Non-transition metal modulated reducibility strategy for highly conductive mixed electronic and ionic (LixLa2/3-x/3)TiO3 perovskite

Abstract

In solid-state batteries, mixed electronic and ionic conductors play a crucial role in enhancing electrode charge transfer. This study proposes a strategy for modulating the reducibility of materials to develop stable and highly conductive mixed conductors based on perovskite-type (Li_xLa_2/3-x/3)TiO₃ oxides. Traditional methods that enhance electronic conductivity through B-site doping with variable valence transition metals have limited improvement on electronic conductivity with presence of significant secondary phases. Therefore, our approach focuses on A-site doping with fixed-valence non-transition metals to affect the reducibility of (Li_xLa_2/3-x/3)TiO₃, thereby regulating its electronic conductance properties. Our findings reveal that co-doping with the alkali metal Na and the alkaline earth metal Sr at the Li-site enhances the reducibility of Ti and doubles the electronic conductivity to 2.89 × 10^–3 S/cm compared to the undoped composition. Meanwhile, Na-Sr co-doping improves the reconfiguration of the crystal lattice during the reduction process, so that it exhibits high sintering activity and thermodynamic stability. These factors together contribute to its outstanding rate capability and long cycle stability, enabling it to maintain over 50% of its initial capacity at a 50 C-rate, and demonstrating over 800 stable cycles at a 2.5 C-rate. This strategy provides a new way to develop high-performance mixed-conductor electrode framework materials for improving the electrode kinetic behavior of solid-state batteries and promoting their practical applications.