Negative electrode material, method for preparing the same, and battery

Abstract

The application relates to the technical field of batteries, in particular to a negative electrode material, a preparation method thereof and a battery. The negative electrode material comprises a substrate and a carbon coating layer coated on at least part of the surface of the substrate; wherein the substrate comprises hard carbon, the hard carbon is a biomass-based hard carbon material, and the hard carbon contains C elements and O elements, and the atomic ratio of O and C satisfies O:C=1:20-1:10. The preparation method of the negative electrode material comprises the following steps: soaking pretreated biomass material in a chloride solution, sintering to obtain a hard carbon precursor; mixing the hard carbon precursor with an acid solution, adding peroxodisulfate, and after mixing, separating and drying, obtaining a hard carbon material containing an epoxy group; performing carbon coating treatment on the hard carbon material containing the epoxy group to form a carbon coating layer on at least part of the surface of the hard carbon, and obtaining the negative electrode material. The application can improve the capacity and kinetic performance of the negative electrode material, and improve the capacity, initial efficiency and cycle performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a negative electrode material, its preparation method, and a battery. Background Technology

[0002] With the introduction of dual-carbon goals and the vigorous development of new energy electric vehicles and clean energy, the energy storage field has broad prospects. Although lithium-ion batteries have been widely used, their further application in large-scale energy storage is limited by factors such as the finite nature of lithium resources, uneven geographical distribution, and high cost. Sodium, belonging to the same main group element as lithium, not only possesses similar physicochemical properties and energy storage mechanisms, but also boasts advantages such as high global abundance, low extraction difficulty, and low cost. Therefore, sodium-ion batteries have a very broad application prospect in large-scale energy storage.

[0003] Carbon-based materials are the most widely developed anode materials for sodium-ion batteries, attracting significant attention due to their abundant resources, stable structure, and low manufacturing cost. While graphite anode materials have achieved relatively successful applications in lithium-ion batteries, their use is limited by the difficulty in embedding sodium ions. Therefore, developing high-capacity sodium-ion anode materials is crucial for advancing sodium-ion battery technology.

[0004] Therefore, the anode materials used in sodium-ion batteries in the present technology still need to be improved and developed. Summary of the Invention

[0005] In view of this, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, the present invention provides a negative electrode material, a method for preparing the same, and a battery, which is beneficial for improving the capacity and kinetic performance of the negative electrode material, facilitating the rapid transport of sodium ions, and thus improving the battery's capacity, initial efficiency, and cycle performance.

[0006] To solve the above-mentioned technical problems, this application is implemented as follows:

[0007] According to one aspect of this application, an embodiment of this application provides a negative electrode material, the negative electrode material comprising a matrix and a carbon coating layer covering at least a portion of the surface of the matrix;

[0008] The matrix comprises hard carbon, which is a biomass-based hard carbon material, and the hard carbon contains C and O elements, wherein the atomic ratio of O to C satisfies:

[0009] O:C = 1:20 to 1:10.

[0010] In addition, the negative electrode material according to this application may also have the following additional technical features:

[0011] In some of these embodiments, the atomic ratio of O to C satisfies:

[0012] O:C = 1:20 to 1:15.

[0013] In some of these embodiments, the hard carbon has a fibrous pleated structure.

[0014] In some of these embodiments, the thickness of the carbon coating layer is 5 nm to 10 nm.

[0015] According to another aspect of this application, embodiments of this application provide a method for preparing a negative electrode material, which includes the following steps:

[0016] The pretreated biomass material was soaked in a chloride solution and sintered to obtain a hard carbon precursor.

[0017] The hard carbon precursor is mixed with an acidic solution, and then peroxydisulfate is added. After mixing, separation and drying, a hard carbon material containing epoxy groups is obtained.

[0018] The hard carbon material containing epoxy groups is subjected to carbon coating treatment to form a carbon coating layer on at least a portion of the surface of the hard carbon, thereby obtaining a negative electrode material.

[0019] In some of these embodiments, the preparation of the pretreated biomass material includes: sequentially subjecting the biomass material to alkali washing, water washing, acid washing, water washing, and drying to obtain the pretreated biomass material.

[0020] In some embodiments, the concentration of the alkaline solution used for the alkaline washing is 0.5 to 1 mol / L.

[0021] In some embodiments, the concentration of the acidic solution used for pickling is 0.5 to 1 mol / L.

[0022] In some of these embodiments, during the alkaline washing, acid washing, or water washing process, the solid-liquid ratio of biomass to solution is 1:50 to 1:200 g / mL.

[0023] In some of these embodiments, the drying temperature is 70°C to 100°C, and the drying time is 10h to 16h.

[0024] In some of these embodiments, the biomass material has a fibrous structure.

[0025] In some of these embodiments, the biomass material includes at least one of cellulose, bamboo, coconut shell, macadamia nut shell, walnut shell, pine nut shell, peanut shell, rice straw, cotton stalk bark, sugarcane bagasse, reed, bamboo shoots, straw, walnut shell, coconut husk, or lignin.

[0026] In some embodiments, the step of obtaining the hard carbon precursor satisfies at least one of the following features (1) to (5): (1) the chloride solution includes at least one of sodium chloride solution, potassium chloride solution or chromium chloride solution; (2) the concentration of the chloride solution is 0.05 to 0.5 mol / L; (3) the solid-liquid ratio of the pretreated biomass material during the soaking process in the chloride solution is 10:1 to 20:1 g / L; (4) the sintering is carried out under an inert gas atmosphere, the flow rate of the inert gas is 40 to 80 mL / min; the heating rate of the sintering is 1 to 5 °C / min; the sintering temperature is 500 to 1000 °C; and the time is 2 to 5 h; (5) the particle size D50 of the hard carbon precursor is 5 μm to 10 μm.

[0027] In some of these embodiments, the step of obtaining the hard carbon material containing epoxy groups satisfies at least one of the following features (1) to (4): (1) the ratio of the hard carbon precursor, the acidic solution, and the peroxydisulfate is 100:10000:1 to 100:5000:2 in g:mL:M; (2) the acidic solution comprises concentrated sulfuric acid with a mass fraction of not less than 98%; (3) the peroxydisulfate comprises at least one of potassium peroxydisulfate, nickel peroxydisulfate, or cobalt peroxydisulfate; and (4) the drying temperature is 70°C to 100°C.

[0028] In some embodiments, the carbon coating layer comprises pyrolytic carbon formed by the thermal decomposition of resins or polymers.

[0029] In some embodiments, the mass ratio of the resin or polymer to the hard carbon material containing epoxy groups is 5:1 to 10:1.

[0030] In some embodiments, the resin or polymer class includes at least one of phenolic resin, epoxy resin, acrylic resin, furfural resin, polyethylene glycol, polyethylene oxide, polyethylene, or polypropylene.

[0031] In some embodiments, the carbon coating treatment is performed by calcination under an inert gas atmosphere.

[0032] In some embodiments, the heating rate of the carbon coating treatment is 1–20 °C / min, the temperature of the carbon coating treatment is 500–700 °C, and the time is 1–8 h.

[0033] In some of these embodiments, the thickness of the carbon coating layer is 5 nm to 10 nm.

[0034] According to another aspect of this application, an embodiment of this application provides a battery, the battery including a negative electrode sheet, the negative electrode sheet including the negative electrode material as described above, or the negative electrode material prepared by the aforementioned method.

[0035] Implementing the technical solution of the present invention has at least the following beneficial effects:

[0036] In this embodiment, the provided negative electrode material includes a matrix and a carbon coating layer. The matrix is ​​a biomass-based hard carbon material containing carbon (C) and oxygen (O) elements, with a defined atomic ratio of C and O. Therefore, by including O in the hard carbon and maintaining the O-C ratio within the defined range, the negative electrode material can exhibit higher capacity and faster kinetics, expand the interlayer spacing, facilitate rapid sodium ion transport, and improve the charge / discharge specific capacity, first-efficiency performance, and cycle performance of the negative electrode material. Simultaneously, the carbon coating layer on the surface of the matrix reduces the specific surface area, increases the mechanical strength and conductivity of the active material (negative electrode material), effectively slows down the structural degradation of the negative electrode material during repeated sodiumification / desodiumification processes, and improves the structural stability of the negative electrode material.

