Interface Modification of LATP-Based Solid-State Li Metal Batteries Using Composite Polymer Electrolyte and Li-in Alloy

NASICON-type Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP) solid electrolyte attracts attention because of its stability in the air and water and its chemical stability with high-voltage cathode materials. However, LATP solid electrolyte has interfacial problems, such as limited contact area. Additionally, Li/LATP interface is deteriorated by structural collapse due to its reduction products. Herein, we modified the electrode interface using PEO based protecting layer (PL) and Li-In alloy anode. PEO based protecting layer (PL) was applied to suppress the Li/LATP interface side reactions and minimize the LiFePO 4 (LFP) /LATP interfacial resistance. We applied two kinds of PLs, solid polymer electrolyte (SPE) and composite polymer electrolyte (CPE). A CPE was prepared using a ceramic filler of LLZTO in order to improve the ionic conductivity and long-term cycling stability of PL. As an anode material Li foil and In 1.5 Li foil were utilized. The symmetric and full cells were prepared with a PL coated on both sides of the electrolyte. The symmetric cell consisted of Li/PL/LATP/PL/Li and the full cell consisted of Li (or In 1.5 Li) /PL/LATP/PL/LFP. The symmetric cell and full cell with CPE exhibited stable cycling performance, compared to that with SPE. The symmetric cell utilizing In 1.5 Li foil showed higher overpotential during the initial cycles, but it showed improved cycling stability, compared to that with Li metal foil. XRD and TOF-SIMS results indicate that there were no structural and chemical changes in the LATP coated with PL. Therefore, the modification strategies of CPE protecting layer and Li-In alloy anode are effective for enhancing cycling performance in all-solid-state batteries.