Resolving the tradeoff between energy storage capacity and charge transfer kinetics of sulfur-doped carbon anodes for potassium ion batteries by pre-oxidation-anchored sulfurization

Sulfur-heteroatom doping is an effective approach to improve the capacity of carbon anodes for potassium-ion batteries due to the reversible K+-sulfur reaction. However, the random sulfur doping induces unresolved tradeoff between capacity and kinetics, which results from the fundamental difficulty in controllable sulfur incorporation using traditional approaches where breaking robust carbon-containing bonds is necessary. Herein, a pre-oxidation-anchored sulfurization approach is proposed to realize site-controlled and content-adjustable sulfur doping, demonstrating the optimum sulfur content of 9.8 at.% in sulfur-doped hollow carbon sphere (S-HCS). Intentional pre-oxidation introduces easy-to-break C-O/C-O-C bond-included oxygen-containing functional groups serving as anchoring sites for substitution with sulfur atoms. Consequently, S-HCS-9.8% achieves superior performance for K+ storage (406.1 mA h g−1 at 0.1 A g−1, 112.6 mA h g−1 at 5 A g−1 and 170 mA h g−1 after 2,000 cycles at 2 A g−1). The enhanced electrochemical performances are attributed to the largest interlayer spacing and highest disorder degree resulting from the thiophene-sulfur-dominated configuration at high sulfur content, which realizes high structure reversibility and stable solid-electrolyte-interface layer. This work provides new insights and guiding principles for the development of heteroatom-doped carbon anodes for next-generation high-performance energy storage applications.