Elastomeric Polyurethane Cathode Binder for Longer Li-Ion Cycle Life
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Solution Overview
Problem
Conventional binders for cathodes in Li-ion batteries, such as PVDF and PTFE, are brittle and have high fluoride content, leading to mechanical integrity issues and increased metal dissolution, which limits the cycle life and environmental sustainability of batteries.
Innovation Solution
A cathode binder comprising elastomeric polyurethane, specifically spandex, with additives like hydrogenated nitrile butadiene rubber (HNBR) is used, which provides improved mechanical strength, adhesion, and reduced metal dissolution, while being environmentally benign and cheaper to produce.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional binders like PVDF or PTFE are used, then the cathode structure is maintained, but the mechanical integrity deteriorates over time due to brittleness and high fluoride content leading to metal dissolution
Solution Approach 1:
The patent changes the chemical composition parameters of the binder from conventional fluorinated polymers (PVDF, PTFE) to elastomeric polyurethane with specific molecular weight ranges (10,000-1,000,000 g/mol). This parameter change eliminates fluoride content while providing superior elasticity and adhesion, directly resolving the contradiction between maintaining mechanical integrity and improving cycle life.
Solution Approach 2:
The patent creates a composite binder system using elastomeric polyurethane combined with conducting agents (carbon black, CNTs, or graphene) in specific ratios. This composite material provides both the mechanical strength needed for cathode structure maintenance and the electrical conductivity required for battery operation, while the elastomeric nature prevents brittleness-induced failure over cycling.
2Strength
If conventional fluorinated binders are used, then adhesion is provided, but metal dissolution increases by up to 175% due to high fluoride content
Solution Approach 1:
The patent extracts and eliminates the harmful fluoride component from conventional binders by completely replacing PVDF/PTFE with elastomeric polyurethane. This extraction removes the source of metal dissolution while retaining the essential adhesion function through the polyurethane's molecular structure and bonding capabilities.
Solution Approach 2:
The patent converts the previously harmful fluoride content into a benefit by replacing it with elastomeric polyurethane that provides enhanced adhesion through its elastic properties and functional groups. The new binder material turns the original problem (need for strong adhesion that causes metal dissolution) into a solution where strong adhesion is achieved without the harmful fluoride that caused dissolution.
3Ease of manufacture
If conventional binders are used, then the cathode is assembled, but the manufacturing cost increases and environmental sustainability is reduced
Solution Approach 1:
The patent adopts elastomeric polyurethane which is inherently cheaper than fluorinated binders like PVDF and PTFE. The material can be procured as off-the-shelf elastomers without requiring complex fluorination processes, reducing manufacturing costs. The binder maintains sufficient longevity for battery operation while being economically replaceable.
Solution Approach 2:
The patent converts the environmental harm caused by fluorinated binders into a benefit by using elastomeric polyurethane that is biodegradable and environmentally benign. The replacement material eliminates persistent fluoride pollution while maintaining all necessary functional properties for cathode operation, turning an environmental liability into a sustainable solution.
Data Source
Figure 1a~1b
Figure 2
Figure 3a~3b
AI summary
A binder for a cathode in a secondary cell, wherein the binder comprises an elastomeric polyurethane; a cathode material as well as a cathode comprising said binder; a method to produce said cathode; a secondary cell comprising said cathode; and a vehicle comprising said secondary cell.