Rational formation of solid electrolyte interface for high-rate potassium ion batteries

Potassium-ion batteries are one of the next-generation energy storage devices that are promising to partly replace lithium-ion batteries, especially in low-cost and large-scale application. However, the poor capacity and cycling stability do not meet the expected requirements. Herein, we synthesize a P–S co-doped flexible carbon fiber film derived from Chinese art paper, which is self-contained with SiO₂ and MgO nanoparticles. Due to the uniform distribution of SiO₂ and MgO on its surface, a reasonable solid electrolyte interphase (SEI) film is formed. The thin SEI layer (2–4 nm) is thick enough to prevent the electron penetration and simultaneously allows unhindered K ion intercalation/deintercalation, and it can also stabilize the interface between active material and electrolyte. Besides, the P–S co-doping can both enhance the K adsorption ability and electronic conductivity, therefore the rate capability is improved. The optimized carbon fiber film shows excellent flexibility and electrochemical performance. A capacity of 171.5 mA h g⁻¹ at 1500 mA g⁻¹ after 500 cycles is obtained. Even at a very high current density of 2500 mA g⁻¹, the capacity can still reach as high as 177.3 mA h g⁻¹. Because of its low cost and sustainability, this work will provide ideas for the development of high-performance potassium-ion battery anodes.