Electrospun Nanofibers Constituted of a Polyimide Core Decorated with Polyhedral Oligomeric Silsesquioxanes and a TiO₂ Shell as Separators for Lithium-Ion Batteries

Conventional polyolefin separators used in lithium-ion batteries face challenges for low porosity, insufficient electrolyte wettability, poor thermal stability, and short circuits caused by dendrite growth. In this work, a unique polyimide/trisilanol isobutyl sesquisiloxane@titanium dioxide fiber separator is prepared by electrospinning and self-assembly, in which polyhedral oligomeric semisiloxane (POSS) serves as a bridge between polyimide (PI) and TiO₂. The PI/trisilanollsobutyl (TS)-POSS@TiO₂ nanofiber separator with a core–shell structure presenting excellent mechanical strength and electrochemical characteristic effectively inhibits the development of lithium dendrites in lithium-ion batteries. The PI/TS-POSS@TiO₂ membrane tensile strength is 17.90 MPa, 152% greater than the pure PI separator tensile strength (7.1 MPa). The lithium-ion battery assembled with a PI/TS-POSS@TiO₂ separator has an excellent conductivity of 1.782 mS/cm, which is 92.44% greater than that of a pure PI separator. Its electrochemical stability window also reaches 5.27 V. The lithium-ion battery assembled by the PI/TS-POSS@TiO₂ separator exhibits excellent rate performance, cycling stability, and preferable resistance to dendritic penetration. The PI/TS-POSS@TiO₂ nanofiber separator has good application prospects in lithium-ion secondary batteries.