CN107834070B - Lithium iron phosphate positive electrode material, lithium ion battery and preparation method thereof - Google Patents

Lithium iron phosphate positive electrode material, lithium ion battery and preparation method thereof Download PDF

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CN107834070B
CN107834070B CN201711388055.4A CN201711388055A CN107834070B CN 107834070 B CN107834070 B CN 107834070B CN 201711388055 A CN201711388055 A CN 201711388055A CN 107834070 B CN107834070 B CN 107834070B
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iron phosphate
lithium
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ionic liquid
sintering
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CN107834070A (en
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王利宣
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Anhui Jiahong New Material Co., Ltd
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    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of or comprising active material
    • H01M4/36Selection of substances as active materials, active masses, active liquids
    • H01M4/58Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825Oxygenated metallic slats or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/05Accumulators with non-aqueous electrolyte
    • H01M10/052Li-accumulators
    • H01M10/0525Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10Energy storage using batteries

Abstract

The invention relates to a lithium iron phosphate cathode material, a lithium ion battery and a preparation method thereof, and belongs to the technical field of lithium batteries. The method comprises the following steps: step 1, mixing 25-45 parts of lithium hydroxide, 25-30 parts of water and 9-15 parts of ethanol, and then adding 12-16 parts of silane coupling agent grafted ionic liquid for modification reaction; step 2, preparing 110-140 parts of iron phosphate into an aqueous solution with a solid content of 30-50 wt.%, adding an anionic surfactant accounting for 2-4% of the weight of the iron phosphate, mixing at a high speed, slowly dropwise adding the mixture into the reactant obtained in the step 1, and uniformly stirring to obtain a slurry; and 3, carrying out spray drying and sintering on the slurry to obtain the lithium iron phosphate material. When the lithium iron phosphate material provided by the invention is applied to the anode material of a lithium ion battery, the lithium iron phosphate material has the advantages of large electric capacity, high discharge efficiency and more cycle discharge times.

Description

Lithium iron phosphate positive electrode material, lithium ion battery and preparation method thereof
Technical Field
The invention relates to a lithium iron phosphate cathode material, a lithium ion battery and a preparation method thereof, and belongs to the technical field of lithium batteries.
Background
When the battery is charged, lithium ions are extracted from the lithium-containing compound of the positive electrode, and the lithium ions move to the negative electrode through the electrolyte. The carbon material of the negative electrode is of a layered structure and has a plurality of micropores, lithium ions reaching the negative electrode are inserted into the micropores of the carbon layer, and the more the lithium ions are inserted, the higher the charge capacity is. When the battery is discharged (i.e., the process we are using the battery), lithium ions embedded in the negative carbon layer are extracted and move back to the positive electrode. The more lithium ions returned to the positive electrode, the higher the discharge capacity. The battery capacity is generally referred to as the discharge capacity. During the charge and discharge of the lithium ion battery, lithium ions are in a state of motion from the positive electrode → the negative electrode → the positive electrode. The battery rocking chair is like a rocking chair, two ends of the rocking chair are two poles of the battery, and lithium ions move back and forth at the two ends of the rocking chair. So the lithium ion battery is also called a rocking chair type battery. The main components of the lithium ion battery comprise: 1) the positive electrode is an active substance and mainly refers to lithium cobaltate, lithium manganate, lithium iron phosphate, lithium nickelate, lithium nickel cobalt manganese and the like, and an aluminum foil with the thickness of 10-20 microns is generally used as a conductive current collector; (2) the separator, which is a special plastic film that allows lithium ions to pass through but is an insulator for electrons, is currently mainly composed of two types of PE and PP, and a combination thereof. There is also a class of inorganic solid membranes, such as an alumina membrane coating, which is an inorganic solid membrane; (3) the negative electrode is an active substance, mainly refers to graphite, lithium titanate or a carbon material similar to a graphite structure, and a copper foil with the thickness of 7-15 microns is generally used as a conductive current collector; (4) the electrolyte is generally an organic system, such as a carbonate solvent dissolved with lithium hexafluorophosphate, and gel electrolyte is used for other polymer batteries; (5) the battery shell is mainly divided into a hard shell (a steel shell, an aluminum shell, a nickel-plated iron shell and the like) and a soft package (an aluminum-plastic film). The charging process of the lithium ion battery is divided into two stages: a constant current charging stage and a constant voltage current decreasing charging stage. The lithium ion battery is permanently damaged by over-charging and discharging of the positive and negative electrodes. Over-discharge causes the collapse of the carbon sheet layer structure of the cathode, and the collapse can cause that lithium ions can not be inserted in the charging process; the overcharge causes excessive lithium ions to be inserted into the carbon structure of the negative electrode, so that part of the lithium ions cannot be released any more.
