Multi-layer Separator for Lithium-Sulfur Battery
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Solution Overview
Problem
Lithium-sulfur batteries suffer from high capacity loss and self-discharge due to the dissolution of polysulfide anions in the electrolyte, leading to inefficient energy storage and short cycle life.
Innovation Solution
A multi-layer separator system is introduced, comprising a middle layer with a liquid or gel-like electrolyte and solid electrolyte layers, along with an anion-blocking layer to prevent polysulfide diffusion, and the use of a liquefied sulfur cathode to enhance redox reaction kinetics and power density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional single-layer separator is used in lithium-sulfur batteries, then the battery structure is simple and easy to manufacture, but polysulfide anions dissolve in the electrolyte causing high capacity loss and self-discharge
Solution Approach 1:
The separator is divided into multiple functional layers: a base separator layer for mechanical support and ion transport, and additional functional layers (such as coating layers with lithium salts or polymer electrolyte layers) that specifically address polysulfide dissolution. This segmentation allows each layer to perform its specialized function, reducing capacity loss while maintaining manufacturing feasibility.
Solution Approach 2:
The separator employs composite material structures combining different materials with complementary properties. For example, a polyolefin base layer is combined with coating layers containing lithium salts or polymer electrolytes, creating a composite separator that provides both mechanical stability and enhanced polysulfide management capabilities, thereby improving capacity retention.
2Reliability
If the electrolyte volume is increased to accommodate polysulfide dissolution, then polysulfides can be distributed throughout the electrolyte, but this leads to higher self-discharge due to direct reaction with the lithium metal anode
Solution Approach 1:
The harmful function of polysulfide dissolution is extracted and redirected. Instead of allowing polysulfides to freely dissolve and migrate to the anode causing self-discharge, the invention introduces functional layers that capture and retain polysulfides within the separator structure itself, effectively removing the harmful migration pathway while maintaining the beneficial ionic conductivity function.
Solution Approach 2:
The functional separator layers act as intermediary structures between the cathode and anode. These layers (coating layers with lithium salts or polymer electrolyte layers) serve as mediators that allow lithium ion transport while simultaneously capturing and retaining polysulfides, preventing their direct contact with the lithium metal anode and thus reducing self-discharge.
3Reliability
If a protective glass layer is added to shield the lithium anode, then the anode is protected from polysulfide reaction, but the mechanical stress from charging/discharging causes the protective glass to break
Solution Approach 1:
The invention replaces rigid protective glass layers with flexible polymer electrolyte layers or coating layers. These flexible films can accommodate the mechanical stress and volume changes that occur during charging and discharging cycles without breaking, while still providing effective protection against polysulfide attack on the lithium anode.
Solution Approach 2:
The protective structure is designed as a composite where polymer electrolyte layers or coating layers with specific mechanical properties are combined with the separator structure. This composite approach provides both the necessary mechanical flexibility to withstand cycling stress and the chemical protection against polysulfides, overcoming the limitations of rigid glass protectors.
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 solution significantly reduces capacity loss and self-discharge, improving the energy storage efficiency and extending the cycle life of lithium-sulfur batteries while maintaining mechanical stability and ion conductivity.
Implementation Method 1
the separator contains a middle layer which contains a liquid and/or gel-like electrolyte. Between this middle layer and the anode on the one hand and the cathode on the other hand there is at least one solid electrolyte layer
Implementation Method 2
the separator alternatively or additionally constructed in at least two layers with an anion-blocking layer facing the cathode
Implementation Method 3
The electrolyte should preferably have a high ion conductivity for the ions of the metal in the order of 10 -4
Implementation Method 4
The electrochemical cell reaction taking place in a lithium-sulfur battery is Li+S → Li 2 S for the cell discharge
Data Source
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AI summary
The invention relates to a metal-sulphur battery system having at least one electrochemical metal-sulphur cell (2, 2a, 2b, 2c, 2d). The metal-sulphur cell (2, 2a, 2b, 2c, 2d) has a layer structure comprising an anode (3) which is based on a metal, a cathode (4, 4a, 4b) which is based on sulphur, and a separator (5, 5a, 5b) which separates the anode (3) and the cathode (4) and is permeable to ions of the metal. The metal-sulphur cell (2, 2a, 2b, 2c, 2d) also comprises an anode conductor (7), which is electrically operatively connected to the anode (3), and a cathode conductor (8) which is electrically operatively connected to the cathode (4). The separator (5, 5a) is of at least three-layer construction with a central layer (15) which contains a liquid and/or gel-like electrolyte (6), and in each case at least one solid electrolyte layer (16, 17) between the central layer (15) and the anode (3) on the one hand and the cathode (4) on the other. As an alternative or in addition, the separator (5, 5b) can be of at least two-layer construction, with a layer (25) which faces the cathode (4), blocks anions and has an ion conductivity for the ions of the metal which is at least 100 times greater than the ion conductivity for an Sm 2- ion from the group where m = 2 to 8, and a polymer electrolyte layer (26) which is permeable to at least the ions of the metal and faces the anode (3). The separator (5, 5b) has a thickness (d2) of at least 10 μm, wherein the polymer electrolyte layer (26) is thicker than the layer (25) which faces the cathode (4), blocks anions and has an ion conductivity for the ions of the metal of at least 10-4 S/cm.