CN104979557A - High-rate lithium iron phosphate positive electrode material and battery electrode sheet - Google Patents

Abstract

The invention discloses a preparation method of a high-rate lithium iron phosphate positive electrode material and a lithium ion battery positive electrode sheet of the material. The preparation method includes: preparation of lithium iron phosphate cathode material; electroless plating of metal aluminum on the surface of lithium iron phosphate; preparation of lithium iron phosphate-graphene composite material. Compared with the prior art, this composite material has the following advantages: 1. The chemical plating method is used to achieve surface coating at the molecular level; 2. Doping with graphene can greatly improve the conductivity of lithium iron phosphate materials, especially suitable for high-power power Lithium Ion Battery.

Description

A high-rate lithium iron phosphate positive electrode material and battery pole piece

technical field

The invention relates to a preparation method of a high-rate lithium iron phosphate positive electrode material and a positive electrode sheet made of the high-rate positive electrode material.

Background technique

The development of cathode materials is closely related to battery performance, so people have been developing new cathode materials. At present, the widely researched lithium-ion battery cathode materials focus on lithium transition metal oxides such as layered LiMO2 (M=Co, Ni, Mn) and spinel-structured LiMn2O4. As cathode materials, they have their own characteristics. LiCoO2 has high cost, poor resources and high toxicity; LiNiO2 is difficult to prepare and has poor thermal stability; LiMn2O4 has low capacity and poor cycle stability. In order to solve the defects of the above materials, a lot of research has been done in the battery industry. In 1997, Padhi et al. reported that olivine-type LiFePO4 has excellent electrochemical properties. Among them, LiFePO4 has a wide range of raw materials, low price, no environmental pollution, good thermal stability of the material, and outstanding safety performance of the prepared battery. A new generation of cathode material for lithium-ion batteries with the most potential for development and application. However, the pure phase LiFePO4 material has no practical value due to the slow diffusion rate of lithium ions and poor electronic conductivity. The conductivity of the material can be improved by coating, ion doping and adding metal conductive powder; the diffusion path of lithium ions can be shortened by nanonization or preparation of porous materials, so as to improve the utilization rate of lithium ions. The common carbon coating method results in that the carbon layer can only partially cover the particles, and it is difficult to completely cover the particles. This results in a certain polarization phenomenon, and it is difficult to meet the requirements of fast charge and discharge performance.

Graphene is a new material that has emerged in recent years. Its structure can be understood as a single layer of graphite, because it has excellent electrical conductivity, and it also has good electrical conductivity to lithium ions, so it can be used as an additive Modified materials have more prominent advantages. Due to the special two-dimensional planar structure of graphene, materials can be grown on its surface or graphene can coat materials to form composite materials.

Through patent retrieval, patent 200910052413.3, a graphene-composite lithium-ion battery positive electrode material lithium iron phosphate and its preparation method uses graphene with high conductivity as the conductive material, but due to the problem that the degree of graphene composite is not high, so A certain degree of polarization occurs during charging and discharging. Patent 201010207516.5, the preparation method of lithium iron phosphate material and lithium ion battery and its positive plate, the lithium iron phosphate composite material is prepared by electroless plating method, because the electroless plating method is used for surface coating to improve the conductivity of the material, but there are The problem of insufficient long-range conductivity. Through the patent search, the following related reports have not been found: combining electroless metal plating on the surface of lithium iron phosphate and doping graphene to improve the conductivity of lithium iron phosphate materials. The composite material has the following advantages: 1. The electroless plating method is used to realize the surface coating at the molecular level; 2. The conductivity of the lithium iron phosphate material can be greatly improved by doping graphene.

Contents of the invention

The purpose of the present invention is to provide a high-rate LiFePO4 composite material and a method for preparing battery pole pieces, comprising the following steps: step 1, preparation of lithium iron phosphate positive electrode material or directly using ready-made lithium iron phosphate positive electrode material on the market; step 2 , the surface of lithium iron phosphate is chemically plated with metal aluminum; step 3, the preparation of lithium iron phosphate-graphene composite material; step 4, a positive electrode sheet made of the above positive electrode material.

