Preparation method of coconut shell-based hard carbon material and sodium ion battery

Abstract

This invention relates to a method for preparing coconut shell-based hard carbon materials and sodium-ion batteries, providing the application of controlling the oxygen content in the material during coconut shell processing to improve the electrochemical performance of coconut shell-based hard carbon materials. This invention also provides a method for pre-treating biomass coconut shells to prepare hard carbon materials. This invention proposes various pre-treatment methods for treating coconut shells as biomass hard carbon precursors to solve problems such as low specific capacity and poor cycle stability of biomass hard carbon. The pre-treatment methods provided by this invention can effectively remove impurities from biomass or effectively improve the cross-linking structure of the coconut shell precursor, providing certain conditions for the subsequent formation of more closed pores. Moreover, the coconut shell precursors used in this invention are low-cost, energy-saving, and environmentally friendly. The processing flow is simple, requiring no complex processes or expensive equipment, is pollution-free, and can be mass-produced, which is conducive to large-scale industrialization and suitable for industrial needs.

Description

Technical Field

[0001] This invention belongs to the technical field of coconut shell-based hard carbon materials, and relates to the application of regulating the oxygen content in the material during the coconut shell processing to improve the electrochemical performance of coconut shell-based hard carbon materials, a method for preparing hard carbon materials from pretreated biomass coconut shells, and sodium-ion batteries, particularly a method for preparing coconut shell-based hard carbon materials and sodium-ion batteries. Background Technology

[0002] Lithium-ion batteries have received continuous attention and research due to their successful application in various portable devices and electric vehicles. However, limited lithium resources have led to a year-on-year increase in the cost of lithium-ion batteries, necessitating the development of other rechargeable batteries to replace them. Sodium ions, belonging to the same group as lithium, have attracted widespread attention due to their similar characteristics, abundant crustal reserves, and low price. Developing high-capacity, high-stability, and high-efficiency anode materials is an unavoidable challenge. Hard carbon anodes, with their high capacity, high efficiency, and high stability, have become the most competitive material for the commercialization of sodium-ion battery anodes. Biomass hard carbon precursors, with their low cost, wide availability, and pollution-free nature, have attracted researchers' attention. Researchers have proposed various precursors, including corn cobs, shrimp shells, camphor wood, nut shells, and grapefruit peels. However, their relatively low specific capacity and low efficiency continue to limit the development of hard carbon.

[0003] Therefore, finding a suitable way to solve the aforementioned problems of biomass hard carbon precursors and further expand the depth and breadth of biomass hard carbon applications is of great significance to the practical application of biomass hard carbon and is also one of the focuses of widespread attention from forward-looking researchers in the industry. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide the application of regulating the oxygen content in the material during the coconut shell processing to improve the electrochemical performance of coconut shell-based hard carbon materials, a method for preparing hard carbon materials by pretreating biomass coconut shells, and a sodium-ion battery. The present invention provides a variety of pretreatment methods to treat biomass hard carbon precursor coconut shells, which can solve the problems of low specific capacity and poor cycle stability of biomass hard carbon.

[0005] This invention provides the application of regulating the oxygen content in coconut shell materials during the processing of coconut shells in improving the electrochemical performance of coconut shell-based hard carbon materials.

[0006] Preferably, the control method includes one or more of the following: hydrothermal pretreatment of coconut shell, low-temperature pretreatment of coconut shell in air atmosphere, low-temperature pretreatment of coconut shell in protective atmosphere, and low-temperature pretreatment of coconut shell in a mixed atmosphere of hydrogen and protective gas.

[0007] The oxygen content includes the oxygen content of the pretreated precursor material and / or the oxygen content in the coconut shell-based hard carbon material.

[0008] Preferably, the temperature of the hydrothermal pretreatment is 100–200°C;

[0009] The hydrothermal pretreatment time is 2–24 hours;

[0010] The temperature for the low-temperature pretreatment in air atmosphere is 100–300°C;

[0011] The time for low-temperature pretreatment in air atmosphere is 1 to 12 hours.

