A method for preparing nitrogen-sulfur-doped graphene-supported crosslinked starch-based hard carbon materials

Abstract

This invention discloses a method for preparing a nitrogen-sulfur-doped graphene-supported crosslinked starch-based hard carbon material, belonging to the field of electrode material technology. Specifically, it involves using water-soluble starch as the main raw material, then adding soluble glucose with a linear structure for crosslinking, followed by the addition of nitrogen-sulfur additives soluble in deionized water, and simultaneously adding nanoscale graphene material. The graphene material acts as a support to form a conductive network, thus preparing a negative electrode hard carbon material. The graphene material includes graphene and graphene derivatives, which are derived from graphene oxide and derivatizing agents, including 3-aminopropyltrimethoxysilane and / or trimethoxy(2-phenylethyl)silane. A sodium-ion battery is further fabricated from the negative electrode hard carbon material. The negative electrode hard carbon material of this invention exhibits good conductivity, resulting in high reversible capacity, high initial efficiency, and a high slope capacity ratio after being fabricated into a battery.

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology, specifically relating to a method for preparing a nitrogen-sulfur-doped graphene-supported crosslinked starch-based hard carbon material. Background Technology

[0002] Compared to lithium-ion batteries, sodium-ion batteries offer advantages such as lower cost, higher charging rate, better low-temperature performance, and improved safety. However, due to current limitations in cycle life and energy density, sodium-ion batteries are more suitable for industries with lower energy density requirements but high cost sensitivity, making them widely applicable in energy storage and low-speed electric vehicles. Hard carbon is an ideal anode material for sodium-ion batteries, possessing a loose, porous, and interwoven layered structure capable of storing large amounts of sodium ions. Currently, biomass hard carbon is the primary anode material for sodium-ion batteries. To improve the electrochemical performance of hard carbon anodes, most companies employ heteroatom doping (mainly nitrogen, phosphorus, sulfur, and boron atoms). Heteroatom doping creates external defects and provides more porosity in the structure, increasing active sites and interlayer spacing. Active sites ensure rapid and efficient electron transport, improving the conductivity of carbon materials, while larger interlayer spacing facilitates sodium ion insertion and extraction.

[0003] Most biomass hard carbon uses solid raw materials such as coconut shells, walnut shells, and wood as raw materials, making it difficult to uniformly dope hard carbon materials with heteroatoms, resulting in less than ideal performance of the manufactured hard carbon materials. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing nitrogen-sulfur-doped graphene-supported crosslinked starch-based hard carbon materials with high reversible capacity, high initial efficiency, high slope capacity ratio, and high powder conductivity after being fabricated into batteries.

[0005] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0006] A method for preparing a negative electrode hard carbon material includes: mixing a matrix raw material with nitrogen and sulfur reagents in deionized water, then adding graphene material to form a slurry, and preparing the negative electrode hard carbon material from the slurry; the matrix raw material protects water-soluble starch, and the nitrogen and sulfur reagents include thiourea and urea; the amount of thiourea is 0.1-2 wt% of the water-soluble starch, and the amount of urea is 0.1-2 wt% of the water-soluble starch. In this invention, the matrix raw material includes water-soluble starch and glucose, with starch as the main raw material and glucose as the cross-linking material. Starch soluble in deionized water is used as the main raw material, and soluble glucose with a linear structure is added for cross-linking. Nitrogen and sulfur additives soluble in deionized water are then added, and nano-scale graphene material is added to the material to provide support and form a conductive network. The synthesized negative electrode hard carbon material is intercalated in the conductive network of graphene, improving the performance of the battery made from the negative electrode hard carbon material.

[0007] The main raw materials of this invention, starch and glucose, are derived from biomass (corn, potatoes, etc.), which are characterized by low cost, abundant resources, renewability, and non-toxicity. Glucose is used to crosslink starch, optimizing the precursor structure at the molecular level. The crosslinking reaction forms a more stable three-dimensional network, reducing excessive increase in specific surface area and the formation of ineffective macropores during carbonization. Crosslinking controls the pore structure of hard carbon from the source, improving initial efficiency. The entire preparation process mainly involves aqueous solution mixing. Liquid-phase mixing can uniformly mix nitrogen, sulfur, and graphene, ensuring the consistency of the hard carbon material. The process is easy to control and scale up, and has good compatibility with existing industrial production equipment (such as spray drying and roller kilns). N and S atoms alter the local electron cloud distribution of carbon atoms, generating more defect sites. These sites can store sodium ions through surface adsorption reactions, providing additional pseudocapacitive capacity besides the intercalation mechanism, thereby improving the overall specific capacity. In particular, the larger radius of S atoms allows for effective expansion of the interlayer spacing of carbon materials, lowering the energy barrier for sodium ion intercalation and deintercalation, and improving rate performance. Hard carbon itself has poor electrical conductivity, but the addition of graphene provides a high-speed electron transport path, which can reduce the internal resistance of the electrode.

