Fluorinated Polymer Separator for Thermal Stability
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Solution Overview
Problem
There is a need for secondary battery separators with outstanding thermal stability and good ionic conductivity to meet performance and safety requirements, particularly in Lithium-ion batteries, which are vulnerable to abuse conditions such as internal shorting, overcharge, and temperature variations.
Innovation Solution
A secondary battery design utilizing a fluorinated polymer separator comprising recurring units derived from vinylidene fluoride (VDF), hexafluoropropylene (HFP), and a (meth)acrylic monomer, such as hydroxyethyl acrylate (HEA), which provides a porous or dense separator structure with enhanced thermal stability and ionic conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional polyolefin separators are used, then manufacturing cost is low and ease of manufacture is good, but thermal stability above 130°C deteriorates leading to loss of mechanical integrity
Solution Approach 1:
The patent employs composite separator structures combining polyolefin layers with PVDF (polyvinylidene fluoride) layers. This composite approach achieves superior thermal stability above 130°C while maintaining mechanical integrity, as the PVDF component provides high-temperature resistance. The layered composite structure allows each material to contribute its strengths: polyolefin for baseline performance and PVDF for thermal stability.
Solution Approach 2:
The invention modifies the chemical composition parameters of the separator by incorporating fluorinated polymers and specific copolymer ratios. By adjusting the composition to include PVDF and controlling the weight percentages of different polymer components, the separator achieves enhanced thermal properties while maintaining manufacturability through established polymer processing techniques.
2Reliability
If separator thickness is increased to improve mechanical integrity, then safety margin improves, but ionic conductivity deteriorates
Solution Approach 1:
The patent implements local quality optimization by creating a multi-layer structure where different regions of the separator have specialized functions. The PVDF-rich layers provide mechanical strength and thermal stability, while thinner polyolefin layers maintain ionic conductivity pathways. This spatial differentiation of material properties allows the separator to simultaneously achieve high safety margins and good ionic conductivity without requiring uniform thickness increase throughout.
Solution Approach 2:
The invention transitions from considering only separator thickness (one dimension) to optimizing a multi-dimensional structure with varying layer compositions and thicknesses. By distributing functional requirements across multiple layers with different thicknesses and material compositions, the separator achieves both mechanical integrity and ionic conductivity through dimensional optimization rather than simple thickness increase.
3Temperature
If PVDF content is increased to improve thermal stability, then high-temperature integrity improves, but manufacturing cost increases
Solution Approach 1:
The patent optimizes the PVDF content parameter within specific weight percentage ranges to achieve the desired thermal stability while controlling costs. By precisely controlling the PVDF concentration and balancing it with other polymer components, the invention achieves high-temperature integrity without excessive material cost, finding an optimal parameter range that satisfies both performance and economic constraints.
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 proposed solution achieves thermal stability and ionic conductivity, ensuring safety and performance compliance with performance and safety requirements, even under extended overcharge or high temperatures, while maintaining the integrity of the battery.
Implementation Method 1
Their main function is to prevent electronic contact, while enabling ionic transport between the positive and negative electrodes of electrochemical cells.
Implementation Method 2
The greater the mechanical integrity of the separator above about 130° C., the greater the margin of safety the separator can provide. The high-temperature melt integrity of the separator is indeed a very important property to keep the battery safe during extended overcharge or during extended exposure to higher temperatures.
Implementation Method 3
The most commonly used separators for secondary batteries are either porous separators made of microporous polymeric films or of non-woven fabrics or dense separators made of polymeric electrolytes.
Data Source
AI summary
The present invention pertains to a secondary battery comprising at least one separator, said separator comprising at least one fluorinated polymer [polymer (F)], said polymer (F) comprising recurring units derived from vinylidene fluoride (VDF), hexafluoropropylene (HFP) and at least one (meth)acrylic monomer (MA) having formula (I) here below, wherein: —R1, R2 and R3, equal to or different from each other, are independently selected from a hydrogen atom and a C1-C3 hydrocarbon group, and —ROH is a C1-C5 hydrocarbon moiety comprising at least one hydroxyl group.