Lignin compounded silicon-carbon negative electrode material and preparation method thereof

Abstract

The invention relates to the technical field of lithium ion battery negative electrode materials, in particular to a lignin compounded silicon-carbon negative electrode material and a preparation method thereof. According to the invention, the defects of low first efficiency and insufficient long circulation capability during application of the existing silicon-carbon negative electrode material are overcome. The preparation method comprises the following steps: preparing phenolic resin, lignin and a cosolvent into a mixed solution; adding deionized water into the mixed solution at a constant temperature to separate out a precipitate, centrifuging, and washing and drying the precipitate to obtain precursor powder; performing three-stage carbonization on the precursor powder to obtain a hard carbon material; performing plasma treatment on the hard carbon material to obtain a plasma hard carbon material; activating and pore-forming the plasma hard carbon material to obtain resin-based porous carbon; after the resin-based porous carbon is subjected to silicon-carbon coating, stepped cooling is adopted, the lignin compounded silicon-carbon negative electrode material is obtained, and the finally obtained silicon-carbon negative electrode material shows excellent performance such as high magnification, long circulation and high first efficiency when being applied to a lithium battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, specifically to a lignin-composite silicon-carbon anode material and its preparation method. Background Technology

[0002] Lithium-ion batteries, with their high energy density and long cycle life, are widely used in consumer electronics, electric vehicles, energy storage systems, and aerospace. Among these, the anode material plays a crucial role, influencing not only the battery's energy density but also its charge / discharge rate and cycle stability. Common anode materials include graphite, lithium titanate, tin-based materials, and silicon-carbon anode materials. Currently, the energy density improvement of graphite anode materials is limited, making it difficult to meet the long-range requirements of electric vehicles; while lithium titanate boasts high safety and long cycle life, its energy density is relatively low; tin-based materials experience significant volume changes during charge and discharge, leading to electrode structural instability. Silicon-carbon anode materials, with their high theoretical specific capacity, hold promise for overcoming the low energy density problem of traditional anode materials and can mitigate volume expansion to some extent. However, current silicon-carbon anode materials still cannot meet the fast-charging time requirements in the electric vehicle field, primarily due to their poor charge transport capabilities, which severely restricts the development of lithium-ion batteries in fast-charging applications and urgently requires further research and improvement.

[0003] To address the shortcomings of existing silicon-carbon anode materials, this invention develops a silicon-carbon anode material that combines high initial efficiency and long cycle life.

[0004] To this end, a lignin-based silicon-carbon composite anode material and its preparation method are proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a lignin-based silicon-carbon anode material and its preparation method. This invention involves preparing a mixed solution from phenolic resin, lignin, and a co-solvent; adding deionized water to the mixed solution at a constant temperature to precipitate a precipitate, centrifuging the precipitate, washing and drying it to obtain a precursor powder; subjecting the precursor powder to three-stage carbonization to obtain a hard carbon material; subjecting the hard carbon material to plasma treatment to obtain a plasma hard carbon material; activating and pore-forming the plasma hard carbon material to obtain resin-based porous carbon; coating the resin-based porous carbon with silicon-carbon, and then using a stepped cooling process to obtain the lignin-based silicon-carbon anode material. The resulting silicon-carbon anode material exhibits excellent performance characteristics such as high initial efficiency, long cycle life, and high rate capability when applied in lithium batteries.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A lignin-based silicon-carbon anode material and its preparation method, comprising:

[0008] On the one hand, the present invention provides a method for preparing a lignin-composite silicon-carbon anode material, specifically including the following steps:

[0009] S1 mixes phenolic resin, lignin, and co-solvent and dissolves them in ethanol to obtain a mixed solution; deionized water is added to the mixed solution at a constant temperature to precipitate the precipitate, and the precipitate is washed and dried after centrifugation to obtain precursor powder.

[0010] S2 involves three-stage carbonization of the precursor powder to obtain hard carbon materials.

[0011] S3 involves plasma treatment of hard carbon materials to obtain plasma hard carbon materials.

[0012] S4 activates and creates pores in plasma hard carbon materials to obtain resin-based porous carbon.

[0013] S5 involves coating resin-based porous carbon with silicon-carbon and then using a stepped cooling process to obtain a lignin-composite silicon-carbon anode material.

[0014] During the activation and pore-forming process, CO2 gas is first introduced to form pores, followed by a mixture of H2O and CO2 gas to form pores.

