Hard carbon negative electrode material synthesized by rhizopus through Maillard reaction and preparation method and application of hard carbon negative electrode material

Abstract

The invention belongs to the technical field of sodium ion batteries, and relates to a hard carbon negative electrode material synthesized by rhizopus through a Maillard reaction, and a preparation method and application thereof. The material is prepared by taking a rhizopus hypha and glucose co-hydrothermal product as a carbon source, carrying out Maillard reaction on the rhizopus hypha and glucose co-hydrothermal reaction, and carrying out high-temperature carbonization on the product, thereby obtaining the hard carbon negative electrode material. The hard carbon negative electrode material prepared by the invention shows high specific capacity, good cycling stability and excellent rate capability and coulombic efficiency. Meanwhile, the preparation method provided by the invention is simple, rapid, efficient and convenient, mild in condition and easy to control, can effectively introduce sodium storage gain impurity elements into the hard carbon material, and is helpful for promoting the development of the hard carbon negative electrode material of the sodium-ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of hard carbon negative electrode materials for sodium ion batteries, and in particular to a method and material for synthesizing hard carbon negative electrode materials using Rhizopus by utilizing the Maillard reaction, and application of the hard carbon negative electrode materials in sodium ion batteries. Background Art

[0002] With the rapid development of science and technology in contemporary society, the demand for electrochemical energy storage devices represented by lithium-ion batteries is increasing. However, the scarcity of lithium resources on the earth has led to large price fluctuations, while sodium is the fourth most abundant element in the earth's crust, with a wide distribution range and is not restricted by resources and regions. At the same time, sodium-ion batteries have better safety performance and a service life comparable to that of lithium-ion batteries, so their application prospects are very broad. Positive and negative electrode materials are the core of the work of sodium-ion batteries. The two are not only the key to improving the performance of sodium-ion batteries, but also the main way to solve the cost bottleneck problem of sodium-ion batteries. Common negative electrode materials for sodium-ion batteries are alloy, conversion and embedded materials. Compared with alloy and conversion materials, embedded materials have Na during the charge and discharge process. + The lattice volume expansion rate during insertion and extraction is small, demonstrating good structural integrity and cycling stability, as well as higher initial Coulombic efficiency and higher rate performance. As a representative of intercalation materials, carbon-based materials are considered the most promising anode materials for sodium-ion batteries due to their abundant resources and environmental friendliness.

[0003] Carbon-based materials are divided into four categories based on the stacking method of carbon atoms: graphite, graphene, soft carbon, and hard carbon. Hard carbon negative electrode materials have low sodium storage potential, high specific capacity, high theoretical reversible capacity, and are rich in resources, widely available, and low in cost. They are the focus of research on negative electrode materials for sodium-ion batteries. Researchers have developed a series of hard carbon negative electrode materials based on carbon-containing raw materials such as asphalt-based, biomass-based, and resin-based. Biomass genes have attracted much attention due to their unique advantages. For example, the raw material sources are abundant, easier to obtain, the carbon yield is high, it is environmentally friendly, and contains multiple elements. It is expected to become an ideal precursor for negative electrode materials for sodium-ion batteries.

[0004] However, hard carbon anodes still face numerous challenges, such as low first coulombic efficiency (ICE), poor rate performance, and low specific capacity. Therefore, it is crucial to develop modification strategies to optimize the ICE, cycle performance, and rate performance of hard carbon anodes. To address these challenges, scientists have proposed numerous strategies. Among them, heteroatom doping with nitrogen, phosphorus, or sulfur (N, P, and S) is an important and effective approach. Hard carbon is synthesized by pyrolyzing a pretreated precursor under an inert atmosphere. During this process, inappropriate heating rates and carbonization temperatures can lead to poor carbon layer development or excessively small interlayer spacing. Furthermore, the release of small precursor molecules during pyrolysis, coupled with a series of crosslinking reactions, results in abundant pores and defects in the hard carbon. However, the small interlayer spacing in hard carbon hinders the intercalation and deintercalation of sodium ions, resulting in poor rate performance and low specific capacity. Heteroatom doping is an effective method for controlling defects and interlayer spacing. Heteroatom doping increases the interlayer spacing of hard carbon, allowing heteroatoms to act as defects within the carbon layers, improving its conductivity and ultimately enhancing its rate performance and specific capacity. Surface engineering offers a promising approach for protecting the anode by creating an artificial interface, effectively reducing the occurrence of side reactions. Furthermore, studies have shown that coatings can effectively increase the sodium ion diffusion coefficient because they provide three-dimensional diffusion rather than two-dimensional diffusion in the anode. Based on this, the present invention proposes a surface engineering method in which a carbon coating with a thickness of approximately 37 nm is synthesized on the surface of spherical hard carbon by hydrothermally forming a composite precursor using Rhizopus and glucose. Summary of the Invention

[0005] The purpose of the present invention is to address a series of problems existing in the first coulombic efficiency, specific capacity and rate performance of hard carbon negative electrode materials in sodium ion battery systems, and provide a method for synthesizing hard carbon negative electrode material precursors by the Maillard reaction of Rhizopus. By regulating parameters such as hydrothermal reaction time, reaction temperature, carbonization process, Rhizopus mycelium mass ratio, and glucose mass ratio, high-performance hard carbon negative electrode materials can be effectively prepared. First, the natural nitrogen source in Rhizopus mycelium is used to achieve self-doping, which can reduce costs. Secondly, mycelium, glucose and water are hydrothermally treated in a certain proportion, and the Maillard reaction is carried out by Rhizopus mycelium and glucose. The pore structure and interlayer spacing of the hard carbon are regulated by co-hydrothermal carbonization, thereby improving the sodium ion diffusion kinetics. At the same time, a carbon coating with consistent morphology can be obtained on the hard carbon surface. The prepared and treated sodium ion battery hard carbon negative electrode material has high specific capacity, good cycle stability, excellent rate performance and coulombic efficiency, which can effectively promote the commercialization process of hard carbon negative electrode materials.

