Biomass charcoal-coated manganese-based material and preparation and application thereof

Abstract

The application discloses a biomass charcoal-coated manganese-based material and a preparation and application thereof. The biomass charcoal material is prepared by taking nut shells as a carbon source and through alkali solution etching and high-temperature heat treatment; the biomass charcoal-coated MnO2 positive electrode material is prepared by taking potassium permanganate as a manganese source and through one-step hydrothermal reaction and heat treatment. The thin carbon layer on the surface of the material can effectively improve the poor conductivity and dissolution of the MnO2. The electrochemical results show that the zinc ion battery assembled by using the biomass charcoal-coated MnO2 positive electrode material has a specific capacity of 292.9 mA / g after stable circulation for 50 times at a current density of 100 mA / g, which is 3 times of that of the uncoated MnO2 positive electrode (specific capacity: 92.5 mA / g).

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and more specifically, to a biochar-coated manganese-based material and its preparation and application. Background Technology

[0002] Over the past few decades, industries such as consumer electronics and electric vehicles have experienced rapid development, presenting many new challenges to the existing energy storage device field and making the development of new high-performance energy storage devices even more urgent. Aqueous zinc-ion batteries have advantages such as safety and environmental friendliness. Currently, their cathode materials are mainly composed of Prussian blue analogues, vanadium-based oxides, organic compounds, and manganese-based oxides. Among them, manganese oxides have been extensively studied due to their diverse crystal structures (α-MnO2, β-MnO2, γ-MnO2, MnO, Mn3O4, etc.) and high theoretical specific capacity. However, Mn... 2+ Problems such as dissolution and poor conductivity of MnO2 limit further improvement in the performance of zinc ions in manganese-based aqueous systems.

[0003] To address the aforementioned issues, we have invented a biochar-coated manganese-based aqueous zinc-ion battery cathode material. Biochar material refers to a stable physicochemical property and carbon content obtained from the ultra-high temperature pyrolysis of biomass under anaerobic or oxygen-deficient conditions. It contains abundant carbon and plant nutrients, possesses a rich porous structure, a large specific surface area, and numerous oxygen-containing active groups, making it a multifunctional material.

[0004] The biochar-coated MnO2 material obtained in this invention has the following advantages: by coating the surface of MnO2 grains with a uniform thin carbon layer, the poor conductivity of MnO2 is effectively improved. Furthermore, the carbon layer effectively suppresses the dissolution of MnO2 in the electrolyte and simultaneously provides channels for ion insertion and extraction. Therefore, it significantly improves the capacity and rate performance of the cathode material and enhances its cycle stability.

[0005] Meanwhile, this invention discloses three complete technical contents: a method for preparing biochar materials using nut shells as a carbon source, a method for preparing biochar-coated MnO2 materials, and the electrochemical performance of biochar-coated MnO2 cathodes. Because this technology is low-cost, simple in procedure, and has significant modification effects, it has good production advantages and can be efficiently applied in industry. Summary of the Invention

[0006] To address the problems in existing technologies, the present invention aims to provide a biochar-coated manganese-based material, its preparation method, and its application. This material mainly comprises two parts: the preparation of biochar and the preparation of biochar-coated MnO2. By uniformly covering the surface of MnO2 particles with biochar to form a carbon coating layer, this material effectively improves the poor conductivity and solubility of MnO2, significantly enhancing battery capacity and cycle stability.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing biochar-coated manganese-based materials includes the following steps:

[0009] (1) Using crushed nut shells as a carbon source, the biochar precursor is obtained by etching through hydrothermal reaction with alkaline solution and drying; biochar material is obtained by heat treatment under a protective atmosphere.

[0010] (2) Using potassium permanganate as the manganese source, biochar is uniformly coated on the surface of the product through hydrothermal reaction, and then dried and heat-treated to obtain biochar-coated manganese-based material.

[0011] The nut shells mentioned include at least one of the following: pistachio, walnut, hazelnut, almond, and pine nut shells.

[0012] Step (1) The mixed suspension of nut shell fragments and inorganic alkaline solution is subjected to hydrothermal reaction. The product is washed, filtered, dried and then heat-treated at high temperature under argon atmosphere to obtain biochar material.

