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      Lithium metal stripping beneath the solid electrolyte interphase

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          Abstract

          <p id="d1986764e235">This study explores the stripping of lithium anodes under various current densities and in different liquid electrolyte systems. We discovered nanovoid formation between the lithium and the solid electrolyte interphase (SEI). Lithium polarization behavior has been systematically investigated with a three-electrode system and ultramicroelectrode. The diffusion and migration of lithium cations across the SEI have been determined to be the main contributors to the stripping overpotential. Two modes of stripping are proposed based on the passivation condition of lithium: stripping on passivated lithium and pitting on lithium after SEI layer breakdown. The present work provides a mechanistic explanation of Coulombic efficiency decay under high charging current density. We also demonstrate that metallurgical factors greatly accelerate the local dissolution of lithium. </p><p class="first" id="d1986764e238">Lithium stripping is a crucial process coupled with lithium deposition during the cycling of Li metal batteries. Lithium deposition has been widely studied, whereas stripping as a subsurface process has rarely been investigated. Here we reveal the fundamental mechanism of stripping on lithium by visualizing the interface between stripped lithium and the solid electrolyte interphase (SEI). We observed nanovoids formed between lithium and the SEI layer after stripping, which are attributed to the accumulation of lithium metal vacancies. High-rate dissolution of lithium causes vigorous growth and subsequent aggregation of voids, followed by the collapse of the SEI layer, i.e., pitting. We systematically measured the lithium polarization behavior during stripping and find that the lithium cation diffusion through the SEI layer is the rate-determining step. Nonuniform sites on typical lithium surfaces, such as grain boundaries and slip lines, greatly accelerated the local dissolution of lithium. The deeper understanding of this buried interface stripping process provides beneficial clues for future lithium anode and electrolyte design. </p>

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          Most cited references27

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          High rate and stable cycling of lithium metal anode

          Lithium metal is an ideal battery anode. However, dendrite growth and limited Coulombic efficiency during cycling have prevented its practical application in rechargeable batteries. Herein, we report that the use of highly concentrated electrolytes composed of ether solvents and the lithium bis(fluorosulfonyl)imide salt enables the high-rate cycling of a lithium metal anode at high Coulombic efficiency (up to 99.1%) without dendrite growth. With 4 M lithium bis(fluorosulfonyl)imide in 1,2-dimethoxyethane as the electrolyte, a lithium|lithium cell can be cycled at 10 mA cm−2 for more than 6,000 cycles, and a copper|lithium cell can be cycled at 4 mA cm−2 for more than 1,000 cycles with an average Coulombic efficiency of 98.4%. These excellent performances can be attributed to the increased solvent coordination and increased availability of lithium ion concentration in the electrolyte. Further development of this electrolyte may enable practical applications for lithium metal anode in rechargeable batteries.
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            Selective deposition and stable encapsulation of lithium through heterogeneous seeded growth

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              The synergetic effect of lithium polysulfide and lithium nitrate to prevent lithium dendrite growth.

              Lithium metal has shown great promise as an anode material for high-energy storage systems, owing to its high theoretical specific capacity and low negative electrochemical potential. Unfortunately, uncontrolled dendritic and mossy lithium growth, as well as electrolyte decomposition inherent in lithium metal-based batteries, cause safety issues and low Coulombic efficiency. Here we demonstrate that the growth of lithium dendrites can be suppressed by exploiting the reaction between lithium and lithium polysulfide, which has long been considered as a critical flaw in lithium-sulfur batteries. We show that a stable and uniform solid electrolyte interphase layer is formed due to a synergetic effect of both lithium polysulfide and lithium nitrate as additives in ether-based electrolyte, preventing dendrite growth and minimizing electrolyte decomposition. Our findings allow for re-evaluation of the reactions regarding lithium polysulfide, lithium nitrate and lithium metal, and provide insights into solving the problems associated with lithium metal anodes.
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                Author and article information

                Journal
                Proceedings of the National Academy of Sciences
                Proc Natl Acad Sci USA
                Proceedings of the National Academy of Sciences
                0027-8424
                1091-6490
                August 21 2018
                August 21 2018
                August 21 2018
                August 06 2018
                : 115
                : 34
                : 8529-8534
                Article
                10.1073/pnas.1806878115
                6112724
                30082382
                ba0aa3e1-19d2-4dad-8206-1d8b88f2f2ce
                © 2018
                History

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