4.8 Article

Additives synergy for stable interface formation on rechargeable lithium metal anodes

Journal

ENERGY STORAGE MATERIALS
Volume 29, Issue -, Pages 377-385

Publisher

ELSEVIER
DOI: 10.1016/j.ensm.2019.12.027

Keywords

Lithium metal anode; Solid electrolyte interphase; Additive; Lithium difluorophosphate; Vinylene carbonate

Funding

  1. National Natural Science Foundation of China [21761132030, 21428303, 21621091]
  2. National Key Research and Development Program of China [2018YFB0905400, 2016YFB0901500]
  3. Chinese Scholarship Council (CSC)
  4. Netherlands Organization for Scientific Research (NWO) under the VICI Grant [16122]

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The attention towards lithium (Li) metal anodes has been rekindled in recent years as it would boost the energydensity of Li batteries. However, notorious safety issues and cycling instability severely hinder their commercialization, especially when cycled in traditional carbonic ester electrolytes that exhibit a wide voltage window and are compatible with most of the cathode materials. Herein, lithium difluorophosphate (LiDFP) and vinylene carbonate (VC) are combined, and demonstrated to be synergistic in constructing in situ a mechanically stable and highly Li-ion conducting surface film on the Li metal anode. This results in uniform and compact Li deposition largely suppressing the formation of Li dendrites, dead lithium and irreversible Li-species as revealed by operando neutron depth profiling (NDP). This enables long-term cycling stability and enhancement of the Coulombic efficiency for rechargeable Li metal anodes. By combining solid state nuclear magnetic resonance (SSNMR) and spectroscopic studies, it is demonstrated that VC slows down the LiDFP reduction, yet promoting the breaking of the P-F bonds, which leads to a protective film. This film is rich in LiF-Li3PO4 inorganic compounds, distributed homogeneously, that is embedded in a matrix of P-O-C species and macromolecular organic compounds like lithium ethylene dicarbonate. This composition is responsible for the improved ionic conductivity and mechanical stability of the protective film during extended cycles. The detailed insight in the additives interaction provides new opportunities for the design of rational surface films necessary for realizing high-performance lithium metal batteries.

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