Cold Sintering of LLTO Composite Electrolytes for Solid‐State Lithium Batteries

Abstract Solid‐state batteries have the potential for higher energy densities and enhanced safety when compared to conventional lithium‐ion batteries. The perovskite‐type Li_3xLa_2/3–xTiO₃ (LLTO) is an attractive ceramic electrolyte due to its high ionic conductivity, broad electrochemical stability window, and thermal and chemical stability. The conventional sintering process for ceramics, typically performed at high temperatures (~1000 °C), poses a critical bottleneck for integrating solid electrolytes with active electrode materials. In this study, Li_0.29La_0.57TiO₃/polypropylene carbonate (PPC) composite electrolytes containing lithium perchlorate (LiClO₄) were densified using cold sintering at 125 °C. The resulting LLTO‐based composite electrolytes exhibit relative densities above 80 % and ionic conductivities exceeding 10⁻⁴ S cm⁻¹ at room temperature. The symmetric Li/LLTO‐PPC‐LiClO₄/Li cell with PVDF interlayers achieves a high critical current density of 1.8 mA cm⁻² at room temperature. Solid‐state lithium batteries fabricated with LLTO composite solid electrolytes deliver a high discharge capacity of 151 mAh g⁻¹ at 0.1 C and 135 mAh g⁻¹ at 0.2 C. Our approach, which integrates ceramic and polymer materials, produces composite electrolytes with superior properties, highlighting the potential of cold sintering for advancing solid‐state batteries.