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

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 Li6.4La3Zr1.4Ta0.6O12 (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. A LiF and Li2PO3F‐rich lithiophilic interface formed by the targeted chemical reactions between LiPO2F2 and the contaminants on the Li6.4La3Zr1.4Ta0.6O12 (LLZTO) surface is designed, which can effectively resist the corrosion of LLZTO surface during air exposure and ensure electrochemical stability of the Li/LLZTO interface with a high critical current density value of 1.2 mA cm−2 of Li|LiF&Li2PO3F‐LLZTO|Li symmetric cells and ultrastable high‐voltage cycling (4.5 V, vs Li/Li+) of LiCoO2|LiF&Li2PO3F‐LLZTO|Li full cells.