High-rate hard carbon material and preparation method thereof, and sodium ion battery

Abstract

The application belongs to the technical field of materials, and provides a high-rate hard carbon material, a preparation method thereof and a sodium ion battery, and comprises the following steps: reacting a hard carbon precursor after pre-carbonization treatment with an alkali under the condition that the temperature is 800-900 DEG C for 1-2 hours to obtain a porous carbon material; the alkali is KOH or K2CO3; the mass ratio of the hard carbon precursor to the alkali is 1:(0.05-0.2); the porous carbon material is subjected to acid washing treatment by using an acid solution to obtain a low-ash carbon material; the low-ash carbon material is subjected to filling treatment by using a carbon filler through liquid phase immersion to obtain a filled carbon material, which is obtained through high-temperature carbonization treatment; and the addition amount of the carbon filler is 5-10 wt% of the mass of the low-ash carbon material. The application realizes high reversible capacity, high initial coulomb efficiency and high rate property by precisely constructing a closed pore structure with a suitable pore size in the hard carbon.

Description

Technical Field

[0001] This application belongs to the field of materials technology, and particularly relates to a high-rate hard carbon material and its preparation method, and a sodium-ion battery. Background Technology

[0002] Rechargeable batteries are playing an increasingly important role in new energy applications. Sodium-ion batteries work on the same principle as lithium-ion batteries, have similar manufacturing processes, and have abundant and inexpensive sodium sources. Therefore, in recent years, sodium-ion batteries have been considered the best complement to lithium-ion batteries in large-scale energy storage. Hard carbon, due to its excellent overall performance, has become the mainstream anode material for sodium-ion batteries.

[0003] Currently, the reversible capacity of hard carbon materials is generally higher than 300 mAh / g, and the initial coulombic efficiency is higher than 88%, meeting the basic requirements for practical applications. However, with the continuous expansion of application scenarios, hard carbon materials have revealed problems such as poor rate performance and poor cycle stability. The reversible capacity of hard carbon mainly originates from the Na in the pseudographite region. + Quasi-metallic sodium deposition within interlayer insertion and closed-pore structures, under high-rate charge-discharge conditions, results in slow interlayer migration of Na. + Excessive metallization of sodium deposits on the surface and in closed pores can lead to severe sodium deposition on the surface of the negative electrode material, resulting in reversible capacity loss and deterioration of battery cycle performance.

[0004] Chen et al. studied a hard carbon prepared by vapor deposition filled with activated carbon, investigating the effect of deposition time on the pore size and porosity of the hard carbon material, which exhibited high reversible capacity. However, they did not study the effect of pore size and porosity on the rate performance of the material, and the vapor deposition process was costly. Zheng et al. studied a high-capacity hard carbon material, which introduced a rich pore structure during the pre-carbonization stage through CO2 etching, followed by high-temperature sintering to close the pores. The hard carbon with abundant closed-pore structure provided high reversible capacity. However, the rate performance of this hard carbon material was poor. Zhao et al. studied a hard carbon material coated with asphalt liquid phase, which exhibited high reversible capacity, high initial coulombic efficiency, and high rate performance. However, this process required the use of precious metal Ni as a catalyst during coating, resulting in high cost, and also required secondary impurity removal of the finished product, making the process relatively complex. Tian et al. prepared a hard carbon by impregnating activated carbon with asphalt solution, which exhibited high reversible capacity and cycle stability. However, this process required multiple impregnations and centrifugation, making the process flow complex. Other existing technologies disclose a hard carbon material with high reversible capacity and high first-time coulombic efficiency, which improves capacity through acid-base treatment for impurity removal and pore formation, and improves first-time coulombic efficiency through coating. However, this process does not investigate the effect of acid-base treatment on pore size, nor does it mention the process's effect on rate performance.

[0005] Given the current state of technology, further research is needed on how to precisely construct closed-pore structures with suitable pore sizes in hard carbon to achieve higher rate performance and better meet market demands. Summary of the Invention

[0006] The purpose of this application is to provide a method for preparing high-rate hard carbon materials, which aims to precisely construct closed-pore structures with suitable pore size in hard carbon to achieve high reversible capacity, high initial coulombic efficiency and high rate performance.

[0007] The embodiments of this application are implemented as follows: a method for preparing a high-ratio hard carbon material includes:

[0008] The pre-carbonized hard carbon precursor is mixed with an alkali to obtain a porous carbon material; the alkali is KOH or K2CO3; the mass ratio of the hard carbon precursor to the alkali is 1:(0.05-0.2).

