A supported biochar material, its preparation method and application, and a composite anode material for lithium metal batteries.

Abstract

This invention belongs to the field of electrode material technology, specifically relating to a supported biochar material, its preparation method and application, and a composite anode for lithium metal batteries. The supported biochar material provided by this invention includes biochar and zinc oxide supported on the surface of the biochar; the biochar is obtained by carbonizing the cambium of a cypress plant. When the supported biochar material is used as the framework material for the lithium battery anode, the zinc oxide particles supported within and on the surface of the biochar pores form an alloy phase with lithium atoms during lithium deposition, enhancing the affinity of lithium atoms for the anode. Furthermore, by altering the chemical environment, it induces lithium to grow in a rounded, larger nucleus morphology, rather than the more common dendritic morphology; thus facilitating the tight deposition of lithium within and on the surface of the biochar, reducing volume expansion. The raw materials for preparing the supported biochar material provided by this invention are widely available and inexpensive, reducing production costs and facilitating industrial production.

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology, specifically relating to a supported biochar material, its preparation method and application, and a composite anode material for lithium metal batteries. Background Technology

[0002] Lithium metal batteries, due to their outstanding advantages such as high energy density, low self-discharge, and no memory effect, have become a major solution for mobile energy and are widely used in mobile phones, tablets, electric vehicles, and home energy storage. The negative electrode material of a lithium battery is a crucial factor affecting its capacity; currently, graphite or lithium metal are commonly used. However, graphite negative electrodes have a relatively low theoretical specific capacity (372 mA hg). -1 This cannot meet the ever-increasing demand for energy supply. In comparison, lithium metal anodes have a higher theoretical specific capacity (3860 mA hg). -1 It has a lower redox potential (-3.04V vs. standard hydrogen electrode). However, lithium metal anodes are difficult to form a stable SEI film, are prone to dendrite formation, and exhibit large volume variations, thus posing serious safety hazards.

[0003] Constructing a three-dimensional framework for lithium anodes is widely considered an effective way to regulate lithium deposition and solve the aforementioned problems. Existing framework materials mainly include lithium alloy-based materials, metal-based materials, carbon-based materials, and polymer-based materials. Among these, carbon-based materials have advantages such as light weight, good chemical stability, and ease of functionalization, making them a recent research hotspot. However, the chemical synthesis of carbon materials often involves toxic organic compounds, and the reaction processes are complex and require harsh conditions (such as high temperature, high pressure, and high vacuum). Furthermore, the precise design of the microstructure of carbon materials faces significant challenges, hindering their industrial application. Summary of the Invention

[0004] In view of this, the present invention provides a supported biochar material, its preparation method and application, and a composite negative electrode material for lithium metal batteries. The raw materials for the preparation of the supported biochar provided by the present invention are widely available and inexpensive, which reduces production costs and is easy to industrialize.

[0005] To address the aforementioned technical problems, the present invention provides a supported biochar material, comprising biochar and zinc oxide supported on the surface of the biochar;

[0006] The biochar is obtained by carbonizing the cambium of a cypress plant.

[0007] Preferably, the biochar contains micropores, mesopores, and macropores, wherein the average diameter of the micropores is 2–10 nm, the average diameter of the mesopores is 30–50 nm, and the average diameter of the macropores is 200 nm; the volume content of the micropores accounts for 15% of the total pore volume; the volume content of the mesopores accounts for 29% of the total pore volume; and the volume content of the macropores accounts for 56% of the total pore volume.

[0008] The biochar has a specific surface area of ​​200–500 m². 2 / g, with a total pore volume of 0.14~0.16cc / g.

[0009] Preferably, the zinc oxide has a mass percentage content of 10-20% in the supported biochar material.

[0010] This invention also provides a method for preparing the supported biochar material described in the above technical solution, comprising the following steps:

[0011] Pre-carbonizing the cambium of Taxodiaceae plants followed by carbonization yields Taxodiaceae-based biochar.

[0012] The cypress-based biochar and an inorganic zinc salt aqueous solution were mixed and adsorbed to obtain a supported biochar precursor.

[0013] The supported biochar precursor is pyrolyzed to obtain the supported biochar material.

[0014] Preferably, the process before pre-carbonization further includes: sequentially crushing, washing, and drying the cambium layer of the cypress plant;

[0015] The pre-carbonization temperature is 200–300°C, and the time is 2–3 hours.

[0016] Preferably, the carbonization temperature is 700–900°C, and the time is 2–3 hours; the heating rate to the required carbonization temperature is 4–6°C / min.

[0017] Preferably, the inorganic zinc salt aqueous solution includes an aqueous solution of zinc nitrate, an aqueous solution of zinc phosphate, or an aqueous solution of zinc sulfate;

[0018] The mass ratio of zinc element to Taxodium cypress-based biochar in the inorganic zinc salt aqueous solution is 1-2:10;

[0019] The adsorption temperature is 20–40°C, and the time is 22–26 h.

[0020] Preferably, the pyrolysis temperature is 350–800°C, the holding time is 1–2 h, and the heating rate to the required pyrolysis temperature is 4–6°C / min.

[0021] The present invention also provides the application of the supported biochar material described in the above technical solution or the supported biochar material prepared by the preparation method described in the above technical solution in the preparation of composite anode materials for lithium metal batteries.

