Sodium-ion battery negative electrode material and preparation method and application thereof

Abstract

The application belongs to the technical field of sodium ion battery negative electrode materials, and discloses a sodium ion battery negative electrode material with high reversible specific capacity, high initial coulomb efficiency and excellent cycle stability, and a preparation method and application thereof. The preparation method comprises the following steps: (1) performing acid washing treatment on a silicon-containing biomass raw material to remove alkali metal elements and alkaline earth metal elements in the silicon-containing biomass raw material and retain silicon dioxide, to obtain an acid-washed raw material; (2) performing carbonization treatment on the acid-washed raw material in an inert atmosphere to obtain a silicon dioxide-containing carbon material; (3) mixing the silicon dioxide-containing carbon material with an alkali solution to perform etching treatment, removing silicon dioxide in the silicon dioxide-containing carbon material, and after washing and drying, obtaining a porous carbon material; and (4) performing chemical vapor deposition treatment on the porous carbon material in a nitrogen-containing carbon source atmosphere, depositing a nitrogen-containing carbon layer at the pores of the porous carbon material, to obtain the sodium ion battery negative electrode material.

Description

Technical Field

[0001] This invention relates to the technical field of sodium-ion battery anode materials, and more specifically, to sodium-ion battery anode materials, their preparation methods, and applications. Background Technology

[0002] Sodium-ion batteries are considered a potential alternative technology to lithium-ion batteries in the field of large-scale energy storage due to the abundance and wide distribution of sodium resources. The anode material is a key component determining the electrochemical performance of sodium-ion batteries. Among them, hard carbon materials have become the most widely studied anode material system for sodium-ion batteries due to their high reversible sodium storage capacity and suitable operating potential.

[0003] Biomass raw materials are widely available and renewable, making them an important precursor for the preparation of hard carbon materials. Silicon-containing biomass such as bamboo, rice husks, wheat straw, and sugarcane bagasse are abundant in nature, offering the advantage of readily available raw materials for the preparation of hard carbon anode materials. However, current technologies for preparing hard carbon anode materials using biomass still face the following technical challenges.

[0004] First, the pore structure of carbon materials significantly impacts their electrochemical performance. An appropriate pore structure shortens the diffusion path of sodium ions, improving rate performance. However, a lack of effective control over the pore structure can lead to significant negative effects. For carbon materials with excessively low porosity, insufficient sodium ion transport channels restrict ion diffusion kinetics, resulting in poor rate performance. Conversely, for carbon materials with high porosity but open pores, the large number of open pores leads to an excessively large specific surface area. During the initial charge-discharge cycle, the electrolyte decomposes extensively on the carbon material surface, forming a solid electrolyte interface film, resulting in increased irreversible capacity loss and a lower initial coulombic efficiency. While existing literature reports methods to control the pore structure of carbon materials using template or activation techniques, these methods typically require the introduction of exogenous templates or activators, making the process cumbersome and difficult to precisely control the pore size and distribution. Even when carbon materials with a certain pore structure are obtained, the high specific surface area problem caused by open pores remains unresolved.

[0005] Secondly, the chemical properties of the hard carbon material surface also significantly influence the adsorption and intercalation behavior of sodium ions. Unmodified carbon materials have a limited variety of active sites, resulting in limited chemisorption capacity for sodium ions and making it difficult to fully utilize the capacity advantage provided by the porous structure. Nitrogen doping is considered an effective means to improve the electrochemical activity of carbon materials. Introducing nitrogen atoms into the carbon framework increases the defects and active sites on the material surface, enhancing the adsorption of sodium ions and thus improving the reversible specific capacity. In existing technologies, nitrogen doping is usually achieved through co-carbonization after mixing with a nitrogen-containing precursor. In this method, the distribution of nitrogen in the carbon material is often random, making it difficult to achieve directional modification of the pore surface. More importantly, the co-carbonization method cannot selectively deposit nitrogen onto the pore walls while maintaining the existing pore morphology, thus failing to simultaneously achieve the dual goals of nitrogen doping and pore sealing. Consequently, the initial coulombic efficiency and reversible specific capacity of carbon materials cannot be improved simultaneously.

[0006] Furthermore, biomass feedstocks typically contain alkali and alkaline earth metals such as potassium, calcium, sodium, and magnesium. These metals can catalyze localized graphitization during high-temperature carbonization, leading to an uneven microstructure in the carbon material and reducing the number of sodium-storing active sites. Simultaneously, residual metal impurities can trigger side reactions during electrochemical cycling, affecting cycle stability.