[0009] The porous carbon material is acid-washed with an acid solution to obtain a low-ash carbon material.

[0010] The low-ash carbon material is subjected to a carbon filler filling treatment by liquid phase impregnation to obtain a filled carbon material, which is then subjected to high-temperature carbonization treatment to obtain a high-ratio hard carbon material.

[0011] Preferably, in the step of mixing the pre-carbonized hard carbon precursor with an alkali to obtain porous carbon material, the reaction temperature is 800-900℃ and the reaction time is 1-2h.

[0012] Preferably, the amount of carbon filler added is 5-10 wt% of the mass of the low-ash carbon material.

[0013] Preferably, the conditions for the high-temperature carbonization treatment are: a temperature of 1100-1300℃.

[0014] Another objective of this application is to provide a high-ratio hard carbon material, which is prepared by the above-described method for preparing high-ratio hard carbon materials.

[0015] Another objective of this application is to provide a sodium-ion battery comprising the aforementioned high-rate hard carbon material.

[0016] The beneficial effects of the embodiments in this application compared with the prior art are:

[0017] (1) High reversible capacity: Alkali etching constructs a rich microporous structure inside the carbon material, and carbon filling transforms the open pores into closed pore structures, thereby increasing the active sites for sodium storage inside the hard carbon material and thus improving the capacity.

[0018] (2) Effective improvement in rate performance: By optimizing the etchant, etching conditions, and carbon filling ratio, the porosity and closed-pore diameter of the hard carbon material can be controlled. The most probable pore size distribution of the optimal hard carbon material is 1-2 nm, providing high capacity while ensuring excellent rate performance.

[0019] (3) High initial coulombic efficiency: Carbon filling simultaneously achieves surface carbon coating on the material. The highly ordered coating layer can induce the formation of a thin and stable electrode electrolyte interfacial film (SEI), reducing the amount of active Na in charge-discharge cycles. + This reduces losses, achieving high initial coulombic efficiency and stable cycling performance. Simultaneously, a thin and stable SEI promotes rapid electrolyte desolvation, thereby improving rate performance.

[0020] (4) Good economic efficiency: The preparation process of this application is simple, and the chemical reagents used are common and inexpensive. The solvent used in the carbon filling process can be recycled, and there are no special equipment requirements. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0022] This application provides a method for preparing a high-ratio hard carbon material, including:

[0023] The pre-carbonized hard carbon precursor is reacted with an alkali at a temperature of 800-900℃ for 1-2 hours to obtain a porous carbon material; the alkali is KOH or K2CO3; the mass ratio of the hard carbon precursor to the alkali is 1:(0.05-0.2).

[0024] The porous carbon material is acid-washed with an acid solution to obtain a low-ash carbon material.

[0025] The low-ash carbon material is subjected to liquid-phase impregnation and carbon filler filling treatment to obtain filled carbon material, which is then subjected to high-temperature carbonization treatment to obtain high-ratio hard carbon material; the amount of carbon filler added is 5-10 wt% of the mass of the low-ash carbon material.

[0026] Optionally, the hard carbon raw material includes one or more of fossil raw materials and biomass raw materials. The pre-carbonization treatment conditions are: heating rate of 2-10℃ / min, pre-treatment temperature of 300-800℃, pre-treatment time of 1-24h, and protective gas of nitrogen and / or argon.

[0027] In the step of reacting the pre-carbonized hard carbon precursor with an alkali at a temperature of 800-900℃ for 1-2 hours to obtain porous carbon material, the protective gas is one or more of nitrogen, argon, and CO2, preferably a mixture of 40% CO2 and nitrogen or argon.

[0028] Optionally, the acid solution is one or more of HCl, HNO3, H2SO4, formic acid, acetic acid, and citric acid. In the step of acid washing the porous carbon material with the acid solution to obtain low-ash carbon material, the mass ratio of porous carbon material to acid solution is 1:5; the reaction temperature is 80℃; and the reaction time is 12h.

[0029] Optionally, the carbon filler includes one or more of asphalt, phenolic resin, epoxy resin, starch, lignin, and bamboo tar; the solvent used includes one or more of deionized water, N,N-dimethylamide, N-methylpyrrolidone, benzene, toluene, and ethanol; the mass ratio of low-ash carbon material to solvent is 1:2; and the impregnation time is 12 hours. The solvent is evaporated by one or more of flash drying, spray drying, and rotary evaporation, and the solvent is recovered through a matching reflux condenser.

