Nickel Cluster-Based Organic Framework-Functionalized Solid-State Electrolyte for Lithium–Metal Batteries

The low ionic conductivity (σ) and poor capacity retention severely hinder the further application of solid-state electrolytes (SSEs) in lithium–metal batteries (LMBs). Herein, novel trinuclear cluster-based metal–organic frameworks (MOFs) with rich cage cavities and characteristic functional group −OH have been synthesized, Ni-MOF–OH ({[H2N(CH3)2]2[Ni3(μ3-O)(XN)(BDC–OH)3]·7.5 DMF}n), and further modified with LiOH into Ni-MOF-OLi-1. The Ni-MOF-OLi-1 SSE exhibits a significant improvement in electrochemical performance with a higher σ of 1.55 × 10–3 S cm–1, a wider electrochemical stability window of 5.3 V, and a better Li+ transference number of 0.69 in comparison with that of Ni-MOF–OH (5.06 × 10–4 S cm–1, 4.9 V, 0.53) at 25 °C. Importantly, Ni-MOF-OLi-1 can maintain excellent σ of 2.49 × 10–4 and 3.18 × 10–3 S cm–1 at −40 and 100 °C, respectively. The activation energy (Ea) is as low as 0.09 eV from 10 to 100 °C. Remarkably, the LiFePO4 (LFP)/Li cell assembled with the Ni-MOF-OLi-1 SSE demonstrates an outstanding capacity retention of 96.33% after 150 charge–discharge cycles at 0.5C and 25 °C. This work provides an effective path for the development of high-performance solid electrolytes of LMBs.