| With the fast development of portable electronic devices, diverse renewable but intermittent energy sources such as solar, tide and wind, and nano-/micro-electronic mechanism systems (NEMS/MEMS), traditional lithium ion battery and supercapacitor is falling behind the needs of cheap, safe, high power density and high energy density for energy storage devices. In recent years, laboratorial studies of energy storage field are concentrating from traditional Lithium ion battery and supercapacitor to new energy storage materials and systems which have novel energy storage mechanisms gradually. Hybrid supercapacitor (HSC), typically consists of a Li-ion battery-type electrode and an electric double-layer supercapacitor electrode, combines the advantages of both LIB and supercapacitor and attracted enormous attention; rechargeable alkali-metal/alkaline-earth metal ion batteries has been became alternative energy storage systems of lithium ion battery due to their safety and sustainability. In this thesis, we designed and fabricated a thin-film HSC with both high volumetric energy and power densities. Both cathode (Multi-Walled carbon nanotube, MWCNT) and anode (Li4Ti5O12) are growing directly on carbon clothes. Moreover, we fabricated Bi2O3 nano-flakes and Bi nano-films, and studied their electrochemical performances and energy storage mechanisms as new aqueous battery electrodes. Compared with slurry-processed electrodes, binder-free and addictive-free nanowire and nano-films electrodes could exhibit the performance of new electrode materials more directly; and without the influence of impurities, it is more convenient to explore the energy storage mechanism of these new electrode materials.The main research contents of my thesis are as follows:1. Anode Li4Ti5O12 nanowire array was obtained by high-temperature solid-state reaction after adding LiOH into Rutile TiO2 nanowire array; and the cathode was binder-free MWCNT. Based these electrodes, we assembled a micro electromechanical hybrid supercapacitor. Both anode and cathode were grown on carbon cloth directly, which could ensure strong machinery and electric connection between electrode materials and current collector and mechanical flexibility. In Li half cell examination, both Li4Ti5O12 nanoarray and MWCNT exhibit excellent cycling and rate capability; as full cell hybrid supercapatitor, our HSC could obtain high single voltage of 3.0 V. The maximum volumetric energy density of our HSC device is～4.38 mWh cm-3, much superior to previous flexible supercapacitors and comparable to the commercial thin-film lithium battery. Under current density of 0.65 mA cm-2, our cell demonstrating 92% energy retention after 3000 cycles, the energy decay per cycle is only～0.0027%, indicating that our HSC device has highly stable cycling performance.2. We synthesized homogeneous and well aligned Bi2O3 nanoflakes which were grown directly on Ti current collector by facile hydrothermal method. For the first time, we systematically investigated the redox reaction reversibility of Bi2O3 electrodes in various aqueous mono-/di-/tri-valent metal ion electrolytes. We found that Bi2O3 could be used as electrode material for aqueous Li, Na, K, Mg, Ca, Sr, Ba and even A1 ion batteries. The highest practical capacity was 357 mAh g-1, which is much superior to normal electrode materials of aqueous rechargeable ion batteries. Furthermore, by using XRD and XPS, we unveiled a distinct "quasi-conversion reaction" mechanism.3. Based on Bi metal thin film, we studied the electrochemical performance of Bi metal in aqueous electrolytes. The capacity, cyclability and energy storage kinetic parameters of Bi electrode in LiOH, NaOH and KOH aqueous solutions is firstly investigated and compared particularly. |
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