CN112331847B - Method for preparing high-electrochemical-activity lithium iron phosphate positive electrode material by using unqualified lithium iron phosphate positive electrode material - Google Patents
Method for preparing high-electrochemical-activity lithium iron phosphate positive electrode material by using unqualified lithium iron phosphate positive electrode material Download PDFInfo
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- CN112331847B CN112331847B CN202011025982.1A CN202011025982A CN112331847B CN 112331847 B CN112331847 B CN 112331847B CN 202011025982 A CN202011025982 A CN 202011025982A CN 112331847 B CN112331847 B CN 112331847B
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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Abstract
The invention discloses a method for preparing a lithium iron phosphate positive electrode material with high electrochemical activity by using an unqualified lithium iron phosphate positive electrode material. The invention adopts a hydrothermal recrystallization method synthesis process, and changes waste into a high-added-value high-electrochemical-activity lithium iron phosphate anode material; the physical property and the electrochemical property of the product prepared by the method are detected for many times and reach an advanced level; the recrystallization process has the advantages of simple flow, mild and easily-controlled process control parameters, suitability for large-scale industrial production and good application prospect in the field of lithium ion batteries.
Description
Technical Field
The invention belongs to the field of electrochemistry, and particularly relates to a method for preparing a lithium iron phosphate positive electrode material with high electrochemical activity by using an unqualified lithium iron phosphate positive electrode material.
Background
Olivine-type LiFePO4Due to the advantages of outstanding safety, low price, environmental protection, excellent cycle performance and the like, the lithium ion battery anode material has great market prospect in the field of mobile power supplies, particularly large power supplies and static energy storage fields required by electric vehicles, and becomes an important lithium ion battery anode material which is currently oriented to large-scale industrialization.
The technology of carbon coating, nanocrystallization, bulk phase doping and the like greatly improves the LiFePO4The electronic conductivity and the ion diffusion rate of the anode material are improved, and the LiFePO is improved4The lithium iron phosphate anode material has the electrochemical properties such as high and low temperature performance, rate performance and the like, and is in an industrial stage at present. However, the main obstacles limiting its scale-up are the cost of the manufacturing process technology, the stability and consistency of the product. The enterprises for producing the lithium iron phosphate material at home are numerous, but the electrochemical activity of the products produced by most of the enterprises has a large gap with the products of the internationally known enterprises, and the products do not have good sales even if the price is 30 percent of the international price of the lithium iron phosphate, and the main reason is that the lithium battery has very strict requirements on the lithium iron phosphate as the anode material, and a large amount of domestic lithium iron phosphate is placed in a storehouse, so that the development of the enterprises is influenced, and the lithium iron phosphate is greatly wasted for lithium resources.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to provide a method for preparing a lithium iron phosphate positive electrode material with high electrochemical activity by using an unqualified lithium iron phosphate positive electrode material aiming at the defects of the prior art.
The technical scheme is as follows: in order to achieve the above object, the present invention is specifically realized as follows: the method for preparing the lithium iron phosphate anode material with high electrochemical activity by using the unqualified lithium iron phosphate anode material adopts the unqualified lithium iron phosphate anode material as a raw material and is prepared by purifying the unqualified lithium iron phosphate anode material by a hydrothermal recrystallization method.
Specifically, the method comprises the following steps:
(1) dispersing the unqualified lithium iron phosphate anode material in an aqueous solution, adding acid to dissolve, controlling the pH value, and filtering and separating undissolved carbon to obtain a lithium iron phosphate aqueous solution;
(2) adding an alkaline substance, and adjusting the pH value of the lithium iron phosphate aqueous solution to 4.5-7.2;
(3) transferring the solution into a hydrothermal recrystallization device, sealing the device, and replacing air with inert gas, wherein the inert gas is N2Or Ar; can be vacuumized to vacuum degree<-0.095, and repeating for three times by introducing nitrogen or argon to normal pressure;
(4) rapidly heating, controlling the temperature of supercritical water thermal recrystallization at 180-220 ℃, and maintaining the recrystallization time for 3-10 hours;
(5) after the reaction is finished, naturally cooling to normal temperature, filtering, separating, washing and drying the suspension to obtain a lithium iron phosphate product with high electrochemical activity;
(6) and uniformly mixing lithium iron phosphate and a carbon source in a high-energy ball mill in the presence of an ethanol solvent, evaporating slurry to remove water, and then carrying out carbon coating under the protection of inert gas at 650-750 ℃ for 1-5 hours to obtain the carbon-coated lithium iron phosphate with high electrochemical activity.
Wherein the concentration of the lithium iron phosphate solution in the step (1) is 0.1-1 mol/L.
Wherein the pH value of the lithium iron phosphate solution in the step (1) is 1-3.
Wherein, the acid in the step (1) is one or a mixture of a plurality of sulfuric acid, phosphoric acid, nitric acid and hydrofluoric acid.
Wherein, the alkaline substance in the step (2) is one or a mixture of several of sodium hydroxide, potassium hydroxide, lithium hydroxide and ammonia water.
