A cyano-modified porous hard carbon negative electrode material and its preparation method and sodium ion battery

Abstract

The present invention discloses a method for preparing a cyano-modified porous hard carbon negative electrode material: (1) impregnating a biomass raw material in an impregnation solution, drying and pre-carbonizing after impregnation to obtain a biomass-based porous pyrolytic carbon; (2) adding an aldose, a nitrogen source, and a copper source into deionized water to react for 10 to 16 hours, then adding an alkaline substance and continuing stirring for 1 to 2 hours, filtering, and drying to obtain a modified aldose; (3) placing the biomass-based porous pyrolytic carbon, the modified aldose, and deionized water in a kneader for kneading to obtain a modified aldose-coated biomass-based porous pyrolytic carbon; (4) high-temperature carbonizing the modified aldose-coated biomass-based porous pyrolytic carbon to obtain a cyano-modified porous hard carbon negative electrode material. The present invention also discloses a cyano-modified porous hard carbon negative electrode material and a sodium ion battery prepared by the preparation method. The cyano-modified porous hard carbon negative electrode material of the present invention has a high adsorption capacity (slope capacity) and excellent rate performance.

Description

Technical Field

[0001] The present invention belongs to the field of sodium ion batteries, and in particular relates to a cyano-modified porous hard carbon negative electrode material, a preparation method thereof, and a sodium ion battery. Background Art

[0002] In recent years, lithium-ion batteries have been widely used in many fields such as electronic equipment and automobiles due to their advantages such as high energy density, long cycle life, high operating voltage and no memory effect. However, the shortage of lithium resources has restricted the development of lithium-ion batteries.

[0003] Sodium-ion batteries and lithium-ion batteries are both secondary batteries, sharing similar operating principles. Sodium is widely available and low-cost. The development of sodium-ion batteries not only mitigates price fluctuations in lithium-ion battery raw materials but is also compatible with existing lithium-ion battery production equipment, offering promising commercial prospects.

[0004] Hard carbon is currently considered the most promising anode material for sodium-ion batteries. However, hard carbon materials still face the problems of low energy density and poor kinetic performance (cycling performance and rate performance).

[0005] The sodium storage mechanism of hard carbon is not clear at present, and it can be mainly divided into "adsorption-pore filling", "adsorption-intercalation", "intercalation-pore filling" and "adsorption-intercalation-pore filling". In general, the sodium storage behavior in hard carbon materials mainly includes: (1) adsorption on the surface, defect sites and functional groups; (2) micropore filling; (3) intercalation of graphitized carbon layers. The electrochemical charge-discharge curve of conventional hard carbon is generally divided into two parts: the platform region (below 0.1V) and the slope region (above 0.1V). The current controversy mainly focuses on the understanding of the sodium storage mechanism corresponding to the platform and slope regions. In the most mainstream view of "adsorption-intercalation-pore filling", adsorption corresponds to the slope region capacity, while the platform region capacity is provided by the combined action of intercalation and pore filling. Among them, the capacity improvement of the platform region is relatively simple, but the lower voltage in the region means that the capacity improvement has little effect on the cycle and rate performance of the battery. The slope region has a faster ion transfer rate and higher voltage, which is conducive to the performance of rate performance and can avoid the safety problem caused by sodium precipitation due to overpotential. The main ways to increase the capacity of the slope section are to increase surface defects, add impurities, introduce active functional groups on the surface, etc. However, the above methods often lead to a lower initial efficiency. Increasing surface defects often means a larger specific surface area, which forms more SEI film during the first charge and discharge process, and inevitably consumes more Na in the process of forming the SEI film. + , resulting in irreversible capacity loss; the addition of miscellaneous elements and the introduction of functional groups on the surface may also cause electrolyte decomposition and irreversible adsorption of Na +The development of hard carbon anode materials with both high ramp capacity and high first-cycle coulombic efficiency is crucial for the development of sodium-ion batteries with high kinetic performance and high energy density. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology and provide a cyanide-modified porous hard carbon negative electrode material and a preparation method thereof and a sodium ion battery.

[0007] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0008] A method for preparing a cyano-modified porous hard carbon negative electrode material comprises the following steps:

[0009] (1) impregnating the biomass raw material in an impregnation solution, drying and pre-carbonizing after the impregnation is completed to obtain biomass-based porous pyrolytic carbon; wherein the impregnation solution is an alkali solution, an acid solution or a salt solution;

[0010] (2) adding the aldose, nitrogen source, and copper source to deionized water and stirring for 10 to 16 hours, then adding an alkaline substance and continuing stirring for 1 to 2 hours, filtering, and drying the filtrate in an inert atmosphere to obtain a modified aldose;

[0011] (3) placing the biomass-based porous pyrolytic carbon, the modified aldose, and deionized water in a kneader and kneading them to obtain a modified aldose-coated biomass-based porous pyrolytic carbon;

[0012] (4) The modified aldose-coated biomass-based porous pyrolytic carbon is subjected to high-temperature carbonization to obtain a cyano-modified porous hard carbon negative electrode material.

