ZnCl2-based activation for converting spent coffee grounds into a robust anode for Li-ion batteries

Achieving a net-zero target via a circular economy approach necessitates maximizing the recycling of waste into higher-value materials. In the present study, spent coffee grounds (SCG) from industrial food processing biomass waste are converted into a high-performance anode material used in lithium-ion batteries via one-step carbonization of ZnCl2 at 550 °C. The hybrid composites (HCs) are collected after the process contained C- and Zn-based mixed oxides, such as zinc silicate (Zn2SiO4) and zinc ferrate (ZnFe2O4). The content of Zn-based mixed oxides in HCs increases with the initial ZnCl2:SCG mass ratio and reaches its maximum at a ratio of 2:1 wt/wt (HCs_2). The electrochemical performance of the HC-based anodes is proportional to the loaded Zn content when the ZnCl2:SCG mass ratio increases from 0 to 2. The optimized anode (HCs_2) exhibits a charge capacity of 692 mAh g−1 and capacity retention of 86 % at the 100th cycle, whereas the corresponding values for HCs_0 anode (without ZnCl2 treatment) are 311 mAh g−1 and 73.3 %. The superior electrochemical performance of the optimized anode is attributed to the nanosized Zn2SiO4 and ZnFe2O4, stabilization effect of activated carbon matrices, and a strategy that increases the proportions of high-capacity components.