Long-cycling and high-rate electrochemical performance of expanded graphite cathode materials with a two-stage aluminum storage mechanism

Graphite materials are of increasing interest as alternative cathodes for aluminum-graphite batteries (AGBs) owing to their low fabrication price and rich resource. The development and design of graphite electrode materials are critical to obtain high electrochemical performance of AGBs. Herein, expanded graphite (EG) with a large interlayer spacing (0.41 nm) has been synthesized via a facile heat treatment. When serving as a cathode material for AGBs, the EG treated at 800 degrees C (800-EG) exhibits a reversible capacity of about 66 mA h g(-1) and no decay occurs after 10 000 cycles at a current density of 5 A g(-1). Even at a high current density of 10 A g(-1), a specific capacity of 47 mA h g(-1) can be achieved. The aluminum storage mechanism and kinetic analyses confirmed by in situ X-ray diffraction (XRD) and systematic electrochemical technology reveal that the good electrochemical performance of EG is largely attributed to the two-stage aluminum storage behavior (adsorption (0.5-1.5 V) and intercalation mechanism (1.5-2.5 V)). Furthermore, the 800-EG also possesses a high pseudocapacitive contribution of 79.27% at 5 mV s(-1) in the voltage range of 1.5-2.5 V induced by the special surface structure. Our work provides a theoretical reference for the structural design of carbon materials and the exploration of aluminum storage mechanisms in energy storage fields.