Sodium ion battery hard carbon negative electrode material and preparation method thereof

Abstract

The application discloses a kind of sodium ion battery hard carbon negative electrode material and preparation method thereof, it is related to the technical field of sodium ion battery.The sodium ion battery hard carbon negative electrode material described in the application is formed by pretreating raw material containing lignocellulose in a eutectic solvent first, then carbonizing after treating in a Lewis acid.The raw material containing lignocellulose is crushed before pretreatment, and the particle size of the crushed raw material containing lignocellulose is 100-200 mesh.The Lewis acid contains a transition metal element.The raw material containing lignocellulose is pretreated with a eutectic solvent and a Lewis acid, which can control the microstructure of lignocellulose-based carbon material, achieve the stable and reversible insertion and extraction of sodium ions in the carbon structure, and the application of the battery has excellent cycle stability and rate performance.

Description

Technical Field

[0001] This invention relates to the technical field of sodium-ion batteries, and more particularly to a hard carbon anode material for sodium-ion batteries and its preparation method. Background Technology

[0002] In recent years, carbon emissions from fossil fuel consumption have led to increasingly prominent environmental problems, making the development of new renewable resources a consensus in society today. Lignocellulose biomass possesses advantages such as abundant resources, renewability, and environmental friendliness. Therefore, utilizing lignocellulose raw materials to develop biomass-based functional materials is of great significance for achieving sustainable social and economic development, and also aligns with the major demand for a shift in the current social energy consumption structure towards low-carbon and clean energy. Carbon materials possess many excellent physicochemical properties, such as high chemical stability, tunable surface chemistry, good electrical conductivity, low density, and large specific surface area, thus showing promising application prospects in catalysis, energy storage and conversion, and adsorption. However, the synthesis of most carbon materials generally relies on non-renewable fossil fuels. Therefore, lignocellulose biomass, as a sustainable carbon source, can alleviate the enormous pressure on energy and the environment in contemporary society.

[0003] Similar to lithium-ion batteries, sodium-ion batteries mainly consist of a positive electrode, a negative electrode, a current collector, an electrolyte, a separator, and a battery casing. Lithium-ion batteries primarily use graphite as their carbon-based negative electrode material. Lithium ions, with their small radius, can effectively intercalate and deintercalate between graphite layers. However, sodium ions have a larger radius, and graphite-based materials cannot effectively store them. Wood-based biomass-based hard carbon materials have attracted widespread attention as negative electrode materials for sodium-ion batteries. Modifying carbonization process parameters (carbonization temperature, temperature variation rate, carbonization method, etc.) is considered a very effective approach to controlling the microstructure of hard carbon. However, increasing the carbonization temperature means increasing energy consumption, and the high-temperature graphitized carbon layer structure is more similar to graphite, with smaller interlayer spacing, which is unfavorable for larger ions such as sodium ions. + The embedding of these molecules affects subsequent ion storage capabilities. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a hard carbon anode material for sodium-ion batteries and its preparation method. This invention pretreats raw materials containing lignocellulose with a eutectic solvent and a Lewis acid, enabling the controllable construction of the microstructure of the lignocellulose bio-based carbon material, such as ordered carbon layer structure, carbon layer spacing, and pore structure. This allows for the stable and reversible insertion and extraction of sodium ions into the carbon structure, and its application in batteries exhibits excellent cycle stability and rate performance.

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

[0006] In a first aspect, the present invention provides a hard carbon anode material for sodium-ion batteries, wherein the hard carbon anode material is formed by pretreating raw materials containing lignocellulose in a eutectic solvent and then carbonizing them in Lewis acid.

[0007] Before pretreatment, the raw material containing lignocellulose is pulverized, and the particle size of the lignocellulose-containing raw material after pulverization is 100-200 mesh.

[0008] The Lewis acid contains transition metal elements.

[0009] The principle of this invention: A raw material containing lignocellulose is pretreated with a eutectic solvent. Because the eutectic solvent has excellent dissolving properties for lignin, it effectively dissolves the hemicellulose and lignin in the raw material. Then, Lewis acid is added for further treatment. Due to the interaction between the transition metal cation hydrates in the Lewis acid and the oxygen atoms at the C5 and C6 positions of cellulose, a cellulose / lignin composite structure chelated with transition metal ions is obtained. This allows the transition metal to catalyze graphitization during subsequent carbonization, improving the graphitization degree and conductivity of the carbon material. The cellulose / lignin composite structure, after carbonization, yields a microstructure conducive to sodium storage. Simultaneously, Cl- ions bound to the metal cations... - This process disrupts the hydrogen bonds in cellulose, thereby increasing the ability to dissolve lignin and cellulose. The more lignin and cellulose are dissolved, the more defects and porous structures the carbon material has, which is beneficial for sodium ion storage.

