成果報告書詳細
管理番号20110000000018
タイトル*平成21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/次世代技術開発/イオン液体電解液を用いたリチウム二次電池の研究開発
公開日2011/1/25
報告書年度2009 - 2009
委託先名学校法人慶應義塾
プロジェクト番号P07001
部署名燃料電池・水素技術開発部
和文要約和文要約等以下本編抜粋:1. 研究開発の内容及び成果等
1-1背景
難揮発性・難燃性のイオン液体をリチウム二次電池の電解液として用いることによって、リチウム二次電池の安全性の大幅な向上が期待される。しかしながら、イオン液体の多くはイオン伝導率が低く、また、正極および負極における電極反応速度が遅いことが実用化への障害となっている。また、従来の炭素より比容量の大きな合金系負極を用いることで、リチウム二次電池のエネルギー密度の向上が期待されるが、イオン液体電解液中での合金負極の反応について検討された例は少ない。本研究開発では、1‐ブチルー1‐メチルピロリジニウム・ビス(トリフルオロメチルスルフォニル)アミド(BMPTFSA)イオン液体にリチウムイオン源としてLiTFSA を加えたものを電解液として用い、スズ負極に対するリチウムのドープ・脱ドープ反応における、各種添加剤および高分子による表面被覆の効果について検討を行った。
英文要約Title : Development of High-performance Battery System for Next-generation Vehicles Next-generation Technology Development
Development of Rechargeable Lithium Batteries with Ionic Liquid Electrolytes
Takashi Miura, Keio University
  Not only high energy density and high power density but also a high-level safety is strictly required for rechargeable lithium batteries employed in practical electric vehicles. By use of non-flammable electrolytes possible, dangerous accidents such as combustion and explosion can be avoided to some extent. Ionic liquids have attracted much attention recently as a promising candidate of non-flammable electrolytes for rechargeable lithium batteries. However, the ionic conductivity of most ionic liquids remains lower than that of conventional organic solvent electrolytes. Moreover, the resistance at the electrode-electrolyte interface is often high in ionic liquids compared with that in organic electrolytes. We have so far found that the interfacial resistance at the Sn electrode can be drastically reduced by addition of a kind of glymes (CH3-O-(CH2-CH2-O)n-CH3, n = 1~4, abbreviated as nG) into an ionic liquid electrolyte, 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)amide (BMP-TFSA) containing LiTFSA. In the present studies, some properties of the ionic liquid electrolyte containing various glymes have been investigated by both electrochemical and spectroscopic methods.
  TFSA- anion is known to have two different conformations, trans- and cis-TFSA-. which can be distinguished by the IR absorption spectroscopy. The SO2 absorption band attributed to cis-TFSA- increased with increasing the LiTFSA/BMPTFSA molar ratio, probably because Li+ ions are coordinated with cis-TFSA- to form [Li(TFSA)2]-. Thus, the concentration of [Li(TFSA)2]- in the electrolytes can be estimated by IR spectroscopy. On the other hand, the concentration of [Li(TFSA)2]- decreased by adding glyme molecules into 1 M LiTFSA / BMPTFSA, suggesting the preferential formation of another complex of [Li(nG)m]+. The coordination numbers of glymes, m, were estimated to be 2.5, 1.2, 1.0 and 0.9 for 1G, 2G, 3G and 4G, respectively. The molar conductivity of the ionic liquid electrolytes became lower almost monotonously with increasing the molar fraction of [Li(TFSA)2]-. Accordingly, the formation of a bulky [Li(TFSA)2]- complex may be suspected to lower the conductivity of these electrolytes.
  The interfacial resistance at LixSn (x = 1.5) determined by AC impedance measurements in these ionic liquid electrolytes was revealed to decrease by addition of the glyme into 1 M LiTFSA / BMPTFSA. For example, the interfacial resistance in the presence of 0.01 M glyme was almost one tenth smaller than that without any additive, suggesting that only a small amount of [Li(nG)m]+ is able to reduce the interfacial resistance considerably.
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