The specific capacity and performance of the negative electrode material in the lithium ion battery are far higher than those of the positive electrode material, so that more research works at present mainly concentrate on improving the specific capacity and the charging and discharging rates of the positive electrode material, and the research of the more mature positive electrode material of the conventional lithium ion battery is concentrated on the layered transition metal oxide L iMO2(M = Co, Ni, Mn, etc.) and spinel-type L iM2O2(M = Co, Ni, Mn, etc..) L iCoO2The anode material is the earliest commercialized anode material of the lithium ion battery, has high theoretical specific capacity (274mAh/g), large open-circuit voltage and stable electrochemical performance, and has the disadvantages of resource shortage, high price, toxicity and explosion at high temperature L iNiO2Large specific capacity (275mAh/g), low price, complex preparation process and poor thermal stability L iMn2O4The material has rich resources, low price and no toxicity, but has lower specific capacity (148mAh/g), fast capacity attenuation at high temperature and poor service life, so a series of defects of the materials seriously influence the application performance of the materials, and the materials are still in the stage of continuous research and development, L iFePO4The lithium ion battery has excellent electrochemical performance, the theoretical specific capacity of 170mAh/g, the voltage to a lithium platform of 3.4V, low cost, environmental friendliness, long cycle life and good safety at high temperature, and takes L i into consideration2CoO2、LiNiO2、LiVO2The main advantages of the material, as the anode material of the lithium ion battery, better solves the problems of cost, environment and safety, and is widely concerned by people L iFePO4Is considered to occur asThe new arrival of lithium ion batteries is marked.
CN103441271A discloses an anion and cation double-doped lithium iron phosphate cathode material, which is a composite of magnesium and fluorine double-doped lithium iron phosphate and carbon, wherein magnesium ions partially replace iron ion positions in lithium iron phosphate crystals, fluorine ions partially replace phosphate ion positions in lithium iron phosphate crystals, and the main component of the cathode material can be L iFe1-xMgx(PO4)1-yF3yThe expression of/C, wherein x is more than or equal to 0.001 and less than or equal to 0.1, y is more than or equal to 0.001 and less than or equal to 0.1, and the preparation method takes a lithium source, a ferrous source, a phosphorus source, a magnesium source, a fluorine source and a carbon source as raw materials and adopts a high-temperature solid phase method. CN104659332A discloses a high magnification lithium iron phosphate battery positive pole, characterized by: the current collector body of the electrode is through-hole foamed nickel with a three-dimensional conductive framework structure, the surface of the foamed nickel conductive framework is coated with an electronically conductive protective layer, the current collector body is foamed nickel with a three-dimensional conductive framework structure, the porosity of the foamed nickel is 50-98%, the through-hole porosity is greater than 98%, and the protective layer is a conductive coating of pvdf or polyacrylic acid containing 5-95% of conductive particles; the conductive particles are one of conductive carbon black, graphite and aluminum powder with the particle size of less than 5 um. CN102569814A discloses rare-earth type lithium iron phosphate used as a lithium secondary battery anode material and a preparation method thereof. The rare-earth type lithium iron phosphate contains 100 mole parts of lithium iron phosphate, 3.9-7.8 mole parts of rare-earth alloy and 1.1-2.2 mole parts of cellulose acetate. The preparation method of the rare-earth type lithium iron phosphate comprises the following steps: putting an iron source compound, a lithium source compound, a phosphorus source compound and a rare earth material into a powder mixing machine for powder mixing, gradually spraying cellulose acetate dissolved in acetone into the powder mixing machine in the powder mixing process to enable the cellulose acetate to be uniformly adhered to mixed material particles of the four materials, and then drying; putting the dried mixture particles into an atmosphere furnace protected by inert gas for presintering; and putting the pre-sintered powder into an atmosphere furnace protected by inert gas for heat preservation treatment to prepare the rare-earth lithium iron phosphate.
