2D Solid-Electrolyte Interphase Built by High-Concentration Polymer Electrolyte for Highly Reversible Silicon Anodes

Silicon anodes with a high capacity of 4200 mAh g-1 and a low potential of 0.3 V (vs Li+/Li) enable lithium-ion batteries with improved energy density. However, the thickened 3D solid-electrolyte interphase (SEI) formation on Si particles in the liquid electrolytes consumes the electrolyte/active Si and blocks the Li+/e- transport, resulting in fast capacity fading. Herein, a high-concentration polymer electrolyte (HCPE) is designed to build 2D SEI on the Si anode surface instead of the particles, which accommodates the volume change and maintains the continuous Li+/e- transport pathways as well. The retarding effect of NO3- lowers the polymerization rate of 1,3-dioxolane (DOL), enabling 6 m LiFSI dissolution. The high concentration of LiFSI takes part in constructing the solvation structure and pulls the DOL away, reducing the decomposition of DOL and poly-DOL (PDOL) and inducing the generation of a LiF- and Li3N-rich SEI with high mechanical strength and fast Li+ transport capability. As a result, the cell using HCPE delivers a high capacity of 1765 mAh g-1 at 2C and maintains a high capacity of 2000 mAh g-1 after 100 cycles at 0.2C, which is superior to that of a liquid electrolyte (617 mAh g-1) and a low-concentration polymer electrolyte (45 mAh g-1). A high-concentration polymer electrolyte (HCPE) with low flowability and high ionic conductivity is developed by retarding the ring-opening polymerization of 1,3-dioxolane (DOL) with a LiNO3 additive. The increased concentration of LiFSI in HCPE reduces the decomposition of DOL and helps induce the formation of a 2D inorganic-rich solid-electrolyte interphase, which accommodates the volume change and maintains the continuous Li+/e- transport pathways as well.image