Sub-Cell Solder Joining for Spatter-Free Battery Tab Welding
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Solution Overview
Problem
Welding spatter occurs during laser welding of cylindrical secondary battery sub cells due to high energy required for joining aluminum or copper current collector plates, leading to metal impurities and electrical shorts, affecting performance and safety.
Innovation Solution
A sub cell design with a solder of lower melting point than the current collector plate and electrode tab, allowing for welding at a lower temperature, and a jelly-roll type electrode assembly with non-coated regions acting as electrode tabs, where the solder penetrates between tabs by capillary action, preventing spatter and ensuring a sufficient welding area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If laser welding is performed at high temperature to join aluminum or copper current collector plate with electrode tab, then welding strength is improved, but welding spatter occurs causing metal impurities and electrical shorts
Solution Approach 1:
A flux composition is introduced as an intermediary substance between the laser beam and the current collector plate. The flux absorbs the high-energy laser irradiation and transfers it to the base material at a lower effective temperature, preventing direct high-temperature melting that causes spatter. The flux layer acts as a thermal mediator, enabling welding without the harmful effects of direct high-energy laser heating.
Solution Approach 2:
The invention changes the thermal parameters of the welding process by introducing a flux with specific thermal properties (melting point, heat capacity, thermal conductivity). The flux composition is designed to absorb laser energy and transfer it at controlled rates, changing the temperature profile during welding from direct high-temperature melting to a controlled lower-temperature process that prevents spatter while maintaining weld strength.
2Productivity
If high energy laser irradiation is used to weld current collector plate, then welding speed is improved, but welding spatter occurs affecting battery safety
Solution Approach 1:
The flux serves as a mediator that enables high welding speeds without spatter by absorbing and redistributing laser energy. The flux layer processes the laser irradiation quickly and efficiently transfers the energy to the joint, maintaining high productivity while eliminating the spatter problem associated with direct high-energy laser welding.
3Ease of manufacture
If direct laser welding of aluminum or copper current collector plate is performed, then manufacturing process is simplified, but welding spatter causes metal impurities and electrical shorts
Solution Approach 1:
The flux is applied in a simple manner (coating or placement) and then activated by laser irradiation to perform the welding function. This adds minimal complexity to the manufacturing process while effectively eliminating spatter. The flux can be applied using conventional coating methods before welding, maintaining ease of manufacture.
Solution Approach 2:
The flux performs multiple functions automatically when activated by laser irradiation: it absorbs the laser energy, controls the heating rate, prevents spatter, and facilitates welding. The flux self-regulates the thermal process without requiring complex external control systems, maintaining manufacturing simplicity while solving the spatter problem.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Prevents welding spatter, enhances safety, and maintains performance by reducing electrical shorts and improving the structural integrity of the battery pack.
Implementation Method 1
The solder may penetrate in between adjacent electrode tabs by capillary action when the solder melts by the welding.
Implementation Method 2
the solder having a lower melting point than the electrode tab and the current collector plate
Implementation Method 3
The welding used to manufacture a sub cell including the electrode assembly and the current collector plate may be laser welding.
Data Source
AI summary
A sub cell includes a jelly-roll type electrode assembly including an electrode tab, a current collector plate joined to one side of the electrode assembly, the current collector plate being electrically connected to the electrode tab, and a solder interposed between the electrode tab and the current collector plate to join the electrode tab and the current collector plate, the solder having a lower melting point than a melting point of the electrode tab and a melting point of the current collector plate.