Selective Copper Electrodeposition to a 3D Copper Nanostructure

Abstract

Introduction Three-dimensional (3D) copper nanostructures are expected to be applied as current collectors for lithium ion battery anodes due to their high electrical conductivity and large specific surface area. The production of 3D copper nanostructures usually requires complicated fabrication steps; however, we have developed a simple method for the production of 3D copper nanostructures.1) There is a disadvantage with this method in that the 3D copper nanostructure is likely to collapse due to low mechanical strength. Reinforcement of the 3D structures is thus considered to be one of the most effective methods to address this problem. This study aims to develop a reinforcement technology using a plating method that is applied after fabrication of the 3D copper nanostructures. The reinforcement technology employed here was viafilling plating technology. This technology is also expected to improve the adhesion to the substrate by selectively depositing copper to the bottom of the 3D nanostructure.Experimental A 3D copper nanostructure plating bath (0.85 M CuSO4·5H2O + 0.55 M H2SO4 + 3×10-4 M polyacrylic acid) and a selective copper plating bath (0.85 M CuSO4·5H2O + 0.55 M H2SO4 + additives) were prepared. A copper sulfate bath that does not contain additives was also employed for comparison. Pure copper and phosphorus-containing copper plates were used as the cathode and anode, respectively. Electrodeposition was conducted under galvanostatic conditions (1 A dm-2) without agitation at 25 °C. In addition, the influence of agitation on selective copper deposition was also investigated. Air agitation, magnetic stirring and a cathode rocker were used. The phase structure and microstructure of the deposits were analyzed using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), respectively. Results and discussion Figures 1a and 1d show a surface and cross-sectional SEM images of the 3D copper nanostructure before selective copper electrodeposition. Figure 1b shows a surface SEM image of the 3D copper nanostructure after electrodeposition without additives. The 3D nanostructure was not observed, because copper was deposited on the surface of the 3D nanostructure. The 3D nanostructure seems to have been deformed by the copper deposited on the surface, according to cross-sectional observations (Fig. 1e).Figure 1c shows a surface SEM image of the 3D copper nanostructure after electrodeposition with additives. The surface morphology is almost the same as the bare 3D nanostructure shown in Figure 1a because copper deposition at the surface of the 3D nanostructure is suppressed. Thus, the 3D nanostructure was maintained, and copper was deposited selectively at the boundary of the 3D nanostructure and the substrate, according to cross-sectional observations (Fig. 1f). Agitation also affected the selective copper deposition, and the results of agitation tests will be discussed at the meeting. References S. Arai and T. Kitamura, ECS Electrochem. Lett., 3(5), D7-D9 (2014). Figure 1