A small metal-air battery based on a wood-based microfluidic chip and its preparation method

Abstract

The present invention discloses a small metal-air battery based on a wood-based microfluidic chip and a preparation method thereof. The above-mentioned wood-based microfluidic chip is prepared by processing wood into wood blocks with mortise and tenon structures and mortise structures, respectively treating them to obtain a wood-based microchannel and a wood-based photothermal evaporator, and connecting them through the mortise and tenon structures; the small metal-air battery based on the wood-based microfluidic chip is prepared by cutting, punching, heat-treating, cleaning, drying, impregnating, drying, and pyrolyzing wood to prepare a self-supporting cathode electrode, using porous metal foam as the anode, and assembling it with the wood-based microfluidic chip through the mortise and tenon structures. The metal-air battery based on the wood-based microfluidic chip prepared by the present invention has a relatively high power density, stable discharge process under light, exhibits relatively high electricity and energy density, simple preparation process, wide range of raw material selection, low cost, and is easy to scale up production.

Description

Technical Field

[0001] The present invention relates to the technical fields of microfluidic chips and battery technologies, and particularly relates to a small metal-air battery based on a wood-based microfluidic chip and a preparation method thereof. Background Art

[0002] With the advent of the Internet of Things era, the market demand for portable electronic devices has been increasing year by year, especially in fields closely related to people's daily lives such as environmental detection, biomedical diagnosis, and drug treatment. And these electronic devices often need to be powered by batteries when in use. Currently, the mainstream small power source is the lithium-ion battery, but the lithium-ion battery has problems such as poor safety, high one-time use cost, complex post-treatment procedures, and potential environmental pollution. Therefore, it is necessary to develop small (disposable) batteries that are safe to use, environmentally friendly, and low in cost.

[0003] Microfluidics is a science and technology involved in precisely controlling fluids at the microscale (<1μm). The microfluidic system is a small reaction platform, specifically manifested as the ability to integrate reactants and chemical reaction processes on a substrate the size of a chip, so it is called a lab-on-a-chip. Using microfluidic technology, the electrodes, catalytic materials, redox substances, and electrochemical reaction processes required during the battery discharge process can be integrated to construct a small battery. In the traditional microfluidic system, the microchannels for liquid flow need to be constructed by etching silicon or polymer organosilicides, and the liquid flow process in the microchannels needs to be driven by a micropump.

[0004] However, the high cost and complex etching process of the silicon-based microchannels, as well as the dependence on micropumps, result in high costs and large volumes of the existing microfluidic technology, which greatly limits the application of the existing microfluidic technology in the field of small (disposable) batteries. Therefore, the development of a new microfluidic system with low cost, flexible structure, and simple usage method has become the key point for constructing a microfluidic small battery with practical application possibilities. Summary of the Invention

[0005] In order to solve the above-mentioned deficiencies existing in the prior art, the purpose of the present invention is to provide a small metal-air battery based on a wood-based microfluidic chip and a preparation method thereof, so as to solve the problems of the too large volume of the system in the existing micropump-driven microfluidic battery and the complex and costly etching process of the silicon-based microchannels.

[0006] The technical solution of the present invention for solving the above technical problems is as follows:

[0007] A preparation method of a wood-based microfluidic chip, comprising the following steps:

[0008] (1) Preparation of wood-based microchannels: Cut wood to form wooden blocks with mortise and tenon joints, heat-treat the wooden blocks with a mixed solution of sodium sulfite and sodium hydroxide, wash with deionized water, and dry to obtain wood-based microchannels;

[0009] (2) Preparation of wood-based photothermal evaporators: Cut wood to form rectangular parallelepiped wooden blocks with tenon joints, spray a ferric chloride solution on one side of the rectangular parallelepiped wooden blocks, dry, and heat-treat this side to carbonize its surface to obtain wood-based photothermal evaporators;

[0010] (3) Preparation of wood-based microfluidic chips: Connect the wood-based microchannels prepared in step (1) and the wood-based photothermal evaporators prepared in step (2) through mortise and tenon joints to obtain them.

