Salt‐Optimized Protection Layers for Stabilizing Lithium Metal Anodes Toward Enhanced Battery Performance

Abstract Lithium (Li) metal anode (LMA) largely increases energy density of Li batteries, but its large‐scale application is hindered by challenges such as formation of dendritic and “dead” Li, electrolyte development and non‐uniform solid electrolyte interphase development. Polymer‐based organic–inorganic composite layers help address these issues by preventing dendritic Li growth, reducing side reactions, and promoting selective Li‐ion (Li + ) transport. Despite lithium bis(fluorosulfonyl)imide (LiFSI) exhibiting higher ionic conductivity than lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), it is used much less in protection layers. This study shows that LiFSI offers superior ionic conductivity and higher transference number, due to its stronger plasticizing effect compared to LiTFSI in a cross‐linked trimethylolpropane propoxylate triacrylate (TPPTA) matrix. This is achieved when the molar ratio between the carbonyl group (C═O) of TPPTA and Li + in Li salts is maintained at 13:1. The TPPTA‐LiFSI (TF) coated LMA (TF@Li) enhances the charge rate capability and cycling performance of Li||LiNi 0.6 Mn 0.2 Co 0.2 O 2 cells, offering better results than TPPTA‐LiTFSI coated LMA (TT@Li). The optimal C═O to Li + ratio at 4.5:1 in TF layer improves cycle life and reduces side reactions of LMA. This TF@Li significantly reduces pit formation and enhances cycle life at faster charging/slower discharging rates, maintaining ≈80% capacity after 200 cycles, nearly double that of Bare Li under the same conditions.