Nano-sized copper tungstate thin films as positive electrodes for rechargeable Li batteries

Nano-sized CuWO4 thin films have been fabricated by radio-frequency (R.F.) sputtering deposition, and are used as positive electrode with both LiClO4 liquid electrolyte and LiPON solid electrolyte in rechargeable lithium batteries. An initial discharge capacity of 192 and 210 mAh/g is obtainable for CuWO4 film electrode with and without coated LiPON in liquid electrolyte, respectively. An all-solid-state cell with Li/LiPON/CuWO4 layers shows a high-volume rate capacity of 145 μAh/cm2 μm in first discharge, and overcomes the unfavorable electrochemical degradation observed in liquid electrolyte system. A two-step reactive mechanism is investigated by both transmission electron microscopy and selected area electron diffraction techniques. Apart from the extrusion and injection of Cu2+/Cu0, additional capacity can be achieved by the reversible reactivity of (WO4)2− framework. The chemical diffusion coefficients of Li intercalation/deintercalation are estimated by cyclic voltammetry. Nano-CuWO4 thin film is expected to be a promising positive electrode material for high-performance rechargeable thin-film lithium batteries.