Composite hard carbon material for sodium ion battery as well as preparation method and application of composite hard carbon material

Abstract

The invention discloses a composite hard carbon material for a sodium ion battery and a preparation method and application thereof, and belongs to the technical field of sodium ion battery production, agricultural wastes and recycled plastics are compounded as precursor raw materials, the raw materials are wide in source and low in price, the production cost is effectively reduced, and the production efficiency is improved. And a new way is provided for high-value resource utilization of wastes, and remarkable cost advantage and environmental benefit are realized. Compared with pure biomass carbon or single polymer derived carbon, the composite hard carbon material disclosed by the invention has high first coulombic efficiency, good rate capability and super-long cycle life while keeping high capacity. In order to solve the problem of two-phase compatibility of biomass and plastic, the compatilizer and the dispersing agent are added into the pretreated powder, so that uniform mixing and dispersion of all the components in the micro-scale are ensured, composite precursor particles with compact structures and uniform components are formed, and the composite hard carbon material with consistent structures and stable performance is obtained.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery production technology, specifically to a composite hard carbon material for sodium-ion batteries, its preparation method, and its application. Background Technology

[0002] With the accelerated transition of the energy structure towards renewable energy, the importance of large-scale energy storage technology is becoming increasingly prominent. Sodium-ion batteries, due to their advantages such as abundant sodium resources, low cost, and relatively high safety, are widely considered an important supplement or even replacement technology for lithium-ion batteries in the field of large-scale energy storage. However, the large ionic radius of sodium ions results in slow insertion and extraction kinetics and low reversible capacity in traditional graphite anode materials, which greatly limits the commercial application of sodium-ion batteries. Therefore, developing anode materials with suitable carbon interlayer spacing, high reversible specific capacity, and excellent cycle stability has become the key to the development of sodium-ion battery technology.

[0003] Among numerous candidate materials, hard carbon materials exhibit great application potential due to their unique disordered microstructure, large interlayer spacing, and abundant nanopores, which provide ample storage space and rapid migration channels for sodium ions. Currently, the precursors for hard carbon material preparation mainly come from biomass, synthetic polymers, and fossil fuels. Among these, the use of agricultural waste such as coconut shells, bamboo powder, and straw as precursors has attracted much attention due to their wide availability, low cost, and renewability.

[0004] However, hard carbon materials prepared from single biomass precursors often suffer from low initial coulombic efficiency, poor rate performance, and poor batch stability. This is mainly due to the complex chemical composition of biomass and its pyrolysis behavior, which is difficult to control precisely. On the other hand, using recycled plastics such as polyethylene terephthalate (PET) and polypropylene (PP) as carbon sources provides a new approach to the resource utilization of "white pollution." However, recycled plastics are prone to melting and coking during pyrolysis, and their carbonization products are usually dense in structure and have an unsuitable specific surface area, making it difficult to meet the high capacity and long lifespan requirements of sodium-ion batteries for anode materials when used alone. In addition, although high-performance hard carbon materials can be obtained by synthesizing polymer precursors such as phenolic resins, the high cost of raw materials and complex process routes limit their application in large-scale energy storage.

[0005] In summary, existing hard carbon materials cannot achieve a balance between performance, cost, and environmental benefits. Relying solely on biomass precursors makes it difficult to overcome performance bottlenecks, while using recycled plastics presents challenges in carbonization control. Furthermore, high-priced synthetic precursors deviate from the original intention of low-cost energy storage. Summary of the Invention

[0006] This invention provides a composite hard carbon material for sodium-ion batteries, its preparation method, and its application. It effectively solves the technical problem that existing hard carbon materials cannot balance performance, cost, and environmental benefits. This invention provides a sodium-ion battery hard carbon material that combines excellent electrochemical performance, low cost, and environmental friendliness, thereby promoting the practical application of sodium-ion battery technology.

[0007] The first objective of this invention is to provide a composite hard carbon material for sodium-ion batteries. The composite hard carbon material is based on a pre-treated powder of agricultural waste and recycled plastics. The matrix is ​​mixed with a compatibilizer and a dispersant and granulated to obtain composite precursor particles. The particles are then pyrolyzed and carbonized under a protective atmosphere. The mass ratio of agricultural waste to recycled plastics is 1:1 / 19 to 19.

[0008] The pre-treatment powder of agricultural waste and recycled plastics is obtained by alkaline washing and acid washing of a mixture of agricultural waste and recycled plastics powder.

[0009] The mass ratio of agricultural waste to recycled plastic is 1:1 / 19 to 19. This ratio is crucial for achieving complementary performance advantages between the two. Within this preferred range, biomass carbon sources can form abundant porous structures to provide high sodium ion storage capacity, while plastic-derived carbon sources can effectively fill and modify these pores and surface defects, thereby improving initial coulombic efficiency and structural stability. If the mass ratio of recycled plastic is too low, i.e., less than 1 / 19, its modification effect is insufficient, making it difficult to effectively suppress side reactions caused by numerous surface defects and complex active sites in biomass carbon. This results in limited improvement in the initial coulombic efficiency of the composite material, and the cycle stability may approach the level of pure biomass carbon. If the mass ratio of recycled plastic is too high, i.e., greater than 19, the plastic is prone to melting and becoming dominant during pyrolysis and carbonization, blocking the favorable pore structure formed by biomass. This leads to a decrease in the specific surface area of ​​the composite material and a reduction in sodium ion insertion / extraction channels, thereby significantly reducing the reversible specific capacity and making it difficult to meet the requirements of high-capacity anode materials.

[0010] In a preferred embodiment, the compatibilizer comprises 1 wt% to 3 wt% of the mass of the mixed powder of agricultural waste and recycled plastic, and the dispersant comprises 0.2 wt% to 1.5 wt%. The ratio of compatibilizer to dispersant used in this invention is crucial for achieving uniform composite of biomass and plastic phases. If the compatibilizer dosage is too low (less than the specified 1 wt%), it is insufficient to form an effective "molecular bridge" at the biomass-plastic interface, resulting in weak interfacial bonding. This leads to phase separation during subsequent heat treatment, resulting in an uneven structure of the final hard carbon material, numerous defective interfaces, decreased electronic conductivity, and deteriorated cycle performance. Conversely, if the compatibilizer dosage is too high (greater than the specified 3 wt%), excessive compatibilizer agglomeration not only fails to improve compatibility but also introduces excessive organic impurities. This generates additional pores or disordered carbon structures during carbonization, reducing the specific capacity of the material and increasing specific surface area and irreversible side reactions, leading to a decrease in initial coulombic efficiency and increased raw material costs. Regarding dispersants, if the amount used is too small (less than the specified 0.2 wt%), it cannot adequately coat the surface of the raw material particles, causing particle agglomeration in the slurry system and making it difficult to achieve initial uniform dispersion. This prevents the compatibilizer from effectively functioning in a homogeneous system, ultimately leading to uneven composition and structure of the composite material. If the amount of dispersant is too large (greater than the specified 1.5 wt%), the pyrolysis products of the excessive dispersant cannot provide sodium storage capacity, effectively diluting the effective content of the activated carbon precursor and resulting in a decrease in the specific capacity of the final material. Furthermore, the pyrolysis of the dispersant introduces residues such as heteroatoms or ash, which can damage the conductive network of the carbon material and may catalyze the formation of unfavorable carbon structures, thereby impairing its overall electrochemical performance, including first-time efficiency, rate capability, and cycle life.

[0011] In a preferred embodiment, the agricultural waste is at least one of coconut shell, rice husk, sugarcane bagasse, cotton stalk, wheat stalk, bamboo powder, and walnut shell; the recycled plastic is at least one of polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), and acrylonitrile-butadiene-styrene copolymer (ABS); the compatibilizer is maleic anhydride-grafted polyolefin and / or ethylene-acrylic acid copolymer; and the dispersant is one or more of sodium polyacrylate, sodium dodecylbenzenesulfonate, and polyvinylpyrrolidone.

[0012] The compatibilizer may be selected from, but is not limited to, the following categories: maleic anhydride-grafted polyolefins (maleic anhydride-grafted polyethylene (PE-g-MAH), maleic anhydride-grafted polypropylene), polyolefin elastomers (ethylene-vinyl acetate copolymer (EVA), styrene-ethylene-butene-styrene block copolymer (SEBS), functionalized copolymers (such as ethylene-acrylic acid copolymer (EAA)). In a preferred embodiment, the compatibilizer is selected from maleic anhydride-grafted polyolefins or ethylene-acrylic acid copolymers.

[0013] The dispersant includes anionic surfactants (sodium dodecylbenzenesulfonate (SDBS), sodium polyacrylate, lignin sulfonate), nonionic surfactants (alkylphenol polyoxyethylene ether, sorbitan fatty acid ester), or polymeric dispersants. In a preferred embodiment, the dispersant is sodium dodecylbenzenesulfonate (SDBS) or polyvinylpyrrolidone (PVP).

[0014] The recycled plastics used in this invention have a weight-average molecular weight (Mw) of 20,000 g / mol to 1,000,000 g / mol, preferably 50,000 g / mol to 300,000 g / mol. In Example 1, the polyethylene terephthalate (PET) used has a weight-average molecular weight (Mw) of approximately 30,000 g / mol. In Example 2, the polypropylene (PP) used has a weight-average molecular weight (Mw) of approximately 50,000 g / mol. In Example 3, the acrylonitrile-butadiene-styrene copolymer (ABS) used has a weight-average molecular weight (Mw) of approximately 75,000 g / mol.

