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A functional SrF2 coated separator enabling a robust and dendrite-free solid electrolyte interphase on a lithium metal anode

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Abstract

An unstable solid electrolyte interphase (SEI) and accompanying Li metal dendrites are the key impediments to commercialization of high-energy lithium metal batteries (LMBs). We employ a strontium fluoride (SrF2) microsphere coated polypropylene (PP) separator to stabilize the SEI and to prevent dendrites from growing. This approach is tested with Li‖Cu half-cells, Li‖Li symmetrical cells, and Li‖NMC full LMBs, there being a major improvement in each case. The Li‖Cu cell with SrF2 maintains a stable coulombic efficiency (CE) of 80% after 100 cycles, when tested at 0.25 mA cm−2 to a capacity of 0.5 mA h cm−2. By comparison, the uncoated PP reference has a CE of 10% in cycle 60. The Li‖Li cell with SrF2 exhibits a markedly smaller voltage polarization and is able to stably cycle for approximately 340 h vs. the reference which begins to display severe voltage instability at 200 h. The Li‖NMC full LMB with SrF2 shows an initial discharge capacity of 173 mA h g−1, with 167 mA h g−1 (96.5%) being retained after 200 cycles at 200 mA g−1 (1C rate). The SrF2 containing LMB also has a substantially improved rate capability over the reference, the difference being drastic even at the highest testing rate of 20C. First-principles calculations based on DFT indicate that lithium ions prefer to adsorb onto the SrF2 surface, which should create a more uniform ion flux and reduce the propensity for dendrite nucleation. In parallel, the SrF2 spheres bind with the SEI layer, creating a tough in situ formed composite membrane that mechanically stabilizes a planar metal interface.

Graphical abstract: A functional SrF2 coated separator enabling a robust and dendrite-free solid electrolyte interphase on a lithium metal anode

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Publication details

The article was received on 27 Jun 2019, accepted on 22 Aug 2019 and first published on 22 Aug 2019


Article type: Paper
DOI: 10.1039/C9TA06908A
J. Mater. Chem. A, 2019, Advance Article

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    A functional SrF2 coated separator enabling a robust and dendrite-free solid electrolyte interphase on a lithium metal anode

    X. Li, Y. Liu, Y. Pan, M. Wang, J. Chen, H. Xu, Y. Huang, W. M. Lau, A. Shan, J. Zheng and D. Mitlin, J. Mater. Chem. A, 2019, Advance Article , DOI: 10.1039/C9TA06908A

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