Toward the realization of reliable Li-ion batteries with high performance and safety, component materials such as those of the current collector and negative electrode require further innovation. Sn, one of the most promising negative-electrode materials, can be electrochemically fixed on a substrate without any binder or conductive additive. However, the pulverization of Snplating films on substrates caused by large volume changes during Li-Sn reactions is the main reason hindering the practical application of Sn-plated electrodes. In the present study, we developed an electrodeposited three-dimensional (3D) Cu substrate applied to underlayer of the electrode. The effect of substrate geometry on the charge-discharge performance of the Sn electrode was investigated. The 3D-Cu/Sn electrode exhibited superior cycling performance with a reversible capacity of 470 mA h g-1 even at the 300th cycle, whereas the Sn-plated electrode prepared on a typical flat Cu substrate showed a capacity of only 20 mA h g-1. The results demonstrated that the 3D structure played a key role in accommodating volumetric changes in the Sn to suppress electrode disintegration. The developed 3D-Cu substrate will be significantly useful as a current collector for alloy-based active materials.

A three-dimensional copper nanostructure architecture (3DC1) coated uniformly with a tin film was fabricated by electrodeposition. In these trials, a pyrophosphate bath was used for tin plating, and the effects of polyethylene glycol and formaldehyde additives on the morphology of the deposited tin were investigated. Relatively large tin particles were electrodeposited in an inhomogeneous manner over the 3DC1 surface when using a plating bath without additives. In contrast, 3DC1 coated with a uniformly thick tin film was fabricated by employing a bath with the additives. have been widely researched. Among these potential uses, the application of 3D copper nanostructured architectures as current collectors in lithium ion battery anodes is one of the most attractive. Consequently, numerous studies have investigated possible tin-based lithium ion battery anodes, including nanoporous copper formed by de-alloying aluminum from an Al-Cu alloy, 4 nanoporous copper generated by electrodeposition using hydrogen bubbles as a template 5-7 and copper nanopillars fabricated by electrodeposition through a porous alumina membrane.8 Although these 3D copper nanostructured architectures are very effective at improving electrode functions, their manufacture requires many steps and is therefore complex. In contrast, our group has previously developed a very straightforward electrodeposition method for the fabrication of these architectures, in which an organic additive is simply added to the electrodeposition bath.9 This process of making 3D copper nanostructure architectures by one-step electrodeposition (the resulting products henceforth being designated as 3DC1) can be expected to have practical applications in the manufacture of various objects, such as current collectors for tin-based lithium ion battery anodes. To ensure the high performance of such anodes, the uniformity of the tin film on the 3DC1 substrate is important. Unfortunately, in general, it is difficult to form metal films with uniform thicknesses on uneven substrates such as 3DC1 by electrodeposition.In this study, therefore, the conditions associated with the electrodeposition of tin on 3DC1 were examined with the aim of fabricating uniformly tin-coated 3DC1. Experimental3DC1 was fabricated on a pure copper plate (JIS C1201P) with an exposed surface area of 10 cm 2 (3.3 × 3 cm) using a plating bath (0.85 M CuSO 4 · 5H 2 O + 0.55 M H 2 SO 4 + 3 × 10 −4 M polyacrylic acid (mean molecular weight 5000; PA-5000)) under galvanostatic conditions (1 A dm −2 ) without agitation at 25• C. 9 The amount of charge applied was 38 C (3.8 C cm −2 ). The continuous electrodeposition of tin was conducted on the resulting 3DC1, employing a pyrophosphate bath 10 (0.25 M Sn 2 P 2 O 7 + 1 M K 4 P 2 O 7 ) as the basic tin plating bath, together with polyethylene glycol (mean molecular weight 600: PEG600) and formaldehyde (HCHO) as additives. 11 * Electrochemical Society Active Member. z E-mail: araisun@shinshu-u.ac.jpThe composition of the tin plating bath with additives was 0.25 M S...

Introduction Lithium-ion batteries (LIBs) are one of the most important energy storage and conversion devices and are widely used in portable electronic devices such as mobile phones and laptops. 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 such as Li4.4Sn with maximum composition　and have a specific capacity of 994 mA h g-1, 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 during the electrochemical alloying-dealloying process. These volume 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 to improve 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 the 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 PEG +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). A cross-section polisher was used to generate cross-sections of the samples. Electrochemical measurements were obtained using coin-type cells assembled in an argon-filled glove box. LiPF6 (1 M) in ethylene carbonate (EC) and diethyl carbonate (DEC) (1:1 vol%) was used as the electrolyte solution. Cycling tests were performed between 0.02-1.5V (vs. Li/Li+) at a constant temperature of 25°C. Results and Discussion Figure 1 (a) shows a surface SEM image of the new tin anode and demonstrates the homogeneous plating of 3D copper nanostructures on the tin film. Figure 1 (b) shows a cross-sectional SEM image of the new tin anode, revealing that the inside of the 3D copper nanostructure is also plated uniformly. This new tin anode exhibits both high reversible capacity and improved cyclability. Charge/discharge characteristics of this anode will be presented in detail at the meeting. References 1)       S.Arai and T.Kitamura, ECS Electrochemistry Letters. 2014, 3 (5), D7-D9. Figure 1

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