[0015] Preferably, the preparation method of the precursor powder is as follows: phenolic resin, lignin, and co-solvent are mixed in a mass ratio of 93-97:1-5:2, and then ethanol is added and stirred to obtain a mixed solution with a mass fraction of 20-30 wt%. The mixed solution is heated to 80°C and held at 2 h. Deionized water is added to the mixed solution, and the temperature is raised to 120°C at 1000 rpm and stirred for 2 h. Then, the mixture is centrifuged, and the centrifuged precipitate is dried to obtain the precursor powder.

[0016] Preferably, the amount of deionized water added is 10 times the volume of ethanol, and the addition rate is 25-40 mL / min.

[0017] Preferably, the three-stage carbonization method is as follows: the precursor powder is transferred to a carbonization furnace. In the first stage, N2 is introduced at a rate of 1 L / min, and the temperature is raised to 400-450℃ at a rate of 2℃ / min and held for 1 hour. In the second stage, the temperature is raised to 500-550℃ at a rate of 3℃ / min and held for 3 hours. In the third stage, the temperature is raised to 800℃ at a rate of 3℃ / min and held for 5 hours to obtain hard carbon material.

[0018] Preferably, the plasma treatment method is as follows: the hard carbon material is subjected to plasma treatment by introducing argon gas at a flow rate of 15 sccm and methane at a flow rate of 3-5 sccm; the treatment is carried out for 30 minutes at a radio frequency power of 100W to obtain plasma hard carbon material.

[0019] Preferably, the activation and pore-forming method is as follows: in a box furnace, CO2 at a flow rate of 0.8-1.1 L / min is first introduced and activated at 850°C for 5 h, and then H2O at a flow rate of 0.2-0.5 L / min is introduced for 2 h to obtain resin-based porous carbon.

[0020] Preferably, the preparation method of lignin-composite silicon-carbon anode material is as follows: resin-based porous carbon is placed in a small fluidized bed, heated to 450°C at 5°C / min, and silane gas is introduced at 1.3-1.6 L / min for deposition for 300 min. After deposition, the temperature is increased to 600°C at 5°C / min, and acetylene gas is introduced at 1.7-2.0 L / min for carbon coating and held for 300 min. Then, the temperature is gradually reduced in a stepwise manner: starting from 600°C, the temperature is reduced to 500°C at a rate of 10°C / min; then reduced to 200°C at a rate of 5°C / min; and finally reduced to 25°C at a rate of 2°C / min. After the cooling is completed, the lignin-composite silicon-carbon anode material is finally obtained.

[0021] On the other hand, the present invention provides a lignin-composite silicon-carbon anode material, specifically comprising the following components: phenolic resin, lignin, and cosolvent;

[0022] Lignin is one or both of sulfate lignin and groundwood lignin;

[0023] The co-solvent is one or more of n-butanol, n-pentanol, and dodecanol.

[0024] Preferably, the lignin is one or both of coniferous lignin and broadleaf lignin; the sulfate lignin is one or more of coniferous sulfate lignin, broadleaf sulfate lignin, and grass sulfate lignin.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. In this invention, by introducing lignin rich in sp2, benzene rings, or unsaturated bonds, the π-electron conjugated system of the benzene rings in the lignin intertwines with the polymer network formed by the phenolic resin, providing a continuous electronic conduction path. During charging and discharging, electrons can be efficiently transported along these conjugated systems, improving the electronic conductivity of the electrode material, thereby achieving high-rate charging and discharging. At the same time, the structure formed by lignin and phenolic resin helps stabilize the electrode / electrolyte interface. The benzene rings and unsaturated bonds of lignin can inhibit the decomposition of the electrolyte and reduce irreversible reactions, thereby effectively preventing excessive reactions between the electrolyte and the electrode material, reducing irreversible capacity loss during the first charge and discharge process, and improving the first efficiency.

[0027] 2. In this invention, staged carbonization better leverages the role of lignin. In the first stage, lignin is rich in structural units such as benzene rings and phenolic hydroxyl groups, which begin to undergo specific changes at this temperature. On one hand, some weaker carbon-oxygen and carbon-hydrogen bonds break, generating a large number of reactive free radicals that interact with free radicals of other surrounding organic molecules, beginning to construct a preliminary carbon network structure. On the other hand, the benzene ring structure in lignin provides stable nodes for the network structure, giving it a preliminary degree of order. In the second stage, the carbonization of lignin deepens, and the side chains in its molecular structure further break and transform into carbon, making the connections between benzene rings even tighter. The presence of lignin promotes further ordering and densification of the carbon skeleton structure in this stage. From a microscopic perspective, the benzene ring structures of lignin are interconnected, forming a more regular rudimentary graphitized microcrystalline structure. Simultaneously, staged carbonization, combined with plasma treatment, enhances the structural stability of lignin in hard carbon materials. Argon ion bombardment makes the connections between the benzene rings of lignin tighter, and the unsaturated bonds rearrange to form a more stable structure. During long-term cycling, this stable structure helps maintain the integrity of the material, reduces capacity decay caused by structural changes, and works synergistically with the carbon skeleton formed by phenolic resin and lignin to improve long-term cycling performance.