[0007] In summary, how to effectively remove metallic impurities from silicon-containing biomass while constructing a reasonable pore structure, and further directionally modifying the pores to simultaneously improve the reversible specific capacity, initial coulombic efficiency, and cycle stability of hard carbon anode materials, is a technical problem that urgently needs to be solved. Summary of the Invention

[0008] The technical problem to be solved by this invention is to provide a sodium-ion battery anode material with high reversible specific capacity, high initial coulombic efficiency and excellent cycle stability, as well as its preparation method and application. The technical solution is as follows: A method for preparing sodium-ion battery anode materials includes the following steps: (1) The silicon-containing biomass raw material is acid-washed to remove alkali metal elements and alkaline earth metal elements from the silicon-containing biomass raw material, while retaining silicon dioxide, to obtain the acid-washed raw material; (2) The acid-washed raw material is carbonized under an inert atmosphere to obtain a carbon material containing silicon dioxide; (3) The silica-containing carbon material is mixed with an alkaline solution and etched to remove the silica from the silica-containing carbon material. After washing and drying, a porous carbon material is obtained. (4) The porous carbon material is subjected to chemical vapor deposition in an atmosphere containing a nitrogen carbon source to deposit a nitrogen-containing carbon layer in the pores of the porous carbon material, thereby obtaining the sodium-ion battery anode material.

[0009] The advantages of the method for preparing the sodium-ion battery anode material of the present invention are: (1) In step (1), the chemical selectivity of acid solutions, which have good solubility for alkali metals and alkaline earth metal compounds but not for silica, is utilized to effectively remove harmful metal impurities such as potassium, calcium, sodium, and magnesium while retaining the naturally occurring silica in the biomass within the raw material system. In step (2), the acid-washed raw material with silica retained undergoes high-temperature carbonization treatment, where the organic components are pyrolyzed into a carbon skeleton, and the silica nanoparticles are uniformly embedded in the carbon matrix in an in-situ dispersed state, acting as a natural hard template. In step (3), an alkaline solution is used to selectively etch away the silica in the carbon matrix, thereby leaving a three-dimensional pore network in situ at its original location that closely matches the spatial distribution of natural silica, thus constructing a porous carbon skeleton with a reasonable pore size distribution and abundant pore volume. Therefore, this invention addresses the inherent characteristic of silicon-containing biomass raw materials containing both harmful metallic impurities and natural silica by innovatively designing a step-by-step processing strategy of "selective acid washing—carbonization—alkali etching." It utilizes the natural silica component of biomass as an in-situ hard template, eliminating the need for additional external template agents. The process is simple and efficient, and the generated pores are naturally and uniformly distributed in the carbon matrix, which is far superior to the problem of local pore aggregation caused by uneven mixing when artificially adding external template agents.

[0010] (2) This invention utilizes chemical vapor deposition to introduce a nitrogen-containing carbon source in gaseous form into the pores of porous carbon materials. Thermal decomposition and deposition reactions occur on the pore wall surface, selectively forming a dense nitrogen-containing carbon layer at the pores. This directional deposition mechanism not only introduces a large number of nitrogen-containing active sites into the inner wall of the pores, enhancing the chemical adsorption of sodium ions by the carbon material and significantly improving the reversible specific capacity, but more importantly, the deposited nitrogen-containing carbon layer can transform the originally open pores in the porous carbon material into closed or semi-closed states. This effectively reduces the specific surface area of ​​the material, decreases the poor contact area between the electrolyte and the carbon material surface, significantly inhibits the excessive growth of the solid electrolyte interface film during the first charge-discharge process, and significantly improves the first coulombic efficiency. Therefore, this invention uses chemical vapor deposition of a nitrogen-containing carbon source to directionally modify the pore structure, achieving a deep synergy between nitrogen doping and pore closure control. In contrast, in the traditional nitrogen-containing precursor co-carburization method, nitrogen is randomly distributed in the carbon matrix, which cannot selectively modify the pore surface. Therefore, it cannot simultaneously achieve the dual technical objectives of nitrogen doping for increased compatibility and improved pore sealing efficiency.

[0011] In summary, this invention employs a four-step synergistic strategy: selective acid washing to retain natural silica, high-temperature carbonization to fix the template pattern, alkaline etching to create pores in situ, and chemical vapor deposition to directionally modify the pores. This strategy successfully prepares a sodium-ion battery hard carbon anode material that combines high reversible specific capacity, high initial coulombic efficiency, and excellent cycle stability. This effectively solves the technical challenge of simultaneously improving reversible specific capacity and initial coulombic efficiency in existing biomass-based hard carbon anode materials.

[0012] As a further improvement to the above preparation method, the silicon-containing biomass raw material is selected from at least one of bamboo, rice husk, wheat straw, and sugarcane bagasse. Therefore, these silicon-containing biomass raw materials are widely available, inexpensive, and renewable, and all contain varying mass fractions of natural silica, providing a sufficient template source for in-situ pore formation.

