Lithium Ion Batteries with Alumina Separator for Improved Safety

Abstract

Lithium ion batteries with inorganic separators offer the advantage of safer and stable operation in a wider temperature range. In this work, lithium ion batteries in both half and full cell configuration with an alumina separator were fabricated by an improved method of blade coating α-Al2O3 slurry directly on either Li4Ti5O12 or LiNi1/3Mn1/3Co1/3O2 electrode followed by drying. The improved separator preparation involves a twice-coating process instead of coating the slurry all at once in order to obtain a thin (∼40 μm) and uniform coat. Unlike state-of-the-art polyolefin separators such as polypropylene (PP) which are selectively wettable with only certain electrolytes, the excellent electrolyte solvent wettability of α-Al2O3 allows the coated alumina separator to function with different electrolytes. The coated α-Al2O3 separator has a much higher resistance to temperature effects than its polyolefin counterparts as it retains its dimensional integrity at temperatures as high as 200°C, eliminating the possibility of a short circuit during thermal runaway. Lithium ion cells with coated α-Al2O3 separator exhibit electrochemical performance comparable to that of polymer separator at room temperature, but the former provide safer operation and shows better cycling performance under extreme temperatures in the range of -30°C to 60°C than the latter.