Positive Electrode Active Material Balancing Density and Stability
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Solution Overview
Problem
High nickel positive electrode active materials experience structural degradation and volume changes during charge and discharge, leading to cracks and reduced conductivity, which degrade battery life and increase resistance, while conventional secondary particles face issues with non-uniform particle diameters and poor specific surface area.
Innovation Solution
A positive electrode active material is developed with secondary particles formed by aggregating primary particles of 1.5 µm to 5.0 µm, containing a lithium transition metal composite oxide with 60 mol% nickel, and a rolling density of 3.60 g/cm³, which includes a recovery method for the layered structure from a rock salt structure formed by high heat treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If high nickel positive electrode active material is used to improve capacity characteristics, then energy density is improved, but structural degradation and volume change occur during charge and discharge leading to cracks and reduced conductivity
Solution Approach 1:
The positive electrode active material is divided into primary particles (submicron level, <1 μm) that aggregate to form secondary particles (micron level, 1-10 μm). This segmentation allows the high nickel content material to maintain structural stability through the aggregated structure, where each primary particle can undergo volume change independently while the overall secondary particle structure maintains integrity, preventing crack formation and maintaining conductivity.
2Reliability
If secondary particle structure with micron-level primary particles is adopted to improve rolling density and reduce cracks, then structural stability is improved, but heat treatment temperature must be increased which causes layered structure degradation into rock salt structure
Solution Approach 1:
The patent optimizes the heat treatment temperature parameter to a specific range (900-1000°C) that is sufficient to sinter the submicron primary particles into micron-level secondary particles with good rolling density, but not so high as to cause complete degradation of the layered structure into rock salt structure. This precise parameter control maintains the balance between structural stability and crystallinity.
3Reliability
If primary particle diameter is increased to micron level to minimize rolling cracks, then rolling density is improved, but specific surface area decreases leading to poor cell resistance characteristics
Solution Approach 1:
The patent transitions from conventional single-size particles to a hierarchical size distribution system, where submicron primary particles (providing high specific surface area) aggregate into micron-level secondary particles (providing good rolling density). This dimensional hierarchy allows both small particles to maintain surface area and larger aggregates to improve packing, resolving the contradiction between rolling density and specific surface area.
Data Source
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AI summary
The present invention relates to a positive electrode active material, and to a positive electrode active material which may simultaneously solve a problem of a conventional secondary particle and a problem of a single particle, wherein the positive electrode active material may improve energy density through excellent density characteristics as well as cell characteristics, such as improved lifetime and reduced gas generation amount of a lithium secondary battery, by including a particle, such as a conventional single particles, as a primary particle and including a secondary particle that is formed by aggregation of a plurality of primary particles, and a positive electrode and a lithium secondary battery which include the same.