[0012] Preferably, the temperature for the low-temperature pretreatment under a protective atmosphere is 100–300°C;

[0013] The time for low-temperature pretreatment under a protective atmosphere is 1 to 12 hours;

[0014] The temperature for the low-temperature pretreatment in the mixed atmosphere of hydrogen and protective gas is 100–300°C.

[0015] The time for low-temperature pretreatment in a mixed atmosphere of hydrogen and protective gas is 1 to 12 hours.

[0016] Preferably, the protective gas includes nitrogen and / or an inert gas;

[0017] The volume ratio of hydrogen to protective gas in the mixed atmosphere is (5-10):100;

[0018] The electrochemical performance includes one or more of the following: initial charge-discharge coulombic efficiency, specific capacity, and cycle performance.

[0019] Preferably, the pretreatment is a pretreatment process to improve the cross-linking structure of the coconut shell precursor;

[0020] The process also includes a carbonization step after pretreatment;

[0021] The hard carbon material is a hard carbon anode material;

[0022] The negative electrode material includes sodium-ion battery negative electrode materials.

[0023] Preferably, the coconut shell comprises coconut shell powder;

[0024] The particle size of the coconut shell powder is 0.5–50 μm;

[0025] The oxygen content specifically refers to the atomic content of oxygen in the material being 1% to 10%;

[0026] The coconut shell includes coconut shell material that has undergone one or more steps of washing, drying, and crushing.

[0027] This invention provides a method for preparing hard carbon materials from pretreated biomass coconut shells, comprising the following steps:

[0028] 1) After pretreatment, the cleaned coconut shell powder is used to obtain the coconut shell precursor;

[0029] 2) Carbonize the coconut shell precursor obtained in step 1) above to obtain coconut shell-based hard carbon material.

[0030] Preferably, the cleaning includes one or more steps of washing, drying and pulverizing;

[0031] The pretreatment includes one or more of the following: hydrothermal pretreatment, low-temperature pretreatment in an air atmosphere, low-temperature pretreatment in a protective atmosphere, and low-temperature pretreatment in a mixed atmosphere of hydrogen and a protective gas.

[0032] The carbonization temperature is 1000–1600°C;

[0033] The carbonization time is 1 to 12 hours.

[0034] The present invention also provides a sodium-ion battery, the sodium-ion battery comprising a negative electrode material;

[0035] The negative electrode material includes coconut shell-based hard carbon material in any of the above technical solutions or coconut shell-based hard carbon material prepared by any of the above technical solutions.

[0036] This invention provides the application of regulating the oxygen content in coconut shell materials during processing to improve the electrochemical performance of coconut shell-based hard carbon materials. Compared with existing technologies, this invention proposes various pretreatment methods for treating coconut shell precursors of biomass hard carbon to solve problems such as low specific capacity and poor cycle stability of biomass hard carbon. The pretreatment methods provided by this invention can effectively remove impurities from biomass or effectively improve the cross-linking structure of coconut shell precursors, providing certain conditions for the subsequent formation of more closed pores. Moreover, the coconut shell precursors used in this invention are low in cost, energy-saving and environmentally friendly, and the processing flow is simple, requiring no complex processes and expensive equipment. It is pollution-free, can be mass-produced, and is conducive to large-scale industrialization, meeting the needs of industrial applications.

[0037] Experimental results show that the biomass hard carbon anode provided by this invention has a first charge-discharge coulombic efficiency of up to 83%, a specific capacity of up to 314 mAh / g, and stable cycle performance, which can meet the requirements of industrial applications. Attached Figure Description

[0038] Figure 1This is a SEM image of coconut shells after hydrothermal pretreatment and high-temperature carbonization in Example 1 of the present invention;

[0039] Figure 2 This is the XRD pattern of coconut shells after hydrothermal pretreatment and high-temperature carbonization in Example 1 of the present invention;

[0040] Figure 3 This is a charge-discharge curve of the battery assembled after hydrothermal pretreatment and high-temperature carbonization of coconut shell in Embodiment 1 of the present invention.