[0008] Preferably, the matrix raw material further includes glucose, the amount of which is 2-24 wt% of the water-soluble starch. More preferably, the amount of glucose is 5-20 wt% of the water-soluble starch.

[0009] Preferably, the graphene material includes graphene and / or graphene derivatives, wherein the graphene derivatives are derived from graphene oxide and a derivatizing agent.

[0010] More preferably, the derivatizing agent includes 3-aminopropyltrimethoxysilane and / or trimethoxy(2-phenylethyl)silane, wherein the amount of 3-aminopropyltrimethoxysilane used is 10-100 wt% of graphene oxide, and the amount of trimethoxy(2-phenylethyl)silane used is 10-100 wt% of graphene oxide. When using graphene derivatives, this invention, by introducing a structure containing 3-aminopropyltrimethoxysilane and / or trimethoxy(2-phenylethyl)silane onto the surface of graphene oxide, and using it in combination with the matrix material and nitrogen-sulfur reagents, can improve the performance of the finally prepared battery, increase the reversible capacity of the battery, and increase the slope capacity ratio of the battery.

[0011] Preferably, in the preparation of graphene derivatives, graphene oxide is added to deionized water and ultrasonically dispersed to obtain a graphene oxide dispersion. The pH is adjusted to 4-5, and then a derivatizing agent is added. The mixture is stirred and reacted at 50-70℃ for 6-24 hours. After the reaction is completed, the mixture is centrifuged to remove the supernatant. The precipitate is washed with ethanol and then with deionized water. The precipitate is then freeze-dried to obtain the graphene derivative.

[0012] More preferably, in the preparation of graphene derivatives, the amount of graphene oxide used is 0.05-0.4 wt% of deionized water.

[0013] More preferably, in the preparation of graphene derivatives, the derivatizing agents include 3-aminopropyltrimethoxysilane and trimethoxy(2-phenylethyl)silane, wherein the amount of 3-aminopropyltrimethoxysilane used is 10-100 wt% of graphene oxide, and the amount of trimethoxy(2-phenylethyl)silane used is 10-100 wt% of graphene oxide.

[0014] Preferably, the slurry is treated with sand milling.

[0015] Preferably, the amount of water-soluble starch used is 10-30 wt% of deionized water.

[0016] Preferably, the amount of graphene material is 1-5 wt% of water-soluble starch.

[0017] Preferably, the preparation of the negative electrode hard carbon material employs spray drying, briquetting, calcination, or pulverization processes.

[0018] Preferably, in the preparation of the negative electrode hard carbon material, water-soluble starch is added to deionized water and mixed and dissolved, then glucose is added and mixed, then nitrogen and sulfur reagents are added and mixed, then graphene material is added and mixed to form a slurry, which is then sand-milled for 10-60 minutes. The slurry after sand milling is spray-dried to obtain powder, which is then calcined under nitrogen protection after being briquetteed, and the calcined briquette is then crushed by jaw crusher and air jet milling to obtain the powder material, i.e., the negative electrode hard carbon material.

[0019] More preferably, in the preparation of the negative electrode hard carbon material, the amount of water-soluble starch used is 10-30 wt% of deionized water.

[0020] More preferably, in the preparation of the negative electrode hard carbon material, the amount of glucose used is 2-24 wt% of water-soluble starch.

[0021] More preferably, in the preparation of the negative electrode hard carbon material, the nitrogen and sulfur reagents include thiourea and urea, with the amount of thiourea used being 0.1-2 wt% of the water-soluble starch and the amount of urea used being 0.1-2 wt% of the water-soluble starch.

[0022] More preferably, in the preparation of the negative electrode hard carbon material, the amount of nitrogen and sulfur reagent used is 0.2-4 wt% of the water-soluble starch. More preferably, the amount of nitrogen and sulfur reagent used is 1-3 wt% of the water-soluble starch.

