Preparation method of sodium titanium phosphate surface modified lithium iron phosphate positive electrode material

Abstract

This invention relates to the field of lithium-ion battery cathode materials, specifically to a method for preparing a lithium iron phosphate cathode material with sodium titanium phosphate surface modification; it addresses the problems of poor rate performance and cycle performance of existing lithium iron phosphate materials. The sodium titanium phosphate surface-modified lithium iron phosphate cathode material comprises sodium titanium phosphate surface-modified lithium iron phosphate powder, acetylene black, and polyvinylidene fluoride. The preparation method first adds gadolinium ions and dysprosium ions during the synthesis of lithium iron phosphate to reduce the electrostatic bonding between lithium ions and surrounding atoms, improving rate performance. Then, sodium titanium phosphate is synthesized. Sodium titanium phosphate has three-dimensional lithium-ion diffusion channels, enhancing the rate performance and cycle performance of the lithium iron phosphate material. It is then co-coated with glucose and polyethylene glycol as a coating layer on the surface of the lithium iron phosphate. This significantly improves the rate performance and cycle performance of existing lithium iron phosphate materials and can be applied in energy storage devices.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode materials, specifically to a method for preparing a lithium iron phosphate cathode material with sodium titanium phosphate surface modification. Background Technology

[0002] Lithium iron phosphate (LFP) is widely used as a cathode material due to its low cost, high safety, and long lifespan. However, some problems still exist in practical applications, such as poor rate performance and poor cycle performance. These problems limit its use in demanding applications. This invention provides a LFP cathode material with sodium titanium phosphate surface modification, thereby effectively improving the cycle stability and rate performance of LFP. Summary of the Invention

[0003] In order to overcome the above-mentioned technical problems, the present invention aims to provide a method for preparing lithium iron phosphate cathode material with sodium titanium phosphate surface modification, which solves the problems of poor rate performance and poor cycle performance of existing lithium iron phosphate.

[0004] In a first aspect, this application provides a lithium iron phosphate cathode material with sodium titanium phosphate surface modification, comprising the following raw materials in parts by weight:

[0005] The mixture consists of 32-64 parts of sodium titanium phosphate / carbon layer coated gadolinium dysprosium co-doped lithium iron phosphate, 4-8 parts of acetylene black, and 4-8 parts of polyvinylidene fluoride.

[0006] The sodium titanium phosphate / carbon layer coated gadolinium dysprosium co-doped lithium iron phosphate is prepared by the following steps:

[0007] Step A1: Add ascorbic acid solution and ethylene glycol solution to a double-necked flask equipped with a magnetic stirrer, stir at 50-100 r / min for 6-10 min, sonicate for 30 min, add lithium hydroxide monohydrate and stir for 6-10 min, add phosphoric acid and stir for 6-10 min, add ferrous sulfate heptahydrate, gadolinium chloride and dysprosium chloride and stir for 10-20 min, transfer to a stainless steel autoclave equipped with a stirrer, react at 180℃ and 300 r / min for 10 h, cool to 24-26℃, wash with deionized water 3-5 times, freeze dry under vacuum for 24 h to obtain gadolinium-dysprosium co-doped lithium iron phosphate precursor powder;

[0008] Step A2: Add sodium acetate and phosphoric acid solution to a two-necked flask equipped with a stirrer and stir for 10-20 min. Dissolve tetraethyl titanate in anhydrous ethanol and add it to the flask and stir for 10-20 min. Transfer to a high-pressure reactor with a polytetrafluoroethylene liner and react at 160°C for 3 h. After filtration, wash with deionized water, centrifuge with anhydrous ethanol, and dry in a forced-air drying oven at 60°C to obtain sodium titanium phosphate precursor powder.

[0009] Step A3: Add sodium titanium phosphate precursor powder, glucose, polyethylene glycol, and deionized water to a three-necked flask equipped with a stirrer and thermometer. Stir at 60-80℃ for 0.5-1h, add gadolinium-dysprosium co-doped lithium iron phosphate precursor powder, sonicate for 0.5-1h, evaporate to dryness at 85-100℃, transfer to a high-temperature furnace, purge with nitrogen for protection, heat to 650-750℃ at a rate of 10℃ / min, sinter for 2-4h, cool to obtain sodium titanium phosphate / carbon layer coated gadolinium-dysprosium co-doped lithium iron phosphate.

