Non‐Flammable and Highly Concentrated Carbonate Ester‐Free Electrolyte Solutions for 5 V‐Class Positive Electrodes in Lithium‐Ion Batteries
Takayuki Doi, Romain Jun Taccori, Ryo Fujii, Tsuyoshi Nagashima, Takatsugu Endo, Yoshifumi Kimura, Minoru Inaba
Abstract
Abstract Non‐flammable and highly concentrated electrolyte solutions were designed using tris(2,2,2‐trifluoroethyl) phosphate (TFEP) as a main solvent toward a radical improvement in the safety and energy density of lithium‐ion batteries. Unlike conventional carbonate ester‐based solutions, simple TFEP‐based electrolyte solutions were not intrinsically compatible with 5 V‐class LiNi 0.5 Mn 1.5 O 4 positive electrodes, even at high concentrations. Based on the degradation mechanism that was analyzed by Raman spectroscopy, scanning electron microscopy/energy dispersive X‐ray spectroscopy, and X‐ray photoelectron spectroscopy, a fluorinated diluent of methyl 3,3,3‐trifluoropropionate (FMP) was introduced to suppress the decomposition of LiBF 4 and TFEP at high potentials. A nearly saturated LiBF 4 /TFEP+FMP electrolyte solution with a specific composition improved the charge and discharge performance of a LiNi 0.5 Mn 1.5 O 4 electrode, and the solution structure was studied by pulsed‐field‐gradient NMR spectroscopy.