[0006] The technical solution adopted by the present invention to solve its technical problem is: The first objective of the present invention is to provide a biomass hard carbon anode material, wherein the biomass precursor of the biomass hard carbon anode material is Rhizopus mycelium. By adopting the technical solution, the Rhizopus mycelium can fix the surrounding free nitrogen through nitrogen fixation, thereby achieving uniform and stable doping of elements such as nitrogen, phosphorus, and sulfur. The result is a biomass hard carbon anode material that is uniformly doped with nitrogen, phosphorus, sulfur, and other elements, has good morphological uniformity, and has high initial efficiency.

[0007] A second object of the present invention is to provide a method for preparing the aforementioned biomass hard carbon anode material, comprising hydrothermally reacting Rhizopus mycelium with glucose to produce a Maillard reaction. This method regulates the pore structure and interlayer spacing of the hard carbon, thereby improving the sodium ion diffusion kinetics. By regulating parameters such as the hydrothermal reaction time, reaction temperature, carbonization process, Rhizopus mycelium mass ratio, and glucose mass ratio, a high-performance hard carbon anode material can be effectively prepared. This ensures that the anode material exhibits excellent electrochemical performance in sodium-ion batteries.

[0008] Specifically, a preparation method for synthesizing a hard carbon negative electrode material using Rhizopus using the Maillard reaction, the method is to use Rhizopus mycelium and glucose as raw materials, add pure water and mix and stir to perform a co-hydrothermal reaction treatment, and then high-temperature carbonization to form hard carbon, specifically comprising the following steps: (1) washing, drying, and crushing the Rhizopus mycelium to obtain Rhizopus mycelium powder; (2) Rhizopus mycelium, glucose and water are mixed and stirred uniformly according to the mass ratio, added into a polytetrafluoroethylene hydrothermal liner, and subjected to hydrothermal reaction at a certain temperature for a certain time, and the product after the hydrothermal reaction is washed and dried to obtain a hard carbon precursor; (3) The dried hard carbon precursor is subjected to high-temperature carbonization treatment to obtain a biomass hard carbon negative electrode material.

[0009] By adopting the above technical solution, In the present invention, various elements in the culture medium of Rhizopus mycelium can be fixed, so that the contents of nitrogen, phosphorus, sulfur and the like in the Rhizopus mycelium are increased and evenly distributed; In the present invention, the co-hydrothermal process can introduce more oxygen-containing functional groups while fixing the carbon skeleton, that is, while maintaining a good surface morphology, it can also provide more Na due to more oxygen-containing functional groups. + Adsorption sites can significantly improve the specific capacity of hard carbon materials; The present invention uses biomass precursors to prepare biomass hard carbon materials, which can achieve uniform doping with nitrogen, phosphorus and sulfur elements, and further improve the electrochemical properties of the material by regulating the preparation process conditions, and has broad market application prospects. At the same time, the preparation method of the present invention is simple and suitable for industrial large-scale production.

[0010] The following is a more preferred technical solution of the present invention: Preferably, in step (1), the Rhizopus hyphae are obtained by culturing Rhizopus species. More preferably, the culturing specifically comprises: first, mixing 10 g of peptone, 10 g of glucose, and 1000 ml of water, sterilizing the mixture at high temperature, and then adding the Rhizopus species to the culture medium, and culturing the mixture on a shaking platform at room temperature of 25°C. The present invention uses the hydrothermal product of Rhizopus and glucose as a matrix, which has the advantages of low cost and a wide source of raw materials.

[0011] Preferably, in step (1), the washing and drying steps are performed by washing with deionized water for more than three times and then freeze-drying to remove moisture. More preferably, the freeze-drying time is 24 hours, and the product is crushed into powder. More preferably, the freeze-drying temperature is -50°C.

[0012] More preferably, in step (1), the crushed product is further sieved, and the sieve preferably has a mesh size of 300-800 mesh, more preferably 300 mesh.

[0013] Preferably, in step (2), in the raw materials, based on the total mass of Rhizopus mycelia, glucose and water as 100%, the mass of Rhizopus mycelia accounts for 10-25%, the mass of glucose accounts for 10-25%, and the mass of water accounts for 50-80%; more preferably, the mass ratio of the Rhizopus mycelia to glucose is 1:1.

[0014] Preferably, in step (2), the temperature condition of the co-hydrothermal treatment is preferably 180-220°C, more preferably 200°C; and / or, in step (2), the time condition of the co-hydrothermal treatment is preferably 8-15 h, more preferably 10-12 h.

[0015] Preferably, in step (2), the product is filtered and washed with deionized water for 3-5 times, the drying temperature is 50-100° C., and the drying time is 1-12 h.

[0016] Preferably, in step (3), the dried product is ground once for pulverization, placed in a porcelain boat, and placed in a tube furnace for high-temperature carbonization reaction.

[0017] Preferably, in step (3), the high-temperature carbonization is carried out under an inert atmosphere, and the inert atmosphere is at least one of nitrogen, helium, and argon.

[0018] Preferably, in step (3), the high-temperature carbonization includes two carbonization processes, the first carbonization process has a calcination temperature heating rate of 2-5 ° C / min, a calcination temperature of 700-900 ° C, and a calcination temperature holding time of 1-3 h; more preferably, the heating rate is 5 ° C / min, the calcination temperature is 800 ° C, and the calcination temperature holding time is 2 h; this carbonization process can promote the full decomposition and cross-linking of the precursor; the second carbonization process has a calcination temperature heating rate of 2-5 ° C / min, a calcination temperature of 1000-1300 ° C, and a calcination temperature holding time of 1-3 h; more preferably, the heating rate is 5 ° C / min, the calcination temperature is 1200 ° C, and the calcination temperature holding time is 2 h; this carbonization process can optimize the formation and ordering of the carbon structure.

