Preparation method of lithium-air battery positive electrode with super-hydrophobicity

Abstract

The application belongs to the field of lithium air battery preparation, and particularly relates to a preparation method of a lithium air battery positive electrode with superhydrophobicity. The technical scheme of the application is as follows: a preparation method of a lithium air battery positive electrode with superhydrophobicity, wherein the material for preparing the positive electrode is a mixture of MSiO2, MWCNTs and MnO2; and the preparation of the positive electrode is implemented by means of roller pressing. The preparation method of the lithium air battery positive electrode with superhydrophobicity is safe, convenient and economical, and can significantly improve the performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-air battery preparation, specifically relating to a method for preparing a lithium-air battery cathode with superhydrophobic properties. Background Technology

[0002] A lithium-air battery mainly consists of a negative electrode shell, spring gaskets, steel sheets, a glass fiber membrane, an electrolyte, a positive electrode sheet, and a positive electrode shell. The positive electrode sheet, as a crucial component, primarily provides the reaction site for the lithium-air battery. Its core working principle is that during discharge, lithium metal loses electrons at the negative electrode to form lithium ions (Li+). These Li+ ions migrate through the electrolyte to the positive electrode, where they combine with oxygen (O2) diffused from the air and electrons (e-) from the external circuit to form lithium peroxide (Li2O2), which is deposited in the pores of the positive electrode. The charging process is the opposite: Li2O2 decomposes, releasing Li+, O2, and e- back into the positive electrode. Throughout the electrochemical reaction, the air positive electrode is not only the catalytic site for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), but also a "triple channel" for oxygen, electrolyte, and electron transport. Its performance directly determines the overall efficiency, rate performance, and cycle life of the battery.

[0003] Therefore, the selection and structural design of air cathode materials are of paramount importance in the development of lithium-air battery technology. An ideal air cathode should possess the following characteristics: high electronic conductivity to promote charge transport; a well-developed porous structure to ensure rapid mass transfer between oxygen and electrolyte; abundant catalytic active sites to reduce reaction overpotential and improve reaction reversibility; and good chemical and electrochemical stability to resist the erosion of reaction intermediates (such as superoxide ions O2-). Currently, the most studied cathode materials include carbon materials (such as carbon nanotubes, graphene, and porous carbon), transition metal oxides (such as MnO2, Co3O4, and RuO2), and noble metals / alloys. Among these, carbon materials have become the most widely used cathode matrix material due to their high specific surface area, excellent conductivity, tunable pore structure, and relatively low cost. However, carbon materials are easily oxidized and decomposed at the high charging potential of the battery, producing byproducts and leading to battery performance degradation.

[0004] Besides the properties of the material itself, the microstructure and macroscopic morphology of the cathode are equally important. The pore structure (pore size, pore volume, porosity) inside the cathode directly affects the oxygen diffusion rate and the storage space of Li2O2. An unreasonable pore structure can lead to the obstruction of reactant transport and the blockage of pores by products, thereby rapidly causing battery failure.

[0005] In summary, developing a novel cathode preparation method that is simple, efficient, and can simultaneously improve the electrochemical performance of lithium-air batteries by optimizing cathode materials and structures has significant research value and application prospects. This invention addresses these needs by proposing an innovative method for preparing high-performance lithium-air battery cathodes through hydrophobic modification of cathode materials combined with a rolling process. Summary of the Invention

[0006] This invention provides a method for preparing a lithium-air battery cathode with superhydrophobicity, which is safe, convenient, and economical, and can significantly improve battery performance.

[0007] The technical solution of the present invention is as follows:

[0008] A method for preparing a superhydrophobic lithium-air battery cathode, wherein the cathode material is a mixture of MSiO2 (methyl-modified silica nanoparticle powder), MWCNTs (multi-walled carbon nanotubes), and MnO2; the cathode is prepared by rolling using a roller press.

[0009] Furthermore, the method for preparing the superhydrophobic lithium-air battery cathode specifically includes the following steps:

[0010] 1) Add SiO2 nanoparticle powder to anhydrous ethanol and sonicate it to disperse it evenly to obtain a nano-SiO2 suspension.

