The Li+ environment and transport in an ionic liquid (IL) comprised of Li+ and an anion of bis(trifluoromethanesulfonyl)imide anion (TFSI-) tethered to oligoethylene oxide (EO) (EO(12)TFSI-/Li+) were determined and compared to those in a binary solution of the oligoethylene oxide with LiTFSI salt (EO(12)/LiTFSI) by using molecular dynamics (MD) simulations and AC conductivity measurements. The latter revealed that the AC conductivity is 1 to 2 orders of magnitude less in the IL compared to the oligoether/salt binary electrolyte with greater differences being observed at lower temperatures. The conductivity of these electrolytes was accurately predicted by MD simulations, which were used in conjunction with a microscopic model to determine mechanisms of Li+ transport. It was discerned that structure-diffusion of the Li+ cation in the binary electrolyte (EO(12)/LiTFSI-) was similar to that in EO(12)TFSI-/Li+ IL at high temperature (>363 K), thus, one can estimate conductivity of IL at this temperature range if one knows the structure-diffusion of Li+ in the binary electrolyte. However, the rate of structure-diffusion of Li+ in IL was found to slow more dramatically with decreasing temperature than in the binary electrolyte. Lithium motion together with EO(12) solvent accounted for 90% of Li+ transport in EO(12)/LiTFSI-, while the Li+ motion together with the EO(12)TFSI- anion contributed approximately half to the total Li+ transport but did not contribute to the charge transport in IL.

Effects of anion size on ionic conductivity were studied for a series of solid polymer electrolytes prepared from lithium polyanionic salts based on a series of lithium bis͓͑perfluoromethyl͒sulfonyl͔imide ͑LiTFSI͒ units connected together by perfluoroalkane linkers to form oligomeric anionic chains of variable length. Solid polymer electrolytes were prepared from the salts using polyethylene oxide as the host and characterized using X-ray diffraction, differential scanning calorimetry, and electrochemical impedance spectroscopy. Ionic conductivities were measured over a temperature range between 120°C and ambient for electrolytes with ethylene oxide ͑EO͒/Li ratios of 30:1 and 10:1. Solid polymer electrolytes prepared from the lithium polyanionic salts exhibited ionic conductivities that were consistently lower ͑by factors of between 2 and 10͒ relative to those of monomeric LiTFSI-based electrolytes over the entire temperature and salt concentration ranges. This finding probably reflects a diminished contribution of anions to the overall conductivity for salts with large, polymeric anions. Trends in ionic conductivity with respect to anion chain length and EO/Li ratio were studied. The existence of an optimal anion chain length that is different for solid polymer electrolytes of differing EO/Li ratio was noted and is rationalized in terms of the cumulative effects of anion mobility, ion-pairing, variations in host chain dynamics in the vicinity of ions as a function of anion structure, and salt-phase segregation on the conductivity.

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A lithium-ion form of a perfluorosulfonate ionomer was used as a binder in LiFePO 4 -based lithium-ion battery cathodes. Carboncoated LiFePO 4 and acetylene carbon black were blended with ionomer to prepare composite cathodes having a composition 60% LiFePO 4 , 20% acetylene carbon black, and 20% binder by weight. Cathodes were tested against Li 4 Ti 5 O 12 anodes using 1.0 M and 0.1 M LiPF 6 -ethylene carbonate/diethyl carbonate ͑EC/DEC͒ electrolytes. Comparison was made with cathodes prepared using poly͑vinylidene͒ difluoride ͑PVDF͒ as binder. At low discharge rates ͑e.g., C/5͒ both cathode types exhibited similar chargedischarge capacities and voltage profiles. However, under higher rate discharge conditions ͑e.g., Ͼ1C, up to 5C͒ cathodes prepared using ionomer binder showed better discharge rate capability than cathodes having PVDF binder. This phenomenon was more pronounced when the salt concentration in the electrolyte was low ͑e.g., 0.1 M LiPF 6 -EC/DEC͒. These findings suggest that use of ionic binders can help to compensate for electrolyte depletion from the electrode porous space as lithium ions are intercalated into lithium-deficient LiFePO 4 particles during rapid discharging. Potential uses for electrodes having ionomer binders in enabling lower cost battery electrolytes ͑because of the reduced need for salt͒ and in developing high rate cathodes that are nonporous or have low porosity are discussed.Lithium-ion batteries are being aggressively developed for hybrid electric vehicle, plug-in hybrid electric vehicle, and electric vehicle applications. For many of these applications, a high rate performance ͑e.g., fast charge and discharge reactions͒ is essential. 1-3 Typical lithium-ion battery electrodes are composite mixtures obtained by blending electroactive material particles with non-electroactive additives such as carbon black and a polymeric binder. Lithium-ion transfer at the interface between the electrode and the electrolyte, as well as lithium transport inside the active materials and in the porous spaces of the electrode, are essential processes during battery charging and discharging, and the rates of these processes in part determine the overall battery performance. Therefore, it is important for the battery electrodes to possess high lithium ion and electron conductivity in order to efficiently transport lithium ions and electrons to and from each active material particle and the current collector, respectively. 4 In a typical lithium-ion battery electrode, the binder provides structural integrity at relatively low mass fractions ͑e.g., Ͻ10 wt %͒, bringing together the electroactive material and the carbon black. Nonionic polymers such as Teflon ͓poly͑tetrafluoroethyl-ene͒, PTFE͔ or poly͑vinylidene͒ difluoride ͑PVDF͒ which do not have any intrinsic ionic functionality are commonly used as electrode binders. Rapid and full penetration of liquid electrolytes into the accessible pores in the composite electrode and rapid transport of lithium ions into and out of the pores, are necessary in s...