A method for preparing lithium iron phosphate positive electrode material using iron phosphate

Abstract

The invention discloses a method for preparing lithium iron phosphate cathode material using iron phosphate, comprising the following steps: 45 55 parts of flaky graphene are first fed into 70 80 parts of hydrochloric acid solution with a mass fraction of 2% and stirred evenly, then washed and dried, and then fed into a proton irradiation box for irradiation treatment, with an irradiation power of 500 800 W and an irradiation time of 20 30 min. The irradiation terminates to obtain an irradiated graphene agent. The lithium iron phosphate cathode material of the present invention adopts flaky graphene to be stirred and activated by hydrochloric acid solution to disperse, improve its activation degree and dispersion, and is further excited by proton treatment, so as to better coordinate with a doped calcium sulfate whisker regulator, and jointly synergize to improve the lithium iron phosphate primary body; optimize the cycle discharge capacity retention rate of the product, and improve the resistivity of the product.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium iron phosphate positive electrode materials, and in particular to a method for preparing lithium iron phosphate positive electrode materials by utilizing iron phosphate. Background Art

[0002] Lithium-ion batteries have high energy density, long cycle life, no memory effect, low self-discharge rate and good environmental compatibility. At a time when fossil energy is becoming increasingly depleted and the environment is deteriorating, they play a vital role in alleviating the energy crisis and curbing environmental degradation. Lithium-ion batteries are mainly composed of positive electrodes, negative electrodes, electrolytes and separators. Among them, the positive and negative electrodes are active substances, which are energy carriers. Currently, commercial lithium-ion positive electrode materials are mainly lithium iron phosphate, ternary materials (nickel-cobalt-manganese ternary material NCM, nickel-cobalt-aluminum ternary material NCA) and lithium manganese oxide. Among them, lithium iron phosphate has attracted widespread attention from the world due to its low price, non-toxicity, environmental friendliness, stable structure and high theoretical specific capacity. Compared with other positive electrode materials, lithium iron phosphate power batteries have obvious advantages in safety performance and cycle life, and their application in the field of electric vehicles is increasing rapidly.

[0003] Chinese patent document CN110857216B discloses a battery-grade iron phosphate precursor, lithium iron phosphate, and its preparation method and application. The document provides the preparation of lithium iron phosphate, but the existing lithium iron phosphate positive electrode material has a high resistivity, which leads to an increase in the internal resistance of the battery. At the same time, the cycle discharge capacity retention rate is poor, making it difficult to coordinately improve the resistivity and cycle discharge capacity retention rate of the product, limiting the product's efficiency. Summary of the Invention

[0004] In view of the defects of the prior art, the purpose of the present invention is to provide a method for preparing a lithium iron phosphate positive electrode material using iron phosphate, so as to solve the problems raised in the above background technology.

[0005] The present invention solves the technical problem by adopting the following technical solutions:

[0006] The present invention provides a method for preparing a lithium iron phosphate positive electrode material using iron phosphate, comprising the following steps:

[0007] Step 1: 45-55 parts of flake graphene are first added to 70-80 parts of 2% hydrochloric acid solution by mass and stirred evenly, then washed with water, dried, and then irradiated in a proton irradiation box with an irradiation power of 500-800W and an irradiation time of 20-30 minutes. After the irradiation is completed, an irradiated graphene agent is obtained;

[0008] Step 2: Mixing the irradiated graphene agent and the doped calcium sulfate whisker regulator in a weight ratio of 3:1 to obtain a composite regulator;

[0009] Step 3: Adding 10-15% of the total amount of the lithium iron phosphate primary body to the composite regulator, stirring evenly, and sending the mixture into a ball mill for ball milling at a ball milling speed of 1000-1500 r / min for 1-2 hours to obtain a ball milled composite body;

[0010] Deionized water, lithium carbonate, and a carbon source mixed with glucose and citric acid (at a molar ratio of 7:3) are added to an iron phosphate precursor to prepare a mixture, the mixture is sand-milled to a particle size of 450 nm, the sand-milled mixture is spray-dried, and the dried material is then calcined at 650° C. for 10 h in a nitrogen atmosphere to obtain lithium iron phosphate;

[0011] The lithium iron phosphate precursor is prepared by using iron phosphate, and the preparation is based on the Chinese patent document CN110857216B. The preparation of the lithium iron phosphate precursor is based on the existing technology;

[0012] Step 4: The ball-milled composite is then placed into a 3-5 times larger modified compounding solution for stirring and modification. After stirring, the mixture is washed with water and dried.

[0013] Step 5: Finally, the lithium iron phosphate positive electrode material of the present invention can be obtained by performing a heat cycle improvement treatment.

[0014] Preferably, the preparation method of the doped calcium sulfate whisker conditioning agent is:

[0015] S01: adding calcium sulfate whiskers to a nitric acid solution at a weight ratio of 1:3, stirring at 55-65° C. for 45-55 minutes at a stirring speed of 350-450 r / min, washing with water, and drying to obtain pretreated calcium sulfate whiskers;

[0016] S02: Add 1-3 parts of sodium methylene bisnaphthalene sulfonate and 2-5 parts of polyaniline to 10-20 parts of ethanol solvent, then add 0.25-0.35 parts of samarium oxide and 0.1-0.4 parts of glycolic acid, and stir evenly to obtain a prepared solution;

[0017] S03: adding the pretreated calcium sulfate whiskers to 3-5 times the prepared liquid, ultrasonically dispersing for 10-20 minutes at 400-500W, washing with water and drying to obtain a doped calcium sulfate whisker regulator.

