# Nickel-based batteries: Science and technology

Three nickel batteries, and why cadmium is the problem child

Source page: https://www.materialinsights.org/energy/e_nickel_batt/sg-sci/

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.

Nickel-based batteries (nickel-cadmium, nickel-metal hydride and nickel-iron) share a nickel oxyhydroxide positive electrode in an alkaline electrolyte. They are rugged and long-lived but store less energy than lithium-ion, and cadmium is toxic and tightly restricted.

#### Mechanism
Mixed

All three chemistries store energy by moving hydrogen ions (protons) between a nickel oxyhydroxide positive electrode and a negative electrode in potassium hydroxide solution. The negative electrode differs: cadmium metal in nickel-cadmium (NiCd), a hydrogen-absorbing metal alloy containing rare earths in nickel-metal hydride (NiMH), and iron in nickel-iron (NiFe, the Edison cell). Cell voltage is lower than lithium-ion (Saft rates its NiCd cells on a 1.0 V per cell basis), so more cells are needed in series. Specific energy is modest: about 40 to 60 Wh/kg for NiCd and 40 to 80 Wh/kg for NiMH in one review table (60 to 100 Wh/kg in a 2015 conference abstract), and only 22 to 25 Wh/kg for commercial nickel-iron, against 100 to 200 Wh/kg for lithium-ion.^[3](https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-rare-earths.pdf)^[11](https://sabik.com/wp-content/uploads/2024/10/sabik_marine_datasheet_saft_sunnicd_batteries_20201.pdf)^[12](https://ecs.confex.com/ecs/227/webprogram/Paper50646.html)^[13](https://jes-eurasipjournals.springeropen.com/articles/10.1186/s13639-016-0032-z/tables/1)
 NiCd specific energy 40-60 Wh/kg^[13](https://jes-eurasipjournals.springeropen.com/articles/10.1186/s13639-016-0032-z/tables/1) NiMH specific energy 40-80 Wh/kg (review); 60-100 Wh/kg (ECS abstract)^[12](https://ecs.confex.com/ecs/227/webprogram/Paper50646.html)^[13](https://jes-eurasipjournals.springeropen.com/articles/10.1186/s13639-016-0032-z/tables/1) Commercial NiFe specific energy 22-25 Wh/kg^[12](https://ecs.confex.com/ecs/227/webprogram/Paper50646.html) Lithium-ion specific energy 100-200 Wh/kg^[13](https://jes-eurasipjournals.springeropen.com/articles/10.1186/s13639-016-0032-z/tables/1)

#### Material scarcity and toxicity
Unfavourable

Cadmium is a toxic heavy metal produced as a by-product of zinc refining; world output was about 23,000 t in 2025, of which China supplied about 41% (calculated). USGS still lists NiCd batteries as the main use of cadmium. Nickel is concentrated in Indonesia, which mined about 2.6 of the world's 3.9 million t in 2025, about 67% (calculated). NiMH depends on rare earths, which are themselves concentrated in China. Nickel-iron uses only nickel and iron, the least problematic mix. Historically NiCd helped remove an even worse metal: USGS lists it among the chemistries that replaced mercury-zinc batteries in the US.^[1](https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-cadmium.pdf)^[2](https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-nickel.pdf)^[3](https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-rare-earths.pdf)^[4](https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-mercury.pdf)
 China share of refined cadmium, 2025 About 41% (calculated from 9,500 of 23,000 t)^[1](https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-cadmium.pdf) Indonesia share of nickel mine output, 2025 About 67% (calculated from 2.6 of 3.9 million t)^[2](https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-nickel.pdf) Nickel price, LME annual average USD 15,000/t (2025) vs USD 25,815/t (2022)^[2](https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-nickel.pdf)

