Preparation and application of a MOFs-modified wood-based self-supporting conductive skeleton

Abstract

A method for preparing a MOFs-modified wood-based self-supporting conductive skeleton comprises the following steps: step (1): cutting and punching a wood block to obtain a thin disc; chemically delignifying the thin disc to obtain a delignified wood chip; step (2): dissolving a metal salt and a surfactant in deionized water to obtain a metal salt solution; obtaining a wood chip metal salt solution; step (3): dissolving an organic ligand and a capping agent in deionized water to obtain a ligand solution, adding the ligand solution to the wood chip metal salt solution, stirring, and aging to obtain a MOFs-modified wood chip; step (4): freezing and drying the MOFs-modified wood chip, and carbonizing it under a reducing gas atmosphere to obtain a MOFs-modified wood-based carbon film; and step (5): adding a DOL / DME mixed solution containing Li2S8 to the MOFs-modified wood-based carbon film to obtain a MOFs-modified wood-based self-supporting conductive skeleton. The present invention can improve the energy density of lithium-sulfur batteries, extend the cycle life, and enhance the electrochemical reaction kinetics.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-sulfur battery electrode materials, and in particular to a preparation method and application of a MOFs-modified wood-based self-supporting conductive skeleton. Background Art

[0002] Lithium-ion batteries have dominated the electronics and power battery markets for over three decades, but they are no longer able to meet current demands for high energy and power density. Lithium-sulfur batteries (LSBs), with their high theoretical specific capacity (1675 mAh / g), low cost, and environmental friendliness, are considered a promising energy storage technology to replace lithium batteries. However, the marketability of LSBs is hampered by several inherent limitations: the low conductivity of sulfur and its final discharge product (Li2S2 / Li2S), volume changes in the cathode, and the polysulfide shuttle effect, all significantly impact the electrochemical performance of LSBs.

[0003] To address the challenges of LSB development, metal-organic frameworks (MOFs) and their derivatives have been used in LSB modification research, improving their electrochemical performance to some extent. However, MOF-derived nanoparticles are independent and unconnected, which severely hinders electron transfer between them. Furthermore, these nanoparticles tend to accumulate and agglomerate, reducing the exposed surface area and active sites, thereby weakening the adsorption of LiPSs.

[0004] In order to fully utilize the active sites of MOFs materials, selecting a suitable catalyst carrier can accelerate the transmission of ions and electrons between nanoparticles and effectively alleviate the shuttling effect of polysulfides. The mainstream solution is to combine it with a carbon matrix. The introduction of conductive agents and binders in traditional coated positive electrodes will reduce the actual energy density and sulfur loading of the electrode. The self-supporting positive electrode is an integrated conductive skeleton with adjustable structure and can be directly used as a positive electrode carrier. Biomass materials are a renewable resource rich in carbon elements, and the most common ones are animal and plant derivatives and agricultural waste. It has outstanding advantages such as wide sources, low cost, environmental sustainability and rich structure, and therefore has broad application prospects in LSB self-supporting positive electrode carbon carriers. Selecting suitable biomass self-supporting materials as catalyst carriers for MOFs is a key issue currently faced. Summary of the Invention

[0005] To overcome the shortcomings of the above-mentioned existing technologies, the present invention proposes a method for preparing and applying a self-supporting conductive framework modified with MOFs (metal organic frameworks) based on wood. This method provides convenient ion and electron pathways and more sulfur loading and reaction sites. Furthermore, the self-supporting cathode is easily adjustable in thickness, allowing for flexible regulation of sulfur loading, achieving a dynamic balance between sulfur loading and electrochemical performance, ultimately achieving improved energy density.