[0013] In the above-mentioned preparation method, preferably, in step (1), the biomass raw material is at least one of coconut shells, walnut shells, and lignin; the alkali solution is at least one of potassium hydroxide solution and sodium hydroxide solution; the acid solution is at least one of phosphoric acid and polyphosphoric acid; and the salt solution is at least one of zinc chloride solution, potassium carbonate solution, ammonium dihydrogen phosphate solution, and ammonium monohydrogen phosphate solution. Relatively cheap biomass shells or lignin are used as the hard carbon main body, and chemical activation is used to etch them with acid, alkali, or salt to form abundant pores and defects inside them, thereby increasing their internal active sodium storage sites and effectively improving the platform capacity of the material.

[0014] In the above preparation method, preferably, in step (1), the mass concentration of the impregnation solution is 40% to 60%; the drying temperature is 100 to 150° C., and the drying time is 12 to 24 hours.

[0015] In the above-mentioned preparation method, preferably, in step (1), the prepared biomass-based porous pyrolytic carbon is washed with deionized water, filtered, and the filter residue is dried and crushed in an inert atmosphere to obtain biomass-based porous pyrolytic carbon powder; wherein the drying temperature is 100-150°C, the drying time is 24-48h, and the crushing is carried out in a jet mill or a mechanical mill, and the Dv50 of the crushed material is 4-20μm.

[0016] In the above preparation method, preferably, in step (1), the pre-carbonization is carried out in an inert atmosphere, the pre-carbonization temperature is 400-700° C., and the holding time is 2-6 hours.

[0017] In the above preparation method, preferably, in step (2), the aldose is at least one of glucose, fructose, mannose, and galactose; further preferably, the aldose is mannose, which has a higher solubility in water, can reduce the amount of deionized water used, and speed up the subsequent drying speed.

[0018] In the above preparation method, preferably, in step (2), the nitrogen source is at least one of ammonium chloride and ammonium acetate; the copper source is at least one of copper chloride and copper acetate; the alkaline substance is at least one of ammonium carbonate, ammonium bicarbonate, and ammonia monohydrate; further preferably, the nitrogen source and the copper source are substances with the same anion.

[0019] In the above preparation method, preferably, in step (2), the mass ratio of the aldose to the nitrogen source is 1.5:1 to 3:1; the mass ratio of the nitrogen source to the copper source is 1:0.04 to 1:0.06; the mass ratio of the aldose to deionized water is 1:2 to 2:1; and the mass ratio of the nitrogen source to the alkaline substance is 1:0.5 to 1:2.5.

[0020] In the above preparation method, preferably, in step (2), the stirring speed is 500 to 2000 rpm.

[0021] In the above preparation method, preferably, in step (2), during the aldose modification process, copper ions (Cu 2+ ) catalyzes the ammonium ion (NH4 + ) oxidizes the aldehyde group (-CHO) to a cyano group (-CN). The reaction equation is as follows: the overall reaction, and the separation steps are as shown in the reaction equations of reactions 1 to 5, wherein R1 is other groups in the aldose that connect to the aldehyde group, and R2 is an ion or group other than the ammonium ion and copper ion in the nitrogen source and the copper source.

[0022]

[0023] The above series of reactions can be carried out at room temperature and air conditions, and the reaction conditions are simple and mild.

[0024] In the above preparation method, preferably, in step (2), the nitrogen source is selected from ammonium salt instead of the commonly used TMSCN (trimethylsilyl cyanide) or metal cyanide (such as potassium cyanide, sodium cyanide) and other highly toxic substances as cyaniding agents, and the nitrogen element is not ionized in the reaction process. - ) exists in the form of, and its operability and safety are relatively high, and it is more operable and safe. The use of water-soluble aldose provides aldehyde groups, so that the reaction can be carried out in deionized water, which reduces costs and also makes the reaction safer for the human body. The reaction is used as a copper source for the catalyst, and then by adding an excess of alkaline substances, the acid generated by the reaction in the solution is first neutralized to make the solution alkaline, and then the hydroxide ions or carbonate ions are combined with the copper ions to form a precipitate and can be removed by filtration, thereby preventing the introduction of magnetic material Cu element from affecting the battery capacity, life and safety. Subsequently, by adding hydrochloric acid or acetic acid to the precipitate (at least one of copper hydroxide and basic copper carbonate), it can be converted back into copper chloride or copper acetate to achieve the reuse of the catalyst; at the same time, the excess alkaline substance and the product formed by the neutralization of the acid (at least one of ammonium chloride and ammonium acetate) can be heated and decomposed into gas or volatilized and removed during the subsequent oven heating or carbonization process, and no residue is left in the material.

