Rate type sodium ion battery hard carbon negative electrode material and preparation method thereof

Abstract

The invention discloses a rate type sodium ion battery hard carbon negative electrode material and a preparation method thereof, and the preparation method comprises the following steps: S1, preparation of a precursor mixed solution: mixing a carbon source, a graphitizing agent, a conductive agent, a dispersing agent and an inorganic acid liquid phase to generate the precursor mixed solution; s2, drying treatment: carrying out drying treatment to obtain a dried precursor mixture; s3, low-temperature catalytic graphitization: carrying out low-temperature carbonization in a protective atmosphere to obtain a graphitized pre-carbonized precursor; s4, alkali washing of the pre-carbonized precursor: washing the pre-carbonized precursor in an alkali washing solution, then washing the pre-carbonized precursor with water until the pH is neutral, and then centrifuging and drying the pre-carbonized precursor to obtain the pre-carbonized precursor without the graphitizing agent; s5, crushing and refining: crushing to obtain a refined carbonized precursor; and S6, high-temperature carbonization: carrying out high-temperature graphitization in a protective atmosphere to obtain the final hard carbon negative electrode material. The preparation method of the rate type sodium ion battery hard carbon negative electrode material has the characteristics of excellent rate performance, high first charge-discharge efficiency and low cost.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and specifically refers to a rate-capable sodium-ion battery hard carbon negative electrode material and a preparation method thereof. Background Art

[0002] With the surging global demand for renewable energy storage, sodium-ion batteries have become an important supplementary technology to lithium-ion batteries due to their advantages such as rich resources, low cost, and high safety.

[0003] Hard carbon materials are regarded as the preferred materials for the negative electrodes of sodium-ion batteries due to their high sodium storage capacity, low expansion rate, and excellent cycle stability. However, existing hard carbon negative electrodes still face problems such as poor rate performance, which has become a key bottleneck in industrial applications.

[0004] The electrochemical performance of hard carbon materials is mainly restricted by problems such as narrow carbon layer spacing, poor electron conductivity, and many internal defects. The kinetics of ion transport inside the hard carbon material is closely related to its layer spacing (d 002 ). The layer spacing (0.36 - 0.42) of hard carbon materials is closely related to their carbonization temperature. Traditional hard carbon preparation processes require high temperatures (≥1300 °C) to increase the degree of graphitization, but high temperatures easily lead to a contraction of the layer spacing (<0.37 nm), increasing the sodium ion diffusion barrier and resulting in a decline in rate performance. Although low-temperature carbonization can retain a relatively large layer spacing (>0.37 nm), it is accompanied by problems such as low graphitization degree, high defect content, and large specific surface area, resulting in a relatively low first-cycle efficiency. The low graphitization degree and structural defects lead to poor electron conductivity of the material, which also restricts the high-rate charge and discharge performance. In addition, the large specific surface area and defect degree are prone to irreversible reactions (irreversible decomposition of the electrolyte on the material surface and irreversible storage of sodium ions inside the material), resulting in a low initial Coulomb efficiency (ICE) and cyclic capacity attenuation.

[0005] Currently, the electronic structure of hard carbon materials can be regulated by heteroatom doping modification (N, S, P, O) to improve the electron conductivity. However, this method simultaneously introduces a large number of defects inside the material, and excessive defects will exacerbate side reactions, reduce the ICE of the material, and affect the cycle stability.

[0006] At the same time, the catalytic carbonization using metal ions (Fe, Ni, Co, etc.) can promote the oriented growth of graphite microcrystals, but it will also cause a large number of carbon layer spacings to narrow (<0.36 nm), making it difficult for sodium ions to be embedded between carbon layers. Coating the surface of soft carbon (pitch coating, CVD, etc.) can repair the surface defects of hard carbon materials and improve the ICE, but this method can only repair the surface defects of hard carbon materials and cannot repair the internal defects of the material body phase. Moreover, the coating layer may hinder ion diffusion, resulting in a decline in rate performance.

[0007] To address the above issues, achieving a hard carbon anode material with a wide carbon layer spacing, high electronic conductivity, and low defect degree is the key to promoting the commercialization of hard carbon anodes for sodium-ion batteries. Summary of the Invention

[0008] The object of the present invention is to provide a hard carbon anode material for high-rate sodium-ion batteries and a preparation method thereof, which have the characteristics of excellent rate performance, high first charge-discharge efficiency, and low cost.

[0009] The present invention can be realized through the following technical solutions:

[0010] The present invention relates to a preparation method of a hard carbon anode material for high-rate sodium-ion batteries, comprising the following steps:

[0011] S1. Preparation of the precursor mixture solution: Mix a carbon source, a graphitizing agent, a conductive agent, a dispersant, and an inorganic acid in liquid phase to generate a precursor mixture solution;

[0012] S2. Drying treatment: Dry the precursor mixture solution obtained in step S1 to obtain a dried precursor mixture;

[0013] S3. Low-temperature catalytic graphitization: Carbonize the precursor mixture obtained in step S2 at low temperature in a protective atmosphere to obtain a pre-carbonized precursor with graphitization;

[0014] S4. Alkaline washing of the pre-carbonized precursor: Wash the pre-carbonized precursor obtained in step S3 in an alkaline washing solution, then wash with water until the pH is neutral, and then centrifuge and dry to obtain a pre-carbonized precursor without a graphitizing agent;

[0015] S5. Crushing and refining: Crush the pre-carbonized precursor without a graphitizing agent obtained in step S4 to obtain a refined carbonized precursor;

[0016] S6. High-temperature carbonization: Graphitize the refined carbonized precursor obtained in step S4 at high temperature in a protective atmosphere to obtain the final hard carbon anode material.

