Synergistic activation of grain boundaries with dual salts enables fast lithium percolation in LATP-based solid state electrolytes

Abstract

In the pursuit of a durable solid-state lithium battery, understanding the mechanism of fast ion transport involving the boundary of electrolytes is imperatively desirable. However, there are limited research studies on the ion transport pathways at the grain-scale. Herein, via combined investigations by ssNMR, TEM, XPS, KPFM and advanced theoretical simulation including MSD and RDF, we discover that non-equilibrium grain boundary structures regulated by the dual-salt strategy during the cold sintering process mainly work synergistically from three aspects, jointly enhancing the lithium percolation at the boundary region. Specifically, the addition of dual lithium salts in the transient liquid phase increased the proportion of lithium occupying the Li₃ sites within the LATP grains, favoring the migration of charge carriers with a lower activation energy. Besides, anions exhibit a competitive substitution on oxygen vacancies, effectively broadening the Li⁺ conduction channels. Moreover, Li⁺ exhibits enrichment and short-range order distribution, which facilitates an increased carrier concentration in an ordered Li conduction matrix, and thus accelerates charge carrier transport. Eventually, we successfully achieved LATP-based solid electrolytes with high room-temperature ionic conductivity, reaching up to 2.02 × 10⁻³ S cm⁻¹—the highest value among those reported for this material. This work provides a guideline for the rational design of electrolytes with fast ion transport.