Edge-rich reduced microcrystalline graphite oxide for Li-ion hybrid capacitors with ultrahigh volumetric energy density

Compact and high-performance carbon cathode materials are vital to improve the gravimetric and volumetric energy/power density of advanced energy storage devices such as lithium-ion hybrid capacitors (LIHCs). Graphite has a high mass density and the areal specific capacitance at the edge plane is far larger than that in the basal plane. Hence, increasing the proportion of edges can effectively improve the specific capacitance of the carbon material. However, it is challenging to expose more edges of graphite due to its high thermal and chemical stability. In this work, a compact cathode is prepared through a facile high-temperature ammonia treatment of microcrystalline graphite oxide (MGO). The obtained edge-rich reduced microcrystalline graphite oxide (ER-RMGO) demonstrates abundant edge sites, a high mass density of 1.48 g cm-3 and an extremely high areal specific capacitance of up to 319.3 mu F cm-2. As a result, the fabricated Li-ion hybrid capacitor delivers an ultrahigh volumetric energy density of 392 Wh L-1 and power density of 9.49 W LkW L-1. This work sheds light on the great potential of microcrystalline graphite derived edge-rich carbon materials for compact capacitive energy storage.