Revealing the interface instability between a lithium metal anode and perovskite solid-state electrolyte

Abstract

Interface instability between the perovskite Li_3xLa_2/3−xTiO₃ (LLTO) and lithium metal anode limits the application in all-solid-state lithium batteries. Direct contact with lithium metal triggers Ti⁴⁺ reduction in crystalline LLTO, including rapid lattice destabilization and performance decay, though the governing mechanisms remain unelucidated. Herein, significant insights from multi-scale characterization technologies and molecular dynamics simulations, reveal the formation of oxygen vacancies in LLTO and lithium oxides at the interface. The mechanical measurements with nanoindentation and Vickers hardness allow us to directly quantify the degradation of hardness and elastic modulus of LLTO. Li|LLTO|Li symmetric cells further confirm the electrochemical decline. We propose a degradation mechanism of the interfacial instability from the perspective of microstructure, mechanical, chemical and electrochemical kinetics. This study provides crucial insights into the microscopic origin to understand the interfacial chemical processes, which is helpful to guide future interface designs.