[0018] Preferably, the concentration of the nitric acid solution is 1-1.5 mol / L.

[0019] Preferably, the stirring temperature of the stirring modification treatment in step 4 is 42-46° C., the stirring reaction is carried out for 35-40 minutes, and the stirring speed is 550-650 r / min.

[0020] Preferably, the preparation method of the modified compounding liquid is:

[0021] S01: 5-9 parts by mass of a 5% aqueous solution of citric acid, 1-3 parts of silica sol, and 1-2 parts of hexadecyltrimethylammonium bromide are stirred and mixed to obtain a modified solution;

[0022] S02: adding a modification liquid of 10-20% of the total amount of nano zinc oxide to the nano zinc oxide, and then ball milling at a speed of 1000-1200 r / min for 1-2 hours. After the ball milling is completed, washing with water and drying to obtain regulated nano zinc oxide;

[0023] S03: 3-6 parts of regulated nano zinc oxide are added to 10-15 parts of deionized water and stirred evenly, and then 1-2 parts of 5% by mass dopamine solution, 0.45-0.55 parts of lanthanum sulfate and 0.2-0.3 parts of phosphate buffer solution are added and stirred evenly to obtain a nano zinc oxide prepared solution;

[0024] S04: Add 5-7 parts of the preparation agent into the nano zinc oxide preparation solution in S03 and stir thoroughly to obtain a modified compounding solution.

[0025] Preferably, the pH value of the phosphate buffer solution is 5.0-5.5.

[0026] Preferably, the preparation method of the formulation is:

[0027] Add 3-5 parts of sodium silicate to 10-15 parts of water, heat to 60-80°C, and stir evenly to prepare a sodium silicate aqueous solution; then place 3-6 parts of nano-bentonite into 10-15 parts of chitosan aqueous solution, followed by adding 1-2 parts of silane coupling agent KH560 and 0.15-0.35 parts of sodium silicate aqueous solution, stir thoroughly, wash with water, and dry to obtain a preparation.

[0028] Preferably, the mass fraction of the chitosan aqueous solution is 6-8%.

[0029] Preferably, the specific steps of the thermal cycle improvement treatment are:

[0030] First, heat the reaction at 75-85°C for 10-20 minutes; then heat to 130-140°C at a rate of 1-3°C / min, keep warm for 5-10 minutes, and then cool to 40-45°C at a rate of 2-4°C / min to obtain a heat-insulated product;

[0031] The heat-insulated product is then stirred and dispersed evenly in a chitosan aqueous solution with a mass fraction of 5% and a volume of 6-8 times the total amount of the heat-insulated product, washed with water, dried, and finally heat-pressed.

[0032] Preferably, the pressure of the hot pressing treatment is 10-15 MPa, the temperature is 55-65° C., and the treatment time is 30-40 min.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. The lithium iron phosphate positive electrode material of the present invention adopts flaky graphene to be stirred and activated and dispersed by hydrochloric acid solution, thereby improving its activation and dispersion. Through proton treatment, the active energy is further stimulated, thereby better coordinating with the doped calcium sulfate whisker regulator to synergistically improve the lithium iron phosphate primary body; optimize the cycle discharge capacity retention rate of the product, and improve the resistivity of the product. The doped calcium sulfate whisker regulator is activated by calcium sulfate whiskers through a nitric acid solution, and is modified and optimized by a mixed solution prepared by sodium methylene bisnaphthalene sulfonate, polyaniline, samarium oxide and glycolic acid. The calcium sulfate whiskers are supported and dispersed in the matrix. Through the optimization and improvement of the mixed solution, the optimized doped calcium sulfate whisker regulator and the flaky graphene have a synergistic effect, optimized and coordinated, and provide a stable cycle discharge capacity for the product;

[0035] 2. The lithium iron phosphate precursor combined with the compound regulator is stirred and ball-milled, and the degree of modification of the lithium iron phosphate precursor is enhanced. The modified lithium iron phosphate precursor has a better effect in the positive electrode material and can optimize the thermal cycle discharge capacity stability;

[0036] 3. Modification of modified compound liquid by stirring: Nano zinc oxide and modifying liquid are pre-modified by ball milling to optimize the activity and dispersibility of nano zinc oxide. Nano zinc oxide compounding liquid is formed by combining dopamine solution, lanthanum sulfate and phosphate buffer solution, and then further coordinated with the compounding agent. The prepared modified compounding liquid further optimizes and modifies the ball milled compound body, further coordinates and optimizes the cyclic discharge capacity and resistivity of the product, and optimizes the thermal stability of the product. The compounding agent adopts nano bentonite, chitosan aqueous solution and silane coupling agent KH560 sodium silicate aqueous solution for coordinated improvement. The lamellar structure of nano bentonite is coordinated and optimized between the raw materials. The compounding agent cooperates with the nano zinc oxide compounding liquid to synergistically enhance the performance of the product.

