The Interface between Li6.5La3Zr1.5Ta0.5O12 and Liquid Electrolyte

Summary An advantageous solid electrolyte/liquid electrolyte interface is crucial for the implementation of a protected lithium anode in liquid electrolyte cells. Li6.5La3Zr1.5Ta0.5O12 (LLZTO) garnet electrolytes are among the few solid electrolytes that are stable in contact with lithium metal. We show LLZTO is unstable in contact with the organic carbonate-based Li+ liquid electrolyte used in conventional Li-ion cells. The interfacial resistance between LLZTO and LiPF6 in (CH2O)2CO: OC(OCH3)2 (1:1 v/v) increases with time due to the growth of a lithium-ion-conducting solid electrolyte interphase (SEI) at the surface of the ceramic electrolyte. The interphase is composed of Li2CO3, LiF, Li2O, and organic carbonates. Even at a rate of 5 mA cm−2, a 3 V potential drop occurs across the LLZTO/liquid electrolyte interface. A practical LLZTO membrane (thickness ∼10 μm), in contact with a lithium anode, gives a potential loss of ∼16 mV, less than 1% of the resistance of the SEI.