Modified Preparation Of Cobalt-based Metal-organic Framework-derived Porous Carbon And Its Application In Lithium-sulfur Cathode

Lithium-sulfur battery(LSB)has become the most applicable due to its high energy density(2600 Wh kg-1)and high specific capacity(1675 mAh g-1),as well as abundant sulfur resources,environmental friendliness and low cost.One of the prospective energy storage secondary batteries.However,the commercial application of lithium-sulfur batteries is still hindered by lithium polysulfide shuttles and the kinetic lag of electron and ion conduction in electrochemical reactions.Studies have found that MOFs-derived porous carbon inherits the porous structure of the precursor,which can buffer the volume effect during the charging and discharging process of lithium-sulfur batteries and provide a place for sulfur electrochemical reactions.At the same time,the metal nanoparticles derived from MOFs can form a chemical adsorption of lithium polysulfide,alleviating the shuttle effect.However,the particle structure of MOFs-derived carbon is not conducive to the formation of a complete ion and electron conduction network,resulting in a lag in ion and electron dynamics.In view of the above problems,this article mainly designs the electron and ion transfer paths of the positive sulfur-carrying substrate,and modifies and regulates the surface chemical adsorption environment of the substrate.The porous carbon material is prepared with the metal Co-based organic framework ZIF-67 as the precursor.Through carbon nanotube modification,magnetic field treatment and bimetallic synergistic effect,the transfer rate of electrons and ions is increased,and the positive electrode material’s resistance to soluble polysulfides is enhanced.Chemical adsorption inhibits the shuttle effect,thereby improving the electrochemical performance of the lithium-sulfur battery cathode.Using the cobalt metal complex ZIF-67 as the precursor,the carbon tube with long-range conductivity is combined with the ZIFs carbon skeleton to form a fast electron and ion conduction channel between the ZIFs carbon skeleton.The composite material can have a rich variety of The chemisorption sites of lithium sulfide and the fast ion and electron conduction network are conducive to improving the electrochemical performance of the battery.The results show that when the content of carbon nanotube(CNT)is 4.5 wt%,the prepared S@Co-NC@CNT-4.5 cathode has the best electrochemical performance.The S@Co-NC@CNT-4.5 positive electrode exhibits a discharge specific capacity of 493 mAh g-1 at a rate of 2C.The initial discharge specific capacity of S@Co-NC@CNT-4.5 positive electrode at 0.2 C rate is 938 mAh g-1,which is 40%higher than the positive electrode capacity without CNT modification.After 100 cycles of stable cycles,the reversible capacity remains At 632 mAh g-1.The results show that the adjustment of the magnetic field during the cathode preparation process can improve the ion transport dynamics of the cathode and improve the electrochemical performance of the battery.When the magnetic field intensity is 200 G,the electrochemical performance improvement effect of S@Co-NC@CNT-4.5 cathode is the best.The initial discharge specific capacity of S@Co-NC@CNT-4.5 cathode material can reach 1160 mAh g-1,and the discharge specific capacity at 0.2 C and 1 C rates are 1033 mAh g-1 and 751 mAh g-1,respectively.When the current density returns to 1 C and 0.2 C again,the specific discharge capacity of the battery can be restored to 688 mAh g-1 and 876 mAh g-1,respectively,and the capacity retention rates are 92%and 86%,respectively.By introducing Ni metal,the synergistic effect of Ni metal and Co metal is used to provide multiple adsorption sites,effectively fix sulfur and improve the ion and electronic conductivity of the matrix,thereby improving the electrochemical performance of the composite cathode material.The results show that the S@Co4Ni--NC@CNT-4.5 composite cathode prepared with the molar ratio of Co and Ni of 4:1 has the best electrochemical performance:it has good high rate performance,and the rate discharge specific capacity at 2 C is still up to 597 mAh g-1,which is 28%higher than the undoped composite cathode capacity.At a rate of 0.2 C,after 300 cycles,the reversible capacity of S@Co4Ni1-NC@CNT-4.5 composite cathode is 34%higher than that of S@Co-NC@CNT-4.5,and the capacity retention rate is increased by 4%.