[0030] The conditions for high-temperature carbonization are as follows: heating rate of 2℃ / min; carbonization temperature of 1000-1400℃, preferably 1100-1300℃; and carbonization time of 3h.

[0031] The following are embodiments of some implementations of this application, which are not intended to limit the scope of this application.

[0032] Additionally, it should be noted that the values ​​given in the following embodiments are as accurate as possible. However, those skilled in the art will understand that due to unavoidable measurement errors and experimental issues, each number should be understood as an approximation rather than an absolutely accurate value.

[0033] Example 1

[0034] S1. Pre-carbonization: The raw bamboo is crushed, passed through a 50-mesh sieve, and pre-fired in a box furnace to obtain hard carbon precursor material. The pre-firing heating rate is 10℃ / min, the temperature is 400℃, and the pre-firing time is 3h; the protective gas is nitrogen.

[0035] S2. Alkali etching for pore formation: The hard carbon precursor material obtained in step S1 and K2CO3 are added to a ball mill jar at a mass ratio of 1:0.1 (ball-to-material ratio 1:5). The mixture is ball-milled for 1 hour at 500 r / min using a planetary ball mill to obtain a mixed material. The mixed material is then heat-treated in a box furnace to obtain porous carbon material. The heating rate is 10℃ / min, the temperature is 800℃, and the heat treatment time is 1 hour. The protective gas is a mixture of 40% CO2 and 60% N2.

[0036] S3. Acid washing and impurity removal: The porous carbon material obtained in step S2 is subjected to acid washing, filtered, washed with water until neutral, and dried to obtain low-ash carbon material. The acid used is concentrated hydrochloric acid, the mass ratio of porous carbon material to concentrated hydrochloric acid is 1:5, the reaction temperature is 80℃, and the reaction time is 12h.

[0037] S4. Carbon Filling: The low-ash carbon material obtained in step S3 is subjected to liquid-phase impregnation filling. The mixture of the low-ash carbon material and the impregnation solution is flash-dried to obtain the filled carbon material. The impregnation solution is an N,N-dimethylformamide solution of asphalt, with the asphalt added at 5 wt% of the mass of the low-ash carbon material. The mass ratio of the low-ash carbon material to the N,N-dimethylformamide solvent is 1:2, and the impregnation time is 12 hours. The flash drying temperature is 180°C, and the solvent is recovered using a condenser.

[0038] S5. High-temperature carbonization: The filled carbon material obtained in step S4 is placed in a high-temperature carbonization furnace and held at 1200℃ for 3 hours in a nitrogen atmosphere to obtain a high-rate performance hard carbon anode material. The heating rate is 2℃ / min.

[0039] Example 2

[0040] S1. Pre-carbonization: The raw bamboo is crushed, passed through a 50-mesh sieve, and pre-fired in a box furnace to obtain hard carbon precursor material. The pre-firing heating rate is 10℃ / min, the temperature is 400℃, and the pre-firing time is 3h; the protective gas is nitrogen.

[0041] S2. Alkali etching for pore formation: The hard carbon precursor material obtained in step S1 and K2CO3 are added to a ball mill jar at a mass ratio of 1:0.05 (ball-to-material ratio 1:5). The mixture is ball-milled for 1 hour at 500 r / min using a planetary ball mill to obtain a mixed material. The mixed material is then heat-treated in a box furnace to obtain porous carbon material. The heating rate is 10℃ / min, the temperature is 800℃, and the heat treatment time is 1 hour. The protective gas is a mixture of 40% CO2 and 60% N2.

[0042] S3. Acid washing and impurity removal: The porous carbon material obtained in step S2 is subjected to acid washing, filtered, washed with water until neutral, and dried to obtain low-ash carbon material. The acid used is concentrated hydrochloric acid, the mass ratio of porous carbon material to concentrated hydrochloric acid is 1:5, the reaction temperature is 80℃, and the reaction time is 12h.

[0043] S4. Carbon Filling: The low-ash carbon material obtained in step S3 is subjected to liquid-phase impregnation filling. The mixture of the low-ash carbon material and the impregnation solution is flash-dried to obtain the filled carbon material. The impregnation solution is an N,N-dimethylformamide solution of asphalt, with the asphalt added at 5 wt% of the mass of the low-ash carbon material. The mass ratio of the low-ash carbon material to the N,N-dimethylformamide solvent is 1:2, and the impregnation time is 12 hours. The flash drying temperature is 180°C, and the solvent is recovered using a condenser.

