PEDOT:PSS Cathode for High-Loading Lithium-Sulfur Batteries
Solution Overview
Problem
Lithium-sulfur secondary batteries face challenges in achieving high sulfur loading and conductivity without using solvents with low flash points or high amounts of binders and carbon-based materials, and with complex process steps.
Innovation Solution
A liquid composition comprising cationic polythiophene, polymeric counterion, elemental sulfur, and a high-boiling-point solvent, along with a conductivity improving agent, is used to create a conductive layer for lithium-sulfur batteries, allowing for high sulfur loading and conductivity without the need for solvents with low flash points or carbon-based materials, and with a simplified process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sulfur is coated with PEDOT using traditional polymerization methods, then conductivity is improved, but the process becomes complex requiring multiple steps including washing out oxidizing agents and purifying sulfur particles
Solution Approach 1:
The patent uses PEDOT:PSS complex as an intermediary substance that already contains the conductive polymer pre-formed. Instead of polymerizing PEDOT in situ which requires multiple purification steps, the pre-formed PEDOT:PSS complex is directly mixed with sulfur particles, serving as a convenient mediator that transfers conductivity to the sulfur cathode without requiring complex washing and purification processes
Solution Approach 2:
The patent changes the physical state and dispersion parameters by using a liquid composition where PEDOT:PSS is dispersed in a high-boiling-point solvent. This allows the conductive polymer to be uniformly distributed throughout the sulfur matrix in liquid form, which then solidifies upon drying, achieving high conductivity without mechanical complex processing steps
2Ease of manufacture
If ethanol is used as dispersing agent for PEDOT:PSS, then coating is facilitated, but safety is compromised due to low flash point
Solution Approach 1:
The patent changes the key parameter of solvent boiling point from low (ethanol at 78°C) to high (solvents with boiling points above 80°C, preferably above 100°C). This parameter change maintains the dispersing and coating facilitation properties while dramatically improving safety by raising the flash point, eliminating the fire hazard associated with ethanol
Solution Approach 2:
The high-boiling-point solvent acts as a safe intermediary medium that replaces ethanol. It performs the same function of dispersing PEDOT:PSS and enabling facile coating but does so without the harmful flammability characteristic, serving as a safer mediator in the manufacturing process
3Quantity of substance
If high sulfur loading is achieved in lithium-sulfur batteries, then energy density is improved, but conductivity deteriorates due to sulfur's electric non-conductor characteristics
Solution Approach 1:
The patent merges sulfur particles with PEDOT:PSS conductive polymer in a liquid composition, creating a composite where the conductive polymer matrix surrounds and connects sulfur particles. This merging allows high sulfur loading while maintaining conductivity through the continuous conductive polymer network that bridges isolated sulfur particles
Solution Approach 2:
The patent creates a composite material system consisting of sulfur particles dispersed in a PEDOT:PSS matrix within a high-boiling-point solvent. This composite structure combines the high capacity advantage of sulfur with the high conductivity advantage of PEDOT, achieving both high sulfur loading and good conductivity simultaneously
4Stability of the object's composition
If binders and carbon-based materials are added to improve electrode structure, then mechanical stability is improved, but the simplicity of the process and composition is reduced
Solution Approach 1:
The patent makes the PEDOT:PSS component multi-functional: it serves simultaneously as the conductive polymer, the binder holding the electrode together, and the matrix for sulfur dispersion. This eliminates the need for separate binder and carbon additive components, achieving mechanical stability without increasing composition complexity
Solution Approach 2:
The patent merges the functions of conductive polymer and binder into a single substance (PEDOT:PSS). Instead of using separate binder materials like PVDF and separate conductive additives like carbon black, the PEDOT:PSS complex performs both functions, simplifying the overall composition while maintaining mechanical integrity
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 approach enables the facile deposition of sulfur films with high sulfur loadings and good conductivity, simplifying the production process and eliminating the need for binders and carbon-based materials, while ensuring safety with solvents having high boiling points.
Implementation Method 1
PEDOT can also be prepared in the presence of polymeric sulfonic acids such as polystyrene sulfonic acid. The resulting complex (PEDOT : PSS) can be dispersed in solvents and allows the facile coating.
Implementation Method 2
A liquid composition comprising cationic polythiophene, polymeric counterion, elemental sulfur, and a high-boiling-point solvent, along with a conductivity improving agent, is used to create a conductive layer for lithium-sulfur batteries
Data Source
Figure 1
AI summary
The present invention relates to a liquid composition comprising a) at least one cationic polythiophene; b) at least one polymeric counterion; c) sulfur; d) at least one solvent having a boiling point of 80°C or more; e) at least one conductivity improving agent; wherein the liquid composition comprises less than 10 wt.-% of components having a boiling point of less than 80°C, based on the total weight of the liquid composition, and wherein the boiling point in each case is determined at a pressure of 1013 mbar. The present invention also relates to a powdered composition comprising components a), b) and c), wherein the cationic polythiophene and the at least one polymeric counterion are present in the form of a cationic polythiophene : polymeric counterion-complex, to a process for preparing a liquid or powdered composition, a liquid or powdered composition obtainable by this process, to a lithium sulfur electrochemical cell and to the use of the liquid or the powdered composition.