[0006] A method for preparing a MOFs-modified wood-based self-supporting conductive skeleton comprises the following steps:

[0007] Step (1): first, cutting a commercially available wood block along the vertical growth direction and punching it with a cutter to obtain thin discs of uniform thickness and diameter; boiling the thin discs in deionized water and then adding a buffer solution containing 1% NaClO2 and 5% CH3COONa to perform chemical delignification treatment; then, removing the thin discs and repeatedly rinsing them with ethanol until neutral, thereby obtaining delignified wood chips;

[0008] Step (2): dissolving metal salts and surfactants of different masses in deionized water to obtain a metal salt solution, adding the delignified wood chips obtained in step (1) to the metal salt solution and stirring with a magnetic stirrer to obtain the wood chip metal salt solution;

[0009] Step (3): dissolving the organic ligand and the capping agent in deionized water to obtain a ligand solution, slowly adding the ligand solution to the wood chip metal salt solution, vigorously stirring with a magnetic stirrer, and then aging at room temperature. After aging, the MOFs-modified wood chip is taken out and washed with deionized water and ethanol;

[0010] Step (4): the MOFs-modified wood chips are frozen and transferred to a freeze dryer for drying, and then neatly arranged and sandwiched between two graphite plates, placed in a tubular furnace, and carbonized under a reducing gas atmosphere to obtain a MOFs-modified wood-based carbon film;

[0011] Step (5): The MOFs-modified wood-based carbon film is placed in a glove box, fixed on a rotating table for rotation, and a DOL / DME mixed solution containing Li2S8 is added dropwise. After standing, a MOFs-modified wood-based carbon film-loaded sulfur self-supporting positive electrode is obtained, that is, a MOFs-modified wood-based self-supporting conductive skeleton.

[0012] Specifically, the commercially available wood block in step (1) is one of balsam, poplar, plank wood, basswood, and pine; the wood chip has a thickness of 1-3 mm and a diameter of 16-20 mm.

[0013] Specifically, the metal salts in step (2) correspond to one or more combinations of Fe, Co, Ni, Zn, and Cu, respectively; the surfactants are one or more combinations of polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG); the concentration of the metal salt is in the range of 1-6 mmol, the surfactant is in the range of 0.01-0.06 g, and the stirring time of the magnetic stirrer is 6-8 h.

[0014] Specifically, the organic ligand described in step (3) is one or a combination of 2-methylimidazole and terephthalic acid, and the concentration range of the organic ligand is 8-144 mmol; the magnetic stirring time is 1-3 h; the aging time is 6-18 h; the capping agent is one or more combinations of hexadecyltrimethylammonium bromide (CTAB) and polyvinyl alcohol (PVA), and the capping agent is 0.01-0.13 g.

[0015] Specifically, the MOFs in step (3) are ZIF-67, ZIF-8, MIL-53 and other types of MOFs materials.

[0016] Specifically, the drying temperature in step (4) is -55°C, 100 Pa, and the drying time is 12 hours.

[0017] Specifically, in step (4), the temperature rise rate of the tube furnace sintering is controlled to be 2-10°C / min, and the high temperature sintering is carried out at 700-900°C for 2-4h.

[0018] Specifically, the MOFs-modified wood chips in step (4) are MOFs-loaded wood matrices, and the MOFs crystals are successfully loaded inside the wood pores to play a filling role. The surface of the MOFs nanoparticles is smooth and presents a granular cubic structure. The particle size of the MOFs is 600-900 nm.

[0019] Specifically, in step (5), the rotation speed of the rotating table is 150 rad / min, and 20 μL of a Li2S8 solution with a concentration of 0.2 g / mL is added dropwise, and the solvent is a mixed solution of DOL / DME (v:v=1:1).

[0020] The MOFs-modified wood-based self-supporting conductive skeleton is applied to assemble a button battery with a MOFs-modified wood-based carbon film sulfur-supported self-supporting positive electrode, and the assembly order is negative electrode shell → lithium sheet → 30 μL / mg(s) DOL / DME mixed solution containing 1M LiTFSI and 1.0% LiNO3 → diaphragm → 30 μL / mg(s) DOL / DME mixed solution containing 1M LiTFSI and 1.0% LiNO3 → MOFs-modified wood-based carbon film sulfur-supported self-supporting positive electrode → gasket → shrapnel → positive electrode shell, thus obtaining an LSB with a MOFs-modified wood-based sulfur-supported self-supporting positive electrode.