[0015] The compatibilizer used in this invention has a weight-average molecular weight (Mw) of 5000 g / mol to 500000 g / mol, preferably 20000 g / mol to 200000 g / mol. In subsequent examples, the maleic anhydride-grafted polyethylene (PE-g-MAH) used has a weight-average molecular weight (Mw) of 100000 g / mol. The ethylene-vinyl acetate copolymer (EVA) has a weight-average molecular weight (Mw) of 80000 g / mol.

[0016] The polyvinylpyrrolidone (PVP) used in this invention has a K value of 15-90, preferably 25-35. The polyvinylpyrrolidone (PVP) used in the examples has a K value of 30.

[0017] The sodium polyacrylate used in the dispersant of this invention has a weight-average molecular weight Mw of 1000 g / mol to 100000 g / mol, preferably 2000 g / mol to 50000 g / mol.

[0018] A second objective of this invention is to provide a method for preparing a composite hard carbon material for sodium-ion batteries, comprising the following steps: The mixed powder of agricultural waste and recycled plastics is subjected to alkaline washing and acid washing to remove organic impurities, dissolve some of the silicon compounds and lignin in the agricultural waste, neutralize the residual alkali solution and dissolve the metal oxides in the agricultural waste, and obtain pretreated powder of agricultural waste and recycled plastics.

[0019] Using the pretreated powder of the agricultural waste and recycled plastics as a matrix, a compatibilizer and a dispersant are added, mixed, dried, and granulated to obtain composite precursor particles.

[0020] Under a protective atmosphere, the composite precursor particles are subjected to programmed temperature pyrolysis to pre-crosslink the recycled plastics in the composite precursor and perform biomass pyrolysis, followed by carbonization to remove non-carbon elements and enrich carbon, thereby obtaining a composite hard carbon material for sodium-ion batteries.

[0021] In the above technical solution, the mixed powder formed by organic waste and recycled plastic is first subjected to alkaline washing and acid washing. The purpose of the alkaline washing step is to remove organic impurities in the raw materials through saponification reaction and dissolve some silicates and lignin. The acid washing step is used to neutralize residual alkali solution and dissolve ash such as metal oxides. To improve the bonding between the biomass and plastic two-phase interface, this invention uses a polymeric compatibilizer, which reduces the interfacial energy and promotes the fusion of the biomass and plastic two phases. The compatibilizer can have good affinity with the plastic phase through specific segments in its molecular structure, and at the same time, it can interact with the biomass phase through polar groups or functional groups, thereby playing a bridging and compatibilizing effect at the two-phase interface, and obtaining a composite precursor with tight interfacial bonding and stable structure. To ensure uniform microscale dispersion of the raw material powder in the slurry and lay the foundation for subsequent uniform composite formation, this invention uses a dispersant. Its function is to prevent particle agglomeration and stabilize the slurry system. The dispersant can effectively adsorb onto the particle surface, and through electrostatic repulsion or steric hindrance, it ensures that the biomass and plastic powders are uniformly and stably dispersed in the slurry, thereby obtaining precursor particles with uniform composition. This invention employs programmed temperature pyrolysis of the composite precursor particles to achieve pre-crosslinking stabilization of the recycled plastic components and preliminary pyrolysis of the biomass components. This prevents the plastic from melting and coking at high temperatures and forms a stable, two-phase uniform composite precursor. The core purpose of the carbonization treatment following programmed temperature pyrolysis is to deeply remove non-carbon elements, enrich the carbon content, and construct a composite hard carbon material with suitable interlayer spacing and pore structure. Through the complementary heat treatment process of heating up and pyrolysis and carbonization, plastic-sourced carbon and biomass-sourced carbon achieve complementary advantages in microstructure. Plastic-sourced carbon effectively fills and modifies the pores and surface defects of biomass carbon, thereby synergistically obtaining a composite hard carbon material with high reversible capacity, high initial coulombic efficiency and long cycle life.

[0022] In a preferred embodiment, the alkaline washing involves using an inorganic alkali to wash the mixed powder of agricultural waste and recycled plastic at 50℃ to 80℃ for 2 to 4 hours to obtain alkaline-washed powder. The acid washing involves using an inorganic acid to wash the alkaline-washed powder at 50℃ to 80℃ for 2 to 4 hours. The alkaline washing and acid washing steps must be performed sequentially. Reversing the order will result in incomplete removal of impurities, affecting the purity and electrochemical performance of the final composite hard carbon material. The alkaline washing temperature and time range are 50℃ to 80℃ and 2 to 4 hours, respectively. Performing alkaline washing within this parameter range effectively balances cleaning efficiency and energy consumption.

[0023] In a preferred embodiment, the inorganic base is a sodium hydroxide solution with a concentration of 2 mol / L to 3 mol / L, and the inorganic acid is sulfuric acid with a concentration of 2 mol / L to 3 mol / L.

[0024] As a preferred embodiment, the programmed temperature pyrolysis specifically involves: heating the composite precursor particles to 200℃~400℃ at a rate of 2℃ / min~5℃ / min for 2 hours to obtain a pyrolytic precursor; the carbonization involves: heating the pyrolytic precursor to 900℃~1400℃ at a rate of 5℃ / min~8℃ / min for 4 hours to obtain a composite hard carbon material for sodium-ion batteries.

[0025] The programmed temperature pyrolysis step employed in this invention is crucial for achieving pre-crosslinking of plastics and initial pyrolysis of biomass. If the degree of pyrolysis is insufficient (e.g., too low a temperature or too short a time), such as pyrolysis at less than 200°C for less than 2 hours, the recycled plastic fails to undergo sufficient crosslinking, and its molecular chains do not form a stable network structure. During the subsequent rapid heating to the high-temperature carbonization stage, the plastic components easily melt, flow, and coke, destroying the homogeneous composite structure already formed in the precursor, leading to a denser product structure, abnormal specific surface area, and deteriorated capacity and rate performance. Conversely, if the degree of pyrolysis is excessive (e.g., too high a temperature or too long a time), such as pyrolysis at greater than 400°C for more than 2 hours, the biomass components prematurely undergo deep carbonization, causing the beneficial pore structure that should have formed during the high-temperature carbonization stage to be partially destroyed or collapsed at the low-temperature stage. Furthermore, excessive pyrolysis causes premature hardening of the precursor, hindering structural optimization and reorganization during the carbonization stage, thus affecting the formation of the optimal carbon layer spacing and porosity in the final material. Furthermore, unnecessarily high pyrolysis temperatures will directly lead to a significant increase in energy consumption, thereby raising production costs and hindering the application of this technology in the field of large-scale energy storage, which contradicts the original intention of this invention to utilize low-cost waste.

[0026] Carbonization temperature and time directly affect the carbon layer structure, graphitization degree, and porosity evolution of the final hard carbon material. Insufficient carbonization (e.g., temperatures below 900℃) results in incomplete removal of non-carbon elements (such as H, O, N, etc.), leading to numerous defects in the carbon material and a low degree of graphitization. This results in poor conductivity, high resistance to sodium ion migration, and poor rate performance. Furthermore, residual heteroatoms can trigger more electrolyte decomposition side reactions, reducing the initial coulombic efficiency. Excessive carbonization (e.g., temperatures above 1400℃) causes the carbon layer structure to develop towards graphitization order, leading to a decrease in interlayer spacing. Since sodium ions have a large radius, excessively small interlayer spacing hinders reversible insertion and extraction of sodium ions, significantly reducing capacity. Additionally, excessively high temperatures can cause some microporous structures to collapse, reducing sodium ion storage space and also negatively impacting capacity retention. More importantly, carbonization temperature is the main source of energy consumption cost in the preparation process. When the temperature exceeds 1400℃, energy consumption will increase exponentially, and the requirements for kiln equipment will be more stringent. This will greatly increase production costs and make the product lose its market competitiveness from an economic point of view, which runs counter to the goal of low cost and high performance pursued by this invention.

[0027] In a preferred embodiment, the agricultural waste has an ash content of ≤10% and a cellulose content of ≥30%.

[0028] A third objective of this invention is to provide an application of the aforementioned composite hard carbon material for sodium-ion batteries as a negative electrode material in sodium-ion batteries.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a composite hard carbon material for sodium-ion batteries. Compared to pure biomass carbon or single polymer-derived carbon, the composite hard carbon material prepared by this invention maintains high capacity while exhibiting high initial coulombic efficiency, good rate performance, and ultra-long cycle life. Addressing the compatibility issue between biomass and plastic phases, this invention adds compatibilizers and dispersants to the pretreated powder, ensuring uniform mixing and dispersion of each component at the microscale. This forms dense, homogeneous composite precursor particles, laying a solid foundation for obtaining structurally consistent and performance-stable composite hard carbon materials, which is beneficial for industrial production. This invention uses agricultural waste and recycled plastics as precursor raw materials. These two raw materials are widely available and inexpensive, effectively reducing production costs and providing a new pathway for the high-value resource utilization of waste, meeting the requirements of green environmental protection and sustainable development. Therefore, this invention achieves significant cost advantages and environmental benefits at the raw material level. Attached Figure Description

[0030] Figure 1 This is a SEM image of the composite hard carbon material for sodium-ion batteries prepared in Example 1 of the present invention. Detailed Implementation

[0031] To enable those skilled in the art to better understand and implement the technical solutions of this invention, the invention is further described below with reference to specific embodiments. However, the embodiments are not intended to limit the invention. Unless otherwise specified, the following test methods and detection methods are conventional methods; unless otherwise specified, the reagents and raw materials are commercially available.

