Titanium Electrochemical Cell Casing for Eddy Current Heating Reduction
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Solution Overview
Problem
Eddy current heating during the recharging of electrochemical cells used in implanted medical devices is a concern due to the conductive nature of existing cell casings, leading to excessive heating, reduced battery charge capacities, and longer recharging times, while materials like Grade 5 and Grade 23 titanium are difficult to form and prone to brittleness.
Innovation Solution
An electrochemical cell casing composed of a combination of high electrical resistivity materials like Grade 5 or Grade 23 titanium for the main body and more ductile Grade 1 or Grade 2 titanium for the lid, joined through welding, which reduces eddy current heating and enhances mechanical robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conductive material is used for the cell casing, then the casing provides good mechanical strength, but eddy current heating occurs during recharging
Solution Approach 1:
The patent applies composite materials by combining two different titanium alloys with complementary properties. Grade 5 or Grade 23 titanium (higher electrical resistivity, lower ductility) is used for the main body to reduce eddy current heating, while Grade 1 or Grade 2 titanium (higher ductility, lower electrical resistivity) is used for the lid to ensure formability and mechanical robustness. This composite construction resolves the contradiction by distributing the functional requirements across different materials.
Solution Approach 2:
The patent applies local quality by assigning different material grades to different parts of the casing based on their specific functional requirements. The main body uses material with higher electrical resistivity (Grade 5 or 23) where eddy current reduction is most critical, while the lid uses more ductile material (Grade 1 or 2) where formability and sealing are prioritized. This localized material selection optimizes each component for its specific role.
2Object-affected harmful factors
If Grade 5 or Grade 23 titanium is used for the casing, then eddy current heating is reduced, but the material is difficult to form and prone to brittleness
Solution Approach 1:
The patent uses composite materials to overcome the manufacturing difficulties of Grade 5 or 23 titanium. The main body is formed from this material for optimal eddy current performance, while the lid is formed from more ductile Grade 1 or 2 titanium that is easier to manufacture and form. This division allows each component to be manufactured with appropriate material properties.
Solution Approach 2:
The patent segments the casing into two distinct components (main body and lid) that can be manufactured separately using materials optimized for their specific requirements. The main body is segmented as the eddy current-resistant component, while the lid is segmented as the formable component. These segments are then joined through welding to create the complete casing.
3Object-affected harmful factors
If Grade 5 or Grade 23 titanium is used for the casing, then eddy current heating is minimized, but the casing becomes brittle
Solution Approach 1:
The patent applies composite materials to balance the brittleness issue. Grade 5 or 23 titanium provides the eddy current resistance for the main body, while Grade 1 or 2 titanium provides the ductility and toughness for the lid. The combination ensures the overall casing has both eddy current performance and mechanical robustness.
Solution Approach 2:
The patent applies local quality by providing different mechanical properties in different locations of the casing. The main body has lower ductility but sufficient structural integrity, while the lid has higher ductility to accommodate forming operations and provide a robust seal. Each location's material properties are optimized for its specific functional demands.
4Productivity
If the magnetic field intensity is increased to improve charging speed, then recharging time is reduced, but eddy current heating increases
Solution Approach 1:
The patent applies parameter changes by modifying the electrical resistivity parameter of the casing material. Grade 5 or 23 titanium has higher electrical resistivity compared to traditional conductive materials, which directly reduces eddy current heating. This parameter change allows the system to tolerate higher magnetic field intensities during charging without excessive heating, thereby enabling faster charging speeds.
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 minimizes eddy current heating and provides a mechanically robust casing that can withstand mechanical stresses and processing steps, ensuring the electrochemical cell's hermeticity and efficiency in energy storage and charging.
Implementation Method 1
Eddy current heating of the cell enclosure generally occurs when eddy currents, emanating from the charging coil, interact with the conductive material of the enclosure or casing. This interaction generates heat there within.
Implementation Method 2
Electro-magnetic (EM) induction in which EM fields are transmitted from an external charger to the cell within the AIMD is a common means through which the electrochemical cell is recharged.
Data Source
AI summary
An electrochemical cell, preferably a secondary, rechargeable cell, including a casing comprised of a main body portion having opposed lower and upper open ends closed by respective lower and upper lids is described. The main body portion is composed of titanium Grades 5 or 23 having a relatively high electrical resistivity material while the lower and upper lids are composed of titanium Grades 1 or 2. The lids are preferably joined to the main body portion using laser welding. The combination of these differing titanium alloys provides a cell casing that effectively retards eddy current induced heating during cell recharging.