Iron Phosphate Cathode Composition for Higher Sodium-Ion Electrode Density
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Solution Overview
Problem
The low compacted density of sodium-ion batteries using Na4Fe3(PO4)2P2O7 (NFPP) as a positive electrode material limits the improvement of energy density.
Innovation Solution
A positive electrode material composed of an iron-based phosphate material with a specific molar ratio of iron to phosphorus (0.55 ≤ A ≤ 0.75) and a mixture of first and second active materials (Na4Fe3(PO4)2P2O7 and Na2FeP2O7) is used, along with a controlled compacted density (2.0 g/cm³ < ρ1 ≤ 2.3 g/cm³) and particle size (2 µm ≤ D50 ≤ 5 µm, 10 µm ≤ D99 ≤ 30 µm) to enhance both discharge performance and energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If NFPP is applied to a positive electrode, then the theoretical capacity per gram is relatively high, but the compacted density of the positive electrode is relatively low
Solution Approach 1:
The patent uses a composite material system consisting of NFPP active material combined with conductive carbon materials and binder materials to form a composite electrode structure. This composite approach allows the electrode to maintain the high theoretical capacity of NFPP while improving compacted density through the synergistic combination of multiple materials with complementary properties.
Solution Approach 2:
The patent optimizes various parameters including the mass ratio of NFPP to other materials, particle size distribution, sintering temperature and time, and pressing pressure to achieve the desired balance between theoretical capacity and compacted density. By carefully controlling these parameters, the electrode structure is optimized to maximize both capacity and density.
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 solution results in a positive electrode with improved compacted density and discharge capacity, leading to higher energy density and performance in sodium-ion batteries.
Implementation Method 1
The intermediate particles are sintered to obtain the positive electrode material. The positive electrode material includes a coating layer and a core. The core is made of the iron-based phosphate material. The coating layer is coated around a surface of the core. A median particle size D50 of the positive electrode material satisfies: 2 μm ≤ D50 ≤ 5 μm.
Implementation Method 2
The slurry is sand milled and spray dried to obtain intermediate particles.
Implementation Method 3
The slurry is sand milled and spray dried to obtain intermediate particles.
Implementation Method 4
The intermediate particles are sintered to obtain the positive electrode material. sintering the intermediate particles to obtain the positive electrode material includes the following. The intermediate particles are sintered at a temperature T, to make the carbon source carbonized to form the coating layer, and make the sodium source, the iron source, and the phosphorus source form the iron-based phosphate material. T satisfies: 470 °C ≤ T ≤ 580 °C.
Data Source
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AI summary
The present disclosure relates to a positive electrode material and a preparation method therefor, a positive electrode, and a battery. 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. In the iron-based phosphate material, a molar ratio of an iron element to a phosphorus element is A, and A satisfies: 0.55 ≤ A ≤ 0.75.