[0021] Beneficial effects of the present invention:

[0022] The present invention provides a method for preparing a MOFs-modified wood-based carbon film and its application as an LSB positive electrode for energy storage after being loaded with sulfur, which has the following beneficial effects:

[0023] (1) By converting traditional powdered carbon materials into self-supporting carbon matrices, the use of conductive agents, binders, and organic solvents is eliminated when acting on the LSBs self-supporting sulfur cathode. The integrated carbon skeleton can provide convenient ion and electron channels and more sulfur loading and reaction sites. In addition, the self-supporting cathode is easy to control in thickness and can flexibly adjust the sulfur loading, achieving a dynamic balance between sulfur loading and electrochemical performance, ultimately achieving the goal of improving energy density.

[0024] (2) The wood used in the present invention can be used as an excellent sulfur carrier. It is cheap and easily available. Its naturally large pores allow it to load sufficient functional components, providing a valuable solution to the contradiction between high sulfur loading density and long cycle life of LSBs. In addition, no toxic or harmful reagents are introduced, which reduces production costs and is conducive to the industrialization of large-scale carbon-based materials.

[0025] (3) The MOFs used in the present invention not only have a high specific surface area and a porous structure, but also have structurally adjustable properties. During the pyrolysis process, they can be converted into an N-doped carbon framework with a large specific surface area and controllable porosity. Combining them with a wood matrix can avoid the large amount of agglomeration produced during the loading and pyrolysis processes. Moreover, combining them with a highly conductive carbon skeleton can overcome the low electronic conductivity of MOFs.

[0026] (4) The wood-based conductive skeleton carbon matrix used in the present invention is composed of a large number of micron-sized pores with orderly orientation and low tortuosity. This pore structure can provide sufficient sulfur storage space and fast ion and electron transmission channels. After loading MOFs, it is beneficial to expose metal catalytic active sites, thereby enhancing the catalytic activity of LiPSs and alleviating the shuttle effect.

[0027] (5) Compared with the aluminum foil-based slurry-coated electrode, the self-supporting electrode prepared by the present invention through a simple delignification pretreatment, freeze drying, and high-temperature carbonization process does not require additional binders, conductive agents, and current collectors and can be used directly as an electrode, which not only improves the positive electrode specific capacity but also simplifies the electrode preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 These are SEM images of the ZIF-8 modified mycelium-based membrane in Example 2 of the present invention; wherein Figures (a) and (c) represent SEM images of the ZIF-8 modified wood-based membrane before carbonization, and (b) and (d) represent SEM images of the ZIF-8 modified wood-based membrane after carbonization.

[0029] Figure 2 This is a 5000-fold EDS graph of the ZIF-67 modified wood-based carbon film in Example 1 of the present invention.

[0030] Figure 3 This is a charge and discharge curve diagram of the Ni-MOF modified wood-based self-supporting positive electrode in Example 4 of the present invention.

[0031] Figure 4 This is a graph showing the rate performance of the MOFs-modified wood-based carbon film self-supporting positive electrode in Examples 1-4 of the present invention.

[0032] Figure 5 This is a long cycle performance diagram of the Mil-53 modified mycelium-based carbon film self-supporting positive electrode in Example 3 of the present invention after 50 weeks at 0.1C. DETAILED DESCRIPTION

[0033] The following is a combination of the embodiments of the present invention Figure 1-5 The technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0034] Example 1

[0035] Step (1): Commercially available balsa wood blocks were cut perpendicular to their growth direction and punched out using a cutter to obtain thin discs 2 mm thick and 16 mm in diameter. The wood chips were boiled in deionized water and then chemically delignified by adding a buffer solution containing 1% NaClO2 and 5% CH3COONa. The wood chips were then removed and repeatedly rinsed with ethanol until neutral, yielding delignified balsa wood chips.

