Topic 5: Battery Separator Failures and Explosions/Fires

From BU-306

The building blocks of a battery are the cathode and anode, and these two electrodes are isolated by a separator. The separator is moistened with electrolyte and forms a catalyst that promotes the movement of ions from cathode (positive) to anode (negative) on charge and in reverse on discharge. Ions are atoms that have lost or gained electrons and have become electrically charged. Although ions pass freely between the electrodes, battery separators provide a barrier between the anode and the cathode. The separator is an isolator with almost no conductivity of current.

The small amount of current that may pass through the separator is self-discharge and this is present in all batteries to varying degrees. Self-discharge eventually depletes the charge of a battery during prolonged storage. Figure 1 illustrates the building block of a lithium-ion cell with the separator and ion flow between the electrodes.

Figure 1. Ion flow through the separator of Li-ion batteries
^{Courtesy of Celgard}