The Solid Electrolyte Interphase a key parameter of the high performance of Sb in sodium-ion batteries: Comparative X-ray Photoelectron Spectroscopy study of Sb/Na-ion and Sb/Li-ion batteries

To understand the origin of the better performance of Sb electrode i) vs Na than vs Li and ii) formulated with CarboxyMethyl Cellulose (CMC) in water rather than with PolyVinylidene diFluoride (PVdF) in N-Methyl-2-Pyrrolidone (NMP), X-ray Photoelectron Spectroscopy (XPS) and electrochemical tests have been carried out to carefully investigate the chemical composition of the SEI layer formed at the Sb electrode surface in the Li- and Na-system, with the different binders. Sb electrodes were cycled using a standard EC/PC/3DMC (1 M LiPF6) electrolyte containing Vinylene Carbonate (VC) and FluoroEthylene Carbonate (FEC) for Li system and a standard Propylene Carbonate PC (1 M NaClO4) electrolyte containing FEC for Na system. Surface analysis was performed by a combined XPS core peaks and quantification data analysis to establish the main components of the Solid Electrolyte Interphase film (SEI). The key observation is that the thickness of the SEI layer is strongly related to the nature of the polymer binder used in the formulation and that its chemical nature is different in Li and Na batteries. Much favorable SEI in the case of Sb-CMC/Na seems to participate to the excellent performance of this electrode.