Porous Cathode Active Material for Lower Initial Resistance
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Solution Overview
Problem
Conventional cathode active materials experience increased initial resistance due to the densification of secondary particles during firing, which inhibits Li ion migration and reduces the reactive area.
Innovation Solution
The cathode active material is designed with secondary particles containing 3 to 20 crystallites, each with a maximum Feret diameter of 1 μm or more, and includes open pores with a diameter of 10 nm to 500 nm and a path length to diameter ratio (L/D) of 0.50 or more, enhancing Li ion access and reaction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the secondary particle becomes dense due to particle growth of crystallites during firing, then the structural integrity is improved, but the migration of Li ions is inhibited and the reactive area decreases
Solution Approach 1:
The invention introduces open pores with specific dimensions (opening diameter of 10 nm to 500 nm, path length to diameter ratio L/D of 0.50 or more) within the secondary particle structure. These pores serve as channels for Li ion migration while maintaining the overall structural integrity of the particle. The porous structure resolves the contradiction by providing dedicated pathways that prevent densification from blocking ion transport, thereby reducing initial resistance while preserving structural strength.
Solution Approach 2:
The secondary particle is segmented into multiple crystallites (3 to 20 crystallites) with controlled sizes (maximum Feret diameter of 1 μm or more). This segmentation creates internal interfaces and potential pore spaces between crystallites, which facilitate Li ion migration pathways. The segmented structure prevents complete densification while maintaining structural coherence, thus reducing initial resistance without compromising structural integrity.
2Reliability
If the reactive area increases to reduce initial resistance, then the Li ion migration is improved, but the particle density decreases
Solution Approach 1:
The open pore structure with controlled dimensions (opening diameter of 10 nm to 500 nm) increases the reactive surface area available for Li ion interaction while occupying minimal volume. The pore walls provide additional reactive interfaces without significantly increasing overall particle volume, thus improving initial resistance without causing excessive density reduction.
Solution Approach 2:
The invention utilizes the three-dimensional pore network within the particle, creating pathways that extend through the particle volume. This dimensional approach allows Li ions to access interior regions more efficiently, effectively increasing the reactive area without requiring proportional increases in particle surface area or volume, thereby maintaining particle density.
Data Source
AI summary
A cathode active material includes a secondary particle. The secondary particle includes 3 to 20 crystallites. Each of the crystallites has a maximum Feret diameter of 1 μm or more. Either or both of the crystallite and the secondary particle have an open pore. The open pore has an opening diameter of 10 nm to 500 nm. The relation of “0.50≤L/D” is satisfied. “L” represents the path length of the open pore. “D” represents the maximum Feret diameter of the secondary particle.