Microporous Battery Separator Using Superabsorbent Polymer
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Solution Overview
Problem
Existing microporous sheet products for battery separators lack optimal properties such as low resistivity, uniform electrolyte distribution, and dimensional stability, particularly in alkaline and lead-acid batteries, and are often not environmentally friendly or cost-effective to produce.
Innovation Solution
A microporous sheet product is created by melt-extruding a mixture of a thermoplastic polymer, a superabsorbent polymer, and a compatibilizing agent, which promotes mixing and forms micropores, allowing for improved electrolyte conductivity and dimensional stability, with the option to remove the compatibilizing agent for enhanced porosity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a nonwoven fibrous material with high porosity is used as separator, then electrolyte uptake and wicking are enhanced, but resistivity increases and manufacturing complexity increases
Solution Approach 1:
The patent uses a microporous polymer matrix with controlled pore structure to achieve electrolyte uptake and wicking while maintaining low resistivity. The porous structure is formed through phase separation during extrusion, creating interconnected pores that facilitate electrolyte transport without requiring complex nonwoven assemblies.
Solution Approach 2:
The separator is formulated as a composite material containing polymer matrix, pore-forming agent, and hydrophilic additive. This composite approach combines the benefits of polymer structural integrity with enhanced electrolyte affinity from hydrophilic components, achieving both low resistivity and improved wicking in a single integrated material.
2Weight of moving object
If separator thickness is reduced to increase energy density, then battery energy density improves, but mechanical strength and dimensional stability deteriorate
Solution Approach 1:
The separator exhibits local quality variations with different regions having distinct properties. The microporous structure provides localized mechanical reinforcement through polymer-rich phases while maintaining thin overall thickness. The phase-separated morphology creates a hierarchical structure that delivers strength where needed while preserving electrolyte transport pathways.
Solution Approach 2:
The patent optimizes multiple material parameters including polymer molecular weight, pore-forming agent concentration, and processing temperature to achieve the desired balance between thickness and mechanical strength. By controlling crystallinity and phase separation morphology, the separator maintains dimensional stability at reduced thickness.
3Reliability
If dendrite formation is inhibited through structure modification, then battery reliability improves, but manufacturing precision requirements increase
Solution Approach 1:
The separator structure is designed in advance to prevent dendrite formation through pre-formed physical barriers. The microporous matrix with controlled pore size distribution and hydrophilic additive distribution creates a uniform electrolyte field that prevents localized current density hotspots before dendrites can form during battery operation.
Solution Approach 2:
The patent uses a standardized extrusion process that replicates the optimal microporous structure consistently across production. The phase separation morphology is controlled to produce uniform pore structures that reliably inhibit dendrite growth while maintaining manufacturability through conventional extrusion equipment and processes.
4Reliability
If superabsorbent polymer is added to enhance electrolyte retention, then electrolyte conductivity improves, but manufacturing complexity and cost increase
Solution Approach 1:
The patent merges the functions of electrolyte retention and structural matrix into a single integrated polymer composite. The superabsorbent polymer particles are incorporated directly into the extruded separator matrix, combining the mechanical support function with the electrolyte retention function in one material system rather than requiring separate components.
Solution Approach 2:
The separator material self-regulates electrolyte distribution through the inherent properties of the hydrophilic additive and microporous structure. The material automatically absorbs and retains electrolyte in the pore spaces during battery assembly and operation, eliminating the need for additional electrolyte management components or complex assembly procedures.
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 resulting sheet product exhibits low resistivity, high electrolyte retention, and resistance to dendrite formation, while being environmentally friendly and cost-effective to produce, with the ability to absorb and retain electrolytes effectively.
Implementation Method 1
the compatibilizing agent promoting mixing of the thermoplastic polymer and the superabsorbent polymer and forming micropores in the sheet material
Implementation Method 2
the superabsorbent polymer, and a compatibilizing agent... high electrolyte retention... the ability to absorb and retain electrolytes effectively
Implementation Method 3
to have the ability to enhance the uptake of the electrolytic composition over the electrode plates and, in so doing, to promote a substantially uniform distribution of the electrolytic composition over the electrode plates (an effect generally referred to as wicking)
Implementation Method 4
to provide the property of freely permitting electrolytic conduction... microporous sheet product... low resistivity
Implementation Method 5
to have a dimensionally stable structure even during thermal excursions (internal or external heating)
Implementation Method 6
melt-extruding an extrusion mixture to produce a sheet material... forming micropores in the sheet material
Data Source
AI summary
Microporous sheet product and methods of making and using the same. In one embodiment, the microporous sheet product is made by a process that includes melt-extruding a sheet material using an extrusion mixture that includes a thermoplastic polymer, a superabsorbent polymer, and a compatibilizing agent. After extrusion, the compatibilizing agent may be removed from the sheet material. When the sheet product is imbibed with a polar or ion-containing liquid, the superabsorbent polymer swells, causing a reduction in the pore size of the sheet product. The exposure also causes some of the superabsorbent polymer to migrate to the exterior of the microporous sheet product. The microporous sheet product may be used, for example, as a battery separator, as a food packaging material, as a diffusion barrier in the ultrafiltration of colloidal matter, and in disposable garments.