[0037] 4. Finally, the thermal cycle improvement treatment is carried out, firstly, the thermal reaction is carried out at a temperature of 75-85°C for 10-20 minutes; then the temperature is raised to 130-140°C at a rate of 1-3°C / min, and the temperature is kept warm for 5-10 minutes, and then the temperature is cooled to 40-45°C at a rate of 2-4°C / min to obtain a heat preservation product, the reactant is activated by thermal reaction, and the stability of the system is optimized by heating and cooling at a constant temperature rate. Then, at 40-45°C, the activity and dispersion of the system are further enhanced by combining with chitosan aqueous solution, and the stability of the system is further enhanced by combining with hot pressing treatment, so that the cyclic discharge capacity retention rate and resistivity of the product are coordinated and optimized, and the thermal stability of the product is further optimized. DETAILED DESCRIPTION

[0038] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0039] A method for preparing a lithium iron phosphate positive electrode material using iron phosphate in this embodiment includes the following steps:

[0040] Step 1: 45-55 parts of flake graphene are first added to 70-80 parts of 2% hydrochloric acid solution by mass and stirred evenly, then washed with water, dried, and then irradiated in a proton irradiation box with an irradiation power of 500-800W and an irradiation time of 20-30 minutes. After the irradiation is completed, an irradiated graphene agent is obtained;

[0041] Step 2: Mixing the irradiated graphene agent and the doped calcium sulfate whisker regulator in a weight ratio of 3:1 to obtain a composite regulator;

[0042] Step 3: Adding 10-15% of the total amount of the lithium iron phosphate primary body to the composite regulator, stirring evenly, and sending the mixture into a ball mill for ball milling at a ball milling speed of 1000-1500 r / min for 1-2 hours to obtain a ball milled composite body;

[0043] Step 4: The ball-milled composite is then placed into a 3-5 times larger modified compounding solution for stirring and modification. After stirring, the mixture is washed with water and dried.

[0044] Step 5: Finally, the lithium iron phosphate positive electrode material of the present invention can be obtained by performing a heat cycle improvement treatment.

[0045] The preparation method of the doped calcium sulfate whisker conditioning agent of this embodiment is:

[0046] S01: adding calcium sulfate whiskers to a nitric acid solution at a weight ratio of 1:3, stirring at 55-65° C. for 45-55 minutes at a stirring speed of 350-450 r / min, washing with water, and drying to obtain pretreated calcium sulfate whiskers;

[0047] S02: Add 1-3 parts of sodium methylene bisnaphthalene sulfonate and 2-5 parts of polyaniline to 10-20 parts of ethanol solvent, then add 0.25-0.35 parts of samarium oxide and 0.1-0.4 parts of glycolic acid, and stir evenly to obtain a prepared solution;

[0048] S03: adding the pretreated calcium sulfate whiskers to 3-5 times the prepared liquid, ultrasonically dispersing for 10-20 minutes at 400-500W, washing with water and drying to obtain a doped calcium sulfate whisker regulator.

[0049] The concentration of the nitric acid solution in this embodiment is 1-1.5 mol / L.

[0050] In step 4 of this embodiment, the stirring temperature for the stirring modification treatment is 42-46° C., the stirring reaction is carried out for 35-40 minutes, and the stirring speed is 550-650 r / min.

[0051] The preparation method of the modified compounding liquid of this embodiment is:

[0052] S01: 5-9 parts by mass of a 5% aqueous solution of citric acid, 1-3 parts of silica sol, and 1-2 parts of hexadecyltrimethylammonium bromide are stirred and mixed to obtain a modified solution;

[0053] S02: adding a modification liquid of 10-20% of the total amount of nano zinc oxide to the nano zinc oxide, and then ball milling at a speed of 1000-1200 r / min for 1-2 hours. After the ball milling is completed, washing with water and drying to obtain regulated nano zinc oxide;

[0054] S03: 3-6 parts of regulated nano zinc oxide are added to 10-15 parts of deionized water and stirred evenly, and then 1-2 parts of 5% by mass dopamine solution, 0.45-0.55 parts of lanthanum sulfate and 0.2-0.3 parts of phosphate buffer solution are added and stirred evenly to obtain a nano zinc oxide prepared solution;

[0055] S04: Add 5-7 parts of the preparation agent into the nano zinc oxide preparation solution in S03 and stir thoroughly to obtain a modified compounding solution.

[0056] The pH value of the phosphate buffer solution of this embodiment is 5.0-5.5.

[0057] The preparation method of the blending agent of this embodiment is as follows:

[0058] Add 3-5 parts of sodium silicate to 10-15 parts of water, heat to 60-80°C, and stir evenly to prepare a sodium silicate aqueous solution; then place 3-6 parts of nano-bentonite into 10-15 parts of chitosan aqueous solution, followed by adding 1-2 parts of silane coupling agent KH560 and 0.15-0.35 parts of sodium silicate aqueous solution, stir thoroughly, wash with water, and dry to obtain a preparation.

[0059] The mass fraction of the chitosan aqueous solution in this embodiment is 6-8%.

[0060] The specific steps of the thermal cycle improvement process of this embodiment are:

[0061] First, heat the reaction at 75-85°C for 10-20 minutes; then heat to 130-140°C at a rate of 1-3°C / min, keep warm for 5-10 minutes, and then cool to 40-45°C at a rate of 2-4°C / min to obtain a heat-insulated product;

[0062] The heat-insulated product is then stirred and dispersed evenly in a chitosan aqueous solution with a mass fraction of 5% and a volume of 6-8 times the total amount of the heat-insulated product, washed with water, dried, and finally heat-pressed.

