Positive Electrode Binder Distribution for Battery Winding Stress
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Solution Overview
Problem
High active material density in non-aqueous electrolyte secondary battery positive electrodes leads to breakage during winding due to stress, as existing solutions either reduce active material content, compromise current-collecting ability, or fail to balance capacity and adhesion effectively.
Innovation Solution
A positive electrode with a binder distribution having a first maximum point near the current collector, a minimum point in the center, and a second maximum point further away, with specific binder ratios and thicknesses to manage stress and adhesion, ensuring high active material density without excessive breakage or deterioration in current-collecting ability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If positive electrode active material particles are densely packed to increase active material density, then battery capacity is improved, but the positive electrode becomes prone to breakage during winding due to stress
Solution Approach 1:
The binder concentration is varied locally across the positive electrode material mixture layer. The concentration is higher near the current collector and lower toward the outer surface, creating different mechanical properties in different regions. This gradient structure allows the inner region to provide strong adhesion to the current collector while the outer region accommodates stress during winding, thereby preventing breakage while maintaining high active material density
Solution Approach 2:
The invention changes the concentration parameter of the binder across the thickness of the positive electrode material mixture layer. By controlling the binder concentration to be 50 to 90% of the concentration near the current collector in the center region, the mechanical properties are optimized to balance adhesion strength and stress resistance, enabling high active material density without breakage during winding
2Strength
If binder concentration is reduced in the center area to suppress breakage, then winding stress is reduced, but adhesion between current collector and electrode material may deteriorate
Solution Approach 1:
The binder concentration is made non-uniform across the positive electrode material mixture layer, with higher concentration near the current collector and lower concentration in the center and outer regions. This local variation ensures strong adhesion at the current collector interface while reducing stress in the bulk material during winding
Solution Approach 2:
The binder concentration parameter is precisely controlled to be 50 to 90% of the concentration near the current collector in the center area. This specific range maintains sufficient adhesion strength while effectively suppressing breakage during winding
Data Source
AI summary
Disclosed is a positive electrode for non-aqueous electrolyte secondary batteries, the positive electrode including a positive electrode material mixture layer which includes positive electrode active material particles and a binder. A curve representing a correlation between a distance from a current collector in the thickness direction of the positive electrode material mixture layer and an amount of the binder has a first maximum point, a minimum point, and a second maximum point. The minimum point corresponds to a position in a center area of the positive electrode material mixture layer in a thickness direction thereof, and the first and second maximum points correspond to a position nearer the current collector and a position further away from the current collector than the position corresponding to the minimum point, respectively. A ratio W1/W2 of an amount W1 at the first maximum point to an amount W2 at the minimum point of the binder per 100 parts by weight of the positive electrode active material particles is greater than 2.