Flat Wound Electrode Body Relaxation Method
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Solution Overview
Problem
Non-aqueous electrolyte secondary cells experience electrode board bending and deterioration of cycle characteristics due to lithium ion intercalation and deintercalation, leading to increased cell thickness and gaps between electrodes, which disrupts lithium ion movement and worsens cell performance.
Innovation Solution
A method involving the use of a winding core to create an approximately cylindrical electrode body, which is then deformed into an oval shape and rotated to relax the winding tension, allowing the swelling to be absorbed without compromising the fixed winding end, thereby preventing electrode board bending and maintaining effective electrode alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If adhesive tape is used to fix the winding end of the flat wound electrode body, then the electrode boards are held in place, but the electrode boards bend due to swelling and contraction during charging and discharging
Solution Approach 1:
The electrode body is divided into multiple electrode boards that are wound in layers. By creating spaces between neighboring strip laminates, the swelling stress is distributed across multiple segments rather than concentrated at the fixed winding end, preventing bending while maintaining structural integrity.
Solution Approach 2:
Spaces are intentionally provided between neighboring strip laminates before the swelling occurs during charging and discharging. These pre-formed spaces act as cushioning regions that absorb the swelling and contraction stresses, preventing the electrode boards from bending at the fixed winding end.
2Shape
If a flat cross section winding core is used to provide space between electrode boards, then electrode board bending is reduced, but winding speed must be reduced
Solution Approach 1:
A winding core with a substantially circular cross section is used instead of a flat cross section core. The circular shape allows for faster winding speeds while the winding process itself creates the necessary spaces between electrode boards through the layer-by-layer winding arrangement, rather than relying on the core shape to provide the spaces.
3Shape
If reduced tension is applied on the electrode boards during winding, then space is provided to absorb swelling, but the quality of winding deteriorates
Solution Approach 1:
Different regions of the wound electrode body have different properties. The spaces between neighboring strip laminates are strategically positioned to absorb swelling, while the fixed winding end maintains strong adhesion through adhesive tape to ensure high winding quality. This local differentiation allows both swelling absorption and winding quality to be optimized in their respective regions.
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 method inhibits electrode board bending, reduces cell thickness, and improves cycle characteristics by maintaining smooth lithium ion movement and reducing stress on cell components, while also enhancing productivity by simplifying the winding process.
Implementation Method 1
the positive and negative electrode boards repeat swelling and contraction because of intercalation and deintercalation of lithium ions through charging and discharging
Implementation Method 2
The adhesive (adhesive tape) that fixes the winding end of the flat wound electrode body restricts the swelling and contraction of the electrode boards
Data Source
AI summary
A method for producing a secondary cell having a flat wound electrode body that inhibits the bending of the electrode board caused by charging and discharging and inhibits resulting swelling of the cell and deterioration of cycle characteristics is provided. The method has the steps of: winding, with a winding core, a positive electrode board, a negative electrode board, and a separator provided between the positive and negative electrode boards, and fixing the winding end, thereby preparing an approximately cylindrical electrode body; after the step of preparing the electrode body, deforming the electrode body into a shape with an approximately oval cross section by pressing the approximately cylindrical electrode body from a direction perpendicular to the winding axis, and rotating the deformed electrode body in the winding direction, thereby relaxing the winding state; and after the relaxation steps, pressing the electrode body into the flat wound electrode body.