Molecular Design of Film-Forming Additives for Lithium-Ion Batteries: Impact of Molecular Substrate Parameters on Cell Performance

Film-forming electrolyte additives are crucial for establishing the performance and safety of high-energy-density lithium-ion batteries (LIBs). Thorough investigation of the solid electrolyte interphase (SEI) formation and of the decomposition mechanisms of the additives is needed. In this work, several derivatives of N-carboxyanhydrides (N-CAs) are synthesized to distinguish relevant molecular substrate parameters crucial for polymerization and film formation and evaluated in LiNi0.8Co0.1Mn0.1O2||Si/graphite cells. Electrochemical performance and laser desorption/ionization mass spectrometry analyses are conducted to elucidate underlying decomposition mechanisms and their dependency on functional moieties. Incorporation of sterically demanding moieties showed beneficial cell performance depending on the size of the functional group. The variation of functionality on the N-CA core shows an influence on the film formation and the flexibility of the formed SEI film rendering steric demand and the electronic properties of a functional group significant molecular parameters. This study is intended to enhance the fundamental understanding of influential substrate parameters of the molecule and to navigate the direction of research toward a both creative and systematic approach of electrolyte additive design for high-energy-density LIB cells.