[0037] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0038] Figure 1 The image shown is a scanning electron microscope (SEM) image of the biomass material provided in Embodiment 1 of the present invention.

[0039] Figure 2 The image shown is a scanning electron microscope (SEM) image of the negative electrode material provided in Embodiment 1 of the present invention.

[0040] Figure 3 The image shown is a transmission electron microscope (TEM) image of the negative electrode material provided in Embodiment 1 of the present invention.

[0041] Figure 4 The figures shown are XRD patterns of the negative electrode materials provided in Example 1 (carbon material rich in epoxy groups) and Comparative Example 1 (original carbon material) of the present invention.

[0042] Figure 5 The image shown is an EDS diagram of the negative electrode material provided in Embodiment 1 of the present invention. Detailed Implementation

[0043] The present application will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0044] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0045] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0046] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0047] While graphite is widely used as an anode material in sodium-ion batteries, it suffers from the drawback of difficulty in intercalating sodium ions. To alleviate this, high-capacity sodium-ion anode materials need to be developed. Hard carbon is considered a promising anode material for sodium-ion batteries due to its advantages such as large interlayer spacing, good structural stability, and low cost. However, existing hard carbon materials, such as some biomass-based hard carbon materials, suffer from low capacity and low initial efficiency, limiting their further development in the field of sodium-ion battery anodes. Therefore, it is necessary to modify hard carbon materials to improve their electrochemical performance and enhance their effectiveness in sodium-ion battery anode applications.

[0048] The inventors of this application have discovered that hard carbon materials, due to their unique microstructure, can effectively insert and remove sodium ions, attracting increasing attention from researchers. Biomass materials are among the best precursor materials for hard carbon, and some biomass-derived hard carbon materials possess unique nanofiber structures that can effectively shorten ion / electron transport paths and improve material conductivity. Furthermore, the disordered arrangement of twisted pseudo-graphene nanocrystals in hard carbon materials at the microscopic level, with larger interlayer distances compared to graphite, reduces the energy barrier during sodium dissociation. Studies have shown that closed nanopores and appropriately spaced carbon layers can accommodate sodium ions with high reversible capacity. However, this capacity is limited to lower current densities and performs poorly at higher current densities. This is attributed to the poor sodium storage kinetics of hard carbon materials. Additionally, biomass hard carbon has a large specific surface area, low initial coulombic efficiency (ICE), and poor cycling performance, hindering the practical application of hard carbon.

[0049] Therefore, the inventors of this application have fully considered the characteristics of hard carbon materials and improved their capacity, initial efficiency, and cycle performance through modification and coating to effectively alleviate the aforementioned problems. In view of this, this application provides a negative electrode material, a method for preparing the negative electrode material, and a battery. The following is a detailed description of this application.

[0050] [Anode Material]

[0051] In some embodiments, this application provides a negative electrode material, which includes a matrix and a carbon coating layer covering at least a portion of the surface of the matrix;

[0052] The matrix includes hard carbon, which is a biomass-based hard carbon material containing carbon (C) and oxygen (O) elements, with the atomic ratio of O to C satisfying the following:

[0053] O:C = 1:20 to 1:10.

[0054] It should be noted that, in this application, the term "coating" is not limited to direct coating, but also includes indirect coating. For example, when a carbon coating layer coats a substrate, it may mean that there are no other structures between the carbon coating layer and the outer surface of the substrate, or it may mean that there are one or more other structures between the carbon coating layer and the outer surface of the substrate. Preferably, there are no other structures between the carbon coating layer and the outer surface of the substrate.

[0055] In this application, the carbon coating layer is formed or coated on at least a portion of the surface of the substrate, which can protect or improve the substrate. It can be used to improve the structural stability of the negative electrode material, increase the first coulombic efficiency of the negative electrode material, and reduce the specific surface area of ​​the negative electrode material. The carbon coating layer coating or forming on at least a portion of the surface of the substrate means that the carbon coating layer can completely encapsulate the substrate within the carbon coating layer, or the carbon coating layer can only coat a portion of the outer surface of the substrate; that is, the carbon coating layer can completely coat the substrate, or it can coat a portion of the substrate surface, preferably completely coat the substrate.

[0056] The provided anode material has a core-shell structure, where the core is hard carbon and the outer shell or shell layer includes a carbon coating layer (carbon material layer). Notably, the hard carbon in this application is a biomass-based hard carbon material, meaning the precursor of the hard carbon can be biomass, making it a biomass-derived hard carbon material. Furthermore, this hard carbon contains both carbon (C) and oxygen (O) elements, such as... Figure 5 The embodiments of this invention show that the negative electrode material contains carbon (C) and oxygen (O) elements, and the atomic ratio of O to C is defined as O:C = 1:20 to 1:10. Therefore, by including C and O elements in the hard carbon and ensuring the ratio of O to C is within the defined range, the material significantly contributes to improving its sodium ion adsorption capacity. Simultaneously, the presence of oxygen in the hard carbon effectively reduces the free volume for sodium ion migration, thus improving the material's kinetics. In other words, by including O elements in the hard carbon and ensuring the ratio of O to C is within the defined range, the negative electrode material can exhibit higher capacity and faster kinetics. During the sodiumification / desodiumification process, the interlayer spacing can be appropriately increased, which is beneficial for achieving rapid sodium ion transport and improving the charge / discharge specific capacity, first-efficiency performance, and cycle performance of the negative electrode material.

[0057] Meanwhile, by setting a carbon coating layer on the surface of the substrate, the specific surface area can be reduced, the mechanical strength and conductivity of the active material (anode material) can be increased, the structural degradation of the anode material during repeated sodiumification / desodiumification processes can be effectively slowed down, the structural stability of the anode material can be improved, and the first coulombic efficiency of the anode material can be improved.

[0058] Moreover, the aforementioned hard carbon is a biomass-based hard carbon material. Using biomass as a precursor to prepare hard carbon materials is widely available and inexpensive, making it a practical industrial production solution for low-cost, large-scale sodium-ion battery anode materials. Furthermore, from a green and recyclable perspective, the strategy of using biomass to synthesize electrode materials is of great significance, and biomass-derived carbon exhibits excellent electrochemical performance.

[0059] Optionally, the matrix hard carbon or anode material has a fibrous structure.

[0060] In some preferred embodiments of this application, the prepared anode material or hard carbon has a fibrous structure, which shortens the ion transport path, improves the electrochemical reaction kinetics, effectively reduces the specific surface area of ​​the material, and has sufficient reactive sites, as well as high specific capacity, making the anode material a potential high-capacity sodium-ion battery anode material.

[0061] As an example, the atomic ratio of O and C mentioned above can be any one of the following values ​​or a range between any two: 1:20, 1:19, 1:18, 1:17, 1:16, 1:15, 1:14, 1:13, 1:12, 1:11, 1:10.

[0062] By maintaining the atomic ratio of O to C within the aforementioned range, the content of oxygen-containing groups or compounds in the hard carbon is kept within an appropriate range. This helps to enhance the material's contribution to sodium ion adsorption capacity and improve the kinetics of the anode material. The oxygen-rich hard carbon material exhibits higher capacity and faster kinetics. During the sodiumification / desodiumification process, the strong attraction of oxygen-containing compounds appropriately expands the interlayer spacing, facilitating rapid sodium ion transport. If the atomic ratio of O to C is too small (close to zero), the oxygen content in the hard carbon is reduced, failing to effectively enhance the material's contribution to sodium ion adsorption capacity and improve the kinetics of the anode material. If the atomic ratio of O to C is too large, the excessive oxygen content results in lower initial efficiency during the first charge-discharge cycle, affecting the battery's cycle life.