[0044] S5. High-temperature carbonization: The filled carbon material obtained in step S4 is placed in a high-temperature carbonization furnace and held at 1200℃ for 3 hours in a nitrogen atmosphere to obtain a high-rate performance hard carbon anode material. The heating rate is 2℃ / min.

[0045] Example 3

[0046] S1. Pre-carbonization: The raw bamboo is crushed, passed through a 50-mesh sieve, and pre-fired in a box furnace to obtain hard carbon precursor material. The pre-firing heating rate is 10℃ / min, the temperature is 400℃, and the pre-firing time is 3h; the protective gas is nitrogen.

[0047] S2. Alkali etching for pore formation: The hard carbon precursor material obtained in step S1 and K2CO3 are added to a ball mill jar at a mass ratio of 1:0.2 (ball-to-material ratio 1:5). The mixture is ball-milled for 1 hour at 500 r / min using a planetary ball mill to obtain a mixed material. The mixed material is then heat-treated in a box furnace to obtain porous carbon material. The heating rate is 10℃ / min, the temperature is 800℃, and the heat treatment time is 1 hour. The protective gas is a mixture of 40% CO2 and 60% N2.

[0048] S3. Acid washing and impurity removal: The porous carbon material obtained in step S2 is subjected to acid washing, filtered, washed with water until neutral, and dried to obtain low-ash carbon material. The acid used is concentrated hydrochloric acid, the mass ratio of porous carbon material to concentrated hydrochloric acid is 1:5, the reaction temperature is 80℃, and the reaction time is 12h.

[0049] S4. Carbon Filling: The low-ash carbon material obtained in step S3 is subjected to liquid-phase impregnation filling. The mixture of the low-ash carbon material and the impregnation solution is flash-dried to obtain the filled carbon material. The impregnation solution is an N,N-dimethylformamide solution of asphalt, with the asphalt added at 5 wt% of the mass of the low-ash carbon material. The mass ratio of the low-ash carbon material to the N,N-dimethylformamide solvent is 1:2, and the impregnation time is 12 hours. The flash drying temperature is 180°C, and the solvent is recovered using a condenser.

[0050] S5. High-temperature carbonization: The filled carbon material obtained in step S4 is placed in a high-temperature carbonization furnace and held at 1200℃ for 3 hours in a nitrogen atmosphere to obtain a high-rate performance hard carbon anode material. The heating rate is 2℃ / min.

[0051] Example 4

[0052] S1. Pre-carbonization: The raw bamboo is crushed, passed through a 50-mesh sieve, and pre-fired in a box furnace to obtain hard carbon precursor material. The pre-firing heating rate is 10℃ / min, the temperature is 400℃, and the pre-firing time is 3h; the protective gas is nitrogen.

[0053] S2. Alkali etching for pore formation: The hard carbon precursor material obtained in step S1 and K2CO3 are added to a ball mill jar at a mass ratio of 1:0.1 (ball-to-material ratio 1:5). The mixture is ball-milled for 1 hour at 500 r / min using a planetary ball mill to obtain a mixed material. The mixed material is then heat-treated in a box furnace to obtain porous carbon material. The heating rate is 10℃ / min, the temperature is 900℃, and the heat treatment time is 1 hour. The protective gas is a mixture of 40% CO2 and 60% N2.

[0054] S3. Acid washing and impurity removal: The porous carbon material obtained in step S2 is subjected to acid washing, filtered, washed with water until neutral, and dried to obtain low-ash carbon material. The acid used is concentrated hydrochloric acid, the mass ratio of porous carbon material to concentrated hydrochloric acid is 1:5, the reaction temperature is 80℃, and the reaction time is 12h.

[0055] S4. Carbon Filling: The low-ash carbon material obtained in step S3 is subjected to liquid-phase impregnation filling. The mixture of the low-ash carbon material and the impregnation solution is flash-dried to obtain the filled carbon material. The impregnation solution is an N,N-dimethylformamide solution of asphalt, with the asphalt added at 5 wt% of the mass of the low-ash carbon material. The mass ratio of the low-ash carbon material to the N,N-dimethylformamide solvent is 1:2, and the impregnation time is 12 hours. The flash drying temperature is 180°C, and the solvent is recovered using a condenser.