[0011] Further, the wood in step (1) and step (2) is any one of pine, fir, spruce, balsa wood, basswood, oak, birch, and poplar.

[0012] Further, in step (1), the wooden blocks are 3 - 20 mm in length, 5 - 22 mm in width, and 10 - 30 mm in height.

[0013] Further, in step (2), the area of the wood-based photothermal evaporator is 1 - 30 cm 2 .

[0014] Further, in step (2), the concentration of the ferric chloride aqueous solution is 0.2 - 2 mol·L –1 .

[0015] Further, in step (2), the amount of the ferric chloride solution sprayed is 0.5 - 15 mL

[0016] Further, in step (2), the heating temperature is 400 - 800 °C and the time is 0.1 - 10 min.

[0017] The wood-based microfluidic chip prepared by the above preparation method.

[0018] A small metal-air battery based on the wood-based microfluidic chip, including the above wood-based microfluidic chip.

[0019] The above small metal-air battery based on the wood-based microfluidic chip includes the following steps:

[0020] (1) Preparation of self-supporting cathode electrode: Cut the wood into rectangular parallelepiped blocks, drill holes perpendicular to the wood growth direction to form a set of hole arrays, heat-treat the blocks with a mixed solution of sodium sulfite and sodium hydroxide, wash with deionized water, dry, soak the treated blocks in an aqueous solution containing a noble metal salt or a mixed solution containing a transition metal salt and a nitrogen-containing organic compound, dry, and pyrolyze in an inert atmosphere to obtain the self-supporting cathode electrode;

[0021] (2) Preparation of metal anode electrode: Cut the porous metal foam into a rectangular parallelepiped as the metal anode electrode;

[0022] (3) Preparation of a small metal-air battery based on a wood-based microfluidic chip: Assemble the above wood-based microfluidic chip, the self-supporting cathode electrode prepared in step (1), and the metal anode electrode prepared in step (2) according to the mortise and tenon structure to obtain it.

[0023] Further, in step (1), the length of the rectangular parallelepiped block is 10 - 50 mm, the width is 4 - 20 mm, and the height is 4 - 20 mm.

[0024] Further, in step (1), the aperture of the hole is 0.5 - 1.5 mm.

[0025] Further, in step (1), the wood is any one of pine, fir, balsa wood, basswood, oak, and birch.

[0026] Further, in step (1), the noble metal salt is any one of palladium nitrate, palladium chloride, chloroplatinic acid, and potassium chloroplatinate, with a concentration of 0.5 - 5 mmol·L –1 .

[0027] Further, in step (1), the transition metal salt is at least one of iron nitrate, cobalt nitrate, copper nitrate, ferric chloride, cobalt chloride, copper chloride, ferrous sulfate, cobalt sulfate, and copper sulfate, with a concentration of 0.02 - 0.5 mol·L –1 .

[0028] Further, in step (1), the nitrogen-containing organic compound is at least one of urea, dicyandiamide, and phthalonitrile, with a concentration of 0.08 - 2.0 mol·L –1 .

[0029] Further, in step (1), the solvent of the mixed solution is any one of water, ethanol, N,N-dimethylformamide, and dimethyl sulfoxide.

[0030] Further, in step (1), the soaking time is 4 - 24 h.

[0031] Further, in step (1), the pyrolysis temperature is 650 - 1100 °C.

[0032] Further, in step (2), the porous metal foam is three-dimensional porous aluminum foam or three-dimensional porous zinc foam.

[0033] Further, in step (2), the cuboid has a length of 3 - 20 mm, a width of 2 - 10 mm, and a height of 2 - 10 mm.

