High-first-effect high-capacity bamboo-based hard carbon material and preparation method thereof

Abstract

The invention discloses a high-first-effect high-capacity bamboo-based hard carbon material and a preparation method thereof, and belongs to the technical field of sodium-ion battery hard carbon negative electrode materials. The preparation method comprises the following steps: uniformly mixing bamboo wood with transition metal salt and alcohol, crushing, stirring and dispersing to obtain uniformly mixed slurry; placing the slurry in a tubular furnace for pre-carbonization to obtain an intermediate product; crushing the intermediate product, removing impurities, and performing high-temperature carbonization to obtain hard carbon; the invention provides a method for generating a low-defect Binchotan layer by using transition metal salt catalysis. A small amount of transition metals such as manganese, iron, cobalt, nickel and the like are introduced. The transition metals are bridged with oxygen-containing defects at 300-400 DEG C and are connected with a short-distance disordered carbon layer, so that the conversion from sp3 carbon to sp2 carbon is promoted. At a high temperature, transition metal is used as a catalyst in a graphitization process to reduce energy of conversion from sp3 carbon to sp2 carbon and promote formation of free radicals, so that defects are repaired to form a long and low-defect carbon layer, formation of a rich closed-pore structure is facilitated, and the capacity performance is considered while the first coulombic efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of hard carbon anode materials for sodium-ion batteries, and particularly relates to a high first-cycle efficiency and high-capacity bamboo-based hard carbon material and a preparation method thereof. Background Art

[0002] Due to advantages such as high reversible capacity and good rate stability, lithium-ion batteries have become the most widely used electrochemical energy storage systems. However, the continuous increase in the cost of lithium resources and limited reserves severely limit the development of lithium-ion batteries. A large number of studies have shown that sodium, which is in the same main group as lithium, is expected to become the next-generation secondary battery due to its rich reserves, uniform distribution, and similar working mechanism to lithium-ion batteries.

[0003] The development of anode materials is the key to the development and application of sodium-ion batteries. Due to thermodynamic limitations, graphite, which is widely used as the anode of lithium-ion batteries, does not form an intercalation compound with sodium. Therefore, using graphite as the anode of sodium-ion batteries will result in the generation of a large amount of dead sodium, causing a great loss of capacity. In recent years, hard carbon, which has unique structural advantages such as short-range order, large interlayer spacing, and abundant closed pores, has stood out and is considered the most suitable anode material for practical sodium-ion batteries. The performance of hard carbon mainly depends on the choice of precursor. Biomass is considered the most commercially promising precursor due to its intrinsic fine structure, wide source, and low cost. Bamboo has been widely used in the synthesis of hard carbon materials due to its natural cross-linked structure, developed pore structure, and other advantages. In the existing technology, patent (202410895140.3) discloses a preparation method of low-ash bamboo-based hard carbon. This method first impregnates bamboo in an aqueous potassium hydroxide solution and then performs carbonization treatment. The prepared hard carbon has good electrochemical performance. However, the treatment with strong alkali solution will cause the collapse of the three-dimensional structure of natural bamboo, resulting in the formation of open pores in the final hard carbon, thus affecting the first Coulombic efficiency of sodium-ion batteries. Patent (202311682100.2) treats bamboo by impregnating it in a saturated sodium salt solution, thereby introducing a large number of mesopores and macropores during the pyrolysis process. The introduction of macropores and mesopores will improve the diffusion kinetics of sodium ions. But it will also cause more electrolyte decomposition, thus affecting the first Coulombic efficiency. Therefore, there is an urgent need for a simple, economical, green and environmentally friendly preparation method to reduce the defect content in bamboo-based hard carbon and thus improve the first Coulombic efficiency and reversible capacity. Summary of the Invention