[0063] Preferably, in some embodiments, the atomic ratio of O to C satisfies: O:C = 1:20 to 1:12.

[0064] Preferably, in some embodiments, the atomic ratio of O to C satisfies: O:C = 1:20 to 1:15.

[0065] Further optimizing the atomic ratio of O and C within the above range can help improve the capacity and kinetic performance of the anode material, and optimize its electrochemical performance.

[0066] In some embodiments, hard carbon has a fibrous, wrinkled structure. Optionally, the biomass used to prepare hard carbon has a fibrous structure.

[0067] In this application, the precursor biomass used to prepare hard carbon can have a fibrous structure, and the resulting hard carbon material can have a high content of epoxy groups, and the hard carbon has a fibrous pleated structure. By giving the hard carbon a fibrous pleated structure or a fibrous structure, it can be used to accelerate ion transport, shorten the transport distance, and improve kinetic performance; that is, it can shorten the ion transport path, improve electrochemical reaction kinetics, effectively reduce the specific surface area of ​​the material, while having sufficient reactive sites, and also enable the material to have a high specific capacity.

[0068] It should be noted that the term "fiber structure" as used herein has a commonly known meaning in the relevant field, referring to a morphological structure with fibers (e.g., a substance composed of continuous or discontinuous filaments). This conventional understanding is sufficient, and this application does not impose any specific limitations on it. Furthermore, "fiber pleated structure" refers to a fiber structure that has a certain degree of pleating; that is, the fiber structure is not linear but has certain curved or bent segments. This is beneficial for providing more reactive sites and improving the kinetic properties and capacity of the material.

[0069] Optionally, the aforementioned biomass includes, but is not limited to, at least one of cellulose, bamboo, coconut shell, macadamia nut shell, walnut shell, pine nut shell, peanut shell, rice straw, cotton stalk husk, sugarcane bagasse, reed, bamboo shoots, straw, walnut shell, coconut husk, or lignin.

[0070] Preferably, the biomass is selected from one or more of cellulose, bamboo fiber, coconut shell, rice straw, cotton stalk husk, and sugarcane bagasse.

[0071] Using the above-mentioned biomass as precursors to prepare hard carbon is not only widely available and low-cost, but also environmentally friendly. In addition, it has a good fiber structure, which enables the prepared hard carbon to have better electrochemical performance.

[0072] In some embodiments, the thickness of the carbon coating layer is 5 nm to 10 nm. Further, the thickness of the carbon coating layer is 6 nm to 9 nm. As an example, the thickness of the carbon coating layer can be any one of 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, or 10 nm, or a range between any two.

[0073] In this application, the thickness of the carbon coating layer can be adjusted according to the size of the core hard carbon. A suitable carbon coating layer thickness can ensure that the anode material has good processing performance, and can also avoid the carbon coating layer being too thick, or the coating material being too much, affecting the timely release of active lithium or the electrochemical performance of the cell or increasing the cost. Alternatively, it can also avoid the carbon coating layer being too thin, which would not be able to effectively exert the modification effect of the carbon coating layer. In other words, it can avoid the carbon coating layer being too thin, which would reduce the effect of improving the first efficiency of the material and reducing the specific surface area of ​​the material.

[0074] Optionally, the aforementioned carbon coating layer comprises pyrolytic carbon formed by the thermal decomposition of resins or polymers. The resins or polymers include, but are not limited to, any one or a mixture of at least two of the following: phenolic resin, urea-formaldehyde resin, epoxy resin, acrylic resin, polyurethane, polyethylene resin, polyaniline, furfural resin, polyethylene glycol, polyethylene oxide, polyacrylonitrile, polyethylene, or polypropylene, in any proportion.

[0075] In this application, the core of the negative electrode material can be a cellulose-derived hard carbon material with rich epoxy groups, and the carbon coating material can be a small molecule carbon material obtained by pyrolysis and volatilization of resins such as phenolic resin or polymers.

[0076] [Preparation methods for negative electrode materials]

[0077] In some embodiments, this application provides a method for preparing a negative electrode material, which includes the following steps:

[0078] The pretreated biomass material was soaked in a chloride solution and sintered to obtain a hard carbon precursor.

[0079] The hard carbon precursor is mixed with an acidic solution, and then peroxydisulfate is added. After mixing, separation and drying, a hard carbon material containing epoxy groups is obtained.

[0080] A carbon coating process is performed on a hard carbon material containing epoxy groups to form a carbon coating layer on at least a portion of the surface of the hard carbon, thereby obtaining a negative electrode material.

[0081] This invention provides a method for preparing a negative electrode material. Biomass is used as a precursor to prepare hard carbon, which undergoes epoxidation during the preparation process to form an oxygen-rich hard carbon material, such as a hard carbon material with potentially residual high levels of epoxy groups. Subsequently, a carbon coating treatment is performed to form a carbon coating layer on the surface of the hard carbon, thus obtaining the negative electrode material. This preparation method is simple, convenient, feasible, environmentally friendly, low-cost, and easy to industrialize. The negative electrode material prepared by this method exhibits good structural stability, excellent kinetic performance, and good electrochemical performance.

[0082] It should be understood that all the features and advantages described above regarding the "anode material" also apply to the "anode preparation method," and will not be repeated here.

[0083] In some specific embodiments, the preparation method of the negative electrode material specifically includes the following steps (a) to (c):

[0084] Step (a): Preparation of hard carbon precursor.

[0085] In some embodiments, in step (a), the pretreated biomass material is soaked in a chloride solution and sintered to obtain a hard carbon precursor.

[0086] In step (a), by immersing the pretreated biomass material in a chloride solution, the chloride solution can be used to shape the material, for example, to facilitate the formation of hard carbon material with a fibrous, wrinkled structure. Furthermore, sintering after immersion in the chloride solution can form a hard carbon precursor through carbonization.

[0087] In some embodiments, in step (a), the biomass material needs to be pretreated to obtain pretreated biomass material. The preparation of the pretreated biomass material includes: sequentially performing alkaline washing, water washing, acid washing, water washing and drying on the biomass material to obtain the pretreated biomass material.

[0088] Thus, by treating biomass materials with alkali washing, water washing, acid washing, and water washing, impurities or dirt in the biomass materials can be removed, improving the purity of the prepared hard carbon materials, which in turn helps to improve the performance of the prepared hard carbon materials.

[0089] Optionally, in the above pretreatment process, the concentration of the alkaline solution used for alkaline washing is 0.5–1 mol / L. During the pretreatment of biomass materials, the alkaline solution used for washing the biomass materials can have a concentration of 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, etc., or other values ​​within the above range; no limitation is made here. Optionally, the alkaline solution can be a conventional alkaline solution, such as sodium hydroxide solution (aqueous solution), potassium hydroxide solution (aqueous solution), etc., but it is not limited to these, as long as it can be used for alkaline washing of biomass materials and does not limit the purpose of this application.

[0090] Optionally, in the above pretreatment process, the concentration of the acidic solution used for pickling is 0.5–1 mol / L. During the pretreatment of biomass materials, the acidic solution is used to clean the biomass materials. The concentration of the acidic solution can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, etc., or other values ​​within the above range, and is not limited here. Optionally, the acidic solution can be a conventional acidic solution, such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, etc. (aqueous solutions of acids), but it is not limited to these, as long as it can be used to pickle biomass materials and is not limited to the purpose of this application. Preferably, hydrochloric acid is used as the acidic solution.

