Fabrication and Electrochemical Evaluation of Tin Plated Three-Dimensional Copper Nanostructured Anode for Lithium Ion Battery

Abstract

Introduction Lithium-ion batteries (LIBs) are among the most important energy storage and power conversion devices, and are widely used in portable electronics such as mobile phones and laptop computers. However, LIBs cannot satisfy the ever-growing needs of high-power applications due to the low energy density of commercial graphite. Tin and lithium form reversible alloys, and for the fully lithiated composition (Li4.4Sn), the specific capacity is 994 mA h g-1, which is almost three times higher than the theoretical value for a conventional graphite anode (372 mA h g-1). However, there are huge variations in the volume occupied by the atoms within the alloy structure because of aggregation of Sn and Li during the electrochemical alloying-dealloying process. These variations result in considerable mechanical stress, which leads to rapid capacity fade (short cycle life) due to pulverization of the material. To address this issue, several strategies have been proposed for improving the cyclability of tin materials by decreasing the particle size and using porous thin films of tin. We have developed a simple method for fabricating a three-dimensional (3D) copper nanostructure using electrodeposition. In this study, the microstructure of a tin-coated anode was analyzed and the charge/discharge characteristics of the anode were evaluated following direct electrodeposition of a pure tin layer on the 3D copper nanostructure. Experimental An acidic copper sulfate bath (0.85 M CuSO4×5H2O + 0.55 M H2SO4 + 3.0´10-4 M polyacrylic acid M.W=5000)1) was used to fabricate the 3D copper nanostructure. Electrodeposition was conducted under galvanostatic conditions (1 A dm-2) at 25°C without agitation. A tin alloy plating bath containing 1 M K4P2O7 + 0.25 M Sn2P2O7+ 0.002 M polyethylene glycol + 0.005 M HCHO was prepared. Electroplating was carried out under galvanostatic conditions at 25°C without agitation. The morphology and structure of the obtained samples were examined by field emission-scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectrometry (EDX). Electrochemical measurements were performed using coin-type cells assembled in an argon-filled glove box. LiPF6 (1 M) in ethylene carbonate and diethyl carbonate (1:1 vol%) was used as the electrolyte solution. Cycling tests were performed between 0.02 and 1.5 V (vs. Li/Li+) at a constant temperature of 25°C. Results and Discussion This new tin anode exhibited both a high reversible capacity and improved cyclability. The reversible capacity was 521.1 mA h g-1 after 100 cycles and 469.3 mA h g-1after 300 cycles at 0.5 C. Figure 1(a) shows a surface SEM image of the new tin anode, demonstrating the homogeneously plated tin film on the 3D copper nanostructure. Figure 1(b) shows an SEM image after 100 cycles, where a small amount of pulverization is evident. Figure 1(c) shows an SEM image of the anode after 300 cycles. Further pulverization is seen to have taken place. The results of a detailed electrochemical evaluation of this anode will be presented at the meeting. Reference 1) S.Arai and T.Kitamura, ECS Electrochem. Lett., 3 (5), D7-D9 (2014). Figure 1