[0011] 2) Add OTMS (octyltrimethoxysilane) to anhydrous ethanol and dissolve it under magnetic stirring; add deionized water and continue stirring to obtain the hydrolyzed OTMS solution;

[0012] 3) The hydrolyzed OTMS solution was added dropwise to the nano-SiO2 suspension and stirred continuously in a constant temperature water bath to modify SiO2 with hydrophobicity using OTMS to obtain MSiO2; MSiO2 was collected using a vacuum filter and washed repeatedly with anhydrous ethanol several times.

[0013] 4) Place the washed MSiO2 into a vacuum drying oven to obtain dried MSiO2;

[0014] 5) Mix MWCNTs, MSiO2 and MnO2 to form an active material powder;

[0015] 6) Add PTFE (polytetrafluoroethylene) emulsion to the active material powder to obtain a mixture;

[0016] 7) Transfer the mixture to an agate mortar, add a small amount of AR grade anhydrous ethanol as a wetting agent to assist in mixing and shaping, and grind into a dough-like substance;

[0017] 8) Roll the dough-like material into a sheet with a thickness of 0.2-0.4 mm using a roller press;

[0018] 9) After the thin sheet is left to stand for 10-14 hours, it is sent into a tube furnace for sintering;

[0019] 10) Use a hydraulic slicer to cut the sintered sheet into positive electrode sheets with a diameter of 11-19 mm for various discharge tests and characterization.

[0020] Furthermore, in the method for preparing the superhydrophobic lithium-air battery cathode, in step 1), 1-3g of SiO2 nanoparticle powder is added to 20-40 ml of anhydrous ethanol and ultrasonically treated for 25-35 minutes to disperse it uniformly, thereby obtaining a nano-SiO2 suspension.

[0021] Furthermore, in the method for preparing the superhydrophobic lithium-air battery cathode, in step 2), 0.1-0.2 g of OTMS is added to 8-12 ml of anhydrous ethanol and dissolved under magnetic stirring; 0.2-0.4 g of deionized water is added to it, and stirring is continued for 25-35 minutes to obtain the hydrolyzed OTMS solution.

[0022] Furthermore, in the method for preparing the superhydrophobic lithium-air battery cathode, in step 3), the hydrolyzed OTMS solution is added dropwise to the nano-SiO2 suspension, and stirred continuously in a constant temperature water bath at 75-85°C for 3-5 hours to modify SiO2 for hydrophobicity using OTMS.

[0023] Furthermore, in the method for preparing the superhydrophobic lithium-air battery cathode, step 4) involves drying at 75-85°C for 2-4 hours.

[0024] Furthermore, in the method for preparing the superhydrophobic lithium-air battery cathode, step 5) involves mixing MWCNTs, MSiO2, and MnO2 in a mass ratio of 3:1:1 to form an active material powder.

[0025] Furthermore, in the method for preparing the superhydrophobic lithium-air battery cathode, in step 6), the mass of PTFE is 30-50% of the mass of MWCNTs.

[0026] Furthermore, in the method for preparing the superhydrophobic lithium-air battery cathode, step 9) involves first preheating at 230-250°C for 0.5-1.5 hours, followed by sintering at 330-350°C for 0.5-1.5 hours.

[0027] Furthermore, in the method for preparing the superhydrophobic lithium-air battery cathode, in step 10), the area of ​​the cathode sheet is 1-3 cm². 2 The thickness is 0.2-0.4mm.

[0028] The beneficial effects of this invention are as follows: Based on the traditional cathode preparation method, this invention incorporates hydrophobic modifications. By improving the cathode material with hydrophobicity, moisture from the air can be effectively prevented from entering the cathode, reducing the possibility of side reactions and thus effectively improving the cycle stability of lithium-air batteries. The rolling process has a short cycle time, low requirements for preliminary material preparation, and no excessive demands on the materials used, enabling more efficient preparation of ultra-thin cathode sheets with higher efficiency. Attached Figure Description

[0029] Figure 1 Metallographic diagram of the positive electrode sheet;

[0030] Figure 2 The diagram shows the elemental composition of the positive electrode; (a) is the elemental composition of the methyl-modified superhydrophobic MSiO2 powder, and (b) and (c) are the standard peak values ​​of SiO2.

[0031] Figure 3 This is a schematic diagram of the hydrophobic angle of the positive electrode surface;

[0032] Figure 4 Electrochemical impedance spectroscopy of the positive electrode;

[0033] Figure 5 This is a cyclic voltammetry test diagram for the positive electrode.

