Composite Polymer Electrolyte Incorporating Metal–Organic Framework Nanosheets with Improved Electrochemical Stability for All-Solid-State Li Metal Batteries

Composite polymer electrolytes using polyethylene oxide (PEO) are highly appealing by virtue of the fine electrochemical stability, inexpensiveness, and easy fabrication. However, their practical application is currently hindered by the insufficient room-temperature ionic conductivity. Herein, nickel-based ultrathin metal–organic framework nanosheets (NMS) are first introduced as a novel 2D filler into the PEO matrix. The introduction of NMS with a high aspect ratio effectively improves the amorphous region proportion of PEO and thus enhances the ionic conductivity of the electrolyte by 1 order of magnitude. In addition, the Lewis acid–base interactions between the surface-coordinated unsaturated Ni atoms in NMS and the anions of lithium salt could promote the dissociation of lithium salt. Hence, the composite electrolyte with NMS achieves a high Li+ transference value of 0.378. Along with the unique nanostructure of NMS, this NMS composite electrolyte also suppresses Li dendrite growth during cycling. As a result, the assembled all-solid-state Li/LiFePO4 battery demonstrates a high reversible capacity of 130 mA h g–1 at 0.1 C and 30 °C for 50 cycles.