[0022] The present invention also provides a lithium metal battery composite anode material, comprising a framework material and lithium deposited in the pores and on the surface of the framework material;

[0023] The framework material is the supported biochar material described in the above technical solution or the supported biochar material prepared by the preparation method described in the above technical solution.

[0024] This invention provides a supported biochar material, comprising biochar and zinc oxide supported on the surface of the biochar; the biochar is obtained by carbonizing the cambium of a cypress plant. In this invention, when the supported biochar material is used as the negative electrode of a lithium battery, the zinc oxide particles supported on the surface of the biochar form an alloy phase with lithium atoms during lithium deposition, enhancing the affinity of lithium atoms for the negative electrode. Furthermore, through changes in the chemical environment (the specific process of lithium deposition is lithium ion desolvation – charge transfer on the electrode to form lithium atoms – lithium atoms adsorbed on the electrode surface. Different chemical compositions of the framework materials result in different surrounding substances and groups when lithium atoms land on the surface; this is a difference in the chemical environment), lithium is induced to grow in a rounded, larger nucleus morphology, rather than the common dendritic morphology; thus facilitating the tight deposition of lithium within and on the surface of the biochar, reducing volume expansion. Simultaneously, the biochar can reduce current density and accommodate lithium deposition, improving the performance of the lithium negative electrode to a certain extent. The supported biochar material provided by this invention exhibits excellent affinity for lithium when used as a negative electrode framework material for lithium metal batteries, and can improve the density of lithium deposition, thereby enhancing the electrochemical performance and safety of lithium metal batteries and extending battery life. The raw materials for preparing the supported biochar material provided by this invention are widely available and inexpensive, reducing production costs and facilitating industrial production. Attached Figure Description

[0025] Figure 1 The images show the SEM and EDS spectra of the supported biochar material prepared in Example 1, where (a), (b), and (c) are SEM images at different magnifications, and (d), (e), and (f) are EDS spectra of C, O, and Zn, respectively.

[0026] Figure 2 The images show the adsorption-desorption isotherms and pore size distribution of the supported biochar material prepared in Example 1.

[0027] Figure 3 The XRD pattern of the supported biochar material prepared in Example 1 is shown below.

[0028] Figure 4The Raman spectrum of the supported biochar material prepared in Example 1 is shown below.

[0029] Figure 5 The XPS spectra of the supported biochar material prepared in Example 1 are shown below, where (a) is the XPS full spectrum scan spectrum, (b) is the C1s high-resolution scan spectrum, (c) is the O1s high-resolution scan spectrum, (d) is the Zn 2p high-resolution scan spectrum, and (e) is the Zn LMM spectrum.

[0030] Figure 6 The half-cell system assembled for Example 1 operates at current densities from 0.5 mA / cm². -2 Up to 2mAcm -2 The capacity is 1mAh cm -2 The lithium nucleation overpotential and long-cycle coulombic efficiency are compared at four current densities, where (a) is the lithium nucleation overpotential at four current densities and (b) is a comparison of the coulombic efficiency at four current densities.

[0031] Figure 7 The Tafel curve for the half-cell system of Example 1;

[0032] Figure 8 The symmetrical battery system assembled in Example 1 was tested at a current density of 1 mA / cm². -2 The capacity is 1mAh cm -2 Under the conditions, the cycling performance and impedance spectrum of the composite electrode are shown, where (a) is the cycling performance curve and (b) is the impedance spectrum.

[0033] Figure 9 SEM image of the unloaded zinc oxide-based biochar material from the Taxodiaceae family in Comparative Example 1;

[0034] Figure 10 The adsorption-desorption isotherm and pore size distribution of the unloaded zinc oxide-based biochar material from the Taxodiaceae family in Comparative Example 1 are shown.

[0035] Figure 11 The XRD pattern of the unloaded zinc oxide-based biochar material from the Taxodiaceae family in Comparative Example 1 is shown.

[0036] Figure 12 The Raman spectrum of the unloaded zinc oxide-based biochar material from the Taxodiaceae family in Comparative Example 1 is shown.

[0037] Figure 13 The half-cell system assembled for Comparative Example 1 was tested at current densities starting from 0.5 mA cm⁻¹. -2 Up to 2mAcm -2 The capacity is 1mAh cm -2The lithium nucleation overpotential and long-cycle coulombic efficiency are compared at four current densities, where (a) is the lithium nucleation overpotential at four current densities and (b) is a comparison of the coulombic efficiency at four current densities.

[0038] Figure 14 Tafel curves for the half-cell system in Comparative Example 1;

[0039] Figure 15 The symmetrical battery system assembled for Comparative Example 1 is shown at a current density of 1 mA cm⁻¹. -2 The capacity is 1mAh cm -2 Under the conditions, the cycling performance and impedance spectrum of the composite electrode are shown, where (a) is the cycling performance curve and (b) is the impedance spectrum.

[0040] Figure 16 For the half-cell system assembled as in Comparative Example 2, the current density starts from 0.5 mA cm⁻¹ -2 Up to 2mAcm -2 The capacity is 1mAh cm -2 The lithium nucleation overpotential and long-cycle coulombic efficiency are compared at four current densities, where (a) is the lithium nucleation overpotential at four current densities and (b) is a comparison of the coulombic efficiency at four current densities.

