Joint Formation in Multi-Layered Ultrasonic Welding of Ni-Coated Cu and the Effect of Preheating

Abstract

Multi-layered ultrasonic welding (USW) is widely used in joining of electrodes or tabs in lithium-ion batteries. To achieve quality joints and enhance the welding process robustness, an improved understanding of the joint formation is highly desirable. In this paper, USW of 4-layered Ni-coated Cu is studied to investigate the joint formation at a single interface and joint propagation from interface to interface under both ambient and preheated conditions. The results indicate that joint formation involves three major mechanisms: Ni-Ni bonding with minimal mechanical interlocking, Ni-Ni bonding with moderate mechanical interlocking, and a combination of Ni-Ni bonding, Cu-Cu bonding, and severe mechanical interlocking. Results also show that joints propagate from the interface close to the sonotrode side to that close to the anvil side. It is further observed that the joint formation can be accelerated and the joint strength can be improved with process preheating, especially at the interface closest to the anvil. The effect of preheating is most significant during the early stage of the process, and diminishes as process progresses. The favorable effects of preheating improve the robustness of multi-layered USW.

A review of quality monitoring for ultrasonic metal welding

“…At present, ultrasonic metal welding is mostly used to connect the battery foil, and the high resistance of the 77 joint will increase the energy loss, hinder the efficiency of the battery pack. Thus, the change of resistivity is also the key to evaluate the quality of ultrasonic welding.…”

“…Luo et al 77 scanned and photographed ultrasonic weld joints of Ni-coated Cu sheet using SEMs, as shown in Figure 14. It can be clearly observed that the interface belongs to the state of discontinuous bonding, and the part that is effective interlocked is scanned.…”

“…Figure 14. The sample welded at 1600 J: (a) optical microscope image, (b) SEM image at region A, (c) EDX composition scan by SEM along the dashed line in (b), (d) SEM image at region B, (e) EDX composition mapping for Cu and (f) EDX composition mapping for Ni 77. …”

Evaluation of Weldability based on Alignment Condition of Horns and Anvils used in Multilayered Battery Cell Welding Process in Ultrasonic Metal Welding

“…배터 리 셀은 소재 조합에 따라 혼(horn)과 앤빌(anvil)의 초음파 금속 용접에서 다층 배터리 셀 용접 공정에 적용되는 혼과 앤빌의 정렬 조건에 따른 용접성 평가 신 승 민 * ․김 동 철 **, † 신 승 민․김 동 철 Journal of Welding and Joining, Epub ahead of print 2 형상을 설계하기 때문에 초음파 금속 용접 공정에서 용 접 품질에 대한 지침이 아직까지 정립되어 있지 않다. 선행 연구로 초음파 금속 용접에서 배터리 셀 소재를 이용한 다층 접합 방식으로 용접 특성 및 현상 등을 연 구한 사례가 있다[6][7][8] . 또한, 구리 소재를 이용하여 통…”