[0019] Preferably, in step (3), after high-temperature carbonization, the product is annealed to 300°C at a cooling rate of 2-10°C / min, and then naturally cooled to room temperature.

[0020] Preferably, in step (3), the high-temperature carbonization product is further ground and sieved, and the mesh size of the sieve is preferably 300-800 mesh, more preferably 300 mesh.

[0021] The present invention provides a biomass hard carbon anode material, the biomass precursor of which is a hydrothermal complex of Rhizopus mycelium and glucose. By employing this technical solution, the composite precursor is formed by co-hydrothermal treatment of Rhizopus and glucose, resulting in a carbon coating with uniform thickness (e.g., 37 nm) and consistent morphology on the surface of spherical hard carbon. Furthermore, the Rhizopus mycelium can fix the surrounding free nitrogen through nitrogen fixation, thereby achieving uniform and stable doping with elements such as nitrogen and phosphorus. This results in a biomass hard carbon anode material with uniform nitrogen and phosphorus doping, good morphological uniformity, and high initial efficiency. To date, there have been no reports in the field of using Rhizopus mycelium in the preparation of hard carbon anode materials for sodium-ion batteries. In this invention, by successfully optimizing the biomass raw material of Rhizopus mycelium through co-hydrothermal treatment with glucose, a hard carbon anode material with a stable structure and excellent performance was synthesized at low temperatures (below 220°C). Mycelium, glucose, and water are co-hydrothermally treated in a certain proportion. The Maillard reaction between Rhizopus mycelium and glucose is then generated. Through co-hydrothermal carbonization, the pore structure and interlayer spacing of the hard carbon are regulated, improving the sodium ion diffusion kinetics. This results in a hard carbon anode material for sodium-ion batteries with high specific capacity, good cycle stability, and excellent rate performance and coulombic efficiency. Therefore, the hard carbon anode material prepared by the co-hydrothermal method of Rhizopus mycelium and glucose exhibits higher capacity, superior rate performance, and coulombic efficiency, providing new commercial application possibilities for sodium-ion batteries.

[0022] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention forms a porous network structure by the Maillard reaction between Rhizopus hyphae and glucose, while the traditional method relies on the structure of the substance itself. Therefore, the present invention can achieve the regulation and optimization of structural properties such as interlayer spacing and pore structure; (2) The present invention uses the Maillard reaction between Rhizopus mycelium and glucose to react at a relatively low temperature to obtain a hard carbon precursor and synthesize a carbon coating on the hard carbon surface; (3) The present invention uses Rhizopus mycelium and glucose as biomass carbon sources, which can effectively achieve uniform and effective doping of heteroatoms such as nitrogen, phosphorus, and sulfur; The hard carbon negative electrode material described in the present invention is prepared by the hydrothermal reaction of Rhizopus mycelium and glucose. After the hydrothermal treatment with glucose, a hydrothermal composite precursor is formed, which successfully regulates the pore structure and interlayer spacing of the hard carbon, and improves the diffusion kinetics of sodium ions. It is beneficial to improve the degree of graphitization of hard carbon and increase the sodium storage sites of the material, and reduce the side reactions occurring when the surface of the hard carbon material contacts the electrolyte. Therefore, the hard carbon negative electrode material exhibits good cycle stability, rate performance and coulombic efficiency. The preparation method of the hard carbon negative electrode material described in the present invention is simple, fast, efficient and convenient, the conditions are mild, and it is easy to control. It can effectively introduce sodium storage gain impurities into the hard carbon material, which is helpful to promote the commercial development of hard carbon negative electrodes for sodium ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a scanning electron microscope (SEM) image of the hard carbon negative electrode material of Example 1; Figure 2 This is a scanning electron microscope (SEM) image of the hard carbon negative electrode material of Comparative Example 1; Figure 3 This is the EDS element distribution diagram of the hard carbon negative electrode material prepared by hydrothermal Maillard reaction of Rhizopus mycelium and glucose in Example 1; Figure 4 Comparison of the cycling performance of the materials of Example 1 and Comparative Example 1 at a current density of 50 mA / g; Figure 5 These are transmission electron microscope (TEM) images of the hard carbon negative electrode materials of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0024] For ease of understanding, the technical solutions and implementation methods of the present invention are further described clearly, completely and in detail through specific examples and in combination with the accompanying drawings. It should be noted that the embodiments described in the present invention are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are given, but they are only part of the embodiments of the present invention, not all of the embodiments. The specific implementation methods described are limited to illustrating and explaining the present invention and do not limit the present invention. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0025] The experimental methods and conditions used in the following examples are conventional methods and conventional conditions unless otherwise specified. The materials, reagents, instruments, devices, etc. used in the examples are conventional substances or equipment known to those skilled in the art and can be obtained from commercial channels unless otherwise specified. The reaction conditions embodied in the summary of the invention are all capable of achieving the described reactions and obtaining products with the desired effects. Due to space limitations, only some examples are listed below to further illustrate the advantages of the technical solutions of the present invention.

[0026] In the present invention, the mycelium of Rhizopus is obtained by culturing Rhizopus species. Specifically, 10g of peptone, 10g of glucose, and 1000ml of water are mixed and sterilized at high temperature to form a culture medium. The Rhizopus species are then added to the culture medium and cultured on a shaking table at room temperature of 25°C. After about seven days, the Rhizopus species grow into spheres.

