Sodium Cathode Composition With Controlled Na Migration for Cycle Stability
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Solution Overview
Problem
Existing sodium-ion secondary batteries face challenges in achieving both high initial capacity and long cycle stability due to the structural limitations and sodium content issues of P2-type and O3-type layered oxide particles.
Innovation Solution
A positive electrode active material is developed by mixing P2-type and O3-type layered oxide particles, followed by sintering to induce sodium migration from the surface of O3-type particles to P2-type particles, while controlling the surface sodium content ratio to enhance structural stability and capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If O3-type layered oxide particles are used to increase energy density, then discharge capacity is improved, but cycle stability deteriorates due to greater structural changes during charge and discharge
Solution Approach 1:
The patent combines P2-type and O3-type layered oxide particles into a composite positive electrode active material. The P2-type particles provide structural stability during cycling, while the O3-type particles contribute high discharge capacity, thereby resolving the contradiction between capacity and cycle stability through synergistic combination of the two phases.
2Reliability
If P2-type layered oxide particles are used to improve cycle stability, then lifespan characteristics are improved, but energy density decreases due to low sodium content
Solution Approach 1:
The composite structure merges the advantages of both P2-type (structural stability) and O3-type (high sodium content and capacity) particles, allowing the electrode to achieve both excellent cycle stability and high energy density that neither phase can provide alone.
3Manufacturing precision
If O3-type oxide particles are washed with water to remove residual Na on the particle surface, then purity is improved, but all internal Na comes out and structural stability deteriorates
Solution Approach 1:
The patent selectively removes only the harmful residual Na on the particle surface through water washing, while the composite P2-O3 structure prevents excessive Na loss from the internal lattice, thereby achieving purification without compromising structural stability.
4Quantity of substance
If mixed particles of P2-type and O3-type are used to achieve high discharge capacity, then initial capacity is improved, but battery lifetime deteriorates due to sodium by-products on the particle surface
Solution Approach 1:
The patent converts the harmful effect of residual Na on the surface into a beneficial process by controlling its removal through water washing. This eliminates sodium by-products that would otherwise cause electrolyte side reactions and gas generation, thereby extending battery lifetime while maintaining high initial 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
The approach results in a positive electrode active material with improved initial capacity and cycle stability, reduced gas generation, and enhanced battery performance by effectively managing sodium distribution and maintaining the structural integrity of the particles.
Implementation Method 1
sintering to induce Na migration from the surface of the O3-type oxide particle to the surface of the P2-type oxide particle
Implementation Method 2
induce Na migration from the surface of the O3-type oxide particle to the surface of the P2-type oxide particle
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
One embodiment of the present invention provides a positive electrode active material for a sodium secondary battery, including P2-type layered oxide particles and O3-type layered oxide particles, wherein in SEM-EDS mapping analysis, an atomic ratio (S3/S2) of a surface Na content (at%) (S3) of the O3-type layered oxide particles to a surface Na content (at%) (S2) of the P2-type layered oxide particles is 0.4 to 1.6.