Porous Polymers as Gallium Ion Carriers for Constructing an SEI with Li–Ga-Rich and LiF-Rich Synergistic Effects in All-Solid-State Lithium Metal Batteries

Lithium fluoride (LiF) is regarded as the core component of the solid electrolyte interphase (SEI). However, LiF exhibits extremely poor ionic conductivity, which is detrimental to the transport of Li+ in the SEI. Li–Ga exhibits excellent lithiophilicity and chemical stability, and its synergistic effect with lithium fluoride can be utilized to construct a high-performance SEI. However, achieving the cogrowth of LiF and Li–Ga is extremely difficult. In this study, polyacetal amine with a porous structure is employed as a Ga3+ carrier and incorporated as a filler into composite solid electrolytes (CSEs). The porous structure facilitates the reduction of TFSI–, thereby promoting the formation of LiF. Moreover, Ga3+ ions readily detach from the porous structure and migrate to the anode, participating in the formation of the SEI, thereby forming an SEI with a synergistic effect rich in both Li–Ga and LiF. The Li–Ga/LiF-rich SEI combines excellent electronic insulation, electrochemical stability, and a high Li+ transport rate, ultimately improving battery performance. At a current density of 0.1 mA cm–2, the Li/PEO–PG/Li cell could cycle for 5000 h. The LFP/PEO–PG/Li full cell delivers a specific discharge capacity of 106.3 mAh g–1 after 700 cycles at 1C and 60 °C while maintaining excellent performance at 100 °C. This study provides new insights for improving the composition of the SEI to enhance battery performance.