A structured three-dimensional polymer electrolyte with enlarged active reaction zone for Li-O2 batteries

The application of conventional solid polymer electrolyte (SPE) to lithium-oxygen (Li-O-2) batteries has suffered from a limited active reaction zone due to thick SPE and subsequent lack of O-2 gas diffusion route in the positive electrode. Here we present a new design for a three-dimensional (3-D) SPE structure, incorporating a carbon nanotube (CNT) electrode, adapted for a gas-based energy storage system. The void spaces in the porous CNT/SPE film allow an increased depth of diffusion of O-2 gas, providing an enlarged active reaction zone where Li+ ions, O-2 gas, and electrons can interact. Furthermore, the thin SPE layer along the CNT, forming the core/shell nanostructure, aids in the smooth electron transfer when O-2 gas approaches the CNT surface. Therefore, the 3-D CNT/SPE electrode structure enhances the capacity in the SPE-based Li-O-2 cell. However, intrinsic instability of poly(ethylene oxide) (PEO) of the SPE matrix to superoxide (O-2(center dot-)) and high voltage gives rise to severe side reactions, convincing us of the need for development of a more stable electrolyte for use in this CNT/SPE design.