NCM Cathode Particle Distribution for Thermal Stability and Density
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Solution Overview
Problem
Lithium-nickel-metal composite oxides exhibit low thermal stability due to the release of lithium and oxygen from the crystal structure during charging, leading to instability at elevated temperatures.
Innovation Solution
A nickel-cobalt-manganese-based positive electrode active material is developed, comprising large and small particle groups with specific particle sizes and crystallite sizes, controlled through calcination conditions, to enhance thermal stability and volumetric energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium-nickel-metal composite oxide is used as positive electrode active material, then high capacity is achieved, but thermal stability deteriorates due to lithium and oxygen release from crystal structure during charging
Solution Approach 1:
The positive electrode active material is divided into two distinct particle groups: a large particle group with average particle size D50 of 12 to 20 μm and a small particle group with average particle size D50 of less than 12 μm. This segmentation allows the large particles to provide high capacity while the small particles enhance thermal stability, resolving the contradiction between capacity and thermal stability.
Solution Approach 2:
Different regions of the particle size distribution are assigned different functional roles. The large particle group primarily contributes to high capacity, while the small particle group specifically addresses thermal stability. This local quality differentiation allows each particle group to optimize its function without compromising the other.
2Volume of moving object
If small particle size is used to improve packing density, then volumetric energy density increases, but thermal stability may deteriorate due to higher surface area to volume ratio
Solution Approach 1:
The particle size distribution is segmented into two groups where the small particle group (D50 < 12 μm) improves packing density and volumetric energy density, while the large particle group (D50 = 12 to 20 μm) maintains thermal stability. This segmentation resolves the contradiction by distributing different functions across different particle sizes.
3Reliability
If polycrystal aggregate structure is used to control crystallite orientation, then thermal stability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent specifies precise parameter ranges for the polycrystal aggregate particles: primary particle size of 2.0 μm or less, crystallite size of (003) plane of 950 to 1210 Å, crystallite size of (104) plane of 500 to 750 Å, and peak intensity ratio I(003)/I(104) of 2.10 or less. By defining these specific parameter ranges, the patent balances thermal stability improvement with achievable manufacturing precision.
Data Source
AI summary
The present disclosure relates to a nickel-cobalt-manganese-based positive electrode active material comprising a large particle group and a small particle group. An average particle size D50 of the large particle group is greater than an average particle size D50 of the small particle group; the average particle size D50 of the large particle group is from 12 to 20 µm; the large particle group includes polycrystal aggregate particles; each polycrystal aggregate particle includes a secondary particle consisting of a plurality of primary particles aggregated together; each polycrystal aggregate particle has a primary particle size of 2.0 µm or less; a crystallite size of a (003) plane of each polycrystal aggregate particle is from 950 to 1210 Å; a crystallite size of a (104) plane of each polycrystal aggregate particle is from 500 to 750 Å; and a peak intensity ratio I(003)/I(104) of the polycrystal aggregate particles is 2.10 or less.