Recent advances in porous carbon nanosheets for high-performance metal-ion capacitors

[Display omitted] •The synthetic strategies of PCNs were presented in detail.•The advantages, optimization strategies, and the energy storage mechanism of PCNs were highlighted.•A systematic and comprehensive review about PCNs as cathode, anode, and matrix for MICs was given.•The future challenges and trends of PCNs-based MICs have been prospected. Metal-ion capacitors (MICs) are considered as highly prospective next-generation energy storage technologies due to the combined merits of metal-ion batteries (MIBs) and supercapacitors (SCs). Nevertheless, the mismatch in reaction kinetics and capacity between the anode and cathode with different energy storage mechanism hinders the practical process. In this regard, porous carbon nanosheets (PCNs) featured by abundant sources, hierarchical porosity, ultrathin two-dimensional structure, and tunable surface properties afford great opportunities for high-performance MICs. In this review, we systematically and critically overview the recent advances of PCNs in MICs, focusing on the synthetic methods, energy storage mechanism, and the structure–activity relationship of PCNs electrode materials. In addition, the device characteristics of MICs and the important research work are briefly described. Finally, the challenges and future trends of PCNs-based MICs are prospected.