Iron Phosphate Cathode Composite for Low-Voltage Capacity Gain
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Solution Overview
Problem
Sodium-ion batteries using Na4Fe3(PO4)2P2O7 (NFPP) as a positive electrode material have low discharge capacity per gram at low voltage, leading to reduced energy density.
Innovation Solution
A positive electrode material composed of an iron-based phosphate material with a mixture of Na4Fe3(PO4)2P2O7 and Na2FeP2O7, where the ratio of these materials is optimized, along with a specific manufacturing process, to enhance the discharge capacity per gram, and a preparation method including mixing, milling, and sintering steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Na4Fe3(PO4)2P2O7 (NFPP) is used as a positive electrode material, then the battery has high stability and safety with three-dimensional sodium-ion diffusion channels, but the discharge capacity per gram at low voltage is low, reducing the energy density of the battery
Solution Approach 1:
The patent uses a composite material system consisting of Na4Fe3(PO4)2P2O7 (NFPP) as the base material combined with Na2FeP2O7 (NFPO) as a coating layer. This composite structure allows the NFPP core to provide high stability and safety with three-dimensional sodium-ion diffusion channels, while the NFPO coating layer compensates for the low discharge capacity per gram at low voltage by providing additional active sites for sodium-ion insertion/extraction, thereby resolving the contradiction between reliability and quantity of substance
Solution Approach 2:
The patent applies local quality modification by coating the surface of NFPP particles with NFPO material. The core NFPP maintains its inherent stability and safety properties, while the surface NFPO layer provides enhanced electrochemical activity and higher discharge capacity at low voltage. This localized modification allows different regions of the electrode material to fulfill different functions, resolving the contradiction between stability and discharge capacity
2Productivity
If the discharge capacity per gram at low voltage is increased, then the energy density of the battery is improved, but the structural stability of the electrode material may be compromised
Solution Approach 1:
The composite structure of NFPP@NFPO resolves this contradiction by combining materials with complementary properties. The NFPP core provides structural stability and three-dimensional sodium-ion diffusion channels, while the NFPO coating enhances discharge capacity at low voltage. The core-shell architecture ensures that the stable NFPP structure remains intact while the NFPO layer provides the additional capacity needed for high energy density
Solution Approach 2:
The NFPO coating layer acts as a protective cushion that prevents structural degradation of the NFPP core during electrochemical cycling. This pre-applied protective layer buffers the mechanical and chemical stresses that would otherwise compromise the structural stability of the electrode material during charge-discharge operations, allowing the material to maintain both high capacity and stability
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 optimized electrode material achieves a higher discharge capacity per gram across the full voltage range, enhancing the energy density of the battery.
Implementation Method 1
As an iron-based phosphate polyanionic material, Na4Fe3(PO4)2P2O7 (NFPP) has three-dimensional sodium-ion diffusion channels
Data Source
AI summary
A positive electrode material and a preparation method therefor, a positive electrode, and a battery are provided. The positive electrode material includes an iron-based phosphate material. The iron-based phosphate material includes a first active material and a second active material. A chemical formula of the first active material is Na4Fe3(PO4)2P2O7. A chemical formula of the second active material is Na2FeP2O7. A mass fraction of the first active material in the iron-based phosphate material is a1. A mass fraction of the second active material in the iron-based phosphate material is a2. a1 and a2 satisfy: 0<a2/a1≤0.2.