[0010] Preferably, the molar ratio of hydrogen bond donor to hydrogen bond acceptor in the eutectic solvent is (2-10):1.

[0011] Preferably, the hydrogen bond donor is at least one selected from oxalic acid, citric acid, ethylene glycol, glycerol, urea, thiourea, and imidazole.

[0012] More preferably, the hydrogen bond donor is a mixture of urea and ethylene glycol, and the molar ratio of urea to ethylene glycol is (0.1-10):1.

[0013] Preferably, the hydrogen bond acceptor is one of quaternary phosphonium salt, quaternary ammonium salt, imidazodium salt, and choline chloride.

[0014] Preferably, the Lewis acid is at least one selected from ferric chloride, cobalt chloride, nickel chloride, copper chloride, manganese chloride, aluminum chloride, and zinc chloride.

[0015] More preferably, the Lewis acid is a mixture of nickel chloride and copper chloride, and the mass ratio of nickel chloride to copper chloride is (0.2-5):1.

[0016] Preferably, the lignocellulose-containing raw material is at least one of wood, bamboo, corn cob, straw, and engineered wood products.

[0017] More preferably, the straw is one of wheat straw, rice straw, sorghum straw, corn straw, soybean stalks, or sugarcane bagasse.

[0018] Preferably, the mass ratio of the precursor particles to the Lewis acid is 1:3.

[0019] Secondly, the present invention also provides a method for preparing a hard carbon anode material for sodium-ion batteries, comprising the following steps:

[0020] (1) The raw material containing lignocellulose is added to a eutectic solvent and pretreated at 80-100℃ for 2-8 hours. After drying, precursor particles are obtained. The mass ratio of the raw material containing lignocellulose to the eutectic solvent is (1-3):20.

[0021] (2) Add the precursor particles to a Lewis acid solution and pretreat at 70-100℃ for 8-12h to obtain a cellulose / lignin composite precursor, wherein the mass ratio of the precursor particles to Lewis acid is 1:(1-4).

[0022] (3) The cellulose / lignin composite precursor is carbonized at high temperature in an inert atmosphere to obtain the hard carbon anode material for sodium-ion batteries.

[0023] The preparation method of this invention is simple, low-cost, safe and environmentally friendly, and can be mass-produced. The prepared sodium-ion battery hard carbon anode material has the characteristics of high graphitization degree, high ionic conductivity and good sodium storage performance.

[0024] This invention controls the mass ratio of lignocellulose-containing raw materials to eutectic solvent within the above-mentioned range, thereby enabling lignin and cellulose in the lignocellulose-containing raw materials to have better solubility, which in turn allows the carbon material to have more pores and defects, which is beneficial for sodium ion storage and thus improves the cycle stability of the battery.

[0025] By controlling the mass ratio of precursor particles to Lewis acid within the aforementioned range, this invention can improve the solubility of lignocellulose. Furthermore, the metal ions in the Lewis acid can catalyze graphitization during the carbonization process, which is beneficial for promoting the graphitization degree of carbon materials and increasing the interlayer spacing of carbon layers, thereby enabling the battery to have excellent cycle stability and rate performance.

[0026] Temperature and time during pretreatment affect the solubility of lignin and cellulose, thus influencing the microstructure of carbon materials. Therefore, this invention controls the temperature and time during pretreatment within the aforementioned range, which is beneficial for improving the solubility of lignin and cellulose, resulting in more pores and defects in the carbon materials, improving sodium ion storage, and thus enabling the battery to have excellent cycle stability.

