This technical report examines the critical role of Mica Gaskets in EV battery safety, focusing on preventing thermal runaway propagation. It provides a detailed comparison between Muscovite and Phlogopite mica, highlighting their dielectric strength ($\ge 20\text{ kV/mm}$) and ability to withstand temperatures exceeding 1000°C. The guide outlines professional selection criteria—including thickness tolerance and resin content—and discusses "Composite Protection" strategies to meet UL 94V-0 flame retardancy. By addressing failure modes like delamination and outgassing, the article assists engineers in optimizing high-voltage battery insulation.