Advances in molten-salt-assisted synthesis of 2D MXenes and their applications in electrochemical energy storage and conversion

Two-dimensional (2D) MXenes have captured inter-disciplinary interest owing to their exceptional electronic conductivities, adjustable layered structures, and controllable interfacial functional groups. Low-cost, efficient, and amicable techniques are urgently desired for synthesizing high-quality and high-yield 2D MXene materials. Recently, molten-salt-assisted methods have been proven to be the promising processes to construct versatile 2D MXenes with metallic-level conductivity, good mechanical strength, low ion diffusion barrier and rich surface chemistries to meet the criteria for practical applications. Herein, the most up-to-date progress of molten-salt-assisted approaches for manufacturing 2D MXene materials and their synthesis mechanisms are comprehensively summarized, introducing the effect on the physical/chemical properties of the obtained MXenes compared with other common synthesis methods. Meanwhile, typical examples of MXenes obtained by tuning surface termination, interlayer spacing, size, and morphology are presented. Further, the focus turns to their structure–property relationships and applications in electrochemical energy storage and conversion, including supercapacitors, Li-batteries, Zn-ion batteries and electrocatalysis. Finally, a discussion about the challenges and prospects of the molten-salt-assisted approaches is put forward. This review will guide and encourage the future rational design and controllable synthesis of 2D MXenes with high performance based on molten-salt-assisted strategies.