SISGR: Linking Ion Solvation and Lithium Battery Electrolyte Properties

Trulove, Paul C.¹  Foley, Matthew P.¹ 

[1] U.S. Naval Academy, Annapolis, MD (United States)

关键词: Lithium ion;    lithium triflate;    ethylene carbonate;    gamma-butyrolactone;    propylene carbonate;   

DOI  :  10.2172/1068557
RP-ID  :  DE-USNA--01419
PID  :  OSTI ID: 1068557

美国|英语

来源: SciTech Connect

【 摘 要 】

The solvation and phase behavior of the model battery electrolyte salt lithium trifluoromethanesulfonate (LiCF₃SO₃) in commonly used organic solvents; ethylene carbonate (EC), gamma-butyrolactone (GBL), and propylene carbonate (PC) was explored. Data from differential scanning calorimetry (DSC), Raman spectroscopy, and X-ray diffraction were correlated to provide insight into the solvation states present within a sample mixture. Data from DSC analyses allowed the construction of phase diagrams for each solvent system. Raman spectroscopy enabled the determination of specific solvation states present within a solvent-salt mixture, and X-ray diffraction data provided exact information concerning the structure of a solvates that could be isolated Thermal analysis of the various solvent-salt mixtures revealed the phase behavior of the model electrolytes was strongly dependent on solvent symmetry. The point groups of the solvents were (in order from high to low symmetry): C2V for EC, CS for GBL, and C1 for PC(R). The low symmetry solvents exhibited a crystallinity gap that increased as solvent symmetry decreased; no gap was observed for EC-LiTf, while a crystallinity gap was observed spanning 0.15 to 0.3 mole fraction for GBL-LiTf, and 0.1 to 0.33 mole fraction for PC(R)-LiTf mixtures. Raman analysis demonstrated the dominance of aggregated species in almost all solvent compositions. The AGG and CIP solvates represent the majority of the species in solutions for the more concentrated mixtures, and only in very dilute compositions does the SSIP solvate exist in significant amounts. Thus, the poor charge transport characteristics of CIP and AGG account for the low conductivity and transport properties of LiTf and explain why is a poor choice as a source of Li⁺ ions in a Li-ion battery.