Influence of lithium phosphate on the structural and lithium-ion conducting properties of lithium aluminum titanium phosphate pellets

Lithium aluminum titanium phosphate (LATP) with a formula of Li1.3Al0.3Ti1.7(PO4)3 has been regarded as one of the most promising inorganic solid-state electrolytes in all-solid-state lithium-ion batteries, and presently, to optimize the structural and electrochemical properties of its ceramic pellets is of crucial importance for potential application purposes. In this paper, chemical lithium phosphate Li3PO4 with a melting point of 837 °C is used as an agglutinant in the ceramics of as-prepared LATP crystallites, aiming to assay its functions in possible performance enhancement. At the sintering temperature of 900 °C, the self-fluxing agglutinant (10.0 wt%) in Li3PO4-LATP composite pellet is expected to fill gaps among close packed particles, and this actually induces an apparent shrinkage in the pellet diameter/thickness, a great decrease in grain-boundary resistance and an obvious increase in total Li+-ion conductivity (e.g., LATP-900 ~ 3.0 × 10−4 S cm−1; Li3PO4-LATP-900 ~ 1.2 × 10−3 S cm−1; at 60 oC). Especially, a polymorphic change of the agglutinant occurring during pellet-sintering process and the in situ formation of ion-conducting interphases may cooperatively explain the improvement of ionic conductivity.