Study of the structure and segmental dynamics of solid-polymer-based composite cathode*

This work examines the structure and segmental dynamics of a model polymer electrolyte in a polymer-based composite cathode consisting of LiFePO4 (LFP), carbon and poly(ethylene oxide) (PEO) with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). By using small angle neutron scattering (SANS) and quasi-elastic neutron scattering (QENS), it is discovered that that a strong interaction between LFP and PEO chains causes the segmental mobility of PEO to decrease by 70% and the Li+ 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. More future effort needs to focus on redesigning the polymer cathode.