Wound Secondary Battery Flat Electrode Joint for High-Rate Discharge
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Solution Overview
Problem
High-rate discharging in lithium ion batteries results in high internal resistance, leading to heat generation and inefficiencies due to unsuitable current extraction configurations.
Innovation Solution
A lithium ion battery design with a band-shaped positive and negative electrode configuration, where the negative electrode active material uncovered parts are bent to form a flat surface and coupled to the battery can using laser welding, reducing internal resistance by optimizing the contact between electrodes and the current collector plate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high-rate discharging is performed to achieve high output power, then the battery can provide high current, but the internal resistance increases causing heat generation and inefficiency
Solution Approach 1:
The negative electrode is divided into multiple uncovered parts that are separately coupled to the battery can bottom, creating multiple parallel current paths. This segmentation reduces the effective resistance by distributing the current flow across multiple connection points rather than a single point contact.
Solution Approach 2:
The negative electrode uncovered parts are bent to form a flat surface configuration, transitioning from a conventional point or line contact to a two-dimensional surface contact with the battery can bottom. This dimensional change increases the contact area and reduces contact resistance, enabling more efficient current extraction.
2Strength
If laser welding is used to couple the negative electrode to the battery can bottom, then the connection strength is improved, but welding defects may occur
Solution Approach 1:
The negative electrode uncovered parts are pre-bent to form a flat surface configuration before the laser welding process. This preliminary action ensures proper alignment and contact between the electrode and battery can bottom, preventing welding defects such as incomplete fusion or misalignment that could compromise reliability.
Solution Approach 2:
The flat surface configuration of the negative electrode changes the welding parameters by providing a uniform contact surface, which allows for more consistent laser energy distribution and reduces the risk of welding defects while maintaining strong connections.
3Area of stationary object
If the negative electrode uncovered parts are bent to form a flat surface, then the contact area with the battery can is increased, but the manufacturing complexity increases
Solution Approach 1:
The negative electrode uncovered parts are designed to be self-bending through their own structural properties or through simple forming processes during assembly. This self-service approach reduces the need for complex external bending equipment or multiple manufacturing steps, thereby limiting the increase in manufacturing complexity while still achieving the desired flat surface configuration.
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
The design achieves lower internal resistance, enabling high-rate discharging while preventing welding defects and ensuring efficient energy transfer, as demonstrated by internal resistance measurements below 11.0 mΩ without defects in the battery cells.
Implementation Method 1
a method is described of welding an exposed part of a negative electrode to a bottom of a battery can by irradiating the exposed part with laser light
Data Source
AI summary
A secondary battery achieves a reduced internal resistance. The secondary battery includes an electrode wound body, a positive electrode current collector plate, and a battery can. The electrode wound body has a structure in which a positive electrode having a band shape and a negative electrode having a band shape are stacked with a separator interposed therebetween. The battery can contains the electrode wound body and the positive electrode current collector plate. The positive electrode includes, on a positive electrode foil having a band shape, a positive electrode active material covered part covered with a positive electrode active material layer, and a positive electrode active material uncovered part. The negative electrode includes, on a negative electrode foil having a band shape, a negative electrode active material covered part covered with a negative electrode active material layer, and a negative electrode active material uncovered part extending at least in a longitudinal direction of the negative electrode foil. The electrode wound body has a flat surface, in which portions of the negative electrode active material uncovered part are bent toward a central axis of the wound structure and overlap with each other in layers to form the flat surface. The flat surface and a bottom part of the battery can are coupled to each other. The secondary battery satisfies 0.05≤Z≤0.5, Z being equal to t×m/T, where t represents a thickness of the negative electrode foil in millimeters, m represents the number of the layers of the negative electrode active material uncovered part at a coupled portion farthest from the central axis, and T represents a thickness of the bottom part of the battery can in millimeters.