Bimodal Positive Electrode Material for Low-Crack Lithium Cathodes
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Solution Overview
Problem
Conventional lithium nickel cobalt manganese oxide positive electrode materials in secondary particle form experience particle breakage and cracking during electrode rolling, leading to degraded life characteristics and increased resistance in lithium secondary batteries.
Innovation Solution
A bimodal positive electrode material comprising large-particle diameter single particles and small-particle diameter pseudo-single particles, where the large-particle diameter material is composed of one nodule and the small-particle diameter material is an aggregate of 2 to 30 nodules, is used to reduce particle cracking and minimize resistance increases during charge and discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium nickel cobalt manganese oxide is used in secondary particle form (aggregated primary particles), then capacity characteristics are improved, but particle breakage and cracking occur during electrode rolling leading to degraded life characteristics
Solution Approach 1:
The invention segments the positive electrode active material into two distinct particle size groups: large particles (10-20 μm) and small particles (3-7 μm). This segmentation allows large particles to maintain structural stability during rolling while small particles fill voids and provide high capacity, resolving the contradiction between capacity and life characteristics.
Solution Approach 2:
The invention applies local quality by creating a bimodal particle size distribution where different regions of the electrode have different particle characteristics. Large particles are distributed throughout to provide structural integrity, while small particles are present to maximize capacity, allowing each region to contribute its optimal properties.
2Strength
If lithium nickel cobalt manganese oxide is used in single particle form, then particle strength is improved preventing cracking during rolling, but lithium mobility decreases leading to increased resistance
Solution Approach 1:
The invention segments particles into two size categories where large particles (10-20 μm) provide the necessary mechanical strength and structural stability to prevent cracking during rolling, while small particles (3-7 μm) maintain high lithium mobility due to their shorter diffusion paths, thus resolving the contradiction between strength and energy loss.
Solution Approach 2:
The invention changes the particle size parameter by creating a bimodal distribution instead of using uniform single particles. This parameter change allows the system to optimize both mechanical strength (through large particles) and lithium mobility (through small particles), preventing the energy loss associated with high resistance in single-particle systems.
3Quantity of substance
If conventional secondary particles with many primary particles are used, then capacity is improved, but particle breakage occurs increasing contact area with electrolyte and causing active material degradation
Solution Approach 1:
The invention segments the particle structure into controlled bimodal sizes (large 10-20 μm and small 3-7 μm) rather than using conventional secondary particles with many aggregated primary particles. This segmentation prevents particle breakage during rolling while maintaining high capacity through the combined surface area of both size groups, thereby reducing active material degradation.
Solution Approach 2:
The invention creates a composite particle system combining large and small particles in specific proportions (70:30 to 80:20 weight ratio). This composite structure provides the mechanical integrity of large particles while incorporating the high surface area of small particles, preventing the harmful effects of particle breakage while maintaining capacity.
Data Source
AI summary
A bimodal positive electrode material includes a large-particle diameter positive electrode active material and a small-particle diameter positive electrode active material, wherein the large-particle diameter positive electrode active material is a single particle composed of one nodule, and the small-particle diameter positive electrode active material is a pseudo-single particle which is an aggregate of 2 to 30 nodules.