Heterojunction-Accelerating Lithium Salt Dissociation in Polymer Solid Electrolytes

Abstract

The practical application of solid-state lithium-metal batteries (SSLMBs) based on polymer solid electrolytes has been hampered by their low ion conductivity and lithium-dendrite-induced short circuits. This study innovatively introduces 1D ferroelectric ceramic-based Bi4Ti3O12-BiOBr heterojunction nanofibers (BIT-BOB HNFs) into poly(ethylene oxide) (PEO) matrix, constructing lithium-ion conduction highways with “dissociators” and “accelerating regions.” BIT-BOB HNFs, as 1D ceramic fillers, not only can construct long-range organic/inorganic interfaces as ion transport pathways, but also install “dissociators” and “accelerating regions” for these pathways through the electric dipole layer and built-in electric field of BIT-BOB HNFs, promoting the dissociation of lithium salts and the transfer of lithium ions. The working mechanisms of BIT-BOB HNFs in the polymer matrix are verified by experimental tests and density functional theory calculations. The obtained composite solid electrolytes exhibit excellent lithium-ion conductivity and migration number (6.67 × 10−4 S cm−1 and 0.54 at 50 °C, respectively). The assembled lithium symmetric battery achieves good cycling stability of over 4500 h. The LiFePO4||Li full battery delivers a high Coulombic efficiency (>99.9%) and discharge capacity retention rate (>87%) after 2200 cycles. In addition, the prepared composite polymer solid electrolyte demonstrates good practical application potential in flexible pouch batteries.