[0032] To address the shortcomings of existing hard carbon materials: First, hard carbon materials prepared from single biomass precursors often suffer from low initial coulombic efficiency, poor rate performance, and poor batch stability. Second, using recycled plastics such as polyethylene terephthalate (PET) and polypropylene (PP) as carbon sources is prone to melting and coking during pyrolysis, resulting in carbonization products with dense structures and unsuitable specific surface areas, making it difficult to meet the high capacity and long lifespan requirements of sodium-ion batteries when used alone. Third, using phenolic resins and other synthetic polymer precursors results in high raw material costs and complex process routes. Based on these technical problems, this invention provides a composite hard carbon material for sodium-ion batteries, its preparation method, and its applications.

[0033] Because agricultural waste and recycled plastics are thermodynamically incompatible, simple mixing can easily lead to phase separation at the microscopic scale, resulting in poor uniformity of the prepared composite precursor. This, in turn, causes structural defects and poor interfacial stability in the final hard carbon material, severely affecting its electrochemical performance. To overcome this key technical challenge, this invention does not employ simple mechanical mixing, but rather a solution using the synergistic effect of compatibilizers and dispersants.

[0034] The technical solution of the present invention will be described in detail below.

[0035] This invention provides a composite hard carbon material for sodium-ion batteries, which uses pretreated agricultural waste and recycled plastic powder as a matrix, and mixes it with a compatibilizer and a dispersant to granulate it to obtain composite precursor particles; the composite precursor particles are then pyrolyzed and carbonized under a protective atmosphere to obtain the composite hard carbon material for sodium-ion batteries.

[0036] The method for preparing the pretreated agricultural waste and recycled plastic powder is as follows: the mixed powder of agricultural waste and recycled plastic is subjected to alkali washing and acid washing to obtain the pretreated agricultural waste and recycled plastic powder.

[0037] In the above technical solution, the mixed powder formed from agricultural waste and recycled plastic is first subjected to alkaline washing and acid washing. The purpose of the alkaline washing step is to remove organic impurities from the raw materials through saponification and dissolve some silicates and lignin. The acid washing step is used to neutralize residual alkali and dissolve ash such as metal oxides. To improve the bonding between the biomass and plastic phases, this invention uses a polymeric compatibilizer, which reduces the interfacial energy and promotes the fusion of the biomass and plastic phases. The compatibilizer has good affinity with the plastic phase through specific segments in its molecular structure, and at the same time interacts with the biomass phase through polar groups or functional groups, thereby playing a bridging and compatibilizing role at the interface between the two phases, and obtaining a composite precursor with tight interfacial bonding and stable structure. To ensure uniform microscale dispersion of raw material powder in the slurry and lay the foundation for subsequent uniform compounding, this invention uses a dispersant. Its function is to prevent particle agglomeration and stabilize the slurry system. The dispersant can be effectively adsorbed on the particle surface and, through electrostatic repulsion or steric hindrance effect, makes biomass and plastic powder uniformly and stably dispersed in the slurry, which is the key to achieving uniformity of precursor components.

[0038] Through in-depth research and extensive experiments, this invention has discovered that the combined use of compatibilizers and dispersants produces a significant synergistic effect. The dispersant first ensures the initial uniform dispersion of each component, providing ideal conditions for the compatibilizer to function. Subsequently, the compatibilizer bridges and fuses at the interface, fixing this uniform microstructure. This stepwise, synergistic mechanism cannot be achieved by a single additive. In particular, the type and ratio of compatibilizer and dispersant have varying effects on the performance of the final composite hard carbon material. Experiments show that different combinations significantly affect the electrochemical performance of the final material. For example, the composite hard carbon material prepared using a specific preferred combination (maleic anhydride-grafted polyolefin and sodium dodecylbenzenesulfonate) exhibits unexpectedly superior performance in initial coulombic efficiency and cycle stability, significantly outperforming single-component carbon sources or other additive combinations (see subsequent examples and comparative examples). Therefore, the synergistic use of the compatibilizer and dispersant is one of the core technical means of achieving high-performance composite hard carbon materials in this invention.

[0039] Furthermore, the core purpose of the present invention in pyrolyzing the composite precursor particles is to achieve pre-crosslinking stabilization of the recycled plastic components and preliminary pyrolysis of the biomass components, preventing the plastic from melting and coking at high temperatures, and forming a stable precursor with uniform two-phase composite structure. The core purpose of the carbonization treatment after pyrolysis is to deeply remove non-carbon elements, enrich the carbon content, and construct a composite hard carbon material with suitable interlayer spacing and pore structure. Through the complementary heat treatment of pyrolysis and carbonization, the plastic-sourced carbon and biomass-sourced carbon achieve complementary advantages in microstructure. The plastic-sourced carbon effectively fills and modifies the pores and surface defects of the biomass carbon, thereby synergistically obtaining a composite hard carbon material with high reversible capacity, high initial coulombic efficiency, and long cycle life.

[0040] The invention will now be described in detail through the following embodiments and comparative examples.

[0041] Example 1 A method for preparing a composite hard carbon material for sodium-ion batteries includes the following steps: S1, using coconut shells as agricultural waste, the coconut shells having an ash content of 5% and a cellulose content of 48%; using PET as recycled plastic, the PET being fragments separated from waste mineral water bottles; crushing the above-mentioned coconut shells and recycled PET plastic to ensure that the particle size can pass through a 200-mesh sieve, and mixing the coconut shells and PET powder in a mass ratio of 90:10 to obtain mixed powder.

[0042] S2, the mixed powder is alkali-washed with 3 mol / L sodium hydroxide solution at 60℃ for 3 h, and then washed with deionized water until neutral to obtain alkali-washed powder; subsequently, the alkali-washed powder is acid-washed with 3 mol / L sulfuric acid solution for 3 h, and then washed with deionized water until neutral, and finally dried at 105℃ to obtain pretreated powder.

[0043] S3, add 2% maleic anhydride-grafted polyethylene (PE-g-MAH) compatibilizer and 0.5% sodium dodecylbenzenesulfonate (SDBS) dispersant to the pretreated powder, and add water to adjust the solid content to 30% to obtain a mixed slurry. Mix the mixed slurry in a high-speed shear mixer at 500 rpm for 30 min to make it uniformly dispersed, and then dry it by flash evaporation, controlling the inlet temperature to 200℃ and the outlet temperature to 90℃ to obtain composite precursor particles.

[0044] S4, the composite precursor particles are subjected to programmed temperature pyrolysis under a nitrogen atmosphere. First, the temperature is increased to 300℃ at 2℃ / min and held for 2 hours for pretreatment. Then, the temperature is increased to 1200℃ at 5℃ / min and held for 4 hours for high-temperature carbonization. After the reaction, the mixture is naturally cooled to room temperature and pulverized using a pulverizer to obtain a composite hard carbon material for sodium-ion batteries, with the following morphology: Figure 1 As shown, Example 1 uses coconut shells and recycled PET as raw materials, and through the addition of additives and heat treatment steps, a high-performance composite hard carbon material was successfully prepared, which exhibits an amorphous porous structure.

[0045] Example 2 The difference from Example 1 is that the agricultural waste is rice husks, the recycled plastic is polypropylene (PP), and the mass ratio of rice husks to PP is 80:20.

[0046] S1, using rice husks as agricultural waste and polypropylene (PP) as recycled plastic; crushing the rice husks and PP to ensure that the particle size can pass through a 200-mesh sieve, and mixing the rice husks and PP powder in a mass ratio of 80:20 to obtain a mixed powder.

[0047] S2, the mixed powder is alkali-washed with 3 mol / L sodium hydroxide solution at 60℃ for 3 h, and then washed with deionized water until neutral to obtain alkali-washed powder; subsequently, the alkali-washed powder is acid-washed with 3 mol / L sulfuric acid solution for 3 h, and then washed with deionized water until neutral, and finally dried at 105℃ to obtain pretreated powder.

[0048] S3, add 2% maleic anhydride-grafted polyethylene (PE-g-MAH) compatibilizer and 0.5% sodium dodecylbenzenesulfonate (SDBS) dispersant to the pretreated powder, and add water to adjust the solid content to 30% to obtain a mixed slurry. Mix the mixed slurry in a high-speed shear mixer at 500 rpm for 30 min to make it uniformly dispersed, and then dry it by flash evaporation, controlling the inlet temperature to 200℃ and the outlet temperature to 90℃ to obtain composite precursor particles.

[0049] S4, the composite precursor particles are subjected to programmed temperature pyrolysis under a nitrogen atmosphere. First, the temperature is increased to 300°C at 2°C / min and held for 2 hours for pretreatment. Then, the temperature is increased to 1200°C at 5°C / min and held for 4 hours for high-temperature carbonization. After the reaction is completed, the mixture is naturally cooled to room temperature and then pulverized using a pulverizer to obtain the composite hard carbon material for sodium-ion batteries.

