Synthesis And Application Of Cathode Host Materials For High Performance Lithium-sulfur Batteries

Energy shortage and environmental pressures have become more urgent and there is increasingly interested in clean energy.Lithium battery has become an ideal system for new energy storage and conversion because of its unique advantages.However,traditional lithium-ion batteries cannot meet future market demands due toits limited capacity and energy density.As a new type of lithium battery,lithium-sulfur batteries(LSBs)have attracted widespread attention due totheir ultra-high specific discharge capacity and energy density.In addition,sulfur as the cathode material is cheap and abundant.However,due tothe insulation of active substance sulfur and discharge product lithium sulfide and the solubility of intermediate product lithium sulfide in electrolyte,which leads tothe low utilization of active species in batteries,the rapid capacity degradation and the short cycle life and hinders the practical process of batteries.In order tosolve these problems,some new inorganic host materials were synthesized via the rational design and modification as the sulfur cathode host materials.The specific works are as follows:(1)MoO₂-Mo₃N₂ heterojunction material was synthesized via partial nitriding with MoO₃ as self-template.The heterojunction material has the advantages of synergistic MoO₂ and Mo₃N₂ due toits unique interface,which has both the strong adsorption ability of MoO₂ and good conductivity of Mo₃N₂.As the host material,MoO₂-Mo₃N₂ heterojunction has sulfur content as high as 75 wt%and electrode sulfur loading(3.2 mg/cm²).During the electrochemical test,the utilization of the sulfur active material is increased.Moreover,it can enhance the discharge specific capacity and the long-term cycling stability of the battery.(2)One sandwich-like MoN-C-MoN trilayers structure material was synthesized and employed as the host material of LSBs.The outer MoN layer can strongly adsorb Li PSs by virtue of its polar surface,while the middle C layer serves as a charge transfer pathway and provides sufficient electron supply for MoN in the surface layer.As an electrode of lithium-sulfur battery,it exhibits good rate performance and has a low capacity decay rate during a long-term cycle.(3)A low-cost,high-efficiency,and green adsorbent:the in-situ N-doped carbon-coated iron sulfide is proposed and as the host material used in Li-S batteries.This material has a sulfiphilic surface and inhibits the shuttle behavior of Li PSs through strong chemical action.The carbon layer generated in-situ could be in close contact with Fe S,ensuring the sample has high conductivity.Cathodes based on this material show higher cyclic stability and lower capacity decay rates.The introduction of green host material can avoid the use of heavy metals and reduce production costs.It provides the possibility for the practical application of Li-S batteries with low cost,eco-friendly and high-performance.In summary,a variety of cathode host materials have been synthesized in this paper.Cathodes based on these materials show good electrochemical performance in batteries.Moreover,the eco-friendly and low-cost cathode materials provide the possibility for the commercialization of batteries.