Improving the Ion Conductivity and Mechanical Performance of Solid Polymer Electrolytes for Energy Storage Safety

Abstract

Lithium-ion batteries have been developed for the high energy efficiency of lithium-ion for application of a wide range of energy storage systems such as portable electronic devices and electric vehicles. However, conventional lithium-ion batteries based on liquid electrolytes are susceptible to external shocks, and the volatility and flammability of the electrolytes, as well as the risk of fire and explosion caused by them, have raised the need for a new type of battery. Solid polymer electrolytes (SPEs) have low volatility, good mechanical performances and electrochemical stability, so solid polymer electrolytes can be used as an alternative to liquid-based electrolytes. However, SPEs have a relatively poor ionic conductivity. In the current study, therefore, several types of SPEs were thoroughly studied in order to overcome the low ionic conductivity while maintain the superior mechanical advantages. Firstly, poly(vinylidene fluoride) (PVDF)-based SPEs were prepared by incorporating two different types of electrolytes to investigate the effect of the lithium salt type on the ionic conductivity. Secondly, PVDF/cellulose nanocrystal (CNC) nanocomposite films were prepared and the lithium salt-containing PVDF/CNC nanocomposite polymer electrolytes were characterized. Interestingly, the incorporation of CNC simultaneously improved the ionic conducting and mechanical performances. Lastly, a bicontinuous SPEs containing polyacrylonitrile (PAN) membrane and an ionic liquid were prepared with different molarities of the lithium salt. Porous PAN membrane was fabricated through a thermally induced phase separation method. Their morphology and ionic conductivity were characterized and then the electrochemical properties of the gel electrolyte-based solid-state supercapacitor were evaluated.