Carbon anode of intercalation capacitive coupling mechanism enabling long term potassium ion capacitors at low temperature

Low temperature comprehensive performance of the dominating lithium ion batteries (LIBs) is a matter of increasing concern. In this work, we screen typical carbon anodes with different structural features such as interlayer spacing, degree of graphitization, porosity, and specific surface area, for sustainable potassium ion capacitors (PICs) at −20 °C. Graphene nanosheet (GN) exhibits much better K+ storage performance over the other carbon materials including graphite, activated carbon, and hard carbon, which is ascribed to the synergistic effects of high conductivity, enlarged interlayer spacing, moderate specific surface area, mesopore structure, and short K+ diffusion path. This screening guides a design direction of carbon anode for K+ storage device at low temperature. Meanwhile, the electrolyte additive of Cs cation could be preferably reduced at the surface of GN during the potassiation, which enables a thin and robust solid electrolyte interphase (SEI) layer and effectively suppresses the co-intercalation induced GN exfoliation and electrolyte decomposition, giving rise to improved cyclic stability at −20 °C. The assembled PICs based on the GN anode and optimized electrolyte enable a comprehensive low temperature performance, especially long-term stability (2000 cycles) over batteries, demonstrating a reliable electrical energy storage device at low temperature.