[0063] The pressure of the hot pressing treatment in this embodiment is 10-15 MPa, the temperature is 55-65° C., and the treatment time is 30-40 minutes.

[0064] Example 1.

[0065] A method for preparing a lithium iron phosphate positive electrode material using iron phosphate in this embodiment includes the following steps:

[0066] Step 1: 45 parts of flake graphene are first added to 70 parts of 2% hydrochloric acid solution by mass and stirred evenly, then washed with water, dried, and then irradiated in a proton irradiation box at an irradiation power of 500 W and an irradiation time of 20 min. After the irradiation is completed, an irradiated graphene agent is obtained;

[0067] Step 2: Mixing the irradiated graphene agent and the doped calcium sulfate whisker regulator in a weight ratio of 3:1 to obtain a composite regulator;

[0068] Step 3: Adding 10% of the total amount of the lithium iron phosphate primary body to the composite regulator to the lithium iron phosphate primary body, stirring evenly, and sending the mixture into a ball mill for ball milling at a ball milling speed of 1000 r / min and a ball milling time of 1 hour to obtain a ball milled composite body;

[0069] Step 4: The ball-milled composite is then placed into a 3-fold modified composite solution for stirring and modification. After stirring is complete, the composite is washed with water and dried.

[0070] Step 5: Finally, the lithium iron phosphate positive electrode material of the present invention can be obtained by performing a heat cycle improvement treatment.

[0071] The preparation method of the doped calcium sulfate whisker conditioning agent of this embodiment is:

[0072] S01: adding calcium sulfate whiskers to a nitric acid solution at a weight ratio of 1:3, stirring at 55°C for 45 minutes at a stirring speed of 350 r / min, washing with water, and drying to obtain pretreated calcium sulfate whiskers;

[0073] S02: Add 1 part of sodium methylene bisnaphthalene sulfonate and 2 parts of polyaniline to 10 parts of ethanol solvent, then add 0.25 parts of samarium oxide and 0.1 parts of glycolic acid, and stir well to obtain a prepared solution;

[0074] S03: Add the pretreated calcium sulfate whiskers to 3 times the prepared liquid, perform ultrasonic dispersion treatment for 10 minutes at 400W, finish the ultrasonic treatment, wash with water, and dry to obtain a doped calcium sulfate whisker regulator.

[0075] The concentration of the nitric acid solution in this embodiment is 1 mol / L.

[0076] In step 4 of this embodiment, the stirring temperature for the stirring modification treatment is 42° C., the stirring reaction is carried out for 35 minutes, and the stirring speed is 550 r / min.

[0077] The preparation method of the modified compounding liquid of this embodiment is:

[0078] S01: 5 parts by mass of a 5% aqueous solution of citric acid, 1 part of silica sol, and 1 part of hexadecyltrimethylammonium bromide were stirred and mixed to obtain a modified solution;

[0079] S02: adding a modification liquid of 10% of the total amount of nano zinc oxide to the nano zinc oxide, and then ball milling at a speed of 1000 r / min for 1 hour. After the ball milling is completed, washing with water and drying are performed to obtain regulated nano zinc oxide;

[0080] S03: 3 parts of regulated nano zinc oxide were added to 10 parts of deionized water and stirred evenly, and then 1 part of 5% dopamine solution, 0.45 parts of lanthanum sulfate and 0.2 parts of phosphate buffer solution were added and stirred evenly to obtain a nano zinc oxide preparation solution;

[0081] S04: Add 5 parts of the preparation agent into the nano zinc oxide preparation solution in S03 and stir thoroughly to obtain a modified compounding solution.

[0082] The pH value of the phosphate buffer solution in this example is 5.0.

[0083] The preparation method of the blending agent of this embodiment is as follows:

[0084] Add 3 parts of sodium silicate to 10 parts of water, heat to 60°C, and stir evenly to prepare a sodium silicate aqueous solution; then place 3 parts of nano-bentonite into 10 parts of chitosan aqueous solution, followed by adding 1 part of silane coupling agent KH560 and 0.15 parts of sodium silicate aqueous solution, stir thoroughly, wash with water, and dry to obtain a preparation.

[0085] The mass fraction of the chitosan aqueous solution in this embodiment is 6%.

[0086] The specific steps of the thermal cycle improvement process of this embodiment are:

[0087] The reaction was first carried out at 75°C for 10 min; then the temperature was raised to 130°C at a rate of 1°C / min, kept at that temperature for 5 min, and then cooled to 40°C at a rate of 2°C / min to obtain a heat-insulated product;

[0088] The heat-insulated product is then stirred and dispersed evenly in a chitosan aqueous solution with a mass fraction of 5% and a volume 6 times the total mass of the heat-insulated product, washed with water, dried, and finally heat-pressed.

[0089] The hot pressing treatment in this embodiment is performed at a pressure of 10 MPa, a temperature of 55° C., and a treatment time of 30 minutes.

[0090] Example 2.

