Sodium metal batteries (SMBs) are receiving broad attention due to the high specific capacity of sodium metal anode and its abundance on earth. However, the growth of dendrites results in poor battery performance and severe safety problems, inhibiting the commercial application of SMBs. In order to stabilize sodium metal anodes, various methods have been developed to optimize the solid electrolyte interphase (SEI) layer and adjust the electroplating/stripping behavior of sodium. Among them, developing anode host materials and adding electrolyte additives to build a protective layer are promising and convenient ways. However, the understanding of the interaction process between sodium metal and those organic materials is still limited, which is essential for the rational design of advanced anode hosts and electrolyte additives. In this paper, we use copper(II) hexadecafluorophthalocyanine (F16CuPc) and copper(II) phthalocyanine (CuPc) as model systems to unravel the sodium interaction with polar functional groups by in-situ photoelectron spectroscopy and density functional theory (DFT) calculations. It is found that sodium atoms prefer to interact with the inner pyrrolic nitrogen sites of CuPc, while they prefer to interact with the outer aza bridge nitrogen atoms owing to Na-F interaction at Na/F16CuPc interface. Besides, for both organic molecules, the central Cu(II) ions are reduced to Cu(I) ions by charge transfer from deposited sodium. The observed fluorination promoted interaction process of sodium in organic materials sheds light on the design of functional interfaces in host materials and anode protective layers for sodium metal anodes.

Probing fluorination promoted sodiophilic sites with model systems of F16CuPc and CuPc

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