Improving Battery Safety With a Light-Conducting Separator

Lithium ion batteries are the battery of choice for laptops, electric vehicles and many other applications due to their high energy density, low maintenance and recharging ability. As electric vehicles become more commonplace and new battery uses are identified for aerospace, industrial and consumer applications, their use continues to grow. However, recent high-profile failures have led to concerns about the safety of large Li-Ion batteries. For example, the batteries can develop internal flaws called dendrites (small tendrils of metal that grow off of one of the electrodes). If the dendrite grows large enough, it can break through the separator that keeps the electrodes apart, causing a short circuit within the battery and potentially leading to fires or explosions. The industry needs better ways to monitor the growth of dendrites and other types of flaws within the battery and predict potential battery failures.

Battelle researchers developed the concept that an optical sensor could be used to monitor the battery for internal flaws such as dendrites. However, in order to make it work, they needed a separator that could conduct light as well as ions. All batteries use separators to keep the two charged electrodes apart. The separators, generally made of very thin plastics, provide a physical barrier between the electrodes while allowing ions to pass back and forth through microscopic holes in the material. However, existing separators did not allow light to pass through. We identified a polymer that would allow sufficient light through for the optical sensors and still provide physical separation and ion transfer between the electrodes. In order to optimize performance, we also changed the formulation of the electrolyte in the battery.

In lab demonstration tests, the new separator and electrolyte combination provided the same level of performance as traditional Li-Ion battery separators with the added function of allowing light to pass through to the optical sensor. This allows the optical sensor to be used to monitor the growth of dendrites and other flaws through the separator material. Optical sensing is a practical solution for monitoring battery health and predicting potential shorts before they occur. This added safety feature could significantly reduce the risks of fires and explosions in Li-Ion batteries used in transportation, aviation and other applications.