[0028] 3. In this invention, the isolated micropores originally created by plasma treatment are interconnected under activation, forming a richer and more efficient lithium-ion transport network. Simultaneously, the activated pore structure acts as a buffer during subsequent charging and discharging. Because plasma treatment enhances the stability of the carbon skeleton, when lithium ions are inserted, the activated pores can accommodate some of the lithium ions, reducing the pressure on the surrounding carbon skeleton structure and adjusting the internal stress distribution of the material. Stress concentration areas that might have existed within the material are released and redistributed through the pores.

[0029] 4. In this invention, after the preceding stages of carbonization, plasma treatment, activation pore formation, and silicon-carbon coating, the lithium-ion transport channels within the material have been initially formed. During the rapid cooling process, the overall structure of the material stabilizes quickly, thus fixing the lithium-ion transport channels. During rapid cooling, the appropriate thickness of the silicon-carbon coating layer, formed by controlling process parameters, and the morphology and connectivity of the lithium-ion transport paths, such as the pore structure and grain boundaries within the hard carbon material, are maintained, preventing damage to the lithium-ion transport channels caused by structural relaxation or deformation due to temperature changes. This ensures that lithium ions can be continuously and efficiently transported between the silicon-carbon coating layer and the hard carbon material during charging and discharging, improving the long-cycle performance of the battery at high rates. Attached Figure Description

[0030] Figure 1 This is a process flow diagram for preparing the silicon-carbon anode material for lithium-ion batteries according to the present invention. Detailed Implementation

[0031] 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Please see Figure 1 This invention provides a lignin-based silicon-carbon anode material and its preparation method, the technical solution of which is as follows:

[0033] Example 1

[0034] The lignin used is coniferous wood lignin, which can be prepared by conventional processes.

[0035] S1. Phenolic resin, lignin, and co-solvent were mixed in ethanol at a mass ratio of 95:3:2. The mixture was stirred at 25°C for 2 hours at a speed of 500 rpm to obtain a 25 wt% mixture. The mixture was heated to 80°C and held at the same speed for 2 hours. Water was added to precipitate the mixture, which was then added to deionized water. The mixture was then heated to 120°C and stirred at a speed of 1000 rpm for 2 hours. The mixture was centrifuged, and the precipitate was dried at 120°C for 10 hours to obtain the precursor powder.

[0036] S2 transfers the precursor powder to a carbonization furnace and introduces N2 at a rate of 1 L / min. In the first stage, the temperature is raised to 400°C at a rate of 2°C / min and held for 1 hour. In the second stage, the temperature is raised to 500°C at a rate of 3°C / min and held for 3 hours. In the third stage, the temperature is raised to 800°C at the same rate and held for 5 hours, finally obtaining hard carbon material.

[0037] Argon gas is introduced into S3 as the working gas at a flow rate of 15 sccm. Under the action of the radio frequency electric field, the argon gas generates plasma, and its high-energy particles can bombard and modify hard carbon materials. At the same time, a small amount of methane is introduced at a flow rate of 3 sccm; the radio frequency power is set to 100W, and the down-processing time is 30 minutes.

[0038] S4 activates and pores the plasma-treated hard carbon material in a box furnace. First, CO2 is introduced at 1L / min and activated at 850℃ for 5h. Then, H2O is introduced at 0.3L / min and activated for 2h to obtain lignin-modified resin-based porous carbon.

[0039] S5. 500g of the above porous carbon was placed in a small fluidized bed, heated to 450℃ at 5℃ / min, and silane gas was introduced at 1.5L / min for deposition for 300min. Then, the temperature was increased to 600℃ at 5℃ / min, and acetylene gas was introduced at 2L / min for carbon coating, which was maintained for 300min. A circulating water cooling jacket was set up outside the reaction vessel. After the reaction was completed, the temperature was rapidly cooled in a stepwise manner: starting from 600℃, the temperature was reduced at a rate of 10℃ / min; from 500℃ to 200℃, the temperature was reduced at a rate of 5℃ / min; and from 200℃ to 25℃, the temperature was reduced at a rate of 2℃ / min. After the cooling was completed, the lignin composite silicon-carbon anode material was finally obtained.