[0025] In the above preparation method, preferably, in step (3), the mass ratio of the biomass-based porous pyrolytic carbon powder to the modified aldose is 100:5 to 100:20; the mass ratio of the biomass-based porous pyrolytic carbon powder to deionized water is 1:1 to 1:3.

[0026] In the above preparation method, preferably, in step (3), during the kneading process, the speed of the kneader is 60-180 rpm, the kneading temperature is 110-150° C., and the kneading time is 4-8 h.

[0027] In the above preparation method, preferably, in step (4), the high-temperature carbonization is carried out in an inert atmosphere, the temperature of the high-temperature carbonization is 1100-1600°C, the holding time is 2-6h; and the heating rate of the high-temperature carbonization is 2-10°C / min.

[0028] In order to improve the slope capacity of the hard carbon negative electrode material without affecting the first effect, the present invention introduces a cyano group (-CN) that can reversibly adsorb sodium ions on the surface of the hard carbon, reducing the hydroxyl group of the carbon-oxygen single bond (CO) structure that brings irreversible adsorption of sodium ions to the surface of the material. Specifically, the outer layer of the raw material aldose coated with the present invention carries 5 alcoholic hydroxyl groups (-OH) and one aldehyde group (-CHO). It is modified by adding a nitrogen source to convert the aldehyde group into a cyano group. Because the bond energy of the carbon-nitrogen triple bond (891kJ / mol) is higher than that of the carbon-oxygen bond (326kJ / mol) and the carbon-hydrogen bond (414kJ / mol), the destruction of the cyano group is more difficult than that of the alcoholic hydroxyl group and the carbon-hydrogen bond during heating. The alcoholic hydroxyl group that irreversibly adsorbs sodium ions is more likely to combine with hydrogen atoms and be removed as water vapor, while the cyano structure that reversibly adsorbs sodium ions is more difficult to destroy. By coating the modified aldose on the surface of pyrolytic carbon and carbonizing it at high temperature, the effect of introducing a group that can reversibly adsorb sodium ions on the surface of the hard carbon is achieved, thereby increasing the slope capacity of the material without affecting the first effect.

[0029] Pore ​​formation can increase the energy density of materials. The pores formed after pore formation shrink or even close during high-temperature carbonization due to the scaling of the material's interlayer spacing and the growth of graphite-like microcrystals. Combined with the effect of coating, the coating agent adheres to the material's surface, blocking its surface pores and making it easier for it to form a closed microporous structure. This provides more internal sodium storage active sites, increasing the material's capacity while avoiding excessive surface defects that would reduce the material's initial efficiency. The small amount of non-closed pore structure remaining after pore formation, coating, and high-temperature carbonization also provides a channel for the electrolyte to enter the material, shortening the diffusion distance of sodium ions in the material and promoting improved rate performance.

[0030] In the above preparation method, preferably, the inert atmosphere is at least one of nitrogen, helium, neon and argon.

[0031] As a general inventive concept, the present invention also provides a cyanide-modified porous hard carbon negative electrode material prepared by the above-mentioned preparation method, wherein the cyanide-modified porous hard carbon negative electrode material includes a porous biomass-based hard carbon matrix and a cyanide-modified aldose hard carbon layer coated on the surface of the porous biomass-based hard carbon matrix.

[0032] The above-mentioned cyano-modified porous hard carbon negative electrode material, preferably, the Dv50 of the cyano-modified porous hard carbon negative electrode material is 5 to 15 μm, and the specific surface area is 2 to 5 m 2 / g, the pore volume is 0.05~0.1cc / g, the buckle battery prepared by this negative electrode material has a first reversible mass specific capacity of more than 340mAh / g at 0.1C, a first coulombic efficiency of more than 88%, a mass specific capacity of more than 200mAh / g at a voltage of 0.1V during discharge, and a reversible mass specific capacity of more than 240mAh / g at 5C.

[0033] As a general inventive concept, the present invention also provides a sodium ion battery, comprising the cyano-modified porous hard carbon negative electrode material prepared by the above-mentioned preparation method or comprising the above-mentioned cyano-modified porous hard carbon negative electrode material.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The cyano-modified porous hard carbon negative electrode material of the present invention has a surface-coated modified aldose that forms hard carbon at high temperature, which can assist the internal biomass-based hard carbon pores to shrink and close at high temperature to form a closed pore structure, thereby reducing the specific surface area of ​​the carbonized material. This improves the subsequent slurry coating performance while avoiding the large specific surface area that causes the battery to form too much SEI film during the first charge and discharge process, consumes too much electrolyte, and consumes too much sodium ions, thereby causing the loss of the first effect. At the same time, the modified aldose is coated on the surface of the material, and the cyano group it brings acts as a surface sodium storage active site, which obtains electrons during the charging process, and the -CN structure is converted into -CN 2- structure, and then combines with sodium ions to form -CN 2- (Na + )2 structure to store sodium, and lose electrons during discharge to convert into -[CN(Na + )2] 2+ structure, and then restore the -CN structure as the sodium ions are removed, realizing reversible sodium storage; the cyanide group on the surface of the material can effectively shorten the diffusion distance inside the material when the sodium ions combine with the material, and reduce the time required for the sodium ions to combine with the material, which is beneficial to improving the slope capacity of the material and improving the rate performance of the material.

