Hygroscopic magnesium air battery positive electrode material as well as preparation method and application thereof

Abstract

The invention discloses a hygroscopic magnesium air battery positive electrode material and a preparation method and application thereof, and belongs to the field of new energy batteries. The hygroscopic magnesium air battery positive electrode material comprises a first porous conductive substrate and a second porous conductive substrate, wherein the first porous conductive substrate comprises sheet-shaped melamine foam and a positive electrode reaction catalyst and a hydrophilic carbon nanotube which are loaded on the surface of the sheet-shaped melamine foam; the perfluorinated sulfonic acid resin is loaded on one side surface of the first porous conductive substrate and forms a hydrophobic surface; the LiCl is loaded on the other side surface of the first porous conductive substrate and in the first porous conductive substrate, and a LiCl hydrophilic surface is formed on the other side surface; wherein in the direction from the hydrophilic surface of the LiCl to the hydrophobic surface of the LiCl, the loading capacity of the LiCl is gradually reduced in a gradient manner. Compared with the prior art, the magnesium air battery positive electrode material disclosed by the invention can directly absorb moisture from air to form electrolyte, so that the weight of a magnesium air battery is effectively reduced, and meanwhile, the discharge duration is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of new energy, and more specifically, relates to a hygroscopic magnesium-air battery cathode material, its preparation method, and its application. Background Technology

[0002] Aqueous magnesium-air batteries are a novel energy storage device that uses magnesium metal as the negative electrode reactant, oxygen from the air as the positive electrode reactant, and an aqueous solution as the electrolyte. They have attracted widespread attention due to their high theoretical energy density, environmental compatibility, high safety, and competitive cost, especially for emergency power applications. However, during discharge, the electrolyte in aqueous magnesium-air batteries is consumed and evaporates, requiring the injection of excessive electrolyte. This results in a large electrolyte mass proportion and a small proportion of the magnesium negative electrode, which acts as the active material. The electrolyte significantly increases the overall mass of the battery, greatly limiting its actual energy density. Furthermore, the magnesium negative electrode is prone to corrosion in the electrolyte, generating hydrogen gas and causing metal dissolution. This corrosion is exacerbated during discharge, manifesting as severe hydrogen evolution and the shedding of negative electrode material (i.e., the "blocking effect"). Simultaneously, corrosion products Mg(OH)₂ adhere to the negative electrode surface, forming a passivation layer, thereby reducing the effective active material and shortening the battery's lifespan.

[0003] To reduce adverse reactions of the negative electrode material in the electrolyte of aqueous magnesium-air batteries, many existing technologies modify the electrolyte by adding corrosion inhibitors and complexing agents to regulate the discharge process of the magnesium negative electrode. Chinese invention patent application CN118472433A discloses a method for preparing a 3-pyridine sulfonic acid-based magnesium-air battery electrolyte. This method involves mixing deionized water, sodium chloride, gadolinium chloride, and a 3-pyridine sulfonic acid compound and adjusting the pH to 7.0 ± 0.3. This electrolyte can improve the discharge voltage and specific energy of the magnesium-air battery, slow down the self-corrosion rate of the negative electrode, and thus significantly improve the battery's discharge performance. However, the modified electrolytes in the above and similar technologies still require a large amount to be added to the magnesium-air battery, making it impossible to reduce battery weight while simultaneously reducing adverse reactions at the negative electrode. Summary of the Invention

[0004] 1. The problem to be solved To address the problems of high electrolyte content, negative electrode corrosion, and passivation reactions leading to short service life in existing magnesium-air batteries, this invention provides a hygroscopic magnesium-air battery cathode material that can directly absorb moisture from the air to form an electrolyte. Compared with traditional batteries, this significantly reduces the electrolyte content during use, slows down negative electrode corrosion and passivation reactions, effectively extends discharge duration, and improves service life.

[0005] Furthermore, the present invention also provides a method for preparing the hygroscopic magnesium-air battery cathode material and its application.

[0006] 2. Technical Solution To address the aforementioned problems, this invention provides a hygroscopic magnesium-air battery cathode material, wherein melamine foam serves as a porous substrate, hydrophilic carbon nanotubes are the electronically conductive component, LiCl is the hygroscopic component, and a cathode reaction catalyst is added. This cathode material can absorb water from the air, and as the hygroscopic time increases, the water content increases, forming a good ion-conducting pathway between the positive and negative electrodes.

