ORCID Profile
0000-0001-5962-5185
Current Organisation
Deakin University
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Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D1EE02929K
Abstract: A non-flammable ionic liquid-ether based hybrid electrolyte shows a robust Li deposition morphology and a very stable cycling of NMC|Li metal cell facilitated by a beneficial interphase formation at the anode surface.
Publisher: The Electrochemical Society
Date: 30-06-2019
DOI: 10.1149/MA2019-04/10/0491
Abstract: Ionic liquids (ILs) are liquids at room temperature which consist of a large variety of cation and anion. The dipolar and van der waals interactions between the cationic and anionic species govern the physical properties of ILs and their applications. Since last few decades, the potential application of ILs in lithium based battery has increased rapidly as some of the ILs offer wide electrochemical stability window, lithium redox compatibility, fast ionic diffusivity and low flammability [1]. Among other Li based battery systems, lithium sulphur (Li-S) battery is one of the most promising candidates for the next generation high energy density battery with high theoretical capacity of 1675 mAh/g [2]. However, the electrochemical redox reaction in Li-S battery is a complex phenomenon. The reduction of elemental sulphur (S 8 ) proceeds via the formation of various intermediate (S n 2- , n ) polysulphides before reaching the final product S 2- . The stability of these polysulphides are highly dependent on the electrolyte medium [3]. Hence the selection of appropriate electrolyte components play an important role in the overall performance of Li-S battery. The electrochemistry of sulphur-polysulphide system has been well studied in organic solvents, however very less literature is reported on the sulphur reduction mechanism in ILs. In this study, we have investigated the sulphur reduction and speciation in three ionic liquids: N -methyl- N -propylpyrrolidinium bis(fluorosulphonyl)imide (Pyr13 FSI), N -methyl- N -propylpyrrolidinium bis(trifluoromethanesulphonyl)imide (Pyr13 TFSI) , trimethyl(isobutyl)phosphonium bis(fluorosulfonyl)imide (P111i4 FSI). The electrochemical redox reactions of sulphur in these ILs have been studied through cyclic voltammetry (CV) and the polysulphide intermediates are simultaneously investigated by in-situ UV Vis method. These studies showed two reductions and one oxidation peak and the plausible pathways have also been identified. The redox behaviour of sulphur speciation in P111i4 FSI is observed to be very similar to Pyr13 TFSI where glassy carbon is used as working electrode in a three electrode electrochemical cell. On the other hand, the redox process of Pyr13 FSI is found to be distinctively different than Pyr13 TFSI. From the in operando UV-vis study, it is found that Pyr13 FSI electrolyte is responsible for the formation of S3 . - radical anion, whereas the Pyr13 TFSI and P111i4FSI electrolyte do not assist the radical formation during the reduction process. Additionally it can also be stated that, in case of P111i4 FSI, the polysulphides are stabilised by small phosphonium cation which protects the FSI anion from the nucleophilic attack of polysulphides, resulting in the stable sulphur redox cycling in P111i4FSI. Thus, based on molecular reactivity, CV and in-situ UV-vis, we propose that a novel phosphonium cation based ionic liquid (P111i4 FSI) is capable of using in Li-S battery. Therefore, this study brings forward a new concept that both of the cation and anion of an IL cumulatively affect the redox behaviour and sulphur speciation in Li-S battery systems. [1] Hallett, J. P. Welton, T., Room-Temperature Ionic Liquids: Solvents for Synthesis and Catalysis. 2. Chemical Reviews 2011, 111 (5), 3508-3576. [2] Ji, X. Nazar, L. F., Advances in Li-S batteries. Journal of Materials Chemistry 2010, 20 (44), 9821-9826. [3] Zhang, S. S., Liquid electrolyte lithium/sulfur battery: Fundamental chemistry, problems, and solutions. Journal of Power Sources 2013, 231 (Supplement C), 153-162.
Publisher: American Chemical Society (ACS)
Date: 06-06-2018
Publisher: American Chemical Society (ACS)
Date: 02-07-2020
DOI: 10.26434/CHEMRXIV.12588059.V1
Abstract: We explore a novel ether aided superconcentrated ionic liquid electrolyte a combination of ionic liquid, N -propyl- N -methylpyrrolidinium bis(fluorosulfonyl)imide (C 3 mpyrFSI) and ether solvent, 1,2 dimethoxy ethane (DME) with 3.2 mol/kg LiFSI salt, which offers an alternative ion-transport mechanism and improves the overall fluidity of the electrolyte. The molecular dynamics (MD) study reveals that the coordination environment of lithium in the ether aided ionic liquid system offers a coexistence of both the ether DME and FSI anion simultaneously and the absence of ‘free’, uncoordinated DME solvent. These structures lead to very fast kinetics and improved current density for lithium deposition-dissolution processes. Hence the electrolyte is used in a lithium metal battery against a high mass loading (~12 mg/cm 2 ) LFP cathode which was cycled at a relatively high current rate of 1mA/cm 2 for 350 cycles without capacity fading and offered an overall coulombic efficiency of .8 %. Additionally, the rate performance demonstrated that this electrolyte is capable of passing current density as high as 7mA/cm 2 without any electrolytic decomposition and offers a superior capacity retention. We have also demonstrated an ‘anode free’ LFP-Cu cell which was cycled over 50 cycles and achieved an average coulombic efficiency of 98.74%. The coordination chemistry and (electro)chemical understanding as well as the excellent cycling stability collectively leads toward a breakthrough in realizing the practical applicability of this ether aided ionic liquid electrolytes in lithium metal battery applications, while delivering high energy density in a prototype cell.
