W-Doped Li7La3Zr2O12 Ceramic Electrolytes for Solid State Li-ion Batteries

W-doped Li 7 La 3 Zr 2 O 12 electrolytes with composition of Li 7-2x La 3 Zr 2-x W x O 12 (LLZWO, x   =   0-0.55) were prepared by conventional solid state reaction. The incorporation of W proves beneficial to stabilization of cubic phase and densification of the ceramic, resulting in relative density of 96% and ionic conductivity of 6.6   ×   10 −4   S   cm −1 at 25   °C. Further analysis indicates that the LLZWO is not only chemically but also electrochemically (at least up to 4.5   V) stable against Li metal anodes. The batteries consisting of Li/LLZWO/Electrolyte-soaked separator/LiNi 0.33 Mn 0.33 Co 0.33 O 2 at 25   °C exhibit the capacity of 142   mAh   g −1 at a constant current of 15   mA   g −1 at the first discharge, which could run for 20 cycles with capacity retention of 94%. These results indicate that the W-doped LLZO ceramics are promising electrolytes for solid state lithium ion batteries.