[0007] The technical solution adopted in this invention is as follows: The first aspect of this invention provides a hygroscopic magnesium-air battery cathode material, comprising: A first porous conductive substrate, comprising sheet-like melamine foam and a positive electrode reaction catalyst and hydrophilic carbon nanotubes supported on the surface of the sheet-like melamine foam. A perfluorosulfonic acid resin loaded on one side of the first porous conductive substrate, wherein the perfluorosulfonic acid resin forms a hydrophobic surface; LiCl loaded on the other side and inside of the first porous conductive substrate forms a LiCl hydrophilic surface on the other side. The loading of LiCl decreases gradually from the hydrophilic surface to the hydrophobic surface along the direction of LiCl.

[0008] As described herein, “surface” includes all surfaces, including the outer and inner surfaces of melamine foam.

[0009] As described herein, "side surface" refers to a surface perpendicular to the thickness direction.

[0010] Preferably, the positive electrode catalyst includes one or two of α-MnO2 and Pt / C, and the mass ratio of the positive electrode catalyst to the hydrophilic carbon nanotubes is (0.3~0.7):1.

[0011] Preferably, the mass ratio of the sheet-like melamine foam to the sum of the masses of the positive electrode catalyst and the hydrophilic carbon nanotubes is 1:(2~7).

[0012] Preferably, the mass ratio of the sheet-like melamine foam to the perfluorosulfonic acid resin is 1:(0.005~0.02).

[0013] Preferably, the mass ratio of the sheet-like melamine foam to LiCl is 1:(1~7).

[0014] Preferably, the thickness of the sheet-like melamine foam is 1-3 mm.

[0015] Preferably, the hydrophilic carbon nanotubes include one or both of hydroxylated carbon nanotubes and carboxylated carbon nanotubes.

[0016] More preferably, the hydrophilic carbon nanotubes are carboxylated carbon nanotubes.

[0017] LiCl is a hygroscopic salt with a strong adsorption effect on water molecules. When the electrode is exposed to air, the LiCl-rich regions rapidly absorb moisture from the air and stabilize it within the porous network through capillary and hydrophilic interactions, thereby maintaining efficient ion conduction and supporting the continuous progress of the positive electrode reaction. Simultaneously, the hydrophobic regions, due to their lower LiCl content, remain dry and form continuous gas diffusion channels, effectively promoting oxygen transport. This salt gradient design based on wettability regulation achieves synergistic optimization of moisture management and gas diffusion within the same electrode, improving the overall performance of the electrode in an air environment.

[0018] The second aspect of the present invention provides a method for preparing a hygroscopic magnesium-air battery cathode material according to any embodiment of the first aspect of the present invention, the steps of which include: S1. The positive electrode catalyst is mixed with the hydrophilic carbon nanotube dispersion to obtain the first solution; S2. The sheet-like melamine foam is repeatedly soaked in the first solution and dried to obtain a first porous conductive substrate loaded with a positive electrode catalyst and hydrophilic carbon nanotubes. S3. A hydrophobic perfluorosulfonic acid resin solution is sprayed onto one side of the first porous conductive substrate, and after drying, a second porous conductive substrate with one side being hydrophobic is obtained. S4. The LiCl solution is dropped onto the second porous conductive substrate from the other side in a direction perpendicular to the other side. After drying, a hygroscopic magnesium-air battery cathode material is obtained. The LiCl on the other side and inside forms a hydrophilic LiCl surface on the other side. The loading of LiCl decreases in a gradient from the hydrophilic to the hydrophobic LiCl surface.

[0019] Preferably, in step S1, the solid mass fraction of the first solution is 1-2%; in step S3, the mass fraction of the perfluorosulfonic acid resin solution is 0.03-0.07%; and in step S4, the concentration of the LiCl solution is 40-60 mg·mL. -1 .

[0020] Preferably, in step S1, the positive electrode catalyst is mixed with a hydrophilic carbon nanotube dispersion and then ultrasonically dispersed. The solvent for the hydrophilic carbon nanotube dispersion is deionized water.

[0021] Preferably, in step S2, the melamine foam is removed immediately after being completely soaked in the first solution and then dried at a temperature of 50-80°C for 1-4 hours.

[0022] More preferably, in step S2, the soaking and drying are performed four times.

[0023] It should be noted that after four soaking-drying cycles, the resistance of the first porous conductive substrate had significantly decreased and entered a plateau phase. Subsequent soaking-drying cycles primarily resulted in the accumulation of substrate quality, with the resistance value no longer showing significant changes. To achieve lower resistance and improve production efficiency, four soaking-drying cycles are optimal.

[0024] Because the surface of the first porous conductive substrate is loaded with hydrophilic carbon nanotubes, its surface is hydrophilic.

[0025] Preferably, in step S3, the perfluorosulfonic acid resin solution has a mass fraction of 0.05%, and the solvent used is ethanol. The drying temperature is 50~80 ℃, and the drying time is 10~30 min.

[0026] After a perfluorosulfonic acid resin solution is sprayed onto one side of the first porous conductive substrate, that side becomes a hydrophobic surface.

