Flat Lithium Primary Battery Cathode Pellet for Stable Case Contact
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Solution Overview
Problem
Flat lithium primary batteries face challenges in maintaining adequate electrical connection between the positive electrode pellet and the case due to expansion issues, leading to increased internal resistance and reduced discharge capacity, particularly because the positive electrode expands uniformly, causing deformation that disrupts contact at the center more than the circumference.
Innovation Solution
The battery design includes a positive electrode pellet with a circular columnar shape divided into first and second portions, where the second portion has a higher graphite content than the first portion, allowing for controlled expansion that maintains electrical contact between the pellet and the case, thereby reducing internal resistance and enhancing discharge capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the positive electrode pellet is made with uniform composition, then the manufacturing process is simple, but the expansion is uniform causing loss of electrical contact at the center
Solution Approach 1:
The positive electrode pellet is designed with non-uniform graphite content distribution, where the center portion has higher graphite content (5-15 parts by mass per 100 parts positive electrode active material) compared to the outer peripheral portion (3-10 parts by mass per 100 parts positive electrode active material). This local quality variation allows the center to expand more during discharge, maintaining contact with the current collector, while the outer peripheral portion provides structural support.
2Stability of the object's composition
If the positive electrode expands uniformly, then the structural integrity is maintained, but the electrical connection at the center is lost
Solution Approach 1:
The patent creates different expansion characteristics in different regions of the positive electrode pellet by varying graphite content. The center portion with higher graphite content expands more, compensating for the deformation caused by uniform expansion and maintaining electrical contact, while the outer peripheral portion with lower graphite content maintains structural stability.
Solution Approach 2:
The patent introduces asymmetry in the composition distribution of the positive electrode pellet, specifically in the graphite content between the center and outer peripheral portions. This asymmetric composition creates differential expansion behavior that counteracts the harmful effects of uniform mechanical expansion, allowing the center to maintain better contact with the current collector.
3Reliability
If a current collector such as L-shaped ring or expanded metal is added, then the electrical connection is improved, but the volume for electricity generation is reduced
Solution Approach 1:
The patent extracts the function of the additional current collector structure by incorporating the necessary conductive material directly into the positive electrode pellet composition. By adjusting the graphite content distribution within the pellet itself, the patent eliminates the need for separate L-shaped rings or expanded metal current collectors, thereby preserving the volume available for electricity generation while maintaining electrical connection reliability.
Solution Approach 2:
The patent merges the function of the current collector with the positive electrode pellet structure itself. The graphite-containing conductive material in the pellet serves dual purposes: maintaining electrical conductivity and providing the necessary expansion characteristics. This integration eliminates the need for separate current collector components and maximizes the active material volume.
Data Source
AI summary
A flat lithium primary battery includes a case, a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. The positive electrode includes a positive electrode pellet containing positive electrode active material, conductive agent, and binder. The positive electrode pellet has a circular columnar shape having a side circumferential surface extending in a circumferential direction surrounding a center axis extending in a center axis direction. The conductive agent contains graphite. The positive electrode pellet is divided into first and second portions. The first portion includes at least a part of the side circumferential surface of the circular columnar shape. The first portion includes an annular portion surrounding at least a part of the second portion. A content of the graphite in the second portion of the positive electrode pellet is higher than in the first portion of the positive electrode pellet.