Hard carbon derived from spent black tea as a high-stability anode for potassium-ion batteries

Hard carbon (HC), composed of disorder graphite domain construction, provides defects, gaps, and nanopores that are beneficial for storing K-ion. In this work, hard carbon derived from spent black tea (THC) is synthesized through a two-step carbonization process. THC is an easy preparation, green, and high-abundance carbon material for highly stable potassium-ion storage. As an anode for potassium-ion batteries, it delivers a high capacity of 203 mA h g(-1) at 30 mA g(-1) and long-term cycling life with 90% capacity retention over 3.6 months. This superior cycle life is attributed to the highly reversible structure, rapid ion diffusion rate, and charge transfer rate of THC. Not only that, a full cell was assembled with THC as the anode and perylene 3,4,9,10-tetracarboxylic dianhydride (PTCDA) as the cathode. The PTCDA//THC delivers a high capacity of 48.6 mA h g(-1) and an energy density of 107 W h kg(-1) at 100 mA g(-1). These findings suggest that THC has considerable promise as a low-cost, high-stability anode material for potassium-ion batteries.