[0013] The inorganic base includes at least one of potassium hydroxide and sodium hydroxide.

[0014] The concentration of the inorganic alkaline solution is 1.5–4.5 M, preferably 2.5–3.5 M.

[0015] The amount of the added fruit shell fragments is 1-3g, preferably 1.0-1.5g.

[0016] The hydrothermal reaction synthesis temperature is 130–170℃, preferably 150℃; the holding time is 4–8h, preferably 6h.

[0017] The heat treatment temperature is 600-850℃, preferably 800℃; the heating rate is 5℃ / min; and the holding time is 1-3h, preferably 2h.

[0018] The preferred method for preparing the biochar material in step (1) of this invention includes the following steps:

[0019] 1) After washing the shells of nuts, process them into fragments (length: 0.2cm, width: 0.2cm, thickness: 0.05cm) and dry them in a 60℃ oven for later use;

[0020] 2) Dissolve the inorganic alkali powder in deionized water and sonicate until completely dissolved to prepare an alkali solution;

[0021] 3) At room temperature, add the fruit shell fragments to 70 mL of alkaline solution and stir for 30 min to obtain a fruit shell suspension;

[0022] 4) Transfer the suspension to a stainless steel reactor with a polytetrafluoroethylene liner (100 mL) for a one-step hydrothermal reaction;

[0023] 5) After the reaction process is complete, the suspension is centrifuged, washed three times with water and ethanol respectively, and dried at 60℃ for 24h to obtain the biochar precursor;

[0024] 6) The precursor is placed in a quartz boat and heat-treated in an argon atmosphere in a tube furnace to obtain biochar material.

[0025] In step (2) of this invention:

[0026] The concentration of the potassium permanganate solution is 0.03-0.05M.

[0027] The amount of biochar powder added shall not exceed 5% of the solution mass, preferably 3%.

[0028] The hydrothermal reaction synthesis temperature is 130–170℃, preferably 150℃; the holding time is 4–8h, preferably 6h.

[0029] The heat treatment temperature is 200-400℃, preferably 350℃; the heating rate is 5℃ / min; and the holding time is 1-3h, preferably 2h.

[0030] The preparation process of biochar-coated MnO2 material in step (2) of this invention preferably includes the following steps:

[0031] 1) Dissolve potassium permanganate in deionized water and sonicate until completely dissolved to prepare a homogeneous solution;

[0032] 2) At room temperature, add biochar powder to 50 mL of potassium permanganate solution and stir for 30 min to obtain a grayish-purple suspension.

[0033] 3) Transfer the suspension to a stainless steel reactor with a polytetrafluoroethylene liner (100 mL) for a one-step hydrothermal reaction;

[0034] 4) After the reaction is complete, the suspension is centrifuged and then washed three times with water and ethanol respectively. It is then dried at 60°C for 24 hours to obtain biochar-coated MnO(OH) (basic manganese oxide) powder.

[0035] 5) Place biochar-coated MnO(OH) powder in a quartz boat and heat-treat it in an air atmosphere in a muffle furnace to obtain biochar-coated MnO2 material.

[0036] This invention also provides a biochar coated with manganese-based materials prepared by the method. The biochar of this invention has a loose texture and a porous structure.

[0037] Furthermore, the specific surface area of ​​biochar materials is 5–9 m². 2 / g, with a pore size of 10–30 nm.

[0038] This invention also provides the application of the aforementioned biochar-coated manganese-based material in the preparation of battery cathode materials, particularly for the preparation of aqueous zinc-ion battery cathode materials.

[0039] Furthermore, the following steps are taken to prepare the zinc-ion battery cathode sheet:

[0040] 1) Biochar-coated MnO2 material, acetylene black and polyvinylidene fluoride are mixed evenly in a ratio of 7:2:1, and then coated evenly on stainless steel foil after being prepared into a paste with N-methylpyrrolidone.

[0041] 2) Dry in a vacuum oven at 100°C for 12 hours.

