Relationship between functionalization and structural defect density of graphite for application in potassium-ion batteries

Potassium-ion batteries (PIBs) have recently gained attention as an alternative to Li-ion batteries (LIBs) because Li and K belong to the same alkali metal group and are replaceable. However, the theoretical capacity of PIBs is hindered by the larger size of potassium ions compared to lithium ions. Generally, the surface treatment of graphite, an anode material in metal-ion batteries, enhances ion diffusivity and improves electrochemical performance. In this study, a straightforward approach is introduced in which graphite is treated with an acid to widen the interlayer spacing and an alkali to create pores. Acid and alkali treatments not only improve ion diffusivity but also control the surface charge of graphite in PIBs. Consequently, acid-treated graphite (AG) displays the highest specific capacity (206.2 mAh g−1 at 0.2 A g−1 after 100 cycles) with good durability. In addition, the trade-off between the physical ion pathway derived from structural defect density and functionalization-induced surface charge improves ion diffusivity.