成果報告書詳細
管理番号20090000000791
タイトル*平成20年度中間年報 次世代自動車用高性能蓄電システム技術開発/要素技術開発/リチウム二次電池の安全性に資するイオン液体電解質の開発
公開日2010/3/24
報告書年度2008 - 2008
委託先名独立行政法人産業技術総合研究所
プロジェクト番号P07001
部署名燃料電池・水素技術開発部 蓄電技術開発室
和文要約以下本編抜粋:1.研究開発の内容及び成果等 1-1 計算科学的手法によるイオン液体電解質の推定 今年度はあまりこれまで報告例があまりないメサイド系アニオン(図1)からなるイオン液体の物性を支配する因子であるイオン間相互作用、拡散挙動に影響を及ぼす側鎖の回転障壁の解析を、第一原理分子軌道法(MO)によって検討した。 メサイドアニオンではTFSAと同様の-SO2CF3基を有するものについては、Covalent AssociatesのKochらによってイミダゾリウム塩の物性とEDLCへの応用について報告例がある。そこで今回は調べた範囲では先例がない、FSAと同様の-SO2F基を有する系について合わせて検討した。まず、最安定構造におけるLiイオンとの相互作用エネルギーの結果(図1)から、メサイド系アニオンとLiイオンの相互作用はアミド系アニオンの場合よりも弱いことが示唆され、Li イオンの輸送には有利な可能性がある事が分かった。
英文要約"Development of Novel Ionic Liquids as Safety Electrolytes for Lithium Secondary Battery"
(National Institute of Advanced Industrial Science and Technology (AIST))
Less-flammability is one of the most valuable properties of ionic liquids (ILs) containing perfluoroanions. Recently, such a unique "liquid" has been expected to be applied to an electrolyte of a lithium secondary battery in order to improve thermal stability and life, which have been increasingly required for an application especially to hybrid vehicles. The aim of this study is to elucidate the molecular design for highly conductive and thermally stable ionic liquids (ca. 2x10-2 S cm-1 at moderate temperature) and to demonstrate that developed ionic liquid sufficiently attains the peak power of 2500 W kg-1 in a practical lithium battery system.
The results obtained in 2008 were descried as follows.
1) Ab initio molecular orbital calculation is used to design new ionic liquids. Furthermore a molecular dynamics calculation (MD) was applied to ionic liquids system to investigate relationship between ionic structure and their diffusivity. We tried to apply these method to methide anions such as [(CF3SO2)3C]- and [(FSO2)3C]- to investigate the possibility of attractive candidate for ionic liquids.
2) New ionic liquids composed of spiro type ammonium cations with FTA. The viscosity and conductivity of this new ionic liquid at 298 K was 44 cP and 7 mS/cm, respectively.
This ionic liquid can be used as over 1 C capable electrolyte for Li/LiCoO2. And we also prepared new perfluoroalkyltrifluoroborate, CF3OCF2CF2BF3. This anion has a significant ability to lower both viscosity and melting point.
3)Ion transport of ionic liquids under electric field studied by pulsed field gradient stimulated echo electrophoretic NMR (PGSTE-ENMR) technique were applied to various ionic liquids composed of amide anions and borate anions for the first time. As a result, the existence of electric field strongly affects the transport properties of ionic liquids and the degree of change of an apparent diffusion coefficient also strongly depend on the structure of anion.
4) Estimation of thermal safety and stability of ionic liquids electrolyte with DSC and TGA-GCMS were applied to various DEME-ILs with a charged cathode (LiCoO2) and a Li metal anode. As a result, an exothermic heat of ILs composed of perfluoroalkyltrifluoroborate anions observed much lower temperature than that for amide anions ( < 500 K), however, no sharp exothermic peak, which usually observed in case of amide system, was detected. This means that borate system is also attractive candidate for a lithium battery without thermorunaway.
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