[0010] As a further aspect of the present invention: the ratio of the amounts of ascorbic acid solution, ethylene glycol solution, lithium hydroxide monohydrate, phosphoric acid, ferrous sulfate heptahydrate, gadolinium chloride and dysprosium chloride in step A1 is 10-20 mL: 30-60 mL: 30-60 mmol: 10-20 mmol: 9-18 mmol: 0.5-1 mmol: 0.5-1 mmol.

[0011] As a further aspect of the present invention: the molar concentration of the ascorbic acid solution in step A1 is 0.03 mol / L.

[0012] As a further aspect of the present invention: the volume fraction of the ethylene glycol solution in step A1 is 12.5%.

[0013] As a further aspect of the present invention: the ratio of sodium acetate, phosphoric acid, tetraethyl titanate and anhydrous ethanol used in step A2 is 10-20 mmol: 30-60 mL: 10-20 mmol: 200-400 mL.

[0014] As a further aspect of the present invention: the mass fraction of the phosphoric acid solution in step A2 is 85%.

[0015] As a further aspect of the present invention: the ratio of sodium titanium phosphate precursor powder, glucose, polyethylene glycol, deionized water and gadolinium-dysprosium co-doped lithium iron phosphate precursor powder in step A3 is 1-2 mmol: 0.15-0.3 mmol: 0.15-0.3 g: 100-200 mL: 150-300 mmol.

[0016] As a further aspect of the present invention: the polyethylene glycol mentioned in step A3 is of type PEG1000.

[0017] Secondly, this invention provides a method for preparing a lithium iron phosphate cathode material with sodium titanium phosphate surface modification, comprising the following steps:

[0018] Step 1: Weigh out 32-64 parts of sodium titanium phosphate / carbon-coated gadolinium dysprosium co-doped lithium iron phosphate, 4-8 parts of acetylene black, and 4-8 parts of polyvinylidene fluoride according to the weight ratio, and set aside; wherein, the polyvinylidene fluoride is of type PVDF5130.

[0019] Step 2: Grind the sodium titanium phosphate / carbon layer coated with gadolinium-dysprosium co-doped lithium iron phosphate, acetylene black, and polyvinylidene fluoride. 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. Then, place it in a roller press to compact it. Finally, use a slicing machine to press it into a circular electrode to obtain the sodium titanium phosphate surface modified lithium iron phosphate cathode material.

[0020] Beneficial effects:

[0021] This invention discloses a sodium titanium phosphate surface-modified lithium iron phosphate cathode material, in which gadolinium ions and dysprosium ions are co-doped into lithium iron phosphate crystals, and glucose and polyethylene glycol are used as carbon layers to co-coat the surface of gadolinium-dysprosium co-doped lithium iron phosphate with sodium titanium phosphate. This effectively solves the problems of poor ion transport performance, interface instability and stress concentration in lithium iron phosphate materials, and significantly improves the rate performance and cycle performance of existing lithium iron phosphate materials.

[0022] A lithium iron phosphate cathode material with sodium titanium phosphate surface modification was prepared. First, gadolinium chloride and dysprosium chloride were added during the preparation of lithium iron phosphate to obtain gadolinium-dysprosium co-doped lithium iron phosphate precursor powder. The radii of gadolinium ions and dysprosium ions are larger than those of iron ions. After doping, the interplanar spacing is expanded, providing a larger migration path for lithium ions. Sodium titanium phosphate was synthesized using sodium acetate, phosphoric acid, and tetraethyl titanate. Sodium titanium phosphate has a three-dimensional ionic conductor structure, which can provide a stable and fast transport path for lithium ions in lithium iron phosphate, thereby improving the poor lithium ion diffusion ability and poor rate performance of lithium iron phosphate materials. Sodium titanium phosphate and carbon layer co-coating improve the coating effect of lithium iron phosphate surface, avoiding the corrosion of lithium iron phosphate by electrolyte due to uneven carbon coating, which leads to a decrease in cycle performance. This effectively improves the rate performance and high and low temperature performance of lithium iron phosphate batteries, ensuring excellent performance of batteries in various operating environments. Detailed Implementation

[0023] 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.

