Bimodal Cathode Active Material for Lithium Secondary Battery
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Solution Overview
Problem
Conventional lithium nickel cobalt manganese oxide positive electrode active materials face issues with particle breakage and cracking during manufacturing and charging/discharging processes, leading to increased gas generation and reduced lifespan and output characteristics due to enhanced contact with electrolyte.
Innovation Solution
A bimodal positive electrode active material comprising lithium nickel-based transition metal oxides with large and small particle diameters, where the large particles are secondary aggregates and small particles are single or quasi-single particles, with a specific B value ratio, to minimize particle breakage and improve rolling density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional lithium nickel cobalt manganese oxide is used in the form of spherical secondary particles with tens to hundreds of primary particles aggregated, then the capacity characteristics are improved, but particle breakage and cracks occur during rolling and charging/discharging processes
Solution Approach 1:
The patent divides the particle structure into two distinct size populations: small particles (D50: 3-8 μm) that maintain structural integrity and resist breakage, and large particles (D50: 15-30 μm) that provide high capacity. This segmentation allows each particle size to fulfill its specific function optimally while reducing overall particle breakage during processing.
Solution Approach 2:
The patent creates a composite particle size distribution system where small and large particles coexist in a specific ratio (30-70 wt% small particles, 70-30 wt% large particles). This composite structure combines the advantages of both size ranges: small particles provide structural stability and resistance to breakage, while large particles contribute to high capacity characteristics.
2Area of stationary object
If particles are broken or cracked, then the contact area with electrolyte increases, but this leads to increased gas generation and deterioration of active material
Solution Approach 1:
The patent employs small particles as a protective matrix that surrounds and cushions large particles during rolling and charging/discharging processes. This beforehand cushioning prevents mechanical stress from concentrating on large particles, thereby preventing cracks and breakage that would otherwise increase harmful electrolyte contact and gas generation.
Solution Approach 2:
The patent changes the particle size parameter by introducing a bimodal distribution with specific size ranges. This parameter change ensures that small particles absorb mechanical stress and prevent crack propagation, thereby controlling the contact area with electrolyte and reducing gas generation and side reactions.
3Volume of stationary object
If a bimodal positive electrode active material is applied to improve energy density, then the rolling density is enhanced, but particle breakage and cracks may still occur
Solution Approach 1:
The patent optimizes the particle size parameters by defining specific ranges: small particles with D50 of 3-8 μm and large particles with D50 of 15-30 μm, with a controlled B value of 0.3-0.7. These parameter changes enable high rolling density while maintaining structural integrity by ensuring small particles provide sufficient cushioning support.
Solution Approach 2:
The patent creates a composite bimodal particle system with optimized weight ratios (30-70 wt% small particles, 70-30 wt% large particles). This composite structure achieves high rolling density through efficient space utilization while the small particles maintain structural integrity of large particles during processing.
Data Source
AI summary
The present invention relates to a positive electrode active material including: a lithium nickel-based transition metal oxide with a large particle diameter and a lithium nickel-based transition metal oxide with a small particle diameter, wherein the lithium nickel-based transition metal oxide with a large particle diameter is in the form of a secondary particle that is an aggregate of primary particles, and the lithium nickel-based transition metal oxide with a small particle diameter is in the form of at least one of a single particle formed of one nodule and a quasi-single particle that is a composite of 30 or less nodules, wherein the volume cumulative particle size distribution graph obtained from particle size analysis (PSD) of the positive electrode active material includes a peak PS on a side with the small particle size and a peak PL on a side with the large particle size, and wherein a B value derived from Equation 1 below is 4.0 to 17.0. The positive electrode active material is applied to a positive electrode to provide a lithium secondary battery in which the breakage of the positive electrode active material particles is suppressed, thereby improving lifespan and output characteristics, and reducing the amount of gas generated. B=Dmax−DL/DS−Dmin wherein Dmax is the maximum particle diameter of the positive electrode active material, Dmin is the minimum particle diameter of the positive electrode active material, DL is the median particle diameter of the peak PL, and DS is the median particle diameter of the peak PS.