[0091] A method for preparing a lithium iron phosphate positive electrode material using iron phosphate in this embodiment includes the following steps:

[0092] Step 1: 55 parts of flake graphene are first added to 80 parts of 2% hydrochloric acid solution by mass and stirred evenly, then washed with water, dried, and then irradiated in a proton irradiation box at an irradiation power of 800 W and an irradiation time of 30 minutes. After the irradiation is completed, an irradiated graphene agent is obtained;

[0093] Step 2: Mixing the irradiated graphene agent and the doped calcium sulfate whisker regulator in a weight ratio of 3:1 to obtain a composite regulator;

[0094] Step 3: Adding 15% of the total amount of the lithium iron phosphate primary body to the composite regulator to the lithium iron phosphate primary body, stirring evenly, and sending the mixture into a ball mill for ball milling at a ball milling speed of 1500 r / min and a ball milling time of 2 h to obtain a ball milled composite body;

[0095] Step 4: The ball-milled composite is then placed into a 5-fold modified composite solution for stirring and modification. After stirring is completed, the composite is washed with water and dried.

[0096] Step 5: Finally, the lithium iron phosphate positive electrode material of the present invention can be obtained by performing a heat cycle improvement treatment.

[0097] The preparation method of the doped calcium sulfate whisker conditioning agent of this embodiment is:

[0098] S01: adding calcium sulfate whiskers to a nitric acid solution at a weight ratio of 1:3, stirring at 65°C for 55 minutes at a stirring speed of 450 r / min, washing with water, and drying to obtain pretreated calcium sulfate whiskers;

[0099] S02: 3 parts of sodium methylene bisnaphthalene sulfonate and 5 parts of polyaniline were added to 20 parts of ethanol solvent, followed by 0.35 parts of samarium oxide and 0.4 parts of glycolic acid, and stirred to obtain a mixed solution;

[0100] S03: adding the pretreated calcium sulfate whiskers to 5 times the prepared liquid, ultrasonically dispersing for 20 minutes at 500W, and washing with water and drying to obtain a doped calcium sulfate whisker regulator.

[0101] The concentration of the nitric acid solution in this embodiment is 1.5 mol / L.

[0102] In step 4 of this embodiment, the stirring temperature for the stirring modification treatment is 46° C., the stirring reaction is carried out for 40 minutes, and the stirring speed is 650 r / min.

[0103] The preparation method of the modified compounding liquid of this embodiment is:

[0104] S01: 9 parts by mass of a 5% aqueous solution of citric acid, 3 parts of silica sol, and 2 parts of cetyltrimethylammonium bromide were stirred and mixed to obtain a modified solution;

[0105] S02: adding a modification liquid of 20% of the total amount of nano zinc oxide to the nano zinc oxide, and then ball milling at a speed of 1200 r / min for 2 hours. After the ball milling is completed, washing with water and drying are performed to obtain regulated nano zinc oxide;

[0106] S03: 6 parts of regulated nano zinc oxide were added to 15 parts of deionized water and stirred evenly, and then 2 parts of 5% by mass dopamine solution, 0.55 parts of lanthanum sulfate and 0.3 parts of phosphate buffer solution were added and stirred evenly to obtain a nano zinc oxide prepared solution;

[0107] S04: Add 7 parts of the preparation agent into the nano zinc oxide preparation solution in S03 and stir thoroughly to obtain a modified compounding solution.

[0108] The pH value of the phosphate buffer solution in this example is 5.5.

[0109] The preparation method of the blending agent of this embodiment is as follows:

[0110] Add 5 parts of sodium silicate to 15 parts of water, heat to 80°C, and stir evenly to prepare a sodium silicate aqueous solution; then place 6 parts of nano-bentonite into 15 parts of chitosan aqueous solution, followed by adding 2 parts of silane coupling agent KH560 and 0.35 parts of sodium silicate aqueous solution, stir thoroughly, wash with water, and dry to obtain a preparation.

[0111] The mass fraction of the chitosan aqueous solution in this embodiment is 8%.

[0112] The specific steps of the thermal cycle improvement process of this embodiment are:

[0113] The reaction was first carried out at 85°C for 20 minutes; then the temperature was raised to 140°C at a rate of 3°C / min, kept at that temperature for 10 minutes, and then cooled to 45°C at a rate of 4°C / min to obtain a heat-insulated product;

[0114] The heat-insulated product is then stirred and dispersed evenly in a chitosan aqueous solution with a mass fraction of 5% and a volume 8 times the total mass of the heat-insulated product, washed with water, dried, and finally heat-pressed.

[0115] The hot pressing treatment in this embodiment is performed at a pressure of 15 MPa, a temperature of 65° C., and a treatment time of 40 minutes.

[0116] Example 3.

[0117] A method for preparing a lithium iron phosphate positive electrode material using iron phosphate in this embodiment includes the following steps:

[0118] Step 1: 50 parts of flake graphene are first added to 75 parts of 2% by mass hydrochloric acid solution and stirred evenly, then washed with water, dried, and then irradiated in a proton irradiation box. The irradiation power is 650W and the irradiation time is 25 minutes. After the irradiation is completed, an irradiated graphene agent is obtained;

[0119] Step 2: Mixing the irradiated graphene agent and the doped calcium sulfate whisker regulator in a weight ratio of 3:1 to obtain a composite regulator;

[0120] Step 3: Adding 12.5% ​​of the total amount of the lithium iron phosphate primary body to the composite regulator to the lithium iron phosphate primary body, stirring evenly, and sending the mixture into a ball mill for ball milling at a ball milling speed of 1250 r / min and a ball milling time of 1.5 h to obtain a ball-milled composite body;

[0121] Step 4: The ball-milled composite is then placed into a 4-fold modified composite solution for stirring and modification. After stirring, the composite is washed with water and dried.

