Insulating Case with Differential Melting Points for Battery Safety
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Solution Overview
Problem
Lithium ion secondary batteries face safety risks due to potential heat-related electrical short circuits between the positive and negative electrode plates when the separator contracts at high temperatures, leading to fires or explosions.
Innovation Solution
An insulating case with a first portion having a melting point between 90% to 110% of the separator's contraction temperature is used to prevent short circuits by melting and filling the gap created by the contracting separator, formed from materials like low-density polyethylene and polypropylene, ensuring the melted material covers the active materials and reduces the reaction area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the separator is used to prevent short circuits between electrode plates, then electrical insulation is improved, but at high temperatures the separator contracts and causes short circuits
Solution Approach 1:
The insulating case acts as an intermediary component between the electrode assembly and the cap assembly. It provides thermal and electrical insulation, preventing direct contact between the electrode plates and the metal cap at high temperatures, thus avoiding short circuits while maintaining electrical insulation functionality.
Solution Approach 2:
The insulating case is designed with specific thermal properties (melting point between 90% to 110% of separator contraction temperature) that change its state at critical temperatures. When the separator contracts due to heat, the insulating case melts to fill the gap and maintain insulation, adapting its physical state to counteract the temperature-induced separator contraction.
2Reliability
If the insulating case melting point is set between 90% to 110% of separator contraction temperature, then safety at high temperatures is improved, but the insulating case may melt during normal operation
Solution Approach 1:
The insulating case utilizes controlled parameter changes in its thermal properties. By setting the melting point within a specific range (90% to 110% of separator contraction temperature), the material transitions from solid to liquid state at critical temperatures, allowing it to flow and fill gaps created by separator contraction, thereby maintaining insulation where needed while sacrificing structural integrity only when necessary for safety.
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 prevents electrical short circuits and enhances safety at high temperatures by ensuring the insulating case melts in sync with the separator contraction, reducing the risk of fires or explosions in lithium ion secondary batteries.
Implementation Method 1
An insulating case with a first portion having a melting point between 90% to 110% of the separator's contraction temperature is used to prevent short circuits by melting and filling the gap created by the contracting separator
Implementation Method 2
If the internal temperature of the secondary battery reaches, for example, 110° C. to 130° C., the upper end of the separator contracts
Data Source
AI summary
An insulating case for a secondary battery and a secondary battery having the same, the insulating case having opposing first and second portions. The first portion faces an electrode assembly of the secondary battery and has a first melting point. The second portion faces a cap assembly of the secondary battery and has a second melting point that is higher than the first melting point. The first melting point is approximately the contraction temperature of a separator of the electrode assembly.