Preparation method and application of hard carbon negative electrode material

Abstract

The application relates to a preparation method and application of a hard carbon negative electrode material, and comprises the following steps: 1) dissolving an epoxy resin derivative and an amine catalyst in an organic solvent to obtain a mixture, ultrasonically dispersing alkali-activated biomass powder in the mixture, and performing reaction by increasing temperature to obtain modified biomass powder; the epoxy resin derivative comprises phenolic epoxy resin and isocyanuric acid triglycidyl ester; 2) carbonizing the modified biomass powder. The reaction in step 1) is used for reinforcing the easily-oxidized and weakly-connected structure on the alkali-activated biomass powder, so that the modified biomass powder with enhanced crosslinking degree and a complex three-dimensional crosslinking structure is obtained; and the modified biomass powder is carbonized in step 2). The hard carbon negative electrode material obtained by the method makes the battery have excellent cycle stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of hard carbon materials, and in particular relates to a preparation method and application of a hard carbon negative electrode material. Background Art

[0002] As the main body of sodium storage in sodium ion batteries, the negative electrode material of sodium ion batteries realizes the insertion / extraction of sodium ions during the charge and discharge process. Therefore, the selection of negative electrode materials plays a decisive role in the development of sodium ion batteries. Since the formation enthalpy of the first-order Na-graphite interlayer spacing compound NaC8 is +19.9kJ / mol, Na + It is difficult to embed into the interlayer of graphite with standard interlayer spacing, and graphite is difficult to use as the negative electrode material of sodium-ion batteries. Therefore, it is necessary to find sodium storage materials with larger interlayer spacing or pores to meet the needs of sodium-ion batteries for negative electrode materials.

[0003] Hard carbon refers to carbon that remains difficult to graphitize even at temperatures of 2500°C. Hard carbon materials have a low degree of graphitization, irregular grain orientation, an underdeveloped layered structure, and large interlayer spacing, making them ideal for the insertion and extraction of sodium ions with large radii. Carbon precursors used to prepare hard carbon primarily include thermoplastic polymers and biomass. With technological advancements and population growth, the consumption of traditional fossil energy is accelerating. The utilization of renewable resources is crucial to addressing the depletion of fossil energy. Due to the advantages of biomass having a wide range of sources and low prices, biomass-based hard carbon as a negative electrode material for sodium ion batteries has received widespread attention. For example, patent CN113666356B discloses a sodium ion battery hard carbon negative electrode material and a preparation method based on fruit shell biomass. The present invention uses fruit shell biomass as a biomass raw material, sequentially immerses the biomass raw material in a hydrochloric acid alcohol solution and a sulfuric acid solution and stirs to obtain a suspension; disperses the suspension in water, filters and dries to obtain a precursor; heats the precursor under inert gas protection for pre-carbonization treatment, cools and then ball mills to obtain pre-carbon powder; heats the pre-carbon powder under inert gas protection for high-temperature carbonization treatment, cools and then dries to obtain a precursor; Patent CN113381016B discloses a biomass hard carbon negative electrode material for sodium ion batteries, and its preparation method and application, comprising the following steps: using one or more of wood, bamboo or oil-tea camellia shells as biomass raw materials, immersing the biomass raw materials in a sulfuric acid solution, stirring at room temperature to obtain a suspension; dispersing the suspension in water, filtering and drying to obtain a precursor; heating the precursor under inert gas protection for pre-carbonization treatment, cooling and ball milling to obtain pre-carbon powder; heating the pre-carbon powder under inert gas protection for high-temperature carbonization treatment, cooling, to obtain a biomass hard carbon negative electrode material for sodium ion batteries.

[0004] All of the above are hard carbon negative electrode materials prepared from biomass and suitable for sodium ion embedding and extraction. However, the use of bio-based hard carbon to prepare the disadvantage of poor cycle stability generally exists. It is necessary to improve the preparation method of biomass hard carbon to improve the cycle stability of sodium ion batteries. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a preparation method and application of hard carbon negative electrode materials. First, epoxy resin derivatives are used to react with alkali-activated biomass powder to "reinforce" its easily oxidized and weakly connected structure, thereby obtaining a modified biomass powder with enhanced cross-linking degree and a complex three-dimensional cross-linked structure; then, this modified biomass powder is carbonized, and the obtained hard carbon negative electrode material is used as a negative electrode material for sodium ion batteries, so that the battery has excellent cycle stability.

