Positive Electrode Sheet Particle Grading for Thick Battery Plate Safety
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Solution Overview
Problem
The increase in energy density of secondary batteries leads to safety issues due to brittle failure of the electrode plates, which can cause short circuits and battery safety problems.
Innovation Solution
A positive electrode plate design with a first region having a uniform particle distribution index and a second region with size gradation, enhancing flexibility and compaction density, while using a reduced binder content in the first region to improve safety and energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the energy density of secondary batteries is increased, then the volumetric energy density is improved, but the safety performance deteriorates due to brittle failure of the electrode plate
Solution Approach 1:
The positive electrode film layer is divided into two distinct regions: a first region adjacent to the current collector with uniform particle distribution (PDI 0.05-0.52) for flexibility, and a second region at the outer surface with graded particle distribution (PDI 0.60-0.82) for high compaction density. This segmentation allows each region to fulfill different functional requirements, resolving the contradiction between safety and energy density.
Solution Approach 2:
Different particle distribution characteristics are applied to different locations within the positive electrode film layer. The first region near the current collector has uniform particle distribution to maintain flexibility and prevent brittle failure, while the second region at the outer surface has graded particle distribution to maximize compaction density and energy density. This local differentiation resolves the contradiction by optimizing each location for its specific function.
2Quantity of substance
If the compaction density of the positive electrode plate is increased, then the volumetric energy density is improved, but the flexibility deteriorates leading to brittle failure
Solution Approach 1:
The positive electrode film layer is segmented into two regions with different particle distribution characteristics. The first region has uniform particle distribution (PDI 0.05-0.52) that maintains flexibility and prevents brittle failure during bending operations. The second region has graded particle distribution (PDI 0.60-0.82) that achieves high compaction density. This segmentation resolves the contradiction by allowing each region to optimize for its primary function.
Solution Approach 2:
Uniform particle distribution is applied locally in the first region adjacent to the current collector to ensure flexibility, while graded particle distribution is applied locally in the second region at the outer surface to maximize compaction density. This local quality differentiation allows the electrode plate to simultaneously achieve both flexibility and high compaction density without brittle failure.
Data Source
Figure 1~2
Figure 3(A)~3(B)
Figure 4~6
AI summary
A positive electrode sheet, a secondary battery, and an electric device. The positive electrode sheet comprises a current collector and a positive electrode film layer located on at least one side of the current collector; the positive electrode film layer comprises a first area and a second area; the particle size distribution index of an active material in the first area is smaller than the particle size distribution index of an active material in the second area, wherein the particle size distribution index is the ratio of the standard deviation of the particle size of an active material to the average particle size thereof, the first area is an area where the positive electrode film layer extends vertically from the surface on the side close to the current collector to the positive electrode film layer within a distance h1, the second area is an area where the positive electrode film layer extends vertically from the surface on the side close to the current collector to the positive electrode film layer with a distance from h1 to H, and H is the thickness of the positive electrode film layer, and h 1 is less than H.