Molten salt dielectric heat conduction chemical preparation and application of flat wood carbon electrode substrate material

Abstract

The invention discloses a molten salt dielectric heat conduction chemical preparation method of a flat wood carbon electrode substrate material, a wood carbon electrode precursor is covered with molten salt, the molten salt dielectric heat conduction chemical synthesis is carried out according to the heating-heat preservation-cooling process, and the molten salt is a mixture formed by mixing inert molten salt and active molten salt; and removing condensed fused salt on the surface of the synthetic product, polishing the surface, and drying to obtain the wood carbon electrode substrate material. According to the preparation method, the problems of high cost, high energy consumption, narrow application range and the like in preparation of a high-performance plate electrode substrate carbon material aiming at integral wood with a specific size are solved, and the self-supporting electrode material substrate which is low in cost, has a hierarchical pore structure and has comprehensive performance is obtained. The obtained wood carbon electrode substrate material can be used as a plate electrode substrate carbon material; alternatively, a high surface capacitance plate electrode is directly used for capacitive deionization or supercapacitors.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials for electrochemical engineering, and particularly relates to the molten salt-mediated thermochemical preparation and application of a flat wood-based carbon electrode substrate material. Background Art

[0002] As the core component in electrochemical engineering equipment, the performance of the electrode directly affects the efficiency and stability of the entire engineering production. Whether it is electrochemical energy storage and conversion engineering technologies (such as batteries, supercapacitors, fuel cells, electrolysis of water, etc.) or electrochemical water treatment technologies (electrooxidation, electro-Fenton, electroadsorption, etc.), most of them cannot directly use existing materials. Therefore, developing suitable electrode materials is one of the research focuses in the field of electrochemical engineering technology. Usually, it is composed of active materials, conductive agents, binders, load (transition) materials, and substrate materials, and is constructed / prepared by methods such as slurry coating, chemical vapor deposition, electrochemical deposition, hydrothermal / solvothermal deposition, 3D printing, molten salt synthesis, etc. The flat electrode substrate material in the most common flat electrode electrochemical reactor can be metal foil, porous metal, polymer film, carbon material, etc., which should be selected according to the working conditions. An ideal substrate material usually should have certain strength, conductivity, functionality, processability, and many other specific requirements. For wood-based carbon substrate materials, due to their unique structures and properties such as high specific surface area, rich pore structure, good conductivity, and environmental friendliness, they show great application potential in the fields of electrochemical energy storage and environmental governance.

[0003] The wood-based carbon substrate material is a porous carbon material prepared by processes such as carbonization and activation using natural wood as a precursor; it can be stably and durably applied within the aqueous electrochemical window; its development not only conforms to the concept of sustainable development but also provides new ideas for the preparation of high-performance carbon-based electrodes. For the development of wood-based carbon substrate materials, the molten salt-mediated thermochemical preparation method is an efficient and controllable preparation technology, showing great potential and advantages. It uses molten salt as a reaction medium and converts natural wood into functional carbon materials through high-temperature carbonization and structure regulation. By adjusting the molten salt composition and process parameters to ensure the obtained carbon materials have a large true surface area, hierarchical pore structure, and excellent electrochemical performance, its technical advantages are as follows: (1) Uniform heating: The molten salt provides a uniform thermal field, avoiding local overheating or incomplete pyrolysis; (2) Catalytic effect: It can catalyze the carbonization reaction through specific molten salts (such as KOH, NaCl-KCl), reducing the reaction temperature; (3) Template effect: The molten salt can act as a soft template to regulate the pore structure of wood-based carbon; (4) Environmentally friendly: The molten salt can be recycled, reducing waste emissions.