[0041] Figure 4 This is a cycle curve of the battery assembled after hydrothermal pretreatment and high-temperature carbonization of coconut shell in Example 1 of the present invention.

[0042] Figure 5 This is a SEM image of the coconut shell after air pretreatment and high-temperature carbonization in Example 2 of the present invention;

[0043] Figure 6 This is the XRD pattern of coconut shell after air pretreatment and high-temperature carbonization in Example 2 of the present invention;

[0044] Figure 7 This is a charge-discharge curve of the battery assembled after coconut shell air pretreatment and high-temperature carbonization in Embodiment 2 of the present invention.

[0045] Figure 8 This is a cycle curve of the battery assembled after coconut shell air pretreatment and high-temperature carbonization in Example 2 of the present invention;

[0046] Figure 9 This is a charge-discharge curve of the battery assembled after coconut shell argon pretreatment and high-temperature carbonization in Example 3 of the present invention.

[0047] Figure 10 This is a charge-discharge curve of the battery assembled after coconut shell pretreatment with 5% H2 / Ar and high-temperature carbonization in Example 4 of the present invention. Detailed Implementation

[0048] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims.

[0049] There are no particular restrictions on the source of any raw materials used in this invention; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0050] There are no particular restrictions on the purity of any raw materials used in this invention. However, this invention preferably uses analytical grade or conventional purity used in the field of bio-based hard carbon material preparation.

[0051] This invention provides the application of regulating the oxygen content in coconut shell materials during the processing of coconut shells in improving the electrochemical performance of coconut shell-based hard carbon materials.

[0052] In this invention, the above application can be a method for regulating the oxygen content in materials during coconut shell processing or a method for regulating the electrochemical performance of coconut shell-based hard carbon materials.

[0053] In this invention, the control method preferably includes one or more of the following: hydrothermal pretreatment of coconut shell, low-temperature pretreatment of coconut shell in air atmosphere, low-temperature pretreatment of coconut shell in protective atmosphere, and low-temperature pretreatment of coconut shell in a mixed atmosphere of hydrogen and protective gas. More preferably, it includes multiple of the following: hydrothermal pretreatment of coconut shell, low-temperature pretreatment of coconut shell in air atmosphere, low-temperature pretreatment of coconut shell in protective atmosphere, and low-temperature pretreatment of coconut shell in a mixed atmosphere of hydrogen and protective gas.

[0054] In this invention, the oxygen content preferably includes the oxygen content of the pretreated precursor material and / or the oxygen content in the coconut shell-based hard carbon material, more preferably the oxygen content of the pretreated precursor material or the oxygen content in the coconut shell-based hard carbon material.

[0055] In this invention, the temperature of the hydrothermal pretreatment is preferably 100-200°C, more preferably 120-180°C, and even more preferably 140-160°C.

[0056] In this invention, the hydrothermal pretreatment time is preferably 2 to 24 hours, more preferably 7 to 19 hours, and even more preferably 12 to 14 hours.

[0057] In this invention, the temperature for low-temperature pretreatment in air atmosphere is preferably 100-300°C, more preferably 140-260°C, and even more preferably 180-220°C.

[0058] In this invention, the time for low-temperature pretreatment in air atmosphere is preferably 1 to 12 hours, more preferably 3 to 10 hours, and even more preferably 5 to 7 hours.

[0059] In this invention, the temperature for the low-temperature pretreatment under a protective atmosphere is preferably 100–300°C, more preferably 140–260°C, and even more preferably 180–220°C.

[0060] In this invention, the time for low-temperature pretreatment under a protective atmosphere is preferably 1 to 12 hours, more preferably 3 to 10 hours, and even more preferably 5 to 7 hours.

[0061] In this invention, the temperature for the low-temperature pretreatment in a mixed atmosphere of hydrogen and protective gas is preferably 100-300°C, more preferably 140-260°C, and even more preferably 180-220°C.

[0062] In this invention, the time for low-temperature pretreatment in a mixed atmosphere of hydrogen and protective gas is preferably 1 to 12 hours, more preferably 3 to 10 hours, and even more preferably 5 to 7 hours.

