In this work, a two-dimensional metal organic framework (MOF) Co(SCN)₂ (pyz)₂ with pore structure was synthesized by liquid-phase diffusion method. The MOF has good adsorption ability for lithium polysulfides and can suppress shuttle effect. By combining it with polypropylene (PP) to form a multifunctional isolation film for lithium sulfur batteries, excellent electrical performance has been demonstrated. Firstly, the preparation of MOF: a mixture of Co(SCN)₂ (3 mg) and water (1 mL) were mixed in a 3 mL small glass bottle; a mixture of pyrazine (10 mg) and acetone (2 mL) were mixed in a 10 mL small glass bottle. Then opened the small bottle and put it into the large bottle, and sealed the large bottle. After standing at room temperature for 12 d, single crystals [Co(SCN)₂(pyz)₂] could be obtained. Then a mixture of Co(SCN)₂(pyz)₂ (5 mg) and polyvinylidene fluoride (PVDF) (1 mg) were mixed in a glass bottle, added 6 mL of methanol, sonicate for 3 h, and filtered under reduced pressure onto a polypropylene (PP) membrane. Placed the composite membrane in a constant temperature oven at 60 ℃ for 12 h, and then used a slicer to make it into a fixed size. Mixed sublimated sulfur powder and Super-P carbon black in a mass ratio of 7:3 and ground them (S/PC). Dried them in an oven at 155 ℃, then weighed 360 mg of S/PC and added it to 800 mg of a 5% (w) PVDF/NMP (NMP=N-methylpyrrolidone) mixed solution. Stirred at room temperature for 12 h at a speed of 350 r/min. Then, the mixed solution was evenly applied onto a 150 μm aluminum foil using a homogenizer, placed in a 60 ℃ constant temperature oven for 12 h, and then sliced using a slicer to obtain a sulfur positive electrode sheet. Then assemble the battery in the order of negative electrode shell, spring sheet, gasket, lithium sheet, electrolyte [electrolyte lithium bis(trifluoromethyl sulfonyl)imide (LiTFSI), 1,3-dioxolane (DOL)/dimethyl ether (DME) (V:V=1:1), 1% (w) LiNO₃], separation composite membrane (the side with MOF material in contact with the sulfur positive electrode), sulfur positive electrode sheet, and positive electrode shell. The electrolyte was 25 μL. After assembly, let it stand at room temperature for 12 h before testing. In constant current testing, during the 0.1 C long cycle test, the initial discharge specific capacity of PC-10Co-PP lithium sulfur battery (2060.48 mAh•g^－1) was much higher than that of PC-PP lithium sulfur battery (883.77 mAh•g^－1); At a rate of 1 C, the initial discharge specific capacity (1095 mAh•g^－1) of PC-10Co-PP lithium sulfur battery is also much higher than that of PC-PP, showing excellent performance improvement, and the coulombic efficiency remained stable, indicating their cycling stability and high service life. This result indicated that porous MOF materials had great potential for application in lithium sulfur batteries, expanding the scope of MOF material applications.

Key words: metal organic framework, lithium sulfur battery, shuttle effect, catalysis, discharge specific capacity