If you’re looking for the available models and specifications, see the our range of sodium-ion batteries.
How a sodium ion battery works: chemistry, cells and BMS (explained well)
A sodium-ion battery works in the same way as a lithium-ion battery: during charging, sodium ions leave the cathode, pass through the electrolyte and enter the anode; during discharging, the process is reversed and the electrons in the external circuit power the load. The Heiwit systems sold in 2025 and 2026 use cells with layered oxide cathodes. The 2027 version features a NFPP polyanionic cathode (sodium iron phosphate-pyrophosphate). In sodium-ion cells, both current collectors can be made of aluminium, which allows for storage at 0 V. An integrated BMS module monitors voltage, temperature and state of charge. The trade-off is energy density, which is lower than that of lithium iron phosphate: for this reason, Heiwit uses these cells in stationary storage systems for photovoltaic applications.
In this in-depth study we explain how a sodium ion battery works from a technical point of view, but in clear language. If you are looking for a more introductory guide, you can start here:
Sodium ion batteries: what they are, advantages and comparison with lithium batteries
What is a sodium ion battery
A sodium-ion battery is an electrochemical storage in which the sodium ions (Na+) move between cathode and anode during charging and discharging, through a electrolyte. The principle is similar to lithium batteries, but with different materials and reactions. Cathode, anode, electrolyte and the other terms are defined in the glossary of sodium-ion terms.
Main components: anode, cathode, electrolyte
- Cathodeion-hosting material at one stage of the cycle.
- AnodeIt accommodates ions in the opposite phase of the cycle.
- Electrolyteallows ionic transport between anode and cathode.
Charge and discharge: what really happens
During the charge, sodium ions move towards the anode; during the download return to the cathode, generating usable current. This cycle is what enables the battery to store and release energy.
The role of the BMS (Battery Management System)
The BMS is the element that handles protections, cell balancing and communication with the inverter:
- Protection against overvoltage, undervoltage and critical temperatures
- Balancing of cells to ensure durability and uniformity
- Communication with inverter and power regulation
Sodium vs. lithium: technical comparison
The main difference is in the energy densitySodium batteries tend to have a lower density than some lithium chemistries. However, in many stationary installations this difference is not binding, whereas stability, reliability and thermal management can be strengths.
| Parameter | Sodium-ion Heiwit | Reference LFP |
|---|---|---|
| Charge carrier | sodium (Na⁺), abundant | lithium (Li⁺) |
| Critical materials | no lithium or cobalt | lithium, iron, phosphorus |
| Energy density | lower: more weight and volume for the same number of kWh | higher, typically 120–180 Wh/kg |
| Temperature range | Battery for sale: discharge from −25 °C to +60 °C, charge from 0 °C to +60 °C; NFPP cells (2027 version): approximately 95 per cent of capacity at −20 °C in qualification tests | marked capacity drop below zero |
| Thermal stability | good; further improvement thanks to the polyanionic structure of the 2027 version | good, the best among lithium chemistries |
| Deep discharge and storage | tolerates zero volts: aluminium collectors on both electrodes | it doesn't tolerate zero volts (copper collector) |
| Self-discharge | 0.35 per cent per month (6 per cent over 539 days), measured on several batteries, at room temperature, at the latitude of Milan | typically between 1 and 3 per cent per month |
| Cycles | over 6,500 estimated for layered oxide cells (2025–2026); 9,000 for the 2027 version with a NFPP cathode; a total of 31,972 cycles across the installed fleet as at 17 September 2026 | high; the value depends on the cell and the test conditions |
| Ideal application | stationary storage, harsh climates, long service life | light mobility, storage where volume is constrained |
The LFP ranges are typical market values and do not describe a single cell; the sodium-ion data relate to Heiwit cells and systems under the relevant test conditions. A comprehensive comparison, including the qualification data, can be found in the page on the range of sodium-ion batteries.
Real performance: what to look at before choosing
- Continuous and peak power
- Operating temperature range
- Guarantees and conditions of use
- Inverter compatibility
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Technical content drafted and subject to internal review by HEIWIT R&D, the function responsible for classifying cells and conducting tests on Heiwit storage systems.
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