[0050] Example 3 The difference from Example 1 is that the agricultural waste is bamboo powder, the recycled plastic is acrylonitrile-butadiene-styrene copolymer (ABS), and the mass ratio of bamboo powder to ABS is 70:30.

[0051] S1, using bamboo powder as agricultural waste and acrylonitrile-butadiene-styrene copolymer (ABS) as recycled plastic; crushing the bamboo powder and ABS to ensure that the particle size can pass through a 200-mesh sieve, and mixing the bamboo powder and ABS powder in a mass ratio of 70:30 to obtain a mixed powder.

[0052] S2, the mixed powder is alkali-washed with 3 mol / L sodium hydroxide solution at 60℃ for 3 h, and then washed with deionized water until neutral to obtain alkali-washed powder; subsequently, the alkali-washed powder is acid-washed with 3 mol / L sulfuric acid solution for 3 h, and then washed with deionized water until neutral, and finally dried at 105℃ to obtain pretreated powder.

[0053] S3, add 2% maleic anhydride-grafted polyethylene (PE-g-MAH) compatibilizer and 0.5% sodium dodecylbenzenesulfonate (SDBS) dispersant to the pretreated powder, and add water to adjust the solid content to 30% to obtain a mixed slurry. Mix the mixed slurry in a high-speed shear mixer at 500 rpm for 30 min to make it uniformly dispersed, and then dry it by flash evaporation, controlling the inlet temperature to 200℃ and the outlet temperature to 90℃ to obtain composite precursor particles.

[0054] S4, the composite precursor particles are subjected to programmed temperature pyrolysis under a nitrogen atmosphere. First, the temperature is increased to 300°C at 2°C / min and held for 2 hours for pretreatment. Then, the temperature is increased to 1200°C at 5°C / min and held for 4 hours for high-temperature carbonization. After the reaction is completed, the mixture is naturally cooled to room temperature and then pulverized using a pulverizer to obtain the composite hard carbon material for sodium-ion batteries.

[0055] Example 4 The difference from Example 1 is that in S3, the compatibilizer is replaced with an equal amount (2%) of ethylene-vinyl acetate copolymer (EVA).

[0056] A method for preparing a composite hard carbon material for sodium-ion batteries includes the following steps: S1, using coconut shells as agricultural waste, the coconut shells having an ash content of 5% and a cellulose content of 48%; using PET as recycled plastic, the PET being fragments separated from waste mineral water bottles; crushing the above-mentioned coconut shells and recycled PET plastic to ensure that the particle size can pass through a 200-mesh sieve, and mixing the coconut shells and PET powder in a mass ratio of 90:10 to obtain mixed powder.

[0057] S2, the mixed powder is alkali-washed with 3 mol / L sodium hydroxide solution at 60℃ for 3 hours, and then washed with deionized water until neutral to obtain alkali-washed powder; subsequently, the alkali-washed powder is acid-washed with 3 mol / L sulfuric acid solution for 3 hours, and then washed with deionized water until neutral, and finally dried at 105℃ to obtain pretreated powder.

[0058] S3, add 2% of the compatibilizer ethylene-vinyl acetate copolymer (EVA) and 0.5% of the dispersant sodium dodecylbenzenesulfonate (SDBS) to the pretreated powder, and add water to adjust the solid content to 30% to obtain a mixed slurry. Mix the mixed slurry in a high-speed shear mixer at 500 rpm for 30 min to make it uniformly dispersed, and then dry it by flash evaporation, controlling the inlet temperature to 200℃ and the outlet temperature to 90℃ to obtain composite precursor particles.

[0059] S4, the composite precursor particles are subjected to programmed temperature pyrolysis under a nitrogen atmosphere. First, the temperature is increased to 300°C at 2°C / min and held for 2 hours for pretreatment. Then, the temperature is increased to 1200°C at 5°C / min and held for 4 hours for high-temperature carbonization. After the reaction is completed, the mixture is naturally cooled to room temperature and then pulverized using a pulverizer to obtain the composite hard carbon material for sodium-ion batteries.

[0060] Example 5 The difference from Example 1 is that in S3, the dispersant is replaced with an equal amount (0.5%) of polyvinylpyrrolidone (PVP).

[0061] A method for preparing a composite hard carbon material for sodium-ion batteries includes the following steps: S1, using coconut shells as agricultural waste, the coconut shells having an ash content of 5% and a cellulose content of 48%; using PET as recycled plastic, the PET being fragments separated from waste mineral water bottles; crushing the above-mentioned coconut shells and recycled PET plastic to ensure that the particle size can pass through a 200-mesh sieve, and mixing the coconut shells and PET powder in a mass ratio of 90:10 to obtain mixed powder.

[0062] S2, the mixed powder is alkali-washed with 3 mol / L sodium hydroxide solution at 60℃ for 3 hours, and then washed with deionized water until neutral to obtain alkali-washed powder; subsequently, the alkali-washed powder is acid-washed with 3 mol / L sulfuric acid solution for 3 hours, and then washed with deionized water until neutral, and finally dried at 105℃ to obtain pretreated powder.

[0063] S3, add 2% maleic anhydride-grafted polyethylene (PE-g-MAH) compatibilizer and 0.5% polyvinylpyrrolidone (PVP) dispersant to the pretreated powder, and add water to adjust the solid content to 30% to obtain a mixed slurry. Mix the mixed slurry in a high-speed shear mixer at 500 rpm for 30 minutes to make it uniformly dispersed, and then dry it by flash evaporation, controlling the inlet temperature to 200℃ and the outlet temperature to 90℃ to obtain composite precursor particles.

[0064] S4, the composite precursor particles are subjected to programmed temperature pyrolysis under a nitrogen atmosphere. First, the temperature is increased to 300°C at 2°C / min and held for 2 hours for pretreatment. Then, the temperature is increased to 1200°C at 5°C / min and held for 4 hours for high-temperature carbonization. After the reaction is completed, the mixture is naturally cooled to room temperature and then pulverized using a pulverizer to obtain the composite hard carbon material for sodium-ion batteries.

[0065] To further illustrate the technical effects of the present invention, a comparative example is also provided, as follows.

[0066] Comparative Example 1 The difference compared to Example 1 is that no compatibilizer or dispersant was added in S3.

[0067] A method for preparing a composite hard carbon material for sodium-ion batteries includes the following steps: S1, using coconut shells as agricultural waste, the coconut shells having an ash content of 5% and a cellulose content of 48%; using PET as recycled plastic, the PET being fragments separated from waste mineral water bottles; crushing the above-mentioned coconut shells and recycled PET plastic to ensure that the particle size can pass through a 200-mesh sieve, and mixing the coconut shells and PET powder in a mass ratio of 90:10 to obtain mixed powder.

[0068] S2, the mixed powder is alkali-washed with 3 mol / L sodium hydroxide solution at 60℃ for 3 hours, and then washed with deionized water until neutral to obtain alkali-washed powder; subsequently, the alkali-washed powder is acid-washed with 3 mol / L sulfuric acid solution for 3 hours, and then washed with deionized water until neutral, and finally dried at 105℃ to obtain pretreated powder.

[0069] S3. Water is added to the pretreated powder to adjust the solid content to 30% to obtain a mixed slurry. The mixed slurry is mixed in a high-speed shear mixer at 500 rpm for 30 minutes to make it uniformly dispersed. Then it is dried by flash evaporation, with the inlet temperature controlled at 200°C and the outlet temperature at 90°C to obtain composite precursor particles.

[0070] S4, the composite precursor particles are subjected to programmed temperature pyrolysis under a nitrogen atmosphere. First, the temperature is increased to 300°C at 2°C / min and held for 2 hours for pretreatment. Then, the temperature is increased to 1200°C at 5°C / min and held for 4 hours for high-temperature carbonization. After the reaction is completed, the mixture is naturally cooled to room temperature and then pulverized using a pulverizer to obtain the composite hard carbon material for sodium-ion batteries.

[0071] Comparative Example 2 The difference compared to Example 1 is that in S3, only 2% of PE-g-MAH compatibilizer was added, and the dispersant SDBS was not added.

[0072] A method for preparing a composite hard carbon material for sodium-ion batteries includes the following steps: S1, using coconut shells as agricultural waste, the coconut shells having an ash content of 5% and a cellulose content of 48%; using PET as recycled plastic, the PET being fragments separated from waste mineral water bottles; crushing the above-mentioned coconut shells and recycled PET plastic to ensure that the particle size can pass through a 200-mesh sieve, and mixing the coconut shells and PET powder in a mass ratio of 90:10 to obtain mixed powder.

[0073] S2, the mixed powder is alkali-washed with 3 mol / L sodium hydroxide solution at 60℃ for 3 hours, and then washed with deionized water until neutral to obtain alkali-washed powder; subsequently, the alkali-washed powder is acid-washed with 3 mol / L sulfuric acid solution for 3 hours, and then washed with deionized water until neutral, and finally dried at 105℃ to obtain pretreated powder.