[0006] In order to achieve the above objectives, the following specific technical solutions are adopted:

[0007] A method for preparing a hard carbon negative electrode material comprises the following steps:

[0008] 1) dissolving an epoxy resin derivative and an amine catalyst in an organic solvent to obtain a mixture, ultrasonically dispersing an alkali-activated biomass powder in the mixture, heating the mixture to react, and filtering, washing, drying, and grinding after the reaction to obtain a modified biomass powder; the epoxy resin derivative includes a novolac epoxy resin and triglycidyl isocyanurate;

[0009] 2) placing the carbon precursor obtained in step 1) in a tube furnace, heating and carbonizing it in an inert atmosphere, maintaining a constant temperature after reaching the carbonization temperature, cooling it naturally to room temperature, and then grinding it to obtain a hard carbon negative electrode material.

[0010] Furthermore, the alkali-activated biomass powder in step 1) is prepared by the following method: crushing the dry biomass into particles, washing, and drying to obtain biomass powder; adding the biomass powder and alkali solution to a reactor, heating to react, cooling to room temperature after the reaction, filtering, washing, and drying to obtain alkali-activated biomass powder.

[0011] Furthermore, the biomass is selected from one or a combination of two or more of rice husks, coconut shells, wood chips, bamboo, rice straw, corn cobs, walnut shells, bagasse, and pistachio shells; the average particle size of the particles is 1-3 mm, the washing is washing with water 1-3 times, and the drying is vacuum drying at 80-100° C. to constant weight.

[0012] Furthermore, the concentration of the alkali solution is 0.5-0.8 mol / L, and the alkali solution is selected from one or a combination of sodium hydroxide solution and potassium hydroxide solution; the mass volume ratio of the biomass powder to the alkali solution is 1 g: (15-20) mL; the temperature is raised to 180-200°C; the reaction time is 1-3 hours; the washing is performed with water until neutral; and the drying is performed at 100-120°C under vacuum to constant weight. The purpose of the alkali activation step is to increase the reactivity of the hydroxyl groups on the biomass powder.

[0013] Furthermore, in step 1), the epoxy resin derivative is prepared by compounding a novolac epoxy resin and triglycidyl isocyanurate in a mass ratio of 3:5-7; the novolac epoxy resin has an epoxy equivalent of 170-190 g / mol and a viscosity of 500-2000 mPa·s; the organic solvent is a mixed solvent composed of DMF and a saturated ketone in a mass ratio of 3-6:1, and the saturated ketone is selected from one or a combination of acetone and methyl ethyl ketone; the epoxy resin derivative accounts for 1% in the mixture. 3-5wt%; the epoxy resin derivative is 7-10wt% of the alkali-activated biomass powder; the amine catalyst is selected from one or a combination of two or more of triethylamine, pyridine, and benzyldimethylamine, and the amount of the catalyst is 1-3wt% of the epoxy resin derivative; the heating is to 80-100°C, the reaction time is 1-5h, the washing is to wash with water 3-5 times, the drying is to vacuum dry at 80-100°C to constant weight, and the grinding is to grind to 1-3mm.

[0014] The purpose of step 1) is to "reinforce" the easily oxidized and weakly connected structures on the biomass with phenolic epoxy resin and triglycidyl isocyanurate, enhance the degree of cross-linking, form a complex three-dimensional cross-linked structure, increase the cyclization and aromatization rate during carbonization, and reduce the probability of gas generation; at the same time, it is beneficial to reduce the surface defects of the generated hard carbon, prevent collapse and closure, and improve the cycle stability of the battery. In the present invention, the epoxy resin derivatives are compounded by phenolic epoxy resin and triglycidyl isocyanurate, and the compounding ratio is relatively important: if the proportion of phenolic epoxy resin is too high, the pore structure of the hard carbon will be underdeveloped and the specific surface area will be too low; if the proportion of phenolic epoxy resin is too small, the triglycidyl isocyanurate will generate more gas during the carbonization process, hard carbon, many surface defects, and the surface structure is prone to collapse and closure, and the cycle stability is poor, so the compounding ratio needs to be strictly controlled.

[0015] Step 2) The carbonization temperature is 1200-1400° C., the heating rate is 3-6° C. / min, the ventilation volume is 100-200 mL / min, the grinding is to 1-20 μm, and the constant temperature is maintained for 3-5 hours.

[0016] The present invention also provides an application of the high-performance hard carbon negative electrode material as a negative electrode material for sodium ion batteries.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] First, epoxy resin derivatives are used to react with alkali-activated biomass powder to "reinforce" its easily oxidized and weakly connected structure, thereby obtaining a modified biomass powder with enhanced cross-linking degree and a complex three-dimensional cross-linked structure; then the modified biomass powder is carbonized, and the resulting hard carbon negative electrode material is used as a negative electrode material for sodium ion batteries, giving the battery excellent cycle stability.

[0019] The preparation method of the hard carbon negative electrode material of the present invention can reduce ash content, reduce surface defects, and have a larger initial reversible capacity; at the same time, the preparation method of the present invention is simple, does not require special complex processes, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is an electron microscope photograph of the hard carbon negative electrode material prepared in Example 1. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with specific embodiment, but is not limited to the content on the specification sheets. Unless otherwise specified, "parts" described in the embodiments of the present invention are all parts by weight. All reagents used are commercially available reagents in this area.