[0091] Optionally, during the above pretreatment processes, the solid-liquid ratio of biomass to solution during alkaline washing, acid washing, or water washing is 1:50 to 1:200 g / mL. That is, during alkaline washing, the solid-liquid ratio of biomass to alkaline solution is 1:50 to 1:200 g / mL; during acid washing, the solid-liquid ratio of biomass to acidic solution is 1:50 to 1:200 g / mL; and during water washing, the solid-liquid ratio of biomass to water is 1:50 to 1:200 g / mL. As examples, this solid-liquid ratio can be 1:50 g / mL, 1:80 g / mL, 1:100 g / mL, 1:150 g / mL, 1:200 g / mL, etc., and of course, other values ​​within the above range are also possible and are not limited here.

[0092] It should be noted that the specific time for the above-mentioned cleaning steps such as alkaline washing, acid washing, and water washing can be selected and set according to the actual situation of the biomass material. For example, the cleaning time for alkaline washing, acid washing, and water washing can be 1 hour to 4 hours, and can be as low as 2 hours.

[0093] Optionally, in the above pretreatment process, the drying temperature is 70℃~100℃, and the drying time is 10h~16h. As an example, the drying temperature can be 70℃, 80℃, 90℃, 100℃, etc., or other values ​​within the above range, which are not limited here; the drying time can be 10h, 11h, 12h, 13h, 15h, 16h, etc., or other values ​​within the above range, which are not limited here. Preferably, the drying temperature is 80℃~90℃, and the drying time is 11h~13h.

[0094] In some embodiments, in step (a), the biomass material has a fibrous structure.

[0095] In some embodiments, in step (a), the biomass mentioned above includes, but is not limited to, any one or at least two of the following in any proportion: cellulose, bamboo, coconut shell, macadamia nut shell, walnut shell, pine nut shell, peanut shell, rice straw, cotton stalk husk, sugarcane bagasse, reed, bamboo shoots, straw, walnut shell, coconut husk, or lignin.

[0096] Preferably, the above-mentioned biomass material is selected from one or more of cellulose, bamboo fiber, coconut shell, rice straw, cotton stalk bark, and sugarcane bagasse.

[0097] Using the above-mentioned biomass as precursors to prepare hard carbon is not only widely available and low-cost, but also environmentally friendly. In addition, it has a good fiber structure, which enables the prepared hard carbon to have better electrochemical performance.

[0098] In some embodiments, in step (a), the biomass material is pretreated, and after obtaining the pretreated biomass material, it is soaked in a chloride solution, wherein the chloride solution includes, but is not limited to, any one or at least two of sodium chloride solution, potassium chloride solution or chromium chloride solution.

[0099] In this application, immersing the treated biomass material in a chloride solution can achieve the effect of material shaping.

[0100] Optionally, the concentration of the chloride solution is 0.05–0.5 mol / L; preferably, the concentration of the chloride solution is 0.08–0.3 mol / L; more preferably, the concentration of the chloride solution is 0.1–0.2 mol / L. The concentration of the chloride solution used can be, for example, 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, 0.12 mol / L, 0.15 mol / L, 0.2 mol / L, 0.3 mol / L, 0.5 mol / L, etc.

[0101] Optionally, the solid-liquid ratio during the soaking process of the pretreated biomass material in the chloride solution is 10:1 to 20:1 g / L; that is, the solid-liquid ratio of the pretreated biomass material to the chloride solution is solid (g):liquid (L) = 10:1 to 20:1. As an example, this solid-liquid ratio can be 10:1 g / L, 12:1 g / L, 15:1 g / L, 20:1 g / L, etc.

[0102] In some embodiments, in step (a), after the pretreated biomass material is immersed in a chloride solution, it is then sintered. The sintering is carried out under an inert gas atmosphere, with an inert gas flow rate of 40–80 mL / min; the sintering heating rate is 1–5 °C / min; the sintering temperature is 500–1000 °C; and the sintering time is 2–5 h. The inert gas can be one or more of nitrogen, argon, helium, etc. For example, the flow rate of the inert gas can be 40 mL / min, 50 mL / min, 60 mL / min, 70 mL / min, 80 mL / min, etc.; the heating rate of sintering can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, etc.; the sintering temperature can be 500℃, 550℃, 600℃, 650℃, 700℃, 800℃, 900℃, 1000℃, etc.; and the sintering time can be 2h, 3h, 4h, 5h, etc.

[0103] Optionally, in step (a), after sintering is completed, the obtained feed can be ground into powder in a mortar and sieved to obtain a hard carbon precursor.

[0104] In some embodiments, in step (a), the particle size D50 of the hard carbon precursor prepared is 5 μm to 10 μm. As an example, the particle size D50 of the hard carbon precursor can be any one of 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, and 10 μm, or a range between any two.

[0105] As an example, step (a) specifically includes: alkali washing of biomass material with a fibrous structure for 1-3 hours (e.g., about 2 hours), then rinsing the material with water, such as deionized water, to bring the pH of the solution to 7; then immersing the material in an acidic solution for 1-3 hours (e.g., about 2 hours), followed by rinsing with water to bring the pH of the solution to 7; and then drying in an oven, for example, at a temperature of 80-90°C for 11-13 hours, to obtain pretreated biomass material. Next, the pretreated biomass material is soaked in a chloride salt solution for 10-30 hours (e.g., about 12 hours), then removed and dried, followed by calcination (sintering) in an inert atmosphere tube furnace. After calcination, the material is ground into powder in a mortar and sieved to obtain a hard carbon precursor with a particle size D50 of 5 μm-10 μm.

[0106] Step (b): Preparation of hard carbon materials.

[0107] In some embodiments, in step (b), the hard carbon precursor obtained in step (a) is mixed with an acidic solution, and then peroxydisulfate is added. After mixing, separation and drying, a hard carbon material containing epoxy groups is obtained.

[0108] In this application, biomass is used as a precursor to prepare hard carbon materials, and hard carbon materials with a high content of epoxy groups are obtained, which have a fibrous pleated structure.

[0109] In step (b), by mixing the hard carbon precursor with an acidic solution, the interlayer spacing can be expanded using the acidic solution; then, peroxydisulfate is added, which can be used to strengthen the material and perform epoxidation treatment. That is, the material with expanded interlayer spacing is epoxidized by the strong oxidizing effect of peroxydisulfate, thereby forming a carbon material with a high content of epoxy groups.

[0110] In some embodiments, in step (b), the acidic solution includes concentrated sulfuric acid with a mass fraction of not less than 98%. Thus, the concentrated sulfuric acid can increase the interlayer spacing.

[0111] In some embodiments, in step (b), the peroxydisulfate includes any one or a mixture of at least two of potassium peroxydisulfate, nickel peroxydisulfate, or cobalt peroxydisulfate in any proportion.

[0112] In this application, the peroxydisulfate provided contains potassium, nickel, and cobalt, all of which catalyze graphitization, and the peroxydisulfate itself possesses strong oxidizing properties. Therefore, by employing these peroxydisulfate compounds, a strong oxidizing effect can be achieved, enabling the epoxidation treatment of materials with expanded interlayer spacing, thereby forming carbon materials with a high content of epoxy groups.

[0113] Furthermore, the catalytic graphitization effect of metal atoms has been demonstrated in many studies to have a good catalytic effect on carbon materials, which can effectively reduce the calcination temperature, reduce the number of defects in the material, and improve the initial efficiency.

[0114] In some embodiments, in step (b), the ratio of hard carbon precursor, acidic solution, and peroxydisulfate is 10:100:1 to 10:500:1, based on g:mL:M; that is, the ratio of hard carbon precursor (g): 98% concentrated sulfuric acid (mL): peroxydisulfate (M) = 100:10000:1 to 100:5000:2, where M refers to the concentration in mol / L. As an example, the ratio of carbon precursor (g): 98% concentrated sulfuric acid (mL): peroxydisulfate (M) is 100:10000:1, 100:8000:1, 100:5000:1, 100:5000:2, etc.

