CN1958441A

CN1958441A - Method for preparing powder of lithium iron phosphate

Info

Publication number: CN1958441A
Application number: CNA2006101367386A
Authority: CN
Inventors: 胡国荣; 彭忠东; 高旭光; 杜柯; 李劼; 刘业翔
Original assignee: Central South University
Current assignee: Qinghai Tuohai New Material Co., Ltd.
Priority date: 2006-11-24
Filing date: 2006-11-24
Publication date: 2007-05-09
Anticipated expiration: 2026-11-24
Also published as: CN100450920C

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

Preparation method of lithium iron phosphate powder

The invention belongs to the technical field of a preparation method of a lithium ion battery anode material, and particularly relates to a method for directly synthesizing a cathode material lithium iron phosphate by improving a reaction system without introducing inert gas protection.

Background art olivine structured LiFePO₄The material has wide source of raw materials and low price, and has excellent high-temperature performance when being used as the anode material of the lithium ion battery, thus being an ideal anode material of the lithium ion secondary power battery.

LiFePO is synthesized at present₄The method mainly comprises a high-temperature solid phase method, a hydrothermal method, a sol-gel method, a liquid phase oxidation-reduction method and a solid phase microwave method.

The high-temperature solid phase method which is widely adopted at present is to mix oxalate or acetate of ferrous iron with ammonium hydrogen phosphate and lithium salt, and then to obtain the product by high-temperature calcination under the protection of argon or nitrogen in inert atmosphere. This method requires the uninterrupted introduction of inert gas to protect against oxidation of the product being produced.

Although the hydrothermal method belongs to a liquid phase reaction environment and does not need to introduce protective gas, the hydrothermal method is only limited to the preparation of a small amount of powder, and the preparation amount is limited if the preparation amount is enlarged, and particularly, the design and manufacture difficulty of a large-scale high-temperature and high-pressure resistant reactor is high, and the manufacturing cost is high.

Thesol-gel method has the advantages of large drying shrinkage of the precursor, high industrial production difficulty and long synthesis period. Furthermore, metal alkoxides are expensive and the solvents for the alkoxides are generally toxic.

The liquid phase oxidation-reduction method uses vitamin C acid and H₂O₂LiI, etc., which increases the cost of the product and the complexity of the process, and is not suitable for industrial production.

Disclosure of Invention

Aiming at the problems of the lithium iron phosphate serving as the cathode material for the lithium ion battery, the invention provides a novel preparation method of the lithium iron phosphate. And secondly, the invention adopts a brand-new reaction system to avoid using a large amount of inert gas, thereby greatly reducing the production cost of the product. The preparation method is simple and easy to implement, and the prepared lithium iron phosphate has excellent physical and electrochemical properties and is suitable for industrial production.

A preparation method of lithium iron phosphate powder mainly comprises the following steps:

lithium salt, iron salt, phosphate, doping elements and a conductive agent are used as raw materials, and the lithium salt, the iron salt and the doping metal ions (Me) are addedⁿ⁺) And phosphate according to the mol ratio of lithium to iron to Meⁿ⁺Phosphoric acid is 1.0: x (1-x) to1.0, wherein x is 0.80-0.99, the raw materials are ball-milled and mixed uniformly, the addition amount of the conductive agent or the precursor of the conductive agent is 5-40% of the generation amount of the lithium iron phosphate, the uniformly mixed precursor is pressed into blocks by a press, then a layer of carbon powder with the thickness of 2-3 cm is covered, the blocks are placed in a muffle furnace, the reaction temperature is 300-800 ℃, the reaction time is 6-12 hours, and the blocks are cooled to room temperature to prepare the lithium iron phosphate powder.

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

the iron salts include: one or more of ferrous oxalate, ferric oxide, ferrous sulfate and ferric phosphate;

the phosphate salts include: one or more of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, iron phosphate and lithium dihydrogen phosphate;

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

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

The main reactions taking place in the reaction system of the invention are as follows (as Fe)₂O₃，LiH₂PO₄And carbon powder as examples):

general reaction

The first reaction with the temperature of the reaction system rising is the reaction of the oxygen left in the material boatCarbon oxide CO₂And then CO is generated, and the surplus reducing gas (CO) in the system plays a role in protecting the reactants in the heat preservation process to maintain the system to have a strong reducing atmosphere, so that the carbothermic reduction reaction can occur (the temperature is higher than 750 ℃). The carbon powder and corundum sheet covered in the cooling process can isolate the product from the outside air, so that the oxidation in the cooling process is avoided.