[0017] In the present invention, during step S1, the conductive agent penetrates into the carbon source, and during the subsequent heat treatment process, the conductive agent is tightly combined with the carbon material under the action of thermodynamics and is uniformly distributed inside the hard carbon material, forming an electrical network inside the hard carbon material to rapidly transport electrons. Combined with a high ion transport rate (wide carbon layer spacing), it exhibits high kinetic characteristics; in step S2, the purpose of this drying is to reduce the moisture content of the material to below 3%, and there is no limitation on the specific drying method, and any drying method that can achieve this purpose is acceptable.

[0018] Further, in step S3, the control conditions for low-temperature catalytic graphitization are as follows: the heating rate is 1-10 °C / min, the heat preservation time is 2-5 h, the heat preservation temperature is 400-1650 °C, and the protective atmosphere is nitrogen and / or argon.

[0019] In step S3, the carbon source is carbonized by heating, and the carbon layers grow directionally under the catalysis of the graphitizing agent, achieving a certain degree of graphitization at a relatively low temperature. The low temperature also ensures a wide carbon layer spacing.

[0020] Further, in step S6, the conditions for high-temperature carbonization are as follows: the heating rate is 1-10 °C / min, the heat preservation time is 2-8 h, the heat preservation temperature is 900-1200 °C, and the protective atmosphere is nitrogen and / or argon.

[0021] Compared with the traditional hard carbon preparation process that requires high temperature (≥1300 °C) to improve the graphitization degree, ensure sufficient electronic conductivity performance and fewer internal and external defects of the material. In the present invention, the graphitizing agent is used to catalyze graphitization at low temperature. While the carbon layers grow, the defects are reduced, and rich graphite-like microcrystalline seeds are in-situ constructed inside the carbon material. During the high-temperature heat treatment process, the carbon layers further grow on the original basis and the defects are reduced. Therefore, the effects of the traditional hard carbon at high treatment temperatures can be achieved at a relatively low treatment temperature (900~1200 °C), and the low treatment temperature ensures a relatively wide carbon layer spacing (≥0.38 nm).

[0022] Further, in step S1, the graphitizing agent is one or more of boron-based substances H3BO3, B2O3, boron powder, Na2B4O7, Na2B4O7, and the addition amount of the graphitizing agent is 0.1-1.5 wt.% of the addition amount of the carbon source. As an efficient graphitization catalyst, the boron-based substance can achieve a good catalytic effect with a relatively small addition amount. Therefore, the addition amount should not be too high. An excessive addition amount will result in too high a graphitization degree of the hard carbon material and too regular a structure, which is not conducive to the rapid transmission of sodium ions.

[0023] Further, the addition amount of the conductive agent is 0.2-1.5 wt.% of the addition amount of the carbon source. The conductive agent is used to construct a conductive network inside the hard carbon material to quickly transport electrons. Its own ion transport performance is not good. Therefore, the addition amount should not be too high, and a balance needs to be built between ionic conductivity and electronic conductivity.

[0024] Further, in step S1, the dispersion system is one or more of sodium dodecylbenzenesulfonate, sodium dodecylsulfonate, cetyltrimethylammonium bromide, polyvinylpyrrolidone (PVP), polyethylene glycol, polyvinyl alcohol, polyacrylamide, polyethyleneimine, sodium carboxymethylcellulose, and polyacrylic acid, and the addition amount of the dispersant is 0.05-1 wt.% of the addition amount of the carbon source. The addition of the dispersant is to disperse the conductive agent with poor hydrophilicity in the aqueous solution to achieve the purpose of uniformly dispersing the conductive agent.

[0025] Further, in step S1, the inorganic acid is one or more of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and the addition amount of the inorganic acid is 0.5-5 wt.% of the addition amount of the carbon source; the liquid-phase reaction is carried out at a temperature of 50-90 °C for a reaction time of 1-5 h.

[0026] In step S1, the addition of the acid solution and heating can hydrolyze the cellulose part in the biomass carbon source, destroy the dense original structure of the biomass, and enable the graphitizing agent and the conductive agent to better penetrate into the interior of the carbon source. If the addition amount of the acid solution or the heating temperature is too low, the purpose of acid hydrolysis of cellulose cannot be achieved. If the addition amount of the acid solution or the heating temperature is too high, the cellulose structure of the biomass will be significantly damaged, resulting in the collapse of the biomass structure and poor electrochemical performance.

[0027] Further, in step S1, the carbon source is one or more of coconut shell powder, apricot shell powder, walnut shell powder, nut shell powder, wood powder, bamboo powder, reed powder, coal powder, phenolic resin, and epoxy resin.

[0028] Further, in step S4, the alkaline cleaning solution is one or more of NaOH, KOH, Na2CO3, and K2CO3. The purpose of alkaline cleaning is to remove the boride in the carbonized precursor to avoid excessive narrowing of the carbon layer spacing during subsequent high-temperature treatment.

[0029] Further, in step S5, the pulverization method is one or more of roll, jaw crusher, mechanical mill, jet mill, Raymond mill, and ball mill, and the carbon particles are pulverized to a D50 of 3-12 μm.

[0030] Another aspect of the present invention is to protect a hard carbon negative electrode material for a high-rate sodium-ion battery, which is prepared by the above preparation method.

[0031] The hard carbon negative electrode material for a high-rate sodium-ion battery and its preparation method of the present invention have the following beneficial effects:

[0032] First, excellent rate performance. The present invention regulates the layer spacing and graphitization degree through a multi-stage temperature carbonization strategy, and at the same time constructs a conductive network inside the material, enabling the hard carbon material to have good ion transport and electron transport characteristics at the same time, and realizing high-rate performance;

[0033] Second, the first charge-discharge efficiency is high. During the preparation process of the present invention, by adding a graphitizing agent and controlling at a lower treatment temperature, a lower defect degree is achieved, ensuring the first charge-discharge efficiency.

