A lithium manganese iron phosphate positive electrode material, a preparation method and application thereof

Abstract

The present application relates to the field of lithium ion batteries, in particular to a kind of lithium manganese iron phosphate positive material and its preparation method and application, for solving the problems of low electrochemical performance, poor charge-discharge efficiency and short cycle life of existing lithium manganese iron phosphate positive material;The lithium manganese iron phosphate positive material is prepared from silver-doped lithium manganese iron phosphate positive material powder, conductive carbon black and polyvinylidene chloride;Wherein the silver-doped lithium manganese iron phosphate positive material powder is doped with divalent silver ions inside, and is coated with three-dimensional interconnected conductive carbon network inside and on the surface, which gives the lithium manganese iron phosphate positive material excellent electrochemical performance, high charge-discharge efficiency and long cycle life, etc., and can meet the demand of high-performance lithium ion batteries.

Description

TECHNICAL FIELD

[0001] The application relates to the field of lithium ion batteries, in particular to a lithium iron manganese phosphate positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries are one of the most popular rechargeable energy devices due to high safety, high energy cyclic use, green environmental protection and other characteristics, and are widely used in the field of power batteries. As an important factor of the performance of lithium ion batteries, the lithium iron manganese phosphate positive electrode material is difficult to meet the requirements of the new generation of high-performance lithium ion batteries due to its low electrochemical performance. In order to improve the performance of lithium ion batteries, the electrochemical performance, charge-discharge performance and cycle life need to be improved. SUMMARY

[0003] In order to overcome the above technical problems, the purpose of the present application is to provide a lithium iron manganese phosphate positive electrode material and a preparation method and application thereof, which partially solve the problems of low electrochemical performance, poor charge-discharge efficiency and short cycle life of the existing lithium iron manganese phosphate positive electrode material.

[0004] The purpose of the present application can be achieved by the following technical solutions:

[0005] In a first aspect, the application provides a preparation method of a lithium iron manganese phosphate positive electrode material, which comprises the following components by weight: 50-100 parts of silver-doped lithium iron manganese phosphate positive electrode material powder, 6.25-12.5 parts of conductive carbon black, and 7-13 parts of polyvinylidene chloride HR460. The components are ground, then N-methylpyrrolidone is added to adjust the solid content to 45%-55%, and the mixture is further ground. After grinding, the mixture is coated on an aluminum foil current collector and dried in a constant-temperature vacuum drying oven for 8-12 hours. The mixture is then compacted in a roller press and punched into a circular electrode by a slicing machine to obtain the lithium iron manganese phosphate positive electrode material.

[0006] In one embodiment, the silver-doped lithium iron manganese phosphate positive electrode material powder is prepared by the following steps:

[0007] Step A1: manganese sulfate, ascorbic acid and deionized water are added to a three-necked flask equipped with a stirrer, and stirred at a stirring rate of 300-400 r / min for 5 min. Then phosphoric acid is added, and stirred at a stirring rate of 500-1000 r / min for 1-2 h. Then iron sulfate and lithium hydroxide are added and stirred. After the reaction, the suspension is placed in a constant-temperature water bath, and stirred at a temperature of 60-80 DEG C for 3-5 h. The obtained suspension is filtered, and the filter cake is centrifuged three times and then placed in a drying oven and vacuum dried at a temperature of 70-90 DEG C for 4-6 h to obtain lithium iron manganese phosphate nanoparticles.

[0008] Step A2: manganese iron phosphate nanoparticles, silver sulfate, distilled water and ethylene glycol were added into a three-necked flask equipped with a stirrer, and stirred at a stirring rate of 500-1000 r / min for 1-2 h, and then the mixture was transferred into a high-pressure reaction kettle, and reacted at a temperature of 170-200 °C for 9-11 h, and then the product was collected by a centrifuge, washed with distilled water for 5-6 times, and dried to obtain silver-doped manganese iron phosphate nanoparticles;

[0009] Step A3: tannic acid solution, glucose and deionized water were added into a three-necked flask equipped with a stirrer, and stirred to obtain a tannic acid-glucose solution; polyurethane and tetrahydrofuran were added into a single-necked flask, and the polyurethane was dissolved to obtain a polyurethane-tetrahydrofuran solution; the polyurethane-tetrahydrofuran solution and the tannic acid-glucose solution were added into a three-necked flask equipped with a stirrer and a thermometer, and reacted at a stirring rate of 500-600 r / min and a temperature of 150-200 °C for 5 h to obtain a carbon source solution;

