Protonic conduction in oxide ceramics under hydrogen-containing atmosphere at elevated temperatures is reviewed with respect to oxide materials, their electrochemical properties, conduction mechanism and possible applications. These oxides are unique in respect of the fact that they have no protons as a host component, but incorporate protons via reactions with the atmosphere. The materials of this class are some perovskite-type oxides and other oxides which contain crystal defects. Defect equilibria for proton formation in these kinds of oxides are discussed citing some experimental results. Possible electrochemical devices using proton conducting ceramics are briefly introduced.
Spherical LiMn2−xMgxO4 powders were prepared by the ultrasonic spray pyrolysis. As-prepared particles had a porous microstructure and were nonagglomerated, which had an average diameter of about 1 µm with narrow size distribution. XRD showed that as-prepared powders were well crystallized to spinel structure with Fd3m space group. ICP analysis revealed that Mg ions were homogeneously doped to LiMn2O4. As-prepared powders were used as cathode active material for lithium secondary battery and its electrochemical properties were investigated between 3.5 and 4.3 V. The first charge/discharge capacity of LiMn2O4 was 145 and 141 mAh g−1 at 0.1 mA cm−2, respectively. The discharge capacity of LiMn2O4 decreased with increasing cycle number. The first charge/discharge capacity of LiMn2−xMgxO4 was less than that of LiMn2O4. However, the cycle performance of LiMn2−xMgxO4 was superior to that of LiMn2O4.
To develop battery technology for a large-sized lithium ion battery, particle size of electrode active material, compression of electrodes, drying conditions of electrodes, and electrolyte identities were examined using a coin-cell, and the treatment of the lower edge of electrodes, electrode size, adhesion of electrode active material and current collector, and impregnation condition of electrolytes, were studied using single cells. The followings are particularly important findings obtained in this study. (1) Residual pyrrolidone caused an increase in water content, and thus, drying of electrodes is important in large-sized batteries. (2) Adhesion of electrode active material and current collector can be improved by either increasing the thickness of the current collector or by using an accurate-sized frame during the compression step of electrodes. (3) Both sides of the lower edge of the electrode were covered by precipitates of the Li dendrite during charge-discharge of the battery, and this precipitation was greatly inhibited by applying paste consisting of 75% natural graphite and 25% PVdF at the edge of the anode. (4) Impregnation of electrolytes to large-sized batteries is very difficult compared to that in small ones, since the uniform contact between electrolytes and electrodes requires a longer time. (5) Sealing of the battery case using a viton o-ring can efficiently avoid the mixing of water inside the battery and the evaporation of solvent outside the battery.
With the aim of developing 1 kWh class lithium ion batteries with long life and high efficiencies, we trial manufactured batteries that were fabricated using LiCoO2and natural graphite as cathode and anode active materials, respectively with 1 mo1 dm−3 LiPF6 or LiBF4 dissolved in EC/DEC as an electrolyte. The construction of the batteries was based on the results of fundamental research done to elucidate the problems encountered with previous models. We achieved 543 cycles with high efficiencies with the 4th battery, exceeding the initial target of 500 cycles. The life and efficiencies of the 4th battery exceed those of large-scale lead storage batteries commercially available. It was noteworthy that engineering factors such as uniform impregnation of the electrolyte into the electrode laminates and maintenance of homogeneous conditions of laminates by the control of expansion and contraction during charge and discharge phases, respectively, were very important for the long life of large-scale lithium ion batteries.
A study was conducted to evaluate corrosion resistance of carbonaceous porous materials made from various fibers and binder as an electrode substrate of phosphoric acid fuel cells. A great improvement in corrosion resistance was achieved by using a high performance carbon fiber as a filler material and by treating at higher temperatures to increase the graphitizability of final products. The corrosion of the product occurred mainly at the surface of fibers because the graphitizability of binder carbon was higher than that of fibers due to the great thermal stress applied during volume shrinkage of binder at carbonization process. Also it became clear that a high corrosion resistance was ensured by good adhesion between fibers and binders. For a product in which fibers separated from binder carbon, its corrosion resistance was low. By using a high performance carbon fiber and by achieving good adhesion of carbon fibers and binder carbon, other properties; e.g. thermal conductivity, electrical conductivity and mechanical strength were also improved greatly.