Lithium Secondary Cell Electrode Bonding With Controlled Penetration
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Solution Overview
Problem
Conventional lithium secondary cells face a challenge in achieving strong bonding of the active material plate to the current collector while minimizing deterioration of cell characteristics due to excessive penetration of the conductive bonding layer.
Innovation Solution
The lithium secondary cell design includes a conductive bonding layer that penetrates the active material plate by 3% to 80% of its thickness, ensuring a balance between bonding strength and cell characteristic preservation, using a conductive bonding layer composed of conductive powder and a binder with an acrylic resin in an aqueous solvent.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the conductive bonding layer is applied to firmly bond the sintered plate to the positive current collector, then the bonding strength is improved, but the cell characteristics deteriorate due to excessive penetration
Solution Approach 1:
The invention controls the penetration depth of the conductive bonding layer as a critical parameter, specifying it should be 5 µm or less (or 1-50% of active material plate thickness). By precisely controlling this parameter, the patent achieves both adequate bonding strength and prevention of cell characteristic deterioration that occurs with excessive penetration.
Solution Approach 2:
The conductive bonding layer is designed with non-uniform distribution - it penetrates into the active material plate at the edges and interfaces where bonding is needed, while maintaining minimal or zero penetration in the central regions where the active material plate thickness is greater. This localized penetration approach ensures strong bonding at critical interfaces while avoiding the harmful effects of excessive penetration in the bulk.
2Strength
If the conductive bonding layer penetrates deeply into the active material plate, then the anchor effect is enhanced for firm bonding, but the cell characteristics deteriorate
Solution Approach 1:
The invention establishes specific parameter ranges for penetration depth (5 µm or less, or 1-50% of thickness) to optimize the balance between anchor effect and cell performance. This parameter control prevents the harmful effects of excessive penetration while maintaining sufficient bonding strength.
Solution Approach 2:
The conductive bonding layer applies partial penetration rather than full penetration throughout the active material plate. By limiting penetration to specific regions and depths (partial action), the invention achieves the necessary anchor effect for bonding while avoiding the excessive penetration that causes cell characteristic deterioration.
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 approach enhances bonding strength while maintaining cell performance by controlling the penetration depth of the conductive bonding layer, thereby reducing capacity loss and negative electrode swelling.
Implementation Method 1
The active material plate is penetrated by the conductive bonding layer through a surface of the active material plate facing the current collector
Implementation Method 2
The sintered plate is bonded to the positive current collector via a conductive bonding layer
Implementation Method 3
an electrolytic solution with which the positive electrode, the negative electrode, and the separator are impregnated
Data Source
AI summary
In a lithium secondary cell, a positive electrode includes a sheet-like positive current collector having conductivity and a positive active material plate that is a plate-like ceramic sintered body containing a lithium composite oxide. The positive active material plate is bonded to the positive current collector via a conductive bonding layer. The positive active material plate is penetrated by the conductive bonding layer through a surface of the positive active material plate facing the positive current collector. A penetration depth of the conductive bonding layer in the positive active material plate with respect to a direction of superposition is 3% or more and 80% or less of a thickness of the positive active material plate.