[0027] Preferably, in step S4, the drying temperature is 70~100 ℃ and the drying time is 8~16 h.

[0028] It should be noted that when adding LiCl solution dropwise to the hydrophilic surface of the second porous conductive substrate, it should be ensured that the liquid can fully and uniformly penetrate into the substrate. Generally, complete penetration is achieved when the solution volume is ≥200 μL per square centimeter. When the solution volume is <200 μL per square centimeter, the second porous conductive substrate needs to be pressed to ensure that the added solution is fully dispersed.

[0029] The second aspect of this invention provides a method for preparing a hygroscopic magnesium-air battery cathode material by uniformly loading a cathode reaction catalyst and carboxylated carbon nanotubes onto a three-dimensional melamine foam framework, constructing a continuous electron conduction network and providing abundant catalytic sites for the oxygen reduction reaction. To further optimize electrode performance, a hydrophobic perfluorosulfonic acid resin is selectively sprayed onto one side of the electrode, thereby creating a difference in wettability on both sides. This difference causes the hydrophilic region to preferentially enrich the hygroscopic component LiCl, forming a salt concentration gradient distribution.

[0030] A third aspect of the present invention provides a magnesium-air battery comprising a hygroscopic magnesium-air battery cathode material as described in any embodiment of the first aspect of the present invention and a hygroscopic magnesium-air battery cathode material prepared by any method described in the second aspect of the present invention.

[0031] Preferably, the mass ratio of LiCl to the negative electrode material in the hygroscopic magnesium-air battery positive electrode material is (0.5~1.5):1.

[0032] More preferably, the mass ratio of LiCl to the negative electrode material in the hygroscopic magnesium-air battery positive electrode material is (0.9~1.5):1.

[0033] When the mass of the negative electrode material in a battery is fixed, the ability of the positive electrode to absorb water from the air increases with the increase of the mass of LiCl in the positive electrode material. As the absorbed moisture increases, the content of the negative electrode capable of battery reactions gradually increases, and the battery's discharge duration gradually lengthens. However, when the mass of LiCl reaches a certain critical value, the battery reaction becomes limited by the mass of the negative electrode material. Further increasing the mass of LiCl at this point will instead lead to an accelerated corrosion rate during discharge, resulting in a decrease in discharge time and negative electrode utilization. When the mass ratio of LiCl to negative electrode material in the positive electrode material is (0.9~1.5):1, the water absorption capacity of the positive electrode material and the reactivity of the negative electrode material are optimally matched, causing the discharge duration to plateau.

[0034] 3. Beneficial effects Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The hygroscopic magnesium-air battery cathode material provided by the present invention, based on the prior art, loads perfluorosulfonic acid resin on one side of the first porous conductive substrate to form a hydrophobic surface, and loads LiCl on the other side and inside to form a LiCl hydrophilic surface. Furthermore, the loading amount of LiCl decreases gradually from the LiCl hydrophilic surface to the hydrophobic surface. The LiCl-rich hydrophilic surface region stabilizes the moisture inside the porous network through capillary action and hydrophilic action, thereby maintaining efficient ion conduction and supporting the continuous progress of the cathode reaction. The hydrophobic region side, due to its lower LiCl content, remains dry and forms a continuous gas diffusion channel, effectively promoting oxygen transport. This salt gradient design based on wettability regulation achieves synergistic optimization of moisture management and gas diffusion within the same electrode. At the same time, the hydrophilic surface of this hygroscopic magnesium-air battery cathode material can directly capture water from the air for ion transport and battery reaction. When using it to prepare magnesium-air batteries, there is no need to inject electrolyte as in traditional magnesium-air batteries, thus reducing the overall mass of the battery and increasing its energy density. Furthermore, the hygroscopic magnesium-air battery cathode material of the present invention absorbs water during use, and the lower electrolyte content in the battery reduces the rate of negative electrode corrosion and passivation reaction, thereby increasing the discharge duration.

[0035] (2) The method for preparing the hygroscopic magnesium-air battery cathode material provided by the present invention involves adding LiCl solution to the second porous conductive substrate from the other side in a direction perpendicular to the other side, thereby obtaining a hygroscopic magnesium-air battery cathode material with a gradient decrease in LiCl loading from the hydrophilic side to the hydrophobic side after drying. The method achieves salt gradient design based on wettability regulation using a simple method, and realizes the synergistic optimization of moisture management and gas diffusion within the same electrode.

