CN112615005A - Method for preparing lithium iron phosphate anode composite material with good electrochemical performance based on waste bagasse - Google Patents

Abstract

The invention discloses a method for preparing a lithium iron phosphate anode composite material with good electrochemical performance based on waste bagasse. So as to achieve the purposes of waste utilization, environmental protection and waste added value improvement. The method comprises the steps of fully grinding a precursor, a lithium source and an antioxidant to obtain a uniform mixture, and performing low-temperature pre-sintering and grinding treatment in a tube furnace in an argon atmosphere. Then fully mixing the pretreated bagasse powder and the pre-sintered sample in absolute ethyl alcohol, then sintering at high temperature in a tubular furnace in argon atmosphere, naturally cooling to room temperature and fully grinding to obtain LiFePO coated with biomass carbon₄A positive electrode composite material. The invention has simple process and low cost, and the prepared similar spherical LiFePO is₄Composite material of/C positive electrodeHigh conductivity, uniform appearance, good dispersibility, and excellent cycle performance and rate capability.

Description

Method for preparing lithium iron phosphate anode composite material with good electrochemical performance based on waste bagasse

Technical Field

The invention relates to the field of lithium ion batteries, in particular to a method for preparing a high-added-value lithium iron phosphate anode composite material by using waste bagasse.

Background

With the development of industry and the increasing use of fossil fuels, environmental issues have become a problem of great global attention and concern. The development and utilization of new energy are necessary ways to reduce environmental pollution and realize sustainable development, and a lot of countries have made great efforts on innovation and development of new energy. In the field of new energy, the lithium ion battery is a very important new energy, and has very obvious advantages in the aspects of power batteries and energy storage. Among various lithium ion positive electrode materials, lithium iron phosphate (LiFePO)₄) The lithium ion anode material has the advantages of good cycle performance, high stability, large theoretical specific capacity (170mAh/g), safety, environmental protection, low cost and the like, and is an extremely important lithium ion anode material which is compatible with ternary materials. However, the defect of extremely low intrinsic conductivity seriously affects the electrochemical performance of the material under high current density, thereby limiting the application of the material in high-power batteries.

Guangxi is a big province of sugar production in China, and a large amount of bagasse is produced in the sugar industry every year. At present, most of bagasse is solid waste except for part of bagasse used for fuel, paper, artificial fiber board and feed. In order to improve the added value of the waste bagasse and change waste into valuable, the application of the waste bagasse in the aspect of new energy is developed, the bagasse is processed by a special process and then is changed into a coated carbon source of lithium iron phosphate, the electrochemical performance of the material is improved by improving the conductivity, regulating the morphology and the particle size, and the rapid development and the marketization application of the new energy industry are promoted.

Disclosure of Invention

The invention aims to coat a layer of biomass carbon converted from waste bagasse on the surface of lithium iron phosphate, regulate the shape and particle size of the lithium iron phosphate by the carbon coating of the biomass, greatly improve the conductivity and further improve the electrochemical performance of the lithium iron phosphate.

The method comprises the following specific steps:

(1) weighing 1-3 g of industrial bagasse, placing the industrial bagasse in 100-500 mL of alkali liquor with the mass percentage concentration of 0.1-10%, transferring the solution into 200mL of a reaction kettle with a polytetrafluoroethylene lining, reacting for 1-10 hours at 50-120 ℃, taking out the reacted bagasse after the reaction kettle is cooled, and washing for 3-5 times by using deionized water until the pH value is neutral; and then baking the bagasse in an oven for 5-40 hours, and grinding the baked bagasse into superfine powder, namely bagasse powder, by using a ball mill.

(2) Weighing 0.01-0.1 mol of FePO₄Grinding a precursor, 0.01-0.1 mol of a lithium source and 1-10% of antioxidant of the sum of the mass of the lithium source and the precursor in absolute ethyl alcohol for 10-120 minutes, fully and uniformly mixing, presintering in a tubular furnace in an argon atmosphere at the sintering temperature of 100-500 ℃ for 2-12 hours, cooling the tubular furnace to room temperature, adding bagasse powder obtained in the step (1) at the mass of 2-10% of the sum of the mass of the lithium source and the precursor, fully grinding in absolute ethyl alcohol, sintering in the tubular furnace in the argon atmosphere again at the sintering temperature of 600-1000 ℃ for 10-12 hours, and cooling to room temperature to obtain the LiFePO4/C positive composite material coated by biomass carbon, namely the lithium iron phosphate positive composite material.

