Lithium-ion (Li-ion) cells are increasingly used in high-voltage and high-capacity modules. The Li-ion chemistry has the highest energy density of all rechargeable battery chemistries, but associated with that energy is the issue of catastrophic thermal runaway with a fire. With recent incidents in the commercial aerospace and electronics sectors, it was necessary to find methods to prevent cell-to-cell thermal runaway propagation.
The work carried out here is not specific to any existing battery design, and was started with the goal of achieving a common method to trigger a cell into thermal runaway and determine if one can consistently obtain this thermal runaway event. The second goal was to determine if cell-to-cell thermal runaway can be prevented.
Li-ion cell-to-cell thermal runaway propagation was studied using a heat-to-vent/thermal runaway method. The trigger method was a commercial heater tape. Different cell designs of various Li-ion chemistries, as well as physical formats, were studied. Testing consisted of designing the cell modules with just spacing between the cells, introduction of a radiant barrier, and placing the cells in a module manufactured using intumescent materials. It was determined that at least 2-mm spacing was required for cylindrical cell designs. For cell formats that had vents on the side, a physical separation between neighboring cells was required. This was achieved by using intumescent materials as well as the radiant barrier.
The methods and designs used to prevent cell-to-cell thermal runaway in Li-ion modules consisted of increased cell-to-cell spacing, introduction of a radiant barrier between the cells, the use of intumescent cell modules that provide physical separation between the cells, and a method to absorb the heat from the cells, preventing the heat from directly affecting the neighboring cells by lowering the heat spread to the neighboring cells.