[0027] Preferably, in step (3), the carbonization temperature is 800-1200℃, the carbonization time is 1-3h, and the heating rate is 3-5℃ / min.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] This invention employs a two-step chemical pretreatment process using a eutectic solvent and Lewis acids to regulate the structure of cellulose / lignin / transition metal composite precursors. By controlling the precursor structure, the type of transition metal ions, and the pyrolysis process conditions, the microstructure of lignocellulose bio-based carbon materials, such as ordered carbon layer structure, interlayer spacing, and pore structure, can be controllably constructed. Furthermore, the sodium storage mechanism of lignocellulose bio-based carbon materials is elucidated, enabling stable and reversible insertion and extraction of sodium ions within the carbon structure. Sodium-ion batteries assembled using hard carbon materials prepared by this method exhibit excellent cycle stability and rate performance. Attached Figure Description

[0030] Figure 1 This is a scanning electron microscope image of the hard carbon anode of the sodium-ion battery prepared in Example 1.

[0031] Figure 2 The rate performance of the hard carbon anode for sodium-ion batteries prepared in Example 4 is shown.

[0032] Figure 3 The sodium-ion battery hard carbon anode prepared in Example 4 was subjected to a 50 mA g... -1 Under charging and discharging conditions.

[0033] Figure 4 The sodium-ion battery hard carbon anode prepared in Example 5 was tested at 1 A g. -1 The loop performance is as follows.

[0034] Figure 5 The sodium-ion battery hard carbon anode prepared in Example 5 was used in a 0.1 A g process. -1 The loop performance is as follows. Detailed Implementation

[0035] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments, but the scope of protection and implementation of the present invention are not limited thereto.

[0036] Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0037] Example 1

[0038] A method for preparing a hard carbon anode material for sodium-ion batteries includes the following steps:

[0039] (1) Eucalyptus wood is used as raw material. It is crushed and ball-milled for 3 hours and then sieved through 100 mesh to obtain eucalyptus wood powder. Then, a eucalyptus solvent is prepared: choline chloride and urea are mixed at a molar ratio of 1:2 and heated at 70°C for 1 hour until a uniform, transparent, colorless liquid is formed, which is the eucalyptus solvent. Finally, 3g of eucalyptus wood powder is weighed and added to 20g of eucalyptus solvent and mixed evenly. The mixture is heated and stirred at 100°C for 2 hours. The pretreated slurry is vacuum filtered and washed with distilled water and then dried at 80°C to obtain precursor particles.

[0040] (2) Then weigh 1g of precursor particles and 3g of copper chloride and mix them evenly with distilled water. Heat and stir at 80℃ for 12h, then wash with deionized water, centrifuge and separate, place the precipitate in a forced-air drying oven and dry at 80℃ for 12h to obtain cellulose / lignin composite precursor chelated with transition metal ions.

[0041] (3) High-temperature carbonization: The pretreated cellulose / lignin composite precursor is placed in a tube furnace and carbonized at 5°C for 5 min under an inert atmosphere (N2). -1 The material was carbonized at 800℃ for 2 hours, then ground into powder, stirred in 10wt% dilute hydrochloric acid solution for 12 hours, washed with deionized water until neutral, and vacuum dried in a vacuum drying oven at 80℃ for 12 hours to obtain the hard carbon anode material for sodium-ion batteries.

[0042] Example 2

[0043] A method for preparing a hard carbon anode material for sodium-ion batteries includes the following steps:

[0044] (1) Using corn stalks as raw material, crush them and ball mill them for 3 hours, then sieve them through a 200-mesh screen to obtain corn stalk powder; then prepare a eutectic solvent: mix imidazole salt and oxalic acid in a molar ratio of 1:5 and heat at 70°C for 1 hour until a uniform, transparent, colorless liquid is formed, which is the eutectic solvent; finally, weigh 1g of corn stalk powder and add it to 20g of eutectic solvent and mix evenly, heat and stir at 100°C for 4 hours, wash the pretreated mixed slurry with distilled water under vacuum, and then dry it at 80°C to obtain precursor particles;

[0045] (2) Then weigh 1g of precursor particles and 1g of ferric chloride and mix them evenly with distilled water. Heat and stir at 80℃ for 12h, then wash with deionized water, centrifuge and separate, place the precipitate in a forced-air drying oven and dry at 80℃ for 12h to obtain cellulose / lignin composite precursor chelated with transition metal ions.

[0046] (3) High-temperature carbonization: The pretreated cellulose / lignin composite precursor is placed in a tube furnace and carbonized at 5°C for 5 min under an inert atmosphere (N2). -1 The material was carbonized at 800℃ for 2 hours, then ground into powder, stirred in 10wt% dilute hydrochloric acid solution for 12 hours, washed with deionized water until neutral, and vacuum dried in a vacuum drying oven at 80℃ for 12 hours to obtain the hard carbon anode material for sodium-ion batteries.

