Positive Electrode Roughness Layout for Brittle Fracture Control
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Solution Overview
Problem
Highly compacted lithium-ion battery positive electrodes are prone to brittle fracture due to active material embedding in the current collector during the cold pressing process, leading to performance loss.
Innovation Solution
The electrochemical device features a current collector with a first region coated with a positive electrode mixture layer and a foil-free second region, where the surface roughness and strength ratios are controlled to reduce damage and enhance flexibility, along with a binder with specific molecular weight and swelling properties to improve binding performance and compacted density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the compacted density of the positive electrode is increased to improve energy density, then the energy density is improved, but the active material particles embed in the current collector during cold pressing, causing damage and brittle fracture
Solution Approach 1:
The current collector is designed with different surface roughness characteristics in different regions: the first region has higher roughness (Sa1) to prevent active material embedding and damage, while the second region has lower roughness (Sa2) to maintain good electrical contact. The roughness ratio Sa1/Sa2 is controlled within 1-20, preferably 10-14, creating localized quality differences that resolve the contradiction between high compacted density and structural integrity.
2Quantity of substance
If the compacted density of the positive electrode is increased to improve energy density, then the energy density is improved, but the positive electrode becomes prone to brittle fracture
Solution Approach 1:
Different regions of the current collector are designed with different surface roughness to create localized mechanical properties that prevent brittle fracture while maintaining high compacted density. The first region's higher roughness provides mechanical cushioning that prevents catastrophic failure, while the overall structure maintains high density for energy density improvement.
Solution Approach 2:
The increased surface roughness in the first region acts as a pre-designed cushioning structure that absorbs stress and prevents active material embedding before damage occurs. This beforehand cushioning prevents the brittle fracture that would otherwise occur during cold pressing at high compacted densities.
3Ease of operation
If the surface roughness of the current collector is increased to prevent active material embedding, then the flexibility is improved, but the manufacturing precision becomes more difficult to control
Solution Approach 1:
The invention specifies a quantitative range for the roughness ratio Sa1/Sa2 (1-20, preferably 10-14) that balances flexibility improvement with manufacturing controllability. This parameter change approach provides clear manufacturing targets while achieving the desired flexibility enhancement without excessive difficulty in controlling the roughness characteristics.
Data Source
AI summary
A positive electrode includes a current collector and a positive electrode mixture layer provided on at least one surface of the current collector, the current collector includes a first region and a second region, the first region is coated with the positive electrode mixture layer, the second region is a foil-free region of the positive electrode, the positive electrode mixture layer includes a positive electrode active material and a binder, and a roughness Sa1 of a surface of a current collector of the first region and a roughness Sa2 of a surface of a current collector of the second region satisfy: 1≤Sa1/Sa2≤20. The positive electrode of the present application has a high compacted density and toughness, thereby improving the problem of brittle fracture of the positive electrode and improving the rate capability of a lithium-ion battery.