[0063] In this invention, the protective gas preferably includes nitrogen and / or an inert gas, more preferably nitrogen or an inert gas.

[0064] In this invention, the volume ratio of hydrogen to protective gas in the mixed atmosphere is preferably (5-10):100, more preferably (6-9):100, and even more preferably (7-8):100.

[0065] In this invention, the electrochemical performance preferably includes one or more of the following: first charge-discharge coulombic efficiency, specific capacity, and cycle performance, and more preferably the first charge-discharge coulombic efficiency, specific capacity, or cycle performance.

[0066] In this invention, the pretreatment is preferably a pretreatment process that improves the cross-linking structure of the coconut shell precursor.

[0067] In this invention, the processing procedure preferably includes a carbonization step after pretreatment.

[0068] In this invention, the hard carbon material is preferably a hard carbon anode material.

[0069] In this invention, the negative electrode material preferably includes a sodium-ion battery negative electrode material.

[0070] In this invention, the coconut shell preferably comprises coconut shell powder.

[0071] In this invention, the particle size of the coconut shell powder is preferably 0.5-50 μm, more preferably 5-40 μm, and even more preferably 15-30 μm.

[0072] In this invention, the oxygen content specifically refers to the atomic content of oxygen in the material, preferably 1% to 10%, more preferably 3% to 8%, and even more preferably 5% to 6%.

[0073] In this invention, the coconut shell preferably comprises coconut shell material that has undergone one or more steps of washing, drying and crushing.

[0074] This invention provides a method for preparing hard carbon materials from pretreated biomass coconut shells, comprising the following steps:

[0075] 1) After pretreatment, the cleaned coconut shell powder is used to obtain the coconut shell precursor;

[0076] 2) Carbonize the coconut shell precursor obtained in step 1) above to obtain coconut shell-based hard carbon material.

[0077] The present invention first pre-treats the cleaned coconut shell powder to obtain a coconut shell precursor.

[0078] In this invention, the cleaning preferably includes one or more steps of washing, drying and pulverizing, more preferably multiple steps of washing, drying and pulverizing.

[0079] In this invention, the pretreatment preferably includes one or more of the following: hydrothermal pretreatment, low-temperature pretreatment in an air atmosphere, low-temperature pretreatment in a protective atmosphere, and low-temperature pretreatment in a mixed atmosphere of hydrogen and protective gas. More preferably, it includes multiple of the following: hydrothermal pretreatment, low-temperature pretreatment in an air atmosphere, low-temperature pretreatment in a protective atmosphere, and low-temperature pretreatment in a mixed atmosphere of hydrogen and protective gas.

[0080] Finally, the coconut shell precursor obtained in the above steps is carbonized to obtain coconut shell-based hard carbon material.

[0081] In this invention, the carbonization temperature is preferably 1000-1600℃, more preferably 1100-1500℃, and even more preferably 1200-1400℃.

[0082] In this invention, the carbonization time is preferably 1 to 12 hours, more preferably 3 to 10 hours, and even more preferably 5 to 7 hours.

[0083] To complete and refine the overall technical solution and better improve the electrochemical performance of biomass hard carbon, the above-mentioned method for preparing hard carbon materials from pretreated biomass coconut shells may specifically include the following:

[0084] Coconut shell pretreatment is used to prepare hard carbon anode materials. The pretreatment method includes hydrothermal treatment, pre-oxidation, pre-carbonization, and acid-base cleaning, and includes the following steps:

[0085] (1) The waste biomass coconut shells are first rinsed with a large amount of clean water, then dried and crushed, and then added to the reactor for low-temperature pretreatment.

[0086] (2) The waste biomass coconut shells are rinsed with a lot of clean water, dried and crushed, and then pretreated at low temperature in the air.

[0087] (3) The waste biomass coconut shells are rinsed with a large amount of clean water, dried and crushed, and then pretreated at low temperature in argon gas.

[0088] (4) The waste biomass coconut shells are rinsed with a large amount of clean water, dried and crushed, and then pretreated at low temperature in an argon-hydrogen mixture.