[0004] Aiming at the problems of reduced first Coulombic efficiency and insufficient reversible capacity caused by preparation process defects when bamboo-based hard carbon is used as the anode material of sodium-ion batteries, the present invention provides a high first-cycle efficiency and high-capacity bamboo-based hard carbon material and a preparation method thereof by introducing a small amount of transition metals such as manganese, iron, cobalt, nickel, etc. These transition metals will bridge with oxygen defects and connect short-range disordered carbon layers at 300 - 400 °C, promoting sp3 Carbon to sp 2 Transformation of carbon. At high temperatures, transition metals act as catalysts for the graphitization process, repairing defects to form longer and less defective carbon layers. Such carbon layers form larger closed pore structures, thereby improving the first Coulombic efficiency and reversible capacity of hard carbon.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A high first-efficiency and high-capacity bamboo-based hard carbon material, wherein the layer spacing of the hard carbon material is 0.35 - 0.4 nm, the crystallite length is 3.5 - 5 nm, and the pore diameter is 0.4 - 1 nm.

[0007] Furthermore, the fractal dimension of the hard carbon material is less than 2.6, the pore connectivity is 0.4 - 1, the defect content I D / I G is less than 1.5, the nitrogen specific surface area is 2 - 15 m 2 / g, and the carbon dioxide specific surface area is 20 - 200 m 2 / g.

[0008] A preparation method of a high first-efficiency and high-capacity bamboo-based hard carbon material, comprising the following steps:

[0009] Step 1, natural bamboo is crushed through an 80-mesh sieve and dried to obtain dried bamboo;

[0010] Step 2, a certain proportion of dried bamboo is mixed with transition metal salts and deionized water, stirred and dispersed to obtain a uniformly mixed slurry; the uniformly mixed slurry is placed in a reaction kettle with a polytetrafluoroethylene inner liner, reacted at 50 - 300 °C for 0.5 - 10 h, cooled to room temperature after the reaction, and then the cooled product is filtered and freeze-dried to obtain modified bamboo;

[0011] Step 3, under an inert atmosphere, the modified bamboo is carbonized at a constant temperature of 400 - 600 °C for 0 - 10 h to obtain an intermediate product;

[0012] Step 4, the intermediate product is pulverized to a suitable particle size by air flow pulverization or ball milling; then washed successively with acid solution, absolute ethanol, and water, and dried to obtain a treated intermediate product;

[0013] Step 5, under an inert atmosphere, the treated intermediate product is carbonized at a constant temperature of 900 - 1500 °C for 0 - 10 h, and after annealing, a high first-efficiency and high-capacity hard carbon negative electrode material for sodium-ion batteries is obtained.

[0014] Further, the types of bamboo for drying in step 1 include, but are not limited to: water bamboo, mottled bamboo, thorny bamboo, asparagus fern, Thai bamboo, Sheng Yin bamboo, Cheng Lu bamboo, turtle shell bamboo, green bamboo or tea pole bamboo, etc.; the age of the bamboo is 0.5 to 10 years; the parts of the bamboo include, but are not limited to: bamboo joints, bamboo poles, bamboo leaves or bamboo flowers, etc.

[0015] The transition metal salts include, but are not limited to: manganese chloride, iron chloride, cobalt chloride, nickel chloride, manganese sulfate or iron sulfate, etc.; the salt concentration of the transition metal salts is 0.0025 to 0.0125 M.

[0016] The inert atmosphere in step 3 and step 5 is any one of nitrogen or argon.

[0017] Further, the dispersion time for stirring and dispersing in step 2 is 1 h to 10 h; the temperature for freeze-drying in step 2 is -50°C to -20°C, and the freeze-drying time is 4 h to 12 h; the washing time in step 6 is 1 h to 10 h, and the washing temperature is 40°C to 95°C.

[0018] Further, in step 3, the isothermal carbonization treatment needs to be heated to 400°C to 600°C at a heating rate of 1 to 10°C / min.

[0019] Further, in step 4, the particle size needs to be controlled such that 0.5 μm < D10 < 2 μm, 4 μm < D50 < 6 μm, and 8 μm < D90 < 12 μm.

[0020] Further, in step 5, the isothermal carbonization treatment needs to be heated to 900°C to 1500°C at a heating rate of 1 to 10°C / min, and the holding time is 0.5 h to 10 h.

