Graphene reinforced lithium iron phosphate material, and preparation method and application thereof

Abstract

The application relates to the field of positive electrode materials, in particular to a graphene-reinforced lithium iron phosphate material and a preparation method and application thereof; the positive electrode material is prepared by doping europium ions into lithium iron phosphate; the europium ion radius is large, lithium ions are provided with larger migration channels, and the binding energy of the lithium ions can be reduced; hydroxyethyl methyl cellulose grafted graphene is coated on the surface of the europium-doped lithium iron phosphate; the hydroxyethyl methyl cellulose reduces the graphene agglomeration phenomenon; after carbonization, the hydroxyethyl methyl cellulose and the graphene jointly form a 3D conductive carbon network, and the electronic conductivity is enhanced; the positive electrode material has high cycle life, charging and discharging efficiency, conductivity and cycle stability, provides a good energy storage basis for a battery, and is suitable for power batteries and energy storage fields.

Description

TECHNICAL FIELD

[0001] The application relates to the field of positive electrode materials, in particular to a graphene-reinforced lithium iron phosphate material and a preparation method and application thereof. BACKGROUND

[0002] As a two-dimensional material, graphene has attracted wide attention in various fields in recent years due to its unique physical and chemical properties. In the field of energy storage, graphene materials are widely used as electrode material enhancers in lithium batteries to improve the energy density, rate performance and cycle stability of the batteries. However, the existing graphene-reinforced lithium iron phosphate material has the problem of poor compatibility between graphene and lithium iron phosphate, which leads to an insufficient direct charge transfer and ion diffusion path between the two, thereby affecting the overall performance of the battery. Therefore, a more efficient and reasonable preparation method needs to be researched to enable the graphene to better combine with the lithium iron phosphate matrix and play its due reinforcing effect. SUMMARY

[0003] In order to overcome the above technical problems, the purpose of the application is to provide a graphene-reinforced lithium iron phosphate material and a preparation method and application thereof, which solve the problems of low coulomb efficiency and poor electrochemical performance of the existing graphene-reinforced lithium iron phosphate material due to poor compatibility between graphene and lithium iron phosphate.

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

[0005] In a first aspect, the application provides a graphene-reinforced lithium iron phosphate material, which comprises the following components by weight:

[0006] Eu-doped lithium iron phosphate@composite graphene 45-90 parts, acetylene carbon black 4-8 parts, butadiene rubber 1.5-3 parts and polyethylene glycol 0.5-1 part;

[0007] The Eu-doped lithium iron phosphate@composite graphene is prepared by the following steps:

[0008] Step A1: Ascorbic acid solution and ethylene glycol solution are added to a three-necked flask equipped with a stirrer, stirred at 50-100 r / min for 10-20 min, ultrasonically dispersed for 20-30 min, lithium hydroxide monohydrate is added and magnetically stirred for 4-6 min, phosphoric acid is added and magnetically stirred for 8-10 min, ferrous sulfate heptahydrate and europium chloride are added and stirred for 10-20 min, the mixed solution is transferred to a stainless steel autoclave, nitrogen is introduced for protection, and the reaction is carried out at 170-180 DEG C and 200-300 r / min for 8-10 h, and then cooled to 24-26 DEG C, washed with deionized water for 3-5 times, and vacuum freeze-dried for 22-24 h to obtain Eu-doped lithium iron phosphate precursor powder;

[0009] Step A2: graphene, strong acid solution into a three-necked flask equipped with a thermometer, placed in a water bath, magnetic stirring at 70-80℃ for 30-60min, ultrasonic dispersion for 2-3h, after filtration with deionized water washing until the pH of the washing liquid is 6-8, placed in a drying oven at 80-90℃ for 10-12h, to obtain graphene oxide;

[0010] Step A3: hydroxyethyl methyl cellulose, N,N-dimethylformamide into a three-necked flask equipped with a stirrer, thermometer, placed in a water bath, stirring at 40-50℃, 50-100r / min for 30-60min, to obtain a first solution;

[0011] Step A4: graphene oxide, N,N-dimethylformamide into a three-necked flask equipped with a stirrer, ultrasonic dispersion for 20-30min, stirring at 300-400r / min, dropwise addition of the first solution, stirring for 20-30min, adding 4-dimethylaminopyridine stirring for 8-10min, control the same amount each time, adding dicyclohexyl carbodiimide in three times stirring for 8-10min, reaction for 22-24h, after centrifugation with absolute ethanol washing 3-5 times, with deionized water washing 2 times, freeze drying for 22-24h, to obtain hydroxyethyl methyl cellulose grafted graphene;

[0012] Step A5: europium doped lithium iron phosphate precursor powder, deionized water into a ball mill tank, ball milling at 400-500r / min for 20-30min, adding hydroxyethyl methyl cellulose grafted graphene, mixing at 900-1000r / min for 4-5h, transfer to a spray dryer for drying, placed in a sintering furnace, nitrogen protection, calcining at 650-750℃ for 4-5h, cooling to 24-26℃, to obtain europium doped lithium iron phosphate@composite graphene.

