Residual stress in battery tab welding processes, particularly ultrasonic and laser welding, plays a critical role in the performance and reliability of current collection in lithium-ion batteries. These welding techniques are widely used to connect electrode tabs to current collectors, but the thermomechanical effects induced during welding can lead to residual stresses that influence electrical conductivity, mechanical integrity, and long-term durability. Understanding these stresses and their implications requires a combination of experimental analysis and thermomechanical simulations.

The welding process introduces localized heating and rapid cooling, creating non-uniform thermal expansion and contraction. This results in residual stresses that remain in the material after welding. Ultrasonic welding generates stress through high-frequency vibrations and pressure, while laser welding produces stress due to concentrated heat input. Both methods can cause microstructural changes, such as grain refinement or recrystallization, which further contribute to residual stress.

Residual stress affects current collection by altering the contact resistance between the tab and the current collector. High residual tensile stress can lead to microcracks or delamination, increasing resistance and reducing efficiency. Compressive stress, on the other hand, may improve contact initially but can cause buckling or deformation over time. The distribution of residual stress is highly dependent on welding parameters such as power, speed, pressure, and cooling rate.

Thermomechanical simulations are essential for predicting residual stress and optimizing welding parameters. Finite element analysis (FEA) models can replicate the heat transfer, phase transformations, and mechanical deformation during welding. These simulations typically incorporate material properties like thermal conductivity, specific heat, and coefficient of thermal expansion. For example, a study on aluminum tab welding showed that peak temperatures exceeding 300°C during laser welding led to residual stresses of up to 200 MPa, with significant stress concentration near the weld zone.

The impact of residual stress on current collection can be quantified through electrical resistance measurements and mechanical testing. Research indicates that residual stress levels above 150 MPa in copper tabs can increase contact resistance by 10-15%, negatively affecting energy efficiency. Additionally, cyclic loading tests reveal that residual stress accelerates fatigue failure, with welded joints showing crack initiation at stress levels 20% lower than non-welded counterparts.

Mitigating residual stress requires careful selection of welding parameters and post-weld treatments. Lower heat input and controlled cooling rates can reduce stress magnitude, while annealing processes can relieve stress after welding. Simulations suggest that reducing laser power by 15% or increasing ultrasonic welding frequency by 10% can decrease residual stress by 25-30%. However, these adjustments must balance stress reduction with weld strength requirements.

In summary, residual stress from tab welding processes significantly impacts current collection in batteries. Thermomechanical simulations provide valuable insights for optimizing welding techniques and minimizing adverse effects. Future research should focus on advanced materials and process controls to further enhance the reliability of battery connections.