[0013] As a further improvement to the above preparation method: In step (1), the acid solution used in the pickling treatment is at least one of hydrochloric acid solution, sulfuric acid solution, and nitric acid solution, the concentration of the acid solution is 0.5-3 mol / L, the pickling temperature is 20-90°C, and the pickling time is 0.5-6 hours. Therefore, the above-mentioned types and concentration ranges of acid can effectively dissolve alkali metals and alkaline earth metals and their compounds without dissolving silica, ensuring that the template material is completely preserved; appropriate temperature and time ensure that metal impurities are fully removed.

[0014] As a further improvement to the above preparation method: in step (2), the carbonization temperature is 800–1400°C, the holding time is 1–6 hours, and the inert atmosphere is argon or nitrogen. Therefore, silicon dioxide remains basically stable under an inert atmosphere and within this temperature range, and does not undergo significant carbothermal reduction reaction with carbon when the carbonization temperature does not exceed 1200°C; when the carbonization temperature approaches the upper limit (e.g., 1400°C), a small amount of carbothermal reduction may occur, but this does not affect the effective removal of most of the silicon dioxide template by the subsequent alkaline etching step.

[0015] As a further improvement to the above preparation method: in step (3), the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution, the concentration of the alkaline solution is 1-3 mol / L, the etching temperature is 40-100°C, and the etching time is 6-18 hours. Thus, the alkaline solution reacts with silicon dioxide to generate soluble silicates, effectively removing silicon dioxide from the carbon skeleton and forming a rich porous structure in situ inside the carbon matrix; the above-mentioned concentration, temperature, and time parameters ensure that the etching reaction proceeds fully without damaging the structural integrity of the carbon skeleton.

[0016] As a further improvement to the above preparation method: In step (4), the nitrogen-containing carbon source is acetonitrile and / or pyridine, and the carrier gas is selected from argon or nitrogen. The carrier gas is introduced into the nitrogen-containing carbon source using a bubbling method to form an atmosphere composed of carrier gas and nitrogen-containing carbon source vapor. The volume fraction of the nitrogen-containing carbon source vapor in the atmosphere is 10-15%. The temperature of the chemical vapor deposition treatment is 600-1000°C, and the time is 30-180 minutes. Thus, acetonitrile and pyridine are both liquid small-molecule organic compounds containing both carbon and nitrogen. Within the above temperature range, they can thermally decompose and deposit on the surface of carbon materials to form a nitrogen-containing carbon layer. By adjusting the volume concentration of the nitrogen-containing carbon source vapor and the deposition time, the thickness and nitrogen doping content of the nitrogen-containing carbon layer can be controlled, thereby achieving the regulation of the pore sealing degree and nitrogen doping level.

[0017] As a further improvement to the above preparation method, after step (3) and before step (4), the method further includes: placing the porous carbon material between two electrodes for pulsed electrothermal treatment. Thus, pulsed electrothermal treatment can instantly heat the carbon material to an extremely high temperature in a very short time, causing rapid rearrangement of the carbon microcrystalline structure, effectively expanding the carbon interlayer spacing, increasing the number of interlayer storage sites where sodium ions can be inserted, and significantly improving the material's reversible specific capacity. At the same time, the extremely short heating duration avoids excessive graphitization due to continuous high temperatures, which would reduce sodium storage performance.

[0018] As a further improvement to the above preparation method: the pulse voltage of the pulsed electrothermal treatment is 30–300V, the single pulse duration is 500–2000ms, and the number of pulses is 1–10. Thus, the above pulse parameter range ensures that the carbon material reaches a sufficiently high temperature instantaneously to achieve effective rearrangement of carbon microcrystals, while the extremely short pulse duration prevents the collapse of the carbon framework and irreversible damage to the pore structure.

[0019] The sodium-ion battery anode material is prepared by the above-described preparation method; the residual silicon content in the sodium-ion battery anode material does not exceed 0.45 wt%, and the nitrogen content is 3.5-6%; the reversible specific capacity at a current density of 0.1 A / g is 280-350 mAh / g, the initial coulombic efficiency is 85-92%, and the capacity retention rate after 500 cycles at a current density of 1 A / g is ≥90%.

[0020] Sodium-ion batteries use the aforementioned sodium-ion battery negative electrode material for their negative electrode.