However, the lithium iron phosphate positive electrode material has a problem of capacity loss after multiple cycle discharge.
Disclosure of Invention
The purpose of the invention is: the lithium iron phosphate material adopts the electrostatic self-assembly principle of the silane coupling agent grafted ionic liquid and the anionic surfactant to prepare the lithium iron phosphate anode material with uniform material coating, and has the advantages of large capacitance and high discharge efficiency when being applied to the anode material of the lithium ion battery.
The technical scheme is as follows:
the preparation method of the lithium iron phosphate anode material comprises the following steps:
step 1, mixing 25-45 parts of lithium hydroxide, 25-30 parts of water and 9-15 parts of ethanol, and then adding 12-16 parts of silane coupling agent grafted ionic liquid for modification reaction;
step 2, preparing 110-140 parts of iron phosphate into an aqueous solution with a solid content of 30-50 wt.%, adding an anionic surfactant accounting for 2-4% of the weight of the iron phosphate, mixing at a high speed, slowly dropwise adding the mixture into the reactant obtained in the step 1, and uniformly stirring to obtain a slurry;
and 3, carrying out spray drying and sintering on the slurry to obtain the lithium iron phosphate material.
In the step 1, the reaction temperature ranges from 15 ℃ to 35 ℃; the reaction time is 1-3 h.
In the step 1, the preparation method of the ionic liquid grafted by the silane coupling agent comprises the following steps: adding 1-5 wt% of silane coupling agent KH560 and 5-10 wt% of imidazole ionic liquid into an alcohol solvent, and reacting at 80-100 ℃ for 10-20 h to obtain a solution of silane coupling agent grafted ionic liquid.
The imidazole ionic liquid is one or a mixture of more of chloridized-1-allyl-3-methylimidazole, chloridized 1-butyl-3-methylimidazole and imidazolyl tetrafluoroborate ionic liquid.
The alcohol solvent is one or more of methanol, ethanol, propylene glycol, butanol and isoamylol.
The anionic surfactant is selected from fatty acids and their salts, such as oleic acid, palmitic acid, sodium oleate, potassium palmitate, and triethanolamine oleate; hydroxy-containing acids and their salts, such as glycolic acid, potassium glycolate, lactic acid and potassium lactate; more preferably glycolic acid.
In the step 2, high-speed mixing means that the mixing and stirring speed is 1000-3000 rpm.
In the step 3, the spray drying temperature is 140-210 ℃; the sintering condition is that the sintering is carried out in an inert gas atmosphere, the sintering temperature is 730-820 ℃, and the sintering time is 6-14 hours.
The lithium iron phosphate cathode material prepared by the method.
The lithium ion battery comprises the lithium iron phosphate anode material.
Advantageous effects
When the lithium iron phosphate material provided by the invention is applied to the anode material of a lithium ion battery, the lithium iron phosphate material has the advantages of large electric capacity, high discharge efficiency and more cycle discharge times.
Detailed Description
The present invention will be described in further detail with reference to the following embodiments. It will be understood by those skilled in the art that the following examples are illustrative of the present invention only and should not be taken as limiting the scope of the invention. The examples do not specify particular techniques or conditions, and are performed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.
