Carbon-Free Cathode Materials for Li-O-2 Batteries

Rechargeable lithium-oxygen batteries, especially the nonaqueous lithium-oxygen batteries have attracted much attention in recent years due to their high energy densities. However, few critical challenges remain to be overcome, including the low round-trip efficiency, high charge overpotential, poor cycling performance, decomposition of electrolyte, and instability of the carbon-based electrode. Among these, the instability of the carbon-based electrode is one of the major problems that hindered the practical application of the Li-O-2 batteries. Much work has been done to solve this problem and there are two widely-applied strategies: modification of carbon and designing a "carbon-free" cathode. In this review, we will introduce recent achievements of both strategies.