[0034] Third, the cost is low. The present invention realizes the purpose of reducing the high-temperature sintering temperature by adding a small amount of graphitizing agent, and prepares the hard carbon material through low-temperature graphitization and high-temperature graphitization, reducing the production energy consumption. Description of the Drawings

[0035] Figure 1 It is the SEM image of the hard carbon material of Application Example 1.

[0036] Figure 2 It is the SEM image of the hard carbon material of Comparative Example 1.

[0037] Figure 3 It is the comparison of the conductivity of the hard carbon materials of the application example and Comparative Example 1 under different pressures. Detailed Embodiments

[0038] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the products of the present invention will be further described in detail below in conjunction with the embodiments.

[0039] The present invention relates to a preparation method of a hard carbon negative electrode material for a high-rate sodium ion battery, comprising the following steps:

[0040] S1. Preparation of the precursor mixed solution: Mix a carbon source, a graphitizing agent, a conductive agent, a dispersant, and an inorganic acid liquid phase to generate a precursor mixed solution;

[0041] S2. Drying treatment: Dry the precursor mixed solution obtained in step S1 to obtain a dried precursor mixture;

[0042] S3. Low-temperature catalytic graphitization: Carbonize the precursor mixture obtained in step S2 at a low temperature in a protective atmosphere to obtain a graphitized pre-carbonized precursor;

[0043] S4. Alkaline washing of the pre-carbonized precursor: Wash the pre-carbonized precursor obtained in step S3 in an alkaline washing solution, then wash with water until the pH is neutral, and then centrifuge and dry to obtain a pre-carbonized precursor without a graphitizing agent;

[0044] S5. Crushing and refining: Crush the pre-carbonized precursor without a graphitizing agent obtained in step S4 to obtain a refined carbonized precursor;

[0045] S6. High-temperature carbonization: Graphitize the refined carbonized precursor obtained in step S4 at a high temperature in a protective atmosphere to obtain the final hard carbon negative electrode material.

[0046] Further, in step S3, the control conditions for low-temperature catalytic graphitization are as follows: the heating rate is 1-10 °C / min, the heat preservation time is 2-5 h, the heat preservation temperature is 400-1650 °C, and the protective atmosphere is nitrogen and / or argon.

[0047] Further, in step S6, the conditions for high-temperature carbonization are as follows: the heating rate is 1-10 °C / min, the heat preservation time is 2-8 h, the heat preservation temperature is 900-1200 °C, and the protective atmosphere is nitrogen and / or argon.

[0048] Further, in step S1, the graphitizing agent is one or more of boron-based substances such as H3BO3, B2O3, boron powder, Na2B4O7, and Na2B4O7, and the addition amount of the graphitizing agent is 0.1-1.5 wt.% of the addition amount of the carbon source.

[0049] Further, the addition amount of the conductive agent is 0.2-1.5 wt.% of the addition amount of the carbon source.

[0050] Further, in step S1, the dispersion system is one or more of sodium dodecylbenzenesulfonate, sodium dodecylsulfonate, cetyltrimethylammonium bromide, polyvinylpyrrolidone (PVP), polyethylene glycol, polyvinyl alcohol, polyacrylamide, polyethyleneimine, sodium carboxymethylcellulose, and polyacrylic acid, and the addition amount of the dispersant is 0.05-1 wt.% of the addition amount of the carbon source.

[0051] Further, in step S1, the inorganic acid is one or more of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and the addition amount of the inorganic acid is 0.5-5 wt.% of the addition amount of the carbon source; the liquid-phase reaction temperature is 50-90 °C, and the reaction time is 1-5 h.

[0052] Further, in step S1, the carbon source is one or more of coconut shell powder, apricot shell powder, walnut shell powder, nut shell powder, wood powder, bamboo powder, reed powder, coal powder, phenolic resin, and epoxy resin.

[0053] Further, in step S4, the alkaline cleaning solution is one or more of NaOH, KOH, Na2CO3, and K2CO3.

[0054] Further, in step S5, the pulverization method is one or more of roll crusher, jaw crusher, mechanical mill, jet mill, Raymond mill, and ball mill, and the carbon particles are pulverized to D50 of 3-12 μm.

[0055] Another aspect of the present invention is to protect a hard carbon negative electrode material for a high-rate sodium-ion battery, which is prepared by the above preparation method.

[0056] Example 1

[0057] This embodiment relates to a hard carbon anode material for a high-rate sodium-ion battery, and its preparation method includes the following steps:

[0058] S1. Preparation of the precursor mixture: Mix the carbon source, graphitizing agent, conductive agent, dispersant, and inorganic acid in liquid phase to generate a precursor mixture. Specifically, the graphitizing agent is a boron-based substance such as H3BO3, B2O3, and Na2B4O7, and the addition amount of the graphitizing agent is 1.5 wt.% of the addition amount of the carbon source; the addition amount of the conductive agent is 1 wt.% of the addition amount of the carbon source; the dispersant is sodium dodecylbenzenesulfonate or sodium dodecylsulfonate, and the addition amount of the dispersant is 0.05 wt.% of the addition amount of the carbon source; the inorganic acid is hydrochloric acid or sulfuric acid, and the addition amount of the inorganic acid is 5 wt.% of the addition amount of the carbon source; the liquid-phase reaction temperature is 70 °C and the reaction time is 1 h; the carbon source is coconut shell powder, apricot shell powder, or walnut shell powder.