[0036] (3) When the hygroscopic magnesium-air battery positive electrode material prepared by the present invention is applied to magnesium-air batteries, the battery structure does not contain moisture during the storage stage, and there will be no adverse reactions of the negative electrode material. It can significantly improve the storage life and capacity retention of magnesium-air batteries. Compared with existing commercial magnesium-air batteries, it does not require the addition of electrolyte, is lighter, has higher energy density, and is more portable, which can greatly expand the practical application scenarios of magnesium-air batteries. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the packaged structure of the magnesium-air battery prepared in Example 1 of the present invention; Figure 2 A photograph of the magnesium-air battery prepared in Example 1 of this invention; Figure 3 The discharge curves of the magnesium-air batteries prepared in Examples 5-8 of this invention are shown. Figure 4 The discharge curves of the magnesium-air batteries prepared in Example 7 and Comparative Examples 1-5 of this invention are shown. Figure 5 The specific capacity of the magnesium-air batteries prepared in Example 7 and Comparative Example 3 of this invention after storage for different times; Figure 6 The discharge voltages of the magnesium-air batteries prepared in Example 7 and Comparative Example 6 of this invention at different current densities; Figure 7 The discharge curves are for the magnesium-air batteries prepared in Examples 7 and 9 of this invention. Detailed Implementation

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0039] Concentration, amount, and other numerical data may be presented in range format herein. It should be understood that such range format is used solely for convenience and brevity and should be flexibly interpreted to include not only the values ​​explicitly stated as the limits of the range, but also all individual values ​​or subranges encompassed within the range, as if each value and subrange were explicitly stated. For example, a range of values ​​from about 1 to about 4.5 should be interpreted to include not only the explicitly stated limits of 1 to 4.5, but also individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that describe only a single value, such as "less than about 4.5," which should be interpreted to include all the values ​​and ranges described above. Furthermore, this interpretation should apply regardless of the breadth of the range or characteristic described.

[0040] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0041] The present invention will be further described below with reference to specific embodiments.

[0042] Example 1 This embodiment discloses a method for preparing a hygroscopic magnesium-air battery cathode material and a method for assembling a magnesium-air battery, including the following steps: S1. Mix 50 mg of α-MnO2 with 10 mL of 1% carboxylated carbon nanotube dispersion and then ultrasonically disperse to obtain the first solution. S2. A melamine foam with a mass of 23.5 mg and dimensions of 1.5 mm × 3 cm × 4 cm was completely immersed in the first solution and immediately removed, then dried at 60 ℃ for 2 h. After immersion-drying four times, a first porous conductive substrate loaded with catalyst α-MnO2 and carboxylated carbon nanotubes was obtained, wherein the total mass of the catalyst α-MnO2 and carboxylated carbon nanotubes was 122.7 mg. S3. Spray approximately 0.6 mL of a 0.05% perfluorosulfonic acid resin solution onto one side of the first porous conductive substrate using a spray gun, and let it stand at 60 °C for 20 min to dry, thus obtaining a second porous conductive substrate with the side sprayed with perfluorosulfonic acid resin being hydrophobic. S4, Prepare a concentration of 50 mg·mL -1 A LiCl solution was added dropwise to the other side of the second porous conductive substrate in a direction perpendicular to the other side. The substrate was then dried in a vacuum oven at 80 °C for 12 h to obtain a hygroscopic magnesium-air battery cathode material in which the LiCl loading decreased in a gradient from the hydrophilic to the hydrophobic side of LiCl.

[0043] S5. Polish the magnesium foil with dimensions of 0.3 mm × 3 cm × 4 cm until it is shiny and clean it with anhydrous ethanol to remove the oxide layer and stains on the magnesium surface.

[0044] S6. Mix dichloromethane and acetone in a mass ratio of 40:1 to obtain a mixed solvent. Mix 0.7 g of polyethylene oxide and 0.6 g of lithium bis(trifluoromethanesulfonyl)imide with 5 mL of the obtained mixed solvent and stir thoroughly to obtain an organic gel membrane precursor solution.

[0045] S7. Coat an organic gel membrane onto magnesium foil, with a coating area of ​​3 × 4 cm. 2 The coating weight is 2.1 mg per square centimeter, and then it is allowed to dry and cure.

[0046] S8. The hydrophilic LiCl surface of the cathode material prepared in S4 is covered on the organic gel separator to obtain a hygroscopic magnesium-air battery.

[0047] Example 2 S1. Mix 50 mg of α-MnO2 with 10 mL of 1% carboxylated carbon nanotube dispersion and then ultrasonically disperse to obtain the first solution. S2. After completely immersing 2.3 mg of melamine foam with dimensions of 1.5 mm × 1 cm × 1 cm in the first solution, remove it immediately and dry it at 60 °C for 2 h. Repeat this immersion-drying operation 6 times.

[0048] Example 3 The process is basically the same as in Example 2, except that the mass of melamine foam in S2 is 2.4 mg.