[0034] The present invention has the following beneficial effects:

[0035] (1) Compared with the common capillary-force-based microfluidic system, the wood-based microfluidic chip of the present invention is a three-dimensional structure, which is spliced by a mortise and tenon structure composed of wood-based microchannels and wood-based photothermal evaporators. The liquid spontaneously flows in the wood-based microfluidic chip by capillary force, thus avoiding the use of micropumps in the traditional microfluidic system. Combining with the photothermal evaporation process, the purpose of driving the flow process to proceed continuously and stably by solar energy can be achieved.

[0036] (2) By using the three-dimensional microfluidic system of the wood-based microfluidic chip, the designed small metal-air battery has a large contact area between the reactants and the electrodes during the electrode reaction process, and at the same time, the mass transfer efficiency is high. Therefore, the power density of the battery is high.

[0037] (3) Based on the characteristic that the liquid can flow continuously for a long time in the wood-based microfluidic chip, the small metal-air battery prepared based on the wood-based microfluidic chip has stable and long-lasting discharge, high energy density, is suitable for long-term power supply to miniaturized electronic devices, has a flexible structure, and can adjust its output voltage and power according to actual needs.

[0038] (4) In the small metal-air battery prepared based on the wood-based microfluidic chip of the present invention, the raw materials of the cathode electrode and the evaporation component are both wood-derived carbon-based materials, which are inexpensive and have a wide range of raw material selection; the main steps for preparing the small metal-air battery are the cutting and carbonization processes of wood, and the whole process has a simple preparation process and is easy to prepare on a large scale. Description of the Drawings

[0039] Figure 1 It is a schematic diagram of the composition structure of a small metal-air battery based on a wood-based microfluidic chip;

[0040] Figure 2 It is a scanning electron microscope image of the wood-based microchannel in the wood-based microfluidic chip prepared in Example 1;

[0041] Figure 3 It is a surface Raman spectrum of the photothermal evaporator in the wood-based microfluidic chip prepared in Example 1;

[0042] Figure 4 It is a Raman spectrum of the cathode electrode prepared in Example 1;

[0043] Figure 5 Scanning electron microscope image of the cathode electrode prepared in Example 1;

[0044] Figure 6 Scanning electron microscope image of the anode electrode prepared in Example 1;

[0045] Figure 7 Voltage-current curve of the batteries prepared in Example 1 and Comparative Example 1 in Test Example 2;

[0046] Figure 8 Discharge curve of the batteries prepared in Example 1 and Comparative Example 2 in Test Example 3;

[0047] Figure 9 Voltage-current curve of the series battery pack in Test Example 4;

[0048] Figure 10 Voltage-current curve of the battery prepared in Example 5 in Test Example 5. Detailed implementation mode

[0049] The following examples are only used to explain the present invention and are not intended to limit the scope of the present invention. For those not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0050] Example 1:

[0051] A small aluminum-air battery based on a wood-based microfluidic chip, and its preparation method includes the following steps:

[0052] (1) Precursor processing: Use a laser cutter to cut pine wood to form wooden blocks with several different geometric structures. Among them, the wooden block with a mortise and tenon structure is the precursor of the wood-based microchannel, the rectangular wooden block with a tenon structure is the precursor of the photothermal evaporator, and the rectangular wooden block is the precursor of the cathode electrode. The geometric shapes of various wooden blocks are as Figure 1 shown.

[0053] (2) Preparation of the wood-based microchannel: Place the wood-based microchannel precursor in a mixed aqueous solution of 0.4 mol·L –1 sodium sulfite and 2.5 mol·L –1 sodium hydroxide, heat and reflux for 6 h, then wash the wood-based microchannel with deionized water until the washing liquid is neutral, and finally dry each wooden block in an oven for 12 h to obtain it.

[0054] (3) Preparation of the photothermal evaporator: Spray 2 mL of 1 mol·L –1into a ferric chloride solution, then taken out and dried in an oven. Heat treatment is carried out on the side sprayed with ferric chloride, the heating temperature is 600 °C, and the heating time is 2 min to carbonize its surface, and the carbonized area is 1 - 30 cm 2 is obtained.

