Design And Preparation Of Carbon-Based And Titanium Carbide-Based Cathode Materials For Lithium-Sulfur Battery And Their Electrochemical Performance

With the emergence and development of electronic equipment and electric vehicles,it has become increasingly urgent to develop efficient and economical energy storage and conversion systems.Lithium-sulfur batteriey?LSB?have been the most specific next-generation high specific energy systems because of its high heoretical specific capacity(1675 mAh g^-1)and volume energy density(2600 Wh kg^-1).And LSB has many advantages,sucj as low cost and environmental friendliness.However,there are several non-ignorable challenges limiting its extensive applications and further practical commercialization.Extra low electronic conductivity and large volume change of sulfur cathode and Li₂S,along with shuttle effects of polysulfides during charge and discharge of sulfur cathodes prevent their commercial application.In this work,carbon and titanium carbide-based lithium-sulfur anode materials are designed and prepared to solve these problems.Main research results are shownblow:?1?Designing and preparation of high-yield and in-situ fabrication of high-content nitrogen-doped graphene nanoribbons@Co/CoOOH.One-dimensional nitrogen-doped graphene nanoribbons loaded with Co/CoOOH or Co nanoparticles in situ by using KOH solution or HNO3 solution,are prepared under mild conditions.As the carbon-based cathode material,it well solved the shuttle effect of polysulfides and the inherent defects of sulfur cathodes and showed great long-cycle performance and high-rate performance.When sulfur loading is 1.1 mg cm^-2,it maintained high discharge specific capacity of 804.9 mAh g^-1 at a current density of 0.2 C after 500 cycles.And the decay is 0.05%at a higher sulfur load(3.9mg cm^-2)and higher current density?0.5 C?after 1000 cycles.?2?Designing and preparation of pod-shaped nano-sulfur particles in-situ wrapped by Ti₃C₂T_x MXenes nanoscrolls.Nano-sulfur particles in-situ wrapped by Ti₃C₂T_x MXenes nanoscrolls were prepared by liquid nitrogen quenching and freeze-drying methods,with a special pod-like morphology.Thanks to its great physical confinement,coupled with the good conductivity of Ti₃C₂T_x MXenes,it well solved the problems of conductivity and shuttle effects.S@Ti₃C₂T_x shows high specific discharge capacity of 937.3 mAh g^-1 at a current density of 0.2 C after 200 cycles amd great rate performance.?3?Designing and preparation of Ti₃C₂T_x MXenes/Co?OH?₂ aerogel.The Ti₃C₂T_x MXenes nanosheets were induced by Co?OH?₂ nanosheets to form hydrogels.And then Ti₃C₂T_x MXenes/Co?OH?₂ aerogel?MXC?was prepared by liquid-nitrogen freezing and freeze-drying method.Thanks to great electrical conductivity of Ti₃C₂T_x MXenes nanosheets and existence of Co?OH?₂,MXC aerogel shows excellent LSB performance.It shows high specific discharge capacity of 1139.0 mAh g^-1 at a current density of 0.2 C after 100 cycles amd great rate performance.If the current density was rised to 1 C,its inicial discharge specific capacity was 1002.2 mAh g^-1 and maintained 801.9 mAh g^-1after 1100 cycles with an extremely low decay of 0.018%.