Li0.33La0.557TiO3@BaTiO3 core–shell fiber as a filler to promote the dissociation and migration of lithium ions in solid polymer electrolytes

Abstract

Incorporating inorganic fillers can significantly enhance the ionic conductivity of solid polymer electrolytes (SPEs). Herein, we report a novel coaxial Li_0.33La_0.557TiO₃@BaTiO₃ (LLTO@BTO) fiber, with BTO as the shell and LLTO as the core, as a filler in PEO (LiTFSI)-based SPEs to utilize passive ferroelectric and ionic conductive properties. Experimental results and DFT calculations confirmed that the ferroelectric BTO shells effectively increased the concentration of free Li⁺ by promoting the dissociation of lithium salts and inhibiting PEO crystallization through surface interactions. Meanwhile, the order of affinity toward Li⁺ was found to be LLTO > BTO > PEO, forming an interface with gradient adsorption properties. Thereby, Li⁺ was adsorbed onto LLTO cores and transported in its phase because of its low transport barriers. Importantly, these additional channels are protected from reduction by the Li anode owing to the protection of the BTO shell. With the LLTO@BTO filler, the PEO-based SPEs (PEO-LLTO@BTO) show a high ionic conduction of 1.44 × 10⁻³ S cm⁻¹ at 30 °C. Li symmetric cells with PEO-LLTO@BTO exhibit a superior cycling stability of >3000 h at a current density of 0.1 mA cm⁻² and 60 °C. The corresponding LiFePO₄/Li battery exhibits excellent cycling and rate performance. This work provides new insights into the design of advanced fiber fillers.