# Joining Characteristics of 60-Layered Cu Foil Stack Using Linear Vibration Ultrasonic Welding

## TL;DR

This study explores how to best weld 60 layers of copper foil for lithium-ion batteries using ultrasonic welding, focusing on optimizing parameters to ensure strong, reliable joints.

## Contribution

The study identifies optimal welding energy and parameters for joining 60-layered copper foil stacks without surface defects.

## Key findings

- Optimal welding energy (500–900 J) produced well-formed joints without surface cracks or tearing.
- Excessive welding energy (>900 J) caused material thinning and interfacial failure.
- The maximum T-peel peak load of 138.7 N was achieved under specific amplitude, time, and pressure conditions.

## Abstract

This study investigates the joint characteristics of a 60-layered copper foil stack using linear vibration ultrasonic welding for lithium-ion pouch cell applications. With increasing demand for high-capacity electric vehicle batteries, ensuring the reliability of multilayer electrode joints is essential. Experiments were conducted by varying vibrational amplitude, welding time, and clamping pressure. Weld quality was analyzed based on indentation profiles, joint strength, and failure modes. Results revealed that optimal welding energy (500–900 J) produced well-formed joints without surface cracks or tearing. Excessive welding energy (>900 J) led to material thinning and interfacial failure. The maximum T-peel peak load of 138.7 N was obtained at the 30th joining interface under 25 µm amplitude, 0.8 s welding time, and 1.5 bar clamping pressure. Interface-dependent optimum conditions were observed, reflecting thickness–direction variations in deformation and bonding within the 60-layer stack. Indentation length and depth correlated linearly with welding energy. Failure modes transitioned from no adhesion to tearing and button-pull types. The findings provide guidelines for optimizing welding parameters for high-quality multilayer foil joints in battery manufacturing.