Preparation method of almond shell-based biomass hard carbon

Abstract

The invention discloses a preparation method of almond shell-based biomass hard carbon, which comprises the following steps: cleaning an almond shell material, drying, and crushing; pre-carbonizing the almond shell powder, so that the almond shell powder is preliminarily carbonized into carbon powder; further crushing, screening, pickling and drying the pre-carbonized carbon powder; and performing high-temperature carbonization on the pre-carbonized carbon powder, and dividing a heating curve into two sections during high-temperature carbonization to finally obtain the hard carbon material. Crushing and screening are carried out before pre-carbonization, the shape and size of a biomass precursor are controlled, the biomass cracking process of the material is more thorough, the defects of terminal hard carbon are reduced, a gap structure is increased, the capacity of the hard carbon material is increased, and the coulombic efficiency of the first round is improved. In the high-temperature carbonization stage, two different heating rates are adopted, the quick heating mode is adopted in the relative low-temperature stage, the preparation efficiency is guaranteed, the slow heating mode is adopted in the relative high-temperature stage, the performance of the material is improved, and especially the first-round coulombic efficiency index of the material is improved.

Description

Technical Field

[0001] The invention relates to a method for preparing almond shell-based biomass hard carbon. Background Art

[0002] Commonly used carbon-based materials mainly include graphite carbon and non-graphite carbon. Among them, non-graphite hard carbon is a more commonly used negative electrode material for sodium ion batteries. Graphite has been widely used in lithium ion batteries. It is the earliest studied and most commercialized negative electrode material. However, compared with the radius of sodium ions, the interlayer spacing of graphite is too small. Researchers obtain expanded graphite by oxidizing graphite, which can be used as a negative electrode material for sodium ion batteries. Non-graphite mainly includes two categories: hard carbon and soft carbon. There is no obvious surface diffraction peak. Both are amorphous structures, composed of graphite microcrystals and amorphous regions. Hard carbon, also known as difficult to graphitize carbon, has attracted widespread attention due to its large interlayer spacing and irregular structure, which is suitable for sodium ion deintercalation. It is a pyrolytic carbon of polymers. It is difficult to graphitize even at a high temperature of 3000°C, and is suitable for use as a negative electrode material for sodium ion batteries. Soft carbon is not directly used as a negative electrode material. It is a raw material for making artificial graphite, or as a coating material to change to natural graphite, alloys and other negative electrode materials.

[0003] So far, the raw materials for synthesizing carbon-based negative electrode materials cannot be completely renewable. With the continuous advancement of the commercialization of sodium-ion batteries, the production of carbon-based negative electrode materials will inevitably consume a large amount of carbon precursors. Exploring low-cost and renewable carbon precursors to prepare carbon-based negative electrode materials for sodium-ion batteries with high reversible capacity and long cycle performance has gradually become a research hotspot in the field of sodium-ion batteries. In the past few years, the synthesis of carbon-based materials with excellent properties such as large specific surface area, controllable porosity and high conductivity using plant fibers as raw materials as negative electrode materials for sodium-ion batteries has attracted the attention of more and more researchers. Based on this, the present invention provides a method for preparing almond shell-based biomass hard carbon, which can make high-value utilization of waste, protect the environment and create high economic value. Summary of the invention

[0004] The present invention provides a method for preparing almond shell-based biomass hard carbon in order to solve the problems existing in the above-mentioned prior art.

[0005] The technical solutions adopted in the present invention are: A method for preparing almond shell-based biomass hard carbon comprises the following steps: S1, washing and drying the almond shell material, then crushing it, and sieving it with a 160-mesh sieve for later use; S2, pre-carbonizing the almond shell powder obtained in S1 to preliminarily carbonize the almond shell powder into carbon powder; S3, further crushing, screening, pickling and drying the carbon powder after pre-carbonization in S2, and the particle size distribution D99 of the material after screening is less than 15 microns and D50 is less than 10 microns; S4, subjecting the pre-carbonized carbon powder dried in S3 to high-temperature carbonization, wherein the temperature rise curve during high-temperature carbonization is divided into two sections, and finally the hard carbon material is obtained.

[0006] Furthermore, in step S1, the cleaning includes two steps. The first step is to use clean water to clean the almond shell material multiple times until the almond shell material is free of dirt and dust; the second step is to immerse the almond shell material free of dirt and dust in deionized water for soaking and cleaning.

[0007] Furthermore, in step S1, the drying temperature does not exceed 140°C.

