Applications Of Carbon-Metal Composites In Long-life Lithium–Oxygen Batteries

Aprotic lithium–oxygen batteries have received widespread attention from researchers around the world due to the ultra-high energy density.At present,the application of aprotic lithium–oxygen batteries still faces many challenges,such as the high charge/discharge overpotential,low practical capacity,poor rate performance and cycling stability.The cathode material is the main area where the charge/discharge reaction takes place.Its structure and catalytic activity have a very important influence on the electrochemical performance of lithium–oxygen batteries.Therefore,it is vital to design a cathode material with both resonable structure and highly effective catalytic activity to enhance the electrochemical performance of lithium–oxygen batteries.The main work of this paper is to study and prepare the cathode materials which possess the usefull structure and highly efficient catalytic performance.The research contents and conclusions are as follows:?1?Using multi-walled carbon nanotubes?MWCNTs?as the template,the three-dimensional?3D?intersected graphene nanoribbons?GNRs?framework was obtained by chemical shear method.Then the RuO₂ modified 3D intersected GNRs cathode?RuO₂@GNRs?was prepared by loading RuO₂ particles on GNRs through a simple dropping method.The electrochemical data suggest that GNRs have a higher specific capacity than MWCNTs.More importantly,the cycling performance of RuO₂@GNRs cathode can last 424 cycles at a curtailed specific capacity of 1000mAh g^–1,showing a very stable long-cycling life.The significantly improved electrochemical performance of RuO₂@GNRs stems from the synergistic catalytic effect between the 3D intersected GNRs skeleton and the highly efficient RuO₂catalyst.?2?The bismuth sulfide/ketjen black hybrid?Bi₂S₃/KB?was prepared by a facile one-step hydrothermal method.The cyclic voltammetry curve?CV?shows that Bi₂S₃/KB hybrid has an excellent ORR/OER bifunctional catalytic ability.In the full charge-discharge mode,the Bi₂S₃/KB cathode shows a higher discharge specific capacity(10475 mAh g^–1)and lower charge-discharge overpotential?1.44 V?than those of bare Bi₂S₃ cathode and bare KB cathode.At a curtailed specific capacity of1000 mAh g^–1,the cycling performance of Bi₂S₃/KB cathode can reach 391 cycles,which demonstrates an excellent cycling stability of Bi₂S₃/KB catalyst.The improved electrochemical performance of Bi₂S₃/KB cathode comes from the good bifunctional catalytic activity of Bi₂S₃/KB and the high electrical conductivity,large specific surface area and rich pores of this hybrid.In addition,the SEM results of different discharge depths show that Li₂O₂ prefers to deposit on the surface of Bi₂S₃ nanorods in the low capacity stage and the existence of Bi₂S₃ can inhibit the deposition of Li₂O₂on KB region in the high capacity stage.This deposition model of Li₂O₂ can effectively defer the electrode deactivation and reduce the side reactions,thus endowing the Bi₂S₃/KB cathode with a stable long-cycling life.?3?The bismuth sulfide/reduced graphene oxide hybrid?Bi₂S₃/rGO?was prepared by a simple one-step hydrothermal method.CV test suggests that Bi₂S₃/rGO has an excellent ORR/OER bifunctional catalytic performance.In the full charge-discharge mode,the Bi₂S₃/rGO cathode has a higher discharge specific capacity(11624 mAh g^–1)and lower charge-discharge overpotential?1.3 V?than those of bare Bi₂S₃ cathode and bare rGO cathode.At a limited specific capacity of1000 mAh g^–1,the Bi₂S₃/rGO cathode has an excellent cycling performance of 305cycles,which shows a stable charge-discharge reversibility.This remarkable improvement of electrochemical performance is determined by the highly efficient bifunctional catalytic activity of Bi₂S₃/rGO and the good electrical conductivity,large specific surface area and porous struture of this hybrid.Similar to the previous chapter,the SEM images under different discharge capacities suggest that Li₂O₂ prefers to deposit on the surface of Bi₂S₃ nanorods,which can effectively prevent the direct contact between Li₂O₂ and carbon materials.It can reduce the corrosion and passivation rate of cathode material,which endows the Bi₂S₃/rGO cathode with a very stable long-life catalytic activity.In addition,the first principle calculations?DFT?reveal that both O₂ and Li₂O₂ have strong adsorption energies on Bi₂S₃?130?surface,which means that Li₂O₂ prefers to deposit on the surface of Bi₂S₃ nanorods as well.Hence,the DFT results are well consitent with the Li₂O₂ deposition mechanism mentioned above.