Li₂S Cathode Modification And Catalytic Mechanism Of LDH For Lithium-Sulfur Batteries

With the increasing prominence of traditional energy problems and the"dual carbon"strategy,new energy sources are gradually being applied in all aspects of society.However,the limited lithium resources have prompted an urgent search for alternatives to lithium-ion batteries.Lithium-sulfur batteries have been the subject of keen interest due to their high theoretical energy density,but their practical applications are challenged by rapid capacity degradation caused by polysulfide shuttling and degradation of the electrode structure.In this thesis,we develop schemes to enhance the performance of lithium-sulfur batteries in two directions,and the results of our study are as follows.Lithium sulfide is a promising cathode material for lithium-sulfur batteries,but the electrical conductivity and electrochemical reactivity severely hinder its application.Herein,Ti₃C₂T_xnanosheets（TNS）-supported nano-Li₂S@Li₃PS₄coating materials（NLi₂S@LPS/TNS）are designed to meet these challenges.The electrochemical redox reaction has fast Li⁺/e^-transfer kinetics and low reaction energy barrier due to the synergistic effect of nano-Li₂S,Li₃PS₄coating and MXene（Ti₃C₂T_x）catalyst,which improves the cycle stability of Li-S batteries.The Li-S batteries with NLi₂S@LPS/TNS electrode have a capacity retention rate of77%after 300 cycles of charge and discharge at 0.5 C rate,corresponding to an average decay rate of 0.08%per cycle.In addition,sulfur as the cathode of lithium-sulfur batteries has a high capacity,but the poor conductivity and as well as the severe shuttle effect seriously hinder its application,and the shuttle phenomenon can be effectively suppressed by catalyst compounding for polysulfide adsorption catalysis.Here we prepared Ni Fe-LDH grown on r GO in a grid-like manner and introduced cation vacancy and oxygen vacancy defects as sulfur cathode catalysts by simple etching treatment,respectively.The experimental analysis shows that the catalytic conversion mechanism of polysulfides is not the same for different vacancies,and the oxygen vacancies are more catalytic for short-chain polysulfides and the nickel vacancies are more catalytic for long-chain polysulfides,and the coexistence of the two catalytic sites significantly enhances the cell performance.Dv-Ni Fe-LDH/r GO@S can maintain a specific capacity of nearly 1100 m Ah g^-1at a 0.2 C,and a capacity retention rate of 75%after 300cycles at a 0.5 C.