[0059] S2. Drying treatment: Dry the precursor mixture obtained in step S1 to obtain a dried precursor mixture.

[0060] S3. Low-temperature catalytic graphitization: Carbonize the precursor mixture obtained in step S2 at low temperature in a protective atmosphere to obtain a pre-carbonized precursor with graphitization. Specifically, the control conditions for low-temperature catalytic graphitization are: heating rate of 10 °C / min, holding time of 3 h, holding temperature of 400 °C, and the protective atmosphere is nitrogen and argon.

[0061] S4. Alkaline washing of the pre-carbonized precursor: Wash the pre-carbonized precursor obtained in step S3 in an alkaline washing solution, then wash with water until the pH is neutral, and then centrifuge and dry to obtain a pre-carbonized precursor without a graphitizing agent. Specifically, the alkaline washing solution is NaOH or KOH.

[0062] S5. Crushing and refinement: Crush the pre-carbonized precursor without a graphitizing agent obtained in step S4 to obtain a refined carbonized precursor. Specifically, the crushing method is roll crushing or jaw crushing.

[0063] S6. High-temperature carbonization: Graphitize the refined carbonized precursor obtained in step S4 at high temperature in a protective atmosphere to obtain the final hard carbon anode material. Specifically, the conditions for high-temperature carbonization are: heating rate of 10 °C / min, holding time of 5 h, holding temperature of 900 °C, and the protective atmosphere is nitrogen and argon.

[0064] Example 2

[0065] This embodiment relates to a hard carbon anode material for a high-rate sodium-ion battery, and its preparation method includes the following steps:

[0066] S1. Preparation of precursor mixture: A carbon source, a graphitizing agent, a conductive agent, a dispersant, and an inorganic acid are mixed in liquid phase to generate a precursor mixture. Specifically, the graphitizing agent is boron powder and Na2B4O7 in the boron series, and the addition amount of the graphitizing agent is 1 wt.% of the addition amount of the carbon source; the addition amount of the conductive agent is 0.2 wt.% of the addition amount of the carbon source; the dispersant is polyethyleneimine, sodium carboxymethylcellulose, and polyacrylic acid, and the addition amount of the dispersant is 1 wt.% of the addition amount of the carbon source; the inorganic acid is sulfuric acid, and the addition amount of the inorganic acid is 3 wt.% of the addition amount of the carbon source; the liquid-phase reaction is carried out at a temperature of 50 °C for a reaction time of 5 h; the carbon source is coconut shell powder, phenolic resin, and epoxy resin.

[0067] S2. Drying treatment: The precursor mixture obtained in step S1 is dried to obtain a dried precursor mixture.

[0068] S3. Low-temperature catalytic graphitization: The precursor mixture obtained in step S2 is carbonized at low temperature in a protective atmosphere to obtain a graphitized pre-carbonized precursor. Specifically, the control conditions for low-temperature catalytic graphitization are: heating rate 5 °C / min, holding time 2 h, holding temperature 1650 °C, and the protective atmosphere is nitrogen.

[0069] S4. Alkaline washing of the pre-carbonized precursor: The pre-carbonized precursor obtained in step S3 is washed in an alkaline washing solution, then washed with water until the pH is neutral, and then centrifuged and dried to obtain a pre-carbonized precursor without a graphitizing agent. Specifically, the alkaline washing solution is NaOH and K2CO3.

[0070] S5. Crushing and refining: The pre-carbonized precursor without a graphitizing agent obtained in step S4 is crushed to obtain a refined carbonized precursor. Specifically, the crushing method is Raymond mill and ball mill.

[0071] S6. High-temperature carbonization: The refined carbonized precursor obtained in step S4 is graphitized at high temperature in a protective atmosphere to obtain the final hard carbon negative electrode material. Specifically, the conditions for high-temperature carbonization are: heating rate 5 °C / min, holding time 2 h, holding temperature 1200 °C, and the protective atmosphere is argon.

[0072] Example 3

[0073] This example relates to a hard carbon negative electrode material for a high-rate sodium-ion battery, and its preparation method includes the following steps:

[0074] S1. Preparation of precursor mixture: A carbon source, a graphitizing agent, a conductive agent, a dispersant, and an inorganic acid are mixed in liquid phase to generate a precursor mixture. Specifically, the graphitizing agent is a boron-based substance, Na2B4O7, and the addition amount of the graphitizing agent is 0.2 wt.% of the addition amount of the carbon source; the addition amount of the conductive agent is 1.5 wt.% of the addition amount of the carbon source; the dispersant is sodium dodecylbenzenesulfonate, polyvinyl alcohol, polyacrylamide, polyethyleneimine, sodium carboxymethyl cellulose, polyacrylic acid, and the addition amount of the dispersant is 0.5 wt.% of the addition amount of the carbon source; the inorganic acid is phosphoric acid, and the addition amount of the inorganic acid is 5 wt.% of the addition amount of the carbon source; the liquid-phase reaction is carried out at a temperature of 80 °C for a reaction time of 1 h; the carbon source is wood powder, bamboo powder, reed powder, coal powder, phenolic resin, and epoxy resin.

[0075] S2. Drying treatment: The precursor mixture obtained in step S1 is dried to obtain a dried precursor mixture.

[0076] S3. Low-temperature catalytic graphitization: The precursor mixture obtained in step S2 is carbonized at low temperature in a protective atmosphere to obtain a graphitized pre-carbonized precursor. Specifically, the control conditions for low-temperature catalytic graphitization are: heating rate of 1 °C / min, holding time of 5 h, holding temperature of 1050 °C, and the protective atmosphere is nitrogen and argon.