[0027] Example 1

[0028] A biomass hard carbon negative electrode material and its specific preparation steps are as follows: (1) The cultured Rhizopus mycelium (applicable to the following examples) was washed three times with deionized water, freeze-dried for 24 hours, crushed into powder, and sieved through a 300-800 mesh sieve to obtain a powdered mycelium precursor for later use, preferably sieved through a 300 mesh sieve; (2) Mix Rhizopus mycelium, glucose and water in a mass ratio of 1:1:4 and stir evenly; (3) Add the stirred product to a polytetrafluoroethylene liner and perform hydrothermal treatment at 200°C for 12 h. Filter, wash, and dry the product after hydrothermal treatment. Preferably, wash with deionized water 3-5 times, dry at 50-100°C, and dry for 1-12 h.

[0029] (4) The dried product was ground once, placed in a porcelain boat, and placed in a tube furnace. Under argon atmosphere, the temperature was raised to 800°C at a rate of 5°C / min and calcined at this temperature for 2 h. The temperature was then raised to 1200°C at a rate of 5°C / min and calcined at this temperature for 2 h. After that, the product was cooled to 300°C at a rate of 10°C / min and then naturally cooled to room temperature. After grinding, the product was sieved with a 300-mesh sieve to obtain a hard carbon material.

[0030] Example 2

[0031] A biomass hard carbon negative electrode material and its specific preparation steps are as follows: (1) Wash the Rhizopus mycelium with deionized water three times, freeze-dry it for 24 h, grind it into powder, and sieve it to obtain a powdered mycelium precursor for later use; (2) Mix Rhizopus mycelium, glucose and water in a mass ratio of 1.5:1:4 and stir evenly; (3) The stirred product was added to a polytetrafluoroethylene liner and hydrothermally treated at 200 °C for 12 h. The hydrothermally treated product was filtered, washed, and dried.

[0032] (4) The dried product was ground once, placed in a porcelain boat, and placed in a tube furnace. Under argon atmosphere, the temperature was raised to 800°C at a rate of 5°C / min and calcined at this temperature for 2 h. The temperature was then raised to 1200°C at a rate of 5°C / min and calcined at this temperature for 2 h. After that, the product was cooled to 300°C at a rate of 10°C / min and then naturally cooled to room temperature. After grinding, the product was sieved with a 300-mesh sieve to obtain a hard carbon material.

[0033] Example 3

[0034] A biomass hard carbon negative electrode material and its specific preparation steps are as follows: (1) Wash the Rhizopus mycelium with deionized water three times, freeze-dry it for 24 h, grind it into powder, and sieve it to obtain a powdered mycelium precursor for later use; (2) Mix Rhizopus mycelium, glucose and water in a mass ratio of 1:1.5:4 and stir evenly; (3) Add the stirred product into a polytetrafluoroethylene liner and perform hydrothermal treatment at 180 °C for 12 h. Filter, wash, and dry the product after hydrothermal treatment.

[0035] (4) The dried product was ground once, placed in a porcelain boat, and placed in a tube furnace. Under argon atmosphere, the temperature was raised to 800°C at a rate of 5°C / min and calcined at this temperature for 2 h. The temperature was then raised to 1200°C at a rate of 5°C / min and calcined at this temperature for 2 h. After that, the product was cooled to 300°C at a rate of 10°C / min and then naturally cooled to room temperature. After grinding, the product was sieved with a 300-mesh sieve to obtain a hard carbon material.

[0036] Example 4

[0037] A biomass hard carbon negative electrode material and its specific preparation steps are as follows: (1) Wash the Rhizopus mycelium with deionized water three times, freeze-dry it for 24 h, grind it into powder, and sieve it to obtain a powdered mycelium precursor for later use; (2) Mix Rhizopus mycelium, glucose and water in a mass ratio of 1:2:4 and stir evenly; (3) Add the stirred product into a polytetrafluoroethylene liner and perform hydrothermal treatment at 180 °C for 12 h. Filter, wash, and dry the product after hydrothermal treatment.

[0038] (4) The dried product was ground once, placed in a porcelain boat, and placed in a tube furnace. Under argon atmosphere, the temperature was raised to 800°C at a rate of 5°C / min and calcined at this temperature for 2 h. The temperature was then raised to 1200°C at a rate of 5°C / min and calcined at this temperature for 2 h. After that, the product was cooled to 300°C at a rate of 10°C / min and then naturally cooled to room temperature. After grinding, the product was sieved with a 300-mesh sieve to obtain a hard carbon material.

[0039] Example 5

[0040] A biomass hard carbon negative electrode material and its specific preparation steps are as follows: (1) Wash the Rhizopus mycelium with deionized water three times, freeze-dry it for 24 h, grind it into powder, and sieve it to obtain a powdered mycelium precursor for later use; (2) Mix Rhizopus mycelium, glucose and water in a mass ratio of 1:2:4 and stir evenly; (3) The stirred product was added to a polytetrafluoroethylene liner and hydrothermally treated at 200 °C for 12 h. The hydrothermally treated product was filtered, washed, and dried.

[0041] (4) The dried product was ground once, placed in a porcelain boat, and placed in a tube furnace. Under argon atmosphere, the temperature was raised to 800°C at a rate of 5°C / min and calcined at this temperature for 2 h. The temperature was then raised to 1000°C at a rate of 5°C / min and calcined at this temperature for 2 h. After that, the product was cooled to 300°C at a rate of 10°C / min and then naturally cooled to room temperature. After grinding, the product was sieved with a 300-mesh sieve to obtain a hard carbon material.

[0042] Example 6

[0043] A biomass hard carbon negative electrode material and its specific preparation steps are as follows: (1) Wash the Rhizopus mycelium with deionized water three times, freeze-dry it for 24 h, grind it into powder, and sieve it to obtain a powdered mycelium precursor for later use; (2) Mix Rhizopus mycelium, glucose and water in a mass ratio of 1:1:4 and stir evenly; (3) The stirred product was added to a polytetrafluoroethylene liner and hydrothermally treated at 200 °C for 12 h. The hydrothermally treated product was filtered, washed, and dried.