[0074] S3, add 2% of maleic anhydride-grafted polyethylene (PE-g-MAH) compatibilizer to the pretreated powder, and add water to adjust the solid content to 30% to obtain a mixed slurry. Mix the mixed slurry in a high-speed shear mixer at 500 rpm for 30 minutes to make it uniformly dispersed. Then dry it by flash evaporation, controlling the inlet temperature to 200℃ and the outlet temperature to 90℃ to obtain composite precursor particles.

[0075] S4, the composite precursor particles are subjected to programmed temperature pyrolysis under a nitrogen atmosphere. First, the temperature is increased to 300°C at 2°C / min and held for 2 hours for pretreatment. Then, the temperature is increased to 1200°C at 5°C / min and held for 4 hours for high-temperature carbonization. After the reaction is completed, the mixture is naturally cooled to room temperature and then pulverized using a pulverizer to obtain the composite hard carbon material for sodium-ion batteries.

[0076] Comparative Example 3 The difference compared to Example 1 is that in S3, only 0.5% of SDBS dispersant was added, and no compatibilizer PE-g-MAH was added.

[0077] A method for preparing a composite hard carbon material for sodium-ion batteries includes the following steps: S1, using coconut shells as agricultural waste, the coconut shells having an ash content of 5% and a cellulose content of 48%; using PET as recycled plastic, the PET being fragments separated from waste mineral water bottles; crushing the above-mentioned coconut shells and recycled PET plastic to ensure that the particle size can pass through a 200-mesh sieve, and mixing the coconut shells and PET powder in a mass ratio of 90:10 to obtain mixed powder.

[0078] S2, the mixed powder is alkali-washed with 3 mol / L sodium hydroxide solution at 60℃ for 3 h, and then washed with deionized water until neutral to obtain alkali-washed powder; subsequently, the alkali-washed powder is acid-washed with 3 mol / L sulfuric acid solution for 3 h, and then washed with deionized water until neutral, and finally dried at 105℃ to obtain pretreated powder.

[0079] S3, add sodium dodecylbenzenesulfonate (SDBS), a dispersant accounting for 0.5% of the total mass of the mixed powder, to the pretreated powder, and add water to adjust the solid content to 30% to obtain a mixed slurry. Mix the mixed slurry in a high-speed shear mixer at 500 rpm for 30 minutes to make it uniformly dispersed, and then dry it by flash evaporation, controlling the inlet temperature to 200℃ and the outlet temperature to 90℃ to obtain composite precursor particles.

[0080] S4, the composite precursor particles are subjected to programmed temperature pyrolysis under a nitrogen atmosphere. First, the temperature is increased to 300°C at 2°C / min and held for 2 hours for pretreatment. Then, the temperature is increased to 1200°C at 5°C / min and held for 4 hours for high-temperature carbonization. After the reaction is completed, the mixture is naturally cooled to room temperature and then pulverized using a pulverizer to obtain the composite hard carbon material for sodium-ion batteries.

[0081] Comparative Example 4 The difference compared to Example 1 is that in S1, no PET plastic was added, and only coconut shell was used as the sole raw material, with the same amount as the total mass of the mixed powder in Example 1.

[0082] A method for preparing a hard carbon material for sodium-ion batteries includes the following steps: S1, using coconut shells as agricultural waste, the coconut shells having an ash content of 5% and a cellulose content of 48%, the coconut shells are crushed to ensure that the particle size can pass through a 200-mesh sieve to obtain coconut shell powder.

[0083] S2, at 60℃, the coconut shell powder is alkali-washed with a 3 mol / L sodium hydroxide solution for 3 hours, and then washed with deionized water until neutral to obtain alkali-washed powder; subsequently, the alkali-washed powder is acid-washed with a 3 mol / L sulfuric acid solution for 3 hours, and then washed with deionized water until neutral, and finally dried at 105℃ to obtain pretreated powder.

[0084] S3, add 2% maleic anhydride-grafted polyethylene (PE-g-MAH) compatibilizer and 0.5% sodium dodecylbenzenesulfonate (SDBS) dispersant to the pretreated powder, and add water to adjust the solid content to 30% to obtain a mixed slurry. Mix the mixed slurry in a high-speed shear mixer at 500 rpm for 30 min to make it uniformly dispersed, and then dry it by flash evaporation, controlling the inlet temperature to 200℃ and the outlet temperature to 90℃ to obtain precursor particles.

[0085] S4, the precursor particles are subjected to programmed temperature pyrolysis under a nitrogen atmosphere. First, the temperature is increased to 300°C at 2°C / min and held for 2 hours for pretreatment. Then, the temperature is increased to 1200°C at 5°C / min and held for 4 hours for high-temperature carbonization. After the reaction is completed, the mixture is naturally cooled to room temperature and then pulverized using a pulverizer to obtain hard carbon material for sodium-ion batteries.

[0086] Comparative Example 5 The difference from Example 1 is that in S1, no coconut shell was added, and only PET was used as the sole raw material, with the same amount as the total mass of the mixed powder in Example 1.

[0087] A method for preparing a composite hard carbon material for sodium-ion batteries includes the following steps: S1, using PET as recycled plastic, the PET being fragments separated from waste mineral water bottles; the recycled PET plastic is crushed to ensure that the particle size can pass through a 200-mesh sieve to obtain plastic powder.

[0088] S2, the plastic powder is alkali-washed with a 3 mol / L sodium hydroxide solution at 60℃ for 3 hours, and then washed with deionized water until neutral to obtain alkali-washed powder; subsequently, the alkali-washed powder is acid-washed with a 3 mol / L sulfuric acid solution for 3 hours, and then washed with deionized water until neutral, and finally dried at 105℃ to obtain pretreated powder.

[0089] S3, add 2% maleic anhydride-grafted polyethylene (PE-g-MAH) compatibilizer and 0.5% sodium dodecylbenzene sulfonate (SDBS) dispersant to the pretreated powder, and add water to adjust the solid content to 30% to obtain a mixed slurry. Mix the mixed slurry in a high-speed shear mixer at 500 rpm for 30 minutes to make it uniformly dispersed, and then dry it by flash evaporation, controlling the inlet temperature to 200℃ and the outlet temperature to 90℃ to obtain precursor particles.

[0090] S4, the precursor particles are subjected to programmed temperature pyrolysis under a nitrogen atmosphere. First, the temperature is increased to 300°C at 2°C / min and held for 2 hours for pretreatment. Then, the temperature is increased to 1200°C at 5°C / min and held for 4 hours for high-temperature carbonization. After the reaction is completed, the mixture is naturally cooled to room temperature and then pulverized using a pulverizer to obtain hard carbon material for sodium-ion batteries.

[0091] Comparative Example 6 The difference compared to Example 1 is that the mass ratio of coconut shell to PET is adjusted to 98:2.

[0092] A method for preparing a composite hard carbon material for sodium-ion batteries includes the following steps: S1, using coconut shells as agricultural waste, the coconut shells having an ash content of 5% and a cellulose content of 48%; using PET as recycled plastic, the PET being fragments separated from waste mineral water bottles; crushing the above-mentioned coconut shells and recycled PET plastic to ensure that the particle size can pass through a 200-mesh sieve, and mixing the coconut shells and PET powder in a mass ratio of 98:2 to obtain mixed powder.

[0093] S2, the mixed powder is alkali-washed with 3 mol / L sodium hydroxide solution at 60℃ for 3 h, and then washed with deionized water until neutral to obtain alkali-washed powder; subsequently, the alkali-washed powder is acid-washed with 3 mol / L sulfuric acid solution for 3 h, and then washed with deionized water until neutral, and finally dried at 105℃ to obtain pretreated powder.

[0094] S3, add 2% maleic anhydride-grafted polyethylene (PE-g-MAH) compatibilizer and 0.5% sodium dodecylbenzenesulfonate (SDBS) dispersant to the pretreated powder, and add water to adjust the solid content to 30% to obtain a mixed slurry. Mix the mixed slurry in a high-speed shear mixer at 500 rpm for 30 min to make it uniformly dispersed, and then dry it by flash evaporation, controlling the inlet temperature to 200℃ and the outlet temperature to 90℃ to obtain composite precursor particles.

[0095] S4, the composite precursor particles are subjected to programmed temperature pyrolysis under a nitrogen atmosphere. First, the temperature is increased to 300°C at 2°C / min and held for 2 hours for pretreatment. Then, the temperature is increased to 1200°C at 5°C / min and held for 4 hours for high-temperature carbonization. After the reaction is completed, the mixture is naturally cooled to room temperature and then pulverized using a pulverizer to obtain the composite hard carbon material for sodium-ion batteries.

[0096] Comparative Example 7 The difference compared to Example 1 is that the mass ratio of coconut shell to PET is adjusted to 5:95.

[0097] A method for preparing a composite hard carbon material for sodium-ion batteries includes the following steps: S1, using coconut shells as agricultural waste, the coconut shells having an ash content of 5% and a cellulose content of 48%; using PET as recycled plastic, the PET being fragments separated from waste mineral water bottles; crushing the above-mentioned coconut shells and recycled PET plastic to ensure that the particle size can pass through a 200-mesh sieve, and mixing the coconut shells and PET powder in a mass ratio of 5:95 to obtain mixed powder.

