Li2CO3 effects: New insights into polymer/garnet electrolytes for dendrite-free solid lithium batteries

Garnet particles are usually introduced into polymer matrices as fillers to fabricate polymer/garnet composite electrolytes (PGEs), which can not only improve the ionic conductivity but also enhance the mechanical strength to suppress Li dendrites. However, the surface Li2CO3 contamination of garnet particles through air exposure has long been overlooked when fabricating the PGEs. Considering the ultralow ionic conductivity and low oxidation voltage of Li2CO3, the effects of Li2CO3 should be taken into consideration. Herein, the PGEs with Li2CO3-containing and Li2CO3-free garnet particles are fabricated from garnet-in-polymer (GIP) to polymer-in-garnet (PIG) electrolyte compositions. The results indicate that Li+ can be transported faster along the polymer/garnet interface in the Li2CO3-free GIP electrolytes, while Li+ migration through the garnet bulk can be improved in the Li2CO3-free PIG electrolytes. The Lewis acid-base interactions between garnet and polymer are enhanced due to the Li2CO3 removal, thus increasing the Li+ transference number. Furthermore, cathode-supported solid-state batteries with vertically aligned LiFePO4 cathodes and Li2CO3-free PIG electrolytes are constructed, which show excellent rate and cycle performance. This work provides new insights into PGEs and the effects of Li2CO3, which can guide the improved design of PGEs for dendrite-free solid garnet batteries.