[0042] The testing methods for the electrochemical performance of electrode materials are as follows:

[0043] 1) The simulated battery adopts the CR2025 button cell system, the electrolyte is a mixed aqueous solution of 1M zinc sulfate and 0.3M manganese sulfate, the negative electrode is a circular zinc sheet, and the battery separator is glass fiber.

[0044] 2) The reversible capacity and cycle performance of the electrode material were tested and analyzed using constant current charge and discharge. The charge and discharge regime was as follows: voltage range: 0.8 to 1.8V; cycle number: generally 1 to 1000 times.

[0045] Due to the implementation of the above technical solutions, the present invention has the following advantages compared with the prior art:

[0046] The biochar-coated MnO2 material obtained in this invention effectively improves the poor conductivity of MnO2 by uniformly coating a thin carbon layer on the surface of MnO2 grains. Furthermore, the carbon layer effectively suppresses the dissolution of MnO2 in the electrolyte and simultaneously provides channels for ion insertion and extraction, making it particularly suitable for zinc-ion batteries. Therefore, it significantly improves the capacity and rate performance of the cathode material and enhances its cycle stability. Attached Figure Description

[0047] Figure 1 This is a comparison chart of the electrochemical performance of the materials prepared in Example 1 and Comparative Example 1.

[0048] Figure 2 The images show the XRD patterns of the products prepared in each stage of Example 1.

[0049] Figure 3 The image shows a SEM image of the biochar prepared in Example 1.

[0050] Figure 4 The image shows a SEM image of the biochar coated with MnO2 prepared in Example 1.

[0051] Figure 5 This is a TEM image of the biochar coated with MnO2 prepared in Example 1. Detailed Implementation

[0052] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The specific embodiments described herein are only for explaining the present invention and do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0053] Example 1

[0054] A method for preparing a biochar-coated manganese-based aqueous zinc-ion battery cathode material includes the following steps:

[0055] Step 1: After washing the pistachio shells, use a knife to process the outer shells into pieces (length: 0.2cm, width: 0.2cm, thickness: 0.05cm), and place them in a 60℃ oven to dry for later use;

[0056] Step 2: At room temperature, add 1.0g of fruit shell fragments to 70mL of 3M potassium hydroxide solution and stir for 30min to obtain a fruit shell suspension;

[0057] Step 3: Transfer the suspension to a stainless steel reactor with a polytetrafluoroethylene liner (100 mL), and hydrothermally react at 150°C for 6 h. After cooling, centrifuge the suspension, wash it three times with water and ethanol respectively, and dry it at 60°C for 24 h to obtain the biochar precursor.

[0058] Step 4: Place the precursor in a quartz boat and heat it to 800°C in an argon atmosphere in a tube furnace at a heating rate of 5°C / min. Hold the temperature for 2 hours and then cool to obtain the biochar material.

[0059] Step 5: At room temperature, add 0.15g of biochar powder to 50mL of 0.04M potassium permanganate solution and stir for 30min to obtain a grayish-purple suspension.

[0060] Step 6: Transfer the suspension to a stainless steel reactor with a polytetrafluoroethylene liner (100 mL), and hydrothermally react at 150 °C for 6 h. After cooling, centrifuge the suspension, wash it three times with water and ethanol respectively, and dry it at 60 °C for 24 h to obtain biochar-coated MnO(OH) powder.

[0061] Step 7: Place the biochar-coated MnO(OH) powder in a quartz boat, heat it to 350°C in an air atmosphere in a muffle furnace at a heating rate of 5°C / min, hold it at that temperature for 2 hours, and then cool it to obtain the biochar-coated MnO2 material.

[0062] To verify the electrochemical performance of the biochar-coated MnO2 cathode material, it was further assembled into a battery application: a CR2025 coin cell system was used, with a 1M zinc sulfate and 0.3M manganese sulfate mixed aqueous solution as the electrolyte, a circular zinc sheet as the negative electrode, and glass fiber as the battery separator. Constant current charge-discharge testing was conducted, with a voltage range of 0.8–1.8V. Electrochemical performance testing showed a capacity of 292.9 mA / g after 50 cycles at a current density of 100 mA / g.