[0010] Step A4: silver-doped manganese iron phosphate nanoparticles and ethanol were added into a single-necked flask, ultrasonically dispersed for 15-30 min, and then added into the carbon source solution, and stirred to react for 5-6 h, and then the product was filtered, washed with ethanol for 5-6 times, and then transferred into a high-temperature furnace, and carbonized at a temperature of 500-1000 °C under nitrogen protection, and then kept for 2-4 h, and then cooled and ground to obtain silver-doped manganese iron phosphate nanoparticle positive electrode material.

[0011] In one embodiment, the amount ratio of manganese sulfate, ascorbic acid, phosphoric acid, iron sulfate and lithium hydroxide in step A1 is 4-8 mmol: 1-2 mmol: 5-10 mmol: 1-2 mmol: 5-10 mmol.

[0012] In one embodiment, the amount ratio of manganese iron phosphate nanoparticles, silver sulfate and ethylene glycol in step A2 is 2.88-5 mmol: 0.02-0.05 mmol: 140-150 mL.

[0013] In one embodiment, the amount ratio of tannic acid solution, glucose and deionized water in step A3 is 5-10 mL: 0.2-0.4 g: 50-100 mL; and the amount ratio of polyurethane and tetrahydrofuran is 30-40 g: 100-150 mL.

[0014] In one embodiment, the mass fraction of the tannic acid solution in step A3 is 25%.

[0015] In one embodiment, the amount ratio of silver-doped manganese iron phosphate nanoparticles and ethanol in step A4 is 0.15-0.2 g: 50-60 mL.

[0016] In a second aspect, the application provides a preparation method of a lithium iron manganese phosphate positive electrode material, comprising the following steps:

[0017] Step one: 50-100 parts of silver-doped lithium iron manganese phosphate positive electrode material powder, 6.25-12.5 parts of conductive carbon black, and 7-13 parts of polyvinylidene chloride are weighed according to weight parts and prepared for use;

[0018] Step two: the silver-doped lithium iron manganese phosphate positive electrode material powder, the conductive carbon black, and the polyvinylidene chloride HR460 are ground, then N-methyl pyrrolidone is added to adjust the solid content to 45%-55% and continue to grind, after grinding, coated on an aluminum foil current collector and placed in a constant temperature vacuum drying oven for drying for 8-12 hours, then placed in a roller press for compaction, and finally punched into a circular electrode by a slicing machine to obtain the lithium iron manganese phosphate positive electrode material.

[0019] In a third aspect, the application provides the application of the lithium iron manganese phosphate positive electrode material prepared by the preparation method of the lithium iron manganese phosphate positive electrode material in a lithium ion battery.

[0020] The application has the following beneficial effects:

[0021] The conductive effect of the lithium iron manganese phosphate positive electrode material is improved by doping divalent silver ions, and the carbon source coated on the surface is introduced into polyurethane to form a conductive carbon network, so that the conductive effect of the lithium iron manganese phosphate positive electrode material is improved.

[0022] In the process of preparing the lithium iron manganese phosphate positive electrode material, lithium iron manganese phosphate nanoparticles are first prepared, then silver sulfate is added to obtain silver-doped lithium iron manganese phosphate nanoparticles, the divalent silver ions can control the cell parameters, the radius of the divalent silver ions is 0.096 mm, which is greater than the radius of the lithium ion 0.076 mm, so the introduction of the divalent silver ions widens the diffusion channel of the lithium ion, the polyurethane is introduced into the carbon source coated on the surface, the stable micelle structure is formed by the rich polar groups of the polyurethane, the three-dimensional interconnected conductive carbon network is formed on the surface and the entire inside of the nanoparticles, and the conductive performance of the nanoparticles and the electrolyte interface and between the nanoparticles is improved. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the embodiments of the application. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0024] Embodiment 1:

[0025] The embodiment is a preparation method of a lithium manganese iron phosphate positive electrode material, including the following steps.

