Use of poly[ionic liquid] as a conductive binder in lithium ion batteries
In the present work, we studied the performance of different new binders based on poly[ionic liquids] (POILs) using a well-known negative electrode material such as Li4Ti5O12 (LTO) compound and ionic liquids (ILs) as solvents. We used an IL formed by Pip1,4Tf2N with N-butyl-N-methyl piperidinium (Pip1,4) as the cation and bis(trifluoromethanesulfonyl)imide (Tf2N−) as the anion. We tested two POILs as binders, composed of either LiTf2N, Pip1,4Tf2N, and PVDF or poly[diallyldimethylammonium]Tf2N (PDDA) as the polymer precursors (PVDF-IL and PDDA-IL, respectively). The best Li+ transport number as well as the smallest contact angle (electrolyte membrane) was obtained for the PDDA-IL polymer. The swelling effect better facilitates impregnation than the other polymers. The LTO/PDDA-IL combination showed the best specific capacity, 70 mAh g−1, and a stable prolonged cycling. We identified the TiIV/TiIII redox reversible processes by cyclic voltammetry experiments and the differential capacity profiles. Additionally, we measured the Li+ diffusion coefficient to be approximately 10−12 cm2 s−1. When different binders and IL-solvents are employed in a typical LTO cell, we demonstrated that the factors that determine cell performance are the ionic conductivity and the swelling effect.
S. Chauque wishes to thank CONICET for the doctoral fellowship. This work was performed at the Instituto de Química of the Universidade de São Paulo in Brazil in collaboration with INFIQC/CONICET—Universidad Nacional de Córdoba and YPF-Tecnología, in Argentina. The authors also acknowledge FAPESP (15/26308-7) for funding.
This work was supported by Program BID-Foncyt (PICT-2015-1605).
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