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High-temperature batteries: Science and technology

How a ceramic tube lets molten sodium store energy

What this tab covers The physics and chemistry: how the energy is stored, which materials it needs (scarcity, toxicity, recyclability) and what makes it age.

High-temperature batteries use molten sodium separated from a sulphur or nickel chloride electrode by a ceramic that passes only sodium ions. The materials are cheap and abundant, but the cells must be held near 300 C, the main NaS supplier (NGK) decided on 31 Oct 2025 to stop taking orders, and a leading European ZEBRA-type factory plan was abandoned in Jul 2026.

Mechanism

Mixed

In a sodium-sulphur (NaS) cell, molten sodium gives up electrons and the sodium ions pass through a solid beta-alumina ceramic tube to react with molten sulphur, forming sodium polysulphide. The ZEBRA (sodium-nickel chloride) cell uses the same ceramic, but the positive side is nickel and salt in a molten sodium aluminium chloride electrolyte. Both need heat to keep the electrodes or electrolyte molten: NaS runs at about 290 to 360 C, and ZEBRA needs at least 250 C and is typically held above 265 C. Cold cells are inert: Altech, a would-be ZEBRA-type maker, reported in 2025 that a cell stored unused for 28 years still worked once reheated (a company claim).136789

NaS operating temperature 290-360 C (cell, BASF 2023); 300-340 C (inside enclosure)13 NaS cell About 2 V, 1.2 kWh, 5.3 kg (about 226 Wh/kg, calculated)3 Sodium metal chloride specific energy (Fuji Electric, manufacturer figure) 135 Wh/kg cell; 100 Wh/kg module7 ZEBRA minimum operating temperature At least 250 C8

Material scarcity and toxicity

Favourable

Sodium, sulphur, aluminium oxide and common salt are abundant and cheap, and there is no lithium or cobalt. ZEBRA needs nickel powder, and nickel mining is concentrated: Indonesia produced about 2.6 million t of the world's 3.9 million t in 2025, about 67% (calculated). Molten sodium reacts violently with water, and hot sodium polysulphide is corrosive, so the cells are hermetically sealed in steel.27812

Indonesia share of nickel mine output, 2025 About 67% (calculated from 2.6 of 3.9 million t)12

Degradation and ageing

Favourable

Ageing comes from ceramic electrolyte cracking, corrosion of seals and containers, and stress from heating and cooling cycles, so the cells are kept hot for their whole life. Ratings have improved: earlier NaS systems were rated at 4,500 cycles and 15 years, while the 2024 BASF-NGK container is rated at 7,300 full cycles or 20 years with capacity fade below 1% a year. EASE's 2016 summary gave 2,000 to 5,000 cycles and under 15 years, reflecting earlier designs. A PNNL test of a ZEBRA module measured fade of only 0.0046% per cycle over 150 cycles.124610

NaS rated life, current product 7,300 cycles or 20 years12 NaS rated life, earlier product 4,500 cycles, 15 years10 NaS capacity fade, 2024 product Below 1% a year1 ZEBRA module fade (PNNL test) 0.0046% per cycle over 150 cycles6

High-temperature variants compared12367810

VariantOperating temperatureLife ratingMain uses
Sodium-sulphur (NaS)290-360 C7,300 cycles or 20 years (current); 4,500 cycles, 15 years (earlier)Grid energy shifting, 6 to 8 h; about 5 GWh installed
Sodium-nickel chloride (ZEBRA)Above 250 C (tests at 265 C)Over 6,000 cycles at 80% depth of discharge; design life over 20 years (Fuji Electric manufacturer claim)Standby and backup power, peak shaving; -40 to 65 C ambient (manufacturer claim)

Sources

  1. Japan's NGK discontinues manufacturing of sodium-sulfur batteries (5 Nov 2025) pv magazine / ESS News, 2025
  2. NAS Battery: product sheet (container specifications and references), dated 02/2024 BASF Stationary Energy Storage, 2024
  3. Sodium Sulfur Batteries NAS for Large Stationary Storage Applications: The time is right! (F. Dötz, NAATBatt Sodium Zinc Battery Workshop, Houston, 30 Nov 2023) BASF Stationary Energy Storage / NAATBatt, 2023
  4. Energy storage technology description: Sodium-Sulphur (NaS) battery European Association for Storage of Energy (EASE), 2016
  5. Evaluating ZEBRA battery module under the peak-shaving duty cycles (Shamim et al., Materials 14(9) 2280) Pacific Northwest National Laboratory, 2021
  6. Salt Battery (sodium metal chloride): product page (manufacturer claims) Fuji SMBE (Fuji Electric group), 2025
  7. Experimental investigation of an electrical model for sodium-nickel chloride batteries (Di Rienzo et al., Energies 13(10) 2652) MDPI, 2020
  8. Altech Batteries: 28-year-old ZEBRA battery confirms extended shelf life of CERENERGY technology (company claim reported 16 May 2025) Small Caps, 2025
  9. NGK's NAS sodium sulfur grid-scale batteries in depth Energy-Storage.news, 2016
  10. Mineral Commodity Summaries 2026: Nickel US Geological Survey, 2026