CN100413781C - Synthetic method of lithium iron phosphate lithium ion battery cathode material - Google Patents

Abstract

The present invention discloses a synthetic method of lithium ferrous phosphate as anode materials of a lithium ion battery. The concrete synthetic method of the present invention is as follows: lithium salt, ferrous salt and ammonium biphosphate are taken and uniformly mixed according to the proportion of the molar ratio that is (0.8 to 1.2): (0.8 to 1.2): (0.8 to 1.2) of lithium ions: ferrous ions: phosphate radical ions to obtain a compound A, a certain quantity of the compound A is put into a certain amount of water solution B containing soluble salt and soluble organic substances and is put into a high-temperature furnace to carry out high-temperature treatment in a non-air or non-oxidization atmosphere, and then, natural cooling is carried out to synthesize ferrous phosphate powder containing carbon simple substances and mixed with metal ions. Synthesized lithium ferrous phosphate powder is milled, and a particle diameter is controlled between 1 to 50 mu m. The distribution of materials after synthesized by the present invention is uniform, and the charging capacity of the battery can be effectively improved when the materials are used as the anode materials of the lithium ion battery.

Description

Synthetic method of lithium iron phosphate lithium ion battery cathode material

technical field

The invention relates to a cathode material of a lithium ion battery, in particular to a synthesis method of lithium iron phosphate, an anode material of a lithium ion battery.

Background technique

As a green high-energy power source, lithium-ion batteries have been widely valued for more than ten years. It has the characteristics of high energy density, good cycle performance and low self-discharge rate. In recent years, the battery industry generally believes that lithium iron phosphate (molecular formula: LiFePO ₄ ) is one of the best new cathode materials for high-energy power batteries. In order to improve the capacity of lithium iron phosphate, carbon and metal doping are generally adopted during the synthesis process. ion. Chinese Patent Publication No. (Patent No.: 200410039176.4) discloses a preparation method of lithium ferrous phosphate, a positive electrode material for lithium ion batteries. It is to mix lithium salt, ferrous salt, phosphate and additives uniformly in proportion and put them into heat treatment equipment , heated in sections under the protection of an inert gas flow with a flow rate of 0.01-50 liters/minute, with a heating rate of 1-20°C/mi. 30 hours, then continue to heat up, carry out high-temperature treatment, keep the temperature at 500-850° C. for 10-48 hours, and then cool down to room temperature to prepare lithium iron phosphate cathode material. This preparation method is simple to operate and easy to control, and the prepared product has excellent electrical conductivity. The disadvantage is that because the added carbon is added in the form of solid, the amount of addition is relatively small, so it is not easy to mix. Thoroughly, so that the positive electrode material in the synthesized ferrous phosphate is not uniform, and the capacity of the material cannot be effectively improved.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art, and provide a method for synthesizing a high-capacity lithium ferrous phosphate battery cathode material with short synthesis time and uniform synthetic materials.

The technical scheme of the present invention is

1. Take lithium source, ferrous salt, and ammonium dihydrogen phosphate, and mix them uniformly in the ratio of lithium ion: ferrous ion: phosphate ion molar ratio (0.8-1.2): (0.8-1.2): (0.8-1.2) Mixture A is obtained in which:

The lithium source is one of lithium carbonate, lithium hydroxide, dilithium hydrogen phosphate, lithium sulfate, lithium acetate, lithium nitrate and lithium oxalate.

The ferrous salt is ferrous acetate or ferrous oxalate.

2. Put a certain amount of mixture A above into a certain amount of aqueous solution B containing soluble salts and soluble organics, stir evenly, put it in a high-temperature furnace, and heat it at 1-30 ° C / Heating at a heating rate of 1 min, when the temperature rises to 50-200°C, heat preservation time of 0-100h, the higher the temperature, the shorter the time, and then perform high-temperature treatment according to the existing one-stage or stage-by-stage heating method, natural cooling, and synthesis of carbon-containing simple substances (expressed by C) and ferrous phosphate powder (expressed by Li _x Fe _y M _z PO ₄ ) doped with metal ions (expressed by M), the values of x, y, and z in the formula are based on the corresponding substances under the following conditions Depends on the dosage;

(1) The mass ratio of the aqueous solution B to the mixture A is = (0.1-10): 1;