The words "include," "have," or any other variation thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
The recitation of values by ranges is to be understood in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a concentration range of "about 0.1% to about 5%" should be interpreted to include not only the explicitly recited concentration of about 0.1% to about 5%, but also include individual concentrations (e.g., 1%, 2%, 3%, and 4%) and sub-ranges (e.g., 0.1% to 0.5%, 1% to 2.2%, 3.3% to 4.4%) within the indicated range. The percentages in the present invention refer to weight percentages unless otherwise specified.
The preparation method of the lithium iron phosphate anode material provided by the invention comprises the following steps:
step 1, mixing 25-45 parts of lithium hydroxide, 25-30 parts of water and 9-15 parts of ethanol, and then adding 12-16 parts of silane coupling agent grafted ionic liquid for modification reaction;
step 2, preparing 110-140 parts of iron phosphate into an aqueous solution with a solid content of 30-50 wt.%, adding an anionic surfactant accounting for 2-4% of the weight of the iron phosphate, mixing at a high speed, slowly dropwise adding the mixture into the reactant obtained in the step 1, and uniformly stirring to obtain a slurry;
and 3, carrying out spray drying and sintering on the slurry to obtain the lithium iron phosphate material.
The preparation method comprises the following steps of firstly, reacting lithium hydroxide with an ionic liquid grafted by a silane coupling agent to enable the ionic liquid grafted by the silane coupling agent to carry out cationization modification on lithium hydroxide slurry, then preparing iron phosphate into slurry containing an anionic surfactant, stirring to enable particles to have electric charge, carrying out electrostatic self-assembly on the slurry obtained in the two steps to realize full adsorption and mixing of materials, and sintering to generate the solid lithium iron phosphate anode material.
In the step 1, the preparation method of the ionic liquid grafted by the silane coupling agent comprises the following steps: adding 1-5 wt% of silane coupling agent KH560 and 5-10 wt% of imidazole ionic liquid into an alcohol solvent, and reacting at 80-100 ℃ for 10-20 h to obtain a solution of silane coupling agent grafted ionic liquid. The imidazole ionic liquid is one or a mixture of more of chloridized-1-allyl-3-methylimidazole, chloridized 1-butyl-3-methylimidazole and imidazolyl tetrafluoroborate ionic liquid. The alcohol solvent is one or more of methanol, ethanol, propylene glycol, butanol and isoamylol. The step has the effect that the lithium hydroxide slurry has positive charges, and after mixing, the iron phosphate and the lithium source are more favorably and uniformly dispersed.
In step 2, anionic surfactants are added in order to impart a negative charge to the iron phosphate slurry, and suitable anionic surfactants in the above-mentioned steps include, for example, fatty acids and their salts such as oleic acid, palmitic acid, sodium oleate, potassium palmitate, and triethanolamine oleate, hydroxy-containing acids and their salts such as glycolic acid, potassium glycolate, lactic acid, and potassium lactate, polyoxyalkylene alkyl ether acetic acids and their salts such as polyoxyalkylene tridecyl ether acetic acid and its sodium salt, salts of carboxy-polysubstituted aromatic compounds such as potassium trimellitate and potassium pyromellitate, alkylbenzene acids and their salts such as dodecylbenzene sulfonic acid and its sodium salt, polyoxyalkylene alkyl ether sulfonic acids and their salts such as polyoxyethylene 2-ethylhexyl ether sulfonic acid and its potassium salt, higher fatty acid amide sulfonic acids and their salts such as stearoyl methyl taurine and its sodium salt, lauroyl methyl taurine and its sodium salt, palmitoyl methyl taurine and its sodium salt, N-acyl sarcosines and their salts such as lauroyl sarcosine and its sodium salt, alkylphosphonic acid and their salts such as octylphosphonic acid and its sodium salt, lauroyl methyl phosphonic acid and its sodium salt, and its salts such as sodium salt, and its salts such as sodium salt, and its salts such as sodium salt, and its salts, and its salts, such as sodium salt, and its salts with the salts, such as sodium salts, and its salts, preferably, and its salts, and.