[0044] (4) The dried product was ground once, placed in a porcelain boat, and placed in a tube furnace. Under argon atmosphere, the temperature was raised to 800°C at a rate of 2°C / min and calcined at this temperature for 2 h. The temperature was then raised to 1200°C at a rate of 2°C / min and calcined at this temperature for 2 h. After that, the product was cooled to 300°C at a rate of 10°C / min and then naturally cooled to room temperature. After grinding, the product was sieved with a 300-mesh sieve to obtain a hard carbon material.

[0045] Example 7

[0046] A biomass hard carbon negative electrode material and its specific preparation steps are as follows: (1) Wash the Rhizopus mycelium with deionized water three times, freeze-dry it for 24 h, grind it into powder, and sieve it to obtain a powdered mycelium precursor for later use; (2) Mix Rhizopus mycelium, glucose and water in a mass ratio of 1:1:4 and stir evenly; (3) The stirred product was added to a polytetrafluoroethylene liner and hydrothermally treated at 200 °C for 12 h. The hydrothermally treated product was filtered, washed, and dried.

[0047] (4) The dried product was ground once, placed in a porcelain boat, and placed in a tube furnace. Under argon atmosphere, the temperature was raised to 800°C at a rate of 10°C / min and calcined at this temperature for 2 h. The temperature was then raised to 1200°C at a rate of 10°C / min and calcined at this temperature for 2 h. After that, the temperature was cooled to 300°C at a rate of 10°C / min and then naturally cooled to room temperature. After grinding, the product was sieved with a 300-mesh sieve to obtain a hard carbon material.

[0048] Example 8

[0049] A biomass hard carbon negative electrode material and its specific preparation steps are as follows: (1) Wash the Rhizopus mycelium with deionized water three times, freeze-dry it for 24 h, grind it into powder, and sieve it to obtain a powdered mycelium precursor for later use; (2) Mix Rhizopus mycelium, glucose and water in a mass ratio of 1:1:4 and stir evenly; (3) The stirred product was added to a polytetrafluoroethylene liner and hydrothermally treated at 200 °C for 16 h. The hydrothermally treated product was filtered, washed, and dried.

[0050] (4) The dried product was ground once, placed in a porcelain boat, and placed in a tube furnace. Under argon atmosphere, the temperature was raised to 800°C at a rate of 5°C / min and calcined at this temperature for 2 h. The temperature was then raised to 1200°C at a rate of 5°C / min and calcined at this temperature for 2 h. After that, the product was cooled to 300°C at a rate of 10°C / min and then naturally cooled to room temperature. After grinding, the product was sieved with a 300-mesh sieve to obtain a hard carbon material.

[0051] Example 9

[0052] A biomass hard carbon negative electrode material and its specific preparation steps are as follows: (1) Wash the Rhizopus mycelium with deionized water three times, freeze-dry it for 24 h, grind it into powder, and sieve it to obtain a powdered mycelium precursor for later use; (2) Mix Rhizopus mycelium, glucose and water in a mass ratio of 1:1:4 and stir evenly; (3) Add the stirred product into a polytetrafluoroethylene liner and perform hydrothermal treatment at 200 °C for 4 h. Filter, wash, and dry the product after hydrothermal treatment.

[0053] (4) The dried product was ground once, placed in a porcelain boat, and placed in a tube furnace. Under argon atmosphere, the temperature was raised to 800°C at a rate of 5°C / min and calcined at this temperature for 2 h. The temperature was then raised to 1200°C at a rate of 5°C / min and calcined at this temperature for 2 h. After that, the product was cooled to 300°C at a rate of 10°C / min and then naturally cooled to room temperature. After grinding, the product was sieved with a 300-mesh sieve to obtain a hard carbon material.

[0054] Example 10

[0055] A biomass hard carbon negative electrode material and its specific preparation steps are as follows: (1) Wash the Rhizopus mycelium with deionized water three times, freeze-dry it for 24 h, grind it into powder, and sieve it to obtain a powdered mycelium precursor for later use; (2) Mix Rhizopus mycelium, glucose and water in a mass ratio of 1:1:4 and stir evenly; (3) The stirred product was added to a polytetrafluoroethylene liner and hydrothermally treated at 200 °C for 12 h. The hydrothermally treated product was filtered, washed, and dried.

[0056] (4) The dried product was ground once, placed in a porcelain boat, and placed in a tube furnace. Under argon atmosphere, the temperature was raised to 800°C at a rate of 5°C / min and calcined at this temperature for 4 h. The temperature was then raised to 1200°C at a rate of 5°C / min and calcined at this temperature for 4 h. After that, the product was cooled to 300°C at a rate of 10°C / min and then naturally cooled to room temperature. After grinding, the product was sieved with a 300-mesh sieve to obtain a hard carbon material.

[0057] Comparative Example 1

[0058] A biomass hard carbon negative electrode material and its specific preparation steps are as follows: (1) Wash the Rhizopus mycelium with deionized water three times, freeze-dry it for 24 h, grind it into powder, and sieve it to obtain a powdered mycelium precursor for later use; (2) The dried product was ground once, placed in a porcelain boat, and placed in a tube furnace. Under argon atmosphere, the temperature was raised to 800°C at a rate of 5°C / min and calcined at this temperature for 2 h. The temperature was then raised to 1200°C at a rate of 5°C / min and calcined at this temperature for 2 h. After that, the product was cooled to 300°C at a rate of 10°C / min and then naturally cooled to room temperature. After grinding, the product was sieved with a 300-mesh sieve to obtain a hard carbon material.