[0034] Figure 6 This is a diagram showing the deep discharge test of a battery with a positive electrode plate installed. Detailed Implementation

[0035] A method for preparing a lithium-air battery cathode with superhydrophobic properties includes the following steps:

[0036] 1) Add 2 g of SiO2 nanoparticle powder to 30 ml of anhydrous ethanol and sonicate for 30 minutes to disperse it evenly, thus obtaining a nano-SiO2 suspension.

[0037] 2) Add 0.15 g OTMS to 10 ml of anhydrous ethanol and dissolve it under magnetic stirring; add 0.3 g of deionized water and continue stirring for 30 minutes to obtain the hydrolyzed OTMS solution;

[0038] 3) The hydrolyzed OTMS solution was added dropwise to the nano-SiO2 suspension and stirred continuously in an 80 °C constant temperature water bath for 4 hours to modify SiO2 into hydrophobicity using OTMS to obtain MSiO2; MSiO2 was collected using a vacuum filter and washed repeatedly with anhydrous ethanol several times.

[0039] 4) Place the washed MSiO2 into a vacuum drying oven and dry it at 80 °C for 3 hours to obtain dried MSiO2;

[0040] 5) Mix MWCNTs, MSiO2 and MnO2 in a mass ratio of 3:1:1 to form an active material powder;

[0041] 6) Add PTFE emulsion to the active material powder, wherein the mass of PTFE is 40% of the mass of MWCNTs, to obtain a mixture;

[0042] 7) Transfer the mixture to an agate mortar, add a small amount of AR grade anhydrous ethanol as a wetting agent to assist in mixing and shaping, and grind into a dough-like substance;

[0043] 8) Roll the dough-like material into a sheet with a thickness of 0.3 mm using a roller press;

[0044] 9) After the sheet is left to stand for 12 hours, it is sent into a tube furnace for sintering; first, it is preheated at 240°C for 1 hour, and then sintered at 340°C for 1 hour;

[0045] 10) Use a hydraulic slicer to cut the sintered sheet into positive electrode sheets with a diameter of 16 mm and an area of ​​2 cm². 2 With a thickness of 0.3 mm, it is used for various discharge tests and characterization.

[0046] like Figure 1 As shown, the microstructure of the cathode is mainly composed of strip-shaped carbon nanotubes and spherical MSiO2 particles, forming a three-dimensional porous structure with the ability to accommodate micro-deposited products.

[0047] like Figure 2 As shown in (a), the main material composition of the modified cathode material shows the presence of methyl groups on the surface of SiO2 nanoparticles, thus successfully modifying the methyl groups and proving that the method successfully modified the nanoparticles; Figure 2 As shown in (b) and (c), the SiO2 content is at its peak.

[0048] like Figure 3 As shown, the hydrophobic angle of the modified cathode surface reached 153.9°, which indicates that the cathode surface has excellent hydrophobicity, thus proving the success of the cathode preparation.

[0049] like Figure 4 As shown, the electrochemical impedance spectroscopy (EIS) results are as follows: The initial ohmic impedance without water and without hydrophobication modification is 23.48 Ω, and the charge transfer impedance is 78.43 Ω; the initial ohmic impedance with water but without hydrophobication modification is 34.70 Ω and 202.27 Ω; the initial ohmic impedance without water but with hydrophobication modification is 20.22 Ω, and the charge transfer impedance is 97.07 Ω; the initial ohmic impedance with water and with hydrophobication modification is 25.62 Ω, and the charge transfer impedance is 145.10 Ω. This demonstrates that after hydrophobication modification, the battery impedance only slightly increases in the absence of water. However, after adding water, the impedance of the battery with the hydrophobicated cathode is significantly lower than that of the battery without the hydrophobicated cathode.

[0050] Cyclic voltammetry (CV) was used to determine the redox potential of battery materials, a key parameter for electron transfer during battery charge and discharge. CV tests were performed on batteries with no water, no hydrophobicity modification, water but no hydrophobicity modification, no water but hydrophobicity modification, and water and hydrophobicity modification. The scan voltage range was 2 V–4.5 V, and the test temperature was room temperature. Figure 5 As shown, the peak value is smallest when water is added and hydrophobicity is improved, and a smaller peak value indicates a more efficient reaction process.

