Critical Length Scales to Inhibit Dendritic Fracture in Ion‐Exchanged LLZTO

ABSTRACT Solid electrolytes (SE) such as Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 (LLZTO) have the potential to enable the production of safe, high‐capacity lithium (Li) metal batteries, but remain vulnerable to Li filaments. Applying in‐plane residual compressive stress to suppress these dendrites provides a possible solution. Herein, we quantify the effectiveness of compressive surface layers over an appropriate thickness and demonstrate that stresses between 300 MPa and 1 GPa can be introduced with a multi‐step process using AgNO 3 to ion‐exchange (IX) smaller Li + ions for larger Ag + ions. This process requires balancing the diffusion kinetics (to create stress) against the thermodynamic factors which cause decomposition of the SE. Surface‐sensitive analysis confirms the presence of silver in the LLZTO, which maintains its cubic structure after high temperature processing while critical current density (CCD) measurements show a threefold increase. These findings demonstrate that dendritic fracture can be inhibited using IX to introduce internal compressive stress at sufficient depths.