[0024] Example 1:

[0025] This embodiment describes a method for preparing a lithium iron phosphate cathode material with sodium titanium phosphate surface modification, including the following steps:

[0026] Step A1: Add 10 mL of ascorbic acid solution and 30 mL of ethylene glycol solution to a two-necked flask equipped with a magnetic stirrer, stir at 50 r / min for 6 min, sonicate for 30 min, add 30 mmol of lithium hydroxide monohydrate and stir for 6 min, add 10 mmol of phosphoric acid and stir for 6 min, add 9 mmol of ferrous sulfate heptahydrate, 0.5 mmol of gadolinium chloride and 0.5 mmol of dysprosium chloride and stir for 10 min, transfer to a stainless steel autoclave equipped with a stirrer, react at 180 °C and 300 r / min for 10 h, cool to 24 °C, wash 3 times with deionized water, and freeze dry under vacuum for 24 h to obtain gadolinium-dysprosium co-doped lithium iron phosphate precursor powder;

[0027] Step A2: Add 10 mmol sodium acetate and 30 mL phosphoric acid solution to a two-necked flask equipped with a stirrer and stir for 10 min. Dissolve 10 mmol tetraethyl titanate in 200 mL anhydrous ethanol and add it to the flask and stir for 10 min. Transfer the solution to a high-pressure reactor with a polytetrafluoroethylene liner and react at 160 °C for 3 h. After filtration, wash with deionized water, centrifuge with anhydrous ethanol, and dry in a forced-air drying oven at 60 °C to obtain sodium titanium phosphate precursor powder.

[0028] Step A3: Add 1 mmol sodium titanium phosphate precursor powder, 0.15 mmol glucose, 0.15 g polyethylene glycol and 100 mL deionized water to a three-necked flask equipped with a stirrer and thermometer. Stir at 60 °C for 0.5 h. Add 150 mmol gadolinium dysprosium co-doped lithium iron phosphate precursor powder and sonicate for 0.5 h. Evaporate to dryness at 85-100 °C. Transfer to a high-temperature furnace, purge with nitrogen for protection, heat to 650 °C at a rate of 10 °C / min, sinter for 2 h, and cool to obtain sodium titanium phosphate / carbon layer coated gadolinium dysprosium co-doped lithium iron phosphate.

[0029] Step A4: Weigh out 32 parts by weight of sodium titanium phosphate / carbon-coated gadolinium dysprosium co-doped lithium iron phosphate, 4 parts by weight of acetylene black and 4 parts by weight of polyvinylidene fluoride, and set aside; wherein, the polyvinylidene fluoride is of type PVDF5130;

[0030] Step A5: Grind the sodium titanium phosphate / carbon layer coated with gadolinium-dysprosium co-doped lithium iron phosphate, acetylene black and polyvinylidene fluoride PVDF5130, then add N-methylpyrrolidone to adjust the solid content to 45% and continue grinding. After grinding, coat it on aluminum foil current collector and dry it in a constant temperature vacuum drying oven for 8 hours. Then place it in a roller press to compact it. Finally, use a slicing machine to press it into a circular electrode to obtain the sodium titanium phosphate surface modified lithium iron phosphate cathode material.

[0031] Example 2:

[0032] This embodiment describes a method for preparing a lithium iron phosphate cathode material with sodium titanium phosphate surface modification, including the following steps:

[0033] Step A1: Add 15 mL of ascorbic acid solution and 45 mL of ethylene glycol solution to a two-necked flask equipped with a magnetic stirrer, stir at 75 r / min for 8 min, sonicate for 30 min, add 45 mmol of lithium hydroxide monohydrate and stir for 8 min, add 15 mmol of phosphoric acid and stir for 8 min, add 13.5 mmol of ferrous sulfate heptahydrate, 0.75 mmol of gadolinium chloride and 0.75 mmol of dysprosium chloride and stir for 15 min, transfer to a stainless steel autoclave equipped with a stirrer, react at 180 °C and 300 r / min for 10 h, cool to 25 °C, wash 4 times with deionized water, and freeze dry under vacuum for 24 h to obtain gadolinium-dysprosium co-doped lithium iron phosphate precursor powder;

[0034] Step A2: Add 15 mmol sodium acetate and 45 mL phosphoric acid solution to a two-necked flask equipped with a stirrer and stir for 15 min. Add 15 mmol tetraethyl titanate solution to 300 mL anhydrous ethanol and stir for 15 min. Transfer to a high-pressure reactor with a polytetrafluoroethylene liner and react at 160 °C for 3 h. After filtration, wash with deionized water, centrifuge with anhydrous ethanol, and dry in a forced-air drying oven at 60 °C to obtain sodium titanium phosphate precursor powder.