[0055] (4) Preparation of the wood-based microfluidic chip: Connect the wood-based microchannel prepared in step (2) and the photothermal evaporator prepared in step (3) through a mortise and tenon structure to obtain it.

[0056] (5) Preparation of the self-supporting cathode electrode: Use a laser cutter to punch holes in a rectangular parallelepiped wooden block (20 mm in length, 6 mm in width, and 6 mm in height) as the cathode electrode precursor to form a 3×6 hole array. The punching direction is perpendicular to the growth direction of the pine wood, and the hole diameter is 1 mm. Place the punched cathode electrode precursor in a mixed aqueous solution of 0.4 mol·L –1 sodium sulfite and 0.25 mol·L –1 sodium hydroxide, heat under reflux for 6 h, then wash the wood-based microchannel with deionized water until the washing liquid is neutral, and finally dry each wooden block in an oven for 12 h. Immerse the dried cathode electrode precursor in a hydrochloric acid solution containing 2.0 mmol·L –1 palladium chloride and 20 mmol·L –1 for 12 h, take it out and dry it in a vacuum drying oven, then place the wooden block impregnated with palladium chloride in a tubular furnace, and under the protection of N2 atmosphere, heat the sample at a rate of 5 °C·min -1 until it is heated to 900 °C and maintained for 2 h, then cool it to room temperature to obtain a carbon-based porous electrode containing a palladium catalyst, and polish the electrode to make its length, width, and height become 6 mm, 3 mm, and 3 mm respectively to obtain it.

[0057] (6) Preparation of the metal anode electrode: Cut the porous aluminum foam into a rectangular parallelepiped, 6 mm in length, 3 mm in width, and 6 mm in height.

[0058] (7) Preparation of the small aluminum-air battery based on the wood-based microfluidic chip: Assemble the wood-based microfluidic chip prepared in step (4), the self-supporting cathode electrode prepared in step (5), and the metal anode electrode prepared in step (6) according to the mortise and tenon structure, as Figure 1 shown, to obtain a small aluminum-air battery based on the wood-based microfluidic chip. Immerse the bottom of the battery in 1.0 mol·L –1In a KOH electrolyte solution, with the top exposed to light, the battery can continuously discharge. At this stage, the product is marked as Wμ-AAB-Pd-A, where Wμ represents wood-based microfluidic, AAB represents Aluminum-air battery, Pd represents palladium as the cathode catalyst, and A represents alkaline electrolyte.

[0059] Example 2:

[0060] A small aluminum-air battery based on a wood-based microfluidic chip, and its preparation method includes the following steps:

[0061] The experimental steps are the same as those in Example 1, except that in step (5), 2.0 mmol·L –1 of palladium chloride and 20 mmol·L –1 of hydrochloric acid aqueous solution are changed to a mixed solution of 0.2 mmol·L –1 of iron nitrate and 0.8 mmol·L –1 of dicyandiamide in N,N-dimethylformamide. After pyrolysis, the sample is placed in 0.5 mol·L –1 of H2SO4 solution at 80 °C for 4 h, then rinsed with deionized water until the cleaning solution is neutral, and finally dried in an oven for 12 h. At this stage, the product is marked as Wμ-AAB-FeNC-A, where FeNC represents iron and carbon co-doped carbon as the cathode catalyst.

[0062] Example 3:

[0063] A small aluminum-air battery based on a wood-based microfluidic chip, and its preparation method includes the following steps:

[0064] The experimental steps are the same as those in Example 1, except that in step (5), 2.0 mmol·L –1 of palladium chloride and 20 mmol·L –1 of hydrochloric acid aqueous solution are changed to a mixed solution of 0.2 mmol·L –1 of cobalt nitrate and 0.8 mmol·L –1 of phthalonitrile in N,N-dimethylformamide. After pyrolysis, the sample is placed in 0.5 mol·L –1 of H2SO4 solution at 80 °C for 4 h, then rinsed with deionized water until the cleaning solution is neutral, and finally dried in an oven for 12 h. At this stage, the product is marked as Wμ-AAB-CoNC-A, where CoNC represents cobalt and carbon co-doped carbon as the cathode catalyst.

