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 SiO<inf>2</inf> nano-fibers, as a separator for lithium-ion batteries. The SiO<inf>2</inf> nano-fibers that were fabricated by a low-cost force spinning technique were deposited by EPD directly onto LiNi<inf>0.8</inf>Co<inf>0.15</inf>Al<inf>0.05</inf>O<inf>2</inf> cathode material. Citric acid charging agent and anhydrous acetone solvent were used. The resulting porosity and tortuosity of the EPD SiO<inf>2</inf> separator were 71.42 %, and 1.70, respectively. The slightly higher tortuosity of the EPD-SiO<inf>2</inf>-fiber separator (60 μm) led to a lower rate capability in comparison to commercial GF/A glass fiber separator (260 μm). 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-SiO<inf>2</inf> 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.