[0035] Step A3: Add 1.5 mmol sodium titanium phosphate precursor powder, 0.225 mmol glucose, 0.225 g polyethylene glycol and 150 mL deionized water to a three-necked flask equipped with a stirrer and thermometer. Stir at 70 °C for 45 min. Add 225 mmol gadolinium dysprosium co-doped lithium iron phosphate precursor powder and sonicate for 45 min. Evaporate to dryness at 90 °C. Transfer to a high-temperature furnace, purge with nitrogen, and heat to 700 °C at a rate of 10 °C / min. Sinter for 3 h. Cool to obtain sodium titanium phosphate / carbon layer coated gadolinium dysprosium co-doped lithium iron phosphate.

[0036] Step A4: Weigh out 48 parts by weight of sodium titanium phosphate / carbon layer coated gadolinium dysprosium co-doped lithium iron phosphate, 6 parts by weight of acetylene black and 6 parts by weight of polyvinylidene fluoride, and set aside; wherein, the polyvinylidene fluoride is of type PVDF5130;

[0037] Step A5: Grind the sodium titanium phosphate / carbon layer coated with gadolinium-dysprosium co-doped lithium iron phosphate, acetylene black, and polyvinylidene fluoride PVDF5130. Then, add N-methylpyrrolidone to adjust the solid content to 50% and continue grinding. After grinding, coat it on an aluminum foil current collector and dry it in a constant temperature vacuum drying oven for 10 hours. Then, place it in a roller press to compact it. Finally, use a slicing machine to press it into a circular electrode to obtain the sodium titanium phosphate surface modified lithium iron phosphate cathode material.

[0038] Example 3:

[0039] This embodiment describes a method for preparing a lithium iron phosphate cathode material with sodium titanium phosphate surface modification, including the following steps:

[0040] Step A1: Add 20 mL of ascorbic acid solution and 60 mL of ethylene glycol solution to a two-necked flask equipped with a magnetic stirrer, stir at 100 r / min for 10 min, sonicate for 30 min, add 60 mmol of lithium hydroxide monohydrate and stir for 10 min, add 20 mmol of phosphoric acid and stir for 10 min, add 18 mmol of ferrous sulfate heptahydrate, 1 mmol of gadolinium chloride and 1 mmol of dysprosium chloride and stir for 20 min, transfer to a stainless steel autoclave equipped with a stirrer, react at 180 °C and 300 r / min for 10 h, cool to 26 °C, wash 5 times with deionized water, and freeze dry under vacuum for 24 h to obtain gadolinium-dysprosium co-doped lithium iron phosphate precursor powder;

[0041] Step A2: Add 20 mmol sodium acetate and 60 mL phosphoric acid solution to a two-necked flask equipped with a stirrer and stir for 20 min. Dissolve 20 mmol tetraethyl titanate in 400 mL anhydrous ethanol and add it to the flask and stir for 20 min. Transfer the solution to a high-pressure reactor with a polytetrafluoroethylene liner and react at 160 °C for 3 h. After filtration, wash with deionized water, centrifuge with anhydrous ethanol, and dry in a forced-air drying oven at 60 °C to obtain sodium titanium phosphate precursor powder.

[0042] Step A3: Add 2 mmol of sodium titanium phosphate precursor powder, 0.3 mmol of glucose, 0.3 g of polyethylene glycol and 200 mL of deionized water to a three-necked flask equipped with a stirrer and thermometer. Stir at 80 °C for 1 h. Add 300 mmol of gadolinium-dysprosium co-doped lithium iron phosphate precursor powder and sonicate for 1 h. Evaporate to dryness at 100 °C. Transfer to a high-temperature furnace, purge with nitrogen for protection, heat to 750 °C at a rate of 10 °C / min, sinter for 4 h, and cool to obtain sodium titanium phosphate / carbon layer coated gadolinium-dysprosium co-doped lithium iron phosphate.