[0059] Comparative Example 2

[0060] A biomass hard carbon negative electrode material and its specific preparation steps are as follows: (1) Wash the Rhizopus mycelium with deionized water three times, freeze-dry it for 24 h, grind it into powder, and sieve it to obtain a powdered mycelium precursor for later use; (2) The dried product was ground once, placed in a porcelain boat, and placed in a tube furnace. Under argon atmosphere, the temperature was raised to 1200°C at a rate of 5°C / min. After calcination at this constant temperature for 2 h, the product was cooled to 300°C at a rate of 10°C / min, and then naturally cooled to room temperature. After grinding, the product was sieved with a 300-mesh sieve to obtain a hard carbon material.

[0061] Comparative Example 3

[0062] A biomass hard carbon negative electrode material and its specific preparation steps are as follows: (1) Wash the Rhizopus mycelium with deionized water three times, freeze-dry it for 24 h, grind it into powder, and sieve it to obtain a powdered mycelium precursor for later use; (2) Mix Rhizopus mycelium, xylose and water in a mass ratio of 1:1:4 and stir evenly; (3) The stirred product was added to a polytetrafluoroethylene liner and subjected to hydrothermal treatment at 200 °C for 12 h. The hydrothermally treated product was filtered, washed, and dried.

[0063] (4) The dried product was ground once, placed in a porcelain boat, and placed in a tube furnace. Under argon atmosphere, the temperature was raised to 800°C at a rate of 5°C / min and calcined at this temperature for 2 h. The temperature was then raised to 1200°C at a rate of 5°C / min and calcined at this temperature for 2 h. After that, the product was cooled to 300°C at a rate of 10°C / min and then naturally cooled to room temperature. After grinding, the product was sieved with a 300-mesh sieve to obtain a hard carbon material.

[0064] Comparative Example 4

[0065] A biomass hard carbon negative electrode material and its specific preparation steps are as follows: (1) Wash the Rhizopus mycelium with deionized water three times, freeze-dry it for 24 h, grind it into powder, and sieve it to obtain a powdered mycelium precursor for later use; (2) Mix Rhizopus mycelium, chitosan and water in a mass ratio of 1:1:4 and stir evenly; (3) The stirred product was added to a polytetrafluoroethylene liner and subjected to hydrothermal treatment at 200 °C for 12 h. The hydrothermally treated product was filtered, washed, and dried.

[0066] (4) The dried product was ground once, placed in a porcelain boat, and placed in a tube furnace. Under argon atmosphere, the temperature was raised to 800°C at a rate of 5°C / min and calcined at this temperature for 2 h. The temperature was then raised to 1200°C at a rate of 5°C / min and calcined at this temperature for 2 h. After that, the product was cooled to 300°C at a rate of 10°C / min and then naturally cooled to room temperature. After grinding, the product was sieved with a 300-mesh sieve to obtain a hard carbon material.

[0067] Comparative Example 5

[0068] A biomass hard carbon negative electrode material and its specific preparation steps are as follows: (1) Wash the Rhizopus mycelium with deionized water three times, freeze-dry it for 24 h, grind it into powder, and sieve it to obtain a powdered mycelium precursor for later use; (2) Mix Rhizopus mycelium, sucrose and water in a mass ratio of 1:1:4 and stir evenly; (3) The stirred product was added to a polytetrafluoroethylene liner and hydrothermally treated at 180 °C for 12 h. The hydrothermally treated product was filtered, washed, and dried.

[0069] (4) The dried product was ground once, placed in a porcelain boat, and placed in a tube furnace. Under argon atmosphere, the temperature was raised to 500°C at a rate of 5°C / min and calcined at this temperature for 2 h. The temperature was then raised to 1200°C at a rate of 5°C / min and calcined at this temperature for 2 h. After that, the product was cooled to 300°C at a rate of 10°C / min and then naturally cooled to room temperature. After grinding, the product was sieved with a 300-mesh sieve to obtain a hard carbon material.

[0070] Comparative Example 6

[0071] A biomass hard carbon negative electrode material and its specific preparation steps are as follows: (1) Wash the Rhizopus mycelium with deionized water three times, freeze-dry it for 24 h, grind it into powder, and sieve it to obtain a powdered mycelium precursor for later use; (2) Mix Rhizopus mycelium, fructose and water in a mass ratio of 1:1:4 and stir evenly; (3) Add the stirred product into a polytetrafluoroethylene liner and perform hydrothermal treatment at 200 °C for 10 h. Filter, wash, and dry the product after hydrothermal treatment.

[0072] (4) The dried product was ground once, placed in a porcelain boat, and placed in a tube furnace. Under argon atmosphere, the temperature was raised to 800°C at a rate of 5°C / min and calcined at this temperature for 2 h. The temperature was then raised to 1200°C at a rate of 5°C / min and calcined at this temperature for 2 h. After that, the product was cooled to 300°C at a rate of 10°C / min and then naturally cooled to room temperature. After grinding, the product was sieved with a 300-mesh sieve to obtain a hard carbon material.

[0073] Comparative Example 7

[0074] A biomass hard carbon negative electrode material and its specific preparation steps are as follows: (1) Wash the Rhizopus mycelium with deionized water three times, freeze-dry it for 24 h, grind it into powder, and sieve it to obtain a powdered mycelium precursor for later use; (2) Mix Rhizopus mycelium, glucose and water in a mass ratio of 1:1:4 and stir evenly; (3) Add the stirred product into a polytetrafluoroethylene liner and perform hydrothermal treatment at 200 °C for 10 h. Filter, wash, and dry the product after hydrothermal treatment.

[0075] (4) The dried product was ground once, placed in a porcelain boat, and placed in a tube furnace. Under argon atmosphere, the temperature was raised to 500°C at a rate of 5°C / min and calcined at this temperature for 2 h. The temperature was then raised to 1200°C at a rate of 5°C / min and calcined at this temperature for 2 h. After that, the product was cooled to 300°C at a rate of 10°C / min and then naturally cooled to room temperature. After grinding, the product was sieved with a 300-mesh sieve to obtain a hard carbon material.