[0098] S2, the mixed powder is alkali-washed with 3 mol / L sodium hydroxide solution at 60℃ for 3 h, and then washed with deionized water until neutral to obtain alkali-washed powder; subsequently, the alkali-washed powder is acid-washed with 3 mol / L sulfuric acid solution for 3 h, and then washed with deionized water until neutral, and finally dried at 105℃ to obtain pretreated powder.

[0099] S3, add 2% maleic anhydride-grafted polyethylene (PE-g-MAH) compatibilizer and 0.5% sodium dodecylbenzenesulfonate (SDBS) dispersant to the pretreated powder, and add water to adjust the solid content to 30% to obtain a mixed slurry. Mix the mixed slurry in a high-speed shear mixer at 500 rpm for 30 min to make it uniformly dispersed, and then dry it by flash evaporation, controlling the inlet temperature to 200℃ and the outlet temperature to 90℃ to obtain composite precursor particles.

[0100] S4, the composite precursor particles are subjected to programmed temperature pyrolysis under a nitrogen atmosphere. First, the temperature is increased to 300°C at 2°C / min and held for 2 hours for pretreatment. Then, the temperature is increased to 1200°C at 5°C / min and held for 4 hours for high-temperature carbonization. After the reaction is completed, the mixture is naturally cooled to room temperature and then pulverized using a pulverizer to obtain the composite hard carbon material for sodium-ion batteries.

[0101] Comparative Example 8 Compared with Example 1, the difference is that in S3, the amount of compatibilizer PE-g-MAH added is changed to 0.5%, and the amount of dispersant SDBS added is changed to 6.0%.

[0102] A method for preparing a composite hard carbon material for sodium-ion batteries includes the following steps: S1, using coconut shells as agricultural waste, the coconut shells having an ash content of 5% and a cellulose content of 48%; using PET as recycled plastic, the PET being fragments separated from waste mineral water bottles; crushing the above-mentioned coconut shells and recycled PET plastic to ensure that the particle size can pass through a 200-mesh sieve, and mixing the coconut shells and PET powder in a mass ratio of 90:10 to obtain mixed powder.

[0103] S2, the mixed powder is alkali-washed with 3 mol / L sodium hydroxide solution at 60℃ for 3 h, and then washed with deionized water until neutral to obtain alkali-washed powder; subsequently, the alkali-washed powder is acid-washed with 3 mol / L sulfuric acid solution for 3 h, and then washed with deionized water until neutral, and finally dried at 105℃ to obtain pretreated powder.

[0104] S3, add 0.5% of maleic anhydride-grafted polyethylene (PE-g-MAH) and 6.0% of sodium dodecylbenzenesulfonate (SDBS) as compatibilizer to the pretreated powder, and add water to adjust the solid content to 30% to obtain a mixed slurry. Mix the mixed slurry in a high-speed shear mixer at 500 rpm for 30 min to make it uniformly dispersed, and then dry it by flash evaporation, controlling the inlet temperature to 200℃ and the outlet temperature to 90℃ to obtain composite precursor particles.

[0105] S4, the composite precursor particles are subjected to programmed temperature pyrolysis under a nitrogen atmosphere. First, the temperature is increased to 300°C at 2°C / min and held for 2 hours for pretreatment. Then, the temperature is increased to 1200°C at 5°C / min and held for 4 hours for high-temperature carbonization. After the reaction is completed, the mixture is naturally cooled to room temperature and then pulverized using a pulverizer to obtain the composite hard carbon material for sodium-ion batteries.

[0106] Comparative Example 9 Compared to Example 1, the temperature of the programmed pyrolysis in S4 was adjusted to 500°C.

[0107] A method for preparing a composite hard carbon material for sodium-ion batteries includes the following steps: S1, using coconut shells as agricultural waste, the coconut shells having an ash content of 5% and a cellulose content of 48%; using PET as recycled plastic, the PET being fragments separated from waste mineral water bottles; crushing the above-mentioned coconut shells and recycled PET plastic to ensure that the particle size can pass through a 200-mesh sieve, and mixing the coconut shells and PET powder in a mass ratio of 90:10 to obtain mixed powder.

[0108] S2, the mixed powder is alkali-washed with 3 mol / L sodium hydroxide solution at 60℃ for 3 h, and then washed with deionized water until neutral to obtain alkali-washed powder; subsequently, the alkali-washed powder is acid-washed with 3 mol / L sulfuric acid solution for 3 h, and then washed with deionized water until neutral, and finally dried at 105℃ to obtain pretreated powder.

[0109] S3, add 2% maleic anhydride-grafted polyethylene (PE-g-MAH) compatibilizer and 0.5% sodium dodecylbenzenesulfonate (SDBS) dispersant to the pretreated powder, and add water to adjust the solid content to 30% to obtain a mixed slurry. Mix the mixed slurry in a high-speed shear mixer at 500 rpm for 30 min to make it uniformly dispersed, and then dry it by flash evaporation, controlling the inlet temperature to 200℃ and the outlet temperature to 90℃ to obtain composite precursor particles.

[0110] S4. The composite precursor particles are subjected to programmed temperature pyrolysis under a nitrogen atmosphere. First, the temperature is increased to 500°C at 2°C / min and held for 2 hours for pretreatment. Then, the temperature is increased to 1200°C at 5°C / min and held for 4 hours for high-temperature carbonization. After the reaction is completed, the mixture is naturally cooled to room temperature and then pulverized using a pulverizer to obtain the composite hard carbon material for sodium-ion batteries.

[0111] Comparative Example 10 Compared to Example 1, the carbonization temperature in S4 was adjusted to 1600°C.

[0112] A method for preparing a composite hard carbon material for sodium-ion batteries includes the following steps: S1, using coconut shells as agricultural waste, the coconut shells having an ash content of 5% and a cellulose content of 48%; using PET as recycled plastic, the PET being fragments separated from waste mineral water bottles; crushing the above-mentioned coconut shells and recycled PET plastic to ensure that the particle size can pass through a 200-mesh sieve, and mixing the coconut shells and PET powder in a mass ratio of 90:10 to obtain mixed powder.

[0113] S2, the mixed powder is alkali-washed with 3 mol / L sodium hydroxide solution at 60℃ for 3 h, and then washed with deionized water until neutral to obtain alkali-washed powder; subsequently, the alkali-washed powder is acid-washed with 3 mol / L sulfuric acid solution for 3 h, and then washed with deionized water until neutral, and finally dried at 105℃ to obtain pretreated powder.

[0114] S3, add 2% maleic anhydride-grafted polyethylene (PE-g-MAH) compatibilizer and 0.5% sodium dodecylbenzenesulfonate (SDBS) dispersant to the pretreated powder, and add water to adjust the solid content to 30% to obtain a mixed slurry. Mix the mixed slurry in a high-speed shear mixer at 500 rpm for 30 min to make it uniformly dispersed, and then dry it by flash evaporation, controlling the inlet temperature to 200℃ and the outlet temperature to 90℃ to obtain composite precursor particles.

[0115] S4. The composite precursor particles are subjected to programmed temperature pyrolysis under a nitrogen atmosphere. First, the temperature is increased to 300°C at 2°C / min and held for 2 hours for pretreatment. Then, the temperature is increased to 1600°C at 5°C / min and held for 4 hours for high-temperature carbonization. After the reaction is completed, the mixture is naturally cooled to room temperature and then pulverized using a pulverizer to obtain the composite hard carbon material for sodium-ion batteries.

[0116] Comparative Example 11 Compared with Example 1, the amount of compatibilizer PE-g-MAH added in S3 was changed to 0.5%, while the amount of dispersant SDBS added remained at 0.5%.

[0117] A method for preparing a composite hard carbon material for sodium-ion batteries includes the following steps: S1, using coconut shells as agricultural waste, the coconut shells having an ash content of 5% and a cellulose content of 48%; using PET as recycled plastic, the PET being fragments separated from waste mineral water bottles; crushing the above-mentioned coconut shells and recycled PET plastic to ensure that the particle size can pass through a 200-mesh sieve, and mixing the coconut shells and PET powder in a mass ratio of 90:10 to obtain mixed powder.

[0118] S2, the mixed powder is alkali-washed with 3 mol / L sodium hydroxide solution at 60℃ for 3 h, and then washed with deionized water until neutral to obtain alkali-washed powder; subsequently, the alkali-washed powder is acid-washed with 3 mol / L sulfuric acid solution for 3 h, and then washed with deionized water until neutral, and finally dried at 105℃ to obtain pretreated powder.

[0119] S3, add 0.5% of maleic anhydride-grafted polyethylene (PE-g-MAH) compatibilizer and 0.5% of sodium dodecylbenzenesulfonate (SDBS) dispersant to the pretreated powder, and add water to adjust the solid content to 30% to obtain a mixed slurry. Mix the mixed slurry in a high-speed shear mixer at 500 rpm for 30 min to make it uniformly dispersed, and then dry it by flash evaporation, controlling the inlet temperature to 200℃ and the outlet temperature to 90℃ to obtain composite precursor particles.

[0120] S4, the composite precursor particles are subjected to programmed temperature pyrolysis under a nitrogen atmosphere. First, the temperature is increased to 300°C at 2°C / min and held for 2 hours for pretreatment. Then, the temperature is increased to 1200°C at 5°C / min and held for 4 hours for high-temperature carbonization. After the reaction is completed, the mixture is naturally cooled to room temperature and then pulverized using a pulverizer to obtain the composite hard carbon material for sodium-ion batteries.

