CN100450920C - Method for preparing powder of lithium iron phosphate - Google Patents

Abstract

This invention relates to a method for synthesizing anode material lithium iron phosphate for lithium-ion batteries by high tecf12 micropowder can be used as filler for epoxy resin to prepare packaging material for large and ultra-large scale integrated circuit, or for other high-quality electronic devices.

Description

A kind of preparation method of lithium iron phosphate powder

technical field

The invention belongs to a method for preparing positive electrode materials of lithium ion batteries, in particular to a method for directly synthesizing the positive electrode material lithium iron phosphate by improving the reaction system without using inert gas protection.

Background technique

Olivine-structured LiFePO ₄ has wide sources of raw materials, low price, and excellent high-temperature performance as a cathode material for lithium-ion batteries, so it is considered to be an ideal cathode material for lithium-ion secondary power batteries.

At present, the methods for synthesizing LiFePO ₄ mainly include high-temperature solid-phase method, hydrothermal method, sol-gel method, liquid-phase redox method, and solid-phase microwave method.

The currently widely used high-temperature solid-phase method is to mix ferrous oxalate or acetate with ammonium hydrogen phosphate and lithium salt, and then calcine at high temperature under the protection of an inert atmosphere of argon or nitrogen to obtain the product. This method requires uninterrupted feeding of inert gas for protection so that the prepared product will not be oxidized.

Although the hydrothermal method belongs to the liquid phase reaction environment and does not need to introduce protective gas, it is limited to the preparation of a small amount of powder. If it is to expand its preparation amount, it is subject to many restrictions, especially the design and manufacture of large-scale high-temperature and high-pressure reactors. Big and expensive.

The sol-gel method has a large drying shrinkage of the precursor, which makes industrial production difficult and the synthesis cycle is long. In addition, metal alkoxides are expensive, and the solvents of the alkoxides are usually toxic.

The liquid-phase redox method uses vitamin C acid, H ₂ O ₂ , LiI, and other chemical products, which increases the cost of the product and the complexity of the process, so it is not suitable for industrial production.

Contents of the invention

Aiming at the above-mentioned problems of lithium iron phosphate, the positive electrode material for lithium ion batteries, the present invention provides a novel preparation method of lithium iron phosphate. The lithium source and the phosphorus source use self-made doped lithium dihydrogen phosphate as raw materials. Secondly, the present invention adopts a brand-new reaction system to avoid the use of a large amount of inert gas, thereby greatly reducing the production cost of the product. The process of the invention is simple and easy, and the prepared lithium iron phosphate has excellent physical properties and electrochemical properties, and is suitable for industrial production.

A preparation method of lithium iron phosphate powder, mainly comprising:

Using lithium salt, iron salt, phosphate, doping element and conductive agent as raw materials, the lithium salt, iron salt, doping metal ion (Me ⁿ⁺ ) and phosphate according to the molar ratio of lithium: iron: ^{Me n+} : phosphoric acid are 1.0 : x: (1-x): 1.0, wherein x=0.80-0.99, the raw materials are uniformly mixed through ball milling, the addition of the conductive agent or the precursor of the conductive agent is 5-40% of the amount of lithium iron phosphate generated, and the uniformly mixed After the precursor is pressed into a block by a press, it is covered with a layer of carbon powder with a thickness of 2-3 cm, placed in a muffle furnace, the reaction temperature is 300-800 ° C, the reaction time is 6-12 hours, cooled to room temperature, and prepared Obtain lithium iron phosphate powder.

The lithium salt includes: one or more of lithium carbonate, lithium hydroxide, lithium nitrate, lithium chloride, lithium dihydrogen phosphate;

The iron salt includes: one or more of ferrous oxalate, ferric oxide, ferrous sulfate, ferric phosphate;

The phosphate includes: one or more of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, iron phosphate, lithium dihydrogen phosphate;

The doping element is one or more of nickel, manganese, zinc, titanium, magnesium, aluminum, zirconium, niobium, chromium and rare earth elements.

The conductive agent is one or more of acetylene black, flake graphite, sucrose, glucose and polyvinyl alcohol.

The main reaction that reaction system of the present invention takes place is as follows (with Fe ₂ O ₃ , LiH ₂ PO ₄ and carbon powder are example):

As the temperature of the reaction system continues to rise, the first reaction is that the residual oxygen in the material boat reacts to form carbon oxide CO ₂ , and then produces CO. During the heat preservation process, the excess reducing gas (CO) in the system will The reactants play a protective role and maintain a strong reducing atmosphere in the system, so that the carbothermal reduction reaction can occur (temperature higher than 750 degrees Celsius). The carbon powder and corundum sheet covered during the cooling process will isolate the product from the outside air to avoid oxidation during the cooling process.

