Near-Atomic-Thick Bismuthene Oxide Microsheets for Flexible Aqueous Anodes: Boosted Performance upon 3D → 2D Transition

Aqueous batteries provide safety, but they usually suffer from low energy and short lifetimes, limiting their use for large-scale energy storage. Two-dimensional materials with infinite lateral dimensions have inherent properties such as high surface area and remarkable power density and cycling stability that are shown to be critical for the next generation of energy storage systems. Here, ultrathin bismuthene oxide with a large aspect ratio is studied as an anode material for rechargeable aqueous metal-ion batteries. The metal oxides are prepared via a novel electrochemical system allowing for a smooth, high-quality transition of bismuthene to bismuthene oxide in a short time. This anodic system is shown to overcome major limiting factors of such batteries, including low capacity and irreversible and unstable redox reactions in aqueous electrolytes. The essential energy storage properties of two-dimensional (2D) microsheets, without the addition of conductive additives and binders, are compared with those of the corresponding three-dimensional (3D) structures. Notably, the battery performance of 2D microsheets is significantly better than that of nanoparticles from all examined aspects, including power density and potential and cycling stability, while exhibiting a capacity density close to their theoretical value. Moreover, 2D microsheets have shown impressive mechanical flexibility related to the ultrathin thickness of individual microsheets and strong interaction between them after film deposition. Combining the excellent energy storage properties of bismuthene oxide, the simple electrode preparation procedure, the inherent flexing characteristic, and the nontoxicity of both the battery material and the electrolyte makes this 2D material an exceptional candidate for large-scale wearable green electronics.