[0122] Step 5: Finally, the lithium iron phosphate positive electrode material of the present invention can be obtained by performing a heat cycle improvement treatment.

[0123] The preparation method of the doped calcium sulfate whisker conditioning agent of this embodiment is:

[0124] S01: adding calcium sulfate whiskers to a nitric acid solution at a weight ratio of 1:3, stirring at 60°C for 50 minutes at a stirring speed of 400 r / min, washing with water, and drying to obtain pretreated calcium sulfate whiskers;

[0125] S02: Add 1-3 parts of sodium methylene bisnaphthalene sulfonate and 2-5 parts of polyaniline to 10-20 parts of ethanol solvent, then add 0.30 parts of samarium oxide and 0.25 parts of glycolic acid, and stir well to obtain a prepared solution;

[0126] S03: adding the pretreated calcium sulfate whiskers to 4 times the prepared solution, ultrasonically dispersing for 15 minutes at 450W, and then washing with water and drying to obtain a doped calcium sulfate whisker conditioning agent.

[0127] The concentration of the nitric acid solution in this embodiment is 1.25 mol / L.

[0128] In step 4 of this embodiment, the stirring temperature for the stirring modification treatment is 44° C., the stirring reaction is carried out for 37 minutes, and the stirring speed is 600 r / min.

[0129] The preparation method of the modified compounding liquid of this embodiment is:

[0130] S01: 7 parts by mass of a 5% aqueous solution of citric acid, 2 parts of silica sol, and 1.5 parts of hexadecyltrimethylammonium bromide were stirred and mixed to obtain a modified solution;

[0131] S02: adding a modifying liquid of 15% of the total amount of nano zinc oxide to the nano zinc oxide, and then ball milling at a speed of 1100 r / min for 1.5 hours. After the ball milling is completed, washing with water and drying are performed to obtain regulated nano zinc oxide;

[0132] S03: 4.5 parts of regulated nano zinc oxide were added to 12 parts of deionized water and stirred evenly, and then 1.5 parts of 5% dopamine solution, 0.50 parts of lanthanum sulfate and 0.25 parts of phosphate buffer solution were added and stirred evenly to obtain a nano zinc oxide prepared solution;

[0133] S04: Add 6 parts of the preparation agent into the nano zinc oxide preparation solution in S03 and stir thoroughly to obtain a modified compounding solution.

[0134] The pH value of the phosphate buffer solution in this example is 5.2.

[0135] The preparation method of the blending agent of this embodiment is as follows:

[0136] Add 4 parts of sodium silicate to 12 parts of water, heat to 70°C, and stir evenly to prepare a sodium silicate aqueous solution; then place 5 parts of nano-bentonite into 12 parts of chitosan aqueous solution, followed by adding 1.5 parts of silane coupling agent KH560 and 0.20 parts of sodium silicate aqueous solution, stir thoroughly, wash with water, and dry to obtain a preparation.

[0137] The mass fraction of the chitosan aqueous solution in this embodiment is 7%.

[0138] The specific steps of the thermal cycle improvement process of this embodiment are:

[0139] The reaction was first carried out at 80°C for 15 minutes; then the temperature was raised to 135°C at a rate of 2°C / min, kept at that temperature for 7.5 minutes, and then cooled to 42°C at a rate of 3°C / min to obtain a heat-insulated product;

[0140] The heat-insulated product is then stirred and dispersed evenly in a chitosan aqueous solution with a mass fraction of 5% and a volume 7 times the total mass of the heat-insulated product, washed with water, dried, and finally heat-pressed.

[0141] The hot pressing treatment in this embodiment is performed at a pressure of 12.5 MPa, a temperature of 60° C., and a treatment time of 35 minutes.

[0142] Comparative Example 1.

[0143] The difference from Example 3 is that the irradiated graphene agent is replaced by graphene.

[0144] Comparative Example 2.

[0145] The difference from Example 3 is that no doped calcium sulfate whisker regulator is added.

[0146] Comparative Example 3.

[0147] The difference from Example 3 is that the doped calcium sulfate whisker regulator is replaced by calcium sulfate whiskers.

[0148] Comparative Example 4.

[0149] The difference from Example 3 is that the preparation method of the doped calcium sulfate whisker regulator is different:

[0150] Add 2-5 parts of polyaniline to 10-20 parts of ethanol solvent, then add 0.30 parts of samarium oxide and stir evenly to obtain a prepared solution;

[0151] S03: Add calcium sulfate whiskers to 4 times the prepared liquid, perform ultrasonic dispersion treatment for 15 minutes at 450W, finish ultrasonication, wash with water, and dry to obtain a doped calcium sulfate whisker regulator.

[0152] Comparative Example 5.

[0153] The difference from Example 3 is that no modified polyhydration liquid treatment was used.

[0154] Comparative Example 6.

[0155] The difference from Example 3 is that the adjustable nano zinc oxide is replaced by nano zinc oxide in the preparation of the modified compounding solution.

[0156] Comparative Example 7.

