Research On Synthesis And Electrochemical Performances Of3D Co₃O₄/Carbon Fiber Cloth Anodes For Flexible Lithium-ion Batteries

Since introduced by Sony Corporation in the early1990s, lithium-ionbatteries have rapidly taken over the miniative and portable electronicconsumption goods market. Flexible lithium-ion batteries are considered asappealing batteries, owing to the improved demand of society for the flexibleelectronic device. Flexible batteries are needed, e.g., for rolled-up displays,active radio-frequency identification tags, integrated circuit smart cards, andimplantable medical devices.Cobalto-cobaltic oxide （Co₃O₄）, as an important transition-metal oxide, isconsidered as a very promising anode material for LIBs, due to the hightheoretical capacity (890mAh·g^-1) and high safety. Carbon fiber cloth （CFC）, onekind of flexible substrate, has high mechanical strength and excellentelectrochemical stability.Herein, the3D Co₃O₄nanowire arrays could be easily grown on the flexiblesubstrate of Carbon fiber cloth by using a facile hydrothermal route. The uniquehierarchical3D Co₃O₄/CFC exhibit high capacity, excellent cycling performanceand good rate capability. The architecture of3D Co₃O₄/CFC is influenced byvarious factors, such as the concentration of Co（NO3）2, reaction time andcalcination temperature. Experiment results demonstrate that3D Co₃O₄nanowirearrays/CFC was obtained in0.05mol·L^-1Co（NO3）2for5h and then heated at400℃for2h. As the integrated anodes of LIBs,3D Co₃O₄nanowire arrays/CFCdelivered high-rate capacity of464mAh·g^-1at5C rate and1261mAh·g^-1after50cycles at1C rate.After soaking3D Co₃O₄nanowire arrays/CFC into the solution of glucose,the solution was maintained at room-temperature for6h and then thermal treatedat350℃for1h. The research demonstrated that the carbon coating was thickerwith the increment of the concentration of the glucose and it’s morehomogeneous with the increase of the holding time. The carbon coatingmodification would cause the reduction of Co3+ion. The carbon can significantlyenhance the rate performances of3D Co₃O₄nanowire arrays/CFC without theadverse on the cycling behavior with an improvement from480mAh·g^-1to697mAh·g^-1at5C rate.The high capacity, excellent cycling stability and good rate capability can beattributed to the unique morphology and structure of the Co₃O₄nanowirearrays/CFC electrodes on the following aspects:（1） The Co₃O₄nanowire arraysdirectly grown on the carbon cloth have an outstanding electronic conductivity because Co₃O₄nanowire arrays sticked tightly to the CFC to form very goodadhesion and electrical contact, building up an expressway for charge transfer.（2）The3D configuration of the Co₃O₄/CFC ensures the loose textures and openspaces between neighboring nanowire arrays, thus greatly enhancing theelectrolyte/Co₃O₄contact area, which would facilitate the diffusion of theelectrolyte and accommodation of the strain induced by the volume changeduring cycling, thus leading to a higher efficiency of lithiation and delithiationunder the electrolyte penetration.（3）The novel3D array structure shortens theLi+ion diffusion paths in the nanowires and enhances the rate capability.