Ferric phosphate, also known as lithium iron phosphate (LFP) or iron phosphate, has the chemical formula FePO₄. Depending on its form, it can exist as the dihydrate FePO₄·2H₂O or the anhydrous form FePO₄, with molecular weights of 186.82 and 150.82, respectively. Below is a detailed analysis of its chemical properties and safety characteristics:
I. Chemical Properties
1. Appearance and Color:
High-purity dihydrate ferric phosphate is a nearly white or pale yellowish-white powder. As crystalline water is lost, its color gradually becomes yellow, with the pure anhydrous form appearing as a yellowish-white powder.
When phosphorus (P) content exceeds the standard in dihydrate ferric phosphate, it appears grayish-white or dark gray; excess iron causes it to appear dark yellow.
If significant amounts of ferrous ions (Fe²⁺), sodium, potassium, sulfate, or ammonium ions are present, the dihydrate ferric phosphate may appear dark gray or black.
2. Physical Properties:
Tapped density: 1.13–1.59 g/cm³
Loose bulk density: 0.75–0.97 g/cm³
Ferric phosphate dissolves easily in hydrochloric acid when heated but is insoluble in most other acids, water, acetic acid, and alcohol.
3. Reaction Characteristics:
During the oxidation synthesis process, hydrogen peroxide is used as an oxidizing agent to fully oxidize Fe²⁺ from ferrous sulfate into Fe³⁺.
The morphology and properties of ferric phosphate are influenced by various factors, including the pH of the reaction solution, stirring speed, and feeding duration.
II. Safety Analysis
1. Thermal Stability:
The decomposition temperature of ferric phosphate used as a cathode material in batteries is approximately 700°C, significantly higher than the decomposition temperature of around 200°C for cathode materials in ternary lithium batteries. This means ferric phosphate batteries have better thermal resistance and are less prone to thermal runaway, which can lead to fires in extreme conditions such as battery short circuits or overheating.
2. Environmental Friendliness:
Ferric phosphate is non-toxic, non-polluting, and free from heavy metals, meeting environmental protection standards.
3. Batch Stability:
Ferric phosphate produced under precise precipitation conditions has a narrow PO₄³⁻/Fe ratio range and excellent batch stability, which helps ensure product consistency.
Ferric phosphate (iron phosphate/lithium iron phosphate) exhibits excellent chemical properties and safety characteristics. As a cathode material for lithium-ion batteries, it has broad application prospects in fields such as electric vehicles and energy storage systems. However, it is essential to adhere to safety protocols during production and use to ensure product quality and safety.
