Abstract
A novel dicationic room temperature ionic liquid, 1,1′-(5,14-dioxo-4,6,13,15-tetraazaoctadecane-1,18-diyl) bis(3-(sec-butyl)-1H-imidazol-3-ium) bis((trifluoromethyl)-sulfonyl) imide has been synthesized and fully characterized. Its thermal and electrochemical analyses along with transport properties have been studied. We propose it as a potential nominal additive to the commonly used conventional organic carbonate electrolyte mixture and study its adaptability in Lithium-ion batteries which are the prime power sources for ultraportable electronic devices. We have compared the performance characteristics of the full cells made without and with this ionic liquid. The cells comprise lithium nickel cobalt manganese oxide cathode, graphite anode and ethylene carbonate - dimethyl carbonate (1:1, v/v + LiPF6) mixture electrolyte with nominal amount of ionic liquid as additive. The major concern with conventional electrolytes such as degradation of the materials inside batteries has been addressed by this electrolyte additive. Additionally, this additive is safer at relatively higher temperature. In its presence, the overall battery life is enhanced and it shows good cycling performance and coulombic efficiency with better discharge capacities (22% higher) after 100 cycles. Even after the increase in current rate from 10 mA/g to 100 mA/g, the cell still retains around 73% of capacity.
Highlights
A novel dicationic room temperature ionic liquid, 1,1′-(5,14-dioxo-4,6,13,15-tetraazaoctadecane-1,18diyl) bis(3-(sec-butyl)-1H-imidazol-3-ium) bis((trifluoromethyl)-sulfonyl) imide has been synthesized and fully characterized
The commercial batteries available in the market are mainly fabricated with organic carbonates along with lithium hexafluorophosphate (LiPF6) as electrolytes[6,7,8], which are prone to ignition or even explosion when cells are damaged or exposed to high temperatures
In order to confirm the purity of synthesized ionic liquid (IL), 1H NMR, 13C NMR and Infrared Spectroscopy (IR) spectroscopy, ESI-mass spectrometry and elemental analyses were carried out
Summary
A novel dicationic room temperature ionic liquid, 1,1′-(5,14-dioxo-4,6,13,15-tetraazaoctadecane-1,18diyl) bis(3-(sec-butyl)-1H-imidazol-3-ium) bis((trifluoromethyl)-sulfonyl) imide has been synthesized and fully characterized. T.Yim et al.[35] elaborately discussed the advantage of room temperature ionic liquid based electrolyte as an alternative to the conventional carbonate based electrolyte in LIBs. Due to the favourable physicochemical and electrochemical properties of the imidazolium-based ionic liquids, they are attractive candidates as non-volatile, non-flammable, and high voltage electrolyte materials for lithium ion batteries[28,36,37] and are expected to enhance its safety performances considerably. A promising approach is demonstrated in this study by using ILs as a nominal additive to a conventional electrolyte consisting of ethylene carbonate and dimethyl carbonate (EC + DMC), leading to beneficial synergistic effects on the physicochemical properties of the resulting mixtures This approach has several techno-commercial benefits: (i) it enhances the cyclability of the cells, (ii) it improves long term capacity retention (iii) significant cost escalation can be avoided because of the nominal use of newly developed material and, (iv) the battery fabrication process will remain similar to the existing protocols. The synthetic protocol, physicochemical and electrochemical properties, the performance of IL and its role as an additive in EC + DMC electrolyte in LIBs are reported here
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