[0041] Figure 17 Tafel curves for the half-cell system in Comparative Example 2;

[0042] Figure 18 The symmetrical battery system assembled for Comparative Example 2 was tested at a current density of 1 mA cm⁻¹. -2 The capacity is 1mAh cm -2 Under the given conditions, the cycling performance and impedance spectrum of the composite electrode are shown, where (a) is the cycling performance curve and (b) is the impedance spectrum. Detailed Implementation

[0043] The present invention provides a supported biochar material, comprising biochar and zinc oxide supported on the surface of the biochar.

[0044] The supported biochar material provided by this invention includes biochar; the biochar is obtained by carbonizing the cambium of a Taxaceae plant. In this invention, the cambium of the Taxaceae plant is mainly composed of sieve tubes, which are straight and tightly and uniformly arranged, with a diameter of 2-10 μm; at the same time, the lignin content of Taxaceae plants is as high as 60%. Carbonization using the cambium of Taxaceae plants as raw material can ensure that the sieve tube structure melts after carbonization to form an ordered microporous structure and retain some channel structure, and the high lignin content is beneficial to the stability of the biochar structure.

[0045] In this invention, the biochar preferably contains micropores, mesopores, and macropores; the average diameter of the micropores is preferably 2–10 nm, more preferably 3–9 nm; the average diameter of the mesopores is preferably 30–50 nm, more preferably 35–45 nm; the average diameter of the macropores is preferably 200 nm; the volume percentage of the micropore volume in the total pore volume is preferably 15%; the volume percentage of the mesopore volume in the total pore volume is preferably 29%; and the volume percentage of the macropore volume in the total pore volume is preferably 56%. In this invention, the specific surface area of ​​the biochar is preferably 200–500 m². 2 / g, more preferably 262-400m 2 / g; the pore volume of the biochar is preferably 0.14-0.16cc / g, more preferably 0.15cc / g.

[0046] The supported biochar material provided by this invention further includes zinc oxide supported on the surface of the biochar. In this invention, the average particle size of the zinc oxide is preferably 20–50 nm, more preferably 30–40 nm. In this invention, the mass percentage of zinc oxide in the supported biochar material is preferably 10–20%, more preferably 12.5–20%, and most preferably 15–18.75%.

[0047] This invention also provides a method for preparing the supported biochar material described in the above technical solution, comprising the following steps:

[0048] Pre-carbonizing the cambium of Taxodiaceae plants followed by carbonization yields Taxodiaceae-based biochar.

[0049] The cypress-based biochar and an inorganic zinc salt aqueous solution were mixed and adsorbed to obtain a supported biochar precursor.

[0050] The supported biochar precursor is pyrolyzed to obtain the supported biochar material.

[0051] This invention involves pre-carbonizing the cambium of Taxaceae plants followed by carbonization to obtain Taxaceae-based biochar. Preferably, the pre-carbonization process further includes pulverizing, washing, and drying the cambium of the Taxaceae plants sequentially. Preferably, the cambium is peeled off from the stems of Taxaceae plants to obtain the cambium itself; the stems preferably include dead branches, thin trunks, or dead roots. In this invention, the Taxaceae plants preferably include Metasequoia glyptostroboides, Sequoia glyptostroboides, Larch, or Pinus tabuliformis, more preferably Metasequoia glyptostroboides. This invention does not have special requirements for the peeling process; conventional methods in the art can be used.

[0052] In this invention, the pulverized material is preferably rectangular, and the length of the rectangle is preferably 1-3 cm, more preferably 2 cm. This invention does not have special requirements for the pulverization process; conventional methods in the art can be used.

[0053] In this invention, the washing process is preferably ultrasonic washing, which preferably includes sequential water washing and ethanol washing; the water used for water washing is preferably deionized water, and the ethanol used for ethanol washing is preferably anhydrous ethanol. In this invention, the power of the ultrasonic washing is preferably 250-350W, more preferably 300W. In this invention, the ultrasonic washing time using water as the detergent is preferably 0.8-1.2 hours, more preferably 1 hour; the ultrasonic washing time using ethanol as the detergent is preferably 0.8-1.2 hours, more preferably 1 hour.

[0054] In this invention, the drying temperature is preferably 75-85°C, more preferably 80°C; the drying time is preferably 22-26 hours, more preferably 24 hours.

[0055] In this invention, the pre-carbonization temperature is preferably 200–300°C, more preferably 230–280°C; the pre-carbonization time is preferably 2–3 hours, more preferably 2.3–2.5 hours. In this invention, the pre-carbonization is preferably carried out under a protective atmosphere, which preferably includes nitrogen or an inert gas, more preferably nitrogen. Pre-carbonizing the cambium of the cypress plant in this invention allows unstable organic matter (such as polysaccharides) in the cambium to fully volatilize and decompose, thereby improving the toughness of the biochar. If the cambium of the cypress plant is directly carbonized, the resulting biochar structure is very brittle, which is not conducive to repeated lithium metal deposition and stripping, and cannot buffer the expansion of lithium volume during volume changes.

[0056] In this invention, the carbonization temperature is preferably 700–900°C, more preferably 800–900°C; the carbonization time is preferably 2–3 hours, more preferably 2.3–2.5 hours. In this invention, the heating rate to the required carbonization temperature is preferably 4–6°C / min, more preferably 5°C / min. In this invention, the carbonization is preferably carried out under a protective atmosphere, which preferably includes nitrogen or an inert gas, more preferably nitrogen.

