Patterned Si thin film electrodes for enhancing structural stability

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Patterned Si thin film electrodes for enhancing structural stability Gyu-bong Cho, Jung-pil Noh, Ho-jin Sung, Sang-hun Lee, Yeon-min Im, Hyo-jun Ahn and Ki-won Kim*

Abstract A patterned film (electrode) with lozenge-shaped Si tiles could be successfully fabricated by masking with an expanded metal foil during film deposition. Its electrochemical properties and structural stability during the chargedischarge process were examined and compared with those of a continuous (conventional) film electrode. The patterned electrode exhibited a remarkably improved cycleability (75% capacity retention after 120 cycles) and an enhanced structural stability compared to the continuous electrode. The good electrochemical performance of the patterned electrode was attributed to the space between Si tiles that acted as a buffer against the volume change of the Si electrode. Keywords: patterned electrode, silicon film, stress, anode

Introduction The secondary Li-ion batteries with a high energy density have gained attention from wide-range applications of power source for the portable electronics, electric vehicle, and electric storage reservoir. In order to increase the energy density in the limited battery volume, the volume of the cathodic electrode having Li sources should be increased, whereas that of the anodic electrode has to be decreased, that is, anode materials with high theoretical capacity are needed to store the large amount of Li ions. For the anodic materials, some of the candidates are Si, Sn, Al, Ge, and compounds including these elements [1,2]. Si has a much higher specific energy (4,200 mAh/ g for Li4.4Si) than commercial graphite (372 mAh/g for LiC6). However, there is a severe practical problem in the application of Si electrodes, i.e., when Si is used as an anode material for Li-ion batteries, a large volume expansion/shrinkage occurs during the charge-discharge (lithiation-delithiation) process. The volume change of Si (310%) causes surface cracking and pulverization of the Si film and leads to a rapid capacity fade during initial cycles. The poor electrochemical performances are ultimately caused by repetitive mechanical stress * Correspondence: [email protected] School of Materials Science and Engineering, Research Institute for Green Energy Convergence Technology, Gyeongsang National University, Gazwadong 900, Jinju, Gyeongnam 660-701, Korea

accompanied by large volume changes [3]. Until now, many attempts have been made to prolong the cycle life of Si film electrodes [4-9]. Most researches focused on enhancing the adhesion between the Si film and a current collector (substrate) because the amount of Li storage was limited and the generation of stress was restrained by the enhanced adhesion. In this work, as a new approach to overcome the problem, space was given to the Si film like a patterned Si film. The Si film including the space is expected to accumulate the stress generated by the volume change during the charge-discharge process. Figure 1 shows schematic diagrams of the e