Permselective Interlayer for Lithium-Sulfur Polysulfide Blocking
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Solution Overview
Problem
Lithium sulfur batteries face challenges such as the insulating nature of solid sulfur, large volume change during charging and discharging, structural damage, and the 'shuttling effect' of lithium polysulfides (LiPS) that lead to irreversible capacity loss and passivation of the lithium anode.
Innovation Solution
A permselective interlayer comprising elastic polyelectrolyte liquids and two-dimensional conducting materials, which facilitates lithium ion transport while hindering polysulfide species, is applied to the separator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If physical barriers or interlayers are provided to suppress the shuttling effect, then polysulfide transport is reduced, but lithium ion transport may be impeded and adhesion to the separator substrate may be insufficient
Solution Approach 1:
The interlayer is designed with spatially differentiated properties: hydrophobic regions (fluorinated polymer segments) provide adhesion to the porous separator substrate and block polysulfides, while hydrophilic regions (ethylene oxide units) create ion-conductive channels for lithium ion transport. This local quality differentiation allows simultaneous achievement of polysulfide suppression and lithium ion conductivity.
Solution Approach 2:
The interlayer comprises a composite polymer structure combining fluorinated hydrophobic segments (for adhesion and polysulfide blocking) with poly(ethylene oxide) hydrophilic segments (for lithium ion conduction). This composite material approach integrates multiple functions within a single interlayer component, resolving the contradiction between polysulfide suppression and lithium ion transport.
2Object-generated harmful factors
If a dense interlayer structure is used to block polysulfides, then polysulfide transport is hindered, but lithium ion transport and electrolyte wetting are reduced
Solution Approach 1:
The interlayer utilizes a porous separator substrate as its foundation, maintaining inherent porosity for electrolyte penetration and ion transport. The fluorinated polymer coating is applied as a thin layer that does not completely block the pores, allowing lithium ions to pass through while the hydrophobic nature of the fluorinated segments blocks polysulfide molecules. This porous structure approach maintains productivity while achieving polysulfide blocking.
Solution Approach 2:
The interlayer creates localized hydrophobic domains (fluorinated polymer regions) within an overall porous structure. These local hydrophobic zones block polysulfides through steric and hydrophobic effects, while the surrounding porous matrix and hydrophilic poly(ethylene oxide) segments maintain channels for lithium ion transport and electrolyte access.
3Strength
If hydrophobic materials are used for adhesion to polyolefin separators, then adhesion strength is improved, but lithium ion conductivity and electrolyte wettability are reduced
Solution Approach 1:
The interlayer employs a composite polymer architecture where fluorinated hydrophobic segments (providing adhesion to polyolefin separators) are chemically linked to poly(ethylene oxide) hydrophilic segments (providing lithium ion conductivity). This composite structure integrates both adhesion and ion transport functions within a single material system, eliminating the trade-off between hydrophobic adhesion and hydrophilic ion conduction.
Solution Approach 2:
The invention merges two previously separate functions (adhesion and ion conduction) into a single dual-functional polymer interlayer. The fluorinated polymer provides adhesion to the separator, while the poly(ethylene oxide) segments provide ion conduction pathways. By combining these functions in one integrated structure, the interlayer simultaneously achieves strong adhesion and high lithium ion conductivity.
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 interlayer effectively mitigates polysulfide transport and accumulation, maintaining lithium ion transport, reducing irreversible capacity loss, and enhancing battery performance.
Implementation Method 1
one or more two dimensional conducting materials
Implementation Method 2
permselective interlayer... facilitates lithium ion transport while hindering polysulfide species
Data Source
AI summary
An interlayer for a lithium sulfur battery is provided. The interlayer is produced from an elastic polyelectrolyte liquid (EPL) and a two dimensional conducting material, such as graphene oxide. The EPL is produced from polyphenol, cationic polymer and facilitated ion transport protein. The interlayers are characterised by ion selective transport behaviour and electrocatalytic properties, and separator substrates coated with the interlayer may be usefully incorporated into lithium sulfur batteries.