[0013] As a further scheme of the application: the amount of ascorbic acid solution, ethylene glycol solution, lithium hydroxide monohydrate, phosphoric acid, ferrous sulfate heptahydrate and europium chloride in step A1 is 10-20mL:30-60mL:30-60mmol:10-20mmol:9-18mmol:1-2mmol.

[0014] As a further scheme of the application: the molar concentration of ascorbic acid solution in step A1 is 0.3mol / L.

[0015] As a further scheme of the application: the mass fraction of ethylene glycol solution in step A1 is 12.5%.

[0016] As a further scheme of the application: the amount of graphene, strong acid solution in step A2 is 5-10g:250-500mL.

[0017] As a further scheme of the present application: the strong acid solution in step A2 is a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1; the mass fraction of the concentrated sulfuric acid is 80%; and the mass fraction of the concentrated nitric acid is 68%.

[0018] As a further scheme of the present application: the amount of the hydroxyethyl methyl cellulose and the N,N-dimethylformamide in step A3 is 20-50 g: 200-500 mL.

[0019] As a further scheme of the present application: the amount of the graphene oxide, the N,N-dimethylformamide, the first solution, the 4-dimethylamino pyridine and the dicyclohexyl carbodiimide in step A4 is 3-5 g: 300-500 mL: 300-500 mL: 6-10 g: 0.3-0.5 g.

[0020] As a further scheme of the present application: the amount of the europium-doped lithium iron phosphate precursor powder, the deionized water and the hydroxyethyl methyl cellulose grafted graphene in step A5 is 5-10 g: 50-100 mL: 0.55-1.1 g.

[0021] In a second aspect, the present application provides a preparation method of a graphene reinforced lithium iron phosphate material, comprising the following steps:

[0022] Step one: according to the weight parts, the europium-doped lithium iron phosphate@composite graphene 45-90 parts, acetylene carbon black 4-8 parts, butadiene rubber 1.5-3 parts and polyethylene glycol 0.5-1 part are weighed and prepared for use; wherein the polyethylene glycol is polyethylene glycol PEG-300; and the butadiene rubber is SBR1502;

[0023] Step two: the europium-doped lithium iron phosphate@composite graphene, acetylene carbon black, butadiene rubber and polyethylene glycol 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 h, placed in a roller compactor for compaction, and finally punched into a circular electrode by a slicing machine to obtain the graphene reinforced lithium iron phosphate material.

[0024] In a third aspect, the present application provides an application of the lithium iron phosphate anode material prepared by the preparation method of the graphene reinforced lithium iron phosphate material in a lithium ion battery.

[0025] The present application has the following beneficial effects:

[0026] The graphene reinforced lithium iron phosphate material of the present application expands the interplanar spacing by doping europium in lithium iron phosphate to provide migration paths for lithium ions, forms a three-dimensional conductive carbon network by grafting graphene on hydroxyethyl methyl cellulose to improve ion transfer efficiency, and improves the conductivity of the lithium iron phosphate positive electrode material through synergistic effect, thereby effectively improving the overall performance of the battery and prolonging its service life.

[0027] A graphene reinforced lithium iron phosphate material is prepared by first adding europium chloride during the preparation of lithium iron phosphate to obtain a europium-doped lithium iron phosphate precursor powder. The radius of europium ions is larger than that of lithium ions, which increases the lattice spacing and provides a larger channel for the migration of lithium ions, and reduces the electrostatic binding between lithium ions and surrounding atoms, thereby enhancing the diffusion of lithium ions. Graphene is oxidized under the action of strong acid to form carboxyl groups on the surface. The carboxyl groups and the hydroxyl groups in hydroxyethyl methyl cellulose undergo amide condensation reaction under the catalysis of 4-dimethylaminopyridine and dicyclohexyl carbodiimide to obtain ester groups. Graphene has high electron mobility, and hydroxyethyl methyl cellulose improves the dispersion performance of graphene, avoids the agglomeration of graphene, and enables graphene to uniformly coat the surface of lithium iron phosphate to avoid excessive looseness between the two and improve their compatibility. The carbon layer formed after calcination and graphene together construct a 3D conductive carbon network to coat the surface of the europium-doped lithium iron phosphate, improve the rate performance and cycle stability of the positive electrode material, and provide efficient energy storage and release capacity, thereby achieving overall improvement of battery performance and having significant advantages in electric vehicles, energy storage systems and other fields. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0029] Embodiment 1:

