: 0.0265 mol... 1-Chloro-4-iodobenzene, 0.0265 mol phenothiazine, 0.006 mol copper powder, and 0.055 mol potassium carbonate were added to a two-necked flask equipped with a stirrer and thermometer. Nitrogen gas was introduced for protection, and the mixture was evacuated and nitrogen replenished three times at 100 rpm, each evacuation lasting ten minutes followed by nitrogen replenishment for one minute. 50 mL of N,N-dimethylformamide was added, and the reaction was carried out at 145 °C for 48 h. The mixture was washed with dichloromethane and extracted three times with saturated brine. The organic layer was collected, dried over anhydrous sodium sulfate, and N,N-dimethylformamide was removed by vacuum distillation. The mixture was then purified by column chromatography with dichloromethane to obtain the first intermediate. Step A4: 0.007 mol of the first intermediate and 25 mL of tetrahydrofuran were added to a two-necked flask equipped with a stirrer and stirred at 100 rpm in the dark. 0.042 mol of the first intermediate was added in four portions. N-Chlorosuccinimide was added in the same amount each time, with half-hour intervals, and reacted in the dark for 24 hours. Tetrahydrofuran was removed by vacuum distillation, and the product was purified by column chromatography with petroleum ether to obtain the second intermediate. Step A5: 0.005 mol of the second intermediate, 0.02 mol of 4-formylphenylboronic acid, 0.0001 mol of triphenylphosphine, and 0.06 mol of potassium carbonate were added to a two-necked flask equipped with a thermometer. Nitrogen gas was introduced for protection, and the mixture was evacuated and nitrogen was added three times, each time for ten minutes and one minute for nitrogen addition. 80 mL of tetrahydrofuran and 20 mL of anoxic water were added, and the mixture was reacted at 95 °C in the dark for 24 hours. The mixture was washed with dichloromethane, extracted three times with saturated brine, and the organic layer was collected, dried with anhydrous sodium sulfate, and the tetrahydrofuran and anoxic water were removed by vacuum distillation. The product was purified by column chromatography with petroleum ether to obtain the third intermediate. Step A6: 1.2 mmol of... 2,4,6-Tricyano-1,3,5-Trimethylbenzene, 1.2 mmol of the third intermediate was added to a Schlenk tube, transferred to an argon glove box, and 6 mL of dimethylamine, 30 mL of N,N-dimethylformamide, and 30 mL of o-dichlorobenzene were added. After sealing, the mixture was sonicated for 30 min, transferred to an oil bath, and reacted at 180 °C and 400 r / min for 72 h. After filtration, the mixture was washed three times with o-dichlorobenzene and dried under vacuum at 160 °C for 12 h to obtain cyanophithitaziazine COF. Step A7: 5 g of neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate and 50 mL of deionized water were added to a ball mill jar and ball-milled at 400 r / min for 15 min. 1 g of cyanophithitaziazine COF was added, and the mixture was mixed at 900 r / min for 4 h. The mixture was then transferred to an oven and dried at 80 °C to obtain COF / neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate. Lithium; Step A8: Weigh 45 parts by weight of COF / NdFeB-doped aluminum titanium phosphate modified lithium iron phosphate, 4 parts by weight of acetylene black, and 1.5 parts by weight of polyethylene glycol, and set aside; wherein, the polyethylene glycol is polyethylene glycol PEG-300; Step A9: Grind the COF / NdFeB-doped aluminum titanium phosphate modified lithium iron phosphate, acetylene black, and polyethylene glycol PEG-300, then add N-methylpyrrolidone to adjust the solid content to 45% and continue grinding. After grinding, coat the mixture onto an aluminum foil current collector and dry it in a constant temperature vacuum drying oven for 8 hours. Then, compact it in a roller press and finally press it into a circular electrode using a slicing machine to obtain a composite solid electrolyte synergistic modified lithium iron phosphate cathode material.

