In situ quantification of interphasial chemistry in Li-ion battery



The solid–electrolyte interphase (SEI) is probably the least understood component in Li-ion batteries. Considerable effort has been put into understanding its formation and electrochemistry under realistic battery conditions, but mechanistic insights have mostly been inferred indirectly. Here we show the formation of the SEI between a graphite anode and a carbonate electrolyte through combined atomic-scale microscopy and in situ and operando techniques. In particular, we weigh the graphitic anode during its initial lithiation process with an electrochemical quartz crystal microbalance, which unequivocally identifies lithium fluoride and lithium alkylcarbonates as the main chemical components at different potentials. In situ gas analysis confirms the preferential reduction of cyclic over acyclic carbonate molecules, making its reduction product the major component in the SEI. We find that SEI formation starts at graphite edge sites with dimerization of solvated Li+ intercalation between graphite layers. We also show that this lithium salt, at least in its nascent form, can be re-oxidized, despite the general belief that an SEI is electrochemically inert and its formation irreversible.

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Fig. 1: In situ, operando and quantitative characterization of live formation and chemistry of the SEI on graphite.
Fig. 2: In situ differential electrochemical mass spectroscopy measurements performed on the graphite electrode during SEI formation.
Fig. 3: Morphological observation of the SEI via in situ and operando AFM measurements during the first lithiation of HOPG.
Fig. 4: Re-oxidation of the nascent interphase observed by EQCM and AFM.
Fig. 5: Schematic illustration of the interphasial formation chemistry during the very first lithiation.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.


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This research was supported financially by the National Materials Genome Project (2016YFB0700600), the Guangdong Innovation Team Project (no. 2013N080) and Shenzhen Science and Technology Research Grants (nos. JCYJ20151015162256516, JCYJ20150729111733470 and JCYJ20160226105838578). J.Lu and K.A. acknowledge support from the US Department of Energy under contract no. DE-AC0206CH11357 with the main support provided by the Vehicle Technologies Office, Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy. Support provided by the China Scholarship Council (CSC) during a visit of T.L. to Argonne National Laboratory is acknowledged.

Author information

F.P., K.X., K.A. and T.L. conceived the work and designed the experiments. L.L., L.T. and K.Y. carried out the in situ AFM results. T.L., X.B., Z.C. and J. Lu performed the electrochemical measurements. T.L., J. Liu and M.L. conducted the TEM measurements. K.A., J. Lu, F.P. and K.X. wrote the manuscript, and all authors edited the manuscript.

Correspondence to Jun Lu or Khalil Amine or Kang Xu or Feng Pan.

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