[0065] Example 4:

[0066] A small zinc-air battery based on a wood-based microfluidic chip, and its preparation method includes the following steps:

[0067] The experimental steps are the same as those in Example 1, except that the porous aluminum foam in step (6) is changed to porous zinc foam. The product at this stage is marked as Wμ-ZAB-Pd-A, where ZAB represents a zinc-air battery.

[0068] Example 5:

[0069] A small aluminum-air battery based on a wood-based microfluidic chip, and its preparation method includes the following steps:

[0070] The experimental steps are the same as those in Example 1, except that the 1.0 mol·L –1 aqueous KOH solution in step (7) is changed to a 2.0 mol·L –1 aqueous NaCl solution. The product at this stage is marked as Wμ-AAB-Pd-N, where N represents a neutral electrolyte.

[0071] Comparative Example 1:

[0072] A small aluminum-air battery based on a wood-based two-dimensional microfluidic chip, and its preparation method includes the following steps:

[0073] The experimental steps are the same as those in Example 1, except that the wood-based microchannel precursor with a mortise and tenon structure in step (1) is changed to a cuboid geometry, and the splicing method of each component in step (7) is changed from a mortise and tenon structure to a sandwich structure. The product at this stage is marked as 2DWμ-AAB-Pd-A, where 2DWμ represents two-dimensional wood-based microfluidics.

[0074] The battery obtained in this preparation process has a two-dimensional microfluidic configuration, that is, the electrodes are laid flat on the left or right side of the microchannel. In this configuration, the electrolyte can only flow through the surface of the electrode catalyst (flow-by), resulting in a smaller electrochemical reaction interface.

[0075] Comparative Example 2:

[0076] A small aluminum-air battery based on a wood-based microfluidic chip without a photothermal evaporation component, and its preparation method includes the following steps:

[0077] The experimental steps are the same as those in Example 1, except that the photothermal evaporator precursor in step (1) is removed, steps (3) and (4) are removed, and the photothermal evaporator component is not introduced when splicing each component in step (7). The product at this stage is marked as W-AAB-Pd-A, where W represents wood-based.

[0078] The battery obtained from this preparation process does not contain a photothermal evaporator component and cannot perform the photothermal evaporation process. It can only drive the flow of the electrolyte in the microchannel and the electrode through natural evaporation. In this microfluidic configuration driven by natural evaporation, the flow rate of the electrolyte is slow, and the mass transfer efficiency of the reactants is low.

[0079] Test Example 1:

[0080] Take the wood-based microfluidic chip, cathode electrode, and anode electrode prepared in Example 1 for performance testing. The test results are as Figure 2 , Figure 3 , Figure 4 , Figure 5 and Figure 6 shown.

[0081] Figure 2 The scanning electron microscope results of the wood-based microchannel show that the wood-based microchannel prepared by the present invention has a regular microporous structure, which is beneficial to the directional flow of the electrolyte and the electrode reactant solution in the wood-based microchannel.

[0082] Figure 3 The Raman test results of the photothermal evaporator show that the main component of the wood block after high-temperature treatment is a carbon material, which can generate heat under the action of light, accelerate the evaporation of water in the electrolyte, and thus maintain the flow process of the electrolyte in the wood-based microchannel.

[0083] Figure 4 The Raman test results of the cathode electrode show that pine wood is converted into a carbon-based material after high-temperature pyrolysis. The carbon-based material has high electrical conductivity, good chemical stability, and mechanical strength, and is suitable as the positive electrode part in metal-air.

[0084] Figure 5 The scanning electron microscope results of the cathode electrode show that pine wood can maintain its pore structure after high-temperature pyrolysis. The pore diameter is 20-40 μm, and the metal nanoparticles acting as the cathode catalyst are evenly distributed in the pore structure. This structure is beneficial to realizing the flow of the electrolyte and the mass transfer process of oxygen to the catalyst surface, thereby accelerating the cathode oxygen reduction reaction.

