Concentrated Ionic‐Liquid‐Based Electrolytes for High‐Voltage Lithium Batteries with Improved Performance at Room Temperature

Abstract

Ionic liquids (ILs) have been widely explored as alternative electrolytes to combat the safety issues associated with conventional organic electrolytes. However, hindered by their relatively high viscosity, the electrochemical performances of IL‐based cells are generally assessed at medium‐to‐high temperature and limited cycling rate. A suitable combination of alkoxy‐functionalized cations with asymmetric imide anions can effectively lower the lattice energy and improve the fluidity of the IL material. The Li/Li1.2Ni0.2Mn0.6O2 cell employing N‐N‐diethyl‐N‐methyl‐N‐(2‐methoxyethyl)ammonium (fluorosulfonyl)(trifluoromethanesulfonyl)imide (DEMEFTFSI)‐based electrolyte delivered an initial capacity of 153 mAh g−1 within the voltage range of 2.5–4.6 V, with a capacity retention of 65.5 % after 500 cycles and stable coulombic efficiencies exceeding 99.5 %. Moreover, preliminary battery tests demonstrated that the drawbacks in terms of rate capability could be improved by using Li‐concentrated IL‐based electrolytes. The improved room‐temperature rate performance of these electrolytes was likely owing to the formation of Li+‐containing aggregate species, changing the concentration‐dependent Li‐ion transport mechanism.

Safe, Stable Cycling of Lithium Metal Batteries with Low‐Viscosity, Fire‐Retardant Locally Concentrated Ionic Liquid Electrolytes

“…Further, the activation energy for ion conduction ( E a ic , Figure 2c) can be deduced from Vogel–Tammann–Fulcher (VTF) analysis (Table S1, Supporting Information), indicating that LCIL exhibited a lower activation energy (5.3 kJ mol −1 ) than DIL and CIL (5.9 and 6.7 kJ mol −1 , respectively). These findings may be attributed to alterations in the conduction mechanism [ 6b,17 ] or nanoscale heterogeneity in the solution structure. [ 18 ]…”

UV-Cured Poly(Siloxane-Urethane)-Based Polymer Composite Materials for Lithium Ion Batteries—The Effect of Modification with Ionic Liquids

“…According to the generally accepted definition [28], ILs are organic-organic or organic-inorganic salts that are liquids at temperatures below 100 • C. ILs have been widely used, mainly as catalysts and solvents in the synthesis of organic compounds [29] and polymers [30], including in mixtures with supercritical CO 2 [31], vulcanization accelerators for rubber [32], and also as electrolytes [33][34][35][36][37][38], specifically for lithium batteries [39][40][41][42][43][44][45][46][47]. A comprehensive literature review concerning ILs in polymer systems was published [48], and the role of ILs in lithium ion batteries was explained in detail in another review [49].…”

Alkoxy-functionalized ionic liquid electrolytes: understanding ionic coordination of calcium ion speciation for the rational design of calcium electrolytes

“…27 The introduction of alkoxy group in the IL's cation structure is known to lower the lattice energy and reduce/ suppress the crystallization of neat ILs as well as IL-based solutions. 28 Indeed, the crystallization of the Pyr 1201 TFSI electrolytes is effectively suppressed while the solubility of Ca(TFSI) 2 is slightly increased to 5 mol%. In the thermograms of Pyr 1201 TFSI with and without Ca-salt ( Fig.…”

“…Substitution of the alkyl-functionalized pyrrolidinium cation with the alkoxyfunctionalized ammonium cation has been shown to reduce the lattice energy and suppress crystallization of the IL solution. Correspondingly, the crystals obtained from N 01 TFSI electrolyte are more fragile than those from [Pyr 1201 ] 2 [Ca(TFSI) 4 ], which makes it impossible to obtain a meaningful XRD analysis.Previous studies about Mg have demonstrated that the nature of the Mg 2+ -ion species is one of the keys to successful Mg deposition/dissolution in IL media 28. For IL-based electrolytes containing only TFSI À anion, Mg ions are typically found as Mg(TFSI) 3À 25,36.…”