[0063] Example 2

[0064] A method for preparing a biochar-coated manganese-based aqueous zinc-ion battery cathode material includes the following steps:

[0065] Step 1: After washing the pistachio shells, use a knife to process the outer shells into pieces (length: 0.2cm, width: 0.2cm, thickness: 0.05cm), and place them in a 60℃ oven to dry for later use;

[0066] Step 2: At room temperature, add 1.0g of fruit shell fragments to 70mL of 3M potassium hydroxide solution and stir for 30min to obtain a fruit shell suspension;

[0067] Step 3: Transfer the suspension to a stainless steel reactor with a polytetrafluoroethylene liner (100 mL), and hydrothermally react at 150°C for 6 h. After cooling, centrifuge the suspension, wash it three times with water and ethanol respectively, and dry it at 60°C for 24 h to obtain the biochar precursor.

[0068] Step 4: Place the precursor in a quartz boat and heat it to 800°C in an argon atmosphere in a tube furnace at a heating rate of 5°C / min. Hold the temperature for 2 hours and then cool to obtain the biochar material.

[0069] Step 5: At room temperature, add 0.10g of biochar powder to 50mL of 0.04M potassium permanganate solution and stir for 30min to obtain a grayish-purple suspension.

[0070] Step 6: Transfer the suspension to a stainless steel reactor with a polytetrafluoroethylene liner (100 mL), and hydrothermally react at 150 °C for 6 h. After cooling, centrifuge the suspension, wash it three times with water and ethanol respectively, and dry it at 60 °C for 24 h to obtain biochar-coated MnO(OH) powder.

[0071] Step 7: Place the biochar-coated MnO(OH) powder in a quartz boat, heat it to 350°C in an air atmosphere in a muffle furnace at a heating rate of 5°C / min, hold it at that temperature for 2 hours, and then cool it to obtain the biochar-coated MnO2 material.

[0072] To verify the electrochemical performance of the biochar-coated MnO2 cathode material, it was further assembled into a battery application: a CR2025 coin cell system was used, with a 1M zinc sulfate and 0.3M manganese sulfate mixed aqueous solution as the electrolyte, a circular zinc sheet as the negative electrode, and glass fiber as the battery separator. Constant current charge-discharge testing was conducted, with a voltage range of 0.8–1.8V. Electrochemical performance testing showed that after 50 cycles at a current density of 100 mA / g, the capacity reached 169.2 mA / g.

[0073] Example 3

[0074] A method for preparing a biochar-coated manganese-based aqueous zinc-ion battery cathode material includes the following steps:

[0075] Step 1: After washing the pistachio shells, use a knife to process the outer shells into pieces (length: 0.2cm, width: 0.2cm, thickness: 0.05cm), and place them in a 60℃ oven to dry for later use;

[0076] Step 2: At room temperature, add 1.0g of fruit shell fragments to 70mL of 3M potassium hydroxide solution and stir for 30min to obtain a fruit shell suspension;

[0077] Step 3: Transfer the suspension to a stainless steel reactor with a polytetrafluoroethylene liner (100 mL), and hydrothermally react at 150°C for 6 h. After cooling, centrifuge the suspension, wash it three times with water and ethanol respectively, and dry it at 60°C for 24 h to obtain the biochar precursor.

[0078] Step 4: Place the precursor in a quartz boat and heat it to 800°C in an argon atmosphere in a tube furnace at a heating rate of 5°C / min. Hold the temperature for 2 hours and then cool to obtain the biochar material.

[0079] Step 5: At room temperature, add 0.20g of biochar powder to 50mL of 0.04M potassium permanganate solution and stir for 30min to obtain a grayish-purple suspension.

[0080] Step 6: Transfer the suspension to a stainless steel reactor with a polytetrafluoroethylene liner (100 mL), and hydrothermally react at 150 °C for 6 h. After cooling, centrifuge the suspension, wash it three times with water and ethanol respectively, and dry it at 60 °C for 24 h to obtain biochar-coated MnO(OH) powder.

