Olivine Cathode Material Balancing Conductivity and Pellet Density
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Solution Overview
Problem
Current cathode materials for lithium ion secondary batteries do not adequately enhance high-rate performance, as they face challenges in balancing lithium ion conductivity, electron conductivity, and pellet density.
Innovation Solution
A cathode material comprising secondary particles with a lithium transition metal compound having an olivine structure, a specific carbon content, and a controlled crystallite size, along with a targeted specific surface area, is developed to improve high-rate performance by optimizing lithium ion migration and electron conductivity while maintaining pellet density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbon content is increased to improve electron conductivity, then high-rate performance improves, but pellet density deteriorates
Solution Approach 1:
The patent optimizes the carbon content parameter to a specific range (0.5-1.8% by mass) to achieve the best balance between electron conductivity and pellet density. This parameter optimization resolves the contradiction by finding the optimal point where carbon provides sufficient conductivity without excessive volume occupation that would reduce density.
Solution Approach 2:
The patent creates a composite structure where carbon is adhered to the surface of primary particles containing lithium transition metal compound. This composite approach allows carbon to provide electron conductivity pathways while the lithium transition metal compound core maintains the active material density, thus resolving the contradiction between conductivity enhancement and density maintenance.
2Reliability
If crystallite size is reduced to improve lithium ion conductivity, then high-rate performance improves, but specific surface area increases
Solution Approach 1:
The patent optimizes the crystallite size parameter to a specific range (50-70 nm) to achieve the best balance between lithium ion conductivity and specific surface area. This parameter optimization resolves the contradiction by finding the optimal point where crystallite size is small enough for good ion conductivity but not so small that excessive surface area causes other performance issues.
3Reliability
If carbon coating is applied to improve electron conductivity, then high-rate performance improves, but lithium ion migration distance increases
Solution Approach 1:
The patent applies carbon coating locally on the surface of primary particles rather than as a thick uniform layer. This local quality approach allows carbon to provide electron conductivity at the particle surface where it is most needed, while keeping the coating thin enough to not significantly increase the lithium ion migration distance through the material.
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 cathode material achieves enhanced high-rate performance and increased capacity density under high-rate conditions without compromising filling property or pellet density, as demonstrated by improved 5C capacity density and pellet density values.
Implementation Method 1
carbon adhering to a surface of the primary particles
Implementation Method 2
lithium ion conductivity
Data Source
AI summary
Provided is a cathode material that can further improve the high-rate performance in a lithium ion secondary battery. The cathode material inculeds secondary particles comprising: primary particles containing a lithium transition metal compound having an olivine structure; and carbon adhering to the surfaces of the primary particles, a plurality of which primary particles are aggregated. The content of the carbon is more than 0.5% by mass and 1.8% by mass or less with respect to the cathode material. The lithium transition metal compound has a crystallite size that is 50 nm to 70 nm. The cathode material has a specific surface area that is 14 m2/g to 45 m2/g.