[0043] Step A4: Weigh out 64 parts by weight of sodium titanium phosphate / carbon layer coated gadolinium dysprosium co-doped lithium iron phosphate, 8 parts by weight of acetylene black and 8 parts by weight of polyvinylidene fluoride, and set aside; wherein, the polyvinylidene fluoride is of type PVDF5130;

[0044] Step A5: Grind the sodium titanium phosphate / carbon layer coated with gadolinium-dysprosium co-doped lithium iron phosphate, acetylene black, and polyvinylidene fluoride PVDF5130. Then, add N-methylpyrrolidone to adjust the solid content to 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 12 hours. Then, place it in a roller press to compact it. Finally, use a slicing machine to press it into a circular electrode to obtain the sodium titanium phosphate surface modified lithium iron phosphate cathode material.

[0045] Comparative Example 1:

[0046] This comparative example illustrates a method for preparing a sodium titanium phosphate surface-modified lithium iron phosphate cathode material, comprising the following steps:

[0047] Step A1: Add 20 mL of ascorbic acid solution and 60 mL of ethylene glycol solution to a two-necked flask equipped with a magnetic stirrer, stir at 100 r / min for 10 min, sonicate for 30 min, add 60 mmol of lithium hydroxide monohydrate and stir for 10 min, add 20 mmol of phosphoric acid and stir for 10 min, add 18 mmol of ferrous sulfate heptahydrate and 1 mmol of gadolinium chloride and stir for 20 min, transfer to a stainless steel autoclave equipped with a stirrer, react at 180 °C and 300 r / min for 10 h, cool to 26 °C, wash 5 times with deionized water, and freeze dry under vacuum for 24 h to obtain gadolinium-doped lithium iron phosphate precursor powder;

[0048] Step A2: Add 20 mmol sodium acetate and 60 mL phosphoric acid solution to a two-necked flask equipped with a stirrer and stir for 20 min. Dissolve 20 mmol tetraethyl titanate in 400 mL anhydrous ethanol and add it to the flask and stir for 20 min. Transfer the solution to a high-pressure reactor with a polytetrafluoroethylene liner and react at 160 °C for 3 h. After filtration, wash with deionized water, centrifuge with anhydrous ethanol, and dry in a forced-air drying oven at 60 °C to obtain sodium titanium phosphate precursor powder.

[0049] Step A3: Add 2 mmol sodium titanium phosphate precursor powder, 0.3 mmol glucose, 0.3 g polyethylene glycol and 200 mL deionized water to a three-necked flask equipped with a stirrer and thermometer. Stir at 80 °C for 1 h, add 300 mmol gadolinium-doped lithium iron phosphate precursor powder and sonicate for 1 h. Evaporate to dryness at 100 °C, transfer to a high-temperature furnace, purge with nitrogen for protection, heat to 750 °C at a rate of 10 °C / min, sinter for 4 h, and cool to obtain sodium titanium phosphate / carbon layer coated gadolinium-doped lithium iron phosphate.

[0050] Step A4: Weigh out 64 parts by weight of sodium titanium phosphate / carbon-coated gadolinium-doped lithium iron phosphate, 8 parts by weight of acetylene black and 8 parts by weight of polyvinylidene fluoride, and set aside; wherein, the polyvinylidene fluoride is of type PVDF5130;

[0051] Step A5: Grind the sodium titanium phosphate / carbon layer coated with gadolinium-doped lithium iron phosphate, acetylene black and polyvinylidene fluoride PVDF5130, then add N-methylpyrrolidone to adjust the solid content to 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 12 hours. Then place it in a roller press to compact it. Finally, use a slicing machine to press it into a circular electrode to obtain the sodium titanium phosphate surface modified lithium iron phosphate cathode material.