[0081] Step 7: Place the biochar-coated MnO(OH) powder in a quartz boat, heat it to 350°C in an air atmosphere in a muffle furnace at a heating rate of 5°C / min, hold it at that temperature for 2 hours, and then cool it to obtain the biochar-coated MnO2 material.

[0082] To verify the electrochemical performance of the biochar-coated MnO2 cathode material, it was further assembled into a battery application: a CR2025 coin cell system was used, with a 1M zinc sulfate and 0.3M manganese sulfate mixed aqueous solution as the electrolyte, a circular zinc sheet as the negative electrode, and glass fiber as the battery separator. Constant current charge-discharge testing was conducted, with a voltage range of 0.8–1.8V. Electrochemical performance testing showed that after 50 cycles at a current density of 100 mA / g, the capacity reached 162.6 mA / g.

[0083] Example 4

[0084] A method for preparing a biochar-coated manganese-based aqueous zinc-ion battery cathode material includes the following steps:

[0085] Step 1: After washing the pistachio shells, use a knife to process the outer shells into pieces (length: 0.2cm, width: 0.2cm, thickness: 0.05cm), and place them in a 60℃ oven to dry for later use;

[0086] Step 2: At room temperature, add 1.0g of fruit shell fragments to 70mL of 3M potassium hydroxide solution and stir for 30min to obtain a fruit shell suspension;

[0087] Step 3: Transfer the suspension to a stainless steel reactor with a polytetrafluoroethylene liner (100 mL), and hydrothermally react at 150°C for 6 h. After cooling, centrifuge the suspension, wash it three times with water and ethanol respectively, and dry it at 60°C for 24 h to obtain the biochar precursor.

[0088] Step 4: Place the precursor in a quartz boat and heat it to 800°C in an argon atmosphere in a tube furnace at a heating rate of 5°C / min. Hold the temperature for 2 hours and then cool to obtain the biochar material.

[0089] Step 5: At room temperature, add 0.25g of biochar powder to 50mL of 0.04M potassium permanganate solution and stir for 30min to obtain a grayish-purple suspension.

[0090] Step 6: Transfer the suspension to a stainless steel reactor with a polytetrafluoroethylene liner (100 mL), and hydrothermally react at 150 °C for 6 h. After cooling, centrifuge the suspension, wash it three times with water and ethanol respectively, and dry it at 60 °C for 24 h to obtain biochar-coated MnO(OH) powder.

[0091] Step 7: Place the biochar-coated MnO(OH) powder in a quartz boat, heat it to 350°C in an air atmosphere in a muffle furnace at a heating rate of 5°C / min, hold it at that temperature for 2 hours, and then cool it to obtain the biochar-coated MnO2 material.

[0092] To verify the electrochemical performance of the biochar-coated MnO2 cathode material, it was further assembled into a battery application: a CR2025 coin cell system was used, with a 1M zinc sulfate and 0.3M manganese sulfate mixed aqueous solution as the electrolyte, a circular zinc sheet as the negative electrode, and glass fiber as the battery separator. Constant current charge-discharge testing was conducted, with a voltage range of 0.8–1.8V. Electrochemical performance testing showed that after 50 cycles at a current density of 100 mA / g, the capacity reached 172.6 mA / g.

[0093] Example 5

[0094] A method for preparing a biochar-coated manganese-based aqueous zinc-ion battery cathode material includes the following steps:

[0095] Step 1: After washing the macadamia nut shells, use a knife to process the outer shells into pieces (length: 0.2cm, width: 0.2cm, thickness: 0.05cm), and place them in a 60℃ oven to dry for later use;

[0096] Step 2: At room temperature, add 1.0g of fruit shell fragments to 70mL of 3M potassium hydroxide solution and stir for 30min to obtain a fruit shell suspension;

[0097] Step 3: Transfer the suspension to a stainless steel reactor with a polytetrafluoroethylene liner (100 mL), and hydrothermally react at 150°C for 6 h. After cooling, centrifuge the suspension, wash it three times with water and ethanol respectively, and dry it at 60°C for 24 h to obtain the biochar precursor.

[0098] Step 4: Place the precursor in a quartz boat and heat it to 800°C in an argon atmosphere in a tube furnace at a heating rate of 5°C / min. Hold the temperature for 2 hours and then cool to obtain the biochar material.

