The Doping Modification And Electrochemical Performance Of SnO₂/graphene Anode Materials For Lithium-ion Batteries

Lithium-ion batteries?LIBs?have been widely used due to their obvious advantages such as high specific capacity,long cycle life,safety,low environmental impact,low memory effect and so on.At present,graphite is the main commercial anode material for LIBs.However,its theoretical capacity is only 372 mAh/g,which can not meet the growing demand for high performance LIBs.SnO₂ is one of the most promising anode materials because of its high theoretical capacity?782 mAh/g?,low cost,environmental benignity and abundance.However,its low conductivity and large volume changes during the lithium insertion/exaction process result in pulverization of the electrodes,leading to poor cycle stability.Graphene has the advantages of large surface area,excellent electronic conductivity and chemical stability.Combining the characteristics of SnO₂ and graphene,we prepared SnO₂/graphene composites for anode materials,and then modified SnO₂/graphene composites by elemental doping,which could improve the electrochemical properties of composites.The main research work is as follows:?1?SnO₂/graphene composites were prepared by the oil bath method,and then the composites were doped with nitrogen by solid-gas reaction.The electrochemical performance was carried out to find out the optimum ratio between SnO₂ and graphene.The experimental results show that the best proportion between SnO₂ and graphene is that the mass of SnO₂ is 63.08wt%in the composite.After 50 cycles at a current density of 0.1 A/g,the SnO₂/nitrogen-doped graphene exhibited a good discharge capacity,which is still high to 891 mAh/g.The excellent electrochemical performance can be attributed to that the graphene can effectively buffer the volume expansion of SnO₂,prevent the agglomeration of SnO₂ nanoparticles,and improve the electrical conductivity of composites.Furthermore,some nitrogen-containing functional groups in the graphene have strong interactions with metal oxides,which would improve the binding between nanoparticles and graphene.?2?Ni-doped SnO₂/graphene composites were prepared by the co-precipitation method and different doping amount of Ni were prepared for comparison.The results suggest that the electrochemical performance of Ni-doped SnO₂/graphene is the best when x is 5.5%in Sn_1-xNi_xO₂.After 50 cycles at a current density of 0.1 A/g,the capacity of Ni-doped SnO₂/graphene was still high to 858 mAh/g.?3?Fe-doped SnO₂/graphene composites were prepared by the co-precipitation method and different doping amount of Fe were prepared for comparison.The results show that the cycle and rate performance of Fe-doped SnO₂/graphene is the best when x is 10%in Sn_1-xFe_xO₂.After 100 cycles at a current density of 0.1 A/g,the Fe-doped SnO₂/graphene exhibited a discharge excellent capacity of 1353 mAh/g,which is far higher than the theoretical capacity of SnO₂?782 mAh/g?.After 100 cycles at a current density of 0.5 A/g,the capacity of Fe-doped SnO₂/graphene was 790 mAh/g.Theiron exert significant catalytic effects on the reaction between Sn and Li₂O,with the synergistic effect between graphene and Fe-doped SnO₂ including its high specific surface area and more active sites,which will make the better embedding of lithium ionsin the crystal as well as the high tolerance to the changes of volume.Therefore,the electrochemical performance of the composites can be effectively improved by elemental doping.