Studies On The Preparation And Performances Of Lithium Sulfide-oriented Cathode For Lithium-sulfur Battery

Lithium sulfide(Li₂S)-oriented cathodes of lithium-sulfur batteries(LSBs)are intensively studied in virtue of high energy density,good volume-exchange accommodation,high melting temperature and safety.However,some issues,such as severe polysulfides shuttle,sluggish sulfur redox kinetics and etc.,obstruct the development of high-performance lithium-sulfur batteries(LSBs).In this study,the above issues are carefully handled by deliberately-designed cathodes.Meanwhile,the electrochemical performances of as-fabricated batteries are significantly elevated.The methodology is briefly stated as follows,1.An in-situ carbothermic reduction method is introduced in this work to investigate the effect of in-situ formed lithium sulfide on lithium sulfur batteries.The fabrication process is achieved with the aid of mesoporous and conductive CMK3 and PF-derived conformal carbon layer.It has been found that the Li₂S@CMK3-C prepared at 835 ^oC has excellent electrochemical performance.The lithium-sulfur battery using Li₂S@CMK3-C as cathode and metal Li as anode can deliver a high initial discharge capacity of 979 m Ah g^-1at 0.1 C.Besides,the discharge specific capacity is still 530 m Ah g^-1at 2 C after 450 cycles.Therefore,the preparation of CMK3-supported Li₂S-based cathode material provides a new approach for the development and industrialization of high-performance Li-S battery.2.A three-dimensional(3D)micro/mesoporous carbon architecture with suitable internal structure is designed in this research for the sake of improvement of electroconductivity and polysulfides confinement.The mesoporous structure can offer considerable voids for volume change as well as fast transfer routes for charges and ions.Meanwhile,the microporous coating layer could physically block polysulfides shuttle.The results show that the as-fabricated Li₂S/CMK3/C has a high lithium sulfide loading of 79 wt.%.In addition,the battery delivers a high specific capacity of848 m Ah g^-1at 0.1 C and a good capability of 410 m Ah g^-1after 400 cycles at 2 C.Therefore,the Li₂S-embedded 3D micro/mesoporous carbon architecture could be a significant option for the development and industrialization of high-performance LSBs.3.A Li₂S-loaded graphene oxide/carbon nanotube matrix wrapped by conductive polymer polypyrrole(PPy)is constructed to localize polysulfides inside cathode.The polypyrrole with pyrrole rings can not only chemically confine lithium polysulfides inside cathode via Li-N interaction,but also physically prevent polysulfides from shuttling.As a result,the Li₂S/CNT/GO/PPy cathode delivers a cycling capacity of 525 m Ah g^-1with a low capacity decay rate of 0.065%cycle^-1at a current density of 2 C after 400 cycles.Therefore,the lithium-sulfur battery with PPy-wrapped and Li₂S-based cathode could reasonably be counted as a potential alternative of Li-ion cells.4.The PANI-derived carbon(PDC)is composited with GO and CNT to promote lithium sulfide activation and electrochemical behaviors.The deliberately designed carbon matrix offers fast electron and ion transfer routes and suitable structure for redox reactions and polysulfide confinement.Furthermore,the PDC could not only chemically immobilize polysulfides inside the cathode,but also play as redox mediator(RM)to facilitate Li₂S oxidation via quinone-based structure.Benefited from the aforementioned advantage,the as-fabricated Li₂S-GO/CNT/PDC composite delivers a high initial capacity of 925 m Ah g^-1at 0.1 C and good retention capability of 550 m Ah g^-1after 400 cycles at 2 C.Therefore,the good electrochemical behavior of the Li₂S-GO/CNT/PDC composite suggests its promising prospect for the commercial application of LSBs in high-energy storage devices.5.The titanium carbide(Ti C)decorates the carbon nanotube(CNT)and forms conductive and polar cathode matrix with superior capability of polysulfides chemisorption and electrochemical catalysis in this research.It has been proved that the conductive and polar titanium carbide can not only chemisorbs lithium polysulfides via titanium-sulfur(Ti-S)coordination,but also optimize the lithium sulfide(Li₂S)nucleation/precipitation mechanism for better redox reaction.Especially,the graphene oxide and carbon nanotube matrix(GO-CNT)in this case can act as both host for Li₂S loading and Ti C precipitation.Accordingly,the as-fabricated lithium sulfide-graphene oxide-carbon nanotube-titanium carbide(LS-GO-CNT-Ti C)cathode delivers the high initial discharge capacity of 956 m Ah g^-1at 0.1 C and good rate capability of 508 m Ah g^-1at 2 C.These results consequently manifest that the conductive and polar matrix of LS-GO-CNT-Ti C can perform as a promising cathode of the high performance LSBs.