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0TA06344D
Abstract: We explore a superconcentrated electrolyte comprising N -propyl- N -methylpyrrolidinium bis(fluorosulfonyl)imide, 1,2 dimethoxyethane and 3.2 mol kg −1 LiFSI. It offers an alternative ion-transport mechanism, improved fluidity and ultra-stable Li metal battery performance.
Publisher: American Chemical Society (ACS)
Date: 16-06-2021
Publisher: The Electrochemical Society
Date: 02-2019
Abstract: The depletion of fossil fuel and strict environmental regulation on carbon footprints has prompted a greater reliability on sustainable energy sources. Batteries represent an important energy storage option due to their wide range of applicability and portability, however, for certain applications such as transportation, a higher energy density battery is required. Beyond the conventional Li-ion battery system, current research is focusing on next-generation cost effective devices. Amongst them, the Li-S battery technology is very promising due to its high theoretical capacity and energy density [1]. However, the chemistry involved in the Li-S battery is a complex process with multiple consecutive electrochemical reactions. Despite having many advantages, its application is still limited by several issues, e.g. , the dissolution and diffusion of intermediate polysulphides, unstable plating and stripping of Li metal, both resulting in rapid capacity fading [2]. Previously, we reported the application of a novel electrolyte system composed of N -propyl- N -methylpyrrolidinium bis(fluorosulfonyl)imide, C 3 mpyrFSI, ionic liquid (IL) and 1,2 dimethoxyethane (DME) in the presence of varying saturated lithium bis(fluorosulfonyl)imide, LiFSI which predominantly suppressed the polysulphide dissolution and diffusion while showing improved lithium plating and stripping behavior [3]. In order to expand our understanding on the role of DME and the lithium salt concentration in this work, we have considered a similar ionic liquid based electrolyte system but at a constant concentration of LiFSI salt. The ionic interactions among different species of the electrolyte system have been extensively studied by nuclear magnetic resonance (NMR) spectroscopy using 1 D chemical shift, PFG-NMR and Heteronuclear Overhauser Effect SpectroscopY (HOESY) measurements. We found that, when increasing the DME concentration in the system, a strong association of Li + cation with the DME occurs due to the electronegative oxygen atoms present in the DME molecules which leads to strong coordination. This leads to a change of the chemical shift of 7 Li nuclei due to them being increasingly de-shielded. Interestingly, we found that the diffusivity of both Li + and DME species are very similar, which also confirms that a Li-DME complex is present with FSI anion associated in the next coordination sphere to counterbalance the positively charged Li complex. MD simulations are underway to better elucidate the molecular shell structure of the system. We have also carried out electrochemical characterizations of these hybrid electrolytes to determine their potential applicability in a lithium sulphur battery. It was apparent using cyclic voltammogram (CV) performed in a three electrode set-up, that an increasing amount of DME increases the ionic conductivity but decreases the lithium plating-stripping efficiency. A coin-cell study of Li/Li symmetrical cycling showed an excellent plating-stripping behaviour for 70%IL-30%DME composition. We have carried out a full cell cycling against sulphur cathode and the optimised electrolyte composition obtained a promising first discharge capacity of 1100mAh/g. Additionally, we have investigated the sulphur speciation in the presence of this ionic liquid in a three-electrode system where platinum mesh has been used as working electrode coupled with in-situ UV-vis spectroscopy. Finally, a time dependent bulk electrolysis study revealed the plausible intermediates formed during the charge-discharge cycle of sulphur redox reaction. From these studies it appears that the composition of this novel hybrid electrolyte system can be tuned to provide a system with improved transport, electrochemical and sulphur speciation properties which lend themselves to a higher performance, next generation lithium sulphur battery technology. References: [1] Ji, X. Nazar, L. F., Advances in Li-S batteries. Journal of Materials Chemistry 2010, 20 (44), 9821-9826. [2] Scheers, J. Fantini, S. Johansson, P., A review of electrolytes for lithium–sulphur batteries.Journal of Power Sources 2014, 255, 204-218. [3] Pal, U. Forsyth, M Improved Li-Ion Transport by DME Chelation in a Novel Ionic Liquid Based Hybrid Electrolyte for Li-S Battery Application. The Journal of Physical Chemistry C, 122 (2018) 14373-14382. Figure 1
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D0CC06184K
Abstract: Solid-state 1 H– 14 N OT HMQC, 11 B MQMAS and 1 H– 11 B HETCOR NMR experiments are used to explore the role of homopolar B–B interaction in the thermal dehydrogenation of pure and supported ammonia borane, for it's potential hydrogen storage applications.
No related grants have been discovered for Urbi Pal.