[0049] Example 4 The process is basically the same as in Example 2, except that the mass of melamine foam in S2 is 2.2 mg.

[0050] Example 5 This embodiment discloses a method for preparing a hygroscopic magnesium-air battery cathode material and a method for assembling a magnesium-air battery, including the following steps: S1. Mix 50 mg of α-MnO2 with 10 mL of 1% carboxylated carbon nanotube dispersion and then ultrasonically disperse to obtain the first solution. S2. A melamine foam with a mass of 2.3 mg and dimensions of 1.5 mm × 1 cm × 1 cm was completely immersed in the first solution and immediately removed, then dried at 60 °C for 2 h. After immersion-drying four times, a first porous conductive substrate loaded with catalyst α-MnO2 and carboxylated carbon nanotubes was obtained, wherein the total mass of the catalyst α-MnO2 and carboxylated carbon nanotubes was 7.25 mg. S3. Spray approximately 0.05 mL of a 0.05% perfluorosulfonic acid resin solution onto one side of the first porous conductive substrate using a spray gun, and let it stand at 60 °C for 20 min to dry, thus obtaining a second porous conductive substrate with the side sprayed with perfluorosulfonic acid resin being hydrophobic. S4, Prepare a concentration of 50 mg·mL -1 A LiCl solution was added dropwise to the other side of the second porous conductive substrate in a direction perpendicular to the other side. The substrate was then dried in a vacuum oven at 80 °C for 12 h to obtain a hygroscopic magnesium-air battery cathode material in which the LiCl loading decreased in a gradient from the hydrophilic to the hydrophobic side of LiCl.

[0051] S5. Polish the magnesium foil until it is shiny and clean it with anhydrous ethanol to remove the oxide layer and stains on the magnesium surface. Cut it into 1×4 cm pieces. 2 The long strips, made of magnesium foil, have a mass of 9 mg per square centimeter; S6. Mix dichloromethane and acetone in a mass ratio of 40:1 to obtain a mixed solvent. Mix 0.7 g of polyethylene oxide and 0.6 g of lithium bis(trifluoromethanesulfonyl)imide with 5 mL of the obtained mixed solvent and stir thoroughly to obtain an organic gel membrane precursor solution; S7. Coat the surface of magnesium foil with an organic gel membrane precursor solution, covering an area of ​​1 × 1 cm. 2 The coating weight is 2.1 mg per square centimeter, and then it is allowed to dry and cure. S8. The hydrophilic LiCl surface of the cathode material prepared in S4 is covered on the organic gel separator to obtain a hygroscopic magnesium-air battery.

[0052] Example 6 The process is basically the same as in Example 5, except that the amount of LiCl solution added in S4 is 0.15 mL.

[0053] Example 7 The process is basically the same as in Example 5, except that the amount of LiCl solution added in S4 is 0.20 mL.

[0054] Example 8 The process is basically the same as in Example 5, except that the amount of LiCl solution added in S4 is 0.25 mL.

[0055] Example 9 The method is basically the same as in Example 7, except that the LiCl solution is loaded by spraying.

[0056] Comparative Example 1 This comparative example discloses a method for preparing a conventional magnesium-air battery cathode material and a method for assembling a magnesium-air battery, including the following steps: S1. Mix 50 mg of α-MnO2 with 10 mL of 1% carboxylated carbon nanotube dispersion and then ultrasonically disperse to obtain the first solution. S2. A melamine foam with a mass of 2.3 mg and dimensions of 1.5 mm × 1 cm × 1 cm was completely immersed in the first solution and immediately removed, then dried at 60 °C for 2 h. After immersion-drying four times, a first porous conductive substrate loaded with catalyst α-MnO2 and carboxylated carbon nanotubes was obtained, wherein the total mass of the catalyst α-MnO2 and carboxylated carbon nanotubes was 7.25 mg. S3. Spray approximately 0.05 mL of a perfluorosulfonic acid resin solution with a mass fraction of 0.05% onto one side of the first porous conductive substrate using a spray gun, and let it stand at 60 ℃ for 20 min to dry, thereby obtaining a second porous conductive substrate with the side sprayed with perfluorosulfonic acid resin being a hydrophobic surface. S4. Polish the magnesium foil until it is shiny and clean it with anhydrous ethanol to remove the oxide layer and stains on the magnesium surface. Cut it into 1×4 cm pieces. 2 The long strips, made of magnesium foil, have a mass of 9 mg per square centimeter; S5. Mix dichloromethane and acetone in a mass ratio of 40:1 to obtain a mixed solvent. Mix 0.7 g of polyethylene oxide and 0.6 g of lithium bis(trifluoromethanesulfonyl)imide with 5 mL of the obtained mixed solvent and stir thoroughly to obtain an organic gel membrane precursor solution.

