Electrochemical characteristics of bundle-type silicon nanorods as an anode material for lithium ion batteries

In order to prepare bundle-type silicon nanorods, a silver-assisted chemical etching technique was used to modify a 1.6 μm silicon thin film, which was deposited on Cu foil by Electron Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition. The bundle-type silicon nanorods on Cu foil were employed as anodes for a lithium secondary battery, without further treatment. The electrochemical characteristics of the pristine silicon thin film anodes and the bundle-type silicon nanorod anodes are different from one another. The electrochemical performance of the bundle-type silicon nanorod anodes exceeded that of the pristine Si thin film anodes. The specific capacity of the bundle-type silicon nanorod anodes is much higher than 3000 mAh g−1 at the first charge (Li insertion) cycle. The coulombic efficiency of bundle-type silicon anodes was stable at more than 97%, and the charge capacity remained at 1420 mAh g−1, even after 100 cycles of charging and discharging. The results from the differential voltage analysis showed a side reaction at around 0.44–0.5 V, and the specific potential of this side reaction decreased after each cycle. The apparent diffusion coefficients of the two anode types were in the range of 10−13–10−16 cm2 s−1 in the first cycle. In subsequent charge cycles, these values for the silicon thin film anodes and the silicon nanorod bundle anode were approximately 10−12–10−14 and 10−13–10−15 cm2 s−1, respectively.

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► A metal-assisted chemical etching technique was performed on Si thin films.
► The etching process resulted in the formation of bundle-type Si nanorods.
► The morphology of Si electrodes closely relate to electrochemical characteristics.