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-O(2) battery (O(2)/KO(2) redox), we originally realize the reversible superoxide/peroxide (KO(2)/K(2)O(2)) interconversion on a KO(2)-based cathode. Controlled within a sealed cell environment, the irreversible O(2) evolution and electrolyte decomposition (induced by superoxide anion (O(2)(−)) formation) are effectively restrained. Rationally controlling the reversible depth-of-charge at 300 mAh/g (based on the mass of KO(2)), no obvious cell degradation can be observed during 900 cycles. Moreover, benefitting from electrolyte modification, the KO(2)-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).