In lithium battery cells, the connection between the electrode and tab is a critical step. The electrode is typically made of copper or aluminum foil with a thickness of 5-20μm, while the tab is made of aluminum or copper alloy with a thickness of 0.1-0.3mm. A reliable connection between them is essential to ensure a smooth current flow path, which directly impacts the performance and safety of lithium batteries.
Traditional welding methods, such as laser welding, have numerous drawbacks when connecting the electrode and tab. The high temperatures generated during the welding process can easily embrittle the electrode. For thin copper foil, burn-through can even occur, severely damaging the electrode structure. Furthermore, high temperatures can cause a brittle alloy layer to form between the tab and the electrode, increasing resistance, affecting the battery's conductivity, and reducing the battery's charge/discharge efficiency and cycle life.
To address these issues, ultrasonic welding technology has emerged and is widely used in lithium battery manufacturing. Ultrasonic welding operates at high frequencies in the 20-60kHz vibration range. When welding the tab and the electrode, high-frequency vibrations cause plastic deformation on both surfaces. This deformation effectively breaks down the oxide layers on the tab and electrode, allowing pure metal surfaces to come into contact. As the vibrations continue, the distance between the metal atoms shrinks, ultimately forming a "mechanical-metallurgical bond." Ultrasonic welding is particularly notable for its minimal heat-affected zone, with the welding temperature typically below 150°C. This characteristic is crucial because it prevents the electrode from breaking due to overheating. Furthermore, since the melting point of the separator inside a lithium-ion battery is approximately 130-160°C, low-temperature welding prevents the separator from melting due to heat, ensuring the stability of the battery cell's internal structure and significantly enhancing the safety and reliability of the lithium-ion battery.
In practical applications, ultrasonic welding significantly improves production efficiency while ensuring weld quality. It eliminates the need for additional solder or flux, reducing production costs and contamination during the welding process. Furthermore, the technology can adapt to welding electrode and tab materials of varying thicknesses, offering excellent process flexibility. By precisely controlling welding parameters such as frequency, amplitude, welding time, and pressure, high-quality welds can be achieved, meeting the stringent requirements of large-scale lithium battery production.
As lithium battery manufacturing progresses toward higher energy density and improved safety, ultrasonic welding technology, with its unique advantages, has become an ideal choice for connecting electrode sheets and tabs, playing a key role in promoting technological advancements in the lithium battery industry.