[0022] The phenolic epoxy resin was purchased from Dow Chemical with the brand name DEN438, an epoxy equivalent weight of 180 g / mol, and a viscosity of 1000 mPa·s.

[0023] Example 1

[0024] 1) 500 g of dried coconut shell was crushed into particles with an average particle size of 3 mm, washed with water three times, and vacuum dried at 100° C. to constant weight to obtain 500 g of biomass powder for later use;

[0025] 2) 500 g of the biomass powder obtained in step 1) and 10,000 mL of a 0.8 mol / L sodium hydroxide solution were added to a reactor, and the temperature was raised to 180° C. for 3 h. After the reaction, the mixture was cooled to room temperature, filtered, washed with water until neutral, and dried under vacuum at 100° C. to constant weight to obtain 492.8 g of alkali-activated biomass powder;

[0026] 3) 49.28 g of a mixture of DEN438 and triglycidyl isocyanurate in a mass ratio of 3:5 and 0.5 g of catalyst triethylamine were dissolved in 949.5 g of a mixed solvent, wherein the mixed solvent was a mixture of DMF and acetone in a mass ratio of 6:1. 492.8 g of the alkali-activated biomass powder obtained in step 2) was ultrasonically dispersed in the mixture, and the temperature was raised to 100° C. for reaction for 3 h. After the reaction was completed, the mixture was filtered, washed with water three times, dried in vacuo at 120° C. to constant weight, and ground to an average particle size of 3 mm to obtain 537.18 g of modified biomass powder;

[0027] 4) 537.18 g of the modified biomass powder obtained in step 3) was placed in a tubular furnace and carbonized in a nitrogen atmosphere at a carbonization temperature of 1400 ° C. The heating rate was 5 ° C / min, and the nitrogen ventilation volume was 150 mL / min. After reaching the carbonization temperature, the temperature was maintained constant for 5 h. After naturally cooling to room temperature, the mixture was ground to an average particle size of 7 μm to obtain 210.5 g of biomass hard charcoal.

[0028] Figure 1 This is an electron microscope photograph of the hard carbon negative electrode material prepared in Example 1. From the SEM image, it can be seen that the hard carbon material prepared in Example 1 has an irregular appearance, a relatively smooth particle surface, and no collapse, closure, or agglomeration defects.

[0029] Example 2

[0030] The rest is the same as Example 1, except that in step 3), the compounding ratio of DEN438 and triglycidyl isocyanurate is 3:7.

[0031] Example 3

[0032] The rest is the same as Example 1, except that in step 3), the compounding ratio of DEN438 and triglycidyl isocyanurate is 3:3.

[0033] Example 4

[0034] The rest is the same as Example 1, except that in step 3), the compounding ratio of DEN438 and triglycidyl isocyanurate is 3:9.

[0035] Example 5

[0036] The rest is the same as Example 1, except that in step 3), the amount of the mixture of DEN438 and triglycidyl isocyanurate prepared in a mass ratio of 3:5 is 34.5 g.

[0037] Comparative Example 1

[0038] 1) 500 g of dried coconut shell was crushed into particles with an average particle size of 3 mm, washed with water three times, and vacuum dried at 100° C. to constant weight to obtain 500 g of biomass powder for later use;

[0039] 2) 500 g of the biomass powder obtained in step 1) and 10,000 mL of a 0.8 mol / L sodium hydroxide solution were added to a reactor, and the temperature was raised to 180° C. for 3 h. After the reaction, the mixture was cooled to room temperature, filtered, washed with water until neutral, and dried under vacuum at 100° C. to constant weight to obtain 492.8 g of alkali-activated biomass powder;

[0040] 2) 492.8 g of alkali-activated biomass powder was placed in a tubular furnace and carbonized in a nitrogen atmosphere at a carbonization temperature of 1400 °C, a heating rate of 5 °C / min, and a nitrogen flow rate of 150 mL / min. After reaching the carbonization temperature, the temperature was maintained constant for 5 h. After naturally cooling to room temperature, the powder was ground to an average particle size of 7 μm to obtain 130.5 g of biomass hard carbon.