[0008] Furthermore, in step S2, during pre-carbonization, the carbonization atmosphere is an inert gas, the carbonization temperature rise rate is 0.5°C / min-20°C / min, the terminal carbonization temperature is 400°C-650°C, and when the temperature reaches the terminal carbonization temperature, it is kept warm for 1-3 hours to initially carbonize the material into carbon powder.

[0009] Furthermore, in step S3, hydrochloric acid is used for pickling at a concentration of 2 mol / L-12 mol / L for 2-24 hours, and after pickling, it is washed with deionized water and dried at a drying temperature of 60°C-140°C.

[0010] Furthermore, in step S4, the heating curve is divided into two sections: In an inert gas carbonization atmosphere, the temperature was first raised from room temperature to 800°C at a rate of 5°C / min -20°C / min; When the temperature reaches 800°C, the heating rate is 0.5°C / min-10°C / min to the terminal carbonization temperature, and the terminal carbonization temperature is 1200°C-1400°C. When the temperature reaches the terminal carbonization temperature, keep it warm for 2-6 hours.

[0011] The present invention has the following beneficial effects: (1) The present invention performs crushing and screening before pre-carbonization, controls the morphology and size of the biomass precursor, makes the biomass cracking process of the material more complete and thorough, reduces the defects of the terminal hard carbon, increases the pore structure, increases the capacity of the hard carbon material, and improves the first-round coulomb efficiency.

[0012] (2) The present invention adopts two different heating rates in the high-temperature carbonization stage. A fast heating method is adopted in the relatively low-temperature stage to ensure the preparation efficiency, and a slow heating method is adopted in the relatively high-temperature stage to improve the performance of the material, especially the first-round coulomb efficiency index of the material.

[0013] (3) The material prepared by the present invention can be widely used in the negative electrode of sodium ion batteries, with a capacity of up to 350 mAh / g and a first-round coulombic efficiency of more than 90%.

[0014] (4) The present invention adopts two cleanings. The first cleaning is to remove impurities and dust, so clean water (i.e. tap water) is used. The first cleaning uses a large amount of water, and the use of clean water can reduce costs. The second cleaning is done with deionized water to remove the influence of ions in the first tap water on the material, and the second cleaning uses less water. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Scanning electron micrograph (SEM) of almond shell-based biomass hard carbon particles.

[0016] Figure 2 This is the charge and discharge curve of almond shell-based biomass sodium-ion battery. DETAILED DESCRIPTION

[0017] The present invention will be further described below in conjunction with the accompanying drawings. Example 1

[0018] The present invention provides a method for preparing almond shell-based biomass hard carbon, comprising the following steps: S1, washing and drying the almond shell material, then crushing it, and sieving it with a 160-mesh sieve for later use; S2, pre-carbonizing the almond shell powder obtained in S1 to preliminarily carbonize the almond shell powder into carbon powder; S3, further crushing, screening, pickling and drying the carbon powder after pre-carbonization in S2, and the particle size distribution D99 of the material after screening is less than 15 microns and D50 is less than 10 microns; S4, subjecting the pre-carbonized carbon powder dried in S3 to high-temperature carbonization, wherein the temperature rise curve during high-temperature carbonization is divided into two sections, and finally the hard carbon material is obtained.

[0019] In step S1, the cleaning includes two steps. The first step is to use clean water (tap water) to clean the almond shell material multiple times until the almond shell material is free of dirt and dust; the second step is to immerse the almond shell material without dirt and dust in deionized water for cleaning. The cleaned almond shell material is drained and dried, and the drying temperature does not exceed 140°C. Finally, the almond shell material is crushed by a crusher and crushed to less than 160 mesh, and sieved with a 160 mesh sieve for standby use.

[0020] In step S2, during pre-carbonization, the carbonization atmosphere is an inert gas (nitrogen or argon), the carbonization temperature heating rate is 0.5°C / min-20°C / min, the terminal carbonization temperature is 400°C-650°C, and when the temperature reaches the terminal carbonization temperature, it is kept warm for 1-3 hours to initially carbonize the material into carbon powder.

[0021] In step S3, hydrochloric acid is used for pickling at a concentration of 2 mol / L-12 mol / L for 2-24 hours. After pickling, the substrate is washed with deionized water and dried at a drying temperature of 60°C-140°C.

