Abstract
Unlike conventional electrolytes, ionic liquid (IL)-based electrolytes offer higher thermal stability, acceptable ionic conductivity, and a higher electrochemical stability window (ESW), which are indispensable for the proper functioning of Li-ion batteries. In this study, fluorine-free electrolytes are prepared by mixing the lithium furan-2-carboxylate [Li(FuA)] salt with the tetra(n-butyl)phosphonium furan-2-carboxylate [(P4444)(FuA)] IL in different molar ratios. The anion of these electrolytes is produced from biomass and agricultural waste on a large scale and, therefore, this study is a step ahead toward the development of renewable electrolytes for batteries. The electrolytes are found to have Tonset higher than 568 K and acceptable ionic conductivities in a wide temperature range. The pulsed field gradient nuclear magnetic resonance (PFG-NMR) analysis has confirmed that the (FuA)− anion diffuses faster than the (P4444)+ cation in the neat (P4444)(FuA) IL; however, the anion diffusion becomes slower than cation diffusion by doping Li salt. The Li+ ion interacts strongly with the carboxylate functionality in the (FuA)− anion and diffuses slower than other ions over the whole studied temperature range. The interaction of the Li+ ion with the carboxylate group is also confirmed by 7Li NMR and Fourier transform infrared (FTIR) spectroscopy. The transference number of the Li+ ion is increased with increasing Li salt concentration. Linear sweep voltammetry (LSV) suggests lithium underpotential deposition and bulk reduction at temperatures above 313 K.
Highlights
The lithium-ion battery (LIB) marketplace is emerging at the fastest rate as batteries are identified as high-performance energy storage devices that can efficiently store and deliver energy on demand along with decreasing the carbon footprint of the transportation sector.[1]
The first descent in the curves represents the weight loss of up to 79% corresponding to the decomposition of the (P4444)+ cation in the ionic liquid (IL) and in the electrolytes, while the second descent represents the decomposition of the (FuA)− anion
The maximum rate of the weight loss of the neat IL and the electrolytes occurs in the temperature range of 588−593 K, which is associated with the degradation of cations
Summary
The lithium-ion battery (LIB) marketplace is emerging at the fastest rate as batteries are identified as high-performance energy storage devices that can efficiently store and deliver energy on demand along with decreasing the carbon footprint of the transportation sector.[1]. The heat generation and thermal runaway are serious issues, which adversely affect the performance of a battery but are connected to water and soil pollution and human health at the battery recycling stages.[10] The large fluorine contents and the flammable organic solvents need to be replaced with nonfluorinated and nonflammable organic electrolytes to improve the safety and performance of next-generation batteries In this regard, new salts were developed during the past few decades,[11−14] but the majority of them were unstable for thermal and electrochemical applications. There is an urge to develop safe electrolytes for LIB applications In this scenario, ILs, which are molten salts at room temperature, are nonflammable, and have high thermal stability, are emerging as promising substitutes for the volatile. The anodic and cathodic limits from LSVs were defined at a current density of 0.1 mA cm−2.29
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