Magnesium Fluoride Interlayers Enabled by Wet-Chemical Process for High-Performance Solid-State Batteries

Garnet-type solid-state electrolytes (SSEs) exemplified by Li6.5La3Zr1.5Ta0.5O12 (LLZT) are chemically unstable when exposed to air, leading to the formation of impurities and poor wettability with Li metal. Herein, a protocol to address this Li/LLZT interface challenge is demonstrated by constructing a lithiophilic MgF2 nanofilm on the LLZT pellet. Specifically, a solution-based process is developed for the surface engineering of LLZT, utilizing magnesium trifluoroacetate (MTF) as the molecular precursor while poly(acrylic acid) (PAA) as the coordinating agent in a sol-gel process. It is demonstrated that a facile spin-coating treatment followed by high-temperature annealing reliably forms crack-free MgF2 nanofilms with precise thickness control. Introduction an MgF2 interlayer transforms the LLZT pellet into a highly lithophilic, facilitating close contact with the lithium anode, thereby leading to a significantly reduced interfacial resistance from 1190 Omega cm(2) to 6 Omega cm(2). Such an interfacial engineering enables stable cycling of full batteries with high reversibility and rate capability using commercial LiFePO4 and LiNi0.83Co0.07Mn0.1O2 as cathodes. This study unfolds the possibility of a solution-based method as a facile and scalable process for the construction of fluoride nanofilms, which is promising to address the critical interfacial challenges of solid-state batteries (SSBs) to facilitate its practical applications.