Weakening Ionic Coordination for High Ionic Conductivity Composite Solid Electrolytes

Abstract

The special chemistry of N,N-dimethylformamide (DMF)-solvated Li+ [Li(DMF)x]+ migration results in polyvinylidene fluoride (PVDF)-based solid polymer electrolytes exhibiting high ionic conductivities. Incorporating ceramic fillers into PVDF electrolytes can further enhance the ionic conductivities. However, there is limited understanding of the desolvation process of Li+ during its transport through the ceramic fillers. Herein, we reveal that this desolvation process exhibits a large energy barrier that hinders the Li+ transport. The introduction of poly(methylhydrosiloxane) (PMHS) can weaken the ion-solvent coordination, forming loosely complexed [Li(DMF)x]+ and reducing their desolvation energy. This promotes rapid ceramic-involved Li+ pathways, enabling the electrolyte with a high ambient ionic conductivity of 7.5 × 10-4 S cm-1. Moreover, the facile desolvation process can enhance the kinetics and reduce side reactions at the electrode/electrolyte interfaces. Therefore, solid-state Li-Li symmetric cells can operate for a record 11 800 h, and LiNi0.8Co0.1Mn0.1O2|Li solid-state batteries also demonstrated exceptional cycling stability for more than 2200 cycles at 2C.