[0057] In this invention, the carbonization process preferably further includes: cooling the carbonized product to room temperature followed by sequential washing and drying. In this invention, the room temperature is preferably 20–30°C. This invention does not have special requirements for the cooling process. In this invention, the water used for washing is preferably deionized water; the number of washes is preferably 2–3. In this invention, the drying temperature is preferably 75–85°C, more preferably 80°C; the drying time is preferably 22–26 hours, more preferably 23–24 hours.

[0058] After obtaining the cypress-based biochar, this invention mixes the cypress-based biochar with an inorganic zinc salt aqueous solution for adsorption to obtain a supported biochar precursor. In this invention, the inorganic zinc salt aqueous solution preferably includes an aqueous solution of zinc nitrate, zinc phosphate, or zinc sulfate, more preferably an aqueous solution of zinc nitrate. This invention preferably dissolves the inorganic zinc salt in deionized water to obtain the inorganic zinc salt aqueous solution. This invention has no special requirements on the amount of deionized water used, as long as it is sufficient for complete dissolution. Taking the zinc nitrate aqueous solution as an example, specifically: zinc nitrate hexahydrate is dissolved in deionized water to obtain the zinc nitrate aqueous solution.

[0059] In this invention, the mass ratio of zinc element to cypress-based biochar in the inorganic zinc salt aqueous solution is preferably 1-2:10, more preferably 1.5-1.9:10.

[0060] This invention does not have special requirements for the mixing process, as long as it is homogeneous. In this invention, the adsorption temperature is preferably 20–40°C, more preferably 25–30°C; the adsorption time is preferably 22–26 hours, more preferably 24 hours. In this invention, the adsorption process is preferably accompanied by stirring or oscillation; this invention preferably uses a magnetic stirrer for stirring, and more preferably uses a mechanical vibrator for oscillation. This invention, through adsorption, causes inorganic zinc salts to be adsorbed onto the pores or surface of biochar.

[0061] In this invention, the post-adsorption process preferably further includes: solid-liquid separation of the adsorption system, followed by sequential washing and drying of the solid obtained from the solid-liquid separation to obtain a supported biochar precursor. In this invention, the solid-liquid separation is preferably performed using vacuum filtration. In this invention, the water used for washing is preferably deionized water, and the number of washing cycles is preferably 2-3. In this invention, the drying temperature is preferably 75-85°C, more preferably 80°C; the drying time is preferably 22-26 hours, more preferably 24 hours.

[0062] After obtaining the supported biochar precursor, the present invention pyrolyzes the supported biochar precursor to obtain the supported biochar material. In the present invention, the pyrolysis temperature is preferably 350–800°C, more preferably 400–700°C; the holding time for pyrolysis is preferably 1–2 hours. In the present invention, the heating rate to the required pyrolysis temperature is preferably 4–6°C / min, more preferably 5°C / min. In the present invention, the pyrolysis is preferably carried out under a protective atmosphere, which preferably includes nitrogen or an inert gas, more preferably nitrogen. In the present invention, the inert gas is preferably argon.

[0063] In this invention, inorganic zinc salts adsorbed on the surface or within the pores of biochar undergo pyrolysis to generate zinc oxide, which adheres to the surface or pores of the biochar. When the inorganic zinc salt is zinc nitrate, the pyrolysis reaction is as shown in Formula 1:

[0064] 2Zn(NO3)2→2ZnO+O2+4NO2 Equation 1.

[0065] In this invention, the pyrolysis process preferably further includes: cooling the pyrolysis product to room temperature and then sequentially washing with water and drying to obtain the supported biochar material. In this invention, the room temperature is preferably 20–30°C, more preferably 25°C. In this invention, the water used for washing is preferably deionized water, and the number of washing cycles is preferably 2–3. In this invention, the drying temperature is preferably 75–85°C, more preferably 80°C; the drying time is preferably 22–26 hours, more preferably 24 hours.

[0066] This invention prepares porous carbon materials loaded with zinc oxide particles through an adsorption-pyrolysis process. The zinc oxide particles significantly improve the lithium affinity of the biochar bulk, which is beneficial for guiding lithium to form rounded crystal nuclei and deposit tightly on the surface of the carbon material through an alloying reaction. Benefiting from the through-hole vessel structure of the cambium of cypress plants, the loaded biochar material obtained after pyrolysis has a unique structure with through-holes with a diameter of 2-10 μm inside and a large number of micropores with a diameter of 2-10 nm on the surface. This structure can effectively accommodate the tight deposition of lithium in the internal space of the framework structure material, thereby improving the lifespan and safety of the lithium anode.

[0067] The preparation method provided by this invention is simple, mild, and has little environmental impact. From the perspective of porous carbon, this invention uses forestry waste—the stems of Taxodiaceae plants—which not only retains some of the unique structures of the cambium of Taxodiaceae plants but also maximizes the resource utilization of forestry waste. From the perspective of metal active sites, the biochar raw materials and zinc used in this invention are widely available and relatively inexpensive, and have a broader application prospect in the field of electrochemistry.

[0068] The present invention also provides the application of the supported biochar material described in the above technical solution or the supported biochar material prepared by the preparation method described in the above technical solution in the preparation of composite anode materials for lithium metal batteries.

[0069] The present invention also provides a lithium metal battery composite anode material, comprising a framework material and lithium deposited in the pores and on the surface of the framework material;

[0070] The framework material is the supported biochar material described in the above technical solution or the supported biochar material prepared by the preparation method described in the above technical solution.

