Hard carbon negative electrode material and preparation method and application thereof

Abstract

The invention discloses a hard carbon negative electrode material and a preparation method and application thereof, and relates to the technical field of batteries, the hard carbon negative electrode material comprises asphalt, cellulose and lignin, in the hard carbon negative electrode material, the mass ratio of the asphalt to the cellulose to the lignin is (3-6): (1-3): (1-3), and the mass ratio of the asphalt to the cellulose to the lignin is (3-6): (1-3): (1-3). According to the hard carbon material prepared by adopting the components, a rich microporous structure and a relatively large specific surface area are formed in the hard carbon material, so that relatively good electrolyte wettability and a lithium ion diffusion channel can be kept even at a low temperature, and the good cycling stability and relatively high capacity of the battery are ensured.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a hard carbon anode material, its preparation method, and its application. Background Technology

[0002] With the growing global demand for renewable energy, lithium-ion batteries (LIBs) have become dominant due to their high energy density and mature technology. However, the low abundance and uneven distribution of lithium resources in the Earth's crust lead to significant fluctuations in raw material prices. In contrast, abundant and inexpensive sodium resources make sodium-ion batteries (SIBs) a highly promising alternative. However, the performance of sodium-ion batteries is limited by the anode material, especially in low-temperature environments.

[0003] In the field of sodium-ion battery anode materials, hard carbon materials have attracted much attention due to their unique disordered structure and abundant sodium storage sites. Currently, commercially applicable hard carbon materials mainly face three key problems: First, hard carbon materials prepared from a single precursor often struggle to achieve both high capacity and long-term cycle stability. For example, while hard carbon derived from pure pitch exhibits good conductivity, its sodium storage capacity is limited, while hard carbon derived from pure biomass has a high initial capacity but poor cycle performance. Second, traditional preparation processes, such as high-temperature graphitization, are not only energy-intensive but also difficult to precisely control the microstructural parameters of the material, such as interlayer spacing and pore distribution. Third, at low temperatures, the conductivity of the material decreases, limiting ion transport and leading to a decline in energy storage capacity. Although existing research has attempted to improve performance through precursor modification or doping, the effects are limited and the processes are complex. Therefore, developing a hard carbon anode material with excellent cycle stability, high capacity, and low cost at low temperatures has become a key technological challenge for promoting the commercial application of sodium-ion batteries. This invention presents an innovative solution against this technological backdrop. Summary of the Invention

[0004] The main objective of this invention is to provide a hard carbon anode material, its preparation method, and its application, aiming to solve the problem that existing hard carbon materials prepared from a single precursor often struggle to achieve both high capacity and long-cycle stability.

[0005] To achieve the above objectives, the present invention proposes a hard carbon anode material, wherein the raw materials of the hard carbon anode material include asphalt, cellulose and lignin, wherein the mass ratio of the asphalt, the cellulose and the lignin in the hard carbon anode material is (3~6): (1~3): (1~3).

[0006] In one implementation, the following steps are included: The asphalt, cellulose and lignin are mixed and dried to obtain a composite precursor; The composite precursor was mechanically processed and then carbonized in an inert atmosphere to obtain a hard carbon anode material.

[0007] In one embodiment, the drying temperature is 80~100°C; and / or, The drying time is 10-16 hours.

[0008] In one embodiment, the mechanical treatment includes grinding or ball milling.

[0009] In one embodiment, the ball milling process is performed at a rotational speed of 800-1000 rpm; and / or, The ball milling process takes 4 to 8 hours.

[0010] In one embodiment, the carbonization process includes heating to 800-1000 °C at a heating rate of 1-5 °C / min and holding at that temperature for 2-4 h.

[0011] The present invention also proposes a hard carbon electrode sheet, which includes a hard carbon anode material, carbon black and additives, wherein the hard carbon anode material includes the hard carbon anode material as described above or the hard carbon anode material prepared by the preparation method of the hard carbon anode material as described above.

[0012] The present invention also proposes a battery comprising the hard carbon electrode as described above.

[0013] The present invention also provides an electrical appliance, which includes the battery described above.