[0115] In some embodiments, in step (b), after adding peroxydisulfate, the mixture is mixed and then separated, such as by filtration, and then placed in an oven for drying, wherein the drying temperature is 70°C to 100°C. As an example, the drying temperature can be 70°C, 80°C, 90°C, 100°C, etc., or other values ​​within the above range, which are not limited here.

[0116] As an example, step (b) specifically includes: mixing the hard carbon precursor obtained in step (a) with an acidic solution such as concentrated sulfuric acid and stirring for 1 to 3 hours (e.g., about 2 hours); then adding peroxydisulfate such as potassium peroxydisulfate, nickel peroxydisulfate, or cobalt peroxydisulfate, and stirring for another 10 to 30 hours (e.g., about 24 hours); after stirring, continuously adding water and stirring to separate the solid; then placing the obtained material in deionized water and stirring until neutral and filtering, i.e., separating; after separation, placing it in an oven for drying, for example, at a drying temperature of 80°C to 90°C, to obtain a hard carbon material containing oxygen elements, such as possibly containing epoxy groups.

[0117] Therefore, the prepared hard carbon contains oxygen, and the above preparation method also indirectly proves that the hard carbon contains epoxy groups, making it an epoxide-rich hard carbon material. The epoxides (epoxy groups) in the hard carbon significantly contribute to improving the material's sodium ion adsorption capacity. Simultaneously, the epoxides or (epoxy groups) in the hard carbon effectively reduce the free volume for sodium ion migration; that is, compared to hydroxyl groups, epoxy groups exhibit better kinetics. Furthermore, this allows the anode material to exhibit higher capacity and faster kinetics. During the sodiumification / desodiumification process, the strong attraction of sodium epoxide appropriately expands the interlayer spacing, which is beneficial for achieving rapid sodium ion transport and improving the charge-discharge specific capacity, first-efficiency performance, and cycle performance of the anode material.

[0118] Step (c): Carbon coating treatment is applied to the hard carbon material.

[0119] In some embodiments, in step (c), the hard carbon material containing epoxy groups obtained in step (b) is subjected to carbon coating treatment to form a carbon coating layer on at least a portion of the surface of the hard carbon, thereby obtaining a negative electrode material.

[0120] In this application, the carbon coating layer comprises pyrolytic carbon formed by the thermal decomposition of resins or polymers. That is, resins or polymers can be thermally decomposed, and small molecule gases are generated during the thermal decomposition process, which can act as a gas source for carbon coating, forming a carbon coating layer on at least a portion of the surface of the hard carbon.

[0121] In some embodiments, the resin or polymer class includes any one or a combination of at least two of phenolic resin, epoxy resin, acrylic resin, furfural resin, polyethylene glycol, polyethylene oxide, polyethylene, or polypropylene. That is, the precursor used to form the carbon coating layer can be selected from resins such as phenolic resin, epoxy resin, acrylic resin, furfural resin, etc.; or the precursor used to form the carbon coating layer can be selected from polymer classes such as polyethylene glycol, polyethylene oxide, polyethylene, or polypropylene.

[0122] Preferably, the resin is selected from phenolic resin.

[0123] In some embodiments, the mass ratio of the resin or polymer to the hard carbon material containing epoxy groups is 5:1 to 10:1. As an example, the mass ratio of the resin or polymer to the hard carbon material containing epoxy groups can be 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc.

[0124] In some embodiments, the hard carbon material contains C and O elements, and the atomic ratio of O to C satisfies: O:C = 1:20 to 1:10.

[0125] In some embodiments, in step (c), the carbon coating process is performed by calcination under an inert gas atmosphere.

[0126] Optionally, the inert gas can be one or more of nitrogen, argon, and helium.

[0127] Optionally, the flow rate of the inert gas is 40–80 mL / min. As an example, the flow rate of the inert gas can be 40 mL / min, 50 mL / min, 60 mL / min, 70 mL / min, 80 mL / min, etc.

[0128] In some embodiments, in step (c), the heating rate of the carbon coating treatment is 1–20 °C / min, the temperature of the carbon coating treatment is 500–700 °C, and the time is 1–8 h. As an example, the heating rate of the carbon coating treatment can be 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 10 °C / min, 15 °C / min, 20 °C / min, etc., the temperature of the carbon coating treatment can be 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, etc., and the time of the carbon coating treatment can be 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 8 h, etc.

[0129] In some embodiments, the thickness of the carbon coating layer is 5 nm to 10 nm.

[0130] As an example, step (c) specifically includes: placing the hard carbon material containing epoxy groups obtained in step (b) and the carbon coating precursor, such as resin or polymer, into two adjacent crucibles respectively (placing them in two crucibles prevents impurities from appearing, resulting in a higher purity of the final product), and performing carbon coating treatment, with the crucible containing the resin or polymer placed at the front end. Then, the two crucibles are transferred to a tube furnace and calcined a second time under an inert gas atmosphere. The collected solid is washed with approximately 3% dilute HCl (dilute hydrochloric acid) to remove residual metal ions from the material, thereby obtaining a high-performance epoxy group-rich biomass sodium-ion battery anode material, i.e., obtaining the anode material.

[0131] Therefore, based on the above settings, the negative electrode material and its preparation method provided by this invention, which uses biomass materials to prepare hard carbon materials, can be used as negative electrode materials for sodium-ion batteries. From the perspective of green and recyclable materials, the strategy of using biomass to synthesize electrode materials is of great significance, and biomass-derived carbon exhibits good electrochemical performance. Furthermore, due to the large specific surface area of ​​hard carbon materials leading to a lower initial efficiency, coating technology is often used to effectively suppress SEI formation and corresponding sodium ion consumption. In this application, a carbon coating layer is formed on the surface of the hard carbon. This carbon coating is an efficient means of reducing the specific surface area, increasing the mechanical strength and conductivity of the active material, and effectively slowing down the structural degradation of the material during repeated sodiumization / desodiumization processes. In addition, electrochemical reaction kinetics is also one of the important indicators for evaluating the quality of materials. The hard carbon core of this invention, i.e., the epoxide-rich hard carbon material, can exhibit higher capacity and faster kinetics. During the sodiumization / desodiumization process, the strong attraction of sodium epoxide is used to appropriately expand the interlayer spacing, which is beneficial for achieving rapid sodium ion transport. In addition, peroxydisulfate was used in the preparation of hard carbon core. Its metal atom catalytic graphitization effect has been proven in many studies to have a good catalytic effect on carbon materials, which can effectively reduce the calcination temperature, reduce the number of defects in the material, and improve the initial efficiency.

[0132] In addition, the sodium-ion battery anode material designed in this invention has a fibrous structure, which can shorten the ion transport path, improve the electrochemical reaction kinetics, effectively reduce the specific surface area of ​​the material, and at the same time have sufficient reactive sites and high specific capacity. It is a promising high-capacity sodium-ion battery anode material.

[0133] [Battery]

[0134] In some embodiments, this application provides a battery, the battery including a negative electrode sheet, the negative electrode sheet including the aforementioned negative electrode material, or a negative electrode material prepared by the aforementioned method.

[0135] Because this battery includes the negative electrode material provided in the embodiments of this application, it can exhibit good electrochemical performance, such as high initial charge-discharge capacity, excellent initial coulombic efficiency, and good cycle stability.

[0136] In this application, the battery can be a sodium-ion battery. The battery stacking type is, for example, a wound or stacked battery, and the structural type is, for example, a prismatic (aluminum, steel, etc.) battery, a pouch battery, or a cylindrical battery, etc., without specific limitations. This battery has a high capacity, good cycle performance, and long service life.

[0137] In some embodiments, the negative electrode sheet includes the aforementioned negative electrode material or a negative electrode material prepared according to the aforementioned method. Further, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. In some embodiments, the negative electrode active material layer includes the negative electrode material described above provided in this application. Further, the negative electrode active material layer may optionally include a conductive agent. Further, the negative electrode active material layer may optionally include a binder.