[0021] The embodiments of the invention provided in this specification will be further described below with reference to the accompanying drawings and specific embodiments. Additional aspects and advantages of the embodiments of the invention provided in this specification will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the embodiments of the invention provided in this specification. Attached Figure Description

[0022] The accompanying drawings, which form part of the embodiments of the invention provided in this specification, are used to aid in understanding the embodiments of the invention provided in this specification. The content provided in the drawings and the related descriptions in the embodiments of the invention provided in this specification can be used to explain the embodiments of the invention provided in this specification, but do not constitute an undue limitation on the embodiments of the invention provided in this specification. In the drawings: Figure 1 This is a SEM image of the silicon dioxide-containing carbon material from step (2) of Embodiment 1 of the present invention.

[0023] Figure 2 This is a SEM image of the porous carbon material in step (3) of Embodiment 1 of the present invention.

[0024] Figure 3 This is a SEM image of the sodium-ion battery anode material in step (4) of Example 1 of the present invention. Detailed Implementation

[0025] The embodiments of the invention provided in this specification will now be clearly and completely described in conjunction with the accompanying drawings. Those skilled in the art will be able to implement the embodiments of the invention provided in this specification based on these descriptions. Before describing the embodiments of the invention provided in this specification in conjunction with the accompanying drawings, it should be particularly noted that: The technical solutions and features provided in the embodiments of the invention provided in this specification, including the following description, can be combined with each other without conflict.

[0026] Furthermore, the embodiments of the inventions provided in this specification mentioned below are generally only a part of the embodiments of the inventions provided in this specification, and not all of them. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the inventions provided in this specification without creative effort should fall within the scope of protection of the embodiments of the inventions provided in this specification.

[0027] Regarding the terminology and units in the embodiments of the invention provided in this specification: The terms "comprising," "including," "having," and any variations thereof in the description, claims, and related parts of the embodiments of the invention provided in this specification are intended to cover non-exclusive inclusion. Furthermore, other relevant terms and units in the embodiments of the invention provided in this specification can be reasonably interpreted based on the relevant content of the embodiments of the invention provided in this specification.

[0028] Example 1

[0029] The sodium-ion battery anode material and its preparation method in this embodiment are as follows: (1) After washing and drying rice husks (60-100 mesh, silicon content is 8.4% as Si), add them to a 1.5 mol / L hydrochloric acid solution (solid-liquid mass-volume ratio of 1 g: 20 mL), stir and acid wash at 60°C for 3 hours, filter, wash with deionized water until the pH of the filtrate is neutral, and dry at 80°C for 12 hours to obtain the acid-washed raw material.

[0030] (2) The pickled raw material is placed in a tube furnace and heated from room temperature to 1100°C at a heating rate of 5°C / min under an argon atmosphere. The temperature is maintained for 3 hours for carbonization treatment. After naturally cooling to room temperature, the material is taken out to obtain carbon material containing silicon dioxide.

[0031] (3) Add the carbon material containing silicon dioxide to a 2 mol / L sodium hydroxide solution (solid-liquid mass-volume ratio of 1 g: 30 mL), stir and etch at 80°C for 6 hours, filter, wash with deionized water and anhydrous ethanol in sequence until the pH of the filtrate is neutral, and vacuum dry at 80°C for 12 hours to obtain the porous carbon material.

[0032] (4) The porous carbon material was placed in a quartz boat in a tube furnace and heated to 600°C at a heating rate of 5°C / min under an argon atmosphere. Then, argon was introduced into a bubble bottle containing acetonitrile at a flow rate of 100 mL / min (the bubble bottle was placed in a 25°C constant temperature water bath) using a bubbling method. The carrier gas containing acetonitrile vapor was introduced into the reaction zone of the tube furnace, and the volume fraction of acetonitrile vapor in the atmosphere was 10%. After deposition at 600°C for 180 minutes, the acetonitrile vapor supply was cut off, and the material was naturally cooled to room temperature under a pure argon atmosphere to obtain the sodium-ion battery anode material.

[0033] Tests showed that the silicon content of the silica-containing carbon material in step (2) was approximately 24.3%. The specific surface area of ​​the porous carbon material in step (3) was 382 m². 2 / g, total pore volume is 0.37cm³ 3 / g. The specific surface area of ​​the sodium-ion battery anode material in step (4) is 8m². 2 The nitrogen content was 5.2 wt%, and the residual silicon content was 0.15 wt%. It can be seen that compared with the raw material in step (1) and the silica-containing carbon material in step (2), the residual silicon content of the sodium-ion battery anode material was significantly reduced, indicating that acid washing can leave silicon elements as a template, while alkaline etching can remove the silica template. Simultaneously, after chemical vapor deposition treatment, the open pores on the surface of the porous carbon material were significantly reduced, and the specific surface area decreased dramatically from 382 m² / g to 8 m² / g. Some pores were covered and sealed by the nitrogen-containing carbon layer, verifying the effective regulation and sealing effect of chemical vapor deposition on the pore structure.