[0089] (5) The precursors obtained by pretreatment in step (1) or (2) or (3) or (4) are carbonized in a high-temperature tube furnace to obtain hard carbon anodes with different pretreatments.

[0090] Specifically, different pretreatment methods control the oxygen content in carbon materials, keeping it within a specific range of 1-10% (atomic ratio), thereby improving the initial charge-discharge coulombic efficiency and specific capacity.

[0091] Specifically, the temperature of the hydrothermal reaction in (1) is 150 to 200 degrees Celsius. Specifically, coconut shell powder is placed in a Teflon reactor, an appropriate amount of deionized water is added, the temperature is raised from room temperature to 150 to 200 degrees Celsius, and the temperature is maintained for 2 to 24 hours.

[0092] Specifically, in step (2), the pre-carbonization temperature in the air is 100-300°C. Specifically, the coconut shell powder is placed in a corundum ceramic boat in a muffle furnace and heated from room temperature to 100-300°C for 1-12 hours.

[0093] Specifically, the pre-carbonization temperature in (3) is 100-300℃. Specifically, the coconut shell powder is placed in a corundum ceramic boat in a tube furnace, and under the protection of argon, the temperature is raised from room temperature to 100-300℃ and kept at that temperature for 1-12 hours.

[0094] Specifically, in step (4), the pre-carbonization temperature of the argon-hydrogen mixture (5-10% H2 / Ar) is 100-300 degrees Celsius. Specifically, the coconut shell powder is placed in a corundum ceramic boat in a tube furnace, and under the protective atmosphere of the argon-hydrogen mixture, the temperature is raised from room temperature to 100-300 degrees Celsius and held for 1-12 hours.

[0095] Furthermore, the method for pretreating biomass coconut shells may also include the following steps:

[0096] (1) Put a certain amount of coconut shell powder into a Teflon reactor and add a certain proportion of deionized water. Then, heat it in a forced-air oven for a certain period of time.

[0097] (2) Place a certain amount of coconut shell powder in a corundum porcelain boat and place it in a muffle furnace for low-temperature carbonization for a period of time.

[0098] (3) Place a certain amount of coconut shell powder in a corundum ceramic boat and place it in a tube furnace for low-temperature carbonization for a period of time, during which argon gas is introduced as a protective gas.

[0099] (4) Place a certain amount of coconut shell powder in a corundum ceramic boat and place it in a tube furnace for low-temperature carbonization for a period of time, during which argon-hydrogen mixture is introduced as a protective gas.

[0100] (5) Place the pretreated coconut shell powder obtained in (1) or (2) or (3) or (4) in a tube furnace and carbonize it at high temperature for a period of time.

[0101] Specifically, the hydrothermal temperature in step (1) is 100-200℃.

[0102] Specifically, in step (2), the pre-carbonization temperature is 100-300℃ and the pre-carbonization time is 1-12h.

[0103] Specifically, in step (3), the pre-carbonization temperature is 100-300℃ and the pre-carbonization time is 1-12h.

[0104] Specifically, in step (4), the pre-carbonization temperature is 100-300℃ and the pre-carbonization time is 1-12h.

[0105] Specifically, in step (5), the carbonization temperature is 1000-1600℃ and the carbonization time is 1-12h.

[0106] The present invention also provides a sodium-ion battery, wherein the sodium-ion battery includes a negative electrode material.

[0107] The negative electrode material includes coconut shell-based hard carbon material in any of the above technical solutions or coconut shell-based hard carbon material prepared by any of the above technical solutions.

[0108] This invention provides the application of regulating the oxygen content in coconut shell processing to improve the electrochemical performance of coconut shell-based hard carbon materials, a method for preparing hard carbon materials from pretreated biomass coconut shells, and a sodium-ion battery. This invention proposes various pretreatment methods for treating coconut shell precursors of biomass hard carbon to address problems such as low specific capacity and poor cycle stability. The pretreatment methods provided by this invention can effectively remove impurities from biomass or effectively improve the cross-linking structure of the coconut shell precursor, providing conditions for the subsequent formation of more closed pores. Furthermore, the coconut shell precursors used in this invention are low-cost, energy-saving, and environmentally friendly. The processing flow is simple, requiring no complex processes or expensive equipment, is pollution-free, and can be mass-produced, facilitating large-scale industrialization and meeting industrial needs.