[0026] Step A1: 4 mmol of manganese sulfate, 1 mmol of ascorbic acid and 100 mL of deionized water are added to a three-necked flask equipped with a stirrer, stirred at a stirring rate of 300 r / min for 5 min, then 5 mmol of phosphoric acid is added, stirred at a stirring rate of 500 r / min for 1 h, then 1 mmol of iron sulfate and 5 mmol of lithium hydroxide are added and stirred, the suspension is placed in a constant-temperature water bath after reaction, stirred at a temperature of 60℃ for 3 h, the obtained suspension is subjected to suction filtration, the filter cake is centrifuged for three times and then placed in a drying oven for vacuum drying at a temperature of 70℃ for 4 h, and lithium manganese iron phosphate nanoparticles are obtained;

[0027] Step A2: 2.88 mmol of lithium manganese iron phosphate nanoparticles, 0.02 mmol of silver sulfate and 140 mL of ethylene glycol are added to a three-necked flask equipped with a stirrer, stirred at a stirring rate of 500 r / min for 1 h, then transferred to a high-pressure reaction kettle, reacted at a temperature of 170℃ for 9 h, and the product is collected by a centrifuge after reaction, washed with distilled water for 5-6 times and dried to obtain silver-doped lithium manganese iron phosphate nanoparticles;

[0028] Step A3: 5 mL of tannic acid solution, 0.2 g of glucose and 50 mL of deionized water are added to a three-necked flask equipped with a stirrer, uniformly stirred to obtain a tannic acid-glucose solution; 30 g of polyurethane and 100 mL of tetrahydrofuran are added to a single-necked flask, and the polyurethane is dissolved to obtain a polyurethane-tetrahydrofuran solution; the polyurethane-tetrahydrofuran solution and the tannic acid-glucose solution are added to a three-necked flask equipped with a stirrer and a thermometer, reacted at a stirring rate of 500 r / min and a temperature of 150℃ for 5 h, and a carbon source solution is obtained;

[0029] Step A4: 0.15 g of silver-doped lithium manganese iron phosphate nanoparticles and 50 mL of ethanol are added to a single-necked flask, ultrasonically dispersed for 15 min, then added to the carbon source solution, stirred and reacted for 5 h, the product is filtered, washed with ethanol for 5-6 times, then transferred to a high-temperature furnace, protected by nitrogen at a temperature of 500℃, subjected to carbonization treatment, and cooled and ground to obtain silver-doped lithium manganese iron phosphate positive electrode material powder.

[0030] Step A5: The silver-doped lithium manganese iron phosphate positive electrode material powder, the conductive carbon black and the polyvinylidene chloride HR460 are weighed according to the weight parts, and reserved.

[0031] Step A6: The silver-doped lithium manganese iron phosphate positive electrode material powder, conductive carbon black, and polyvinylidene chloride HR460 are ground, then N-methyl pyrrolidone is added to adjust the solid content to 45% and continue to grind, after grinding, coated on an aluminum foil current collector, placed in a constant temperature vacuum drying oven for drying for 8h, placed in a rolling machine for compaction, and finally punched into a circular electrode with a slicer, to obtain a lithium manganese iron phosphate positive electrode material.

[0032] Example 2:

[0033] The present embodiment is a preparation method of a lithium manganese iron phosphate positive electrode material, comprising the following steps:

[0034] Step A1: 6mmol of manganese sulfate, 1.5mmol of ascorbic acid, and 120mL of deionized water are added to a three-necked flask equipped with a stirrer, stirred at a stirring rate of 350r / min for 5min, then 7mmol of phosphoric acid is added, stirred at a stirring rate of 700r / min for 1.5h, then 1.5mmol of ferric sulfate and 7mmol of lithium hydroxide are added and stirred, after the reaction, the suspension is placed in a constant temperature water bath, stirred at a temperature of 70℃ for 4h, the obtained suspension is filtered, the filter cake is centrifuged for three times, and then placed in a drying oven for vacuum drying at a temperature of 80℃ for 5h, to obtain lithium manganese iron phosphate nanoparticles;

[0035] Step A2: 4mmol of lithium manganese iron phosphate nanoparticles, 0.035mmol of silver sulfate, and 145mL of ethylene glycol are added to a three-necked flask equipped with a stirrer, stirred at a stirring rate of 750r / min for 1.5h, then transferred to a high-pressure reaction kettle, reacted at a temperature of 180℃ for 10h, after the reaction, the product is collected with a centrifuge, washed with distilled water for 5-6 times, and dried to obtain silver-doped lithium manganese iron phosphate nanoparticles;

