成果報告書詳細
管理番号20140000000194
タイトル*平成25年度中間年報 革新型蓄電池先端科学基礎研究事業 革新型蓄電池先端科学基礎研究開発 (2)
公開日2014/5/17
報告書年度2013 - 2013
委託先名国立大学法人九州大学
プロジェクト番号P09012
部署名スマートコミュニティ部
和文要約
英文要約In this project, we have investigated cryolite Li3MF6, trirutile-type Li2MF6, inverse spinel-type Li2MF4 and perovskite-type NaFeF3 as new fluoride cathodes up to now. Among them, FeOF cathode has the highest energy density. However, the conversion-type cathodes without Li cannot be applicable for Li-ion batteries with carbon anode.
To dissolve this problem, we tried to reconversion reaction by there 3 type composite cathodes as follows;
(1) The electrochemical properties for LiF-FeO composite cathode
The mixture of LiF and FeO particulate was milled by dry-mechanical ball-milling. The reversible capacity of the obtained mixed cathode was 292 mAh/g with an average voltage of 2.5 V and an energy density over 700 mWh/g, which is higher than the theoretical energy density of LiFePO4. In addition, we confirmed that it can actually work as cathode in Li-ion type cell with LTO anode.
(2) The structure and valance change of LiFeOF cathode during initial charge and discharge cycle
To determine the charge and discharge reaction mechanism of LiFeOF cathode, the valance of iron and crystal structure changes during the charge-discharge reaction were investigated by synchrotron-based X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) measurement.
(3) The electrochemical properties for LiF-MnO and LiF-TiO composite cathode
The LiF-MnO and LiF-TiO composite cathodes were prepared by the dry ball-milling method under ambient pressure. The obtained LiF-MnO and LiF-TiO composite were indexed as the mixture of NaF and these metal oxides. At a rate of 0.2 mA/cm2, the initial charge/discharge capacities of LiF-MnO and LiF-TiO cathode were 219/218 mAh/g and 387/302 mAh/g, respectively. Although the charge/discharge overpotentials are not small, LiF-MnO and LiF-TiO composites also showed a reversible reconversion reaction.

 Air electrode activity of meso-porous or oxygen deficient perovskite oxide for Zn-air battery was studied in this year. Since it is reported that Ruddlesden- Popper type perovskite oxide, La-Sr-Fe-O, shows extremely high activity to oxygen reduction reaction, effects of rare earth cations in Ln-Sr-Fe-O was studied for air electrode. Among the examined rare earth cation, it was found that conductivity increased the following order; Pr>Gd>La>Sm, and on-set potential for oxygen reduction reaction is the following order ; Er>La>Pr>Sm. Considering the activity to oxygen evolution reaction, it was found that Pr-Sr-Fe-O shows the most reversible as a rechargeable air electrode. Effects of rare earth cations in Ln-Sr-Fe-O on discharge capacity in Zn-O2 battery was further studied and it is seen that Pr-Sr-Fe-O shows the discharge capacity close to 750 mAh/g-Zn which is close to the theoretical discharge capacity (820 mAh/g-Zn) and reasonably high discharge potential (1.25V). Effects of concentration of KOH on cycle stability on Zn-O2 battery were also studied by using Pr-Sr-Fe-O for air electrode. It was found that cycle stability was much increased by using 8MKOH solution for electrolyte and almost theoretical capacity could be sustained up to 60 cycles. However, discharge potential decreased with cycle number, in particular, after 20 cycles. Therefore, stable conducting binder for air electrode is strongly requested.
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