The 0.1C discharge capacity of the high electrochemical activity lithium iron phosphate positive electrode material is more than or equal to 155mAh/g, the 1C discharge capacity is more than or equal to 145mAh/g, the 10C discharge capacity is more than or equal to 115mAh/g, and the 20C discharge capacity is more than or equal to 100 mAh/g.
Has the advantages that: compared with the prior art, the invention has the following advantages:
(1) the invention adopts a hydrothermal recrystallization method synthesis process, and changes waste into a high-added-value high-electrochemical-activity lithium iron phosphate anode material;
(2) the physical property and the electrochemical property of the product prepared by the method are detected for many times and reach an advanced level;
(3) the recrystallization process has the advantages of simple flow, mild and easily-controlled process control parameters, suitability for large-scale industrial production and good application prospect in the field of lithium ion batteries.
Drawings
Fig. 1 is a schematic diagram of a hydrothermal recrystallization process of lithium iron phosphate with high electrochemical activity.
Fig. 2 is an XRD diffractogram of the carbon-coated lithium iron phosphate crystal prepared in example 1.
Fig. 3 is a graph showing the initial specific capacity of rate discharge of the carbon-coated lithium iron phosphate powder prepared in example 1.
Detailed Description
Example 1:
dropwise adding 98% sulfuric acid to adjust the pH value of the solution to be 2.5, adjusting the concentration of the lithium iron phosphate in the filtrate after filtering and separating to be 0.5mol/L, adopting potassium hydroxide as an alkaline substance, adjusting the pH value of the solution to be 6.5, transferring the solution into a hydrothermal crystallizer, sealing the reaction crystallizer, replacing air with inert gas, wherein the inert gas is N2, and replacing for three times. Performing hydrothermal reaction at 180 ℃, keeping the reaction time for 4 hours, naturally cooling to room temperature after the reaction is finished, performing solid-liquid separation on the slurry, washing the slurry with water and an ethanol solution for three times respectively, drying the slurry in a vacuum drying oven at 100 ℃ for 4 hours, and removing free water to obtain the carbon-coated lithium iron phosphate precursor powder material. Mixing a carbon-coated lithium iron phosphate precursor powder material and 12% sucrose in a high-energy ball mill for 60min in the presence of an ethanol solvent, taking out, evaporating to remove the solvent, placing in a tube furnace, carrying out high-temperature heat treatment at 650 ℃ for 5 hours under the protection of inert gas, and cooling to obtain a black carbon-coated lithium iron phosphate cathode material.
As shown in fig. 1 to 3, the carbon-coated lithium iron phosphate powder prepared in the embodiment is pure-phase lithium iron phosphate, has high crystallinity, stable electrochemical performance and excellent high rate performance, has a specific discharge capacity of 112mAh/g at room temperature during charging and discharging at a rate of 20C, and has a good application prospect in the field of lithium ion batteries.
Example 2:
dropwise adding 65% nitric acid to adjust the pH value of the solution to be 3, adjusting the concentration of the lithium iron phosphate in the filtrate to be 0.3mol/L after filtering and separating, adopting sodium hydroxide as an alkaline substance, adjusting the pH value of the solution to be 5.5, transferring the solution to a hydrothermal heavy crystallizer, sealing the reaction crystallizer, replacing air with inert gas, wherein the inert gas is N2, and replacing for three times. Performing hydrothermal reaction at 200 ℃, keeping the reaction time for 3 hours, naturally cooling to room temperature after the reaction is finished, performing solid-liquid separation on the slurry, washing the slurry with water and an ethanol solution for three times respectively, drying the slurry in a vacuum drying oven at 100 ℃ for 4 hours, and removing free water to obtain the carbon-coated lithium iron phosphate precursor powder material. Mixing a carbon-coated lithium iron phosphate precursor powder material and 12% sucrose in a high-energy ball mill for 60min in the presence of an ethanol solvent, taking out, evaporating to remove the solvent, placing in a tube furnace, carrying out high-temperature heat treatment at 650 ℃ for 5 hours under the protection of inert gas, and cooling to obtain a black carbon-coated lithium iron phosphate cathode material.
The carbon-coated lithium iron phosphate powder prepared by the embodiment is pure-phase lithium iron phosphate, has high crystallinity, stable electrochemical performance and excellent high rate performance, has a specific discharge capacity of 108mAh/g during charging and discharging at a rate of 20C at room temperature, and has good application prospect in the field of lithium ion batteries.