[0023] Example 2: This example describes a method for preparing a composite solid electrolyte synergistically modified lithium iron phosphate cathode material, comprising the following steps: Step A1: 0.0773 mol lithium carbonate, 0.075 mol iron phosphate, and 27 mL ethanol are added to a ball mill jar. The mass ratio of raw materials to milling beads is 1:20. The mixture is ball-milled for 4 hours and then vacuum-dried in a drying oven to obtain lithium iron phosphate. Step A2: 0.12 mol lithium carbonate, 0.0113 mol alumina, 0.1275 mol titanium dioxide, 0.225 mol ammonium dihydrogen phosphate, and 0.003 mol... Neodymium oxide and 0.5475 mol of isopropanol were added to a ball mill jar, with a raw material to milling beads mass ratio of 1:2. The mixture was ball-milled for 10 hours. Then, 7.5 g of lithium iron phosphate was added and ball-milled for 2 hours. The mixture was then dried in a drying oven at 70°C for 12 hours, and sintered in a muffle furnace at 650°C for 10 hours. The mixture was then added back to the ball mill jar, with a raw material to milling beads mass ratio of 1:2. The mixture was ball-milled for 12 hours, dried in a drying oven at 70°C for 12 hours, and sintered in a muffle furnace at 950°C for 12 hours. Finally, the mixture was ground to obtain neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate. Step A3: 0.04 mol... 1-Chloro-4-iodobenzene, 0.04 mol phenothiazine, 0.009 mol copper powder, and 0.0825 mol potassium carbonate were added to a two-necked flask equipped with a stirrer and thermometer. Nitrogen gas was introduced for protection, and the mixture was evacuated and nitrogen replenished three times at 150 rpm, each evacuation lasting ten minutes followed by nitrogen replenishment for one minute. 75 mL of N,N-dimethylformamide was added, and the reaction was carried out at 145 °C for 48 h. The mixture was washed with dichloromethane and extracted four times with saturated brine. The organic layer was collected, dried over anhydrous sodium sulfate, and N,N-dimethylformamide was removed by vacuum distillation. The mixture was then purified by column chromatography with dichloromethane to obtain the first intermediate. Step A4: 0.0105 mol of the first intermediate and 37 mL of tetrahydrofuran were added to a two-necked flask equipped with a stirrer and stirred at 150 rpm in the dark. 0.063 mol of the first intermediate was added in four portions. N-Chlorosuccinimide was added in the same amount each time, with half-hour intervals, and reacted in the dark for 24 hours. Tetrahydrofuran was removed by vacuum distillation, and the product was purified by column chromatography with petroleum ether to obtain the second intermediate. Step A5: 0.0075 mol of the second intermediate, 0.03 mol of 4-formylphenylboronic acid, 0.00015 mol of triphenylphosphine, and 0.09 mol of potassium carbonate were added to a two-necked flask equipped with a thermometer. Nitrogen gas was introduced for protection, and the mixture was evacuated and nitrogen was added three times, each time for ten minutes and one minute for one minute. 120 mL of tetrahydrofuran and 30 mL of anoxic water were added, and the mixture was reacted at 95 °C in the dark for 24 hours. The mixture was washed with dichloromethane, extracted four times with saturated brine, and the organic layer was collected, dried with anhydrous sodium sulfate, and the tetrahydrofuran and anoxic water were removed by vacuum distillation. The product was purified by column chromatography with petroleum ether to obtain the third intermediate. Step A6: 1.4 mmol of... 2,4,6-Tricyano-1,3,5-Trimethylbenzene, 1.4 mmol of the third intermediate was added to a Schlenk tube, transferred to an argon glove box, and 7 mL of dimethylamine, 35 mL of N,N-dimethylformamide, and 35 mL of o-dichlorobenzene were added. After sealing, the mixture was sonicated for 45 min, transferred to an oil bath, and reacted at 180 °C and 400 r / min for 72 h. After filtration, the mixture was washed three times with o-dichlorobenzene and dried under vacuum at 160 °C for 12 h to obtain cyanophithitaziazine COF. Step A7: 7.5 g of neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate and 75 mL of deionized water were added to a ball mill jar and ball-milled at 450 r / min for 17 min. 1.5 g of cyanophithitaziazine COF was added, and the mixture was mixed at 950 r / min for 4.5 h. The mixture was then transferred to an oven and dried at 80 °C to obtain COF / neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate. Lithium iron phosphate; Step A8: Weigh 67.5 parts by weight of COF / NdFeB-doped aluminum titanium phosphate modified lithium iron phosphate, 6 parts by weight of acetylene black, and 2.25 parts by weight of polyethylene glycol, and set aside; wherein, the polyethylene glycol is polyethylene glycol PEG-300; Step A9: Grind the COF / NdFeB-doped aluminum titanium phosphate modified lithium iron phosphate, acetylene black, and polyethylene glycol PEG-300, then add N-methylpyrrolidone to adjust the solid content to 50% and continue grinding. After grinding, coat the mixture onto an aluminum foil current collector and dry it in a constant temperature vacuum drying oven for 10 hours. Then, compact it in a roller press and finally press it into a circular electrode using a slicing machine to obtain a composite solid electrolyte synergistic modified lithium iron phosphate cathode material.