[0004] At present, the molten salt preparation of wood-derived carbon can be divided into three categories: (1) extracting lignin from wood and then mediating lignin-derived carbon materials by molten salt; (2) removing lignin and hemicellulose components from wood and performing molten salt-assisted carbonization of the wood cell wall to obtain elastic wood sponges; (3) directly performing molten salt-mediated thermochemical preparation on wood precursors. The cores of the first two preparations are respectively carried out in response to the complex composition of wood, where lignin, hemicellulose, and cellulose are intertwined, resulting in wood-derived carbon materials with smaller pore sizes and dense structures after carbonization, which are not conducive to applications such as ion transport and storage. Both involve multiple steps such as raw material selection, pretreatment, carbonization, and post-treatment. Comparing (2) and (3), both are obtained by carbonizing the natural wood cell wall structure. However, the former first pre-treats the wood (dissolving some chemical components, namely cellulose, hemicellulose, and lignin, on the basis of not destroying the basic skeleton of the wood to increase the porosity inside the wood) and then carbonizes, usually resulting in powdery carbon materials, which is an energy-consuming and inefficient process; the latter directly utilizes the natural pores of the wood to form channels and genetically obtains a complete carbon sheet, using it as a self-supporting electrode, which is a more energy-saving and simpler approach. In this technical approach, no binder needs to be added; at the same time, the mechanical strength of the wood itself is fully utilized; moreover, the longitudinally through pores and internal micro / mesopores synergistically promote ion transport, and this structural feature endows wood-derived carbon materials with an irreplaceable efficacy in electrode applications that is difficult to achieve by artificial preparation. However, for the production of specific-sized whole wood, how to break the tight barrier of different components of the wood cell wall, introduce functional groups to overcome the problems of underdeveloped pore structure, uneven pore distribution, low reactivity, and the flatness of the overall structure in molten salt-mediated thermochemical preparation is the main challenge faced by the processing of such flat electrode substrate carbon materials.

[0005] Capacitive deionization technology has attracted much attention in the field of water treatment due to its characteristics such as low energy consumption, environmental friendliness, and easy regeneration of electrodes. Aqueous supercapacitors, as a very promising new energy technology, have advantages such as high efficiency, environmental protection, sustainability, and safety, and are widely used in fields such as new energy, electric vehicles, and smart grids. Flat electrode substrate carbon materials have obvious material advantages and high-compatibility technical characteristics in the core component of these two, namely the electrode, and have great application prospects. Therefore, effectively using wood precursors for molten salt-mediated thermochemical preparation to obtain a material that not only retains the natural pore structure but also may generate new micropores and mesopores, in order to obtain high-performance flat electrode substrate carbon materials and direct applications, is of great engineering value for these two types of devices and technologies. Summary of the Invention

[0006] To overcome the above-mentioned disadvantages of the prior art, the object of the present invention is to provide a molten salt-mediated thermochemical preparation and application of a flat wood-based carbon electrode substrate material, so as to solve the problems of high cost, high energy consumption, narrow application range, etc. faced in the preparation of high-performance flat electrode substrate carbon materials for whole wood of specific sizes, and obtain a self-supporting electrode material substrate with low cost, multi-level pore structure, and balanced comprehensive performance.

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

[0008] A molten salt-mediated thermochemical preparation method of a flat wood-based carbon electrode substrate material, comprising the following steps:

[0009] Step 1, covering the wood-based carbon electrode precursor with molten salt, and performing molten salt-mediated thermochemical synthesis according to the process of heating - heat preservation - cooling, wherein the molten salt is a mixture composed of an inert molten salt and an active molten salt;

[0010] Step 2, removing the condensed molten salt on the surface of the synthesis product, polishing the surface and drying it to obtain the wood-based carbon electrode substrate material.

[0011] In one embodiment, the wood-based carbon electrode precursor is air-dried wood, and the compensation coefficient of its size to the size of the finally obtained wood-based carbon electrode substrate material is 1.2 - 1.7∶1.

[0012] In one embodiment, the inert molten salt is KCl, and the active molten salt is ZnCl2, and the mass ratio of the two is 1∶1 - 1∶4.

[0013] In one embodiment, covering the wood-based carbon electrode precursor with molten salt means completely coating the wood-based carbon electrode precursor with molten salt.

[0014] In one embodiment, in Step 1, the depth of the container for accommodating the wood-based carbon electrode precursor covered with molten salt is 2 - 3 times the thickness of the wood-based carbon electrode precursor.

[0015] In one embodiment, the process of heating - heat preservation - cooling is as follows:

[0016] The heating rate is 3 - 5°C / min, and the temperature is raised to 800 - 850°C; the heat preservation time is 180 - 300 min; the cooling rate is 3 - 5°C / min, and the temperature is lowered to room temperature.

[0017] In one embodiment, the process of heating - heat preservation - cooling is carried out in an air atmosphere.

[0018] In one embodiment, the condensed molten salt is removed by dissolving it with deionized water, and then the oil stain is removed by washing with acetone and absolute ethanol, and finally it is thoroughly rinsed with deionized water.

[0019] In one embodiment, deionized water is used to remove residual salts, acetone and absolute ethanol are used to remove residual oil stains, and the material is thoroughly cleaned with flowing deionized water until the pH value of the aqueous solution reaches 6 - 8 and the conductivity is 1 - 20 μS / cm, and the drying temperature is 60 - 80 °C.