In the preparation method of a high-rate LiFePO4 composite material and a battery pole piece according to the present invention, in the first step, the lithium iron phosphate positive electrode material can be synthesized by a common method or directly purchase a ready-made lithium iron phosphate positive electrode on the market Material. If you synthesize lithium iron phosphate by yourself, the sintering temperature is 600-850 degrees, the holding time is 1-10 hours, and there is argon or nitrogen protective gas.

In the preparation method of a high-rate LiFePO4 composite material and battery pole piece according to the present invention, in the second step, the electroless metal plating on the surface of lithium iron phosphate (taking metal aluminum as an example) includes the following sub-steps:

1. Prepare metal molten salt electroplating solution: the metal molten salt electroplating solution includes aluminum metal room temperature molten salt;

2. Configuration of activation solution: add the chloride salt solution containing active metal Pd, Ru or Rh ions to ethanol, propanol or ethylene glycol, and configure the activation solution of alcohol-water mixture;

3. Activation of lithium iron phosphate cathode material: Under nitrogen or argon inert atmosphere, immerse lithium iron phosphate material in the above activation solution, and reflux under the protection of inert gas, so that the active metal is deposited on the activated matrix lithium iron phosphate material On the surface, the activated lithium iron phosphate positive electrode material is washed, filtered and vacuum-dried;

4. Under the protection of an inert gas, put the activated lithium iron phosphate positive electrode material in the electroplating solution, control the reduction conditions, and layer the metal element on the surface of the lithium iron phosphate, and the redox reaction temperature is 25-50 degrees;

5. Wash the metal-plated lithium iron phosphate positive electrode material with absolute ethanol, and dry the cleaned lithium iron phosphate composite material in vacuum.

In the preparation method of a high-rate LiFePO4 composite material and battery pole piece according to the present invention, in the third step, the lithium iron phosphate/graphene composite material is prepared. After fully mixing the lithium iron phosphate composite material with a certain weight of graphene or graphite oxide, calcining in an inert gas protection at 500-800 degrees for a period of time and then cooling to obtain the high-rate lithium iron phosphate material to be prepared.

In the preparation method of a high-rate LiFePO4 composite material and battery pole piece according to the present invention, in the step 4, after mixing the above-mentioned lithium iron phosphate composite material, conductive agent and binder uniformly according to a certain proportion, apply Cover the surface of the foil, dry and compact to obtain the battery pole piece.

According to a high-rate LiFePO4 composite material and battery pole piece of the present invention, preferably, the inorganic metal aluminum salt includes aluminum halide, and the content of the aluminum halide accounts for 20-50% of the total amount of molten salt; Organic halide onium salts include halide quaternary ammonium salts, halide imidazolium salts, pyridinium salts, and the organic halide onium salt content stands at 30-80% of the total amount of molten salt; the concentration range of the organic reducing agent in the electroplating solution is 0.005- 0.5mol/L, the molar ratio of the organic reducing agent to the aluminum salt in the molten aluminum metal salt is 0.5-5.0.

In a high rate LiFePO4 composite material and battery pole piece according to the present invention, preferably, the activation solution further includes a polymer stabilizer with a concentration not greater than 0.01mol/L, and the stabilizer includes polyvinyl alcohol or poly ethylene glycol.

In the high-rate LiFePO4 composite material and the battery pole piece according to the present invention, preferably, the amount of aluminum coating accounts for 0.1-5.0% of the total amount of the composite material.

According to a kind of high rate LiFePO4 composite material and battery pole piece of the present invention, preferably, the preparation method of lithium iron phosphate/graphene composite material, described graphene material is by single-layer or the number of layers is between 1-20 layers between carbon materials.

According to a kind of high rate LiFePO of the present invention Composite material and battery pole piece, preferably, the preparation method of lithium iron phosphate/graphene composite material, raw material uniform mixing method is that solid phase or solid-liquid machinery fully mixes, and liquid phase material can be Ethanol or acetone is used, the mixing time is 2-50 hours, and the graphene content is between 0.1-5% of the weight of the lithium iron phosphate cathode material.

