Material Insights · Understanding the Material World

Other and primary batteries: Engineering and performance

Why non-flammable zinc still loses to lithium on the grid

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

Engineering data for emerging chemistries are thin; zinc-based grid systems cost more than lithium-ion in PNNL's 2021 estimate and were not yet available at 100 MW scale. Primary cells are judged on shelf life and energy per cell rather than efficiency.

Round-trip efficiency

Mixed

Lithium-ion reaches about 85 to 90% (Sandia). Water-based zinc chemistries are less efficient because of side reactions: Sandia gives about 75% for zinc-manganese dioxide, and a 2025 review reports energy efficiency from below 64% to above 89% depending on the cathode. Round-trip efficiency does not apply to primary cells, which are used once.1315

Lithium-ion benchmark About 85-90%15 Zinc-manganese dioxide About 75%15 Aqueous zinc cells by cathode Below 64% to above 89%13

Power and energy decoupling

Unfavourable

These are solid-electrode batteries, so power and energy are fixed by cell design and cannot be sized separately. PNNL estimated a 10 MW, 10-hour zinc-based system at USD 449/kWh in 2021, above a 100 MW, 10-hour lithium iron phosphate system at USD 356/kWh, partly because zinc systems were not yet available at the larger scale.1

Zinc system, 10 MW / 10 h, 2021 USD 449/kWh1 LFP system, 100 MW / 10 h, 2021 USD 356/kWh1

Footprint and siting flexibility

Mixed

Zinc-ion and potassium-ion store less energy per kg than lithium-ion, so systems are larger. Their water-based or less reactive designs may allow denser indoor siting with fewer fire setbacks, but this depends on certification results that are not yet widely published.

Safety and thermal runaway risk

Mixed

Zinc-ion's water-based electrolyte does not burn, the main safety advantage over lithium-ion. Potassium-ion uses organic electrolytes like lithium-ion and needs similar fire testing (UL 9540A and NFPA 855 in the US). Among primary cells, lithium coin cells are a known child-ingestion hazard and lithium metal can ignite if crushed. The EU caps mercury at 0.0005% in all batteries and lead at 0.01% in portable batteries from 18 Aug 2024, and requires portable batteries in products to be removable by the user.9

EU mercury limit 0.0005% by weight9 EU lead limit, portable batteries 0.01% from 18 Aug 20249

Sources

  1. 2022 Grid Energy Storage Technology Cost and Performance Assessment (PNNL-33283), Executive Summary p. vii Pacific Northwest National Laboratory for US Department of Energy, 2022
  2. SafeGuardS 115/23: EU issues new regulation on batteries and waste batteries (summary of Regulation (EU) 2023/1542) SGS, 2023
  3. Several concerns about aqueous zinc metal batteries: from components to unit cells (Li, Liang and Fang, EES Batteries, first published 22 Dec 2025) Royal Society of Chemistry, 2025
  4. Energy Storage Overview (H. Passell, NECPUC Energy Storage Webinar Series, 19 Mar 2021) Sandia National Laboratories, 2021