[0077] S4. Alkaline washing of the pre-carbonized precursor: The pre-carbonized precursor obtained in step S3 is washed in an alkaline washing solution, then washed with water until the pH is neutral, and then centrifuged and dried to obtain a pre-carbonized precursor without a graphitizing agent. Specifically, the alkaline washing solution is KOH, Na2CO3.

[0078] S5. Crushing and refining: The pre-carbonized precursor without a graphitizing agent obtained in step S4 is crushed to obtain a refined carbonized precursor. Specifically, the crushing method is jet milling and ball milling.

[0079] S6. High-temperature carbonization: The refined carbonized precursor obtained in step S4 is graphitized at high temperature in a protective atmosphere to obtain the final hard carbon negative electrode material. Specifically, the conditions for high-temperature carbonization are: heating rate of 1 °C / min, holding time of 8 h, holding temperature of 1100 °C, and the protective atmosphere is nitrogen and argon.

[0080] Example 4

[0081] This example relates to a hard carbon negative electrode material for a rate-type sodium-ion battery, and its preparation method includes the following steps:

[0082] S1. Preparation of precursor mixture: A carbon source, a graphitizing agent, a conductive agent, a dispersant, and an inorganic acid are mixed in liquid phase to form a precursor mixture. Specifically, the graphitizing agent is a boron-based substance H3BO3 or Na2B4O7, and the addition amount of the graphitizing agent is 0.5 wt.% of the addition amount of the carbon source; the addition amount of the conductive agent is 0.5 wt.% of the addition amount of the carbon source; the dispersant is polyvinylpyrrolidone (PVP), polyethylene glycol, polyvinyl alcohol, polyacrylamide, or polyvinyl iminodiacetic acid, and the addition amount of the dispersant is 0.1 wt.% of the addition amount of the carbon source; the inorganic acid is hydrochloric acid or sulfuric acid, and the addition amount of the inorganic acid is 2 wt.% of the addition amount of the carbon source; the liquid-phase reaction is carried out at a temperature of 60 °C for 3 h; the carbon source is coconut shell powder, apricot shell powder, or walnut shell powder.

[0083] S2. Drying treatment: The precursor mixture obtained in step S1 is dried to obtain a dried precursor mixture.

[0084] S3. Low-temperature catalytic graphitization: The precursor mixture obtained in step S2 is carbonized at low temperature in a protective atmosphere to obtain a graphitized pre-carbonized precursor. Specifically, the control conditions for low-temperature catalytic graphitization are: heating rate 4 °C / min, holding time 4 h, holding temperature 1250 °C, and the protective atmosphere is nitrogen and argon.

[0085] S4. Alkaline washing of the pre-carbonized precursor: The pre-carbonized precursor obtained in step S3 is washed in an alkaline washing solution, then washed with water until the pH is neutral, and then centrifuged and dried to obtain a pre-carbonized precursor without a graphitizing agent. Specifically, the alkaline washing solution is NaOH or Na2CO3.

[0086] S5. Crushing and refining: The pre-carbonized precursor without a graphitizing agent obtained in step S4 is crushed to obtain a refined carbonized precursor. Specifically, the crushing method is mechanical grinding or jet milling.

[0087] S6. High-temperature carbonization: The refined carbonized precursor obtained in step S4 is graphitized at high temperature in a protective atmosphere to obtain the final hard carbon negative electrode material. Specifically, the conditions for high-temperature carbonization are: heating rate 6 °C / min, holding time 4 h, holding temperature 1000 °C, and the protective atmosphere is argon.

[0088] Example 5

[0089] This example relates to a hard carbon negative electrode material for a rate-type sodium-ion battery, and its preparation method includes the following steps:

[0090] S1. Preparation of precursor mixture: A carbon source, a graphitizing agent, a conductive agent, a dispersant, and an inorganic acid are mixed in liquid phase to form a precursor mixture. Specifically, the graphitizing agent is a boron-based substance such as H3BO3, B2O3, Na2B4O7, Na2B4O7, and the addition amount of the graphitizing agent is 0.9 wt.% of the addition amount of the carbon source; the addition amount of the conductive agent is 0.7 wt.% of the addition amount of the carbon source; the dispersant is sodium dodecylbenzenesulfonate, polyethylene glycol, polyvinyl alcohol, polyacrylamide, polyethyleneimine, sodium carboxymethylcellulose, polyacrylic acid, and the addition amount of the dispersant is 1 wt.% of the addition amount of the carbon source; the inorganic acid is hydrochloric acid and phosphoric acid, and the addition amount of the inorganic acid is 2 wt.% of the addition amount of the carbon source; the liquid-phase reaction is carried out at a temperature of 70 °C for a reaction time of 1 - 5 h; the carbon source is coconut shell powder, apricot shell powder, or walnut shell powder.

[0091] S2. Drying treatment: The precursor mixture obtained in step S1 is dried to obtain a dried precursor mixture.

[0092] S3. Low-temperature catalytic graphitization: The precursor mixture obtained in step S2 is carbonized at low temperature in a protective atmosphere to obtain a graphitized pre-carbonized precursor. Specifically, the control conditions for low-temperature catalytic graphitization are: heating rate of 7 °C / min, holding time of 3 h, holding temperature of 850 °C, and the protective atmosphere is nitrogen.

[0093] S4. Alkaline washing of the pre-carbonized precursor: The pre-carbonized precursor obtained in step S3 is washed in an alkaline washing solution, then washed with water until the pH is neutral, and then centrifuged and dried to obtain a pre-carbonized precursor without a graphitizing agent. Specifically, the alkaline washing solution is NaOH, KOH, Na2CO3, or K2CO3.

