Phonon Engineering in Solid Polymer Electrolyte toward High Safety for Solid‐State Lithium Batteries

Extensively‐used rechargeable lithium‐ion batteries (LIBs) face challenges in achieving high safety and long cycle life. To address such challenges, ultrathin solid polymer electrolyte (SPE) is fabricated with reduced phonon scattering by depositing the composites of ionic‐liquid (1‐ethyl‐3‐methylimidazolium dicyamide, EMIM:DCA), polyurethane (PU) and lithium salt on the polyethylene separator. The robust and flexible separator matrix not only reduces the electrolyte thickness and improves the mobility of Li+, but more importantly provides a relatively regular thermal diffusion channel for SPE and reduces the external phonon scattering. Moreover, the introduction of EMIM:DCA successfully breaks the random intermolecular attraction of the PU polymer chain and significantly decreases phonon scattering to enhance the internal thermal conductivity of the polymer. Thus, the thermal conductivity of the as‐obtained SPE increases by approximately six times, and the thermal runaway (TR) of the battery is effectively inhibited. This work demonstrates that optimizing thermal safety of the battery by phonon engineering sheds a new light on the design principle for high‐safety Li‐ion batteries. This work focuses on the influence of phonon scattering on solid‐state‐polymer electrolytes (SPEs), and designs an ultrathin PPIL electrolyte with high thermal stability by phonon engineering to optimize the high‐safety of solid‐state lithium batteries (SSLBs). Herein, a new way to enable SSLBs with high‐safety and high‐energy‐density is shown, and the importance of phonon engineering in high‐safety of SSLBs is highlighted.