Insights into the local structure, microstructure and ionic conductivity of silicon doped NASICON-type solid electrolyte Li1.3Al0.3Ti1.7P3O12

NASICON-type solid electrolyte Li1.3Al0.3Ti1.7P3O12 (LATP) is attractive because of the cheap raw materials, ex-cellent air stability, and high ionic conductivity. Silicon doping is generally adopted to improve its conductivity further, but the corresponding mechanism is vacant. Herein, we synthesize the silicon doped LATP electrolyte with a simple solution-based method and systemically investigate the effects of different silicon doping level on the local structure, microstructure and ionic diffusion kinetics of the solid electrolytes. We firstly put forward the octahedral occupation of silicon in Li1.3Al0.3Ti1.7P3O12 electrolyte instead of tetrahedral sites. Silicon doping is found to be negative for the ionic transportation in grain bulk, however, the grain boundary conductivity can be increased after a small amount of silicon doping due to the modification of micro-structure, i, e., the silicon doping induces the segregation of LiTiOPO4 in the grain boundary, which can effectively suppress the abnormal growth of electrolyte grains and concomitant gas pores and cracks during sintering. As a result, the total conduc-tivity can reach similar to 10(-3) S.cm(-1) after silicon doping with this simple method. Our results demonstrate the critical importance of adjusting secondary phase on the micro-structure and ionic conductivity of electrolyte during the development of inorganic fast ionic conductors.

Automated summary

Silicon doping negatively affects the ionic transportation in grain bulk, but can increase grain boundary conductivity and total conductivity to around 10(-3) S.cm(-1) by inducing the segregation of LiTiOPO4. This finding highlights the critical importance of adjusting secondary phase for microstructure and ionic conductivity of solid electrolytes in the development of inorganic fast ionic conductors.