[0024] Example 3: This example describes a method for preparing a lithium iron phosphate cathode material synergistically modified with a composite solid electrolyte, comprising the following steps: Step A1: 0.103 mol lithium carbonate, 0.1 mol iron phosphate, and 50 mL ethanol are added to a ball mill jar. The mass ratio of raw materials to milling beads is 1:20. The mixture is ball-milled for 4 hours and then vacuum-dried in a drying oven to obtain lithium iron phosphate. Step A2: 0.16 mol lithium carbonate, 0.015 mol aluminum oxide, 0.17 mol titanium dioxide, 0.3 mol ammonium dihydrogen phosphate, and 0.004 mol neodymium oxide are added to the mixture. Add 0.73 mol of isopropanol to a ball mill jar, with a raw material to ball milling beads mass ratio of 1:2, and ball mill for 10 h. Add 10 g of lithium iron phosphate and ball mill for 2 h. Place in a drying oven and dry at 70 °C for 12 h. Place in a muffle furnace and sinter at 650 °C for 10 h. Then add to a ball mill jar, with a raw material to ball milling beads mass ratio of 1:2, and ball mill for 12 h. Place in a drying oven and dry at 70 °C for 12 h. Place in a muffle furnace and sinter at 950 °C for 12 h. Grind to obtain neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate; Step A3: Add 0.053 mol of isopropanol to a ball mill jar. 1-Chloro-4-iodobenzene, 0.053 mol phenothiazine, 0.012 mol copper powder, and 0.11 mol potassium carbonate were added to a two-necked flask equipped with a stirrer and thermometer. Nitrogen gas was introduced for protection, and the mixture was evacuated and nitrogen replenished three times at 200 rpm, each evacuation lasting ten minutes followed by nitrogen replenishment for one minute. 100 mL of N,N-dimethylformamide was added, and the reaction was carried out at 145 °C for 48 h. The mixture was washed with dichloromethane and extracted five times with saturated brine. The organic layer was collected, dried over anhydrous sodium sulfate, and N,N-dimethylformamide was removed by vacuum distillation. The mixture was then purified by column chromatography with dichloromethane to obtain the first intermediate. Step A4: 0.014 mol of the first intermediate and 50 mL of tetrahydrofuran were added to a two-necked flask equipped with a stirrer and stirred at 200 rpm in the dark. 0.084 mol of the first intermediate was added in four portions. N-Chlorosuccinimide was added in the same amount each time, with half-hour intervals, and reacted in the dark for 24 hours. Tetrahydrofuran was removed by vacuum distillation, and the product was purified by column chromatography with petroleum ether to obtain the second intermediate. Step A5: 0.01 mol of the second intermediate, 0.04 mol of 4-formylphenylboronic acid, 0.0002 mol of triphenylphosphine, and 0.12 mol of potassium carbonate were added to a two-necked flask equipped with a thermometer. Nitrogen gas was introduced for protection, and the mixture was evacuated and nitrogen was added three times, each time for ten minutes and one minute for one minute. 160 mL of tetrahydrofuran and 40 mL of anoxic water were added, and the mixture was reacted at 95 °C in the dark for 24 hours. The mixture was washed with dichloromethane, extracted five times with saturated brine, and the organic layer was collected, dried with anhydrous sodium sulfate, and the tetrahydrofuran and anoxic water were removed by vacuum distillation. The product was purified by column chromatography with petroleum ether to obtain the third intermediate. Step A6: 1.6 mmol of the second intermediate, 0.04 mol of 4-formylphenylboronic acid, 0.0002 mol of triphenylphosphine, and 0.12 mol of potassium carbonate were added to a two-necked flask equipped with a thermometer. Nitrogen gas was introduced for protection, and the mixture was evacuated and nitrogen was added three times, each time for ten minutes and nitrogen was added for one minute. 160 mL of tetrahydrofuran and 40 mL of anoxic water were added, and the mixture was reacted at 95 °C in the dark to obtain the third intermediate. The mixture was washed with dichloromethane, extracted five times with saturated brine, and the organic layer was collected and dried with anhydrous sodium sulfate. Tetrahydrofuran and anoxic water were removed 2,4,6-Tricyano-1,3,5-Trimethylbenzene, 1.6 mmol of the third intermediate was added to a Schlenk tube, transferred to an argon glove box, and 8 mL of dimethylamine, 40 mL of N,N-dimethylformamide, and 40 mL of o-dichlorobenzene were added. After sealing, the mixture was sonicated for 60 min, transferred to an oil bath, and reacted at 180 °C and 400 r / min for 72 h. After filtration, the mixture was washed three times with o-dichlorobenzene and dried under vacuum at 160 °C for 12 h to obtain cyanophithitaziazine COF. Step A7: 10 g of neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate and 100 mL of deionized water were added to a ball mill jar and ball-milled at 500 r / min for 20 min. 2 g of cyanophithitaziazine COF was added, and the mixture was mixed at 1000 r / min for 5 h. The mixture was then transferred to an oven and dried at 80 °C to obtain COF / neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate. Lithium iron phosphate; Step A8: Weigh 90 parts by weight of COF / NdFeB-doped aluminum titanium phosphate modified lithium iron phosphate, 8 parts by weight of acetylene black, and 3 parts by weight of polyethylene glycol, and set aside; wherein, the polyethylene glycol is polyethylene glycol PEG-300; Step A9: Grind the COF / NdFeB-doped aluminum titanium phosphate modified lithium iron phosphate, acetylene black, and polyethylene glycol PEG-300, then add N-methylpyrrolidone to adjust the solid content to 55% and continue grinding. After grinding, coat the mixture onto an aluminum foil current collector and dry it in a constant temperature vacuum drying oven for 12 hours. Then, compact it in a roller press and finally press it into a circular electrode using a slicing machine to obtain a composite solid electrolyte synergistic modified lithium iron phosphate cathode material.