(2) The soluble salts in aqueous solution B include at least: nitrates, acetates, and sulfates of metal elements such as aluminum, titanium, magnesium, zirconium, vanadium, manganese, nickel, cobalt, niobium, rhodium, barium, and chromium and one of hydrochloride, its dosage must meet the following conditions: the molar ratio of the metal ion (M) in the soluble salts to the lithium ion in the lithium source is ≤0.3;

(3) The soluble organic substances in the aqueous solution B include at least one of: sucrose, glucose, and one of the soluble polymer compounds that can be decomposed into conductive carbon substances by pyrolysis, and the dosing amount must meet the following conditions: The mass ratio of simple carbon to Li _x Fe _y M _z PO ₄ in the composition is ≤1.0;

3. Grinding the lithium iron phosphate powder synthesized above, and controlling the particle size between 1-50 μm.

Because the present invention adopts the above-mentioned solution mixing method, it is easy to mix and thoroughly mixed, so that the material after synthesis is distributed evenly. When the material is used as the positive electrode material of lithium ion battery, the charging capacity of the battery can be effectively improved.

Detailed ways

In order to illustrate the present invention more clearly, the following examples are cited, but they do not limit the present invention in any way.

Embodiment one:

(1) First, lithium oxalate, ferrous oxalate and ammonium dihydrogen phosphate are uniformly mixed in a ratio of lithium ion: ferrous ion: phosphate ion molar ratio of 1:1:1 to obtain mixture A

(2) Take 1 kg of mixture A and put it into 1 kg of aqueous solution B containing glucose and zirconium nitrate, stir evenly, heat at a heating rate of 20°C/min under a nitrogen atmosphere, keep it warm for 5 hours when the temperature reaches about 100°C, and then continue to heat up , kept at 700°C for 10 hours, cooled naturally, and synthesized lithium ferrous phosphate powder containing carbon simple substance and doped metal zirconium ions, wherein:

It is required that 1 kg of aqueous solution B contains 10 g of glucose and 1 g of zirconium nitrate (Zr(NO ₃ ) ₄ ) (about 0.003 mol);

According to step (1), it can be seen that 1 kg of mixture A contains 1.62 moles of lithium oxalate (Li ₂ C ₂ O ₄ molecular weight: 102), 3.24 moles of ferrous oxalate (FeC ₂ O ₄ . Molecular weight: 143) and 3.24 moles of ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ molecular weight: 115), so the finally synthesized lithium ferrous phosphate positive electrode material containing carbon simple substance and doped metal zirconium ions is represented by LiFeZr _{0 0009} PO ₄ ;

(3) Grinding the synthesized lithium iron phosphate powder, and controlling the particle size between 1-50 μm.

Embodiment two:

(1) First, lithium carbonate, ferrous oxalate and ammonium dihydrogen phosphate are uniformly mixed in a ratio of lithium ion: ferrous ion: phosphate ion molar ratio of 1:1:1 to obtain mixture A

(2) Take 1kg of mixture A and put it into 1kg of aqueous solution B containing polyvinyl alcohol and magnesium nitrate, stir evenly, heat at a heating rate of 30°C/min under a nitrogen atmosphere, and keep it warm for 4 hours when the temperature rises to about 110°C. Continue to heat up, when the temperature reaches 300 ° C, keep the temperature for 5 hours, then continue to heat up to 700 ° C, keep the temperature for 5 hours, cool naturally, and synthesize lithium ferrous phosphate powder containing carbon element and doped metal magnesium ions, wherein:

It is required that 1 kg of aqueous solution B contains 10 g of polyvinyl alcohol and 1 g of magnesium nitrate (about 0.004 moles);

According to step (1), it can be seen that 1 kg of mixture A contains 1.70 moles of lithium carbonate (Li ₂ CO ₃ molecular weight 74), 3.48 moles of ferrous oxalate (FeC ₂ O ₄ molecular weight: 143) and 3.4 moles of ammonium dihydrogen phosphate (NH ₄ H ₂ PO _Molecular weight: 115), so the finally synthesized lithium iron phosphate positive electrode material containing simple carbon and doped metal magnesium ions can be expressed as LiFeMg _{0 0013} PO ₄ ;

(3) Grinding the synthesized lithium iron phosphate powder, and controlling the particle size between 1-50 μm.

