In Situ Preparation And Electrochemical Performance Study Of Cobalt And Manganese Oxides/Carbon Composites

Nowadays,the theoretical capacity of widely commercial graphite anode in lithium ion battery industry could not cope with the demands of large-scale energy storage equipment.Thus,it is urgent to develop a new lithium ion battery anode material,which has high theoretical capacity,long cycle life and safety performance.Cobalt-manganese-based metal oxides have become a promising anode material for lithium-ion batteries due to their high energy density and high power density.Nevertheless,the disadvantages of cobalt-manganese-based metal oxides material,poor conductivity and large volume change during intercalating and deintercalating of Li+,have greatly limit the widely application in industry.In this paper,using the graphene oxide with high conductivity,good flexibility and metal-organic frameworks with plentiful porous structure,adjustable porous volume as basement,in situ synthesized the cobalt-manganese-based oxide/carbon composites by several principles and preparation methods.In order to improve the conductivity and structure stability of material,and get a new anode material for lithium-ion battery with high reversible capacity,long cycle life and good rate capability.Firstly,using GO as basement and the electrostatic coupling between Co2+ and oxygen-containing groups on the surface of GO,this paper synthesized interconnected network structured with rich porous Co O/RGO composite material by solvothermal method and heat treatment,which Co O nanoparticles in-situ growth on ultra-thin graphene sheet surface.The composite material exhibited well electrochemical performance.After 80 cycles at 100 mA/g,the specific discharge capacity reach 1327.3 mAh/g,the capacity retention rate can reach100%.However,Co is an expensive and toxic metal,we added Mn into the composite material,for Mn is green initiative and abundant in resources.We synthesized the CoMn_xO_y/RGO bimetallic oxide/carbon composite material.By using the complementary and cooperative effects between Co and Mn,hoping to improve the conductivity and structural stability of the composites.And MnCo₂O₄/RGO exhibited better cycle stability and rate performance.It maintains 918.7 mAh after100 cycles at 200 mA/g.Compared with the first cycle.At 3200 mA/g,the capacity can reach 692 mAh/g,and the capacity can recover to 1306.8 mAh/g when the current density went back to 100 mA/g after high current discharge cycle.Secondly,in this part,we synthesized hierarchical structured hollow spherical MnO@C composite material by coprecipitation and high temperature sintering method,using the MOFs as precursor.Porous amorphous carbon was coated on thesurface of nanocrystalline MnO particles,mixing uniform.The structure can shorten the transmission path of Li+,buffer the volume change of material and improve the conductivity.After 80 cycles at 100 mAh/g current density,the discharge specific capacity of 813.7 mAh/g can still be maintained.Later,we prepared CoMn_xO_y@C composites on the basis of MnO@C.The results showed that MnCo₂O₄@C exhibited better cycle stability and rate performance.The discharge specific capacity was 820.5 mAh/g after 100 cycles at current density of 200 mAh/g.And the discharge specific capacity is 682.4 mAh/g at high current density of 3200 mAh/g.The discharge specific capacity reaches 1227.7 mAh/g when the current density went back to 100 mA/g.