[0025] Comparative Example 1: This comparative example describes a method for preparing a lithium iron phosphate cathode material synergistically modified with a composite solid electrolyte, comprising the following steps: Step A1: 0.103 mol lithium carbonate, 0.1 mol iron phosphate, and 50 mL ethanol were added to a ball mill jar, with a raw material to milling ball mass ratio of 1:20. The mixture was ball-milled for 4 hours and then vacuum-dried in a drying oven to obtain lithium iron phosphate. Step A2: 0.16 mol lithium carbonate, 0.015 mol alumina, 0.17 mol titanium dioxide, 0.3 mol ammonium dihydrogen phosphate, 0.004 mol neodymium oxide, and 0.73 mol isopropanol were added to a ball mill jar, with a raw material to milling ball mass ratio of 1:2. The mixture was ball-milled for 10 hours, then 10 g of lithium iron phosphate was added and ball-milled for 2 hours. The mixture was then dried in a drying oven at 70°C for 12 hours, sintered in a muffle furnace at 650°C for 10 hours, and then added back to the ball mill jar. The mass ratio of the material to the ball milling beads is 1:2. The mixture is ball milled for 12 hours, dried in a drying oven at 70°C for 12 hours, sintered in a muffle furnace at 950°C for 12 hours, and then ground to obtain neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate. Step A3: Weigh 90 parts of neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate, 8 parts of acetylene black, and 3 parts of polyethylene glycol according to their weight proportions, and set aside. The polyethylene glycol is polyethylene glycol PEG-300. Step A4: Grind the neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate, acetylene black, and polyethylene glycol PEG-300. Then add N-methylpyrrolidone to adjust the solid content to 55% and continue grinding. After grinding, coat the mixture onto an aluminum foil current collector and dry it in a constant temperature vacuum drying oven for 12 hours. Compact the mixture in a roller press and finally press it into a circular electrode using a slicing machine to obtain a composite solid electrolyte synergistic modified lithium iron phosphate cathode material.