And 3, performing high-temperature sintering reaction on the obtained material to generate a solid lithium iron phosphate material.
The percentages recited in the present invention are all percentages by mass unless otherwise specified.
Example 1
The preparation method of the cathode material comprises the following steps:
step 1, mixing 25 parts of lithium hydroxide, 25 parts of water and 9 parts of ethanol, and then adding 12 parts of a solution of silane coupling agent grafted ionic liquid for modification reaction, wherein the reaction temperature range is 15 ℃; the reaction time is 1 h; the preparation method of the silane coupling agent grafted ionic liquid comprises the following steps: adding 1wt% of silane coupling agent KH560 and 5wt% of chlorinated-1-allyl-3-methylimidazole ionic liquid into ethanol, and reacting at 80 ℃ for 10 hours to obtain a solution of the silane coupling agent grafted ionic liquid.
Step 2, preparing 110 parts of iron phosphate into an aqueous solution with a solid content of 30wt.%, adding 2% glycolic acid based on the weight of the iron phosphate, stirring at a high speed of 1000rpm, slowly dropwise adding the mixture into the reactant obtained in the step 1, and uniformly stirring to obtain a slurry;
step 3, spray drying and sintering the slurry to obtain a lithium iron phosphate material, wherein the spray drying temperature is 140 ℃; the sintering condition is that the sintering is carried out in an inert gas atmosphere, the sintering temperature is 730 ℃, and the sintering time is 6 hours.
Example 2
The preparation method of the cathode material comprises the following steps:
step 1, mixing 45 parts of lithium hydroxide, 30 parts of water and 15 parts of ethanol, and then adding 16 parts of a solution of silane coupling agent grafted ionic liquid for modification reaction, wherein the reaction temperature range is 35 ℃; the reaction time is 3 h; the preparation method of the silane coupling agent grafted ionic liquid comprises the following steps: adding 5wt% of silane coupling agent KH560 and 10 wt% of chlorinated-1-allyl-3-methylimidazole ionic liquid into ethanol, and reacting at 100 ℃ for 20 hours to obtain a solution of silane coupling agent grafted ionic liquid.
Step 2, preparing 140 parts of iron phosphate into an aqueous solution with a solid content of 50wt.%, adding 4% glycolic acid based on the weight of the iron phosphate, stirring at a high speed of 3000rpm, slowly dropwise adding the mixture into the reactant obtained in the step 1, and uniformly stirring to obtain a slurry;
step 3, spray drying and sintering the slurry to obtain a lithium iron phosphate material, wherein the spray drying temperature is 210 ℃; the sintering condition is carried out in an inert gas atmosphere, the sintering temperature is 820 ℃, and the sintering time is 14 h.
Example 3
The preparation method of the cathode material comprises the following steps:
step 1, mixing 30 parts of lithium hydroxide, 28 parts of water and 12 parts of ethanol, and then adding 13 parts of a solution of silane coupling agent grafted ionic liquid for modification reaction, wherein the reaction temperature range is 20 ℃; the reaction time is 2 h; the preparation method of the silane coupling agent grafted ionic liquid comprises the following steps: adding 2wt% of silane coupling agent KH560 and 8 wt% of chlorinated-1-allyl-3-methylimidazole ionic liquid into ethanol, and reacting at 90 ℃ for 15 hours to obtain a solution of silane coupling agent grafted ionic liquid.
Step 2, preparing 120 parts of iron phosphate into an aqueous solution with a solid content of 40wt.%, adding glycolic acid with a weight of 3% of that of the iron phosphate, stirring at a high speed of 2000rpm, slowly dripping the mixture into the reactant obtained in the step 1, and uniformly stirring to obtain a slurry;
step 3, spray drying and sintering the slurry to obtain a lithium iron phosphate material, wherein the spray drying temperature is 170 ℃; the sintering condition is that the sintering is carried out in an inert gas atmosphere, the sintering temperature is 750 ℃, and the sintering time is 10 hours.