[0036] (2) The cyano-modified porous hard carbon negative electrode material of the present invention has a Dv50 of 5 to 15 μm and a specific surface area of ​​2 to 5 m 2 / g, the pore volume is 0.05-0.1cc / g, the button battery prepared by the negative electrode material has the first reversible mass specific capacity of more than 340mAh / g at 0.1C, the first coulombic efficiency is more than 88%, and the mass specific capacity of 0.1V voltage during discharge is more than 200mAh / g.

[0037] (3) The present invention adopts a chemical activation method to etch micropores in biomass raw materials, increase the internal defects of the material, and close the pores by surface coating auxiliary materials to form closed micropores. While ensuring that the negative electrode material has a smaller specific surface area, its internal defects provide more sodium storage active sites, thereby improving the capacity of the material without affecting the primary effect of the material; at the same time, a small amount of unclosed pores provides a channel for the electrolyte to enter the interior of the material, shortening the diffusion distance of sodium ions in the material, which is beneficial to the improvement of the material's rate performance.

[0038] (4) The present invention introduces cyanide groups as active sodium storage sites by coating the surface of the material, thereby improving the slope capacity and rate performance of the negative electrode material.

[0039] (5) The present invention uses copper ions as catalysts to allow ammonium ions to oxidize the aldehyde groups in aldose to cyano groups; less toxic ammonium salts are used instead of conventional TMSCN or metal cyanide and other highly toxic substances as cyaniding agents; the reactants and catalysts are all well soluble in water, and the reaction can be carried out directly in water without the need to use organic solvents such as THF (tetrahydrofuran), DMF (N,N-dimethylformamide), DMSO (dimethyl sulfoxide) as reaction solvents, nor is it necessary to add organic solvents such as THF (tetrahydrofuran), DMF (N,N-dimethylformamide), DMSO (dimethyl sulfoxide) to water to increase the solubility of the reactants and catalysts, thereby reducing the solvent cost and preventing the organic solvents from causing harm to the human body through volatilization, inhalation, contact with the skin, etc.; the reaction is carried out in air at room temperature, the reaction is mild, and the environmental requirements are low; the nitrogen element is not always in the form of ionized cyanide (CN - ) form, and its operability and safety are relatively high.

[0040] (6) The synthesis process of the present invention is simple, highly operable, and has low raw material costs, making it easy to achieve mass production and commercialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is an SEM image of the cyano-modified porous hard carbon negative electrode material in Example 1 of the present invention;

[0042] Figure 2 This is a TEM image of the cyano-modified porous hard carbon negative electrode material in Example 1 of the present invention;

[0043] Figure 3 This is a charge-discharge curve diagram of the cyano-modified porous hard carbon negative electrode material prepared in Example 1 of the present invention under 0.1C conditions. DETAILED DESCRIPTION

[0044] To facilitate understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0045] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0046] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0047] Example 1:

[0048] A cyano-modified porous hard carbon negative electrode material of the present invention comprises a porous lignin-based hard carbon matrix and a cyano-modified mannose hard carbon layer coated on the surface of the porous lignin-based hard carbon matrix.

[0049] The preparation method of the cyanide-modified porous hard carbon negative electrode material of this embodiment includes the following steps:

[0050] (1) After immersing lignin in a potassium hydroxide solution with a mass concentration of 40% for 1 hour, the lignin was placed in an oven and dried at 110°C in a nitrogen atmosphere for 24 hours; then the lignin was placed in a box furnace and heated to 650°C at a rate of 5°C / min in a nitrogen atmosphere and kept at this temperature for 2 hours for pre-carbonization; after the pre-carbonization was completed, the temperature was cooled to room temperature, the material was taken out and washed with deionized water to pH = 8, filtered, and the filter residue was placed in an oven and dried at 110°C under nitrogen protection for 24 hours. The dried material was then placed in a jet mill and pulverized to a Dv50 of about 7 μm to obtain lignin-based porous pyrolytic carbon powder.

[0051] (2) Mannose, ammonium chloride, copper chloride, and deionized water were placed in a high-speed shearing machine at a mass ratio of 150:100:4:75 and stirred at 1000 rpm for 14 h. Then, ammonium carbonate of the same mass as the ammonium chloride was added and stirred at 1000 rpm for 1 h to allow the copper ions, carbonate ions, and hydroxide ions in the solution to combine with each other to form basic copper carbonate and copper hydroxide precipitates. The mixture was filtered and the filtrate was dried at 150°C under a nitrogen atmosphere for 24 h to obtain modified mannose. Hydrochloric acid was added to the filter residue and stirred until completely dissolved. The residue was then dried in an oven at 150°C until the liquid was completely volatilized, and the catalyst copper chloride was recovered.