[0030] The present embodiment is a preparation method of a graphene reinforced lithium iron phosphate material, comprising the following steps:

[0031] Step A1: 10 mL ascorbic acid solution, 30 mL ethylene glycol solution was added to a three-necked flask equipped with a stirrer, stirred at 50 r / min for 10 min, ultrasonic dispersion for 20 min, 30 mmol lithium hydroxide monohydrate was added by magnetic stirring for 4 min, 10 mmol ferrous sulfate heptahydrate and 1 mmol europium chloride were added by stirring for 10 min, the mixed solution was transferred to a stainless steel autoclave, protected by nitrogen, reacted at 170℃, 200 r / min for 8 h, cooled to 24℃, washed with deionized water for 3 times, vacuum freeze-dried for 22 h, to obtain europium-doped lithium iron phosphate precursor powder;

[0032] Step A2: 5 g graphene, 250 mL strong acid solution was added to a three-necked flask equipped with a thermometer, placed in a water bath, stirred at 70℃ by magnetic stirring for 30 min, ultrasonic dispersion for 2 h, after suction filtration, washed with deionized water until the pH of the washing liquid was 6, placed in a drying oven and dried at 80℃ for 10 h, to obtain graphene oxide;

[0033] Step A3: 20 g hydroxyethyl methyl cellulose, 200 mL N,N-dimethylformamide was added to a three-necked flask equipped with a stirrer and a thermometer, placed in a water bath, stirred at 40℃, 50 r / min for 30 min, to obtain a first solution;

[0034] Step A4: 3 g graphene oxide, 300 mL N,N-dimethylformamide was added to a three-necked flask equipped with a stirrer, ultrasonic dispersion for 20 min, stirred at 300 r / min, 300 mL of the first solution was added dropwise, stirred for 20 min, 6 g 4-dimethylaminopyridine was added by stirring for 8 min, the same amount was added each time, 0.3 g dicyclohexyl carbodiimide was added in three portions by stirring for 8 min, reacted for 22 h, after centrifugation, washed with anhydrous ethanol for 3 times, washed with deionized water for 2 times, freeze-dried for 22 h, to obtain hydroxyethyl methyl cellulose grafted graphene;

[0035] Step A5: 5 g europium-doped lithium iron phosphate precursor powder, 50 mL deionized water was added to a ball mill tank, ball milled at 400 r / min for 20 min, 0.55 g hydroxyethyl methyl cellulose grafted graphene was added, mixed at 900 r / min for 4 h, transferred to a spray dryer for drying, placed in a sintering furnace, protected by nitrogen, calcined at 650℃ for 4 h, cooled to 24℃, to obtain europium-doped lithium iron phosphate@composite graphene;

[0036] Step A6: The europium-doped lithium iron phosphate@composite graphene 45 parts, acetylene black 4 parts, butadiene rubber 1.5 parts and polyethylene glycol 0.5 parts were weighed according to the weight parts, and prepared for use; wherein the polyethylene glycol was polyethylene glycol PEG-300; the butadiene rubber was SBR1502;

[0037] Step A7: Lithium iron phosphate doped with europium@composite graphene, acetylene carbon black, butadiene rubber SBR1502 and polyethylene glycol PEG-300 were ground, then N-methyl pyrrolidone was added to adjust the solid content to 45% and continue to grind, after grinding, coated on aluminum foil current collector, put into constant temperature vacuum drying oven and dried for 8h, placed in a roller press and compacted, finally punched into a circular electrode with a slicer, to obtain a graphene reinforced lithium iron phosphate material.

[0038] Example 2:

[0039] The present embodiment is a preparation method of a graphene reinforced lithium iron phosphate material, comprising the following steps:

[0040] Step A1: 15mL ascorbic acid solution, 45mL ethylene glycol solution were added to a three-necked flask equipped with a stirrer, stirred at 75r / min for 15min, ultrasonic dispersion for 25min, 45mmol lithium hydroxide monohydrate was added and magnetically stirred for 5min, 15mmol phosphoric acid was added and magnetically stirred for 9min, 13.5mmol ferrous sulfate heptahydrate and 1.5mmol europium chloride were added and stirred for 15min, the mixed solution was transferred to a stainless steel autoclave, protected by nitrogen, reacted at 175℃, 250r / min for 9h, cooled to 25℃, washed with deionized water for 4 times, vacuum freeze-dried for 23h, to obtain a lithium iron phosphate doped with europium precursor powder;

[0041] Step A2: 7.5g graphene, 325mL strong acid solution were added to a three-necked flask equipped with a thermometer, placed in a water bath, magnetically stirred at 75℃ for 45min, ultrasonic dispersion for 2.5h, after suction filtration, washed with deionized water until the pH of the washing liquid was 7, placed in a drying oven and dried at 85℃ for 11h, to obtain graphene oxide;

[0042] Step A3: 35g hydroxyethyl methyl cellulose, 350mL N,N-dimethylformamide were added to a three-necked flask equipped with a stirrer and a thermometer, placed in a water bath, stirred at 45℃, 75r / min for 45min, to obtain a first solution;

[0043] Step A4: 4g graphene oxide, 400mL N,N-dimethylformamide were added to a three-necked flask equipped with a stirrer, ultrasonic dispersion for 25min, stirred at 350r / min, 400mL first solution was added dropwise, stirred for 25min, 8g 4-dimethylaminopyridine was added and stirred for 9min, the same amount was added each time, 0.4g dicyclohexyl carbodiimide was added in three portions and stirred for 9min, reacted for 23h, after centrifugation, washed with anhydrous ethanol for 4 times, washed with deionized water for 2 times, freeze-dried for 23h, to obtain hydroxyethyl methyl cellulose grafted graphene;

[0044] Step A5: 7.5 g of europium-doped lithium iron phosphate precursor powder, 75 mL of deionized water were added to a ball mill tank, ball milling at 450 r / min for 25 min, 0.825 g of hydroxyethyl methyl cellulose grafted graphene was added, mixing at 950 r / min for 4.5 h, transferred to a spray dryer for drying, placed in a sintering furnace, protected by nitrogen, calcined at 700℃ for 4.5 h, cooled to 25℃, to obtain europium-doped lithium iron phosphate@composite graphene;

[0045] Step A6: The europium-doped lithium iron phosphate@composite graphene 67.5 parts, acetylene black 6 parts, butadiene rubber 2.25 parts and polyethylene glycol 0.75 parts were weighed according to the weight parts, and prepared for use; wherein the polyethylene glycol is polyethylene glycol PEG-300; the butadiene rubber is SBR1502;

[0046] Step A7: The europium-doped lithium iron phosphate@composite graphene, acetylene black, butadiene rubber SBR1502 and polyethylene glycol PEG-300 were ground, then N-methyl pyrrolidone was added to adjust the solid content to 50% and continue to grind, after grinding, coated on an aluminum foil current collector and dried in a constant temperature vacuum drying oven for 10 h, pressed in a roller press, and finally punched into a circular electrode with a slicing machine to obtain a graphene reinforced lithium iron phosphate material.

[0047] Example 3:

[0048] The present embodiment is a preparation method of a graphene reinforced lithium iron phosphate material, comprising the following steps:

[0049] Step A1: 20 mL of ascorbic acid solution, 60 mL of ethylene glycol solution were added to a three-necked flask equipped with a stirrer, stirred at 100 r / min for 20 min, ultrasonic dispersed for 30 min, 60 mmol of lithium hydroxide monohydrate was added and magnetically stirred for 6 min, 20 mmol of phosphoric acid was added and magnetically stirred for 10 min, 18 mmol of ferrous sulfate heptahydrate and 2 mmol of europium chloride were added and stirred for 20 min, the mixed solution was transferred to a stainless steel autoclave, protected by nitrogen, reacted at 180℃, 300 r / min for 10 h, cooled to 26℃, washed with deionized water for 5 times, vacuum freeze-dried for 24 h, to obtain europium-doped lithium iron phosphate precursor powder;

[0050] Step A2: 10 g of graphene, 500 mL of strong acid solution were added to a three-necked flask equipped with a thermometer, placed in a water bath, magnetically stirred at 80℃ for 60 min, ultrasonic dispersed for 3 h, after filtration, washed with deionized water until the pH of the washing liquid was 8, placed in a drying oven and dried at 90℃ for 12 h, to obtain graphene oxide;

[0051] Step A3: 50 g of hydroxyethyl methyl cellulose, 500 mL of N, N-dimethylformamide were added to a three-necked flask equipped with a stirrer, a thermometer, and placed in a water bath, stirred at 50 DEG C, 100 r / min for 60 min to obtain a first solution;

[0052] Step A4: 5 g of graphene oxide, 500 mL of N, N-dimethylformamide were added to a three-necked flask equipped with a stirrer, ultrasonic dispersion for 30 min, stirred at 400 r / min, 500 mL of the first solution was added dropwise, stirred for 30 min, 10 g of 4-dimethylamino pyridine was added and stirred for 10 min, the same amount was controlled each time, 0.5 g of dicyclohexyl carbodiimide was added in three times and stirred for 10 min, reacted for 24 h, washed with anhydrous ethanol for 5 times and deionized water for 2 times after centrifugation, and freeze-dried for 24 h to obtain hydroxyethyl methyl cellulose grafted graphene;

[0053] Step A5: 10 g of europium-doped lithium iron phosphate precursor powder, 100 mL of deionized water were added to a ball mill tank, ball milled at 500 r / min for 30 min, 1.1 g of hydroxyethyl methyl cellulose grafted graphene was added, mixed at 1000 r / min for 5 h, transferred to a spray dryer for drying, placed in a sintering furnace, protected by nitrogen, calcined at 750 DEG C for 5 h, and cooled to 26 DEG C to obtain europium-doped lithium iron phosphate@composite graphene;

[0054] Step A6: according to the weight part, 90 parts of europium-doped lithium iron phosphate@composite graphene, 8 parts of acetylene black, 3 parts of butadiene rubber and 1 part of polyethylene glycol were weighed, and the polyethylene glycol was polyethylene glycol PEG-300; the butadiene rubber was SBR1502;

[0055] Step A7: The europium-doped lithium iron phosphate@composite graphene, acetylene black, butadiene rubber SBR1502 and polyethylene glycol PEG-300 were ground, then N-methyl pyrrolidone was added to adjust the solid content to 55%, and then ground, coated on an aluminum foil current collector, dried in a constant temperature vacuum drying box for 12 h, pressed in a roller press, and finally punched into a circular electrode with a slicing machine to obtain a graphene reinforced lithium iron phosphate material.

[0056] Comparative Example 1:

[0057] The present comparative example is a preparation method of a graphene reinforced lithium iron phosphate material, comprising the following steps:

[0058] Step A1: 20 mL ascorbic acid solution, 60 mL ethylene glycol solution were added into a three-necked flask equipped with a stirrer, stirred at 100 r / min for 20 min, ultrasonic dispersion for 30 min, 60 mmol lithium hydroxide monohydrate was added and magnetically stirred for 6 min, 20 mmol of ferrous sulfate heptahydrate and 2 mmol of europium chloride were added and stirred for 20 min, the mixed solution was transferred to a stainless steel autoclave, protected by nitrogen, reacted at 180℃, 300 r / min for 10 h, cooled to 26℃, washed with deionized water for 5 times, vacuum freeze-dried for 24 h, to obtain a lithium iron phosphate doped with europium precursor powder;

[0059] Step A2: 10 g of lithium iron phosphate doped with europium precursor powder, 100 mL of deionized water were added into a ball mill tank, ball milled at 500 r / min for 30 min, 1.1 g of graphene was added and mixed at 1000 r / min for 5 h, transferred to a spray dryer for drying, placed in a sintering furnace and protected by nitrogen, calcined at 750℃ for 5 h, cooled to 26℃, to obtain lithium iron phosphate doped with europium@graphene;

[0060] Step A3: lithium iron phosphate doped with europium@graphene 90 parts, acetylene carbon black 8 parts, butadiene rubber 3 parts and polyethylene glycol 1 part were weighed according to weight parts, for standby; wherein the polyethylene glycol is polyethylene glycol PEG-300; the butadiene rubber is SBR1502;

[0061] Step A4: lithium iron phosphate doped with europium@graphene, acetylene carbon black, butadiene rubber SBR1502 and polyethylene glycol PEG-300 were ground, then N-methyl pyrrolidone was added to adjust the solid content to 55% and continue to grind, after grinding, coated on an aluminum foil current collector and dried in a constant temperature vacuum drying box for 12 h, placed in a roller press for compaction, and finally punched into a circular electrode with a slicing machine, to obtain a graphene reinforced lithium iron phosphate material.

[0062] Comparative Example 2:

[0063] The present comparative example is a preparation method of a graphene reinforced lithium iron phosphate material, comprising the following steps:

[0064] Step A1: 20 mL ascorbic acid solution, 60 mL ethylene glycol solution were added into a three-necked flask equipped with a stirrer, stirred at 100 r / min for 20 min, ultrasonic dispersion for 30 min, 60 mmol lithium hydroxide monohydrate was added and magnetically stirred for 6 min, 20 mmol of ferrous sulfate heptahydrate and 2 mmol of europium chloride were added and stirred for 20 min, the mixed solution was transferred to a stainless steel autoclave, protected by nitrogen, reacted at 180℃, 300 r / min for 10 h, cooled to 26℃, washed with deionized water for 5 times, vacuum freeze-dried for 24 h, to obtain a europium-doped lithium iron phosphate precursor powder;

[0065] Step A2: 10 g of europium-doped lithium iron phosphate precursor powder, 100 mL of deionized water were added into a ball mill tank, ball milled at 500 r / min for 30 min, 1.1 g of hydroxyethyl methyl cellulose was added, mixed at 1000 r / min for 5 h, transferred to a spray dryer for drying, placed in a sintering furnace, protected by nitrogen, calcined at 750℃ for 5 h, cooled to 26℃, to obtain europium-doped lithium iron phosphate@carbonized hydroxyethyl methyl cellulose;

[0066] Step A3: The europium-doped lithium iron phosphate@carbonized hydroxyethyl methyl cellulose 90 parts, acetylene black 8 parts, butadiene rubber 3 parts and polyethylene glycol 1 part were weighed according to the weight parts, and reserved; wherein the polyethylene glycol is polyethylene glycol PEG-300; the butadiene rubber is SBR1502;

[0067] Step A4: The europium-doped lithium iron phosphate@carbonized hydroxyethyl methyl cellulose, acetylene black, butadiene rubber SBR1502 and polyethylene glycol PEG-300 were ground, then N-methyl pyrrolidone was added to adjust the solid content to 55%, and then ground, after grinding, coated on an aluminum foil current collector, dried in a constant temperature vacuum drying box for 12 h, placed in a roller press, and finally punched into a circular electrode with a slicing machine, to obtain a graphene reinforced lithium iron phosphate material.

[0068] Comparative Example 3:

[0069] The present comparative example is a preparation method of a graphene reinforced lithium iron phosphate material, comprising the following steps:

[0070] Step A1: 20 mL ascorbic acid solution, 60 mL ethylene glycol solution was added to a three-necked flask equipped with a stirrer, stirred at 100 r / min for 20 min, ultrasonic dispersion for 30 min, 60 mmol lithium hydroxide monohydrate was added by magnetic stirring for 6 min, 20 mmol phosphoric acid was added by magnetic stirring for 10 min, 18 mmol ferrous sulfate heptahydrate was added by stirring for 20 min, the mixed solution was transferred to a stainless steel autoclave, protected by nitrogen, reacted at 180℃, 300 r / min for 10 h, cooled to 26℃, washed with deionized water for 5 times, vacuum freeze-dried for 24 h, to obtain lithium iron phosphate precursor powder;

[0071] Step A2: 10 g graphene, 500 mL strong acid solution was added to a three-necked flask equipped with a thermometer, placed in a water bath, stirred at 80℃ by magnetic stirring for 60 min, ultrasonic dispersion for 3 h, after suction filtration, washed with deionized water until the pH of the washing liquid was 8, placed in a drying oven and dried at 90℃ for 12 h, to obtain graphene oxide;

[0072] Step A3: 50 g hydroxyethyl methyl cellulose, 500 mL N, N-dimethylformamide was added to a three-necked flask equipped with a stirrer and a thermometer, placed in a water bath, stirred at 50℃, 100 r / min for 60 min, to obtain a first solution;

[0073] Step A4: 5 g graphene oxide, 500 mL N, N-dimethylformamide was added to a three-necked flask equipped with a stirrer, ultrasonic dispersion for 30 min, stirred at 400 r / min, 500 mL of the first solution was added dropwise, stirred for 30 min, 10 g 4-dimethylaminopyridine was added by stirring for 10 min, the same amount was added each time, 0.5 g dicyclohexyl carbodiimide was added in three portions by stirring for 10 min, reacted for 24 h, after centrifugation, washed with anhydrous ethanol for 5 times, washed with deionized water for 2 times, freeze-dried for 24 h, to obtain hydroxyethyl methyl cellulose grafted graphene;

[0074] Step A5: 10 g lithium iron phosphate precursor powder, 100 mL deionized water was added to a ball mill tank, ball milled at 500 r / min for 30 min, 1.1 g hydroxyethyl methyl cellulose grafted graphene was added, mixed at 1000 r / min for 5 h, transferred to a spray dryer for drying, placed in a sintering furnace, protected by nitrogen, calcined at 750℃ for 5 h, cooled to 26℃, to obtain lithium iron phosphate@composite graphene;

[0075] Step A6: lithium iron phosphate@composite graphene 90 parts, acetylene black 8 parts, butadiene rubber 3 parts and polyethylene glycol 1 part were weighed according to the weight parts, for standby use; wherein the polyethylene glycol was polyethylene glycol PEG-300; the butadiene rubber was SBR1502;

[0076] Step A7: Lithium iron phosphate@composite graphene, acetylene black, butadiene rubber SBR1502 and polyethylene glycol PEG-300 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 and dried for 12h, placed in a roller press and compacted, finally punched into a circular electrode with a slicer, to obtain a graphene reinforced lithium iron phosphate material.

[0077] Performance test

[0078] The lithium iron phosphate materials of examples 1-3 and comparative examples 1-3 were used as positive electrodes, CR2032 button cell shells were used for assembly, lithium sheets were used as negative electrodes, Celgard2400 battery separators were used, and 1M LiPF6 / EC+DEC+EMC (1:1:1, v / v / v) was added dropwise as electrolyte to obtain sample batteries.

[0079] The sample batteries were tested on a Wuhan Land battery test system using a constant current charge-discharge program, the test environment was constant temperature 25℃, the voltage range was 2.7-4.3V, the reference current density was set to 180mAh / g, and the batteries were activated for three cycles at 0.1C before testing; the cycle test program was 100 cycles of charge-discharge at 1C; the rate test program entered the next condition after 5 complete cycles at 1C current density, and finally returned to 1C condition and continued to cycle to the 100th cycle to obtain the initial discharge capacity, the remaining capacity after 100 cycles and the coulombic efficiency data.

[0080] Table 1: Initial discharge capacity, remaining capacity after 100 cycles, coulombic efficiency data

[0081]

[0082] Referring to the table above, according to the comparison between examples 1-3 and comparative examples 1-3, it can be seen that the coulombic efficiency of the europium-doped lithium iron phosphate@composite graphene positive electrode material is high, and the cycle and rate performance is excellent.

[0083] According to the comparison between example 3 and comparative example 1, it can be seen that the coulombic efficiency of the europium-doped lithium iron phosphate@composite graphene positive electrode material is higher than that of the europium-doped lithium iron phosphate@graphene positive electrode material, indicating that the europium-doped lithium iron phosphate@composite graphene positive electrode material has excellent electrochemical performance;

[0084] According to the comparison between example 3 and comparative example 2, it can be seen that the coulombic efficiency of the europium-doped lithium iron phosphate@composite graphene positive electrode material is higher than that of the europium-doped lithium iron phosphate@hydroxyethyl methyl cellulose carbonized positive electrode material, indicating that the europium-doped lithium iron phosphate@composite graphene positive electrode material has excellent electrochemical performance;

[0085] According to the comparison between the embodiment 3 and the comparative example 3, it can be seen that the coulomb efficiency of the europium-doped lithium iron phosphate@composite graphene positive electrode material is higher than that of the lithium iron phosphate@composite graphene positive electrode material, which indicates that the europium-doped lithium iron phosphate@composite graphene positive electrode material has excellent electrochemical performance.

[0086] In the description of the present specification, the description referring to 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 a suitable manner.

[0087] The above is only an example and 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, which shall belong to the protection scope of the present application.

