Heat-Sealed Cell Separator to Minimize Voids in Bobbin Cells
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Solution Overview
Problem
Alkaline electrochemical cells face challenges in maximizing discharge performance while adhering to fixed dimensional standards, necessitating the optimization of cell characteristics to increase active material content and minimize non-active material volume, such as separators, to enhance run-time.
Innovation Solution
The implementation of a hollow container with a tubular cathode ring and a compressed separator within, where the separator is steamed in situ to minimize creases and voids, and heat-sealed to prevent direct contact between active materials, utilizing a nonwoven fibrous separator with thermoplastic fibers and a specialized insertion tool for radial pressure and heat application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the separator is made larger to reduce creases and voids, then the discharge performance is improved, but the cell volume is exceeded
Solution Approach 1:
The separator is subjected to steam treatment which changes its physical parameters (temperature, humidity, flexibility) to enable it to conform to the cathode surface without increasing its nominal size. This parameter change allows the separator to reduce creases and voids while maintaining compliance with cell volume standards.
Solution Approach 2:
The separator is pre-formed into a convolute configuration with overlapping portions before insertion into the cell. This preliminary shaping action prepares the separator to fit tightly against the cathode, minimizing voids and creases from the outset without requiring additional space during final assembly.
2Quantity of substance
If the separator is compressed to minimize voids, then the active material volume is maximized, but the separator structure may be damaged
Solution Approach 1:
Steam treatment modifies the physical parameters of the separator material, making it more pliable and resistant to structural damage during compression. The heat and moisture from steaming temporarily alter the material properties, allowing compression without compromising separator integrity.
Solution Approach 2:
The separator utilizes a composite structure with overlapping portions that are heat-sealed together. This composite construction provides structural reinforcement, allowing the separator to withstand compression forces while minimizing voids between the separator and cathode.
3Reliability
If heat is applied to seal the separator, then the separator integrity is improved, but the active material may be affected
Solution Approach 1:
Heat sealing is applied locally only to the overlapping portions of the separator where it is needed for structural integrity. This localized heat application avoids exposing the active materials to excessive temperatures that could degrade their performance, while still achieving the desired separator sealing.
Solution Approach 2:
The overlapping portions of the separator act as an intermediary structure that can be heat-treated separately from the active materials. By concentrating heat application on these non-active portions, the separator integrity is improved without adversely affecting the temperature-sensitive active materials.
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 configuration enhances discharge performance by maximizing active material volume, reducing internal gaps, and preventing short circuits, thereby extending the operational time of electrical devices.
Implementation Method 1
The separator according to the present invention is steamed in situ to further decrease the number of creases within the separator
Implementation Method 2
The electrochemical cell according to claim 12 is heat-sealed to prevent the positive and negative active materials from coming in direct contact
Implementation Method 3
The separator sheet of certain embodiments may be a nonwoven fibrous separator sheet comprising thermoplastic fibers, and heating the at least a part of the overlapping portion may melt at least a portion of the thermoplastic fibers
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A separator for a bobbin-style electrochemical cell is inserted into an interior opening within a ring-shaped cathode in an electrochemical cell can. An expansion force is then applied to an interior surface of the separator to press the separator against the interior walls of the cathode. A tool may then remove various creases and/or wrinkles in the separator and/or may then heat seal at least a portion of the tubular walls of the separator to minimize the void space between the separator and active material (e.g., cathode and/or anode) within the electrochemical cell.