Sulfur-Based Active Material Composition for Dense, Stable Li-Ion Electrodes
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Solution Overview
Problem
Lithium-ion secondary batteries face challenges with polymer-based active materials having low true density and poor cycle characteristics due to large volume changes during lithium ion absorption and release, and carbon materials have reached capacity limits.
Innovation Solution
A sulfur-based active material is produced by mixing acrylic resin, sulfur, and an iron compound with divalent or trivalent iron ions, then baked to create a material with improved volume energy density and capacity retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If polymer-based active materials are used, then charge and discharge capacity per unit mass is large, but true density decreases and volume energy density becomes inferior
Solution Approach 1:
The invention uses composite materials consisting of sulfur particles dispersed in a porous carbon matrix. This composite structure combines the high capacity of sulfur with the high density and structural stability of carbon, achieving both high mass capacity and high volume energy density. The carbon matrix provides a dense packing structure while accommodating sulfur particles, thus resolving the contradiction between mass capacity and volume density.
Solution Approach 2:
The invention employs porous carbon materials as the base structure to hold sulfur particles. The porous structure allows for high sulfur loading while maintaining structural integrity and enabling lithium ion transport. The porosity provides space for sulfur particles without significantly increasing the overall volume, thus improving volume energy density while maintaining high capacity.
2Quantity of substance
If materials that can absorb and release more lithium ions are used, then battery capacity is increased, but volume changes during charging and discharging cause poor cycle characteristics
Solution Approach 1:
The porous carbon matrix acts as a flexible container that accommodates the volume changes of sulfur during lithium ion absorption and release. The carbon structure can expand and contract without compromising structural integrity, preventing particle cracking and maintaining electrical contact throughout cycling. This resolves the contradiction between high capacity and cycle stability.
Solution Approach 2:
The composite structure of sulfur particles embedded in porous carbon provides both high capacity (from sulfur) and excellent cycle characteristics (from carbon's structural stability). The carbon matrix constrains sulfur volume expansion while allowing lithium ion transport, enabling the material to withstand repeated charging and discharging cycles without degradation.
3Reliability
If carbon materials such as graphite and hard carbon are used, then cycle characteristics are maintained, but capacity has almost reached theoretical limit and cannot be increased significantly
Solution Approach 1:
The invention changes the active material from conventional carbon (graphite, hard carbon) to sulfur-based composite materials. This parameter change transitions from carbon-limited capacity (theoretical limit already reached) to sulfur-based capacity (theoretical limit much higher at ~1675 mAh/g vs. graphite's ~372 mAh/g). The porous carbon matrix is used not as the active material but as a structural support, enabling sulfur to serve as the capacity-providing component.
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 sulfur-based active material achieves a good balance of volume energy density and capacity retention, enhancing the performance of lithium-ion secondary batteries.
Implementation Method 1
baking the raw material
Implementation Method 2
materials that can absorb and release more lithium ions
Data Source
AI summary
Provided is a method of producing a sulfur-based active material, the method comprising the steps of: (1) mixing an acrylic resin, sulfur, and an iron compound comprising a divalent or trivalent iron ion to obtain a raw material; and (2) baking the raw material, characterized in that a volume energy density is improved while maintaining a capacity retention rate of the active material that constitutes an electrode of a lithium-ion secondary battery.