Improvement of Electrochemical Stability Using the Eutectic Composition of a Ternary Molten Salt System for Highly Concentrated Electrolytes for Na-Ion Batteries
Jinkwang Hwang, Ashvini Nair Sivasengaran, Huan Yang, Hiroki Yamamoto, Takashi Takeuchi, Kazuhiko Matsumoto, Rika Hagiwara
Abstract
The increase in the concentration of electrolytes for secondary batteries has significant advantages in terms of physicochemical and electrochemical performance. This study aims to explore a highly concentrated electrolyte for Na-ion batteries using a ternary salt system. The eutectic composition of the Na[N(SO2F)2]–Na[N(SO2F)(SO2CF3)]–Na[SO3CF3] ternary molten salt system increases solubility into an organic solvent, enabling the use of highly concentrated electrolytes for Na-ion batteries. The ternary salt system achieved concentrations of 5.0 m (m = mol kg–1) with propylene carbonate (PC), 2.9 m with dimethoxyethane, 2.0 m with ethylene carbonate/dimethyl carbonate, and 3.9 m with ethylene carbonate/diethyl carbonate. The highly concentrated electrolyte of 5.0 m in PC suppressed Al corrosion and exhibited better oxidative stability. Stable electrochemical performance using hard carbon/NaCrO2 in the full-cell configuration introduces a new strategy to explore highly concentrated electrolytes for secondary batteries.