[0021] Further, the acid solution in step 4 is any one or several of hydrochloric acid, sulfuric acid, nitric acid or acetic acid, and the concentration of the acid solution is 0.5 to 5 mol / L.

[0022] A sodium-ion battery, the negative electrode of the sodium-ion battery includes the bamboo-based hard carbon material prepared by the above preparation method.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) The present invention proposes to use transition metal salts to catalyze the formation of low-defect long carbon layers. By introducing a small amount of transition metals such as manganese, iron, cobalt, nickel, etc. These transition metals will bridge and connect short-range disordered carbon layers with oxygen defects at 300 - 400°C, promoting sp 3 carbon to sp 2Carbon conversion. At high temperatures, transition metals act as catalysts for the graphitization process, repairing defects to form longer and less defective carbon layers. Such carbon layers form larger closed pore structures, thereby improving the first Coulombic efficiency and reversible capacity of hard carbon.

[0025] (2) The present invention uses environmentally friendly transition metal salts to modify the pyrolysis process of bamboo, reducing the content of open pores during pyrolysis and the content of defects in the final hard carbon, and having advantages such as high first Coulombic efficiency and high reversible capacity. It solves the problem of low first-cycle Coulombic efficiency of existing hard carbon anode materials. At the same time, the preparation method of the present invention has simple equipment, easy operation control, and is easy to realize large-scale production.

[0026] (3) The present invention uses low-cost bamboo as a precursor, supplemented with a very low content of transition metal salts to prepare a hard carbon anode material for a sodium-ion battery with high first efficiency and high capacity. It has advantages such as low cost, simple equipment for the preparation method, easy operation control, and easy to realize large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0028] Figure 1 It is the X-ray diffraction pattern of the hard carbon after being treated with manganese chloride in Example 2 of the present invention.

[0029] Figure 2 It is the Raman spectrum of the hard carbon after being treated with manganese chloride in Example 2 of the present invention.

[0030] Figure 3 It is the charge-discharge curve of the hard carbon after being treated with manganese chloride in Example 2 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] To understand the present invention in depth, we will describe it comprehensively and meticulously. However, the present invention has multiple implementation manners and is not limited to the specific examples listed herein. The presentation of these examples aims to deepen the comprehensive understanding of the disclosed content of the present invention.

[0032] The present invention uses bamboo as a precursor and uses transition metal salts to generate a low-defect long carbon layer structure. These transition metals will bridge and connect short-range disordered carbon layers with oxygen-containing defects at 300°C to 400°C, promoting the conversion of sp 3 carbon to sp 2Carbon conversion. At high temperatures, transition metals act as catalysts for the graphitization process, repairing defects to form longer and less defective carbon layers, thereby greatly improving the first Coulombic efficiency and reversible capacity of this hard carbon. The experimental results show that the bamboo-based hard carbon material provided by the present invention exhibits longer carbon layers and abundant closed pores. As the negative electrode of a sodium-ion battery, it demonstrates high first-cycle efficiency performance while maintaining its high capacity.

[0033] Example 1

[0034] This example provides a high first-cycle efficiency and high-capacity moso bamboo-based hard carbon negative electrode material;

[0035] The graphite layer spacing of the hard carbon negative electrode material is 0.384 nm; the crystallite length of the hard carbon negative electrode material is 3.9 nm; the nitrogen specific surface area of the hard carbon negative electrode material is 8.7 m 2 / g; the carbon dioxide specific surface area of the hard carbon negative electrode material is 50 m 2 / g;

[0036] The hard carbon negative electrode material is a material rich in closed pores, and the closed pore volume of the hard carbon negative electrode material is 0.104 m 3 / g; the pore diameter of the hard carbon negative electrode material is 0.6 nm;

[0037] The hard carbon negative electrode material has a low defect content, and the I D / I G is 1.3.

