In Situ Formed Layered-Layered Metal Oxide as Bifunctional Catalyst for Li-Air Batteries

• Published in: Journal of the Electrochemical Society Vol. 163; no. 10; pp. A2464 - A2474
• Main Authors: Ates, Mehmet Nurullah, Gunasekara, Iromie, Mukerjee, Sanjeev, Plichta, Edward J., Hendrickson, Mary A., Abraham, K. M.
• Format: Journal Article
• Language: English
• Published: The Electrochemical Society 01.01.2016
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/2.0111613jes

The electrochemical activity of a Li-air battery cathode catalyst derived from the lithium rich layered-layered metal oxide of the formula 0.5Li2MnO3.0.5LiMn0.5Ni0.35Co0.15O2 is reported. The catalyst formed in-situ by electrochemically de-lithiating this metal oxide embedded in a high surface area carbon matrix behaved as a bifunctional catalyst for O2 reduction reaction (ORR) and O2 evolution reaction (OER) in a non-aqueous Li-O2 cell. Cyclic voltammetry (CV) in both half and full cells revealed enhanced OER and ORR catalytic activity by: i-) displaying a more positive potential shift during ORR, ii-) stabilizing the initial ORR product LiO2, and iii-) showing an additional potential step in the oxidation of the ORR products. In the CV of catalyzed cells, a reduction peak appeared before the main peroxide (O22−) formation peak suggesting that the catalyst stabilizes the superoxide (O2−) formed prior to the formation of peroxide. Evidence for LiO2 as the initial discharge product was obtained from both the Raman spectrum and X-ray diffraction (XRD) pattern of Li-air cell cathodes after galvanostatic discharge to 2 V. Surface features for the discharged cathodes obtained from Field Emission Scanning Electron Microscope (FESEM) unveiled dissimilar morphologies for the discharge products from catalyzed and uncatalyzed cells, originating from different nucleation mechanisms. The catalyzed cells exhibited longer cycle life than uncatalyzed cells under similar cycling conditions.