Two-dimensional redox polydopamine with in-plane cylindrical mesochannels on graphene for high-energy and high-power lithium-ion capacitors

Lithium-ion capacitors (LICs) are distinguished for bridging the gap of energy and power densities between lithium-ion batteries and supercapacitors. However, the kinetic mismatch between the slow diffusion and fast adsorption/desorption of lithium ions usually leads to the sacrifice of high power density or high energy density. Here, we report a general "one-for-two" strategy for controllable construction of 2D mesoporous polydopamine/reduced-graphene-oxide heterostructure (mPDA/rGO) with ordered in-plane cylindrical mesochannels as cathode and mPDA/rGO derived nitrogen-doped carbon nanosheets (mNC/rGO) as anode of LIC to achieve fast electrochemical kinetics. The in-plane cylindrical mesochannels and surface redox reactions of 2D mPDA/rGO and mNC/rGO ensure rapid reaction kinetics in both cathode and anode. As a result, mPDA/rGO shows remarkable specific capacity of 133 mAh/g, and excellent rate capability of 94 mAh/g even at 5 A/g. Meanwhile, 2D mNC/rGO exhibits high capacitance of 550 mAh/g at 0.1 A/g and 225 mAh/g at 5 A/g. The as-assembled LIC with these two electrodes offers a high energy density of 208 Wh kg−1 at a power density of 176 W kg−1, which can retain as high as 102.2 Wh kg−1 at 8.8 kW kg−1. This study demonstrates the control of porosity and morphology as an appealing strategy for rational construction of 2D electrode materials to boost high-energy and high-power LICs.