[0056] S5. High-temperature carbonization: The filled carbon material obtained in step S4 is placed in a high-temperature carbonization furnace and held at 1200℃ for 3 hours in a nitrogen atmosphere to obtain a high-rate performance hard carbon anode material. The heating rate is 2℃ / min.

[0057] Example 5

[0058] S1. Pre-carbonization: The raw bamboo is crushed, passed through a 50-mesh sieve, and pre-fired in a box furnace to obtain hard carbon precursor material. The pre-firing heating rate is 10℃ / min, the temperature is 400℃, and the pre-firing time is 3h; the protective gas is nitrogen.

[0059] S2. Alkali etching for pore formation: The hard carbon precursor material obtained in step S1 and K2CO3 are added to a ball mill jar at a mass ratio of 1:0.1 (ball-to-material ratio 1:5). The mixture is ball-milled for 1 hour at 500 r / min using a planetary ball mill to obtain a mixed material. The mixed material is then heat-treated in a box furnace to obtain porous carbon material. The heating rate is 10℃ / min, the temperature is 800℃, and the heat treatment time is 2 hours. The protective gas is a mixture of 40% CO2 and 60% N2.

[0060] S3. Acid washing and impurity removal: The porous carbon material obtained in step S2 is subjected to acid washing, filtered, washed with water until neutral, and dried to obtain low-ash carbon material. The acid used is concentrated hydrochloric acid, the mass ratio of porous carbon material to concentrated hydrochloric acid is 1:5, the reaction temperature is 80℃, and the reaction time is 12h.

[0061] S4. Carbon Filling: The low-ash carbon material obtained in step S3 is subjected to liquid-phase impregnation filling. The mixture of the low-ash carbon material and the impregnation solution is flash-dried to obtain the filled carbon material. The impregnation solution is an N,N-dimethylformamide solution of asphalt, with the asphalt added at 5 wt% of the mass of the low-ash carbon material. The mass ratio of the low-ash carbon material to the N,N-dimethylformamide solvent is 1:2, and the impregnation time is 12 hours. The flash drying temperature is 180°C, and the solvent is recovered using a condenser.

[0062] S5. High-temperature carbonization: The filled carbon material obtained in step S4 is placed in a high-temperature carbonization furnace and held at 1200℃ for 3 hours in a nitrogen atmosphere to obtain a high-rate performance hard carbon anode material. The heating rate is 2℃ / min.

[0063] Example 6

[0064] S1. Pre-carbonization: The raw bamboo is crushed, passed through a 50-mesh sieve, and pre-fired in a box furnace to obtain hard carbon precursor material. The pre-firing heating rate is 10℃ / min, the temperature is 400℃, and the pre-firing time is 3h; the protective gas is nitrogen.

[0065] S2. Alkali etching for pore formation: The hard carbon precursor material obtained in step S1 and K2CO3 are added to a ball mill jar at a mass ratio of 1:0.1 (ball-to-material ratio 1:5). The mixture is ball-milled for 1 hour at 500 r / min using a planetary ball mill to obtain a mixed material. The mixed material is then heat-treated in a box furnace to obtain porous carbon material. The heating rate is 10℃ / min, the temperature is 800℃, and the heat treatment time is 1 hour. The protective gas is a mixture of 40% CO2 and 60% N2.

[0066] S3. Acid washing and impurity removal: The porous carbon material obtained in step S2 is subjected to acid washing, filtered, washed with water until neutral, and dried to obtain low-ash carbon material. The acid used is concentrated hydrochloric acid, the mass ratio of porous carbon material to concentrated hydrochloric acid is 1:5, the reaction temperature is 80℃, and the reaction time is 12h.

[0067] S4. Carbon Filling: The low-ash carbon material obtained in step S3 is subjected to liquid-phase impregnation filling. The mixture of the low-ash carbon material and the impregnation solution is flash-dried to obtain the filled carbon material. The impregnation solution is an N,N-dimethylformamide solution of asphalt, with the asphalt added at 10 wt% of the mass of the low-ash carbon material. The mass ratio of the low-ash carbon material to the N,N-dimethylformamide solvent is 1:2, and the impregnation time is 12 hours. The flash drying temperature is 180°C, and the solvent is recovered using a condenser.