[0157] The difference from Example 3 is that no dopamine solution or lanthanum sulfate is added in the preparation of the nano zinc oxide preparation solution of the modified compounding solution.

[0158] Comparative Example 8.

[0159] The difference from Example 3 is that no adjusting agent is added in the preparation of the modified compounding solution.

[0160] Comparative Example 9.

[0161] The difference from Example 3 is that the preparation method of the adjustable nano zinc oxide is different.

[0162] S01: 7 parts of deionized water and 1.5 parts of cetyltrimethylammonium bromide were stirred and mixed to obtain a modified solution;

[0163] S02: adding a modifying liquid of 15% of the total amount of nano zinc oxide to the nano zinc oxide, and then ball milling at a rotation speed of 1100 r / min for 1.5 hours. After the ball milling is completed, washing with water and drying are performed to obtain regulated nano zinc oxide.

[0164] Comparative Example 10.

[0165] The difference from Example 3 is that the thermal cycle improvement treatment is not adopted.

[0166] The products of Examples 1-3 and Comparative Examples 1-10 were subjected to performance tests under normal conditions and at 70°C;

[0167]

[0168]

[0169] As can be seen from Comparative Examples 1-10 and Example 3, the product of Example 3 can achieve a capacity retention rate of up to 96% and a resistivity of 4.5Ω.cm after 100 cycles under normal conditions; and can reach 95% and 4.7Ω.cm at 70°C. The capacity retention rate and resistivity after cycling can achieve a coordinated improvement effect, and the product has excellent temperature resistance and stability.

[0170] The product did not add the doped calcium sulfate whisker regulator, the doped calcium sulfate whisker regulator was replaced by calcium sulfate whiskers, and the preparation methods of the doped calcium sulfate whisker regulator were different. The performance of the product showed a trend of deterioration. At the same time, the performance of the product at 70°C when the doped calcium sulfate whisker regulator was replaced by calcium sulfate whiskers was worse than that without the doped calcium sulfate whisker regulator. It can be seen that only the doped calcium sulfate whisker regulator prepared by the method of the present invention has the best performance effect.

[0171] Without using any of the modified compounding liquid treatment, without adding the doped calcium sulfate whisker regulator, and without using the thermal cycle improvement treatment, the product performance deteriorates significantly. By using the three coordinated treatments, the product performance is synergistically enhanced.

[0172] In the preparation of the modified multiplexing liquid, the adjustable nano-zinc oxide is replaced by nano-zinc oxide; no dopamine solution and lanthanum sulfate are added in the preparation of the nano-zinc oxide preparation liquid of the modified multiplexing liquid; no adjusting agent is added in the preparation of the modified multiplexing liquid. The preparation methods of the adjustable nano-zinc oxide are different, and the performance of the products tends to deteriorate. Only the modified multiplexing liquid prepared by the method of the present invention and combined with the doped calcium sulfate whisker adjusting agent has the most significant performance effect of the product; in addition, the inventors of the present invention also found that when no adjusting agent is added in the preparation of the modified multiplexing liquid, the performance of the product deteriorates more significantly. Based on this, the present invention further explores and processes it.

[0173] The present invention further explores the product performance by mixing and adjusting the agent

[0174] The preparation method of the blending agent is as follows:

[0175] Add 4 parts of sodium silicate to 12 parts of water, heat to 70°C, and stir evenly to prepare a sodium silicate aqueous solution; then place 5 parts of nano-bentonite into 12 parts of chitosan aqueous solution, followed by adding 1.5 parts of silane coupling agent KH560 and 0.20 parts of sodium silicate aqueous solution, stir thoroughly, wash with water, and dry to obtain a preparation.

[0176] Experimental Example 1.

[0177] The same as Example 3, the only difference is that no sodium silicate aqueous solution is added during the preparation of the formulation.

[0178] Experimental Example 2.

[0179] The same as Example 3, the only difference is that deionized water is used instead of chitosan aqueous solution in the preparation of the formulation.

[0180] Experimental Example 3.

[0181] The same as Example 3, the only difference is that nano-bentonite is replaced by nano-rectorite.

[0182] Experimental Example 4.

[0183] The same as Example 3, the only difference is that the silane coupling agent KH560 is not added in the preparation of the formulation.

[0184]

[0185] As can be seen from Experimental Examples 1-4, sodium silicate aqueous solution was not added in the preparation of the dispensing agent. Among the other factors in the preparation of the dispensing agent, the performance of the product deteriorated most significantly. Silane coupling agent KH560 was not added in the preparation of the dispensing agent, and the chitosan aqueous solution was replaced by deionized water. The performance of the product showed a trend of deterioration. Only by using sodium silicate aqueous solution with silane coupling agent KH560 and chitosan aqueous solution, the performance effect of the product was the most significant. At the same time, nano-bentonite was replaced by nano-rectorite, and the performance of the product showed a trend of deterioration. The selection of nano-bentonite is proprietary. Only by using nano-bentonite to match the other raw materials in the dispensing agent of the present invention, the performance effect of the product was the most significant. Using other raw material ratios, the technical effect of the present invention could not be achieved.

