Optimization of Lithium Content and Sintering Aid for Maximized Li + Conductivity and Density in Ta‐Doped Li 7 La 3 Zr 2 O 12

Ta‐doped cubic phase Li 7 La 3 Zr 2 O 12 ( LLZ ) lithium garnet received considerable attention in recent times as prospective electrolyte for all‐solid‐state lithium battery. Although the conductivity has been improved by stabilizing the cubic phase with the Ta 5+ doping for Zr 4+ in LLZ , the density of the pellet was found to be relatively poor with large amount of pores. In addition to the high Li + conductivity, density is also an essential parameter for the successful application of LLZ as solid electrolyte membrane in all‐solid‐state lithium battery. Systematic investigations carried out through this work indicated that the optimal Li concentration of 6.4 (i.e., Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 ) is required to obtain phase pure, relatively dense and high Li + conductive cubic phase in Li 7− x La 3 Zr 2− x Ta x O 12 solid solutions. Effort has been also made in this work to enhance the density and Li + conductivity of Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 further through the Li 4 SiO 4 addition. A maximized room‐temperature (33°C) total (bulk + grain boundary) Li + conductivity of 3.7 × 10 −4 S/cm and maximized relative density of 94% was observed for Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 added with 1 wt% of Li 4 SiO 4 .