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Iron-Air Battery

Ultra-low cost multi-day storage using abundant iron and air

Overview

Iron-air batteries use the reversible oxidation of iron to store energy. By breathing in oxygen from the air during discharge and releasing it during charge, they achieve extremely low costs using abundant materials.

How It Works

Iron-air batteries operate on the principle of reversible rusting. During discharge, iron pellets react with oxygen from the air to form iron oxide (rust), releasing electrons. During charge, an electrical current reverses the process, converting iron oxide back to iron and releasing oxygen. The electrolyte is typically a potassium hydroxide (KOH) solution.

Advantages & Disadvantages

✓ Advantages

  • Extremely low cost ($20-80/kWh targeted)
  • Abundant, non-toxic materials (iron + air)
  • Very long duration capability (10-100+ hours)
  • No rare earth metals or lithium required
  • Safe: non-flammable, non-explosive
  • Scalable to very large capacities

✕ Disadvantages

  • Low round-trip efficiency (40-55%)
  • Slow charge and discharge rates
  • Still in early commercial stages
  • Iron oxidation degradation over time
  • Large system footprint
  • Limited power density

Applications

Multi-day grid storage Renewable energy seasonal storage Backup power for critical infrastructure Peak demand management Transmission and distribution deferral Island grids with high renewable penetration

Cost Breakdown

Iron electrode: 25-35% | Air cathode: 20-30% | Electrolyte: 10-15% | Power conversion: 10-15% | Balance of plant: 15-20% | Installation: 5-10%

Market Outlook

Iron-air batteries represent a transformative approach to multi-day energy storage. Form Energy's 100-hour battery has secured major utility contracts, signaling strong market interest in ultra-long-duration storage solutions.