Conductivity, Thermal and Electrochemical Stability of Solutions of Lithium Bis(Oxalato) Borate in Sulfolane
Authors: Sheina Ludmila , Kuzmina Elena , Karaseva Elena , Ivanov Alexey , Kolosnitsyn Vladimir 
Published: February 2020

Lithium bis(oxalato) borate (LiBoB) is promising lithium salt for electrolyte solutions of lithium-ion and lithium batteries because of high thermal and hydrolytic stability as well as high electrochemical stability of BoB- anion in wide potential range [1,2].

Sulfones are promising solvents and co-solvents for high-voltage batteries [3-7]. Sulfolane (tetramethylene sulfone) is the most known representative of sulfones. It has high dielectric permittivity (43.3 at 30 °C), high oxidizing stability (≥5 V vs. Li/Li+), high flash point (> 166 °C [8]) and low toxicity [3-5].

This work summarizes the results of studies on the conductivity, viscosity, electrochemical and thermal stability of LiBoB solutions in sulfolane with concentration range of 6·10-4 – 1.1 mol L-1.

The maximum of specific conductivity is 1,7·10-3 S·cm-1 at 30 ºС and corresponds to ~0.8 mol L-1 (Fig. a). Activation energy of conductivity of 1M LiBoB in sulfolane is 23.3±0.5 kJ mol-1.

Solutions of LiBoB in sulfolane are viscous (Fig. b). Activation energy of viscous flow for 1M LiBoB in sulfolane is 29.4±0.5 kJ mol-1.

Association constant and limiting molar conductivity (λ0) of LiBoB in sulfolane are 6 mol-1·L and 8·10-4 S·m2·mol-1, correspondingly.

The decomposition temperature (temperature at the initial decomposition) of 1M LiBoB in sulfolane is 286 °C, estimated by DSC method (Fig. c), and 260 °C, estimated by DTA method (Fig. d).

Anodic stability of 1M LiBoB in sulfolane is ~5.8 V vs. Li/Li+, estimated at Pt working electrode.

Therefore, lithium bis(oxalato) borate dissociates well in sulfolane, its solution has moderate conductivity, high thermal and electrochemical stability.

Figure. Isotherms of specific conductivity (a) and dynamic viscosity (b) of LiBoB solutions in sulfolane; DSC (c) and DTA (d) of 1M LiBoB in sulfolane.

This work was performed as part of a Government Order to Ufa Institute of Chemistry of the Russian Academy of Sciences by the Ministry of Science and Higher Education of the Russian Federation (Theme No. AAAA-A17-117011910031-7).

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Figure 1