Development and characterization of a bilayer separator for lithium ion batteries

A battery separator is placed between the positive and negative electrodes to prevent electric contact of the electrodes while maintaining good ionic flow. The most commonly used separators for lithiumion batteries are porous polyolefin membranes. However, they generally do not have good dimentional stability at elevated temperatures. In this study, a bilayer separator has been formed directly on an anode. This bilayer separator comprised a ceramic layer and a porous polyvinylidene fluoride (PVDF) layer. Coin cells with this type of separators showed stable cycling performance at room temperature. They also showed significantly improved rate capabilities compared to the reference cell with a conventional polyolefin separator. An oven test has been used to characterize the cells thermal stability. Charged cells were kept in an oven at 150 degrees C and their voltage drop was recorded. The reference cell with a conventioal separator failed within about SO min. while no noticeable voltage drop was observed for the cells with the new bilayer separator within the measured 2 h. (C) 2011 Elsevier B.V. All rights reserved.