[0138] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on the two opposite surfaces of the negative electrode current collector. It can be understood that the negative electrode active material layer can also be stacked on either of the two surfaces of the negative electrode current collector.

[0139] This application does not impose any particular restrictions on the material of the negative electrode current collector, as long as it can achieve the purpose of this application, and can be selected according to actual needs. As an example, the negative electrode current collector can be made of metal materials such as aluminum, copper, nickel, stainless steel, or nickel-plated steel, or it can be a foil material with a surface coating layer. This coating layer has one or more functionalities such as improved conductivity, improved adhesion, improved safety, reduced DCR, and increased lithium-ion conductivity. For example, it can be a carbon coating layer, a carbon coating + graphene / conductive carbon nanotube / boehmite, or alumina, and a solid electrolyte coating. Of course, in other embodiments, a composite current collector can also be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming metal materials such as aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys on a polymer material substrate such as polypropylene, polyethylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, etc.

[0140] This application does not impose any particular limitations on the types of conductive agents and binders in the negative electrode active material layer, as long as they can achieve the purpose of this application. For example, the binder may include, but is not limited to, one or more of polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene-butadiene copolymer (styrene-butadiene rubber), polyvinyl alcohol, polytetrafluoroethylene, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, or sodium carboxymethyl cellulose. The conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), conductive graphite, carbon nanotubes (CNTs), carbon fibers, graphene, or conductive polymers. The aforementioned conductive carbon black includes Ketjen black, acetylene black, etc., and the aforementioned carbon nanotubes include single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

[0141] This application does not impose any particular restrictions on the mass ratio of negative electrode material, conductive agent, and binder in the negative electrode active material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0142] In some embodiments, the battery further includes a positive electrode, an electrolyte, and a separator. That is, the battery includes a positive electrode, a negative electrode, an electrolyte, and a separator.

[0143] In this embodiment of the application, the specific materials and structures of the positive electrode, separator, and electrolyte are not limited. Any components and structures known in the art that can be used in secondary batteries can be selected, as long as they can achieve the purpose of this application.

[0144] Since the battery provided in this embodiment of the invention adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, and will not be described in detail here.

[0145] The following describes the implementation methods of this application. The implementation methods described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the implementation methods, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents, materials, or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0146] Example 1

[0147] The preparation of the negative electrode material includes the following steps:

[0148] (a) The biomass material (cellulose) with fibrous structure is alkali washed for 2 hours, then rinsed with water such as deionized water to make the pH of the solution reach 7, and then placed in an acidic solution for acid washing for 2 hours, and then rinsed with water to make the pH of the solution reach 7. Then it is placed in an oven for drying at a temperature of 80°C for 12 hours to obtain the pretreated biomass material.

[0149] Then, 50g of pretreated biomass material (cellulose material) was soaked in 2.5L of chloride salt solution (0.1mol / L chromium chloride solution) for 12h. After soaking, it was taken out and dried, and then placed in an inert atmosphere (nitrogen atmosphere) tube furnace for calcination (sintering). The sintering temperature was 900℃ and the time was 2h. The sintering heating rate was 5℃ / min. After calcination, the material was ground into powder in a mortar and sieved to obtain a hard carbon precursor with a particle size D50 of 5-7μm.

[0150] (b) Mix 10g of the hard carbon precursor obtained in step (a) with 500mL of concentrated sulfuric acid and stir for 2h. Then add 0.54g of potassium peroxydisulfate solution (the concentration of potassium peroxydisulfate salt is 0.2M) and stir for another 24h. After stirring, add water continuously and stir to separate the solid. Then put the obtained material into deionized water and stir to neutralize it and filter it, that is, separate it. After separation, put it into an oven for drying at a temperature of 80℃ to obtain hard carbon material containing epoxy groups.

[0151] In hard carbon materials, the atomic ratio of O to C satisfies: O:C = 1:20.

[0152] (c) Take 2g of the hard carbon material containing epoxy groups obtained in step (b), and put the hard carbon material containing epoxy groups and phenolic resin into two adjacent crucibles at a mass ratio of 1:5 for carbon coating treatment. The crucible containing phenolic resin is placed at the front end. Then, transfer the two crucibles to a tube furnace and perform secondary calcination in an inert gas atmosphere. The inert gas is nitrogen, the flow rate of the inert gas is 80mL / min, the heating rate of the carbon coating treatment is 15℃ / min, the temperature of the carbon coating treatment is 500℃, and the time is 2h. The collected solid is washed with about 3% dilute HCl and cooled to room temperature to obtain the negative electrode material.

[0153] Example 2

[0154] The negative electrode material in Example 2 was prepared according to the preparation method of Example 1, with the only difference being:

[0155] In step (a), coconut shells are used as the biomass material.

[0156] Example 3

[0157] The negative electrode material in Example 3 was prepared according to the preparation method of Example 1 above, with the only difference being:

[0158] In step (a), the biomass material used is bagasse.

[0159] Example 4

[0160] The negative electrode material in Example 4 was prepared according to the preparation method of Example 1 above, with the only difference being:

[0161] In step (a), the biomass material used is bamboo fiber.

[0162] Example 5

[0163] The negative electrode material in Example 5 was prepared according to the preparation method of Example 1 above, with the only difference being:

[0164] In step (a), 50g of pretreated biomass material is soaked in 5L of chloride salt solution (0.2mol / L sodium chloride solution) for 12h. After soaking, it is taken out and dried, and then placed in an inert atmosphere (nitrogen atmosphere) tube furnace for calcination (sintering). The sintering temperature is 600℃ and the time is 5h. The heating rate of sintering is 5℃ / min. After calcination, the material is ground into powder in a mortar and sieved to obtain a hard carbon precursor with a particle size D50 of 5-8μm.

[0165] Example 6

[0166] The negative electrode material in Example 6 was prepared according to the preparation method of Example 1 above, with the only difference being:

[0167] In step (a), 50g of pretreated biomass material is soaked in 5L of chloride salt solution (0.3mol / L potassium chloride solution) for 12h. After soaking, it is taken out and dried, and then placed in an inert atmosphere (nitrogen atmosphere) tube furnace for calcination (sintering). The sintering temperature is 1000℃ and the time is 2h. The sintering heating rate is 3℃ / min. After calcination, the material is ground into powder in a mortar and sieved to obtain a hard carbon precursor with a particle size D50 of 6-9μm.

[0168] Example 7

[0169] The negative electrode material in Example 7 was prepared according to the preparation method of Example 1 above, with the only difference being:

[0170] In step (b), 10g of the hard carbon precursor obtained in step (a) is mixed with 800mL of concentrated sulfuric acid and stirred for 2 hours. Then, 24g of potassium peroxydisulfate solution (the concentration of potassium peroxydisulfate salt is 0.2M) is added and stirred for another 24 hours. After stirring, water is continuously added and stirred to separate the solid. The obtained material is then placed in deionized water and stirred until neutral and filtered, i.e., separated. After separation, it is placed in an oven for drying at a temperature of 85℃ to obtain hard carbon material containing epoxy groups.

[0171] In hard carbon materials, the atomic ratio of O to C satisfies: O:C = 1:15.

[0172] Example 8

[0173] The negative electrode material in Example 8 was prepared according to the preparation method of Example 1 above, with the only difference being:

[0174] In step (b), 10g of the hard carbon precursor obtained in step (a) is mixed with 1000mL of concentrated sulfuric acid and stirred for 2 hours. Then, 24g of potassium peroxydisulfate solution (the concentration of potassium peroxydisulfate salt is 0.1M) is added and stirred for another 24 hours. After stirring, water is continuously added and stirred to separate the solid. The obtained material is then placed in deionized water and stirred until neutral and filtered, i.e., separated. After separation, it is placed in an oven for drying at a temperature of 90℃ to obtain hard carbon material containing epoxy groups.

[0175] In hard carbon materials, the atomic ratio of O to C satisfies: O:C = 1:10.

