Investigation of the Interface Between Graphite Electrode and Ionic Liquid Based Electrolyte
From the literature it is known, that for IL-electrolytes the addition of organic carbonates is crucial for improving the performance of the carbon based batteries (5). Their role is associated to the creation of interfacial compatibility between the Cgr/IL and formation of Solid Electrolyte Interphase (SEI) (6). Several studies concern the SEI characterization on Cgr surface with organic carbonates (7) or neat IL based electrolytes (8) but few with IL based electrolytes doped by carbonate. Recently, we have tested safe and low-cost full cell configuration based on Cgr//LiFePO4 (LFP) with as electrolyte a mixture of (1‑hexyl-3-methylimidazolium (bis(trifluoromethanesulfonyl) imide) C1C6ImNTf2 with LiNTf2 (1mol.L-1) and vinylene carbonate, VC (5% vol.) (5).
In this work, we report the evolution of Cgr electrode, before and after one and 400 cycling (at 60°C) by FIB-SEM and XPS techniques. FIB-SEM method shows the presence IL components inside the graphite particles and formation of non-homogenous film. The post mortem XPS analyses indicated that the surfaces were covered by an IL layer. The appearance of peak associated to LiF on the graphite surface after the first cycle is clearly observed, nonetheless its intensity does not change after 400 cycles as the ratio F / N, Table 1. In the N 1s region the peaks due to both the cation and anion, in pure ILs show a relative ratio of Ncation/Nanion close to stoichiometry (2:1). This ratio changes with the number of cycling from 0,8 to 0,6; suggesting a higher degradation of cation. Further results will be discussed during the poster presentation.
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