成果報告書詳細
管理番号20090000000759
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/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2010/3/24
報告書年度2008 - 2008
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 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 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有機電解液中に比べてイオン液体中では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修飾の効果について検討を行った.
英文要約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
Ionic liquids have been studied as alternative electrolytes for rechargeable lithium batteries because of their non-flammability, which is expected to improve safety of the batteries in case of accidents. However, the ionic conductivities of most of ionic liquids are often lower than those of conventional organic electrolytes. Furthermore, the charge transfer resistances at negative and positive electrodes in ionic liquids are known to be generally higher than those in conventional organic electrolytes. In the present development, the effect of some additives on the charge transfer resistance has been studied on a tin electrode in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) ionic liquid. In addition, the surface modification of a tin electrode with thin polymer films has been also examined in order to reduce the charge transfer resistances and to improve cycle performance of alloying anodes.
The lithium dope and undope reactions for a tin electrode were found to be possible in 1 M LiTFSA/BMPTFSA electrolyte both with and without addition of some glymes (CH3-O-(CH2-CH2-O)n-CH3, n = 1 ~ 4). The charge transfer resistance was examined for the electrode with a composition of LiSn at the open circuit potential using electrochemical impedance spectroscopy. The charge transfer resistances in the electrolyte with the glymes were smaller than that in the electrolyte without glymes, indicating the addition of the glymes is effective for enhancement of the electrode kinetics probably due to the selective coordination of the glymes against lithium ions in the ionic liquid. It was found that the charge transfer resistance in the electrolyte with 0.2 M monoglyme (n = 1) was one fifth of that in the neat electrolyte.
The tin electrode modified with lithium polyacrylate (PAALi) or polyethylene oxide with LiTFSA (PEO/LiTFSA) was prepared by a casting method. Charge and discharge were found to be impossible when the tin electrode was modified with thick PAALi film (200 -g cm-2). On the other hand, lithium dope and undope reactions were possible on the tin electrode modified with PEO/LiTFSA. The charge transfer resistance for the PEO/LiTFSA modified electrode was a little smaller than that for the unmodified electrode, probably because the reaction occurs at the interface between the electrode and the polymer film, in which lithium ions are dissociated with ether oxygen atoms. Furthermore, cycle performance of the PEO/LiTFSA modified electrode was superior to that of unmodified electrode. It has been known that the cycle performance of a tin anode is poor due to embrittlement caused by swelling and shrinking along charge and discharge process. The modification of the tin electrode with PEO/LiTFSA is considered to prevent the active material from falling off the electronic pathways.
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