Abstract
Ionic liquids (ILs) are used as electrolytes in high-performance lithium-ion batteries, which can effectively improve battery safety and energy storage capacity. All atom molecular dynamics simulation and experiment were combined to investigate the effect of the concentration of lithium salt on the performance of electrolytes of four IL solvents ([Cnmim][TFSI] and [Cnmim][FSI], n = 2, 4). The IL electrolytes exhibit higher density and viscosity; meanwhile, larger lithium ion transfer numbers as the concentration of LiTFSI increases. Furthermore, in order to explore the effect of the concentration of lithium salt on the ionic associations of Li+ and anion of IL, the microstructures of the lithium salt in various IL electrolytes at different concentrations were investigated. The structural analysis indicated that strong bidentate and monodentate coordination was found between Li+ and anion of all IL electrolytes. Both cis and trans isomerism of [FSI]− were observed in [FSI]−-type IL electrolyte systems. Furthermore, the existence of the ion cluster [Li[anion]x](x−1)− in IL electrolytes and the cluster became more closed and compact as the concentration of LiTFSI increases.
Highlights
With the popularity of personal portable electronic devices, new energy vehicles and renewable energy are developing rapidly
By comparing 2 mol/L lithium salt (LiTFSI) with pure organic solvents (DMC and DEC) and Ionic liquids (ILs) solvents ([Cnmim][BF4] and [Cnmim][TFSI] (n = 2, 4)), we found that IL electrolytes had higher conductivity than organic solvents at high concentration of Li salt; the dissolution of lithium bis(trifluoromethylsulfonyl) imide (LiTFSI) in the IL solvents was an anion-driven process (Tong et al, 2019)
ILs are used as electrolytes in energy storage devices due to their unique characteristics, thereby improving the safety and energy storage capacity of lithium ion batteries
Summary
With the popularity of personal portable electronic devices, new energy vehicles and renewable energy are developing rapidly. Lithium ion batteries have dominated the battery market since their successful commercialization in the early 1990s due to their high voltage, high specific energy, and long cycle life (Scrosati and Garche, 2010; Goodenough and Kim, 2011). The concern of the safety for lithium ion battery has been exposed and increased prominent, as it is difficult to meet the requirements of lightweight, high-capacity, long-life electronic equipment, electric vehicles, and other technologies. The development of a new generation of green battery systems with high performance and environmental protection has become a common challenge for the international community
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