Bimodal Cathode Active Material with Over-Sintered Fine Particles
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Solution Overview
Problem
Current lithium secondary batteries face challenges in achieving high energy density, thermal stability, and preventing cracks and breakage of positive electrode active materials during rolling, while also reducing gas generation during high-temperature storage.
Innovation Solution
A bimodal positive electrode active material is developed by blending large and small particles, where the small particles are over-sintered to have a crystallite size of 200 nm or more, improving packing density and stability, and the mixture is used in a lithium composite transition metal oxide composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If large particles and small particles are blended to increase rolling density, then energy density is improved, but cracks and breakage of positive electrode active material occur during rolling
Solution Approach 1:
The positive electrode active material is segmented into two distinct particle size ranges: large particles (D50: 8 μm to 30 μm) and small particles (D50: 1 μm to 9 μm). This segmentation allows the large particles to provide structural stability while small particles fill voids to increase rolling density, thereby improving energy density without causing particle breakage during rolling.
Solution Approach 2:
Different regions of the electrode structure are assigned different particle sizes: large particles are distributed throughout to provide mechanical strength and structural integrity, while small particles are concentrated in void spaces to maximize packing density. This local quality differentiation resolves the contradiction between increasing density and maintaining particle stability.
2Productivity
If rolling density is increased by blending large and small particles, then capacity per unit volume is improved, but thermal stability deteriorates
Solution Approach 1:
The particle size distribution parameters are precisely controlled within specific ranges: large particles with D50 of 8-30 μm and small particles with D50 of 1-9 μm. This parameter optimization ensures that the bimodal mixture achieves high rolling density while maintaining thermal stability through the presence of structurally sound large particles that resist thermal degradation.
3Productivity
If small particles are used to increase packing density, then energy density is improved, but particle breakage during rolling increases
Solution Approach 1:
The electrode utilizes a composite particle system combining large particles (D50: 8-30 μm) with small particles (D50: 1-9 μm). The large particles serve as structural scaffolds providing mechanical strength, while small particles fill interstitial voids to maximize packing density. This composite approach enables high energy density without sacrificing particle strength or increasing breakage during rolling.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances energy density, improves high-temperature life characteristics, reduces particle breakage, and decreases gas generation during storage, leading to improved capacity and stability of the secondary battery.
Implementation Method 1
the small particles are over-sintered to have a crystallite size of 200 nm or more
Data Source
AI summary
The present invention relates to a positive electrode active material for a secondary battery which includes a first positive electrode active material and a second positive electrode active material, wherein an average particle diameter (D50) of the first positive electrode active material is twice or more an average particle diameter (D50) of the second positive electrode active material, and the second positive electrode active material has a crystallite size of 200 nm or more.