Example 3:
dropwise adding 85% phosphoric acid to adjust the pH value of the solution to be 1.5, adjusting the concentration of lithium iron phosphate in the filtrate to be 1mol/L after filtering and separating, adopting lithium hydroxide as an alkaline substance, adjusting the pH value of the solution to be 6.8, transferring the solution to a hydrothermal heavy crystallizer, sealing the reaction crystallizer, replacing air with inert gas, wherein the inert gas is N2, and replacing for three times. Performing hydrothermal reaction at 220 ℃, keeping the reaction time for 2 hours, naturally cooling to room temperature after the reaction is finished, performing solid-liquid separation on the slurry, washing the slurry with water and an ethanol solution for three times respectively, drying the slurry in a vacuum drying oven at 100 ℃ for 4 hours, and removing free water to obtain the carbon-coated lithium iron phosphate precursor powder material. Mixing a carbon-coated lithium iron phosphate precursor powder material and 12% sucrose in a high-energy ball mill for 60min in the presence of an ethanol solvent, taking out, evaporating to remove the solvent, placing in a tube furnace, carrying out high-temperature heat treatment at 650 ℃ for 5 hours under the protection of inert gas, and cooling to obtain a black carbon-coated lithium iron phosphate cathode material.
The carbon-coated lithium iron phosphate powder prepared by the embodiment is pure-phase lithium iron phosphate, has high crystallinity, stable electrochemical performance and excellent high rate performance, has a specific discharge capacity of 105mAh/g during charging and discharging at 20C rate at room temperature, and has good application prospect in the field of lithium ion batteries.
Claims (6)
1. A method for preparing a lithium iron phosphate positive electrode material with high electrochemical activity by using an unqualified lithium iron phosphate positive electrode material is characterized in that the unqualified lithium iron phosphate positive electrode material is adopted as a raw material and is purified by a hydrothermal recrystallization method; the method specifically comprises the following steps:
(1) dispersing the unqualified lithium iron phosphate anode material in an aqueous solution, adding acid to dissolve, controlling the pH value, and filtering and separating undissolved carbon to obtain a lithium iron phosphate aqueous solution;
(2) adding an alkaline substance, and adjusting the pH value of the lithium iron phosphate aqueous solution to 4.5-7.2;
(3) transferring the solution into a hydrothermal recrystallization device, sealing the device, and replacing air with inert gas, wherein the inert gas is N2Or Ar;
(4) rapidly heating, controlling the temperature of supercritical water thermal recrystallization at 180-220 ℃, and maintaining the recrystallization time for 3-10 hours;
(5) after the reaction is finished, naturally cooling to normal temperature, and filtering, separating, washing and drying the suspension to obtain a lithium iron phosphate product with high electrochemical activity;
(6) and uniformly mixing lithium iron phosphate and a carbon source in a high-energy ball mill in the presence of an ethanol solvent, evaporating slurry to remove water, and then carrying out carbon coating under the protection of inert gas at 650-750 ℃ for 1-5 hours to obtain the carbon-coated lithium iron phosphate with high electrochemical activity.
2. The method for preparing the lithium iron phosphate positive electrode material with high electrochemical activity by using the unqualified lithium iron phosphate positive electrode material according to claim 1, wherein the concentration of the lithium iron phosphate solution in the step (1) is 0.1-1 mol/L.
3. The method for preparing the lithium iron phosphate positive electrode material with high electrochemical activity by using the unqualified lithium iron phosphate positive electrode material according to claim 1, wherein the pH value of the lithium iron phosphate solution in the step (1) is 1-3.
4. The method for preparing the lithium iron phosphate positive electrode material with high electrochemical activity by using the unqualified lithium iron phosphate positive electrode material according to claim 1, wherein the acid in the step (1) is one or a mixture of sulfuric acid, phosphoric acid, nitric acid and hydrofluoric acid.
5. The method for preparing the lithium iron phosphate positive electrode material with high electrochemical activity by using the unqualified lithium iron phosphate positive electrode material according to claim 1, wherein the alkaline substance in the step (2) is one or a mixture of several of sodium hydroxide, potassium hydroxide, lithium hydroxide and ammonia water.
6. The method for preparing the lithium iron phosphate positive electrode material with high electrochemical activity by using the unqualified lithium iron phosphate positive electrode material according to claim 1, wherein the 0.1C discharge capacity of the lithium iron phosphate positive electrode material with high electrochemical activity is more than or equal to 155mAh/g, the 1C discharge capacity is more than or equal to 145mAh/g, the 10C discharge capacity is more than or equal to 115mAh/g, and the 20C discharge capacity is more than or equal to 100 mAh/g.
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| CN102569792A (en) * | 2011-11-07 | 2012-07-11 | 四川大学 | Preparation method for one-step synthesis of high-rate-performance carbon-coated lithium iron phosphate cathode material by in-situ hydrothermal carbonization |
| CN102790216A (en) * | 2012-08-24 | 2012-11-21 | 广州市香港科大霍英东研究院 | Supercritical solvent thermal preparation method of cathode material lithium iron phosphate of lithium ion battery |
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| CN102569792A (en) * | 2011-11-07 | 2012-07-11 | 四川大学 | Preparation method for one-step synthesis of high-rate-performance carbon-coated lithium iron phosphate cathode material by in-situ hydrothermal carbonization |
| CN102790216A (en) * | 2012-08-24 | 2012-11-21 | 广州市香港科大霍英东研究院 | Supercritical solvent thermal preparation method of cathode material lithium iron phosphate of lithium ion battery |
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