Lithium-Iron Disulfide Cell Anode Patch Design
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Lithium-iron disulfide electrochemical cells with spirally wound electrode assemblies experience premature voltage drop-off on intermittent discharge tests due to radial expansion forces and internal disconnects, limiting their capacity and reliability in consumer devices.
Innovation Solution
A localized area of increased thickness on the anode, specifically a lithium or lithium alloy patch positioned underneath the cathode's terminal edge, helps retain the anode's integrity during discharge and enhances lithium utilization, mitigating premature voltage drop-off and improving capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a cathode outer wrap design is used to maximize active material utilization, then capacity is improved, but premature voltage drop-off occurs on intermittent discharge tests due to radial expansion forces causing internal disconnects
Solution Approach 1:
The anode is designed with non-uniform thickness, featuring a localized thicker region (anode extension) at the outermost wind position. This local structural modification provides enhanced mechanical support and maintains electrical connectivity at the critical interface between cathode and anode during intermittent discharge, preventing internal disconnects while preserving overall capacity.
Solution Approach 2:
The extended anode structure acts as a pre-positioned mechanical buffer that compensates for radial expansion forces before they can cause damage. By having additional anode material in advance at the outermost region, the design prevents separator puncture and maintains electrical contact during volume changes that occur during intermittent discharge cycles.
2Ease of manufacture
If uniform thickness electrodes are used to simplify manufacturing, then ease of manufacture is improved, but capacity is limited due to insufficient lithium utilization
Solution Approach 1:
Instead of uniform thickness throughout, the anode employs local quality variation with a thicker region specifically at the outermost wind. This targeted thickening increases lithium content where it is most needed for maintaining connectivity during discharge, while keeping the rest of the electrode structure simple and manufacturable.
Solution Approach 2:
The anode thickness is segmented into two distinct regions: a standard thickness region for ease of manufacture and a localized extended thickness region for enhanced lithium utilization and mechanical stability. This segmentation allows the electrode to benefit from both simple fabrication processes and improved performance characteristics.
3Quantity of substance
If thicker electrodes are used to increase capacity, then quantity of active material is improved, but device complexity increases due to additional safety devices and design considerations
Solution Approach 1:
Rather than uniformly increasing electrode thickness throughout the entire cell, the invention applies thickness enhancement locally only at the outermost anode region. This localized approach increases active material content and improves reliability without requiring proportional increases in safety devices or other design elements that would accompany a uniform thickening of all components.
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 solution effectively increases the overall capacity and reliability of lithium-iron disulfide cells on intermittent discharge tests by up to 7% compared to anode outer wrap designs, while maintaining manufacturing simplicity and reducing lithium usage.
Implementation Method 1
a lithium-based negative electrode including a small region of increased thickness proximate to/under the terminal end of the outermost edge of the cathode strip
Data Source
Figure 1
Figure 2A~2B
Figure 2C~2D
AI summary
The invention relates to primary electrochemical cells having a jellyroll electrode assembly that includes a lithium-based negative electrode, a positive electrode with a coating comprising iron disulfide deposited on a current collector and a polymeric separator. More particularly, the invention relates to a cell design which optimizes cell capacity and substantially eliminates premature voltage drop-off on intermittent service testing. The resulting cell has a region of increased lithium thickness proximate to/under the terminal end of the outermost edge of the cathode strip.