[0014] In the technical solution of this invention, the raw materials of the hard carbon anode material include asphalt, cellulose, and lignin. The mass ratio of the asphalt, cellulose, and lignin in the hard carbon anode material is (3~6):(1~3):(1~3). On the one hand, using low-cost, widely available, and relatively inexpensive raw materials not only reduces production costs but also benefits environmental protection. Asphalt can serve as a carbon source, forming a graphitized carbon structure with good conductivity during high-temperature pyrolysis. Simultaneously, its rich aromatic layered structure helps improve the mechanical strength of the final hard carbon material. Cellulose is a natural polymer compound rich in hydroxyl groups (-OH). These functional groups can promote the formation of microporous structures during pyrolysis, increasing the specific surface area of ​​the material, thereby facilitating electrolyte wetting and rapid lithium-ion diffusion, and improving battery charging efficiency. Discharge efficiency and capacity are improved, while lignin contains more aromatic ring structures and fewer hydrophilic groups. During carbonization, it can provide an additional carbon source and help form a more complex three-dimensional network structure, which is very beneficial for improving the cycle stability and mechanical properties of the material. On the other hand, the hard carbon material prepared by controlling the above components within the above range has obtained the formation of graphite-like microcrystals and rich micropore / closed-pore structures due to the rich microporous structure and large specific surface area formed inside. This allows it to maintain good electrolyte wettability and sodium ion diffusion channels even at low temperatures, thereby ensuring good cycle stability and high capacity of the battery. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0016] Figure 1 This is a SEM image of the hard carbon anode material obtained in Example 1 of the present invention; Figure 2 The images show the first three charge-discharge test diagrams (left) and the rate performance test diagram (right) of the hard carbon anode material obtained in Example 1 of this invention. Figure 3 This is a qualitative diagram of the cycle stability of the hard carbon anode material obtained in Example 1 of the present invention; Figure 4 The diagram shows the first three charge-discharge test results of the hard carbon anode material obtained in Example 1 of this invention at low temperature (-20℃) and the cycle performance diagram of the hard carbon anode material obtained in Example 2 at low temperature (-20℃). Figure 5This is a SEM image of the hard carbon anode material obtained in Example 2 of the present invention; Figure 6 The first three charge-discharge test diagrams and rate performance test diagrams of the hard carbon anode material obtained in Example 2 of this invention are shown. Figure 7 This is a qualitative diagram of the cycle stability of the hard carbon anode material obtained in Example 2 of the present invention; Figure 8 The diagram shows the first three charge-discharge test results and the cycle performance at low temperature (-20°C) of the hard carbon anode material obtained in Example 2 of this invention. Figure 9 This is a SEM image of the hard carbon anode material obtained in Example 3 of the present invention; Figure 10 The first three charge-discharge test diagrams and rate performance test diagrams of the hard carbon anode material obtained in Example 3 of this invention are shown. Figure 11 This is a qualitative diagram of the cycle stability of the hard carbon anode material obtained in Example 3 of the present invention; Figure 12 The diagram shows the first three charge-discharge test results and the cycle performance at low temperature (-20°C) of the hard carbon anode material obtained in Example 3 of this invention. Figure 13 This is a SEM image of the hard carbon anode material obtained in Example 4 of the present invention; Figure 14 The first three charge-discharge test diagrams and rate performance test diagrams of the hard carbon anode material obtained in Example 4 of this invention are shown. Figure 15 This is a qualitative diagram of the cycle stability of the hard carbon anode material obtained in Example 4 of the present invention; Figure 16 The diagram shows the first three charge-discharge test results and the cycle performance at low temperature (-20°C) of the hard carbon anode material obtained in Example 4 of this invention. Figure 17 This is a SEM image of the hard carbon anode material obtained in Comparative Example 1 of this invention; Figure 18 The first three charge-discharge test diagrams and rate performance test diagrams of the hard carbon anode material obtained in Comparative Example 1 of this invention are shown. Figure 19 This is a qualitative diagram of the cycle stability of the hard carbon anode material obtained in Comparative Example 1 of this invention; Figure 20 The diagram shows the first three charge-discharge test results and the cycle performance at low temperature (-20°C) of the hard carbon anode material obtained in Comparative Example 1 of this invention. Figure 21This is a SEM image of the hard carbon anode material obtained in Comparative Example 2 of this invention; Figure 22 The first three charge-discharge test diagrams and rate performance test diagrams of the hard carbon anode material obtained in Comparative Example 2 of this invention are shown. Figure 23 This is a qualitative diagram of the cycle stability of the hard carbon anode material obtained in Comparative Example 2 of the present invention; Figure 24 The diagram shows the first three charge-discharge test results and the cycle performance at low temperature (-20°C) of the hard carbon anode material obtained in Comparative Example 2 of this invention. Figure 25 This is a SEM image of the hard carbon anode material obtained in Comparative Example 3 of this invention; Figure 26 The first three charge-discharge test diagrams and rate performance test diagrams of the hard carbon anode material obtained in Comparative Example 3 of this invention are shown. Figure 27 This is a qualitative diagram of the cycle stability of the hard carbon anode material obtained in Comparative Example 3 of the present invention; Figure 28 The diagram shows the first three charge-discharge test results and the cycle performance at low temperature (-20°C) of the hard carbon anode material obtained in Comparative Example 3 of this invention. Figure 29 This is a SEM image of the hard carbon anode material obtained in Comparative Example 4 of this invention; Figure 30 The first three charge-discharge test diagrams and rate performance test diagrams of the hard carbon anode material obtained in Comparative Example 4 of this invention are shown. Figure 31 This is a qualitative diagram of the cycle stability of the hard carbon anode material obtained in Comparative Example 4 of the present invention; Figure 32 The diagram shows the first three charge-discharge test results and the cycle performance at low temperature (-20°C) of the hard carbon anode material obtained in Comparative Example 4 of this invention. Figure 33 These are Raman test graphs for Examples 1, 2, 3 and Comparative Examples 1, 2 of the present invention.