[0052] (3) The modified mannose prepared in step (2), the lignin-based porous pyrolytic carbon powder prepared in step (1), and deionized water are placed in a kneader at a ratio of 100:10:150. Under a nitrogen atmosphere, the kneader is heated to 110°C and kneaded at a rate of 120 rpm for 6 hours to obtain modified mannose-coated lignin-based porous pyrolytic carbon.

[0053] (4) The modified mannose-coated lignin-based porous pyrolytic carbon was heated to 1400°C at a rate of 5°C / min in a nitrogen atmosphere and kept at a constant temperature for 2 h for high-temperature carbonization. After carbonization, the temperature was cooled to room temperature to obtain a cyano-modified porous hard carbon negative electrode material.

[0054] The SEM and TEM images of the cyano-modified porous hard carbon anode material prepared in this example are shown in Figure 2. Figure 1 and Figure 2 As shown, from Figure 1From the SEM image, it can be seen that the morphology of the cyanide-modified porous hard carbon anode material of this embodiment is similar to that of conventional hard carbon; Figure 2 In the TEM image, the material with lighter outer color and disordered grain distribution is the coating modified mannose-based hard carbon, and the material with darker inner color and disordered grain distribution is the lignin-based hard carbon; Figure 1 and Figure 2 , it can be seen that the modified mannose is well coated on the lignin-based pyrolysis carbon and completes the carbonization to form a hard carbon material.

[0055] Example 2:

[0056] A cyano-modified porous hard carbon negative electrode material of the present invention comprises a porous coconut shell-based hard carbon matrix and a cyano-modified fructose hard carbon layer coated on the surface of the porous coconut shell-based hard carbon matrix.

[0057] The preparation method of the cyanide-modified porous hard carbon negative electrode material of this embodiment includes the following steps:

[0058] (1) Coconut shells were immersed in a phosphoric acid solution with a mass concentration of 40% for 1 hour, and then placed in an oven and dried at 150°C for 12 hours in a nitrogen atmosphere; then placed in a box furnace, heated to 450°C at a rate of 5°C / min in a nitrogen atmosphere, and kept at this temperature for 2 hours for pre-carbonization; after the pre-carbonization was completed, the temperature was cooled to room temperature, the material was taken out and washed with deionized water to pH = 6, filtered, and the filter residue was placed in an oven and dried at 150°C for 24 hours under nitrogen protection. The dried material was then placed in a jet mill and crushed to a Dv50 of about 5 μm to obtain coconut shell-based porous pyrolytic carbon powder.

[0059] (2) Fructose, ammonium acetate, copper acetate, and deionized water were placed in a high-speed shearing machine at a mass ratio of 150:100:6:150 and stirred at 1200 rpm for 12 hours. Ammonia monohydrate was then added at 70% of the mass of ammonium acetate and stirred at 1200 rpm for 1 hour to allow the copper ions in the solution to combine with the hydroxide ions generated by water ionization to form copper hydroxide precipitate. The mixture was filtered and the filtrate was dried at 150°C under a nitrogen atmosphere for 48 hours to obtain modified fructose. Acetic acid was added to the filter residue and stirred until completely dissolved. The mixture was then dried in an oven at 150°C until the liquid was completely volatilized, and the catalyst copper acetate was recovered.

[0060] (3) The modified fructose prepared in step (2), the coconut shell-based porous pyrolytic carbon powder prepared in step (1), and deionized water are placed in a kneader at a ratio of 100:20:150. Under a nitrogen atmosphere, the kneader is heated to 110° C. and kneaded at a rate of 120 rpm for 6 h to obtain modified fructose-coated coconut shell-based porous pyrolytic carbon.

[0061] (4) The modified fructose-coated coconut shell-based porous pyrolytic carbon was heated to 1300°C at a rate of 2°C / min in a nitrogen atmosphere and kept at this temperature for 2 h for high-temperature carbonization. After the carbonization, the temperature was cooled to room temperature to obtain a cyano-modified porous hard carbon negative electrode material.

[0062] Example 3:

[0063] A cyano-modified porous hard carbon negative electrode material of the present invention comprises a porous coconut shell-based hard carbon matrix and a cyano-modified glucose hard carbon layer coated on the surface of the porous coconut shell-based hard carbon matrix.

