Lithium intercalation properties of V205-based thin films and their application to thin film batteries

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Polymolybdovanadate(VィイD22ィエD20ィイD25ィエD2-MoOィイD23ィエD2) can intercalate lithium reversibly and perform as cathode of secondary battery. Moreover its film can be fabricated with ease. We built all solid state secondary batteries with films of polymolybdovanadate as cathode and tested for the purpose of evaluating the film cathode.Polymolybdovanadic acid was synthesized by the reaction of hydrogen peroxide water solution with a mixture of vanadium and molybdenum (V/Mo = 1/9). The acid thus obtained was spin-coated or cast on ITO glass substrate. Solid electrolyte (LiClOィイD24ィエD2/PEO-PPO) was prepared as following ; The mixture of 1M LiClOィイD24ィエD2/PC(propylene carbonate) and liquid monomer EO(ethylene oxide)/PPO(propylene oxide) was cast and polymerized by irradiation of UV ray. The mixing ratio of LiClOィイD24ィエD2/PC and EO/PPO was optimized to be 20 and 80wt%, respectively to give resultant higher conductivity and lower interracial resistance. The cathode and electrolyte, thus prepared, w … More ere pressed and integrated. All solid state cell,Li|LiClOィイD24ィエD2/PEO-PPO|VィイD22ィエD20ィイD25ィエD2-MoOィイD23ィエD2, ITOwas constructed using lithium metal as a counter electrode and sealed by epoxy resin.The cell with thin cathode (〜0.5μm) showed lower deterioration of battery capacity with increasing current density than one with thick cathode (〜5μm). The ratio of actual capacity to ideal one estimated by open circuit voltage measurements, however, did not depend on cathode thickness very much. This means that the cell with thick VィイD22ィエD20ィイD25ィエD2-MoOィイD23ィエD2 cathode may have effective high capacity due to increase in cathode quantity, even if suffer some degree of reduction. In this stage, the cell with 4.2 μm VィイD22ィエD20ィイD25ィエD2-MoOィイD23ィエD2 cathode performed with 10 μAcm-2 of capacity under 20 μAcm-2 of current density.The largest cause of the reduction of battery capacity is the interfacial resistance between electrolyte and cathode VィイD22ィエD20ィイD25ィエD2-MoOィイD23ィエD2 film. Thin film battery using VィイD22ィエD20ィイD25ィエD2-MoOィイD23ィエD2 film nay show still higher capacity, because we preliminary confirmed that such interracial resistance can be overcome by a certain device while cell construction. Less