Sodium-Ion Cathode Doping to Suppress Cycling Gas Release
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Solution Overview
Problem
Nickel-iron-manganese polycrystalline materials in sodium-ion batteries generate excessive gas during cycling, leading to volume expansion, structural instability, and safety issues such as swelling, deformation, or explosion, which affect cycle life and energy density.
Innovation Solution
Doping two elements with different properties, M and A, where M has a bond energy greater than 500 kJ/mol and an ionic radius of 0.06 nm or higher, and A has a valence state of +3 or higher, to confine oxygen and stabilize the structure, combined with a coating layer and a specific sintering process to improve gas generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If nickel-iron-manganese polycrystalline materials are used as positive electrode material, then high capacity and good processability are achieved, but excessive gas generation occurs during cycling
Solution Approach 1:
The patent applies local quality by doping specific elements (M and A) at particular sites within the layered oxide structure. Element M is doped at interstitial positions with high M-O bond energy to locally strengthen oxygen binding, while element A is doped at transition metal sites to provide structural support. This localized modification addresses gas generation at specific problematic sites without compromising the overall high capacity of the nickel-iron-manganese material.
Solution Approach 2:
The patent creates a composite doped layered oxide material by combining nickel-iron-manganese base material with dopant elements M and A. The composite structure integrates the high capacity characteristics of the original nickel-iron-manganese polycrystalline material with the oxygen-stabilizing properties of element M and the structural-supporting properties of element A, achieving both high capacity and reduced gas generation.
2Ease of operation
If layered oxide positive electrode material undergoes intercalation and deintercalation of sodium ions, then battery operation is enabled, but volume expansion and stress accumulation occur
Solution Approach 1:
The patent modifies the structural parameters of the layered oxide by introducing dopant elements with specific ionic radii and valence states. Element A with ionic radius ≥0.06 nm and valence ≥+3, when doped at transition metal sites, adjusts the lattice parameters and strengthens the structural framework. This parameter modification enables the material to accommodate sodium ion intercalation/deintercalation while maintaining structural stability and preventing excessive volume expansion.
Solution Approach 2:
The patent applies preliminary action by pre-doping elements M and A into the layered oxide structure before battery operation. This pre-modification of the crystal structure creates a more robust framework that can withstand the stress of subsequent sodium ion intercalation and deintercalation cycles, preventing structural degradation and volume expansion issues that would otherwise occur during battery operation.
3Object-generated harmful factors
If water-washing method is used to reduce gas generation, then gas generation is reduced, but preparation process complexity and manufacturing cost increase
Solution Approach 1:
The patent extracts the need for post-synthesis water-washing treatment by incorporating dopant elements M and A during the synthesis process itself. The doping elements M (with high M-O bond energy >500 kJ/mol) and A (with ionic radius ≥0.06 nm and valence ≥+3) are integrated into the crystal structure during sintering, providing inherent oxygen stabilization and structural support that eliminates gas generation issues without requiring subsequent water-washing steps to remove carbonates or other byproducts.
4Object-generated harmful factors
If operating voltage is reduced to minimize gas generation, then gas generation is reduced, but capacity and energy density decrease
Solution Approach 1:
The patent changes the chemical and structural parameters of the positive electrode material by doping elements M and A, which modify the electronic structure and redox potentials of the material. These parameter changes enable the material to operate at higher voltages with reduced gas generation, as the dopants stabilize the structure against oxygen release and facilitate electron transfer, thereby maintaining or even enhancing capacity and energy density while suppressing harmful gas evolution.
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 doped positive electrode material exhibits improved structural stability, reduced gas generation, enhanced cycle performance, and increased capacity, addressing safety and performance issues in sodium-ion batteries.
Implementation Method 1
a M-O bond of the element M has a bond energy of greater than 500 kJ/mol, the function of the element M is to be doped at a position of an interstitial atom, to confine oxygen and restrict oxygen release
Implementation Method 2
an element A has an ionic radius of greater than or equal to 0.06 nm and a valence state of +3 or higher. The doping of the element A may preferentially replace a transition metal at a transition metal site, playing a supporting role in the internal structure of the layered material
Implementation Method 3
a layered oxide positive electrode material has a main reaction of intercalation and deintercalation of sodium ions. When sodium ions are intercalated into the layered oxide positive electrode material from the electrolyte, the structure of the positive electrode material changes, and the layered oxide layers expand outward
Data Source
Figure 1~3
Figure 4~5
AI summary
A positive electrode material for a sodium-ion battery, and a preparation method thereof and use thereof, where the positive electrode material for the sodium-ion battery has a chemical general formula NaaNibFecMndMcAfO2, where the element M and the element A are doping elements, M-O of the element M has a bond energy of greater than 500 kJ/mol, the element A has an ionic radius of greater than or equal to 0.06 nm, and the element A has a valence state of +3 of higher, and a XRD pattern of the positive electrode material for the sodium-ion battery is free of impurity phase diffraction peak in a range of 42.5°-43.5°. The element M is doped at a position of an interstitial atom, which can confine oxygen and restrict oxygen release in a desodiation state, and the element A can preferentially replace a transition metal at a transition metal site, playing a supporting role, and thus improving the gas generation problem of the positive electrode material for the sodium-ion battery during cycling.