Lithium-Sulfur Battery Sulfur Ratio to Limit Polysulfide Dissolution
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Solution Overview
Problem
Lithium-sulfur batteries exhibit lower specific capacity than theoretical due to the dissolution of lithium polysulfide in the electrolyte solution during charging and discharging, leading to shuttle reactions and capacity degradation.
Innovation Solution
A lithium-sulfur battery design with a sulfur-carbon composite positive electrode and a controlled weight ratio of sulfur in the electrolyte solution to the positive electrode (WSE/WSP ≤ 0.15) to minimize sulfur loss and enhance capacity retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If sulfur-based compound is used as positive electrode active material, then theoretical specific capacity of 1,675 mAh/g is achieved, but lithium polysulfide dissolves in electrolyte solution causing shuttle reactions and capacity degradation
Solution Approach 1:
A diaphragm coated with sulfur-based compound is introduced as an intermediary between the positive and negative electrodes. This diaphragm acts as a mediator that allows ion transport while preventing direct contact and shuttle reactions between lithium polysulfide and the negative electrode, thereby maintaining high specific capacity while improving capacity retention.
Solution Approach 2:
The patent employs a thin film diaphragm structure that physically confines lithium polysulfide and prevents its dissolution into the bulk electrolyte. This thin film barrier maintains the integrity of the sulfur-based active material while allowing necessary ion transport, thus resolving the contradiction between achieving high specific capacity and preventing capacity degradation.
2Use of energy by moving object
If sulfur-based compound is used as positive electrode active material, then theoretical energy density of 2,600 Wh/kg is achieved, but dissolution of lithium polysulfide leads to capacity degradation
Solution Approach 1:
The diaphragm coated with sulfur-based compound serves as an intermediary that enables the system to achieve high energy density while preventing the harmful dissolution of lithium polysulfide. By mediating the interaction between electrodes, it preserves the energy storage capability of sulfur while preventing capacity degradation through shuttle reactions.
Solution Approach 2:
The patent extracts and isolates the sulfur-based compound into a separate diaphragm structure, removing it from direct contact with the electrolyte and negative electrode. This extraction prevents lithium polysulfide dissolution while maintaining the high energy density benefits of sulfur-based active material.
3Quantity of substance
If sulfur-based compound is used as positive electrode active material, then high capacity is achieved, but shuttle reactions occur due to polysulfide dissolution
Solution Approach 1:
The diaphragm coated with sulfur-based compound acts as an intermediary barrier that physically separates the positive and negative electrodes. This mediator prevents lithium polysulfide from dissolving into the electrolyte and participating in shuttle reactions, while still allowing necessary ion transport to maintain high capacity.
Solution Approach 2:
The patent converts the potentially harmful sulfur-based compound that causes shuttle reactions into a beneficial coating on the diaphragm. By coating the diaphragm with sulfur-based compound, the system transforms the source of harm into a protective barrier that prevents polysulfide dissolution while maintaining high capacity.
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 achieves a specific capacity of 1,000 mAh/g or more and energy density of 300 Wh/kg or more, closely approaching theoretical limits by reducing polysulfide dissolution and shuttle reactions.
Implementation Method 1
lithium-sulfur batteries have theoretical specific capacity (specific capacity) of 1,675 mAh/g by conversion reaction (S8+16Li++16e−→8Li2S) of lithium ion and sulfur at the positive electrode
Implementation Method 2
lithium metals, carbon-based materials capable of intercalation/deintercalation of lithium ions, or silicon and tin that can be alloyed with lithium for the negative electrode active material
Implementation Method 3
the dissolution of lithium polysulfide in the electrolyte solution during charging and discharging, leading to shuttle reactions and capacity degradation
Data Source
AI summary
A lithium-sulfur battery having a high capacity and a method for manufacturing the same are provided. The lithium sulfur battery comprises a positive electrode and an electrolyte solution, and has a weight ratio, WSE/WSP, of a weight of a sulfur element (S) of a sulfur-based compound present in the electrolyte solution to a weight of a sulfur element (S) of a sulfur-based compound present in the positive electrode of 0.15 or less.