[0071] In this invention, the deposition capacity of lithium deposited within the pores of the framework material is preferably 1.4–1.6 mAh / cm³. -2 More preferably 1.5mAh / cm -2 The lithium deposition capacity on the surface of the framework material is preferably 3.5–4.5 mAh / cm³. -2 More preferably 4mAh / cm -2 .

[0072] This invention preferably utilizes an electrode deposition method to prepare a composite electrode composed of lithium metal and an electrode sheet prepared during half-cell assembly, with the lithium deposition capacity preferably being 4 mAh cm⁻¹. -2 ~6mAh cm -2 This invention limits the lithium deposition capacity within the aforementioned range to ensure that lithium completely fills the pores of the carbon framework material. Specifically, the electrodeposition method involves assembling the electrodes used in the half-cell system, along with two 0.5mm spacers, a 0.6mm lithium sheet, and a Celgard separator, into a coin cell with a diameter of 20mm and a thickness of 1.6mm. The coin cell is then placed on a battery tester, and a discharge program is set with a certain current density and deposition capacity. Lithium will be deposited onto the electrode surface during the discharge process. After deposition is complete, the battery is disassembled to obtain the composite electrode after lithium deposition.

[0073] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0074] Example 1

[0075] Collect fallen branches of dawn redwood, peel off the outermost green bark, and peel off the cambium layer of the red-orange part inside the bark. Cut the cambium layer into rectangles with an average length of 2 cm and place them in 200 mL of deionized water for ultrasonic washing at 300 W for 1 h. Then place them in 200 mL of anhydrous ethanol for ultrasonic washing at 300 W for 1 h. After washing, place the cambium layer in an 80 °C oven and dry for 24 h. Then place it in a corundum ark and pre-carbonize it at 200 °C for 2 h under a nitrogen protective atmosphere. Then heat it to 800 °C for 2 h at a heating rate of 5 °C / min. After cooling to 25 °C, wash it twice with deionized water and dry it in an 80 °C oven for 24 h to obtain cypress-based biochar.

[0076] 168 mg of zinc nitrate hexahydrate was dissolved in 20 mL of deionized water to obtain an aqueous solution of zinc nitrate; 200 mg of cypress-based biochar was added to the zinc nitrate aqueous solution, mixed evenly, and then adsorbed at 30 °C for 24 h under the stirring of a magnetic stirrer; after vacuum filtration, the solid was washed twice with deionized water and dried in an 80 °C forced-air oven for 24 h to obtain a supported biochar precursor.

[0077] The supported biochar precursor was placed in a corundum ark and pyrolyzed at 400℃ for 1 h under a nitrogen protective atmosphere. After cooling to 25℃, it was washed with deionized water until the pH was neutral and then dried in an 80℃ forced-air oven for 24 h to obtain the supported biochar material.

[0078] Lithium was deposited on the surface and pores of supported biochar material using electrodeposition to obtain a lithium metal battery composite anode; the electrodeposition conditions were 0.1 mA cm⁻¹. -2 Current density, 4mAh cm -2 The deposition capacity.

[0079] Comparative Example 1

[0080] The cypress-based biochar prepared in Example 1 was used as a comparative example.

[0081] Lithium was deposited on the surface and pores of cypress-based biochar using electrodeposition to obtain a lithium metal battery composite anode; the electrodeposition conditions were 0.1 mA cm⁻¹. -2 Current density, 4mAh cm -2 The deposition capacity.

[0082] Comparative Example 2

[0083] Copper foil was cut into circular pieces with a diameter of 11 mm and a thickness of 10 μm as a comparative example.

[0084] Lithium was deposited on the surface of copper foil using electrodeposition to obtain a composite anode for lithium metal batteries; the electrodeposition conditions were 0.1 mA / cm². -2 Current density, 4mAh cm -2 The deposition capacity.

[0085] Using the materials from Example 1 and Comparative Examples 1-2 as substrates for lithium deposition, lithium metal battery composite anodes were prepared and then used to form half-cells and symmetrical cells for electrochemical testing.

[0086] The supported biochar material prepared in Example 1 was examined by scanning electron microscopy, and SEM images and energy dispersive spectroscopy (EDS) spectra were obtained, as shown below. Figure 1 As shown, (a), (b), and (c) are SEM images at different magnifications, and (d), (e), and (f) are EDS images of C, O, and Zn, respectively.

[0087] As shown in SEM image (a), the surface of the prepared supported biochar material is uneven, with a small number of through-channels with diameters of 2–10 μm and a small number of open macropores with diameters of several hundred nanometers. These channels and macropores originate from the melting and reorganization of the sieve tubes themselves. Under magnification, image (b) shows a large number of micropores with diameters of 2–10 nm on the surface of the supported biochar material, indicating that during carbonization, cellulose and hemicellulose decomposed and melted, the material melted and reorganized into amorphous carbon, and the organic matter in the biomass was released in gaseous form. The pores are mainly micropores. The surface of the zinc oxide-supported cypress-based biochar is covered with a large number of crystals, which are visible under high magnification (c). These crystals appear as clusters with diameters of 50–200 nm, uniformly covering the surface and internal channels of the biochar. The EDS diagram shows that O is uniformly dispersed on the material surface, while the positions of Zn overlap with those of O, indicating that zinc oxide clusters are distributed on the surface of biochar and that oxygen-containing functional groups may exist. This suggests that metal oxides have been successfully modified on the surface of biochar.

