Interphase Formed at Li_6.4La₃Zr_1.4Ta_0.6O₁₂/Li Interface Enables Cycle Stability for Solid‐State Batteries

Abstract

Abstract Garnet‐type Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTaO) is considered a promising solid‐state electrolyte (SSE) for all‐solid‐state batteries (SSBs), but LLZTaO/Li interfacial issues limit their power density. The key question of whether LLZTaO does or does not form an interphase layer before and at the initial stage of electrochemical cycling remains debatable. An XPS interface approach, electrochemical cycling, and an electrochemically coupled phase field model to study the dynamic changes of interfacial resistance during cycling are utilized, and it is found that the generation rate of the interphase via electrochemical reaction processes at the LLZTaO/Li interface depends on the applied current density. For a Li/LLZTaO/Li cell, the impedance and overpotential increase gradually at the initial stage of electrochemical cycling at a current density of 0.1 mA cm –2 due to the formation of a passivating reaction zone (interphase) at LLZTaO/Li interface, which can protect the LLZTaO from being continuously reacted. With increasing the current density to 0.5 mA cm –2 , the electrochemical reaction is suppressed and tied to uneven Li ion transport across the LLZTaO/Li interface on plating, leading to a short circuit of the cell. Understanding how interface dynamic transformations influence electrochemical degradation is helpful to stabilize these interfaces in SSBs.