[0052] Comparative Example 2:

[0053] This comparative example illustrates a method for preparing a sodium titanium phosphate surface-modified lithium iron phosphate cathode material, comprising the following steps:

[0054] Step A1: Add 20 mL of ascorbic acid solution and 60 mL of ethylene glycol solution to a two-necked flask equipped with a magnetic stirrer, stir at 100 r / min for 10 min, sonicate for 30 min, add 60 mmol of lithium hydroxide monohydrate and stir for 10 min, add 20 mmol of phosphoric acid and stir for 10 min, add 18 mmol of ferrous sulfate heptahydrate and 1 mmol of dysprosium chloride and stir for 20 min, transfer to a stainless steel autoclave equipped with a stirrer, react at 180 °C and 300 r / min for 10 h, cool to 26 °C, wash 5 times with deionized water, and freeze dry under vacuum for 24 h to obtain dysprosium-doped lithium iron phosphate precursor powder;

[0055] Step A2: Add 20 mmol sodium acetate and 60 mL phosphoric acid solution to a two-necked flask equipped with a stirrer and stir for 20 min. Dissolve 20 mmol tetraethyl titanate in 400 mL anhydrous ethanol and add it to the flask and stir for 20 min. Transfer the solution to a high-pressure reactor with a polytetrafluoroethylene liner and react at 160 °C for 3 h. After filtration, wash with deionized water, centrifuge with anhydrous ethanol, and dry in a forced-air drying oven at 60 °C to obtain sodium titanium phosphate precursor powder.

[0056] Step A3: Add 2 mmol of sodium titanium phosphate precursor powder and 200 mL of deionized water to a three-necked flask equipped with a stirrer and thermometer. Stir at 80 °C for 1 h, add 300 mmol of dysprosium-doped lithium iron phosphate precursor powder, sonicate for 1 h, evaporate to dryness at 100 °C, transfer to a high-temperature furnace, purge with nitrogen for protection, heat to 750 °C at a rate of 10 °C / min, sinter for 4 h, cool to obtain sodium titanium phosphate coated dysprosium-doped lithium iron phosphate.

[0057] Step A4: Weigh out 64 parts by weight of sodium titanium phosphate coated with dysprosium-doped lithium iron phosphate, 8 parts by weight of acetylene black and 8 parts by weight of polyvinylidene fluoride, and set aside; wherein, the polyvinylidene fluoride is of type PVDF5130;

[0058] Step A5: Coated sodium titanium phosphate with dysprosium-doped lithium iron phosphate, acetylene black and polyvinylidene fluoride PVDF5130 is ground, then N-methylpyrrolidone is added to adjust the solid content to 55% and grinding is continued. After grinding, it is coated on aluminum foil current collector and placed in a constant temperature vacuum drying oven to dry for 12 hours. It is then placed in a roller press to compact it, and finally punched into a circular electrode by a slicing machine to obtain sodium titanium phosphate surface modified lithium iron phosphate cathode material.

[0059] Comparative Example 3:

[0060] This comparative example illustrates a method for preparing a sodium titanium phosphate surface-modified lithium iron phosphate cathode material, comprising the following steps:

[0061] Step A1: Add 20 mL of ascorbic acid solution and 60 mL of ethylene glycol solution to a two-necked flask equipped with a magnetic stirrer, stir at 100 r / min for 10 min, sonicate for 30 min, add 60 mmol of lithium hydroxide monohydrate and stir for 10 min, add 20 mmol of phosphoric acid and stir for 10 min, add 18 mmol of ferrous sulfate heptahydrate, 1 mmol of gadolinium chloride and 1 mmol of dysprosium chloride and stir for 20 min, transfer to a stainless steel autoclave equipped with a stirrer, react at 180 °C and 300 r / min for 10 h, cool to 26 °C, wash 5 times with deionized water, and freeze dry under vacuum for 24 h to obtain gadolinium-dysprosium co-doped lithium iron phosphate precursor powder;

[0062] Step A2: Add 20 mmol sodium acetate and 60 mL phosphoric acid solution to a two-necked flask equipped with a stirrer and stir for 20 min. Dissolve 20 mmol tetraethyl titanate in 400 mL anhydrous ethanol and add it to the flask and stir for 20 min. Transfer the solution to a high-pressure reactor with a polytetrafluoroethylene liner and react at 160 °C for 3 h. After filtration, wash with deionized water, centrifuge with anhydrous ethanol, and dry in a forced-air drying oven at 60 °C to obtain sodium titanium phosphate precursor powder.

