Abstract
Electrolytes play an integral role in the successful operation of any battery chemistry. The reemergence of the sodium-ion battery (SIB) chemistry has therefore rejuvenated the search for optimized SIB salts and solvents. Recent experiments have found that 1 M NaPF 6 in ethylene carbonate (EC) and propylene carbonate (PC), EC 0.5 : PC 0.5 (w/w) is the best binary electrolyte for SIBs. However, mathematical models, to elucidate these experimental findings, have so far been lacking. Furthermore, no attempts to understand the effect of EC composition on the conductivity and electrolyte stability have been performed. Herein, the viscosity and conductivity profiles of NaPF 6 in EC 0.5 : PC 0.5 electrolyte are unraveled, using experimental and modeling approaches at different temperatures and salt concentrations. The viscosity is measured in a double-wall Couette cell and for the first time, the ionic conductivity is determined using two Pt blocking electrodes in a PAT-Cell electrochemical setup. Modeling is performed using the Advanced Electrolyte Model (AEM), a statistical mechanics software. It is shown that the conductivity and viscosity relationship follows a simple Stokes' law even at a low temperatures and high concentrations. In addition, the stability of binary and ternary electrolytes on hard carbon is shown to correlate with the preferential ion solvation of EC. • Electrolyte conductivity and viscosity profiles of the NaPF 6 in EC and PC. • Conductivity and viscosity results over a wide concentration and temperature range. • The Advanced Electrolyte Model accurately predicts the experimental results. • NaPF 6 -based have higher conductivity compared to LiPF 6 -based electrolytes. • The cationic preferential ion solvation of EC correlates with electrode stability.
Highlights
Over the last decade, efforts to develop and commercialize sodiumion batteries (SIBs) have been propelled by the supply shortage risk of lithium-ion battery (LIB) components and the need to avert overreliance on LIBs in emerging, large scale applications [1]
Recent experiments have found that 1 M NaPF6 in ethylene carbonate (EC) and propylene carbonate (PC), EC0.5 : PC0.5 (w/w) is the best binary electrolyte for sodium-ion battery (SIB)
1 M NaClO4 salt was selected from the Advanced Electrolyte Model (AEM) library, in order to match the conditions in the respective literature studies
Summary
Efforts to develop and commercialize sodiumion batteries (SIBs) have been propelled by the supply shortage risk of lithium-ion battery (LIB) components and the need to avert overreliance on LIBs in emerging, large scale applications [1]. In the aftermath of these achievements, SIBs have emerged as the most prominent "post lithium" energy storage technology, with the potential to complement and match the perfor mances of LIBs in electric vehicles and grid energy storage applications In this battery chemistry transition endeavor, it is important to optimize SIB electrolytes and to elucidate their properties at different. Based on the experimental and AEM results, it is shown that the conductivity and viscosity relation ship for the EC0.5 : PC0.5 electrolyte, follows a simple Stokes’ law This demonstrates that ion pairing effects in the liquid organic electrolyte remain low over the concentration and temperature range studied and validates the use of the dilute solution theory in electrochemical models of this SIB electrolyte. These results encourage the explora tion of highly concentrated SIB electrolytes, which have improved safety and charge transfer kinetics [18,19]
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