Square Lithium Battery Electrode Openings for Bend Stress Relief
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Solution Overview
Problem
The challenge in manufacturing square lithium secondary batteries lies in forming an active material mixture layer without bends with a small radius of curvature, which leads to reduced discharge capacity and reliability due to stress concentration and potential short-circuits, especially when using silicon as the negative electrode active material.
Innovation Solution
Incorporating a structure with openings in the active material mixture layer on the electrode sheets, specifically designed to reduce stress at bends by allowing misalignment compensation and using graphene to enhance conductivity and prevent electrolyte solution wastage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the active material mixture layer is formed continuously without removing material at bends, then the manufacturing process is simpler and productivity is higher, but the active material layer cracks and flakes at bends causing short-circuits and reduced reliability
Solution Approach 1:
The patent applies local quality by forming openings selectively at bend portions of the electrode sheet while maintaining continuous active material layer in non-bend areas. This localized modification allows the active material mixture layer to be formed continuously without material removal at bends, preventing cracks and flakes at critical locations while maintaining manufacturing efficiency and battery reliability
2Quantity of substance
If silicon is used as negative electrode active material to increase capacity, then the battery capacity increases significantly, but the volume change during charge/discharge causes adhesion degradation and active material damage
Solution Approach 1:
The patent applies porous materials by forming openings at bend portions of the electrode sheet. This porous structure accommodates the volume expansion and contraction of silicon during charge/discharge cycles, reducing stress concentration and preventing adhesion degradation and active material damage, thereby maintaining reliability while utilizing high-capacity silicon
Solution Approach 2:
The patent applies segmentation by creating discrete openings at specific bend locations rather than removing material continuously. This segmented approach allows the active material layer to maintain integrity in non-bend areas while providing stress relief at critical bend portions, solving the adhesion stability problem without sacrificing battery capacity
3Reliability
If the active material mixture layer is removed at bend portions to prevent cracking, then short-circuits are prevented, but the discharge capacity is reduced due to loss of active material
Solution Approach 1:
The patent applies local quality by forming openings selectively only at bend portions where stress concentration occurs, rather than removing active material from the entire electrode. This localized approach prevents short-circuits at critical locations while preserving active material in non-bend areas, maintaining discharge capacity
Solution Approach 2:
The patent applies taking out by extracting material only at specific critical locations (bend portions) where openings are formed, rather than removing material uniformly. This selective extraction prevents short-circuits at vulnerable points while minimizing the loss of active material and preserving overall discharge capacity
Data Source
AI summary
A square lithium secondary battery includes a wound body in which a collective sheet in which a positive electrode sheet and a negative electrode sheet overlap each other with a first separator interposed therebetween is wound while a second separator is put inside the collective sheet. An active material mixture layer on one or both surfaces of at least one of the positive electrode sheet and the negative electrode sheet includes a region with a plurality of openings and a region with no opening. At least a bent portion of the collective sheet is covered with the region with the plurality of openings.