Ionic Conductivity of Electrolytes Composed of Oleate-Capped Yttria-Stabilized Zirconia Nanoparticles.

Yttria-stabilized zirconia (YSZ) is a highly promising electrolyte material for solid oxide fuel cells (SOFCs). We investigated the conductivity-enhancing effect of nanosized YSZ to explore key techniques to decrease the operating temperature. YSZ nanoparticles ranging from 2 to 4 nm were synthesized with oleate groups by the hydrothermal method at various oleate/metal ion ratios (Ole/M = 1.00, 0.75, and 0.50). The nanoparticles were sintered, and the ionic conductivities were evaluated. The 1.00 Ole/M sample exhibited high dispersibility in cyclohexane and showed a nearly monodispersed distribution. The other samples possessed agglomerated nanoparticles. The sintered YSZ nanoparticles had densities of 3.36-2.80 g/cm3 and ionic conductivities of 2.52-1.16 mS/cm at 750 °C, which are higher than those of commercial 8 mol % YSZ. Furthermore, the sintered YSZ nanoparticles exhibited higher activation energies than the commercial samples in the lower temperature range (550-650 °C). The ionic conductivity enhancement despite the high activation energy is likely due to the increased grain boundary volume. This study demonstrated the successful production of YSZ with high ionic conductivity and sinterability upon sintering at 1050 °C using YSZ nanoparticles.

Large Charge-Transfer Energy in LiFePO4 Revealed by Full-Multiplet Calculation for the Fe L3 -edge Soft X-ray Emission Spectra.

We analyzed the Fe 3d electronic structure in LiFePO4 /FePO4 (LFP/FP) nanowire with a high cyclability by using soft X-ray emission spectroscopy (XES) combined with configuration-interaction full-multiplet (CIFM) calculation. The ex situ Fe L2,3 -edge resonant XES (RXES) spectra for LFP and FP are ascribed to oxidation states of Fe2+ and Fe3+ , respectively. CIFM calculations for Fe2+ and Fe3+ states reproduced the Fe L3 RXES spectra for LFP and FP, respectively. In the calculations for both states, the charge-transfer energy was considerably larger than those for typical iron oxides, indicating very little electron transfer from the O 2p to Fe 3d orbitals and a weak hybridization on the Fe-O bond during the charge-discharge reactions.

Investigation of the relationship between the cycle performance and the electronic structure in LiAlxMn2-xO4 (x = 0 and 0.2) using soft X-ray spectroscopy.

Al doping into LiMn2O4 is one of the well-known methods to improve the cycle performance of the LiMn2O4 cathode. We carried out soft X-ray emission spectroscopy (XES) for LiMn2O4 and LiAl0.2Mn1.8O4 to elucidate the relationship between the Mn 3d electronic structures and cycle performances. After the first cycle, the XES spectra of LiAl0.2Mn1.8O4 are almost unchanged compared to the initial state. In contrast, charge-transfer excitation for the XES of LiMn2O4 is significantly reduced, indicating that the Mn 3d-O 2p hybridization in LiMn2O4 should be easily weakened by charge-discharge. In LiAl0.2Mn1.8O4, the Mn-O bond becomes more stable due to the decrease of Mn3+ ions with Jahn-Teller distortion by Al3+ doping, resulting in the improved cycle performance.