Hard carbon negative electrode material of high-first-effect fast-charging sodium-ion battery and preparation method of hard carbon negative electrode material

Abstract

The invention discloses a high-first-effect fast-charging sodium ion battery hard carbon negative electrode material and a preparation method thereof, and belongs to the technical field of sodium ion batteries. The hard carbon negative electrode material comprises a hard carbon inner core and a conductive coating layer coating the surface of the hard carbon inner core, the hard carbon core is prepared from a carbon source through pre-carbonization and acid pickling treatment, and the carbon source comprises at least one of coconut shells and an epoxy resin carbon material; the conductive coating layer is a composition of glucose, single-layer graphene and water. The high-first-effect fast-charging sodium ion battery hard carbon negative electrode material disclosed by the invention has the advantages of low specific surface area, high first efficiency and high reversible capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and particularly to a hard carbon negative electrode material for a high first-efficiency fast-charging sodium-ion battery and a preparation method thereof. Background Art

[0002] With the continuous increase in the global demand for lithium resources, the development of lithium-ion batteries is facing double constraints of resource scarcity and rising costs. Against this background, sodium-ion batteries are regarded as one of the most promising alternative energy storage technologies due to their similar working principles to lithium-ion batteries, lower raw material costs, and richer resource reserves. As the negative electrode material of sodium-ion batteries, hard carbon has become a current research hotspot due to its advantages such as rich resources, low cost, and suitable working potential. However, there are still two key technical bottlenecks in this material: one is the relatively low initial Coulomb efficiency, and the other is the poor rate performance. These problems seriously restrict the practical application performance of sodium-ion batteries. In addition, the existing preparation processes of hard carbon negative electrode materials generally have defects such as complex processes, high energy consumption, and easy damage to the surface structure, further exacerbating the problem of low first efficiency. Therefore, developing hard carbon negative electrode materials with excellent fast-charging performance and high first efficiency has become a key technical problem in promoting the commercial application of sodium-ion batteries. Summary of the Invention

[0003] The purpose of the present invention is to provide a hard carbon negative electrode material for a high first-efficiency fast-charging sodium-ion battery and a preparation method thereof, reduce the specific surface area of the hard carbon negative electrode material, optimize the electrochemical performance of the assembled sodium-ion battery, and improve the first efficiency and reversible capacity of the hard carbon negative electrode material.

[0004] The technical solution adopted by the present invention to achieve the above purpose is as follows: A hard carbon negative electrode material for a high first-efficiency fast-charging sodium-ion battery, comprising a hard carbon core and a conductive coating layer coated on the surface of the hard carbon core; the hard carbon core is prepared from a carbon source through pre-carbonization and pickling treatment.

[0005] The present invention provides a hard carbon negative electrode material for a high first-efficiency fast-charging sodium-ion battery. Coating a conductive coating layer on the surface of the hard carbon core not only significantly reduces the specific surface area of the hard carbon negative electrode material, reduces the amount of electrolyte consumed in the formation of the SEI film during the first charge and discharge process, thereby improving its first efficiency; but also increases the closed pore structure of the hard carbon material and increases the sodium storage active sites by coating a conductive coating layer on the surface of the hard carbon core, which helps to improve the sodium storage capacity of the hard carbon negative electrode material, thereby improving the reversible capacity.

[0006] Preferably, the carbon source includes at least one of coconut shell and epoxy resin carbon material.

[0007] More preferably, the epoxy resin carbon material is obtained by curing gallic acid epoxy resin and 1,2-epoxy resin-3-(di-2,6-dimethylphenylmethoxy) propane. The epoxy resin carbon material obtained by curing gallic acid epoxy resin and 1,2-epoxy resin-3-(di-2,6-dimethylphenylmethoxy) propane used in the present invention is rich in active epoxy groups and has a tightly crosslinked network structure. When compounded with coconut shell to prepare a hard carbon core, it helps to reduce the specific surface area of the hard carbon material and construct an optimized porous structure, thereby improving the electrochemical performance of the prepared hard carbon negative electrode material and increasing the first efficiency and reversible capacity of the sodium ion battery assembled with the hard carbon negative electrode material.