[0121] Comparative Example 12 Compared with Example 1, the difference is that the amount of compatibilizer PE-g-MAH added in S3 is changed to 5.0%, while the amount of dispersant SDBS added remains at 0.5%.

[0122] A method for preparing a composite hard carbon material for sodium-ion batteries includes the following steps: S1, using coconut shells as agricultural waste, the coconut shells having an ash content of 5% and a cellulose content of 48%; using PET as recycled plastic, the PET being fragments separated from waste mineral water bottles; crushing the above-mentioned coconut shells and recycled PET plastic to ensure that the particle size can pass through a 200-mesh sieve, and mixing the coconut shells and PET powder in a mass ratio of 90:10 to obtain mixed powder.

[0123] S2, the mixed powder is alkali-washed with 3 mol / L sodium hydroxide solution at 60℃ for 3 h, and then washed with deionized water until neutral to obtain alkali-washed powder; subsequently, the alkali-washed powder is acid-washed with 3 mol / L sulfuric acid solution for 3 h, and then washed with deionized water until neutral, and finally dried at 105℃ to obtain pretreated powder.

[0124] S3, add 5.0% of maleic anhydride-grafted polyethylene (PE-g-MAH) and 0.5% of sodium dodecylbenzenesulfonate (SDBS) as compatibilizer to the pretreated powder, and add water to adjust the solid content to 30% to obtain a mixed slurry. Mix the mixed slurry in a high-speed shear mixer at 500 rpm for 30 min to make it uniformly dispersed, and then dry it by flash evaporation, controlling the inlet temperature to 200℃ and the outlet temperature to 90℃ to obtain composite precursor particles.

[0125] S4, the composite precursor particles are subjected to programmed temperature pyrolysis under a nitrogen atmosphere. First, the temperature is increased to 300°C at 2°C / min and held for 2 hours for pretreatment. Then, the temperature is increased to 1200°C at 5°C / min and held for 4 hours for high-temperature carbonization. After the reaction is completed, the mixture is naturally cooled to room temperature and then pulverized using a pulverizer to obtain the composite hard carbon material for sodium-ion batteries.

[0126] Comparative Example 13 Compared with Example 1, the difference is that the amount of compatibilizer PE-g-MAH added in S3 is kept at 2.0%, and the amount of dispersant SDBS added is changed to 0.1%.

[0127] A method for preparing a composite hard carbon material for sodium-ion batteries includes the following steps: S1, using coconut shells as agricultural waste, the coconut shells having an ash content of 5% and a cellulose content of 48%; using PET as recycled plastic, the PET being fragments separated from waste mineral water bottles; crushing the above-mentioned coconut shells and recycled PET plastic to ensure that the particle size can pass through a 200-mesh sieve, and mixing the coconut shells and PET powder in a mass ratio of 90:10 to obtain mixed powder.

[0128] S2, the mixed powder is alkali-washed with 3 mol / L sodium hydroxide solution at 60℃ for 3 h, and then washed with deionized water until neutral to obtain alkali-washed powder; subsequently, the alkali-washed powder is acid-washed with 3 mol / L sulfuric acid solution for 3 h, and then washed with deionized water until neutral, and finally dried at 105℃ to obtain pretreated powder.

[0129] S3, add 2% of maleic anhydride-grafted polyethylene (PE-g-MAH) compatibilizer and 0.1% of sodium dodecylbenzenesulfonate (SDBS) dispersant to the pretreated powder, and add water to adjust the solid content to 30% to obtain a mixed slurry. Mix the mixed slurry in a high-speed shear mixer at 500 rpm for 30 min to make it uniformly dispersed, and then dry it by flash evaporation, controlling the inlet temperature to 200℃ and the outlet temperature to 90℃ to obtain composite precursor particles.

[0130] S4, the composite precursor particles are subjected to programmed temperature pyrolysis under a nitrogen atmosphere. First, the temperature is increased to 300°C at 2°C / min and held for 2 hours for pretreatment. Then, the temperature is increased to 1200°C at 5°C / min and held for 4 hours for high-temperature carbonization. After the reaction is completed, the mixture is naturally cooled to room temperature and then pulverized using a pulverizer to obtain the composite hard carbon material for sodium-ion batteries.

[0131] Comparative Example 14 Compared with Example 1, the difference is that the amount of compatibilizer PE-g-MAH added in S3 is kept at 2.0%, and the amount of dispersant SDBS added is changed to 3.0%.

[0132] A method for preparing a composite hard carbon material for sodium-ion batteries includes the following steps: S1, using coconut shells as agricultural waste, the coconut shells having an ash content of 5% and a cellulose content of 48%; using PET as recycled plastic, the PET being fragments separated from waste mineral water bottles; crushing the above-mentioned coconut shells and recycled PET plastic to ensure that the particle size can pass through a 200-mesh sieve, and mixing the coconut shells and PET powder in a mass ratio of 90:10 to obtain mixed powder.

[0133] S2, the mixed powder is alkali-washed with 3 mol / L sodium hydroxide solution at 60℃ for 3 h, and then washed with deionized water until neutral to obtain alkali-washed powder; subsequently, the alkali-washed powder is acid-washed with 3 mol / L sulfuric acid solution for 3 h, and then washed with deionized water until neutral, and finally dried at 105℃ to obtain pretreated powder.

[0134] S3, add 2% maleic anhydride-grafted polyethylene (PE-g-MAH) compatibilizer and 3.0% sodium dodecylbenzenesulfonate (SDBS) dispersant to the pretreated powder, and add water to adjust the solid content to 30% to obtain a mixed slurry. Mix the mixed slurry in a high-speed shear mixer at 500 rpm for 30 min to make it uniformly dispersed, and then dry it by flash evaporation, controlling the inlet temperature to 200℃ and the outlet temperature to 90℃ to obtain composite precursor particles.

[0135] S4, the composite precursor particles are subjected to programmed temperature pyrolysis under a nitrogen atmosphere. First, the temperature is increased to 300°C at 2°C / min and held for 2 hours for pretreatment. Then, the temperature is increased to 1200°C at 5°C / min and held for 4 hours for high-temperature carbonization. After the reaction is completed, the mixture is naturally cooled to room temperature and then pulverized using a pulverizer to obtain the composite hard carbon material for sodium-ion batteries.

[0136] The performance of the sodium-ion composite hard carbon materials provided in Examples 1 to 5 and Comparative Examples 1 to 14, and the sodium-ion battery hard carbon materials provided in Comparative Examples 4 to 5 were tested, and the results are as follows.

[0137] Table 1. Performance of hard carbon materials from the embodiments of the present invention and Comparative Examples 1 to 5. Table 2. Performance of hard carbon materials of Examples 1 and Comparative Examples 6 to 14 of the present invention As shown in Tables 1 and 2 above, using the composite hard carbon material of Example 1 as the negative electrode and a sodium metal sheet as the counter electrode, a CR2032 button cell was assembled. Test results show that the initial discharge capacity of this composite hard carbon negative electrode material reaches 350 mAh / g, with an initial coulombic efficiency of 91.2%. After 100 cycles at a charge-discharge rate of 0.1C, the capacity retention rate is 99.5%. The composite hard carbon material for sodium-ion batteries prepared in Example 2 has an initial discharge capacity of 335 mAh / g, an initial coulombic efficiency of 90.5%, and a capacity retention rate of 99.3% after 100 cycles. The composite hard carbon material for sodium-ion batteries prepared in Example 3 has an initial discharge capacity of 320 mAh / g, an initial coulombic efficiency of 93.5%, and a capacity retention rate of 98.9% after 100 cycles. This scheme exhibits the best initial efficiency and cycle performance. The sodium-ion battery composite hard carbon material prepared in Example 4 had an initial discharge capacity of 338 mAh / g, an initial coulombic efficiency of 86.0%, and a capacity retention of 83.0% after 100 cycles. This performance was superior to the additive-free control group of Comparative Example 1, but inferior to Example 1, demonstrating the advantage of the preferred compatibilizer (PE-g-MAH) in forming strong interfacial chemical bonds. The sodium-ion battery composite hard carbon material prepared in Example 5 had an initial discharge capacity of 345 mAh / g, an initial coulombic efficiency of 89.5%, and a capacity retention of 85.0% after 100 cycles. This performance was superior to the additive-free control group of Comparative Example 1, but inferior to Example 1, demonstrating the advantage of the preferred ionic dispersant (SDBS) in achieving initial uniform particle dispersion.