Comparative example 1
The difference from example 3 is that: the ionic liquid solution is not modified by a silane coupling agent.
Step 1, mixing 30 parts of lithium hydroxide, 28 parts of water and 12 parts of ethanol, and then adding 13 parts of ionic liquid solution for modification reaction, wherein the reaction temperature range is 20 ℃; the reaction time is 2 h; the preparation method of the ionic liquid solution comprises the following steps: adding 8% of chloride-1-allyl-3-methylimidazole ionic liquid into ethanol, and uniformly stirring.
Step 2, preparing 120 parts of iron phosphate into an aqueous solution with a solid content of 40wt.%, adding glycolic acid with a weight of 3% of that of the iron phosphate, stirring at a high speed of 2000rpm, slowly dripping the mixture into the reactant obtained in the step 1, and uniformly stirring to obtain a slurry;
step 3, spray drying and sintering the slurry to obtain a lithium iron phosphate material, wherein the spray drying temperature is 170 ℃; the sintering condition is that the sintering is carried out in an inert gas atmosphere, the sintering temperature is 750 ℃, and the sintering time is 10 hours.
Comparative example 2
The difference from example 3 is that: no anionic surfactant glycolic acid was added in step 2.
The preparation method of the cathode material comprises the following steps:
step 1, mixing 30 parts of lithium hydroxide, 28 parts of water and 12 parts of ethanol, and then adding 13 parts of a solution of silane coupling agent grafted ionic liquid for modification reaction, wherein the reaction temperature range is 20 ℃; the reaction time is 2 h; the preparation method of the silane coupling agent grafted ionic liquid comprises the following steps: adding 2wt% of silane coupling agent KH560 and 8 wt% of chlorinated-1-allyl-3-methylimidazole ionic liquid into ethanol, and reacting at 90 ℃ for 15 hours to obtain a solution of silane coupling agent grafted ionic liquid.
Step 2, preparing 120 parts of iron phosphate into an aqueous solution with a solid content of 40wt.%, mixing at a high speed of 2000rpm, slowly dripping the mixture into the reactant obtained in the step 1, and uniformly stirring to obtain a slurry;
step 3, spray drying and sintering the slurry to obtain a lithium iron phosphate material, wherein the spray drying temperature is 170 ℃; the sintering condition is that the sintering is carried out in an inert gas atmosphere, the sintering temperature is 750 ℃, and the sintering time is 10 hours.
Comparative example 3
And the negative and positive ions in CN103441271A are double-doped with the lithium iron phosphate positive electrode material.
Comparative example 4
A lithium iron phosphate positive electrode material in CN 102569814A.
Testing performance
1. Preparation of test cells:
(1) preparing a positive plate: respectively taking the lithium iron phosphate materials prepared in the examples and the comparative examples as positive electrode active materials, and mixing the positive electrode material, acetylene black and PVDF in a weight ratio of 100: 4: 5 dissolving in N-methyl pyrrolidone, stirring, coating on aluminum foil, baking at 100 + -5 deg.C, rolling to a certain thickness with a tablet machine, and rolling to obtain positive plate;
(2) preparing a negative plate: graphite, acetylene black and PVDF are mixed in a weight ratio of 100: 3: 6, dissolving in N-methyl pyrrolidone, uniformly stirring, coating on a copper foil, baking at the temperature of 100 +/-5 ℃, rolling to a certain thickness by using a tablet press, and rolling and cutting into a negative plate;
(3) coiling the positive and negative plates and the polypropylene diaphragm into a square lithium ion battery cell, collecting the cell in a battery case, welding, and injecting 1.0 mol/L L iPF6And (3) adding an electrolyte of/EC + EMC + DMC (wherein the mass ratio of EC, EMC and DMC is 1: 1: 1), sealing, and preparing the test battery.
