Nonaqueous electrolyte solutions in current lithium-ion cells achieve stability toward the graphite anode (negative electrode) via the formation of passive surface films on the anode surface. These films are composed of reaction products resulting from electrolyte reduction and some reduced lithium. These films reportedly contain various lithium compounds, such as lithium carbonate (Li 2 CO 3 ), lithium oxide (Li 2 O), lithium hydroxide (LiOH), lithium alkoxides, lithium fluoride (LiF), as well as electrolyte salt reduction products that are still to be accurately characterized. 1 Relative amounts of these constituents are also equally uncertain. In addition to the expense of lithium for such surface films, termed solid electrolyte interphase (SEI), 2 a portion of lithium might be "trapped" in the anode material and is "kinetically inaccessible." Consequently, a differential exists between the intercalated lithium (charge capacity) and deintercalated lithium (discharge capacity), which is loosely termed irreversible capacity. This irreversible capacity depends not only on the rate of lithiation during the formation cycles and the temperature, but also on the extent of charge-discharge cycling, during which the surface film may grow. Irreversible capacity is typically estimated as the cumulative differential in the capacity after five cycles (one cycle in some reports), when the charge capacity/discharge capacity ratio approaches unity.It is difficult to separate the irreversible capacity into a component involving SEI formation and a component involving capacity loss due to kinetic effects, unless one of the components is estimated by a nonelectrochemical method. In this work, we attempted such a study on SEI formation on graphite in different electrolyte solutions using solid-state 7 Li nuclear magnetic resonance (NMR). Solid-state 7 Li NMR has been commonly used for qualitative detection and characterization of lithium intercalation in (and the SEI formation on) graphite and disordered carbons. 3-8 However, this technique has not been used extensively for quantitative determinations. In this work, the surface films were also examined ex situ by transmission electron microscopy (TEM) for elucidating the microstructure of film-covered graphite electrodes. These studies were further complemented by electrochemical impedance spectroscopy (EIS) measurements to understand the surface film characteristics of graphite anodes in different electrolytes.Improving low-temperature performance of lithium-ion cells remains a formidable technical challenge. The present investigation is an outgrowth of our previous studies 9 of novel electrolyte formulations for low-temperature performance. Similar efforts to improve the properties of electrolytes at low temperatures are being made elsewhere. 10-14 Our recent results have shown that a ternary mixture of alkyl carbonates, i.e., 1:1:1 (vol. %) of EC (ethylene carbonate):DEC (diethyl carbonate):DMC (dimethyl carbonate) with 1 M LiPF 6 exhibits favorable electrochemical characteris...