In the present invention, by briquetting the reactant, the air content in the reactant precursor can be greatly reduced, and the synthesized material and carbon powder can be easily separated, and the precursor and air can be further avoided by covering the briquette body with carbon powder. The consumption of carbon powder can be further reduced by adding a corundum sheet on the charging crucible, that is to say, as long as there is covered carbon powder in the final calcined product, the phase of the reactant can be guaranteed to be olivine Structure of lithium iron phosphate. It avoids the problems of using ammonium dihydrogen phosphate or ammonium monohydrogen phosphate as raw materials in the traditional high-temperature solid-phase method or common carbothermal reduction reaction solid-phase method, which is not conducive to environmental protection and has too long reaction time.

The reaction system of the invention is changed from a traditional inert atmosphere to a strong reducing atmosphere, and the production cost is greatly reduced without the protection of an inert gas flow, and the prepared lithium iron phosphate has high purity and excellent electrochemical and physical properties.

Description of drawings

Fig. 1 is a schematic diagram of the reaction system of the present invention; wherein: 1-corundum sheet, 2-ground corundum crucible, 3-carbon powder, 4-block precursor;

Fig. 2 is the XRD figure of the LiFePO ₄ /C composite material prepared by the embodiment;

Fig. 3 is the first charging curve of the LiFePO ₄ /C composite material prepared by the embodiment (test conditions: the test of the battery is carried out at room temperature (20 ° C), with the metal lithium sheet as the negative electrode, and the positive electrode sheet is composed of 80% ( Mass ratio) of electrode material powder, 10% acetylene black, 10% binder (polytetrafluoroethylene, PTFE) pressed, the electrolyte is 1mol/l LiPF ₆ /(EC+DME). The diaphragm adopts Celgard 2400 film, the charge and discharge rate is 0.2C. The battery is made in a glove box filled with high-purity argon.)

FIG. 4 is a graph of cycle performance of the LiFePO ₄ /C composite material prepared in Example 1. FIG.

Detailed ways

Example 1: 10.58 grams of lithium dihydrogen phosphate, 8.025 grams of ferric oxide, and 4.72 grams of sucrose were added at the same time, and ball milled and mixed together, dried and pressed into blocks, and finally the block precursor was placed in the corundum material boat at the grinding port , and then cover the bulk precursor with 2-3 cm thick carbon powder, place the material boat at the temperature control point of the muffle furnace to start heating up, the reaction condition is 700 ° C, the reaction time is 12 hours, and then wait for the vacuum furnace to cool The sample was taken out at room temperature to obtain a LiFePO ₄ /C composite material.

Example 2: A mixture containing 3.71 grams of lithium carbonate, 18 grams of ferrous oxalate, 0.37 grams of NiO, 11.52 grams of ammonium dihydrogen phosphate, and 3.2 grams of sucrose was subjected to high-energy ball milling, dried, and briquetted, and then the bulk precursor Put it in the ground corundum material boat, and then cover the block precursor with 2-3 cm thick carbon powder, place the material boat at the temperature control point of the muffle furnace to start heating, the reaction condition is 750 °C, and the reaction time is 10 hours, and then the sample was taken out after the vacuum furnace was cooled to room temperature, and the LiFePO ₄ /C composite material was obtained.

Claims (6)

1. a preparation method of lithium iron phosphate powder, is characterized in that: adopt lithium salt, iron salt, phosphate, doping element and conductive agent as raw material, lithium salt, iron salt, doping metal ion and phosphate According to the molar ratio of lithium: iron: Me ⁿ⁺ : phosphoric acid is 1.0: x: (1-x): 1.0, wherein x = 0.80-0.99, the raw materials are mixed uniformly by ball milling, and the addition amount of the conductive agent or the precursor of the conductive agent is phosphoric acid 5-40% of the amount of lithium iron produced, the uniformly mixed precursor is pressed into a block by a press, covered with a layer of carbon powder with a thickness of 2-3 cm, placed in a muffle furnace, and the reaction temperature is 300-800 ° C. The reaction time is 6-12 hours, and the mixture is cooled to room temperature to obtain lithium iron phosphate powder. 2. The method for preparing lithium iron phosphate powder according to claim 1, wherein the lithium salt comprises one or more of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate. 3. The method for preparing lithium iron phosphate powder according to claim 1, wherein the iron salt comprises one or more of ferrous oxalate, ferric oxide, and ferrous sulfate. 4. The preparation method of lithium iron phosphate powder according to claim 1, characterized in that: the phosphate comprises: one or more of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, iron phosphate, lithium dihydrogen phosphate . 5 . The method for preparing lithium iron phosphate powder according to claim 1 , wherein the doping element is one or more of nickel, manganese, zinc, titanium, magnesium, and aluminum. 6. The method for preparing lithium iron phosphate powder according to claim 1, wherein the conductive agent is one or more of acetylene black, flake graphite, sucrose, and glucose.

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