Sealed Battery Safety Valve Slit Design for Annealing Prevention
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Solution Overview
Problem
Conventional safety valves in sealed batteries undergo softening due to annealing during the welding process, causing them to open at a lower pressure than intended, making it difficult to predict the valve opening pressure across all batteries in a production line.
Innovation Solution
A safety valve design with a slit surrounding the thin portion to prevent heat conduction from the case, ensuring the valve opens at the predetermined pressure, and enhancing vibration attenuation characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the thin portion of the safety valve is formed by pressing to induce work hardening, then the tensile strength increases, but the heat from welding during sealing causes annealing that softens the thin portion, resulting in unpredictable valve opening pressure
Solution Approach 1:
The safety valve is divided into two functional zones: a thin portion for pressure-sensitive opening and a thick peripheral portion for structural support and heat shielding. This segmentation allows the thin portion to maintain work hardening without annealing, preserving tensile strength and predictable valve opening pressure while the thick portion absorbs welding heat.
Solution Approach 2:
Different wall thicknesses are applied to different parts of the safety valve: the thin portion (first wall thickness) is optimized for pressure response and work hardening, while the peripheral portion (second wall thickness greater than the first) provides localized heat resistance during welding. This local quality differentiation resolves the contradiction between strength enhancement through work hardening and protection against annealing.
2Stress or pressure
If the wall thickness of the thin portion is reduced to enable splitting at predetermined pressure, then the valve opening pressure is achieved, but the physical strength and mechanical integrity are compromised
Solution Approach 1:
The safety valve employs non-uniform wall thickness distribution: a thin portion with first wall thickness for pressure-sensitive splitting at predetermined pressure, and a thick peripheral portion with second wall thickness for maintaining overall mechanical strength and structural integrity. This local differentiation allows the valve to open at the desired pressure while preserving sufficient strength.
Solution Approach 2:
The safety valve structure is segmented into a thin portion for pressure response and a thick peripheral portion for structural support. This segmentation enables the thin portion to split at the predetermined valve opening pressure while the thick peripheral portion maintains the mechanical strength necessary for withstanding assembly forces and operational stresses.
3Reliability
If welding is performed to seal the battery case, then the sealing is achieved, but heat is transmitted to the thin portion causing annealing and softening
Solution Approach 1:
The peripheral portion of the safety valve is designed with greater wall thickness (second wall thickness) specifically to provide thermal mass and heat resistance during the welding sealing process. This local quality enhancement protects the thin portion from annealing while allowing effective welding sealing of the battery case.
Solution Approach 2:
The safety valve is segmented into a thin portion for pressure sensitivity and a thick peripheral portion for heat shielding during welding. This segmentation allows the welding heat to be absorbed and dissipated by the thick peripheral portion, preventing heat transmission to the thin portion and avoiding annealing-induced softening.
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 slit effectively suppresses annealing and mechanical strength loss, allowing the safety valve to open reliably at the set pressure, preventing premature opening and ensuring the battery's reliability.
Implementation Method 1
the physical strength (specifically, the tensile strength) of the thin safety valve increases on account of metal hardening (work hardening) that is elicited during such press working
Implementation Method 2
The heat generated during the heating treatment such as welding is transmitted to the thin portion of the safety valve. As a result, the thin portion of the safety valve and that has undergone work hardening may now soften, contrariwise, on account of so-called annealing elicited by the heat input.
Data Source
AI summary
A sealed battery is provided in which a case is partially provided with a safety valve that is provided with a thin portion, which is formed thinner than the peripheral portion of the safety valve. A portion of the safety valve surrounding the thin portion is provided with a slit for preventing heat conduction from the other portions of the case to the thin portion, said slit being formed so as to surround the thin portion.