[0138] For the hard carbon materials prepared in Comparative Examples 1 to 5, the initial discharge capacity of the composite hard carbon material for sodium-ion batteries prepared in Comparative Example 1 was 273 mAh / g, the initial coulombic efficiency was 85.1%, and the capacity retention after 100 cycles was 80.2%. The results indicate that without additives, the interfacial bonding between the two phases was extremely poor, leading to a significant deterioration in electrochemical performance. The initial discharge capacity of the composite hard carbon material for sodium-ion batteries prepared in Comparative Example 2 was 287 mAh / g, the initial coulombic efficiency was 88.0%, and the capacity retention after 100 cycles was 83.5%. The results indicate that the lack of a dispersant resulted in poor initial dispersion uniformity, limiting the effectiveness of the compatibilizer. The initial discharge capacity of the composite hard carbon material for sodium-ion batteries prepared in Comparative Example 3 was 270 mAh / g, the initial coulombic efficiency was 86.5%, and the capacity retention after 100 cycles was 82.0%. The results indicate that the lack of a compatibilizer prevented strong interfacial bonding between the two phases, resulting in weak interparticle bonding. The hard carbon material for sodium-ion batteries prepared in Comparative Example 4 had an initial discharge capacity of 290 mAh / g, an initial coulombic efficiency of 82.3%, and a capacity retention of 85.0% after 100 cycles. The results indicate that the lack of modification of surface defects on biomass carbon by plastic-sourced carbon led to the low initial coulombic efficiency. The hard carbon material for sodium-ion batteries prepared in Comparative Example 5 had an initial discharge capacity of only 120 mAh / g. The results show that the lack of abundant pore structure provided by biomass resulted in a severe shortage of sodium storage active sites, failing to meet the capacity requirements of the anode material.

[0139] For the hard carbon materials prepared in Comparative Examples 6 to 14, in Comparative Example 6, due to the insufficient plastic content, its effect on filling pores and modifying defects was negligible, and the material performance would approach that of pure biomass carbon. Compared with Example 1, the initial coulombic efficiency was significantly reduced, and the cycle stability deteriorated, proving that too little plastic cannot effectively improve material performance. In Comparative Example 7, due to the excessive plastic content, its molten carbonization resulted in a dense structure, blocking the favorable pores formed by biomass, leading to a sharp drop in capacity. Although the initial efficiency was acceptable, the reversible capacity was severely degraded, only 150 mAh / g, which could not meet the requirements of the anode material, proving that an excessive plastic ratio would sacrifice the core capacity advantage of the material. In Comparative Example 8, insufficient compatibilizer led to poor interfacial bonding; excessive dispersant introduced too many impurities, diluted the active ingredients, and damaged performance. All performance indicators of the composite hard carbon material prepared in Comparative Example 8 were significantly lower than those of Example 1, proving that the compatibilizer and dispersant need to work synergistically within the preferred range, and deviation from any parameter will lead to performance deterioration, especially since excessive dispersant did indeed reduce capacity and efficiency as expected. In Comparative Example 9, excessive pyrolysis caused premature carbonization of the biomass, damaging its pore structure and increasing energy consumption. Although the efficiency was acceptable, the capacity was significantly lower than in Example 1, demonstrating that excessively high pyrolysis temperatures impair the material's ability to form high-capacity structures. Furthermore, this process consumed more energy and was less economical. In Comparative Example 10, excessively high carbonization temperatures led to graphitization of the carbon layers, reducing interlayer spacing and hindering sodium ion insertion / extraction, resulting in a sharp decrease in capacity and enormous energy consumption. In Comparative Example 11, the dispersant ensured initial uniform dispersion, but due to insufficient compatibilizer, a strong interfacial bond could not be formed between the uniformly dispersed two-phase particles. During subsequent heat treatment, separation at the interface was common, leading to defects. The hard carbon material prepared in Comparative Example 11 exhibited significantly better performance than the material in Comparative Example 1 without any additives, demonstrating the positive role of the dispersant in achieving initial uniform dispersion. However, the performance of the hard carbon material prepared in Comparative Example 11 was significantly worse than that in Example 1, especially in terms of poor cycling stability. This directly reflects that insufficient compatibilizer leads to weak interfacial bonding, resulting in gradual structural deterioration during long-term cycling. In Comparative Example 12, the dispersant functioned normally, but excessive compatibilizer itself agglomerated, becoming a new source of impurities, and introduced too much disordered structure after carbonization, increasing side reactions. The capacity of the hard carbon material prepared in Comparative Example 12 was slightly improved compared to Comparative Example 11, because the excessive compatibilizer may have enhanced interfacial coverage to some extent. However, the initial coulombic efficiency failed to improve further, and was even slightly lower than that of Example 1. This is consistent with the conclusion that excessive compatibilizer introduces impurities and increases side reactions, while also significantly increasing costs. In Comparative Example 13, the compatibilizer was sufficient, but insufficient dispersant caused the raw material powder to agglomerate in the slurry, forming localized biomass-rich and plastic-rich areas. The compatibilizer could not effectively function between macroscopic agglomerates, resulting in poor microscopic dispersion.The hard carbon material prepared in Comparative Example 13 outperformed that of Comparative Example 2 (which only added a compatibilizer), but was far inferior to that of Example 1. This indicates that even with sufficient compatibilizer, its effectiveness is greatly reduced if the initial dispersion is uneven, and the low cycle retention rate particularly illustrates the stability problems caused by structural inhomogeneity. In Comparative Example 14, the dispersion effect may have been good due to the sufficient amount of dispersant, but the excessive dispersant, acting as an impurity precursor, left residual ash or damaged the carbon layer structure after carbonization, diluted the active material, and impaired conductivity. The capacity of the hard carbon material prepared in Comparative Example 14 was lower than that of Example 1, and its initial coulombic efficiency was the lowest (85.0%) among all the comparative groups involving additives, demonstrating that the excessive dispersant introduced impurities, leading to serious side reactions and poor cycle performance.

[0140] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

[0141] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A composite hard carbon material for sodium-ion batteries, characterized in that, The composite hard carbon material is made by using pre-treated powder of agricultural waste and recycled plastic as a matrix, mixing the matrix with compatibilizer and dispersant and granulating to obtain composite precursor particles; then pyrolyzing and carbonizing under a protective atmosphere; the mass ratio of agricultural waste to recycled plastic is 1:1 / 19 to 19. The pre-treatment powder of agricultural waste and recycled plastics is obtained by alkaline washing and acid washing of a mixture of agricultural waste and recycled plastics powder.

2. The composite hard carbon material for sodium-ion batteries according to claim 1, characterized in that, Based on the mass of the mixed powder of agricultural waste and recycled plastics, the compatibilizer accounts for 1 wt% to 3 wt% of the mass, and the dispersant accounts for 0.2 wt% to 1.5 wt% of the mass.

3. The composite hard carbon material for sodium-ion batteries according to claim 1, characterized in that, The agricultural waste is at least one of coconut shell, rice husk, sugarcane bagasse, cotton stalk, wheat stalk, bamboo powder, and walnut shell; the recycled plastic is at least one of polyethylene terephthalate, polypropylene, polyethylene, polyvinyl chloride, polystyrene, and acrylonitrile-butadiene-styrene copolymer; the compatibilizer is maleic anhydride-grafted polyolefin and / or ethylene-acrylic acid copolymer; and the dispersant is one or more of sodium polyacrylate, sodium dodecylbenzenesulfonate, and polyvinylpyrrolidone.

4. A method for preparing a composite hard carbon material for sodium-ion batteries according to any one of claims 1 to 3, characterized in that, Includes the following steps: The mixed powder of agricultural waste and recycled plastic is subjected to alkaline washing and acid washing to remove organic impurities from the mixed powder, dissolve some of the silicates and lignin in the agricultural waste, neutralize the residual alkali solution and dissolve the metal oxides of the agricultural waste, and obtain pretreated powder of agricultural waste and recycled plastic. Using pretreated powders of agricultural waste and recycled plastics as a matrix, compatibilizers and dispersants are added, and the mixture is granulated to obtain composite precursor particles; Under a protective atmosphere, the composite precursor particles are subjected to programmed temperature pyrolysis to pre-crosslink the recycled plastics in the composite precursor and perform biomass pyrolysis, followed by carbonization to obtain a composite hard carbon material for sodium-ion batteries.

5. The method for preparing the composite hard carbon material for sodium-ion batteries according to claim 4, characterized in that, The alkaline washing is performed by using an inorganic alkali to wash the mixed powder of agricultural waste and recycled plastic at 50℃ to 80℃ for 2 to 4 hours to obtain alkaline washed powder; the acid washing is performed by using an inorganic acid to wash the alkaline washed powder at 50℃ to 80℃ for 2 to 4 hours.

6. The method for preparing the composite hard carbon material for sodium-ion batteries according to claim 5, characterized in that, The inorganic base is a sodium hydroxide solution with a concentration of 2 mol / L to 3 mol / L, and the inorganic acid is sulfuric acid with a concentration of 2 mol / L to 3 mol / L.

7. The method for preparing the composite hard carbon material for sodium-ion batteries according to claim 4, characterized in that, The programmed temperature-increasing pyrolysis is as follows: the composite precursor particles are heated to 200℃~400℃ at a rate of 2℃ / min~5℃ / min and pyrolyzed for 2h to obtain a pyrolytic precursor; the carbonization is as follows: the pyrolytic precursor is heated to 900℃~1400℃ at a rate of 5℃ / min~8℃ / min and carbonized for 4h to obtain a composite hard carbon material for sodium-ion batteries.

8. The method for preparing composite hard carbon material for sodium-ion batteries according to claim 4, characterized in that, The agricultural waste has an ash content of ≤10% and a cellulose content of ≥30%.

9. The application of the composite hard carbon material for sodium-ion batteries as described in any one of claims 1 to 3 as a negative electrode material in sodium-ion batteries.

Images