[0068] S5. High-temperature carbonization: The filled carbon material obtained in step S4 is placed in a high-temperature carbonization furnace and held at 1200℃ for 3 hours in a nitrogen atmosphere to obtain a high-rate performance hard carbon anode material. The heating rate is 2℃ / min.

[0069] Example 7

[0070] S1. Pre-carbonization: The raw bamboo is crushed, passed through a 50-mesh sieve, and pre-fired in a box furnace to obtain hard carbon precursor material. The pre-firing heating rate is 10℃ / min, the temperature is 400℃, and the pre-firing time is 3h; the protective gas is nitrogen.

[0071] S2. Alkali etching for pore formation: The hard carbon precursor material obtained in step S1 and K2CO3 are added to a ball mill jar at a mass ratio of 1:0.1 (ball-to-material ratio 1:5). The mixture is ball-milled for 1 hour at 500 r / min using a planetary ball mill to obtain a mixed material. The mixed material is then heat-treated in a box furnace to obtain porous carbon material. The heating rate is 10℃ / min, the temperature is 800℃, and the heat treatment time is 1 hour. The protective gas is a mixture of 40% CO2 and 60% N2.

[0072] S3. Acid washing and impurity removal: The porous carbon material obtained in step S2 is subjected to acid washing, filtered, washed with water until neutral, and dried to obtain low-ash carbon material. The acid used is concentrated hydrochloric acid, the mass ratio of porous carbon material to concentrated hydrochloric acid is 1:5, the reaction temperature is 80℃, and the reaction time is 12h.

[0073] S4. Carbon Filling: The low-ash carbon material obtained in step S3 is subjected to liquid-phase impregnation filling. The mixture of the low-ash carbon material and the impregnation solution is flash-dried to obtain the filled carbon material. The impregnation solution is an N,N-dimethylformamide solution of asphalt, with the asphalt added at 5 wt% of the mass of the low-ash carbon material. The mass ratio of the low-ash carbon material to the N,N-dimethylformamide solvent is 1:2, and the impregnation time is 12 hours. The flash drying temperature is 180°C, and the solvent is recovered using a condenser.

[0074] S5. High-temperature carbonization: The filled carbon material obtained in step S4 is placed in a high-temperature carbonization furnace and held at 1300℃ for 3 hours in a nitrogen atmosphere to obtain a high-rate performance hard carbon anode material. The heating rate is 2℃ / min.

[0075] Example 8

[0076] S1. Pre-carbonization: The raw bamboo is crushed, passed through a 50-mesh sieve, and pre-fired in a box furnace to obtain hard carbon precursor material. The pre-firing heating rate is 10℃ / min, the temperature is 400℃, and the pre-firing time is 3h; the protective gas is nitrogen.

[0077] S2. Alkali etching for pore formation: The hard carbon precursor material obtained in step S1 and K2CO3 are added to a ball mill jar at a mass ratio of 1:0.1 (ball-to-material ratio 1:5). The mixture is ball-milled for 1 hour at 500 r / min using a planetary ball mill to obtain a mixed material. The mixed material is then heat-treated in a box furnace to obtain porous carbon material. The heating rate is 10℃ / min, the temperature is 800℃, and the heat treatment time is 1 hour. The protective gas is a mixture of 40% CO2 and 60% N2.

[0078] S3. Acid washing and impurity removal: The porous carbon material obtained in step S2 is subjected to acid washing, filtered, washed with water until neutral, and dried to obtain low-ash carbon material. The acid used is concentrated hydrochloric acid, the mass ratio of porous carbon material to concentrated hydrochloric acid is 1:5, the reaction temperature is 80℃, and the reaction time is 12h.

[0079] S4. Carbon Filling: The low-ash carbon material obtained in step S3 is subjected to liquid-phase impregnation filling. The mixture of the low-ash carbon material and the impregnation solution is flash-dried to obtain the filled carbon material. The impregnation solution is an N,N-dimethylformamide solution of asphalt, with the asphalt added at 5 wt% of the mass of the low-ash carbon material. The mass ratio of the low-ash carbon material to the N,N-dimethylformamide solvent is 1:2, and the impregnation time is 12 hours. The flash drying temperature is 180°C, and the solvent is recovered using a condenser.

[0080] S5. High-temperature carbonization: The filled carbon material obtained in step S4 is placed in a high-temperature carbonization furnace and held at 1100℃ for 3 hours in a nitrogen atmosphere to obtain a high-rate performance hard carbon anode material. The heating rate is 2℃ / min.

