Separator media for electrochemical cells
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Solution Overview
Problem
Current separators in nickel metal hydride batteries suffer from high self-discharge rates due to ammonia-shuttle mechanisms, where nitrogen impurities oxidize and form ammonia, leading to inefficient charge retention.
Innovation Solution
A separator medium comprising sulfonated polymeric nonwoven sheets with specific pore size and sulfur content, retaining high tensile strength and enhanced ammonia absorption capabilities, is developed to improve electrolyte distribution and electrical resistance in alkaline batteries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional polyolefin nonwoven separators are used in NiMH batteries, then the battery structure is simple and manufacturing is easy, but the self-discharge rate is high due to ammonia-shuttle mechanism
Solution Approach 1:
The patent converts the harmful ammonia-shuttle mechanism into a beneficial ammonia-trapping function by incorporating sulfonated polymeric fibers with specific nitrogen content (0.1-5.0 mmol/g) into the separator. The sulfonated groups actively trap ammonia molecules, preventing their migration between electrodes and transforming the separator from a passive barrier into an active ammonia-scavenging component that reduces self-discharge.
Solution Approach 2:
The patent changes the chemical composition parameters of the separator by using sulfonated polymeric fibers with controlled nitrogen content (0.1-5.0 mmol/g) and specific surface area (0.5-1.5 m²/g). These parameter modifications enable the separator to effectively trap ammonia while maintaining structural integrity and electrical insulation properties.
2Reliability
If the separator has high ammonia absorption capability, then self-discharge is reduced, but the separator material becomes more complex
Solution Approach 1:
The patent maintains separator simplicity by controlling key parameters: nitrogen content (0.1-5.0 mmol/g), surface area (0.5-1.5 m²/g), and fiber diameter (1-20 μm). By optimizing these parameters within specific ranges, the separator achieves high ammonia absorption while using a single nonwoven layer, avoiding the need for complex multi-layer structures.
3Object-generated harmful factors
If the nonwoven sheet has larger surface area, then ammonia absorption is enhanced, but the mechanical strength may be reduced
Solution Approach 1:
The patent balances surface area and strength by specifying optimal ranges: surface area (0.5-1.5 m²/g) and fiber diameter (1-20 μm). The sulfonated polymeric fibers within this parameter range provide sufficient ammonia-trapping capacity while maintaining the mechanical integrity needed for battery operation.
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 self-discharge rates by maintaining high tensile strength and ammonia absorption, enhancing the performance and longevity of nickel metal hydride batteries.
Implementation Method 1
retaining high tensile strength and enhanced ammonia absorption capabilities
Data Source
AI summary
A separator medium for electrochemical cells that contains at least one nonwoven sheet of polymeric fibers. The nonwoven sheet has a surface area of about 0.5 to about 1.5 m2/g and has a maximum pore size that is equal to or more than 2.5 times the mean flow pore size and more than 11 times the minimum pore size. The sheet may be sulfonated to a level of 0.67% and demonstrates superior tensile properties after sulfonation and relative to previously known separators.