From Contaminated to Highly Lithiated Interfaces: A Versatile Modification Strategy for Garnet Solid Electrolytes

Abstract The surface chemistry of garnet electrolyte is sensitive to air exposure. The poor LLZO/Li interface caused by Li₂CO₃/LiOH contaminants on garnet electrolyte surface easily induces large interfacial resistance resulting in the growth of Li dendrites. Herein, a versatile modification strategy is designed to convert the contaminants on Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) surface into a LiF and Li₂PO₃F‐rich lithiophilic interface by targeted chemical reactions at the interface between LiPO₂F₂ and Li₂CO₃/LiOH. The newly formed LiF‐Li₂PO₃F interfacial layer not only facilitates the interface wettability between Li and LLZTO, but also helps to resist corrosion of the LLZTO surface by moisture in the air. The Li|LiF&Li₂PO₃F‐LLZTO|Li symmetric cell exhibits a low interfacial resistance of 5.1 Ω cm² and ultrastable galvanostatic cycling, over 1500 h at 0.6 mA cm⁻² and over 70 h at 1.0 mA cm⁻². In addition, LiCoO₂|LiF&Li₂PO₃F‐LLZTO|Li hybrid solid‐state full cells display high initial specific capacity of 192 mAh g⁻¹ at 0.1 C, and excellent cycling stability with a capacity retention over 76% even after 1000 cycles at 0.5 C at a high cut‐off voltage of 4.5 V. This study provides a simple and practical strategy for the feasibility of the application of high‐voltage cathodes in this modified garnet all‐solid‐state batteries.