[0109] Experimental results show that the biomass hard carbon anode provided by this invention has a first charge-discharge coulombic efficiency of up to 83%, a specific capacity of up to 314 mAh / g, and stable cycle performance, which can meet the requirements of industrial applications.

[0110] To further illustrate the present invention, the following embodiments are provided to describe in detail the application of the present invention in improving the electrochemical performance of coconut shell-based hard carbon materials by regulating the oxygen content in the coconut shell processing process, a method for preparing hard carbon materials from pretreated biomass coconut shells, and sodium-ion batteries. However, it should be understood that these embodiments are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are given only to further illustrate the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention. The scope of protection of the present invention is not limited to the following embodiments.

[0111] Example 1

[0112] Waste biomass coconut shells were crushed and washed, then dried in an oven. The dried coconut shells were placed in a reaction vessel, and a certain amount of deionized water was added. After sealing, the vessel was placed in a forced-air oven and heated from room temperature to 200°C for 12 hours to obtain a pretreated coconut shell precursor. After natural cooling, the precursor was centrifuged, filtered, washed, and dried. The dried particles were placed in a corundum ceramic boat and transferred to a tube furnace under argon protection. The temperature was raised from room temperature to 1300°C and held for 2 hours. After cooling to room temperature, the final product was obtained.

[0113] See Figure 1 , Figure 1 This is a SEM image of coconut shells after hydrothermal pretreatment and high-temperature carbonization in Example 1 of the present invention.

[0114] See Figure 2 , Figure 2 The image shows the XRD pattern of coconut shells after hydrothermal pretreatment and high-temperature carbonization in Example 1 of this invention.

[0115] Product SEM, such as Figure 1 As shown, XRD is as follows Figure 2 As shown, a hard carbon negative electrode, conductive agent, and binder were mixed evenly in water at a mass ratio of 94:2:4, and coated onto copper foil. After vacuum drying, the mixture was cut to obtain electrode sheets. Using metallic sodium as the counter electrode, 1M NaPF6 EC DMC (1:1) electrolyte, and Whatman glass fiber as the separator, a 2032 battery was assembled. The test was conducted using a Newway battery testing system under the following conditions: charge / discharge current 30mA / g, voltage range 0.01–2.5V vs Na / Na + .

[0116] See Figure 3 , Figure 3 This is a charge-discharge curve of the battery assembled after hydrothermal pretreatment and high-temperature carbonization of coconut shells in Example 1 of the present invention.

[0117] See Figure 4 , Figure 4This is a cycle curve of the battery assembled after hydrothermal pretreatment and high-temperature carbonization of coconut shells in Example 1 of the present invention.

[0118] The initial charge-discharge curve is as follows Figure 3 As shown, the specific capacity is 296 mAh / g, and the initial charge / discharge efficiency is 83%; the cycle performance is as follows. Figure 4 As shown, after 100 cycles, there is still 85% capacity retention.

[0119] Example 2

[0120] Waste biomass coconut shells were crushed and washed, then dried in an oven. The dried coconut shells were placed in a corundum ceramic boat and kept at a constant temperature of 200°C for 6 hours in a muffle furnace to obtain an air-pretreated coconut shell precursor. The ground particles were placed in a corundum ceramic boat and transferred to a tube furnace protected by argon gas. The temperature was raised from room temperature to 1300°C and held for 2 hours. After cooling to room temperature, the final product was obtained.

[0121] See Figure 5 , Figure 5 This is a SEM image of the coconut shell after air pretreatment and high-temperature carbonization in Example 2 of the present invention.

[0122] See Figure 6 , Figure 6 This is the XRD pattern of coconut shell after air pretreatment and high-temperature carbonization in Example 2 of the present invention.

