Drawing from the Old‐The First Ever Sultone as Electrolyte Additive in High‐Voltage NMC811 || AG+SiOx Multilayer Pouch Cells

Abstract The addition of a small amount of silicon to the anode material is a widely used approach to increase the energy density of lithium‐ion batteries (LIBs). However, its (de‐)lithiation leads to volume changes, resulting in structural degradation and the formation of an insufficient solid‐electrolyte interphase (SEI), limiting the cycle life and electrochemical performance. Therefore, the formation of an effective SEI is imperative to overcome these challenges. Sulfur‐containing electrolyte additives are garnering attention due to their abundant supply and advantageous chemistry in LIBs. With 1,8‐naphthosultone (1,8‐NS) as an electrolyte additive, a notably enhanced electrochemical performance in high‐voltage NMC811 || artificial graphite(AG) + 20 % SiO x cells is observed. Employing advanced spectrometric and spectroscopic characterization techniques, complemented with theoretical calculations, the degradation products and pathways of 1,8‐NS in the cell are elucidated. This includes 1,8‐NS reduction, sultone ring opening, and chemical degradation with electrolyte solvent degradation products. The formation of these products is traced back to the SiO x anode, where an effective, layered SEI with various 1,8‐NS degradation products is formed. This SEI is suggested to exhibit improved mechanical and electrochemical parameters, resulting in the observed improvement of the electrochemical performance of the cells.