[0047] Example 3

[0048] A method for preparing a hard carbon anode material for sodium-ion batteries includes the following steps:

[0049] (1) Using soybean stalks as raw material, crush them and ball mill them for 3 hours, then sieve them through a 150-mesh screen to obtain soybean stalk powder; then prepare a eutectic solvent: mix quaternary phosphonium salt and thiourea at a molar ratio of 1:10 and heat them at 70°C for 1 hour until a uniform, transparent, colorless liquid is formed, which is the eutectic solvent; finally, weigh 2g of soybean stalk powder and add it to 20g of eutectic solvent and mix them evenly. Heat and stir at 100°C for 8 hours. Wash the pretreated mixed slurry with distilled water under vacuum and then dry it at 80°C to obtain precursor particles;

[0050] (2) Then weigh 1g of precursor particles and 4g of cobalt chloride and mix them evenly with distilled water. Heat and stir at 80℃ for 12h, then wash with deionized water, centrifuge and separate, place the precipitate in a forced-air drying oven and dry at 80℃ for 12h to obtain cellulose / lignin composite precursor chelated with transition metal ions.

[0051] (3) High-temperature carbonization: The pretreated cellulose / lignin composite precursor is placed in a tube furnace and carbonized at 5°C for 5 min under an inert atmosphere (N2). -1 The material was carbonized at 800℃ for 2 hours, then ground into powder, stirred in 10wt% dilute hydrochloric acid solution for 12 hours, washed with deionized water until neutral, and vacuum dried in a vacuum drying oven at 80℃ for 12 hours to obtain the hard carbon anode material for sodium-ion batteries.

[0052] Example 4

[0053] A method for preparing a hard carbon anode material for sodium-ion batteries includes the following steps:

[0054] (1) Eucalyptus wood is used as raw material. It is crushed and ball-milled for 3 hours and then sieved through 150 mesh to obtain eucalyptus wood powder. Then, a eucalyptus solvent is prepared: imidazolium salt and ethylene glycol are mixed at a molar ratio of 1:10 and heated at 70°C for 1 hour until a uniform, transparent, colorless liquid is formed, which is the eucalyptus solvent. Finally, 3g of eucalyptus wood powder is weighed and added to 20g of eucalyptus solvent and mixed evenly. The mixture is heated and stirred at 100°C for 8 hours. The pretreated slurry is vacuum filtered and washed with distilled water, and then dried at 80°C to obtain precursor particles.

[0055] (2) Then weigh 1g of precursor particles, 1g of copper chloride and 2g of nickel chloride and mix them evenly with distilled water. Heat and stir at 80℃ for 12h, then wash with deionized water, centrifuge and separate, place the precipitate in a forced-air drying oven and dry at 80℃ for 12h to obtain cellulose / lignin composite precursor chelated with transition metal ions.

[0056] (3) High-temperature carbonization: The pretreated cellulose / lignin composite precursor is placed in a tube furnace and carbonized at 5°C for 5 min under an inert atmosphere (N2). -1 The material was carbonized at 1000℃ for 2 hours, then ground into powder, stirred in 10wt% dilute hydrochloric acid solution for 12 hours, washed with deionized water until neutral, and vacuum dried in a vacuum drying oven at 80℃ for 12 hours to obtain the hard carbon anode material for sodium-ion batteries.

[0057] Example 5

[0058] The difference from Example 4 is that in step (1), imidazole salt, urea and ethylene glycol are mixed in a molar ratio of 1:5:5 and heated at 70°C for 1 hour until a uniform, transparent, colorless liquid is formed, thus obtaining a eutectic solvent system. All other steps are the same as in Example 4.

[0059] Example 6

[0060] The difference from Example 4 is that in step (1), imidazole salt, urea and ethylene glycol are mixed in a molar ratio of 1:9:1 and heated at 70°C for 1 hour until a uniform, transparent, colorless liquid is formed, thus obtaining a eutectic solvent system. All other steps are the same as in Example 4.

[0061] Comparative Example 1

[0062] The difference from Example 1 is that the mass ratio of eucalyptus powder to eutectic solvent in step (1) is 1:1, while the other steps are the same as in Example 1.

