EAGER: Investigation of Lithium-Air Battery Cathode Reaction Mechanisms through SERS-Active Electrode

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Zhu - 1505943This project is aimed at developing lithium-air batteries for use in electrically powered vehicles as alternatives to vehicles that run on fossil fuels. To compete with commercial internal combustion engines, electricity storage systems have to be significantly improved in energy density, power density and reversibility. Lithium-air batteries have the potential to significantly enhance the energy density but they are still immature and suffer from many issues, including the fact that they have sluggish and irreversible cathode reactions. Because the cathode reaction mechanism of the lithium-air battery is unclear, it is very difficult to design electrodes and electrolytes that cycle better. The primary objective in this research is to synthesize a bicontinuous, SERS (surface-enhanced Raman spectroscopy)-active electrode for lithium-air batteries and study the mechanism of charging/discharging processes by Raman spectroscopy. This is an EAGER grant to demonstrate the feasibility of the fabrication process.Intellectual Merit: This project seeks to fabricate the SERS-active electrodes to study the products formed on the cathode. The rationale for fabricating well organized bi-continuous 3D porous electrodes is to provide, simultaneously, a large effective surface area and an improvement in the electrolyte and oxygen diffusion. Lithium-air battery cathode reactions are complicated and sensitive to the local electrochemical environment. It is important to study the mechanisms of the battery electrode reactions to gain chemical information about the electrode throughout the charging/discharging process. In this work, the PI plans to use polymer templates to fabricate well-organized bicontinuous electrodes made of pristine chemical vapor deposited graphene. The bi-continuous electrodes can enhance the lithium-air battery kinetic performance and reduce the clog induced degradationTo enhance the Raman signals, the bi-continuous electrodes will be modified by the adsorption of uniform and regularly assembled gold nanoparticles. The modified electrodes may allow the detection, by surface-enhanced Raman spectroscopy, of trace intermediate compounds deposited on the electrodes. The PI proposes to use the modified electrode with stable solvents (Dimethoxyethane, Dimethyl sulfoxide and Tetra(ethylene) glycol dimethyl ether etc.) to fabricate lithium-air battery. A suite of characterization tools (including Raman, FTIR, TEM, XPS, and XRD) should enable the investigation of the materials on the air-cathode. Of particular interest are intermediate compounds deposited on the cathode during the charging and discharging processes that will be elucidated by SERS Raman spectroscopy to address fundamental material challenges associated with electrolyte/electrode stability. This research will provide the bases to design in-situ SERS Raman characterization techniques in the future, which may elucidate the cathode reaction mechanisms through the continuous investigation of the chemical information on the electrodes. Ultimately this may point to new engineering solutions for high performance, reversible lithium-air batteries.Broader Impacts: Understanding the electrode reaction mechanism is needed to improve capacity and cyclability of electrochemical energy storage system. This is also pivotal for material and process design. Due to the high theoretical capacitance of lithium-air battery and the possible high demand for these batteries in consumer and industrial applications, the potential impact from even a modest advance in cyclability or efficiency is quite large. There are both economic and environmental benefits to consider because increased battery capacity will decrease the replacement rate and may allow for the substitution of new technology for old. This could include the replacement of the internal combustion engine with electrical motors for uses in transportation systems. Dissemination of concepts associated with this research will be to a broader, public audience through various outreach programs. Local outreach efforts will include Science Olympiad weekend for students in grades 4-6, the UA-Harker program for high-school students working with professors in the institute of polymer science and polymer engineering. Additionally, the PI's group is active in ACS SEED program to promote the research activities of economically disadvantaged local high school students. The goal of these outreach activities are to (1) illustrate hands-on nanotechnology, (2) excite students about science and technology so that they may be encouraged to consider careers in STEM fields, and (3) teach about challenges and opportunities associated with the engineering of chemical processes.