Interphase Optimum via Synergistic Effect of Poly(1,3‐dioxolane) Electrolytes and Lithium Difluorophosphate for Stable Lithium Metal Batteries

Abstract Solid polymer electrolytes (SPEs) hold great promise for future applications of high‐energy lithium metal batteries (LMBs). Unfortunately, inadequate room‐temperature ionic conductivity, sluggish interfacial charge transport, and uncontrolled electrode/electrolyte interface reactions severely limit their widespread applications. Herein, poly(1,3‐dioxolane) electrolytes (PDEs) are prepared in situ by introducing lithium difluorophosphate (LiDFP, LiPO₂F₂) as a multifunctional additive, which not only achieves excellent ionic conductivity but facilitates interfacial charge transport. Meanwhile, a high‐mechanical‐stability organic–inorganic hybrid solid electrolyte interphase (SEI) is formed by the synergistic effect of PDEs and LiDFP. The enrichment of LiF and Li_xPO_yF_z species in SEI formed by the preferential reduction of LiDFP ensures outstanding mechanical stability, and the ring‐opening polymerization of 1,3‐dioxolane provides the SEI excellent adaptability to the repetitive volume changes of lithium metal anode, which mitigates crack and regeneration of SEI and reduces side reactions between active Li and electrolytes. Therefore, based on PDEs, the symmetric Li cell enables steady cycling for 2000 h. The Li‐LiFePO₄ cell achieves superior long‐term cycling stability (over 1200 cycles) and wide operating temperature (−20 ∼ 60 °C). Also, the Li‐LiNi_0.6Mn_0.2Co_0.2O₂ exhibits favorable cycling stability. This study provides solutions to ongoing pain point issues of SPEs and facilitates practical applications of SPEs in high‐energy LMBs.