Li-Substituted Layered-Spinel Cathode for Sodium Ion Batteries
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Solution Overview
Problem
Cycling stability of O3-type layered cathodes for sodium-ion batteries remains an issue, particularly at high voltages, due to phase transitions that affect charge storage and material stability, and existing solutions do not adequately address this challenge.
Innovation Solution
A Li-substituted layered-tunneled O3/spinel Na(NixFeyMnz)O2 cathode material, Na0.87Li0.25Ni0.4Fe0.2Mn0.4O2+, is developed, with a mixed-phase structure comprising 94% layered and 6% spinel components, enhancing structural stability and Na mobility through the integration of spinel and layered phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If O3-type layered cathodes are used for sodium-ion batteries, then high capacity is achieved, but cycling stability deteriorates at high voltages due to phase transitions
Solution Approach 1:
The patent creates a composite material by introducing Li ions into the O3-type layered cathode structure, forming a Li-substituted composite that combines the high capacity characteristics of the original O3-phase with enhanced structural stability. The Li substitution at transition metal sites creates a composite structure that resists harmful phase transitions while maintaining electrochemical activity, thereby achieving both high capacity and improved cycling stability at high voltages
Solution Approach 2:
The patent modifies the compositional parameters of the cathode material by substituting Li ions at transition metal sites with specific stoichiometric ratios. This parameter change (Li content optimization) transforms the material properties to suppress phase transitions at high voltages while preserving the high capacity characteristics of the O3-type structure, resolving the contradiction between capacity and cycling stability
2Stability of the object's composition
If Li ions are introduced to maintain pure layered structures, then structural stability is improved, but phase transitions still occur at high voltages
Solution Approach 1:
The patent applies local quality modification by selectively substituting Li ions at specific transition metal sites within the layered structure. This localized substitution creates regions of enhanced structural stability that act as anchors to prevent global phase transitions at high voltages, while maintaining the overall layered structure's electrochemical activity and 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 Li-substituted cathode exhibits improved cycling stability and rate capability, maintaining 95% capacity retention after 50 cycles at high current density and showing enhanced Na ion diffusivity, contributing to superior electrochemical performance compared to un-doped controls.
Implementation Method 1
When Li ions are introduced to the O3-type layered cathodes, Li ions are thermodynamically favored at the transition metal sites due to the similarity of its ionic radii (0.76 Å) to that of the transition metals ( ̃0.5-0.7 Å)
Implementation Method 2
The Na+/vacancy ordering in O3 structures triggers the phase transitions by the gliding of TMO2 layers through vector (1⁄3, 2⁄3, 0) without breaking TM-O bonds. With partial extraction of Na ions during charging process
Implementation Method 3
With partial extraction of Na ions during charging process, the O3 structure gradually transforms to the P3 structure; namely, Na ions are located at prismatic sites with a stacking sequence of AB-BC-CA
Implementation Method 4
enhancing structural stability and Na mobility through the integration of spinel and layered phases
Data Source
AI summary
Systems, methods, and compositions are disclosed for a Li-substituted layered-tunneled O3/spinel Na(NixFeyMnz)O2 cathode material, Na0.87Li0.25Ni0.4Fe0.2Mn0.4O2+∂ (LS-NFM) for enhanced sodium ion storage and cycling stability. The LS-NFM electrode is prepared by adjusting the stoichiometric ratio of the Na ion over the sum of Li and transition metal ions below 1. The Rietveld refinement of XRD data indicates that the cathode is composed of 94% layered and 6% spinel components. When cycled at a high current density of 100 mA g−1, LS-NFM cathode exhibited a first-cycle Coulombic efficiency of 88% and reversible discharge capacity of 107 mAh g−1 after 50 cycles with the capacity retention of 95%.