Substituted Garnet Materials for Safer Lithium Ion Batteries: Composition Optimisation and Full Cell Application
Our work has been dedicated to identifying suitable substitution strategies in order to stabilize the cubic phase at lower temperature while maintaining a high density for the material. In addition to studying the effect of Al substitution on the Li site, we have explored the benefits of partially replacing Li+ by Ga3+. The substitution of Li+ by a cation with higher oxidation state decreases the number of charge carriers (Li+) in the structure and could be detrimental to the conductivity of the material. Nevertheless, the preferential location of Ga3+ on the Li tetrahedral sites forces Li+ onto the distorted octahedral sites, thereby increasing the disorder on the Li sites and stabilizing the cubic phase of the garnet. This substitution leads to a considerable gain in conductivity, with values as high as 1.3 mS.cm-1 for Li6.55Ga0.150La3Zr2O12 at 25ºC . Alternative substitutions on the Zr4+site will also be discussed, leading to a wider range of compositional possibilities.
In order to demonstrate the applicability of the garnet electrolytes to commercial systems, the implementation of these substituted garnets in full cell Li-ion batteries will also be reported.
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(a) Crystal structure of garnet Li7-3xGax□2xLa3Zr2O12 where La (dodecahedral), Zr (octahedral) and O atoms are represented by dark red, blue, and red circles respectively. Li (octahedral), Li (tetrahedral), and Ga (tetrahedral) are represented in grey, turquoise blue, and green respectively. (b) Enlarged area of the Li vacancy highlighted in (a) showing the Li+ pathways. (c) Arrhenius plot of Li6.55Ga0.150La3Zr2O12between 340 and 180 K.