Construction of Anion-Adsorbing UiO-67 Functionalized Polyimide Separator for Boosting Electrochemical Performance of Lithium-Metal Batteries

Abstract The development of high-energy-density lithium-metal batteries (LMBs) has imposed increasingly stringent requirements on the thermal stability, ionic conductivity, and interfacial compatibility of separators. To address the inherent drawbacks of conventional polypropylene (PP) separators, such as inadequate thermal stability and poor electrolyte wettability, a polyimide (PI) separator was fabricated via the nonsolvent induced phase separation (NIPS) method in this work. Furthermore, by introducing metal-organic framework (MOF) materials (UiO-67) into PI slurry, a PI/UiO-67 composite separator was successfully constructed, which achieves the synergistic optimization of the pore structure, surface morphology, and mechanical properties of the separator. The results demonstrate that the PI/UiO-67 composite separator retains the excellent thermal stability of the PI matrix, with no thermal shrinkage observed at 200 °C, while simultaneously exhibiting significantly improved electrode–electrolyte interfacial compatibility. Compared with the commercial PP separator (bulk resistance 2.97 Ω, interfacial impedance 165 Ω), the composite separator possesses a lower bulk resistance (2.28 Ω) and interfacial impedance(122 Ω). Additionally, integrating UiO-67 considerably improves the wettability of the electrolyte and the lithium-ion transference number (0.61) in the separator, which in turn markedly boosts the electrochemical stability and the long-cycle performance of LMBs. LMBs utilizing the PI/UiO-67 separator achieve a notable capacity retention of 87.4% after 150 cycles at a rate of 0.5 C. In tests conducted with lithium symmetric cells, stable cycling performance is observed for more than 600 h at a current density of 0.2 mA cm–2. This study offers a valuable composite approach and theoretical insights for advancing the development of separators that ensure high safety and performance in LMBs.