[0040] The difference between Examples 2-16 and Example 1 is that the mass ratio of added phenolic resin, lignin, and cosolvent (hereinafter referred to as mass ratio in Table 1) is different, the mass fraction of the mixed solution is different, and the rate of addition of deionized water is different. The difference between Example 17 and Example 1 is that the lignin is a mixture of coniferous wood lignin and hardwood sulfate lignin in a mass ratio of 1:1. The specific parameters are shown in Table 1.

[0041] Table 1 Parameter Table for Examples 1-17

[0042]

[0043]

[0044] Comparative Example 1

[0045] The difference from Example 1 is that the mass ratio of phenolic resin, lignin, and co-solvent is 92:6:2, while the other parameters and conditions are the same.

[0046] Comparative Example 2

[0047] The difference from Example 1 is that no lignin is added, the mass ratio of phenolic resin to cosolvent is 98:2, and the other parameters and conditions are the same.

[0048] Comparative Example 3

[0049] The difference from Example 1 is that the lignin is straw-ground wood lignin, while the other parameters and conditions are the same;

[0050] Comparative Example 4

[0051] The difference from Example 1 is that the lignin is coniferous alkali lignin, while the other parameters and conditions are the same.

[0052] Experimental Example 1

[0053] Lignin-based silicon-carbon composite anode material was used as the anode active material. It was mixed with polyacrylic acid resin, single carbon nanotubes, and conductive carbon black in a mass ratio of 90:5:1:4, and deionized water was added to form a slurry. The slurry was then uniformly coated on copper foil and vacuum dried at 80°C for 24 hours to obtain the battery electrode for the experiment. A lithium sheet was used as the counter electrode, and a 1.1 mol / L LiPF6 electrolyte was used. The solvent was a four-component mixed solvent with a volume ratio of ethylene carbonate: vinylene carbonate: dimethyl carbonate: fluoroethylene carbonate = 1:1:1:1. A polypropylene microporous membrane was used as the separator, and the CR2025 coin cell was assembled in a vacuum glove box (Labstar (1200 / 780) glove box of Braun GmbH, Germany).

[0054] Half-cell testing employed the Arbin multi-channel battery testing system to measure capacity, initial charge / discharge efficiency (first efficiency), and cycle retention (50 cycles at 5C for coin cell), along with Raman spectroscopy testing (I...). D / I G The full-embedded expansion rate and the test results are shown in Table 2.

[0055] Table 2 Test Results of Examples 1-17 and Comparative Examples 1-4

[0056] By changing the mass ratio of phenolic resin, lignin, and co-solvent, as well as the mass fraction of the mixed solution, during the preparation of silicon-carbon anode materials, the mass percentage of lignin after mixing phenolic resin, lignin, and co-solvent was between 1% and 5%. Within this range, the performance of the obtained silicon-carbon anode materials was basically similar. Among them, the silicon-carbon anode material with the best performance was obtained under the parameters of Example 15, i.e., a lignin content of 3% and a mass ratio of phenolic resin, lignin, and co-solvent of 95:3:2. Comparative Example 2, combined with Example 1, shows that with the addition of lignin, the initial efficiency of the material is improved. This is because the addition of lignin reduces the defects in the porous carbon skeleton of the material, thereby improving conductivity. However, as can be seen from Comparative Example 1, when the lignin content is too high, mechanical strength is lost. D / I G An increase in the value indicates a decrease in the degree of graphitization of the material, resulting in a reduction in initial performance. Therefore, the optimal range for adding lignin is 1-5 parts. Furthermore, combining Examples 15 and 17 shows that when softwood lignin is replaced with a mixture of softwood lignin and hardwood sulfate lignin in a 1:1 mass ratio, the material's performance remains essentially unchanged. This is because both softwood and hardwood lignin, or sulfate lignin, are rich in sp2, benzene rings, or unsaturated bonds, which have a good effect on the final carbon structure. However, when lignin is replaced with lignin from other raw materials or softwood lignin prepared by other processes, the resulting silicon-carbon material exhibits poorer performance.

[0057] As can be seen from Example 1 and Comparative Example 3, when straw-based lignin replaces the original softwood lignin, the structure of straw-based lignin is relatively more complex. Compared with softwood lignin, the orderliness and content of its benzene rings, unsaturated bonds, and other structures may differ. In terms of high-rate performance, due to its slightly inferior structural order, the straw-based lignin structure cannot form a highly efficient lithium-ion transport network after plasma treatment and activation pore-forming, as is the case with softwood lignin, resulting in a slightly lower lithium-ion transport rate. Simultaneously, straw-based lignin has more surface impurities and defects. Although plasma treatment and activation pore-forming can optimize this, they still lead to slightly poorer controllability of the reaction between the electrode material and the electrolyte, increased irreversible reactions, and reduced first-time efficiency. The poor stability of the pore structure and carbon skeleton of straw-based lignin makes the expansion control during lithium-ion insertion and extraction less effective than that using softwood lignin, ultimately resulting in a slightly higher expansion rate.