[0064] The preparation method of the cyanide-modified porous hard carbon negative electrode material of this embodiment includes the following steps:

[0065] (1) Coconut shells were immersed in a phosphoric acid solution with a mass concentration of 60% for 1 hour, and then placed in an oven and dried at 150°C for 12 hours in a nitrogen atmosphere; then placed in a box furnace, heated to 450°C at a rate of 5°C / min in a nitrogen atmosphere, and kept at this temperature for 2 hours for pre-carbonization; after the pre-carbonization was completed, the temperature was cooled to room temperature, the material was taken out and washed with deionized water to pH = 5, filtered, and the filter residue was placed in an oven and dried at 150°C for 24 hours under nitrogen protection. The dried material was then placed in a jet mill and pulverized to a Dv50 of about 7 μm to obtain coconut shell-based porous pyrolytic carbon powder.

[0066] (2) Glucose, ammonium acetate, copper acetate, and deionized water were placed in a high-speed shearing machine at a mass ratio of 150:100:6:200 and stirred at 1000 rpm for 14 h. Then, ammonium carbonate of the same mass as the ammonium acetate was added and stirred at 1000 rpm for 1 h to allow the copper ions in the solution to combine with the carbonate ions and the hydroxide ions generated by water ionization to form basic copper carbonate and copper hydroxide precipitates. The mixture was filtered and the filtrate was dried at 150°C under a nitrogen atmosphere for 48 h to obtain modified glucose. Acetic acid was added to the filter residue and stirred until completely dissolved. The mixture was then dried in an oven at 150°C until the liquid was completely volatilized, and the catalyst copper acetate was recovered.

[0067] (3) The modified glucose prepared in step (2), the coconut shell-based porous pyrolytic carbon powder prepared in step (1), and deionized water are placed in a kneader at a ratio of 100:10:150. Under a nitrogen atmosphere, the kneader is heated to 110° C. and kneaded at a rate of 120 rpm for 6 h to obtain modified glucose-coated coconut shell-based porous pyrolytic carbon.

[0068] (4) The modified glucose-coated coconut shell-based porous pyrolytic carbon was heated to 1300°C at a rate of 2°C / min in a nitrogen atmosphere and kept at this temperature for 2 h for high-temperature carbonization. After the carbonization, the temperature was cooled to room temperature to obtain a cyano-modified porous hard carbon negative electrode material.

[0069] Example 4:

[0070] A cyano-modified porous hard carbon negative electrode material of the present invention comprises a porous coconut shell-based hard carbon matrix and a cyano-modified galactose hard carbon layer coated on the surface of the porous coconut shell-based hard carbon matrix.

[0071] The preparation method of the cyanide-modified porous hard carbon negative electrode material of this embodiment includes the following steps:

[0072] (1) Coconut shells were immersed in a potassium carbonate solution with a mass concentration of 40% for 1 hour, and then placed in an oven and dried at 150°C for 12 hours in a nitrogen atmosphere; then placed in a box furnace, heated to 700°C at a rate of 5°C / min in a nitrogen atmosphere, and kept at this temperature for 2 hours for pre-carbonization; after the pre-carbonization was completed, the temperature was cooled to room temperature, the material was taken out and washed with deionized water to pH = 8, filtered, and the filter residue was placed in an oven and dried at 110°C for 24 hours under nitrogen protection. The dried material was then placed in a jet mill and pulverized to a Dv50 of about 7 μm to obtain coconut shell-based porous pyrolytic carbon powder.

[0073] (2) Galactose, ammonium acetate, copper acetate, and deionized water were placed in a high-speed shearing machine at a mass ratio of 150:100:6:300 and stirred at 1500 rpm for 16 hours. Then, ammonium carbonate of the same mass as the ammonium acetate was added and stirred at 1500 rpm for 2 hours to allow the copper ions in the solution to combine with the carbonate ions and the hydroxide ions ionized from the water to form basic copper carbonate and copper hydroxide precipitates. The mixture was filtered and the filtrate was dried at 150°C for 48 hours under a nitrogen atmosphere to obtain modified galactose. Acetic acid was added to the filter residue and stirred until completely dissolved. The mixture was then dried in an oven at 150°C until the liquid was completely volatilized, and the catalyst copper acetate was recovered.

[0074] (3) The modified galactose prepared in step (2), the coconut shell-based porous pyrolytic carbon powder prepared in step (1), and deionized water are placed in a kneader at a ratio of 100:20:150. Under a nitrogen atmosphere, the kneader is heated to 110° C. and kneaded at a rate of 120 rpm for 6 h to obtain modified galactose-coated coconut shell-based porous pyrolytic carbon.

[0075] (4) The obtained modified galactose-coated coconut shell-based porous pyrolytic carbon was heated to 1300°C at a rate of 2°C / min in a nitrogen atmosphere and kept at a constant temperature for 2 h for high-temperature carbonization. After the carbonization was completed, the temperature was cooled to room temperature to obtain a cyano-modified porous hard carbon negative electrode material.

