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

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.