Issue No. 3, December

Abstract

A sago-based gel polymer electrolyte (GPE) was prepared by mixing native sago with potassium hydroxide (KOH) aqueous in order to investigate the applicability of GPE to zinc-air (Zn-air) battery. The viscosity and conductivity of the sago GPE were evaluated using varying sago amounts and KOH concentrations. The viscosity of the sago GPE was kept as a reserve in the region of ~ 0.2 Pa s as the KOH concentration was increased from 2 to 8 M. Sago GPE was found to have an excellent ionic conductivity of (4.45 ± 0.1) x 10^-1 S cm^-1 with 6 M KOH. GPE was also employed in an experimental Zn-air battery using porous Zn electrode as the anode. The battery shows outstanding discharge capacity and practical capacity obtained of 505 mA h g^-1.

Abstract

Polyanionic cathode/anode active materials such as olivine and NASICON-type phosphates with the high thermal stability and low environmental impact have been expected for next generation Li-ion battery. In addition, we have also focused on the other characters such as 3D framework and the flat charge/discharge voltage profiles, because they should be also suitable for solid-state and aqueous Li-ion batteries, respectively. In this presentation, the cell performances of Li₃V₂(PO₄)3/Li_1.5Al_0.5Ge_1.5(PO₄)₃/Li₃V₂(PO₄)₃ and Na₃V₂(PO₄)₃/Na₃Zr₂(SiO₄)₂PO₄/Na₃V₂(PO₄)₃ are demonstrated as all NASICON phosphate symmetric solid-state Li-ion and Na-ion battery, respectively. In addition, LiFePO₄/1M Li₂SO₄ aqueous electrolyte/LiTi2(PO₄)₃ is also introduced as an aqueous Li-ion battery with olivine cathode and NASICON anode. They are two prototypes of the next generation safe secondary batteries with polyanionic cathode/anode active materials.

Abstract

The thermal and transport properties of PYR_1(2O1)TFSI-PYR₁₃FSI ionic liquid binary mixtures as electrolytes for low temperature electrochemical devices are reported in the present paper. The DSC measurements are in good agreement with the conductivity results. It is shown that the incorporation of even small mole fractions (x ≤ 0.3) of PYR_1(2O1)TFSI into PYR₁₃FSI strongly hinders the ability of the samples to crystallize. This results in a very large conductivity enhancement for the PYR_1(2O1)TFSI-PYR₁₃FSI binary mixtures, particularly at low temperatures, that were seen to approach conduction values of 10^-4 Scm^-1 and 10^-3 Scm^-1 at -40°C and -20°C, respectively. Such an interesting behavior makes PYR_1(2O1)TFSI-PYR₁₃FSI binary mixtures particularly appealing for low temperature applications.

Abstract

The present paper focuses on a nanostructured SnCo alloy electrochemically prepared by template method in view of its use as anode material alternative to graphite in lithium-ion batteries. The fabrication of SnCo nanowire arrays was carried out by potentiostatic co-deposition of the two metals by using nanostructured anodic alumina membranes as template. Electrochemical tests on lithiation-delithiation of these SnCo electrodes in conventional organic electrolyte (EC:DMC LiPF₆) at 30°C showed that their specific capacity was stable for about the first 12 cycles at a value near to the theoretical one for Li₂₂Sn₅ and, hence, progressively decayed.

Abstract

In addition to cost and lifetime, important factors in using lithium-ion (Li-ion) batteries as a backup power supply in telecommunication applications are safety and the flatness of discharge voltage to maintain compatibility with existing systems based on lead storage batteries. We have been researching Li-ion batteries using manganese spinel as cathode material from the viewpoints of flat discharge voltage and thermal stability in the event of overcharging or internal short-circuits. The safety of the Li-ion battery was improved by adding a phosphazene flame retardant to the electrolytic solution and cathode of the battery. Then, with the aim of extending battery lifetime, some of the manganese in the cathode was replaced by another metallic element, which showed favorable results.

Abstract

Low cost printable power sources are needed e.g. in sensors and RFID applications. As manufacturing method printing techniques are preferred in order to keep the costs low. The materials should also be easily disposable. Enzymatic bio-fuel cells are an alternative for printable primary batteries. Since one drawback of bio-fuel cells is their low power, we have developed supercapacitors that can be combined with enzymatic bio-fuel cells to provide the power peaks necessary in the applications. The materials for the supercapacitors have been chosen to be compatible with the fuel cell and with printing methods, e.g. the activated carbon powder in the electrodes was bound with chitosan. As printing substrates we have used paperboards. The current collectors have been made of graphite and metal inks. Since the voltage requirement is limited to approximately 1 V, aqueous electrolytes have been used. Printed supercapacitors of various sizes have been prepared. The geometrical electrode areas have been between 0.5 and 2 cm². The maximum feasible output current has been in the order of 50 mA corresponding to about 50 mW power. When the capacitor is used together with an enzymatic power source, the leakage current must be as low as possible. Typical leakage current values have been in the order of 10 μA.

Abstract

The pressure dependence of the diffusion coefficient in the superionic α- and β-phases of Ag₃SI has been studied by using the method of molecular dynamics. It is shown that in the high temperature α-phase, the Ag diffusion coefficient decreases with pressure. On the hand, in the intermediate temperature β-phase, the Ag diffusion coefficient exhibits a maximum at around 2.8 GPa. The structural origin of this behavior is discussed through the pressure dependence of the pair distribution functions.

Abstract

In complex perovskite-type oxides which have been studied as cathode materials, the thermal expansion coefficient increases with the increase in the oxygen ionic conductivity. In the present study, with the aim to explain such a behavior, a research has been carried out from a chemical bond point of view. For oxides A₁-xA′_xB_1-yB′_yO_3-δ with perovskite structure, the ionicity of the individual bond, A-O and B-O, and the thermal expansion coefficient of mixed compounds were estimated by using semiempirical methods. It has been shown that the thermal expansion coefficient and the oxygen ionic conductivity decrease with the increase in the difference of the ionicity between A-O and B-O bonds. It is also found that the tolerance factor and the specific free volume are linearly correlated with the difference of ionicity.