Safety electrochemical stability

The general capacitance of a capacitor is determined by the voltage range, in which it is operated. Furthermore, the voltage range depends on the electrochemical stability of the electrolyte. Because some ILs are known to be electrochemically stable toward oxidation and reduction processes, they become - next to the safety issue - also in terms of capacity very interesting candidates for this appHcation. 

Inorganic solid lithium ion conductors provide advantages compared with liquid electrolytes, such as safety and durability due to their mechanical, thermal, and electrochemical stabilities. They were usually synthesized via glass material conventional methods, but in recent years the sol-gel method was used. 

To resolve the problems associated with safety, thermal and electrochemical stability and conductivity, new syntheses of new electrolytes are the subject of new and important studies. Not withstanding the importance of the methide salt for which commercial availabhity is expected shortly, a number of important new developments are worth highhghting. Lithium bis(perfluoro-ethyl-sulfonyl)imide, liNCSOzCzFjjz or IJBETI, is very similar to that for the imide salt as it is stable up to 330°C [26]. hi addition to its high thermal stabhity, the LiBElT salt was also shown to be unreactive towards water [27]. The studies by Barthel et al. on chelatoborates [32] such as bis[2,3-pyridinediolato(2-)-0,0"]borate are of special interest as are studies on new methide salts such as Li[C2(S02CF3)4(S204C3F6)] [32]. 

Liquid organic solutions High conductivity over a wide temperature range. Liquid state. Narrow electrochemical stability window. Safety. ... 

In the drive towards expanding the range of useful ionic liquids (ILs), with suitably low viscosities, sufficient stability, and conductivity for electrochemical uses, phosphonium-based ionic liquids (PILs) are exceptionally promising compounds. Due to the high thermal and electrochemical stabilities of PILs compared to ammonium-based ILs (allq l-ammonium, imidazolium, pyridinium, pyrrolidinium, and piperidinium compounds), phosphonium salts have been especially considered for applications as electrolytes. Their properties (both thermal and electrochemical stabilities) are in fact crucial to improve safety, durability, power and energy densities of electrochemical devices such as electric double layer capacitors. 

Catalytic oxidation reactions in ionic liquids have been investigated only very recently. This is somewhat surprising in view of the well loiown oxidation stability of ionic liquids, from electrochemical studies [11], and the great commercial importance of oxidation reactions. Moreover, for oxidation reactions with oxygen, the nonvolatile nature of the ionic liquid is of real advantage for the safety of the reaction. While the application of volatile organic solvents may be restricted by the formation of explosive mixtures in the gas phase, this problem does not arise if a nonvolatile ionic liquid is used as the solvent. 

In addition, the use of ionic liquids is often prompted by safety and environmental considerations, where their negligible volatility and nonflammability makes them ideal replacements for more toxic molecular solvents and, importantly, overcomes the problem of solvent evaporation that exists with the long-term use of volatile solvents in electrochemical applications. The wide liquid range and good thermal stability are also extremely advantageous for device applications. 

---