Optimization and Analysis of Ultrasonic Wedge Bonding Parameters for Enhanced Bonding Performance in 21700 Cylindrical Lithium Battery Modules

The 21700 cylindrical lithium battery module uses ultrasonic wedge bonding technology to connect the positive terminal and negative terminal of the cell to the busbars. The weak bond of the negative terminal. This paper studied the wire bonding parameter of the negative terminal (Al wire and Fe-base Ni-top can). We aim to analyze the reasons for the poor bonding performance of the central area of the joint. Through stress and strain simulation, the result shows that the stress at the center region is lower than that in the circumference region, and the high-stress region corresponds to the ridges’ vein-shaped elliptical rings of the bonding interface (i.e., the effective bonding area). The model was further validated through experimental design. The unbonded area in the center region of the joint can be limitedly reduced by optimizing key parameters, and the influencing parameters in the order of most to least critical are bond power, force, and time. Shear strength and tensile tests were used to evaluate bonding qualities. The regression equations of Al wire deformation and joint width corresponding to key parameters were established. The optimal range of Al wires deformation and joint width is proposed. The minimum value of the deformation was 174 μm, and the maximum value was 248 μm. The minimum value of the joint width was 560 μm, and the maximum value was 1110 μm. The optimal bonding parameters obtained by the response optimizer are bond force 1250 gf and bond power 100.