Controllable Preparation And Electrochemical Performance Of The Co₃O₄Nanomaterials

Cubic spinel Co₃O₄has been demonstrated to be a promising safety anodeelectrode material for lithium ion batteries（LIBs） due to its advantages such as facilepreparation, low environmental footprint, inexpensiveness and extremely hightheoretical specific capacity (892mAh·g^-1). However they exhibit the poor capacityretention performance owning to the inherent low electrical conductivity of the Co₃O₄electrode materials and the volume expansion indused by the Li intercalated to theelectrode during the charging and discharging process. Moreover, its high rateproperties are very poor. Therefore it needs long time for finding a way to develop thecommercial Co₃O₄anode material.In recent years, the transition metal oxides electrode material directly grown onthe corrent collector has drawn increasing attention. The special structure has not nolyimproved electrical conductivity, high special capacity and cycling performance dueto excellent electrical connection between active nanostructure and the currentcollector, but also has a simple preparation process without the utilization of carbonconductive additives and polymer binder when compared with the traditionalelectrode. In this paper, the spinel Co₃O₄active nanomaterials with differentmorphologies directly grown on nickel foam were prepared, and then the Ag@Co₃O₄electrode material with the coating of nano-silver was obtained, their morphology,crystal structure and electrochemical properties were characterized by the physicaland electrochemical methods. The main research results are as follows:1. The well organized flower-like Co₃O₄anode nanomaterial directly grown onthe Nickel foam was prepared by the solvothermal-thermal decomposition method.The results from SEM and TEM show that: the well organized flower-like Co₃O₄iscomposed of mesoporous Co₃O₄nanosheet networks with a favorablemacro/meso-porous structrues. Its pore size is about7nm. When compared with theCo₃O₄anode material prepared in the same conditions without the current collector ofnickel foam, the results of electrochemical performance show that: The wellorganized flower-like Co₃O₄anode achives a discharge capacity of883.3mAh·g^-1at0.5C after30cycles, corresponding to82.3%of the capacity retention, but the Co₃O₄anode without the collector only delivers a discharge capacity of591.1mAh·g^-1with55.9%of the capacity retention. Thus the flower-like Co₃O₄anode has excellent electrochemical performance than that of the Co₃O₄anode without the collector.2. We developed a cost-efficiency hydrothermal-thermal decomposition methodto fabricate well organized Co₃O₄nanosheets with uniform sheet stucture.Experimental results show that: The thickness of the nanosheets is estimated to bearound10nm, its height are about3.2μm. The networks are consisted of mesoporousCo₃O₄nanosheets which are interconnected with each other to form1.5μmmacropores. The discharge capacity is maintained at about1000mAh·g^-1at a rate of0.5C after30cycles.3. Ag@Co₃O₄composite anode material was prepared by coating the Co₃O₄nanosheet anode material with Ag using the silver mirror reaction method. In thissection, the relation between the morphology, electrochemical properties and Agcoating was studied in detail. The results indicate that the electrochemical propertiescoulde be improved by coating of Ag on the Co₃O₄nanosheet. Ag@Co₃O₄nanocomposite material shows excellent lithium storage capacity and cycleperformance(more than1100mAh·g^-1of the capacity after40cycles).