| Energy shortage and environment pollution threat the survival and development of humanbeing. The most effective solution is to develop renewable resources. However, those resources, because of instability and discontinuity, need large-energy energy storage equipment which could achieve energy storage and transfer between different energy resources. As energy storage equipment, lithium ion batteries have been considered as promising stationary batteries because of their high output voltage, high energy density, high power density, long cycle life, no memory and environmental friendly features; sodium ion batteries could also be used as stationary batteries because of their abundant resources and low cost. In this Ph. D. dissertation, we coated the Li4Ti5O12with a few-layer graphene via a new low-temperature coating technique; secondly, we introduce a novel material of LiNb3O8with high capacity as an anode electrode for lithium ion batteries; we report the use of carbon coated Na3V2(PO4)3as a promising cathode material for sodium ion batteries and investigate the sodium storage mechanism. The main findings and conclusions are as follows:As far as we know, carbon coating is a powerful method to enhance the surface electrical conductivity of electrode materials. It is an effective way of improving electrochemical performance. Typically, carbon coating of electrode materials is conducted over700℃. Under such a high temperature, some electrode materials, including lithium transition metal oxides, may be reduced or may become unstable during the carbon coating process. We successfully coated few-layer graphene on the surface of Li4Ti5O12by a low-temperature carbon coating technique at400℃. Capacities of131and104mAh/g can be reached at current rates of5C and10C, respectively. Moreover, cyclic performance is significantly improved after coating. The capacity decreases from144.6to124.4mAh/g after2400cycles at a current rate of2C in a half cell versus Li+/Li, with high capacity retention of86%. Furthermore, few-layer graphene coated Li2MnO3was also prepared using the same approach. The crystalline structure and chemical state of Mn remain unchanged after few-layer graphene coating. The cyclic performance is also significantly improved. This new graphene-coating technique could be easily extended to other active electrode materials for electrochemical devices.Nevertheless, the theoretical capacity of Li4Ti5O12is only175mAh/g. In order to further improve the energy density of a battery, it is desirable to explore new anode materials with high reversible capacity. Here we exploited a novel anode material of LiNb3O8. For enhancing electrical contact and deducing the particle size of electrode material, the pure LiNb3O8was ball-milled with carbon black. The initial discharge/charge capacities of the resulting sample are351and212mAh/g, respectively. The partial two-electron transfer reaction from Nb5+to Nb3+is realized in this material The result is confirmed by XANES and ex-situ XRD.Due to the low abundance of lithium in the earth's crust, large-scale applications of lithium ion batteries become questionable. We first report the use of carbon to coat Na3V2(PO4)3materials by one-step solid state reaction approach. The sample shows flat voltage plateaus at3.4V and1.63V vs. Na+/Na. The storage voltage of3.4V is relatively higher than the average voltage of other cathode materials for sodium ion batteries. The capacity is improved by reducing carbon content of Na3V2(PO4)3/C and coulombic efficiency is enhanced by optimized electrolytes. The initial coulombic efficiency for sample after reducing carbon content inNaFSI/PC is up to98.7%and it can maintain at99.8%in the subsequent cycles. The initial reversible capacity is107.1mAh/g, which is close to its theoretical capacity and its capacity retention is92.9%after80cycles. The behavior of structural changes between charge/discharge of Na3V2(PO4)3/C is a typical two-phase reaction between Na3V2(PO4)3to NaV2(PO4)3with volume change of ca.8.26%.
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