Core-Shell Cathode Material Balancing Porosity and Particle Strength
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Solution Overview
Problem
Existing lithium-metal composite oxides with high porosity or complex structures suffer from reduced particle strength and insufficient durability, compromising battery performance.
Innovation Solution
A lithium-metal composite oxide with a core-shell structure is developed, where the core has a porous structure with 20-60% porosity and the shell has a solid structure with 5% or less porosity, maintaining overall porosity between 10-50%, enhancing particle strength to 10-50 MPa.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a lithium-metal composite oxide with high porosity or complex structure is used to improve battery characteristics, then battery performance is enhanced, but particle strength is reduced and durability is insufficient
Solution Approach 1:
The particle is segmented into distinct functional zones: a porous core region (5-45% porosity) for electrochemical activity and a dense shell section (0-20% porosity) for mechanical strength. This segmentation allows each region to optimize its function independently, resolving the contradiction between porosity-driven performance and density-driven strength.
Solution Approach 2:
Different regions of the particle are assigned different porosity characteristics: the core has higher porosity (5-45%) to enhance electrolyte penetration and lithium ion diffusion, while the shell has lower porosity (0-20%) to provide mechanical strength and structural stability. This local differentiation of properties resolves the contradiction between overall porosity benefits and particle strength requirements.
2Productivity
If porosity is increased to improve electrolyte penetration and lithium ion diffusion, then reaction resistance is reduced, but particle structural stability deteriorates
Solution Approach 1:
The particle structure is divided into a porous core zone for high reaction activity and a dense shell zone for structural stability. The core porosity (5-45%) facilitates rapid electrolyte penetration and lithium ion diffusion, while the shell porosity (0-20%) maintains structural integrity during charge-discharge cycles, resolving the contradiction between reaction rate and structural stability.
Solution Approach 2:
The particle functions as a composite structure combining high-porosity and low-porosity regions within a single material phase. This internal composite architecture enables simultaneous achievement of high reaction productivity in the core and structural stability in the shell, resolving the contradiction between these opposing requirements.
Data Source
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AI summary
Provided is a positive electrode active material for a lithium ion secondary battery excellent in particle strength while maintaining favorable battery characteristics. The positive electrode active material for a lithium ion secondary battery includes a lithium-metal composite oxide composed of secondary particles formed by aggregation of primary particles or both the primary particles and the secondary particles. The lithium-metal composite oxide contains lithium, nickel, manganese, and cobalt. The lithium-metal composite oxide has a particle strength of 10 to 50 MPa. The secondary particles each include a core occupying an inside of the particle and a shell section surrounding the core and covering its outside. When the cross section of the secondary particle is observed by imaging, the secondary particle has the conditions of: (a) the core having the porous structure with a porosity of 20 to 60%; (b) the shell section having the solid structure with a porosity of 5% or less; and (c) an overall porosity of the secondary particle of 10 to 50%.