MBenes beyond MXenes: the next frontier of 2D boride materials for multivalent ion energy storage devices

A novel class of two-dimensional (2D) transition metal borides (MBenes) has emerged as a promising boride-based platform for advanced energy storage devices (ESDs), complementing established 2D materials such as graphene and MXenes. While MXenes have demonstrated remarkable electrical conductivity and electrochemical versatility, their long-term stability and multivalent-ion storage behavior can be influenced by surface terminations, defects, oxidation susceptibility, and electrolyte environments. MBenes, featuring strong metal–boron bonding, metallic conductivity, and diverse surface chemistry, have recently attracted attention as an emerging 2D boride platform for energy storage applications. This review systematically examines the synthesis, crystal chemistry, surface characteristics, and charge-storage mechanisms of MBenes, with a primary focus on their emerging role in multivalent-ion electrochemical energy-storage devices. Selected applications beyond electrochemical energy storage are briefly discussed to highlight future research opportunities. Recent theoretical and early experimental studies highlight the potential of MBenes in multivalent-ion batteries (Mg 2+ , Zn 2+ , and Al 3+ ), with predicted high storage capacities and favorable electrochemical characteristics. However, practical advantages over conventional Li-ion systems depend on electrode architecture, electrolyte chemistry, and device-level validation. Their enlarged interlayer spacing, high conductivity, and flexible frameworks may facilitate ion transport and structural tolerance, although these effects remain dependent on composition, surface termination, and operating conditions. Computational studies predict significant capacities and low diffusion barriers for Mg 2+ storage, while early experimental results indicate stable cycling. Beyond multivalent-ion batteries, MBenes have also demonstrated promising performance in Li-ion, Na-ion, Li-S batteries, and supercapacitors, highlighting the versatility of their layered structures and charge-storage chemistry. Recent advances in heterostructure, interface, and defect engineering have further expanded their electrochemical capabilities. Despite significant progress, challenges remain in scalable synthesis, precise control over surface termination, long-term oxidation stability, and maintaining performance under realistic mass loading. Emerging HF-free, and in some cases fully fluorine-free, synthesis routes, together with interface engineering approaches, may help overcome these hurdles. MBenes represent an emerging family of 2D borides with potential applications spanning high-energy-density batteries and high-power electrochemical capacitors. Addressing challenges in scalable synthesis, defect control, multivalent-ion storage, and device integration requires synergistic theoretical, materials-engineering, and electrochemical approaches to advance MBenes toward practical energy-storage technologies.