Self-standing porous LiMn₂O₄ nanowall arrays as promising cathodes for advanced 3D microbatteries and flexible lithium-ion batteries

Three-dimensional self-supported cathode nanoarchitectures are the key to develop high-performance thin film lithium-ion microbatteries and flexible lithium-ion batteries. In this work, we have developed a facile "hydrothermal lithiation" strategy to prepare vertically aligned porous LiMn₂O₄ nanowall arrays, comprising highly crystallized spinel nanoparticles, on various conductive substrates without high temperature treatment. The "hydrothermal lithiation" can effectively convert Mn₃O₄ spinel nanowall arrays into LiMn₂O₄ spinel nanowall arrays without severe morphology change. The binder-free three-dimensional porous LiMn₂O₄ nanowall arrays exhibit high specific reversible capacity up to 131 mA h g^-1 (or 0.29 mA h cm^-2) as well as outstanding cycling stability and rate capability, making them promising as cathodes for both three-dimensional thin film lithium-ion microbatteries and flexible lithium-ion batteries. A flexible lithium-ion full cell is demonstrated by using LiMn₂O₄ nanowall arrays on carbon cloth as the cathode and Li₄Ti₅O₁₂ nanowall arrays on carbon cloth as the anode. The flexible Li₄Ti₅O₁₂//LiMn₂O₄ full cell device, employing three-dimensional nanoarchitectures for both cathode and anode, can deliver specific reversible capacities of 124.8 mA h g^-1 (based on the weight of cathode material) at 1 C and 92.1 mA h g^-1 at 20 C with excellent cycle performance. Our work demonstrates the great potential for flexible energy storage technology using low cost fabrication method of nanoarchitectures.