Cathode Active Material Particle Size Control for Battery Stability
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Solution Overview
Problem
Nickel-based lithium transition metal oxides used in cathodes for lithium secondary batteries have low discharge capacity and stability issues, especially at high voltages, due to low mixture density and thermal instability.
Innovation Solution
A cathode active material comprising secondary particles with specific size ranges and a method of preparing nickel-based lithium transition metal oxides through heat treatment processes to enhance mixture density, crystallinity, and stability, including adjusting the size of primary and secondary particles and controlling the weight ratio of lithium to transition metals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If nickel-based lithium transition metal oxides are used to provide high discharge capacity per unit weight, then the discharge capacity per unit weight is improved, but the mixture density and discharge capacity per unit volume deteriorate
Solution Approach 1:
The cathode active material is divided into primary particles (3-6 μm) that aggregate to form secondary particles (10-20 μm). This segmentation allows optimization of both weight-based and volume-based capacity by creating a hierarchical structure where smaller primary particles provide high surface area for lithium insertion while larger secondary particles improve packing density in the cathode mixture.
2Quantity of substance
If nickel-based lithium transition metal oxides are used to achieve high discharge capacity, then the discharge capacity is improved, but the thermal stability and battery stability at high voltage deteriorate
Solution Approach 1:
The particle size parameters are precisely controlled with primary particles in the 3-6 μm range and secondary particles in the 10-20 μm range. This parameter optimization reduces surface area to volume ratio, minimizing thermal runaway risk while maintaining high discharge capacity. The specific particle size distribution also improves electrochemical stability at high operating voltages.
3Volume of stationary object
If the particle size of cathode active material is increased to improve mixture density, then the mixture density is improved, but the discharge capacity per unit weight may deteriorate
Solution Approach 1:
The cathode active material employs a nested structure where multiple primary particles (3-6 μm) are aggregated within each secondary particle (10-20 μm). This nested arrangement allows the material to achieve high mixture density through compact secondary particle packing while maintaining high discharge capacity per unit weight through the cumulative effect of numerous high-capacity primary particles within each secondary particle.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The approach results in a lithium secondary battery with improved high-voltage stability, reduced gas generation, and increased reliability and safety by enhancing mixture density and crystallinity of the cathode active material.
Implementation Method 1
performing a first heat treatment on a nickel-based transition metal hydroxide precursor at a temperature in a range from about 400° C. to about 600° C.
Implementation Method 2
performing a second heat treatment thereon at a temperature of 1,000° C. to about 1,050° C.
Data Source
AI summary
A cathode active material including at least two agglomerates of primary particles and a cathode and a lithium secondary battery containing the same are disclosed. In the cathode active material, a secondary particle includes a nickel-based lithium transition metal oxide, an average particle diameter of each primary particle is in a range from about 2 to about 3 μm, and an average particle diameter of the secondary particle is in a range from about 5 to about 8 μm.