[0088] Nitrogen adsorption-desorption experiments were conducted on the supported biochar material prepared in Example 1, and adsorption-desorption isotherms and pore size distribution maps were obtained, as shown below. Figure 2 As shown. By Figure 2 The BET specific surface area of ​​the supported biochar material is known to be 316.53 m². 2 The average pore size is 2.5 nm. The adsorption-desorption isotherm curve shows a sharp increase in adsorption within a very small relative pressure range (approximately P / P0 = 0.1), followed by a near-horizontal increase within a relative pressure range of 0.1–0.9, conforming to the IUPAC Type I isotherm, indicating that the surface of the supported biochar material is mainly microporous. The presence of an H4 hysteresis loop under high pressure indicates the presence of a small amount of mesopores on the surface. When the material is used as a negative electrode framework, the micropores can generate capillary action, thereby increasing the wettability of the electrolyte. Furthermore, they can promote lithium-ion adsorption on the material, improving its lithiophilicity to some extent.

[0089] The supported biochar material prepared in Example 1 was analyzed using an X-ray diffractometer, and the XRD pattern was obtained, as shown below. Figure 3 As shown. By Figure 3 It can be seen that amorphous carbon diffraction peaks (002) and (100) crystal planes were detected at 24° and 44°, and ZnO (100), (002), (101) and (110) crystal planes were detected at 32°, 34.5°, 36° and 56.5°, indicating that the zinc oxide exists in the form of hexagonal wurtzite P63mc structure.

[0090] The supported biochar material prepared in Example 1 was analyzed using Raman spectroscopy, and the Raman spectrum was obtained, as shown below. Figure 4 As shown. By Figure 4 It can be seen that at 1350cm -1 and 1590cm -1 The presence of distinct D and G peaks indicates a lower degree of graphitization and a higher content of disordered carbon. The D peak is wider, while the G peak shifts to higher frequencies relative to the position of the graphite crystal, suggesting a lower degree of graphitization and a higher content of disordered carbon.

[0091] The supported biochar material prepared in Example 1 was analyzed using X-ray photoelectron spectroscopy, and XPS spectra were obtained, as shown below. Figure 5 As shown, (a) is the XPS full-spectrum scan spectrum, (b) is the C1s high-resolution scan spectrum, (c) is the O1s high-resolution scan spectrum, (d) is the Zn 2p high-resolution scan spectrum, and (e) is the Zn LMM spectrum. Figure 5 Image (a) shows the presence of a C1s peak (285 eV), an O 1s peak (533 eV), a Zn 2p 1 / 2 peak (1044 eV), and a Zn 2p 3 / 2 peak (1021 eV). The C1s spectrum (...) Figure 5 (b) Separate the C, CO, and C=O bonds in the O1s spectrum. Figure 5 (c) Separates lattice oxygen and adsorbed oxygen, with a higher content of adsorbed oxygen due to the smaller size of the zinc oxide particles, resulting in more defects and vacancies. In the Zn spectrum ( Figure 5 In (d), an energy loss peak appears near the Zn 2p 1 / 2 peak, which is a characteristic peak that only appears when divalent zinc is present. This is consistent with the Zn LMM spectrum. Figure 5 (e)) The calculated Auger peak matches the Auger electron kinetic energy of ZnO (987.7 eV). Combined with the presence of characteristic peaks of ZnO in the XRD pattern, this confirms that the metal compound supported on the biochar is zinc oxide.

[0092] The above test results prove that the cypress-based biochar prepared in Example 1 has a porous structure and is loaded with zinc oxide particles on its surface.

[0093] The biochar material prepared in Comparative Example 1 was examined by scanning electron microscopy, and the SEM images were obtained, as shown below. Figure 9 As shown. From SEM Figure 9 As can be seen, the porous biochar surface without metal oxide particles exhibits a complex pore structure, including through-holes with a diameter of about 2 μm, open macropores of several hundred nanometers (derived from the sieve tube structure), and micropores with a diameter of 2–10 nm. Figure 1 In contrast, the chemical modification process of zinc oxide did not significantly change the structure of the carbon material itself, nor did it show any obvious blockage of the pore structure by zinc oxide particles.

[0094] Nitrogen adsorption-desorption experiments were conducted on the biochar material of Comparative Example 1, and adsorption-desorption isotherms and pore size distribution diagrams were obtained, as shown below. Figure 10 As shown, the BET specific surface area of ​​the biochar material is 352.10 m². 2 / g, with an average pore size of 2.5nm; the adsorption-desorption isotherm and pore size distribution curve of the unloaded zinc oxide biochar material are almost identical to those of the loaded zinc oxide in Example 1, further demonstrating that the surface modification of zinc oxide did not significantly change the pore structure of the porous carbon material.

[0095] The biochar material of Comparative Example 1 was analyzed using an X-ray diffractometer, and the XRD pattern was obtained, as shown below. Figure 11 As shown, amorphous carbon diffraction peaks (002) and (100) crystal planes were detected at 24° and 44°, respectively, while zinc oxide diffraction peaks did not appear as in Example 1. This indicates that the carbon material without zinc oxide does not contain zinc oxide and only exhibits the morphology of amorphous carbon.

[0096] The unloaded zinc oxide biochar material of Comparative Example 1 was analyzed using Raman spectroscopy, and the Raman spectrum was obtained, as shown below. Figure 12 As shown. By Figure 12 It can be seen that at 1350cm -1 and 1590cm -1 The presence of distinct D and G peaks indicates a lower degree of graphitization and a higher content of disordered carbon. The D peak is wider, while the G peak shifts to higher frequencies relative to the position of the graphite crystal, suggesting a lower degree of graphitization and a higher content of disordered carbon.

