Protective Element Rectangular Conductor Flux Body Arrangement
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Solution Overview
Problem
The existing protective elements for lithium ion secondary batteries face challenges in miniaturization and improving ratings due to high conductor resistance, which is not adequately addressed by increasing the cross-sectional area of the meltable conductor, and the elliptical flux body tends to deviate from the center, leading to insufficient oxidation resistance and wettability.
Innovation Solution
A protective element with a rectangular meltable conductor and multiple circular flux bodies disposed along the heat-generating resistor, ensuring even coverage and improved wettability, and a holding mechanism to maintain the flux bodies' position, facilitating rapid current path interruption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the cross-sectional area of the meltable conductor is increased to reduce conductor resistance, then the conductor resistance decreases, but the device size increases
Solution Approach 1:
The patent transitions from increasing cross-sectional area (2D approach) to optimizing the longitudinal arrangement and contact area (1D approach) to reduce resistance without increasing overall device volume. The meltable conductor is arranged with extended contact areas along the current path direction rather than expanding perpendicular to the current flow.
Solution Approach 2:
The patent applies flux bodies in advance to the meltable conductor surface before operation. This preliminary application of flux ensures that the conductor surface is pre-protected from oxidation and pre-conditioned for optimal electrical contact, reducing contact resistance without requiring larger conductor dimensions.
2Area of stationary object
If an elliptical flux body is used to cover the meltable conductor, then the flux coverage area increases, but the flux body deviates from the center position
Solution Approach 1:
The patent divides a single large elliptical flux body into multiple smaller circular flux bodies arranged in an array. This segmentation allows each small flux body to be precisely positioned independently, preventing the centering deviation issues that occur with large elliptical flux bodies while collectively providing adequate coverage of the meltable conductor surface.
Solution Approach 2:
The patent uses multiple identical circular flux bodies with uniform dimensions and properties. This homogeneity ensures consistent performance across all flux bodies and simplifies the manufacturing process, as each flux body can be produced with the same precision standards rather than requiring a single large elliptical flux body with complex positioning requirements.
3Length of stationary object
If the meltable conductor is made thinner to reduce device thickness, then the device becomes thinner, but the conductor resistance increases
Solution Approach 1:
The patent compensates for reduced thickness (1D reduction) by increasing the longitudinal extent and contact area of the meltable conductor along the current path direction. The conductor is designed with extended contact regions at its ends that overlap with the electrodes, effectively reducing resistance through increased path length and contact area rather than through increased thickness.
Solution Approach 2:
The flux bodies are applied in advance to the thin meltable conductor to reduce contact resistance at the interfaces with the electrodes. This preliminary flux application ensures optimal electrical contact despite the reduced conductor thickness, compensating for the increased resistance that would otherwise result from the thinner geometry.
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 solution effectively reduces conductor resistance, enhances oxidation resistance, and improves wettability, allowing for rapid and reliable interruption of the current path, thereby enhancing the protective element's performance and safety.
Implementation Method 1
the meltable conductor 83 on the current path is blown by self-heating caused by an overcurrent or by a heat-generating resistor 84 provided within the protective element 80
Implementation Method 2
the meltable conductor 83 on the current path is blown by self-heating caused by an overcurrent
Implementation Method 3
because heating the meltable conductor 83 causes oxidation which inhibits blowout, a flux body 85 is laminated thereon in order to remove oxide film generated on the meltable conductor 83 and improve wettability
Data Source
AI summary
To spread flux evenly across the entire surface of a rectangular meltable conductor, a protective element includes: an insulating substrate; a heat-generating resistor disposed on the insulating substrate; a first and a second electrodes laminated onto the insulating substrate; a heat-generating element extracting electrode overlapping the heat-generating resistor in a state electrically insulated therefrom and electrically connected to the heat-generating resistor on a current path between the first and the second electrodes; a rectangular meltable conductor laminated between the heat-generating element extracting electrode and the first and the second electrodes for interrupting a current path between the first electrode and the second electrode by being melted by heat; and a plurality of flux bodies disposed on the meltable conductor; wherein the flux bodies are disposed along the heat-generating resistor.