[0008] More preferably, the preparation of the epoxy resin carbon material is specifically as follows: Under a nitrogen atmosphere, the resin raw materials are mixed evenly, maleic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol are added under the condition of 40-60 °C, and then heated at 120-160 °C for 4-12 h under dry conditions to obtain the epoxy resin carbon material.

[0009] Even more preferably, the resin raw materials include at least one of gallic acid epoxy resin, 1,2-epoxy resin-3-(di-2,6-dimethylphenylmethoxy) propane, and 1-(2,4-bis(benzyloxy)phenyl)ethanone. The present invention further uses 1-(2,4-bis(benzyloxy)phenyl)ethanone to prepare the epoxy resin carbon material, which helps to improve the density of the three-dimensional structure of the epoxy resin carbon material, thereby increasing the closed pore structure of the hard carbon negative electrode material and increasing the sodium storage active sites, further improving the first efficiency and reversible capacity of the hard carbon negative electrode material.

[0010] Even more preferably, the mass ratio of maleic anhydride to gallic acid epoxy resin is 1:0.8-1.2.

[0011] Even more preferably, the mass ratio of maleic anhydride to 1,2-epoxy resin-3-(di-2,6-dimethylphenylmethoxy) propane is 1:0.5-1.

[0012] Even more preferably, the mass ratio of maleic anhydride to 1-(2,4-bis(benzyloxy)phenyl)ethanone is 1:0.2-0.5.

[0013] Even more preferably, the mass ratio of maleic anhydride to 2,4,6-tris(dimethylaminomethyl)phenol is 1:0.01-0.05.

[0014] Even more preferably, the preparation of gallic acid epoxy resin is specifically as follows: Mix gallic acid and epichlorohydrin and stir. Add tetrabutylammonium iodide at 90 - 100 °C, react for 4 - 6 h. After the reaction is completed, cool to room temperature, slowly add sodium hydroxide solution. After the reaction ends, wash with water until the pH is neutral, and distill under reduced pressure to obtain gallic acid epoxy resin. The dosage ratio of gallic acid to epichlorohydrin is 1 g : 5 - 20 mL; the mass ratio of tetrabutylammonium iodide to gallic acid is 1 : 15 - 50; the mass concentration of the sodium hydroxide solution is 5 - 20%, and the dosage ratio of gallic acid to the sodium hydroxide solution is 1 g : 5 - 20 mL.

[0015] The present invention also discloses a preparation method of the hard carbon negative electrode material for the high-first-efficiency fast-charging sodium-ion battery described in claim 1, including, S1. Pre-carbonize the carbon source to obtain biochar; S2. Add pickling solution to the biochar and stir for 4 - 8 h to obtain a hard carbon core; S3. Mix the hard carbon core and the conductive coating layer, and obtain precursor powder by air flow pulverization; S4. Carbonize the precursor powder to obtain the hard carbon negative electrode material for the high-first-efficiency fast-charging sodium-ion battery.

[0016] Preferably, the temperature of the pre-carbonization treatment is 400 - 600 °C.

[0017] Preferably, the pre-carbonization treatment time is 1 - 4 h.

[0018] Preferably, the pickling solution is a phosphoric acid solution, and the concentration of the phosphoric acid solution is 0.2 - 1 mol / L.

[0019] Preferably, the temperature of the carbonization treatment is 1000 - 1500 °C.

[0020] Preferably, the carbonization treatment time is 2 - 5 h.

[0021] Preferably, the preparation of the hard carbon negative electrode material for the high-first-efficiency fast-charging sodium-ion battery is specifically as follows: S1. Crush and grind the carbon source and mix. Under an argon atmosphere, heat the temperature at a rate of 2 - 10 °C / min to 400 - 600 °C, and pre-carbonize for 1 - 4 h to obtain biochar.

[0022] S2. Add phosphoric acid solution to the biochar and stir for 2 - 8 h to obtain a hard carbon core.

[0023] S3. Dissolve glucose in water, add graphene and mix evenly, then add the hard carbon core and stir evenly, dry, and obtain precursor powder by air flow pulverization.

[0024] S4. Under an argon atmosphere, the temperature is raised to 1000 - 1500 °C at a rate of 2 - 10 °C / min, and the precursor powder is carbonized for 2 - 5 h to obtain the hard carbon material.

