Sodium Secondary Cell Positive Electrode Material Composition
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Solution Overview
Problem
Sodium secondary cells using existing sodium-containing composite metal oxides as positive electrode-active materials have insufficient discharge voltage and lower energy density, limiting their application as nonaqueous electrolyte secondary cells.
Innovation Solution
A positive electrode-active material with an α-NaFeO2 type crystal structure, represented by the formula Naa(FewNixMny-zTiz)O2, is developed, where a ≥ 0.6 and ≤ 1, w ≥ 0 and ≤ 0.5, y ≥ 0.03 and ≤ 0.5, z ≥ 0.03 and ≤ 0.5, w+x+y=1, and y>z, optimized to enhance capacitance and energy density, and further improved by specific ranges for w, x, and y to maximize discharge capacitance and energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If existing sodium-containing composite metal oxide (NaFe0.4Ni0.3Mn0.3O2) is used as positive electrode-active material, then the cell can operate as a sodium secondary cell, but the discharge voltage is insufficient and energy density is lower
Solution Approach 1:
The patent applies parameter changes by systematically varying the compositional parameters (a, w, x, y, z) of the composite metal oxide Naa(FewNixMnym-zTiz)O2 to optimize discharge voltage and energy density. Specifically, the patent identifies optimal ranges: a≥0.6, w≥0.03, x≥0.03, y≥0.1, z≥0.03, which directly change the material's electrochemical properties to achieve higher discharge voltage and energy density compared to existing materials like NaFe0.4Ni0.3Mn0.3O2
Solution Approach 2:
The patent employs composite materials by creating a multi-element composite metal oxide Naa(FewNixMnym-zTiz)O2 combining Fe, Ni, Mn, and Ti in specific ratios. This composite structure leverages the synergistic effects of different metal elements: Fe provides high voltage, Ni enhances capacity, Mn stabilizes structure, and Ti improves conductivity, collectively resolving the contradiction between discharge voltage and energy density
2Quantity of substance
If sodium is used instead of lithium in secondary cells, then resource abundance and cost are improved, but discharge voltage and energy density are insufficient
Solution Approach 1:
The patent changes the compositional parameters of the positive electrode material to compensate for sodium's lower standard potential compared to lithium. By optimizing the ratio of high-potential elements (particularly Fe with a≥0.6) and adjusting the overall composition within specified ranges, the patent achieves discharge voltages and energy densities that make sodium-based cells competitive with lithium-based cells while maintaining resource abundance advantages
Data Source
AI summary
A positive electrode-active material is provided for use in a positive electrode for a sodium secondary cell and a sodium secondary cell. Also provided is a positive electrode for a sodium secondary cell and a sodium secondary cell having a high energy density. The positive electrode-active material for a sodium secondary cell includes a composite metal oxide, which has an α-NaFeO2 type crystal structure and is denoted by Formula (1) described below:Naa(FewNixMny-zTiz)O2 (1),wherein a is greater than or equal to 0.6 and less than or equal to 1.0, w is greater than 0 and less than 0.5, x is greater than 0 and less than 0.5, y is greater than 0.03 and less than or equal to 0.5, z is greater than or equal to 0.03 and less than 0.5, and w+x+y=1.0, and y>z.