[0036] Step (2): Dissolve 3 mmol of Co(NO3)2·6H2O and 0.03 g of polyvinylpyrrolidone (PVP) in 50 mL of deionized water to obtain a metal salt solution, and add the delignified wood chips obtained in step (1) thereto and stir for 6 hours.

[0037] Step (3): Dissolve 144 mmol of dimethylimidazole (2-MI) and 13 mg of hexadecyltrimethylammonium bromide (CTAB) in 150 mL of deionized water to obtain a ligand solution, which is slowly added to the metal salt solution of delignified wood chips obtained in step (2), stirred vigorously for 2 h, and then aged at room temperature for 12 h. After aging, the wood chips are taken out and washed with deionized water and ethanol.

[0038] Step (4): Freeze the wood chips obtained in step (3) and transfer them to a freeze dryer for drying for 12 hours (-55°C, 100Pa) to obtain a ZIF-67-loaded wood matrix, which is neatly arranged and sandwiched between two graphite plates, placed in a tubular furnace, and heated and sintered in a reducing atmosphere furnace at a controlled rate of 5°C / min, and sintered at a high temperature of 800°C for 3 hours; obtaining a MOFs-modified wood-based carbon matrix.

[0039] Step (5): The MOFs-modified wood-based carbon film obtained in step (4) was sent into a glove box, fixed on a rotating table at a rotation speed of 150 rad / min, and 20 μL of a Li2S8 solution with a concentration of 0.2 g / mL was added dropwise, and the solvent was a mixed solution of DOL / DME (v:v=1:1). After standing, a MOFs-modified wood-based carbon film-loaded sulfur self-supporting positive electrode was obtained.

[0040] Step (6): Assemble the MOFs-modified wood-based carbon film sulfur-loaded self-supporting positive electrode into a button battery, and the assembly order is negative electrode shell → lithium sheet → 30 μL / mg(s) DOL / DME mixed solution containing 1M LiTFSI and 1.0% LiNO3 → diaphragm → 30 μL / mg(s) DOL / DME mixed solution containing 1M LiTFSI and 1.0% LiNO3 → MOFs-modified wood-based carbon film sulfur-loaded self-supporting positive electrode → gasket → spring → positive electrode shell, thus obtaining an LSB with a MOFs-modified wood-based sulfur-loaded self-supporting positive electrode.

[0041] The electrochemical performance test of the ZIF-67 modified wood-based carbon film self-supporting cathode prepared in Example 1 proved its excellent electrochemical performance as a framework material. Figure 4 As shown, at current densities of 0.1C, 0.2C, 0.5C, and 1C, the first discharge specific capacity was nearly 1142mAh / g, 1012mAh / g, 817mAh / g, and 541mAh / g, respectively. When the current density returned to 0.1C, the positive electrode discharge specific capacity could reach 1133mAh / g, indicating that the ZIF-67 modified wood-based membrane has excellent rate performance. Figure 2 As shown in the figure, after high-temperature carbonization, C, N, O, and Co are evenly distributed on the wood carbon skeleton without obvious agglomeration, indicating that the metal Co and N elements are successfully introduced and cooperate well with the carbon skeleton.

[0042] Example 2

[0043] Step (1): Commercially available basswood blocks were cut perpendicular to their growth direction and punched out using a cutter to obtain thin discs 2 mm thick and 16 mm in diameter. The wood chips were boiled in deionized water and then chemically delignified by adding a buffer solution containing 1% NaClO2 and 5% CH3COONa. The wood chips were then removed and repeatedly rinsed with ethanol until neutral, thereby obtaining delignified basswood chips.

[0044] Step (2): Dissolve 1 mmol of Zn(NO3)2·6H2O and 0.01 g of polyvinylpyrrolidone (PVP) in 50 mL of deionized water to obtain a metal salt solution, and add the delignified forged wood chips obtained in step (1) thereto and stir for 8 hours.