[0058] As can be seen from Example 1 and Comparative Example 4, when alkali-containing lignin is used to replace the original coniferous wood lignin, the structure of alkali-containing lignin undergoes significant changes under alkaline preparation conditions. The ordered structure of the benzene ring and the conjugated system are more severely damaged, and the active sites are altered. This results in lower lithium-ion transport rates in high-rate performance because the lithium-ion transport channel construction is not as ideal as that of coniferous wood lignin. In terms of long-cycle performance, due to the poor stability of the carbon skeleton, structural damage is more likely to occur during charge-discharge cycles, leading to significant capacity decay.

[0059] Example 18

[0060] The difference from Example 15 is that in the three-stage carbonization process, N2 is introduced at a rate of 1 L / min in the first stage, and the temperature is raised to 430°C at a rate of 2°C / min and held for 1 hour; in the second stage, the temperature is raised to 520°C at a rate of 3°C / min and held for 3 hours; during plasma treatment, the flow rate of methane gas is 4 sccm; and the other parameters and conditions are the same.

[0061] Example 19

[0062] The difference from Example 15 is that in the three-stage carbonization process, N2 is introduced at a rate of 1 L / min in the first stage, and the temperature is raised to 450°C at a rate of 2°C / min and held for 1 hour; in the second stage, the temperature is raised to 550°C at a rate of 3°C / min and held for 3 hours; during plasma treatment, the flow rate of methane gas is 5 sccm; and the other parameters and conditions are the same.

[0063] Comparative Example 5

[0064] The difference from Example 15 is that, in the preparation process of hard carbon material, a two-stage carbonization is carried out. In the first stage, N2 is introduced at a rate of 1 L / min, and the temperature is raised to 500-550°C at a rate of 3°C / min and held for 3 hours. In the second stage, the temperature is raised to 800°C at a rate of 3°C / min and held for 5 hours. All other parameters and conditions are the same.

[0065] Comparative Example 6

[0066] The difference from Example 15 is that no plasma treatment is performed during the preparation of the hard carbon material; all other parameters and conditions are the same.

[0067] Comparative Example 7

[0068] The difference from Example 15 is that methane is not introduced during plasma treatment in the preparation of hard carbon materials; all other parameters and conditions are the same.

[0069] Experimental Example 2

[0070] Examples 18-19 and Comparative Examples 5-7 were tested according to the test method of Experimental Example 1, and the test results are shown in Table 3.

[0071] Table 3 Test Results of Examples 15, 18-19 and Comparative Examples 5-7

[0072] By changing the heating rate of the carbonization stage and the flow rate of methane gas, it can be seen that the overall performance of the anode material reaches its optimal state under the conditions of Example 18.

[0073] Comparative Example 5 employed a two-stage carbonization method in the preparation of hard carbon materials, unlike the segmented precise heating method in Example 15. The first stage directly raised the temperature to 500℃ at a relatively rapid rate of 3℃ / min, lacking the initial pyrolysis and molecular structure rearrangement stage at 400℃ as in Example 15. This resulted in insufficient precursor reaction and an incomplete initial carbon structure. This leads to a decrease in the orderliness of the subsequently formed carbon framework structure, affecting the construction of electron conduction and lithium-ion transport pathways. D / I G The value reflects the degree of order in the carbon structure. It will increase as the degree of structural order decreases. An imperfect structure will make the controllability of the reaction between the electrode and the electrolyte worse and increase the irreversible reaction. At the same time, the capacity retention rate is affected by the stability of the carbon skeleton. Decreased stability leads to faster capacity decay. The initial full insertion expansion rate of the coin cell negative electrode is increased because the carbon skeleton structure weakens, which reduces the buffering capacity of the structure against the volume changes of lithium ion insertion and extraction. Therefore, the overall performance of the material ultimately decreases.

[0074] Comparative Example 6 did not perform plasma treatment during the preparation of hard carbon materials, which prevented the optimization of the material's surface and pore structure. Plasma treatment could have opened the pores through argon ion bombardment and then modified the surface with active carbon atoms generated from methane decomposition, increasing surface active sites and enhancing structural stability. Without this step, the material surface has more impurities and defects, which is detrimental to the adsorption and desorption of lithium ions on the electrode surface; the carbon framework structure lacks stability and is more susceptible to damage during multiple charge-discharge cycles, resulting in reduced capacity retention; at the same time, due to the lack of plasma treatment to optimize the pore structure and enhance the stability of the carbon framework, the material's expansion control during lithium ion insertion and extraction is also worse, leading to an increase in the initial full-intercalation expansion rate of the coin cell anode.

