Ferrous Oxalate (Iron(II) Oxalate): From Battery Precursors to Pigments

Ferrous oxalate (iron(II) oxalate), with the chemical formula FeC₂O₄ (anhydrous) or FeC₂O₄·2H₂O (dihydrate), is a vital inorganic industrial chemical. As the key precursor for lithium iron phosphate (LiFePO₄) battery cathode materials, ferrous oxalate occupies a central position in the new energy supply chain — this single application accounts for over 90% of global consumption. In addition, ferrous oxalate is widely used across multiple industrial sectors including ceramic and glass coloring, magnetic material synthesis, photocatalytic degradation, photographic development, and metal surface treatment.

1. Basic Chemical Profile

2. Core Application Areas

2.1 Lithium-Ion Battery Cathode Precursor (>90% Share)

This is by far the largest and most strategic application for ferrous oxalate.

Ferrous oxalate serves as the iron source, reacting with a lithium source (lithium carbonate or lithium hydroxide) and a phosphate source via solid-phase synthesis to produce lithium iron phosphate (LiFePO₄) cathode material.

Key advantages of the ferrous oxalate route in LiFePO₄ production:

Downstream applications:

EV batteries: Lithium iron phosphate batteries for new energy vehicles

Energy storage systems: Grid-scale and residential energy storage cells

Consumer electronics: Power tools, e-bikes, and portable devices

2.2 Pigments and Colorants

Ferrous oxalate is a versatile precursor for iron oxide pigments. Upon thermal decomposition under controlled conditions, it yields various iron oxide pigments:

Specific application fields:

2.3 Photocatalysis and Environmental Remediation

Ferrous oxalate and its derivatives play an important role in the photocatalytic degradation of organic pollutants:

Photo-Fenton reaction

● : The ferrous oxalate–ferrioxalate system acts as a highly efficient photocatalyst, generating hydroxyl radicals (·OH) to degrade dyes, pesticide residues, and phenolic compounds in organic wastewater

Porous material precursor

● : Thermally decomposed porous iron oxides are used in

supercapacitor

electrode materials and gas sensors

Visible-light response

● : Compared to conventional TiO₂ photocatalysts, iron-based photocatalytic materials exhibit superior absorption in the visible-light range

2.4 Photographic Development

Ferrous oxalate is employed as a developing agent component in traditional photographic processes. The reducing power of Fe²⁺ reduces photosensitive silver ions to metallic silver, forming the visible image.

2.5 Metal Surface Treatment and Electroplating

2.6 Leather Tanning and Textile Finishing

3. Product Grades and Specifications

4. Packaging, Storage, and Handling

Packaging

● Standard: 25 kg/bag (PE inner liner + woven outer bag or fiber drum)

● Custom options available: 500 kg supersacks, 1000 kg supersacks

Storage and Handling Requirements

Frequently Asked Questions

Q1: What is the difference between ferrous oxalate and ferric oxalate?

Ferrous oxalate (FeC₂O₄) contains iron in the +2 oxidation state, appearing as a yellow powder. Ferric oxalate (Fe₂(C₂O₄)₃) contains iron in the +3 oxidation state, appearing yellow-green. Their chemical properties and applications differ significantly — ferrous oxalate is primarily used in LiFePO₄ precursors and pigments, while ferric oxalate serves more in photocatalysis and photographic processes.

Q2: What are the key differences between battery-grade and industrial-grade ferrous oxalate?

The critical differences lie in metal impurity content and particle size control. Battery-grade product requires strict ppm-level control of Na, K, Ca, Cu, Zn, and other impurities, with D50 particle size typically in the 2–8 μm range and a narrow distribution. Industrial-grade product has wider tolerances for impurities and particle size.

Q3: How is ferrous oxalate converted into lithium iron phosphate?

Ferrous oxalate serves as the iron source and is mixed with lithium carbonate (lithium source) and ammonium dihydrogen phosphate (phosphate source) in stoichiometric proportions. After ball milling and drying, the mixture is sintered at 600–800 °C under an inert gas atmosphere (e.g., nitrogen or argon), undergoing a solid-phase reaction to form olivine-type lithium iron phosphate (LiFePO₄).

Q4: How does ferrous oxalate compare with ferrous sulfate as an iron source?

Q5: Is ferrous oxalate classified as a hazardous chemical?

Ferrous oxalate is not classified as a hazardous chemical and can be transported and stored under standard chemical handling conditions. However, its GHS classification is "Warning" — inhalation of dust or skin contact may be harmful. Appropriate personal protective equipment is recommended during handling.

Q6: What is the shelf life of ferrous oxalate? How should it be stored?

Under dry, cool, and sealed conditions, ferrous oxalate typically remains stable for 12–24 months. As the dihydrate is hygroscopic, it should be used promptly after opening and stored away from strong oxidizers and strong acids.