[0045] Step (3): 48 mmol of dimethylimidazole (2-MI) and 6 mg of hexadecyltrimethylammonium bromide (CTAB) were dissolved in 150 mL of deionized water to obtain a ligand solution, which was slowly added to the metal salt solution of the delignified forged wood chips obtained in step (2), stirred vigorously for 2 h, and then aged at room temperature for 18 h. After aging, the wood chips were taken out and washed with deionized water and ethanol.

[0046] Step (4): Freeze the wood chips obtained in step (3) and transfer them to a freeze dryer for drying for 12 hours (-55°C, 100Pa) to obtain a ZIF-8-loaded wood matrix, which is neatly arranged and sandwiched between two graphite plates. The matrix is ​​placed in a tubular furnace and sintered in a reducing atmosphere furnace at a controlled rate of 10°C / min and sintered at 800°C for 4 hours to obtain a MOFs-modified wood-based carbon matrix.

[0047] Step (5): The MOFs-modified wood-based carbon film obtained in step (4) was sent into a glove box, fixed on a rotating table at a rotation speed of 150 rad / min, and 20 μL of a Li2S8 solution with a concentration of 0.2 g / mL was added dropwise, and the solvent was a mixed solution of DOL / DME (v:v=1:1). After standing, a MOFs-modified wood-based carbon film-loaded sulfur self-supporting positive electrode was obtained.

[0048] Step (6): Assemble the MOFs-modified wood-based carbon film sulfur-loaded self-supporting positive electrode into a button battery, and the assembly order is negative electrode shell → lithium sheet → 30 μL / mg(s) DOL / DME mixed solution containing 1M LiTFSI and 1.0% LiNO3 → diaphragm → 30 μL / mg(s) DOL / DME mixed solution containing 1M LiTFSI and 1.0% LiNO3 → MOFs-modified wood-based carbon film sulfur-loaded self-supporting positive electrode → gasket → spring → positive electrode shell, thus obtaining an LSB with a MOFs-modified wood-based sulfur-loaded self-supporting positive electrode.

[0049] The morphology of the ZIF-8 modified wood-based precursor and sintered body prepared in Example 2 is as follows: Figure 1 (a) Figure 1 (b) Figure 1 (c) and Figure 1 As shown in (d), before sintering, ZIF-8 crystals are successfully loaded inside the wood pores, playing a filling role. The surface of the ZIF-8 nanoparticles is smooth and has a granular cubic structure. The particle size of ZIF-8 is approximately 600-900nm. After sintering, ZIF-8 is successfully converted into Zn nanoparticles, and the ZIF-8 skeleton collapses to form Zn / N@CBW with the wood.

[0050] Example 3

[0051] Step (1): Commercially available poplar wood blocks were cut perpendicular to their growth direction and punched using a cutter to obtain thin discs 2 mm thick and 16 mm in diameter. The wood chips were boiled in deionized water and then chemically delignified by adding a buffer solution containing 1% NaClO2 and 5% CH3COONa. The wood chips were then removed and repeatedly rinsed with ethanol until neutral, thereby obtaining delignified poplar wood chips.

[0052] Step (2): 3 mmol of FeCl3·6H2O and 0.03 g of polyethylene glycol (PEG) were dissolved in 50 mL of deionized water to obtain a metal salt solution, and the delignified poplar wood chips obtained in step (1) were added thereto and stirred for 8 h;

[0053] Step (3): 48 mmol of terephthalic acid and 6 mg of cetyltrimethylammonium bromide (CTAB) were dissolved in 150 mL of deionized water to obtain a ligand solution, which was slowly added to the metal salt solution of delignified poplar wood chips obtained in step (2), stirred vigorously for 2 h, and then aged at room temperature for 18 h. After aging, the wood chips were removed and washed with deionized water and ethanol;

[0054] Step (4): The wood chips obtained in step (3) were frozen and transferred to a freeze dryer for drying for 12 h (-55 ° C, 100 Pa) to obtain a MIL-53 (Fe)-loaded wood matrix, which was neatly arranged and sandwiched between two graphite plates, placed in a tubular furnace, and sintered in a reducing atmosphere furnace at a controlled rate of 5 ° C / min, and sintered at a high temperature of 800 ° C for 4 h to obtain a MOFs-modified wood-based carbon matrix;

