Silicon/graphene-sheet hybrid film as anode for lithium ion batteries Y.Q. Zhang, X.H. Xia, X.L. Wang, Y.J. Mai, S.J. Shi, Y.Y. Tang, L. Li, J.P. Tu ⁎ State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China abstract article info Article history: Received 21 May 2012 Received in revised form 23 June 2012 Accepted 1 July 2012 Available online 7 July 2012 Keywords: Silicon Graphene Lithium ion battery Magnetron sputtering We report a silicon/graphene-sheet hybrid film prepared by combining electrophoretic deposition and radiofrequency magnetron deposition methods. The constructed hybrid film shows rough morphology with wrinkles and scrolling edges. As anode material for lithium ion batteries, the silicon/graphene-sheet hy- brid film exhibits enhanced electrochemical performances with weaker polarization, higher capacity, better rate capability and cycling performance as compared to the bare silicon film. The silicon/graphene-sheet hy- brid film delivers a high initial reversible capacity of 2204 mAh g -1 and quite good cycling life (capacity maintenance is 87.7%) after 150 cycles. The graphene-sheet in the hybrid film is responsible for the improve- ment of the electrochemical properties. The introduction of the graphene-sheet film not only enhances the adhesion between silicon and the current collector, but also alleviates the structure degradation caused by volume expansion and the shrinkage of silicon film during lithium-ion insertion/extraction, resulting in im- proved electrochemical performances. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Among the explored anode systems for lithium-ion batteries, silicon is considered to be one of the most promising anode materials due to its low discharge potential and extremely high theoretical capacity (add theoretical capacity) [1–5]. Great efforts have been dedicated to silicon film anodes due to their attractive advantages such as good electric con- tact with current collectors and no polymer binders [6–12]. However, its practical application is restrained by the poor cycling stability resulting from the large specific volume change (>300%) causing pul- verization and deterioration of active materials during cycling. This phenomenon is particularly serious in the combining area between Si films and substrate. Based on above thoughts, enhancing the adhesion between the Si film and current collector is the key strategy to obtain high-performance Si film lithium ion batteries. In the research on supe- rior Si film electrodes, several strategies are regarded promising for the construction of high-performance Si film electrodes. The first is to design substrates with rough morphologies. Recent research demon- strated that constructing a substrate with rough morphologies can ef- fectively accommodate strain of silicon anode caused by lithium-ion insertion/extraction and improve electrochemical performance [7–9]. Takamura et al. [7] reported a roughened Ni foil supported Si film anode and demonstrated its enhanced electrochemical performance. The second way is to add a buffer layer between Si films and the sub- strate to improve the adhesion and release the strain through the buffer layer. Wei's group [11] employed single-walled carbon nanotubes as the buffer layer between the Si film and current collector to obtain high-performance Si anode material. Since discovered in 2004, graphene has attracted tremendous research interest in energy storage technologies due to its novel prop- erties such as extraordinarily high electrical conductivity, great mechanical strength and large specific surface area. Compared with the single-walled carbon nanotubes film, the graphene-sheet film shows wrinkled paper-like morphology with good flexibility, which is much more favorable to release strain and keep structure integrity. Besides, the graphene sheet film prepared by electrophoretic deposi- tion (EPD) exhibits noticeable adhesion with the substrate and can resist harsh volume change during cycling. Here, we report a silicon/graphene-sheet hybrid film prepared by combining EPD and radiofrequency (RF) magnetron sputtering methods. Remarkably, the as-prepared hybrid film exhibits superior performance with ex- cellent capacity retention and high specific capacity during cycling and thus promising application. 2. Experimental The graphene-sheet film grown on Cu foil (G-Cu) was prepared by EPD method as described in our previous work [13]. The load weight of graphene-sheet was about 0.08 mg cm -2 . The deposition of Si was synthesized via the method mentioned in reference [9]. The average loading was about 0.3 mg cm -2 . The gravimetric capacity was only calculated by the weight of Si. The structure and morphology of the as-deposited films were analyzed by Raman spectroscopy (LABRAM HR-800), transmission electron microscopy (TEM, CM200) and field emission scanning elec- tron microscopy (FESEM, S-4800). The silicon/graphene-sheet hybrid Electrochemistry Communications 23 (2012) 17–20 ⁎ Corresponding author. Tel.: +86 571 87952573; fax: +86 571 87952856. E-mail addresses: tujp@zju.edu.cn, tujplab@zju.edu.cn (J.P. Tu). 1388-2481/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2012.07.001 Contents lists available at SciVerse ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom