A positive electrode material for lithium iron phosphate battery and preparation method thereof

Abstract

The invention discloses a positive electrode material for a lithium iron phosphate battery and a preparation method thereof. A precursor and a modified carrier are ground and blended, and then calcined in a nitrogen atmosphere to obtain the positive electrode material. The positive electrode material contains a silicon-based material silicon that can combine with lithium to increase the theoretical capacity. At the same time, the lithium iron phosphate is embedded in the gaps of the carrier to stabilize the structure of the material. Lithium dendrites are not easily formed on the surface of the positive electrode material. Doping with nitrogen, sulfur and boron elements and lanthanum metal can expand the lattice structure of the positive electrode material, expand the diffusion channel of lithium ions, increase the diffusion rate of lithium ions, and improve the rate performance. The surface is coated with graphene carbon material to increase the conductivity of the material, stabilize its structure, and improve the cycle performance of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of positive electrode material preparation, and in particular to a positive electrode material for a lithium iron phosphate battery and a preparation method thereof. Background Art

[0002] With the progress and development of science, human beings are increasingly dependent on energy demand. While traditional energy represented by coal and oil has promoted the development of human society, it has also brought a series of problems. As a non-renewable energy source, with the exploitation and utilization of human beings, the reserves are constantly decreasing and becoming exhausted, and gradually unable to meet the energy needs of human beings and society. As a representative of new clean energy, lithium-ion batteries have achieved rapid development due to their many advantages. Compared with traditional petroleum and coal energy, it has the advantages of cleanness and pollution-free, relatively higher safety, and better energy storage efficiency compared to traditional secondary energy, which have alleviated the problems in the energy field to a certain extent. At present, it has become the preferred energy source for portable electronic products and new energy vehicles. The positive electrode is one of the main sources of lithium ions in lithium batteries. The positive electrode materials mainly include high-safety lithium iron phosphate and high-energy-density nickel cobalt manganese oxide. Lithium iron phosphate exhibits low intrinsic electronic conductivity and slow ion diffusion coefficient, which affects the normal use of the battery. Summary of the invention

[0003] The purpose of the present invention is to provide a positive electrode material for lithium iron phosphate batteries and a preparation method thereof, which solves the problem that the positive electrode material for lithium iron phosphate batteries at the current stage has low lithium battery capacity and short cycle life.

[0004] The purpose of the present invention can be achieved through the following technical solutions:

[0005] A method for preparing a positive electrode material for a lithium iron phosphate battery comprises the following steps:

[0006] Step A1: dispersing graphene oxide in anhydrous ethanol, stirring and adding KH550 and deionized water at a speed of 150-200 r / min and a temperature of 40-50° C., reacting for 3-5 hours to obtain pretreated graphene, uniformly mixing polyvinyl alcohol, epichlorohydrin, tetrabutylammonium bromide and DMF, introducing nitrogen protection, reacting for 2-3 hours at a speed of 120-150 r / min and a temperature of 110-115° C., cooling to 50-55° C., adding sodium hydroxide solution, reacting for 5-7 hours to obtain a modifier;

[0007] Step A2: The pretreated graphene, the modifier and DMF are mixed evenly, and the reaction is carried out for 4-6 hours at a speed of 120-150r / min, a temperature of 20-25°C and a pH value of 10-11 to obtain modified graphene. Polyethylene glycol, boric acid, boron trichloride and toluene are mixed evenly, and the reaction is carried out for 2-3 hours at a speed of 150-200r / min and a temperature of 70-80°C. Then, the modified graphene is added and the reaction is continued for 5-7 hours to obtain a precursor. The precursor, the modified carrier and ethanol are mixed and ground evenly, and then calcined for 2-3 hours at a temperature of 750-800°C and a nitrogen atmosphere to obtain a positive electrode material.

[0008] Furthermore, the amount of KH550 described in step A1 is 2-3% of the mass of graphene oxide, the amount ratio of polyvinyl alcohol, epichlorohydrin, tetrabutylammonium bromide and sodium hydroxide solution is 20g:4.5g:0.5g:30mL, the mass fraction of sodium hydroxide solution is 50%, and the molecular weight of polyvinyl alcohol is 2000.

[0009] Furthermore, the molar ratio of the amino group on the pretreated graphene and the epoxy group on the modifier described in step A2 is 1:1, the dosage ratio of polyethylene glycol, boric acid and modified graphene is 10mmo l:10mmo l:1g, the dosage of boron trichloride is 3% of the mass of boric acid, the molecular weight of polyethylene glycol is 2000, and the mass ratio of the precursor and the modified carrier is 1:10.

[0010] Further, the modified carrier is prepared by the following steps:

[0011] Step B1: 2,2'-diamino-4,4'-bithiazole, epoxy octane and DMF are mixed evenly, and reacted for 3-5 hours at a speed of 150-200 r / min, a temperature of 30-40°C and a pH value of 10-11 to obtain intermediate 1; intermediate 1, terephthalaldehyde, p-toluenesulfonic acid and toluene are mixed evenly, and reacted for 5-7 hours at a speed of 60-80 r / min and a temperature of 110-120°C to obtain intermediate 2;

[0012] Step B2: Mix the intermediate 2, (3-aminopropyl) dimethylethoxysilane and DMF, react for 3-5 hours at a speed of 200-300 r / min and a temperature of 40-50° C. to obtain a modified monomer, mix the modified monomer, dimethyldichlorosilane and deionized water, stir for 10-15 minutes at a speed of 200-300 r / min and a temperature of 60-70° C., add concentrated sulfuric acid and hexamethyldisiloxane, react for 4-6 hours, and adjust the pH to neutral to obtain a modified ligand;

[0013] Step B3: The modified ligand, lanthanum nitrate hexahydrate, DMF and deionized water are mixed, and the reaction is carried out for 2-3 hours at a frequency of 20-30kHz and a temperature of 25-30°C, and the temperature is raised to 150-155°C, and the reaction is continued for 10-15 hours to obtain a carrier. Phosphoric acid, lithium hydroxide, ferrous sulfate heptahydrate and deionized water are mixed evenly, and the reaction is carried out for 1-1.5 hours at a speed of 300-500r / min and a temperature of 180-185°C, and the carrier is added, and the reaction is continued for 8-10 hours, and then filtered and dried. The substrate is calcined at a temperature of 800-850°C and a nitrogen atmosphere for 2-3 hours to obtain a modified carrier.

[0014] Furthermore, the molar ratio of 2,2'-diamino-4,4'-bithiazole to octane oxide in step B1 is 1:4, the molar ratio of intermediate 1 to terephthalaldehyde is n:n+1, and the amount of p-toluenesulfonic acid used is 1% of the mass of intermediate 1.

[0015] Furthermore, the molar ratio of the intermediate 2 and (3-aminopropyl)dimethylethoxysilane described in step B2 is 1:2, the amount ratio of the modified monomer, dimethyldichlorosilane, deionized water and hexamethyldisiloxane is 1mmol:3mmo1:20mL:2mmo1, and the amount of concentrated sulfuric acid is 1-2% of the mass of the modified monomer.

[0016] Further, the usage ratio of the modified ligand and lanthanum nitrate hexahydrate described in step B3 is 1.1g:2mmo l, and the usage ratio of phosphoric acid, lithium hydroxide, ferrous sulfate heptahydrate, deionized water and carrier is 10.6mmo l:30mmo l:10mmo l:40mL:2g.

[0017] The beneficial effects of the present invention are as follows: the positive electrode material for lithium iron phosphate battery disclosed by the present invention uses graphene oxide as a raw material and is treated with KH550 to graft active amino groups on the surface, polyvinyl alcohol and epichlorohydrin are reacted to make the hydroxyl groups on the polyvinyl alcohol react with the epoxy groups on the epichlorohydrin, and then a ring-closing reaction is carried out under the condition of sodium hydroxide solution to prepare a modifier, the pretreated graphene is reacted with the modifier to make the amino groups on the pretreated graphene react with the epoxy groups on the modifier to form new hydroxyl groups, polyethylene glycol is reacted with boric acid to make the hydroxyl groups on the polyethylene glycol react with the epoxy groups on the modifier, and the modifier is prepared by reacting the pretreated graphene with the epoxy groups on the modifier. The boric acid group is reacted, and then modified graphene is added so that the remaining boric acid group reacts with the hydroxyl group on the modified graphene to obtain a precursor. The precursor and the modified carrier are ground and blended, and then calcined under a nitrogen atmosphere to obtain a positive electrode material. The modified carrier is reacted with 2,2'-diamino-4,4'-bithiazole and octane oxide so that the amino group on 2,2'-diamino-4,4'-bithiazole reacts with the epoxy group on octane oxide to form a new hydroxyl group to obtain an intermediate 1. The intermediate 1 is reacted with terephthalaldehyde so that the two hydroxyl groups on one side of the intermediate 1 react with the terephthalaldehyde. The aldehyde group on diformaldehyde reacts with diacetal to obtain intermediate 2, intermediate 2 reacts with (3-aminopropyl) dimethylethoxysilane so that the aldehyde group on intermediate 2 reacts with the amino group on (3-aminopropyl) dimethylethoxysilane to obtain a modified monomer, the modified monomer and dimethyldichlorosilane are hydrolyzed, and then condensed with hexamethyldisiloxane to obtain a modified ligand, the modified ligand reacts with lanthanum nitrate hexahydrate so that the thiazole on the modified ligand cooperates with lanthanum ions to form an organic framework of lanthanum, phosphoric acid, lithium hydroxide and ferrous sulfate heptahydrate are reacted, and a modified ligand is prepared on the surface of the carrier. The surface of the positive electrode material forms a lithium iron phosphate load to obtain a modified carrier. The positive electrode material contains silicon-based materials. Silicon can combine with lithium to increase the theoretical capacity. At the same time, the lithium iron phosphate is embedded in the gaps of the carrier, which can stabilize the structure of the material. Lithium dendrites are not easy to form on the surface of the positive electrode material. The doping with nitrogen, sulfur, boron elements and lanthanum metal can expand the lattice structure of the positive electrode material, expand the diffusion channel of lithium ions, increase the diffusion rate of lithium ions, and improve the rate performance. The surface contains graphene carbon material coating, which can increase the conductivity of the material, stabilize its structure, and improve the cycle performance of the battery. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] Example 1

[0020] A method for preparing a positive electrode material for a lithium iron phosphate battery comprises the following steps:

[0021] Step A1: dispersing graphene oxide in anhydrous ethanol, stirring and adding KH550 and deionized water at a speed of 150 r / min and a temperature of 40° C., reacting for 3 hours to obtain pretreated graphene, uniformly mixing polyvinyl alcohol, epichlorohydrin, tetrabutylammonium bromide and DMF, introducing nitrogen protection, reacting for 2 hours at a speed of 120 r / min and a temperature of 110° C., cooling to 50° C., adding sodium hydroxide solution, and reacting for 5 hours to obtain a modifier;

[0022] Step A2: The pretreated graphene, modifier and DMF are mixed evenly, and the reaction is carried out for 4 hours at a speed of 120r / min, a temperature of 20°C and a pH value of 10 to obtain modified graphene. Polyethylene glycol, boric acid, boron trichloride and toluene are mixed evenly, and the reaction is carried out for 2 hours at a speed of 150r / min and a temperature of 70°C. Then, the modified graphene is added and the reaction is continued for 5 hours to obtain a precursor. The precursor, modified carrier and ethanol are mixed and ground evenly, and then calcined for 2 hours at a temperature of 750°C and a nitrogen atmosphere to obtain a positive electrode material.

[0023] The amount of KH550 described in step A1 is 2% of the mass of graphene oxide, the amount ratio of polyvinyl alcohol, epichlorohydrin, tetrabutylammonium bromide and sodium hydroxide solution is 20g:4.5g:0.5g:30mL, the mass fraction of sodium hydroxide solution is 50%, and the molecular weight of polyvinyl alcohol is 2000.

[0024] The molar ratio of the amino group on the pretreated graphene and the epoxy group on the modifier described in step A2 is 1:1, the dosage ratio of polyethylene glycol, boric acid and modified graphene is 10mmo l:10mmo l:1g, the dosage of boron trichloride is 3% of the mass of boric acid, the molecular weight of polyethylene glycol is 2000, and the mass ratio of the precursor and the modified carrier is 1:10.

[0025] The modified carrier is prepared by the following steps:

[0026] Step B1: 2,2'-diamino-4,4'-bithiazole, epoxy octane and DMF were mixed evenly, and reacted for 3 hours at a speed of 150 r / min, a temperature of 30° C. and a pH value of 10 to obtain intermediate 1; intermediate 1, terephthalaldehyde, p-toluenesulfonic acid and toluene were mixed evenly, and reacted for 5 hours at a speed of 60 r / min and a temperature of 110° C. to obtain intermediate 2;

[0027] Step B2: Intermediate 2, (3-aminopropyl)dimethylethoxysilane and DMF were mixed, and the mixture was reacted for 3 hours at a speed of 200 r / min and a temperature of 40° C. to obtain a modified monomer. The modified monomer, dimethyldichlorosilane and deionized water were mixed, and the mixture was stirred for 10 minutes at a speed of 200 r / min and a temperature of 60° C., and concentrated sulfuric acid and hexamethyldisiloxane were added. The mixture was reacted for 4 hours, and the pH was adjusted to neutral to obtain a modified ligand.

[0028] Step B3: The modified ligand, lanthanum nitrate hexahydrate, DMF and deionized water are mixed, and the reaction is carried out at a frequency of 20 kHz and a temperature of 25°C for 2 hours, and then the temperature is raised to 150°C and the reaction is continued for 10 hours to obtain a carrier. Phosphoric acid, lithium hydroxide, ferrous sulfate heptahydrate and deionized water are evenly mixed, and the reaction is carried out at a speed of 300 r / min and a temperature of 180°C for 1 hour. The carrier is added, and the reaction is continued for 8 hours. After that, it is filtered and dried, and the substrate is calcined at a temperature of 800°C in a nitrogen atmosphere for 2 hours to obtain a modified carrier.

[0029] The molar ratio of 2,2'-diamino-4,4'-bithiazole to octane oxide in step B1 is 1:4, the molar ratio of intermediate 1 to terephthalaldehyde is 1:2, and the amount of p-toluenesulfonic acid used is 1% of the mass of intermediate 1.

[0030] The molar ratio of intermediate 2 and (3-aminopropyl)dimethylethoxysilane described in step B2 is 1:2, the usage ratio of modified monomer, dimethyldichlorosilane, deionized water and hexamethyldisiloxane is 1mmol:3mmol:20mL:2mmol, and the usage of concentrated sulfuric acid is 1% of the mass of modified monomer.

[0031] The usage ratio of the modified ligand and lanthanum nitrate hexahydrate described in step B3 is 1.1g:2mmo l, and the usage ratio of phosphoric acid, lithium hydroxide, ferrous sulfate heptahydrate, deionized water and carrier is 10.6mmo l:30mmo l:10mmo l:40mL:2g.

[0032] Example 2

[0033] A method for preparing a positive electrode material for a lithium iron phosphate battery comprises the following steps:

[0034] Step A1: dispersing graphene oxide in anhydrous ethanol, stirring and adding KH550 and deionized water at a speed of 150 r / min and a temperature of 45° C., reacting for 4 hours to obtain pretreated graphene, uniformly mixing polyvinyl alcohol, epichlorohydrin, tetrabutylammonium bromide and DMF, introducing nitrogen protection, reacting for 3 hours at a speed of 120 r / min and a temperature of 115° C., cooling to 50° C., adding sodium hydroxide solution, and reacting for 6 hours to obtain a modifier;

[0035] Step A2: The pretreated graphene, modifier and DMF are mixed evenly, and the reaction is carried out for 5 hours at a speed of 120r / min, a temperature of 25°C and a pH value of 10 to obtain modified graphene. Polyethylene glycol, boric acid, boron trichloride and toluene are mixed evenly, and the reaction is carried out for 2.5 hours at a speed of 150r / min and a temperature of 75°C. Then, the modified graphene is added and the reaction is continued for 6 hours to obtain a precursor. The precursor, modified carrier and ethanol are mixed and ground evenly, and then calcined for 2.5 hours at a temperature of 780°C and a nitrogen atmosphere to obtain a positive electrode material.

[0036] The amount of KH550 described in step A1 is 2% of the mass of graphene oxide, the amount ratio of polyvinyl alcohol, epichlorohydrin, tetrabutylammonium bromide and sodium hydroxide solution is 20g:4.5g:0.5g:30mL, the mass fraction of sodium hydroxide solution is 50%, and the molecular weight of polyvinyl alcohol is 2000.

[0037] The molar ratio of the amino group on the pretreated graphene and the epoxy group on the modifier described in step A2 is 1:1, the dosage ratio of polyethylene glycol, boric acid and modified graphene is 10mmo l:10mmo l:1g, the dosage of boron trichloride is 3% of the mass of boric acid, the molecular weight of polyethylene glycol is 2000, and the mass ratio of the precursor and the modified carrier is 1:10.

