Iron Phosphate Cathode Composition for Low-Voltage Capacity Balance
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Solution Overview
Problem
Sodium-ion batteries using Na4Fe3(PO4)2P2O7 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 specific ratio of Na4Fe3(PO4)2P2O7 and Na2FeP2O7 active materials, coated with a carbon layer, is prepared through staged sintering to enhance discharge capacity and energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Na4Fe3(PO4)2P2O7 is used as a positive electrode material, then the battery has high theoretical capacity per gram, but the discharge capacity per gram at low voltage is low, reducing energy density
Solution Approach 1:
The patent uses a composite material system consisting of Na4Fe3(PO4)2P2O7 as the base material combined with a carbon coating layer. This composite structure allows the material to maintain its high theoretical capacity while the carbon layer enhances electronic conductivity and enables additional capacity contributions at low voltage, thereby resolving the contradiction between theoretical capacity and actual discharge capacity at low voltage
Solution Approach 2:
The patent modifies the physical and chemical parameters of the Na4Fe3(PO4)2P2O7 material by applying a carbon coating and controlling particle size distribution. These parameter changes improve the material's electrochemical performance, particularly enhancing low-voltage discharge capacity while preserving the high theoretical capacity characteristics of the base material
2Use of energy by moving object
If the carbon source is carbonized to form a coating layer, then the discharge capacity per gram is improved, but the manufacturing process complexity increases
Solution Approach 1:
The patent incorporates the carbon source into the slurry mixture before sintering, performing the carbonization action preliminarily during the sintering process itself rather than as a separate post-treatment step. This preliminary action simplifies the manufacturing process while still achieving the desired carbon coating that enhances discharge capacity
Solution Approach 2:
The patent merges the carbonization process with the sintering process by adding the carbon source to the initial slurry mixture. This combination allows both the formation of the active material and the carbon coating to occur in a single integrated manufacturing step, reducing process complexity while maintaining the capacity-enhancing benefits of the carbon layer
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 material achieves high energy density by balancing the discharge capacity across the full voltage range, maintaining structural stability and extending cycle life.
Implementation Method 1
The carbon source is carbonized to form the coating layer
Implementation Method 2
The slurry is sand milled and spray dried to obtain first intermediate particles
Implementation Method 3
Staged sintering is performed to obtain the positive electrode material
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. 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.