A high-capacity cathode for rechargeable K-metal battery based on reversible superoxide-peroxide conversion

As a promising low-cost energy storage device, the development of a rechargeable potassium-ion battery (KIB) is severely hindered by the limited capacity of cathode candidates. Regarded as an attractive capacity-boosting strategy, triggering the O-related anionic redox activity has not been achieved within a sealed KIB system. Herein, in contrast to the typical gaseous open K-O₂ battery (O₂/KO₂ redox), we originally realize the reversible superoxide/peroxide (KO₂/K₂O₂) interconversion on a KO₂-based cathode. Controlled within a sealed cell environment, the irreversible O₂ evolution and electrolyte decomposition (induced by superoxide anion (O₂ ^-) formation) are effectively restrained. Rationally controlling the reversible depth-of-charge at 300 mAh/g (based on the mass of KO₂), no obvious cell degradation can be observed during 900 cycles. Moreover, benefitting from electrolyte modification, the KO₂-based cathode is coupled with a limited amount of K-metal anode (merely 2.5 times excess), harvesting a K-metal full-cell with high energy efficiency (∼90%) and long-term cycling stability (over 300 cycles).