Positive Electrode Active Material with Radial Particle Orientation
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Solution Overview
Problem
The use of positive electrode active materials with mixed primary particles of different aspect ratios in secondary particles leads to decreased discharging capacity and cycling performance in non-aqueous electrolyte secondary batteries.
Innovation Solution
A positive electrode active material comprising a secondary particle with primary particles aggregated into a lithium transition metal composite oxide, having a lamellar crystal structure, with specific molar ratios of Li, Ni, Mn, and Co, and oriented second particles radially disposed within the secondary particle, enhancing isotropic expansion/contraction of first particles at the outer periphery and anisotropic expansion/contraction of second particles within, thus reducing stress and improving cycling performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If primary particles of different aspect ratios are mixed in the secondary particle, then cycling performance may be improved, but discharging capacity decreases
Solution Approach 1:
The patent applies local quality by differentiating the roles of primary particles based on their aspect ratios. High aspect ratio particles (≥1.2) are positioned at the outer periphery to provide isotropic expansion/contraction and maintain discharging capacity, while low aspect ratio particles (<1.2) are positioned inside to provide anisotropic expansion/contraction and improve cycling performance. This spatial differentiation of particle functions resolves the contradiction between capacity and cycling performance.
Solution Approach 2:
The patent employs asymmetry in the distribution of particles with different aspect ratios within the secondary particle structure. Rather than uniform mixing, it creates an asymmetric arrangement where peripheral particles have different geometric properties than internal particles. This asymmetric configuration optimizes both capacity (through peripheral high aspect ratio particles) and cycling performance (through internal low aspect ratio particles).
2Quantity of substance
If high aspect ratio primary particles are used, then discharging capacity is maintained, but cycling performance deteriorates
Solution Approach 1:
The patent merges particles of different aspect ratios within a single secondary particle structure, combining the advantages of both high aspect ratio particles (isotropic expansion, high capacity) and low aspect ratio particles (anisotropic expansion, good cycling performance). This merging approach allows the battery to achieve both high discharging capacity and excellent cycling stability simultaneously.
3Reliability
If low aspect ratio primary particles are used, then cycling performance is improved, but discharging capacity decreases
Solution Approach 1:
The patent assigns low aspect ratio particles to specific locations (inside the secondary particle) where they can fulfill their function of providing anisotropic expansion/contraction to improve cycling performance, while high aspect ratio particles are assigned to the periphery to maintain discharging capacity. This local quality differentiation resolves the contradiction.
Data Source
Figure 1~2
AI summary
A positive electrode active material includes a secondary particle (1) in which primary particles (10) are aggregated. A ratio (L11/L12) of an average value of maximum lengths L11 of first particles (11) in a first direction (d1) and an average value of maximum lengths L12 of the first particles (11) in a second direction (d2) as defined in the claims is 0.5 to 1.10. A ratio (L21/L22) of an average value of maximum lengths L21 of second particles (12) in the first direction (d1) and an average value of maximum lengths L22 of the second particles (12) in the second direction (d2) as defined in the claims is 1.40 or more. The second particles (12) include oriented particles that have major axis directions (d3) radially oriented in the first direction and that have the average value of the maximum lengths L21 of 640 nm or less.