[0081] Example 9

[0082] S1. Pre-carbonization: The raw bamboo is crushed, passed through a 50-mesh sieve, and pre-fired in a box furnace to obtain hard carbon precursor material. The pre-firing heating rate is 10℃ / min, the temperature is 400℃, and the pre-firing time is 3h; the protective gas is nitrogen.

[0083] S2. Alkali etching for pore formation: The hard carbon precursor material obtained in step S1 and KOH are added to a ball mill jar at a mass ratio of 1:0.1 (ball-to-material ratio 1:5). The mixture is ball-milled for 1 hour at 500 r / min using a planetary ball mill to obtain a mixed material. The mixed material is then heat-treated in a box furnace to obtain porous carbon material. The heating rate is 10℃ / min, the temperature is 800℃, and the heat treatment time is 1 hour. The protective gas is a mixture of 40% CO2 and 60% N2.

[0084] S3. Acid washing and impurity removal: The porous carbon material obtained in step S2 is subjected to acid washing, filtered, washed with water until neutral, and dried to obtain low-ash carbon material. The acid used is concentrated hydrochloric acid, the mass ratio of porous carbon material to concentrated hydrochloric acid is 1:5, the reaction temperature is 80℃, and the reaction time is 12h.

[0085] S4. Carbon Filling: The low-ash carbon material obtained in step S3 is subjected to liquid-phase impregnation filling. The mixture of the low-ash carbon material and the impregnation solution is flash-dried to obtain the filled carbon material. The impregnation solution is an N,N-dimethylformamide solution of asphalt, with the asphalt added at 5 wt% of the mass of the low-ash carbon material. The mass ratio of the low-ash carbon material to the N,N-dimethylformamide solvent is 1:2, and the impregnation time is 12 hours. The flash drying temperature is 180°C, and the solvent is recovered using a condenser.

[0086] S5. High-temperature carbonization: The filled carbon material obtained in step S4 is placed in a high-temperature carbonization furnace and held at 1200℃ for 3 hours in a nitrogen atmosphere to obtain a high-rate performance hard carbon anode material. The heating rate is 2℃ / min.

[0087] Comparative Example 1

[0088] Replace K2CO3 in step S2 with Na2CO3, and the rest is the same as in Example 1.

[0089] Comparative Example 2

[0090] Replace K2CO3 in step S2 with NaOH, and the rest is the same as in Example 1.

[0091] Comparative Example 3

[0092] Replace K2CO3 in step S2 with CaCO3, and the rest is the same as in Example 1.

[0093] Comparative Example 4

[0094] The mass ratio of hard carbon precursor material to K2CO3 in step S2 is adjusted to 1:0, and the rest is the same as in Example 1.

[0095] Comparative Example 5

[0096] The mass ratio of hard carbon precursor material to K2CO3 in step S2 was adjusted to 1:0.3, and the rest was the same as in Example 1.

[0097] Comparative Example 6

[0098] The alkaline etching temperature in step S2 is adjusted to 600°C, and the rest is the same as in Example 1.

[0099] Comparative Example 7

[0100] The alkaline etching temperature in step S2 is adjusted to 1000℃, and the rest is the same as in Example 1.

[0101] Comparative Example 8

[0102] The alkaline etching time in step S2 was adjusted to 3 hours, and the rest was the same as in Example 1.

[0103] Comparative Example 9

[0104] The amount of asphalt added in step S4 was adjusted to 15 wt% of the mass of the low-ash carbon material, and the rest was the same as in Example 1.

[0105] Comparative Example 10

[0106] Step S4 is omitted; the rest is the same as in Example 1.

[0107] Comparative Example 11

[0108] The high-temperature carbonization temperature in step S5 is adjusted to 1000℃, and the rest is the same as in Example 1.

[0109] Comparative Example 12

[0110] The high-temperature carbonization temperature in step S5 is adjusted to 1400℃, and the rest is the same as in Example 1.

[0111] Comparative Example 13

[0112] JH3-5 bamboo-based activated carbon from Zhejiang Jizhu Biotechnology Co., Ltd. was purchased directly as a low-ash carbon material, and steps S4 and S5 were performed under the same conditions as in Example 1.