[0020] The wood-based carbon electrode substrate material obtained by the present invention can be used as a flat electrode substrate carbon material; or, it can be directly used as a flat electrode with high surface capacitance for capacitive deionization or supercapacitors.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. The present invention uses molten salt-mediated thermochemical synthesis to synchronously complete carbonization and activation in an air atmosphere. Compared with the traditional method that requires separate steps of carbonization (in a high-temperature inert atmosphere) and chemical activation (such as KOH corrosion treatment), the inert gas protection is omitted, reducing the equipment cost and energy consumption.

[0023] 2. The natural pores of wood are further expanded under the action of molten salt to form hierarchical pores, which is beneficial to promoting the ion adsorption capacity (applicable to capacitive deionization) and charge storage capacity (applicable to supercapacitors).

[0024] 3. The surface of the flaky carbon synthesized by molten salt-mediated thermochemical synthesis is flat. After polishing, the thickness is controllable and smooth, and it can be directly used as an electrode without additional binder. Its mechanical strength is superior to that of powdered activated carbon electrodes, avoiding structural collapse.

[0025] 4. The natural hierarchical pores are suitable for both capacitive deionization and meet the requirements of supercapacitors for high specific capacitance, broadening the application range of wood-based carbon electrodes. Description of the Drawings

[0026] Figure 1(a) is a cross-sectional SEM image of the wood-based carbon prepared in the embodiment of the present invention.

[0027] Figure 1(b) is the pore wall thickness of the wood-based carbon prepared in the embodiment of the present invention.

[0028] Figure 1(c) is a longitudinal-sectional SEM image of the wood-based carbon prepared in the embodiment of the present invention

[0029] Figure 2 is the Raman spectrum of the wood-based carbon electrode prepared by the present invention.

[0030] Figure 3 is the CV diagram of the wood-based carbon electrode prepared by the present invention.

[0031] Figure 4 is the EIS diagram of the wood-based carbon electrode prepared by the present invention. Detailed Embodiments

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below in conjunction with specific embodiments and comparative examples. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope protected by the present invention.

[0033] Unless otherwise specified, the equipment used in this embodiment and the comparative examples are all conventional experimental equipment. The materials and reagents used are commercially available without special instructions, and the experimental methods without special instructions are also conventional experimental methods.

[0034] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0035] The present invention relates to a molten salt-mediated thermochemical preparation method for a flat woody carbon electrode substrate material. This preparation method uses a covered corundum boat to coat the whole wood with a preferably low-melting-point mixed molten salt, and through a preferably heating and carbonization process, high-temperature synergistic etching-activation is achieved to finally obtain a high-performance flat electrode substrate carbon material with an optimized pore structure. This preparation is a one-step molten salt-mediated synthesis without the protection of inert gas in an air atmosphere. After washing off the molten salt, a flaky woody carbon with a relatively high surface flatness can be obtained. With further mechanical polishing, woody carbon with a certain thickness and surface roughness requirements can be obtained and directly used as a self-supporting electrode, which is an energy-saving and simple method. In this technical approach, no binder needs to be added, and the mechanical strength of the wood itself is fully utilized. Moreover, the longitudinally through pores and the internal micro / mesopores also promote ion transport. This preparation endows the wood-derived carbon material with an irreplaceable efficacy in electrode applications. The prepared woody carbon electrode has good mechanical strength and a natural pore structure, excellent adsorption performance, and can be directly used for flat electrode applications with high surface capacitance for capacitive deionization or supercapacitors. The process and principle of the present invention can be specifically described as the following steps:

[0036] Step 1: Prepare for molten salt-mediated synthesis.

[0037] Cut the air-dried wood (such as poplar wood) into blocks of a set size to be used as the precursor of the woody carbon electrode substrate material; according to the mass of the wood precursor, appropriately weigh a molten salt system composed of an inert molten salt and an active molten salt in a corresponding proportion. Each component of the molten salt is dried in an oven to remove moisture, and then ground and mixed evenly in a mortar to finally prepare a molten salt mixture with a specific composition.

