High performance lithium-ion hybrid capacitors with pre-lithiated hard carbon anodes and bifunctional cathode electrodes

Lithium-ion hybrid capacitor is a type of energy storage device that bridge the gap between lithium-ion battery and electrical double layer capacitor. We have developed a facile approach to achieve the pre-lithiation of carbonaceous anode, and then fabricated lithium-ion hybrid capacitors with bifunctional cathode containing capacitor material (activated carbon) and battery material (LiNi0.5Co0.2Mn0.3O2). The hybrid capacitor with 25 wt.% LiNi0.5Co0.2Mn0.3O2 addition in bifunctional cathode (denoted as LAN25) exhibits excellent rate capability and high energy density. The rate capability of LAN25 is comparable to that with pure AC cathode (denoted as LAC), while the volumetric energy density is 1.36 times higher than the latter one. The continuous galvanostatic charge–discharge cycling tests reveal that the lithium-ion hybrid capacitor remains more than 98% capacity after 20,000 cycles, and nearly 100% coulombic efficiency over entire cycles. The superior performance is ascribed to the synergy effect of the active components in bifunctional cathode and the effective pre-lithiation of hard carbon anode. The present work makes the study of lithium-ion hybrid capacitor easily accessible and broadens roads to hybrid devices with high energy density, high power density and long cycle life.