[0025] More preferably, in step S1, the carbon source includes at least one of coconut shell and epoxy resin carbon material.

[0026] Even more preferably, the mass ratio of coconut shell to epoxy resin carbon material is 1:0.2 - 1.

[0027] More preferably, in step S2, the concentration of the phosphoric acid solution is 0.2 - 1 mol / L.

[0028] More preferably, the dosage ratio of biochar to phosphoric acid solution in step S2 is 1 g:2 - 10 mL.

[0029] More preferably, the mass ratio of glucose to the hard carbon core in step S3 is 1:1 - 5.

[0030] More preferably, the dosage ratio of glucose to water in step S3 is 1 g:2 - 15 mL.

[0031] More preferably, the mass ratio of graphene to the hard carbon core in step S3 is 1:50 - 200.

[0032] Since the present invention uses coconut shell and epoxy resin carbon material as carbon sources to prepare the hard carbon core, and then coats a conductive coating layer on the surface of the hard carbon core to obtain the hard carbon negative electrode material for a high first - efficiency fast - charging sodium - ion battery, it has the following beneficial effects: The present invention prepares epoxy resin carbon material by using gallic acid epoxy resin, 1,2 - epoxy - 3 - (di - 2,6 - dimethylphenylmethoxy) propane, and 1 - (2,4 - bis(benzyloxy)phenyl)ethanone, and then composes it with coconut shell to prepare the hard carbon core, increasing the closed - pore structure of the hard carbon negative electrode material for a high first - efficiency fast - charging sodium - ion battery, increasing the sodium - storage active sites, so that the sodium - storage capacity of the hard carbon material is improved, and the reversible capacity is increased. The reversible capacity is 311.8 - 410.8 mA / g; then a conductive coating layer is coated on the surface of the hard carbon core, significantly reducing the specific surface area of the hard carbon negative electrode material for a high first - efficiency fast - charging sodium - ion battery, resulting in a reduction in the amount of electrolyte consumed in forming the SEI film during the first - cycle charge - discharge process, reducing the irreversible capacity loss, and thus improving the first - cycle efficiency. The first - cycle efficiency is 89.90 - 94.95%. Therefore, the present invention provides a hard carbon negative electrode material for a high first - efficiency fast - charging sodium - ion battery with a high first - cycle efficiency and a high reversible capacity and its preparation method. Description of the Drawings

[0033] Figure 1 SEM image of the hard carbon negative electrode material for a high first - efficiency fast - charging sodium - ion battery prepared in Example 1.

[0034] Figure 2It is the nitrogen adsorption - desorption test curve.

[0035] Figure 3 It is the first - week discharge curve.

[0036] Figure 4 It is the rate performance test chart. Specific embodiments

[0037] The present invention will be further described in detail below in conjunction with specific embodiments. The provided embodiments are only for clarifying the present invention, rather than limiting the scope of the present invention. The following provided embodiments can be used as a guide for those of ordinary skill in the art to make further improvements, and do not limit the present invention in any way.

[0038] In the experimental methods of the following embodiments, unless otherwise specified, they are all conventional methods. The materials, reagents, etc. used in the following embodiments, unless otherwise specified, can all be obtained from commercial channels.

[0039] Example 1: The preparation of a hard - carbon negative electrode material for a high - first - efficiency fast - charging sodium - ion battery includes: S1. Crush coconut shells, and under an argon atmosphere, heat the temperature to 500 °C at a rate of 5 °C / min and perform pre - carbonization treatment for 2 h to obtain biochar.

[0040] S2. Add phosphoric acid solution to the biochar and stir for 4 h to obtain a hard - carbon core. The concentration of the phosphoric acid solution is 1 mol / L, and the dosage ratio of the biochar to the phosphoric acid solution is 1 g:5 mL.

[0041] S3. Dissolve glucose in water, add single - layer graphene and mix evenly, then add the hard - carbon core and stir evenly, dry, and obtain precursor powder by air - flow pulverization. The mass ratio of glucose to the hard - carbon core is 1:3, the dosage ratio of glucose to water is 1 g:7 mL; the mass ratio of single - layer graphene to the hard - carbon core is 1:100.