[0034] Figure 1 The image shows a SEM image (including a partial cross-section) of the silica-containing carbon material from step (2). Figure 2 The image shows a SEM image of the porous carbon material from step (3). Figure 3 The image shows a SEM image of the sodium-ion battery anode material from step (4). Figure 1 As shown, the silica-containing carbon material from step (2) exhibits the natural fibrous / layered morphology retained after rice husk carbonization, with a relatively dense overall structure but a small number of pores. Figure 2 As shown, the porous carbon material in step (3) exhibits a highly open, sponge-like porous structure, with numerous interconnected cavities separated by thin carbon walls, resulting in extremely abundant pores. Figure 3 As shown, the surface of the sodium-ion battery anode material in step (4) is extremely smooth and flat, with only some incompletely closed circular holes remaining. The surface between the holes is very uniform. This highly smooth surface morphology is a typical feature of carbon layers after chemical vapor deposition.

[0035] The sodium-ion battery anode material of this embodiment has a reversible specific capacity of 328 mAh / g at a current density of 0.1 A / g, an initial coulombic efficiency of 88.6%, and a capacity retention rate of 94.2% after 500 cycles at a current density of 1 A / g.

[0036] Example 2

[0037] Compared with Example 1, the difference between the sodium-ion battery anode material and its preparation method in this example is that the hydrochloric acid concentration in step (1) is 3 mol / L, and the mixture is stirred and acid-washed at 20°C for 0.5 hours.

[0038] The specific surface area of ​​the porous carbon material in step (3) was tested to be 370 m². 2 / g, total pore volume is 0.35cm³ 3 / g. The specific surface area of ​​the sodium-ion battery anode material in step (4) is 12m². 2 The nitrogen content is 5.1 wt%, and the residual silicon content is 0.21 wt%. The reversible specific capacity at a current density of 0.1 A / g is 315 mAh / g, the initial coulombic efficiency is 86.2%, and the capacity retention after 500 cycles at a current density of 1 A / g is 92.5%.

[0039] Example 3

[0040] Compared with Example 1, the difference between the sodium-ion battery anode material and its preparation method in this example is that the hydrochloric acid concentration in step (1) is 0.5 mol / L, and the mixture is stirred and acid-washed at 90°C for 6 hours.

[0041] The specific surface area of ​​the porous carbon material in step (3) was tested to be 378 m².2 / g, total pore volume is 0.36cm³ 3 / g. The specific surface area of ​​the sodium-ion battery anode material in step (4) is 9m². 2 The nitrogen content is 5.2 wt%, and the residual silicon content is 0.16 wt%. The reversible specific capacity at a current density of 0.1 A / g is 325 mAh / g, the initial coulombic efficiency is 88.2%, and the capacity retention after 500 cycles at a current density of 1 A / g is 93.8%.

[0042] Example 4

[0043] Compared with Example 1, the difference between the sodium-ion battery anode material and its preparation method in this example is that the carbonization temperature in step (2) is 800°C and the holding time is 6 hours.

[0044] The specific surface area of ​​the porous carbon material in step (3) was tested to be 350 m². 2 / g, total pore volume is 0.33cm³ 3 / g. The specific surface area of ​​the sodium-ion battery anode material in step (4) is 14m². 2 The nitrogen content is 5.5 wt%, and the residual silicon content is 0.18 wt%. The reversible specific capacity at a current density of 0.1 A / g is 308 mAh / g, the initial coulombic efficiency is 86.1%, and the capacity retention after 500 cycles at a current density of 1 A / g is 92.2%.

[0045] Example 5

[0046] Compared with Example 1, the difference between the sodium-ion battery anode material and its preparation method in this example is that the carbonization temperature in step (2) is 1400°C and the holding time is 1 hour.

[0047] The specific surface area of ​​the porous carbon material in step (3) was tested to be 305 m². 2 / g, total pore volume is 0.27cm³ 3 / g. The specific surface area of ​​the sodium-ion battery anode material in step (4) is 16m². 2 The nitrogen content is 4.5wt%, and the residual silicon content is 0.42wt%. The reversible specific capacity at a current density of 0.1A / g is 292mAh / g, the initial coulombic efficiency is 86.5%, and the capacity retention after 500 cycles at a current density of 1A / g is 90.8%.

[0048] Example 6

[0049] Compared with Example 1, the difference between the sodium-ion battery anode material and its preparation method in this example is that the sodium hydroxide solution concentration in step (3) is 1 mol / L, and the etching is carried out by stirring at 100°C for 6 hours.

