Coupling Super-Delocalized Sulfonimide Anions with Inorganic Nanofillers for Better Composite Polymer Electrolytes: (I) Thermal and Transport Properties

Composite polymer electrolytes (CPEs), harmonizing the advantageous features of organic and inorganic components, appear to be a tantalizing solution to enhance inherent safety and energy density of today's rechargeable lithium batteries. In light of the significant impact of salt anions on electrolyte properties, we herein delve into a family of CPEs based on a super-delocalized sulfonimide anion (i.e., sTFSI(-)) and inorganic nanofillers (i.e., alumina), to provide more precise molecular design and property turning of solid-state electrolytes and their batteries. The fundamental properties of sTFSI-based CPEs are systematically investigated and compared with those based on classical bis(trifluoromethanesulfonyl)imide anion (i.e., TFSI-), enlisting surface morphology, phase transition, and ion transport, etc. Our results show that the content of nanosized Al2O3 filler serves as a critical factor affecting the mechanical properties and crystallization behavior of the resulting CPEs. The replacement of TFSI- with sTFSI(-) anion enables a higher portion of nanosized Al2O3 filler (>10 wt%) in the resulting CPEs, at only a minor expense of the ionic conductivity. This work unveils significant synergy between salt anions and inorganic fillers in modulating fundamental properties of polymer electrolytes, offering critical insights into the performance enhancement of the polymer-based solid-state batteries.