[0038] This example also provides a preparation method for the above hard carbon negative electrode material, and the preparation method includes the following steps:

[0039] (1) First, crush moso bamboo and pass it through an 80-mesh sieve. Then, place it in a forced-air drying oven and treat it at 70 °C for 24 h until constant weight to obtain dried moso bamboo;

[0040] (2) Immerse 30 g of dried moso bamboo in 450 mL of 0.0025 M manganese chloride solution, stir at 450 rpm for 30 min, place the mixed slurry in a reaction kettle with a polytetrafluoroethylene liner, react at 50 - 300 °C for 0.5 - 10 h, cool to room temperature after the reaction, and then filter the solution. The obtained filter residue is dried in an oven at 70 °C for 24 h to obtain modified moso bamboo.

[0041] (3) Place the modified moso bamboo in a tubular furnace, heat it to 600 °C at a rate of 2 °C / min in an argon atmosphere, perform constant-temperature carbonization treatment for 10 min, and cool to room temperature to obtain bamboo-based low-temperature pyrolysis carbon.

[0042] (4) Crush the bamboo-based low-temperature pyrolysis carbon to a particle size with D10 being 1.8 μm, D50 being 4.5 μm, and D90 being 9.5 μm. Subsequently, wash the crushed bamboo-based low-temperature pyrolysis carbon successively with 0.5 mol / L hydrochloric acid, absolute ethanol, and water until the pH reaches 7 to obtain the impurity-removed and crushed bamboo-based low-temperature pyrolysis carbon.

[0043] Among them, the pickling time with hydrochloric acid is 12 h, and the pickling temperature is 25 °C;

[0044] (5) Place the impurity-removed and crushed bamboo-based low-temperature pyrolysis carbon in a tubular furnace, heat it to 1300 °C at a rate of 2 °C / min in an argon atmosphere, carry out isothermal carbonization treatment for 2 h, and cool it to room temperature to obtain the bamboo-based hard carbon negative electrode.

[0045] Example 2

[0046] This example provides a high first-cycle efficiency and high-capacity moso bamboo-based hard carbon negative electrode material;

[0047] The graphite layer spacing of the hard carbon negative electrode material is 0.37 nm; the crystallite length of the hard carbon negative electrode material is 4 nm; the nitrogen specific surface area of the hard carbon negative electrode material is 10 m 2 / g; the carbon dioxide specific surface area of the hard carbon negative electrode material is 80 m 2 / g;

[0048] The hard carbon negative electrode material is a material rich in closed pores, and the closed pore volume of the hard carbon negative electrode material is 0.154 m 3 / g; the pore diameter of the hard carbon negative electrode material is 0.8 nm;

[0049] The hard carbon negative electrode material has a low defect content, and the I D / I G is 1.1.

[0050] This example also provides a preparation method of the above hard carbon negative electrode material, and the preparation method includes the following steps:

[0051] (1) First, crush the moso bamboo and pass it through an 80-mesh sieve, and then, in a blast drying oven, after treating it at 70 °C for 24 h until it reaches a constant weight, obtain the dried moso bamboo;

[0052] (2) Immerse 30 g of the dried moso bamboo in 450 mL of 0.01 M manganese chloride solution, stir it at 450 rpm for 30 min, place the mixed slurry in a reaction kettle with a polytetrafluoroethylene inner lining, react at 50 - 300 °C for 0.5 - 10 h, after the reaction, cool it to room temperature, and then filter the solution. The obtained filter residue is dried in an oven at 70 °C for 24 h to obtain the modified moso bamboo.

[0053] (3) Place the modified moso bamboo in a tubular furnace, heat it to 600 °C at a rate of 2 °C / min in an argon atmosphere, carry out isothermal carbonization treatment for 10 min, and cool it to room temperature to obtain bamboo-based low-temperature pyrolysis carbon.