[0038] The modified carrier is prepared by the following steps:

[0039] Step B1: 2,2'-diamino-4,4'-bithiazole, epoxy octane and DMF were mixed evenly, and the mixture was reacted for 4 hours at a speed of 150 r / min, a temperature of 35° C. and a pH of 11 to obtain intermediate 1; intermediate 1, terephthalaldehyde, p-toluenesulfonic acid and toluene were mixed evenly, and the mixture was reacted for 6 hours at a speed of 60 r / min and a temperature of 115° C. to obtain intermediate 2;

[0040] Step B2: Intermediate 2, (3-aminopropyl)dimethylethoxysilane and DMF were mixed, and the mixture was reacted at a speed of 200 r / min and a temperature of 45° C. for 4 h to obtain a modified monomer. The modified monomer, dimethyldichlorosilane and deionized water were mixed, and the mixture was stirred at a speed of 200 r / min and a temperature of 65° C. for 15 min. Concentrated sulfuric acid and hexamethyldisiloxane were added, and the mixture was reacted for 5 h. The pH was adjusted to neutral to obtain a modified ligand.

[0041] Step B3: The modified ligand, lanthanum nitrate hexahydrate, DMF and deionized water are mixed, and the reaction is carried out at a frequency of 25 kHz and a temperature of 28°C for 3 hours, and then the temperature is raised to 150°C and the reaction is continued for 13 hours to obtain a carrier. Phosphoric acid, lithium hydroxide, ferrous sulfate heptahydrate and deionized water are evenly mixed, and the reaction is carried out at a speed of 300 r / min and a temperature of 185°C for 1.3 hours. The carrier is added, and the reaction is continued for 9 hours. After that, it is filtered and dried, and the substrate is calcined at a temperature of 830°C in a nitrogen atmosphere for 2.5 hours to obtain a modified carrier.

[0042] The molar ratio of 2,2'-diamino-4,4'-bithiazole to octane oxide in step B1 is 1:4, the molar ratio of intermediate 1 to terephthalaldehyde is 2:3, and the amount of p-toluenesulfonic acid used is 1% of the mass of intermediate 1.

[0043] The molar ratio of intermediate 2 and (3-aminopropyl)dimethylethoxysilane described in step B2 is 1:2, the usage ratio of modified monomer, dimethyldichlorosilane, deionized water and hexamethyldisiloxane is 1mmol:3mmol:20mL:2mmol, and the usage of concentrated sulfuric acid is 1.5% of the mass of modified monomer.

[0044] The usage ratio of the modified ligand and lanthanum nitrate hexahydrate described in step B3 is 1.1g:2mmo l, and the usage ratio of phosphoric acid, lithium hydroxide, ferrous sulfate heptahydrate, deionized water and carrier is 10.6mmo l:30mmo l:10mmo l:40mL:2g.

[0045] Example 3

[0046] A method for preparing a positive electrode material for a lithium iron phosphate battery comprises the following steps:

[0047] Step A1: dispersing graphene oxide in anhydrous ethanol, stirring and adding KH550 and deionized water at a speed of 200 r / min and a temperature of 50° C., reacting for 5 hours to obtain pretreated graphene, and uniformly mixing polyvinyl alcohol, epichlorohydrin, tetrabutylammonium bromide and DMF, introducing nitrogen protection, reacting for 3 hours at a speed of 150 r / min and a temperature of 115° C., cooling to 55° C., adding sodium hydroxide solution, and reacting for 7 hours to obtain a modifier;

[0048] Step A2: The pretreated graphene, modifier and DMF are mixed evenly, and the reaction is carried out for 6 hours at a speed of 150r / min, a temperature of 25°C and a pH value of 11 to obtain modified graphene. Polyethylene glycol, boric acid, boron trichloride and toluene are mixed evenly, and the reaction is carried out for 3 hours at a speed of 200r / min and a temperature of 80°C. Then, the modified graphene is added and the reaction is continued for 7 hours to obtain a precursor. The precursor, modified carrier and ethanol are mixed and ground evenly, and then calcined for 3 hours at a temperature of 800°C and a nitrogen atmosphere to obtain a positive electrode material.

[0049] The amount of KH550 described in step A1 is 3% of the mass of graphene oxide, the amount ratio of polyvinyl alcohol, epichlorohydrin, tetrabutylammonium bromide and sodium hydroxide solution is 20g:4.5g:0.5g:30mL, the mass fraction of sodium hydroxide solution is 50%, and the molecular weight of polyvinyl alcohol is 2000.

