Li-ion battery shut-off at high temperature caused by polymer phase separation in responsive electrolytes.

For the purpose of realizing inherently safe high-power Li-ion batteries, a model Li4Ti5O12/LiFePO4 rechargeable battery is investigated using the thermally responsive polymer, poly(benzyl methacrylate), in an ionic liquid. At high temperature, battery operation is inhibited as a result of increased internal resistance caused by polymer and ionic liquid phase separation. Li-ion concentration is shown to affect the phase transition temperature and the extent to which batteries are deactivated.