Research On Fe₃O₄/Rebar Graphene Composite As Binder Free Anode For Lithium Ion Battery

Lithium-ion batteries?LIBs?share prospect of application in portable electronic devices,electric vehicles?EVs?and hybrid-electric vehicles?HEVs?due to their superior properties such as high energy density,fast charge/discharge rate,long lifetime and environment friendly.Carbon material and transition metal oxides are considered as promising anode materials for LIBs.Carbon material possesses excellent electrical conductivity,but low specific capacity?372 mAh/g?while transition metal oxides hold specific capacity?926 mAh/g?,but poor electrical conductivity and huge volume change.Among all the carbon allotrope,graphene has become research hotspot due to its outstanding electrical conductivity,large specific surface area and fast and stable electron and ion transport ability.In the group of transition metal oxides,Fe₃O₄ has captured lots of attention as a promising anode material for LIBs for its high theoretical reversible capacity?926 mAh/g?and abundant resources.Anode material for LIBs with excellent electrochemical properties can be obtained by combining the advantages of both carbon and Fe₃O₄.In this paper,we prepared rebar graphene?RG?via in-situ synthesis method which overcame the weakness of traditional CVD synthesized graphene,such as low production,troubles in transferring onto target substrate,low electrical conductivity and poor mechanical properties.Fe₃O₄/rebar graphene?FRG?composite was obtained through solvothermal route and used as anode for lithium ion batteries.Ratio of raw materials,solution concentration and calcination time were adjusted for the preparation of rebar graphene and ratio of raw materials,temperature and time of hydrothermal process were optimized for the preparation of FRG.Furthermore,the electrochemical performance of the obtained products were tested as binder free and carbon black free anode for lithium ion battery.The results show that RG is a free-standing film which is interconnected by single-wall carbon nanotube and graphene through covalent bonding.FRG composite is obtained by coating a layer of Fe₃O₄ nanoparticles with particle size of approximately 200 nm on the matrix of RG uniformly which also forms a free-standing film.The specific capacities at the 100 th cycle of the RG and FRG as binder free and carbon black free anode materials for lithium ion battery are 545 mAh/g and 1038 mAh/g,respectively,which suggests that the specific capacity of FRG is twice as that of RG.After high rate cycling at 10 A/g,the specific capacities of RG and FRG achieve at 482 mAh/g and 955 mAh/g at 0.1 A/g,respectively.The FRG electrode has achieved much higher energy and power density,reaching 1202 mAh/g at the first cycle at 0.1 A/g,owing to the synergistic effects between RG and the homogeneously dispersed Fe₃O₄ nanoparticles.