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Matthew McDowell1

1, Georgia Institute of Technology, Atlanta, Georgia, United States

The vast majority of solid-state electrolyte (SSE) materials are unstable in contact with lithium metal, and (electro)chemical reactions between SSEs and lithium result in the formation of an interphase region [1]. Understanding the growth kinetics and chemo-mechanical consequences of interphase formation is key for controlling solid-state interfaces, which may enable the use of a wider variety of SSE materials within lithium metal batteries. Here, we investigate NASICON-structured L1+xAlxGe2-x(PO4)3 (LAGP), as well as sulfide-based SSEs. For LAGP, multi-modal in situ investigation of interfacial reactions combined with electrochemical experiments reveal how the formation of the interphase is linked to cell failure. In situ transmission electron microscopy (TEM) shows that the reaction of LAGP with lithium is similar to a conversion reaction, in which lithium insertion causes amorphization and volume expansion of ~130% [2]. The interphase is a mixed ionic-electronic conductor, resulting in continuous growth. In situ X-ray tomography experiments of operating LAGP-based cells reveal that the growth of the interphase causes fracture of the SSE, and quantification of the crack network shows that the extent of fracture with time is directly correlated to impedance increases within the cell [3]. Finite-element analysis is used to model stress evolution during interphase formation, and the initial fracture locations predicted from modeling correspond well to experimental observations. Interestingly, we have found that interphase growth trajectories can be modulated through the deposition of interfacial protection layers. Controlling the morphology of the interphase with protection layers results in the ability to extend cycling stability of symmetric cells from ~30 hours with unprotected SSEs to >1000 hours with protected materials. Overall, these results provide fundamental insight into interfacial transformations in SSEs, and they show that control over interfacial transformation processes could enable a wider variety of materials to be used in solid-state lithium metal batteries.

1. V. Augustyn, M. T. McDowell, A. Vojvodic “Towards an Atomistic Understanding of Solid-State Electrochemical Interfaces for Energy Storage,” Joule, 2018, 2, (11), 2189-2193.

2. J. A. Lewis, F. J. Q. Cortes, M. G. Boebinger, J. Tippens, T. S. Marchese, N. Kondekar, X. Liu, M. Chi, M. T. McDowell “Interphase Morphology Between a Solid-State Electrolyte and Lithium Controls Cell Failure” ACS Energy Letters, 2019, 4, (2), 591-599.

3. J. Tippens, J. C. Miers, A. Afshar, J. A. Lewis, F. J. Q. Cortes, H. Qiao, T. S. Marchese, C. V. Di Leo, C. Saldana, M. T. McDowell “Visualizing Chemo-Mechanical Degradation of a Solid-State Battery Electrolyte” ACS Energy Letters, 2019, DOI: 10.1021/acsenergylett.9b00816.

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