Polymer electrolytes are hailed as a possible means to mitigate these issues. Their lack of rigidity is advantageous in circumventing the denouement that arises from volumetric changes during ionic shuttle across the membrane; however, their ionic conductivities lag severely behind their liquid counterparts.
To ameliorate the ionic conductivities of these polymers, suitable filler materials are needed to appropriately limit the crystallinity of the host polymer and improve the ionic hopping during cycling. Plasticizers widen the amorphous regions where ionic conductivity takes place and more importantly lower the glass transition temperature of the polymer and its crystallinity to make the polymer more pliable and easier to process. Inorganic and organic filler are utilized to further widen the ionic pathways in the polymer structure as well as increase the mechanical stability of the membrane by providing structural reinforcement. Inorganic fillers can also contribute to the ionic conductivity by creating either Lewis acid or base sites which interact with ionic species and facilitate transport.
Poly (ethylene glycol) diacrylate (PEGDA) polymer membranes were synthesized using UV curing techniques. Succinonitrile (SCN) was incorporated as a plasticizer to enhance amorphous regions and reduce the glass transition temperature. Vanadium pentoxide (V₂O₅) was added as an inorganic filler to provide structural reinforcement and create Lewis acid/base sites for ionic transport. Additionally, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid was introduced to further improve ionic conductivity. The polymer films were cast and cured under controlled UV exposure conditions to ensure uniform cross-linking.
After curing, the polymer films were cut into electrodes and sandwiched between stainless steel electrodes to form blocker cells. EIS measurements were conducted using a frequency range of 1 MHz to 1 kHz. The resistance was determined from the intersection of the Warburg tail with the x-axis in the Nyquist plot.
Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were applied to investigate the electrochemical stability window of the membranes.
We find that the interplay of these fillers greatly enhances the ionic conductivity of the final formed membrane (5.24x10-4 S/cm) as well as its voltage stability window making it a suitable candidate for lithium-based batteries as a solid polymer electrolyte.