[0023] More preferably, in the preparation of the negative electrode hard carbon material, the amount of graphene material used is 1-5 wt% of the water-soluble starch. More preferably, the amount of nitrogen and sulfur reagents used is 2-4 wt% of the water-soluble starch.

[0024] More preferably, in the preparation of the negative electrode hard carbon material, the calcination temperature is 1200-1500℃, and the calcination time is 2-5h; the particle size (D) of the powder material... 50 The thickness is 3-10 μm.

[0025] More preferably, p-aminobenzenesulfonic acid is added during the preparation of the negative electrode hard carbon material, and the amount of p-aminobenzenesulfonic acid used is 0.1-1 wt% of the water-soluble starch. When graphene derivatives are used to prepare the negative electrode hard carbon material, p-aminobenzenesulfonic acid can also be added. Under the combined action of water-soluble starch, glucose, and nitrogen and sulfur reagents, the performance of the finally prepared battery can be improved, the reversible capacity of the battery can be increased, and the slope capacity ratio of the battery can be increased.

[0026] This invention discloses the negative electrode hard carbon material prepared by the above method.

[0027] A battery comprising: the aforementioned negative electrode hard carbon material.

[0028] This invention utilizes water-soluble starch as the main raw material, then adds soluble glucose with a linear structure for cross-linking, followed by the addition of nitrogen- and sulfur-containing additives soluble in deionized water, and simultaneously incorporates nanoscale graphene material. The graphene material acts as a support to form a conductive network, thus preparing a negative electrode hard carbon material. The graphene material includes graphene and graphene derivatives, which are derived from graphene oxide and derivatizing agents, including 3-aminopropyltrimethoxysilane and / or trimethoxy(2-phenylethyl)silane. Furthermore, a sodium-ion battery is fabricated from the negative electrode hard carbon material, resulting in the following beneficial effects: the negative electrode hard carbon material exhibits good conductivity, leading to high reversible capacity, high initial efficiency, and a high slope capacity ratio after battery fabrication. Therefore, this invention provides a method for preparing a nitrogen- and sulfur-doped graphene-supported cross-linked starch-based hard carbon material with high reversible capacity, high initial efficiency, high slope capacity ratio, and high powder conductivity after battery fabrication. Attached Figure Description

[0029] Figure 1 This is a charge / discharge curve.

[0030] Figure 2 This is a reversible capacity graph.

[0031] Figure 3 This is a diagram showing the capacity percentage of the slope section.

[0032] Figure 4 This is a powder resistivity diagram. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] The concepts involved in this application will first be described with reference to the accompanying drawings. It should be noted that the following descriptions of various concepts are only for the purpose of making the content of this application easier to understand and do not constitute a limitation on the scope of protection of this application; furthermore, the embodiments and features in the embodiments of this application can be combined with each other unless otherwise specified. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0035] Example 1: A method for preparing a nitrogen-sulfur-doped graphene-supported crosslinked starch-based hard carbon material

[0036] Preparation of the anode hard carbon material: Water-soluble starch was dissolved in deionized water, then glucose was added and mixed, followed by nitrogen-sulfur reagents and then graphene to form a slurry. The slurry was milled for 30 minutes, and then spray-dried to obtain powder. The powder was briquetteed and calcined under nitrogen protection. The calcined briquette was then subjected to jaw crushing and air jet milling to obtain the powder material, i.e., the anode hard carbon material. The amount of water-soluble starch used was 20 wt% of deionized water, the amount of glucose used was 10 wt% of water-soluble starch, the nitrogen-sulfur reagents included thiourea and urea, the amount of thiourea used was 1.5 wt% of water-soluble starch, the amount of urea used was 1.5 wt% of water-soluble starch, and the amount of graphene used was 3 wt% of water-soluble starch; the calcination temperature was 1300℃, and the calcination time was 4 hours; the particle size of the powder material (D...)... 50 The thickness is 4-6 μm.