[0036] Step A3: 7mL of tannic acid solution, 0.3g of glucose, and 70mL of deionized water are added to a three-necked flask equipped with a stirrer, stirred uniformly to obtain a tannic acid-glucose solution; 35g of polyurethane and 130mL of tetrahydrofuran are added to a single-necked flask, and the polyurethane is dissolved to obtain a polyurethane-tetrahydrofuran solution; the polyurethane-tetrahydrofuran solution and the tannic acid-glucose solution are added to a three-necked flask equipped with a stirrer and a thermometer, reacted at a stirring rate of 550r / min and a temperature of 170℃ for 5h to obtain a carbon source solution;

[0037] Step A4: 0.17 g of silver-doped lithium manganese iron phosphate nanoparticles and 55 mL of ethanol were added to a single-neck flask and ultrasonically dispersed for 20 min, then added to the carbon source solution, and stirred for 5.5 h. The product was filtered and washed with ethanol for 5-6 times, then transferred to a high-temperature furnace, and carbonized at 750℃ under nitrogen protection for 3 h. After cooling, the silver-doped lithium manganese iron phosphate anode material powder was obtained by grinding.

[0038] Step A5: The silver-doped lithium manganese iron phosphate anode material powder, conductive carbon black, and polyvinylidene chloride HR460 were weighed according to the proportions of 70 parts, 9.5 parts, and 10 parts, respectively, and reserved.

[0039] Step A6: The silver-doped lithium manganese iron phosphate anode material powder, conductive carbon black, and polyvinylidene chloride HR460 were ground, then N-methyl pyrrolidone was added to adjust the solid content to 50%, and the grinding was continued. After grinding, it was coated on an aluminum foil current collector and placed in a constant-temperature vacuum drying oven for 10 h. It was then pressed in a roller press and finally punched into a circular electrode using a slicing machine to obtain the lithium manganese iron phosphate anode material.

[0040] Example 3:

[0041] The present embodiment is a method for preparing a lithium manganese iron phosphate anode material, comprising the following steps:

[0042] Step A1: 8 mmol of manganese sulfate, 2 mmol of ascorbic acid, and 150 mL of deionized water were added to a three-neck flask equipped with a stirrer, and stirred at a stirring rate of 400 r / min for 5 min. Then 10 mmol of phosphoric acid was added, and stirred at a stirring rate of 1000 r / min for 2 h. Then 2 mmol of iron sulfate and 10 mmol of lithium hydroxide were added and stirred. After the reaction, the suspension was placed in a constant-temperature water bath at a temperature of 80℃ and stirred for 5 h. The obtained suspension was filtered, and the filter cake was centrifuged three times and then placed in an oven at a temperature of 90℃ for vacuum drying for 6 h to obtain lithium manganese iron phosphate nanoparticles.

[0043] Step A2: 5 mmol of lithium manganese iron phosphate nanoparticles, 0.05 mmol of silver sulfate, and 150 mL of ethylene glycol were added to a three-neck flask equipped with a stirrer, and stirred at a stirring rate of 1000 r / min for 2 h. Then it was transferred to a high-pressure reaction kettle and reacted at a temperature of 200℃ for 11 h. After the reaction, the product was collected using a centrifuge, washed with distilled water for 5-6 times, and dried to obtain silver-doped lithium manganese iron phosphate nanoparticles.

[0044] Step A3: 10 mL of tannic acid solution, 0.4 g of glucose and 100 mL of deionized water were added to a three-necked flask equipped with a stirrer, stirred uniformly to obtain a tannic acid-glucose solution; 40 g of polyurethane and 150 mL of tetrahydrofuran were added to a single-necked flask, and the polyurethane was dissolved to obtain a polyurethane-tetrahydrofuran solution; the polyurethane-tetrahydrofuran solution and the tannic acid-glucose solution were added to a three-necked flask equipped with a stirrer and a thermometer, and reacted at a stirring rate of 600 r / min and a temperature of 200℃ for 5 h to obtain a carbon source solution;

[0045] Step A4: 0.2 g of silver-doped manganese iron phosphate lithium nanoparticles and 60 mL of ethanol were added to a single-necked flask and ultrasonically dispersed for 30 min, then added to the carbon source solution, and stirred for 6 h. The product was filtered, washed with ethanol for 5-6 times, then transferred to a high-temperature furnace, carbonized at a temperature of 1000℃ under nitrogen protection, and kept for 4 h. After cooling, the product was ground to obtain silver-doped manganese iron phosphate lithium anode material powder.

