Macro-Particle Cathode Structure for Thermal Stability and Low Resistance
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Solution Overview
Problem
Conventional nickel-based lithium transition metal oxide positive electrode active materials in lithium secondary batteries face issues with thermal stability, lifespan reduction, and increased resistance due to their secondary particle structure formed by agglomeration of primary micro particles, which leads to gas generation and output performance degradation.
Innovation Solution
A nickel-based lithium transition metal oxide positive electrode active material is developed in the form of secondary particles formed by agglomeration of primary macro particles with a coating layer of lithium-metal oxide, where the primary particles have a larger average size and crystal size, reducing the interface and minimizing the washing process to maintain low resistance and improved output characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional nickel-based lithium transition metal oxide is used in the form of secondary particles formed by agglomeration of primary micro particles, then high capacity can be achieved, but thermal stability deteriorates and particle cracking occurs during rolling
Solution Approach 1:
The invention divides the secondary particle into multiple primary macro particles (0.5-3 μm) as building blocks. This segmentation approach maintains the high capacity advantage of secondary particles while reducing the specific surface area compared to primary micro particles, thereby improving thermal stability and reducing particle cracking during electrode manufacturing
Solution Approach 2:
The invention changes the particle size parameter from conventional primary micro particles to primary macro particles with D50 of 0.5-3 μm. This parameter change reduces the specific surface area, minimizing side reactions and improving thermal stability while maintaining high capacity through the secondary particle structure
2Object-generated harmful factors
If washing process is applied to reduce lithium impurities, then gas generation is reduced, but surface damage occurs and lifespan is reduced
Solution Approach 1:
The invention performs preliminary action by controlling the synthesis process to minimize lithium impurity formation from the beginning, and by using primary macro particles that are less susceptible to surface damage. This eliminates the need for aggressive washing processes that would damage the surface and reduce lifespan
Solution Approach 2:
The invention accepts low levels of lithium impurities that do not require expensive or damaging washing processes to remove. The primary macro particle structure is robust enough to handle minimal impurities without requiring intensive surface treatment, thus avoiding lifespan reduction
3Reliability
If primary macro particles with large size are used to form secondary particles, then thermal stability is improved, but output performance may be reduced due to intrinsic low conductivity
Solution Approach 1:
The invention creates a composite structure where primary macro particles are agglomerated into secondary particles with controlled morphology. This composite approach combines the thermal stability benefits of larger particles with enhanced output performance through optimized secondary particle structure that facilitates electron and ion transport
Solution Approach 2:
The invention transitions from considering only primary particle size to optimizing the secondary particle structure formed by agglomeration. This dimensional change allows simultaneous achievement of thermal stability (through primary macro particle size) and output performance (through secondary particle morphology and arrangement)
Data Source
AI summary
A positive electrode active material for a lithium secondary battery includes a secondary particle having an average particle size (D50) of 1 to 10 μm formed by agglomeration of at least two primary macro particles having an average particle size (D50) of 0.5 to 3 μm; and a coating layer of lithium-metal oxide formed on a surface of the secondary particle. The primary macro particle is represented by LiaNi1-b-c-dCobMncQdO2+δ, wherein 1.0≤a≤1.5, 0<b<0.2, 0<c<0.2, 0≤d≤0.1, 0<b+c+d≤0.2, −0.1≤δ≤1.0, Q is at least one type of metal selected from the group consisting of Al, Mg, V, Ti and Zr. The metal of the lithium-metal oxide is at least one type of metal selected from the group consisting of manganese, nickel, vanadium and cobalt, and an amount of lithium impurities is 0.25 weight % or less.