[0063] Step A3: Add 2 mmol of sodium titanium phosphate precursor powder and 200 mL of deionized water to a three-necked flask equipped with a stirrer and thermometer. Stir at 80 °C for 1 h. Add 300 mmol of gadolinium-dysprosium co-doped lithium iron phosphate precursor powder and sonicate for 1 h. Evaporate to dryness at 100 °C. Transfer to a high-temperature furnace, purge with nitrogen for protection, heat to 750 °C at a rate of 10 °C / min, sinter for 4 h, and cool to obtain sodium titanium phosphate coated gadolinium-dysprosium co-doped lithium iron phosphate.

[0064] Step A4: Weigh out 64 parts by weight of sodium titanium phosphate coated with gadolinium dysprosium co-doped lithium iron phosphate, 8 parts by weight of acetylene black and 8 parts by weight of polyvinylidene fluoride, and set aside; wherein, the polyvinylidene fluoride is of type PVDF5130;

[0065] Step A5: Grind the sodium titanium phosphate coated with gadolinium-dysprosium co-doped lithium iron phosphate, acetylene black, and polyvinylidene fluoride PVDF5130. Then, add N-methylpyrrolidone to adjust the solid content to 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 12 hours. Then, place it in a roller press to compact it. Finally, use a slicing machine to press it into a circular electrode to obtain the sodium titanium phosphate surface modified lithium iron phosphate cathode material.

[0066] Performance testing

[0067] The lithium iron phosphate cathode materials of Examples 1-3 and Comparative Examples 1-3 were assembled using a CR2032 button cell casing, with lithium sheets as the negative electrode and a Celgard2400 battery separator. 1M LiPF6 / EC+DEC+EMC (1:1:1, v / v / v) electrolyte was added to obtain the sample battery.

[0068] The Wuhan Landian LAND-CT2001A battery testing system was used, with a test voltage of 2.5-3.75V. During testing, a charge-then-discharge method was employed. Cyclic performance testing was performed at a current density of 1C for 200 cycles to obtain the capacity retention rate after 200 cycles. Rate performance testing was conducted at current densities of 0.2C, 0.5C, 1C, and 5C to obtain the rate performance.

[0069]

[0070] Referring to the table above, based on the comparison between Examples 1-3 and Comparative Examples 1-3, it can be seen that the rate performance and capacity retention of gadolinium-dysprosium co-doped lithium iron phosphate coated with sodium titanium phosphate / carbon layer are good.

[0071] Based on the comparison between Example 3 and Comparative Example 1, it can be seen that the discharge specific capacity and capacity retention of the cathode material obtained by coating gadolinium-dysprosium co-doped lithium iron phosphate with sodium titanium phosphate / carbon layer are higher than those of the cathode material obtained by coating gadolinium-doped lithium iron phosphate with sodium titanium phosphate / carbon layer. This indicates that the cathode material obtained by coating gadolinium-dysprosium co-doped lithium iron phosphate with sodium titanium phosphate / carbon layer has excellent rate capability and cycle performance.

[0072] Based on the comparison between Example 3 and Comparative Example 2, it can be seen that the discharge specific capacity and capacity retention of the cathode material obtained by coating gadolinium dysprosium with sodium titanium phosphate / carbon layer are higher than those of the cathode material obtained by coating dysprosium with sodium titanium phosphate, indicating that the cathode material obtained by coating gadolinium dysprosium with sodium titanium phosphate / carbon layer has excellent rate capability and cycle performance.

[0073] Based on the comparison between Example 3 and Comparative Example 3, it can be seen that the discharge specific capacity and cycle retention rate of the cathode material obtained by coating gadolinium dysprosium co-doped lithium iron phosphate with sodium titanium phosphate / carbon layer are higher than those of the cathode material obtained by coating gadolinium dysprosium co-doped lithium iron phosphate with sodium titanium phosphate. This indicates that the cathode material obtained by coating gadolinium dysprosium co-doped lithium iron phosphate with sodium titanium phosphate / carbon layer has excellent rate capability and cycle performance.

[0074] 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.

