Achieving Low-Energy-Barrier Ion Hopping in Adhesive Composite Polymer Electrolytes by Nanoabsorption
Xuewei He, Ang Ye, Xuewei Fu, Wei Yang, Yu Wang
Abstract
Adhesive polymer electrolytes are of great interest for next-generation high-energy-density solid-state batteries but their practical applications have been blocked by extremely low ionic conductivity that is fundamentally caused by a coupling transport mechanism. Here, to boost the ionic conductivity, we propose a decoupled low-energy-barrier ion-hopping mechanism that is realized by surface absorption from nanoparticles. To test this model, Al2O3 nanoparticles are composited with a fully amorphous and adhesive ultrahigh-molecular-weight poly(ethylene oxide) (UHMWPEO)–Li+ complex. It is found that the ion conductivity can be improved to 9.94 ± 1.57 × 10–5 S cm–1 at 20 °C, ca. about 20 times of the pure complex electrolyte. Meanwhile, the ion-hopping energy barrier is reduced by 67%, yielding a low activation energy of 0.25 eV. This phenomenon is further explained by the nanoabsorption effects on shrinking the free volume (the hopping distance) and stabilizing the hopping sites. Further, the strong nanoabsorption effects also notably improve the mechanical properties as well as the electrochemical stability of the resultant nanocomposite electrolyte. When the adhesive composite electrolyte is coated onto a commercial separator, it effectively improves the stability of Li metal and the cycling performance lasts for 2000 h before its failure, demonstrating the potential applications in Li–metal batteries.