[0046] Step A5: The silver-doped manganese iron phosphate lithium anode material powder, conductive carbon black and polyvinylidene chloride HR460 were weighed according to the weight parts, and used as prepared.

[0047] Step A6: The silver-doped manganese iron phosphate lithium anode material powder, conductive carbon black and polyvinylidene chloride HR460 were ground, then N-methyl pyrrolidone was added to adjust the solid content to 55%, and the grinding was continued. After grinding, it was coated on an aluminum foil current collector and dried in a constant-temperature vacuum drying box for 12 h. It was then pressed in a roller press and finally punched into a circular electrode using a slicing machine to obtain a lithium manganese iron phosphate anode material.

[0048] Comparative Example 1

[0049] This comparative example is a preparation method of a lithium manganese iron phosphate anode material, comprising the following steps:

[0050] Step A1: 8 mmol of manganese sulfate, 2 mmol of ascorbic acid and 150 mL of deionized water were added to a three-necked flask equipped with a stirrer, stirred at a stirring rate of 400 r / min for 5 min, then 10 mmol of phosphoric acid was added, stirred at a stirring rate of 1000 r / min for 2 h, then 2 mmol of ferric sulfate and 10 mmol of lithium hydroxide were added and stirred, and the suspension was placed in a constant-temperature water bath at a temperature of 80℃ and stirred for 5 h. The obtained suspension was filtered, and the filter cake was centrifuged three times and then placed in an oven at a temperature of 90℃ and vacuum dried for 6 h to obtain manganese iron phosphate lithium nanoparticles;

[0051] Step A2: 5 mmol of lithium manganese iron phosphate nanoparticles, 0.05 mmol of silver sulfate and 150 mL of ethylene glycol were added to a three-necked flask equipped with a stirrer, stirred at a stirring rate of 1000 r / min for 2 h, then transferred to a high-pressure reaction kettle, reacted at a temperature of 200℃ for 11 h, and after the reaction was completed, the product was collected by a centrifuge, washed with distilled water for 5-6 times and dried to obtain silver-doped lithium manganese iron phosphate nanoparticles;

[0052] Step A3: 10 mL of tannic acid solution and 100 mL of deionized water were added to a three-necked flask equipped with a stirrer, stirred uniformly to obtain a tannic acid solution; 40 g of polyurethane and 150 mL of tetrahydrofuran were added to a single-necked flask, and after the polyurethane was dissolved, a polyurethane-tetrahydrofuran solution was obtained; the polyurethane-tetrahydrofuran solution and the tannic acid solution were added to a three-necked flask equipped with a stirrer and a thermometer, reacted at a stirring rate of 600 r / min and a temperature of 200℃ for 5 h to obtain a carbon source solution;

[0053] Step A4: 0.2 g of silver-doped lithium manganese iron phosphate nanoparticles and 60 mL of ethanol were added to a single-necked flask, ultrasonically dispersed for 30 min, then added to the carbon source solution, stirred and reacted for 6 h, the product was filtered, washed with ethanol for 5-6 times, then transferred to a high-temperature furnace, carbonized at a temperature of 1000℃ under nitrogen protection, and after heat preservation for 4 h, cooled and ground to obtain silver-doped lithium manganese iron phosphate positive electrode material powder.

[0054] Step A5: The silver-doped lithium manganese iron phosphate positive electrode material powder, conductive carbon black and polyvinylidene chloride HR460 were weighed according to the weight parts, and the total weight was 125.5 parts.

[0055] Step A6: The silver-doped lithium manganese iron phosphate positive electrode material powder, conductive carbon black and polyvinylidene chloride HR460 were ground, then N-methyl pyrrolidone was added to adjust the solid content to 55%, and the grinding was continued. After grinding, it was coated on an aluminum foil current collector and dried in a constant-temperature vacuum drying box for 12 h, pressed in a roller press, and finally punched into a circular electrode by a slicing machine to obtain a lithium manganese iron phosphate positive electrode material.

