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Discrete Graphitic Crystallites Promise High‐rate Ion Intercalation for KC8 Formation in Potassium Ion Batteries

Graphite has paved the way for commercial lithium‐ion batteries and shows great potential as an anode for high‐energy potassium‐ion batteries (PIBs) due to its low‐potential charge/discharge plateau. However, the restricted diffusion of large K+ in graphite causes difficulties in generating the stage‐one graphite‐intercalation compound (GIC) KC8 at high rates and results in a low plateau capacity and an inferior rate performance. It is discovered that the formation of high‐stage GICs (prior to KC24) is the rate‐controlling step of K+ intercalation, which is key to forming KC8. Here, a carbon anode material containing the medium‐size discrete graphitic crystallites is reported, produced by heating non‐graphitizable carbon above 2800 °C. This carbon anode material promotes the formation of KC8 due to the accelerated K+ diffusion especially at the rate‐controlling step and the sufficient reactive sites, which leads to a record‐high plateau capacity of 293 mAh g−1 and an excellent rate performance with 180 mAh g−1 at 500 mA g−1. For comparison, the respective values for graphite are only 242 and 51 mAh g−1. This study provides new insights into K+‐intercalation chemistry and shall promote the design of carbon anode materials for high‐energy and high‐power PIBs and even other energy storage systems.