Cathode Active Material Structure to Minimize Rolling Cracks
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Solution Overview
Problem
Conventional lithium secondary battery positive electrode active materials, such as NCM based lithium composite transition metal oxides, suffer from particle cracking during the rolling process due to their secondary particle structure, leading to poor cycling performance and low stability, especially in high-Ni variants which have low structural and chemical stability.
Innovation Solution
A positive electrode active material comprising secondary particles formed by agglomeration of primary macro particles with an average size of 2 μm or more, a crystal density of 4.74 or more, and a specific ratio of particle size to crystal size, which are synthesized using a method involving primary and secondary sintering to enhance stability and resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional NCM based lithium composite transition metal oxide is used with secondary particle structure, then high capacity can be achieved, but particle cracking occurs during rolling process leading to poor cycling performance and low stability
Solution Approach 1:
The invention segments the positive electrode active material into primary particles (0.5-5 μm) that agglomerate to form secondary particles (3-10 μm). This segmentation allows the primary particles to maintain structural integrity during rolling while the secondary particles provide the necessary capacity, resolving the contradiction between capacity and stability.
2Quantity of substance
If high-Ni NCM based lithium composite transition metal oxide is used, then high capacity is achieved, but structural and chemical stability deteriorates and thermal stability becomes difficult to ensure
Solution Approach 1:
The invention applies local quality by creating a core-shell structure where the inner core contains high-Ni NCM material for high capacity, while the outer shell contains low-Ni NCM material with superior structural and chemical stability. This allows the high-capacity material to benefit from the stabilizing effect of the low-Ni shell, resolving the contradiction between capacity and stability.
3Ease of manufacture
If secondary particle structure with small primary particles is used, then conventional electrode manufacturing can be achieved, but particle cracking occurs during rolling process
Solution Approach 1:
The invention changes the critical parameter of primary particle size from conventional small sizes to 0.5-5 μm, which provides sufficient rigidity to prevent cracking during rolling while maintaining manufacturability. This parameter change resolves the contradiction between ease of manufacture and particle strength.
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
The solution provides improved resistance and life characteristics by minimizing particle cracking and ensuring stable lithium ion movement, resulting in enhanced performance of lithium secondary batteries.
Implementation Method 1
a method for preparing the same involving primary and secondary sintering
Data Source
AI summary
A positive electrode active material including at least one secondary particle comprising an agglomerate of primary macro particles is provided. A method for preparing the same and a lithium secondary battery containing the same are also provided. The positive electrode active material contains secondary particle with improved resistance by simultaneous growth of the average particle size D50 and the crystal size of the primary macro particle. The positive electrode active material has high crystal density and improved life and resistance characteristics by ensuring the movement path of lithium ions and minimizing defects in the crystal structure of the positive electrode active material.