Regulating the Inner Helmholtz Plane for Stable Solid Electrolyte Interphase on Lithium Metal Anodes

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Abstract
The stability of a battery is strongly depended on the feature of solid electrolyte interphase (SEI). The electrical double layer forms prior to the formation of SEI at the interface between Li metal anode and electrolyte. The fundamental understanding on the regulation of the SEI structure and stability on Li surface through structure of electrical double layer is highly necessary for safe batteries. Herein the interfacial chemistry of SEI is correlated with the initial Li surface adsorption electrical double layer at nanoscale through theoretical and experimental analysis. Under the premise of the constant solvation sheath structure of Li+ in bulk electrolyte, a trace amount of lithium nitrate (LiNO3) and copper fluoride (CuF2) were employed into electrolytes to build robust electric double layer structures on Li metal sur-face. The distinct results were achieved with the initial competitive adsorption of bis(fluorosulfonyl)imide ion (FSI−), fluoride ion (F−) and nitrate ion (NO3−) in inner Helmholtz plane. As a result, Cu–NO3− complexes are preferentially adsorbed and reduced to form SEI. The modified Li metal electrode can achieve an average Coulombic efficiency of 99.5% over 500 cycles, enabling a long lifespan and high capacity retention of practical rechargeable batteries. The mechanism as-proposed bridges the gap between Li+ solvation and the adsorption about the electrode interface formation in a working battery.
Funding Information
  • Ministry of Science and Technology of the People's Republic of China (2016YFA0200102, 2016YFA0202500)
  • Tsinghua University
  • National Natural Science Foundation of China (21676160, 21776019, 21805161, 21825501, U1801257)

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