[0055] Step (5): The MIL-53 (Fe) modified wood-based carbon film obtained in step (4) was placed in a glove box, fixed on a rotating table at a rotation speed of 150 rad / min, and 20 μL of a 0.2 g / mL Li2S8 solution was added dropwise, and the solvent was a mixed solution of DOL / DME (v:v=1:1). After standing, a MIL-53 (Fe) modified wood-based carbon film-loaded sulfur self-supporting positive electrode was obtained;

[0056] Step (6): Assemble the button battery with the MIL-53(Fe) modified wood-based carbon film sulfur-loaded self-supporting positive electrode, and the assembly order is negative electrode shell → lithium sheet → 30 μL / mg(s) DOL / DME mixed solution containing 1M LiTFSI and 1.0% LiNO3 → diaphragm → 30 μL / mg(s) DOL / DME mixed solution containing 1M LiTFSI and 1.0% LiNO3 → MIL-53(Fe) modified wood-based carbon film sulfur-loaded self-supporting positive electrode → gasket → spring → positive electrode shell, thus obtaining an LSB using a MIL-53(Fe) modified wood-based sulfur-loaded self-supporting positive electrode.

[0057] The electrochemical performance of the MIL-53 (Fe) modified wood-based carbon film self-supporting cathode prepared in Example 3 was tested. Figure 5 The capacity of approximately 814 mAh / g was maintained after 50 cycles at a current density of 0.1 C, with a single-cycle decay rate of 0.56%. This is attributed to the fact that the Fe-MOFs-derived carbon material can fully expose Fe catalytic sites and nitrogen doping sites, enabling more efficient chemical adsorption and catalytic conversion of LiPSs, thereby improving their conversion kinetics.

[0058] Example 4

[0059] Step (1): Commercially available pine wood blocks were cut perpendicular to their growth direction and punched using a cutter to obtain thin discs 2 mm thick and 16 mm in diameter. The wood chips were boiled in deionized water and then chemically delignified by adding a buffer solution containing 1% NaClO2 and 5% CH3COONa. The wood chips were then removed and repeatedly rinsed with ethanol until neutral, obtaining delignified pine wood chips.

[0060] Step (2): 3 mmol Ni(NO3)2·6H2O and 0.03 g polyethylene glycol (PEG) were dissolved in 50 mL deionized water to obtain a metal salt solution, and the delignified pine wood chips obtained in step (1) were added thereto and stirred for 8 h;

[0061] Step (3): 24 mmol of 2-MI and 3 mg of hexadecyltrimethylammonium bromide (CTAB) were dissolved in 150 mL of deionized water to obtain a ligand solution, which was slowly added to the metal salt solution of delignified pine wood chips obtained in step (2), stirred vigorously for 2 h, and then aged at room temperature for 18 h. After aging, the wood chips were removed and washed with deionized water and ethanol;

[0062] Step (4): Freeze the wood chips obtained in step (3) and transfer them to a freeze dryer for drying for 12 hours (-55°C, 100Pa) to obtain a Ni-MOF-loaded wood matrix, which is neatly arranged and sandwiched between two graphite plates, placed in a tubular furnace, and heated and sintered in a reducing atmosphere furnace at a controlled rate of 5°C / min. Sinter at a high temperature of 900°C for 2 hours to obtain a MOFs-modified wood-based carbon matrix.