[0099] Step 5: At room temperature, add 0.25g of biochar powder to 50mL of 0.04M potassium permanganate solution and stir for 30min to obtain a grayish-purple suspension.

[0100] Step 6: Transfer the suspension to a stainless steel reactor with a polytetrafluoroethylene liner (100 mL), and hydrothermally react at 150 °C for 6 h. After cooling, centrifuge the suspension, wash it three times with water and ethanol respectively, and dry it at 60 °C for 24 h to obtain biochar-coated MnO(OH) powder.

[0101] Step 7: Place the biochar-coated MnO(OH) powder in a quartz boat, heat it to 350°C in an air atmosphere in a muffle furnace at a heating rate of 5°C / min, hold it at that temperature for 2 hours, and then cool it to obtain the biochar-coated MnO2 material.

[0102] To verify the electrochemical performance of the biochar-coated MnO2 cathode material, it was further assembled into a battery application: a CR2025 coin cell system was used, with a 1M zinc sulfate and 0.3M manganese sulfate mixed aqueous solution as the electrolyte, a circular zinc sheet as the negative electrode, and glass fiber as the battery separator. Constant current charge-discharge testing was conducted, with a voltage range of 0.8–1.8V. Electrochemical performance testing showed that after 50 cycles at a current density of 100 mA / g, the capacity reached 118.6 mA / g.

[0103] Comparative Example 1

[0104] A method for preparing a manganese-based aqueous zinc-ion battery cathode material includes the following steps:

[0105] Step 1: At room temperature, stir 50 mL of 0.04 M potassium permanganate solution for 30 min.

[0106] Step 2: Transfer the solution to a stainless steel reactor with a polytetrafluoroethylene liner (100 mL), and perform hydrothermal reaction at 150 °C for 6 h. After cooling, centrifuge the suspension, wash it three times with water and ethanol respectively, and dry it at 60 °C for 24 h to obtain MnO(OH) powder.

[0107] Step 3: Place MnO(OH) powder in a quartz boat, heat it to 350℃ in an air atmosphere in a muffle furnace at a heating rate of 5℃ / min, hold it at that temperature for 2 hours, and then cool it to obtain MnO2 material.

[0108] To verify the electrochemical performance of the MnO2 cathode material, it was further assembled into a battery application: a CR2025 coin cell system was used, with a 1M zinc sulfate and 0.3M manganese sulfate mixed aqueous solution as the electrolyte, a circular zinc sheet as the negative electrode, and glass fiber as the battery separator. Constant current charge-discharge testing was conducted, with a voltage range of 0.8–1.8V. Electrochemical performance testing revealed a capacity of 92.5 mA / g after 50 cycles at a current density of 100 mA / g.

[0109] Comparative Example 2

[0110] A method for preparing a biochar-coated manganese-based aqueous zinc-ion battery cathode material includes the following steps:

[0111] Step 1: After washing the bamboo skewers, cut them into pieces with a knife (length: 0.2cm, width: 0.2cm, thickness: 0.05cm), and dry them in a 60℃ oven for later use;

[0112] Step 2: At room temperature, add 1.0g of bamboo skewer fragments to 70mL of 3M potassium hydroxide solution and stir for 30min to obtain a fruit shell suspension;

[0113] Step 3: Transfer the suspension to a stainless steel reactor with a polytetrafluoroethylene liner (100 mL), and hydrothermally react at 150°C for 6 h. After cooling, centrifuge the suspension, wash it three times with water and ethanol respectively, and dry it at 60°C for 24 h to obtain the biochar precursor.

[0114] Step 4: Place the precursor in a quartz boat and heat it to 800°C in an argon atmosphere in a tube furnace at a heating rate of 5°C / min. Hold the temperature for 2 hours and then cool to obtain the biochar material.

[0115] Step 5: At room temperature, add 0.25g of biochar powder to 50mL of 0.04M potassium permanganate solution and stir for 30min to obtain a grayish-purple suspension.

