Fig. 3: Systematic Investigation of Physicochemical and Electrochemical Property Alterations in SMTA Electrolyte.

a Optical photographs of SMT electrolyte after storage at 55 °C and –60 °C. ¹H NMR of long-stored SMT (b) and SMTA (c) electrolytes at 25 °C (two weeks) and 55 °C (two days). d Differential scanning calorimetry (DSC) heating curves of SMTA electrolyte. e The viscosity and ionic conductivity of SMTA electrolyte were measured at different temperatures from –60 °C to 25 °C. f The GCD curves of HC | |Na cells equipped with the SMTA electrolyte at 55 °C, 25 °C, 0 °C, −20 °C, −40 °C, −50 °C, and −60 °C. g The GCD curve of the HC | |Na cell with SMT and SMTA electrolytes at –50 °C. h Cycling performance of HC | |Na cells with SMT and SMTA electrolytes at 55 °C. i Cycling performance of HC | |Na cells with the SMTA electrolyte at 25 °C and −40 °C at a specific current of 100 mA g^-1. j The desolvation energy of THF, MeTHF in SMTA electrolyte at 55 °C and –40 °C (above). ΔE(-THF) represents the energy required to remove one THF molecule from each solvation structure, while ΔE(-MeTHF) indicates the energy for removing one MeTHF molecule. Arrhenius behaviour of the resistance corresponding to Na⁺ transport through SEI and charge-transfer processes (below). The semicircles in the mid-frequency and high-frequency regions represent charge transfer and ion transport properties in the SEI, respectively.