[0085] Figure 6 The scanning electron microscope results of the anode electrode show that the porous metal foam has an open-cell structure with a pore diameter of 150-300 μm. This structure ensures that the electrolyte can smoothly pass through the anode electrode to initiate the metal oxidation reaction.

[0086] Test Example 2:

[0087] Take the small aluminum-air batteries prepared in Example 1 and Comparative Example 1 for performance testing. The test results are as Figure 7 shown.

[0088] According toFigure 7 It can be seen that the open-circuit voltage of the battery is 1.2V, and the maximum output power density of the three-dimensional microfluidic aluminum-air battery based on the wood-based microfluidic chip in Example 1 can reach 200 mW·cm –3 , while that of the two-dimensional microfluidic aluminum-air battery based on the wood-based microfluidic chip in Comparative Example 1 is only 50 mW·cm –3 , indicating that the three-dimensional microfluidic configuration obtained by splicing the wood-based microfluidic chip and the self-supporting electrode using the mortise and tenon structure in the present invention is beneficial to improving the power density of the battery.

[0089] Test Example 3:

[0090] The small aluminum-air batteries prepared in Example 1 and Comparative Example 2 were taken for performance testing, and the test results are as Figure 8 shown.

[0091] According to Figure 8 it can be seen that the microfluidic aluminum-air battery driven by photothermal evaporation in Example 1 can stably discharge continuously at 200 mA·cm –3 for 11 h, with the electricity quantity reaching 800 Ah·Kg -1 , and the energy density reaching 640 Wh·Kg -1 , while the microfluidic aluminum-air battery driven by natural evaporation in Comparative Example 2 can only discharge for 1.5 h at 200 mA·cm –3 , and the discharge voltage continuously decreases. The electricity quantity and energy density are only 110 Ah·Kg -1 and 55 Wh·Kg -1 respectively. The test results prove that the battery prepared in the present invention has significant improvements in terms of sustainable discharge time, electricity quantity, and energy density after introducing the photothermal evaporator assembly.

[0092] Test Example 4:

[0093] Two small aluminum-air batteries based on the wood-based microfluidic chip prepared in Example 1 were taken for a series connection test, and the test results are as Figure 9 shown. [[ID= forty]]

[0094] According to Figure 9 it can be seen that the open-circuit voltage of the battery pack formed by connecting two small aluminum-air batteries based on the wood-based microfluidic chip in series reaches 2.1V, and the maximum output power reaches 17 mW.

[0095] Test Example 5:

[0096] The small aluminum-air battery based on the wood-based microfluidic chip prepared in Example 5 was taken for performance testing, and the test results are as [[ID= fifty]] Figure 10 shown.

[0097] According to Figure 10It can be seen that the open-circuit voltage of the battery is 0.6 V, and the maximum output power density is 40 mW·cm –3 , and the result is relatively lower than that of the small aluminum-air battery based on the wood-based microfluidic chip prepared in Example 1, indicating that the discharge performance of the wood-based microfluidic aluminum-air battery prepared by the present invention in neutral electrolyte is lower than its discharge performance in alkaline electrolyte. However, due to the fact that neutral electrolyte is safer, more environmentally friendly and has greater application potential than alkaline electrolyte.

[0098] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a wood-based microfluidic chip, characterized in that, It includes the following steps: (1) Preparation of wood-based microchannels: Cut wood to form wooden blocks with mortise and tenon structures, heat-treat the wooden blocks with a mixed solution of sodium sulfite and sodium hydroxide, wash with deionized water, and dry to obtain wood-based microchannels; (2) Preparation of wood-based photothermal evaporators: Cut wood to form rectangular wooden blocks with mortise structures, spray a ferric chloride solution on one side of the rectangular wooden blocks, dry, and heat-treat this side to carbonize its surface to obtain wood-based photothermal evaporators; (3) Preparation of wood-based microfluidic chips: Connect the wood-based microchannels prepared in step (1) and the wood-based photothermal evaporators prepared in step (2) through mortise and tenon structures to obtain wood-based microfluidic chips.

