Nonaqueous Battery Separator Layout for Controlled Overcharge Shorting
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries face challenges in preventing rapid temperature increases during overcharge, leading to potential internal short-circuits and safety risks due to the rapid melting of separators, which can cause excessive heat generation before the shutdown function effectively stops charging.
Innovation Solution
A nonaqueous electrolyte secondary battery design featuring a recessed short-circuit promoting portion in the separator, which melts at a controlled position to induce an internal short-circuit between the electrode mixture layer and the current collector foil, thereby preventing rapid temperature increases by adjusting the formation position of this portion to ensure charging stops before a high-temperature range is reached.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separator with shutdown function is provided to prevent temperature increase during overcharge, then battery safety is improved, but internal short-circuit may occur before charging stops due to rapid separator melting, causing rapid temperature increase to high-temperature range
Solution Approach 1:
A short-circuit promoting portion is formed in advance in the separator at a position where the electrode mixture layer does not face (mixture layer non-facing portion). This preliminary structural feature ensures that when the separator melts during overcharge, the short-circuit occurs at a controlled location between the electrode mixture layer and current collector foil, preventing more severe short-circuits in the core portion while maintaining the shutdown function.
Solution Approach 2:
The harmful effect of separator melting during overcharge is converted into a beneficial controlled short-circuit. By pre-forming the short-circuit promoting portion, the separator melting is directed to create a controlled short-circuit between the electrode mixture layer and current collector foil in the mixture layer non-facing portion, which stops charging before the temperature reaches the high-temperature range, thus preventing more severe damage.
2Loss of time
If the separator melts rapidly to stop charging during overcharge, then charging is stopped earlier, but internal short-circuit occurs before shutdown due to excessive heat generation, causing temperature to rapidly increase
Solution Approach 1:
The separator is given different local properties: a short-circuit promoting portion is formed only in the mixture layer non-facing portion, while other regions maintain normal separator structure. This local differentiation ensures that melting occurs preferentially at the promoted portion, creating a controlled short-circuit location that prevents rapid temperature increase in the core portion.
Solution Approach 2:
The short-circuit promoting portion acts as an intermediary structure that mediates between the separator melting and electrode contact. It provides a controlled pathway for short-circuit occurrence, ensuring that the short-circuit happens between the electrode mixture layer and current collector foil rather than between opposing electrode mixture layers, thereby controlling the temperature increase rate.
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 design effectively prevents sudden temperature increases to the high-temperature range during overcharge, enhancing safety by ensuring that charging stops before significant heat buildup occurs, thus securing higher safety standards compared to previous technologies.
Implementation Method 1
the separator having such a structure is heated, the separator starts to melt from a position where the short-circuit promoting portion is formed
Data Source
AI summary
An electrode body of a secondary battery described herein includes: a core portion where electrode mixture layers of a plurality of electrode sheets are laminated; terminal connecting portions where respective current collector foil exposed portions are laminated, and a mixture layer non-facing portion where the electrode mixture layer faces the current collector foil exposed portion, the mixture layer non-facing portion being formed in a boundary between the terminal connecting portion and the core portion. In the secondary battery described herein, a short-circuit promoting portion having a predetermined depth (d) is formed in a separator provided between the electrode sheets in the mixture layer non-facing portion. Hereby, before a battery temperature rapidly increases to a high-temperature range due to occurrence of internal short-circuit between the electrode mixture layers, internal short-circuit is caused between the electrode mixture layer and the current collector foil exposed portion, so that charging can be stopped.