[0022] In step S4, the heating curve is divided into two sections: in an inert gas (nitrogen or argon) carbonization atmosphere, first the temperature is raised from room temperature to 800°C, and the heating rate is 5°C / min-20°C / min; when reaching 800°C, the heating rate is 0.5°C / min-10°C / min to the terminal carbonization temperature, and the terminal carbonization temperature is 1200°C-1400°C. When the temperature reaches the terminal carbonization temperature, it is kept warm for 2-6 hours to complete the final carbonization of the material. Figure 1 Scanning electron micrograph (SEM) of almond shell-based biomass hard carbon particles. Example 2

[0023] After the hard carbon material is prepared, it is dispersed in deionized water with conductive carbon black, hydroxymethyl cellulose and styrene butadiene rubber, and stirred at a speed of 2000 for 2 hours to form a negative electrode active material slurry. Among them, the weight ratio of hard carbon: conductive carbon black: hydroxymethyl cellulose: styrene butadiene rubber is 92%: 3%: 2%: 3%. The slurry is coated on copper foil, then dried at 100°C for 10 minutes, and rolled to obtain a negative electrode sheet.

[0024] In the glove box, CR2032 button cells are assembled in the order of negative electrode shell, shrapnel, steel sheet, sodium sheet, glass fiber diaphragm, negative electrode sheet, and positive electrode shell. 40 µL of electrolyte is dripped on both sides of the diaphragm. The electrolyte is sodium hexafluorophosphate electrolyte (1 mol NaPF6 is dissolved in a mixed solvent of EC / PC / EMC=35:5:60 (mass ratio)). The assembled battery is charged and discharged between 0V-2V. When assembling the battery, in order to ensure that the electrolyte does not decompose and the metal sodium sheet is not oxidized, the entire assembly process is carried out in a glove box environment filled with high-purity argon. When the water content and oxygen content in the glove box are not higher than 0.01ppm, the sodium ion button cell is assembled.

[0025] Figure 2 This is the charge and discharge curve of almond shell-based biomass hard carbon particles. The gram capacity is 340mAh / g and the first-round coulomb efficiency is 91.5%.

[0026] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be regarded as within the protection scope of the present invention.

Claims

1. A method for preparing almond shell-based biomass hard carbon, characterized in that: The steps include: S1, washing and drying the almond shell material, then crushing it, and sieving it with a 160-mesh sieve for later use; S2, pre-carbonizing the almond shell powder obtained in S1 to preliminarily carbonize the almond shell powder into carbon powder; S3, further crushing, screening, pickling and drying the carbon powder after pre-carbonization in S2, and the particle size distribution D99 of the material after screening is less than 15 microns and D50 is less than 10 microns; S4, subjecting the pre-carbonized carbon powder dried in S3 to high-temperature carbonization, wherein the temperature rise curve during high-temperature carbonization is divided into two sections, and finally the hard carbon material is obtained.

2. The method for preparing almond shell-based biomass hard carbon according to claim 1, characterized in that: In step S1, the cleaning includes two steps. The first step is to use clean water to clean the almond shell material multiple times until the almond shell material is free of dirt and dust; the second step is to immerse the almond shell material free of dirt and dust in deionized water for cleaning.

3. The method for preparing almond shell-based biomass hard carbon according to claim 1, characterized in that: In step S1, the drying temperature does not exceed 140°C.

4. The method for preparing almond shell-based biomass hard carbon according to claim 1, characterized in that: In step S2, during pre-carbonization, the carbonization atmosphere is an inert gas, which can be high-purity nitrogen or high-purity argon. The carbonization temperature rise rate is 0.5°C / min-20°C / min, and the terminal carbonization temperature is 400°C-650°C. When the temperature reaches the terminal carbonization temperature, it is kept warm for 1-3 hours to initially carbonize the material into carbon powder.

5. The method for preparing almond shell-based biomass hard carbon according to claim 1, characterized in that: In step S3, hydrochloric acid is used for pickling at a concentration of 2 mol / L-12 mol / L for 2-24 hours. After pickling, the substrate is washed with deionized water and dried at a drying temperature of 60°C-140°C.

6. The method for preparing almond shell-based biomass hard carbon according to claim 1, characterized in that: In step S4, the heating curve is divided into two sections: In the inert gas carbonization atmosphere, the inert gas can be high-purity nitrogen or high-purity argon. The temperature is first raised from room temperature to 800°C at a rate of 5°C / min -20°C / min. When the temperature reaches 800°C, the heating rate is 0.5°C / min-10°C / min to the terminal carbonization temperature, and the terminal carbonization temperature is 1200°C-1400°C. When the temperature reaches the terminal carbonization temperature, keep it warm for 2-6 hours.

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