[0186] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

[0187] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for preparing lithium iron phosphate positive electrode material using iron phosphate, characterized in that: The following steps are involved: Step 1: 45-55 parts of flake graphene are first added to 70-80 parts of a 2% by mass hydrochloric acid solution and stirred evenly, then washed with water, dried, and then irradiated in a proton irradiation box. The irradiation power is 500-800W and the irradiation time is 20-30 minutes. After the irradiation is completed, an irradiated graphene agent is obtained; Step 2: Mixing the irradiated graphene agent and the doped calcium sulfate whisker regulator in a weight ratio of 3:1 to obtain a composite regulator; Step 3: Add deionized water, lithium carbonate, glucose and citric acid to the iron phosphate in a molar ratio of 7:3, mix with a carbon source to prepare a mixture, sand grind the mixture, control the sand grinding particle size to 450nm, spray dry the sand milled mixture, and then place the dried material in a nitrogen atmosphere at 650°C for 10 hours to obtain a lithium iron phosphate precursor; Adding 10-15% of the total amount of the lithium iron phosphate primary body to the composite regulator, stirring evenly, and sending the mixture into a ball mill for ball milling at a ball milling speed of 1000-1500 r / min for 1-2 hours to obtain a ball-milled composite body; Step 4: The ball-milled composite is then placed into a 3-5 times larger modified compounding solution for stirring and modification. After stirring, the mixture is washed with water and dried. Step 5: Finally, the lithium iron phosphate positive electrode material is obtained by heat-cycle improvement treatment; the preparation method of the doped calcium sulfate whisker regulator is: S01: adding calcium sulfate whiskers to a nitric acid solution at a weight ratio of 1:3, stirring at 55-65° C. for 45-55 minutes at a stirring speed of 350-450 r / min, washing with water, and drying to obtain pretreated calcium sulfate whiskers; S02: Add 1-3 parts of sodium methylene bisnaphthalene sulfonate and 2-5 parts of polyaniline to 10-20 parts of ethanol solvent, then add 0.25-0.35 parts of samarium oxide and 0.1-0.4 parts of glycolic acid, and stir evenly to obtain a prepared solution; S03: adding the pretreated calcium sulfate whiskers to 3-5 times the prepared liquid, ultrasonically dispersing for 10-20 minutes at 400-500W, and then washing with water and drying to obtain a doped calcium sulfate whisker conditioning agent; the preparation method of the modified compounding liquid is as follows: S01: 5-9 parts by mass of a 5% aqueous solution of citric acid, 1-3 parts of silica sol, and 1-2 parts of hexadecyltrimethylammonium bromide are stirred and mixed to obtain a modified solution; S02: adding a modification liquid of 10-20% of the total amount of nano zinc oxide to the nano zinc oxide, and then ball milling at a speed of 1000-1200 r / min for 1-2 hours. After the ball milling is completed, washing with water and drying to obtain regulated nano zinc oxide; S03: 3-6 parts of regulated nano zinc oxide are added to 10-15 parts of deionized water and stirred evenly, and then 1-2 parts of 5% by mass dopamine solution, 0.45-0.55 parts of lanthanum sulfate and 0.2-0.3 parts of phosphate buffer solution are added and stirred evenly to obtain a nano zinc oxide preparation solution; S04: Add 5-7 parts of the preparation agent to the nano zinc oxide preparation solution in S03 and stir thoroughly to obtain a modified compound solution; the specific steps of the thermal cycle improvement treatment are: First, heat the reaction at 75-85°C for 10-20 minutes; then heat to 130-140°C at a rate of 1-3°C / min, keep warm for 5-10 minutes, and then cool to 40-45°C at a rate of 2-4°C / min to obtain a heat-insulated product; The heat-insulated product is then stirred and dispersed evenly in a chitosan aqueous solution with a mass fraction of 5% which is 6-8 times the total amount of the heat-insulated product, washed with water, dried, and finally heat-pressed.

2. The method for preparing a lithium iron phosphate positive electrode material using iron phosphate according to claim 1, characterized in that: The concentration of the nitric acid solution is 1-1.5 mol / L.

3. The method for preparing a lithium iron phosphate positive electrode material using iron phosphate according to claim 1, characterized in that: The stirring temperature of the stirring modification treatment in step 4 is 42-46° C., the stirring reaction is carried out for 35-40 minutes, and the stirring speed is 550-650 r / min.

4. The method for preparing a lithium iron phosphate positive electrode material using iron phosphate according to claim 1, characterized in that: The pH value of the phosphate buffer solution is 5.0-5.

5.

5. The method for preparing a lithium iron phosphate positive electrode material using iron phosphate according to claim 1, characterized in that: The preparation method of the blending agent is as follows: Add 3-5 parts of sodium silicate to 10-15 parts of water, heat to 60-80°C, and stir evenly to prepare a sodium silicate aqueous solution; then place 3-6 parts of nano-bentonite into 10-15 parts of chitosan aqueous solution, followed by adding 1-2 parts of silane coupling agent KH560 and 0.15-0.35 parts of sodium silicate aqueous solution, stir thoroughly, wash with water, and dry to obtain a preparation.

6. The method for preparing a lithium iron phosphate positive electrode material using iron phosphate according to claim 5, characterized in that: The mass fraction of the chitosan aqueous solution is 6-8%.

7. The method for preparing a lithium iron phosphate positive electrode material using iron phosphate according to claim 1, characterized in that: The pressure of the hot pressing treatment is 10-15 MPa, the temperature is 55-65° C., and the treatment time is 30-40 minutes.

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