[0042] S4. Under an argon atmosphere, heat the temperature to 1300 °C at a rate of 5 °C / min and perform carbonization treatment on the precursor powder for 2 h to obtain a hard - carbon negative electrode material for a high - first - efficiency fast - charging sodium - ion battery.

[0043] Example 2: The preparation of gallic acid epoxy resin includes: Mix gallic acid and epichlorohydrin and stir. Add tetrabutylammonium iodide at 100 °C and react for 6 h. After the reaction is completed, cool to room temperature, slowly add sodium hydroxide solution. After the reaction ends, wash with water until the pH is neutral, and perform vacuum distillation to obtain gallic acid epoxy resin. The dosage ratio of gallic acid to epichlorohydrin is 1 g:10 mL; the mass ratio of tetrabutylammonium iodide to gallic acid is 1:30; the mass concentration of the sodium hydroxide solution is 10%, and the dosage ratio of gallic acid to the sodium hydroxide solution is 1 g:10 mL.

[0044] The preparation of epoxy resin carbon material includes Under a nitrogen atmosphere, mix gallic acid epoxy resin and 1,2-epoxy resin-3-(di-2,6-dimethylphenylmethoxy)propane evenly. Add maleic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol and mix at 60 °C, then heat at 140 °C under dry conditions for 8 h to obtain epoxy resin carbon material. The mass ratio of maleic anhydride to gallic acid epoxy resin is 1:1.2, the mass ratio of maleic anhydride to 1,2-epoxy resin-3-(di-2,6-dimethylphenylmethoxy)propane is 1:1, and the mass ratio of maleic anhydride to 2,4,6-tris(dimethylaminomethyl)phenol is 1:0.03.

[0045] The preparation of a hard carbon anode material for a high-efficiency fast-charging sodium-ion battery includes S1. Crush and grind coconut shell and epoxy resin carbon material and mix them. Under an argon atmosphere, heat the temperature to 500 °C at a rate of 5 °C / min and perform pre-carbonization treatment for 2 h to obtain biochar. The mass ratio of coconut shell to epoxy resin carbon material is 1:0.4.

[0046] S2. Add phosphoric acid solution to the biochar and stir for 4 h to obtain a hard carbon core. The concentration of the phosphoric acid solution is 1 mol / L, and the dosage ratio of biochar to phosphoric acid solution is 1 g:5 mL.

[0047] S3. Dissolve glucose in water, add monolayer graphene and mix evenly, then add the hard carbon core and stir evenly. Dry and obtain precursor powder by air flow pulverization. The mass ratio of glucose to the hard carbon core is 1:3, the dosage ratio of glucose to water is 1 g:7 mL; the mass ratio of monolayer graphene to the hard carbon core is 1:100.

[0048] S4. Under an argon atmosphere, heat the temperature to 1300 °C at a rate of 5 °C / min and perform carbonization treatment on the precursor powder for 2 h to obtain a hard carbon anode material for a high-efficiency fast-charging sodium-ion battery.

[0049] Example 3: The preparation of gallic acid epoxy resin is the same as that in Example 2.

[0050] Preparation of epoxy resin carbon material. Compared with Example 2, except that the mass ratio of maleic anhydride to gallic acid epoxy resin is changed to 1:0.8, other conditions are the same as those in Example 2.

[0051] Preparation of hard carbon anode material for high-first-efficiency fast-charging sodium-ion battery. Compared with Example 2, except that the epoxy resin carbon material is replaced with the epoxy resin carbon material prepared in this example, other conditions are the same as those in Example 2.

[0052] Example 4: Preparation of gallic acid epoxy resin is the same as that in Example 2.

[0053] Preparation of epoxy resin carbon material. Compared with Example 2, except that the mass ratio of maleic anhydride to 1,2-epoxy resin-3-(di-2,6-dimethylphenylmethoxy)propane is changed to 1:0.5, other conditions are the same as those in Example 2.

[0054] Preparation of hard carbon anode material for high-first-efficiency fast-charging sodium-ion battery. Compared with Example 2, except that the epoxy resin carbon material is replaced with the epoxy resin carbon material prepared in this example, other conditions are the same as those in Example 2.

[0055] Example 5: Preparation of gallic acid epoxy resin is the same as that in Example 2.

