Three-dimensional heterogeneity in liquid electrolyte structures promotes Na ion transport and storage performance in Na-ion batteries

Abstract

Unlike solid materials, the molecular structure and chemical distribution in electrolyte solutions have been considered in isotropic states. Herein, we reveal controllable regulation of solution structures in electrolytes by manipulating solvent interactions for Na-ion batteries. Low-solvation fluorocarbons as diluents in concentrated phosphate electrolytes induce adjustable heterogeneity in electrolyte structures through variable intermolecular forces between high-solvation phosphate and diluents. An optimal trifluorotoluene (PhCF₃) diluent weakens the solvation strength around Na⁺ and spontaneously leads to a locally enlarged Na⁺ concentration and global 3D continuous Na⁺ transport path thanks to the appropriate electrolyte heterogeneity. Besides, strong correlations between the solvation structure and the Na⁺ storage performance and interphases are demonstrated. PhCF₃ diluted concentrated electrolyte enables superior operations of Na-ion batteries at both room temperature and a high temperature of 60 °C. A hard carbon anode exhibits a reversible capacity of 300 mA h g^-1 at 0.2C and excellent life over 1200 cycles without decay.