The solid–electrolyte interphase (SEI) dictates the performance of most batteries, but the understanding of its chemistry and structure is limited by the lack of in situ experimental tools. In this work, we present a dynamic picture of the SEI formation in lithium-ion batteries using in operando liquid secondary ion mass spectrometry in combination with molecular dynamics simulations. We find that before any interphasial chemistry occurs (during the initial charging), an electric double layer forms at the electrode/electrolyte interface due to the self-assembly of solvent molecules. The formation of the double layer is directed by Li+ and the electrode surface potential. The structure of this double layer predicts the eventual interphasial chemistry; in particular, the negatively charged electrode surface repels salt anions from the inner layer and results in an inner SEI that is thin, dense and inorganic in nature. It is this dense layer that is responsible for conducting Li+ and insulating electrons, the main functions of the SEI. An electrolyte-permeable and organic-rich outer layer appears after the formation of the inner layer. In the presence of a highly concentrated, fluoride-rich electrolyte, the inner SEI layer has an elevated concentration of LiF due to the presence of anions in the double layer. These real-time nanoscale observations will be helpful in engineering better interphases for future batteries.
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All data that support the findings of this study have been included in the main text and Supplementary Information. The original data are archived at the Environmental Molecular Sciences Laboratory at Pacific Northwest National Laboratory and are available from the corresponding authors upon reasonable request.
The original code for MD simulation is kept at the Environmental Molecular Sciences Laboratory at Pacific Northwest National Laboratory and is available from the corresponding authors upon reasonable request.
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This work was supported by Laboratory Directed Research and Development (LDRD) programs (mainly an FY 16 Open Call LDRD and partially Chemical Dynamics Initiative) at Pacific Northwest National Laboratory (PNNL). C.W. thanks the support of the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the US Department of Energy under the Advanced Battery Materials Research (BMR) Program and the US–Germany Cooperation on Energy Storage. O.B. and K.X. at ARL were supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the US Department of Energy, Office of Science, Basic Energy Sciences (agreement SN2020957). Battelle operates PNNL for the US Department of Energy (DOE) under Contract DE-AC05- 76RL01830. The research was performed using the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the Department of Energy’s Office of Biological and Environmental Research and located at PNNL.
A US patent (10,505,234 B2) was granted to Battelle Memorial Institute for the protection of the innovation of the liquid battery cell used in this work.
Peer review information Nature Nanotechnology thanks Bing Joe Hwang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Zhou, Y., Su, M., Yu, X. et al. Real-time mass spectrometric characterization of the solid–electrolyte interphase of a lithium-ion battery. Nat. Nanotechnol. 15, 224–230 (2020). https://doi.org/10.1038/s41565-019-0618-4
ACS Energy Letters (2020)