CN1958440A - Method for synthesizing Nano level powder of lithium iron phosphate - Google Patents

Abstract

This invention relates to a quenching method for preparing nanoscale anode material lithium iron phosphate for lithium-ion batteries. The method comprises: mixing lithium salt, iron salt, phosphate, organic precursor of carbon, and doping metal ions by high energy ball milling, oven-drying, loading into an inert atmosphere furnace, reacting at 300-400 deg.C for 2-6 h, cooling to room temperature, taking out the powder, pressing into block, loading into a stainless steel container, vacuumizing, sealing, placing the sealed stainless steel container into a muffle furnace, calcining, taking out the stainless steel container at the calcining temperature, and quenching to obtain nanoscale anode material lithium iron phosphate, which has such advantages as high electronic-ionic conductivity and excellent electrochemical properties.

Description

A method for synthesizing nanoscale lithium iron phosphate powder

Technical field The present invention belongs to a method for preparing a cathode material for a nanoscale lithium ion battery, in particular a method for synthesizing a cathode material lithium iron phosphate with high electron-ion conductivity by a quenching method.

Background technology LiFePO ₄ with olivine structure 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. However, LiFePO ₄ has the disadvantage of poor electron-ion conductivity, so improving its electron-ion conductivity is a problem that lithium iron phosphate must solve for its application.

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. The crystal grains of lithium iron phosphate synthesized by this method are coarse, and the ion-electronic conductivity of the material is poor.

The carbothermal reduction method is also one of the high-temperature solid-phase methods. Generally, ferric oxide or ferric oxide is used as the iron source. Under the protection of high temperature and argon or nitrogen, carbon reduces ferric iron to ferrous iron. The problem that the reaction time of this method is too long and the crystal grains grow too much still exists, so it is difficult to prepare positive electrode materials with excellent electrochemical performance.

Although the hydrothermal method can prepare nano-scale lithium iron phosphate cathode materials with high electron-ion conductivity, the hydrothermal method needs to use a high-temperature and high-pressure reactor, and the final product is often accompanied by impurities, and the preparation process is difficult to control. .

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.

SUMMARY OF THE INVENTION Aiming at the disadvantages of poor lithium iron phosphate ion-electron conductivity, the present invention aims at preparing nanometer-sized lithium iron phosphate with high electron-ion conductivity and proposes a preparation method of lithium iron phosphate, which uses quenching The preparation of nano-scale lithium iron phosphate by cold technology can prepare electrode materials with high electron-ion conductivity and excellent electrochemical performance.

The present invention prepares the practice of lithium iron phosphate cathode material as follows:

A method for synthesizing nanoscale lithium iron phosphate powder, using lithium salt, iron salt, phosphate, doping element and conductive agent as raw materials, lithium salt, iron salt, doping metal ion (Me ⁿ⁺ ) and phosphate According to the molar ratio: Lithium: Iron: Me ⁿ⁺ : Phosphoric acid 1.0: x (x = 0.80-0.99): (1-x): 1.0, at the same time, add a conductive agent of 0.5-2.0% of the total mass of the above raw materials; mix evenly through ball milling Then put it in an inert atmosphere reaction furnace, the reaction temperature is 300-400°C, the holding time is 2-6 hours, then cool to room temperature; take out the powder, briquetting, and then put the block precursor in a heat-resistant stainless steel container , vacuum-sealed, placed in a muffle furnace and calcined at 500-800°C for 10-20 hours, then the sealed heat-resistant stainless steel container was taken out at the calcining temperature for quenching, and nano-scale lithium iron phosphate was obtained after quenching Powder material.

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 manganese, zinc, titanium, magnesium, aluminum, zirconium, niobium, chromium and rare earth elements,

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

The present invention decomposes by-products by calcining at a low temperature of 300-400°C, and then briquetting the resulting precursor can significantly increase the tap density of the product; applying the quenching technology to the present invention has the characteristics of short cooling time and low synthesis temperature , and the prepared lithium iron phosphate product has high purity, low carbon content, excellent electrochemical and physical properties, and the material synthesized by quenching technology has nano-sized grain size and high electronic-ionic conductivity.

The nanometer-sized lithium iron phosphate prepared by the present invention can effectively reduce the diffusion path of lithium ions in the electrode reaction process, and because the particles are small, the material can be fully contacted with the electrolyte to improve the utilization rate of the active material. Through bulk phase doping and Surface coating can improve the intrinsic conductivity of the material and improve the interfacial charge transfer capability of the electrode-electrolyte solution, and the first discharge capacity can reach 155mAh/g, while the lithium iron phosphate prepared by the traditional high-temperature solid-phase method can reach 0.2C rate. The first discharge capacity is only 110mAh/g.

