Mechanically induced surface defect engineering in expanded graphite to boost the low-voltage intercalation kinetics for advanced potassium-ion batteries

Enhancing carbon materials' low-potential K⁺ intercalation capacity is an essential topic in potassium-ion batteries (PIBs). Nevertheless, conventional methods effectively improve performance by increasing the surface area and active sites, but always at the expense of initial coulombic efficiency (ICE). Herein, an efficient and convenient strategy is proposed to construct self-doped defective carbon nanosheets (SDCS) using the mechanical ball-milling technique. This in situ defect engineering increases K⁺ intercalation sites and shortens the ionic pathway, enhancing the ionic intercalation kinetics, specific capacity, and ICE. As expected, the SDCS-24 electrode delivers an ultra-high low-potential capacity of 314.3 mAh g⁻¹ below 0.5 V, high ICE of 76.1 %, and long-term cycle stability (300.1 mAh g⁻¹ after 1800 cycles at 1 C). The K⁺ storage mechanism is determined by ex situ XRD and in situ Raman. The full-cell with 3,4,9,10-Perylenetetracarboxylic dianhydride cathode and SDCS-24 anode further confirms its promising application. This work presents a strategy for designing self-doped defective carbons in situ and provides insights into the potassium storage mechanism at low potential.