Could sodium-ion super-charge Africa’s battery rental market?

The smaller packs are used for charging mobile phones. They can also power household lighting, which is where the biggest social impact is felt as, for example, it gives children more time to do their homework. The packs are a much better alternative to using noisy, polluting petrol generators. The larger packs can be used to replace petrol generators or to power higher-demand electrical items such as electric motor bikes.”

A sodium-ion solution

Use of faster-charging batteries has the potential to increase the profitability of MOPO’s business model, allowing the company to expand further. This was the driver behind the NaBEDA project, part of the Ayrton Challenge on Energy Storage (ACES), which investigated the use of sodium-ion batteries – an emerging battery chemistry with potential benefits over lithium-ion.

Sodium is more widely available than lithium – making it less susceptible to supply chain shocks. Over certain time periods sodium has been less expensive to source than lithium. Na-ion batteries also have safety and life cycle advantages over other types of cells.

Some sodium-ion batteries can safely reach zero volts, which means you can completely discharge the battery, recharge it, and it still works,” he explains. “If you did that to a lithium-ion battery it would be severely damaged. That advantage of sodium-ion has potentially big implications, not just for MOPO but for industry as a whole. You could potentially build and ship packs with all the cells discharged, which would make the manufacturing and shipping processes much safer and reduce the risk of fire.”

But as a relatively untested chemistry, little was known about how sodium-ion cells would perform in harsh environments such as sub-Saharan Africa.

For the NaBEDA project, MOPO sourced three different types of commercially available sodium-ion cells. The Sheffield team incorporated the cells into the 4-cell MOPO50 battery packs and cycled them in environmental chambers at high temperatures.

MOPO50 batteries of 50Wh for flexible household energy for 24 hours.

The team discovered that the cells do not degrade any faster at temperatures of 35°C or above, and that they actually produce less heat during operation than other battery chemistries. This is something that could lead to shorter charging cycles and extend the lifespan of battery packs.

We didn’t see any performance drop off when we took the cells right down to zero volts and charged them up again. We even short-circuited the cells for several weeks, then put them back in operation and they functioned normally.”

Sodium-ion cells have lower energy density than Li-ion. Because of this, Dan says, making a business case to use them in small battery packs is currently difficult.

To achieve the desired density with what’s on the market at the moment you need big cells. That doesn’t make a lot of sense for MOPO’s small rental product because they become too big to carry around. But we’ve shown that for larger battery packs like the MOPO Max there’s potentially a viable business case.”

The next steps

Proving the practicality of larger battery packs using Na-ion batteries will be the aim of a follow-on project, NaSEMA, which will begin in July 2025 under a second ACES “concept-to-demonstrator” project.

Dan’s team will assemble a batch of the larger, recently launched MOPO Max 1 kWh battery packs with sodium-ion cells and send them to Liberia. The packs will be deployed to MOPO customers to assess their performance in real-world applications like e-motorcycle batteries, generator replacement, and cooking. The project will determine whether Na-ion is a commercially viable alternative to lithium iron phosphate (LFP) cells for MOPO.

MOPOMax of 1,000Wh for flexible energy for households, businesses & e-mobility.

Further lab work will also be carried out looking at factors including calendar ageing – how fast cells degrade at high temperature when not being used, and the effect of storage at zero Volts. This will help quantify potential cost savings in logistics and operational resilience, particularly for deployment in remote, off-grid environments where traditional battery technologies face challenges in storage and transport.

Dan says working with the Faraday Institution as part of ACES has been “refreshing”.

I like the approach where seed funding is awarded to set up a small project to see if a technology has potential. I’m really pleased we’ve been able to produce outputs that are worthy of further investigation.

What we’re doing here isn’t fundamental research, but it’s equally important. It’s finding out how technologies can be applied, and the impact they can have on lives and livelihoods.”

Jono West Co-Founder and Chairman of MOPO concludes:

Our latest collaboration with Professor Dan Gladwin and the University of Sheffield marks an exciting step forward as we trial sodium-ion cell chemistry in Liberia. The potential impact is truly transformative, not only on our business model but also offering a pathway to significantly disrupt the global battery supply chain and reduce reliance on critical minerals. We are deeply grateful to the Faraday Institution for their crucial support in bringing this project to fruition.”