[0097] The results above show that the biochar material prepared in Comparative Example 1 has the same microporous structure as the supported biochar material in Example 1. The supported zinc oxide did not block the pores of the biochar, but was uniformly distributed in the pores of the biochar and on the surface of the material.

[0098] The electrochemical performance of the supported biochar material prepared in Example 1, and the materials of Comparative Example 1 and Comparative Example 2, was tested according to the following method. Half-cell system performance testing: The carbon-coated electrode was prepared as follows: First, the supported biochar material from Example 1 or the unsupported biochar material from Comparative Example 1, conductive carbon (SuperP), and binder polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 8:1:1, using N-methylpyrrolidone (NMP) as a solvent, and stirred to form a uniform slurry. The active material mass was 40 mg. The slurry was uniformly coated onto a rectangular copper foil with a length of 20 cm, a width of 7 cm, and a thickness of 10 μm using a scraper, with a coating thickness of 100–200 μm. The coated copper foil was dried in a vacuum drying oven at 80°C for 12 h. After drying, it was cut into circular electrodes with a diameter of 11 mm and coated with active material. The copper disc from Comparative Example 2 was used directly as the electrode. Using 1M LiTFSI, DME:DOL = 1:1, and 5% wt LiNO3 as the electrolyte, the above three types of electrodes, along with a 16mm diameter lithium metal sheet and a Celgard separator, were assembled into a 20mm diameter, 1.6mm thick button cell as the positive electrode, negative electrode, and separator, respectively.

[0099] The performance of the symmetric battery system was tested as follows: A composite electrode composed of lithium metal and electrodes prepared during half-cell assembly was fabricated using an electrodeposition method. The lithium deposition capacity was 4 mAh cm⁻¹. -2 ~6mAh cm -2 Between, in this embodiment 4mAh cm -2 The amount of lithium deposited is ensured to completely fill the pores of the carbon framework material. Specifically, the electrodeposition method involves assembling the electrodes used in the half-cell system, along with two 0.5mm spacers, a 0.6mm lithium sheet, and a Celgard separator, into a coin cell with a diameter of 20mm and a thickness of 1.6mm. The coin cell is then placed on a battery tester and subjected to a 0.1mA cm-wave pressure. -2 Current density and 4mAhcm -2 To achieve the desired deposition capacity, lithium is deposited onto the electrode surface. After deposition, the battery is disassembled to obtain the composite electrode with deposited lithium. The two composite electrodes are used as the positive and negative electrodes, respectively, and assembled with a Celgard separator and electrolyte into a coin cell with a diameter of 20 mm and a thickness of 1.6 mm.

[0100] The battery tester (LAND-CT2001A) is used for constant current discharge / charge testing and cycle performance testing; linear sweep voltammetry (LSV) measurement and electrochemical impedance spectroscopy (EIS) testing are performed on the CHI920C electrochemical workstation using a dual-electrode system.

[0101] Figure 6 , Figure 13and Figure 16 The half-cell systems assembled in Example 1, Comparative Example 1, and Comparative Example 2, respectively, were tested at current densities ranging from 0.5 mA / cm². -2 Up to 2mAcm -2 The capacity is 1mAh cm -2 The lithium nucleation overpotential and long-cycle coulombic efficiency exhibited at different current densities are compared, with (a) showing the lithium nucleation overpotential at four current densities and (b) showing the coulombic efficiency at four current densities. Figure 6 It can be seen that 0.5mA cm -2 At the specified current density, the nucleation overpotential of the material in Example 1 was 16.1 mV, the cycle life was over 3200 h, and the coulombic efficiency was over 98%; 1.0 mA cm -2 The nucleation overpotential at current density is 32.2 mV, the cycle life is over 1200 h, and the coulombic efficiency is over 97.5%; 1.5 mA cm -2 The nucleation overpotential at current density is 69.4 mV, the cycle life is over 400 h, and the coulombic efficiency is over 97.5%; 2.0 mA cm -2 The nucleation overpotential at the specified current density was 275.3 mV, the cycle life was over 200 h, and the coulombic efficiency was over 97.5%. This indicates that the supported biochar material exhibited a very low nucleation overpotential and maintained a cycle life of several hundred cycles and a coulombic efficiency of over 98% at different current densities. Compared to Example 1, the materials in Comparative Examples 1 and 2 showed significantly larger nucleation overpotentials and lower cycle lives. Figure 13 , Figure 16 ): 0.5mA cm -2 The nucleation overpotentials of the materials in Comparative Example 1 and Comparative Example 2 at current densities were 39.2 mV and 55.2 mV, respectively, and their cycle lifetimes were 1600 h and 1200 h, respectively; 1.0 mA cm -2 The nucleation overpotentials at the current densities were 97.9 mV and 132.6 mV, respectively, and the cycle lifetimes were 450 h and 300 h; 1.5 mA cm -2 The nucleation overpotentials at the current densities were 133 mV and 196.4 mV, respectively, and the cycle lifetimes were 300 h and 80 h, respectively; 2.0 mA cm -2 The nucleation overpotentials at different current densities were 363.2 mV and 576 mV, with cycle lifetimes of 175 h and 10 h, respectively. Over a wider potential range, at 20 mV / s... -1 The half-cell system was subjected to linear voltammetric scanning tests at a certain scan rate. Figure 7 The Tafel curve of the half-cell system assembled from supported biochar materials was obtained, and the calculated exchange current density was 0.609 mA / cm². -2This demonstrates that the supported biochar material possesses excellent kinetic properties. The Tafel curves for Comparative Example 1 and Comparative Example 2 are shown below. Figure 14 and Figure 17 As shown, the calculated exchange current density is 0.182 mA / cm². -2 and 0.264mA cm -2 This demonstrates that the dynamic performance of the comparative material is far weaker than that of the material in Example 1.