The alkali liquor is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate and sodium bicarbonate.

The lithium source is one or more of lithium acetate, lithium carbonate and lithium hydroxide.

The antioxidant is one or more of citric acid monohydrate, cysteine beta-mercaptoethanol and ascorbic acid.

The invention relates to a bagasse treatment process and a preparation method of a biomass carbon-coated LiFePO4/C anode composite material by high-temperature carbon thermal reduction. The surface of the material is coated with the biomass carbon to improve the conductivity of the material, regulate and control the size and the morphology of particles, improve the electrochemical performance of the material under high magnification, and the result shows that:

when the voltage range is 2.5-4.2V, the first discharge specific capacity of the prepared LiFePO4/C anode composite material coated by the biomass carbon can reach 156.1mAh/g under the multiplying power of 0.2C, the discharge specific capacity retention rate is 91.1% after 100 cycles, and the composite material has excellent cycle stability. Under the high multiplying power of 10C, the discharge specific capacity is still 85.5 mAh/g. The conductivity of the lithium iron phosphate without being coated with the bagasse is 0.163S/m, and the conductivity is improved to 0.718S/m after coating.

The invention has low cost and little environmental pollution, and the prepared LiFePO4/C anode composite material coated by the biomass carbon has excellent electrochemical performance, and is especially obviously improved in the aspects of circulation and rate capability. Therefore, the LiFePO coated with the biomass carbon is prepared by combining the carbon thermal reduction process after the waste bagasse is subjected to special process treatment₄the/C anode composite material can effectively improve the cycle and rate performance of the material, so that the marketization process of the material in the field of power batteries can be promoted, the sugar industry can be helped to solve the environmental problem caused by waste residues, and the high-added-value resource utilization of wastes can be improved.

Drawings

FIG. 1 shows LiFePO of examples 1 and 2₄XRD pattern of (a).

The labels in the figure are: LFP is the blank lithium iron phosphate positive electrode material synthesized in example 1; the LFP-10% is the lithium iron phosphate cathode composite material synthesized in the embodiment 2 by using bagasse as a biomass-coated carbon source.

FIG. 2 shows LiFePO of examples 1 and 2₄SEM image of (d).

FIG. 3 shows LiFePO of examples 1 and 2₄Cycling performance plots at 0.2C magnification.

FIG. 4 shows LiFePO of examples 1 and 2₄The rate performance graph of (1).

FIG. 5 is LiFePO of example 2₄A TEM image of (a).

FIG. 6 is LiFePO of example 2₄EDS map of (a).

Detailed Description

Example 1:

synthesis of LiFePO₄A positive electrode material:

0.5g of FePO was weighed out in a molar ratio (precursor: lithium source: 1), respectively₄Precursor, 0.1391g LiOH. H₂O, 0.0639g ascorbic acid (LiOH. H) was added₂O and FePO₄10 percent of the total mass) Fully grinding in absolute ethyl alcohol until the mixture is uniform, then presintering in a tubular furnace in an argon atmosphere for 5 hours, wherein the sintering temperature is 350 ℃ (the heating rate of 5 ℃/min), continuing to fully grind in absolute ethyl alcohol after the tubular furnace is cooled to the room temperature, putting the sample into the tubular furnace in the argon atmosphere again, sintering for 10 hours under the condition of 650 ℃ (the heating rate of 5 ℃/min), and cooling to the room temperature to obtain the LiFePO₄And (3) a positive electrode material.

Example 2:

synthesizing LiFePO4/C anode composite material coated by biomass carbon by using waste bagasse:

(1) weighing 1g of industrial bagasse, placing the industrial bagasse into 200mL of sodium hydroxide with the mass percentage concentration of 0.1-10%, transferring the solution into a 200mL reaction kettle with a polytetrafluoroethylene lining, reacting for 5 hours at 100 ℃, taking out the reacted bagasse after the reaction kettle is cooled, and washing the bagasse with deionized water for 4 times until the pH value is neutral; then, the bagasse was roasted in an oven for 20 hours, and the roasted bagasse was ground into ultrafine powder, i.e., bagasse powder, by a ball mill.