[0026] Comparative Example 2: This comparative example describes a method for preparing a lithium iron phosphate cathode material synergistically modified with a composite solid electrolyte, comprising the following steps: Step A1: 0.103 mol lithium carbonate, 0.1 mol iron phosphate, and 50 mL ethanol are added to a ball mill jar. The mass ratio of raw materials to milling beads is 1:20. The mixture is ball-milled for 4 hours and then vacuum-dried in a drying oven to obtain lithium iron phosphate. Step A2: 0.16 mol lithium carbonate, 0.015 mol alumina, 0.17 mol titanium dioxide, 0.3 mol ammonium dihydrogen phosphate, and 0.7 mol... 3 mol of isopropanol was added to a ball mill jar, with a raw material to milling beads mass ratio of 1:2. The mixture was ball-milled for 10 hours. Then, 10 g of lithium iron phosphate was added and ball-milled for 2 hours. The mixture was then dried in a drying oven at 70°C for 12 hours, and sintered in a muffle furnace at 650°C for 10 hours. The mixture was then added back to the ball mill jar, with a raw material to milling beads mass ratio of 1:2. The mixture was ball-milled for 12 hours, dried in a drying oven at 70°C for 12 hours, and sintered in a muffle furnace at 950°C for 12 hours. Finally, the mixture was ground to obtain lithium iron phosphate modified with lithium aluminum titanium phosphate. Step A3: 0.053 mol... 1-Chloro-4-iodobenzene, 0.053 mol phenothiazine, 0.012 mol copper powder, and 0.11 mol potassium carbonate were added to a two-necked flask equipped with a stirrer and thermometer. Nitrogen gas was introduced for protection, and the mixture was evacuated and nitrogen replenished three times at 200 rpm, each evacuation lasting ten minutes followed by nitrogen replenishment for one minute. 100 mL of N,N-dimethylformamide was added, and the reaction was carried out at 145 °C for 48 h. The mixture was washed with dichloromethane and extracted five times with saturated brine. The organic layer was collected, dried over anhydrous sodium sulfate, and N,N-dimethylformamide was removed by vacuum distillation. The mixture was then purified by column chromatography with dichloromethane to obtain the first intermediate. Step A4: 0.014 mol of the first intermediate and 50 mL of tetrahydrofuran were added to a two-necked flask equipped with a stirrer and stirred at 200 rpm in the dark. 0.084 mol of the first intermediate was added in four portions. N-Chlorosuccinimide was added in the same amount each time, with half-hour intervals, and reacted in the dark for 24 hours. Tetrahydrofuran was removed by vacuum distillation, and the product was purified by column chromatography with petroleum ether to obtain the second intermediate. Step A5: 0.01 mol of the second intermediate, 0.04 mol of 4-formylphenylboronic acid, 0.0002 mol of triphenylphosphine, and 0.12 mol of potassium carbonate were added to a two-necked flask equipped with a thermometer. Nitrogen gas was introduced for protection, and the mixture was evacuated and nitrogen was added three times, each time for ten minutes and one minute for one minute. 160 mL of tetrahydrofuran and 40 mL of anoxic water were added, and the mixture was reacted at 95 °C in the dark for 24 hours. The mixture was washed with dichloromethane, extracted five times with saturated brine, and the organic layer was collected, dried with anhydrous sodium sulfate, and the tetrahydrofuran and anoxic water were removed by vacuum distillation. The product was purified by column chromatography with petroleum ether to obtain the third intermediate. Step A6: 1.6 mmol of the second intermediate, 0.04 mol of 4-formylphenylboronic acid, 0.0002 mol of triphenylphosphine, and 0.12 mol of potassium carbonate were added to a two-necked flask equipped with a thermometer. Nitrogen gas was introduced for protection, and the mixture was evacuated and nitrogen was added three times, each time for ten minutes and nitrogen was added for one minute. 160 mL of tetrahydrofuran and 40 mL of anoxic water were added, and the mixture was reacted at 95 °C in the dark to obtain the third intermediate. The mixture was washed with dichloromethane, extracted five times with saturated brine, and the organic layer was collected and dried with anhydrous sodium sulfate. Tetrahydrofuran and anoxic water were removed 2,4,6-Tricyano-1,3,5-Trimethylbenzene, 1.6 mmol of the third intermediate was added to a Schlenk tube, transferred to an argon glove box, and 8 mL of dimethylamine, 40 mL of N,N-dimethylformamide, and 40 mL of o-dichlorobenzene were added. After sealing, the mixture was sonicated for 60 min, transferred to an oil bath, and reacted at 180 °C and 400 r / min for 72 h. After filtration, the mixture was washed three times with o-dichlorobenzene and dried under vacuum at 160 °C for 12 h to obtain cyanophithitaziazine COF. Step A7: 10 g of lithium aluminum titanium phosphate modified lithium iron phosphate and 100 mL of deionized water were added to a ball mill jar and ball milled at 500 r / min for 20 min. 2 g of cyanophithitaziazine COF was added, and the mixture was mixed at 1000 r / min for 5 h. The mixture was then transferred to an oven and dried at 80 °C to obtain COF / neodymium-doped lithium aluminum titanium phosphate modified... Lithium iron phosphate; Step A8: Weigh 90 parts by weight of COF / lithium aluminum titanium phosphate modified lithium iron phosphate, 8 parts by weight of acetylene black, and 3 parts by weight of polyethylene glycol, and set aside; wherein, the polyethylene glycol is polyethylene glycol PEG-300; Step A9: Grind the COF / lithium aluminum titanium phosphate modified lithium iron phosphate, acetylene black, and polyethylene glycol PEG-300, then add N-methylpyrrolidone to adjust the solid content to 55% and continue grinding. After grinding, coat the mixture onto an aluminum foil current collector and dry it in a constant temperature vacuum drying oven for 12 hours. Then, compact it in a roller press and finally press it into a circular electrode using a slicing machine to obtain a composite solid electrolyte synergistic modified lithium iron phosphate cathode material.