[0056] The difference from Example 3 is that no glucose is added to the carbon source solution.

[0057] Comparative Example 2:

[0058] The present comparative example is a preparation method of a lithium manganese iron phosphate positive electrode material, comprising the following steps:

[0059] Step A1: 8 mmol of manganese sulfate, 2 mmol of ascorbic acid and 150 mL of deionized water were added to a three-neck flask equipped with a stirrer, stirred at a stirring rate of 400 r / min for 5 min, then 10 mmol of phosphoric acid was added, stirred at a stirring rate of 1000 r / min for 2 h, then 2 mmol of ferric sulfate and 10 mmol of lithium hydroxide were added and stirred, the obtained suspension was placed in a constant temperature water bath, stirred at a temperature of 80℃ for 5 h, the obtained suspension was filtered, the filter cake was centrifuged for three times and then placed in a drying oven, vacuum dried at a temperature of 90℃ for 6 h to obtain manganese iron lithium phosphate nanoparticles;

[0060] Step A2: 5 mmol of manganese iron lithium phosphate nanoparticles, 0.05 mmol of silver sulfate and 150 mL of ethylene glycol were added to a three-neck flask equipped with a stirrer, stirred at a stirring rate of 1000 r / min for 2 h, then transferred to a high-pressure reaction kettle, reacted at a temperature of 200℃ for 11 h, after the reaction, the product was collected by a centrifuge, washed with distilled water for 5-6 times and dried to obtain silver-doped manganese iron lithium phosphate nanoparticles;

[0061] Step A3: 0.4 g of glucose and 100 mL of deionized water were added to a three-neck flask equipped with a stirrer, stirred uniformly to obtain a glucose solution; 40 g of polyurethane and 150 mL of tetrahydrofuran were added to a single-neck flask, and the polyurethane was dissolved to obtain a polyurethane-tetrahydrofuran solution; the polyurethane-tetrahydrofuran solution and the glucose solution were added to a three-neck flask equipped with a stirrer and a thermometer, reacted at a stirring rate of 600 r / min and a temperature of 200℃ for 5 h to obtain a carbon source solution;

[0062] Step A4: 0.2 g of silver-doped manganese iron lithium phosphate nanoparticles and 60 mL of ethanol were added to a single-neck flask, ultrasonically dispersed for 30 min, then added to the carbon source solution, stirred for 6 h, the product was filtered, washed with ethanol for 5-6 times, then transferred to a high-temperature furnace, protected by nitrogen gas at a temperature of 1000℃, carbonized and treated for 4 h, cooled and ground to obtain silver-doped manganese iron lithium phosphate positive electrode material powder.

[0063] Step A5: The silver-doped manganese iron lithium phosphate positive electrode material powder, the conductive carbon black and the polyvinylidene chloride HR460 were weighed according to the weight parts, and were ready for use.

[0064] Step A6: The silver-doped manganese iron phosphate positive electrode material powder, conductive carbon black, and polyvinylidene chloride HR460 were ground, then N-methyl pyrrolidone was added to adjust the solid content to 55%, and the grinding was continued. After grinding, it was coated on an aluminum foil current collector, dried in a constant temperature vacuum drying oven for 12 h, placed in a roll press for compaction, and finally punched into a circular electrode with a slicer. A manganese iron phosphate positive electrode material was obtained.

[0065] The difference from Example 3 is that tannic acid is not added to the carbon source solution.

[0066] Comparative Example 3:

[0067] This comparative example is a method for preparing a manganese iron phosphate positive electrode material, comprising the following steps:

[0068] Step A1: 8 mmol of manganese sulfate, 2 mmol of ascorbic acid, and 150 mL of deionized water were added to a three-necked flask equipped with a stirrer, stirred at a stirring rate of 400 r / min for 5 min, then 10 mmol of phosphoric acid was added, stirred at a stirring rate of 1000 r / min for 2 h, then 2 mmol of ferric sulfate and 10 mmol of lithium hydroxide were added and stirred, after the reaction, the suspension was placed in a constant temperature water bath, stirred at a temperature of 80℃ for 5 h, the suspension obtained by reaction was filtered, the filter cake was centrifuged three times and then placed in an oven dryer at a temperature of 90℃ for vacuum drying for 6 h, and manganese iron phosphate nanoparticles were obtained;

