Battery Electrode Peel Strength for Crack-Free Winding
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Solution Overview
Problem
Secondary batteries with wound electrode structures often experience cracking at inner sections due to stress, leading to reduced battery capacity and potential short circuits, as high peel strength between the active material-containing layer and current collector can cause the electrode to break at inner sections rather than the outer surface.
Innovation Solution
An electrode with a peel strength between 0.2 kN/m to 0.7 kN/m is achieved by using a current collector and an active material-containing layer containing titanium-containing oxide particles of 0.1 μm to 3 μm in size, ensuring the active material-containing layer is partially unbound at inner bent sections, reducing stress concentration and preventing cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the peel strength between the active material-containing layer and current collector is increased to improve electrode integrity, then the electrode becomes more resistant to delamination, but the electrode cracks at inner bent sections subjected to stress during winding
Solution Approach 1:
The invention applies different properties to different parts of the electrode by creating an unbound state specifically at the inner bent section. The active material-containing layer is intentionally designed to be unbound from the current collector at the innermost bent section, allowing this local region to peel and absorb stress, while the rest of the electrode maintains strong adhesion for structural integrity.
Solution Approach 2:
Instead of making the entire electrode uniformly strong through high peel strength, the invention inverts the approach by creating a deliberately weak unbound region at the inner bent section. This inverted strategy allows the electrode to sacrifice a small unbound area to prevent catastrophic cracking throughout the wound structure.
2Strength
If the electrode is made stiff to maintain structural integrity during winding, then the electrode holds its shape better, but cracking occurs at innermost bent sections due to stress concentration
Solution Approach 1:
The invention converts the harmful effect of stress concentration at the inner bent section into a beneficial outcome. By allowing the active material-containing layer to be unbound and peel at this high-stress region, the stress concentration that would normally cause cracking is instead absorbed by the controlled peeling of the unbound layer, protecting the rest of the electrode from damage.
Solution Approach 2:
The unbound state of the active material-containing layer at the inner bent section acts as a pre-prepared cushioning mechanism. Before winding occurs and stress is applied, the unbound region is already in place to absorb and dissipate the stress concentration that will occur during the winding process, preventing crack initiation.
3Quantity of substance
If the active material-containing layer is fully bound to the current collector to maximize active material utilization, then battery capacity is maximized, but the electrode cannot accommodate bending stress without cracking
Solution Approach 1:
The invention applies partial action by having the active material-containing layer bound to the current collector in most regions while intentionally leaving it unbound at the inner bent section. This partial unbinding sacrifices a small portion of active material utilization in the unbound region but enables successful winding without cracks, achieving the greater good of overall electrode integrity and functional capacity.
Data Source
AI summary
According to one embodiment, provided is an electrode including a current collector and an active material-containing layer in contact with the current collector. The active material-containing layer contains a carbon nanotube and particles of titanium-containing oxide having an average particle size or 0.1 μm to 3 μm. A peel strength between the current collector and the active material-containing layer is within a range of 0.2 kN/m to 0.7 kN/m.