[0076] Comparative Example 8

[0077] A biomass hard carbon negative electrode material and its specific preparation steps are as follows: (1) Wash the Rhizopus mycelium with deionized water three times, freeze-dry it for 24 h, grind it into powder, and sieve it to obtain a powdered mycelium precursor for later use; (2) Mix Rhizopus mycelium, glucose and water in a mass ratio of 4:4:3 and stir evenly; (3) The stirred product was added to a polytetrafluoroethylene liner and hydrothermally treated at 200 °C for 10 h. The hydrothermally treated product was filtered, washed, and dried.

[0078] (4) The dried product was ground once, placed in a porcelain boat, and placed in a tube furnace. Under argon atmosphere, the temperature was raised to 800°C at a rate of 5°C / min and calcined at this temperature for 2 h. The temperature was then raised to 1200°C at a rate of 5°C / min and calcined at this temperature for 2 h. After that, the product was cooled to 300°C at a rate of 10°C / min and then naturally cooled to room temperature. After grinding, the product was sieved with a 300-mesh sieve to obtain a hard carbon material.

[0079] Comparative Example 9

[0080] A biomass hard carbon negative electrode material and its specific preparation steps are as follows: (1) Wash the Rhizopus mycelium with deionized water three times, freeze-dry it for 24 h, grind it into powder, and sieve it to obtain a powdered mycelium precursor for later use; (2) Mix Rhizopus mycelium, glucose and water in a mass ratio of 1:1:4 and stir evenly; (3) The stirred product was added to a polytetrafluoroethylene liner and hydrothermally treated at 200 °C for 12 h. The hydrothermally treated product was filtered, washed, and dried.

[0081] (4) The dried product was ground once, placed in a porcelain boat, and placed in a tube furnace. Under argon atmosphere, the temperature was raised to 800°C at a rate of 5°C / min and calcined at this temperature for 2 h. The temperature was then raised to 1400°C at a rate of 5°C / min and calcined at this temperature for 2 h. After that, the product was cooled to 300°C at a rate of 10°C / min and then naturally cooled to room temperature. After grinding, the product was sieved with a 300-mesh sieve to obtain a hard carbon material.

[0082] Comparative Example 10

[0083] A biomass hard carbon negative electrode material and its specific preparation steps are as follows: (1) Wash the Rhizopus mycelium with deionized water three times, freeze-dry it for 24 h, grind it into powder, and sieve it to obtain a powdered mycelium precursor for later use; (2) Mix Rhizopus mycelium, glucose and water in a mass ratio of 1:1:4 and stir evenly; (3) The stirred product was added to a polytetrafluoroethylene liner and hydrothermally treated at 200 °C for 12 h. The hydrothermally treated product was filtered, washed, and dried.

[0084] (4) The dried product was ground once, placed in a porcelain boat, and placed in a tube furnace. Under argon atmosphere, the temperature was raised to 500°C at a rate of 5°C / min and calcined at this temperature for 2 h. The temperature was then raised to 1400°C at a rate of 5°C / min and calcined at this temperature for 2 h. After that, the product was cooled to 300°C at a rate of 10°C / min and then naturally cooled to room temperature. After grinding, the product was sieved with a 300-mesh sieve to obtain a hard carbon material.

[0085] Performance Testing

[0086] The materials prepared in the above examples and comparative examples were assembled into button-type half-cells for electrochemical testing. The electrolyte was 1 mol / L NaPF6 in DME (100 vol %) (DME: ethylene glycol dimethyl ether), and the separator was Whatman GF / F glass fiber. The cells were assembled in the order of positive electrode shell, hard carbon negative electrode sheet, electrolyte, separator, sodium sheet, and negative electrode shell, and sealed using a packaging machine. The hard carbon negative electrode sheet was composed of the Rhizopus hard carbon negative electrode material prepared in each example, conductive carbon black, and sodium carboxymethyl cellulose in a mass ratio of 8:1:1. An appropriate amount of deionized water was added and stirred in a homogenizer for 30 minutes to form a slurry. The slurry was then evenly coated onto bright aluminum foil and vacuum-dried at 80°C for 12 hours. The electrode sheets were finally cut into circular electrodes with a diameter of 12 mm. The active material loading for each electrode was 0.9-1.5 mg. After the cells were allowed to rest for 24 hours, electrochemical testing was performed using a Xinwei testing system and a Chenhua electrochemical workstation. The electrochemical tests were performed at 30 o The constant current charge and discharge test was conducted at a constant temperature of 1000 °C, primarily for constant current charge and discharge testing. The constant current charge and discharge test primarily assesses reversible capacity, cycle life, and coulombic efficiency. The battery's long-term cycling performance was tested at a current density of 50 mA / g. The constant current charge and discharge test cycle consisted of 50 cycles of resting for 5 minutes, constant current discharge, resting for 5 minutes, and constant current charge.

[0087] The specific surface area and average pore size of the materials obtained in Examples 1-10 and Comparative Examples 1-10 were tested. The specific parameters are shown in Table 1:

[0088] The batteries obtained in Examples 1-10 and Comparative Examples 1-10 were tested for indicators such as the initial coulombic efficiency and the 50th cycle discharge capacity, further demonstrating that the sodium ion battery using the hard carbon negative electrode sheet of the present application maintained a relatively high charge and discharge capacity after cycling, as shown in Table 2.

[0089] Figure 1 and Figure 2 Transmission electron microscopy (SEM) images of the hard carbon negative electrode materials prepared in Example 1 and Comparative Example 1 show that the hard carbon material prepared by the Maillard reaction of Rhizopus mycelium and glucose exhibits fewer aggregates and a more complete tubular structure. The SEM images also demonstrate that the hard carbon material prepared by the Maillard reaction of Rhizopus mycelium and glucose exhibits a more stable structure and a more complete and abundant tubular structure, which facilitates sodium ion migration.

