Metal Foil Stack Laser Welding With Deep-Penetration Weld Nuggets
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Solution Overview
Problem
Conventional welding techniques struggle to reliably join large stacks of metal foils to a metal substrate in lithium-ion battery production, limiting the number of layers and energy density of battery cells.
Innovation Solution
A method using deep-penetration laser welds to securely attach a stack of metal foils to a metal substrate, employing a composite laser beam with a narrow center beam and annular beam to deliver highly localized energy, forming weld nuggets that secure the foil stack with high strength while minimizing damage to the foils.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional welding techniques are used to join metal foils to a metal substrate, then the welding process is simple and fast, but the reliability of joining large stacks of metal foils is poor
Solution Approach 1:
The laser beam is divided into two distinct segments: a center beam for deep penetration welding and an annular beam for surface heating and contaminant removal. This segmentation allows each beam component to perform its specific function optimally, achieving reliable welding of large foil stacks without requiring complex multi-step processes
Solution Approach 2:
The welding process uses a composite laser beam structure combining two different beam profiles (center and annular) into a single integrated welding system. This composite approach enables simultaneous deep penetration and surface treatment, resolving the contradiction between welding reliability and process simplicity
2Quantity of substance
If the number of metal foil layers in a stack is increased to improve energy density, then the energy density increases, but the difficulty of detecting and measuring weld quality increases
Solution Approach 1:
The annular beam extracts and removes contaminants from the foil surfaces before welding, preventing defects that would be difficult to detect in thick stacks. This extraction function improves weld quality consistency across large numbers of foils, making quality detection more manageable
Solution Approach 2:
The annular beam performs preliminary surface preparation and contaminant removal before the center beam creates the weld. This preliminary action ensures clean welding surfaces throughout the entire foil stack, maintaining detectable weld quality even when joining 100+ foils
3Productivity
If conventional laser welding is used to join metal foils, then the process is faster than ultrasonic welding, but the heat accumulation damages the thin metal foils
Solution Approach 1:
The center beam delivers highly localized energy to create deep penetration welds with minimal heat spread to surrounding areas. This localized heating allows fast welding speeds while protecting the thin foils from heat damage, as the energy is concentrated precisely where needed
Solution Approach 2:
The laser system uses pulsed operation with specific duty cycles, allowing rapid heating during pulse on-time and cooling during pulse off-time. This periodic action enables high productivity while preventing excessive heat accumulation that would damage the thin metal foils
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
This method enables the reliable welding of stacks containing over 100 foils, withstanding shear forces greater than 700 Newtons, and significantly increases the energy density of stacked-structure battery cells by allowing for more layers without compromising the integrity of the foils.
Implementation Method 1
irradiating the stack of metal foils with a beam of laser pulses to weld the stack of metal foils to the metal substrate
Implementation Method 2
The peak power of the center beam is at least 0.5 kilowatt for each of the laser pulses... focusing the composite beam such that a largest transverse 1/e2 extent of the center beam is less than 150 μm at the stack
Implementation Method 3
employing a composite laser beam with a narrow center beam and annular beam to deliver highly localized energy, forming weld nuggets that secure the foil stack with high strength while minimizing damage to the foils
Data Source
AI summary
A method for laser welding a metal foil stack to a metal substrate includes clamping the foil stack against a support surface of a substrate and irradiating the stack with a beam of laser pulses to weld the foils to the substrate. The beam is a composite beam including a center beam and a surrounding annular beam. An initial series of the laser pulses are incident on the stack at mutually distinct locations on a top surface of the stack, and a subsequent series of the laser pulses are incident on the stack at mutually distinct locations on a side of the stack. The resulting weld nuggets penetrate deeply into the stack, with an average penetration depth that exceeds an average pitch between the weld nuggets. The method is capable of welding more than 100 foils to the substrate. Welded assemblies have been demonstrated to withstand large shear forces.