Ultrathin Two-Dimensional Metal Oxides for Advanced Electrochemical Energy Storage

Rechargeable batteries have been recognized as one of the most promising energy storage systems for the wide applications ranging from consumer electronics to electric transport. The great success achieved in the mature market of commercialized Li-ion batteries motivates us to explore advanced energy storage techniques to meet the ever-increasing energy demand of our society, especially in the areas require high-energy density. The traditional battery technology could not provide reliable high energy density and satisfied cycle life, limited by the current electrode materials and preparation process, however, severely impede its large-scale practical application. Therefore, exploring novel electrode materials with high capacity to break the bottleneck of development next-generation battery technology is urgently needed. It is well established that 2D structures could be fantastic candidate materials for energy-related applications, due to the distinctive properties, such as large surface areas, rapid ion/electron diffusion kinetics, abundant active sites and good mechanical strength, which may greatly enhance the electrochemical properties, especially the high-rate capability and long-term cycling stability. Furthermore, the conversion/alloying-based anode materials, such as metal oxides typically have much higher theoretical specific capacity, thus leading to higher energy density than commercial graphite electrodes. Hence, this doctoral work will mainly focus on the rational design and controllable synthesis of novel 2D metal oxide materials and their hierarchical structure assembled by 2D building blocks for energy storage applications. More specifically, by employing the facile moderate “bottom-up” approach, a series of metal oxides, including the 3D hierarchical ultrathin δ-Bi2O3 nanosheets, atomically thin Bi2MoO6 nanosheets and the hierarchical porous NiO/β-NiMoO4 heterostructured microspheres have been successfully synthesized and used as anode materials towards lithium ion batteries. Impressively, those as-prepared 2D electrode materials exhibited superior reversible capacity, excellent high-rate capability and good long cycling stability, which are much better than those of corresponding bulk counterparts. In addition, to further deeply understand the mechanism of enhancement Li-ion storage properties, the DFT calculation and the in-situ synchrotron XRPD techniques have been applied to analyse the reaction dynamics and the evolution of crystal structure during the charging/discharging processes. It is believed that the excellent electrochemical performance benefits from the strong interface effect, the unique 2D ultrathin configuration, and the superior structural stability of the crystal.