[0037] Example 2: A method for preparing a nitrogen-sulfur-doped graphene-supported crosslinked starch-based hard carbon material

[0038] Preparation of the anode hard carbon material: Water-soluble starch was dissolved in deionized water, then glucose was added and mixed, followed by nitrogen and sulfur reagents, and finally graphene was added to form a slurry. The slurry was milled for 30 minutes, and then spray-dried to obtain powder. The powder was then briquetteed and calcined under nitrogen protection. The calcined briquette was then subjected to jaw crushing and air jet milling to obtain the powder material, i.e., the anode hard carbon material. The amount of water-soluble starch used was 20 wt% of deionized water, the amount of glucose used was 20 wt% of water-soluble starch, the nitrogen and sulfur reagents included thiourea and urea, with thiourea used at 1 wt% of water-soluble starch, urea used at 1 wt% of water-soluble starch, and graphene used at 3 wt% of water-soluble starch; the calcination temperature was 1400℃, and the calcination time was 3 hours; the particle size (D) of the powder material was specified. 50 The thickness is 4-6 μm.

[0039] Example 3: A method for preparing a nitrogen-sulfur-doped graphene-supported crosslinked starch-based hard carbon material

[0040] Preparation of the anode hard carbon material: Water-soluble starch was dissolved in deionized water, then glucose was added and mixed, followed by nitrogen-sulfur reagents, and finally graphene was added to form a slurry. The slurry was milled for 30 minutes, and then spray-dried to obtain powder. The powder was briquetteed and calcined under nitrogen protection. The calcined briquette was then subjected to jaw crushing and air jet milling to obtain the powder material, i.e., the anode hard carbon material. The amount of water-soluble starch used was 20 wt% of deionized water, the amount of glucose used was 5 wt% of water-soluble starch, the nitrogen-sulfur reagents included thiourea and urea, with thiourea and urea used at 0.5 wt% and urea respectively, and graphene used at 2 wt% of water-soluble starch; the calcination temperature was 1500℃, and the calcination time was 2 h; the particle size (D) of the powder material was specified. 50 The thickness is 4-6 μm.

[0041] Example 4: A method for preparing a nitrogen-sulfur-doped graphene-supported crosslinked starch-based hard carbon material

[0042] Preparation of the anode hard carbon material: Water-soluble starch was dissolved in deionized water, then glucose was added and mixed, followed by nitrogen and sulfur reagents, and finally graphene was added to form a slurry. The slurry was milled for 30 minutes, and then spray-dried to obtain powder. The powder was then briquetteed and calcined under nitrogen protection. The calcined briquette was then subjected to jaw crushing and air jet milling to obtain the powder material, i.e., the anode hard carbon material. The amount of water-soluble starch used was 20 wt% of deionized water, and the amount of glucose used was 5 wt% of water-soluble starch. The nitrogen and sulfur reagents included thiourea and urea; the amount of thiourea used was 1 wt% of water-soluble starch, the amount of urea used was 1 wt% of water-soluble starch, and the amount of graphene used was 3 wt% of water-soluble starch. The calcination temperature was 1300℃, and the calcination time was 3 hours. The particle size (D) of the powder material was specified. 50 The thickness is 4-6 μm.

[0043] Example 5: A method for preparing a nitrogen-sulfur-doped graphene-supported crosslinked starch-based hard carbon material

[0044] Preparation of the anode hard carbon material: Water-soluble starch was dissolved in deionized water, then glucose was added and mixed, followed by nitrogen-sulfur reagents and then graphene to form a slurry. The slurry was milled for 30 minutes, and then spray-dried to obtain powder. The powder was then briquetteed and calcined under nitrogen protection. The calcined briquette was then subjected to jaw crushing and air jet milling to obtain the powder material, i.e., the anode hard carbon material. The amount of water-soluble starch used was 20 wt% of deionized water, the amount of glucose used was 10 wt% of water-soluble starch, the nitrogen-sulfur reagents included thiourea and urea, the amount of thiourea used was 1.5 wt% of water-soluble starch, the amount of urea used was 1.5 wt% of water-soluble starch, and the amount of graphene used was 4 wt% of water-soluble starch; the calcination temperature was 1400℃, and the calcination time was 3 hours; the particle size of the powder material (D...)... 50 The thickness is 4-6 μm.

[0045] Example 6: A method for preparing a nitrogen-sulfur-doped graphene-supported crosslinked starch-based hard carbon material

[0046] The difference between this embodiment and Example 1 is that the graphene in the preparation of the negative electrode hard carbon material is replaced with a graphene derivative.

