Mildly-expanded graphite with adjustable interlayer distance as high-performance anode for potassium-ion batteries

As a promising anode for potassium-ion batteries (PIBs), graphite has drawn great attention due to easy availability, low cost and formation of potassium-based intercalation compound. However, poor cyclic and rate performances due to severe structural degradation limit the practical application of graphite anode. Herein, a low cost mildly-expanded graphite (MEG) with adjustable interlayer lattice distance is synthesized through a wet chemical oxidation route. As anode for PIBs, the MEG exhibited stable intercalation/deintercalation plateaus, outstanding cyclic stability and rate performance. By optimizing the mass ratio between graphite and potassium permanganate oxidant, the MEG anode retaining long-range-ordered domains of graphite delivers a capacity of 88 mAh/g at 1500 mA/g and a capacity retention of 72.3% after 200 cycles at 100 mA/g. The potassium ion full cell assembled with MEGs anode exhibites high energy density and outstanding cyclic stability. Our results demonstrate a promising graphite-based anode for PIBs and provide guidance for the designing of novel carbonic electrodes for PIBs.