Preparation Of Three-dimensional Conductive Porous Carbon Based On CNTs And Its Electrochemical Properties In Lithium Sulfur Cathode

The theoretical specific capacity of lithium sulfur battery is 1675 m Ah?g^-1 and the theoretical energy density is 2600 Wh·kg^-1,which has broad application prospects.However,the poor conductivity,"shuttle effect"and volume expansion of sulfur cathode lead to its poor actual electrochemical performance.In this paper,ZIF-67 and HCS with good conductivity,high specific surface area and mature technology were selected to grow CNTs in situ.Nitrogen doped three-dimensional porous carbon materials were prepared with melamine as the carbon source and Co as the catalyst。The effects of synthesis conditions on the structure and electrochemical properties of the products were studied,the specific discharge capacity and cycle stability of lithium sulfur battery were improved.The main results and conclusions are as follows:1.Preparation and electrochemical properties of Co-NC@CNTs/S composite sulfur cathodeUsing ZIF-67 and melamine as precursors,CNTs were grown in situ to prepare Co-NC@CNTs.The effects of heat treatment temperature and precursor ratio on the structure of three-dimensional porous carbon and the electrochemical properties of sulfur cathode were studied.It is found that the heat treatment temperature and the ratio of precursors have an important influence on the length and diameter of CNTs.When the heat treatment temperature is 650℃,the ratio of ZIF-67 to melamine is 1:1.5,Co-NC@CNTs has the most complete CNTs wrapped cube structure,and the diameter of CNTs is about 20 nm.When applied to sulfur cathode,the specific capacity of the first discharge is 1252 m Ah?g^-1,and the capacity retention rate is 83.1%.2.Preparation and electrochemical properties of HCS@CNTs/S composite sulfur cathodeWith Si O₂@RF and melamine as precursors,Co as catalyst,HCS@CNTs was prepared by high temperature sintering.The effects of precursor ratio and catalyst ratio on three-dimensional porous carbon materials were studied.The appropriate addition amount of melamine and Co is conducive to the formation of CNTs with high specific surface area and high aspect ratio HCS@CNTs three dimensional porous carbon structure.When the ratio of Si O₂@RF to melamine is 1:2.5 and the ratio of Co to melamine is 0.1:1,HCS@CNTs has the highest aspect ratio and graphitization degree.The first discharge specific capacity of sulfur carbon cathode at 0.1 C rate is 1318.4m Ah?g^-1,and the capacity retention rate is 62.8%.By comprehensively comparing the structures of Co-NC@CNTs and HCS@CNTs and their effects on the performance of lithium sulfur battery,HCS@CNTs/S system shows higher specific capacity and cycle performance.By optimizing its preparation process,the electrochemical performance of lithium sulfur cathode of this system is expected to be further improved.