[0094] S5. Crushing and refining: The pre-carbonized precursor without a graphitizing agent obtained in step S4 is crushed to obtain a refined carbonized precursor. Specifically, the crushing method is roll crushing or jaw crushing.

[0095] S6. High-temperature carbonization: The refined carbonized precursor obtained in step S4 is graphitized at high temperature in a protective atmosphere to obtain the final hard carbon negative electrode material. Specifically, the conditions for high-temperature carbonization are: heating rate of 8 °C / min, holding time of 7 h, holding temperature of 1100 °C, and the protective atmosphere is nitrogen and argon.

[0096] Application Example 1

[0097] This example relates to a hard carbon negative electrode material for a high-rate sodium-ion battery, and its preparation method includes the following steps:

[0098] S1. Preparation of precursor mixture: walnut shell powder, boric acid, carbon nanotubes, PVP and sulfuric acid are mixed in liquid phase and reacted for a certain time to generate a precursor mixture; wherein the addition amounts of boric acid, carbon nanotubes, PVP and sulfuric acid are 0.5, 0.8, 0.1 and 3 wt.% of the carbon source addition amount, respectively; the reaction temperature is 80°C and the reaction time is 2h.

[0099] S2, drying treatment: drying the precursor mixture obtained in step S1 to obtain a dry precursor mixture;

[0100] S3, low-temperature catalytic graphitization: the precursor mixture obtained in step S2 is carbonized at low temperature in a nitrogen atmosphere, with a heating rate of 5°C / min, a holding time of 2.5 h, and a holding temperature of 550°C to obtain a graphitized pre-carbonized precursor;

[0101] S4, alkaline washing of the pre-carbonized precursor: washing the pre-carbonized precursor obtained in step S3 in a NaOH washing solution, then washing with water until the pH is neutral, then centrifuging and drying to obtain a pre-carbonized precursor free of a graphitizing agent;

[0102] S5, pulverizing and refining: the pre-carbonized precursor without graphitizing agent obtained in step S4 is pulverized by air flow to obtain a refined carbonized precursor with a D50 of 8 μm;

[0103] S6. High-temperature carbonization: The refined carbonized precursor obtained in step S4 is graphitized at high temperature in an inert gas atmosphere at a heating rate of 5°C / min, a holding time of 4 h, and a holding temperature of 1100°C to obtain a final hard carbon negative electrode material.

[0104] The electrochemical performance of the obtained material was tested according to the following method: hard carbon material, Super P, CMC, SBR were mixed into a homogenous slurry at a mass ratio of 94: 1.5: 2: 2.5, and the black slurry was coated on copper foil using a 120 um four-sided preparation device, and then the film was dried in a vacuum drying oven at 100°C for 2 hours. The electrode film was punched into a disc with a radius of 0.6 mm using a punching machine, and metallic sodium was used as the counter electrode, 1 mol / L NaClO4 EC+DEC (1:1 vol%) was used as the electrolyte, and the diaphragm was a PP / PE / PP three-layer diaphragm, and assembled into a CR2016 button cell in a glove box. The above button cell was subjected to constant current charge and discharge tests, with a current density of 0.1C (1C=300 mAh / g) and a voltage range of 1-0.005 V.

[0105] Comparative Example 1

[0106] This embodiment relates to a hard carbon negative electrode material for a sodium ion battery, and a preparation method thereof comprises the following steps:

[0107] S1. Preparation of precursor mixture: Mix walnut shell powder, carbon nanotubes, PVP, and sulfuric acid in liquid phase, react for a certain period of time to generate a precursor mixture; the addition amounts of carbon nanotubes, PVP, and sulfuric acid are 0.8, 0.1, and 3 wt.% of the carbon source addition amount respectively, the reaction temperature is 80 °C, and the reaction time is 2 h.

[0108] S2. Drying treatment: Dry the precursor mixture obtained in step S1 to obtain a dry precursor mixture;

[0109] S3. Low-temperature graphitization: Carbonize the precursor mixture obtained in step S2 at low temperature in a nitrogen atmosphere, with a heating rate of 5 °C / min, a holding time of 2.5 h, and a holding temperature of 550 °C to obtain a pre-carbonized precursor;

[0110] S4. Alkaline washing of pre-carbonized precursor: Wash the pre-carbonized precursor obtained in step S3 in a NaOH washing solution, then wash with water until the pH is neutral, and then centrifuge and dry to obtain an alkali-washed pre-carbonized precursor;

[0111] S5. Crushing and refinement: Crush the pre-carbonized precursor obtained in step S4 by air flow to obtain a refined carbonized precursor with a D50 of 8 μm;

[0112] S6. High-temperature carbonization: Graphitize the refined carbonized precursor obtained in step S4 at high temperature in an inert gas atmosphere, with a heating rate of 5 °C / min, a time of 4 h, and a temperature of 1100 °C to obtain the final hard carbon negative electrode material.

[0113] The obtained material is tested for electrochemical performance according to the following method: The hard carbon material, Super P, CMC, and SBR are mixed into a homogeneous slurry in a mass ratio of 94:1.5:2:2.5, and then the black slurry is coated on the copper foil using a 120-μm four-sided coater. Then, the film is dried in a vacuum drying oven at 100 °C for 2 hours. The electrode film is punched into a disc with a radius of 0.6 mm using a punching machine. Using metallic sodium as the counter electrode, 1 mol / L NaClO4 EC+DEC (1:1 vol%) as the electrolyte, and a PP / PE / PP three-layer separator, a CR2016-type button battery is assembled in a glove box. The above button battery is subjected to a constant current charge-discharge test, with a current density of 0.1C (1C = 300 mAh / g) and a voltage range of 1 - 0.005 V.

