Spherical Na-Fe Pyrophosphate Cathode Structure for Higher Compaction
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Solution Overview
Problem
The compacted density of sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2(P2O7) remains relatively low, limiting its potential as a positive electrode material for sodium-ion batteries.
Innovation Solution
A positive electrode design with spheroidal or spherical sodium iron phosphate particles partially embedded into the positive electrode particles are partially embedded into the positive current collector, and the positive electrode is designed with specific geometric relationships to enhance the compacted density, including embedding depth, angle, and distance parameters, using spherical or spherical sodium iron phosphate pyrophosphate particles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If sodium iron phosphate pyrophosphate is used as positive electrode material, then high voltage plateau and high capacity are achieved, but compacted density remains relatively low
Solution Approach 1:
The patent employs spheroidal or spherical positive electrode particles made from sodium iron phosphate pyrophosphate. The spherical morphology allows for better packing efficiency and higher compacted density compared to irregular shapes, directly addressing the low compacted density issue while maintaining the high capacity and voltage characteristics of the material
Solution Approach 2:
The patent embeds positive electrode particles partially into the positive current collector, creating a nested structure where particles are integrated within the collector matrix. This embedding approach increases the effective density by utilizing the space within and around the current collector more efficiently
2Quantity of substance
If positive electrode particles are embedded into positive current collector, then compacted density increases, but mechanical performance may deteriorate
Solution Approach 1:
The patent applies partial embedding rather than complete embedding of particles into the current collector. This local quality approach ensures that particles are anchored sufficiently to improve density while leaving portions exposed to maintain mechanical integrity and flexibility of the electrode structure
Solution Approach 2:
The patent implements partial embedding of particles into the current collector, where only a portion of each particle is embedded. This partial action provides enough anchoring to improve compacted density while avoiding excessive embedding that would compromise mechanical performance and electrode flexibility
3Quantity of substance
If rolling pressure is increased to embed particles, then compacted density improves, but particle fracture risk increases
Solution Approach 1:
The spherical or spheroidal particle morphology inherently provides better resistance to fracture during rolling compared to irregular shapes. The curved surfaces distribute stress more evenly, allowing effective embedding at moderate rolling pressures without causing particle fracture
Solution Approach 2:
The patent optimizes the rolling pressure parameter to achieve effective particle embedding while avoiding excessive pressure that would cause fracture. By controlling the rolling pressure within an appropriate range and combining it with spherical particle morphology, the process achieves high compacted density while maintaining particle integrity
Data Source
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AI summary
A positive electrode includes a positive current collector and a positive active layer. The positive active layer is disposed on a preset surface of the positive current collector. The positive active layer includes positive electrode particles partially embedded into the positive current collector. The positive electrode particles are made from sodium iron phosphate pyrophosphate. The positive electrode particles are spheroidal or spherical. The positive electrode satisfies: b≤c•α/180°, where b denotes a depth to which the positive electrode particles are embedded into the positive current collector, α denotes an included angle between tangents at two points farthest away from each other on an intersection line of the preset surface and a surface of each of the positive electrode particles partially embedded, and c denotes a distance between an intersection of the tangents at two points farthest away from each other on the intersection line and the preset surface.