Embodiment three:

(1) At first three kinds of materials dilithium hydrogen phosphate, ferrous oxalate and ammonium dihydrogen phosphate are uniformly mixed in the ratio of lithium ion: ferrous ion: phosphate ion molar ratio is 1: 1: 1 to obtain mixture A;

(2) Take 1 kg of mixture A and put it into 1 kg of aqueous solution B containing sucrose and magnesium nitrate and stir evenly. Under nitrogen atmosphere, heat at a heating rate of 5°C/min. When the temperature reaches about 90°C, keep it warm for 6 hours, and continue heating. When the temperature reaches 300°C, keep the temperature for 5 hours, then continue to heat up to 700°C, keep the temperature for 5 hours, cool naturally, and synthesize lithium ferrous phosphate powder containing carbon element and doped metal magnesium ions, wherein:

It is required to contain 10 g of sucrose and 1 g of magnesium nitrate (about 0.004 mole) in 1 kg of aqueous solution B;

According to step (1), it can be known that 1 kg of mixture A contains 1.6 moles of dilithium hydrogen phosphate (Li ₂ HPO ₄ molecular weight 110), 3.2 moles of ferrous oxalate (FeC ₂ O ₄ molecular weight: 143) and 3.2 moles of ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ molecular weight: 115), so the finally synthesized lithium iron phosphate positive electrode material containing carbon simple substance and doped metal magnesium ions can be represented by LiFeMg _{0 0011} PO ₄ ;

(3) Grinding the synthesized lithium iron phosphate powder, and controlling the particle size between 1-50 μm.

For ease of calculation, when the lithium source, ferrous salt, and ammonium dihydrogen phosphate in the examples of the present invention are mixed, they are all carried out according to the ratio of lithium ion: iron ion: phosphate ion molar ratio is 1: 1: 1, thus Make the values of X, Y, and Z in the finally synthesized lithium iron phosphate powder molecular formula LiFeMg _{0 0013} PO ₄ equal, but this should not be used as a limitation to the technical solution of the present invention.

Claims (1)

1. A synthetic method of lithium-ion battery cathode material lithium ferrous phosphate, its concrete synthetic method is as follows: (1) Get lithium source, ferrous salt, ammonium dihydrogen phosphate, and press lithium ion: ferrous ion: phosphate ion molar ratio is (0.8-1.2): (0.8-1.2): (0.8-1.2) evenly Mix to obtain mixture A, wherein: The lithium source is one of lithium carbonate, lithium hydroxide, dilithium hydrogen phosphate, lithium sulfate, lithium acetate, lithium nitrate and lithium oxalate, and the ferrous salt is ferrous acetate or ferrous oxalate; (2) Put a certain amount of mixture A above into a certain amount of aqueous solution B containing soluble salts and soluble organics, stir evenly, put it in a high-temperature furnace, and heat it at 1-30°C in a non-oxidizing atmosphere. Heating at a heating rate of /min, when the temperature rises to 50-200°C, keep it warm for 0-100h, the higher the temperature, the shorter the time, then perform high-temperature treatment according to the existing heating method, cool naturally, and synthesize carbon containing C and doped Lithium ferrous phosphate powder Li _x Fe _y M _z PO ₄ of metal ion M, where the values of x, y, and z are determined according to the dosing amount of the corresponding substance under the following conditions; ① The mass ratio of aqueous solution B to mixture A is (0.1-10): 1; ②The soluble salts in aqueous solution B include at least: nitrate, acetate, sulfate and hydrochloric acid of aluminum, titanium, magnesium, zirconium, vanadium, manganese, nickel, cobalt, niobium, rhodium, barium, chromium metal elements One of the salts, the doping amount must meet the following conditions: the molar ratio of the metal ion M in the soluble salt to the lithium ion in the lithium source is ≤0.3; ③ The soluble organic substances in the aqueous solution B include at least one of: sucrose, glucose and one of the soluble polymer compounds that can be decomposed into conductive carbon substances by pyrolysis, and the dosage must meet the following conditions: the final composition The mass ratio of carbon simple substance in Li _x Fe _y M _z PO ₄ is ≤1.0; (3) Grinding the lithium iron phosphate powder synthesized above, and controlling the particle size between 1-50 μm.