[0017] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0020] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0021] Currently, commercially available hard carbon materials face three main challenges: First, hard carbon materials prepared from a single precursor often struggle to achieve both high capacity and long-term cycle stability. For example, while hard carbon derived from pure pitch exhibits good conductivity, its sodium storage capacity is limited, whereas hard carbon derived from pure biomass has a high initial capacity but poor cycle performance. Second, traditional preparation processes, such as high-temperature graphitization, are not only energy-intensive but also difficult to precisely control the microstructural parameters of the material, such as interlayer spacing and pore distribution. Third, at low temperatures, the conductivity of the material decreases, limiting ion transport and leading to a decline in energy storage capacity. Although existing research has attempted to improve performance through precursor modification or doping, the effects have been limited and the processes complex. Therefore, developing a hard carbon anode material with excellent cycle stability, high capacity, and low cost at low temperatures has become a key technological challenge for promoting the commercial application of sodium-ion batteries. This invention presents an innovative solution against this technological backdrop.

[0022] In view of this, the present invention proposes a hard carbon anode material, wherein the raw materials of the hard carbon anode material include asphalt, cellulose and lignin, wherein the mass ratio of the asphalt, the cellulose and the lignin in the hard carbon anode material is (3~6): (1~3): (1~3).

[0023] In the technical solution of this invention, on the one hand, the use of low-cost, widely available, and relatively inexpensive raw materials not only reduces production costs but also benefits the environment. Asphalt can serve as a carbon source, forming a graphitized carbon structure with good conductivity during high-temperature pyrolysis. Simultaneously, its abundant aromatic layered structure helps improve the mechanical strength of the final hard carbon material. Cellulose is a natural polymer compound rich in hydroxyl groups (-OH). These functional groups promote the formation of microporous structures during pyrolysis, increasing the specific surface area of ​​the material, thus facilitating electrolyte wetting and rapid lithium-ion diffusion, improving battery charge-discharge efficiency and capacity. Lignin contains more aromatic ring structures and fewer hydrophilic groups. During carbonization, it can provide additional carbon sources and help form more complex three-dimensional network structures, which is highly beneficial for improving the material's cycle stability and mechanical properties. On the other hand, the hard carbon material prepared from the above components, due to its abundant microporous structure and large specific surface area, maintains good electrolyte wetting and lithium-ion diffusion channels even at low temperatures, thereby ensuring good battery cycle stability and high capacity.

[0024] It is understood that in the hard carbon anode material, the mass ratio between the asphalt, the cellulose, and the lignin is (3~6): (1~3): (1~3). Specifically, the mass ratio between the asphalt, the cellulose, and the lignin can be, but is not limited to, a variety of combinations of proportions such as 3:2:2, 3:1:1, 3:1:3, 4:2:2, 5:2:1, 6:1:1, or 3:3:2. By precisely controlling the material ratio in the hard carbon anode material, the material structure is optimized, and graphite-like microcrystals and abundant micropore / closed-pore structures can be formed. This can be obtained from the scanning electron microscope (SEM) and Raman images in the attached figures.

[0025] In some embodiments, the following steps are included: The asphalt, cellulose and lignin are mixed and dried to obtain a composite precursor; The composite precursor was mechanically processed and then carbonized in an inert atmosphere to obtain a hard carbon anode material.

[0026] In the preparation steps of this invention, firstly, a multi-layered pore structure and a stable carbon network are constructed by utilizing the synergistic effect of pitch, cellulose, and lignin. Then, through low-temperature drying, high-energy ball milling, and gradient carbonization treatment, the carbon structure is precisely controlled, balancing performance and cost, making it suitable for large-scale industrial production. In some embodiments, the drying temperature is 80~100℃ and the drying time is 10~16h. Specifically, the drying temperature can be 80℃, 90℃ or 100℃, and the drying time can be 10h, 13h or 16h, etc. Within the above range, moisture or solvents (such as water, ethanol, etc.) can be effectively removed, avoiding the generation of violent steam during the subsequent carbonization process, which may cause the material to crack or the pore structure to be damaged.

[0027] In some embodiments, the mechanical treatment includes grinding or ball milling. Mechanical treatment can refine the precursor particles to the micrometer or even submicrometer level. Small particle size is beneficial to increasing the electrode / electrolyte contact area and improving lithium-ion transport efficiency, especially at low temperatures. It can also improve the uniformity of heat conduction during subsequent carbonization and reduce local overheating or uneven carbonization. Therefore, grinding or ball milling is used to achieve the above functions.

