3D-structured bifunctional MXene paper electrodes for protection and activation of Al metal anodes

Multivalent Al metal anodes (AMAs) can deliver high specific/volumetric capacities (2980 mA h g⁻¹/8046 mA h cm⁻³) in chloroaluminate ionic liquid-based electrolytes (ILEs). However, strong corrosion of their surfaces and poor charge transfer kinetics in acidic ILEs remain critical obstacles to realizing high-performance AMAs. In this study, a 3D-structured bifunctional MXene paper electrode (3D-BMPE), which has distinctive material properties, such as high electrical conductivity, high elastic modulus, a large number of nanopores, and multitudinous oxygen functional groups, was fabricated to protect Al deposition/dissolution reactions with improved redox kinetics. The 3D-BMPE obstructed Al corrosion during the long rest time in the ILE and consecutive cycling process, resulting in a significantly stable cycling performance of the 3D-BMPE-based AMA over 2000 cycles. Furthermore, Al nucleation and growth reactions were catalyzed in the nanoporous structure surrounded by the highly functionalized MXene surfaces, which reduced overpotentials by one-sixth, resulting in highly improved coulombic efficiencies of ∼99.9%. Moreover, the excellent electrochemical performance of the 3D-BMPE-based AMA was confirmed in Al-based dual-ion battery full cells, demonstrating the significant role played by 3D-BMPEs for AMAs.