ABSTRACT
Portable consumer electronics, spanning from wristwatches, mobile phones, laptops, and cameras, to electric vehicles and stationary power supply, are turning out to be an everyday necessity, demanding superior energy storage devices with improved safety [1, 2]. Among the different energy storage devices, batteries and supercapacitors (SCs) have been the most promising candidates in the arena [3]. The wide 74combination of electrodes and electrolytes has enabled the tailored use of these energy storage devices in extensive applications. However, heavy-duty applications such as electric vehicles or batteries used in abusive environments, such as petroleum mines, demand high tolerance of temperature and pressure [4, 5]. For the development of batteries or SCs with improved safety, the electrolyte plays a major role, unlike other device components, such as cathode, anode, or packaging materials. The conventional batteries had been using single-phase electrolytes (liquid electrolytes prepared by dissolving a suitable lithium salt in organic aprotic solvents, e.g., 1 M lithium hexafluorophosphate ( LiPF6 ) in ethylene carbonate (EC)/dimethyl carbonate (DMC), or all-solid-state electrolyte prepared by mixing solid-state matrix with a lithium salt, e.g.. poly(ethylene oxide) (PEO) mixed with lithium perchlorate ( LiPF6 ) along with a polymeric separator (Celgard®), which have higher ionic conductivity, but shows severe safety issues, even at room temperature applications, due to the low boiling point of the aprotic solvents, such as ethylene carbonate (EC), dimethyl carbonate (DMC), or propylene carbonate (PC). On that account, the development of electrolytes for high temperature applications remains a great challenge. For high temperature applications, conventional battery electrodes (carbon or metal oxide-based electrodes) are employable, but an electrolyte alternative was little known. Molten salt electrolytes came as a temporary solution, but it demanded higher operating temperatures to ensure the best conductivity properties. Solid-state electrolytes based on polymeric materials and lithium ion (Li-ion) conducting ceramic materials such as lithium superionic conductor (LISICON) and sodium superionic conductor (NASICON) were studied; however, they possessed poor ionic conductivity and pro-cessability, but they were safer. Ergo, there was a need to bring the safety offered by solid electrolytes and the superior conductivity offered by the liquid electrolytes into a single frame covering a wide range of operating temperatures [6-10].