[0063] Step (5): The Ni-MOF modified wood-based carbon film obtained in step (4) was placed in a glove box, fixed on a rotating table at a rotation speed of 150 rad / min, and 20 μL of a 0.2 g / mL Li2S8 solution was added dropwise, and the solvent was a mixed solution of DOL / DME (v:v=1:1). After standing, a Ni-MOF modified wood-based carbon film-loaded sulfur self-supporting positive electrode was obtained;

[0064] Step (6): Assemble the Ni-MOF modified wood-based carbon film sulfur-loaded self-supporting positive electrode into a button battery, and the assembly order is negative electrode shell → lithium sheet → 30 μL / mg(s) DOL / DME mixed solution containing 1M LiTFSI and 1.0% LiNO3 → diaphragm → 30 μL / mg(s) DOL / DME mixed solution containing 1M LiTFSI and 1.0% LiNO3 → Ni-MOF modified wood-based carbon film sulfur-loaded self-supporting positive electrode → gasket → spring → positive electrode shell, thus obtaining an LSB using a Ni-MOF modified wood-based sulfur-loaded self-supporting positive electrode.

[0065] The electrochemical performance of the Ni-MOF modified wood-based carbon film self-supporting cathode prepared in Example 4 was tested. Figure 3 From the constant current charge-discharge curves of the first week at 0.1C, it can be seen that the Ni-MOF modified wood-based carbon film self-supporting positive electrode has two typical discharge platforms and one charging platform. The voltage platform around 2.3V corresponds to the transformation of S8 to long-chain LiPSs, and the 2.1V platform corresponds to the transformation of long-chain LiPSs to Li2S. The charging platform around 2.4V is the reverse reaction of the above reaction, that is, the oxidation reaction of Li2S to S8.

[0066] The above results demonstrate that the wood substrate used in this invention is an excellent conductive substrate capable of supporting excellent catalysts, making it a promising self-supporting cathode material for LSBs. This not only simplifies the process but also increases the sulfur loading capacity of LSBs. The wood-based self-supporting cathode was prepared using biomass wood as raw material, which was pretreated by cutting and delignification. The material was loaded with MOFs containing Co, Zn, Fe, and Ni as metal active centers and dimethylimidazole and terephthalic acid as organic ligands. The resulting wood-based self-supporting cathode was then freeze-dried. The freeze-dried mycelial membrane was sandwiched between two graphite plates and placed in a tubular furnace. Nitrogen was used as the shielding gas and heated in a stepwise manner to produce the resulting material.

[0067] The present invention utilizes natural wood with a directional ordered pore array with low curvature and good structural stability, and the thickness is easy to control. On the one hand, the appropriate thickness and rich pores of the wood can greatly increase the sulfur loading capacity. The appropriate thickness needs to be determined as a standard through sandpaper polishing. On the other hand, its continuous conductive framework and low curvature are conducive to electrolyte penetration to achieve rapid transfer of ions and electrons. However, the ordered pores of wood are large-sized channels at the micron level and lack functional micro-mesopores, which can easily cause sulfur loss, resulting in serious capacity decay. Therefore, filling and modifying the pores of wood by loading catalysts is an effective way to improve the electrochemical performance of wood-based self-supporting positive electrodes. The wood used in the present invention is bio-macro-renewable, cheap and easy to obtain. The self-supporting positive electrode sheet obtained is assembled into a stacked battery, and the battery performance test shows good electrochemical performance.

