Abstract

Introduction Lithium ion batteries employing graphite as the anode active material exhibit higher energy densities than conventional rechargeable batteries, although increasing the capacity of these devices will require the use of alternative anode compounds. Since tin (Sn) has a higher theoretical capacity (991 mAh g-1) than graphite (372 mAh g-1), it has been considered for this role. However, Sn tends to fall off the current collector during charge-discharge cycles due to significant volume variations, degrading the battery performance. One approach to avoiding this problem is to anchor the Sn layer to an underlying copper (Cu) layer using fibrous materials. We have already reported the excellent charge-discharge characteristics of a new tin anode reinforced with multiwalled carbon nanotubes (MWCNTs), formed by a combination of Cu/MWCNT composite plating and electroless tin plating.In this study, we examined a new fabrication process for the MWCNT-reinforced tin anode structure based on tin electrodeposition using a sulfuric acid bath, and explored the correlation between the new negative electrode structure and its electrochemical characteristics. Experimental A Cu/MWCNT composite plating bath (0.85 M CuSO4 ●5H2O + 0.55 M H2SO4 + MWCNT + polyacrylic acid), and a tin plating bath (0.2 M SnSO4 + 0.5 M H2SO4 + additive) were prepared. Using these baths, a Cu/MWCNT film was applied to a pure copper plate and tin was subsequently electrodeposited on the Cu/MWCNT film, resulting in the MWCNT-reinforced tin anode structure. For comparison purposes, tin was also electrodeposited on a pure copper plate. Electroplating was carried out under galvanostatic conditions at 25 °C. The microstructure of the new tin anode was examined by field emission scanning electron microscopy (FE-SEM). The phase structure of the deposits was analyzed by X-ray diffraction (XRD). Electrochemical studies of the tin-based anodes were carried out using coin cells (2032) assembled in an Ar-filled glove box. Each coin cell consisted of a lithium foil counter and reference electrodes and a tin-based anode as the working electrode. The electrolyte was 1 M LiPF6in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (1:1 vol%). Cycling tests were performed at a constant temperature of 25 °C. Results and Discussion Figure 1 shows a surface SEM image of the tin anode fabricated by the new process. MWCNTs are seen to be uniformly dispersed over the Sn layer. Figure 2 presents a cross-sectional SEM image of the tin anode. It can be seen that MWCNTs connect the Sn and Cu layers. No defects, such as voids or cracks, are observed between the two layers.The electrochemical characteristics of the tin anode will be discussed in detail during the presentation. References 1) S. Arai and R. Fukuoka, J. Appl. Electrochem., 46, 331 (2016). Figure 1

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