Synthesis Of Ultrathin 3D Metal Oxides Nanosheets And Their Energy Storage Performance

The two-dimensional (2D) ultrathin nanosheets can effectively combine the microscopic electronic, magnetic and optical properties with macroscopic ultrathin, transparent and flexible devices, guaranteeing a maximum functionality while keeping the size minimized. It possesses huge surface area, minimize Li+ ion diffusion distance as well as open channel buffering large volume variation during cycling processes, endowing 2D ultrathin nanosheets with superior energy storage performance. However, the study of 2D ultrathin nanosheets mainly restrict on the layered materials with weak van der Waals force between the layers. Expanding the study area to 2D ultrathin nanosheets with nonlayered structure or quasi-layered structure with relatively strong bonds between the layers will not only significantly enrich the families of 2D ultrathin nanosheets, but also optimize energy storage by rational materials design and synthesis. The goal of this dissertation is to rational design and controllable synthesis of 3d metal oxides ultrathin nanosheets, as well as energy storage performance. The details are summarized briefly as follows:1. Inspired by the detailed structural analysis between metal hydroxides and corresponding metal oxide, taking Co3O4 as an example, we first demonstrate the rational design and fabrication of novel atomically-thick Co3O4 nanosheets with specific facet exposed by topochemical transformation from layered intermediate precursors, opening the window for the preparation of non-layered ultrathin nanosheets. The novel ultrathin nanosheets possess the huge surface area, open channel and atomic thickness, endowing it well-suited for lithium ion batteries (LIBs). Thus, the designed electrodes display remarkable improvement in LIBs compared with Co3O4 nanoparticles. The eminently enhanced lithium storage performance can be attributed not only to the joint advantages of inorganic graphene analogues but also the enhancement of Co2+ atoms and charge redistribution for ultrathin Co3O4 nanosheets.2. We put forward an ultra-rapid and facile microwave-assisted strategy to prepare ultrathin birnessite K0.17MnO2 nanosheets with a thickness of only 2 nm. Notably, this novel route can also be extended to the synthesis of ultrathin Na-type birnessite nanosheets, revealing the universality of this synthetic strategy in extension to those layered compounds. We also investigated as-prepared ultrathin birnessite K0.17MnO2 nanosheets as electrodes for supercapacitors and LIBs, exhibiting remarkable improvement in electrochemical characteristics compared with corresponding bulk counterpart. Such intriguing behaviors are mainly attributed to the intrinsic crystal structure and the synergistic effect of inorganic graphene analogues, such as huge surface area, facile guest ion diffusion and electron transport. This study opens the window for the ultra-rapid and facile preparation of ultrathin nanosheets, which will significantly expand the studies of inorganic graphene analogues and optimize energy storage by reasonable materials design and synthesis.3. We put forward a novel route to eminently enhance the lithium storage performance by doping and carbon-supporting. Taking classical intercalation TiO2 anode material as an example, carbon-supported ultrathin reduced TiO2 nanosheets will drastically improved the electronic conductivity. Also, these nano-carbon pillars not only strengthen the stacked ultrathin layers and prevent complete condensation, but also offer ample space for Li+ ion diffusion. We also investigated as-prepared carbon-supported ultrathin reduced TiO2 nanosheets as anode materials for LIBs, exhibiting remarkably enhanced their electrochemical behaviors compared with common TiO2 nano-discs.4. Herein, a new approach, coupled with variation in the crystal structure and stoichiometry, has been developed to tune the electrical and optical properties of P-Cu2Se hyperbranched structures by regulated solid-state phase conversion. We present a facile wet-chemical strategy to access single-crystalline metastable β-Cu2Se hyperbranched architectures for the first time after 35 years delay, An increase in electrical conductivity and a tunable optical response were observed under ambient conditions. This behavior can be explained by the oxidation of the surface of the P-Cu2Se hyperbranched structures, ultimately leading to solid-state phase conversion from P-Cu2Se into superionic conductor a-Cu1.8Se, which has potential applications in energy-related devices and sensors.