Solid electrolyte interphase layer formation on mesophase graphite electrodes with different electrolytes studied by small‐angle neutron scattering.

Relative solid electrolyte interphase (SEI) film thickness investigation on graphite electrodes after the first charge state in the lithium‐ion battery was successfully demonstrated by the ex‐situ small‐angle neutron scattering technique. Here, for both the mesophase graphite powder (MGP) and the fine‐mesophase graphite powder (FMGP) anodes, with two different particle sizes was analyzed precisely by the Guinier–Porod model. The data revealed a stable, maximum (~tens of nm) bi‐layer SEI film formed on MGP anode in ethylene‐carbonate/dimethyl‐carbonate (EC/DMC) at a capacity of 50 mAh/g and sluggish above 100 mAhg‐1. The SEI formed on FMGP with and without 3 wt% fluoroethylene‐carbonate additive in EC/DMC showed the relative thickness greater than that only in ethylene‐carbonate/diethyl‐carbonate. Lithiation initiated the rapid SEI formation on the graphite surface and achieved a maximum thickness in the cell potential ≤0.2 V, and became thinner when the graphite particle expanded after Li+ intercalation. It was observed that the SEI thickness influenced the electrolytes and additives, which might ultimately impact battery performance. Our preliminary results make evident that small‐angle neutron scattering could be employed to better understand the complex microstructure solid electrolyte interphase formation and its accurate thickness, on a mesophase graphite anode. [ABSTRACT FROM AUTHOR]