[0075] Comparative Example 7 did not introduce methane during plasma treatment. Compared to Example 15, the material surface lacked the modification of active carbon atoms generated from methane decomposition. The active carbon atoms generated from methane decomposition can react with the unsaturated bonds on the surface of hard carbon materials, further optimizing the surface structure and enhancing surface activity. The absence of this modification process reduces the number of active sites on the material surface, ultimately leading to a decrease in the overall performance of the material.

[0076] The difference between Examples 20-25 and Example 18 is that the flow rates of CO2 and H2O introduced during the activation and pore-forming process are different; the other parameters are the same.

[0077] The specific parameters of Examples 18 and 20-25 are shown in Table 4.

[0078] Table 4 Parameter Table for Examples 18 and 20-25

[0079] serial number <![CDATA[CO2 flow rate / L / min]]> <![CDATA[H2O flow rate / L / min]]> Example 18 1.0 0.3 Example 20 0.8 0.3 Example 21 0.9 0.3 Example 22 1.1 0.3 Example 23 0.9 0.2 Example 24 0.9 0.4 Example 25 0.9 0.5

[0080] Comparative Example 8

[0081] The difference from Example 18 is that the plasma treatment and activation pore-forming steps are interchanged. That is, the hard carbon material is first activated to form pores to obtain resin-based porous carbon, then the resin-based porous carbon is subjected to plasma treatment to obtain plasma-treated resin-based porous carbon, and finally the plasma-treated resin-based porous carbon is coated with silicon carbon and then cooled in stages to obtain lignin composite silicon carbon anode material.

[0082] Comparative Example 9

[0083] The difference from Example 18 is that, during the activation and pore-forming process, only CO2 gas is introduced to form pores, and no mixture of H2O and CO2 gas is introduced to form pores; the other parameters and conditions are the same.

[0084] Comparative Example 10

[0085] The difference from Example 18 is that, during the activation and pore-forming process, a mixture of H2O and CO2 gas is first introduced to form pores, followed by CO2 gas; all other parameters and conditions are the same.

[0086] Comparative Example 11

[0087] The difference from Example 18 is that, during the activation and pore-forming process, only a mixture of H2O and CO2 gas is introduced to form pores; the other parameters and conditions are the same.

[0088] Experimental Example 3

[0089] Examples 20-25 and Comparative Examples 8-11 were tested according to the parameters and conditions of Experimental Example 1, and the test results are shown in Table 5.

[0090] Table 5. Test Results of Examples 18, 20-25, and Comparative Examples 8-11

[0091] During the activation and pore-forming stage, parameters were optimized by changing the CO2 and H2O flow rates. When the CO2 flow rate was 0.9 L / min and the H2O flow rate was 0.4 L / min, that is, under the conditions of Example 24, the overall performance of the material basically reached its optimal level.

[0092] Comparative Example 8 swapped the plasma treatment and activation-based pore formation steps. Originally, plasma treatment first optimized the surface and pore structure of the hard carbon material, enhancing surface active sites and providing a better foundation for subsequent activation-based pore formation, resulting in a more ordered pore structure that facilitates lithium-ion transport. However, by first activating-based pore formation, although the material surface and pores are formed, the lack of pre-optimization by plasma results in more surface impurities and defects. Subsequent plasma treatment is less effective at enhancing structural stability and surface activity as in the original sequence. This primarily leads to a significant reduction in the orderliness and stability of the carbon framework, therefore... D / I G The higher the value, the worse the controllability of the reaction between the electrode and the electrolyte during charging and discharging, the more irreversible reactions occur, which also leads to a decrease in capacity retention. At the same time, the overall structure of the material becomes less adaptable to lithium ion insertion and extraction, and the initial full insertion expansion rate of the coin cell negative electrode increases.