[0123] The reagents were mixed evenly in water at a mass ratio of 94:2:4 and coated onto copper foil. After vacuum drying, the electrode sheets were cut to obtain electrode plates. Using metallic sodium as the counter electrode, 1M NaPF6 EC DMC (1:1) electrolyte, and Whatman glass fiber as the separator, a 2032 battery was assembled. The battery was tested using a Newway battery testing system under the following conditions: charge / discharge current 30mA / g, voltage range 0.01-2.5V vsNa / Na + .

[0124] See Figure 7 , Figure 7 This is a charge-discharge curve of the battery assembled after coconut shell air pretreatment and high-temperature carbonization in Example 2 of the present invention.

[0125] See Figure 8 , Figure 8 This is a cycle curve of the battery assembled after coconut shell air pretreatment and high-temperature carbonization in Example 2 of the present invention.

[0126] The initial charge-discharge curve is as follows Figure 7 As shown, the specific capacity is 314 mAh / g, and the initial charge / discharge efficiency is 83%; the cycle performance is as follows. Figure 8 As shown, after 100 cycles, there is still 86% capacity retention.

[0127] Example 3

[0128] Waste biomass coconut shells were crushed and washed, then dried in an oven. The dried coconut shells were placed in a corundum ceramic boat and kept at a constant temperature of 200℃ for 6 hours in a tube furnace with argon gas as a protective gas to obtain a pretreated coconut shell precursor. The ground particles were placed in a corundum ceramic boat and transferred to a tube furnace with argon protection. The temperature was raised from room temperature to 1300℃ and held for 2 hours. After cooling to room temperature, the final product was obtained.

[0129] Hard carbon negative electrode, conductive agent, and binder were mixed evenly in water at a mass ratio of 94:2:4 and coated onto copper foil. The mixture was then vacuum dried and cut to obtain electrode sheets. Using metallic sodium as the counter electrode, 1M NaPF6 EC DMC (1:1) electrolyte, and Whatman glass fiber as the separator, a 2032 battery was assembled. The battery was tested using a Newway battery testing system under the following conditions: charge / discharge current 30mA / g, voltage range 0.01-2.5V vs Na / Na + .

[0130] See Figure 9 , Figure 9 This is a charge-discharge curve of the battery assembled after coconut shell argon pretreatment and high-temperature carbonization in Example 3 of the present invention.

[0131] The initial charge-discharge curve is as follows Figure 9 As shown, the specific capacity is 305mAh / g, and the initial charge / discharge efficiency is 78%.

[0132] Example 4

[0133] Waste biomass coconut shells were crushed and washed, then dried in an oven. The dried coconut shells were placed in a corundum ceramic boat and kept at a constant temperature of 200℃ for 6 hours in a tube furnace, with an argon-hydrogen mixture (5% hydrogen) as a protective gas, to obtain a pretreated coconut shell precursor. The ground particles were placed in a corundum ceramic boat and transferred to a tube furnace with argon protection. The temperature was raised from room temperature to 1300℃ and held for 2 hours. After cooling to room temperature, the final product was obtained.

[0134] Hard carbon negative electrode, conductive agent, and binder were mixed evenly in water at a mass ratio of 94:2:4 and coated onto copper foil. The mixture was then vacuum dried and cut to obtain electrode sheets. Using metallic sodium as the counter electrode, 1M NaPF6 EC DMC (1:1) electrolyte, and Whatman glass fiber as the separator, a 2032 battery was assembled. The battery was tested using a Newway battery testing system under the following conditions: charge / discharge current 30mA / g, voltage range 0.01-2.5V vs Na / Na + .

[0135] See Figure 10 , Figure 10 This is a charge-discharge curve of the battery assembled after coconut shell pretreatment with 5% H2 / Ar and high-temperature carbonization in Example 4 of the present invention.

[0136] The initial charge-discharge curve is as follows Figure 10 As shown, the specific capacity is 326mAh / g, and the initial charge / discharge efficiency is 81%.

