Significant electrochemical performance improvement of an anion MOF-based solid-state electrolyte across a wide temperature range via an ion exchange strategy

Low ionic conductivity (σ) and high activation energy (E_a) seriously hinder the development of solid-state electrolytes (SSEs). Herein, a series of post-modified Li⁺@Ni-MOF-X (X = 1, 2, and 3) materials were synthesized via an ion exchange method based on a 3D anionic trinuclear cluster-based metal-organic framework (MOF) (Ni-MOF: {[H₂N(CH₃)₂]₂[Ni₃(μ₃-O) (XN)(BDC)₃]·6DMF}_n). Compared with the pristine Ni-MOF, Li⁺@Ni-MOF-2 exhibited significantly enhanced performance as SSEs, featuring a higher σ of 1.28 × 10^-3 S cm^-1, a larger lithium-ion transference number (t_Li⁺) of 0.76, and a wider electrochemical stability window (ESW) of 5.3 V at room temperature (Ni-MOF: 2.19 × 10^-4 S cm^-1, 0.57, and 5.0 V). Notably, Li⁺@Ni-MOF-2 maintained excellent σ even at -40 °C (2.12 × 10^-4 S cm^-1) and exhibited an ultra-low E_a (0.08 eV) from 10 to 100 °C, demonstrating potential practical application over a wide temperature range. Moreover, LiFePO₄|Li⁺@Ni-MOF-2|Li full cells stably cycled for 150 cycles at 0.1 C with a capacity retention of 81.30%. This work has enriched the types of MOF-based SSEs, providing the possibility for the application of lithium-ion SSEs in a wide temperature range.