WO2012062110A1

WO2012062110A1 - Preparing method of composite lithium iron phosphate/carbon for lithium ion battery

Info

Publication number: WO2012062110A1
Application number: PCT/CN2011/075932
Authority: WO
Inventors: 朱杰; 杜振山
Original assignee: 河北力滔电池材料有限公司
Priority date: 2010-11-10
Filing date: 2011-06-20
Publication date: 2012-05-18
Also published as: CN102013477B; CN102013477A

Abstract

A preparing method of a composite lithium iron phosphate/carbon for a lithium ion battery is provided. The method includes steps as follows: 1) preparing a suspension graphene-scattered aqueous solution system: crushing a graphite to 1-5μm, adding a distilled water or a purified water, adding 0.1-5% a surfactant under the stirring condition, increasing the temperature to 180-250℃ under the sealing condition, stirring for 2-6 hours, and cooling; 2) crushing a lithium iron phosphate to 1-5μm, adding the distilled water or the purified water, adding 0.01-1% a coupling agent under stirring condition, uniformly stirring, adding the graphene-scattered aqueous solution, stirring and filtering; 3) vacuum-drying solid powder obtained by filtering, sintering for 2-12 hours, and obtaining the graphene-coated lithium iron phosphate positive material. The method has simple technique, and the material prepared by the method has the advantages of excellent performance, high conductive ability, high stacking and compaction intensity and so on.

Description

Method for preparing lithium ion battery composite material lithium iron phosphate/carbon

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a preparation method of a lithium ion battery composite material lithium iron phosphate/carbon. Background technique

At present, the synthesis method of lithium iron phosphate material is mainly divided into a solid phase method and a liquid phase method. The solid phase method mainly utilizes iron salt, lithium salt and phosphate to synthesize lithium iron phosphate at high temperature sintering. In the liquid phase method, a soluble iron salt, a lithium salt, and a phosphoric acid salt are dissolved in a solvent, and lithium iron phosphate or a precursor thereof is prepared by ion reaction, and then a high-temperature sintering is performed to obtain a finished product. The solid phase reaction is simple, the raw materials are easy to handle, and the yield is high, but the morphology of the raw materials is not easy to control, and the tap density and compaction density of the product are low. For example, the invention patents CN101200289, CN1762798, CN101140985, etc. all adopt a solid phase synthesis process route. Some new synthetic methods, such as microwave synthesis (CN101172597, CN101807692A) and ultrasonic coprecipitation (CN101800311A), can be attributed to solid phase synthesis. The liquid phase method requires the use of a reactor for pre-treatment, and also requires drying, filtration, etc., and the process is complicated. However, the sphericity of the product is generally good, the tap density is high, and the capacity and high rate performance are excellent. The invention patents CN101172599, CN101047242, and CN101121509 all adopt the above process route.

A successful application of iron phosphate materials is that their surfaces are coated with a conductive carbon layer. It is actually a lithium iron phosphate/carbon composite. Only the lithium iron phosphate material coated with carbon can exert its electrochemical performance normally. However, the carbon added by the general process is loosely distributed and loosely distributed among the lithium iron phosphate particles, which seriously reduces the bulk density of the lithium iron phosphate material, making its tap density much lower than its theoretical density, and affecting the subsequent The compact density of the pole piece. How to minimize the carbon content in the cathode material without reducing the carbon coating effect of the material, without reducing the conductivity, electrochemical capacity and cycle performance, is a concern of materials research. Summary of the invention

The present invention provides a method for preparing a lithium ion battery composite lithium iron phosphate/carbon in order to solve the problems existing in the prior art.

SUMMARY OF THE INVENTION The object of the present invention is to provide a lithium ion battery composite lithium iron phosphate/carbon preparation method which has the advantages of simple process, convenient operation, excellent material performance, high electrical conductivity, high bulk density and high compaction density, and stable product quality.