[0028] In some embodiments, the ball milling speed is 800~1000 rpm; the ball milling time is 4~8 h. Specifically, the ball milling speed can be 800 rpm, 900 rpm or 1000 rpm. Within the above ball milling range, effective crushing and mixing can be achieved, but it is not too high, which may cause equipment wear or excessive material disorder. The specific ball milling time can be 4 h, 6 h or 8 h. If the time is too short, the mixing will be insufficient, and if the time is too long, it may lead to excessive amorphization or introduce too many defects.

[0029] In some embodiments, the carbonization process includes heating to 800-1000°C at a heating rate of 1-5°C / min and holding at that temperature for 2-4 hours. Specifically, the heating rate of the carbonization process can be 1°C / min, 3°C / min, 4°C / min, 5°C / min, etc., the temperature of the carbonization process can be 800°C, 900°C, 1000°C, etc., and the carbonization time can be 2 hours, 3 hours, 4 hours, etc. Within the above heating range, volatile components can be gradually released, while internal pressure accumulation can be avoided to prevent cracks or pore collapse, thereby improving the structural integrity of the carbonized product.

[0030] Furthermore, by holding the temperature at 800~1000℃ for 2~4 h, a typical hard carbon structure of "graphite-like microcrystals + abundant micropores / closed pores" can be formed. It has a large interlayer spacing, which is conducive to lithium ion insertion and can store a large number of lithium ions, contributing high capacity. Appropriate defects and functional groups help lithium ion adsorption and diffusion at low temperature. An excellent microstructure was obtained through the above gradient carbonization process.

[0031] The present invention also proposes a hard carbon electrode sheet, which includes a hard carbon anode material, carbon black and additives, wherein the hard carbon anode material includes the hard carbon anode material as described above or the hard carbon anode material prepared by the preparation method of the hard carbon anode material as described above.

[0032] The present invention also proposes a battery comprising the hard carbon electrode as described above.

[0033] The present invention also provides an electrical appliance, which includes the battery described above.

[0034] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0035] Example 1 Step 1: 4 g of pitch, 2 g of cellulose, and 2 g of lignin were dried at 80 °C for 12 h to remove moisture. They were then placed in a ball mill jar and ball-milled at 900 rpm for 6 hours to ensure thorough mixing. After ball milling, the mixture was evenly spread in a ceramic boat and placed in a tube furnace. The furnace was heated to 800 °C at a rate of 5 °C / min under a nitrogen atmosphere and held at the target temperature for 2 hours for carbonization. After carbonization, the mixture was allowed to cool naturally to room temperature to obtain the hard carbon anode material. Its SEM image is shown below. Figure 1 As shown.

[0036] Step 2: The hard carbon anode material obtained in Step 1 is prepared into a slurry according to the ratio of hard carbon anode material: carbon black: PVDF = 8:1:1, and coated onto copper foil to obtain a hard carbon electrode sheet. This hard carbon electrode sheet is used as the anode of a sodium-ion battery, and the battery is assembled in an argon-filled glove box. The hard carbon electrode sheet, glass fiber, and sodium sheet are used as the working electrode, separator, and counter electrode, respectively. The electrolyte is 1M NaSO3CF3 / Diglyme solvent. After assembly, the battery is allowed to stand at 25°C for 8 hours, and then subjected to a 25 mAg test. -1 It was subjected to charge-discharge cycles at current density. Its first-cycle discharge specific capacity reached 346.5 mAh g⁻¹, and its first-cycle charge-discharge efficiency reached 79.5%. Figure 2 (Left figure in the image) The current density is increased to 0.1 A g⁻¹, while the capacity remains at 163.1 mAh g⁻¹.-1 ( Figure 2 (The right figure in the image), and at 25 mA g -1 and 500 mA g -1 After 100 and 1000 cycles of stability testing, the initial capacity was maintained at 74.5%. Figure 3 (Figure a) and 69.1% ( Figure 3 (See Figure b in the text). Furthermore, at a low temperature of -20°C and at 25 mA g... -1 It still exhibits a capacity of 302.1 mAh g. -1 initial capacity ( Figure 4 (Left image in the image) and maintaining 60.3% after 100 cycles ( Figure 4 (The right image in the image).

[0037] Example 2 4 g of pitch, 3 g of cellulose, and 3 g of lignin were dried at 100°C for 10 h to remove moisture. They were then placed in a ball mill jar and ball-milled at 850 rpm for 7 h to ensure thorough mixing. After ball milling, the mixture was evenly spread in a ceramic boat and placed in a tube furnace. The furnace was heated to 750°C at a rate of 3°C / min under a nitrogen atmosphere and held at the target temperature for 3 h for carbonization. After carbonization, the mixture was naturally cooled to room temperature to obtain the TCLHC anode material. Its SEM image is shown below. Figure 5 As shown.

