Dual-Layer Electrode Coating with Localized H-NBR for Flexibility
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Solution Overview
Problem
Existing electrodes for lithium secondary batteries face challenges in achieving both strong adhesion to the current collector and flexibility, particularly when using active materials with small particle diameters, which can lead to reduced energy density and productivity issues when attempting to add soft materials for flexibility.
Innovation Solution
The electrode employs a dual-layer structure with a lower layer containing a first active material and a non-rubbery binder, and an upper layer with a second active material, a non-rubbery binder, and a rubbery binder, specifically hydrogenated nitrile butadiene rubber (H-NBR), optimized in weight ratios to enhance flexibility and adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a soft material is added as a binder to improve flexibility, then flexibility is improved, but solid content of slurry is reduced causing degradation of coating productivity
Solution Approach 1:
The electrode active material layer is divided into a lower layer region (without rubbery binder) and an upper layer region (with rubbery binder). This segmentation allows the rubbery binder to be localized only where flexibility is needed, rather than throughout the entire layer, thus maintaining coating productivity while achieving the desired flexibility.
Solution Approach 2:
The rubbery binder is selectively applied to the upper layer region of the electrode active material layer, creating local quality differentiation. The lower layer region maintains high solid content for productivity, while the upper layer region contains the rubbery binder for flexibility, optimizing both properties in their respective zones.
2Reliability
If an excessively small particle diameter active material is used, then electrode performance is improved, but adhesion to current collector is reduced
Solution Approach 1:
The electrode active material layer is formulated as a composite structure containing both small particle diameter active material (for performance) and rubbery binder (for adhesion). The rubbery binder compensates for the poor adhesion of small particles while maintaining their performance benefits, creating a composite material system that achieves both goals.
3Ease of operation
If a large amount of soft material is added to improve flexibility, then flexibility is improved, but electrode thickness increases resulting in decrease in energy density
Solution Approach 1:
The rubbery binder is segmented and confined to the upper layer region only, rather than being distributed throughout the entire electrode active material layer. This reduces the total amount of soft material needed while still achieving the required flexibility, thereby preserving energy density.
Solution Approach 2:
Flexibility is provided locally in the upper layer region where it is most needed for wearable device applications, while the lower layer region maintains higher density. This localized approach to quality differentiation achieves flexibility without the penalty of overall thickness increase and energy density loss.
Data Source
AI summary
An electrode including a current collector; and an electrode active material layer disposed on at least one surface of the current collector is disclosed. The electrode active material layer includes a lower layer region facing the current collector, and an upper layer region facing the lower layer region and extended to the surface of the electrode active material layer. The lower layer region includes a first active material and a first non-rubbery binder and is free from a rubbery binder. The upper layer region includes a second active material, a second non-rubbery binder, and a rubbery binder. The rubbery binder is a hydrogenated nitrile butadiene rubber (H-NBR). Each of the first non-rubbery binder and the second non-rubbery binder includes a polyvinylidene fluoride (PVDF)-based polymer, and the weight ratio of the second non-rubbery binder to the rubbery binder in the upper layer region is 1:0.03-1:0.07.