Flexible Quasi-Solid-State Supercapactors From V- And Mn-Based Oxide Nanostructured Arrays

With the rapid development of the wearable electronic devices and microelectronic devices, we have put forward higher requirements in energy storage device, especially flexible energy storage device. Compared with other electrochemical energy storage device, supercapacitors have a lot of advantages, such as fast charge-discharge ability, high power density and excellent cycling stability, thus attracted enormous attentions and willing to be one of the most prospective energy storage devices. Although supercapacitors especially electric double layer carbon based supercapacitors have been commercialized, the existing problems, specifically, low specific/volumetric capacitance and low energy density, need further studies to solve. One of the basic research directions of supercapacitors is to design new type of electrodes which has wide working potential and large capacitance. In this thesis, we designed and prepared flexible V- and Mn-based electrodes. Through doping and surface modification, we improved their electron conductivity and diffusion transportability to get high electrochemical performances of both supercapacitor electrodes and devices. In this way, we try to provide several practical methods to enhance the performance of supercapacitors. The main contents of this thesis as follows:1. By using improved hydrothermal route, VO2 nanosheet arrays were uniformly grow on ultra-thin (10μm) titanium plate. Then adding glucose solution on the VO2 nanosheets arrays directly, under high temperature annealing, VO2 nanosheet were converted to uniform V2O3@C composite nanosheets arrays. Carbon coating not only increased the conductivity but also reduce the dissolution of Vanadium Oxides in the liquid electrolyte. The three-electrode-testing results showed that by combining the advantages of both structural design and carbon coating, our V2O3@C composite nanosheets arrays could exhibit excellent energy density and stable cycling performance.2. By using LiCl/PVA gel as electrolyte, our V2O3@C nanosheet arrays as both positive and negative electrodes, we composed a quasi-solid flexible supercapacitor. The results show that our ultrathin flexible film supercapacitor (only 40 micrometre thick) has wide voltage window of 2.0 V, high volumetric energy density (maximum 15.9 mWh cm-3) and power density (maximum 6900 mW cm-3), outstanding rate capability and cyclic stability.3. Doping and surface modification of Manganese Oxide. By facile hydrothermal method, we synthesized Ni doped Manganese Oxide nanorod arrays on ultrathin Ti plate substrate successfully. Then we coated a lay of conductive Polymer Polypyrrole (PPy) on the Ni0.25Mn0.75O surface to get an ultrathin Ni0.25Mn0.75O@PPY composite electrode. By using Nio.25Mno.750@PPY nanorod arrays as cathode, V2O3@C nanosheet arrays as anode, LiCl/PVA gel as electrolyte, we composed a quasi-solid flexible supercapacitor. The electrochemical results showed that our flexible supercapacitor device could obtain 2.4 V super-wide voltage window, high volume energy densities (26.8 mWh cm-3) and flexibility.