[0038] The carbonized hard carbon material was prepared into a slurry with a hard carbon:carbon black:PVDF ratio of 8:1:1 and coated onto copper foil to obtain a hard carbon electrode sheet. This hard carbon electrode sheet was used as the negative electrode of a sodium-ion battery, and the battery was assembled in an argon-filled glove box. The hard carbon electrode sheet, glass fiber, and sodium sheet were used as the working electrode, separator, and counter electrode, respectively, and the electrolyte was 1M NaSO3CF3 / Diglyme solvent. After assembly, the battery was allowed to stand at 25°C for 8 h, and then subjected to a 25 mA g... -1 Under charge-discharge cycling at current density, its first-cycle discharge specific capacity reaches 341.2 mAh g⁻¹. -1 The first charge-discharge efficiency reached 78.8% ( Figure 6 (Left figure in the image), current density increased to 0.1 A g. -1 The capacity remains at 162.9 mAh g. -1 ( Figure 6 (The right figure in the image), and at 25 mA g -1 and 500 mA g -1 After 100 and 1000 lap cycle stability tests, the initial capacity was maintained at 77.5%. Figure 7 (Figure a) and 67.3% ( Figure 7(See Figure b in the original text). Furthermore, it still exhibits a capacity of 300.5 mAh g⁻¹ at a low temperature of -20°C. -1 initial capacity ( Figure 8 (Left figure in the image) and at 25 mA g -1 After 100 cycles, it remains at 59.3%. Figure 8 (The right image in the image).

[0039] Example 3 3g of asphalt, 2g of cellulose, and 2g of lignin were dried at 90°C for 11 hours to remove moisture. They were then placed in a ball mill jar and ball-milled at 1000 rpm for 5 hours to ensure thorough mixing. After ball milling, the mixture was evenly spread in a ceramic boat and placed in a tube furnace. The furnace was heated to 900°C at a rate of 2°C / min under a nitrogen atmosphere and held at the target temperature for 2 hours for carbonization. After carbonization, the mixture was allowed to cool naturally to room temperature to obtain a hard carbon anode material. Its SEM image is shown below. Figure 9 As shown.

[0040] The carbonized hard carbon material was prepared into a slurry with a hard carbon:carbon black:PVDF ratio of 8:1:1 and coated onto copper foil to obtain a hard carbon electrode sheet. This hard carbon electrode sheet was used as the negative electrode of a sodium-ion battery, and the battery was assembled in an argon-filled glove box. The hard carbon electrode sheet, glass fiber, and sodium sheet were used as the working electrode, separator, and counter electrode, respectively, and the electrolyte was 1M NaSO3CF3 / Diglyme solvent. After assembly, the battery was allowed to stand at 25°C for 8 h, and then subjected to a 25 mA g... -1 It was subjected to charge-discharge cycles at current density. Its first-cycle discharge specific capacity reached 340.1 mAh g⁻¹. -1 The first charge-discharge efficiency reached 79.9% ( Figure 10 (Left figure in the image), current density increased to 0.1 A g. -1 The capacity remains at 135.5 mAh g⁻¹. Figure 10 (The right figure in the image), and at 25 mAg -1 and 500 mA g -1 After 100 and 1000 lap cycle stability tests, the initial capacity was maintained at 77.3%. Figure 11 (Figure a) and 70.2% ( Figure 11 (See Figure b in the image). Furthermore, it still exhibits a capacity of 298.5 mAh g⁻¹ at a low temperature of -20°C. -1 initial capacity ( Figure 12 (Left figure in the image) and at 25 mA g -1 After 100 cycles, it remains at 58.2%. Figure 12 (The right image in the image).

[0041] Example 4 3 g of pitch, 3 g of cellulose, and 3 g of lignin were dried at 80°C for 12 h to remove moisture. They were then placed in a ball mill jar and ball-milled at 900 rpm for 6 h to ensure thorough mixing. After ball milling, the mixture was evenly spread in a ceramic boat and placed in a tube furnace. The furnace was heated to 800°C at a rate of 5°C / min under a nitrogen atmosphere and held at the target temperature for 3 hours for carbonization. After carbonization, the mixture was allowed to cool naturally to room temperature to obtain a hard carbon anode material. Its SEM image is shown below. Figure 13 As shown.