[0057] S6. Coat the surface of magnesium foil with an organogel membrane precursor solution, covering an area of ​​1 × 1 cm. 2 The coating weight is 2.1 mg per square centimeter, and then it is allowed to dry and cure. S7, using an area of ​​1×1 cm 2 The glass fiber diaphragm is loaded with an electrolyte, which is a 25 μL sodium chloride aqueous solution with a mass fraction of 3.5%. S8. Magnesium foil coated with an organic gel separator, glass fiber loaded with electrolyte, and a second porous conductive substrate are stacked in the order of magnesium foil-glass fiber-conductive substrate to obtain a magnesium-air battery.

[0058] Comparative Example 2 The results are basically the same as those in Comparative Example 1, except that the electrolyte loading in S7 is 50 μL.

[0059] Comparative Example 3 The results are basically the same as those in Comparative Example 1, except that the electrolyte loading in S7 is 100 μL.

[0060] Comparative Example 4 The results are basically the same as those in Comparative Example 1, except that the electrolyte loading in S7 is 150 μL.

[0061] Comparative Example 5 The results are basically the same as those in Comparative Example 1, except that the electrolyte loading in S7 is 200 μL.

[0062] Comparative Example 6 S1. Mix 50 mg of α-MnO2 with 10 mL of 1% carboxylated carbon nanotube dispersion and then ultrasonically disperse to obtain the first solution. S2. A melamine foam with a mass of 2.3 mg and dimensions of 1.5 mm × 1 cm × 1 cm was completely immersed in the first solution and immediately removed, then dried at 60 °C for 2 h. After immersion-drying four times, a first porous conductive substrate loaded with catalyst α-MnO2 and carboxylated carbon nanotubes was obtained, wherein the total mass of the catalyst α-MnO2 and carboxylated carbon nanotubes was 7.25 mg. S3, Prepare a concentration of 50 mg·mL -1 A LiCl solution was added dropwise to the side of the first porous conductive substrate in a direction perpendicular to the side, and then dried in a vacuum oven at 80 °C for 12 h to obtain a hygroscopic magnesium-air battery cathode material with a uniform LiCl loading. S4. Polish the magnesium foil until it is shiny and clean it with anhydrous ethanol to remove the oxide layer and stains on the magnesium surface. Cut it into 1×4 cm pieces. 2 The long strips, made of magnesium foil, have a mass of 9 mg per square centimeter; S5. Mix dichloromethane and acetone in a mass ratio of 40:1 to obtain a mixed solvent. Mix 0.7 g of polyethylene oxide and 0.6 g of lithium bis(trifluoromethanesulfonyl)imide with 5 mL of the obtained mixed solvent and stir thoroughly to obtain an organic gel membrane precursor solution; S6. Coat the surface of magnesium foil with an organogel membrane precursor solution, covering an area of ​​1 × 1 cm. 2 The coating weight is 2.1 mg per square centimeter, and then it is allowed to dry and cure. S7. The positive electrode material prepared in S3 is coated onto an organic gel separator to obtain a hygroscopic magnesium-air battery.

[0063] Test Example 1 The positive and negative electrodes of the magnesium-air battery prepared in Example 1 were led out with conductive adhesive and encapsulated with an aluminum-plastic film with holes punched on the positive electrode side. An encapsulation film was added to the perforated side of the aluminum-plastic film. The schematic diagram of the encapsulated battery structure is shown below. Figure 1 As shown. Keep the battery sealed when it is not discharging, and open the sealing film when the battery needs to be discharged.

[0064] like Figure 2 As shown, when the battery is fully sealed, the open-circuit voltage is zero. At room temperature, after the outer packaging film of the aluminum-plastic film is torn off, the battery captures moisture from the air (with a relative humidity of approximately 80%) as an electrolyte, and the open-circuit voltage gradually increases.

[0065] Test Example 2 In Examples 2-4, the mass and longitudinal resistance of the first porous conductive substrate were measured after each soaking and drying. The mass was obtained using an analytical balance with an accuracy of 0.1 mg, and the resistance was measured using a multimeter. To significantly reduce contact resistance, test signals were introduced on the upper and lower surfaces of the first porous conductive substrate using nickel foam. Given the extremely low resistance of nickel foam, its effect was negligible in the tests. The mass and resistance results of the first porous conductive substrate after each soaking and drying in Examples 2-4 are shown in Table 1.

[0066] As shown in Table 1, after four soaking-drying cycles, the resistance of the first porous conductive substrate decreased significantly and entered a plateau phase. Subsequent soaking-drying operations mainly reflected the accumulation of substrate quality, while the resistance value no longer changed significantly. To obtain lower resistance and improve production efficiency, four soaking-drying cycles are optimal.

