Cathode Active Material Particle Mixing to Suppress Ni/Mn Dissolution
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Solution Overview
Problem
Non-aqueous electrolyte secondary batteries face challenges in achieving high capacity, good cyclic characteristics, and high rate discharge characteristics while minimizing the dissolution of Ni and Mn from the positive electrode active material, which can lead to increased resistance and reliability issues.
Innovation Solution
A positive electrode active material comprising Ni-containing lithium composite oxides with specific particle size and composition ratios, where Ni-containing lithium composite oxide a has a larger primary particle size and smaller secondary particle size, and Ni-containing lithium composite oxide b has a smaller primary particle size and larger secondary particle size, is used, incorporating Mn, B, and Al to enhance lithium ion conductivity and stabilize the crystal structure, thereby suppressing the dissolution of Ni and Mn.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a combination of large particle and small particle having particle size difference is used to enhance packing density, then battery capacity is improved, but dissolution of Ni and Mn increases compromising reliability
Solution Approach 1:
The positive electrode active material is segmented into two distinct particle types (a and b) with different primary and secondary particle size relationships. Type (a) particles have larger primary particles aggregated into smaller secondary particles, while type (b) particles have smaller primary particles aggregated into larger secondary particles. This segmentation allows optimization of both capacity and dissolution resistance through complementary characteristics
Solution Approach 2:
Different regions of the particle structure are assigned different qualities: the primary particle size controls surface area and dissolution resistance, while the secondary particle size controls packing density and capacity. By independently optimizing these two levels of structure, the invention achieves both high capacity and low dissolution
2Quantity of substance
If Ni-containing lithium composite oxide with high Ni content is used to achieve large capacity, then battery capacity is improved, but dissolution of Ni and Mn increases leading to increased resistance and reliability issues
Solution Approach 1:
The invention changes the particle size parameters at two different levels (primary and secondary) to resolve the contradiction. By adjusting the primary particle size to be larger in type (a) and smaller in type (b), and accordingly adjusting secondary particle sizes, the surface area to volume ratio is optimized to reduce dissolution while maintaining capacity
Solution Approach 2:
The invention uses a composite structure of Ni-containing lithium composite oxides with specific particle size characteristics. The composite consists of two types of particles with complementary properties, creating a material system that achieves both high capacity and low dissolution through the synergistic effect of the two particle types
Data Source
AI summary
A positive electrode active material for a nonaqueous electrolyte secondary battery, the positive electrode active material comprising a Ni-containing lithium composite oxide a, b, wherein the Ni-containing lithium composite oxide a has an average primary particle size of 1 μm or more which is larger than the average primary particle size of the Ni-containing lithium composite oxide b, the Ni-containing lithium composite oxide a has an average secondary particle size of 2 to 6 μm, the Ni-containing lithium composite oxide b has an average primary particle size of 0.05 μm or more and an average secondary particle size of 10 to 20 μm, the Ni-containing lithium composite oxide a contains Mn and at least one of B and Al, the Ni-containing lithium composite oxide b contains Mn, and the ratio of the Ni-containing lithium composite oxide a to the Ni-containing lithium composite oxide b is 5:95 to 55:45.