Co-free LiNi_0.5Mn_0.5O₂ shows better thermostability and higher discharge capacity than LiCoO₂. We investigate the effects of Li content and cation mixing on electronic structure in Li_xNi_0.5Mn_0.5O₂ (x=1.00∼1.08) by Rietveld analysis and first principle calculation. The crystal structures were well refined and excess Li existed at transition-metal site without any change of the Li and Ni occupancies at Li site. It suggests that the amount of the cation mixing has no relation with Li content. From the result of structure relaxation by calculation, it was found that the structure was stabilized by cation mixing and thus cation mixing is possible to happen theoretically. This result is caused by increase of covalent bond near the cation mixing atom. In the sample of Li_1.03Ni_0.5Mn_0.5O₂ which shows good discharge performance, electron density between the transition metal and oxygen showed maximum among the investigated samples by MEM (experiment) and WIEN2k (calculation). Such result suggests that host structure stability plays an important role for the discharge performance.

View full abstract

Lignophenols as the additive for the negative active materials of lead-acid batteries were synthesized, by use of the phase-separation system, as the controlled molecular structures from native lignins based on the softwood (chamaecyparis obtuse) and the hardwood (fagus crenata). The relationship between molecular structures of the prepared lignophenols and the performance of batteries with the addition of the lignophenols to negative active materials has been investigated. The role of aromatic methoxyl groups of the lignophenols on the battery performance has been mainly investigated. Employed batteries were 2 V-3.3 Ah flooded cells consisting of one negative plate and two positive plates. When the methoxyl group contents in the lignophenols increased, the discharge capacity increased but the charge capacity decreased. It was considered that the methoxyl groups of the lignophenols were demethylated in the batteries. The discharge performance was improved because the particle growth and the reaction area of negative active materials were respectively suppressed and increased. Despite the increase in the reaction area, the charge reaction was suppressed. The difference of the effects of the demethylated lignophenols on the discharge and the charge performance was thought to be due to the behavior of the adsorption of the demethylated lignophenols on mainly lead ion.

View full abstract

The dependences of the CO₂ concentration and the effects of electric current on the ionic conduction properties of anion exchange membranes (AEMs) in fuel cells were investigated. The ionic conductivity of AEMs was measured by AC impedance method at 40°C in various atmospheres. After the initial ion exchange process, contact with air containing 38% CO₂ caused the ionic conductivity of AEMs to decrease to 40% of the value measured immediately after the initial ion exchange process. However, exposing the AEMs in a CO₂-free air atmosphere increased the ionic conductivity to 50% of the value measured immediately after the initial ion exchange process. Then 89 C cm⁻² of direct current (DC) was applied in a CO₂-free atmosphere to the AEMs. The ionic conductivity increased close to the value measured immediately after the initial ion exchange process. These results are discussed by assuming that bicarbonate (HCO₃⁻) is produced in the AEMs.

View full abstract