We have synthesized LiNi0.5−xMn1.5−xM2xO4 (M=Al, Cr) materials by polyvinyl alcohol (PVA) method, and investigated the effect of the synthetic condition on the electrochemical performance including charge-discharge cycling tests. The characterization of the materials obtained was performed by X-ray diffraction, BET measurement, chemical analysis, and galvanostatic electrochemical measurements. It was found that all synthesized LiNi0.5−xMn1.5−xM2xO4 (M=Al, Cr) materials consist of LiNi0.5Mn1.5O4 phase including a small amount of impurity NiO phase. Al and Cr substituted LiNi0.45Mn1.45M0.10O4 (M=Al, Cr) samples showed better C-rate performance, e.g., with a main discharge plateau of ∼4.7 V, and the discharge capacity of ∼100 mAh (g-oxide)−1 at a 10C rate and 25°C, compared to LiNi0.5Mn1.5O4.
The kinetic parameters, such as Tafel slope, charge transfer coefficient and the diffusion coefficient of formic acid electrooxidation were obtained under the quasi steady-state conditions. The Tafel plot exhibits two linear regions with the same values of 340 mV. The charge transfer coefficient is 0.32 and the diffusion coefficient is calculated to be 1.01×10−7 cm2 s−1. The temperature dependence of the formic acid oxidation in the temperature range of 20∼60°C was also investigated. The results have shown that the oxidation reaction was sensitive to temperature and the activation energy was increased with increasing potential at the potential range of 0.1–0.5 V.
In order to check whether the alloys in the system Mg–Ge can be prepared by sintering method or not, the Mg2Ge powder was fired in argon atmosphere at high temperatures. As a result, it was found that the samples were obtained as sintered alloys. From the electrochemical measurements, next, the sintered materials including copper as a conductive agent were found to work as anode active materials for lithium secondary batteries. When they were fired with the additive component such as ammonium hydrogen carbonate (NH4HCO3), polyvinyl alcohol (PVA) or magnesium powder vanishing during firing, the porous sintered alloys could be prepared, which also worked as anode materials with better cyclic stability than the nonporous ones. These results denoted that the sintering method is valuable and developing for preparation of the alloy materials.
Current collecting property in micro tubular solid oxide fuel cell (SOFC) was evaluated by using electrochemical impedance spectroscopy. A micro tubular cell was composed of NiO/(ZrO2)0.9(Y2O3)0.1 anode-substrate, (Ce0.6La0.4)O1.8 and La0.8Sr0.2Ga0.8Mg0.2O2.8 double layer electrolyte, and La0.6Sr0.4Co0.2Fe0.8O3 cathode. The effects of different current collecting types, i.e., short-current path or long-current path were discussed. These results were simulated to the equivalent circuit consisting of four resistances and three capacitances, and accuracy of these estimated values were investigated in nonlinear least square techniques. As the results, short-current path type showed high performance and ohmic resistance was dependent of current collect types.