[0114] Comparative Example 2

[0115] This example relates to a hard carbon negative electrode material for sodium-ion batteries, and its preparation method includes the following steps:

[0116] S1. Preparation of precursor mixture: Mix walnut shell powder, carbon nanotubes, PVP, and sulfuric acid in liquid phase, react for a certain time to generate a precursor mixture; the addition amounts of carbon nanotubes, PVP, and sulfuric acid are 0.8, 0.1, and 3 wt.% of the carbon source addition amount respectively, the reaction temperature is 80 °C, and the reaction time is 2 h.

[0117] S2. Drying treatment: Dry the precursor mixture obtained in step S1 to obtain a dry precursor mixture;

[0118] S3. Low-temperature graphitization: Carbonize the precursor mixture obtained in step S2 at low temperature in a nitrogen atmosphere, with a heating rate of 5 °C / min, a holding time of 2.5 h, and a holding temperature of 550 °C to obtain a pre-carbonized precursor;

[0119] S4. Alkaline washing: Wash the pre-carbonized precursor obtained in step S3 in a NaOH washing solution, then wash with water until the pH is neutral, then centrifuge and dry to obtain an alkali-washed pre-carbonized precursor;

[0120] S5. Crushing and refining: Crush the pre-carbonized precursor obtained in step S4 by air flow to obtain a refined carbonized precursor with a D50 of 8 μm;

[0121] S6. High-temperature carbonization: Graphitize the refined carbonized precursor obtained in step S4 at high temperature in an inert gas atmosphere, with a heating rate of 5 °C / min, a holding time of 4 h, and a holding temperature of 1100 °C to obtain the final hard carbon negative electrode material.

[0122] The obtained material is tested for electrochemical performance according to the following method: The hard carbon material, Super P, CMC, and SBR are mixed into a homogeneous slurry in a mass ratio of 94:1.5:2:2.5, and then the black slurry is coated on a copper foil using a 120-μm four-sided coater, and then the film is dried in a vacuum drying oven at 100 °C for 2 hours. The electrode film is punched into a disc with a radius of 0.6 mm using a punching machine, a metal sodium is used as the counter electrode, 1 mol / L NaClO4 EC+DEC (1:1 vol%) is used as the electrolyte, and a PP / PE / PP three-layer separator is used to assemble a CR2016 type button battery in a glove box. The above button battery is subjected to a constant current charge-discharge test with a current density of 0.1 C (1 C = 300 mAh / g) and a voltage range of 1 - 0.005 V.

[0123] Comparative Example 3

[0124] This example relates to a hard carbon negative electrode material for a sodium-ion battery, and its preparation method includes the following steps:

[0125] S1. Preparation of precursor mixture: Mix walnut shell powder, boric acid, carbon nanotubes, PVP and sulfuric acid in liquid phase, react for a certain time to generate a precursor mixture; the addition amounts of boric acid, carbon nanotubes, PVP and sulfuric acid are 0.5, 0.8, 0.1, 3 wt.% of the carbon source addition amount respectively, the reaction temperature is 80 °C, and the reaction time is 2 h.

[0126] S2. Drying treatment: Dry the precursor mixture obtained in step S1 to obtain a dried precursor mixture;

[0127] S3. Low-temperature catalytic graphitization: Carbonize the precursor mixture obtained in step S2 at low temperature in a nitrogen atmosphere, with a heating rate of 5 °C / min, a holding time of 2.5 h, and a holding temperature of 550 °C to obtain a pre-carbonized precursor for graphitization;

[0128] S4. Crushing and refinement: Crush the pre-carbonized precursor for graphitization obtained in step S3 by air flow to obtain a refined carbonized precursor, with D50 being 8 μm;

[0129] S5. High-temperature carbonization: Graphitize the refined carbonized precursor obtained in step S4 at high temperature in an inert gas atmosphere, with a heating rate of 5 °C / min, a time of 4 h, and a temperature of 1100 °C to obtain the final hard carbon negative electrode material.

[0130] The obtained material was tested for electrochemical performance according to the following method: The hard carbon material, Super P, CMC, and SBR were mixed into a homogeneous slurry in a mass ratio of 94:1.5:2:2.5, and then the black slurry was coated on the copper foil using a 120-μm four-sided coater. Then, the film was dried in a vacuum drying oven at 100 °C for 2 hours. The electrode film was punched into a disc with a radius of 0.6 mm using a punching machine. Using metallic sodium as the counter electrode, 1 mol / L NaClO4 EC+DEC (1:1 vol%) as the electrolyte, and a PP / PE / PP three-layer separator, a CR2016 type button battery was assembled in a glove box. The above button battery was subjected to a constant current charge-discharge test, with a current density of 0.1C (1C = 300 mAh / g) and a voltage range of 1 - 0.005 V.

[0131] Figure 1 and Figure 2 are the TEM images of Application Example 1 and Comparative Example 1 respectively. There are obvious lattice fringes inside the material of Application Example 1, and almost no lattice fringes can be seen in the TEM image of Comparative Example 1, indicating that the B-based substance can effectively promote the growth of lattice fringes (graphite microcrystals) and promote the graphitization of carbon materials. The Raman test fitting results show that I D / I GAsking 1.60 and 1.92 respectively further proves that the B series substances can effectively promote graphitization and reduce the defect degree of carbon materials.

[0132] The crystal structures of the application examples and comparative examples were measured by XRD. The fitting of the (002) peak of the XRD pattern and the results show that the average carbon layer spacings of Application Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 are 0.385, 0.392, 0.371, and 0.354 nm respectively. The comparison results show that a low sintering temperature ensures a wider carbon layer spacing for the hard carbon material. The comparison results between Application Example 1 and Comparative Example 2 fully prove the importance of the multi-stage temperature carbonization strategy.