[0038] The molten salt of the present invention has both the functions of a templating agent and an activating agent. Among them, the inert molten salt acts as a sealant to prevent the oxidation or even spontaneous combustion of the woody carbon precursor during air carbonization; the active molten salt forms pore structures in the carbon matrix through its own etching characteristics, and synchronously completes the morphology regulation and pore microstructure construction during the carbonization process. Exemplarily, the inert molten salt in the present invention is KCl, and the active molten salt is ZnCl2, and the mass ratio of the two is 1:1 to 1:4. In the molten salt system of this example, KCl provides a stable physical template as an inert component, and ZnCl2, as an active component, realizes the efficient construction of pores through the corrosive chemical reaction of chloride ions, forming a synergistic effect between the two during the carbonization process. By adjusting the mass ratio of KCl to ZnCl2, a balance is achieved between morphology regulation and pore activation.

[0039] Step 2, molten salt-mediated synthesis.

[0040] According to the volume and processing amount of the woody carbon electrode precursor, select a corundum boat with an appropriate processing volume, cover the precursor poplar blocks with molten salt and place them in the corundum boat. Preferably, the depth of the inner groove of the corundum boat is 2 to 3 times the total thickness of the placed precursor. Subsequently, cover it with a matching corundum lid and transfer it to a muffle furnace, and carry out molten salt-mediated thermochemical synthesis without inert gas protection according to the preferred heating-holding-cooling procedure.

[0041] The preferred heating-holding-cooling procedure for this step is: the heating rate is 3 - 5 °C / min; when heating up to 850 °C, the holding time is 180 - 300 min; the cooling rate is 3 - 5 °C / min. The temperature program of this example avoids the severe shrinkage of the woody carbon precursor due to thermal stress and the resulting structure collapse by slowly heating up, and at the same time, the molten salt uniformly, slowly and fully penetrates into the precursor; long-time holding at a high temperature range ensures the full carbonization of the precursor and the full activation of the molten salt, and regulates the degree of carbonization within an appropriate time window; the slow cooling process ensures the orderly rearrangement of the carbon skeleton, reduces microcracks, and at the same time inhibits pore collapse.

[0042] This step does not need to use an inert atmosphere as in the traditional molten salt solid-phase mixing carbonization process. The reason is that before the melting point temperature, heat causes the system to exhaust gas outward, and the oxidation damage can be ignored; after reaching the melting point temperature, the molten salt covering the precursor forms a liquid seal effect, which can shield air and prevent the precursor from undergoing severe oxidation or even spontaneous combustion. While shielding air, its high heat capacity also helps to promote rapid heat conduction and carbonization.

[0043] Step 3, post-treatment.

[0044] For the wood carbon that has completed molten salt-mediated thermochemical synthesis and cooled to room temperature, it is taken out of the corundum boat, and deionized water and absolute ethanol are used to dissolve and remove the condensed molten salt and wash the wood carbon clean. According to the surface roughness control requirements for the wood carbon used as an electrode substrate and a capacitive electrode application, mechanical polishing is used to control the surface roughness, and finally it is dried with hot air. Specifically, the synthesized wood carbon can be alternately mechanically polished with coarse and fine water sandpapers and coarse sandpaper until the surface roughness reaches the required control.

[0045] Exemplarily, in this step, deionized water is used to remove the residual salt, and it is thoroughly washed with flowing deionized water until the pH value of the aqueous solution reaches 6 - 8 and the conductivity is 1 - 20 μS / cm. The drying temperature is 60 - 80 °C.

[0046] The volume of the wood precursor will shrink after carbonization. Using a compensation coefficient can ensure the effective size of the electrode after carbonization. The compensation coefficient of the size of the wood precursor to the size of the final wood carbon substrate material in the present invention is preferably 1.2 - 1.7:1.

[0047] The wood carbon electrode prepared by the present invention can provide a flat electrode with a high surface capacitance directly applicable to capacitive deionization and supercapacitors. The treatment solution of the capacitive deionization flat electrode is an aqueous solution containing heavy metals such as nickel or an aqueous medium supercapacitor such as Na2SO4 and KOH.

[0048] The following are several specific embodiments of the present invention.

[0049] Example 1

[0050] A molten salt-mediated thermochemical preparation method for a flat wood carbon electrode substrate material. First, poplar wood blocks are sliced to obtain wood chips with dimensions of 70×70×3 mm. Then the wood chips are weighed, and according to the mass of the wood chips, ZnCl2 and KCl are weighed in a mass ratio of wood chips:ZnCl2:KCl = 1:1:4 and ground in a mortar until ZnCl2 and KCl are evenly mixed. The wood chips and the mixed molten salt are placed in a covered corundum boat with dimensions of 100×100×20 mm, so that the molten salt completely covers and wraps the wood chips, and the lid is covered. The boat is placed in a muffle furnace and heated to 850 °C at a heating rate of 3 °C / min in an air atmosphere. After holding for 180 min, it is naturally cooled to room temperature. The carbonized wood chips are taken out, washed with deionized water and absolute ethanol until the pH value of the solution is 6 - 8 and the conductivity is 1 - 20 μS / cm, and then placed in an oven and dried at a constant temperature of 60 °C. The wood carbon is alternately polished with 800 - mesh fine sandpaper and 220 - mesh coarse sandpaper to obtain a wood carbon electrode material with a thickness of about 1.5 mm.

