Nitrogen, phosphorus co-doped holey rGO as a cathode material for Li-ion capacitors (LICs)

Graphene-based materials are considered as ideal cathode materials for lithium-ion capacitors (LICs). However, the ion-accessible surface area of graphene is restricted by the restacking of graphene nanosheets, resulting in a limited specific capacity. Fabricating porous graphene with an appropriate pore structure and introducing heteroatom doping can improve the capacity of graphene and increase the energy outputs of graphene-based LICs. Herein, we use an easy and low-cost hydrothermal method to create a 3D nitrogen and phosphorus co-doped holey rGO (NPHG) aerogel. In a half-cell system, NPHG delivers a specific capacity of ∼120 mAh/g at 0.1 A/g and maintains 92% of its initial capacity after 1000 cycles at 1 Ag−1. Moreover, when used as a cathode with a pre-lithiated nitrogen-doped rGO-siloxene (NGSil-4) anode to construct an NGSil-4//NPHG LIC, a high energy density of 145.86 Wh Kg−1 is obtained at a power density of 200.2 W Kg−1, while retaining 15.35 Wh Kg−1 at 14550 W Kg−1.This work demonstrates the great potential of NPHG cathodes, with the integration of the appropriate porosity and N and P co-doping using a simple and low cost hydrothermal method, for high-performance LICs.