[0056] Preparation of epoxy resin carbon material includes: Under a nitrogen atmosphere, gallic acid epoxy resin, 1,2-epoxy resin-3-(di-2,6-dimethylphenylmethoxy)propane and 1-(2,4-bis(benzyloxy)phenyl)ethanone are mixed evenly, maleic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol are added at 60 °C, and then heated at 140 °C for 8 h under dry conditions to obtain epoxy resin carbon material. The mass ratio of maleic anhydride to gallic acid epoxy resin is 1:1.2, the mass ratio of maleic anhydride to 1,2-epoxy resin-3-(di-2,6-dimethylphenylmethoxy)propane is 1:1, the mass ratio of maleic anhydride to 1-(2,4-bis(benzyloxy)phenyl)ethanone is 1:0.5, and the mass ratio of maleic anhydride to 2,4,6-tris(dimethylaminomethyl)phenol is 1:0.03.

[0057] Preparation of hard carbon anode material for high-first-efficiency fast-charging sodium-ion battery. Compared with Example 2, except that the epoxy resin carbon material is replaced with the epoxy resin carbon material prepared in this example, other conditions are the same as those in Example 2.

[0058] Example 6: Preparation of gallic acid epoxy resin is the same as that in Example 2.

[0059] Preparation of epoxy resin carbon material. Compared with Example 5, except that the mass ratio of maleic anhydride to 1-(2,4-bis(benzyloxy)phenyl)ethanone is changed to 1:0.2, other conditions are the same as those in Example 5.

[0060] Preparation of hard carbon anode material for high-first-efficiency fast-charging sodium-ion battery. Compared with Example 2, except that the epoxy resin carbon material is replaced with the epoxy resin carbon material prepared in this example, other conditions are the same as those in Example 2.

[0061] Comparative Example 1: Preparation of hard carbon anode material for high-first-efficiency fast-charging sodium-ion battery, including, S1. Crush coconut shells, and under an argon atmosphere, heat the temperature to 500 °C at a rate of 5 °C / min, and perform pre-carbonization treatment for 2 h to obtain biochar.

[0062] S2. Add phosphoric acid solution to the biochar and stir for 4 h to obtain a hard carbon core. The concentration of the phosphoric acid solution is 1 mol / L, and the dosage ratio of the biochar to the phosphoric acid solution is 1 g:5 mL.

[0063] S3. Under an argon atmosphere, heat the temperature to 1300 °C at a rate of 5 °C / min, and perform carbonization treatment on the hard carbon core for 2 h to obtain a hard carbon material.

[0064] Comparative Example 2: Preparation of gallic acid epoxy resin is the same as that in Example 2.

[0065] Preparation of epoxy resin carbon material. Compared with Example 2, except that 1,2-epoxy resin-3-(di-2,6-dimethylphenylmethoxy)propane is not added, other conditions are the same as those in Example 2.

[0066] Preparation of hard carbon anode material for high-first-efficiency fast-charging sodium-ion battery. Compared with Example 2, except that the epoxy resin carbon material is replaced with the epoxy resin carbon material prepared in this example, other conditions are the same as those in Example 2.

[0067] Comparative Example 3: Preparation of epoxy resin carbon material. Compared with Example 2, except that gallic acid epoxy resin is not added, other conditions are the same as those in Example 2.

[0068] Preparation of hard carbon anode material for high-first-efficiency fast-charging sodium-ion battery. Compared with Example 2, except that the epoxy resin carbon material is replaced with the epoxy resin carbon material prepared in this example, other conditions are the same as those in Example 2.

[0069] Comparative Example 4: Preparation of epoxy resin carbon material. Compared with Example 5, except that gallic acid epoxy resin and 1,2-epoxy resin-3-(di-2,6-dimethylphenylmethoxy) propane were not added, other conditions were the same as those in Example 5.

[0070] Preparation of hard carbon anode material for high-first-efficiency fast-charging sodium-ion battery. Compared with Example 2, except that the epoxy resin carbon material was replaced with the epoxy resin carbon material prepared in this example, other conditions were the same as those in Example 2.

[0071] Experimental examples: 1. Material characterization The hard carbon anode material for high-first-efficiency fast-charging sodium-ion battery prepared in Example 1 was analyzed by scanning electron microscopy using a scanning electron microscope.

