Multi-Phase NaxMO2 Cathode for Sodium-Ion Battery Reversibility
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Solution Overview
Problem
Sodium-based layered oxides in sodium-ion batteries face issues with reversibility and structural stability, particularly above 4.0 V, leading to irreversible capacity loss and degradation due to sodium-driven structural changes and electrolyte decomposition, which affects full cell cycling and balancing.
Innovation Solution
An integrated cathode active material with a composition of NaxMO2, where M is a transition metal, comprising at least three distinguishable phases (Pm or On) that are concurrently formed during the quenching process, enhancing sodiation/desodiation reversibility and stability through a solvothermal or co-precipitation method involving specific salts, precipitation agents, and calcination steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If O3-type material is charged above 4.0 V, then high voltage charge capability is achieved, but reversibility deteriorates with large irreversible capacity loss
Solution Approach 1:
The patent creates an integrated multi-phase composite material combining P2, P3, and O3 phases in a single bulk structure. This composite approach allows the material to benefit from the high voltage capability of O3 phase while the P2/P3 phases provide structural stability and prevent irreversible degradation, resolving the contradiction between achieving high charge voltage and maintaining reversibility.
Solution Approach 2:
Different phases are distributed throughout the bulk material with each phase performing its specific function: P2 and P3 phases provide structural stability in regions prone to degradation, while O3 phases enable high voltage charge capability in appropriate regions. This local differentiation allows simultaneous optimization of voltage and reversibility.
2Stability of the object's composition
If P2 phase is used for structural stability, then structural stability is improved, but initial coulombic efficiency exceeds 100% causing full cell cycling problems
Solution Approach 1:
The patent adjusts the composition parameters by incorporating P3 phase alongside P2 phase, changing the overall sodium content and distribution. This parameter adjustment reduces the excessive initial sodium reservoir problem of pure P2 phase while maintaining the structural stability benefits, enabling proper full cell cycling.
3Device complexity
If single phase material is used, then material simplicity is maintained, but electrochemical behavior is limited by phase-specific drawbacks
Solution Approach 1:
The patent employs an integrated multi-phase composite structure where P2, P3, and O3 phases coexist in the bulk material. This composite design overcomes the limitations of single-phase materials by combining the advantages of each phase while mitigating their individual drawbacks, achieving superior electrochemical performance.
Solution Approach 2:
The integrated multi-phase material performs multiple functions simultaneously: P2 and P3 phases provide structural stability and prevent slab gliding, O3 phases enable high voltage charge capability, and the combined structure ensures reversible sodiation/desodiation. This multi-functionality resolves the contradiction between simplicity and performance.
4Quantity of substance
If extensive Na extraction is performed, then charge capacity is increased, but structural stability deteriorates with P2 to O2 transition
Solution Approach 1:
The patent incorporates P3 phase alongside P2 phase as a preventive measure before extensive sodium extraction occurs. The P3 phase acts as a cushioning structure that maintains stability during deep charge states, preventing the detrimental P2 to O2 transition that would otherwise occur upon extensive Na extraction.
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 integrated phase material maintains multiple phases below 300°C, improving sodium ion insertion/extraction efficiency and reversibility during high voltage charge and discharge cycling, resulting in higher coulombic efficiency and capacity retention.
Implementation Method 1
reacting under solvothermal or co-precipitation condition salts of sodium and M in the presence of a precipitation agent and solvent to form a mixture
Implementation Method 2
reacting under solvothermal or co-precipitation condition salts of sodium and M in the presence of a precipitation agent and solvent to form a mixture
Implementation Method 3
calcining the mixture at a first calcination temperature to form a first calcination composition; calcining the calcination composition at a second calcination temperature
Implementation Method 4
calcining the mixture at a first calcination temperature to form a first calcination composition
Implementation Method 5
thermally quenching the second calcined composition via rapid cooling to form the NaxMO2
Data Source
AI summary
A cathode active material includes NaxMO2 having at least a first phase, a second phase different from the first phase, and a third phase that is different from the first and second phases, wherein each phase is independently selected from Pm or On, where m and n are individually an integer, M is a transition metal or a mixture of transition metals, and x is greater than 0 and less than or equal to 1.