Non-lithium-based metal ion capacitors: recent advances and perspectives

Metal ion capacitors (MICs), as the combination of supercapacitors and rechargeable batteries, are endowed with higher energy density and longer cycle life but not at the expense of high-power properties. The low reserves and uneven geographical distribution of lithium resources stimulate enormous interest in alternative non-lithium based MICs (NLMICs). In recent years, tremendous efforts have been devoted to design and fabricate high performance NLMIC systems. Although still facing many challenges, the development of NLMICs has been made great progress. In this review, we first discuss the operating mechanisms of the NLMIC systems, and then mainly review the research progresses of the involved electrode materials, aqueous/organic electrolytes, and device design toward monovalent (Na + and K + ) and multivalent (Mg 2+ , Ca 2+ , Zn 2+ , and Al 3+ ) MICs. Finally, an outlook on the involved challenges and future perspective of the NLMICs is also proposed. A comprehensive overview of the research progress toward non-lithium metal ion capacitors, including the mechanisms, electrode materials, electrolytes, and novel device designs, is presented with further perspectives.