[0051] Battery discharge performance testing: such as Figure 6 As shown, at a current density of 0.2 mA / cm² 2 At that time, the discharge capacity achievable without adding water and without hydrophobic modification was 21.29 mA / cm². 2 The discharge capacity achievable by adding water but without hydrophobication modification is 22.02 mA / cm². 2 The discharge capacity achievable without water but through hydrophobic modification is 25.57 mA / cm². 2 The discharge capacity achievable by adding water and hydrophobicating the sample is 29.59 mA / cm². 2 Therefore, it can be seen that the hydrophobicity improvement enhances the battery's discharge performance.

Claims

1. A method for preparing a lithium-air battery cathode with superhydrophobic properties, characterized in that, The positive electrode is a mixture of MSiO2, MWCNTs, and MnO2; the positive electrode is prepared by rolling using a roller press.

2. The method for preparing a superhydrophobic lithium-air battery cathode according to claim 1, characterized in that, Specifically, the steps include the following: 1) Add SiO2 nanoparticle powder to anhydrous ethanol and sonicate it to disperse it evenly to obtain a nano-SiO2 suspension. 2) Add OTMS to anhydrous ethanol and dissolve it under magnetic stirring; add deionized water and continue stirring to obtain the hydrolyzed OTMS solution; 3) The hydrolyzed OTMS solution was added dropwise to the nano-SiO2 suspension and stirred continuously in a constant temperature water bath to modify SiO2 with hydrophobicity using OTMS to obtain MSiO2; MSiO2 was collected using a vacuum filter and washed repeatedly with anhydrous ethanol several times. 4) Place the washed MSiO2 into a vacuum drying oven to obtain dried MSiO2; 5) Mix MWCNTs, MSiO2 and MnO2 to form an active material powder; 6) Add PTFE emulsion to the active material powder to obtain a mixture; 7) Transfer the mixture to an agate mortar, add a small amount of AR grade anhydrous ethanol as a wetting agent to assist in mixing and shaping, and grind into a dough-like substance; 8) Roll the dough-like material into a sheet with a thickness of 0.2-0.4 mm using a roller press; 9) After the thin sheet is left to stand for 10-14 hours, it is sent into a tube furnace for sintering; 10) Use a hydraulic slicer to cut the sintered sheet into positive electrode sheets with a diameter of 11-19 mm for various discharge tests and characterization.

3. The method for preparing a superhydrophobic lithium-air battery cathode according to claim 2, characterized in that, In step 1), 1-3g of SiO2 nanoparticle powder is added to 20-40ml of anhydrous ethanol and ultrasonically treated for 25-35 minutes to disperse it evenly, thus obtaining a nano SiO2 suspension.

4. The method for preparing a superhydrophobic lithium-air battery cathode according to claim 2, characterized in that, In step 2), 0.1-0.2 g of OTMS is added to 8-12 ml of anhydrous ethanol and dissolved under magnetic stirring; 0.2-0.4 g of deionized water is added and stirring is continued for 25-35 minutes to obtain the hydrolyzed OTMS solution.

5. The method for preparing a superhydrophobic lithium-air battery cathode according to claim 2, characterized in that, In step 3), the hydrolyzed OTMS solution is added dropwise to the nano-SiO2 suspension and stirred continuously in a constant temperature water bath at 75-85°C for 3-5 hours to modify SiO2 for hydrophobicity using OTMS.

6. The method for preparing a superhydrophobic lithium-air battery cathode according to claim 2, characterized in that, In step 4), the product is dried at 75-85°C for 2-4 hours.

7. The method for preparing a superhydrophobic lithium-air battery cathode according to claim 2, characterized in that, In step 5), MWCNTs, MSiO2 and MnO2 are mixed in a mass ratio of 3:1:1 to form an active material powder.

8. The method for preparing a superhydrophobic lithium-air battery cathode according to claim 2, characterized in that, In step 6), the mass of PTFE is 30-50% of the mass of MWCNTs.

9. The method for preparing a superhydrophobic lithium-air battery cathode according to claim 2, characterized in that, In step 9), the temperature is first preheated at 230-250℃ for 0.5-1.5 hours, and then sintered at 330-350℃ for 0.5-1.5 hours.

10. The method for preparing a superhydrophobic lithium-air battery cathode according to claim 2, characterized in that, In step 10), the area of ​​the positive electrode is 1-3 cm². 2 The thickness is 0.2-0.4 mm.

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