Controllable Synthesis And Electrochemical Properties Of Modified Chalcogenides Cathodes

The energy density and cycle life of existing lithium-ion batteries remain insufficient for many of the applications,prompting the urgent need for new electrode materials with much higher specific capacities.Lithium-chalcogenides batteries,such as S,Se,Te,and Li₂S based batteries,have been considered as the good candidates as the high-performance and noval rechargeable batteries,owing to their high theoretical specific capacity,abundant resources and low competitive cost.However,so far,the lithium-chalcogenides batteries are plagued by a series of problems before their practical application,such as low active utilization,poor cycling performance,and low rate capability.In order to address those issues,in this article,several highly conductive carbonaceous materials with the well-designed the architecture,such as graphene,carbon nanotube and metal-organic frameworks derived materials,are employed as chalcogenides host for the high performance lithium-chalcogenides batteries.And then we systermly investigate the electrochemical performance and reveal the redox chemistry of those cathodes to provides insights to design new open structured and high-performance cathode materials for lithium-chalcogenides battery.The main content and results are summarized as follows.Part I.Synthesis and properties of sulfur/carban composite cathode1.Wrinkled sulfur@graphene microspheres（WSGM）composite were prepared through a facile,low cost and large-scale spray drying method and its electrochemical properties were investigated.to prepare.Benifiting from its unique wrinkled porous architecture and the highly conductive N-doped graphene matrix,when WSGM with very high mass（82.3 wt%）sulfur loading is used as the cathode for lithium-sulfur（Li-S）cells,it delivers superior electrochemical performance:the reversible specific capacity at 0.1C is as large as 1165.7 m Ah g^-1;even after 200 cycles with a high capacity retention of82.9%.2.Three-dimensional CNT/graphene/sulfur aerogels（3DCGS）were designed and prepared,and the electrochemical performance of high sulfur loading was studied.The results show that the porous,highly conductive 3DCG can be prepared by the freeze drying method and solvothermal reaction.The bimodal mesopores（with sizes of 3.5 and32.1 nm）in 3DCG can accommodate plenty of sulfur（80.1 wt%）,and facilitate the charge transportation and electrolyte penetration.Such unique architecture in 3DCG result in its superior electrochemical performance:the discharge capacity for sulfur is 1217 mAh g^-1and the high-rate capacity up to 4 C is as large as 653.4 mAh g^-1.3.We report well-designed yolk-shelled carbon@Fe₃O₄（YSC@Fe₃O₄）nanoboxes as sulfur hosts and investigate their electrochemical performance.The results show that YSC@Fe₃O₄ can be prepared through simple coprecipitation method and hydrochloric acid etching reaction.And then,S/YSC@Fe₃O₄ was obtained by a melt-diffusion method.With both physical entrapment by carbon shells and strong chemical interaction with Fe₃O₄ cores,this unique architecture immobilizes the active material and inhibits diffusion of the polysulfide intermediates.Moreover,due to their high conductivity,the carbon shells and the polar Fe₃O₄ cores facilitate fast electron/ion transport during the charge/discharge process,resulting in improved electrochemical utilization and reversibility.With these merits,the S/YSC@Fe₃O₄ cathodes support high sulfur loading(5.5 mg cm^-2)exhibit excellent performance.Part II.Synthesis and properties of Li₂S/C composite cathode1.Three-dimensional Li₂S/graphene hierarchical architecture（3DLG）was designed and prepared by in-situ depositing Li₂S nanoparticles into three-dimensional graphene foam（3DGF）network with high surface area and porosity through a facile drop-cast method,and its electrochemical properties were studied.The results show that 3DLG can be employed as flexible,free-standing and binder-free cathode and exhibits a high capacity retention of 87.7%after 300 cycles,and the high-rate capacity up to 4 C reaches598.6 mAh g^-1.2.Three-dimensional CNT/graphene/lithium sulfide（3DCG-Li₂S）aerogel was designed and prepared through facile solvothermal reaction and a subsequent liquid infiltration-evaporation coating method,and its electrochemical performance was studied.The results show that owing to the highly flexible,conductive and unique bimodal mesoporous 3DCG,the free-standing 3DCG-Li₂S with a high Li₂S loading of 81.4 wt%exhibits excellent electrochemical performance including a high discharge capacity of1123.6 mAh g^-11 at the initial cycle and 914.6 mAh g^-1 after 300 cycles.3.Nanoporous carbon-cobalt-nitrogen/Li₂S（Li₂S@C-Co-N）cathode materials were designed and prepared by liquid infiltration-evaporation of ultrafine Li₂S nanoparticles into graphitic carbon co-doped with cobalt and nitrogen derived from metal-organic frameworks,and their electrochemical properties were studied.In this report,the obtained Li₂S@C-Co-N architecture remarkably immobilizes Li₂S within the cathode structure through physical and chemical molecular interactions.Owing to the synergistic interactions between C-Co-N and Li₂S,Li₂S@C-Co-N composite delivers a reversible capacity of 1155.3 mAh g^-1 at the initial cycle,and 929.6 mAh g^-1 after 300 cycles.Part III.Synthesis and properties of Se/C composite cathode1.Three-dimensional graphene-carbon nanotubes@selenium（3DG-CNT@Se）aerogel was designed and prepared,and its electrochemical properties were studied.The3DG-CNT@Se can be used as freestanding cathode and demonstrates excellent electrochemical performance:at 1 C,4 C,and 10 C,the cathode owns reversible specific capacities of 558.3 mAh g^-1,436.4 mAh g^-1,and 192.9 mAh g^-1,respectively.2.Three-dimensional hierarchical carbon-cobalt-nitrogen/selenium（C-Co-N/Se）cathode materials were designed and prepared,and their electrochemical properties were studied.The C-Co-N is prepared with metal-organic framework and employed as matrix to host selenium.Owing to the unique structure with abundant meso-pores and the homogenous distribution of cobalt nanoparticles and nitrogen-group in C-Co-N composite,polyselenides can be immobilized through strong chemical interaction.With a very high Se loading of 76.5 wt%,the C-Co-N/Se cathode delivers superior electrochemical performance with an ultrahigh reversible capacity of 672.3 mAh g^-1 and a capacity of 574.2 mAh g^-1 after 200 cycle.Part IV.Synthesis and properties of Te/C composite cathode1.Three-dimensional aerogel with ultrathin tellurium nanowires wrapped homogenously by reduced graphene oxide（3DGT）was designed and prepared via a facile hydrothermal method,and its electrochemical performance was studied.The obtained3DGT can be used as a free-standing,binder-free cathode for lithium-tellurium（Li-Te）batteries and exhibits excellent electrochemical performances:it shows a high initial capacity of 2611 mAh cm^-3(418.4 mAh g^-1)at 0.2 C,a high retention of 88%after 200cycles and a high-rate capacity of 1083 mAh cm^-3(173.5 mAh g^-1)at 10 C.2.A tellurium@carbon-cobalt-nitrogen（Te@C-Co-N）cathode material was designed and prepared,and its electrochemical performance was studied.Research indicates:highly nanoporous cobalt and nitrogen co-doped carbon polyhedra derived from metal-organic framework is synthesized and employed as tellurium host for Li-Te batteries.The Te@C-Co-N cathode with a high Te loading of 77.2 wt%exhibits excellent electrochemical performances including an ultrahigh initial capacity of 2615.2 mAh cm^-3,a superior cycling stability with a high capacity retention of 94.6%after 800 cycles.