[0076] Comparative Example 1:

[0077] The preparation method of the hard carbon negative electrode material of this comparative example comprises the following steps:

[0078] (1) After immersing lignin in a potassium hydroxide solution with a mass concentration of 40% for 1 hour, the lignin was placed in an oven and dried at 110°C in a nitrogen atmosphere for 24 hours; then the lignin was placed in a box furnace and heated to 650°C at a rate of 5°C / min in a nitrogen atmosphere and kept at this temperature for 2 hours for pre-carbonization; after the pre-carbonization was completed, the temperature was lowered to room temperature, the material was taken out and washed with deionized water to pH = 8, filtered, and the filter residue was placed in an oven and dried at 110°C for 24 hours under nitrogen protection. The dried material was then placed in a jet mill and pulverized to a Dv50 of about 7 μm to obtain lignin-based porous pyrolytic carbon powder.

[0079] (2) Mannose, the lignin-based porous pyrolytic carbon powder prepared in step (1), and deionized water were placed in a kneader at a ratio of 100:10:150. Under a nitrogen atmosphere, the kneader was heated to 110° C. and kneaded at a rate of 120 rpm for 6 h to obtain mannose-coated lignin-based porous pyrolytic carbon.

[0080] (3) The mannose-coated lignin-based porous pyrolytic carbon was heated to 1400°C at a rate of 5°C / min in a nitrogen atmosphere and kept at this temperature for 2 h for high-temperature carbonization. After the carbonization, the temperature was cooled to room temperature to obtain a hard carbon negative electrode material.

[0081] Comparative Example 2:

[0082] The preparation method of the hard carbon negative electrode material of this comparative example comprises the following steps:

[0083] (1) After immersing lignin in a potassium hydroxide solution with a mass concentration of 40% for 1 hour, the lignin was placed in an oven and dried at 110°C in a nitrogen atmosphere for 24 hours; then the lignin was placed in a box furnace and heated to 650°C at a rate of 5°C / min in a nitrogen atmosphere and kept at this temperature for 2 hours for pre-carbonization; after the pre-carbonization was completed, the temperature was lowered to room temperature, the material was taken out and washed with deionized water to pH = 8, filtered, and the filter residue was placed in an oven and dried at 110°C for 24 hours under nitrogen protection. The dried material was then placed in a jet mill and pulverized to a Dv50 of about 7 μm to obtain lignin-based porous pyrolytic carbon powder.

[0084] (2) The lignin-based porous pyrolytic carbon powder was heated to 1400°C at a rate of 5°C / min in a nitrogen atmosphere and kept at this temperature for 2 hours for high-temperature carbonization. After the carbonization, the temperature was cooled to room temperature to obtain a porous hard carbon negative electrode material.

[0085] Comparative Example 3:

[0086] The preparation method of the hard carbon negative electrode material of this comparative example comprises the following steps:

[0087] (1) The lignin was placed in a box furnace, heated to 650°C at a rate of 5°C / min under a nitrogen atmosphere, and kept at this temperature for 2 h for pre-carbonization. The material was then placed in a jet mill and pulverized to a Dv50 of approximately 7 μm to obtain lignin-based pyrolytic carbon powder.

[0088] (2) The lignin-based pyrolysis carbon powder was heated to 1400°C at a rate of 2°C / min in a nitrogen atmosphere and kept at this temperature for 2 h for high-temperature carbonization. After cooling to room temperature, a hard carbon negative electrode material was obtained.

[0089] The hard carbon negative electrode materials prepared in the above examples and comparative examples were placed in a Mastersizer 3000 to test the particle size; the BET specific surface area and pore volume were tested in a Mike 3030. The results are shown in Table 1.

[0090] The hard carbon negative electrode materials prepared in the above embodiments and comparative examples were mixed with SP carbon black, CMC, SBR, and deionized water, and then coated on aluminum foil to prepare negative electrode sheets. The dried negative electrode sheets were used as negative electrodes, sodium sheets were used as positive electrodes, glass fibers were used as separators, and 1.0M NaPF6 in diglyme = 100 Vol% was used as electrolyte. Coin-type batteries were assembled and their mass specific capacity at 0.1C, initial coulombic efficiency, and mass specific capacity at 0.1V voltage during discharge were tested. The mass specific capacity at 5C was then tested. The data obtained are shown in Table 1 below. The charge and discharge curves of the hard carbon negative electrode material in Example 1 are shown in Table 1 below. Figure 3 shown.

[0091] Table 1 Material parameters of each embodiment and comparative example

[0092]

[0093] From the comparison between Example 1 and Comparative Example 1, it can be seen that at 0.1C, the reversible mass specific capacity and 0.1V mass specific capacity of Example 1 are higher than those of Comparative Example 1, and the difference between the two is close, indicating that after the aldose modification, the porous hard carbon material is coated, and the cyanide group on the surface of the material improves the slope capacity of the material; and the reversible mass specific capacity of Example 1 at 5C is higher than that of Comparative Example 1, indicating that the slope capacity brought by the cyanide group also has a positive effect on improving the rate performance of the material.