[0050] The specific surface area of ​​the porous carbon material in step (3) was tested to be 398 m². 2 / g, total pore volume is 0.41cm³ 3 / g. The specific surface area of ​​the sodium-ion battery anode material in step (4) is 10m². 2 The nitrogen content is 5.2 wt%, and the residual silicon content is 0.12 wt%. The reversible specific capacity at a current density of 0.1 A / g is 323 mAh / g, the initial coulombic efficiency is 87.8%, and the capacity retention after 500 cycles at a current density of 1 A / g is 93.8%.

[0051] Example 7

[0052] Compared with Example 1, the difference between the sodium-ion battery anode material and its preparation method in this example is that the sodium hydroxide solution concentration in step (3) is 3 mol / L, and the etching is carried out by stirring at 40°C for 18 hours.

[0053] The specific surface area of ​​the porous carbon material in step (3) was tested to be 345 m². 2 / g, total pore volume is 0.31cm³ 3 / g. The specific surface area of ​​the sodium-ion battery anode material in step (4) is 13m². 2 The nitrogen content is 4.8 wt%, and the residual silicon content is 0.28 wt%. The reversible specific capacity at a current density of 0.1 A / g is 308 mAh / g, the initial coulombic efficiency is 86.2%, and the capacity retention after 500 cycles at a current density of 1 A / g is 92.5%.

[0054] Example 8

[0055] Compared with Example 1, the difference between the sodium-ion battery anode material and its preparation method in this example is that: in step (4), the nitrogen-containing carbon source is pyridine, and the volume fraction of pyridine vapor in the atmosphere is 15%; and it is deposited at 1000°C for 30 minutes.

[0056] Tests showed that the specific surface area of ​​the sodium-ion battery anode material is 6 m². 2 The nitrogen content is 4.1 wt%, and the residual silicon content is 0.14 wt%. The reversible specific capacity at a current density of 0.1 A / g is 318 mAh / g, the initial coulombic efficiency is 89.2%, and the capacity retention after 500 cycles at a current density of 1 A / g is 93.4%.

[0057] Example 9

[0058] Compared with Example 1, the difference between the sodium-ion battery anode material and its preparation method in this example is that after step (3) and before step (4), the following pulse electric heating treatment step is also included: the porous carbon material is loaded between two graphite electrodes and pressed tightly, and a pulse voltage of 150V is applied at room temperature and under an argon atmosphere. The pulse duration is 1000ms, and the pulse is repeated 5 times with a 10-second interval between each pulse, thus completing the pulse electric heating treatment.

[0059] Tests showed that the specific surface area of ​​the sodium-ion battery anode material is 5 m². 2 The nitrogen content is 5.3 wt%, and the residual silicon content is 0.11 wt%. The reversible specific capacity at a current density of 0.1 A / g is 348 mAh / g, the initial coulombic efficiency is 91.5%, and the capacity retention after 500 cycles at a current density of 1 A / g is 95.8%.

[0060] Example 10

[0061] Compared with Example 1, the difference between the sodium-ion battery anode material and its preparation method in this example is that bamboo powder (60-100 mesh, silicon content of about 0.5wt%, calculated as Si element) is used instead of rice husk in step (1), and the conditions of the other steps are the same as in Example 1.

[0062] The specific surface area of ​​the porous carbon material in step (3) was tested to be 165 m². 2 / g, total pore volume is 0.18cm³ 3 / g; The specific surface area of ​​the sodium-ion battery anode material in step (4) is 18m². 2 The nitrogen content is 4.8 wt%, and the residual silicon content is 0.08 wt%. The reversible specific capacity at a current density of 0.1 A / g is 288 mAh / g, the initial coulombic efficiency is 85.8%, and the capacity retention after 500 cycles at a current density of 1 A / g is 91.5%.

[0063] Compare with Example 1 Compared with Example 1, the difference between the sodium-ion battery anode material and its preparation method in this comparative example is that the acid washing treatment in step (1) is not performed, and the dried rice husk raw material is directly used for the carbonization treatment in step (2). The conditions of the remaining steps are the same as those in Example 1.

[0064] Tests showed that the silicon content of the silica-containing carbon material in step (2) was approximately 23.8%. The specific surface area of ​​the porous carbon material in step (3) was 295 m². 2 / g, total pore volume is 0.28cm³ 3 / g. The nitrogen content of the sodium-ion battery anode material in step (4) is 3.6wt%, and the residual silicon content is 0.35wt%; the reversible specific capacity at a current density of 0.1A / g is 255mAh / g, the initial coulombic efficiency is 66.8%, and the capacity retention rate after 500 cycles at a current density of 1A / g is 74.2%.

