Nitrogen-Doped Sulfur Cathode Material for Li-Ion Battery Cyclability
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Solution Overview
Problem
Lithium-ion secondary batteries using sulfur as a positive-electrode active material face challenges in maintaining cyclability and charging/discharging capacity due to sulfur's tendency to form soluble compounds with lithium, leading to capacity degradation over repeated charging and discharging.
Innovation Solution
A sulfur-based positive-electrode active material is developed by heat-treating a starting material comprising a chain organic compound and sulfur under a nitrogen atom-doping gas atmosphere, specifically using ammonia gas, to introduce doped nitrogen atoms, which enhances the material's cyclability and charging/discharging capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If sulfur is used as a positive-electrode active material to achieve larger charging and discharging capacity, then the battery capacity increases, but the cyclability deteriorates due to sulfur elution into the electrolyte
Solution Approach 1:
The patent uses a composite material consisting of sulfur and a nitrogen-containing compound. The nitrogen-containing compound forms a coating layer on the sulfur particles, creating a composite structure that prevents sulfur elution while maintaining high capacity. This resolves the contradiction by combining two materials with complementary properties: sulfur provides high capacity while the nitrogen-containing compound provides structural stability and prevents dissolution.
Solution Approach 2:
The patent changes the chemical composition parameters by introducing nitrogen-containing compounds with specific molecular structures and nitrogen content ratios. By controlling the ratio of nitrogen-containing compound to sulfur (0.01-10 mass ratio) and selecting compounds with specific nitrogen content (10-50 at%), the patent optimizes both capacity and cyclability, resolving the contradiction through precise parameter control.
2Reliability
If a material other than sulfur is added to inhibit sulfur elution and improve cyclability, then the cyclability improves, but the charging and discharging capacity may be reduced
Solution Approach 1:
The patent precisely controls the amount of nitrogen-containing compound added, maintaining a mass ratio between 0.01 and 10 relative to sulfur. This optimized ratio ensures sufficient coverage to prevent sulfur elution while minimizing the dilution effect on capacity. The patent also controls the nitrogen content (10-50 at%) and molecular weight (100-10,000 Da) of the nitrogen-containing compound to balance protection and capacity.
Solution Approach 2:
The nitrogen-containing compound forms a localized coating layer on the surface of sulfur particles rather than uniformly mixing throughout. This local quality approach allows the sulfur core to maintain its high-capacity properties while the surface coating provides protective functionality, resolving the contradiction between capacity and cyclability.
3Ease of manufacture
If elemental sulfur is used as the positive-electrode active material, then the battery is inexpensive and has low reactivity, but the battery capacity deteriorates through repeated charging and discharging due to soluble compound formation
Solution Approach 1:
The patent creates a composite material where inexpensive elemental sulfur is combined with a nitrogen-containing compound. This composite maintains the cost-effectiveness and low reactivity of sulfur while adding the functional benefits of the nitrogen-containing compound to prevent polysulfide dissolution and improve cyclability.
Solution Approach 2:
The nitrogen-containing compound acts as an intermediary between sulfur and the electrolyte, forming a protective barrier that prevents direct interaction between sulfur and the electrolyte. This intermediary layer stops the formation of soluble lithium polysulfides while allowing lithium ion transport, thus improving cyclability without sacrificing the inherent advantages of sulfur.
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 improves the cyclability of lithium-ion secondary batteries by reducing the degradation of charging and discharging capacity, ensuring a higher capacity retention rate through the effective adsorption of polysulfide ions on doped nitrogen sites, thereby extending the battery's lifespan.
Implementation Method 1
heat-treating a starting material comprising a chain organic compound and sulfur under an atmosphere of a nitrogen atom-doping gas, wherein the nitrogen atom-doping gas is ammonia gas
Implementation Method 2
introduce doped nitrogen atoms, which enhances the material's cyclability and charging/discharging capacity
Implementation Method 3
the effective adsorption of polysulfide ions on doped nitrogen sites, thereby extending the battery's lifespan
Data Source
Figure 1
Figure 2~3
AI summary
An object of the present disclosure is to provide a new sulfur-based positive-electrode active material which can improve cyclability of a lithium-ion secondary battery while maintaining a charging and discharging capacity, 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 doped nitrogen atoms obtainable by heat-treating a starting material comprising a chain organic compound and sulfur under an atmosphere of a nitrogen atom-doping gas.