[0093] As shown in Comparative Examples 9-11, when plasma-treated hard carbon materials are activated and pore-forming, the order of gas introduction cannot be changed under fixed activation and pore-forming temperatures and times. Before activation and pore-forming, plasma treatment can clean the surface of the resin-based porous carbon, introduce active sites, and enhance its reactivity with subsequent treatment gases. Comparative Example 9 only uses activation and pore-forming. When reacting with the plasma-treated carbon material, the relatively low reactivity means that although plasma treatment introduces active sites, these sites are difficult to fully utilize. This makes the pore-forming process slow, resulting in a limited number of pores and uneven pore size distribution, negatively impacting subsequent silicon-carbon coating. Silicon particles cannot be uniformly embedded in the carbon material, the contact area between silicon and carbon is small, and the interfacial bonding is weak, leading to a decrease in the material's electrical properties. Comparative Example 10 first introduces a mixed gas for pore-forming, which has high reactivity with the carbon material and quickly forms a large number of pores. However, during subsequent gas introduction, the already formed pore structure and the secondary reaction with the carbon material altered some of the pore structure, resulting in impaired pore regularity and connectivity. This change affected the silicon-carbon composite effect, leading to uneven distribution of silicon particles within the pores and weak bonding with the carbon material, thus impacting the overall performance of the material. Comparative Example 11 only introduced a mixed gas to create pores, which, while forming pores, resulted in differences in pore size, porosity, and shape. These differences led to suboptimal dispersion and fixation of silicon particles within the carbon material, resulting in poor structural stability of the silicon-carbon composite material and significantly affecting the initial full-intercalation expansion rate.

[0094] The difference between Examples 26-31 and Example 24 lies in the different rates of introducing silane and acetylene gases during the final preparation of lignin-based composite silicon-carbon anode materials using resin-based porous carbon; all other parameters are the same. Specific parameters are shown in Table 6.

[0095] Table 6 Parameter Table for Examples 24 and 26-31

[0096] serial number Silane gas flow rate / L / min Acetylene gas flow rate / L / min Example 24 1.4 1.8 Example 26 1.3 1.8 Example 27 1.5 1.8 Example 28 1.6 1.8 Example 29 1.5 1.7 Example 30 1.5 1.9 Example 31 1.5 2.0

[0097] Comparative Example 12

[0098] The difference from Example 24 is that, after the silicon-carbon coating was completed, a natural cooling method was used; all other parameters and conditions were the same.

[0099] Comparative Example 13

[0100] The difference from Example 24 is that after silicon-carbon coating, a rapid cooling method was used, starting from 600°C and cooling down to 25°C at a rate of 15°C / min; the other parameters and conditions were the same.

[0101] Experiment Example 4

[0102] Examples 26-31 and Comparative Examples 12-13 were tested according to the parameters and conditions of Experimental Example 1, and the test results are shown in Table 7.

[0103] Table 7 Test Results of Examples 24, 26-31, and Comparative Examples 12-13

[0104] By changing the flow rates of silane gas and acetylene gas as further optimization, the optimal degree of silicon-carbon coating was determined. In Example 30, the silicon-carbon coating effect was optimal when the flow rate of silane gas was 1.5 L / min and the flow rate of acetylene gas was 1.9 L / min. The electrode sheet material prepared under this condition had the best overall performance.

[0105] Comparative Example 12 employed natural cooling after silicon-carbon coating. Compared to the rapid cooling in Example 23, the natural cooling rate was slow, resulting in a longer time the material remained at high temperatures. At high temperatures, intense atomic thermal motion occurs, allowing more time for the atoms in the silicon-carbon coating and internal carbon structure to diffuse and rearrange, making it difficult to fix them in ideal positions and disrupting the originally tight interfacial bonding and stable structure. From the perspective of first-efficiency performance, the change in interfacial structure makes the electrode-electrolyte reaction more complex, increasing irreversible reactions and ultimately reducing the 0.8V first-efficiency. Simultaneously, the structural disorder increases, leading to... D / I G As the value increases, the unstable structure becomes more susceptible to lithium-ion insertion and extraction during charge-discharge cycles, resulting in a decrease in capacity retention.

[0106] Comparative Example 13 employed rapid cooling after silicon-carbon coating, but the cooling rate remained consistently at 15°C / min, which was too fast compared to the gradient cooling in Example 23. This rapid cooling caused instantaneous changes in internal stress, preventing uniform release and leading to stress concentration. Stress concentration easily induces microcracks or structural defects within the material, resulting in abnormal electrode-electrolyte reactions and increased irreversible capacity loss, thus reducing the initial efficiency to 0.8V. Damage to the internal structure and a decrease in the orderliness of the carbon structure also contribute to this. D / I G As the lithium-ion concentration increases, microcracks and defects continuously expand during cycling, ultimately leading to a decrease in capacity retention. The integrity of the material's structure is compromised, weakening its resistance to volume changes during lithium-ion insertion and extraction. The initial full-intercalation expansion rate of the coin cell anode increases, but due to rapid cooling which stabilizes the structure to some extent, the increase is smaller compared to natural cooling. After plasma treatment, the material's microstructure is in a relatively active but ordered state. Simultaneously, stepwise rapid cooling helps to stabilize the structural optimization resulting from plasma treatment. This is because rapid cooling quickly stabilizes the structure of surface active sites, preventing changes in subsequent processes and ensuring that lithium-ion adsorption and desorption on the electrode surface can continue efficiently, further improving the material's electrochemical performance.

