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| Author(s): |
Marcelo José Monteiro
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ) |
| Defense date: | 2010-09-03 |
| Examining board members: |
Roberto Manuel Torresi;
Rômulo Augusto Ando;
Paulo Sergio Santos;
Munir Salomão Skaf;
Edson Antonio Ticianelli
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| Advisor: | Roberto Manuel Torresi; Mauro Carlos Costa Ribeiro |
| Abstract | |
The searching for reliable power sources for electrical engines has lead to great efforts in order to synthesize new electrolytes to be used in Li-ion batteries in order to make them powerful and safe. Ionic liquids have been widely studied for this purpose. Lithium salt solutions of Li(CF3SO2)2N, LiTf2N, in a room-temperature ionic liquid (RTIL), 1-butyl-2,3-dimethyl-imidazolium cation, BMMI, and the (CF3SO2)2N-, bis(trifluoromethanesulfonyl)imide anion, Tf2N, were prepared in different concentrations. The addition of a lithium salt to this RTIL decreases the mobility of all species, especially Li+. Estimated conductivities (NMR-PGSE), Raman spectroscopy and Molecular Dynamics Simulation data suggest the formation of aggregates formed by [Tf2N] anions around Li+, with [Tf2N]´s oxygen atoms pointing toward Li+. These aggregates increase as LiTf2N content is increased, thus contributing to diminish conductivity. To overcome this obstacle, it was synthesized ionic liquids with ether-function-containing cations, so, oxygen atom from the ether group could compete for Li+ against the oxygen atoms from [Tf2N], preventing Li+ to form high mass aggregates improving the Li+ diffusion process. The chosen cations were the 1,2-dimethyl-imidazolium and N-methylmorpholine. RTILs were represented by [Et2OMMI][Tf2N] and [Et2OMor][Tf2N], respectively. Results show that [Et2OMMI][Tf2N] has a lower electrochemical window (3,8V) than [BMMI][Tf2N] (4,6V), but their reduction potential is equal, which makes them resistant to reduction by metallic lithium. These two RTIL´s have almost the same density and the viscosity of [Et2OMMI][Tf2N] is 20% lower than that of [BMMI][Tf2N]. Being less viscous, it is expected that [Et2OMMI][Tf2N] had a higher conductivity. It has in fact a conductivity 40% higher than [BMMI][Tf2N], which suggests that the ether chain add some structural modification to the system, showing that in this case, changes in charge transport is not only a function of the fluidity. Diffusion coefficients of [Et2OMMI][Tf2N] are higher than those of [Et2OMor][Tf2N], but a little bit lower than those of [BMMI][Tf2N]. It was also addressed the physical property changes in [BMMI][Tf2N] with the increasing addition of SO2. All the transport properties have improved and a decrease in ionic pair formation was suggested by experiment data (AU) | |