Carbon nanotube fiber is a promising material in electrical and electronic applications, such as, wires, cables, batteries, and supercapacitors. But the problem of joining carbon nanotube fiber is a main obstacle for its practical development. Since the traditional joining methods are unsuitable because of low efficiency or damage to the fiber structure, new methods are urgently required. In this study, the joining between carbon nanotube fiber was realized by deposited nickel–copper doublelayer metal via a meniscus-confined localized electrochemical deposition process. The microstructures of the double-layer metal joints under different deposition voltages were observed and studied. It turned out that a complete and defect-free joint could be fabricated under a suitable voltage of 5.25 V. The images of the joint cross section and interface between deposited metal and fiber indicated that the fiber structure remained unaffected by the deposited metal, and the introduction of nickel improved interface bonding of double-layer metal joint with fiber than copper joint. The electrical and mechanical properties of the joined fibers under different deposition voltages were studied. The results show that the introduction of nickel significantly improved the electrical and mechanical properties of the joined fiber. Under a suitable deposition voltage, the resistance of the joined fiber was 37.7% of the original fiber, and the bearing capacity of the joined fiber was no less than the original fiber. Under optimized condition, the fracture mode of the joined fibers was plastic fiber fracture.

    Abstract
    1 Introduction
    2 Experimental
        2.1 Materials
        2.2 Methods
        2.3 Characterization
    3 Results and discussion
        3.1 Deposition processes
        3.2 Morphology and microstructure
        3.3 Mechanism
        3.4 Electrical properties
        3.5 Mechanical properties and fracture analysis
    4 Conclusions
    Acknowledgements 
    References

• Yecheng Wang(School of Materials Science and Engineering, Tianjin University, Tianjin Key Laboratory of Advanced Joining Technology)
• Zhen Luo(School of Materials Science and Engineering, Tianjin University, Tianjin Key Laboratory of Advanced Joining Technology)
• Di Zhang(Central Research Institute of Building and Construction CO., Ltd)
• Yue Yang(School of Materials Science and Engineering, Tianjin University, Tianjin Key Laboratory of Advanced Joining Technology)
• Jianming Hu(School of Materials Science and Engineering, Tianjin University, Tianjin Key Laboratory of Advanced Joining Technology)
• Muse Degefe Chewaka(School of Materials Science and Engineering, Tianjin University, Tianjin Key Laboratory of Advanced Joining Technology)
• Sansan Ao(School of Materials Science and Engineering, Tianjin University, Tianjin Key Laboratory of Advanced Joining Technology)
• Yang Li(School of Materials Science and Engineering, Tianjin University, Tianjin Key Laboratory of Advanced Joining Technology)