[0027] Comparative Example 3: This comparative example describes a method for preparing a lithium iron phosphate cathode material synergistically modified with a composite solid electrolyte, comprising the following steps: Step A1: 0.103 mol lithium carbonate, 0.1 mol iron phosphate, and 50 mL ethanol were added to a ball mill jar. The mass ratio of raw materials to milling beads was 1:20. The mixture was ball-milled for 4 hours, then vacuum-dried in a drying oven and sintered in a muffle furnace at 950 °C for 12 hours to obtain lithium iron phosphate. Step A2: 0.053 mol 1-chloro-4-iodobenzene, 0.053 mol phenothiazine, 0.012 mol copper powder, and 0.11 mol potassium carbonate were added to a two-necked flask equipped with a stirrer and thermometer. Nitrogen gas was introduced for protection, and the mixture was evacuated and replenished with nitrogen three times at 200 r / min. Each evacuation lasted for ten minutes, and the nitrogen replenishment lasted for one minute. 100 mL of ethanol was added at each evacuation. N,N-Dimethylformamide was reacted at 145℃ for 48 h, washed with dichloromethane, extracted five times with saturated brine, and the organic layer was collected, dried with anhydrous sodium sulfate, and N,N-dimethylformamide was removed by vacuum distillation. The mixture was then purified by column chromatography with dichloromethane to obtain the first intermediate. Step A3: 0.014 mol of the first intermediate and 50 mL of tetrahydrofuran were added to a two-necked flask equipped with a stirrer and stirred at 200 rpm in the dark. 0.084 mol of N-chlorosuccinimide was added in four equal portions, half an hour apart, and reacted in the dark for 24 h. Tetrahydrofuran was removed by vacuum distillation, and the mixture was purified by column chromatography with petroleum ether to obtain the second intermediate. Step A4: 0.01 mol of the second intermediate and 0.04 mol of... 4-Formylphenylboronic acid, 0.0002 mol triphenylphosphine, and 0.12 mol potassium carbonate were added to a two-necked flask equipped with a thermometer. Nitrogen gas was introduced for protection, and the mixture was evacuated three times, with each evacuation lasting ten minutes and nitrogen replenishment lasting one minute. 160 mL of tetrahydrofuran and 40 mL of anoxic water were added, and the mixture was reacted at 95 °C in the dark for 24 h. The mixture was washed with dichloromethane and extracted five times with saturated brine. The organic layer was collected, dried with anhydrous sodium sulfate, and the tetrahydrofuran and anoxic water were removed by vacuum distillation. The mixture was purified by column chromatography with petroleum ether to obtain the third intermediate. Step A5: 1.6 mmol of 2,4,6-tricyano-1,3,5-trimethylbenzene, 1...6 mmol of the third intermediate was added to a Schlenk tube, transferred to an argon glove box, and 8 mL of dimethylamine, 40 mL of N,N-dimethylformamide, and 40 mL of o-dichlorobenzene were added. After sealing, the mixture was sonicated for 60 min, transferred to an oil bath, and reacted at 180 °C and 400 rpm for 72 h. After filtration, the mixture was washed three times with o-dichlorobenzene and dried under vacuum at 160 °C for 12 h to obtain cyanophithitaziazine COF. Step A6: 10 g of lithium iron phosphate and 100 mL of deionized water were added to a ball mill jar and ball-milled at 500 rpm for 20 min. 2 g of cyanophithitaziazine COF was added, and the mixture was mixed at 1000 rpm for 5 h. The mixture was then transferred to an oven and dried at 80 °C to obtain COF-modified phosphoric acid. Lithium iron phosphate; Step A7: Weigh 90 parts by weight of COF-modified lithium iron phosphate, 8 parts by weight of acetylene black, and 3 parts by weight of polyethylene glycol, and set aside; wherein, the polyethylene glycol is polyethylene glycol PEG-300; Step A8: Grind the COF-modified lithium iron phosphate, acetylene black, and polyethylene glycol PEG-300, then add N-methylpyrrolidone to adjust the solid content to 55% and continue grinding. After grinding, coat the mixture onto an aluminum foil current collector and dry it in a constant temperature vacuum drying oven for 12 hours. Then, compact it in a roller press and finally press it into a circular electrode using a slicing machine to obtain a composite solid electrolyte synergistic modified lithium iron phosphate cathode material.

