Battery Cell Bus Bar Welding Structure With IMC Gap Control
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Solution Overview
Problem
Dissimilar metal welding in battery cell assemblies often results in defects such as cracks and voids due to differences in thermal characteristics, particularly when using laser welding between metals like aluminum and steel, which have incompatible weldability.
Innovation Solution
A welding structure that minimizes thermal characteristic differences by using an intermetallic compound (IMC) between the terminal and connector of a battery cell and a bus bar, with a space formed at opposite sides of the IMC to prevent excessive diffusion and crack formation, where the terminal and connector are laser-welded with a pulse-wave or continuous-wave laser.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If laser welding is used to join dissimilar metals (aluminum bus bar and steel terminal), then welding speed and production efficiency are improved, but thermal characteristic differences cause defects such as cracks and voids in the welded portion
Solution Approach 1:
An intermetallic compound (IMC) layer is intentionally formed as an intermediary between the aluminum bus bar and steel terminal. This IMC layer acts as a mediator that facilitates bonding between the dissimilar metals while managing the thermal characteristic differences, preventing direct contact that would cause cracking and voids during laser welding.
Solution Approach 2:
The thermal characteristics of the welded portion are modified by changing the material composition parameter - introducing an IMC layer with intermediate thermal properties between aluminum and steel. This gradient structure reduces the thermal shock and stress concentration that occur when directly welding dissimilar metals with vastly different thermal conductivities.
2Device complexity
If direct welding is performed between aluminum bus bar and steel terminal, then manufacturing process is simplified, but excessive diffusion and crack formation occur due to incompatible weldability
Solution Approach 1:
The IMC layer serves as a mediator that enables welding of incompatible metals without requiring complex pre-treatment processes. Instead of complicating the process with multiple steps, the IMC forms naturally during welding and provides the necessary interface for strong bonding between aluminum and steel.
Solution Approach 2:
The welded joint is designed as a composite structure consisting of three distinct layers: aluminum bus bar, IMC intermediate layer, and steel terminal. This composite structure leverages the advantages of each material - the ductility of aluminum, the bonding capability of IMC, and the strength of steel - to achieve a joint stronger than the individual components.
3Reliability
If IMC is formed between terminal and connector, then thermal characteristic difference is minimized, but IMC diffusion must be controlled to prevent excessive growth and defects
Solution Approach 1:
The welding process is designed to form a partial IMC layer - enough to provide thermal compatibility and bonding, but not so much that it causes excessive diffusion and defects. The laser welding parameters are optimized to achieve the minimum necessary IMC thickness for reliable bonding while preventing over-diffusion.
Solution Approach 2:
The laser welding process rapidly forms the IMC layer in a controlled timeframe, rushing through the diffusion process before excessive growth can occur. This short-duration high-energy input creates the necessary IMC interface quickly, minimizing the time available for uncontrolled diffusion and defect formation.
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 structure enhances the strength and electrical conductivity of the welded portion, reducing defects like cracks and voids, and improving tensile strength and electrical conductivity compared to existing methods.
Implementation Method 1
The terminal of the battery cell and the connector of the bus bar may be laser-welded
Implementation Method 2
the terminal and the connector are connected to each other through an intermetallic compound (IMC) therebetween
Data Source
AI summary
A battery cell assembly includes a battery cell with a terminal, and a bus bar electrically connected to the battery cell, the bus bar including a connector connected to the terminal of the battery cell, the connector and the terminal being connected to each other through an intermetallic compound (IMC), and a space being defined between the terminal and the connector at opposite sides of the IMC, and a connection portion extending from the connector in a direction oriented away from the terminal.