Highly Stable Carbon-Free Ag/Co3O4 Cathodes for Li-Air Batteries with Aqueous Alkaline Electrolyte: Electrochemical and Structural Investigations

Kurzfassung

Highly Stable Carbon-Free Ag/Co3O4 Cathodes for Li-Air Batteries with Aqueous Alkaline Electrolyte: Electrochemical and Structural Investigations Dennis Wittmaier 1,*, Norbert Wagner 1, K. Andreas Friedrich 1,2 1 German Aerospace Center (DLR), Institute of Technical Thermodynamics, Pfaffenwaldring 38-40, 70569 Stuttgart, Germany 2 Institute for Energy Storage, University of Stuttgart, Pfaffenwaldring 31, Germany *Corresponding author. Phone: +4971168628068; Fax +497116862747; E-mail: dennis.wittmaier@dlr.de The operation of a secondary lithium-air battery requires to run the battery in oxygen reduction reaction (ORR) as well as in oxygen evolution reaction (OER). OER represents the charge reaction and requires a sufficient catalyst for oxygen evolution. Currently carbon materials are widely used in cathodes of aqueous alkaline lithium-air batteries due to their high electronic conductivity, stability, relatively low costs and catalytic activity towards oxygen reduction reaction (ORR) [1, 2]. However, carbon-based cathode materials are non-stable in the potential range of OER as they start to corrode at potentials higher than open circuit voltage (OCV) [3, 4]. Corrosion leads to high degradation corresponding to successive capacity loss and ultimately destruction of the cathode. To improve long-term stability and reduce side reactions such as H2 and CO2 evolution carbon-free bifunctional cathodes for aqueous alkaline lithium-air batteries are of need [5, 6]. In this poster we present cathodes with a combination of Ag and Co3O4. Those were prepared with a dry-processed and solvent-free preparation method [7, 8]. Electrocatalytic activity regarding both ORR and OER was investigated by cyclic voltammetry (CV) for up to 300 cycles in half-cells. In addition structural and surface characteristics were investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). These combined measurements give new insights in the materials’ oxidation states and the stability of Ag oxides in Ag/Co3O4 cathodes throughout a complete battery cycle [9]. Cathodes with the combination of Ag and Co3O4 show high activity for both reactions ORR and OER and a significant improvement in performance compared to both pure Ag and pure Co3O4 cathodes. Long-term tests show superior stability of the bimetal cathodes [6]. [1] H. Ohkuma, I. Uechi, M. Matsui, Y. Takeda, O. Yamamoto, N. Imanishi, J. Power Sources 245 (2014) 947. [2] H. Arai, S. Müller, O. Haas, J. Electrochem. Soc. 147 (2000) 3584. [3] P. N. Ross, M. Sattler, J. Electrochem. Soc. 135 (1988) 1464. [4] P. N. Ross, H. Sokol, J. Electrochem. Soc. 131 (1984) 1742. [5] D. Wittmaier, T. Danner, N. Wagner, K. A. Friedrich, J. App. Electrochem. 43 (2013) 73. [6] D. Wittmaier, N. Wagner, K. A. Friedrich, H.A. Amin, H. Baltruschat, J. Power Sources 265 (2014) 299. [7] D. Wittmaier, N. Wagner, H.A. Amin, H. Baltruschat, Patent App. PCT/EP2015/053586. [8] D. Wittmaier, N. Wagner, H.A. Amin, H. Baltruschat, Patent App. DE 102014102304 A1. [9] D. Wittmaier, Natalia A. Canas, I. Biswas, K. A. Friedrich, Adv. Energy Mater. 2015, doi: 10.1002/aenm.201500763.