Department of Physics

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Author: search.filters.author.Sivasubramanian, S.C.Subject: search.filters.subject.Ionic Liquid

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    Preparation and characterization of novel solid electrolytes based on [EMIM] BF4 and lithium nitrate confined silica gels
    (Elsevier, 2019-11) Sivasubramanian, S.C.; Dalvi, Anshuman
    Novel ionic liquid ([EMIM]BF4) and lithium nitrate confined silica gel composites have been prepared via hydrolytic sol-gel process and found to exhibit electrical conductivity up to 10−4 Ω−1cm−1 in the temperature range 150–300 °C. The composites are thermally stable at this temperature range and measurements are repeatable. Powder X-ray diffraction patterns suggest that the composites are amorphous in nature. FE-SEM (EDS elemental mapping) and DSC measurements further confirm IL confinement in the matrix. Electrical conductivity (150–300 °C) has been studied as a function of IL and Li+ ion content. The samples with no IL content are essentially electronic in nature. Addition of IL in small amounts (1 mol%) enhances the total conductivity at least by an order of magnitude. Further addition of salt (LiNO3) enhances ionic transport by orders of magnitude. The electronic conductivity and ionic mobility along with OCV measurements on cells of type Li/composite/LiCoO2 suggests facilitation of Li+ ion transport in presence of IL in small amount. However, further increasing the content of IL in the composition while keeping the salt ion concentration same, does not improve conductivity, rather reduces it. This complex behavior may be due to possibility of Li+ ions forming complex with IL anion and further investigations are required in this regard. Preliminary findings suggest that these materials have good potential for their applications in all-solid-state supercapacitors.
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    Solid-state supercapacitors using ionic liquid dispersed Li+-NASICONs as electrolytes
    (Elsevier, 2022-12) Dalvi, Anshuman; Sivasubramanian, S.C.
    Ceramic ionic conductors exhibit inadequate ionic conductivity for device applications. However, when added with a small amount of ionic liquid (IL), exhibit a substantial conductivity rise. This research demonstrates the use of such IL-ceramic composites, with IL content ≤ 13 wt%, for capacitor applications. These supercapacitors are designed using IL dispersed Li+ ion conducting fast ionic ceramics as an electrolyte, viz; LiTi2(PO4)3 (LTP) and Li1.3Al0.3Ti1.7(PO4)3 (LATP). The cells are fabricated in 2032-coin cells using these composites and activated charcoal coated on the copper foil as the electrode. A typical supercapacitor containing LATP-13 wt% EMIM BF4 as electrolyte at ∼ 35 °C exhibits high specific capacitance of ∼181 F-g−1, specific energy ∼ 6.1 Wh-kg−1, and power of ∼140 W-kg−1 at 0.65 mA/cm2 (0.56 A-g−1) and 1 V. Importantly, the choice of IL (size of the ions), as well as the composition of fast ionic ceramic, influences the device performance. For a discharge at 0.56 A-g−1, a supercapacitor with this composite electrolyte exhibit stability at least up to ∼ 13,000 charge/discharge cycles with a fairly stable coulomb efficiency of ∼ 99%. At ∼ 100 °C these cells exhibit a maximum specific capacitance up to ∼ 600 F-g−1. These supercapacitors exhibit appreciable cycling performance at 30–100 °C. At higher discharge currents (≥ 0.34 A-g−1) electric double layer capacitor behavior is witnessed. A stack of two cells is able to glow a white light-emitting diode (3 V) successfully for ∼30 min.