[0069] Step A2: 10 mL of tannic acid solution, 0.4 g of glucose, and 100 mL of deionized water were added to a three-necked flask equipped with a stirrer, stirred uniformly to obtain a tannic acid-glucose solution; 40 g of polyurethane and 150 mL of tetrahydrofuran were added to a single-necked flask, and after the polyurethane was dissolved, a polyurethane-tetrahydrofuran solution was obtained; the polyurethane-tetrahydrofuran solution and the tannic acid-glucose solution were added to a three-necked flask equipped with a stirrer and a thermometer, and reacted at a stirring rate of 600 r / min and a temperature of 200℃ for 5 h to obtain a carbon source solution;

[0070] Step A3: 0.2 g of manganese iron phosphate nanoparticles and 60 mL of ethanol were added to a single-necked flask, ultrasonically dispersed for 30 min, then added to the carbon source solution, and stirred for 6 h. The product was filtered, washed with ethanol for 5-6 times, then transferred to a high-temperature furnace, protected by nitrogen at a temperature of 1000℃, and subjected to carbonization treatment for 4 h, cooled, and ground to obtain manganese iron phosphate positive electrode material powder.

[0071] Step A4: The manganese iron phosphate positive electrode material powder 100 parts, conductive carbon black 12.5 parts, and polyvinylidene chloride HR460 13 parts were weighed according to the weight parts, and reserved.

[0072] Step A5: Lithium manganese iron phosphate positive electrode material powder, conductive carbon black, polyvinylidene chloride HR460 were ground, then N-methyl pyrrolidone was added to adjust the solid content to 55% and continue to grind, after grinding, coated on aluminum foil current collector, put into constant temperature vacuum drying oven for 12h, placed in a roller press, finally punched into a circular electrode with a slicer, to obtain a lithium manganese iron phosphate positive electrode material.

[0073] The difference from Example 3 is that silver is not doped in the lithium manganese iron phosphate positive electrode material powder.

[0074] The circular electrodes of Examples 1-3 and Comparative Examples 1-3 were assembled using a R2032 button cell shell, using lithium sheet as the negative electrode, using a PE membrane, and adding electrolyte 1MLiPF6 / EC+DEC+EMC (1:1:1, v / v / v) dropwise.

[0075] The sample battery was tested for 1C cycle performance at 25°C using a blue light tester: the prepared sample battery was placed in a high temperature oven at 25°C for charge and discharge test, the voltage range was 2.0V-4.35V, 0.1C charge and discharge activation for one cycle, then 0.5C constant current and constant voltage charging, the cutoff current was 0.05C, 1C current constant current discharge, 50 cycles, to obtain the first discharge specific capacity, the 100th cycle capacity retention rate and other parameters.

[0076] The test results are shown in the following table:

[0077]

[0078] Referring to the above table, according to the comparison between Examples 1-3 and Comparative Examples 1-3, it can be seen that the electrochemical performance of the silver-doped lithium manganese iron phosphate positive electrode material is good, the capacity retention rate is high, and the cycle performance is excellent.

[0079] According to the comparison between Example 3 and Comparative Example 1, it can be seen that using tannic acid-glucose as a carbon source solution has better conductivity than using tannic acid alone as a carbon source solution, because the carbon content of tannic acid alone is lower, resulting in incomplete coating and affecting the conductivity.

[0080] According to the comparison between Example 3 and Comparative Example 2, it can be seen that using tannic acid-glucose as a carbon source solution has better conductivity than using glucose alone as a carbon source solution, because the carbon content of glucose alone is lower, resulting in incomplete coating and reducing the conductivity.

[0081] According to the comparison between Example 3 and Comparative Example 3, it can be seen that the introduction of silver ions into the lithium manganese iron phosphate positive electrode material has better conductivity than the ordinary lithium manganese iron phosphate positive electrode material, the introduction of silver ions widens the diffusion channel of lithium ions and improves the conductivity.

[0082] In the description of the present specification, the description of the terms "one embodiment", "an example", "a specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Also, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in an appropriate manner.

[0083] The above is only an example and a description of the present application, and those skilled in the art can make various modifications or supplements to the described specific embodiments or replace them with similar ways, as long as they do not deviate from the invention or exceed the scope defined in the present application.