[0047] Preparation of graphene derivatives: Graphene oxide was ultrasonically dispersed in deionized water to obtain a graphene oxide dispersion. The pH was adjusted to 4.5, and then a derivatizing agent was added. The mixture was stirred at 60°C for 12 hours. After the reaction was complete, the mixture was centrifuged, the supernatant was removed, and the precipitate was washed with ethanol, then with deionized water, and freeze-dried to obtain the graphene derivatives. The amount of graphene oxide used was 0.2 wt% of deionized water. The derivatizing agents included 3-aminopropyltrimethoxysilane and trimethoxy(2-phenylethyl)silane, with 3-aminopropyltrimethoxysilane and trimethoxy(2-phenylethyl)silane each accounting for 90 wt% of the graphene oxide.

[0048] Example 7: A method for preparing a nitrogen-sulfur-doped graphene-supported crosslinked starch-based hard carbon material

[0049] The difference between this embodiment and Example 1 is that the graphene in the preparation of the negative electrode hard carbon material is replaced with a graphene derivative.

[0050] Preparation of graphene derivatives: Graphene oxide was ultrasonically dispersed in deionized water to obtain a graphene oxide dispersion. The pH was adjusted to 4.5, and then a derivatizing agent was added. The mixture was stirred at 60°C for 12 hours. After the reaction was complete, the mixture was centrifuged, the supernatant was removed, and the precipitate was washed with ethanol, then with deionized water, and freeze-dried to obtain the graphene derivatives. The amount of graphene oxide used was 0.2 wt% of deionized water. The derivatizing agents included 3-aminopropyltrimethoxysilane and trimethoxy(2-phenylethyl)silane. The amount of 3-aminopropyltrimethoxysilane used was 20 wt% of graphene oxide, and the amount of trimethoxy(2-phenylethyl)silane used was 20 wt% of graphene oxide.

[0051] Example 8: A method for preparing a nitrogen-sulfur-doped graphene-supported crosslinked starch-based hard carbon material

[0052] The difference between this embodiment and Embodiment 6 is that p-aminobenzenesulfonic acid is added in the preparation of the negative electrode hard carbon material.

[0053] Preparation of the anode hard carbon material: Water-soluble starch was dissolved in deionized water, then glucose was added and mixed, followed by nitrogen and sulfur reagents. Graphene derivatives and p-aminobenzenesulfonic acid were then added to form a slurry, which was milled for 30 minutes. The milled slurry was then spray-dried to obtain powder. The powder was briquetteed and calcined under nitrogen protection. The calcined briquette was then subjected to jaw crushing and air jet milling to obtain the powder material, i.e., the anode hard carbon material. The amount of water-soluble starch used was 20 wt% of deionized water, and the amount of glucose used was 10 wt% of water-soluble starch. The nitrogen and sulfur reagents included thiourea and urea; the amount of thiourea used was 1.5 wt% of water-soluble starch, the amount of urea used was 1.5 wt% of water-soluble starch, the amount of graphene derivative used was 3 wt% of water-soluble starch, and the amount of p-aminobenzenesulfonic acid used was 0.9 wt% of water-soluble starch. The calcination temperature was 1300℃, and the calcination time was 4 hours. The particle size (D) of the powder material was... 50 The thickness is 4-6 μm.

[0054] Example 9: A method for preparing a nitrogen-sulfur-doped graphene-supported crosslinked starch-based hard carbon material

[0055] The difference between this embodiment and Example 8 lies in the preparation of the negative electrode hard carbon material.

[0056] Preparation of the anode hard carbon material: Water-soluble starch was dissolved in deionized water, then glucose was added and mixed, followed by nitrogen and sulfur reagents. Graphene derivatives and p-aminobenzenesulfonic acid were then added to form a slurry. The slurry was milled for 30 minutes, and then spray-dried to obtain powder. The powder was briquetteed and calcined under nitrogen protection. The calcined briquette was then subjected to jaw crushing and air jet milling to obtain the powder material, i.e., the anode hard carbon material. The amount of water-soluble starch used was 20 wt% of deionized water, and the amount of glucose used was 10 wt%. The nitrogen and sulfur reagents included thiourea and urea. The amount of thiourea used was 1.5 wt% of water-soluble starch, the amount of urea used was 1.5 wt% of water-soluble starch, the amount of graphene derivative used was 3 wt% of water-soluble starch, and the amount of p-aminobenzenesulfonic acid used was 0.2 wt% of water-soluble starch. The calcination temperature was 1300℃, and the calcination time was 4 hours. The particle size (D) of the powder material was... 50 The thickness is 4-6 μm.