[0042] The carbonized hard carbon material was prepared into a slurry with a hard carbon:carbon black:PVDF ratio of 8:1:1 and coated onto copper foil to obtain a hard carbon electrode. This hard carbon electrode was used as the negative electrode of a sodium-ion battery, and the battery was assembled in an argon-filled glove box. The hard carbon electrode, glass fiber, and sodium sheet were used as the working electrode, separator, and counter electrode, respectively. The electrolyte was 1M NaSO3CF3 in Diglyme. After assembly, the battery was allowed to stand at 25°C for 8 h, and then subjected to a 25 mA g... -1 It was subjected to charge-discharge cycles at current density. Its first-cycle discharge specific capacity reached 341.6 mAh g⁻¹. -1 The first charge-discharge efficiency reached 76.4% ( Figure 14 (Left figure in the image), current density increased to 0.1 A g. -1 The capacity remains at 143.2 mAh g. -1 ( Figure 14 (The right figure in the image), and at 25 mAg -1 and 500 mA g -1 After 100 and 1000 lap cycle stability tests, the initial capacity was maintained at 69.7% ( Figure 15 (Figure a) and 64.2% ( Figure 15 (See Figure b in the image). Furthermore, it still exhibits a capacity of 201.2 mAh g⁻¹ at a low temperature of -20°C. -1 initial capacity ( Figure 16 (Left figure in the image) and at 25 mA g -1 After 100 cycles, maintain 63.5% ( Figure 16 (The right image in the image).

[0043] Comparative Example 1 4 g of pitch, 2 g of cellulose, and 2 g of lignin were dried at 80 °C for 12 h to remove moisture. They were then placed in a ball mill jar and ball-milled at 900 rpm for 6 hours to ensure thorough mixing. After ball milling, the mixture was evenly spread in a ceramic boat and placed in a tube furnace. The furnace was heated to 600 °C at a rate of 5 °C / min under a nitrogen atmosphere and held at the target temperature for 2 hours for carbonization. After carbonization, the mixture was naturally cooled to room temperature to obtain the hard carbon anode material. Its SEM image is shown below. Figure 17 As shown.

[0044] The carbonized hard carbon material was prepared into a slurry with a ratio of hard carbon:carbon black:PVDF = 8:1:1 and coated onto copper foil to obtain a hard carbon electrode sheet. This hard carbon electrode sheet was used as the negative electrode of a sodium-ion battery. The battery was assembled in an argon-filled glove box. The hard carbon electrode sheet, glass fiber, and sodium sheet were used as the working electrode, separator, and counter electrode, respectively. The electrolyte was 1M NaSO3CF3 in Diglyme. After assembly, the battery was allowed to stand at 25°C for 8 hours, followed by loading at 25 mA g. -1 Charge-discharge cycles were performed at the specified current density. The first-cycle discharge specific capacity was 279.1 mAh g⁻¹. -1 The first-cycle charge-discharge efficiency was nearly 55.6% ( Figure 18 (Left figure in the image), current density increased to 0.1 A g. -1 The capacity remains at only 61.7 mAh g. -1 ( Figure 18 (The right image in the image) and at 25 mAg -1 and 500 mA g -1 After 100 and 1000 lap cycle stability tests, the initial capacity was maintained at 36.5%. Figure 19 (Figure a) and 20.8% Figure 19 (See Figure b in the original text). Furthermore, at a low temperature of -20°C, it only exhibited a capacity of 109.3 mAh g⁻¹. -1 initial capacity ( Figure 20 (Left figure in the image) and at 25 mA g -1 After 100 cycles, it remains at 24.8%. Figure 20 (The right image in the image).

[0045] Comparative Example 2 2 g of cellulose and 2 g of lignin were dried at 80 °C for 12 hours to remove moisture, then placed in a ball mill jar and ball-milled at 900 rpm for 6 hours to ensure thorough mixing. After ball milling, the mixture was evenly spread in a ceramic boat and placed in a tube furnace. The furnace was heated to 800 °C at a rate of 5 °C / min under a nitrogen atmosphere and held at the target temperature for 2 hours for carbonization. After carbonization, the mixture was allowed to cool naturally to room temperature to obtain hard carbon material, the SEM image of which is shown below. Figure 21 As shown.

[0046] The carbonized hard carbon material was prepared into a slurry with a ratio of hard carbon material: carbon black: PVDF = 8:1:1 and coated onto copper foil to obtain a hard carbon electrode sheet. This hard carbon electrode sheet was used as the negative electrode of a sodium-ion battery. The battery was assembled in an argon-filled glove box. The hard carbon electrode sheet, glass fiber, and sodium sheet were used as the working electrode, separator, and counter electrode, respectively. The electrolyte was 1M NaSO3CF3 in Diglyme. After assembly, the battery was allowed to stand at 25°C for 8 hours, followed by loading at 25 mA g. -1 Charge-discharge cycles were performed at the specified current density. The first discharge specific capacity was 184.4 mAh g⁻¹. -1 The first charge-discharge efficiency was 64.7% ( Figure 22 (Left figure in the image) The current density is increased to 0.1 A g⁻¹, but the capacity remains at only 32.8 mAh g⁻¹. -1 ( Figure 22 (The right figure in the image), and at 25 mAg -1 and 500 mA g -1 After 100 and 1000 lap cycle stability tests, the initial capacity was maintained at 54.8%. Figure 23 (Figure a) and 34.3% ( Figure 23 (See Figure b in the original text). Furthermore, at a low temperature of -20°C, it only exhibited a capacity of 119.5 mAh g⁻¹. -1 initial capacity ( Figure 24 (Left figure in the image) and at 25 mA g -1 After 100 cycles, it remains at 33.4%. Figure 24 (The right image in the image).