Description of drawings

Figure 1: SEM image of the sample, wherein A-sample obtained in Example 1, B-sample obtained in Example 2, C-sample obtained in Example 3;

Figure 2: XRD pattern of the sample, wherein A-sample obtained in Example 1, sample obtained in B-Example 2, and sample obtained in C-Example 3;

Figure 3: The charge and discharge curve-voltage diagram of the sample, where A-the sample obtained in Example 1, B-the sample obtained in Example 2, and C-the sample obtained in Example 3.

Detailed ways

Example 1: 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, 11.52 grams of sucrose and 1.2 grams of sucrose was passed through high-energy ball milling, dried at a low temperature of 60°C and placed in a self-made inert atmosphere reaction furnace , start to heat up, the reaction temperature is 300-400°C and the holding time is 4 hours, decompose and discharge by-products, then cool to room temperature, and pass inert gas for protection during the whole process. The powder is taken out and compacted, and then the bulk precursor is placed in a heat-resistant stainless steel container and vacuum-sealed. Place the sealed heat-resistant stainless steel container in a muffle furnace for a certain period of calcination at 650°C, then take out the sealed heat-resistant stainless steel container at the calcination temperature for quenching, and take out the product to obtain nano-scale lithium iron phosphate doped with nickel ions Powder material. The specific capacity of the prepared material was tested to be 155mAh/g. Example 2: A mixture containing 3.71 grams of lithium carbonate, 18 grams of ferrous oxalate, MnCO _0.114 grams of ammonium dihydrogen phosphate, 11.52 grams of sucrose, and 1.2 grams of sucrose was passed through high-energy ball milling, dried at a low temperature of 60°C and placed in a self-made inert atmosphere reaction furnace During the process, the temperature starts to rise, the reaction temperature is 300-400°C and the holding time is 4 hours, the by-products are decomposed and discharged, and then cooled to room temperature, and an inert gas is introduced for protection during the whole process. The powder is taken out and compacted, and then the bulk precursor is placed in a heat-resistant stainless steel container and vacuum-sealed. Place the sealed heat-resistant stainless steel container in a muffle furnace for a certain period of calcination at 650°C, then take out the sealed heat-resistant stainless steel container at the calcination temperature for quenching, and take out the product to obtain nano-scale lithium iron phosphate doped with manganese ions Powder material. The specific capacity of the prepared material was tested to be 149mAh/g.

Example 3: A mixture containing 3.71 grams of lithium carbonate, 18 grams of ferrous oxalate, 0.236 grams of CoCO ₃ , 11.52 grams of ammonium dihydrogen phosphate, 11.52 grams of sucrose and 1.2 grams of sucrose was passed through high-energy ball milling, dried at a low temperature of 60°C and placed in a self-made inert atmosphere reaction furnace During the process, the temperature starts to rise, the reaction temperature is 300-400°C and the holding time is 4 hours, the by-products are decomposed and discharged, and then cooled to room temperature, and an inert gas is introduced for protection during the whole process. The powder is taken out and compacted, and then the bulk precursor is placed in a heat-resistant stainless steel container and vacuum-sealed. Place the sealed heat-resistant stainless steel container in a muffle furnace for a certain period of calcination at 650°C, then take out the sealed heat-resistant stainless steel container at the calcination temperature for quenching, and take out the product to obtain cobalt-doped nano-scale lithium iron phosphate powder body material. The specific capacity of the prepared material was tested to be 145mAh/g.

Claims (6)

1. A method for synthesizing nanoscale lithium iron phosphate powder, characterized in that: lithium salt, iron salt, phosphate, doping element and conductive agent are used as raw materials, lithium salt, iron salt, doping metal ion and According to the molar ratio of lithium: iron: Me ⁿ⁺ : phosphoric acid, the phosphate is 1.0: x: (1-x): 1.0, wherein x = 0.80-0.99, and at the same time, add a conductive agent of 0.5-2.0% of the total mass of the above raw materials; mix by ball milling After uniformity, place in an inert atmosphere reaction furnace, the reaction temperature is 300-400°C, the holding time is 2-6 hours, and then cool to room temperature; take out the powder, briquette, and then place the block precursor in a heat-resistant stainless steel container inside, vacuum sealed, placed in a muffle furnace and calcined at 500-800°C for 10-20 hours, then take out the sealed heat-resistant stainless steel container at the calcining temperature for quenching, and obtain nano-scale ferric phosphate after quenching Lithium powder material. 2. The preparation method of lithium iron phosphate powder according to claim 1, wherein the lithium salt comprises: one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium chloride, lithium dihydrogen phosphate or Various. 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, ferrous sulfate, and ferric phosphate. 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 of elements such as manganese, zinc, titanium, magnesium, aluminum, zirconium, niobium, chromium and rare earth one or more species. 6. The preparation method of lithium iron phosphate powder according to claim 1, characterized in that: the conductive agent is carbon or a carbon precursor, including one of acetylene black, flake graphite, sucrose, glucose, and polyvinyl alcohol one or more species.

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