[0057] Comparative Example 1: A method for preparing a nitrogen-sulfur-doped graphene-supported crosslinked starch-based hard carbon material

[0058] Preparation of the negative electrode hard carbon material: Water-soluble starch was dissolved in deionized water, then glucose was added and mixed, followed by nitrogen and sulfur reagents to form a slurry. The slurry was milled for 30 minutes, and then spray-dried to obtain powder. The powder was briquetteed and calcined under nitrogen protection. The calcined briquette was then subjected to jaw crushing and air jet milling to obtain the powder material, i.e., the negative electrode hard carbon material. The amount of water-soluble starch used was 20 wt% of deionized water, and the amount of glucose used was 10 wt% of the water-soluble starch. The nitrogen and sulfur reagents included thiourea and urea, with thiourea and urea each accounting for 1.5 wt% of the water-soluble starch. The calcination temperature was 1300℃, and the calcination time was 4 hours. The particle size (D) of the powder material was... 50 The thickness is 4-6 μm.

[0059] Comparative Example 2: A method for preparing a nitrogen-sulfur-doped graphene-supported crosslinked starch-based hard carbon material

[0060] Preparation of the anode hard carbon material: Water-soluble starch was dissolved in deionized water, then glucose was added and mixed, followed by graphene to form a slurry. The slurry was milled for 30 minutes, and then spray-dried to obtain powder. The powder was briquetteed and calcined under nitrogen protection. The calcined briquette was then subjected to jaw crusher and air jet milling to obtain the powder material, i.e., the anode hard carbon material. The amount of water-soluble starch used was 20 wt% of deionized water, the amount of glucose was 10 wt% of water-soluble starch, and the amount of graphene was 3 wt% of water-soluble starch; the calcination temperature was 1300℃, and the calcination time was 4 hours; the particle size (D) of the powder material was specified.50 The thickness is 4-6 μm.

[0061] Comparative Example 3: A method for preparing a nitrogen-sulfur-doped graphene-supported crosslinked starch-based hard carbon material

[0062] The difference between this comparative example and Example 6 is that the graphene in the preparation of the negative electrode hard carbon material is replaced with a graphene derivative.

[0063] Preparation of graphene derivatives: Graphene oxide was ultrasonically dispersed in deionized water to obtain a graphene oxide dispersion. The pH was adjusted to 4.5, and then a derivatizing agent was added. The mixture was stirred at 60°C for 12 hours. After the reaction was complete, the mixture was centrifuged, the supernatant was removed, and the precipitate was washed with ethanol, then with deionized water, and freeze-dried to obtain the graphene derivatives. The amount of graphene oxide used was 0.2 wt% of deionized water. The derivatizing agents included 3-aminopropyltrimethoxysilane and trimethoxy(2-phenylethyl)silane, with each accounting for 3 wt% of the graphene oxide.

[0064] Comparative Example 4: A method for preparing a nitrogen-sulfur-doped graphene-supported crosslinked starch-based hard carbon material

[0065] The difference between this comparative example and Example 6 is that the graphene in the preparation of the negative electrode hard carbon material is replaced with graphene oxide.

[0066] Experimental example:

[0067] Preparation of the test battery: The negative electrode hard carbon material, SP, SBR and CMC were mixed with pure water at a mass ratio of 95:1.5:2:1.5 to obtain a slurry. The mass ratio of the negative electrode hard carbon material to pure water was 1:3. The slurry was uniformly coated on aluminum foil with a coating thickness of 25μm. After drying, it was punched into electrode sheets and assembled with sodium sheet, glass fiber separator and electrolyte (1.4M NaPF6) into coin cells for testing.

[0068] The test battery was charged and discharged on a button cell battery tester under the following conditions: left to stand at room temperature for 4 hours, discharged at a constant current of 0.1C (25 mA / g) to 0.01V, left to rest for 5 minutes, and charged at a constant current of 0.1C to 2.5V.

