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Sodium-ion batteries: Engineering and performance

The cold-proof, fire-resistant battery that ships fully discharged

What this tab covers Engineering and operating performance: round-trip efficiency, whether power and energy can be scaled separately, footprint and siting, and safety.

Sodium-ion is efficient, works over a wider temperature range than lithium-ion and carries less fire risk, but needs more space for the same energy.

Round-trip efficiency

Favourable

IRENA puts sodium-ion round-trip efficiency at about 92%, within the 85 to 95% lithium-ion range. Cells can reach 80% charge in about 15 minutes.1

Round-trip efficiency about 92%1 Fast charge to 80% about 15 minutes1

Power and energy decoupling

Mixed

As with lithium-ion, energy and power scale together with the number of cells, and only inverters and grid connections are sized independently. No published cost split for sodium-ion grid systems was found; because the cells drop into the same kind of containers, inverters and grid connections as lithium-ion, the power-related costs per kW should be similar.1

Footprint and siting flexibility

Favourable

Sodium-ion cells hold 250 to 375 kWh per cubic metre, which is within the lithium-ion range but below its upper end, so a grid site needs somewhat more space than for nickel-rich cells. The bigger siting advantage is temperature: it works from about -40 C to 80 C and keeps about 90% of capacity at -40 C, which suits very cold sites and reduces cooling needs in hot climates such as much of India.12

Volumetric energy density 250-375 kWh/m31 Operating temperature range -40 to 80 C1 Capacity retained at -40 C about 90%2

Safety and thermal runaway risk

Favourable

Sodium-ion cells can be stored and shipped at zero charge, whereas lithium-ion usually travels at 30 to 50% charge, which removes a major source of transport and warehouse fires. The study for the European Economic and Social Committee (EESC) reports a lower thermal runaway risk and a safe operating ceiling of about 100 C against about 60 C for lithium-ion. The organic electrolyte is still flammable, so grid systems need the same NFPA 855 fire testing and design as lithium-ion.35

Shipping state of charge, sodium vs lithium-ion 0% vs 30-50%3 Approximate safe operating ceiling, sodium vs lithium-ion about 100 C vs about 60 C3

Sources

  1. Sodium-ion batteries: Technology brief IRENA, 2025
  2. Global EV Outlook 2026: Electric vehicle batteries International Energy Agency, 2026
  3. Energy resilience of households in a prepared union: the potential of a sodium battery-based solution (study by Milieu, WSP and CE Delft) European Economic and Social Committee, 2026
  4. NFPA 855: 2026 edition updates and what they mean for energy storage projects Energy-Storage.news, 2026