Preparation of a Self-Supported SiO2 Membrane as a Separator for Lithium-Ion Batteries

For the first time, electrophoretic deposition (EPD) has been employed to prepare a self-supported, inorganic membrane consisting of SiO2 nano-fibers, as a separator for lithium-ion batteries. The SiO2 nano-fibers that were fabricated by a low-cost force spinning technique were deposited by EPD directly onto LiNi0.8Co0.15Al0.05O2 cathode material. Citric acid charging agent and anhydrous acetone solvent were used. The resulting porosity and tortuosity of the EPD SiO2 separator were 71.42 %, and 1.70, respectively. The slightly higher tortuosity of the EPD-SiO2-fiber separator (60 mu m) led to a lower rate capability in comparison to commercial GF/A glass fiber separator (260 mu m). On the other hand, the latter exhibited lower self-discharge than the former in full-cells with a graphite anode; this is proposed to be related to the different purities of the two materials that impart different electronic properties or the presence of 20 wt % PVDF in the EPD-SiO2 separator. Indeed, the deposited membrane has good characteristics as a battery separator and the EPD process is extremely feasible for the fabrication of miniaturized lithium-ion batteries on wafer level.