[0176] Example 9

[0177] The negative electrode material in Example 9 was prepared according to the preparation method of Example 1 above, with the only difference being:

[0178] In step (c), 2g of the hard carbon material containing epoxy groups obtained in step (b) is taken, and the hard carbon material containing epoxy groups and polyethylene are placed in two adjacent crucibles at a mass ratio of 1:10 for carbon coating treatment. The crucible containing polyethylene is placed at the front end, and the two crucibles are then transferred to a tube furnace for secondary calcination in an inert gas atmosphere. The inert gas is nitrogen, the flow rate of the inert gas is 80mL / min, the heating rate of the carbon coating treatment is 15℃ / min, the temperature of the carbon coating treatment is 600℃, and the time is 4h. The collected solid is washed with approximately 3% dilute HCl and cooled to room temperature to obtain the negative electrode material.

[0179] Example 10

[0180] The negative electrode material of Example 10 was prepared according to the preparation method of Example 1 above, with the only difference being:

[0181] In step (c), 2g of the hard carbon material containing epoxy groups obtained in step (b) is taken, and the hard carbon material containing epoxy groups and acrylic resin are placed in two adjacent crucibles at a mass ratio of 1:8 for carbon coating treatment. The crucible containing acrylic resin is placed at the front end, and the two crucibles are then transferred to a tube furnace for secondary calcination in an inert gas atmosphere. The inert gas is nitrogen, the flow rate of the inert gas is 80mL / min, the heating rate of the carbon coating treatment is 20℃ / min, the temperature of the carbon coating treatment is 700℃, and the time is 1h. The collected solid is washed with approximately 3% dilute HCl and cooled to room temperature to obtain the negative electrode material.

[0182] Comparative Example 1

[0183] The preparation of the negative electrode material includes the following steps:

[0184] (a) 10g of cellulose is alkali washed for 2h, then rinsed with water such as deionized water to bring the pH of the solution to 7. Then the material is placed in an acidic solution for acid washing for 2h, and then rinsed with water to bring the pH of the solution to 7. Then it is placed in an oven for drying at 80℃ for 12h to obtain the pretreated biomass material.

[0185] (b) The pretreated biomass material (cellulose) obtained in step (a) is placed in a crucible and placed in a tube furnace. The atmosphere inside the tube furnace is nitrogen, and the gas flow rate can be 80 mL / min. The heating rate is 2℃ / min, the calcination time is 2 h, and the calcination temperature is 1300℃. After calcination, cellulose-derived hard carbon sodium-ion battery anode material is obtained.

[0186] The negative electrode material prepared in Comparative Example 1 is a conventional cellulose-derived hard carbon material.

[0187] Comparative Example 2

[0188] The preparation of the negative electrode material includes the following steps:

[0189] (a) The cellulose material containing fibrous structure is alkali washed for 2 hours, then rinsed with water such as deionized water to make the pH of the solution reach 7, and then placed in an acidic solution for acid washing for 2 hours, and then rinsed with water to make the pH of the solution reach 7. Then it is placed in an oven for drying at a temperature of 80°C for 12 hours to obtain the pretreated biomass material.

[0190] (b) The pretreated biomass material (cellulose) obtained in step (a) is placed in an inert atmosphere tube furnace for one calcination. After the first calcination, it is ground in a mortar and sieved to obtain intermediate material.

[0191] (c) Take 2g of the intermediate material obtained in step (b), and put the intermediate material and phenolic resin into two adjacent crucibles at a mass ratio of 1:5, with the crucible containing the phenolic resin placed at the front end. Then transfer the two crucibles to a tube furnace and perform a second calcination in an inert gas atmosphere, wherein the inert gas is nitrogen, the inert gas flow rate is 80mL / min, the heating rate of the second calcination is 15℃ / min, the calcination temperature is 500℃, the calcination time is 2h, and cool to room temperature to obtain the negative electrode material.

[0192] The negative electrode material prepared in Comparative Example 2 is a conventional cellulose-derived hard carbon material with a carbon coating layer.

[0193] Comparative Example 3

[0194] The preparation of the negative electrode material includes the following steps:

[0195] (a) The cellulose material containing fibrous structure is alkali washed for 2 hours, then rinsed with water such as deionized water to make the pH of the solution reach 7, and then placed in an acidic solution for acid washing for 2 hours, and then rinsed with water to make the pH of the solution reach 7. Then it is placed in an oven for drying at a temperature of 80°C for 12 hours to obtain the pretreated biomass material.

[0196] (b) The pretreated biomass material (cellulose) obtained in step (a) is placed in an inert atmosphere tube furnace for one calcination. After the first calcination, it is ground in a mortar and sieved to obtain intermediate material.

[0197] (c) Add 3g of the intermediate material obtained in step (b) and 3g of sodium nitrate to a round-bottom flask. Place the flask in an ice bath, add 375ml of 98% concentrated sulfuric acid, and stir for 2 hours. Add 30g of potassium dichromate and stir for 2 hours, then stir at room temperature for 48 hours. Subsequently, add 750ml of 5% sulfuric acid and stir for 1 hour. The temperature is maintained at 98℃ throughout the mixing process. After stirring, continuously add water and stir to lower the temperature of the mixture to room temperature. Then, separate the solid. Wash the collected solid alternately with 3% dilute H2SO4 and 3% dilute HCl. Then, place the obtained material in deionized water, stir and wash until neutral, and filter. After drying in an 80℃ oven, the material obtained is designated as the biomass sodium ion anode material, i.e., the anode material.

[0198] The negative electrode material prepared in Comparative Example 3 was an uncoated epoxide carbon material.

[0199] Performance testing

[0200] 1. Preparation of sodium-ion batteries

[0201] (1) The negative electrode materials prepared in the above embodiments and comparative examples are used as negative electrode active materials, conductive carbon black (Super P) is used as conductive agent, and sodium carboxymethyl cellulose (CMC) is used as binder.

[0202] The negative electrode active material, binder, and conductive agent are mixed in a mass ratio of 8:1:1 to obtain a mixed material. The mixed material is then thoroughly stirred in deionized water to obtain the corresponding negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector copper foil, and after drying, pressing, and other processes, a negative electrode sheet is obtained.

[0203] (2) Provide a sodium metal sheet as the positive electrode.

[0204] (3) Provide a glass fiber membrane as a separation membrane.

[0205] (4) Provide an electrolyte prepared by dissolving 1.0 mol / L NaPF6 in an organic solvent composed of diethylene glycol dimethyl ether.

[0206] (5) Assemble the negative electrode, separator and positive electrode in the order of negative electrode, separator and positive electrode, and wet them with electrolyte respectively. Assemble the NCF2032 button cell in an argon glove box.

[0207] 2. Perform electrochemical performance testing on the battery.

[0208] GCD tests were performed using the LAND battery testing system within a voltage window of 0.01-2V.

[0209] (1) Initial discharge capacity and initial charge capacity test: Under constant temperature conditions of 25℃, discharge at a constant current of 0.1C to 0.01V and record the discharge capacity at this time = initial discharge capacity; continue charging at a constant current of 0.1C from 0.01V to 2V and record the charging capacity at this time as the initial charge capacity.

[0210] (2) Initial Coulomb efficiency test: Initial Coulomb efficiency = Initial charge capacity / Initial discharge capacity * 100%.

[0211] (3) Capacity retention rate (cycle performance and rate performance) test: Under constant temperature conditions of 25℃, discharge at a constant current rate of 1.0C to 0.01V, and then charge at a constant current rate of 1.0C to 2V. This constitutes one complete charge-discharge cycle, which is recorded as one cycle. Repeat this process until the number of cycles equals 200, at which point the test ends. The charging capacity of the last cycle is the reversible specific capacity. The charging specific capacity of the last cycle / the charging specific capacity of the first cycle = the capacity retention rate after 200 cycles.