[0137] Example 5

[0138] Waste biomass coconut shells were crushed and washed, then dried in an oven. The dried coconut shells were placed in a beaker and soaked and stirred in 1M NaOH solution for 12 hours. After filtration and washing, 1M HCl was added and soaked and stirred for 12 hours. After filtration, washing, and drying, a pretreated coconut shell precursor was obtained. The ground particles were placed in a corundum ceramic boat and transferred to a tube furnace protected by argon. The temperature was raised from room temperature to 1300℃ and held for 2 hours. After cooling to room temperature, the final product was obtained.

[0139] The above provides a detailed description of the application of the present invention in regulating the oxygen content in the coconut shell processing process to improve the electrochemical performance of coconut shell-based hard carbon materials, a method for preparing hard carbon materials from pretreated biomass coconut shells, and sodium-ion batteries. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The above descriptions of the embodiments are only for the purpose of helping to understand the method and core ideas of the present invention, including the best mode, and also to enable any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention. The scope of protection of this patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements that are not different from the textual description of the claims, or if they include equivalent structural elements that are not substantially different from the textual description of the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. Use of regulating oxygen content of a material in a pretreatment step in a coconut shell treatment process in improving electrochemical performance of a coconut shell-based hard carbon material. The method of regulating comprises one or more of hydrothermal pretreatment of the coconut shell, low-temperature pretreatment of the coconut shell in an air atmosphere, low-temperature pretreatment of the coconut shell in a protective atmosphere, and low-temperature pretreatment of the coconut shell in a mixed atmosphere of hydrogen and a protective gas. The oxygen content comprises oxygen content of the precursor material after pretreatment and / or oxygen content in the coconut shell-based hard carbon material. The pretreatment is a pretreatment process for improving cross-linking structure of the coconut shell precursor.

2. Use according to claim 1, characterized in that, The hydrothermal pretreatment has a temperature of 100-200℃. The hydrothermal pretreatment has a time of 2-24h.

3. Use according to claim 1, characterized in that, The low-temperature pretreatment in the air atmosphere has a temperature of 100-300℃. The low-temperature pretreatment in the air atmosphere has a time of 1-12h.

4. Use according to claim 2, characterized in that, The low-temperature pretreatment in the protective atmosphere has a temperature of 100-300℃. The low-temperature pretreatment in the protective atmosphere has a time of 1-12h. The low-temperature pretreatment in the mixed atmosphere of hydrogen and a protective gas has a temperature of 100-300℃. The low-temperature pretreatment in the mixed atmosphere of hydrogen and a protective gas has a time of 1-12h.

5. Use according to claim 4, characterized in that, The protective gas comprises nitrogen and / or an inert gas. The mixed atmosphere has a volume ratio of hydrogen to the protective gas of (5-10):

100. The electrochemical performance comprises one or more of initial charge-discharge coulombic efficiency, specific capacity, and cycle performance.

6. Use according to claim 2, characterized in that, The treatment process further comprises a carbonization step after the pretreatment. The hard carbon material is a hard carbon negative electrode material. The negative electrode material comprises a sodium-ion battery negative electrode material.

7. The use according to claim 1, characterized in that, The coconut shell comprises coconut shell powder. The coconut shell powder has a particle size of 0.5-50μm. The oxygen content specifically refers to atomic content of oxygen in the material being 1%-10%. The coconut shell comprises one or more steps of coconut shell material after cleaning, drying, and crushing.

8. The use according to claim 1, characterized in that, The coconut shell treatment process comprises the following steps: 1) obtaining a coconut shell precursor by pretreating cleaned coconut shell powder; 2) obtaining a coconut shell-based hard carbon material by carbonizing the coconut shell precursor obtained in step 1).

9. Use according to claim 8, characterized in that, The cleaning comprises one or more steps of cleaning, drying, and crushing. The carbonization has a temperature of 1000-1600℃. The carbonization has a time of 1-12h.

10. A sodium-ion battery, characterized in that, The sodium-ion battery comprises a negative electrode material. The negative electrode material comprises the coconut shell-based hard carbon material in the use according to any one of claims 1-9.

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