The surface reactions of electrolytes with the graphitic anode of lithium ion batteries have been investigated. The investigation utilizes two novel techniques, which are enabled by the use of binder-free graphite anodes. The first method, transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy, allows straightforward analysis of the graphite solid electrolyte interphase (SEI). The second method utilizes multi-nuclear magnetic resonance (NMR) spectroscopy of D 2 O extracts from the cycled anodes. The TEM and NMR data are complemented by XPS and FTIR data, which are routinely used for SEI studies. Cells were cycled with LiPF 6 and ethylene carbonate (EC), ethyl methyl carbonate (EMC), and EC/EMC blends. This unique combination of techniques establishes that for EC/LiPF 6 electrolytes, the graphite SEI is ∼50 nm thick after the first full lithiation cycle, and predominantly contains lithium ethylene dicarbonate (LEDC) and LiF. In cells containing EMC/LiPF 6 electrolytes, the graphite SEI is nonuniform, ∼10−20 nm thick, and contains lithium ethyl carbonate (LEC), lithium methyl carbonate (LMC), and LiF. In cells containing EC/EMC/LiPF 6 electrolytes, the graphite SEI is ∼50 nm thick, and predominantly contains LEDC, LMC, and LiF.

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The performance of the novel lithium salt, lithium tetrafluorooxalatophopshate (LiPF 4 (C 2 O 4 )) has been investigated as electrolyte solution in carbonate solvents. Investigation of the performance of LiPF 4 (C 2 O 4 ) electrolytes in the presence of different types of anode materials, Mesocarbon Microbead (MCMB) graphite and Nature Graphite (NG), has uncovered a dependence of a first cycle shoulder at 1.75 V and irreversible capacity on the structure of the anodic graphite. Andoes with more irreversible capacity have a thicker anode solid electrolyte interphase (SEI) which is most likely caused by differences in the surface of the graphite. Appropriate choice of graphite leads to first cycle efficiencies which are very similar for LiPF 4 (C 2 O 4 ) and LiPF 6 electrolytes.