While eyed for their high energy density and ability to recharge over hundreds of cycles, Li-ion batteries are also known for their risk of catching fire or exploding. Though used commercially and in electric vehicles from companies like Tesla and General Motors, research continues to improve them. examine how to improve their failure rate in commercial production.
An important area of research is thermal runaway, which is initiated by a short circuit within a battery cell. This internal short circuit (ISC) can be an effect of an impurity that made its way in during production. The short circuit causes heating, which quickly escalates inside the battery as a positive feedback loop. Thermal runaway happens in seconds, raising the temperature across the cells in the battery, and possibly escalating to a fire or explosion.
A patented ISC device (left) from NREL and NASA integrates within layers of Li-ion batteries (right) to enable controlled shorting and observation of thermal runaway in experiments.
It is not very easy to investigate thermal runaway because it happens inside the battery at unexpected times, and at a fast rate. To enable examination of the process, two scientists from NASA and NREL came up with a device that could be built into a battery cell and activated to initiate thermal runaway under controlled conditions.
Since being patented in 2015, a team from the University College of London finally presents Phase I research results with the device. They used rapid X-Ray imaging at 2000 frames per second to capture thermal runaway as it happened.
The paper is published in Energy and Environmental Science. It shows how the battery reacted with the activated ISC device emulating an impurity at deliberate locations within the battery. Scientists could use the ISC device to observe thermal runaway initiated at the cathode and anode, and other locations. With the snapshots taken over the course of a few seconds, they could also observe the intermediate steps, causes and effects, and rate of propagation through battery cells.
