Browsing by Subject "rechargeable batteries"

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    Advanced Materials for Rechargeable Lithium-Sulfur Batteries
    (Office of the Vice Chancellor for Research, 2014-04-11) Fu, Yongzhu
    Rechargeable batteries are essential power supplies for our daily life, and they are widely used in portable electronics, hybrid electric vehicles, and grid energy storage. Lithium-ion (Li-ion) batteries, which have the highest energy density among rechargeable batteries, have reached the capacity limits of current electrode materials, such as transition metal oxides (e.g., LiCoO2, LiMn2O4, and LiFePO4). To meet the increasing demand of high energy density batteries, rechargeable lithium-sulfur (Li-S) batteries are considered as one of the most promising systems with significant potential for many practical applications. Sulfur has a theoretical capacity of 1,672 mAh/g by taking two electrons per atom, which is an order of magnitude higher than those of transition metal oxides. However, several challenges impede practical application of Li-S batteries, such as high resistivity of sulfur, dissolution of intermediate polysulfides, and shuttle of these polysulfides from cathode to anode in Li-S batteries. Significant improvements have been achieved over the past years, but further improvements and better understanding of Li-S batteries are still needed. This poster will present several strategies that have been developed including sulfur-conductive polymer nanocomposites, lithium/dissolved polysulfide cells, sandwiched Li2S electrodes, and in situ formed Li2S cathodes. A nanolayer of conductive polypyrrole was fabricated on sulfur particles, which can enhance electrical conductivity and reduce dissolution of polysulfides. Binder-free carbon nanotube current collector was used in lithium/dissolved polysulfide cells, which exhibit unprecedented capaciteis of 1,600 mAh/g in the first cycle and over 1,400 mAh/g after 50 cycles. Lithium metal anode is used in current Li-S batteries since the sulfur cathodes do not have any lithium in the initial stage, which is a safety hazard. Lithium-rich sulfur cathode materials such as Li2S can allow a variety of non-lithium metal anodes to be used, which can advance the Li-S battery technology to an unprecedented level. However, the high reactivity of Li2S results in limited approaches that have been explored. A sandwiched Li2S electrode consisting of two layers of carbon nanotube paper has been developed which shows high capacities and high rate capabilities. In addition, a novel in situ formed Li2S cathode is developed, which utilizes lithiated graphite as a lithium donor to convert lithium polysulfide Li2S6 to the end discharge product Li2S. These materials and strategies are promising for practical applications.
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    CHEMICAL AND PHASE TRANSFORMATION FROM VANADIUM SULFIDE TO OXIDE VIA A NEW CHEMICAL ROUTE FOR THE SYNTHESIS OF Βʹ-LIXV2O5 AS A HIGH PERFORMANCE CATHODE
    (Office of the Vice Chancellor for Research, 2014-04-11) Lee, Wen Chao; Mahootcheian Asl, Nina; Kim, Youngsik; Zhu, Likun
    The used of rechargeable lithium ion batteries are so widely nowadays on consumer electronics especially portable devices such as cellphones, laptops and etc. The advancement of technology has created batteries with providing high energy density without memory effect and minimum the self-discharge on standby mode. Even with these features, researchers are still trying to improve the batteries with more energy density, low cost, better safety and high durability. The energy density improves with high operation voltage and high capacity. All these features came from one source, material. The resources for current commercial cathode material are decreasing and so new alternative cathode with high performance is needed to replace the commercial cathode in the future. The high temperature vanadium pentoxide phase, βʹ-LixV2O5, was synthesized via a new chemical synthesis involving the evolution of vanadium oxides from the 600°C heat treatment of the pure LiVS2 in air. By employing this method of synthesis, well-crystalized, rod-shaped βʹ-LixV2O5 particles 20 – 30 μm in length and 3 – 6 μm in width were obtained. Moreover, the surface of βʹ-LixV2O5 particles was found to be coated by an amorphous vanadium oxysulfide film (~20 nm in thickness). In contrast to a low temperature vanadium pentoxide phase (LixV2O5), the electrochemical intercalation of lithium into the βʹ-LixV2O5 was fully reversible where 0.0 < x < 2.0, and it delivered a capacity of 310 mAh/g at a current rate of 0.07 C between 1.5 V and 4 V. Good capacity retention of more than 88% was also observed after 50 cycles even at a higher current rate of 2 C.
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    First principles study on the electrochemical, thermal and mechanical properties of LiCoO2 for thin film rechargeable battery
    (2014) Wu, Linmin; Hoh Lee, Weng; Zhang, Jing
    Thin film rechargeable battery has become a research hotspot because of its small size and high energy density. Lithium cobalt oxide as a typical cathode material in classical lithium ion batteries is also widely used in thin film rechargeable batteries. In this work, the electrochemical, mechanical and thermal properties of LiCoO2 were systematically investigated using the first principles method. Elastic constants under hydrostatic pressures between 0 to 40 GPa were computed. Specific heat and Debye temperature at low temperature were discussed. Thermal conductivity was obtained using the imposed-flux method. The results show good agreements with experimental data and computational results in literature.