Three-dimensional nitrogen–sulfur codoped layered porous carbon nanosheets with sulfur-regulated nitrogen content as a high-performance anode material for potassium-ion batteries

Abstract

Three-dimensional nitrogen–sulfur codoped layered porous carbon nanosheets (3D-NSCNs) with sulfur-regulated nitrogen content are constructed as a high-performance anode material for potassium-ion batteries (KIBs) through a gel and nitrogen–sulfur codoping process. Compared with the sample without sulfur doping, the 3D-NSCNs reveal enhanced electrical conductivity, specific surface area, and pyrrolic (N-5) and pyridinic (N-6) nitrogen contents, all of which are beneficial for increased electrochemical performances. After 200 cycles at a current density of 100 mA g⁻¹, the 3D-NSCNs anode exhibits a specific capacity of 254.9 mA h g⁻¹. After 2900 cycles at a higher charge–discharge current density of 1 A g⁻¹, the specific capacity is still 171.1 mA g⁻¹, and the capacity retention is 78.9%, indicating the application potential of the as-synthesized 3D-NSCNs as an anode material for KIBs. Domination by a surface-driven mechanism is proposed to explain the excellent rate and cycle performances and can also be validated by galvanostatic intermittent titration results, which show that the K⁺ diffusion coefficient in the 3D-NSCNs is improved after nitrogen–sulfur doping. This work demonstrates a new strategy to improve the electrochemical properties of carbon-based K-storage materials by increasing the N-5 and N-6 contents through sulfur doping while also producing micropores to increase the number of active sites.