[0069] The charge-discharge curves of batteries made from different negative electrode hard carbon materials obtained in Example 1 and Comparative Examples 1-2 of this invention are as follows: Figure 1As shown, the reversible capacity of the hard carbon material in Example 1 was 316.0 mAh / g, with an initial efficiency of 88.2%; the reversible capacity of the hard carbon material in Comparative Example 1 was 307.5 mAh / g, with an initial efficiency of 87.7%; and the reversible capacity of the hard carbon material in Comparative Example 2 was 290.5 mAh / g, with an initial efficiency of 88.2%. This indicates that doping hard carbon materials with nitrogen and sulfur increases the interlayer spacing, increases the number of sodium storage active sites, and improves the reversible capacity.

[0070] In this invention, batteries made from the negative electrode hard carbon materials prepared in Examples 1, 6-9, and Comparative Examples 1-4 were subjected to charge-discharge tests. The reversible capacity of the obtained batteries is as follows: Figure 2 As shown, in the preparation of the negative electrode hard carbon material of this invention, water-soluble starch is used as the main raw material, and then soluble glucose with a linear structure is added for cross-linking. Nitrogen-sulfur additives soluble in deionized water are then added, along with nanoscale graphene material. The graphene material acts as a support to form a conductive network, thus preparing the negative electrode hard carbon material. After the battery is fabricated, charge-discharge tests are conducted, and the battery made of the negative electrode hard carbon material shows good reversible capacity. The reversible capacity of the battery obtained after using nitrogen-sulfur reagents and graphene is high, superior to batteries using only nitrogen-sulfur reagents or graphene alone, indicating that the combined use of nitrogen-sulfur reagents and graphene has a better effect. The graphene material in this invention can also use graphene derivatives. In this invention, derivatizing agents are used to derivatize graphene, including 3-aminopropyltrimethoxysilane and trimethoxy(2-phenylethyl)silane. After propyltrimethoxysilane and trimethoxy(2-phenylethyl)silane react with graphene oxide to generate graphene derivatives, these derivatives are applied to the preparation of hard carbon negative electrode materials. When these derivatives are then used to fabricate batteries, the reversible capacity of the resulting batteries is improved, indicating that the graphene derivatives are more effective than graphene oxide. The amount of 3-aminopropyltrimethoxysilane and trimethoxy(2-phenylethyl)silane used cannot be too low; if the amount is too low, there is no significant improvement in the reversible capacity of the battery, indicating that the amount of 3-aminopropyltrimethoxysilane and trimethoxy(2-phenylethyl)silane used needs to be controlled within a certain range. Furthermore, this invention can also add p-aminobenzenesulfonic acid during the preparation of the hard carbon negative electrode material. The further use of p-aminobenzenesulfonic acid after the use of graphene derivatives further improves the reversible capacity of the prepared batteries.

[0071] In this invention, the slope section capacity of batteries made from different negative electrode hard carbon materials obtained in Example 1 and Comparative Examples 1-2 accounts for, for example, Figure 3 As shown, the slope capacity ratio refers to the proportion of specific capacity above 0.1V to the total specific capacity. The slope capacity ratios of Example 1, Comparative Example 1, and Comparative Example 2 are 41.6%, 41.3%, and 35.4%, respectively. After doping, the number of defect sites in the hard carbon material increases, and the proportion of sodium storage capacity in the slope section increases.

[0072] In this invention, batteries made from the negative electrode hard carbon materials prepared in Examples 1, 6-9, and Comparative Examples 1-4 were subjected to charge-discharge tests. The resulting battery ramp capacity is as follows: Figure 3 As shown, the slope capacity ratio refers to the proportion of specific capacity above 0.1V to the total specific capacity. A high slope capacity ratio indicates an increased sodium storage capacity ratio in the slope section. In this invention, the preparation of the negative electrode hard carbon material uses water-soluble starch as the main raw material, then adds soluble glucose with a linear structure for cross-linking, followed by nitrogen-sulfur additives soluble in deionized water, and simultaneously adds nanoscale graphene material. The graphene material acts as a support to form a conductive network, thus preparing the negative electrode hard carbon material. After battery fabrication, charge-discharge tests show that the battery made with the negative electrode hard carbon material has a high slope section capacity ratio. The use of nitrogen-sulfur reagents and graphene results in a higher slope section capacity ratio than batteries using only nitrogen-sulfur reagents or graphene alone, indicating that the combined use of nitrogen-sulfur reagents and graphene has a better effect. The graphene material in this invention can also use graphene derivatives. In this invention, a derivatizing agent is used to derivatize graphene, including 3-aminopropyltrimethoxysilane. The invention utilizes 3-aminopropyltrimethoxysilane and trimethoxy(2-phenylethyl)silane. After reacting 3-aminopropyltrimethoxysilane and trimethoxy(2-phenylethyl)silane with graphene oxide to generate graphene derivatives, these derivatives are applied to the preparation of hard carbon negative electrode materials. When these derivatives are then used to fabricate batteries, the slope capacity ratio of the resulting batteries increases, indicating that the graphene derivatives are more effective than graphene oxide. However, the amount of 3-aminopropyltrimethoxysilane and trimethoxy(2-phenylethyl)silane used cannot be too low. If the amount of 3-aminopropyltrimethoxysilane and trimethoxy(2-phenylethyl)silane is too low, there is no significant improvement in the slope capacity ratio of the prepared batteries, indicating that the amount of 3-aminopropyltrimethoxysilane and trimethoxy(2-phenylethyl)silane used needs to be controlled within a certain range. Furthermore, this invention can also add p-aminobenzenesulfonic acid during the preparation of hard carbon negative electrode materials. The further use of p-aminobenzenesulfonic acid after the use of graphene derivatives further increases the slope capacity ratio of the prepared batteries.

