Edge‑nitrogen/sulfur co-doping boost high potassium ion storage of carbon nanosheet anode materials

Abstract

Potassium-ion batteries (PIBs) have garnered considerable attention as a potential alternative to lithium-ion batteries. However, the larger radius of K⁺ poses challenges, including slow kinetic processes and significant volume changes, which adversely affect the rate performance and cycling stability of electrode materials. Herein, N, S co-doped carbon nanosheets (xNS-HC) are synthesized as anode materials of PIBs by carbonization of citric acid and CH₄N₂S precursors in LiCl/KCl molten salts. Of these, 5NS-HC possesses a high N content of 20.19 at.% with 90.90 % of edge N-species and a S content of 2.53 at.%. The 5NS-HC material exhibits a high specific K⁺ storage capacity of 368.2 mAh g⁻¹ at 0.1 A g⁻¹, superior rate capability (106.1 mAh g⁻¹ at 10 A g⁻¹), and long-term cycling stability (205.8 mAh g⁻¹ after 2800 cycles at 1 A g⁻¹). In-depth analysis via in-situ XPS and DFT calculations reveals that the active sites doped with edge-N/S exhibit a profound affinity towards K⁺, thus contributing to the outstanding electrochemical K⁺ storage performance observed in 5NS-HC. The full cell of K_0.4Mn_0.9Li_0.1O₂·0.33H₂O||5NS-HC exhibits a high specific capacity of 141.2 mAh g⁻¹, supporting a high energy density of 147.1 Wh kg⁻¹. These compelling results illustrate that edge-N/S co-doping can significantly enhance the K⁺ storage of carbon anode materials.