[0050] The molar ratio of the amino group on the pretreated graphene and the epoxy group on the modifier described in step A2 is 1:1, the dosage ratio of polyethylene glycol, boric acid and modified graphene is 10mmo l:10mmo l:1g, the dosage of boron trichloride is 3% of the mass of boric acid, the molecular weight of polyethylene glycol is 2000, and the mass ratio of the precursor and the modified carrier is 1:10.

[0051] The modified carrier is prepared by the following steps:

[0052] Step B1: 2,2'-diamino-4,4'-bithiazole, epoxy octane and DMF were mixed evenly, and reacted for 5 hours at a speed of 200 r / min, a temperature of 40°C and a pH value of 11 to obtain intermediate 1; intermediate 1, terephthalaldehyde, p-toluenesulfonic acid and toluene were mixed evenly, and reacted for 7 hours at a speed of 80 r / min and a temperature of 120°C to obtain intermediate 2;

[0053] Step B2: Intermediate 2, (3-aminopropyl)dimethylethoxysilane and DMF were mixed, and the mixture was reacted at a speed of 300 r / min and a temperature of 50° C. for 5 h to obtain a modified monomer. The modified monomer, dimethyldichlorosilane and deionized water were mixed, and the mixture was stirred at a speed of 300 r / min and a temperature of 70° C. for 15 min. Concentrated sulfuric acid and hexamethyldisiloxane were added, and the mixture was reacted for 6 h. The pH was adjusted to neutral to obtain a modified ligand.

[0054] Step B3: The modified ligand, lanthanum nitrate hexahydrate, DMF and deionized water are mixed, and the reaction is carried out at a frequency of 30 kHz and a temperature of 30°C for 3 hours, and then the temperature is raised to 155°C and the reaction is continued for 15 hours to obtain a carrier. Phosphoric acid, lithium hydroxide, ferrous sulfate heptahydrate and deionized water are evenly mixed, and the reaction is carried out at a speed of 500 r / min and a temperature of 185°C for 1.5 hours. The carrier is added, and the reaction is continued for 10 hours. After that, it is filtered and dried, and the substrate is calcined at a temperature of 850°C in a nitrogen atmosphere for 3 hours to obtain a modified carrier.

[0055] The molar ratio of 2,2'-diamino-4,4'-bithiazole to octane oxide in step B1 is 1:4, the molar ratio of intermediate 1 to terephthalaldehyde is 3:4, and the amount of p-toluenesulfonic acid used is 1% of the mass of intermediate 1.

[0056] The molar ratio of intermediate 2 and (3-aminopropyl)dimethylethoxysilane described in step B2 is 1:2, the amount ratio of modified monomer, dimethyldichlorosilane, deionized water and hexamethyldisiloxane is 1mmol:3mmol:20mL:2mmol, and the amount of concentrated sulfuric acid is 2% of the mass of the modified monomer.

[0057] The usage ratio of the modified ligand and lanthanum nitrate hexahydrate described in step B3 is 1.1g:2mmo l, and the usage ratio of phosphoric acid, lithium hydroxide, ferrous sulfate heptahydrate, deionized water and carrier is 10.6mmo l:30mmo l:10mmo l:40mL:2g.

[0058] Comparative Example 1

[0059] Compared with Example 1, this comparative example uses a modified carrier instead of a positive electrode material, and the remaining steps are the same.

[0060] Comparative Example 2

[0061] The local proportion is compared with Example 1, in which the precursor is replaced by modified graphene, and the other steps are the same.

[0062] Comparative Example 3

[0063] Compared with Example 1, this comparative example uses 2,2'-diamino-4,4'-bithiazole to replace the modified ligand, and the remaining steps are the same.

[0064] The positive electrode materials prepared in Examples 1-3 and Comparative Examples 1-3, acetylene black, polyvinylidene fluoride and N-methylpyrrolidone were mixed into a slurry in a mass ratio of 8:1:1:1, and then coated on an aluminum foil, dried and cut into pieces with a diameter of 13 mm. Celgard 2500 diaphragm, gasket, and shrapnel nuclear battery shell were used as a set of CR2032 button battery materials, and the electrolyte was LiPF6 (ethylene carbonate, dimethyl carbonate and diethyl carbonate in a volume ratio of 1:1:1) to make battery samples.