[0041] The hard carbons prepared in the above examples and comparative examples were subjected to the following performance tests:

[0042] Cycling stability: In order to test the electrochemical performance of the hard carbon prepared in the examples and comparison, the obtained carbon material was mixed with PVDF (NMP solution) at a mass ratio of 90:10, slurried, and then coated on copper foil, placed in a vacuum drying oven at 120°C for 12 hours, and cut into circular electrodes with a diameter of 10 mm. The circular electrode with a diameter of 10 mm was used as the working electrode, the sodium sheet was used as the counter electrode, and the glass fiber was used as the diaphragm. 1 mol L -1 NaClO4 / EC+DEC (volume ratio 1:1) was used as the electrolyte and button half-cells (C2025) were assembled in a glove box (Mikrouna, H2O, O2 <0.1ppm) for a series of electrochemical tests. The charge and discharge cycle tests were performed using a (LandBT2000) battery test system with a test voltage range of 0.01-3.0V (vs. Na + / Na), test rate 1C.

[0043] Specific surface area: measured by NOVA 1000e pore structure specific surface area tester. The sample was degassed at 350℃ for 2h and adsorbed with liquid nitrogen at 77K and relative pressure (P / P0) 10 -6 The N2 adsorption measurement was performed within the range of -1. The specific surface area was calculated using the BET equation.

[0044] Ash content: The carbon precursors prepared in the examples and comparative examples were tested with reference to the standard GB / T 1429-2009, "Determination of ash content in carbon materials."

[0045] Table 1

[0046]

[0047] As can be seen from Table 1, the hard carbon negative electrode material prepared from biomass in the present invention has excellent cycle stability. The preparation method of the hard carbon negative electrode material in the present invention can reduce ash content, reduce surface defects, and have a larger first reversible capacity. At the same time, the preparation method of the present invention is simple, does not require special complex processes, and is suitable for industrial production.

[0048] The above detailed description is a specific description of one feasible embodiment of the present invention. This embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or modification that does not depart from the present invention should be included in the scope of the technical solution of the present invention.

Claims

1. A method for preparing a hard carbon negative electrode material, characterized in that: The steps include: 1) dissolving an epoxy resin derivative and an amine catalyst in an organic solvent to obtain a mixture, ultrasonically dispersing an alkali-activated biomass powder in the mixture, heating the mixture to react, and filtering, washing, drying, and grinding the mixture after the reaction to obtain a modified biomass powder; the epoxy resin derivative is prepared by compounding a phenolic epoxy resin and triglycidyl isocyanurate in a mass ratio of 3:5-7; 2) The modified biomass powder obtained in step 1) is placed in a tubular furnace and heated to carbonize in an inert atmosphere. After reaching the carbonization temperature, the temperature is maintained constant, and the powder is naturally cooled to room temperature and then ground to obtain a hard carbon negative electrode material.

2. The method for preparing the hard carbon negative electrode material according to claim 1, characterized in that: In step 1), the epoxy equivalent weight of the novolac epoxy resin is 170-190 g / mol and the viscosity is 500-2000 mPa·s.

3. The method for preparing the hard carbon negative electrode material according to claim 1, characterized in that: Step 1) The organic solvent is a mixed solvent of DMF and a saturated ketone in a mass ratio of 3-6:1, and the saturated ketone is selected from one or a combination of acetone and methyl ethyl ketone.

4. The method for preparing the hard carbon negative electrode material according to claim 1, wherein: Step 1) The epoxy resin derivative accounts for 3-5 wt% of the mixture; the epoxy resin derivative accounts for 7-10 wt% of the alkali-activated biomass powder.

5. The method for preparing the hard carbon negative electrode material according to claim 1, wherein: In step 1), the temperature is raised to 80-100° C., the reaction time is 1-5 hours, and the grinding is performed to a particle size of 1-3 mm.

6. The method for preparing the hard carbon negative electrode material according to claim 1, characterized in that: Step 1) The amine catalyst is selected from one or a combination of two or more of triethylamine, pyridine, and benzyldimethylamine, and the amount of the catalyst is 1-3 wt% of the epoxy resin derivative.

7. The method for preparing the hard carbon negative electrode material according to claim 1, characterized in that: Step 2) The carbonization temperature is 1200-1400°C, the heating rate is 3-6°C / min, the ventilation volume is 100-200 mL / min, the grinding is to 1-20 μm, and the constant temperature is maintained for 3-5 hours.

8. The method for preparing the hard carbon negative electrode material according to claim 1, characterized in that: Step 1) The alkali-activated biomass powder is prepared by the following method: crushing dry biomass into particles, washing, and drying to obtain biomass powder; adding the biomass powder and alkali solution to a reactor, heating to react; cooling to room temperature after the reaction, filtering, washing, and drying to obtain alkali-activated biomass powder.

9. The method for preparing the hard carbon negative electrode material according to claim 8, characterized in that: The biomass is selected from one or a combination of two or more of rice husks, coconut shells, wood chips, bamboo, rice straw, corn cobs, walnut shells, bagasse, and pistachio shells; and the average particle size of the particles is 1-3 mm.

10. Use of the hard carbon negative electrode material prepared by the preparation method according to any one of claims 1 to 9 as a negative electrode material for sodium ion batteries.

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