Carbon-Sulfur Structure for Lithium-Ion Battery Cathode
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Solution Overview
Problem
Lithium-ion secondary batteries using elemental sulfur as a positive-electrode active material suffer from reduced cyclability due to sulfur elution into the electrolyte, leading to a decline in charging and discharging capacity over repeated cycles.
Innovation Solution
A sulfur-based positive-electrode active material is developed, comprising a carbon-sulfur structure with a long-chain polymer thienoacene structure, formed by compounding sulfur with an unvulcanized diene rubber and a vulcanization accelerator, and heat-treating the mixture, which creates a three-dimensional network to enclose and fix elemental sulfur, preventing its elution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If elemental sulfur is used as a positive-electrode active material, then charging and discharging capacity is increased, but cyclability deteriorates due to sulfur elution into the electrolyte
Solution Approach 1:
The patent uses a composite material consisting of sulfur combined with conductive polymer particles and carbon particles. The conductive polymer forms a matrix that encapsulates sulfur, preventing its elution into the electrolyte while maintaining electrical conductivity. The carbon particles further enhance conductivity and structural stability, resolving the contradiction between high capacity and good cyclability.
Solution Approach 2:
The conductive polymer forms a flexible matrix or shell around the sulfur particles, creating a confined structure that prevents sulfur from dissolving into the electrolyte. This flexible encapsulation allows the sulfur to maintain its electrochemical activity while preventing harmful elution, thus improving cyclability without sacrificing capacity.
2Reliability
If sulfur is bound to a carbon skeleton as carbon polysulfide, then cyclability is improved to a certain degree, but the improvement is restrictive and not enough
Solution Approach 1:
The patent creates a multi-component composite material combining sulfur, conductive polymer particles, and carbon particles. This composite structure provides superior cyclability compared to simple carbon polysulfide by preventing sulfur elution through the polymer matrix while maintaining high capacity through the synergistic effects of all components.
Solution Approach 2:
The conductive polymer acts as an intermediary between sulfur and the electrolyte, providing a physical barrier that prevents direct contact between sulfur and electrolyte molecules. This intermediary structure eliminates the root cause of sulfur elution while maintaining electrical pathways for charge transfer, achieving both improved cyclability and capacity retention.
3Reliability
If polyacrylonitrile is added to polyisoprene, then cyclability is improved slightly, but the effect is still restrictive
Solution Approach 1:
The patent employs a composite material system where conductive polymer particles are dispersed in a sulfur matrix along with carbon particles. This composite approach achieves superior cyclability improvement without the need for complex polymer blends, simplifying the material composition while maximizing performance benefits.
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
This approach significantly improves the cyclability of lithium-ion secondary batteries by maintaining a large charging and discharging capacity and preventing sulfur elution, resulting in enhanced battery performance.
Implementation Method 1
a carbon-sulfur structure which has Raman shift peaks at around 500 cm−1, at around 1,250 cm−1 and at around 1,450 cm−1 in a Raman spectrum. The carbon-sulfur structure is assumed to have a long-chain polymer thienoacene structure in which thiophene rings are fused and linked... creates a three-dimensional network to enclose and fix elemental sulfur, preventing its elution
Data Source
AI summary
An object of the present invention is to provide a positive-electrode active material comprising a carbon-sulfur structure which has Raman shift peaks at around 500 cm−1, at around 1,250 cm−1 and at around 1,450 cm−1 in a Raman spectrum, and by using the positive-electrode active material, it is possible to greatly improve cycling characteristics of a lithium-ion secondary battery.