[0212] The test results are shown in Table 1 below.

[0213] Table 1

[0214]

[0215] As shown in Table 1, compared to Comparative Examples 1-3, the coin cells prepared using the negative electrode materials provided in Examples 1-10 all exhibit higher initial charge / discharge capacity, higher first-in-stock efficiency, and better cycle performance and rate performance. It should be understood that the current density used in the capacity retention test of this invention is 1.0C, i.e., a high current density is used for testing. The higher capacity retention obtained under this high current density indicates that the negative electrode material of this invention has better rate performance, and further indicates that the negative electrode material exhibits good kinetics.

[0216] Furthermore, a comparative analysis of Examples 1 and 2-10 reveals that the performance of the anode materials prepared using the biomass materials, the specified operating parameters for preparing the hard carbon precursor, the specified operating parameters for preparing the hard carbon material containing epoxy groups, and the specified operating parameters for carbon coating treatment, as defined in this invention, is not significantly different. All materials exhibit high initial charge-discharge capacity, high first-cycle efficiency, and good cycle performance and rate performance. A comparative analysis of Example 1 and Comparative Example 1 shows that the conventional cellulose-derived hard carbon material prepared in Comparative Example 1 lacks oxygen and a carbon coating layer. Consequently, Comparative Example 1 exhibits lower initial charge-discharge capacity and first-cycle efficiency, lower capacity retention after 200 cycles, and poor rate performance.

[0217] The analysis and comparison between Example 1 and Comparative Example 2 show that the conventional cellulose-derived hard carbon material with carbon coating prepared in Comparative Example 2 does not contain oxygen. Therefore, Comparative Example 2 has a lower initial charge-discharge capacity and initial inventory efficiency, a lower capacity retention rate after 200 cycles, and poor rate performance.

[0218] The analysis and comparison between Example 1 and Comparative Example 3 show that the uncoated epoxide carbon material prepared in Comparative Example 3 has lower initial charge-discharge capacity and initial stock efficiency, lower capacity retention after 200 cycles, and poor rate performance.

[0219] in addition, Figure 1 This displays an SEM image of the biomass material provided in Embodiment 1 of the present invention, that is, an electron microscope image of the morphology of the raw material in the embodiment of the present invention. Figure 1 It can be observed that the biomass material used in this invention has a fibrous structure. Figure 2 The SEM image of the negative electrode material provided in Embodiment 1 of the present invention is shown. Figure 2 It can be seen that the negative electrode material (hard carbon material) prepared by this invention retains the fibrous structure of the precursor. Figure 3 The TEM image of the negative electrode material provided in Embodiment 1 of the present invention is shown. Figure 3 It can be seen that the negative electrode material prepared in the embodiments of the present invention has a good coating effect. Figure 4 The XRD patterns of the negative electrode materials provided in Example 1 (epoxy-rich carbon material) and Comparative Example 1 (original carbon material) of the present invention are shown. Figure 4 It can be seen that the 002 characteristic peak of the hard carbon material shifts to a lower angle, which represents an increase in interlayer spacing. In other words, it indicates that the negative electrode material prepared by this invention has a large interlayer spacing. Figure 5 The EDS diagram of the negative electrode material provided in Embodiment 1 of the present invention is shown. Figure 5 This demonstrates the successful doping of oxygen in the negative electrode material of this invention.

[0220] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0221] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0222] It should be noted that the terms "and / or" or " / " used herein are merely descriptions of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The singular forms "a," "described," and "the" used in the embodiments of the invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0223] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0224] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode material, characterized in that, The negative electrode material includes a matrix and a carbon coating layer covering at least a portion of the surface of the matrix; The matrix comprises hard carbon, which is a biomass-based hard carbon material, and the hard carbon contains C and O elements, wherein the atomic ratio of O to C satisfies: O:C = 1:20 to 1:10; The hard carbon has a fibrous pleated structure; The hard carbon contains epoxy groups; The carbon coating layer comprises pyrolytic carbon formed by the thermal decomposition of a polymer. The thickness of the carbon coating layer is 5 nm to 10 nm.

2. The negative electrode material according to claim 1, characterized in that, The atomic ratio of O and C satisfies: O:C = 1:20 to 1:

15.

3. A method for preparing the negative electrode material as described in claim 1 or 2, characterized in that, Includes the following steps: The pretreated biomass material was soaked in a chloride solution and sintered to obtain a hard carbon precursor. The hard carbon precursor is mixed with an acidic solution, and then peroxydisulfate is added. After mixing, separation and drying, a hard carbon material containing epoxy groups is obtained. The hard carbon material containing epoxy groups is subjected to carbon coating treatment to form a carbon coating layer on at least a portion of the surface of the hard carbon, thereby obtaining a negative electrode material.

4. The method for preparing the negative electrode material according to claim 3, characterized in that, The preparation of the pretreated biomass material includes: The biomass material was subjected to alkali washing, water washing, acid washing, water washing and drying in sequence to obtain pretreated biomass material; The concentration of the alkaline solution used in the alkaline washing is 0.5–1 mol / L; The concentration of the acidic solution used for pickling is 0.5–1 mol / L; During the alkaline washing, acid washing, or water washing process, the solid-liquid ratio of biomass and solution is 1:50 to 1:200 g / mL; The drying temperature is 70℃~100℃, and the drying time is 10h~16h; The biomass material has a fibrous structure; The biomass materials include at least one of bamboo, coconut shell, macadamia nut shell, walnut shell, pine nut shell, peanut shell, cotton stalk husk, sugarcane bagasse, reed, bamboo shoots, straw, or coconut husk.

5. The method for preparing the negative electrode material according to claim 3, characterized in that, The step of obtaining the hard carbon precursor satisfies at least one of the following features (1) to (5): (1) The chloride solution includes at least one of sodium chloride solution, potassium chloride solution or chromium chloride solution; (2) The concentration of the chloride solution is 0.05–0.5 mol / L; (3) The solid-liquid ratio of the pretreated biomass material during the soaking process in the chloride solution is 10:1 to 20:1 g / L; (4) The sintering is carried out in an inert gas atmosphere, and the flow rate of the inert gas is 40-80 mL / min; The sintering heating rate is 1-5℃ / min, the sintering temperature is 500-1000℃, and the time is 2-5h. (5) The particle size D50 of the hard carbon precursor is 5μm to 10μm.

6. The method for preparing the negative electrode material according to claim 3, characterized in that, The step of obtaining the hard carbon material containing epoxy groups satisfies at least one of the following characteristics (1) to (4): (1) The ratio of the hard carbon precursor, acidic solution and peroxydisulfate is 100:10000:1 to 100:5000:2, based on g:mL:M. (2) The acidic solution includes concentrated sulfuric acid with a mass fraction of not less than 98%; (3) The peroxydisulfate includes at least one of potassium peroxydisulfate, nickel peroxydisulfate, or cobalt peroxydisulfate; (4) The drying temperature is 70℃~100℃.

7. The method for preparing the negative electrode material according to any one of claims 3 to 6, characterized in that, The carbon coating layer comprises pyrolytic carbon formed by the thermal decomposition of a polymer. The mass ratio of the polymer to the hard carbon material containing epoxy groups is 5:1 to 10:1; The polymer includes at least one of phenolic resin, epoxy resin, acrylic resin, furfural resin, polyethylene, or polypropylene. The carbon coating treatment is carried out by calcination under an inert gas atmosphere; The heating rate of the carbon coating treatment is 1-20℃ / min, the temperature of the carbon coating treatment is 500-700℃, and the time is 1-8h. The thickness of the carbon coating layer is 5 nm to 10 nm.

8. A battery, said battery comprising a negative electrode, characterized in that, The negative electrode sheet comprises the negative electrode material as described in any one of claims 1 to 2; Alternatively, the negative electrode material prepared by the method according to any one of claims 3 to 7.

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