Thermal runaway is a major issue facing widespread adaptation of lithium-ion batteries. To achieve safe, thermally stable energy storage, various approaches have been proposed to regulate exothermic electrochemical reactions at high temperature, yet these have could only be either applied in aqueous systems or impractical in large-format cells. In this communication, we demonstrate that a copolymer, poly(2-chloroethyl vinyl ether-alt-maleic anhydride), or poly(CVE-MA), which exhibits a temperature-activated phase transition in organic solvents at high temperature, can be utilized as a thin film to inhibit lithium-ion migration/intercalation chemistries at the electrode/electrolyte interface. A large voltage drop and capacity decrease were observed at 80 °C due to interfacial hindrances imposed by the phase transition and resultant precipitation of poly(CVE-MA). This development of responsive polymers in organic solvents holds great potential for the future thermal safety of lithium-ion batteries.