[0065] The electrochemical properties of the positive electrode material were tested using the Blue Electric Battery Test System: the battery was tested for the first charge and discharge at a rate of 0.1C at a constant temperature of 25°C, with a test voltage range of 2.0-3.8V; the cycle life test was performed at a charge and discharge rate of 1C, with a test voltage range of 2.0-3.8V; the number of cycles was 500, and the test results are shown in the following table.

[0066]

[0067] It can be seen from the above table that the present application has very good cycle performance and charge-discharge capacity.

[0068] The above contents are merely examples and explanations of the concept of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing a positive electrode material for a lithium iron phosphate battery, characterized in that: The specific steps include: Step A1: dispersing graphene oxide in anhydrous ethanol, stirring and adding KH550 and deionized water to react to obtain pretreated graphene, uniformly mixing polyvinyl alcohol, epichlorohydrin, tetrabutylammonium bromide and DMF, introducing nitrogen protection to react, cooling and adding sodium hydroxide solution to react to obtain a modifier; Step A2: pretreated graphene, a modifier and DMF are mixed and reacted to obtain modified graphene, polyethylene glycol, boric acid, boron trichloride and toluene are mixed and reacted, and then the modified graphene is added and the reaction is continued to obtain a precursor, the precursor, the modified carrier and ethanol are mixed and ground evenly, and then calcined under a nitrogen atmosphere to obtain a positive electrode material; The modified carrier is prepared by the following steps: Step B1: 2,2'-diamino-4,4'-bithiazole, octyl oxide and DMF are mixed for reaction to obtain intermediate 1, and intermediate 1, terephthalaldehyde, p-toluenesulfonic acid and toluene are mixed for reaction to obtain intermediate 2; Step B2: The intermediate 2, (3-aminopropyl)dimethylethoxysilane and DMF are mixed and reacted to obtain a modified monomer, the modified monomer, dimethyldichlorosilane and deionized water are mixed and stirred, concentrated sulfuric acid and hexamethyldisiloxane are added, reacted, and the pH is adjusted to neutral to obtain a modified ligand; Step B3: After the modified ligand, lanthanum nitrate hexahydrate, DMF and deionized water are mixed and reacted, the temperature is increased to continue the reaction to obtain a carrier, phosphoric acid, lithium hydroxide, ferrous sulfate heptahydrate and deionized water are mixed and reacted, and the carrier is added, and the reaction is continued, and then filtered and dried. The substrate is calcined under a nitrogen atmosphere to obtain a modified carrier.

2. The method for preparing a positive electrode material for a lithium iron phosphate battery according to claim 1, characterized in that: The amount of KH550 used in step A1 is 2-3% of the mass of graphene oxide, and the amount ratio of polyvinyl alcohol, epichlorohydrin, tetrabutylammonium bromide and sodium hydroxide solution is 20g:4.5g:0.5g:30mL.

3. The method for preparing a positive electrode material for a lithium iron phosphate battery according to claim 1, characterized in that: The molar ratio of the amino group on the pretreated graphene and the epoxy group on the modifier in step A2 is 1:1, the amount ratio of polyethylene glycol, boric acid and modified graphene is 10mmol:10mmol:1g, and the mass ratio of the precursor and the modified carrier is 1:

10.

4. The method for preparing a positive electrode material for a lithium iron phosphate battery according to claim 1, characterized in that: The molar ratio of 2,2'-diamino-4,4'-bithiazole to octane oxide in step B1 is 1:4, and the molar ratio of intermediate 1 to terephthalaldehyde is n:n+1, where n is a natural number greater than 0.

5. The method for preparing a positive electrode material for a lithium iron phosphate battery according to claim 1, characterized in that: The molar ratio of intermediate 2 and (3-aminopropyl)dimethylethoxysilane in step B2 is 1:2, and the amount ratio of modified monomer, dimethyldichlorosilane, deionized water and hexamethyldisiloxane is 1mmol:3mmol:20mL:2mmol.

6. The method for preparing a positive electrode material for a lithium iron phosphate battery according to claim 1, characterized in that: The modified ligand and lanthanum nitrate hexahydrate used in step B3 are in a ratio of 1.1 g:2 mmol, and the phosphoric acid, lithium hydroxide, ferrous sulfate heptahydrate, deionized water and carrier are in a ratio of 10.6 mmol:30 mmol:10 mmol:40 mL:2 g.

7. A positive electrode material for lithium iron phosphate battery, characterized in that: Prepared according to any one of claims 1 to 6.

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