[0065] Compare with Example 2 Compared with Example 1, the difference between the sodium-ion battery anode material and its preparation method in this comparative example is that the acid solution in step (1) is replaced by a 10% hydrofluoric acid solution instead of a hydrochloric acid solution, while the remaining acid washing conditions and subsequent step conditions are the same as in Example 1. Since hydrofluoric acid can dissolve silicon dioxide, silicon dioxide and metal impurities in the raw materials are removed simultaneously after acid washing.

[0066] Testing revealed that the silicon content of the silica-containing carbon material in step (2) was approximately 0.1%, significantly lower than the 24.3% in Example 1. The specific surface area of ​​the porous carbon material in step (3) was 78 m². 2 / g, total pore volume is 0.07cm³ 3 / g. The specific surface area of ​​the sodium-ion battery anode material in step (4) is 10m². 2 The nitrogen content is 1.8 wt%, and the residual silicon content is 0.03 wt%. The reversible specific capacity at a current density of 0.1 A / g is 248 mAh / g, the initial coulombic efficiency is 84.5%, and the capacity retention after 500 cycles at a current density of 1 A / g is 86.2%.

[0067] Compare with Example 3 Compared with Example 1, the difference between the sodium-ion battery anode material and its preparation method in this comparative example is that the alkaline etching treatment in step (3) is not performed, that is, the silicon dioxide-containing carbon material obtained in step (2) is directly used for the chemical vapor deposition treatment in step (4), and the conditions of the remaining steps are the same as those in Example 1.

[0068] Tests showed that the specific surface area of ​​the sodium-ion battery anode material is 21 m². 2 The nitrogen content is 2.8% and the residual silicon content is 20.3wt%. The reversible specific capacity at a current density of 0.1A / g is 218mAh / g, the initial coulombic efficiency is 52.8%, and the capacity retention after 500 cycles at a current density of 1A / g is 75.5%.

[0069] Compare with Example 4 Compared with Example 1, the difference between the sodium-ion battery anode material and its preparation method in this comparative example is that the chemical vapor deposition treatment in step (4) is not performed, that is, the porous carbon material obtained in step (3) is directly used as the anode material, and the conditions of the remaining steps are the same as those in Example 1.

[0070] Tests showed that the specific surface area of ​​the porous carbon material (i.e., the anode material) was 382 m². 2 The nitrogen content is 0.2 wt%, the reversible specific capacity at a current density of 0.1 A / g is 275 mAh / g, the initial coulombic efficiency is 49.2%, and the capacity retention after 500 cycles at a current density of 1 A / g is 82.2%.

[0071] Compare with Example 5 Compared with Example 1, the difference between the sodium-ion battery anode material and its preparation method in this comparative example is that the chemical vapor deposition treatment in step (4) is not performed. Instead, before the carbonization treatment in step (2), the acid-washed raw material and melamine are uniformly mixed at a mass ratio of 1:0.3 and then subjected to the same carbonization treatment and alkaline etching treatment as in Example 1. The etched product is directly used as the anode material.

[0072] Tests showed that the specific surface area of ​​the porous carbon material (i.e., the negative electrode material) was 365 m². 2 The nitrogen content is 3.0 wt%, and the residual silicon content is 0.14 wt%. The reversible specific capacity at a current density of 0.1 A / g is 282 mAh / g, the initial coulombic efficiency is 56.2%, and the capacity retention after 500 cycles at a current density of 1 A / g is 83.5%.

[0073] In the above embodiments and comparative examples, the testing methods for each performance data are as follows: Specific surface area and total pore volume testing: Nitrogen adsorption-desorption tests were conducted at 77 K using a fully automated specific surface area and porosity analyzer. The specific surface area was calculated using the Brunauer-Emmett-Teller (BET) method, and the total pore volume was converted from the amount of nitrogen adsorbed at a relative pressure P / P0 = 0.99.

[0074] Nitrogen content test: The sample was completely burned in an oxygen atmosphere using an elemental analyzer, and the generated nitrogen-containing gas was quantitatively detected by a thermal conductivity detector to calculate the mass fraction of nitrogen in the material.

[0075] Residual silicon content test: A certain amount of sample was weighed and completely dissolved using an acid digestion method (microwave digestion of nitric acid-hydrofluoric acid mixed acid). The concentration of silicon in the solution was determined by inductively coupled plasma optical emission spectrometry (ICP-OES) and converted into the mass fraction of silicon in the sample.

