成果報告書詳細
管理番号20140000000242
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 (11)
公開日2014/5/17
報告書年度2013 - 2013
委託先名国立大学法人横浜国立大学
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We are attempting to develop a novel lithium-air secondary battery by using solvate ionic liquid electrolytes. Owing to their chemical and physical properties, ionic liquids have attracted much attention in many applications. We can exploit these advantages in the ionic liquids for designing battery electrolytes applicable to lithium-air battery with ultrahigh energy density. Thus developed lithium solvate ionic liquids are inherently non-flammable, less-volatile, highly lithium-conductive, and highly stable against oxidative reaction. Therefore, they are a promising electrolyte of the lithium-air batteries operated in open-air conditions. Moreover, a variety of the design routes enables us to introduce more hydrophobic property into the solvate ionic liquids. In this project, we also attempt to fabricate lithium-air battery systems composed of not only lithium metal but also graphite as the negative electrode. The final goals in this project are (i) to evaluate the possibility of the battery operation with humidified oxygen or real air using the solvate ionic liquid electrolytes, and (ii) to realize the lithium-air battery that allows the energy density of 500 Wh/kg over 50 cycles of reversible charge-discharge.
From the set of data on various analytical methods such as XRD, SEM, GC-MS, XPS with electrochemical measurements including RRDE voltammetry, we conclude that main reduction and re-oxidation products are lithium peroxide and oxygen, respectively during reversible redox reactions of oxygen in the solvate ionic liquid electrolyte. In the solvate ILs, the reaction intermediates were less soluble, and the side reactions of oxidative decomposition during charging reaction were greatly suppressed, compared to organic electrolytes. We prepared more hydrophobic ionic liquids. The novel hydrophobic electrolyte allowed equilibrium moisture content lower than 1 wt% at 90% RH. To develop a moisture-blocking membrane for the air cathode, water vapor permeability for a range of polymers were studied. Fluorinated polymer membranes showed outstandingly low permeability of water vapor. It was found that both lithium metal and graphite anodes showed highly reversible charge-discharge reactions in the solvate ionic liquids. Reversible charge-discharge cycle was successfully performed under pure oxygen flow using lithium metal as the negative electrode, the solvate ionic liquid as the electrolyte, and porous carbon (Ketjen Black)-polytetrafluoroethylene (PTFE) composite electrode as the positive air electrode.
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