Piston-Type Battery Design for Axial Expansion
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Solution Overview
Problem
Existing electrochemical cells, particularly those used in miniaturized medical devices like leadless pacemakers, face challenges in achieving maximum energy density due to suboptimal designs that result in unutilized casing volume and radial expansion of the cathode, limiting their size reduction and longevity.
Innovation Solution
The electrochemical cell is designed with a 'piston-type' configuration where the anode/cathode interface is oriented perpendicular to the cell length, utilizing a fluorinated carbon cathode and lithium anode, and featuring a cathode current collector with angled or corrugated configurations to minimize radial expansion and maximize axial movement, thereby increasing energy density and reducing unoccupied casing volume.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bobbin-type cell construction is used, then reliable discharge characteristics are provided, but energy density is reduced due to unutilized casing volume
Solution Approach 1:
The patent inverts the conventional bobbin-type construction by switching to a piston-type configuration where the anode/cathode interface is oriented perpendicular to the cell length rather than parallel. This inversion allows the electrodes to expand axially during discharge rather than radially, fully utilizing the casing volume and eliminating the interfacial gap that reduces energy density in traditional designs.
Solution Approach 2:
The patent changes the expansion dimension from radial (in bobbin-type) to axial (in piston-type). By reorienting the electrode interface perpendicular to the cell length, the design exploits the axial dimension for expansion, thereby utilizing the full casing volume including the previously wasted interfacial gap region, and achieving higher energy density while maintaining reliable discharge.
2Productivity
If the cathode is allowed to expand during discharge, then electrochemical reaction occurs, but radial expansion interferes with cell operation and increases device size
Solution Approach 1:
The patent introduces asymmetry in the expansion behavior by using a piston-type configuration where the anode and cathode are positioned at opposite ends of the cell with their interface perpendicular to the length. This asymmetric arrangement directs expansion axially in one direction toward the other electrode, rather than allowing symmetric radial expansion in all directions, thereby containing the volume increase within the cell length rather than increasing the device diameter.
Solution Approach 2:
The patent inverts the conventional radial expansion pattern by designing the electrode interface perpendicular to the cell length. This causes the cathode to expand axially toward the anode during discharge rather than radially outward, converting what would be harmful radial expansion into useful axial movement that maintains compact device dimensions while enabling continuous electrochemical reaction.
3Quantity of substance
If a piston-type configuration is used, then energy density is increased by reducing unoccupied volume, but device complexity increases due to specialized current collector design
Solution Approach 1:
The cathode current collector in the piston-type configuration serves multiple functions: it provides electrical conductivity, supports the cathode active material, and acts as a mechanical constraint that directs axial expansion while accommodating volume changes during discharge. This multi-functionality reduces the need for separate expansion management components, thereby limiting the increase in device complexity despite the advanced configuration.
Solution Approach 2:
The patent changes the geometric parameters of the current collector, specifically orienting the anode/cathode interface perpendicular to the cell length and designing the current collector to accommodate axial expansion. This parameter change enables the piston-type configuration that increases energy density by eliminating the interfacial gap, while the current collector's adapted geometry manages the complexity through optimized structural design rather than additional 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
This design enhances energy density and cell life by minimizing unoccupied casing volume and radial expansion, making it suitable for powering smaller, more invasive medical devices with increased capacity and reduced size.
Implementation Method 1
The cell comprises a Group IA anode or negative electrode and a fluorinated carbon (CFx) cathode or positive electrode
Data Source
AI summary
An electrochemical cell comprising a cathode and an anode residing within a casing, the anode being positioned distal of the cathode. The cathode having a cathode current collector having an angled configuration that encourages the cathode active material to move in an axial distal direction during cell discharge. The cathode current collector may be configured having at least one fold thereby dividing the current collector into at least two portions having an angle therebetween. The cathode current collector may comprise a wire having a helical configuration or the cathode current collector may comprise a post with a thread having a helical orientation about the post exterior. A preferred chemistry is a lithium/CF.sub.x activated with a nonaqueous electrolyte.