[0107] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a lignin-composite silicon-carbon anode material, characterized in that: Specifically, the following steps are included: S1 mixes phenolic resin, lignin, and a co-solvent and dissolves them in ethanol to obtain a mixed solution; deionized water is added to the mixed solution at a constant temperature to precipitate the precipitate, and the precipitate is washed and dried after centrifugation to obtain a precursor powder. S2 performs three-stage carbonization on the precursor powder to obtain hard carbon material; S3. The hard carbon material is subjected to plasma treatment to obtain plasma hard carbon material. S4 activates and creates pores in the plasma hard carbon material to obtain resin-based porous carbon. S5 After coating the resin-based porous carbon with silicon carbon, a step-down cooling method is used to obtain the lignin-composite silicon carbon anode material. In the activation and pore-forming process, CO2 gas is first introduced to form pores, and then a mixture of H2O and CO2 gas is introduced to form pores.

2. The method for preparing a lignin-composite silicon-carbon anode material according to claim 1, characterized in that: The precursor powder is prepared by mixing the phenolic resin, lignin, and cosolvent in a mass ratio of 93-97:1-5:2, then adding ethanol and stirring to obtain a mixed solution with a mass fraction of 20-30 wt%. The mixed solution is heated to 80°C and held at that temperature for 2 hours. Deionized water is added to the mixed solution, and the temperature is raised to 120°C at 1000 rpm and stirred for 2 hours. The mixture is then centrifuged, and the centrifuged precipitate is dried to obtain the precursor powder.

3. The method for preparing a lignin-composite silicon-carbon anode material according to claim 2, characterized in that: The amount of deionized water added is 10 times the volume of ethanol, and the addition rate is 25-40 mL / min.

4. The method for preparing a lignin-composite silicon-carbon anode material according to claim 1, characterized in that: The three-stage carbonization method is as follows: the precursor powder is transferred to a carbonization furnace. In the first stage, N2 is introduced at a rate of 1 L / min, and the temperature is raised to 400-450℃ at a rate of 2℃ / min and held for 1 hour. In the second stage, the temperature is raised to 500-550℃ at a rate of 3℃ / min and held for 3 hours. In the third stage, the temperature is raised to 800℃ at a rate of 3℃ / min and held for 5 hours to obtain the hard carbon material.

5. The method for preparing a lignin-composite silicon-carbon anode material according to claim 1, characterized in that: The plasma treatment method is as follows: the hard carbon material is subjected to plasma treatment by introducing argon gas at a flow rate of 15 sccm and methane at a flow rate of 3-5 sccm; the treatment is carried out for 30 minutes at a radio frequency power of 100W to obtain the plasma hard carbon material.

6. The method for preparing a lignin-composite silicon-carbon anode material according to claim 1, characterized in that: The activation and pore-forming method is as follows: In a box furnace, CO2 at a flow rate of 0.8-1.1 L / min is first introduced and activated at 850°C for 5 hours, followed by H2O at a flow rate of 0.2-0.5 L / min for 2 hours to obtain the resin-based porous carbon.

7. The method for preparing a lignin-composite silicon-carbon anode material according to claim 1, characterized in that: The preparation method of the lignin-composite silicon-carbon anode material is as follows: the resin-based porous carbon is placed in a small fluidized bed, heated to 450°C at 5°C / min, and silane gas is introduced at 1.3-1.6 L / min for deposition for 300 min. After deposition, the temperature is increased to 600°C at 5°C / min, and acetylene gas is introduced at 1.7-2.0 L / min for carbon coating and held for 300 min. Then, the temperature is gradually reduced in a stepwise manner: starting from 600°C, the temperature is reduced to 500°C at a rate of 10°C / min; then reduced to 200°C at a rate of 5°C / min; and finally reduced to 25°C at a rate of 2°C / min. After the cooling is completed, the lignin-composite silicon-carbon anode material is finally obtained.

8. A lignin-composite silicon-carbon anode material prepared by any one of the preparation methods described in claims 1-7, characterized in that: Specifically, it includes the following components: phenolic resin, lignin, and cosolvent; The lignin is one or both of sulfate lignin and groundwood lignin; The co-solvent is one or more of n-butanol, n-pentanol, and dodecanol.

9. The lignin-composite silicon-carbon anode material according to claim 8, characterized in that: The lignin is one or both of coniferous lignin and broadleaf lignin; the sulfate lignin is one or more of coniferous sulfate lignin, broadleaf sulfate lignin, and grass sulfate lignin.

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