Lithium-ion batteries are finding increasing application due to their high voltage, high power density, and low weight compared to competing battery chemistries. Assembling lithium-ion batteries, however, presents new manufacturing challenges.
One major challenge is that Lithium-ion cell technology requires dissimilar tab materials. Assembling these batteries requires joining of the thin aluminum, copper, or nickel tabs, often in multiple-layers and to thicker (and often dissimilar) interconnects. When compared with other potential welding processes, ultrasonic welding is able to consistently produce reliable joints. Additionally, the process produces minimal heat, requires no flux, can be used with coated materials, produces low-resistance joints, and is low cost.
The most critical process parameter is the ultrasonic tooling, especially the knurl pattern; the knurl pattern is the texture that is used to couple the ultrasonic weld energy into the work pieces. The knurl pattern influences weld strength and repeatability. Battery packs can have 100’s of welds or more in series, all of which are required to maintain functionality of the battery pack.
A study was recently completed at EWI in conjunction with the Ohio State Welding Engineering Department to investigate Ultrasonic Metal Welding of Lithium-Ion tabs to buss bar connections. A model was developed that can be used to predict the ‘best practice’ welding conditions for various numbers of tabs, which also takes into account the weld tool knurl pattern, knurl geometry, and the weld process parameters