Study On Doped FeOOH/Graphene Composites As Anode Material For Lithium-ion Batteries

Lithium-ion batteries(LIBs)have become an important energy storage device due to their high energy density and long cycling life.At present,the commercial anode material of LIBs is graphite.However,its theoretical specific capacity is only 372 m Ah g^-1,which cannot meet the demand of high energy density.Recent studies have shown that iron oxides have high theoretical specific capacity(?900-1007 m Ah g^-1).In addition,with the advantages of resource abundance,low cost,environmental friendliness and large-scale production,iron oxides have been regarded as promising anode materials for the next-generation LIBs.However,the practical application of iron oxides is seriously restricted due to the issues of large volume change,poor structural stability,low reaction kinetics and rapid capacity fading.Therefore,in this paper,we improve the electrochemical performance of FeOOH by element doping and graphene composition.It is found that these strategies can effectively alleviate the above mentioned issues,thereby improving the electrochemical reaction kinetics and lithium storage property.The specific research contents are as follows:(1)The silicon-doped FeOOH/graphene(Si-FeOOH@G)composite is prepared through a facile one-pot hydrothermal method.Study shows that the composite fabricated with the Na₂Si O₃/Fe Cl₂ molar ratio of 2.2%has the best cycling and rate performance.It exhibits a very high specific discharge capacity of 1370.5 m Ah g^-1 at 0.1 A g^-1 after 200 cycles.Besides,it also delivers average discharge capacities of 599.2 m Ah g^-1 at the high current densities of 2 A g^-1.The doping of Si can effectively inhibit the agglomeration of active nanoparticles,promote the diffusion of Li⁺ions and the conversion reaction of FeOOH.Therefore,graphene composition and proper Si doping can greatly improve the reversible capacity,cycling and rate performances of FeOOH.(2)A one-pot hydrothermal method was applied to prepare Sn-doped FeOOH/graphene(Sn-FeOOH/rGO)composite.According to the electrochemical results,the Sn-FeOOH/rGO composite has the best cycle performance when the molar ratio of Na₂Sn O₃ to Fe Cl₂ is 5%.The 5%Sn-FeOOH/rGO composite can deliver a high reversible specific capacity of 1445.0 m Ah g^-1 after 200 cycles at0.1 A g^-1.Moreover,5%Sn-FeOOH/rGO exhibits excellent rate performance,delivering average discharge capacities of 677.2 m Ah g^-1 at 2 A g^-1.Sn doping in FeOOH can prevent the agglomeration of FeOOH nanoparticles and provide a considerable pseudocapacitance capacity.In addition,doped Sn can also provide the lithium storage capacity,and the synergic effect between doped Sn and iron oxide can further improve the electrochemical reaction kinetics of material.Thus,the 5%Sn-FeOOH/rGO composite material exhibits excellent electrochemical performance with the combination of conductive graphene.(3)The F-doped Fe(O,F)OH/rGO composite material is directly prepared by a simple one-pot hydrothermal process.F doping can make FeOOH nanoparticles more uniformly dispersed on graphene,and enhancing the transport of electrons and lithium ions.The prepared 0.04-Fe(O,F)OH/rGO material has a reversible specific capacity of 1209.3 m Ah g^-1 after 135 cycles at 0.1 A g^-1.Besides,this material also exhibits excellent rate performance,providing average discharge capacities of 744.8 m Ah g^-1 at 2 A g^-1.The doping of F can solve the problem of slow kinetics,and the conductive graphene network can effectively improve the conductivity of composite.As a consequence,the 0.04-Fe(O,F)OH/rGO composite exhibits excellent rate performance and good cycling ability at high current density.Overall,the advantageous combination of element doping and graphene composition can effectively improve the electrochemical performance of FeOOH anode material.This study can provide experimental support and theoretical guidance for the design and development of transition metal oxide-based anode materials with high LIB performance.