[0090] Figure 3It can be found from the EDS element distribution diagram of the hard carbon negative electrode material that the hard carbon negative electrode material after hydrothermal treatment with Rhizopus and glucose can detect the presence of phosphorus in the EDS test and the distribution is relatively uniform.

[0091] Figure 4 The cycle performance diagrams of the hard carbon negative electrode materials of Example 1 and Comparative Example 1 show that the hard carbon negative electrode material prepared by co-hydrothermal treatment of Rhizopus mycelium and glucose exhibits excellent cycle performance. At a current density of 50 mA / g, the initial charge capacity is 270.19 mAh / g, the first-cycle coulomb efficiency reaches 86.97%, and after 50 cycles, the capacity retention rate is 96.7%. The unmodified hard carbon material negative electrode material has a low discharge capacity and decays rapidly, with an initial charge capacity of only 220.99 mAh / g, a first-cycle coulomb efficiency of less than 70%, and a capacity of only 87.5% after 50 cycles. This shows that the hard carbon material prepared by co-hydrothermal treatment of Rhizopus mycelium and glucose can effectively improve the material's sodium storage reversible capacity and cycle stability.

[0092] Figure 5 TEM images of the hard carbon negative electrode materials of Example 1 and Comparative Example 1; Figure 5 The TEM image shows that a carbon layer of about 37 nm is generated on the surface of the hard carbon material prepared by the hydrothermal Maillard reaction of Rhizopus mycelium and glucose, which makes the hard carbon structure more stable and is conducive to the migration of sodium ions.

[0093] This application presents a sodium-ion battery hard carbon anode material prepared by hydrothermal synthesis of Rhizopus mycelium and glucose. This material has a higher number of sodium storage sites, resulting in lower impedance and excellent cycling and rate performance. This material holds great promise for applications in small mobile electronic devices, electric vehicles, solar power generation, and aerospace.

[0094] The above-described embodiments are only preferred solutions of the present invention and are not intended to limit the present invention in any form. Other variations and modifications are possible without exceeding the technical solutions described in the claims.

Claims

1. A method for preparing a hard carbon negative electrode material by using Rhizopus to synthesize a Maillard reaction, characterized in that: The preparation method is to carry out a co-hydrothermal reaction with Rhizopus mycelium and glucose as raw materials, and prepare the hard carbon negative electrode material through a high-temperature carbonization reaction of the reaction product; in the co-hydrothermal reaction, based on the total mass of Rhizopus mycelium, glucose and water as 100%, the mass of Rhizopus mycelium accounts for 10-25%, the mass of glucose accounts for 10-25%, and the mass of water accounts for 50-80%.

2. The method for preparing a hard carbon negative electrode material by using the Maillard reaction of Rhizopus according to claim 1, wherein: The Rhizopus mycelium is cleaned, dried and crushed.

3. The method for preparing a hard carbon negative electrode material by using the Maillard reaction of Rhizopus according to claim 1, wherein: The mass ratio of the Rhizopus mycelium to glucose is 1:

1.

4. The method for preparing a hard carbon negative electrode material by using the Maillard reaction of Rhizopus according to claim 1, wherein: In the co-hydrothermal reaction, the temperature is 180-220°C and the time is 8-15 hours; the high-temperature carbonization reaction includes two carbonization processes, the heating rate of the first carbonization process is 2-5°C / min, the calcination temperature is 700-900°C, and the holding time is 1-3 hours; the heating rate of the second carbonization process is 2-5°C / min, the calcination temperature is 1000-1300°C, and the holding time is 1-3 hours.

5. The method for preparing a hard carbon negative electrode material by using the Maillard reaction of Rhizopus according to claim 4, wherein: In the co-hydrothermal reaction, the temperature is 200°C and the time is 10-12 h; the heating rate of the first carbonization process is 5°C / min, the calcination temperature is 800°C, and the holding time is 2 h; the heating rate of the second carbonization process is 5°C / min, the calcination temperature is 1200°C, and the holding time is 2 h.

6. The method for preparing a hard carbon negative electrode material by using the Maillard reaction of Rhizopus according to claim 1, wherein: After the co-hydrothermal reaction, the product is washed, dried and crushed, and then subjected to a high-temperature carbonization reaction under an inert atmosphere.

7. The method for preparing a hard carbon negative electrode material by using the Maillard reaction of Rhizopus according to claim 1, wherein: After the high-temperature carbonization reaction, the sample was annealed to 300°C at a cooling rate of 2-10°C / min and then naturally cooled to room temperature.

8. The method for preparing a hard carbon negative electrode material by using the Maillard reaction of Rhizopus according to claim 1, wherein: The specific steps include: (1) washing, drying and crushing the Rhizopus mycelium to obtain Rhizopus mycelium powder; (2) Rhizopus mycelium powder, glucose and water are subjected to a co-hydrothermal reaction at 180-220 °C for 8-15 h, and the reaction product after the hydrothermal reaction is washed, dried and crushed at a drying temperature of 50-100 °C for 1-12 h; (3) The product is subjected to high-temperature carbonization treatment, firstly, the first stage of carbonization treatment is carried out at a heating rate of 2-5 °C / min, a calcination temperature of 700-900 °C, and a holding time of 1-3 h, and then the second stage of carbonization treatment is carried out at a heating rate of 2-5 °C / min, a calcination temperature of 1000-1300 °C, and a holding time of 1-3 h to obtain a hard carbon negative electrode material.

9. A hard carbon negative electrode material synthesized by using the Maillard reaction of Rhizopus prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the hard carbon negative electrode material synthesized by the Rhizopus as claimed in claim 9 using the Maillard reaction in the field of sodium ion batteries.

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