ZIF-based heterojunction filler enhancing Li-ion transport of composite solid-state electrolytes

Composite solid electrolytes (CSEs) are considered among the most promising candidates for solid-state batteries. However, their practical application is hindered by low ionic conductivity and a limited lithium-ion transference number, primarily owing to the insufficient mobility of Li⁺. In this work, we design a heterojunction nanoparticle composed of bimetallic zeolitic imidazolate frameworks (ZIFs) coupled with amorphous titanium oxide (TiO₂@Zn/Co–ZIF) as a filler to fabricate a composite solid-state electrolyte (PVZT). The amorphous TiO₂ coating facilitates salt dissociation through Lewis acid–base interactions with the anions of the lithium salt. Meanwhile, the Zn/Co–ZIF framework not only provides additional selective pathways for Li⁺ transport but also effectively restricts anion migration through its confined pore size. The synergistic effect results in a high room-temperature ionic conductivity (8.8 × 10⁻⁴ S·cm⁻¹) and a lithium-ion transference number of 0.47 for PVZT. A symmetrical cell using PVZT demonstrates stable Li⁺ deposition/stripping for over 1100 h at a current density of 0.1 mA·cm⁻². Additionally, a LiNi_0.8Co_0.1Mn_0.1O₂/Li full cell using PVZT retains 75.0% of its capacity after 1200 cycles at a 2 C rate. This work offers valuable insights into the design of functional fillers for CSEs with highly efficient ion transport.