Ultra-Thin Wrinkled Carbon Sheet as an Anode Material of High-Power-Density Potassium-Ion Batteries.

Although K is readily inserted into graphite, the volume expansion of graphite of up to 60% upon the formation of KC, together with its slow diffusion kinetics, prevent graphite from being used as an anode for potassium-ion batteries (PIBs). Soft carbon with low crystallinity and an incompact carbon structure can overcome these shortcomings of graphite. Here, ultra-thin two-dimensional (2D) wrinkled soft carbon sheets (USCs) are demonstrated to have high specific capacity, excellent rate capability, and outstanding reversibility. The wrinkles themselves prevent the dense stacking of micron-sized sheets and provide sufficient space to accommodate the volume change of USCs during the insertion/extraction of K. The ultra-thin property reduces strain during the formation of K-C compounds, and further maintains structural stability. The wrinkles and heteroatoms also introduce abundant edge defects that can provide more active sites and shorten the K migration distance, improving reaction kinetics. The optimized USC electrode exhibits a reversible capacity of 151 mAh g even at 6400 mA g, and excellent cyclic stability up to 2500 cycles at 1000 mA g. Such comprehensive electrochemical performance will accelerate the adoption of PIBs in electrical energy applications.