Sodium Layered Oxide Composition for Moisture-Stable High Capacity
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Solution Overview
Problem
Sodium layered oxides in sodium ion batteries are sensitive to moist air, leading to structural deterioration and poor electrochemical performance due to phase transitions and the formation of secondary phases like Na2CO3 and NaOH, which complicates electrode processing and increases parasitic reactions with the electrolyte.
Innovation Solution
A sodium layered oxide compound with a specific formula, Na x M1 a+ 1-y-z-n M2 b+ y M3 c+ z M4 d+ n O 2, where M1, M2, M3, and M4 are different transition metal ions, and the cumulative oxidation state of these ions is adjusted to achieve a stable P2-O3 or O3 phase structure, reducing moisture sensitivity and enhancing cycling performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If sodium layered oxide with high sodium content (x ~ 1) is used to achieve high capacity, then electrochemical capacity is improved, but moisture sensitivity increases leading to structural deterioration
Solution Approach 1:
The patent applies parameter changes by precisely controlling the sodium content parameter (x) to be in the range 0.95 ≤ x < 1, and adjusting the cumulative oxidation state of transition metals to be more than +4-x. This parameter optimization resolves the contradiction by achieving high capacity (close to theoretical maximum) while simultaneously improving moisture stability compared to x=1 materials.
Solution Approach 2:
The patent uses composite materials by creating a multi-element transition metal system (M1, M2, M3, M4) with specific oxidation states. This composite approach allows tuning of both electrochemical performance and structural stability, resolving the contradiction between high capacity and moisture resistance through synergistic element combinations.
2Object-affected harmful factors
If sodium content is reduced to improve moisture stability, then resistance to humid air is improved, but phase transitions occur and secondary phases form reducing electrochemical performance
Solution Approach 1:
The patent resolves this contradiction by identifying and controlling critical parameters: sodium content (x ≥ 0.95) and cumulative oxidation state (> +4-x). These parameter changes ensure the material maintains single-phase P2-O3 structure without secondary phases, achieving both moisture stability and high electrochemical performance simultaneously.
3Stability of the object's composition
If strict moisture-free conditions are maintained during electrode processing, then structural stability is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent applies preliminary action by pre-optimizing the material composition (sodium content and oxidation states) during synthesis to inherently confer moisture resistance. This preliminary compositional design allows subsequent electrode processing to be performed under normal conditions without requiring stringent moisture-free environments, thus reducing manufacturing complexity while maintaining structural stability.
4Stability of the object's composition
If co-doping with Zn and Ti is applied to reduce phase transitions, then structural stability is improved, but sensitivity to moist air increases requiring fully dried conditions
Solution Approach 1:
The patent resolves this contradiction by changing the compositional parameters beyond simple co-doping. By controlling sodium content (x ≥ 0.95) and cumulative oxidation state (> +4-x) in the Zn-Ti co-doped system, the patent achieves both phase stability and reduced moisture sensitivity, allowing processing under less stringent conditions compared to previous co-doped materials.
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 proposed sodium layered oxide exhibits improved moisture stability, maintaining electrochemical performance and capacity retention, allowing for the production of high-capacity sodium ion batteries with reduced sensitivity to humid environments and minimized parasitic reactions.
Implementation Method 1
On exposure to moist air, the sodium from the alkali layer is replaced/ ion exchanged by H+
Implementation Method 2
the formation of secondary phases like Na2CO3 and NaOH
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
The invention relates to A sodium layered oxide of formula I: NaxM1a+1-y-z-nM2b+yM3c+zM4d+nO2, (I), wherein: M1a+, M2b+, M3c+ and M4d+ are different transition metal ions or mixtures thereof, x is a number ranging from 0.5 to strictly less than 1; y, z and n are numbers ranging from 0.01 to 0.85; y + z + n is less than 1; a, b, c and d are the respective oxidation number of the transition metal ions M1, M2, M3 and M4, respectively; and the cumulative oxidation state of transition metal ions a∗(1-y-z-n)+(b∗y)+(c∗z)+(d∗n) is equal to 4-x; and wherein said sodium layered oxide of formula I is not P2-Na2/3Ni1/4Mn1/2Ti1/6Zn1/12O2, P2-Na2/3Ni1/4Mn1/2Ti1/6Mg1/12O2, or P2-Na2/3Ni1/4Mn1/2Ti1/6Mg1/12O2.