According to a high-rate LiFePO4 composite material and battery pole piece of the present invention, preferably, the preparation method of the lithium iron phosphate/graphene composite material is calcined at 550°C for 0.5-5h under the protection of nitrogen, and then cooled naturally. The lithium iron phosphate/graphene composite material of the present invention is obtained.

The high-magnification LiFePO4 composite material of the present invention is characterized in that the surface of lithium iron phosphate is uniformly coated with a layer of aluminum metal, and then forms a composite material with graphene, and graphene is distributed inside or on the surface of lithium iron phosphate particles to form a long-range conductive network.

The beneficial effects of the present invention are as follows: 1. The electroless plating method is used to realize surface coating at the molecular level; 2. The conductivity of the lithium iron phosphate material can be greatly improved by doping graphene.

In view of the object of the present invention, in a second aspect of the present invention, the present invention provides a positive electrode sheet of a lithium iron phosphate lithium battery, the positive electrode sheet comprising the above-mentioned lithium iron phosphate composite material.

In view of the object of the present invention, in a third aspect of the present invention, the present invention provides a lithium iron phosphate battery, wherein the positive electrode sheet of the lithium iron phosphate battery contains the above-mentioned lithium iron phosphate composite material.

Description of drawings

Fig. 1 is an XRD diffraction pattern of a high-magnification lithium iron phosphate positive electrode material prepared by the pole piece of the present invention.

Detailed ways

Embodiment one:

Step 1: Preparation of lithium iron phosphate powder by sintering: Lithium carbonate and iron phosphate are used as raw materials, and the ratio of Li, Fe and PO4 is controlled to be 1.05:1:1 for ball milling, with acetone as the medium, and the ball-to-material ratio is 5:1. After milling for 12 hours, the mixture was placed in a tube furnace at 650°C, calcined for 8 hours, protected by argon, and lithium iron phosphate powder was obtained after cooling.

Step 2: Prepare aluminum metal molten salt electroplating solution: the inorganic metal aluminum salt is usually aluminum chloride, and its content accounts for 25% of the total amount of molten salt; 60%, the organic solvent is benzene, and its dosage is to make the final concentration of trivalent aluminum salt 0.05mol/L, the organic reducing agent is lithium hydride, and the molar ratio of organic aluminum salt is 2:1, and the organic reducing agent in the electroplating solution The concentration is 0.25mol/L.

Step 3: Prepare a chloride salt solution containing active metal Pd ions: the concentration of chloride salt is 0.005mol/L, and the volume of the added ethanol and chloride salt solution is equal to configure a 50% alcohol-water mixture. During the preparation process Stir in medium to make the two evenly mixed.

Step 4: Activation of the lithium iron phosphate positive electrode material: Under an argon inert atmosphere, soak the lithium iron phosphate material in the above activation solution, and add a polyethylene glycol stabilizer, the concentration of the stabilizer is 0.005mol/L, inert Stirring and reflux are carried out under gas protection, the reaction temperature is controlled at 30-40 degrees, the active metal is deposited on the surface of the activated matrix lithium iron phosphate material, and the activated lithium iron phosphate positive electrode material is washed, filtered and vacuum-dried.

Step 5: Layer metal elemental aluminum on the surface of lithium iron phosphate: under the protection of argon, place the activated lithium iron phosphate cathode material in the electroplating solution, and stir it with low-speed magnetic force for 3 hours to fully mix the material with the electroplating solution and control the reduction conditions The temperature is 35-45°C.

Step 6: Preparation of high-rate LiFePO4 composite material: Mix the above-mentioned metal-coated lithium iron phosphate material with graphene at 2% of the weight of lithium iron phosphate for 10 hours, and calcinate at 550 degrees for 1.5 hours under the protection of nitrogen. h, natural cooling to obtain the lithium iron phosphate/graphene composite material of the present invention.

Step 7: Make the above-mentioned lithium iron phosphate/graphene composite material into a soft-packed 503759-800mAh high-rate battery according to the current common lithium-ion battery manufacturing process on the market, and then conduct a rate performance test. The test results are as follows:

It can be seen from the data that the internal resistance of the battery made of the lithium iron phosphate/graphene composite material of the present invention is 13.2% lower than that of the conventional aluminum foil battery, and the rate performance is significantly improved.