[0063] Comparative Example 2

[0064] The difference from Example 1 is that the mass ratio of precursor particles to copper chloride in step (2) is 2:1, while the other steps are the same as in Example 1.

[0065] Comparative Example 3

[0066] The difference from Example 1 is that the particle size of the eucalyptus powder in step (1) is 80 mesh, while the other steps are the same as in Example 1.

[0067] experiment

[0068] The sodium-ion battery hard carbon anode material prepared in the above examples and comparative examples was mixed with the conductive agent acetylene black and the binder sodium carboxymethyl cellulose to form a uniform slurry, which was then coated onto copper foil. The mass ratio of carbon material to conductive agent and binder was 8:1:1. A sodium-ion half-cell was assembled using a coin cell, and its performance at 50 mA g was tested. -1 Charge and discharge at 1A g and at 1A g -1 Cyclic stability under [condition / condition].

[0069] Capacity retention (%) = Discharge capacity after 300 cycles / Discharge capacity after 1 cycle × 100%.

[0070] The experimental results of Examples 1-6 and Comparative Examples 1-4 are shown in Table 1.

[0071] Table 1

[0072]

[0073] Depend on Figure 1 The scanning images show that the sodium-ion battery hard carbon anode material prepared in Example 1 has a certain porous structure, which is mainly due to the dissolution and etching effect of the lignocellulose during the pretreatment process. Figure 2 As can be seen, Example 4 exhibited excellent rate performance, even at rates as high as 10A g. -1 Under high current density, the obtained carbon material maintains a high capacity retention rate. Figure 3 The charge-discharge curves for Example 4 show a high-voltage ramp region and a low-voltage plateau region. This indicates that the two-step pretreatment dissolved more lignocellulose, thereby etching the carbon material. The more defective structures are more conducive to the storage of sodium ions.

[0074] Depend on Figure 4 and Figure 5As can be seen from the cycling performance graph of Example 5, the battery showed no significant capacity decay after 2000 charge-discharge cycles at high current density, exhibiting excellent cycling performance. Even after 300 cycles at low current density, the capacity showed no significant decay, indicating that the defects and porous structure introduced by the etching effect of pretreated lignocellulose on the final carbon material are conducive to stable sodium ion storage, thus demonstrating good electrochemical performance as a negative electrode material for sodium-ion batteries.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A hard carbon anode material for sodium-ion batteries, characterized in that, The sodium-ion battery hard carbon anode material is made by pretreating raw materials containing lignocellulose in a eutectic solvent, then treating them in Lewis acid and carbonizing them. Before pretreatment, the raw material containing lignocellulose is pulverized, and the particle size of the lignocellulose-containing raw material after pulverization is 100-200 mesh. The Lewis acid contains a transition metal element; The eutectic solvent is a mixture of imidazolium salt, urea, and ethylene glycol in a molar ratio of 1:5:5; The Lewis acid is at least one of ferric chloride, cobalt chloride, nickel chloride, copper chloride, manganese chloride, aluminum chloride, and zinc chloride.

2. The sodium-ion battery hard carbon anode material as described in claim 1, characterized in that, The Lewis acid is a mixture of nickel chloride and copper chloride, with a mass ratio of nickel chloride to copper chloride of (0.2-5):

1.

3. The sodium-ion battery hard carbon anode material as described in claim 1, characterized in that, The raw material containing lignocellulose is at least one of wood, bamboo, corn cob, straw, and engineered wood products.

4. The method for preparing the hard carbon anode material for sodium-ion batteries according to any one of claims 1-3, characterized in that, Includes the following steps: (1) The raw material containing lignocellulose is added to a eutectic solvent and pretreated at 80-100℃ for 2-8 hours. After drying, precursor particles are obtained. The mass ratio of the raw material containing lignocellulose to the eutectic solvent is (1-3):

20. (2) Add the precursor particles to a Lewis acid solution and pretreat at 70-100℃ for 8-12h to obtain a cellulose / lignin composite precursor, wherein the mass ratio of the precursor particles to Lewis acid is 1:(1-4). (3) The cellulose / lignin composite precursor is carbonized at high temperature in an inert atmosphere to obtain the hard carbon anode material for sodium-ion batteries.

5. The method for preparing the hard carbon anode material for sodium-ion batteries as described in claim 4, characterized in that, In step (3), the carbonization temperature is 800-1200℃, the carbonization time is 1-3h, and the heating rate is 3-5℃ / min.

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