Significantly enhanced lithium-ion conductivity of solid-state electrolytes via flower-like structured lamellar metal–organic frameworks with open metal sites

Abstract

Solid-state electrolytes (SSEs) are a frontier topic in battery technology with the potential to solve the safety problem of lithium ion batteries (LIBs). Metal organic frameworks (MOFs) are regarded as promising candidates for a new type of solid-state ion conductor, but the low ionic conductivity and unstable interface contact still seriously hinder the application of MOF based solid state electrolytes (SSEs). Herein, a HKUST-1 based solid-state electrolyte (SSE) was designed and prepared, which possess both a flower-like lamellar structure and sufficient accessible open metal sites (OMSs). These sites could capture anions and release free lithium ions (Li⁺), and the ultra-thin thickness shortened the Li⁺ transmission path. The lamellar HKUST-1 exhibits an ionic conductivity of 1.6 × 10⁻³ S cm⁻¹ at 25 °C with an activation energy of 0.12 eV, Li-ion transference number of 0.73 and electrochemical stability window of 0–5.5 V. The MOF based electrolyte has been assessed with Li|MOFs|LiFePO₄ cells at 25 °C, which showed a high capacity retention of 93% at 0.1C after 100 cycles and excellent rate capability. It also exhibited excellent cycle stability in Li symmetric cells. This Li⁺ conduction strategy of modulating the morphology and modifying pore walls provides a new research idea for designing advanced SSEs.