Li/CFx Cell Swelling Reduction via Porous Separator
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Solution Overview
Problem
Lithium/fluorinated carbon (Li/CFx) electrochemical cells used in implantable medical devices experience significant swelling during discharge, leading to mechanical deformation and capacity loss due to lack of electrolyte contact with solid particles, which complicates device design and increases total device volume.
Innovation Solution
The electrochemical cell design incorporates a perforated metal cathode and anode current collector, a stepped header, and an optimized electrolyte formulation with a specific ratio of lithium salt in a mixed solvent, minimizing swelling by ensuring adequate void space and electrolyte contact, resulting in a cell swelling of less than or equal to 2% after discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If traditional Li/CFx electrochemical cells are used, then high energy capacity is achieved, but significant swelling occurs during discharge leading to mechanical deformation and capacity loss
Solution Approach 1:
The patent employs a porous separator with specific pore size and distribution to accommodate cell swelling during discharge. The porous structure allows the separator to expand and contract with the cell volume changes while maintaining electrolyte pathways, thus preventing mechanical deformation and capacity loss associated with traditional non-porous separators.
Solution Approach 2:
The patent modifies key parameters including electrolyte composition (using specific lithium salt concentrations and solvent ratios), separator properties (porosity, thickness, material composition), and cell design parameters to optimize performance. These parameter changes enable the cell to achieve high energy capacity while minimizing swelling-induced mechanical deformation and capacity loss.
2Volume of moving object
If cell swelling is minimized to reduce device volume, then implantable medical device size is reduced, but electrolyte contact with solid particles may be insufficient leading to capacity loss
Solution Approach 1:
The porous separator maintains adequate electrolyte distribution throughout the cell even at minimal swelling states. The interconnected pore network ensures electrolyte reaches all solid particle surfaces, preventing capacity loss while allowing the cell to maintain a compact size suitable for implantable medical devices.
Solution Approach 2:
The patent uses composite electrolyte formulations combining multiple solvents and lithium salts to optimize both cell swelling characteristics and electrolyte distribution. This composite approach enables adequate electrolyte contact with solid particles while minimizing overall cell volume expansion.
3Reliability
If more void space is reserved for cell volume change, then swelling-induced damage to device circuitry is prevented, but total device volume increases
Solution Approach 1:
By optimizing separator thickness, porosity, and material composition, the patent reduces the magnitude of cell swelling during discharge. This parameter optimization allows the cell to accommodate volume changes within a smaller overall size while still protecting device circuitry from damage, eliminating the need for excessive void space.
Solution Approach 2:
The porous separator acts as a buffer that absorbs and distributes mechanical stress from cell swelling, protecting circuitry while maintaining a compact cell structure. The porous network provides compliance that prevents stress concentration, allowing circuitry protection with minimal void space.
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 optimized design reduces cell swelling, maintains electrolyte contact, and enhances energy density, making it suitable for implantable medical devices by minimizing volume expansion and maintaining high energy capacity.
Implementation Method 1
an electrochemical cell that converts chemical energy to electrical energy
Data Source
AI summary
An electrochemical cell that converts chemical energy to electrical energy includes a cathode with an active material of fluorinated carbon on a perforated metal cathode current collector, a lithium anode on a perforated metal anode current collector, a stepped header, a stable electrolyte, and a separator. In various embodiments, an anode current collector design, a cathode current collector design, a stepped header design, a cathode formulation, an electrolyte formulation, a separator, and a battery incorporating the electrochemical cell are provided.