[0054] (4) Crush the bamboo-based low-temperature pyrolysis carbon to a particle size with D10 of 1.7 μm, D50 of 4.8 μm, and D90 of 9.7 μm. Subsequently, wash the crushed bamboo-based low-temperature pyrolysis carbon successively with 0.5 mol / L hydrochloric acid, absolute ethanol, and water until the pH is 7 to obtain the impurity-removed and crushed bamboo-based low-temperature pyrolysis carbon. Among them, the hydrochloric acid pickling time is 12 h, and the pickling temperature is 25 °C;

[0055] (5) Place the impurity-removed and crushed bamboo-based low-temperature pyrolysis carbon in a tubular furnace, heat it to 1300 °C at a rate of 2 °C / min in an argon atmosphere, carry out isothermal carbonization treatment for 2 h, and cool it to room temperature to obtain the bamboo-based hard carbon negative electrode.

[0056] Example 3

[0057] This example provides a moso bamboo-based hard carbon negative electrode material with high initial efficiency and high capacity;

[0058] The graphite layer spacing of the hard carbon negative electrode material is 0.36 nm; the crystallite length of the hard carbon negative electrode material is 4.5 nm; the nitrogen specific surface area of the hard carbon negative electrode material is 6 m 2 / g; the carbon dioxide specific surface area of the hard carbon negative electrode material is 40 m 2 / g;

[0059] The hard carbon negative electrode material is a closed-pore-rich material, and the closed-pore pore volume of the hard carbon negative electrode material is 0.154 m 3 / g; the pore diameter of the hard carbon negative electrode material is 0.6 nm;

[0060] The hard carbon negative electrode material has a low defect content, and the I D / I G is 1.0.

[0061] This example also provides a preparation method of the above hard carbon negative electrode material, and the preparation method includes the following steps:

[0062] (1) First, crush the moso bamboo and pass it through an 80-mesh sieve, and then place it in a forced-air drying oven and treat it at 70 °C for 24 h until it reaches constant weight to obtain dried moso bamboo;

[0063] (2) Immerse 30 g of dry bamboo in 450 mL of 0.0125 M manganese chloride solution, stir at 450 rpm for 30 min, place the mixed slurry in a reaction kettle lined with polytetrafluoroethylene, react at 50 - 300 °C for 0.5 - 10 h, cool to room temperature after the reaction, and then filter the solution. The obtained filter residue is dried in an oven at 70 °C for 24 h to obtain modified bamboo.

[0064] (3) Place the modified bamboo in a tubular furnace, heat it to 600 °C at a rate of 2 °C / min in an argon atmosphere, carry out isothermal carbonization treatment for 10 min, and cool to room temperature to obtain bamboo-based low-temperature pyrolysis carbon.

[0065] (4) Crush the bamboo-based low-temperature pyrolysis carbon to a particle size with D10 being 1.6 μm, D50 being 5.3 μm, and D90 being 9.2 μm. Then wash the crushed bamboo-based low-temperature pyrolysis carbon successively with 0.5 mol / L hydrochloric acid, absolute ethanol, and water until the pH is 7 to obtain the impurity-removed and crushed bamboo-based low-temperature pyrolysis carbon. Among them, the pickling time with hydrochloric acid is 12 h, and the pickling temperature is 25 °C;

[0066] (5) Place the impurity-removed and crushed bamboo-based low-temperature pyrolysis carbon in a tubular furnace, heat it to 1300 °C at a rate of 2 °C / min in an argon atmosphere, carry out isothermal carbonization treatment for 2 h, and cool to room temperature to obtain the bamboo-based hard carbon negative electrode.

[0067] Example 4

[0068] This example provides a bamboo-based hard carbon negative electrode material with high initial efficiency and high capacity;

[0069] The graphite layer spacing of the hard carbon negative electrode material is 0.374 nm; the crystallite length of the hard carbon negative electrode material is 4.2 nm; the nitrogen specific surface area of the hard carbon negative electrode material is 8.7 m 2 / g; the carbon dioxide specific surface area of the hard carbon negative electrode material is 55 m 2 / g;

[0070] The hard carbon negative electrode material is a material rich in closed pores, and the closed pore volume of the hard carbon negative electrode material is 0.173 m 3 / g; the pore diameter of the hard carbon negative electrode material is 0.7 nm;

[0071] The hard carbon negative electrode material has a low defect content, and the I D / I G is 1.12.

