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Diffusion: a comparision between liquid and solid polymer LiTFSI electrolytes
Umeå University, Faculty of Science and Technology, Chemistry.
Umeå University, Faculty of Science and Technology, Chemistry.
2001 (English)In: 13th International Conference on Solid State Ionics (8-14 July 2001), Cairns, AUSTRALIA, 2001Conference paper (Refereed)
Abstract [en]

From careful analyses of pfg-NMR data, it is demonstrated that the size of the diffusing Li+·xH2O complex in an aqueous solution of LiTFSI is strongly dependent on salt concentration, with the number of solvating water units ranging from six in dilute (H2O)500LiTFSI to two in highly concentrated (H2O)5LiTFSI. Such a relationship is explained by a mass tendency toward a lower solvation number as the number of available H2O molecules per lithium ion decreases. In a liquid (PEO)nLiTFSI system, a contrasting situation prevails, since the size of the diffusing Li+ complex is almost constant over a large salt concentration range (5≤n≤50). Our interpretations of these data imply that one PEO chain, containing on average nine ether oxygen units, is able to dissolve up to two lithium ions, but exclude the possibility of cationic crosslinks between different PEO chains and direct ionic interactions. For solid P(EO)nLiTFSI eletrolytes, a significantly lower value for the diffusion coefficient of the small lithium ions as compared to that of the large TFSI ions (DLi=0.2DTFSI) was found for all salt concentrations investigated (5≤n≤50). This observation fits in with recent structural observations, which suggest that lithium ions move as single entities in this specific system and require a rather complicated solvation–desolvation step for long-range motion. In all electrolytes investigated, both liquid and solid, the large and bulky TFSI ion appears to be moving as a single unit, thus manifesting the excellent ionization properties of the LiTFSI salt.

Place, publisher, year, edition, pages
Keyword [en]
Solid polymer electrolyte, Liquid electrolyte, PEO, H2O, LiTFSI, Ionic self-diffusion, pfg-NMR
URN: urn:nbn:se:umu:diva-10027DOI: doi:10.1016/S0167-2738(02)00364-8OAI: diva2:149698
Solid State Ionics 2002, volumes 152-153, pages 131-6Available from: 2008-06-11 Created: 2008-06-11Bibliographically approved

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