| Due to the outstanding advantages such as low Li+intercalation voltage, high capacityintensity, excellent safety, rich resource and low cost, SnO2is considered to be an attractivesubstitute of carbon negative materials for Li-ion batteries. However, the main obstacles forthe industrialization of SnO2as negative material are its drawbacks: relatively low cyclingreversibility, poor rate capability and low power density, which makes it can’t fulfill therequirement of Li-ion batteries for electric vehicles. To overcome those drawbacks of SnO2, Itried two ways:1) electrodeposited SnO2on planar Cu foils to fabricate SnO2nano-filmnegative electrodes,2) electrodeposited Cu nanorods on planar Cu foils to obtain, thenelectrodeposited SnO2nano particles around Cu nanorods to fabricate nano-structured SnO2negative electrodes based on Cu nanorods current collectors. A systematic and detailed studyon the fabricated nano SnO2negative electrodes has been carried out. Main research resultsare listed as below:1) Arrays of Cu nanorod were fabricated by cathodic electrodeposition inside thenanopores of anodized alumina oxide (AAO) templates. Three electrolyte systemswere tested and compared. Two of them were acid copper sulfate based solutions,including conventional solution A and high-throw solution B. The third one wasalkaline solution. The influence of electrodeposition conditions, such aspredeposition polishing, deposition voltage, and deposition duration, on theaggregation and Cu nanorod arrays were investigated in detail. It was found thatcareful mechanical polishing effectively reduced the surface roughness of Cucathodes and avoided the formation of continuous Cu layer. Properties of electrolytesand form of copper ions in the electrolytes greatly affected the uniformity ofdeposited Cu nanorods. Nanorods electrodeposited in electrolyte B with the highestH2SO4concentration demonstrated the worst uniformity, while the most uniformnanorods were fabricated in alkaline electrolyte C. Using the weight gain per unitarea of cathode as a direct measure of average length of deposited Cu nanorods andby controlling the weight gain to be in the range of1.2～1.4mg/cm2, free-standingCu nanorod arrays have been successfully obtained by electrodeposition inelectrolyte A and C.2) Pure SnO2films were successfully fabricated on Cu substrates by one-step cathodicelectrodeposition without the pretreatment of electrolytes. Electrodepositionparameters, such as the concentration of HNO3, aging of the electrolyte, thedeposition voltage, and temperature, were demonstrated to be critical to eliminate theco-deposition of Sn. It was found that the ratio of the concentration of HNO3to SnCl4, aging of the electrolytes, the electrodeposition temperature, and the depositionvoltage were important parameters impacting both the morphology and the phase ofthe deposits. By carefully controlling these processing conditions, dense SnO2filmswith good adherence to the Cu substrate were successfully obtained. The electrodesloaded with SnO2films were annealed, then fabricated into coin cells. The cellstesting results showed that their electrochemical properties were not improvedcompared to the electrode without annealing.3) To fabricate nano-structured SnO2electrodes based on Cu nanorods currentcollectors, we prepared Cu current collectors loaded with Cu nanorod arrays, thenload SnO2active materials on the Cu nanorod arrays by catholic potentiostaticdeposition technique. It was found that electrodes prepared under85℃electrodeposition temperature and0.4V electrodeposition voltage had the bestelectrochemical properties, and their morphology were rather different from that ofelectrodes prepared under other electrodeposition conditions. Besides, the weightgain of SnO2on per unit area of Cu nanorods current collectors should be carefullycontrolled to avoid that the space between Cu nanorods are fully occupied by SnO2particles, thus lose the advantages brought by nano structure and worsen theelectrochemical properties of fabricated cells.4) Electrochemical properties of three types of nano electrodes were tested andcompared: SnO2electrodes based on Cu nanorods current collectors, SnO2electrodesbased on planar Cu current collectors and nano-powder SnO2electrodes based onplanar Cu current collectors. The results showed that the discharging specificcapacity of SnO2electrodes based on Cu nanorods current collectors was muchhigher than that of other two types of electrodes, especially under high dischargingrate. The morphology of SnO2electrodes based on Cu nanorods current collectorshad minor changes after many cycles, and no crackles were found. This kind ofnano-structured electrodes showed excellent structure stability and cyclingperformance. |
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