[0075] 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 sodium titanium phosphate surface-modified lithium iron phosphate cathode material, characterized in that, Raw materials comprising the following components by weight: 32-64 parts of sodium titanium phosphate / carbon layer coated gadolinium dysprosium co-doped lithium iron phosphate, 4-8 parts of acetylene black and 4-8 parts of polyvinylidene fluoride; The sodium titanium phosphate / carbon layer coated gadolinium dysprosium co-doped lithium iron phosphate is prepared by the following steps: Step A1: Ascorbic acid, ethylene glycol solution, and deionized water are stirred and sonicated. Lithium hydroxide monohydrate is added and stirred, followed by phosphoric acid and stirring. Ferrous sulfate heptahydrate, gadolinium chloride, and dysprosium chloride are added and stirred. The mixture is then transferred to a stainless steel autoclave for reaction. After cooling, the mixture is washed and dried to obtain gadolinium-dysprosium co-doped lithium iron phosphate precursor powder. The ratio of ascorbic acid solution, ethylene glycol solution, deionized water, lithium hydroxide monohydrate, phosphoric acid, ferrous sulfate heptahydrate, gadolinium chloride, and dysprosium chloride in step A1 is 10-20 mL: 3.75-7.5 mL: 26.25-52.5 mL: 30-60 mmol: 10-20 mmol: 9-18 mmol: 0.5-1 mmol: 0.5-1 mmol. The molar concentration of the ascorbic acid solution is 0.03 mol / L. The volume fraction of the ethylene glycol solution is 12.5%. Step A2: Sodium acetate and phosphoric acid solution were added to a flask and stirred. Tetraethyl titanate dissolved in anhydrous ethanol was added to the flask and stirred. The mixture was then transferred to an autoclave for reaction. After filtration, washing, centrifugation, and drying, sodium titanate precursor powder was obtained. The ratio of sodium acetate, phosphoric acid, tetraethyl titanate, and anhydrous ethanol in step A2 was 10-20 mmol: 30-60 mL: 10-20 mmol: 200-400 mL. The mass fraction of the phosphoric acid solution was 85%. Step A3: Stir sodium titanium phosphate precursor powder, glucose, polyethylene glycol, and deionized water. Add gadolinium-dysprosium co-doped lithium iron phosphate precursor powder, sonicate, evaporate to dryness, transfer to a high-temperature furnace, purge with nitrogen for protection, heat, sinter, and cool to obtain sodium titanium phosphate / carbon layer coated gadolinium-dysprosium co-doped lithium iron phosphate. The ratio of sodium titanium phosphate precursor powder, glucose, polyethylene glycol, deionized water, and gadolinium-dysprosium co-doped lithium iron phosphate precursor powder in step A3 is 1-2 mmol: 0.15-0.3 mmol: 0.15-0.3 g: 100-200 mL: 150-300 mmol.

2. A method for preparing a lithium iron phosphate cathode material with sodium titanium phosphate surface modification, characterized in that, The preparation of the sodium titanium phosphate surface-modified lithium iron phosphate cathode material as described in claim 1 includes the following steps: Step 1: Weigh out 32-64 parts of sodium titanium phosphate / carbon-coated gadolinium-dysprosium co-doped lithium iron phosphate, 4-8 parts of acetylene black, and 4-8 parts of polyvinylidene fluoride according to the weight ratio, and set aside. Step 2: Grind the sodium titanium phosphate / carbon layer coated with gadolinium-dysprosium co-doped lithium iron phosphate, acetylene black and polyvinylidene fluoride, then add N-methylpyrrolidone to adjust the solid content and continue grinding. After grinding, coat it on aluminum foil current collector and dry it in a constant temperature vacuum drying oven. Then place it in a roller press to compact it. Finally, use a slicing machine to press it into a circular electrode to obtain the sodium titanium phosphate surface modified lithium iron phosphate cathode material.

3. The method for preparing a sodium titanium phosphate surface-modified lithium iron phosphate cathode material according to claim 2, characterized in that, The solid content is adjusted to 45%-55%.

4. The method of claim 2, wherein the lithium iron phosphate cathode material is surface modified with sodium titanium phosphate. The drying time in the constant temperature vacuum drying oven is 8-12h.

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