[0072] The nitrogen isothermal adsorption and desorption tests were carried out on the hard carbon anode materials for high-first-efficiency fast-charging sodium-ion battery prepared in Example 1 and Comparative Example 1 using a fully automatic specific surface area and porosity analyzer. The degassing temperature was 200 °C and the degassing time was 7 h.

[0073] Figure 1 It is the SEM image of the hard carbon anode material for high-first-efficiency fast-charging sodium-ion battery prepared in Example 1. This shows that the preparation method of the present invention can prepare the hard carbon anode material for high-first-efficiency fast-charging sodium-ion battery.

[0074] Figure 2 It is the nitrogen adsorption and desorption test curve. The specific surface area of the hard carbon anode material for high-first-efficiency fast-charging sodium-ion battery prepared in Example 1 of the present invention is 4.6 m 2 / g, and the specific surface area of the hard carbon anode material for high-first-efficiency fast-charging sodium-ion battery prepared in Comparative Example 1 is 141.7 m 2 / g. This shows that in the preparation of the hard carbon anode material for high-first-efficiency fast-charging sodium-ion battery of the present invention, using glucose and monolayer graphene to coat on the surface of the hard carbon core helps to significantly reduce the specific surface area of the prepared hard carbon anode material for high-first-efficiency fast-charging sodium-ion battery. The significant reduction of the specific surface area results in a decrease in the amount of electrolyte consumed in the formation of the SEI film during the first-cycle charge and discharge process, thereby improving the first efficiency.

[0075] 2. Electrochemical performance test The button sodium-ion batteries were assembled using the hard carbon anode materials of the high-first-efficiency fast-charging sodium-ion batteries prepared in Examples 1-6 and Comparative Examples 1-4 of the present invention, and the sodium-ion batteries prepared in Examples 1-6 and Comparative Examples 1-4 were correspondingly obtained. The specific steps are as follows: The hard carbon anode material of the high-first-efficiency fast-charging sodium-ion battery, conductive carbon black, styrene-butadiene rubber, and sodium carboxymethylcellulose were mixed with pure water to obtain the anode slurry. The mass ratio of conductive carbon black to the hard carbon anode material of the high-first-efficiency fast-charging sodium-ion battery is 1:18, the mass ratio of conductive carbon black to styrene-butadiene rubber is 1:0.8, the mass ratio of conductive carbon black to sodium carboxymethylcellulose is 1:0.2, and the dosage ratio of the hard carbon anode material of the high-first-efficiency fast-charging sodium-ion battery to pure water is 1 g:3 mL. Then, the anode slurry was evenly coated on the aluminum foil with a coating thickness of 25 μm, and after drying, it was punched into electrode sheets and assembled with sodium sheets and a sodium perchlorate solution with a concentration of 1 mol / L into button sodium-ion batteries.

[0076] 2.1 First-cycle charge and discharge test The sodium-ion batteries prepared in Examples 1-6 and Comparative Examples 1-4 were tested using a button battery tester. The test method is as follows: The sodium-ion batteries were left standing for 4 h, discharged at a constant current of 0.1 C (25 mA / g) to 0.01 V, left standing for 5 min, and then charged at a constant current of 0.1 C to 2.5 V.

[0077] Figure 3 is the first-cycle discharge curve, Figure 4 is the rate test chart. Tables 1 and 2 show the first efficiency and reversible capacity of the sodium-ion batteries prepared in Examples 1-6 and Comparative Examples 1-4 under the condition of 0.1 C, respectively.

[0078] Table 1 First efficiency (%)

[0079] Under the condition of 0.1 C, the first efficiency of Example 1 is higher than that of Comparative Example 1 because in the preparation of the hard carbon anode material of the high-first-efficiency fast-charging sodium-ion battery, glucose and single-layer graphene were used in Example 1 for coating on the surface of the precursor, reducing the specific surface area of the hard carbon anode material of the high-first-efficiency fast-charging sodium-ion battery, reducing the irreversible capacity loss, and thus improving the first efficiency.

