Multi-Layer Li-S Battery Separator for Polysulfide Control
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Solution Overview
Problem
Lithium-sulfur batteries face issues with low energy density, rapid degradation due to polysulfide dissolution, and non-uniform reactivity of the positive electrode material, leading to reduced capacity and cycle lifetime.
Innovation Solution
A multi-layer separator with a first layer having a porosity of 50 vol% or more and a second layer with a porosity of 25 vol% or less is used, along with a sulfur-carbon composite positive electrode active material, to enhance energy density and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional single-layer separator is used, then the manufacturing process is simple, but the battery energy density is low and life characteristics are poor
Solution Approach 1:
The separator is divided into multiple layers with different porosity characteristics. The first layer has porosity of 30-60% and the second layer has porosity of 10-30%, creating a segmented structure that addresses different functional requirements separately rather than using a single uniform layer
Solution Approach 2:
Different regions of the separator have different porosity values optimized for their specific functions. The first layer with higher porosity (30-60%) is positioned to handle electrolyte distribution, while the second layer with lower porosity (10-30%) is positioned to prevent polysulfide dissolution, creating local quality variations that optimize overall performance
2Productivity
If the separator porosity is increased to improve electrolyte distribution, then ion transport is enhanced, but polysulfide dissolution increases leading to rapid degradation
Solution Approach 1:
The separator is segmented into two layers with different porosity values. The first layer has porosity of 30-60% for efficient ion transport, while the second layer has porosity of 10-30% to restrict polysulfide dissolution, allowing each layer to optimize for its specific function
Solution Approach 2:
The separator exhibits local quality variations through different porosity values in different layers. The first layer has higher porosity (30-60%) localized for ion transport, while the second layer has lower porosity (10-30%) localized for polysulfide containment, resolving the contradiction between transport efficiency and stability
3Quantity of substance
If the positive electrode material reactivity is increased to improve capacity, then energy density increases, but non-uniform reactivity leads to reduced cycle lifetime
Solution Approach 1:
The multi-layer separator acts as an intermediary between the positive electrode material and the electrolyte. It mediates the interaction by controlling electrolyte distribution and restricting polysulfide dissolution, allowing high-capacity materials to be used without suffering from their non-uniform reactivity issues
Solution Approach 2:
The harmful effect of non-uniform reactivity is extracted and isolated by the separator structure. The separator takes out the polysulfides that cause degradation and prevents them from dissolving into the electrolyte, allowing the positive electrode material to maintain high capacity without the detrimental effects of non-uniform reactivity
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 separator and sulfur-carbon composite improve energy density to 400 Wh/kg or higher and extend the battery's life characteristics, reducing non-uniform reactivity and manufacturing costs.
Implementation Method 1
a first layer having a porosity of 50 vol% or more... a second layer having a porosity of 25 vol% or more and less than 50 vol%... capable of locking the polysulfide formed at the positive sulfur electrode
Implementation Method 2
a first layer having a porosity of 50 vol% or more... a second layer having a porosity of 25 vol% or more and less than 50 vol%
Data Source
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AI summary
The present invention relates to a separator for a lithium-sulfur battery, comprising: a first layer having a porosity of 50 vol% or more, wherein the first layer is on a first surface of the separator, wherein a thickness of the first layer is 50% or more of 100% of a thickness of the; and a lithium-sulfur battery, comprising: an electrode assembly and an electrolyte, wherein the electrode assembly comprises a positive electrode, a negative electrode and a separator between the negative electrode and the positive electrode, wherein the positive electrode comprises a positive electrode active material layer, and the positive electrode active material layer comprises a sulfur and/or a sulfur compound, wherein the separator is as defined in the application, and wherein the first layer of the separator is in contact with the positive electrode active material layer.