[0047] Comparative Example 3 4 g of pitch and 2 g of lignin were dried at 80 °C for 12 hours to remove moisture, then placed in a ball mill jar and ball-milled at 900 rpm for 6 hours to ensure thorough mixing. After ball milling, the mixture was evenly spread in a ceramic boat and placed in a tube furnace. The furnace was heated to 800 °C at a rate of 3 °C / min under a nitrogen atmosphere and held at the target temperature for 3 hours for carbonization. After carbonization, the mixture was allowed to cool naturally to room temperature to obtain hard carbon material, the SEM image of which is shown below. Figure 25 As shown.

[0048] The carbonized hard carbon material was prepared into a slurry with a ratio of hard carbon material: carbon black: PVDF = 8:1:1 and coated onto copper foil to obtain a hard carbon electrode sheet. This hard carbon electrode sheet was used as the negative electrode of a sodium-ion battery. The battery was assembled in an argon-filled glove box. The hard carbon electrode sheet, glass fiber, and sodium sheet were used as the working electrode, separator, and counter electrode, respectively. The electrolyte was 1M NaSO3CF3 / Diglyme solvent. After assembly, the battery was allowed to stand at 25°C for 8 hours, followed by a test at 25 mA g. -1 Charge-discharge cycles were performed at the specified current density. The first-cycle discharge specific capacity was 262.4 mAh g⁻¹. -1 The first charge-discharge efficiency was 75.2% ( Figure 26 (Left figure in the image) The current density is increased to 0.1 A g⁻¹, but the capacity remains at only 64.6 mAh g⁻¹. -1 ( Figure 26 (The right figure in the image), and at 25 mA g -1 and 500 mA g -1 After 100 and 1000 lap cycle stability tests, the initial capacity was maintained at 65.7% ( Figure 27 (Figure a) and 52.6% ( Figure 27 (See Figure b in the original text). Furthermore, at a low temperature of -20°C, it only exhibited a capacity of 119.5 mAh g⁻¹. -1 initial capacity ( Figure 28 (Left figure in the image) and at 25 mA g -1 After 100 cycles, maintain 38.5% ( Figure 28 (The right image in the image).

[0049] Comparative Example 4 4 g of pitch and 2 g of cellulose were dried at 80 °C for 12 hours to remove moisture, then placed in a ball mill jar and ball-milled at 900 rpm for 6 hours to ensure thorough mixing. After ball milling, the mixture was evenly spread in a ceramic boat and placed in a tube furnace. The furnace was heated to 800 °C at a rate of 5 °C / min under a nitrogen atmosphere and held at the target temperature for 2 hours for carbonization. After carbonization, the mixture was allowed to cool naturally to room temperature to obtain hard carbon material, the SEM image of which is shown below. Figure 29 As shown.

[0050] The carbonized hard carbon material was prepared into a slurry with a ratio of hard carbon material: carbon black: PVDF = 8:1:1 and coated onto copper foil to obtain a hard carbon electrode sheet. This hard carbon electrode sheet was used as the negative electrode of a sodium-ion battery. The battery was assembled in an argon-filled glove box. The hard carbon electrode sheet, glass fiber, and sodium sheet were used as the working electrode, separator, and counter electrode, respectively. The electrolyte was 1M NaSO3CF3 / Diglyme solvent. After assembly, the battery was allowed to stand at 25°C for 8 hours, followed by a test at 25 mA g. -1 Charge-discharge cycles were performed at the specified current density. The first discharge specific capacity was 241.1 mAh g⁻¹. -1 The first charge-discharge efficiency was 69.7% ( Figure 30 (Left figure in the image) The current density is increased to 0.1 A g⁻¹, but the capacity remains at only 42.9 mAh g⁻¹. -1 ( Figure 30 (The right figure in the image), and at 25 mA g -1 and 500 mA g -1 After 100 and 1000 lap cycle stability tests, the initial capacity was maintained at 59.3%. Figure 31 (Figure a) and 41.2% ( Figure 31 (See Figure b in the original text). Furthermore, at a low temperature of -20°C, it only exhibited a capacity of 184.3 mAh g⁻¹. -1 initial capacity ( Figure 32 (Left figure in the image) and at 25 mA g -1 After 100 cycles, maintain 40.7% ( Figure 32 (The right image in the image).

[0051] Comparative Example 5 The difference between Comparative Example 5 and Example 1 lies in the proportions of each component.

[0052] Comparative Example 6 The difference between Comparative Example 6 and Example 1 lies in the proportions of each component.

[0053] The differences between the above embodiments and the comparative examples are shown in Tables 1 and 2.