2.1, specific capacity test:
at room temperature, the test cell is placed for 5min, and is charged at a constant current of 0.8mA, the voltage is cut off to 3.8V, the constant voltage charging is carried out at 3.8V, the current is cut off to 0.1mA, the test cell is placed for 5min, and is discharged at a constant current of 0.8mA, and the voltage is limited to 2.5V. The specific capacity was calculated and the results are shown in the table below.
2.2 testing of cycle Performance
At room temperature, the test cell is charged at constant current of 0.8mA, the voltage is limited to 3.8V, the cell is charged at constant voltage of 3.8V, the current is cut off to 0.1mA, the cell is placed for 5min, and the cell is discharged at constant current of 0.8 mA. The capacity retention was calculated 500 times by repeating 500 times, and the results are shown in the following table.
2.5~3.8V specific capacity 1(mAh/g) 2.5 to 3.8V specific capacity 2(mAh/g) 2.5 to 3.8V specific capacity 3(mAh/g) Capacity retention ratio at 200 times (%) Discharge efficiency (%)
Example 1 166 167 168 96.5 98
Example 2 167 166 168 96.2 97
Example 3 168 167 169 97.5 99
Comparative example 1 152 151 153 93.5 96
Comparative example 2 150 152 152 92.8 95
Comparative example 3 156 157 157 93.6 95
Comparative example 4 152 153 152 92.4 94
The lithium iron phosphate material prepared by the preparation method provided by the embodiment of the invention has large specific capacity and longer cyclic discharge life; compared with the comparative example 1, in the embodiment 3, the lithium hydroxide slurry is subjected to ionic liquid modification, so that better mixing of materials can be effectively realized through electrostatic self-assembly, and the prepared cathode material has higher circulating discharge capacity retention; in contrast to comparative example 2, in example 3, the iron phosphate slurry was stirred with an anionic surfactant, so that the electronegativity of the slurry was improved, which was beneficial to the process of electrostatic self-assembly. The capacity retention rate of the material after 200-cycle discharge is superior to that of the anode material in the prior art.

Claims (1)

1. A preparation method of a lithium iron phosphate anode material is characterized by comprising the following steps:
step 1, mixing 25-45 parts of lithium hydroxide, 25-30 parts of water and 9-15 parts of ethanol, and then adding 12-16 parts of silane coupling agent grafted ionic liquid for modification reaction;
step 2, preparing 110-140 parts of iron phosphate into an aqueous solution with a solid content of 30-50 wt.%, adding an anionic surfactant accounting for 2-4% of the weight of the iron phosphate, mixing at a high speed, slowly dropwise adding the mixture into the reactant obtained in the step 1, and uniformly stirring to obtain a slurry;
step 3, spray drying and sintering the slurry to obtain a lithium iron phosphate material;
in the step 1, the reaction temperature ranges from 15 ℃ to 35 ℃; the reaction time is 1-3 h;
in the step 1, the preparation method of the ionic liquid grafted by the silane coupling agent comprises the following steps: adding 1-5 wt% of silane coupling agent KH560 and 5-10 wt% of imidazole ionic liquid into an alcohol solvent, and reacting at 80-100 ℃ for 10-20 h to obtain a solution of silane coupling agent grafted ionic liquid;
the imidazole ionic liquid is selected from one or a mixture of more of chloridized-1-allyl-3-methylimidazole, chloridized 1-butyl-3-methylimidazole or imidazolyl tetrafluoroborate ionic liquid;
the alcohol solvent is selected from one or a mixture of methanol, ethanol, propylene glycol, butanol or isoamylol;
the anionic surfactant is selected from oleic acid, palmitic acid, sodium oleate, potassium palmitate or triethanolamine oleate;
in the step 2, high-speed mixing means that the mixing and stirring speed is 1000-3000 rpm;
in the step 3, the spray drying temperature is 140-210 ℃; the sintering condition is that the sintering is carried out in an inert gas atmosphere, the sintering temperature is 730-820 ℃, and the sintering time is 6-14 hours.
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