[0051] Example 2

[0052] A molten salt mediated thermochemical preparation method for flattening a woody carbon electrode substrate material. First, poplar wood blocks are sliced to obtain wood chips with dimensions of 70×70×3 mm. Then, the wood chips are weighed, and according to the mass of the wood chips, ZnCl2 and KCl are weighed in a mass ratio of wood chips:ZnCl2:KCl = 1:1:4, and ground in a mortar until ZnCl2 and KCl are evenly mixed. The wood chips and the mixed molten salt are placed in a covered corundum ark with dimensions of 100×100×20 mm, such that the molten salt completely covers and wraps the wood chips, and then the lid is covered. The ark is placed in a muffle furnace and heated to 850 °C at a heating rate of 5 °C / min in an air atmosphere. After holding for 180 min, it is naturally cooled to room temperature. The carbonized wood chips are taken out, rinsed with deionized water and absolute ethanol until the pH value of the solution is 6 - 8 and the conductivity is 1 - 20 μS / cm, and then placed in an oven for drying at a constant temperature of 60 °C. The woody carbon is alternately polished with 800-mesh fine sandpaper and 220-mesh coarse sandpaper to obtain a woody carbon electrode material with a thickness of about 1.5 mm.

[0053] According to the comparison results of Examples 1 and 2, it can be seen that woody carbon with better initial surface flatness can be obtained by reducing the heating rate.

[0054] In the present invention, a CDI device is composed of a worthy woody carbon electrode as the negative electrode material and graphite paper as the positive electrode material for the adsorption of heavy metal ions. Using nickel ions as the target pollutant, a simulated heavy metal wastewater containing Ni with a concentration of 50 mg / L is prepared. 2+ Under the conditions of a voltage of 1.6 V, a temperature of 20 °C, a pH of 6, and a flow rate of 10 mL / min, 100 mL of wastewater containing Ni 2+ is electro-adsorbed. After 180 min of adsorption, the removal rate of Ni 2+ is 18.65%.

[0055] The SEM images of the woody carbon electrode prepared in Example 1 of the present invention are shown in Figures 1(a), 1(b), and 1(c). It can be seen from the SEM images that the main pore channels are large pores with a size of 5 - 10 μm, containing a small amount of micro and mesopores, and the pore wall thickness is about 1.5 μm.

[0056] Figure 2 This is the Raman spectrum of the woody carbon electrode prepared in Example 1 of the present invention. The D peak appearing at 1340 cm -1 reflects the disorder and structural defects of carbon, and the G peak appearing at 1585 cm -1 indicates the presence of a two-dimensional hexagonal lattice with E 2g symmetry and a sp 2 carbon atom structure. The intensity ratio of the D and G peaks, I D / I G = 0.98, indicates that the prepared woody carbon material is a typical amorphous carbon structure.

[0057] Figure 3 This is the CV diagram of the wood-based carbon electrode prepared in Example 1 of the present invention. It can be seen that the wood-based carbon has typical electric double layer characteristics as an electrode and can be used as an electrode material for capacitive deionization. The electric double layer capacitance generated on its surface is used to adsorb ions in the aqueous solution. According to calculations, the specific capacitance of this wood-based carbon electrode is 2.95 F / g at a scanning rate of 50 mV / s. Although a relatively low specific capacitance value is presented under the current experimental conditions due to the influence of high scanning rates, a quasi-rectangular CV curve is still maintained at high scanning rates, indicating that the material has excellent rate performance. This wood-based carbon is used as a substrate to be compounded with pseudocapacitive materials, and a hybrid supercapacitor can be constructed to break through the energy density limitation of traditional electric double layer carbon materials.

[0058] Figure 4 This is the EIS diagram of the wood-based carbon electrode prepared in Example 1 of the present invention. It can be seen that the wood-based carbon has a low charge transfer resistance, which is beneficial to the rapid adsorption / desorption of target ions and reduces the overall energy consumption.

