Nickel-Based Cathode Particle Structure for Crack-Limited Cycle Life
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Solution Overview
Problem
Lithium nickel-based oxide positive electrode active materials for rechargeable lithium batteries suffer from decreased long-term cycle-life, increased resistance, and unsatisfactory capacity characteristics due to cracking during repeated charging and discharging.
Innovation Solution
A lithium nickel-based composite oxide positive electrode active material is developed with a secondary particle structure where primary particles are radially arranged, having a high ratio of particles with cross-sectional areas less than 0.1 µm² and a full width at half maximum (FWHM) of the (003) plane peak in X-ray diffraction analysis less than 0.125, enhancing lithium diffusion and mitigating cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a lithium nickel-based oxide positive electrode active material is used, then high energy density is achieved, but long-term cycle-life decreases and resistance increases due to cracks generated during repeated charging and discharging
Solution Approach 1:
The positive electrode active material is divided into multiple primary particles (5-50 nm in size) aggregated into secondary particles. This segmentation reduces internal stress and prevents crack propagation during charging-discharging cycles, thereby improving cycle-life while maintaining high energy density through the nickel-based composition
Solution Approach 2:
The patent employs a hierarchical structure where primary particles are nested within secondary particles, which in turn are distributed on the electrode. This nested architecture allows the smaller primary particles to accommodate volume changes independently, protecting the overall structure from cracking while maintaining the high-capacity nickel-based material's energy density
2Productivity
If the positive electrode active material undergoes repeated charging and discharging, then capacity is realized, but cracks are generated causing resistance to increase and capacity characteristics to deteriorate
Solution Approach 1:
The aggregated secondary particle structure acts as a cushioning mechanism that absorbs and distributes the mechanical stress generated during lithium insertion and extraction. The spaces between primary particles within secondary particles provide buffer zones that prevent crack formation before it can propagate, thereby protecting capacity characteristics during repeated cycling
Solution Approach 2:
The secondary particle structure functions as a flexible framework that can accommodate volume expansion and contraction during charging-discharging cycles. This flexible architecture prevents rigid crack formation while allowing the material to maintain its capacity through reversible lithium insertion and extraction
3Quantity of substance
If high capacity is targeted, then energy density improves, but initial charge/discharge efficiency and high-rate charging capacity are reduced
Solution Approach 1:
The patent transitions from considering only particle size to implementing a multi-dimensional hierarchical structure with primary particles (5-50 nm) aggregated into secondary particles with controlled size distribution. This dimensional approach provides both short diffusion paths within primary particles (improving rate capability) and sufficient active material volume in secondary particles (maintaining capacity), thereby achieving high initial charge/discharge efficiency alongside high capacity
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
This structure improves initial charge/discharge efficiency, high-rate charging capacity, and cycle-life characteristics by reducing lithium diffusion resistance and stress during contraction and expansion, leading to enhanced performance in rechargeable lithium batteries.
Implementation Method 1
enhancing lithium diffusion and mitigating cracking
Implementation Method 2
full width at half maximum (FWHM) of the (003) plane peak in X-ray diffraction analysis
Data Source
Figure 1(A)~1(C)
Figure 2
Figure 3
AI summary
Provided are a positive electrode active material for a rechargeable lithium battery, and a rechargeable lithium battery including the same, the positive electrode active material including a lithium nickel-based composite oxide wherein the positive electrode active material is in a form of a secondary particle in which a plurality of primary particles are aggregated and at least a portion of the primary particles are radially arranged, in a cross-section of the secondary particle, a number ratio of primary particles having a cross-sectional area of less than about 0.1 µm2 is greater than or equal to about 65%, and a full width at half maximum (FWHM) of the peak corresponding to the (003) plane in the X-ray diffraction analysis for the positive electrode active material is less than or equal to about 0.125.