[0116] Step 6: Transfer the suspension to a stainless steel reactor with a polytetrafluoroethylene liner (100 mL), and hydrothermally react at 150 °C for 6 h. After cooling, centrifuge the suspension, wash it three times with water and ethanol respectively, and dry it at 60 °C for 24 h to obtain biochar-coated MnO(OH) powder.

[0117] Step 7: Place the biochar-coated MnO(OH) powder in a quartz boat, heat it to 350°C in an air atmosphere in a muffle furnace at a heating rate of 5°C / min, hold it at that temperature for 2 hours, and then cool it to obtain the biochar-coated MnO2 material.

[0118] To verify the electrochemical performance of the biochar-coated MnO2 cathode material, it was further assembled into a battery application: a CR2025 coin cell system was used, with a 1M zinc sulfate and 0.3M manganese sulfate mixed aqueous solution as the electrolyte, a circular zinc sheet as the negative electrode, and glass fiber as the battery separator. Constant current charge-discharge testing was conducted, with a voltage range of 0.8–1.8V. Electrochemical performance testing showed that after 50 cycles at a current density of 100 mA / g, the capacity reached 94.4 mA / g.

Claims

1. A method for preparing biochar-coated manganese-based materials, characterized in that, Includes the following steps: (1) Using crushed nut shells as a carbon source, the biochar precursor is obtained by etching through hydrothermal reaction with alkaline solution and drying. (1) Biochar material is obtained by heat treatment under a protective atmosphere; (2) Using potassium permanganate as the manganese source, biochar is uniformly coated on the surface of the product by hydrothermal reaction, dried and then heat-treated in air atmosphere to obtain biochar-coated manganese-based material; biochar powder is added to potassium permanganate solution, the amount of biochar powder added does not exceed 5% of the solution mass, and the biochar powder is obtained from the biochar material; the heat treatment temperature in step (2) is 200-400℃; the heat treatment time is 1-3h.

2. The preparation method according to claim 1, characterized in that, The nut shells mentioned include at least one of the following: pistachio, walnut, hazelnut, almond, and pine nut shells.

3. The preparation method according to claim 1, characterized in that, Step (1) The mixed suspension of nut shell fragments and inorganic alkaline solution is subjected to hydrothermal reaction. The product is washed, filtered, dried and then heat-treated at high temperature under argon atmosphere to obtain biochar material.

4. The preparation method according to claim 3, characterized in that, The inorganic alkali includes at least one of potassium hydroxide and sodium hydroxide; the concentration of the inorganic alkali solution is 1.5–4.5 M; and the amount of fruit shell fragments added is 1–3 g.

5. The preparation method according to claim 4, characterized in that, The concentration of the inorganic alkaline solution is 2.5–3.5 M; the amount of fruit shell fragments added is 1.0–1.5 g.

6. The preparation method according to claim 3, characterized in that, The hydrothermal reaction synthesis temperature in step (1) is 130-170℃; the holding time is 4-8h; the heat treatment temperature in step (1) is 600-850℃; the holding time is 1-3h.

7. The preparation method according to claim 6, characterized in that, The hydrothermal reaction synthesis temperature in step (1) is 150℃; the holding time is 6h; the heat treatment temperature in step (1) is 800℃; the heating rate is 5℃ / min; and the holding time is 2h.

8. The preparation method according to claim 1, characterized in that, In step (2): the concentration of the potassium permanganate solution is 0.03-0.05M; the amount of biochar powder added does not exceed 3% of the solution mass.

9. The preparation method according to claim 1, characterized in that, In step (2): the hydrothermal reaction synthesis temperature is 130-170℃; the heat preservation time is 4-8h.

10. The preparation method according to claim 9, characterized in that, In step (2): the hydrothermal reaction synthesis temperature is 150℃; the holding time is 6h; the heat treatment temperature is 350℃; the heating rate is 5℃ / min; and the holding time is 2h.

11. The biochar-coated manganese-based material prepared by the method according to any one of claims 1-10.

12. The application of the biochar-coated manganese-based material according to claim 11, characterized in that, Used to prepare battery cathode materials.

13. The application according to claim 12, characterized in that, Used to prepare cathode materials for aqueous zinc-ion batteries.

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