Sulfurized Polyacrylonitrile as a High-Performance and Low-Volume Change Anode for Robust Potassium Storage

Potassium-ion batteries (KIBs) are considered as low-cost electrochemical energy storage technologies because of the abundant potassium resources. However, the practical applications of KIBs are mainly hampered by the unsatisfactory electrochemical performance of anode materials which often undergo large volume variations during potassiation-depotassiation, limiting their cycling life. Here, low-cost sulfurized polyacrylonitrile (S-PAN) is reported as an attractive anode candidate for KIBs. It provides a high potassium storage capacity of 569 mAh g_(S-PAN)^-1 with decent rate capability and cycling stability (no capacity loss after 1500 cycles, running time ∼188 days). Detailed ex situ spectroscopic and in situ microscopic characterizations reveal that the distinguished electrochemical performance of S-PAN is attributed to the high reversibility of its covalent C-S and S-S bonds which undergo repeated cleavage-redimerization during potassiation-depotassiation concomitant with relatively small volume variation (less than 24.2%). Subsequently, a full-cell constructed by pairing high-voltage K₂MnFe(CN)₆ cathode with high-capacity S-PAN anode demonstrates an attractive energy density (290.9 Wh kg^-1) and long-term cycling stability (1200 cycles with 95.4% capacity retention). Given the high performance and low cost of both anode and cathode materials, it is believed that the present full-cell promises it as a competitive energy storage system for the cost-sensitive grid-scale applications.