## 2 Topical Research Areas Related to Ionic Liquids and the Contribution of Spiroammonium Compounds
### Azoniaspiroalkanes with IL Properties Used as Electrolytes
Organic onium cation--5-azoniaspiro-[4.4]-nonane (AS 44), a non-aqueous electrolyte component, has become the subject of inventions [102; 103], with reference to a secondary magnesium battery that has a high theoretical capacitive density, long life, and high safety. Secondary magnesium batteries are expected to be introduced into practical use due to their superiority to secondary lithium batteries. A non-aqueous electrolyte consists of an ionic liquid in which the anion is bis((trifluoromethyl)sulfonyl)]methanide [N(SO\({}_{2}\)CF\({}_{3}\))\({}_{2}\)]\({}^{-}\), and the cation includes Mg\({}^{2+}\) and an organic onium cation--of 5-azoniaspiro-[4.4]-nonane (AS 44):  
Quaternary ammonium tetrafluoroborate (QA BF\({}_{4}\)) salts are highly soluble in non-aqueous solvents, conferring high conductivity [104]. Two series of tetrafluoroborates (C80, C6, and C60 and C8, C9, and C10) have been synthesized so that the cations of each series had almost the same molecular weight, with the number of carbon atoms being 6, 8, and 10; however, different structures were achieved in terms of whether it is cyclic or not (Figure 5) [105]. The experiment was performed using acetonitrile on carbon catalysts with a 40 \(\upmu\) thick cellulose separator that was placed between the two electrodesThe effect of the presence of a cyclic structure and its size on the conductivity of the electrolyte has been tested. Cyclic ions have a smaller effective radius than that of corresponding acyclic ions due to fewer degrees of conformational freedom, such as the rotational, bending, and stretching modes. This circumstance leads to the higher capacitances of the cyclic quaternary salts than that of those with their acyclic counterparts. The viscosity (and conductivity) versus the ion size relationship is linear for spiro salts. Thus, an increase in cation size results in higher viscosity and lower conductivity than those in the case of smaller cations. Electrolytes with high conductivity based on spiro-type quaternary ammonium salts, such as 1,1'-spirobipyrrolidinium tetrafluoroborate (SBP BF\({}_{4}\)) and 4-azoniaspiro-[4.4]-nonane tetrafluoroborate, are being widely investigated for applications in electric double-layer capacitors (EDLCs) [106]. Currently, lithium-ion batteries (LIBs) are the dominant power sources used in portable electronic devices. However, these batteries have problematic aspects in terms of use due to the fact that they are equipped with fluorinated lithium salts (e.g., LiPF\({}_{6}\)) and organic solvents. Lithium salts are quite expensive for synthesis and unsafe in the presence of moisture; organic solvents have high vapor pressure and are also flammable. Therefore, the design and development of more stable salts and electrolytes are highly desirable [107; 108]. In order to mitigate the challenges with the current fluorine-containing electrolytes, the synthesis and evaluation of a new class of fluorine-free lithium and sodium salts based on a pseudo-delocalized concept has been carried out. The representatives of azoniaspiro compounds in the \"spiro\" group are 2,4,8,10-tetraoxo-3,6,9-triazaspiro-[5.5]-undecan-6-ium-3,9-diide and (ethylsulfonyl)((1,1,3,3-tetraoxido-4H-1,3,2,5-dithiadiazol-5-ium-2-id-5-yl)methyl)sulfonyl)imide (Figure 6) [109].