Sodium-Rich Polyanionic Cathode Composition for Stable High Capacity
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Solution Overview
Problem
Current sodium-ion battery positive electrode materials exhibit limitations such as poorer stability and lower specific capacity, hindering the performance of sodium-ion secondary batteries.
Innovation Solution
A polyanionic compound with the chemical formula Na 2+x Mn 1-y M y Si 2-z M' z O 6-t N k X p Y q is developed, featuring a novel composition and structure with high sodium content, orthorhombic crystal structure, and specific doping elements to enhance stability and capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional positive electrode materials (oxides, fluorides, sulfides, phosphates, pyrophosphates) are used, then the battery can operate, but the stability and specific capacity are limited
Solution Approach 1:
The patent employs composite materials by combining multiple elements (Mn, Si, M, M', X, Y) to form a polyanionic compound with formula Na2+xMn1-yMySi2-zM'zO6-tNkXpYq. This composite structure integrates the advantages of different elements: Mn provides electrochemical activity, Si enhances structural stability, M and M' dopants optimize electronic conductivity and ion diffusion, while X and Y halogens improve overall stability. The synergistic combination resolves the contradiction between stability and specific capacity.
Solution Approach 2:
The patent applies local quality through selective doping at different crystal structure sites. M elements substitute at Mn sites to enhance local electrochemical activity, while M' elements substitute at Si sites to strengthen local structural stability. The non-uniform distribution of different elements at specific lattice positions allows simultaneous optimization of stability and capacity in different regions of the material.
2Quantity of substance
If high sodium content is increased to improve specific capacity, then capacity extraction improves, but structural stability may deteriorate
Solution Approach 1:
The patent utilizes parameter changes by precisely controlling the sodium content parameter (2+x where x ranges from -0.2 to 0.1) and adjusting doping levels (y, z, t, k, p, q parameters) to achieve optimal balance. The structural stability is maintained through the polyanionic framework which provides robust bonding, while sodium content is optimized within specific ranges to maximize capacity without compromising stability.
Solution Approach 2:
The composite polyanionic compound structure combines sodium-rich composition with a stable framework formed by MnO6 octahedra and SiO4 tetrahedra connected through oxygen bridges. This composite architecture allows high sodium content (2+x) while maintaining structural integrity through the rigid polyanionic backbone and stabilizing dopant elements.
3Reliability
If structural stability is enhanced through crystal structure optimization, then cycling performance improves, but manufacturing complexity increases
Solution Approach 1:
The patent achieves cycling performance improvement through parameter optimization of the orthorhombic crystal structure (space group Pnnm), including unit cell parameters a=7.5±1.5Å, b=10.5±1.5Å, c=10.5±1.5Å. These parameter specifications provide clear manufacturing targets while ensuring structural stability for reversible sodium ion insertion/extraction, balancing performance requirements with manufacturability.
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 polyanionic compound improves specific capacity and cycling stability of secondary batteries, providing a high sodium ion content and stable crystal structure for reversible intercalation and deintercalation, resulting in enhanced electrochemical performance.
Implementation Method 1
smaller structural changes during intercalation and deintercalation of sodium ions, thereby constructing a main body for reversible intercalation and deintercalation of sodium ions
Data Source
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AI summary
A polyanionic compound has the following chemical formula: Na2+xMn1-yMySi2-zM'zO6-tN1XpYq (1), where in formula (1), M is selected from Ni, Fe, Cu, Zn, Mg, Al, or a combination thereof, M' is selected from Ge, Sn, Ti, or a combination thereof, X is selected from S, Se, or a combination thereof, and Y is selected from F, Cl, or a combination thereof, where -0.2<x<0.2, 0≤y<0.1, 0≤z<0.1, 0≤t≤0.5, 0≤k≤2t/3, 0≤p≤t, 0≤q≤t/2, and k+1/2p+3/2q=t.