[0028] For performance testing, the composite solid electrolyte synergistically modified lithium iron phosphate cathode material of Examples 1-3 and Comparative Examples 1-3 was used as the cathode, lithium sheet as the anode, Celgard2400 as the battery separator, and 1M LiPF6 / EC+DEC+EMC (1:1:1, v / v / v) electrolyte was used. The battery was assembled using a CR2032 button cell casing. After injecting the electrolyte, a 12kN pressure was applied using a packaging machine to seal the battery, ensuring that the sealing ring was fully pressed together to obtain the lithium battery. The lithium battery was used as the sample battery.

[0029] Conductivity tests were performed on the sample batteries. The multimeter was set to the resistance setting, and its two probes were connected to the positive and negative terminals of the battery, respectively. The voltage values ​​across the battery were recorded, and the conductivity was calculated. A CHI660C electrochemical workstation was used for the button batteries in this experiment. The test conditions were: AC voltage amplitude of 5mV, frequency range of 1Hz~100kHz, and test temperature of 25℃. The interfacial impedance value was obtained. The sample batteries were then subjected to 0.1C cycle performance tests at 25℃ using a blue electric current tester. The prepared sample batteries were placed in a 25℃ constant temperature chamber for charge-discharge testing. The voltage range was 2.5-3.75V, and charge-discharge cycles were performed at 0.1C current (constant current charging) for 100 cycles. The 0.1C discharge specific capacity and capacity retention rate after 100 cycles were obtained. The test results are shown in Table 1: Table 1: Schematic diagram of test results for conductivity, interfacial impedance, 0.1C discharge specific capacity, and capacity retention rate after 100 cycles.

[0030] Referring to the table above, based on the comparison between Examples 1-3 and Comparative Examples 1-3, it can be seen that COF / neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate has high conductivity and good interface stability.

[0031] Comparing Example 3 and Comparative Example 1, it can be seen that the interface impedance value of the cathode material obtained by modifying lithium iron phosphate with COF / neodymium-doped aluminum titanium phosphate is lower than that of the cathode material obtained by modifying lithium iron phosphate with neodymium-doped aluminum titanium phosphate, indicating that the cathode material obtained by modifying lithium iron phosphate with COF / neodymium-doped aluminum titanium phosphate has a lower interface impedance. Similarly, comparing Example 3 and Comparative Example 2, it can be seen that the interface impedance value of the cathode material obtained by modifying lithium iron phosphate with COF / neodymium-doped aluminum titanium phosphate is lower than that of the cathode material obtained by modifying lithium iron phosphate with COF / neodymium-doped aluminum titanium phosphate, indicating that the cathode material obtained by modifying lithium iron phosphate with COF / neodymium-doped aluminum titanium phosphate has a lower interface impedance. Again, comparing Example 3 and Comparative Example 3, it can be seen that the interface impedance value of the cathode material obtained by modifying lithium iron phosphate with COF / neodymium-doped aluminum titanium phosphate is lower than that of the cathode material obtained by modifying lithium iron phosphate with COF, indicating that the cathode material obtained by modifying lithium iron phosphate with COF / neodymium-doped aluminum titanium phosphate has a lower interface impedance.

[0032] 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.

[0033] 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 composite solid electrolyte synergistically modified lithium iron phosphate cathode material, characterized in that, The product comprises the following components by weight: 45-90 parts of COF / neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate, 4-8 parts of acetylene black, and 1.5-3 parts of polyethylene glycol; wherein the COF / neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate is prepared by the following steps: Step A1: ball milling lithium carbonate, iron phosphate, and ethanol to obtain lithium iron phosphate; Step A2: ball milling lithium carbonate, alumina, titanium dioxide, ammonium dihydrogen phosphate, neodymium oxide, isopropanol, and lithium iron phosphate to obtain neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate; Step A3: reacting 1-chloro-4-iodobenzene, phenothiazine, copper powder, potassium carbonate, and N,N-dimethylformamide to obtain the product... A first intermediate; Step A4: React the first intermediate, tetrahydrofuran, and N-chlorosuccinimide to obtain the second intermediate; Step A5: React the second intermediate, 4-formylphenylboronic acid, triphenylphosphine, potassium carbonate, tetrahydrofuran, and deoxygenated water to obtain the third intermediate; Step A6: React 2,4,6-tricyano-1,3,5-trimethylbenzene, the third intermediate, dimethylamine, N,N-dimethylformamide, and o-dichlorobenzene to obtain cyanophenothiazine COF; Step A7: Ball mill neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate, deionized water, and cyanophenothiazine COF to obtain COF / neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate.

