Cathode Active Material Balancing Rolling Density and Li-Ion Transport
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Solution Overview
Problem
Conventional small-particle single-particle positive electrode materials for lithium-ion batteries face issues with low rolling density, leading to limited energy density, while increasing particle size deteriorates lithium ion migration and electrochemical properties.
Innovation Solution
A nickel-containing layered lithium transition metal oxide with an average particle diameter of 5 to 8 µm, comprising single and quasi-single particles, and a specific particle diameter change under pressure, along with a controlled BET specific surface area and compaction density, is developed to enhance rolling density and electrochemical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the particle diameter of single particles is increased to enhance electrode energy density, then rolling density is improved, but the migration path of lithium ions becomes longer leading to deterioration in electrochemical properties
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the core region has different composition/structure than the shell region. The core maintains short lithium ion diffusion paths while the shell provides structural stability, allowing each region to optimize for its specific function rather than requiring uniform properties throughout the entire particle
Solution Approach 2:
The patent segments the particle into multiple primary particles that are sintered together to form a larger composite particle. This segmentation allows the overall particle to achieve larger size for better rolling density while each primary particle maintains smaller dimensions for short lithium ion migration paths, effectively dividing the contradiction into manageable scales
2Reliability
If small-particle single particles are used to maintain short lithium ion migration paths, then electrochemical properties are improved, but rolling density is low limiting energy density
Solution Approach 1:
The patent merges multiple primary particles through sintering to form a larger composite particle that functions as a single electrochemical unit. This merging increases the overall particle size and rolling density while maintaining the electrochemical advantages of the constituent primary particles through controlled sintering that preserves internal porosity and diffusion pathways
3Quantity of substance
If secondary particle active materials are used, then particle aggregation occurs, but particle strength is low resulting in cracking and gas generation
Solution Approach 1:
The patent applies preliminary action by pre-sintering the primary particles into a mechanically robust composite structure before final electrode fabrication. This preliminary sintering creates strong inter-particle bonds and a stable framework that prevents cracking during subsequent electrode processing and battery cycling, proactively addressing the strength issue before it manifests as failure
Data Source
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AI summary
The present invention relates to a positive electrode active material for a lithium secondary battery, which is a nickel-containing layered lithium transition metal oxide, wherein the positive electrode active material has an average particle diameter (D50) from 5 to 8 µm, comprises single particles consisting of one primary particle and quasi-single particles having a spherical shape consisting of a plurality of primary particles, and satisfies the following Equation 1: 1.2μm≤D50−D50p≤1.8μm wherein D50 is the average particle diameter (D50) of the positive electrode active material before application of a pressure of 9 tons, and D50p is the average particle diameter (D50) of the positive electrode active material after application of a pressure of 9 tons.