[0072] This example also provides a preparation method for the above hard carbon negative electrode material, and the preparation method includes the following steps:

[0073] (1) First, crush the moso bamboo and pass it through an 80-mesh sieve. Then, place it in a forced-air drying oven and treat it at 70 °C for 24 h until it reaches a constant weight to obtain dried moso bamboo;

[0074] (2) Immerse 30 g of the dried moso bamboo in 450 mL of 0.01 M cobalt chloride solution, stir at 450 rpm for 30 min, place the mixed slurry in a reaction kettle with a polytetrafluoroethylene inner lining, react at 50 - 300 °C for 0.5 - 10 h, cool to room temperature after the reaction, and then filter the solution. The obtained filter residue is dried in an oven at 70 °C for 24 h to obtain modified moso bamboo.

[0075] (3) Place the modified moso bamboo in a tubular furnace, heat it to 600 °C at a rate of 2 °C / min in an argon atmosphere, carry out constant-temperature carbonization treatment for 10 min, and cool to room temperature to obtain bamboo-based low-temperature pyrolysis carbon.

[0076] (4) Crush the bamboo-based low-temperature pyrolysis carbon to a particle size with D10 of 1.5 μm, D50 of 4.9 μm, and D90 of 9.1 μm. Then, wash the crushed bamboo-based low-temperature pyrolysis carbon successively with 0.5 mol / L hydrochloric acid, absolute ethanol, and water until the pH reaches 7 to obtain impurity-removed and crushed bamboo-based low-temperature pyrolysis carbon. Among them, the hydrochloric acid pickling time is 12 h and the pickling temperature is 25 °C;

[0077] (5) Place the impurity-removed and crushed bamboo-based low-temperature pyrolysis carbon in a tubular furnace, heat it to 1300 °C at a rate of 2 °C / min in an argon atmosphere, carry out constant-temperature carbonization treatment for 2 h, and cool to room temperature to obtain the bamboo-based hard carbon negative electrode.

[0078] Example 5

[0079] This example provides a high-first-efficiency and high-capacity pleioblastus amarus-based hard carbon negative electrode material;

[0080] The graphite layer spacing of the hard carbon negative electrode material is 0.378 nm; the crystallite length of the hard carbon negative electrode material is 4.15 nm; the nitrogen specific surface area of the hard carbon negative electrode material is 9.5 m 2 / g; the carbon dioxide specific surface area of the hard carbon negative electrode material is 60 m 2 / g;

[0081] The hard carbon negative electrode material is a closed-pore-rich material, and the closed-pore pore volume of the hard carbon negative electrode material is 0.168 m 3 / g; the pore diameter of the hard carbon negative electrode material is 0.7 nm;

[0082] The hard carbon negative electrode material has a low defect content, and the I D / I G is 1.05.

[0083] This embodiment also provides a method for preparing the above-mentioned hard carbon anode material, and the preparation method includes the following steps:

[0084] (1) First, crush the bitter bamboo and pass it through an 80-mesh sieve. Then, place it in a forced-air drying oven and treat it at 70 °C for 24 h until it reaches a constant weight to obtain dried bitter bamboo;

[0085] (2) Immerse 30 g of dried bamboo in 450 mL of 0.01 M manganese chloride solution, stir at 450 rpm for 30 min, place the mixed slurry in a reaction kettle with a polytetrafluoroethylene inner lining, react at 50 - 300 °C for 0.5 - 10 h, cool to room temperature after the reaction, and then filter the solution. The obtained filter residue is dried in an oven at 70 °C for 24 h to obtain modified bitter bamboo.

[0086] (3) Place the modified bitter bamboo in a tube furnace, heat it to 600 °C at a rate of 2 °C / min in an argon atmosphere, perform constant-temperature carbonization treatment for 10 min, and cool to room temperature to obtain bamboo-based low-temperature pyrolysis carbon.

