Advanced Electrolyte Additives for Lithium-Ion Batteries: Classification, Function, and Future Directions

Lithium-ion batteries (LIBs) are widely employed as energy storage devices, particularly in portable electronics and electric vehicles, owing to their high energy density and efficiency. Among the key components of LIBs, the electrolyte plays a crucial role in determining capacity, cycling stability, rate performance, the electrode/electrolyte interface, and overall battery efficiency. However, traditional electrolytes face significant challenges, including severe structural degradation and interfacial side reactions under high-voltage and high-temperature conditions. Protective layers, such as the cathode-electrolyte interphase (CEI) and solid-electrolyte interphase (SEI), are essential for addressing these issues. These layers inhibit electron transfer while allowing lithium-ion (Li+) transport, preserving the structural and electrochemical integrity of the battery. A cost-effective strategy to further enhance the electrode–electrolyte interface and boost LIB performance is the incorporation of carefully designed electrolyte additives. While some articles discuss the use of electrolyte additives in LIBs, there is a lack of detailed studies classifying these additives based on their chemical composition-based grouping. Such a classification enables a more focused examination of the roles and mechanisms by which these additives improve LIB performance. This review paper bridges this gap by examining various electrolyte additives and their contributions to enhancing the safety and performance of next-generation LIBs. It provides valuable insights into the current progress and challenges associated with additives in liquid electrolytes. The article is organized into seven sections, addressing boron-based electrolyte additives (Section 2), sulfur-based electrolyte additives (Section 3), phosphorus-based electrolyte additives (Section 4), fluorine-based electrolyte additives (Section 5), and nitrogen-based electrolyte additives (Section 6). Each section discusses specific examples, the formation of SEI and CEI layers, and the electrochemical properties of these additives. Furthermore, the article concludes with a summary and outlook, advocating for continued advancements in electrolyte engineering for LIBs.