The effect of crown ether additives for the electrolyte solution containing Mg(N(CF3SO2)2)2 (Mg(TFSA)2) was studied. Mg(TFSA)2 salt hardly dissolved in tetrahydrofuran, while 1 mol dm−3 solution was obtained by 18-crown-6 (18C6) ether addition and the 10−3 S cm−1 order of ionic conductivity was achieved. From the FT-IR spectrum, the predominantly coordination between Mg2+-ion and 18C6 was indicated. Cyclic voltammogram showed the redox current, which indicated that the reversible Mg plating and stripping reaction took place, while the clear redox current did not appear in the additive-free solution. From the results, we concluded the specific solvation structure of Mg2+-ion by 18C6 ether would play the effective role for the reversible Mg plating and stripping reaction.
Three reference electrodes (Li/Li+) were embedded to the three sides (symmetrical (R1), Extra Positive-side (R2) and Extra Negative-side (R3)) of a square lithium-ion battery (LIB) cell, and electrical potential changes of the positive (P) and negative (N) electrodes against the reference electrodes during charge and discharge were studied. AC impedance measurement also was conducted with the cell. During charge of the cell, the negative electrode potential at the Extra Positive-side (N-R2(+)) was maintained below 0 V vs. Li/Li+ which means the high risk of Li metal deposition at that area. Contrary to this, at the Extra Negative-side (N-R3(−)), the potential was maintained above 0 V vs. Li/Li+ during and after charge and discharge of the cell. AC impedance spectra of the positive electrode or the negative one against the three reference electrodes were quite different with each other. AC impedance spectra can be influenced by the relaxation current between the positive electrode (P) and the Extra Positive-side (P-Extra) or by that between the negative electrode (N) and the Extra Negative-side (N-Extra).
To control the packing surface density of carbon nanotubes (CNTs) and the defects and numbers of graphene layers, graphene is grown on nickel foil by chemical vapor deposition (CVD) with different time periods and flow rates of methane. CNTs are then grown on the cobalt-coated (by sputtering of Co with different time) graphene/nickel foil prepared by CVD. Longer sputtering time for cobalt leads to lower capacitance of carbon nanotube/graphene composites. Furthermore, shorter growing time of graphene results in higher capacitance of carbon nanotube/graphene composites. Higher flow rates of methane for CVD lead to higher capacitance of carbon nanotube/graphene composites.
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