[0067] Table 1. Mass and resistance of the first porous conductive substrate after the first to sixth immersion and drying in Examples 2-4 of the present invention.

[0068] Test Example 3 The hygroscopic magnesium-air batteries prepared in Examples 5-8 were tested in an air battery mold at a speed of 0.1 mA·cm⁻¹. -2 Discharge tests were conducted using the current density of the sample. The test conditions were room temperature and relative humidity of approximately 80%. The results are as follows: Figure 3 As shown. By Figure 3It is known that as the mass ratio of LiCl to magnesium anode in the battery increases, the discharge duration of the battery is correspondingly extended. However, when the mass ratio of LiCl to magnesium anode reaches 1.11 (Example 7), the discharge duration of the battery no longer changes significantly. This is because as the mass ratio of LiCl to magnesium anode gradually increases, the hygroscopic cathode's ability to capture moisture from the air is enhanced, which helps to form a continuous ion transport pathway and stabilize the electrode interface reaction. However, when the mass ratio of LiCl to magnesium anode reaches a certain value, the battery reaction begins to be mainly limited by the capacity of the magnesium anode itself, and excess LiCl cannot be converted into effective discharge gain, causing the discharge duration to plateau.

[0069] Test Example 4 The batteries prepared in Example 7 and Comparative Examples 1-5 were tested in an air battery mold at 0.1 mA·cm⁻¹. -2 Discharge tests were conducted using the current density of the sample. The test conditions were room temperature and relative humidity of approximately 80%. The results are as follows: Figure 4 As shown.

[0070] Depend on Figure 4 It is evident that in conventional magnesium-air batteries (Comparative Examples 1-5), the discharge duration increases with increasing electrolyte loading. However, when the electrolyte volume exceeds 100 μL, the discharge duration plateaus. With lower electrolyte levels, the amount of reactive negative electrode material increases, leading to a higher discharge duration. However, once the negative electrode can fully react, further increases in electrolyte content do not change the battery capacity.

[0071] Compared with Comparative Examples 1-5, the discharge duration of the hygroscopic magnesium-air battery prepared in Example 7 is significantly improved. This is because the hygroscopic magnesium-air battery has a much lower moisture content than batteries using liquid electrolytes during discharge, and the large number of carboxyl groups on the carbon nanotubes in the positive electrode can form hydrogen bonds with water. This interaction reduces the reactivity of water, thus the adverse reactions occurring at the negative electrode are weaker, the utilization rate of the negative electrode is higher, and the discharge capacity of the battery increases accordingly.

[0072] Test Example 5 The batteries prepared in Example 7 and Comparative Example 3 were tested in an air battery mold at 0.1 mA·cm⁻¹ -2The current density was used for discharge testing under room temperature and relative humidity of approximately 80%. In Example 7, the battery's encapsulation film was removed only during testing and then resealed until the next testing period. The specific capacity was measured after storage for 0, 1, 2, 7, and 30 days. In Comparative Example 3, the battery was stored immediately after encapsulation (day 0). Since electrolyte had been added, the battery continued to react, and its specific capacity was measured on days 0, 1, 2, and 7. The specific capacity results for both sets of batteries are as follows: Figure 5 As shown.

[0073] Depend on Figure 5 It can be seen that the specific capacity of the hygroscopic magnesium-air battery prepared in Example 7 only decreased slightly with the extension of storage time. However, the conventional magnesium-air battery prepared in Comparative Example 3 experienced a continuous decrease in battery capacity over 7 days because the reaction could not be stopped, until the negative electrode was completely corroded.

[0074] Test Example 6 The batteries prepared in Example 7 and Comparative Example 6 were tested in an air battery mold at a speed of 0.05 mA·cm⁻¹. -2 0.1 mA·cm -2 0.2 mA·cm -2 and 0.5 mA·cm -2 Discharge tests were conducted using the current density of the sample. The test conditions were room temperature and relative humidity of approximately 80%. The results are as follows: Figure 6 As shown.

[0075] Depend on Figure 6 It can be seen that, compared with the hygroscopic magnesium-air battery with uniformly distributed LiCl loading prepared in Comparative Example 6, the hygroscopic magnesium-air battery with gradient LiCl loading prepared in Example 7 exhibits a higher discharge voltage under different discharge currents. This is because there is a hydrophilic-hydrophobic gradient in the cathode material treated with perfluorosulfonic acid resin. On the hydrophilic side of the electrode, LiCl aggregates and forms a continuous ion pathway after absorbing moisture. On the hydrophobic side of the electrode, LiCl is less distributed. After absorbing moisture, the porous structure of the electrode is still preserved, and oxygen can reach the reaction site unimpeded, which is conducive to the efficient progress of the cathode reaction.

