TY - JOUR
T1 - Recent strategies for improving the performance of ionic liquids as battery electrolytes
AU - Roy, Binayak
AU - Pal, Urbi
AU - Kar, Mega
AU - MacFarlane, Douglas R.
N1 - Funding Information:
The optimal performance of a conventional organic solvent-based electrolyte often appears at around 1 mol L−1 (or 1 M) concentration of the metal salt, since above 1 M, the metal ion–solvent co-ordination increases their mutual coupling, thereby increasing the viscosity and decreasing the charge transport properties [23]. However, the extent and nature of the co-ordination of metal ions in IL electrolytes change at higher salt concentrations where the solvent becomes a limited component [24]. The solubility of metal salts in ILs has been reported to vary depending on their chemical structures; however, a concentration of ∼3.2–3.8 mol kg−1 (m) or ∼50 mol% has often elicited the best battery performance [6,23, 25–27]. Yoon et al. have reported that a 3.2 m LiFSI in N-propyl-N-methyl pyrrolidinium bis(fluorosulfonyl)imide (or [C3mpyr][FSI]) electrolyte significantly improves Li metal battery cycling, compared to both the lower concentration IL electrolytes and conventional organic solvent electrolytes [6]. Higher ionic dissociation between Li+ and [FSI−] ions and the preferential formation of the cis-conformer of the [FSI−] species at high salt concentration are thought to be responsible for this improvement, as indicated by physical and spectroscopic analyses [7]. Tong et al. have also reached a similar conclusion through their RDF analysis and further added that the co-ordination between Li+ and the cis-conformer of [FSI−] is more monodentate in nature at high salt concentration [28]. Further, MD simulation work by Chen and Forsyth [29] has demonstrated that at a high concentration of the Li salt (50 mol%) in IL electrolyte, the diffusion of small metal ion-anion clusters is more facile than the larger IL cation–anion clusters. These features together improve the Li+ transference number and thereby assist the Li+ transport through the bulk of the HCIL electrolyte. This was also supported in a recent study by Heist and Lee, who attributed the stable performance of 3.6 m LiFSI in [C3mpyr][FSI] HCIL electrolyte in a high voltage (4.3 V) Li metal battery to its high Li transference number, despite showing low ionic conductivity [25].The authors acknowledge the Australian Research Council funded StorEnergy Industrial Transformation Training Centre (IC180100049) for their support. The authors are also thankful to Calix Ltd. for their support.
Funding Information:
The authors acknowledge the Australian Research Council funded StorEnergy Industrial Transformation Training Centre ( IC180100049 ) for their support. The authors are also thankful to Calix Ltd. for their support.
Publisher Copyright:
© 2022 Elsevier B.V.
PY - 2022/10
Y1 - 2022/10
N2 - Ionic liquids (ILs) are widely known for their intriguing properties, such as low flammability, high electrochemical stability, etc., and therefore are considered as promising alternatives to conventional organic solvent-based battery electrolytes. Yet, IL-based electrolytes have rarely been used for practical battery applications, mostly due to their high viscosity and limited transport properties. Recent research efforts attempt to overcome these drawbacks by increasing the salt concentration in electrolytes and exploring the addition of solvents in hybrid ILs, as well as designing solvate IL electrolytes. This review aims to briefly discuss these recent strategies adopted with regard to Li-based and other advanced battery systems. This work also outlines the design of novel ILs where the tuneable chemistry of ILs can play a role in providing a pathway to battery applications.
AB - Ionic liquids (ILs) are widely known for their intriguing properties, such as low flammability, high electrochemical stability, etc., and therefore are considered as promising alternatives to conventional organic solvent-based battery electrolytes. Yet, IL-based electrolytes have rarely been used for practical battery applications, mostly due to their high viscosity and limited transport properties. Recent research efforts attempt to overcome these drawbacks by increasing the salt concentration in electrolytes and exploring the addition of solvents in hybrid ILs, as well as designing solvate IL electrolytes. This review aims to briefly discuss these recent strategies adopted with regard to Li-based and other advanced battery systems. This work also outlines the design of novel ILs where the tuneable chemistry of ILs can play a role in providing a pathway to battery applications.
KW - Ionic Liquid
KW - lithium battery
KW - electrolytes
KW - high voltage electrolytes
KW - Sodium Battery
KW - solvate ionic liquid
KW - hybrid ionic liquids
KW - Circular economy
UR - http://www.scopus.com/inward/record.url?scp=85138025039&partnerID=8YFLogxK
U2 - 10.1016/j.cogsc.2022.100676
DO - 10.1016/j.cogsc.2022.100676
M3 - Review Article
AN - SCOPUS:85138025039
SN - 2452-2236
VL - 37
JO - Current Opinion in Green and Sustainable Chemistry
JF - Current Opinion in Green and Sustainable Chemistry
M1 - 100676
ER -