Claims

1. A method for preparing a MOFs-modified wood-based self-supporting conductive skeleton, characterized in that: The following steps are involved: Step (1): first, cut a commercially available wood block along the vertical growth direction and punch it with a cutter to obtain a thin disc with uniform thickness and diameter; boil the thin disc in deionized water and then add a buffer solution containing NaClO2 and CH3COONa to perform chemical delignification treatment; then take out the thin disc and repeatedly rinse it with ethanol until it is neutral to obtain delignified wood chips; Step (2): dissolving metal salts and surfactants of different masses in deionized water to obtain a metal salt solution, adding the delignified wood chips obtained in step (1) to the metal salt solution and stirring with a magnetic stirrer to obtain a wood chip metal salt solution; The metal salts in step (2) correspond to metal species selected from one or more combinations of Fe, Co, Ni, Zn, and Cu; Step (3): dissolving the organic ligand and the capping agent in deionized water to obtain a ligand solution, slowly adding the ligand solution to the wood chip metal salt solution, vigorously stirring with a magnetic stirrer, and then aging at room temperature. After aging, the MOFs-modified wood chips are taken out and washed with deionized water and ethanol; The organic ligand in step (3) is one or a combination of 2-methylimidazole and terephthalic acid; Step (4): the MOFs-modified wood chips are frozen and transferred to a freeze dryer for drying, and then neatly arranged and sandwiched between two graphite plates, placed in a tubular furnace, and carbonized under a reducing gas atmosphere to obtain a MOFs-modified wood-based carbon film; Step (5): The MOFs-modified wood-based carbon film is placed in a glove box, fixed on a rotating table for rotation, and a DOL / DME mixed solution containing Li2S8 is added dropwise. After standing, a MOFs-modified wood-based carbon film-loaded sulfur self-supporting positive electrode is obtained, that is, a MOFs-modified wood-based self-supporting conductive skeleton.

2. The method for preparing a MOFs-modified wood-based self-supporting conductive skeleton according to claim 1, characterized in that: The commercially available wood block in step (1) is one of balsa wood, poplar wood, plank wood, basswood, and pine wood; the wood chip has a thickness of 1-3 mm and a diameter of 16-20 mm; The buffer solution is an aqueous solution of 1% NaClO2 and 5% CH3COONa.

3. The method for preparing a MOFs-modified wood-based self-supporting conductive skeleton according to claim 2, characterized in that: The surfactant is one or more combinations of polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG), the metal salt is 1-6 mmol, the surfactant is 0.01-0.06 g, and the stirring time of the magnetic stirrer is 6-8 h.

4. The method for preparing a MOFs-modified wood-based self-supporting conductive skeleton according to claim 3, characterized in that: The organic ligand is 8-144 mmol; the magnetic stirring time is 1-3 h; the aging time is 6-18 h; the capping agent is one or more combinations of cetyltrimethylammonium bromide (CTAB) and polyvinyl alcohol (PVA), and the capping agent is 0.01-0.13 g.

5. The method for preparing a MOFs-modified wood-based self-supporting conductive skeleton according to claim 1, characterized in that: The drying in step (4) is carried out at a temperature of -55°C, 100 Pa, and a time of 12 h. The heating rate of the tubular furnace in step (4) is controlled to be 2-10°C / min, and the high-temperature sintering is carried out at 700-900°C for 2-4 h.

6. The method for preparing a MOFs-modified wood-based self-supporting conductive skeleton according to claim 5, characterized in that: The MOFs-modified wood chips in step (4) serve as a MOFs-loaded wood matrix. The MOFs crystals are successfully loaded inside the wood pores, playing a filling role. The surface of the MOFs nanoparticles is smooth and presents a granular cubic structure. The particle size of the MOFs is 600-900 nm.

7. The method for preparing a MOFs-modified wood-based self-supporting conductive skeleton according to claim 1, characterized in that: In step (5), the rotation speed of the rotating table is 150 rad / min, and 20 μL of Li2S8 solution with a concentration of 0.2 g / mL is added dropwise. The solvent is a mixed solution of DOL / DME, v:v=1:

1.

8. Application of the MOFs modified wood-based self-supporting conductive skeleton obtained by the method according to any one of claims 1 to 7, characterized in that: The MOFs-modified wood-based carbon film sulfur-loaded self-supporting positive electrode was assembled into a button cell. The assembly order was negative electrode shell → lithium sheet → 30 μL / mg(s) DOL / DME mixed solution containing 1M LiTFSI and 1.0% LiNO3 → diaphragm → 30 μL / mg(s) DOL / DME mixed solution containing 1M LiTFSI and 1.0% LiNO3 → MOFs-modified wood-based carbon film sulfur-loaded self-supporting positive electrode → gasket → shrapnel → positive electrode shell, thus obtaining a lithium-sulfur battery with MOFs-modified wood-based sulfur-loaded self-supporting positive electrode.

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