[0087] (4) Crush the bamboo-based low-temperature pyrolysis carbon to a particle size with D10 of 1.4 μm, D50 of 4.5 μm, and D90 of 8.9 μm. Then, wash the crushed bamboo-based low-temperature pyrolysis carbon successively with 0.5 mol / L hydrochloric acid, absolute ethanol, and water until the pH is 7 to obtain impurity-removed and crushed bamboo-based low-temperature pyrolysis carbon. Among them, the hydrochloric acid pickling time is 12 h, and the pickling temperature is 25 °C;

[0088] (5) Place the impurity-removed and crushed bamboo-based low-temperature pyrolysis carbon in a tube furnace, heat it to 1300 °C at a rate of 2 °C / min in an argon atmosphere, perform constant-temperature carbonization treatment for 2 h, and cool to room temperature to obtain the bamboo-based hard carbon anode.

[0089] Comparative Example 1

[0090] The difference between this comparative example and Example 1 is that no manganese chloride is introduced, that is, the bamboo is directly immersed in an aqueous solution.

[0091] The remaining preparation methods and parameters are the same as those in Example 1.

[0092] Performance Test

[0093] Based on the bamboo-based hard carbon anode material prepared in the above-mentioned examples and comparative examples, a CR2032 button cell is fabricated. The specific steps include:

[0094] Mix the prepared hard carbon anode material with carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber in a mass ratio of 91:2:2:5 to form a slurry. Then, uniformly scrape the slurry onto a current collector carbon foil. After drying, cut the electrode sheet. The battery is assembled in a glove box under an Ar atmosphere, using metallic sodium as the counter electrode, and 1M NaClO 4A solution with a volume ratio of ethylene carbonate to diethyl carbonate of 1:1 was used as the electrolyte to assemble a CR2032 coin cell.

[0095] The CR2032 coin cell was subjected to charge-discharge tests under the following conditions: a current density of 30 mA / g and a voltage of 0.001 - 3 V.

[0096] The test results are shown in Table 1.

[0097] Table 1

[0098] Reversible specific capacity (mAh / g) Initial Coulombic efficiency (%) Example 1 306.7 88 Example 2 320 92 Example 3 306 90 Example 4 315 91.5 Example 5 313 91 Comparative Example 1 287 85

[0099] Analysis:

[0100] As can be seen from the above table, the present invention utilizes transition metal salts to achieve the formation of a low-defect long carbon layer structure. These transition metals will bridge and connect short-range disordered carbon layers with oxygen defects at 300 - 400 °C, promoting the conversion of sp 3 carbon to sp 2 carbon. At high temperatures, the transition metals act as catalysts for the graphitization process, repairing defects to form longer and lower-defect carbon layers, thereby greatly improving the first Coulombic efficiency and reversible capacity of the hard carbon.

[0101] As can be seen from Examples 1 - 3, when the concentration of manganese chloride is low, the defects cannot be effectively repaired; when the concentration of manganese chloride is high, excessive defect repair leads to a higher degree of graphitization of the hard carbon, reducing the closed pore volume in the hard carbon, thereby reducing the reversible capacity and the first Coulombic efficiency.

[0102] As can be seen from Comparative Example 1 and Example 4, cobalt chloride solution can effectively improve the reversible capacity and the first Coulombic efficiency.

[0103] As can be seen from Example 2 and Example 5, the present invention can effectively improve the reversible capacity and the first Coulombic efficiency of different varieties of bamboo-based hard carbon.

[0104] The content not described in detail in the specification of the present invention belongs to the prior art well-known to those skilled in the art. Although the above-described illustrative specific embodiments of the present invention have been described to facilitate the understanding of the present invention by those skilled in the art, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions created using the concept of the present invention are within the scope of protection.

Claims

1. A bamboo-based hard carbon material with high initial efficiency and high capacity, characterized in that: The interlayer distance of the hard carbon material is 0.35-0.4 nm, the crystallite length is 3.5-5 nm, and the pore diameter is 0.4-1 nm.