#### Degradation and ageing
Favourable

Nickel-based cells tolerate deep discharge, overcharge and extreme temperatures better than most chemistries, which is why USGS notes the reliability and longevity of industrial NiCd. Ageing comes from electrolyte loss and gassing on overcharge, electrode swelling and, in NiCd, the memory effect, a voltage depression after repeated shallow cycling. Nickel-iron is known for very long life but high self-discharge. A review gives 1,000 to 2,000 cycles for both NiCd and NiMH at deep discharge, but shallow cycling extends life greatly: Saft's datasheet (a manufacturer rating) claims up to 8,000 cycles at 15% depth of discharge for its solar NiCd cells, a life expectancy above 20 years and operation from -50 to +70 C. Improved nickel-iron cells reached nearly 3,000 cycles in University of Southern California laboratory tests.^[1](https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-cadmium.pdf)^[11](https://sabik.com/wp-content/uploads/2024/10/sabik_marine_datasheet_saft_sunnicd_batteries_20201.pdf)^[12](https://ecs.confex.com/ecs/227/webprogram/Paper50646.html)^[13](https://jes-eurasipjournals.springeropen.com/articles/10.1186/s13639-016-0032-z/tables/1)
 NiCd and NiMH cycle life (deep cycling) 1,000-2,000 cycles^[13](https://jes-eurasipjournals.springeropen.com/articles/10.1186/s13639-016-0032-z/tables/1) Saft solar NiCd (manufacturer rating) Up to 8,000 cycles at 15% depth of discharge; over 20 years^[11](https://sabik.com/wp-content/uploads/2024/10/sabik_marine_datasheet_saft_sunnicd_batteries_20201.pdf) Saft NiCd operating range -50 C to +70 C^[11](https://sabik.com/wp-content/uploads/2024/10/sabik_marine_datasheet_saft_sunnicd_batteries_20201.pdf) Advanced NiFe, lab Nearly 3,000 cycles^[12](https://ecs.confex.com/ecs/227/webprogram/Paper50646.html)

#### Nickel-based variants compared^[1](https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-cadmium.pdf)^[3](https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-rare-earths.pdf)^[5](https://www.sgs.com/en/news/2023/09/safeguards-11523-eu-issues-new-regulation-on-batteries-and-waste-batteries)

| Variant | Negative electrode | Key material concern | Main remaining uses |
|---|---|---|---|
| **Nickel-cadmium (NiCd)** | Cadmium | Toxic; EU limits portable batteries to 0.002% cadmium | Industrial backup, aviation and rail, harsh climates |
| **Nickel-metal hydride (NiMH)** | Rare-earth based hydrogen-storage alloy | Rare earth supply concentration | Consumer AA/AAA cells, hybrid vehicles |
| **Nickel-iron (NiFe)** | Iron | Low; nickel only | Off-grid and long-life niche backup |

#### Sources

1. [Mineral Commodity Summaries 2026: Cadmium](https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-cadmium.pdf) US Geological Survey, 2026
2. [Mineral Commodity Summaries 2026: Nickel](https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-nickel.pdf) US Geological Survey, 2026
3. [Mineral Commodity Summaries 2026: Rare Earths](https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-rare-earths.pdf) US Geological Survey, 2026
4. [Mineral Commodity Summaries 2026: Mercury](https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-mercury.pdf) US Geological Survey, 2026
5. [SafeGuardS 115/23: EU issues new regulation on batteries and waste batteries (summary of Regulation (EU) 2023/1542)](https://www.sgs.com/en/news/2023/09/safeguards-11523-eu-issues-new-regulation-on-batteries-and-waste-batteries) SGS, 2023
6. [Saft Sun+ (Sunica) nickel-cadmium batteries for solar systems: datasheet (undated; file name suggests 2020; hosted by distributor Sabik Marine)](https://sabik.com/wp-content/uploads/2024/10/sabik_marine_datasheet_saft_sunnicd_batteries_20201.pdf) Saft, distributed by Sabik Marine
7. [Properties of nickel-iron batteries with high-performance iron electrodes (Yang, Manohar, Prakash and Narayanan, University of Southern California; 227th ECS Meeting conference abstract)](https://ecs.confex.com/ecs/227/webprogram/Paper50646.html) The Electrochemical Society, 2015
8. [E-transportation: the role of embedded systems in electric energy transfer from grid to vehicle (Baronti, Chow, Ma, Rahimi-Eichi and Saletti), Table 1, EURASIP Journal on Embedded Systems 2016](https://jes-eurasipjournals.springeropen.com/articles/10.1186/s13639-016-0032-z/tables/1) SpringerOpen, 2016

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_nickel_batt/index.md)
- [Overview](https://www.materialinsights.org/energy/e_nickel_batt/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_nickel_batt/correlation/index.md)
- [Engineering and performance](https://www.materialinsights.org/energy/e_nickel_batt/sg-eng/index.md)
- [Economics](https://www.materialinsights.org/energy/e_nickel_batt/sg-econ/index.md)
- [Impact and additionality](https://www.materialinsights.org/energy/e_nickel_batt/sg-impact/index.md)
- [What to track](https://www.materialinsights.org/energy/e_nickel_batt/tracking/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_nickel_batt/links/index.md)