Research progress on cathode electrolyte interphase in high-voltage lithium batteries

Achieving high energy density batteries is currently a key focus in the field of energy storage. Lithium batteries, due to their high energy density, have garnered significant attention in research. Increasing the upper limit of the battery's cut-off voltage can boost the energy density of lithium batteries. However, high-voltage conditions can lead to irreversible phase transitions and side reactions in cathode materials, which can degrade battery performance and even result in safety risks, including explosions. The electrolyte can also decompose, causing capacity loss and releasing flammable gases when subjected to high voltage, which can lead to battery swelling and potential combustion and explosions. Designing an ideal cathode electrolyte interphase (CEI) on the cathode's surface to regulate the electrode-electrolyte interface reaction can effectively enhance the cycling stability of the battery, reduce irreversible phase transitions in the cathode, and improve the oxidation stability of the electrolyte. The ideal CEI should possess high ion conductivity, high thermal stability, and should minimize interface side reactions to ensure optimal battery performance. Understanding the formation and development of CEI is crucial for enhancing battery performance under high voltage. Apart from creating artificial CEI, modifying electrolytes has gained significant attention. By altering the electrolyte recipe, an ideal CEI can be achieved. Electrolyte engineering is considered an effective strategy for attaining an ideal CEI and enhancing the stability of high nickel positive electrodes. This approach is simple, cost-effective, and holds great promise for achieving higher energy density in lithium batteries. To provide a better understanding of CEI in lithium ion batteries (LIBs), this article reviews the latest advancements in CEI, including the formation mechanism of CEI, the key factors influencing CEI, methods for modifying CEI, and techniques for characterizing CEI. Additionally, it summarizes the current status of artificial CEI development and in situ CEI generation through electrolyte design. The aim is to offer fundamental guidance for future research and the design of high-voltage battery CEI. Finally, the article outlines the opportunities and challenges in electrolyte engineering for modified CEI, pointing towards the future direction of constructing an ideal CEI.