Thermal switch material suitable for use in controlling short circuits in lithium-ion batteries and method of making the thermal switch material

A composite thermal switch material suitable for use in controlling short circuits in lithium ion batteries. The switch material comprises a substantially homogeneous matrix of metallic nanoparticles and non-electrically conductive polymeric nanoparticles, the non-electrically conductive polymeric nanoparticles being fused to one another and having a greater thermal expansion coefficient than the metallic nanoparticles, the metallic nanoparticles and the non-electrically conductive polymeric nanoparticles being present in said substantially homogeneous matrix in relative proportions such that the composite thermal switch material is electrically conductive below a switching temperature and is substantially non-electrically conductive at or above the switching temperature.