(2) 0.5g of FePO was weighed out in a molar ratio (precursor: lithium source: 1), respectively₄Precursor, 0.1391g LiOH. H₂O, 0.0639g ascorbic acid (LiOH. H) was added₂O and FePO₄10 percent of the total mass), grinding the bagasse powder in absolute ethyl alcohol for 100 minutes, then placing the bagasse powder into a tube furnace in an argon atmosphere for presintering for 5 hours, wherein the sintering temperature is 350 ℃ (the heating rate of 5 ℃/min), after the tube furnace is cooled to the room temperature, 0.0639g of bagasse powder (occupying LiOH. H) obtained in the step (1) is added₂O and FePO ₄10 percent of the total mass), fully grinding in absolute ethyl alcohol, then placing into a tubular furnace in an argon atmosphere again, sintering for 10 hours under the condition of 650 ℃ (the heating rate of 5 ℃/min), and cooling to room temperature to obtain the LiFePO4/C composite material coated by the biomass carbon, namely the lithium iron phosphate anode composite material.

And manufacturing the synthesized sample into a circular pole piece, and assembling the circular pole piece into the button cell.

The specific operation is as follows: according to the active substance (LiFePO)₄) Of polyvinylidene fluoride (PVDF) acetylene black (C)Weighing corresponding mass substances respectively, placing the weighed substances in an agate mortar, grinding the weighed substances in an infrared oven for about 1 hour, then dripping a proper amount of NMP (N-methyl-2-pyrrolidone), fully grinding the weighed substances for 1 hour to form a paste, and uniformly coating the material on the surface of a smooth aluminum foil by using a coater to form a uniform sheet. And then, putting the coated pole pieces in a vacuum drying oven at 80 ℃ for drying at night, punching the materials into circular pole pieces with the diameter of 14mm by using a punching machine, and weighing and recording the mass of active substances contained in each pole piece. LiPF with 1mol/L concentration and using metal lithium sheet as cathode and Celgard2400 microporous polypropylene film as diaphragm₆The mixed solution of/EC + DMC + EMC (l: l: l volume ratio) is used as electrolyte, and then the CR2016 type button cell is assembled in a glove box in argon atmosphere, wherein the environment in the glove box requires that the oxygen pressure is less than 10ppm and the relative humidity is less than 5%. And finally, standing the assembled button-type battery for 12 hours, and then carrying out charging and discharging, alternating current impedance and cyclic voltammetry tests.

The blank lithium iron phosphate positive electrode material synthesized in the embodiment 1 is marked as follows: LFP; example 2 a lithium iron phosphate positive electrode composite material synthesized using bagasse as a biomass-coated carbon source was labeled: LFP-10%.

Claims (1)

1. A method for preparing a lithium iron phosphate anode composite material with good electrochemical performance based on waste bagasse is characterized by comprising the following steps:

(1) weighing 1-3 g of industrial bagasse, placing the industrial bagasse in 100-500 mL of alkali liquor with the mass percentage concentration of 0.1-10%, transferring the solution into 200mL of a reaction kettle with a polytetrafluoroethylene lining, reacting for 1-10 hours at 50-120 ℃, taking out the reacted bagasse after the reaction kettle is cooled, and washing for 3-5 times by using deionized water until the pH value is neutral; then baking the bagasse in an oven for 5-40 hours, and grinding the baked bagasse into ultrafine powder, namely bagasse powder, by using a ball mill;

(2) weighing 0.01-0.1 mol of FePO₄Grinding a precursor, 0.01-0.1 mol of lithium source and 1-10% of antioxidant of the sum of the mass of the lithium source and the precursor in absolute ethyl alcohol for 10-120 minutes, fully and uniformly mixingPresintering in a tubular furnace in an argon atmosphere, wherein the sintering temperature is 100-500 ℃, the sintering time is 2-12 hours, adding bagasse powder obtained in the step (1) and accounting for 2-10% of the sum of the mass of a lithium source and a precursor after the tubular furnace is cooled to room temperature, fully grinding the bagasse powder in absolute ethyl alcohol, putting the bagasse powder into the tubular furnace in the argon atmosphere again for sintering, wherein the sintering temperature is 600-1000 ℃, the sintering time is 10-12 hours, and cooling to room temperature to obtain a LiFePO4/C positive composite material coated by biomass carbon, namely a lithium iron phosphate positive composite material;

the alkali liquor is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate and sodium bicarbonate;

the lithium source is one or more of lithium acetate, lithium carbonate and lithium hydroxide;

the antioxidant is one or more of citric acid monohydrate, cysteine beta-mercaptoethanol and ascorbic acid.

Images