Amorphous Sodium-Ion Cathode Material for High Discharge Capacity
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Solution Overview
Problem
Conventional positive electrode active materials for sodium-ion secondary cells, such as those containing Na2FeP2O7, exhibit low discharge capacity.
Innovation Solution
A positive electrode active material with a composition of 8 to 55% Na2O, 10 to 70% NiO, 0 to 60% CrO+FeO+MnO+CoO, and 15 to 70% P2O5+SiO2+B2O3, incorporating an amorphous phase, which enhances sodium ion insertion and extraction capabilities and facilitates the formation of a dense ion-conducting path with the solid electrolyte.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional positive electrode active materials containing Na2FeP2O7 are used, then the cell structure is simple and easy to manufacture, but the discharge capacity is low
Solution Approach 1:
The patent applies composite materials by combining multiple metal oxides (NiO, CrO, FeO, MnO, CoO) with phosphates (P2O5) and other components (SiO2, B2O3) to create a composite positive electrode active material. This composite structure enables higher discharge capacity through synergistic effects of different components, particularly NiO which provides redox reactions, while maintaining structural stability through the phosphate matrix.
2Productivity
If the positive electrode active material contains amorphous phase, then the diffusion path for sodium ions expands and insertion/extraction is facilitated, but the manufacturing precision and phase control become more difficult
Solution Approach 1:
The patent applies parameter changes by controlling the composition ratios of multiple oxides and phosphates within specific ranges to stabilize the amorphous phase. By adjusting parameters such as NiO content (10-70%), CrO+FeO+MnO+CoO content (0-60%), and P2O5+SiO2+B2O3 content (15-70%), the patent achieves optimal balance between amorphous phase stability and sodium ion diffusion performance, preventing crystallization while maintaining manufacturing control.
3Quantity of substance
If NiO content is increased to enhance redox reaction and discharge capacity, then the energy density increases, but the material becomes more prone to decomposition and manufacturing difficulties arise
Solution Approach 1:
The patent applies local quality by creating distinct functional zones within the composite material: NiO-rich regions provide redox reactions and high capacity, while phosphate-rich regions (P2O5, SiO2, B2O3) provide structural stability and prevent decomposition. This spatial differentiation of functionality allows high NiO content (10-70%) to be maintained without compromising overall material stability, as the phosphate matrix locally supports and protects the NiO regions.
4Duration of action of stationary object
If the positive electrode active material is used with solid electrolyte, then the ion-conducting path is improved and cycle characteristics increase, but the firing process becomes more complex and decomposition risks increase
Solution Approach 1:
The patent applies preliminary action by pre-forming the positive electrode active material with controlled amorphous phase and specific composition before assembly with the solid electrolyte. This preliminary preparation ensures that during subsequent firing, the material is already optimized for interface formation with the solid electrolyte, reducing decomposition risks and simplifying the overall manufacturing process while maintaining excellent cycle characteristics.
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 proposed active material significantly increases discharge capacity, rapid charge/discharge characteristics, and cycle stability, while inhibiting electrolyte decomposition and maintaining high redox potential.
Implementation Method 1
NiO changes the valence of Ni ions during charge and discharge to cause a redox reaction and thus act as a drive force for insertion and extraction of sodium ions
Implementation Method 2
the amorphous phase softens and flows during firing to fusion bond the positive electrode active material and a sodium-ion conductive solid electrolyte together
Data Source
AI summary
Provided is a novel positive electrode active material for a sodium-ion secondary cell having a good discharge capacity. A positive electrode active material for a sodium-ion secondary cell, the positive electrode active material containing, in terms of % by mole of oxide, 8 to 55% Na2O, 10 to 70% NiO, 0 to 60% CrO+FeO+MnO+CoO, and 15 to 70% P2O5+SiO2+B2O3 and containing an amorphous phase.