Studies have shown that reducing carbon content without lowering the conductivity of lithium iron phosphate/carbon systems can only be achieved by introducing carbon materials with higher electrical conductivity. In actual production, the higher the synthesis temperature, the higher the degree of graphitization of the carbon material and the better the conductivity. However, the high synthesis temperature causes the crystal grains of the lithium iron phosphate material to be excessively large, and the lithium ion diffusion distance is increased to lower the discharge capacity of the material. The appearance of graphene materials provides a theoretical basis for the advancement of lithium iron phosphate/carbon materials. Graphene is a two-dimensional network of carbon materials with sp2 hybrid orbitals. Its conductivity is 100 times that of copper due to its remarkable quantum tunneling effect. Graphene is extremely thin, very soft and has excellent flexibility. It is an ideal material for coating lithium iron phosphate. It is conceivable that the lithium iron phosphate material coated with an appropriate amount of graphene has a small carbon content, but the electrical conductivity of the material is lowered. At the same time, since the graphene is tightly coated on the surface of the lithium iron phosphate particles, there is no loose carbon between the grains, and the density of the material is greatly increased.

The invention provides a preparation and synthesis method of a lithium iron phosphate/carbon composite material, wherein carbon is tightly coated on the surface of lithium iron phosphate in the form of graphene, thereby reducing the carbon content in the positive electrode material to less than 1% (in general materials) Containing more than 3% carbon), the material is densely distributed, increasing the density of lithium iron phosphate material.

The process route adopted by the invention is as follows: Firstly, a graphene stable dispersion aqueous solution system is prepared by using a thermal differential layer stripping technique, and then the pure lithium iron phosphate material is treated with the solution to adsorb the graphene on the surface of the lithium iron phosphate particles, and then subjected to heat treatment. The combination of graphene and lithium iron phosphate provides the desired lithium iron phosphate/carbon composite.

The preparation method of the lithium ion battery composite material lithium iron phosphate/carbon of the invention adopts the following technical solutions:

A lithium ion battery composite material lithium iron phosphate / carbon preparation method, coated with lithium iron phosphate, characterized by: composite lithium iron phosphate / carbon preparation process includes:

1. Preparing a suspended graphene dispersed aqueous solution system: preparing a suspended graphene dispersed aqueous solution system by using a hot differential layer stripping method; pulverizing the natural graphite to a particle size of 1-5 micrometers, and adding it to steamed water or purified water. Adding 0.1-5% of the surfactant, under shear and stirring, the temperature of the seal is raised to 180-250 ° C, stirred for 2-6 hours, and the temperature is lowered;

2. Treat the pure lithium iron phosphate material with the above solution: pulverize the lithium iron phosphate to a particle size of 1-5 μm, and add steamed water or purified water according to the ratio of lithium iron phosphate: water = 1: 1-10; , adding a total weight of 0. 01-1% of the coupling agent, stirring evenly; adding the above graphene dispersed aqueous solution, stirring, filtering;

3. Heat treatment of graphene and lithium iron phosphate material: The solid powder obtained by filtration is vacuum dried, calcined at 250-350 ° C under nitrogen or argon atmosphere for 2-12 hours to obtain graphene-coated lithium iron phosphate. Cathode material.

The preparation method of the lithium ion battery composite material lithium iron phosphate/carbon of the invention can also adopt the following technical measures: The preparation method of the lithium ion battery composite material lithium iron phosphate/carbon, characterized in that: the surfactant is phenylenediamine , polyvinylpyrrolidone, alkylphenol ethoxylates, and the like. It can be peeled off between the graphite layers in the hydrothermal state and stabilizes the graphene/water system.

The preparation method of the lithium ion battery composite material lithium iron phosphate/carbon is characterized in that: the coupling agent is Y-mercaptopropyltrimethoxysilane, methyl isobutyl ketone decyl silane, vinyl triethoxy Silane and the like. It can adhere to the surface of lithium iron phosphate and is easily crosslinked with graphene.

The method for preparing a lithium ion battery composite lithium iron phosphate/carbon is characterized in that: the weight percentage concentration of graphene in the graphene-dispersed aqueous solution is ι-ιο%.