According to the invention, the reactant is briquetted, so that the air content in the precursor of the reactant is greatly reduced, the synthesized material is easily separated from carbon powder, the contact between the precursor and the air can be further avoided by covering the carbon powder on the briquetting body, and the consumption of the carbon powder can be further reduced by covering a corundum piece on the charging crucible, namely, the phase of the reactant is lithium iron phosphate with an olivine structure as long as the covered carbon powder exists in the final calcined product. The problems that the traditional high-temperature solid phase method or the common carbothermic reduction reaction solid phase method uses ammonium dihydrogen phosphate or ammonium monohydrogen phosphate as raw materials to generate ammonia gas, which is not beneficial to environmental protection and has overlong reaction time are solved.

The reaction system is changed from the traditional inert atmosphere to the strong reducing atmosphere, the inert gas flow is not used for protection, the production cost is greatly reduced, and the prepared lithium iron phosphate has high purity and excellent electrochemical and physical properties.

Drawings

FIG. 1 is a schematic diagram of a reaction system according to the present invention; wherein: 1-corundum piece, 2-ground corundum crucible, 3-carbon powder and 4-blocky precursor;

FIG. 2 shows LiFePO prepared in the examples₄XRD pattern of the/C composite material;

FIG. 3 shows the LiFePO content prepared in the examples₄The first charging curve diagram of the/C composite material (test condition: the test of the battery is carried out at room temperature (20 ℃), a metal lithium sheet is taken as a negative electrode, and a positive electrode sheet is formed by pressing 80% (mass ratio) of electrode material powder, 10% of acetylene black and 10% of adhesive (polytetrafluoroethylene, PTFE)Prepared by using 1mol/l LiPF as electrolyte₆/(EC + DME). The diaphragm adopts Celgard 2400 membrane, and the charge-discharge multiplying power is 0.2C. The cell was made in a glove box filled with high purity argon. )

FIG. 4 shows LiFePO prepared in example 1₄Cycle performance diagram of the/C composite.

Detailed Description

Example 1: 10.58 g of lithium dihydrogen phosphate and 8.025 g of ferric oxide are added with 4.72 g of cane sugar at the same time, ball milling and mixing are carried out, drying and briquetting are carried out, then the massive precursor is placed in a ground corundum material boat, carbon powder with the thickness of 2-3 cm is covered on the massive precursor, the material boat is placed at the temperature control point of a muffle furnace to start heating, the reaction condition is 700 ℃, the reaction time is 12 hours, then the sample is taken out after the vacuum furnace is cooled to the room temperature, and LiFePO is prepared₄a/C composite material.

Example 2: the method comprises the steps of carrying out high-energy ball milling on a mixture containing 3.71 g of lithium carbonate, 18 g of ferrous oxalate, 0.37 g of NiO, 11.52 g of ammonium dihydrogen phosphate and 3.2 g of cane sugar, drying and briquetting the mixture, then placing a massive precursor into a ground corundum material boat, covering carbon powder with the thickness of 2-3 cm on the massive precursor, placing the material boat at a temperature control point of a muffle furnace to start heating, wherein the reaction condition is 750 ℃, the reaction time is 10 hours, then taking out a sample after the vacuum furnace is cooled to room temperature, and obtaining LiFePO₄a/C composite material.

Claims

1. A preparation method of lithium iron phosphate powder is characterized by comprising the following steps: lithium salt, ferric salt, phosphate, doping elements and conductive agent are adopted as raw materials, and the lithium salt, the ferric salt, the doping metal ions and the phosphate are mixed according to the mol ratio of lithium to iron to Meⁿ⁺1.0: x: 1-x: 1.0, wherein x is 0.80-0.99, the raw materials are ball-milled and mixed uniformly, the addition amount of the conductive agent or the precursor of the conductive agent is 5-40% of the generation amount of the lithium iron phosphate, the uniformly mixed precursor is pressed into blocks by a press, covered with a layer of carbon powder with the thickness of 2-3 cm, placed in a muffle furnace,the reaction temperature is 300-800 ℃, the reaction time is 6-12 hours, and the lithium iron phosphate powder is prepared after cooling to room temperature.

2. The method for producing lithium iron phosphate powder according to claim 1, characterized in that: the lithium salt includes: one or more of lithium carbonate, lithium hydroxide, lithium nitrate, lithium chloride and lithium dihydrogen phosphate.

3. The method for producing lithium iron phosphate powder according to claim 1, characterized in that: the iron salts include:one or more of ferrous oxalate, ferric oxide, ferrous sulfate and ferric phosphate.

4. The method for producing lithium iron phosphate powder according to claim 1, characterized in that: the phosphate salts include: one or more of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, iron phosphate and lithium dihydrogen phosphate.

5. The method for producing lithium iron phosphate powder according to claim 1, characterized in that: the doping element is one or more of manganese, zinc, titanium, magnesium, aluminum, zirconium, niobium, chromium, rare earth and the like.

6. The method for producing lithium iron phosphate powder according to claim 1, characterized in that: the conductive agent is one or more of acetylene black, crystalline flake graphite, sucrose, glucose and polyvinyl alcohol.