Modified Polypropylene Separator for Lithium-Sulfur Polysulfide Control

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Solution Overview

Problem

Lithium-sulfur batteries face issues with lithium polysulfides dissolving into the electrolyte and shuttling through the separator, leading to capacity loss due to thick coating separators that increase internal resistance.

Innovation Solution

Grafting Lewis acid monomers onto polypropylene molecules to form a modified separator that inhibits polysulfide shuttling and reduces thickness, using a grafting reaction without a coating step.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a coating separator is used to inhibit polysulfide shuttling, then the separator's ability to prevent capacity loss is improved, but the separator thickness increases and internal resistance increases

Engineering Contradiction:

Improveseparator's ability to prevent capacity lossVSAvoidseparator thickness

Core Design Contradiction:

ReliabilityVSLength of stationary object

Solution Approach 1:

The patent combines the polysulfide inhibition function directly into the separator base material by grafting Lewis acid monomers onto polypropylene molecules, merging the separator structure and functional coating into a single integrated component, thereby eliminating the need for a separate coating layer

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent creates a composite material by grafting Lewis acid monomers (containing carbonyl groups) onto polypropylene chains, forming a modified polypropylene with both the mechanical properties of polypropylene and the polysulfide inhibition capability of Lewis acid groups

Inventive Principle:

Principle #40Composite materials

2Reliability

If a coating separator is used to inhibit polysulfide shuttling, then the separator's ability to prevent capacity loss is improved, but the internal resistance increases

Engineering Contradiction:

Improveseparator's ability to prevent capacity lossVSAvoidinternal resistance

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent introduces Lewis acid functional groups at specific locations along the polypropylene chains where they can interact with polysulfides, creating localized active sites for polysulfide inhibition without requiring a thick uniform coating across the entire separator

Inventive Principle:

Principle #3Local quality

3Length of stationary object

If Lewis acid monomers are grafted onto polypropylene molecules, then the separator thickness is reduced and internal resistance is reduced, but the manufacturing process becomes more complex

Engineering Contradiction:

Improveseparator thicknessVSAvoidmanufacturing process complexity

Core Design Contradiction:

Length of stationary objectVSDevice complexity

Solution Approach 1:

The patent divides the modification process into distinct stages: free radical generation from peroxide, hydrogen abstraction to form polypropylene radicals, and sequential grafting of Lewis acid monomers, allowing each step to be optimized and controlled independently

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent controls the grafting process by adjusting parameters such as peroxide concentration, monomer concentration, temperature, and reaction time to optimize the degree of substitution and grafting efficiency, thereby controlling the final separator properties

Inventive Principle:

Principle #35Parameter changes

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 modified separator enhances electrochemical performance by reducing internal resistance and improving cycle stability and capacity retention.

Implementation Method 1

the polypropylene undergoes a hydrogen elimination reaction under the action of peroxide free radicals to form polypropylene macromolecular free radicals

Methodology Applied

Scientific EffectFree radical reaction:

Implementation Method 2

the polypropylene macromolecular free radicals may undergo a grafting or chain-scission reaction, so that Lewis acid monomers can be grafted onto polypropylene molecules

Methodology Applied

Scientific EffectGrafting reaction: Chemical Bonding

Implementation Method 3

the Lewis acid selected also has the effect of a catalyst, which enables unsaturated carbon-carbon double bonds contained in the polypropylene molecules to undergo a polyaddition reaction

Methodology Applied

Scientific EffectCatalysis: Catalysis

Data Source

PatentEP4477677B1Modified polypropylene and a preparation method therefor, a separator and a preparation method therefor, and a lithium-sulfur battery

Publication Date: 2026.01.28 JIANGSU ZENIO NEW ENERGY BATTERY TECH CO LTD

Figure 1

AI summary

Disclosed is a preparation method for modified polypropylene, comprising the following steps: dissolving polypropylene in a solvent; and adding a Lewis acid and an initiator into the solution in which the polypropylene is dissolved, and then performing a grafting reaction, to obtain the modified polypropylene; wherein the Lewis acid is selected from at least one of boron trifluoride diethyl etherate, boron trifluoride methyl ether, boron trifluoride acetic acid and boron trifluoride propionic acid; and the initiator is an organic peroxide initiator. Further disclosed are modified polypropylene prepared by the described method, a separator and a preparation method therefor, and a lithium-sulfur battery. Lewis acid monomers are grafted onto molecules of the modified polypropylene provided in the present disclosure, and therefore the modified polypropylene is suitable for being prepared into a separator of a lithium-sulfur battery, and can improve the electrochemical performance of the lithium-sulfur battery.