High-Voltage Electrolytes Based on Nitrile Containing Disiloxanes for Lithium-Ion Batteries

Two nitrile containing disiloxanes were investigated as non-volatile solvent for electrochemically stable electrolytes suitable for high energy and high power density lithium-ion batteries. The investigated disiloxanes show an excellent thermal behaviour (bp = 106 °C, 0.1 mbar) with a very low glass transition temperature T_gdown to -107 °C.

Fig. 1 a) CV of TmdSx-PN and b) Arrhenius plot of nitrile containing disiloxane TmdSx-OPN with different LiTFSI salt concentrations.

Electrochemical characterization was performed by temperature dependent impedance spectroscopy, differential scanning calorimetry, cyclic voltammetry and constant current cycling. The siloxane electrolytes showed a wide electrochemical window up to 5.4 V vs. Li/Li⁺ using LiTFSI as lithium salt. High ionic conductivity was found up to 1 mS∙cm^-1 at 30 °C and a molality of 0.7 mol/Kg (CN:Li = 11:1).[1] These are the highest reported ionic conductivities and anodic stability for a liquid siloxane electrolyte.[2] Charge-discharge half-cell test were done with LiFePO₄cathode materials. These results show that nitrile functionalized disiloxanes are very promising electrolyte solvents for the use in lithium-ion batteries with high energy densities. In addition, nitrile functionalized disiloxanes are very suitable as liquid solvent in polymer based gel electrolytes.

The authors acknowledge funding by the German federal ministry of education and research (BMBF) within the project “MEET Hi-EnD”.

[1] B. Pohl, M.M. Hiller, S.M. Seidel, M. Grünebaum, H.-D. Wiemhöfer, submitted, (2014).

[2] S. Jeschke, A.-C. Gentschev, H.-D. Wiemhöfer, Chem. Commun., 49 (2013) 1190-1192.