[0076] Test Example 7 The batteries prepared in Examples 7 and 9 were tested in an air battery mold at 0.1 mA·cm⁻¹ -2 Discharge tests were conducted using the current density of the sample. The test conditions were room temperature and relative humidity of approximately 80%. The results are as follows: Figure 7 As shown.

[0077] Depend on Figure 7It can be seen that, compared with Example 7 which used dropwise addition of LiCl solution, the discharge capacity of the battery in Example 9, which used spraying LiCl solution, decreased slightly. This may be because the dropwise addition method facilitates the penetration of LiCl solution into the porous substrate through capillary action, easily forming a gradient distribution along the thickness direction; while the spraying method causes a large amount of LiCl solution to accumulate on the substrate surface, and after drying, LiCl is mainly enriched in the surface layer of the positive electrode. This surface-enriched structure prevents the internal porous structure from forming an effective ion-conducting network due to salt deficiency, thus limiting the overall utilization of the active material.

[0078] The above description provides an illustrative overview of the present invention and its embodiments. This description is not restrictive, and the embodiments shown are merely one example of the invention's implementation. Actual implementations are not limited to these examples. Therefore, if those skilled in the art are inspired by this description and design similar implementations and examples without departing from the spirit of the invention, such designs should fall within the scope of protection of the present invention.

Claims

1. A hygroscopic magnesium-air battery cathode material, characterized in that, include: A first porous conductive substrate, comprising sheet-like melamine foam and a positive electrode reaction catalyst and hydrophilic carbon nanotubes supported on the surface of the sheet-like melamine foam. A perfluorosulfonic acid resin loaded on one side of the first porous conductive substrate, wherein the perfluorosulfonic acid resin forms a hydrophobic surface; LiCl loaded on the other side and inside of the first porous conductive substrate forms a LiCl hydrophilic surface on the other side. The loading of LiCl decreases gradually from the hydrophilic surface to the hydrophobic surface along the direction of LiCl.

2. The hygroscopic magnesium-air battery cathode material according to claim 1, characterized in that: The positive electrode catalyst includes one or both of α-MnO2 and Pt / C; The mass ratio of the positive electrode catalyst to the hydrophilic carbon nanotubes is (0.3~0.7):

1.

3. The hygroscopic magnesium-air battery cathode material according to claim 1 or 2, characterized in that: The mass ratio of the sum of the masses of the sheet-like melamine foam, the positive electrode catalyst, and the hydrophilic carbon nanotubes is 1:(2~7).

4. The hygroscopic magnesium-air battery cathode material according to claim 1 or 2, characterized in that: The mass ratio of the sheet-like melamine foam to the perfluorosulfonic acid resin is 1:(0.005~0.02).

5. The hygroscopic magnesium-air battery cathode material according to claim 1 or 2, characterized in that: The mass ratio of the sheet-like melamine foam to LiCl is 1:(1~7).

6. The hygroscopic magnesium-air battery cathode material according to claim 1 or 2, characterized in that: The thickness of the sheet-like melamine foam is 1~3 mm.

7. The method for preparing the hygroscopic magnesium-air battery cathode material according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. The positive electrode catalyst is mixed with the hydrophilic carbon nanotube dispersion to obtain the first solution; S2. The sheet-like melamine foam is repeatedly soaked in the first solution and dried to obtain a first porous conductive substrate loaded with a positive electrode catalyst and hydrophilic carbon nanotubes. S3. A hydrophobic perfluorosulfonic acid resin solution is sprayed onto one side of the first porous conductive substrate, and after drying, a second porous conductive substrate with one side being hydrophobic is obtained. S4. The LiCl solution is dropped onto the second porous conductive substrate from the other side in a direction perpendicular to the other side. After drying, a hygroscopic magnesium-air battery cathode material is obtained. The LiCl on the other side and inside forms a hydrophilic LiCl surface on the other side. The loading of LiCl decreases in a gradient from the hydrophilic to the hydrophobic LiCl surface.

8. The method for preparing the hygroscopic magnesium-air battery cathode material according to claim 7, characterized in that: In step S1, the solid mass fraction of the first solution is 1-2%; In step S3, the mass fraction of the perfluorosulfonic acid resin solution is 0.03~0.07%; In step S4, the concentration of the LiCl solution is 40~60 mg·mL. -1 .

9. A magnesium-air battery, characterized in that: It includes the hygroscopic magnesium-air battery cathode material according to any one of claims 1 to 6 and the hygroscopic magnesium-air battery cathode material prepared by the method according to any one of claims 7 to 8.

10. The magnesium-air battery according to claim 9, characterized in that: The mass ratio of LiCl to the negative electrode material in the hygroscopic magnesium-air battery positive electrode material is (0.5~1.5):1.

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