Impact of Lithium‐Free Borate Additives on the Cycle Life and Calendar Aging of Silicon‐Based Lithium‐Ion Batteries

Silicon‐anode lithium‐ion batteries (LIBs) suffer from limited cycle life and poor calendar life, constraining their large‐scale commercialization. Integrating additives into electrolytes is a simple and cost‐effective strategy to improve these aspects. The effects of lithium‐free boron‐based additives on cycling and calendar performance of high‐loading Si‐anode LIBs remain largely unexplored. In this work, the influence of five Li‐free borate additives, each with distinct molecular structures and elemental compositions, is systematically investigated. All additives enhance cycle life to varying extents. Notably, the addition of 1 v/v% tri(2,2,2‐trifluoroethyl) borate to the baseline electrolyte nearly doubles the cycle life at 50% state of health. This enhancement is attributed to three key factors. Specifically, borate additives 1) improve electrochemical activity, 2) act as anion receptors that interact with [PF 6 ] − anions and carbonate solvents to reduce electrolyte decomposition, and 3) promote the formation of a stable and polymeric solid electrolyte interphase layer. Furthermore, these additives exhibited negligible impact in mitigating leakage current during a 180 h voltage‐hold calendar‐aging test, indicating their limited effect in calendar life. These findings provide insight into the role of Li‐free borate additives in improving cycle life while addressing the knowledge gap regarding their influence on calendar aging.