2. The preparation method of the wood-based microfluidic chip according to claim 1, characterized in that, The wood in step (1) and step (2) is any one of pine, fir, spruce, balsa, basswood, oak, birch, and poplar; the length of the wooden blocks in step (1) is 3-20 mm, the width is 5-22 mm, and the height is 10-30 mm.

3. The preparation method of the wood-based microfluidic chip according to claim 1, characterized in that, The area of the wood-based photothermal evaporator described in step (2) is 1-30 cm 2 ; the concentration of the ferric chloride aqueous solution is 0.2-2 mol·L –1 ; The amount of ferric chloride solution sprayed is 0.5-15 mL, the heating temperature is 400-800 °C, and the time is 0.1-10 min.

4. A wood-based microfluidic chip prepared by the preparation method according to any one of claims 1-3.

5. A small metal-air battery based on a wood-based microfluidic chip, characterized in that, It includes the wood-based microfluidic chip according to claim 4.

6. The preparation method of the small metal-air battery based on the wood-based microfluidic chip according to claim 5, characterized in that, It includes the following steps: (1) Preparation of self-supporting cathode electrodes: Cut wood into rectangular wooden blocks, drill holes perpendicular to the wood growth direction to form a set of hole arrays, heat-treat the wooden blocks with a mixed solution of sodium sulfite and sodium hydroxide, wash with deionized water, dry, soak the treated wooden blocks in an aqueous solution containing precious metal salts or a mixed solution containing transition metal salts and nitrogen-containing organic compounds, dry, and pyrolyze in an inert atmosphere to obtain self-supporting cathode electrodes; (2) Preparation of metal anode electrodes: Cut porous metal foam into a rectangular shape as the metal anode electrode; (3) Preparation of a small metal-air battery based on a wood-based microfluidic chip: Assemble the wood-based microfluidic chip according to claim 4, the self-supporting cathode electrode prepared in step (1), and the metal anode electrode prepared in step (2) according to the mortise and tenon structure to obtain a small metal-air battery based on a wood-based microfluidic chip.

7. The preparation method of the small metal-air battery based on the wood-based microfluidic chip according to claim 6, characterized in that, The length of the rectangular wooden block in step (1) is 10-50 mm, the width is 4-20 mm, the height is 4-20 mm, and the pore diameter of the holes is 0.5-1.5 mm.

8. The preparation method of the small metal-air battery based on the wood-based microfluidic chip according to claim 6, characterized in that, The wood in step (1) is any one of pine, fir, balsa, basswood, oak and birch; the noble metal salt is any one of palladium nitrate, palladium chloride, chloroplatinic acid and potassium chloroplatinate, with a concentration of 0.5~5 mmol·L –1 ; the transition metal salt is at least one of ferric nitrate, cobalt nitrate, copper nitrate, ferric trichloride, cobalt chloride, copper chloride, ferric sulfate, cobalt sulfate and copper sulfate, with a concentration of 0.02~0.5 mol·L –1 ; the nitrogen-containing organic compound is at least one of urea, dicyandiamide and phthalonitrile, with a concentration of 0.08~2.0 mol·L –1 ; the solvent of the mixed solution is any one of water, ethanol, N,N-dimethylformamide and dimethyl sulfoxide.

9. The preparation method of the small-sized metal-air battery based on the wood-based microfluidic chip according to claim 6, characterized in that, The soaking time in step (1) is 4-24 h, and the pyrolysis temperature is 650-1100 °C.

10. The preparation method of the small metal-air battery based on the wood-based microfluidic chip according to claim 6, characterized in that, The porous metal foam in step (2) is three-dimensional porous aluminum foam or three-dimensional porous zinc foam, and the length of the rectangle is 3-20 mm, the width is 2-10 mm, and the height is 2-10 mm.

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