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 electrolyte is imperatively desirable. However, there are limited research on the ion transport pathways in 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 cold sintering process mainly works synergistically from three aspects, jointly enhancing the lithium percolation at boundary region. Specifically, the addition of dual lithium salts in transient liquid phase increased proportion of lithium occupying the Li3 sites within the LATP grains, favoring the migration of charge carriers along the shorter Li1-Li3-Li1 pathway. Besides, anions exhibit a competitive substitution on oxygen vacancies, effectively broadening the Li⁺ conduction channels.Moreover, the Li+ exhibits enrichment and short-range order distribution, which facilitates an increased carrier concentration in an ordered Li conduction matrix, 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 reported for this material. This work provides a guideline for rational design of electrolytes with fast ion transport.