[0102] Figure 8 , Figure 15 and Figure 18 Symmetrical battery systems assembled in Example 1, Comparative Example 1, and Comparative Example 2, respectively, were tested at a current density of 1 mA cm⁻¹. -2 The capacity is 1mAh cm -2 Under the given conditions, the cycling performance and impedance spectrum of the composite electrode are shown, where (a) is the cycling performance curve and (b) is the impedance spectrum (EIS). Figure 8 Image (a) shows that the composite electrode exhibits stable cycling for up to 1200 hours in a symmetrical battery system. Figure 8 As can be seen in (b), the impedances representing the SEI film and bulk charge transfer on the composite electrode surface are 7 Ωcm, respectively. -2 and 37.97Ωcm -2 The composite electrodes of Comparative Example 1 and Comparative Example 2 exhibited cycle lives of 1000 h and 800 h, respectively, in the symmetrical battery system. Figure 15 and Figure 18 Furthermore, the impedances of the SEI film on the electrode surface and the charge transfer in the bulk phase are 7 Ωcm, respectively. -2 15Ωcm -2 and 45Ωcm -2 63Ωcm -2 .

[0103] The test results of the above lithium metal battery system show that the supported biochar material provided by the present invention, due to its large specific surface area and abundant pore structure, can reduce local current density and alleviate volume changes during lithium deposition / stripping. In addition, the material surface contains a high content of zinc oxide active sites, thus exhibiting higher electronic conductivity and lithiophilicity. This helps to regulate the formation of more rounded lithium-zinc alloy phase nuclei with lower reactivity, reducing electrolyte consumption and allowing lithium to be deposited in a uniform and compact morphology, thereby improving the cycle life and coulombic efficiency of the lithium metal battery. Therefore, the prepared composite anode exhibits excellent electrochemical behavior.

[0104] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A supported biochar material, characterized in that, Includes biochar and zinc oxide supported on the surface of the biochar; The biochar is obtained by carbonizing the cambium of cypress plants; the specific surface area of ​​the biochar is 200-500 m². 2 / g, with a total pore volume of 0.14~0.16cc / g; The zinc oxide content in the supported biochar material is 10-20% by mass. The preparation method of the supported biochar material includes the following steps: Pre-carbonizing the cambium of Taxodiaceae plants followed by carbonization yields Taxodiaceae-based biochar. The cypress-based biochar and an inorganic zinc salt aqueous solution were mixed and adsorbed to obtain a supported biochar precursor. The supported biochar precursor is pyrolyzed to obtain the supported biochar material.

2. The supported biochar material according to claim 1, characterized in that, The biochar contains micropores, mesopores, and macropores. The average diameter of the micropores is 2-10 nm, the average diameter of the mesopores is 30-50 nm, and the average diameter of the macropores is 200 nm. The volume content of the micropores accounts for 15% of the total pore volume; the volume content of the mesopores accounts for 29% of the total pore volume; and the volume content of the macropores accounts for 56% of the total pore volume.

3. A method for preparing the supported biochar material according to claim 1 or 2, comprising the following steps: Pre-carbonizing the cambium of Taxodiaceae plants followed by carbonization yields Taxodiaceae-based biochar. The cypress-based biochar and an inorganic zinc salt aqueous solution were mixed and adsorbed to obtain a supported biochar precursor. The supported biochar precursor is pyrolyzed to obtain the supported biochar material.

4. The preparation method according to claim 3, characterized in that, The process before pre-carbonization also includes: sequentially crushing, washing, and drying the cambium layer of the cypress plant; The pre-carbonization temperature is 200~300℃, and the time is 2~3h.

5. The preparation method according to claim 3, characterized in that, The carbonization temperature is 700~900℃, and the time is 2~3h; the heating rate to the required carbonization temperature is 4~6℃ / min.

6. The preparation method according to claim 3, characterized in that, The inorganic zinc salt aqueous solution includes zinc nitrate aqueous solution, zinc phosphate aqueous solution, or zinc sulfate aqueous solution; The mass ratio of zinc element to Taxodium cypress-based biochar in the inorganic zinc salt aqueous solution is 1~2:10; The adsorption temperature is 20~40℃ and the time is 22~26h.

7. The preparation method according to claim 3, characterized in that, The pyrolysis temperature is 350~800℃, and the holding time is 1~2h; the heating rate to the required pyrolysis temperature is 4~6℃ / min.

8. The application of the supported biochar material according to claim 1 or 2 or the supported biochar material prepared by the preparation method according to any one of claims 3 to 7 in the preparation of composite anodes for lithium metal batteries.

9. A composite negative electrode material for lithium metal batteries, characterized in that, Includes a frame material and lithium deposited within and on the surface of the frame material's pores; The framework material is the supported biochar material according to claim 1 or 2, or the supported biochar material prepared by the preparation method according to any one of claims 3 to 7.

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