Bi-modal Lithium Battery Positive Electrode Active Material
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Solution Overview
Problem
Rechargeable lithium batteries face challenges in achieving high active mass density without fracturing the active material particles during the rolling process, which affects their cycle-life characteristics at both low and high temperatures.
Innovation Solution
A positive electrode is designed with a bi-modal size distribution of active materials, featuring small particle size active materials with an average diameter of 2-4 μm and large particle size active materials with an average diameter of 17-21 μm, each coated with a specific layer, to enhance active mass density and cycle-life characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high active mass density is pursued in the positive electrode, then energy density is improved, but plate fractures and particle cracks occur during the rolling process
Solution Approach 1:
The positive electrode active material is segmented into two distinct particle size ranges: small particles (2-4 μm) and large particles (17-21 μm). This segmentation allows the small particles to fill voids between large particles, increasing active mass density while the larger particles provide structural integrity to withstand rolling pressure without fracturing.
Solution Approach 2:
Different regions of the particle size distribution are assigned different functional roles: small particles (2-4 μm) primarily fill spaces and increase density, while large particles (17-21 μm) primarily provide mechanical strength and structural stability. This local quality differentiation resolves the contradiction between density and strength.
2Quantity of substance
If high active mass density is achieved through rolling process, then energy density is improved, but cycle-life characteristics at low and high temperatures deteriorate
Solution Approach 1:
The bi-modal particle size distribution segments the active material into small (2-4 μm) and large (17-21 μm) particles, allowing the small particles to densely pack and increase active mass density while the larger particles maintain structural integrity during cycling, thereby improving both density and cycle-life characteristics at various temperatures.
3Quantity of substance
If particle size is reduced to increase active mass density, then energy density is improved, but particle strength decreases and fractures increase
Solution Approach 1:
Instead of uniformly reducing particle size, the invention segments particles into two size categories: small particles (2-4 μm) that increase density by filling voids, and large particles (17-21 μm) that maintain structural strength. This segmentation avoids the weakness of uniformly small particles while achieving high density.
Solution Approach 2:
The positive electrode uses a composite structure of two different particle size ranges, combining the density advantages of small particles with the strength advantages of large particles, creating a composite material system that achieves both high active mass density and adequate particle strength.
Data Source
AI summary
The present invention relates to a positive electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same. The positive electrode includes: a current collector; and a positive electrode active material positioned on at least one surface of the active material layer current collector. The positive electrode active material layer includes a small particle size active material having an average particle diameter D50 of 2 μm to 4 μm and a first coating layer positioned at a surface thereof, and a large particle size active material having an average particle diameter D50 of 17 μm to 21 μm and a second coating layer positioned at the surface thereof.