[0073] The powder resistivity of different negative electrode hard carbon materials obtained in Example 1 and Comparative Examples 1-2 under different pressures in this invention is as follows: Figure 4 As shown, the powder conductivity is: Comparative Example 2 > Example 1 > Comparative Example 1. The addition of graphene improves the conductivity of the hard carbon material and reduces the powder resistivity.

[0074] The embodiments and / or implementation methods described above are merely preferred embodiments and / or implementation methods for implementing the technology of the present invention, and are not intended to limit the implementation methods of the technology of the present invention in any way. Any person skilled in the art can make some modifications or alterations to other equivalent embodiments without departing from the scope of the technical means disclosed in the content of the present invention, but they should still be regarded as the technology or embodiments that are substantially the same as the present invention.

[0075] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. The above descriptions are only preferred embodiments of this application. It should be noted that due to the limitations of written expression, while there are objectively infinite specific structures, those skilled in the art can make several improvements, modifications, or changes without departing from the principles of this application, and can also combine the above technical features in an appropriate manner. These improvements, modifications, changes, or combinations, or the direct application of the inventive concept and technical solution to other situations without modification, should all be considered within the scope of protection of this application.

Claims

1. A method of preparing a negative electrode hard carbon material, comprising: The base raw material is mixed with a nitrogen-sulfur reagent in deionized water, and then graphene material is added to form a slurry, and the negative electrode hard carbon material is prepared from the slurry; the base raw material comprises water-soluble starch and glucose, and the nitrogen-sulfur reagent comprises thiourea and urea; the amount of thiourea is 0.1-2wt% of the water-soluble starch, the amount of urea is 0.1-2wt% of the water-soluble starch, and the amount of glucose is 2-24wt% of the water-soluble starch; The graphene material comprises graphene and / or graphene derivative, and the graphene derivative is derived from graphene oxide and a derivative agent.

2. The method of claim 1, wherein the method is characterized by: The derivative agent comprises 3-aminopropyltrimethoxysilane and / or trimethoxy(2-phenylethyl)silane, the use amount of 3-aminopropyltrimethoxysilane is 10-100wt% of the graphene oxide, and the use amount of trimethoxy(2-phenylethyl)silane is 10-100wt% of the graphene oxide.

3. The method of claim 1, wherein the method is characterized by: The slurry is subjected to sanding treatment.

4. The method of claim 1, wherein the method is characterized by: The use amount of the water-soluble starch is 10-30wt% of the deionized water.

5. The method of claim 1, wherein the negative electrode hard carbon material is prepared by the steps of: preparing a mixture of a carbon source and a solvent; and performing a carbonization process on the mixture. The amount of the graphene material is 1-5wt% of the water-soluble starch.

6. The method of claim 1, wherein the negative electrode hard carbon material is prepared by the steps of: preparing a mixture of a carbon source and a solvent; and performing a carbonization process on the mixture. The preparation of the negative electrode hard carbon material adopts spray drying treatment, briquetting treatment, calcination treatment or crushing treatment.

7. The negative electrode hard carbon material prepared by the method of any one of claims 1-6.

8. A battery comprising: The negative electrode hard carbon material of claim 7.

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