Preparation And Electrochemical Performance Of Cobalt Oxides/Carbon Composites

Among transition metal oxides,Co O and Co₃O₄ are considered to be promising anode materials due to their high theoretical capacity,wide source,and ease of preparation.However,because of the poor conductivity and severe volume expansion effect of CoO and Co₃O₄,the electrode materials was eased to pulverize and then the capacity decreased,which limited their application.The common methods to solve such problems include nanocrystallization,doping,and compositing with carbon materials,among which the compositing with carbon materials is a more common and efficient method.In this paper,three different carbon sources were used to composite with cobalt oxides through hydrothermal-heating treatment,solvothermal-heating treatment and impregnation-heating treatment methods to obtain cobalt oxides/carbon composites with different morphologies and phases.The relationship of structure,composition and properties were studied.?1?Using Super P as a carbon source,Co O/Super P composites were prepared by hydrothermal following with heating treatment method.Super P can not only effectively reduce the size of CoO particles,but also improve the electrochemical performance of CoO.The CoO/Super P composite electrode exhibited a cycling capacity of 1020 mAh g^-1 at 0.1 A g^-1.The higher reversible capacity can be attributed to the fact that Super P can effectively promote the electron transfer of Co during the delithiation process and accelerate the electrochemical reaction rate,which in turn allows Co and Li₂O to be completely converted to CoO.Then decrease the loss of active material meanwhile improve the capacity and rate performance.In order to further modify the structure of the material,the Super P is activated and the ethanol solution is used as a solvent.The morphology of the products can be controlled by changing the volume ratio of ethanol to water in the solvent.When the volume ratio of ethanol to water is 3:4,the CoO in the product has three structures:porous rods,porous sheets and porous blocks.After 30 cycles,the capacity of the CoO/Super P can reach 1466 mAh g^-1,and the capacity after100 cycles is stable at 794 mAh g^-1.The synergistic effect of three porous structures of CoO with different dimensions and Super P contributes to increase the electrochemical performance of electrode.?2?CoO/graphene composites were prepared by solvothermal-heating treatment.The self-assembled structure of CoO can be controlled by changing the mass fraction of oleic acid in the solvent.Changing the heat treatment temperature can effectively change the phase composition of the product.When the mass fraction of oleic acid is 1.6%and the heat treatment temperature is 500?C,the product is Co₃O₄/CoO/Co/graphene composites with a three-dimensional?3D?porous structure.After 100 cycles,the discharge capacity of it was 1209 mA h g^-1,and the capacity retention rate was 98.2%.The presence of metal Co and graphene increases the conductivity of the material,accelerates the electrochemical reaction,reduces the residue of Li₂O,and then maintains the reversibility of the charge and discharge process of the electrode.The presence of Co₃O₄ and CoO increases the capacity of the electrode,and the synergistic effect of the four elements enhance the electrochemical performance of the electrode.?3?Taking nostoc commune as the carbon source of biomass,the adsorption of cobalt nitrate is the most obvious,which makes the content of Co₃O₄ in the product Co₃O₄/C is 76.4%,and the surface of Co₃O₄ particles is covered by a layer of graphitizing carbon derived from the nostoc commune itself.When the carbonization temperature is 1000?C and the activation time is 2 h,the carbon matrix in the product exhibits a 3-D porous structure,and the carbon-coated Co₃O₄ particles are loading on it uniformly.The capacity stable at 1072 mAh g^-1 in the 100 cycles,the capacity retention rate was 93.1%,and the capacity at the current density of 2 A g^-1 was 866 mAh g^-1.