Synthesis And Electrochemical Performances Of Novel Carbon-Based Nanohybrids For Lithium-air And Sodium-ion Batteries

With the rapid development of electric vehicle industry and renewable energy technologies,the electrochemical performance of traditional lithium-ion batteries is too low to meet their requirements.Therefore,it is highly desired to develop two new kinds of secondary batteries:lithium-air battery with much higher energy density;sodium-ion battery using lower cost and being suitable for the large-scale application.The development of new secondary batteries,as well as highlighting their inherent advantages,strongly depends on the configuration of advanced electrode materials with excellent comprehensive properties.In this study,we focus on the enhancement of electrochemical performance of secondary batteries.With this aim in mind,novel design idea and synthetic technology were employed to configure multiscale and multilevel microstructure and nanostructure to achieve the excellent mass transport,electron transfer,structure stability,and catalystic activity by reasonably optimizing the composition,morphology,porous structure,surface characteristics,and electrical conductivity of electrochemically active materials.The detailed study are as follows:N-doped porous graphene aerogels made of interconnected nanocages?NPGA?were constructed by the template-assisted reduced self-assembly of graphene oxide.The unique nanocages are in favor of enhancing the transport of O₂ and electrolyte and increasing tri-phase interfaces for reactions.When employed as the cathode materials for Li-air batteries,it delivers ultrahigh specific capacity?10081 mA h g'1?and ultrahigh rate capability(the capacity of 5978 mAh g'1 can be kept at the current density of 3.2 A g^-1).Based on the total mass of carbon and Li₂O₂,a gravimetric energy density of 2400 W h kg^-1 for the NPGA-O₂//Li cell is delivered at a power density of 1300 W kg^-1.The composite film with interconnected porous structure and high conductivity was prepared by a vacuum filtration assembly strategy.Then,advanced atomic layer deposition method was employed to uniformly and controllably deposit extremely low amount of RuO₂?just 2.84 wt%,Mn3O4/CNTs-RuO₂?.As evidenced by the characterizations for structure and surface,the RuO₂ nanoparticles with modulated electronic structure as the result of the interaction with substrate can enhance the adsorption ability of the intermediate of LiO₂,confine the chemical disproportionation reactions of LiO₂ happened on the surface of catalysts and further form the ultrathin nanosheet-shaped discharge product.As the cathode materials for Li-air batteries,it demonstrates the ultralong cycle life up to 251 cycles and 1700 h.Core-shell nanorods functionalized with the ultrafine MoO₂ nanoparticles?TiO₂@MoO₂-C?were synthesized by a in-situ complexation and polymerization reactions followed by high-temperature annealing approach and using TiO₂ nanotube clusters as templates.The ultrafine MoO₂ nanoparticles can decrease the length of ion diffusion,and TiO₂ nanotube clusters play the role of cable core for enhancing the electron transfer.When employed as the anode for sodium-ion batteries,it delivers a high rate capacity of 76 mA h g^-1 at the ultrahigh current density of 20 A g^-1 and an ultralong cycle life up to 10000 cycles at a current density of 10 A g^-1.Based on the electrochemical qualitative and quantitative analysis,the excellent rate performance is attributed to the high capacitance contribution.MoS₂ with super wide interlayer spacing?1.34 nm?supported on carbon fibers?named as E-MoS₂/carbon fibers?were synthesized by a polyvinylpyrrolidone-assisted hydrothermal reaction and following annealing.Carbon fibers are in favor of enhancing the conductivity,and the MoS₂ with super wide interlayer spacing is beneficial for decreasing the intercalation and diffusion resistance of Na+.As the anode materials for sodium-ion batteries,it shows the ultrahigh rate capacity of 104 mA h g^-1 at a current density of 20 A g'1.With this current density,the battery can be fully charged in ca.18.7 s.Also,a long cycle life up to 3000 cycles was achieved at 10 A g^-1.The sandwich-type nano-architecture of G@MoS₂-C was synthesized by a in-situ complexation and polymerization reactions guided by graphene.The few-layered MoS₂ with expanded interlayer spacing is in favor of decreasing the ion diffusion length and resistance.The graphene in the sandwich-type structure as the electron channels helps to enhance electrical conductivity.Benefiting from the unique structure merits,the G@MoS₂-C delivers the ultrahigh rate capability,as evidenced by the high capacity of 93 mA h g^-1 at 50 A g^-1.