Olivine Phosphate Cathode Particles With Strain-Relief Voids
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Solution Overview
Problem
Olivine-type phosphate compounds used as positive electrode active materials face capacity degradation due to strain accumulation from volume changes during charge-discharge cycles, leading to tertiary particle structure destruction and metal elution.
Innovation Solution
Incorporating vacant spaces between secondary particles in tertiary particles, with a proportion of 4.8% to 29% of the cross-sectional area, to absorb and relax strain, using a method involving slurry formation, spray drying, and heat treatment to produce a positive electrode active material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If tertiary particles are formed by aggregating secondary particles to enhance electrode density, then productivity and electrode density are improved, but strain accumulates during charge-discharge cycles causing tertiary particle structure destruction and capacity degradation
Solution Approach 1:
The patent introduces vacant spaces (porosity) between secondary particles within tertiary particles. This porous structure provides buffer space that absorbs strain generated during charge-discharge cycles, preventing the tertiary particle structure from breaking down while maintaining high electrode density. The vacant spaces act as stress relief zones that accommodate volume changes of the active material.
Solution Approach 2:
The patent creates non-uniform density distribution within tertiary particles by concentrating vacant spaces at specific locations between secondary particles. This local quality adjustment allows the structure to maintain high density in active material regions while providing strategic buffer zones for strain accommodation, resolving the contradiction between density and endurance.
2Quantity of substance
If the volume of active material changes greatly during charge-discharge cycles, then capacity is improved, but strain accumulates within tertiary particles leading to structure destruction and metal elution
Solution Approach 1:
The patent pre-configures vacant spaces between secondary particles before charge-discharge cycles begin. These预先 prepared buffer spaces cushion the strain that will be generated during volume changes, preventing structure destruction and metal elution while allowing full capacity utilization.
3Reliability
If vacant space is formed between secondary particles to absorb strain, then endurance is improved, but electrode density decreases
Solution Approach 1:
The patent optimizes the distribution and proportion of vacant spaces within tertiary particles, concentrating them at specific interfaces between secondary particles rather than uniformly throughout. This allows the electrode to maintain high overall density while providing localized buffer zones for strain absorption, resolving the contradiction between density and endurance.
Solution Approach 2:
The patent controls the proportion of vacant spaces within specific ranges (5-30% of tertiary particle volume, with optimal ranges of 10-20% or 15-25%) to balance strain absorption capability with electrode density. By optimizing these parameters, both endurance and density requirements are satisfied simultaneously.
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
Enhances the endurance of the electrode by maintaining the tertiary particle structure and preventing capacity degradation.
Implementation Method 1
a vacant space formed between the secondary particles inside the tertiary particle can absorb and relax the strain that can be produced by volume changes of the active material
Implementation Method 2
forming tertiary particles by spray drying the slurry
Implementation Method 3
performing heat treatment of the tertiary particles to produce a positive electrode active material
Data Source
AI summary
A positive electrode active material comprises tertiary particles. Each of the tertiary particles includes secondary particles. Each of the secondary particles includes primary particles. Each of the primary particles includes an olivine-type phosphate compound. In at least part of the tertiary particle, a vacant space is formed between the secondary particles.