K0.6CoO2-xNx Porous Nanoframe: a Co-enhanced Ionic and Electronic Transmission for Potassium Ion Batteries

Abstract Potassium-ion batteries (PIBs) have been regarded as a promising alternative to lithium-ion batteries (LIBs) due to their low cost and decent operational voltage. Layer-structured cobalt oxides are attractive as cathodes for PIBs, but suffer from poor rate performance and unsatisfied cycling stability. Here, K0.6CoO2-xNx porous nanoframe is rationally designed as a promising cathode for PIBs. Both experimental results and DFT calculations reveal that the partial substitution of O with N atoms can enlarge the interlayer spacing, which can accommodate more K+ intercalation and speed up K+ migration. Meanwhile, the electronic conductivity is effectively improved after N doping. Moreover, the unique hollow nanoframe structure can provide more electrochemical active sites for K+. As a consequence, the K0.6CoO2-xNx porous nanoframe delivers a reversible capacity of 86 mAh g-1 at 50 mA g-1 and the capacity retains 66 mAh g-1 over 400 cycles. Combined with a commercial graphite anode, the K0.6CoO2-xNx full cell with good reversibility is demonstrated. This work opens up a new way to prepare high-performance layered metal oxides cathodes for PIBs.