(Invited) Ion Transport and Interface Resistance in Polymer-Based Composite Electrolytes and Composite Cathode

Abstract

Solid-state electrolytes are promising to enable the next generation batteries with higher energy density and improved safety. However, each major class of solid electrolytes has intrinsic weaknesses. By combining different classes of solid electrolytes, such as a polymer electrolyte and an oxide ceramic electrolyte, one can potentially overcome the intrinsic weaknesses of each component and develop a composite electrolyte to achieve high ionic conductivity, good mechanical properties, good chemical stability, and adhesion with the electrodes.In this presentation, we show that the interfacial resistance strongly affects the ionic conductivity of polymer/oxide ceramic composite electrolytes, in both the ceramic-in-polymer design where ceramic particles are dispersed within the polymer electrolyte matrix as well as the polymer-in-ceramic design where a three dimensionally interconnected ceramic scaffold is developed. The quantification of the interfacial resistance, the origin of this resistance, as well as the strategies to minimize it are discussed.In a second case, we examine the effect of interfaces on ion transport in a polymer based composite cathode consisting of LiFePO4 (LFP), carbon and poly(ethylene oxide) (PEO) with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The structure and dynamics of PEO and lithium ion mobility are studied by small angle neutron scattering and quasi-elastic neutron scattering. The results show that Li ion mobility in PEO/LiTFSI in the composite cathode is only 30% of the bulk electrolyte. This suggests a key bottleneck that limits the rate performance of polymer-based solid-state batteries originates from the sluggish ion transport in the polymer electrolyte confined in the cathode.