The method for preparing a lithium ion battery composite material lithium iron phosphate/carbon, characterized in that: adding graphene dispersion After the aqueous solution, the mixture was stirred at 20 to 40 ° C for 4 to 10 hours, and then allowed to stand for 12 to 36 hours, followed by stirring.

The lithium ion battery composite material lithium iron phosphate / carbon preparation method is characterized in that: when the solid powder is dried by vacuum, the vacuum drying temperature is 120-150 ° C.

The invention has the advantages and positive effects:

Lithium ion battery composite material lithium iron phosphate / carbon preparation method, due to the adoption of the novel technical solution of the present invention, compared with the prior art, the iron phosphate/carbon material prepared by the invention, the graphene is completely nanometerly distributed in the phosphoric acid The surface of the iron-lithium material forms a surface carbon layer with extremely high electrical conductivity and does not produce a loose bulk carbon layer. The bulk density and compaction density of the lithium iron phosphate cathode material are effectively increased.约。 The measured, the carbon content of the material was reduced to 0. 8-1%, the body conductivity was maintained at 0. 01S / cm. The tap density is increased to 1. 8g/cm3, the 0. 1C capacity is 155mAh/g, and the compact density of the capacity pole piece is increased from 2. 2 g/cm3 to 2. 6-2. 7 g/cm3. The overall performance of the lithium iron phosphate material has been greatly improved. The invention has the advantages of simple process, convenient operation, excellent material performance, high electrical conductivity, high bulk density and compact density, and stable product quality. detailed description

In order to further understand the technical content, features and effects of the present invention, the following examples are listed, and the following details are as follows:

Example 1

A method for preparing a lithium ion battery composite lithium iron phosphate/carbon, firstly preparing a stable suspended graphene-water system. The concentration of graphene in the system is 1%. The natural graphite is first pulverized to an average particle size of about 1 micrometer, and then added to the distilled water, and 0.1% of the surfactant phenylenediamine is added, and the temperature is raised to 180 ° C under high shear agitation. Stirring was continued for 6 hours under high temperature and high pressure, and the temperature was lowered to obtain a stable suspended graphene-water system.

Pure lithium iron phosphate was pulverized to an average particle diameter of 1 μm, and pure water was added in a ratio of lithium iron phosphate: water = 1:1. Under stirring, a total weight of 0.01% by weight of the coupling agent Y-mercaptopropyltrimethoxysilane was used to enhance the adsorption capacity of the lithium iron phosphate material for graphene, and the stirring was uniform. The dispersed graphene solution was slowly added and stirred at 20 ° C for 4 hours. Allow to stand for 12 hours. After stirring for another hour, the liquid was filtered, and the obtained solid powder was dried under vacuum at 120 ° C to remove water, and then calcined under a nitrogen atmosphere at 250 ° C for 2 hours to obtain a graphene-coated lithium iron phosphate cathode material. .

Example 2

A method for preparing a lithium ion battery composite lithium iron phosphate/carbon, firstly preparing a stable suspended graphene-water system. The concentration of graphene in the system is generally 10%. The natural graphite was first pulverized to an average particle size of 5 μm, and then added to purified water, and 5% of a surfactant polyvinylpyrrolidone was added, and the temperature was raised to 250 ° C under high-speed shear stirring. Stirring was continued for 2 hours under high temperature and high pressure, and the temperature was lowered to obtain a stable suspended graphene-water system.

Pure lithium iron phosphate was pulverized to an average particle diameter of 5 μm, and purified water was added in a ratio of lithium iron phosphate: water = 1:10. Under stirring, a total weight of 1% by weight of the coupling agent methyl isobutyl ketone silane is added to enhance the iron phosphate. The adsorption capacity of lithium material for graphene is evenly stirred. The dispersed graphene solution was slowly added and stirred at 40 ° C for 10 hours. Allow to stand for 36 hours. After stirring for another 2 hours, the liquid was filtered, and the obtained solid powder was dried under vacuum at 150 ° C to remove water, and then calcined under an argon atmosphere at 350 ° C for 12 hours to obtain a graphene-coated lithium iron phosphate positive electrode. material.