Claims

1. A lithium iron manganese phosphate cathode material, characterized in that, The following components are included by mass parts: 50-100 parts of silver-doped lithium manganese iron phosphate positive electrode material powder, 6.25-12.5 parts of conductive carbon black, and 7-13 parts of polyvinylidene chloride; The silver-doped lithium manganese iron phosphate positive electrode material powder is prepared by the following steps: Step A1: manganese sulfate, ascorbic acid, and deionized water are stirred, phosphoric acid is added and stirred, then iron sulfate and lithium hydroxide are added and stirred, after reaction, the suspension is placed in a constant temperature water bath and stirred, filtered, the filter cake is centrifuged and vacuum dried to obtain lithium manganese iron phosphate nanoparticles; Step A2: lithium manganese iron phosphate nanoparticles, silver sulfate, and ethylene glycol are stirred, then transferred to a high-pressure reaction kettle for reaction, after reaction, the product is collected by centrifugation, washed with distilled water and dried to obtain silver-doped lithium manganese iron phosphate nanoparticles; Step A3: tannic acid solution, glucose, and deionized water are stirred to obtain a tannic acid-glucose solution; polyurethane and tetrahydrofuran are added to a flask, the polyurethane is dissolved to obtain a polyurethane-tetrahydrofuran solution; the polyurethane-tetrahydrofuran solution and the tannic acid-glucose solution are stirred to react to obtain a carbon source solution; Step A4: the silver-doped lithium manganese iron phosphate nanoparticles are ultrasonically dispersed in ethanol and then added to the carbon source solution, stirred to react, filtered, washed with ethanol, then transferred to a high-temperature furnace, protected by nitrogen, carbonized, heat preserved, cooled, and ground to obtain silver-doped lithium manganese iron phosphate positive electrode material powder.

2. The lithium iron manganese phosphate cathode material of claim 1, characterized in that, The amount ratio of manganese sulfate, ascorbic acid, deionized water, phosphoric acid, iron sulfate, and lithium hydroxide in step A1 is 4-8 mmol:1-2 mmol:100-150 mL:5-10 mmol:1-2 mmol:5-10 mmol.

3. The lithium iron manganese phosphate cathode material of claim 1, wherein, The amount ratio of lithium manganese iron phosphate nanoparticles, silver sulfate, and ethylene glycol in step A2 is 2.88-5 mmol:0.02-0.05 mmol:140-150 mL.

4. The lithium iron manganese phosphate cathode material of claim 1, wherein, The amount ratio of tannic acid solution, glucose, and deionized water in step A3 is 5-10 mL:0.2-0.4 g:50-100 mL.

5. The lithium iron manganese phosphate cathode material of claim 1, wherein, The amount ratio of polyurethane and tetrahydrofuran in step A3 is 30-40 g:100-150 mL.

6. The lithium iron manganese phosphate cathode material of claim 1, wherein, The mass fraction of the tannic acid solution in step A3 is 25%.

7. The lithium iron manganese phosphate cathode material of claim 1, wherein, The amount ratio of silver-doped lithium manganese iron phosphate nanoparticles and ethanol in step A4 is 0.15-0.2 g:50-60 mL.

8. A method for preparing a lithium iron manganese phosphate cathode material, characterized in that, A method for preparing lithium manganese iron phosphate positive electrode material as claimed in any one of claims 1-7, comprising the following steps: Step one: 50-100 parts of silver-doped lithium manganese iron phosphate positive electrode material powder, 6.25-12.5 parts of conductive carbon black, and 7-13 parts of polyvinylidene chloride as claimed in any one of claims 1-7 are weighed according to weight parts and prepared for use; Step two: the silver-doped lithium manganese iron phosphate positive material powder in any one of claims 1-7, conductive carbon black, polyvinylidene chloride are ground, then N-methyl pyrrolidone is added to adjust the solid content, and then grinding, coating on the aluminum foil current collector, drying in a constant temperature vacuum drying oven for 8-12h, compaction in a roller press, and finally punching into a circular electrode with a slicer, to obtain a lithium manganese iron phosphate positive material.

9. The method for preparing a lithium manganese iron phosphate cathode material according to claim 8, characterized in that, The solid content is 45%-55%.

10. The application of the lithium manganese iron phosphate positive material prepared by the preparation method of the lithium manganese iron phosphate positive material according to claim 8 in a lithium ion battery.

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