2. The high initial efficiency and high capacity bamboo-based hard carbon material according to claim 1, characterized in that: The fractal dimension of the hard carbon material is less than 2.6, the pore connectivity is 0.4 to 1, and the defect content is I D / I G Less than 1.

5.

3. A method for preparing a high initial efficiency and high capacity bamboo-based hard carbon material as claimed in any one of claims 1 to 2, characterized in that: The following steps are involved: Step 1, natural bamboo is crushed and passed through an 80-mesh sieve, and dried to obtain dried bamboo; Step 2, mixing a certain proportion of dried bamboo with transition metal salt and deionized water, stirring and dispersing to obtain a mixed slurry; placing the mixed slurry in a polytetrafluoroethylene-lined reactor, reacting at 50-300° C. for 0.5-10 hours, cooling to room temperature after the reaction, filtering and freeze-drying the cooled product to obtain modified bamboo; Step 3, in an inert atmosphere, carbonizing the modified bamboo at 400-600° C. for 0-10 h to obtain an intermediate product; Step 4, the intermediate product is crushed by air flow or ball milling to a suitable particle size; then washed in acid, anhydrous ethanol, and water in sequence, and dried to obtain the treated intermediate product; Step 5, under an inert atmosphere, carbonizing the treated intermediate product at a constant temperature of 900-1500° C. for 0-10 hours, and annealing to obtain a high-efficiency and high-capacity hard carbon negative electrode material for sodium ion batteries.

4. The method for preparing a high initial efficiency and high capacity bamboo-based hard carbon material according to claim 3, characterized in that: The types of bamboo dried in step 1 include: water bamboo, spotted bamboo, thorny bamboo, asparagus bamboo, Thai bamboo, holy sound bamboo, supporting green bamboo, tortoise shell bamboo, green skin bamboo or tea stem bamboo; the age of the bamboo is 0.5 to 10 years; the parts of the bamboo include: bamboo nodes, bamboo stems, bamboo leaves or bamboo flowers; The transition metal salt in step 2 includes: manganese chloride, ferric chloride, cobalt chloride, nickel chloride, manganese sulfate or ferric sulfate; the salt concentration of the transition metal salt is 0.0025-0.0125M; The inert atmosphere in step 3 and step 5 is any one of nitrogen or argon.

5. The method for preparing a high initial efficiency and high capacity bamboo-based hard carbon material according to claim 3, characterized in that: The dispersion time of the stirring dispersion in step 2 is 1 h to 10 h; the freeze-drying temperature in step 2 is -50°C to -20°C, and the freeze-drying time is 4 h to 12 h.

6. The method for preparing a high initial efficiency and high capacity bamboo-based hard carbon material according to claim 3, characterized in that: In step 3, the constant temperature carbonization treatment needs to be heated to 400°C to 600°C at a heating rate of 1 to 10°C / min; in step 5, the constant temperature carbonization treatment needs to be heated to 900°C to 1500°C at a heating rate of 1 to 10°C / min, and the insulation time is 0.5h to 10h.

7. The method for preparing a high initial efficiency and high capacity bamboo-based hard carbon material according to claim 3, characterized in that: The particle size in step 4 needs to be controlled at 0.5 μm <D10<2μm,4μm<D50<6μm,8μm<D90<12μm。 8. The method for preparing a high initial efficiency and high capacity bamboo-based hard carbon material according to claim 3, characterized in that: In step 4, the washing time is 1 h to 10 h, and the washing temperature is 40° C. to 95° C.

9. The method for preparing a high initial efficiency and high capacity bamboo-based hard carbon material according to claim 3, characterized in that: The acid solution in step 4 is any one or more of hydrochloric acid, sulfuric acid, nitric acid or acetic acid, and the concentration of the acid solution is 0.5-5 mol / L.

10. A sodium ion battery, characterized in that: The negative electrode of the sodium ion battery comprises the bamboo-based hard carbon material prepared by the preparation method according to any one of claims 3 to 9.

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