Example 3

A method for preparing a lithium ion battery composite lithium iron phosphate/carbon, firstly preparing a stable suspended graphene-water system. The concentration of graphene in the system was 2%. The natural graphite was first pulverized to an average particle diameter of 2 μm, and then added to pure water, and 1% of a surfactant alkylphenol ethoxylate was added, and the temperature was raised to 200 ° C under high-speed shear stirring. Stirring was continued for 4 hours under high temperature and high pressure, and the temperature was lowered to obtain a stable suspended graphene-water system.

Pure lithium iron phosphate was pulverized to an average particle diameter of 3 μm, and pure water was added in a proportion of lithium iron phosphate: water = 1:5. Under stirring, a total weight of 0.1% by weight of the coupling agent vinyltriethoxysilane was added to enhance the adsorption capacity of the lithium iron phosphate material for graphene, and the stirring was uniform. The dispersed graphene solution was slowly added and stirred at 25 ° C for 6 hours. Allow to stand for 24 hours. After stirring for 1.5 hours, the liquid was filtered, and the obtained solid powder was dried at 135 degree under vacuum to remove water, and then calcined under an argon atmosphere at 300 ° C for 8 hours to obtain graphene-coated lithium iron phosphate. Cathode material.

The lithium iron phosphate/carbon composite material of the lithium ion battery prepared by the invention has the graphene completely distributed on the surface of the lithium iron phosphate material, forming a surface carbon layer having extremely high conductivity, and effectively increasing the lithium iron phosphate positive electrode. The bulk density and compaction density of the material, the lithium iron phosphate/carbon composite material has the positive positive effects described.

Claims

Claim

1) preparing a suspended graphene dispersed aqueous solution system: preparing a suspended graphene dispersed aqueous solution system by using a hydrothermal difference layer stripping method; pulverizing natural graphite to a particle size of 1-5 micrometers, adding to distilled water or purified water , adding 0.1-5% of the surfactant, under the condition of shear stirring, the temperature is raised to 180-250 ° C, stirred for 2-6 hours, and the temperature is lowered;

2), treating the pure lithium iron phosphate material with the above solution: crushing lithium iron phosphate to a particle size of 1-5 micrometers, adding distilled water or purified water according to the ratio of lithium iron phosphate: water = 1: 1-10; stirring state Next, adding 0.01-1% of the total weight of the coupling agent, stirring uniformly; adding the above graphene dispersed aqueous solution, stirring, filtering;

3) heat treatment of graphene and lithium iron phosphate material: the solid powder obtained by filtration is vacuum dried and calcined at 250-350 ° C for 2-12 hours under a nitrogen or argon atmosphere to obtain graphene-coated iron phosphate. Lithium cathode material.

The method for preparing a lithium ion battery composite lithium iron phosphate/carbon according to claim 1, wherein the surfactant is phenylenediamine, polyvinylpyrrolidone or alkylphenol ethoxylate.

The method for preparing a lithium ion battery composite lithium iron phosphate/carbon according to claim 1, wherein the coupling agent is Y-mercaptopropyltrimethoxysilane or methyl isobutyl ketone sulfonylsilane. Or vinyl triethoxysilane.

The method for preparing a lithium ion battery composite lithium iron phosphate/carbon according to claim 1, 2 or 3, wherein the graphene-dispersed aqueous solution has a graphene concentration of from 1 to 10% by weight.

The method for preparing a lithium ion battery composite lithium iron phosphate/carbon according to claim 1, 2 or 3, characterized in that after adding a graphene dispersed aqueous solution, stirring at 20-40 ° C is carried out 4- 10 hours, then let stand for 12-36 hours, then stir.

The method for preparing a lithium ion battery composite lithium iron phosphate/carbon according to claim 1, 2 or 3, characterized in that: when the solid powder is vacuum dried, the vacuum drying temperature is 120-150 °C.