[0094] From the comparison of comparative example 1 and comparative example 2, it can be seen that the capacity difference between the two at 0.1C is small, but the first efficiency of comparative example 1 is higher, and the reversible mass specific capacity of comparative example 2 at 5C is slightly higher than that of comparative example 1. This is because comparative example 2 is not coated, and the unclosed pores on the surface are more than those in comparative example 1. The unclosed pores shorten the Na + The distance diffused within a material.

[0095] From the comparison between Comparative Example 2 and Comparative Example 3, it can be seen that at 0.1C, the reversible mass specific capacity of Comparative Example 2 is higher than that of Comparative Example 3, while at 0.1V, the mass specific capacities of the two are close, indicating that the capacity improved by pore formation is mainly in the platform area of ​​<0.1V.

[0096] From the comparison between comparative examples 1 and 3, it can be seen that at 5C, the reversible capacity of comparative example 1 is higher than that of comparative example 3, which indicates that after coating, there are still a small amount of unclosed pores that are entered by the electrolyte after the battery is assembled, shortening the Na + The diffusion distance within the material is increased, thereby improving the rate performance of the material.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the scope of protection of the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a cyano-modified porous hard carbon negative electrode material, characterized in that: The following steps are involved: (1) impregnating the biomass raw material in an impregnation solution, drying and pre-carbonizing the raw material after impregnation to obtain a biomass-based porous pyrolytic carbon; wherein the impregnation solution is an alkali solution, an acid solution or a salt solution; (2) adding an aldose, a nitrogen source, and a copper source to deionized water and stirring for 10 to 16 hours, then adding an alkaline substance and continuing stirring for 1 to 2 hours, filtering, and drying the filtrate in an inert atmosphere to obtain a modified aldose; the nitrogen source is at least one of ammonium chloride and ammonium acetate; (3) placing the biomass-based porous pyrolytic carbon, the modified aldose, and deionized water in a kneader and kneading them to obtain a modified aldose-coated biomass-based porous pyrolytic carbon; (4) The modified aldose-coated biomass-based porous pyrolytic carbon is carbonized at high temperature to obtain a cyano-modified porous hard carbon negative electrode material.

2. The preparation method according to claim 1, wherein In step (1), the biomass raw material is selected from at least one of coconut shells, walnut shells, and lignin; the alkali solution is at least one of potassium hydroxide solution and sodium hydroxide solution; the acid solution is at least one of phosphoric acid and polyphosphoric acid; and the salt solution is at least one of zinc chloride solution, potassium carbonate solution, ammonium dihydrogen phosphate solution, and ammonium monohydrogen phosphate solution.

3. The preparation method according to claim 1, wherein In step (1), the pre-carbonization is carried out in an inert atmosphere, the pre-carbonization temperature is 400-700° C., and the holding time is 2-6 hours.

4. The preparation method according to claim 1, wherein In step (2), the aldose is at least one of glucose, fructose, mannose, and galactose; the copper source is at least one of copper chloride and copper acetate; and the alkaline substance is at least one of ammonium carbonate, ammonium bicarbonate, and ammonia monohydrate.

5. The preparation method according to claim 4, wherein In step (2), the mass ratio of the aldose to the nitrogen source is 1.5:1 to 3:1; the mass ratio of the nitrogen source to the copper source is 1:0.04 to 1:0.06; the mass ratio of the aldose to deionized water is 1:2 to 2:1; and the mass ratio of the nitrogen source to the alkaline substance is 1:0.5 to 1:2.

5.

6. The preparation method according to claim 1, wherein In step (3), the mass ratio of the biomass-based porous pyrolytic carbon to the modified aldose is 100:5-100:20; the mass ratio of the biomass-based porous pyrolytic carbon to deionized water is 1:1-1:

3.

7. The preparation method according to claim 1, wherein In step (3), during the kneading process, the speed of the kneader is 60-180 rpm, the kneading temperature is 110-150° C., and the kneading time is 4-8 h.

8. The preparation method according to claim 1, wherein In step (4), the high-temperature carbonization is carried out in an inert atmosphere, the temperature of the high-temperature carbonization is 1100-1600° C., and the holding time is 2-6 hours.

9. A cyano-modified porous hard carbon negative electrode material prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The cyano-modified porous hard carbon negative electrode material comprises a porous biomass hard carbon matrix and a modified aldose hard carbon layer with cyano groups coated on the surface of the porous biomass hard carbon matrix.

10. A sodium ion battery, characterized in that: The invention comprises the cyano-modified porous hard carbon negative electrode material prepared by the preparation method according to any one of claims 1 to 8, or the cyano-modified porous hard carbon negative electrode material according to claim 9.

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