Claims

1. A graphene-reinforced lithium iron phosphate material, characterized in that, The following components are included by weight parts: The europium-doped lithium iron phosphate@composite graphene 45-90 parts, acetylene carbon black 4-8 parts, butadiene rubber 1.5-3 parts and polyethylene glycol 0.5-1 parts; The europium-doped lithium iron phosphate@composite graphene is prepared by the following steps: Step A1: Stir the ascorbic acid solution, ethylene glycol solution, add lithium hydroxide monohydrate, stir, add phosphoric acid, stir, add ferrous sulfate heptahydrate and europium chloride, stir, react in a high-pressure kettle, cool, wash and dry to obtain the europium-doped lithium iron phosphate precursor powder; Step A2: Stir the graphene and strong acid solution, ultrasonic, filter and wash, and dry to obtain the graphene oxide; Step A3: Stir the hydroxyethyl methyl cellulose and N,N-dimethylformamide to obtain a first solution; Step A4: Ultrasonic the graphene oxide and N,N-dimethylformamide, stir, add the first solution, stir, add 4-dimethylaminopyridine, stir, control the amount of addition, add dicyclohexyl carbodiimide in three times, stir, react, centrifugal wash and dry to obtain the hydroxyethyl methyl cellulose grafted graphene; Step A5: Ball mill the europium-doped lithium iron phosphate precursor powder and deionized water, mix with the hydroxyethyl methyl cellulose grafted graphene, dry, calcine under nitrogen, cool and obtain the europium-doped lithium iron phosphate@composite graphene.

2. The graphene reinforced lithium iron phosphate material of claim 1, wherein, The amount ratio of the ascorbic acid solution, ethylene glycol solution, lithium hydroxide monohydrate, phosphoric acid, ferrous sulfate heptahydrate and europium chloride in step A1 is 10-20 mL:30-60 mL:30-60 mmol:10-20 mmol:9-18 mmol:1-2 mmol.

3. The graphene reinforced lithium iron phosphate material of claim 1, wherein the graphene is present in an amount of 0.1 to 5 wt%. The molar concentration of the ascorbic acid solution in step A1 is 0.3 mol / L; the mass fraction of the ethylene glycol solution is 12.5%.

4. The graphene reinforced lithium iron phosphate material of claim 1, wherein, The amount ratio of the graphene and strong acid solution in step A2 is 5-10 g:250-500 mL.

5. The graphene reinforced lithium iron phosphate material of claim 1, wherein the graphene is present in an amount of 0.1 to 5 wt%. The strong acid solution in step A2 is a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1; the mass fraction of the concentrated sulfuric acid is 80%; the mass fraction of the concentrated nitric acid is 68%.

6. The graphene reinforced lithium iron phosphate material of claim 1, wherein, The amount ratio of the hydroxyethyl methyl cellulose and N,N-dimethylformamide in step A3 is 20-50 g:200-500 mL.

7. The graphene reinforced lithium iron phosphate material of claim 1, wherein the graphene is present in an amount of 0.1 to 5 wt%. The amount ratio of the graphene oxide, N,N-dimethylformamide, first solution, 4-dimethylaminopyridine and dicyclohexyl carbodiimide in step A4 is 3-5 g:300-500 mL:300-500 mL:6-10 g:0.3-0.5 g.

8. The graphene reinforced lithium iron phosphate material of claim 1, wherein, The amount ratio of the europium-doped lithium iron phosphate precursor powder, deionized water and hydroxyethyl methyl cellulose grafted graphene in step A5 is 5-10 g:50-100 mL:0.55-1.1 g.

9. A method of preparing a graphene-reinforced lithium iron phosphate material, characterized by, The method for preparing the graphene reinforced lithium iron phosphate material as claimed in any one of claims 1-8 comprises the following steps: Step one: Take the europium-doped lithium iron phosphate@composite graphene 45-90 parts, acetylene carbon black 4-8 parts, butadiene rubber 1.5-3 parts and polyethylene glycol 0.5-1 parts by weight parts, and reserve for use; Step two: grind the europium-doped lithium iron phosphate@composite graphene, acetylene carbon black, butadiene rubber and polyethylene glycol, then add N-methyl pyrrolidone to adjust the solid content to 45%-55%, continue to grind, coat on the aluminum foil current collector after grinding, put into a constant temperature vacuum drying oven and dry for 8-12h, place in a roller compactor to compact, and finally use a slicing machine to punch into a circular electrode to obtain the graphene-enhanced lithium iron phosphate material.

10. Use of the graphene reinforced lithium iron phosphate material according to any one of claims 1 to 8 or of the graphene reinforced lithium iron phosphate material prepared by the method of preparation of the graphene reinforced lithium iron phosphate material according to claim 9, characterized in that, The graphene-enhanced lithium iron phosphate material is used for the preparation of a lithium ion battery.

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