[0059] In summary, compared with the traditional molten salt solid-phase mixing carbonization process, the significant advantages of the present invention are as follows: First, the molten salt has both the functions of a templating agent and an activating agent, and simultaneously completes the morphology regulation and pore microstructure construction during the carbonization process. The molten salt forms a uniform liquid environment at high temperature, provides a physical template for the carbon precursor, guides the directional growth of its morphology, and simultaneously generates volatile substances through chemical reactions, thereby forming micropores and mesopores in the carbon matrix. Second, the process flow is simplified, avoiding subsequent washing and binder addition steps. The molten salt can be removed by simple water washing after carbonization without complex post-treatment processes, significantly reducing production costs and environmental pollution. Third, the prepared flat electrode substrate has a high flatness and good surface hydrophilicity. The micropores and mesopores introduced by the molten salt during the carbonization process increase the specific surface area of the material, retain heteroatoms and enhance the surface hydrophilicity, which is beneficial to the penetration of the electrolyte and the transport of ions. Fourth, the carbon material salt medium can be recycled, which conforms to the concept of green chemistry. The molten salt can be removed by simple water washing after carbonization without using toxic chemicals, reducing environmental pollution. In addition, the raw materials of the molten salt are simple and easy to obtain, with low economic and energy costs, and the post-treatment operation is simple and convenient, which is a green and sustainable preparation method.

Claims

1. A molten salt-mediated thermochemical preparation method for a flat wood carbon electrode substrate material, characterized in that: The steps include: Step 1, covering the wood carbon electrode precursor with molten salt, and performing molten salt-mediated thermochemical synthesis according to the process of heating-heat preservation-cooling, wherein the molten salt is a mixture of inert molten salt and active molten salt; Step 2, removing the condensed molten salt on the surface of the synthetic product, polishing the surface and drying it to obtain the wood carbon electrode base material.

2. The molten salt-mediated thermochemical preparation method of the flattened wood carbon electrode substrate material according to claim 1, characterized in that: The wood carbon electrode precursor is air-dried wood, and the compensation coefficient between the size of the wood carbon electrode precursor and the size of the finally obtained wood carbon electrode substrate material is 1.2-1.7:

1.

3. The molten salt-mediated thermochemical preparation method of the flattened wood carbon electrode substrate material according to claim 1, characterized in that: The inert molten salt is KCl, and the active molten salt is ZnCl2, and the mass ratio of the two is 1:1 to 1:

4.

4. The molten salt-mediated thermochemical preparation method of the flattened wood carbon electrode substrate material according to claim 1, characterized in that: Covering the wood-carbon electrode precursor with molten salt means that the wood-carbon electrode precursor is completely covered with molten salt.

5. The molten salt-mediated thermochemical preparation method of the flat wood carbon electrode substrate material according to claim 1, characterized in that: In the step 1, the depth of the container for containing the wood-carbon electrode precursor covered with molten salt is 2 to 3 times the thickness of the wood-carbon electrode precursor.

6. The molten salt-mediated thermochemical preparation method of a flat wood carbon electrode substrate material according to any one of claims 1 to 5, characterized in that: The heating-keeping-cooling process is as follows: The heating rate is 3-5°C / min, and the temperature is raised to 800-850°C; the heat preservation time is 180-300min; the cooling rate is 3-5°C / min, and the temperature is cooled to room temperature.

7. The molten salt-mediated thermochemical preparation method of the flattened wood carbon electrode substrate material according to claim 6, characterized in that: The heating-heat preservation-cooling process is carried out in an air atmosphere.

8. The molten salt-mediated thermochemical preparation method of the flattened wood carbon electrode substrate material according to claim 1, characterized in that: Use deionized water to dissolve and remove the condensed molten salt, then use acetone and anhydrous ethanol to clean and remove oil stains, and finally rinse thoroughly with deionized water.

9. The molten salt-mediated thermochemical preparation method of the flattened wood carbon electrode substrate material according to claim 8, characterized in that: Deionized water is used to remove residual salt, acetone and anhydrous ethanol are used to remove residual oil, and flowing deionized water is used for thorough cleaning until the pH value of the aqueous solution reaches 6-8, the conductivity is 1-20μS / cm, and the drying temperature is 60-80℃.

10. The wood carbon electrode substrate material obtained by the molten salt-mediated thermochemical preparation method of the flat wood carbon electrode substrate material according to any one of claims 1 to 9 is used as a flat plate electrode substrate carbon material; or directly used in the application of high surface capacitance flat plate electrodes for capacitor deionization or supercapacitors.

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