[0054] Table 1. Preparation parameters of the examples and comparative examples

[0055] Table 2 Preparation parameters for the examples and comparative examples

[0056] The performance test results of the above embodiments and comparative examples are shown in Table 3; Table 3 Performance test results of the examples and comparative examples

[0057] As shown in Table 1, the electrochemical performance of the hard carbon anode materials prepared using asphalt, cellulose, and lignin as raw materials in the embodiments of the present invention is better than that of Comparative Example 1. Among them, Comparative Example 1 suffers from insufficient temperature during carbonization, resulting in a low degree of graphitization and generally poor mechanical strength, which affects the conductivity and ion transport rate, ultimately reducing the rate performance and cycle stability of the battery. Comparative Examples 2-4 have poor performance because they lack asphalt material and cannot form a good graphitized carbon structure. Comparative Example 3 cannot form a three-dimensional network structure due to the lack of cellulose or lignin, thus failing to form a graphite-like microcrystalline structure, leading to poor performance. Comparative Example 5 has insufficient asphalt addition, resulting in a discontinuous carbon skeleton and an inability to form graphite-like microcrystalline structures. The excessive specific surface area reduces the initial efficiency and leads to poor cycle stability. Comparative Example 6 has excessive cellulose, which causes the carbon skeleton to "fragment," resulting in excessive pore formation, lack of continuous conductive pathways, and many residual oxygen-containing functional groups in the cellulose, increasing side reactions, excessive SEI film formation, and reducing the initial efficiency.

[0058] Figure 33 The Raman spectra of Examples 1, 2, 3 and Comparative Examples 1, 2 of this invention are shown. All samples exhibit a typical D peak (approximately 1350 cm⁻¹). -1 ) and G peak (approximately 1600 cm) -1 The D peak is associated with defects and disordered structures in carbon materials, while the G peak reflects the degree of graphitization. The samples treated at 600℃ in Comparative Examples 1 and 2, as well as the cellulose / lignin composite samples, exhibited high ID / IG values ​​(1.738, 1.621), indicating extremely high disorder and abundant defect structures. While this structure may provide more sodium ion storage sites, excessive disorder can lead to excessive defects, affecting electrochemical performance. In contrast, the ID / IG ratios of Examples 1, 2, and 3 were all around 0.9, indicating that they retained a moderate degree of disorder to provide sufficient sodium ion insertion sites while maintaining a high degree of graphitization to ensure good conductivity.

[0059] It should be noted that ID refers to the intensity of the D peak (approximately 1350 cm^-1) in the Raman spectrum. This peak is related to defects and disordered structures in carbon materials. The D peak originates from the breathing vibration mode of carbon atoms, which requires a defect to activate. Therefore, the intensity of the D peak can reflect the number of defects in the material.

[0060] IG refers to the intensity of the G peak (approximately 1600 cm^-1). The G peak reflects the degree of sp² hybridization of ordered graphite structure in carbon materials. The G peak originates from the in-plane vibration mode of carbon atoms and is a characteristic of highly ordered graphene layers. The ID / IG ratio is obtained by dividing ID by IG.

[0061] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A hard carbon anode material, characterized in that, The raw materials of the hard carbon anode material include asphalt, cellulose and lignin, wherein the mass ratio of the asphalt, the cellulose and the lignin in the hard carbon anode material is (3~6): (1~3): (1~3).

2. A method for preparing the hard carbon anode material as described in claim 1, characterized in that, Includes the following steps: The asphalt, cellulose and lignin are mixed and dried to obtain a composite precursor; The composite precursor was mechanically processed and then carbonized in an inert atmosphere to obtain a hard carbon anode material.

3. The method for preparing the hard carbon anode material as described in claim 2, characterized in that, The drying temperature is 80~100℃; and / or, The drying time is 10-16 hours.

4. The method for preparing the hard carbon anode material as described in claim 2, characterized in that, The mechanical treatment includes grinding or ball milling.

5. The method for preparing the hard carbon anode material as described in claim 2, characterized in that, The ball milling process is performed at a rotation speed of 800-1000 rpm; and / or, The ball milling process takes 4 to 8 hours.

6. The method for preparing the hard carbon anode material as described in claim 2, characterized in that, The carbonization process includes heating to 800-1000℃ at a heating rate of 1-5℃ / min and holding at that temperature for 2-4 hours.

7. A hard carbon electrode, characterized in that, The hard carbon electrode sheet includes a hard carbon anode material, carbon black, and additives, wherein the hard carbon anode material includes the hard carbon anode material as described in claim 1 or the hard carbon anode material prepared by the preparation method of the hard carbon anode material as described in any one of claims 2 to 7.

8. A battery, characterized in that, The battery includes the hard carbon electrode as described in claim 7.

9. An electrical device, characterized in that, The electrical device includes the battery as described in claim 8.

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