Full cells consisting of nanocrystalline Li3V2(PO4)3 (LVP) positive and standard commercial Li4Ti5O12 (LTO) negative electrodes demonstrated outstanding cyclability: capacity retention of 77% over 10,000 cycles. We achieved this stable cycle performance by electrochemical preconditioning of LTO with Li prior to full-cell cycling. The strategy of Li preconditioning not only allows adjustment of the state of charge (SOC) between negative and positive electrodes, but also gives rise to the formation of a protective covering layer on the LTO surface. As we show, this covering layer plays an important role in preventing a key performance-limiting phenomenon—namely, the deposition of vanadium eluted from LVP onto LTO, which degrades the coulombic efficiency of Li+ intercalation/deintercalation into LTO crystals—yielding minimal SOC shifts and stable full-cell cycling.
Stable high-voltage operation of LiCoPO4 (LCP) was successfully achieved via crystal-structure-matched surface coating using FePO4 (FP) with an identical olivine structure to the LCP. The efficient formation of Fe3+-rich surface together with the partial dissolution of Fe3+ into LCP matrix yielded the excellent cycle performance with 99% of capacity retention at 100th cycle, with a minimized Fe3+ dosage compared to the methods previously reported. This work confirms that the existence of the Fe3+ on the LCP surface is an important factor to bring about the stability of electrode/electrolyte interface.
In this work, IV characteristic and efficiency of protonic ceramic fuel cells and electrolysis cells were discussed based on the oxygen potential profile in mix conductive electrolyte. In protonic electrolyte such as barium zirconate, which exhibits partial hole conductivity in oxygen atmosphere, oxygen potential profile shows a steep slope where hole conductivity is low. As the result, hole blocking layer becomes extremely thin and the rest of the electrolyte shows a significant hole conductivity. Therefore, current leakage cannot be ignored even when the electrolyte material shows quite low electronic conductivity in one side of the electrolyte. When electronic leakage is significant, the analysis of electrochemical measurements becomes complicated. In such case, focusing on the net ionic current is a useful approach to evaluate the cell characteristics. Considering the effect of electrode polarization on the oxygen potential gap at electrode/electrolyte interface, electronic leakage becomes more serious in electrolysis mode. The simulation results showed that both improvement of ionic transportation number of electrolyte and reduction of polarization resistance of oxygen electrode are critical to achieve high efficiency in electrolysis cells.
The measurements on the activity and solvation of H2O in hydrate melts and aqueous electrolyte solutions containing various metal chlorides were carried out by a vapor pressure measurement using a transpiration method and 1H quantitative NMR (1H qNMR). The electrolyte concentration dependence of the detection rate of H2O by 1H qNMR reflected the change of the hydration structure of the first hydration shell, and the activity of H2O by the vapor pressure measurement clearly showed the change of the network structure of water including the first and second hydration spheres. The correlation between the enthalpy and entropy of vaporization showed the existence of different kinds of water-cation interactions.