Spherical P2 Cathode Particles for Higher Sodium-Ion Capacity
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Solution Overview
Problem
Positive electrode active materials with a P2-type structure have low reversible capacity.
Innovation Solution
Development of spherical positive electrode active material particles with a P2-type structure comprising transition metal elements like Mn, Ni, and Co, and O, with surface crystallites less than 1 μm in diameter, and a chemical composition represented by NaaMnx−pNiy−qCoz−rMp+q+rO2, produced through a method involving precursor particles covered with a Na salt and fired to form a Na-containing transition metal oxide with a P2-type structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If P2-type structure positive electrode active material is used, then the battery can be constructed with available materials, but the reversible capacity is low
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the interior maintains the P2-type structure for stability while the surface develops an O3-type structure with higher reversible capacity. This spatial differentiation of crystal structures allows different regions to fulfill different functional requirements simultaneously.
Solution Approach 2:
The patent utilizes parameter changes by controlling the Na content (x value in NaxMnO2) and processing conditions to induce a phase transformation from P2 to O3 structure at the particle surface. By adjusting composition parameters and thermal treatment, the material transitions between different crystal structures with distinct electrochemical properties.
2Speed
If conventional P2-type positive electrode material is used, then the structure is stable, but the reaction resistance and diffusion resistance are high
Solution Approach 1:
The patent applies preliminary action by pre-forming spherical precursor particles with controlled size and composition before the phase transformation process. This preliminary structuring ensures that when the O3 phase forms on the surface, the underlying P2 structure remains intact, creating the desired core-shell configuration with optimized ion transport pathways.
Solution Approach 2:
The patent employs spheroidality by maintaining spherical particle morphology throughout the synthesis and transformation process. The spherical shape provides uniform stress distribution during phase transformation and creates consistent surface-to-volume ratios, facilitating uniform O3 layer formation and optimal ion diffusion from all directions.
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
The spherical particles exhibit high reversible capacity due to reduced reaction and diffusion resistance, improved rate characteristics, and increased sodium ion conductivity.
Implementation Method 1
covering the surface of the precursor particle with a Na salt to obtain a covered particle
Implementation Method 2
firing the covered particle to obtain a Na-containing transition metal oxide particle having a P2-type structure
Data Source
AI summary
The reversible capacity of P2-type positive electrode active material particle is increased. A positive electrode active material particle of the present disclosure has a P2-type structure, comprises at least one transition metal elements from among Mn, Ni and Co, with Na and O, as constituent elements, and is spherical.