Stabilizing the Li1.3Al0.3Ti1.7(PO4)3|Li Interface for High Efficiency and Long Lifespan Quasi‐Solid‐State Lithium Metal Batteries

To tackle the poor chemical/electrochemical stability of Li1+xAlxTi2‐x(PO4)3 (LATP) against Li and poor electrode|electrolyte interfacial contact, a thin poly[2,3‐bis(2,2,6,6‐tetramethylpiperidine‐N‐oxycarbonyl)norbornene] (PTNB) protection layer is applied with a small amount of ionic liquid electrolyte (ILE). This enables study of the impact of ILEs with modulated composition, such as 0.3 lithium bis(fluoromethanesulfonyl)imide (LiFSI)‐0.7 N‐butyl‐N‐methylpyrrolidinium bis(fluoromethanesulfonyl)imide (Pyr14FSI) and 0.3 LiFSI‐0.35 Pyr14FSI‐0.35 N‐butyl‐N‐methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI), on the interfacial stability of PTNB@Li||PTNB@Li and PTNB@Li||LiNi0.8Co0.1Mn0.1O2 cells. The addition of Pyr14TFSI leads to better thermal and electrochemical stability. Furthermore, Pyr14TFSI facilitates the formation of a more stable Li|hybrid electrolyte interface, as verified by the absence of lithium “pitting corrosion islands” and fibrous dendrites, leading to a substantially extended lithium stripping‐plating cycling lifetime (>900 h). Even after 500 cycles (0.5C), PTNB@Li||LiNi0.8Co0.1Mn0.1O2 cells achieve an impressive capacity retention of 89.1 % and an average Coulombic efficiency of 98.6 %. These findings reveal a feasible strategy to enhance the interfacial stability between Li and LATP by selectively mixing different ionic liquids. Incorporating a small amount of ionic liquid electrolyte (0.3LiFSI‐0.35Pyr14FSI‐0.35Pyr14TFSI) within a hybrid electrolyte that also contains Li1.3Al0.3Ti1.7(PO4)3 (LATP) and the polymer PVDF‐TrFE yields drastically enhances interfacial stability against lithium metal, prolonging the lithium stripping‐plating lifetime by a factor of 3.7 and giving superior cycling stability over 500 cycles (0.5C) in full cells with LiNi0.8Co0.1Mn0.1O2 (NCM811) as the cathode material.