Novel Electrolyte Systems for Improving Energy Density and Power Density of Li-O2 Batteries

Abstract

Capacities and power density of Li-O2 batteries are closed contacted with physical properties of electrolyte. In this work, we research the electrochemical performance of the mixed electrolyte between dimethylsulfoxide (DMSO) and N, N-dimethylacetamide (DMA), firstly. The cell with 70% of DMA mixed electrolyte exhibited high discharge rate capability and low over-potential that the charge platform is below 3.6V at a current density of 0.2 mA cm-2. The titration result showed that DMA is more stable than DMSO in Li-O2 batteries. It is because that the stability of high donor number (DN) solvent is less than that of the low DN solvent in Li-O2 batteries, even though high DN solvent has a high discharge capacities. 1, 2 Based on this, we proposed a new strategy; namely, by combining a relative stable solvent with low DN and a stable additive as the cell electrolyte, the relationship between high capacity and high stability could be balanced. A novel type electrolyte additive, octamethylcyclotetrasiloxane (OMTS), is applied to Li-O2 batteries with TEGDME-based electrolyte with low DN. The electrochemical tests show that, With an optimal OMTS content (10% OMTS), the cell displayed a discharge capacity of 6778 mAh g-1 at 0.05 mA cm-2, and its discharge capacity still has an acceptable capacity of 1823mAh g-1 at an ultra-high current density of 1 mA cm-2. Specially, the capacity retention of the cell with optimal OMTS content is more than double that of the cell with no OMTS additive at large current density of 1 mA cm-2. The further NMR and Li2O2 yield measurements during discharge indicate that OMTS additive does not alter the discharge product and compromise the stability of electrolyte. Figure 1