NONAQUEOUS ELECTROLYTE SOLUTIONS FOR Li-O₂ CELLS

Pairing lithium and oxygen in aprotic solvents can theoretically lead to one of the most promising electrochemical cells available. If successful, this system can compete with technologies such as the internal combustion engine and provide an energy density that can accommodate electric vehicle demands. However, there are many problems that have held this technology back from becoming a reality. One of the main reasons is capacity fading after only a few cycles, which is caused by the instability of electrolyte solutions in the presence of reduced oxygen species like O₂^-. and O₂^-2.

In recent years, use of various analytical tools, has enabled researchers to characterize the breakdown products resulting from the reactions of the reduced oxygen species with aprotic solvents. No electrolyte solution has yet been found which is fully stable throughout the reduction and oxidation processes. We believe, however, that an understanding of these decomposition mechanisms can help us in designing new systems which are more stable toward the aggressive conditions taking place in the Li-O₂ cell.

The addition of a redox mediator - a soluble electroactive molecule that can interact with the oxides on the cathode surface - can help to oxidize the nonconductive ORR products. The addition of different salts - that keep a redox couple`s behavior within the desired voltage range - can help to reduce the OER voltage below 4 V using high currents densities. Despite these improvements, the capacity fading remains, and it appears that a parasitic reaction still governs the cell performance.