Lithium-Nickel Cathode Crystal Structure for Low-Expansion Cycling
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Solution Overview
Problem
Lithium-nickel composite oxide-based lithium-ion secondary batteries suffer from poor cycle characteristics and significant battery expansion due to gas generation during charge and discharge cycles.
Innovation Solution
A positive electrode active material for lithium-ion secondary batteries is developed, comprising a lithium-nickel composite oxide with a hexagonal layered structure, configured by either single primary particles or secondary particles with a small number of aggregated primary particles, and a specific mole ratio of lithium, nickel, and optional metal elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium-nickel composite oxide is used as positive electrode active material, then battery capacity and energy density are improved, but cycle characteristic deteriorates and battery expansion occurs
Solution Approach 1:
The positive electrode active material is divided into multiple primary particles (0.5-5 μm) that aggregate to form secondary particles (5-20 μm). This segmentation reduces the size of individual crystallites, limiting the propagation of cracks during charge-discharge cycles and improving cycle characteristic while maintaining high battery capacity.
Solution Approach 2:
The patent applies different characteristics to different levels of particle structure: primary particles have small size (0.5-5 μm) to reduce internal stress and prevent cracking, while secondary particles have larger size (5-20 μm) to maintain good electrode morphology and electrical contact. This hierarchical structure optimizes both cycle characteristic and battery capacity.
2Quantity of substance
If lithium-nickel composite oxide is used as positive electrode active material, then energy density is improved, but battery expansion due to gas generation increases
Solution Approach 1:
By segmenting the active material into small primary particles (0.5-5 μm) that form secondary particles, the patent reduces the generation and accumulation of gas during charge-discharge cycles. The smaller particle size reduces internal stress and prevents large-scale structural degradation that would otherwise generate significant gas, thereby reducing battery expansion while maintaining high energy density.
3Shape
If secondary particles with multiple aggregated primary particles are used, then electrode morphology is improved, but cycle characteristic deteriorates due to cracking at interfaces
Solution Approach 1:
The patent optimizes the segmentation level by creating secondary particles composed of multiple small primary particles (0.5-5 μm). This hierarchical segmentation provides good electrode morphology at the secondary particle level while the small primary particle size prevents crack propagation, thereby improving cycle characteristic despite the presence of interfaces.
Solution Approach 2:
The patent applies different size characteristics to different structural levels: primary particles are kept small (0.5-5 μm) to prevent cracking at interfaces, while secondary particles are larger (5-20 μm) to ensure good electrode morphology and electrical contact. This local differentiation of particle size optimizes both electrode morphology and cycle characteristic.
Data Source
AI summary
A positive electrode active material for a lithium ion secondary battery, the positive electrode active material including a lithium-nickel composite oxide having a hexagonal layered structure and configured by particles including at least either single primary particles or secondary particles with a plurality of aggregated primary particles, wherein the particles of the positive electrode active material have a cross section having an area proportion of a crystal face having a maximum area in the particle of 80% or more when one crystal face is defined as a region having a crystal misorientation of 15° or less.