[0133] The galvanostatic charge-discharge tests (0.1C) show that the first-cycle charge specific capacities of Application Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 are 307, 276, 298, and 265 respectively, and the ICEs are 91.2%, 84.1%, 89.6%, and 90.6% respectively. The galvanostatic charge-discharge test results show that after adding the graphitizing agent, a lower treatment temperature (1100 °C) can achieve the capacity and first efficiency at a higher temperature (1300 °C). The capacity of Comparative Example 3 is lower because the graphitizing agent continues to catalyze graphitization at high temperature, resulting in too narrow a carbon layer spacing (0.354 nm) and making it difficult for sodium ions to be inserted into the carbon layer.

[0134] Although the capacities and ICEs of the application example and Comparative Example 2 are relatively close, the rate performance test results show that the capacity retention rates of the example and Comparative Example 2 are 75.6% and 64.8% respectively at a 5C current density. The rate performance of Comparative Example 2 is poor because its carbon layer spacing (0.371 nm) is too narrow, resulting in a low rate of sodium ion deintercalation and intercalation between the carbon layers.

[0135] The above embodiments are only specific embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can be made, and these obvious replacement forms all belong to the protection scope of the present invention.

Claims

1. A preparation method of a hard carbon negative electrode material for a high-rate sodium-ion battery, characterized in that It includes the following steps: S1. Preparation of precursor mixture: Carbon source, graphitizing agent, conductive agent, dispersant and inorganic acid are mixed in liquid phase to generate a precursor mixture; S2. Drying treatment: The precursor mixture obtained in step S1 is dried to obtain a dried precursor mixture; S3. Low-temperature catalytic graphitization: The precursor mixture obtained in step S2 is carbonized at low temperature in a protective atmosphere to obtain a graphitized pre-carbonized precursor; S4. Alkaline washing of pre-carbonized precursor: The pre-carbonized precursor obtained in step S3 is washed in an alkaline washing solution, then washed with water until the pH is neutral, and then centrifuged and dried to obtain a pre-carbonized precursor without graphitizing agent; S5. Crushing and refining: The pre-carbonized precursor without graphitizing agent obtained in step S4 is crushed to obtain a refined carbonized precursor; S6. High-temperature carbonization: The refined carbonized precursor obtained in step S4 is graphitized at high temperature in a protective atmosphere to obtain the final hard carbon anode material.

2. The preparation method of the hard carbon negative electrode material for the multiple-rate sodium ion battery according to claim 1, wherein: In step S3, the control conditions for low-temperature catalytic graphitization are: heating rate 1 - 10 °C / min, heat preservation time 2 - 5 h, heat preservation temperature 400 - 1650 °C, and the protective atmosphere is nitrogen and / or argon.

3. The preparation method of the hard carbon negative electrode material for the rate-type sodium ion battery according to claim 1, wherein: In step S6, the conditions for high-temperature carbonization are: heating rate 1 - 10 °C / min, heat preservation time 2 - 8 h, heat preservation temperature 900 - 1200 °C, and the protective atmosphere is nitrogen and / or argon.

4. The preparation method of the hard carbon negative electrode material for the multiple-rate sodium-ion battery according to claim 1, wherein: In step S1, the graphitizing agent is one or more of boron-based substances H3BO3, B2O3, boron powder, Na2B4O7, Na2B4O7, and the addition amount of the graphitizing agent is 0.1 - 1.5 wt.% of the addition amount of the carbon source.

5. The preparation method of the hard carbon negative electrode material for the magnification type sodium ion battery according to claim 1, wherein: In step S1, the conductive agent is one or more of carbon nanotubes, graphene, pitch; the addition amount of the conductive agent is 0.2 - 1.5 wt.% of the addition amount of the carbon source.

6. The preparation method of the hard carbon negative electrode material for the multiple-rate sodium ion battery according to claim 1, wherein: In step S1, the dispersant is one or more of sodium dodecylbenzenesulfonate, sodium dodecylsulfonate, cetyltrimethylammonium bromide, polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, polyacrylamide, polyethyleneimine, sodium carboxymethylcellulose, polyacrylic acid, and the addition amount of the dispersant is 0.05 - 1 wt.% of the addition amount of the carbon source.

7. The preparation method of the hard carbon anode material for the high-rate sodium-ion battery according to claim 1, wherein: In step S1, the inorganic acid is one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and the addition amount of the inorganic acid is 0.5 - 5 wt.% of the addition amount of the carbon source; the liquid-phase reaction temperature is 50 - 90 °C, and the reaction time is 1 - 5 h.

8. The preparation method of the hard carbon negative electrode material for the rate-type sodium ion battery according to claim 1, characterized in that: In step S1, the carbon source is one or more of coconut shell powder, apricot shell powder, walnut shell powder, nut shell powder, wood powder, bamboo powder, reed powder, coal powder, phenolic resin, epoxy resin.

9. The preparation method of the hard carbon negative electrode material for the multiple-rate sodium ion battery according to claim 8, wherein: In step S4, the alkaline washing solution is one or more of NaOH, KOH, Na2CO3, K2CO3; In step S5, the crushing method is one or more of roll crusher, jaw crusher, mechanical mill, jet mill, Raymond mill and ball mill, and crushed to a carbon particle D50 of 3 - 12 μm.

10. A hard carbon anode material for a high-rate sodium-ion battery, characterized in that: Prepared by the preparation method described in any one of claims 1 - 9.

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