Extended Data Fig. 6: Properties of the optimized electrolyte containing DMSO.
From: A rechargeable calcium–oxygen battery that operates at room temperature
a, Dependence of apparent viscosity on the electrolyte formula containing different volume ratio of DMSO, demonstrating that the electrolyte of EMIM-BF4/DMSO (50:50 vol%) has the lowest apparent viscosity. b, Dependence of ionic conductivity on the electrolyte formula containing different volume ratio of DMSO, showing that the electrolyte of EMIM-BF4/DMSO (50:50 vol%) has the highest ionic conductivity (11.5 mS/cm). c, Steady-state current density of electrolytes containing different volume ratio of DMSO upon varying applied polarization potentials. The electrolyte of EMIM-BF4/DMSO (50:50 vol%) demonstrates the comparably higher steady-state current densities, pointing to the facilitated Ca2+ transportation. d–f, Potentiostatic polarization curves of the EMIM-BF4/DMSO (50:50 vol%) electrolyte (d), EMIM-BF4/DMSO (75:25 vol%) electrolyte (e), and EMIM-BF4 electrolyte without DMSO (f). Inset, corresponding Nyquist plots of the electrolyte. Among the various electrolytes, our optimized electrolyte (d) has the highest Ca2+ transference number \(({t}_{{{Ca}}^{2+}}=0.43)\). g, h, Linear sweep voltammetry curves of the O2 reduction reaction in electrolytes with DMSO (EMIM-BF4/DMSO, 50:50 vol%, in g) and without DMSO (only EMIM-BF4, in h) at a scan rate of 100 mV/s with rotating disc electrode rotation rates from 400 to 1,200 rpm and an increment of 200 rpm. The comparably higher limiting current densities in the electrolytes with DMSO (EMIM-BF4/DMSO, 50:50 vol%) indicates the improved O2 reduction reaction kinetics by the introduction of DMSO. The clear observation of O2 reduction at about 1.5 V originates from the maximized exposure of working electrode to the continuously applied O2 flux. i, The fitted linear Levich plots of the limiting current density (O2 reduction reaction) versus the square root of rotation rate (ω1/2), deducing a higher O2 diffusion coefficient of 1.69 × 10−6 cm2/s in the electrolyte with DMSO (EMIM-BF4/DMSO, 50:50 vol%) than 4.47 × 10−7 cm2/s in the electrolyte without DMSO. Error bars represent the standard deviations of the results from five samples.