2. The composite solid electrolyte synergistic modification of lithium iron phosphate cathode material according to claim 1, characterized in that, The ratio of lithium carbonate, iron phosphate, and ethanol used in step A1 is 0.0515-0.103 mol: 0.05-0.1 mol: 25-50 mL.

3. The composite solid electrolyte synergistic modification of lithium iron phosphate cathode material according to claim 1, characterized in that, The volume fraction of ethanol mentioned in step A1 is 95%.

4. The composite solid electrolyte synergistic modification of lithium iron phosphate cathode material according to claim 1, characterized in that, The ratio of lithium carbonate, aluminum oxide, titanium dioxide, ammonium dihydrogen phosphate, neodymium oxide, isopropanol, and lithium iron phosphate used in step A2 is 0.08-0.16 mol: 0.0075-0.015 mol: 0.085-0.17 mol: 0.15-0.3 mol: 0.002-0.004 mol: 0.365-0.73 mol: 5-10 g.

5. The composite solid electrolyte synergistic modification of lithium iron phosphate cathode material according to claim 1, characterized in that, The ratio of 1-chloro-4-iodobenzene, phenothiazine, copper powder, potassium carbonate, and N,N-dimethylformamide used in step A3 is 0.0265-0.053 mol: 0.0265-0.053 mol: 0.006-0.012 mol: 0.055-0.11 mol: 50-100 mL.

6. The composite solid electrolyte synergistic modification of lithium iron phosphate cathode material according to claim 1, characterized in that, In step A4, the ratio of the first intermediate, tetrahydrofuran, and N-chlorosuccinimide is 0.007-0.014 mol: 25-50 mL: 0.042-0.084 mol.

7. The composite solid electrolyte synergistic modification of lithium iron phosphate cathode material according to claim 1, characterized in that, In step A5, the ratio of the second intermediate, 4-formylphenylboronic acid, triphenylphosphine, potassium carbonate, tetrahydrofuran, and deoxygenated water is 0.005-0.01 mol: 0.02-0.04 mol: 0.0001-0.0002 mol: 0.06-0.12 mol: 80-160 mL: 20-40 mL.

8. The composite solid electrolyte synergistic modification of lithium iron phosphate cathode material according to claim 1, characterized in that, The ratio of 2,4,6-tricyano-1,3,5-trimethylbenzene, the third intermediate, dimethylamine, N,N-dimethylformamide, and o-dichlorobenzene in step A6 is 1.2-1.6 mmol: 1.2-1.6 mmol: 6-8 mL: 30-40 mL: 30-40 mL.

9. The composite solid electrolyte synergistic modification of lithium iron phosphate cathode material according to claim 1, characterized in that, In step A7, the ratio of neodymium-doped lithium aluminum titanium phosphate modified lithium iron phosphate, deionized water, and cyanophethiazine COF is 5-10g: 50-100mL: 1-2g.

10. A method for preparing lithium iron phosphate cathode materials synergistically modified with composite solid electrolytes, characterized in that, This material is used to prepare the composite solid electrolyte synergistic modification of lithium iron phosphate cathode material as described in any one of claims 1-9. The process includes the following steps: Step 1: Weigh 45-90 parts by weight of COF / NdFeB-doped aluminum titanium phosphate modified lithium iron phosphate, 4-8 parts by weight of acetylene black, and 1.5-3 parts by weight of polyethylene glycol, and set aside; Step 2: Grind the COF / NdFeB-doped aluminum titanium phosphate modified lithium iron phosphate, acetylene black, and polyethylene glycol, then add N-methylpyrrolidone to adjust the solid content to 45%-55% and continue grinding. After grinding, coat the mixture onto an aluminum foil current collector and dry it in a constant temperature vacuum drying oven for 8-12 hours. Then, place it in a roller press to compact it, and finally use a slicing machine to press it into a circular electrode to obtain a composite solid electrolyte synergistic modified lithium iron phosphate cathode material.

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