Ionic Percolation Networks in Composite Electrodes for All-Solid-State Batteries

Abstract

Solid-state composite electrolytes made of polymers and ceramics can balance the need for high ionic-conductivity and mechanical flexibility in constructing all-solid-state lithium batteries. Although the interface of solid composite electrolytes and Li-metal anodes have been well studied, the ionic conduction through the interface with porous electrodes has not received the same level of attention. In this study, we fabricated ion-conductors used as both flowable gel-like ionic fillers and stiff ion-conducting separators to address interfacial ionic conduction challenges with porous electrodes. A composite electrolyte made of Li6.4La3Zr1.4Ta0.6O12 (LLZTO) and a poly(ethylene oxide) (PEO)-lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) matrix was chosen as a model system to study interfacial ionic conduction properties. This solid composite electrolyte exhibits a room temperature ionic conductivity of 1.2×10-4 S cm-1. The bulk moduli of these ionic conductors were adjusted by varying polymer molecular weight, filler content, and salt concentration. In order to minimize the impact of porosity induced interfacial impedance on the overall cell performance, an ionic percolation network within the electrode pores was created using flowable ionic filler. We built symmetric cells that are made of cathodes or ionically percolated cathodes to determine the impact of having ionic fillers on the interfacial impedance of porous electrodes. In conclusion, ionic conductors filled solid-state battery cells with zero porosity promise a reduction in the interfacial impedance of the composite electrode.