[0076] Electrochemical performance testing: The negative electrode material, acetylene black conductive agent, and polyvinylidene fluoride binder were mixed in a mass ratio of 8:1:1, and N-methyl-2-pyrrolidone was used as a solvent to prepare a slurry. This slurry was uniformly coated onto a copper foil current collector, vacuum dried at 120°C for 12 hours, and then punched into circular electrodes with a diameter of 12 mm. The surface loading of the active material was approximately 1.0–1.5 mg / cm³. 2 CR2032 coin cells were assembled in an argon-filled glove box (water and oxygen content both below 0.1 ppm). A sodium metal sheet was used as the counter / reference electrode, a Whatman GF / D glass fiber membrane as the separator, and a solution of 1 mol / L NaClO4 dissolved in ethylene carbonate / propylene carbonate (volume ratio 1:1) with 5 vol% fluoroethylene carbonate added as the electrolyte. Constant current charge-discharge tests were conducted at 25°C using a battery testing system, with a voltage window of 0.01–2.0 V (vs. NaClO4). + / Na). The reversible specific capacity and initial coulombic efficiency were derived from the discharge specific capacity and charge-discharge efficiency at the initial cycle density of 0.1 A / g; the cycle stability test was performed by first activating the device at 0.1 A / g for 3 cycles, followed by 500 cycles at a current density of 1 A / g, and the capacity retention was calculated using the following formula: Capacity retention rate = (specific capacity of discharge cycle 100 / specific capacity of discharge cycle 1) × 100%.

[0077] The embodiments of the invention provided in this specification have been described above. Those skilled in the art will be able to implement the embodiments of the invention provided in this specification based on these descriptions. All other preferred embodiments and implementations obtained by those skilled in the art based on the above description of the embodiments of the invention provided in this specification without inventive effort should fall within the protection scope of the embodiments of the invention provided in this specification.

Claims

1. A method for preparing a sodium-ion battery anode material, characterized in that: Includes the following steps: (1) The silicon-containing biomass raw material is subjected to acid washing treatment to remove alkali metal elements and alkaline earth metal elements from the silicon-containing biomass raw material, while retaining silicon dioxide, to obtain the acid-washed raw material; the acid solution used in the acid washing treatment is at least one of hydrochloric acid solution, sulfuric acid solution, and nitric acid solution, the concentration of the acid solution is 0.5-3 mol / L, the acid washing temperature is 20-90°C, and the acid washing time is 0.5-6 hours; (2) The acid-washed raw material is carbonized under an inert atmosphere to obtain a carbon material containing silicon dioxide; (3) The silica-containing carbon material is mixed with an alkaline solution and etched to remove the silica from the silica-containing carbon material. After washing and drying, a porous carbon material is obtained. The concentration of the alkaline solution is 1-3 mol / L, the etching temperature is 40-100°C, and the etching time is 6-18 hours. (4) The porous carbon material is subjected to chemical vapor deposition in an atmosphere containing a nitrogen carbon source to deposit a nitrogen-containing carbon layer in the pores of the porous carbon material to obtain the sodium-ion battery anode material; the nitrogen-containing carbon source is acetonitrile and / or pyridine.

2. The preparation method according to claim 1, characterized in that: The silicon-containing biomass raw material is selected from at least one of bamboo, rice husk, wheat straw, and sugarcane bagasse.

3. The preparation method according to claim 1, characterized in that: In step (2), the carbonization temperature is 800-1400°C, the holding time is 1-6 hours, and the inert atmosphere is argon or nitrogen.

4. The preparation method according to claim 1, characterized in that: In step (3), the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution.

5. The preparation method according to claim 1, characterized in that: In step (4), the carrier gas is selected from argon or nitrogen. The carrier gas is introduced into the nitrogen-containing carbon source by bubbling to form an atmosphere composed of carrier gas and nitrogen-containing carbon source vapor. The volume fraction of the nitrogen-containing carbon source vapor in the atmosphere is 10-15%. The temperature of the chemical vapor deposition treatment is 600-1000°C and the time is 30-180 minutes.

6. The preparation method according to any one of claims 1-5, characterized in that: After step (3) and before step (4), the process also includes: placing the porous carbon material between the two electrodes for pulsed electric heating treatment.

7. The preparation method according to claim 6, characterized in that: The pulse voltage of the pulsed electric heating treatment is 30-300V, the single pulse duration is 500-2000ms, and the number of pulses is 1-10.

8. The sodium-ion battery anode material prepared by the preparation method according to any one of claims 1-7, characterized in that: The residual silicon content is no more than 0.45 wt%, and the nitrogen content is 3.5-6%; the reversible specific capacity at a current density of 0.1 A / g is 280-350 mAh / g, and the initial coulombic efficiency is 85-92%; the capacity retention after 500 cycles at a current density of 1 A / g is ≥90%.

9. A sodium-ion battery, characterized in that: Its negative electrode uses the sodium-ion battery negative electrode material as described in claim 8, or the sodium-ion battery negative electrode material prepared by any one of the preparation methods described in claims 1-7.

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