[0080] The initial efficiency of Examples 2-4 is higher than that of Example 1 because in the preparation of the hard carbon anode material for high initial efficiency fast charging sodium ion batteries, Examples 2-4 use epoxy resin carbon materials and coconut shells as carbon sources to prepare the hard carbon core, while Example 1 does not use epoxy resin carbon materials. This shows that the use of epoxy resin carbon materials can improve the initial efficiency of sodium ion batteries. The initial efficiency of Examples 2-4 is higher than that of Comparative Examples 2-3 because in the preparation of the epoxy resin material, Examples 2-4 use gallic acid epoxy resin and 1,2-epoxy-3-(di-2,6-dimethylphenylmethoxy) propane synergistically to prepare the epoxy resin carbon material, Comparative Example 2 only uses gallic acid epoxy resin alone, and Comparative Example 3 only uses 1,2-epoxy-3-(di-2,6-dimethylphenylmethoxy) propane alone. The initial efficiency of Example 2 is higher than that of Example 3 and Example 4 because in the preparation of the epoxy resin carbon material, the usage amounts of gallic acid epoxy resin and 1,2-epoxy-3-(di-2,6-dimethylphenylmethoxy) propane are different. This shows that compared with the epoxy resin carbon material prepared by using gallic acid epoxy resin and 1,2-epoxy-3-(di-2,6-dimethylphenylmethoxy) propane alone, the epoxy resin carbon material prepared by using gallic acid epoxy resin and 1,2-epoxy-3-(di-2,6-dimethylphenylmethoxy) propane synergistically in an appropriate amount is more conducive to improving the initial efficiency of sodium ion batteries.

[0081] The initial efficiency of Examples 5-6 is higher than that of Example 2 and Comparative Example 4 because in the preparation of the epoxy resin material, Examples 5-6 further use 1-(2,4-bis(benzyloxy)phenyl)ethanone to prepare the epoxy resin material, Example 2 does not use 1-(2,4-bis(benzyloxy)phenyl)ethanone, and Comparative Example 4 only uses 1-(2,4-bis(benzyloxy)phenyl)ethanone alone; the initial efficiency of Example 5 is higher than that of Example 6 because in the preparation of the epoxy resin material, the usage amount of 1-(2,4-bis(benzyloxy)phenyl)ethanone is different. This shows that further using 1-(2,4-bis(benzyloxy)phenyl)ethanone to prepare the epoxy resin material can further improve the initial efficiency of sodium ion batteries.

[0082] Table 2 Reversible capacity (mAh / g)

[0083] Under the condition of 0.1C, the reversible capacity of Example 1 is higher than that of Comparative Example 1 because in the preparation of the hard carbon anode material for high initial efficiency fast charging sodium ion batteries, Example 1 uses glucose and single-layer graphene to coat the surface of the precursor, increasing the closed pore structure of the hard carbon anode material for high initial efficiency fast charging sodium ion batteries, and the sodium storage active sites increase, resulting in an increase in the sodium storage capacity of the hard carbon material.

[0084] The reversible capacity of Examples 2-4 is higher than that of Example 1 because in the preparation of the hard carbon anode material for high first-efficiency fast-charging sodium-ion batteries, epoxy resin carbon materials and coconut shells are used as carbon sources to prepare the hard carbon core in Examples 2-4, while epoxy resin carbon materials are not used in Example 1. This shows that the use of epoxy resin carbon materials can improve the reversible capacity of sodium-ion batteries. The reversible capacity of Examples 2-4 is higher than that of Comparative Examples 2-3 because in the preparation of epoxy resin materials, gallic acid epoxy resin and 1,2-epoxy resin-3-(di-2,6-dimethylphenylmethoxy) propane are used synergistically to prepare epoxy resin carbon materials in Examples 2-4, gallic acid epoxy resin is used alone in Comparative Example 2, and 1,2-epoxy resin-3-(di-2,6-dimethylphenylmethoxy) propane is used alone in Comparative Example 3. The reversible capacity of Example 2 is higher than that of Example 3 and Example 4 because the usage amounts of gallic acid epoxy resin and 1,2-epoxy resin-3-(di-2,6-dimethylphenylmethoxy) propane are different in the preparation of epoxy resin carbon materials. This shows that compared with the epoxy resin carbon materials prepared by using gallic acid epoxy resin and 1,2-epoxy resin-3-(di-2,6-dimethylphenylmethoxy) propane alone, the epoxy resin carbon materials prepared by using gallic acid epoxy resin and 1,2-epoxy resin-3-(di-2,6-dimethylphenylmethoxy) propane synergistically in appropriate amounts are more conducive to improving the reversible capacity of sodium-ion batteries.

