Progress and perspectives of 2D materials as anodes for potassium-ion batteries

The development of rechargeable batteries using potassium instead of lithium as charge carrier is being studied with increasing interest. Potassium ion batteries (PIBs) are considered as a promising technology for large-scale energy storage, due to the advantages of using K, such as earth-abundance and cost effectiveness. Nevertheless, research on PIBs is still in its infancy and faces numerous challenges. Among these, a primary one is to identify a suitable anode material which has multiple properties, specifically high specific capacity, long-term life cycle, fast charging, low-cost, environmental friendliness and meets safety standards. Two-dimensional (2D) materials show great potential in battery applications due to their properties, such as large specific area, enlarged interlayer distance and surface modifiability. We review the state of the art on the synthesis and application of 2D materials in PIBs, including graphene, MXenes, transition-metal dichalcogenide materials, graphene-analogous materials and porous polymer materials. The electrochemical characteristics of different materials and K+ storage mechanisms are presented, and current challenges as well as some promising approaches for the future development of PIBs are also proposed.