High sulfur-doped hard carbon anode from polystyrene with enhanced capacity and stability for potassium-ion storage

Carbonaceous materials are regarded as a promising anode material for potassium ion batteries (PIBs) due to their high electronic conductivity, abundant resources and low cost. However, relatively low storage capacity and structural instability still hinder their practical application. Herein, high sulfur-doped hard carbon (SHC-3) with a sulfur up to 27.05 at% is synthesized from polystyrene and sulfur as precursors. As an anode for PIBs, the SHC-3 delivers a superb cycling stability and rate performance (298.1 mAh g−1 at 100 mA g−1 for 1000 cycles, a capacity retention of 95.2%; 220.2 mAh g−1 at 500 mA g−1 after 5200 cycles). The potassium storage of SHC-3 exhibits excellent cyclic stability at both low and high rates. Structure and kinetic studies demonstrate that the larger interlayer spacing (0.382 nm) of the SHC-3 accelerates the diffusion of potassium ions and effectively alleviates the volume expansion, and thus maintains the structure stability during the process of potassization/de-potassization. Meanwhile, the density functional theory calculation shows that the doped sulfur atoms provide abundant active sites for the adsorption of potassium ions, thereby increasing the reversible capacity of PIBs. This work provides a new scheme for the design of carbonaceous anode materials with high capacity and long cycle life.