Stabilizing Lithium Anode Via Separator Engineering and in-Situ Electrolyte Additive Tuned SEI

Abstract

Li metal anode is regarded as one of the rising stars in secondary batteries systems. Safety issues attributing from lithium dendrites, however, greatly hinders its practical application. Here we present an effective and scalable way of protecting lithium metal anode via separator engineering, and further through the tuning of solid electrolyte interface (SEI) via Li+/functional group bonding. The novel separator exhibits much higher specific surface area (~16.9x) and enhanced ionic conductivity (~3.25x) than Celgard separator. The -COOH/separator bonding is flexible and Li+/COOH is easily coupled thus a lower interfacial resistance and a more dynamically stable SEI are achieved. FTIR and UV-vis have confirmed the flexible bonding of –COOH. Contact angle measurements confirm the lithiophilic characteristic of the novel separator, which indicates a easy and homogenous absorption of the –COOH functional groups onto the Li metal surface. Consequently, the Li||Li symmetric cell achieves 3 times longer stable cycling. CV, Nyquist plots and in-depth XPS further confirm the chemically and physically stable SEI after fewer cycles with this novel separator than that with Celgard separator. In-situ optical microscopy reveals dendrites inhibition from Li+/COOH coupling effect under extreme current density of 10 mA cm-2. Cross-sectional SEM illustrates the dense, uniform and stable SEI on Li metal anode with novel separator, volume expansion problem is also tackled to a large degree. This separator can stand 43% of elastic deformation under more than 40 MPa of stress, and its structural stability is confirmed by SEM and AFM even after the separator loses the functional groups. It fits well with both LIBs and L-S batteries systems, and is promising for scalable manufacturing.