Physicochemical properties and application of ionic liquids with N-P bonds as lithium secondary battery electrolytes

Nobuyuki Serizawa, Shiro Seki, Seiji Tsuzuki, Kikuko Hayamizu, Yasuhiro Umebayashi, Katsuhito Takei, Hajime Miyashiro

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

Physicochemical properties such as density, viscosity, ionic conductivity, and self-diffusion coefficient of two types of room-temperatureionic liquids composed of cations with N-P bonds were investigated. One is an ionic liquid composed of cations with N-P-O bond, namely, tri(N,N-dimethylamino)-n- butoxyphosphonium bis(trifluoromethanesulfonyl)amide (TABP-TFSA) and has a relatively low viscosity (38 mPa s at 30C) due to the high internal mobility of the cation, despite its large ion size. TABP-TFSA showed a characteristic electrochemical oxidation behavior, such as a wide electrochemical potential window of stability without gas evolution. Formation of passivation film on a Pt electrode was suggested from the results of potential sweep experiments. The lithium secondary battery ([LiCoO2Li] cell) using TABP-TFSA as the electrolyte achieved stable charge-discharge operations in over 500 cycles. For another ionic liquid with N-P bond, namely, TAEP-TFSA (TAEP+ tri(N-methyl-N-(n-butylamino))ethylphosphonium), less battery cycle stability and low rate performances were observed, despite the higher ionic dissociation than TABP-TFSA, probably because of the high viscosity and low electrochemical oxidative stability. It is shown that the introduction of oxygen in the cation like N-P-O produces better performances compared with the cation having N-P structure.

Original languageEnglish
Pages (from-to)A1023-A1030
JournalJournal of the Electrochemical Society
Volume158
Issue number9
DOIs
Publication statusPublished - 2011 Aug 3
Externally publishedYes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Renewable Energy, Sustainability and the Environment
  • Surfaces, Coatings and Films
  • Electrochemistry
  • Materials Chemistry

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