Electrochemical stability of non-aqueous electrolytes for sodium-ion batteries and their compatibility with Na_0.7CoO₂

Abstract

The present study compares the physico-chemical properties of non-aqueous liquid electrolytes based on NaPF6, NaClO4 and NaCF3SO3 salts in the binary mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC). The ionic conductivity of the electrolytes is determined as a function of salt concentration and temperature. It is found that the electrolytes containing NaClO4 and NaPF6 exhibit ionic conductivities ranging from 5 mS cm(-1) to 7 mS cm(-1) at ambient temperature. The electrochemical stability window of the different electrolytes is studied by linear sweep voltammetry (LSV) and cyclic voltammetry (CV) measurements with respect to a variety of working electrodes (WE) such as glassy carbon (GC), graphite and a carbon gas diffusion layer (GDL). Electrolytes containing NaPF6 and NaClO4 are found to be electrochemically stable with respect to GC and GDL electrodes up to 4.5 V vs. Na/Na(+), with some side reactions starting from around 3.0 V for the latter salt. The results further show that aluminium is preferred over different steels as a cathode current collector. Copper is stable up to a potential of 3.5 V vs. Na/Na(+). In view of practical Na-ion battery systems, the electrolytes are electrochemically tested with Na0.7CoO2 as a positive electrode. It is inferred that the electrolyte NaPF6-EC : DMC is favorable for the formation of a stable surface film and the reversibility of the above cathode material.

Vinylene Carbonate as Co-Solvent for Low-Temperature Mixed Electrolyte Based Supercapacitors

“…2b, κ nearly exponentially decreases with the decrease of temperature. The measured values of κ, ∼9 mS cm −1 at room temperature, are somewhat higher than for traditional propylene carbonate and ethylene carbonate -dimethyl carbonate based Na-ion battery electrolytes [23][24][25][26] but somewhat lower Cyclic voltammetry data.-The cyclic voltammograms (CVs) were measured in two-electrode test cells at potential scan rate (ν) of 5 mV s −1 to establish the region of ideal polarizability of the C(Mo 2 C) electrodes in the tested electrolytes (Fig. 3a).…”

Electrolytes for electrochemical energy storage

“…266 Please do not adjust margins Please do not adjust margins Comparative studies were reported on electrolytes based on commercially available sodium salts, namely NaPF6, NaClO4 and NaCF3SO3 in a binary mixture of EC and DMC. 268 It was found that the ionic conductivity of the two solutions of 0.6 mol L ─1 NaPF6 and 1.0 mol L ─1 NaClO4 in EC and DMC were 6.8 and 5.0 mS cm ─1 , respectively. These values are somewhat higher than that of NaOTf (3.7 mS cm ─1 , 0.8 mol L ─1 ).…”

“…Unfortunately, NaOTf, NaFSI and NaTFSIbased electrolytes had the major drawback of being unable to form a passivation layer on the Al current collector. 268,269 A systematic evaluation of the intrinsic Al stability in electrolytes based on various NaX [X=PF6, ClO4, TFSI, FTFSI, FSI] salts dissolved in solvent mixtures showed a trend of the Al dissolution increasing in an order of NaPF6 < NaClO4 < NaTFSI < NaFTFSI < NaFSI. 270 When adding 5 wt.% NaPF6 to the base electrolyte, the stability of Al in imide-based electrolytes could be improved, which may be attributed to the formation of a protection passivation layer on the Al surface.…”

Review—Practical Issues and Future Perspective for Na-Ion Batteries

“…89 Bhide and Adelhelm et al proved the presence of NaF in NaPF 6 (99.0%, Alfa Aesar) using X-ray diffraction and the observation of the insoluble fraction in NaPF 6 /EC:DMC solution by eyes. 92 Detailed study on influence of impurities contained in NaPF 6 salts on sodium insertion properties is required for further understanding. Therefore, influence of the NaPF 6 salts with different purity on electrochemical properties has been investigated using the salts supplied different companies.…”