Preparation Of Al-MOF-based Porous Carbons And Their Application In Lithium-sulfur Batteries

Lithium-sulfur batteries had high theoretical specific capacity and energy density,which can meet the needs of next-generation batteries and were expected to become candidates for next-generation rechargeable batteries.Nevertheless,in the typical lithium-sulfur batteries,highly soluble lithium polysulfide can readily diffuse out from the cathode into the electrolyte and then shuttle between the cathode and anode during cycling,leading to capacity decay and raising the electrode resistance to limit rate performance.Therefore,suppression of the shuttle effect of polysulfide was one of the key factors in the development of lithium-sulfur batteries.In this project,Al-MOF derived porous carbon materials to prepare flexible interlayers and modified separators for lithium-sulfur batteries.The microstructure and chemical composition of the MOFS-derived porous materials were analyzed by various characterization methods,and the effects of the compositions and synthesis conditions of the materials on the electrochemical performance were also studied.The main contents was as follows:The Al-MOF precursor was self-assembled and grown on the cotton substrate by a simple hydrothermal method,and the flexible Al₂O₃/porous carbon derivative composite interlayer material was obtained after heat treatment.Through investigation,we found that 180?was the best synthesis temperature,and Al₂O₃/C@CC-180derived from Al-MOF showed excellent electrochemical performance.The reversible discharge specific capacity was as high as 870.5 m Ah/g after 100 cycles at 0.2 C,and it was still as high as 477.8 m Ah/g after 300 cycles at 5 C.Under the condition of sulfur loading of 5.2 mg/cm²,it can still maintain a specific discharge capacity of723.5 m Ah/g after 80 cycles,indicating that it had excellent fast charge-discharge performance and cycle stability.This derivatized interlayer material had many advantages.First,the porous carbon material and the carbonized cotton cloth substrate can effectively promote the transmission of electron ions.Second,the polar metal ions can slow down the shuttle of polysulfide through strong chemical and physical restrictions.The Al-MOF precursor was carbonized to obtain derivative Al₂O₃/porous carbon and conductive agent Super P to prepare a mixed slurry,which was coated on one side of the diaphragm to form a 50?m polysulfide barrier layer for lithium-sulfur batteries.The results showed that the Al₂O₃/C@Super P@PP modified separator had good cycle stability.The discharge specific capacity of first cycle was 1372.4 m Ah/g and the specific discharge capacity remained 986.9 m Ah/g in the 50th cycles at 0.2 C.When the current density was 1 C,the average specific discharge capacity of about 537.8m Ah/g can be maintained after 150 cycles,and it had an excellent cycle life.The polar Al₂O₃ and porous carbon coatings in the modified separator alleviate the shuttle effect through chemical interactions and physical barriers.At the same time,good electrolyte wettability promotes lithium ion migration,ensurde the rapid diffusion of Li⁺/electrons and improved reaction kinetics.