Claims (8)

1. high magnification lithium iron phosphate positive material and a battery pole piece, comprise the steps: step one, the preparation of lithium iron phosphate positive material or directly use lithium iron phosphate positive material ready-made on the market; Step 2, LiFePO4 surface chemical metal plating aluminium simple substance; Step 3, the preparation of LiFePO4-graphene composite material; Step 4, the positive plate made with above-mentioned positive electrode.

2. high magnification lithium iron phosphate positive material and a battery pole piece, is characterized in that, comprises in described step 2:

Sub-step one: prepare metal fused salt electroplate liquid;

Sub-step two: the configuration of activating solution

Sub-step three: the activation of lithium iron phosphate positive material

Sub-step four: LiFePO4 surface lamination metal simple-substance.

3. a kind of high magnification lithium iron phosphate positive material as claimed in claim 2 and battery pole piece, is characterized in that, the sub-step one described in it prepares metal fused salt electroplate liquid, and described metal fused salt electroplate liquid comprises aluminum metal room temperature fused salt;

The configuration of sub-step two activating solution: the chlorate solution containing active metal Pd, Ru or Rh ion is joined ethanol, in propyl alcohol or ethylene glycol, is configured to the activating solution of alcohol-water mixture;

The activation of sub-step triphosphoric acid iron lithium ion anode material: under nitrogen or argon inert atmosphere, LiFePO 4 material is immersed in above-mentioned activating solution, reflux under inert gas shielding, make reactive metal deposits activated matrix LiFePO 4 material surface, by activation after lithium iron phosphate positive material washing and filtering and vacuumize;

Sub-step four LiFePO4 surface lamination metal simple-substance: under inert gas shielding, by the lithium iron phosphate positive material after activation as in electroplate liquid, control reducing condition, LiFePO4 surface lamination metal simple-substance, described redox reaction temperature is 25-50 degree.

4. a kind of high magnification lithium iron phosphate positive material as claimed in claim 3 and battery pole piece, is characterized in that, in the sub-step one described in it: described inorganic metal aluminium salt comprises aluminum halide, and the content of described aluminum halide accounts for the 20-50% of molten fuse salt total amount; Described organic halogenation salt comprises halogenation quaternary amine, imidazolium halide salt, pyridiniujm, the 30-80% of described organic halogenation salt content station fuse salt total amount; The concentration range of described organic reducing agent in electroplate liquid is 0.005-0.5mol/L, and in described organic reducing agent and described aluminum metal fused salt, the mol ratio of aluminium salt is 0.5-5.0;

In sub-step two: described activating solution also comprises the polymer stabilizer that concentration is not more than 0.01mol/L, described stabilizer comprises, polyvinyl alcohol or polyethylene glycol;

In sub-step four: LiFePO4 covers the 0.1-5.0% that aluminum amount accounts for composite material total amount.

5. a kind of high magnification lithium iron phosphate positive material as claimed in claim 1 and battery pole piece; it is characterized in that; in step 3 described in it; raw material uniform mixing method is solid phase or the fully mixing of solid-liquid machinery; liquid phase substance can adopt ethanol or acetone; incorporation time is 2-50h; wherein Graphene content is between the 0.1-5% of lithium iron phosphate positive material weight; then 550 DEG C of calcining 0.5-5h when there being nitrogen to protect, namely cooling obtains LiFePO4/graphene composite material of the present invention naturally.

6. a kind of high magnification lithium iron phosphate positive material according to claim 1 and battery pole piece, is characterized in that, in the step 3 described in it, grapheme material is that the material with carbon element between 1-20 layer forms by individual layer or the number of plies.

7. high magnification lithium iron phosphate positive material and a battery pole piece, is characterized in that the high magnification lithium iron phosphate positive material that described positive electrode comprises any one in 1-6 and prepares.

8. high magnification lithium iron phosphate positive material and a battery pole piece, is characterized in that the high magnification lithium iron phosphate positive material that described positive plate comprises any one in 1-6 and prepares.