Sulfur-Based Positive Electrode Active Material for Lithium-Ion Battery
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Solution Overview
Problem
Lithium-ion secondary batteries using elemental sulfur as a positive-electrode active material face capacity deterioration due to sulfur compounds dissolving in the electrolyte, leading to reduced cyclability.
Innovation Solution
A sulfur-based positive-electrode active material is developed by heat-treating a polymer with a hetero atom-containing moiety and sulfur under a non-oxidizing atmosphere, forming a carbon skeleton that enhances charging and discharging capacity and cyclability.
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 is deteriorated due to sulfur compounds dissolving in the electrolyte
Solution Approach 1:
The patent uses a composite material consisting of sulfur and a heteroatom-containing compound (such as nitrogen-containing or oxygen-containing compounds). This composite structure allows sulfur to provide high capacity while the heteroatom-containing compound prevents sulfur compounds from dissolving in the electrolyte, thus maintaining cyclability. The heteroatom-containing compound acts as a matrix or support that holds sulfur in an insoluble state.
Solution Approach 2:
The heteroatom-containing compound serves as an intermediary substance between sulfur and the electrolyte. It mediates the interaction by providing a barrier that prevents direct contact between sulfur compounds and the electrolyte, thereby preventing dissolution while still allowing lithium ion transport. This intermediary layer resolves the contradiction by decoupling the capacity-providing function of sulfur from the stability-providing function.
2Object-affected harmful factors
If sulfur is used as a positive-electrode active material, then the risk of firing and explosion is reduced compared to oxygen-containing materials, but sulfur compounds still dissolve in the electrolyte causing capacity loss
Solution Approach 1:
By creating a composite material where sulfur is combined with heteroatom-containing compounds, the patent achieves both safety and stability. The heteroatom-containing compound provides a stable matrix that prevents sulfur compound dissolution while maintaining the inherent safety advantage of sulfur over oxygen-containing materials.
Solution Approach 2:
The patent applies local quality by creating a specific microstructure where sulfur is distributed within or on the surface of heteroatom-containing compound particles. This local arrangement ensures that sulfur provides high capacity where needed while the heteroatom-containing compound provides protection against dissolution at the interface with the electrolyte.
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 significantly improves the retention of charging and discharging capacity over repeated cycles, offering superior cyclability and reduced risk of capacity loss.
Implementation Method 1
heat-treating a polymer with a hetero atom-containing moiety and sulfur under a non-oxidizing atmosphere, forming a carbon skeleton
Implementation Method 2
heat-treating a mixture of polyisoprene and sulfur powder
Data Source
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AI summary
An object of the present invention is to provide a novel sulfur-based positive-electrode active material which can largely improve cyclability of a lithium-ion secondary battery, a positive electrode comprising the positive-electrode active material and a lithium-ion secondary battery comprising the positive electrode. The sulfur-based positive-electrode active material is one comprising: a carbon skeleton derived from a polymer composed of a monomer unit having at least one hetero atom-containing moiety, and sulfur incorporated into the carbon skeleton as the carbon skeleton is formed from the polymer by heat treatment; wherein the hetero atom-containing moiety is pyrrolidone or the polymer is polyvinylpyridine.