[0113] First, the pore size distribution of hard carbon was analyzed by small-angle X-ray scattering (SAXS) measurement and SASFIT software. The specific surface area of ​​hard carbon was obtained by N2 desorption test based on BET theory. The true density of hard carbon was obtained by a true density meter. The results are shown in Table 1.

[0114] Furthermore, the hard carbon materials prepared in the various embodiments and comparative examples were used as negative electrode active materials for sodium-ion secondary batteries. According to a mass ratio of 92%:3%:1.5%:3.5%, 184 mg of the above-mentioned hard carbon powder, 6 mg of conductive carbon black, 6 mg of a 2% (w / w) carboxymethyl cellulose solution, and 17.5 mg of a 40% (w / w) styrene-butadiene rubber were weighed out, and an appropriate amount of deionized water was added. The mixture was stirred for 20 minutes until a uniform slurry was formed. This slurry was then uniformly coated onto the surface of a copper (Cu) foil using a 100 μm scraper. The slurry was dried in a 105°C forced-air drying oven for 2 hours. The Cu foil containing the active material was then cut into circular negative electrode sheets and transferred to a glove box for later use.

[0115] The simulated battery assembly was carried out in a MIKROUNA glove box filled with Ar atmosphere. A prepared carbon material electrode was used as the negative electrode, 1.0 mol / L NaPF6 in DME as the electrolyte, and a Na metal sheet as the counter electrode to assemble a 2016 coin cell. After resting for 12 hours, the battery underwent its first charge-discharge test at 0.1C, with a voltage range of 0–2V. Rate charge-discharge tests were then conducted at rates from 0.1 to 5C. The test results are shown in Table 1.

[0116] Table 1

[0117]

[0118]

[0119] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

[0120] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a high-ratio hard carbon material, characterized in that, include: The pre-carbonized hard carbon precursor was reacted with an alkali at a temperature of 800-900℃ for 1 hour to obtain a porous carbon material; the alkali was KOH or K2CO3; the mass ratio of the hard carbon precursor to the alkali was 1:0.

2. The porous carbon material is acid-washed with an acid solution to obtain a low-ash carbon material. The low-ash carbon material is subjected to liquid-phase impregnation and carbon filler filling treatment to obtain filled carbon material, which is then subjected to high-temperature carbonization treatment at 1100-1200℃ to obtain high-ratio hard carbon material; the amount of carbon filler added is 5wt% of the mass of the low-ash carbon material. The low-ash carbon material is subjected to a carbon filler filling treatment by liquid phase impregnation to obtain a filled carbon material. The solvent used is one or more of deionized water, N,N-dimethylamide, N-methylpyrrolidone, benzene, toluene, and ethanol. The mass ratio of the low-ash carbon material to the solvent is 1:

2. The impregnation time is 12 hours.

2. The method for preparing high-ratio hard carbon material according to claim 1, characterized in that, In the step of reacting the pre-carbonized hard carbon precursor with an alkali at a temperature of 800-900℃ for 1-2 hours to obtain porous carbon material, the protective gas is one or more of nitrogen, argon, and CO2.

3. The method for preparing high-ratio hard carbon material according to claim 1, characterized in that, The conditions for the high-temperature carbonization treatment are: a heating rate of 2℃ / min and a carbonization time of 3h.

4. The method for preparing high-ratio hard carbon material according to claim 1, characterized in that, The carbon filler is one or more of asphalt, phenolic resin, epoxy resin, starch, lignin, and bamboo tar.

5. The method for preparing high-ratio hard carbon material according to claim 1, characterized in that, In the step of acid washing the porous carbon material with an acid solution to obtain low-ash carbon material, the mass ratio of porous carbon material to acid solution is 1:5; the reaction temperature is 80℃; and the reaction time is 12h.

6. The method for preparing high-ratio hard carbon material according to claim 1, characterized in that, The acid solution is one or more of HCl, HNO3, H2SO4, formic acid, acetic acid, and citric acid.

7. The method for preparing high-ratio hard carbon material according to claim 1, characterized in that, The pre-carbonization treatment conditions are as follows: heating rate of 2-10℃ / min, pretreatment temperature of 300-800℃, pretreatment time of 1-24h, and protective gas of nitrogen and / or argon.

8. A high-ratio hard carbon material, characterized in that, The high-ratio hard carbon material is prepared by the preparation method of the high-ratio hard carbon material according to any one of claims 1-7.

9. A sodium-ion battery, characterized in that, The sodium-ion battery includes the high-rate hard carbon material as described in claim 8.

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