Multifunctional polymer electrolyte networks for energy harvesting and storage

A novel polymer electrolyte membrane (PEM) was developed based on poly(ethylene imine) (PEI)-co-polyethylene glycol diglycidyl ether (PEGDGE) network, containing lithium tri(fluoromethane sulphonyl) imide (LiTFSI) salt and succinonitrile (SCN) plasticizer. The polymer electrolyte multifunctional-networks have numerous advantages by virtue of the ion-dipole complexation facilitating facile ion conduction, multi-hydrogen bonding for self-healing to prevent electrode cracking, and covalently bonded networks to afford mechanical support. The tensile strength, modulus, and elongation-to-break of the PEI-co-PEGDGE/SCN/LiTFSI PEM films are all high, suggestive of highly flexible and stretchable nature. A wide electrochemical stability window of -0.5 ~ 5.1 V was achieved. In the symmetric Li/PEM/Li cell tests, dendrite formation of lithium crystal was discerned after cycling for 720 h, which motivates us to investigate the mechanism of Li⁺ dendritic growth through the solid PEM network and develop strategy for preventing such dendritic growth during charge/discharge cycling. The same polymer network showed mechanoelectrical response to bending, exhibiting a flexoelectric coefficient of ~190 μC/m due to polarization/depolarization of oppositely charge dipoles, and dissociated ions.