Application Of Titanium Nitride Composites In Lithium-sulfur Battery Cathode Materials

With the development of portable appliances and electric vehicles,energy storage devices with high theoretical energy density are urgently needed.Lithium-sulfur batteries are considered as one of the most promising energy storage devices due to their high theoretical energy density(2600 Wh kg^-1),abundant resources,non-toxicity,and low economic cost,which are suitable for large-scale energy storage devices.However,some inherent problems,such as the poor electrical conductivity of sulfur and discharge products Li₂S₂/Li₂S as well as the volume expansion of sulfur during cycling,the dissolution of polysulfides(Li PSs)during charge-discharge process causing the“shuttle effect”impede their widely practical applications.In addition,the above issues would lead to low active material utilization,inferior coulombic efficiency,and poor cycling stability.Based on the design and preparation of cathode carrier materials for lithium-sulfur batteries,this thesis aims to solve the problems existing in lithium-sulfur batteries.Two novel cathode support materials are prepared through rational structural design and action mechanism study.The specific research results are as follows:(1)A novel sulfur support material was prepared by uniform Ly dispersing polar Ti N nanoparticles in N-doped carbon nanocages(Ti N@C NCs)by hydrothermal method.The structure has high electrical conductivity and sufficient space to alleviate sulfur volume expansion.Morever,the polar Ti N nanoparticles not only exhibit strong chemisorption capacity for Li PSs,but also can catalyze the conversion of long-chain Li PSs to short-chain Li₂S₂/Li₂S during the reduction process,effectively suppressing the shuttle effect and significantly improving electron/ion transport,thereby enhancing the electrochemical performance of Li-S batteries.Therefore,the S/Ti N@C NCs electrode has an electrochemical capacity of 1485.7 m Ah g^-1 at 0.1 C.In particular,the capacity retention rate after 500 cycles at 3 C is about 73.1%,and the capacity decay.(2)2D Ti₃C₂ and graphene oxide were prepared into 3D Ti N nanoflakes(Ti N NFs@r GO)with directional exposed(001)crystal planes by spray drying.Theoretical calculations and electrochemical tests confirm that Ti N nanosheets dominated by(001)planes have a significant catalytic effect in the oxidation and reduction processes.During the oxidation process,the decomposition energy barrier of Li₂S can be lowered and the reaction kinetics can be enhanced.Ti N NFs@r GO and Li PSs enhanced the adsorption and catalytic ability of Li PSs through chemical bonding during the reduction process.The r GO three-dimensional carbon framework can support more active species and relieve the volume expansion caused by sulfur reaction,and can improve the conductivity of electrode materials.Based on the above advantages of materials,Ti N NFs@r GO exhibits a high discharge capacity of 949 m Ah g^-1 at 1 C and maintains a high capacity after 800 cycles with a cycle decay rate of 0.033%per cycle.Long-term stable cycling of lithium-sulfur batteries is achieved.