[0085] The reversible capacity of Examples 5-6 is higher than that of Example 2 and Comparative Example 4 because in the preparation of epoxy resin carbon materials, 1-(2,4-bis(benzyloxy)phenyl)ethanone is further used to prepare epoxy resin carbon materials in Examples 5-6, 1-(2,4-bis(benzyloxy)phenyl)ethanone is not used in Example 2, and 1-(2,4-bis(benzyloxy)phenyl)ethanone is used alone in Comparative Example 4; the reversible capacity of Example 5 is higher than that of Example 6 because the usage amount of 1-(2,4-bis(benzyloxy)phenyl)ethanone is different in the preparation of epoxy resin materials. This shows that further using 1-(2,4-bis(benzyloxy)phenyl)ethanone to prepare epoxy resin materials can further improve the reversible capacity of sodium-ion batteries.

[0086] It can be seen that Figure 4 at 2C discharge, the reversible capacity of Example 1 is 117 mAh / g, which is 6 times that of Comparative Example 1, and the sodium-ion battery prepared in Example 1 has good cycle stability because in the preparation of the hard carbon anode material for high first-efficiency fast-charging sodium-ion batteries, glucose and single-layer graphene are used to coat the surface of the hard carbon core, improving the conductivity and reducing the resistance.

[0087] The conventional operations in the operation steps of the present invention are well known to those skilled in the art and will not be elaborated here.

[0088] The embodiments described above have elaborated on the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, supplements, or substitutions in a similar manner within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A hard carbon negative electrode material for a high-first-efficiency fast-charging sodium-ion battery, comprising a hard carbon core and a conductive coating layer coated on the surface of the hard carbon core; the hard carbon core is prepared from a carbon source through pre-carbonization and pickling treatment.

2. The hard carbon negative electrode material of a high-first-efficiency fast-charging sodium-ion battery according to claim 1, characterized in that, The carbon source includes at least one of coconut shell and epoxy resin carbon material.

3. The hard carbon negative electrode material of a high-first-efficiency fast-charging sodium-ion battery according to claim 2, characterized in that, The epoxy resin carbon material is obtained by curing gallic acid epoxy resin and 1,2-epoxy-3-(di-2,6-dimethylphenylmethoxy) propane.

4. The hard carbon negative electrode material for a high-first-efficiency fast-charging sodium ion battery according to claim 1, wherein, The conductive coating layer is a composition of glucose, single-layer graphene and water.

5. A preparation method of the hard carbon negative electrode material for the high-first-efficiency fast-charging sodium-ion battery as described in claim 1, comprising: S1. Pre-carbonize the carbon source to obtain biochar; S2. Add pickling solution to the biochar and stir for 4 - 8 h to obtain a hard carbon core; S3. Mix the hard carbon core and the conductive coating layer, and obtain precursor powder through air-flow pulverization; S4. Carbonize the precursor powder to obtain the hard carbon negative electrode material for the high-first-efficiency fast-charging sodium-ion battery.

6. The preparation method of a hard carbon negative electrode material for a high-first-efficiency fast-charging sodium ion battery according to claim 5, characterized in that, The temperature of the pre-carbonization treatment is 400 - 600 °C.

7. The preparation method of a hard carbon negative electrode material for a high-first-efficiency fast-charging sodium-ion battery according to claim 5, characterized in that, The time of the pre-carbonization treatment is 1 - 4 h.

8. The preparation method of a hard carbon anode material for a high-first-efficiency fast-charging sodium-ion battery according to claim 5, characterized in that, The pickling solution is a phosphoric acid solution, and the concentration of the phosphoric acid solution is 0.2 - 1 mol / L.

9. The preparation method of a hard carbon negative electrode material for a high-first-efficiency fast-charging sodium-ion battery according to claim 5, characterized in that, The temperature of the carbonization treatment is 1000 - 1500 °C.

10. The preparation method of a hard carbon negative electrode material for a high-first-efficiency fast-charging sodium-ion battery according to claim 5, characterized in that, The time of the carbonization treatment is 2 - 5 h.

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