Cobalt-Gradient Cathode Material for Crack-Resistant Li-Ion Batteries
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Solution Overview
Problem
Lithium composite oxides used in positive electrode active materials for lithium secondary batteries face issues with volume change and stress during charging and discharging, leading to particle damage, such as cracks and structural changes, which affect stability and reliability.
Innovation Solution
A lithium composite oxide with a concentration gradient of cobalt that decreases from the surface to the central portion, having different slopes with the same sign, and a coating layer covering the interface between primary particles, enhances particle stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a lithium composite oxide with high nickel content is used to increase energy capacity, then the energy density is improved, but the particle stability and structural integrity deteriorate due to cation mixing and volume changes during charging and discharging
Solution Approach 1:
The patent applies local quality by creating a non-uniform cobalt concentration distribution within the lithium composite oxide particles. The cobalt concentration is higher at the surface portion and lower at the central portion, forming distinct regions with different functional properties. The surface region with higher cobalt content provides structural stability and protects against particle degradation, while the central region with lower cobalt content maintains high nickel content for energy density. This spatial variation in composition resolves the contradiction between energy density and particle stability.
Solution Approach 2:
The patent employs composite materials by combining nickel and cobalt in a specific spatial arrangement within the lithium composite oxide structure. The material consists of multiple phases or regions: a surface layer enriched with cobalt (forming a protective shell) and a core region with higher nickel content. This composite structure leverages the advantages of both elements - cobalt's structural stability at the surface and nickel's high capacity in the interior - thereby achieving both high energy density and particle stability.
2Ease of manufacture
If the cobalt concentration is uniformly distributed throughout the lithium composite oxide, then the manufacturing process is simplified, but the particle stability at both surface and central portions deteriorates under repeated charging and discharging stress
Solution Approach 1:
The patent implements local quality by establishing a non-uniform cobalt concentration profile within the lithium composite oxide particles. The cobalt concentration varies spatially, being higher at the surface portion and lower at the central portion. This creates functionally distinct regions: the cobalt-rich surface layer provides structural reinforcement and protects against particle degradation during charging/discharging cycles, while the cobalt-poor core maintains high nickel content for capacity. This spatially differentiated composition resolves the contradiction between manufacturing simplicity and particle stability.
3Productivity
If the lithium composite oxide particles undergo volume change during charging and discharging, then the electrochemical activity is maintained, but cracks and structural collapse occur due to accumulated stress
Solution Approach 1:
The patent applies parameter changes by modifying the compositional parameters of the lithium composite oxide - specifically, the spatial distribution of cobalt concentration. By creating a gradient where cobalt concentration decreases from the surface toward the center, the material's physical and chemical properties are optimized: the surface region's higher cobalt content provides structural rigidity and stress resistance, while the core region's lower cobalt content maintains electrochemical activity. This parameter modification resolves the contradiction between maintaining electrochemical activity and preserving structural integrity during volume changes.
Data Source
AI summary
The present invention relates to a positive electrode active material and a lithium secondary battery including the same, and more particularly, to a positive electrode active material including a lithium composite oxide containing at least nickel and cobalt, wherein since the cobalt in the lithium composite oxide has a concentration gradient having at least different slopes from a surface portion toward a central portion, it is possible to improve the stability of particles not only in a surface portion of the lithium composite oxide but also in a central portion thereof, a positive electrode including the positive electrode active material, and a lithium secondary battery using the negative electrode.