When discussing electrification in off-highway applications, lithium-ion (Li-ion) technology tends to dominate the conversation, and rightfully so. It compares favorably to combustion engines in certain metrics and offers clear advantages over other battery electric options. Yet, it’s still maturing and is yet to reach its full potential.
However, given supply chain constraints and costs associated with mining lithium, alternatives to lithium-ion batteries (LIBs) are being sought. One of the suggested solutions is an element that sits right below lithium in the periodic table, sodium. Sharing similar characteristics with lithium, research on sodium batteries began in the 1970s; however, they were far from as successful as lithium, leading to rapid commercialization of the latter.
The revived interest in sodium as a viable commercial alternative to lithium throws an interesting curveball in the battery electric field as it could positively disrupt the market. However, how do sodium-ion batteries (SIBs) compare to lithium-ion batteries, and what could their introduction to the off-highway vehicle market mean?
Cost and safety as driving factors
The first thing to note about sodium is its availability; it’s the sixth most common element and can even be extracted from seawater. It requires little treatment and processing, which lowers the cost and time it takes to render it battery ready. The vast availability of sodium also means it’s unlikely there will ever be any supply chain issues, as almost any country with adequate infrastructure can produce it.
Sodium-ion batteries are non-flammable and, therefore, not susceptible to thermal events and can operate across a vast temperature spectrum. Data suggests that sodium batteries maintain a 90% capacity-retention rate when running in -20°C and can continue functioning in temperatures of up to 60°C. This makes them a safer option than most comparable battery technologies, leading to increased research in recent years.
Furthermore, extracting sodium from the Earth or the seas has a much lower environmental impact, and its abundance means less energy is required. Sodium-ion batteries are also marginally easier to recycle, making them relatively more sustainable.
Where sodium has the edge over lithium
The rarity of lithium is a common theme whenever talking about li-ion batteries; however, it’s worth noting that it’s unlikely the world will run out of lithium any time soon. There’s enough to power billions of EVs, so what “rarity” means here is more about the limited number of locations equipped to handle adequate mining, treating, and processing of the material sustainably.
This has created a somewhat gated industry where large quantities of lithium are controlled by a few countries, which drives up the price, considering the “limited” supply for such high demand. The fact that it could easily take ten years to open a new mine ready for lithium extraction doesn’t help satisfy demand either. And it’s well known that demand is likely only to increase unless a suitable alternative is found that at least supplements the EV market demand for rechargeable batteries rather than outright replacing lithium-ion.
It’s here that sodium’s abundance is put in sharp focus. There’s also a massive difference in raw material price; as of late 2022, lithium carbonate cost $570,000 per ton, while sodium carbonate was priced at less than $3,000 per ton.
Sodium salts’ better conductivity also allows for lower electrolyte concentration, and aluminum can be used for both the anode and the cathode, which further drives down costs. On the other hand, lithium requires aluminum and copper, which is slightly heavier and more expensive.
SIBs’ capacity to operate under a broader temperature spectrum makes them an exciting prospect for OEMs and companies operating in harsh weather conditions. The power supply retention rate is 90% at -20°C and only drops to 70% at -40°C.
It’s a considerable feat, considering Li-ion batteries can lose almost half their capacity when exposed to temperatures below 0°C and drop to 12% capacity at -40°C. For Li-ion batteries, the optimal operating temperature is 0°C to 50°C, although thermal management systems go a considerable way towards ensuring functionality on either side of this range.
Sodium-ion batteries also don’t suffer from any over-discharge problems and can be discharged to 0 volts, while lithium-ion batteries cannot, as otherwise, the interlayer structure of the cathode graphite might collapse, affecting the secondary insertion of lithium ions. The LFP chemistry can come close to full discharge, although battery manufacturers still wouldn’t recommend doing so.
Why lithium-ion still leads the way
While sodium-ion batteries might supply power to battery electric vehicles and applications in the future, it’s unlikely that they’ll unseat Li-ion batteries any time soon. Firstly, despite SIBs offering three main cathode types (oxide, polyanions, and Prussian blue analogs), there’s no consensus on which one should be commercialized first. On the other hand, the six main types of lithium-ion battery chemistries are well-defined for various applications.
Sodium-ion batteries also have far lower power and energy densities, and while this does mean increased safety, lithium-ion battery manufacturers alleviate these worries with various safety measures. In Xerotech’s case, for example, our patented Xerotherm® technology is a world-leading solution that snuffs out the threat of thermal propagation at the source. We also have safety controls at cell, module, and pack levels, ensuring that our Hibernium® battery packs are among the safest on the market, with no performance compromises.
In practical terms, less power and energy density mean SIBs store far less power than LIBs. This means that a sodium-ion battery of similar size to a lithium-ion battery will give much less range or operational time before the next required charge. And in the off-highway market, that means increased downtime. To make up for that, Sodium-ion batteries would need to be larger, which is slightly prohibitive to a market where vehicles are likely to operate in tight spaces.
Lithium-ion batteries are also slightly more efficient when using the energy stored in the battery, as they use 90% of energy stored, compared to 80-85% for sodium-ion. Lithium-ion batteries are also more efficient when it comes to charging; they charge faster and can withstand far more charge cycles.
The sodium-ion electrode suffers structural degradation under repeat charge-discharge cycles (generally around 3,000 cycles), whereas the Li-ion chemistries used for off-highway applications can withstand between up to 10,000 charge cycles, depending on the cell chemistry of choice. In some ways, this might mitigate Sodium-ion batteries’ cost advantage in the long run, as they’ll need to be replaced more often than LIBs.
What this could mean for the OHEV market
For off-highway electric vehicles (OHEVs), it’s unlikely that sodium-ion batteries represent a like-for-like replacement with lithium-ion batteries. They certainly carry notable advantages, especially regarding production costs, practically infinite supply, and safety, but lithium-ion batteries stand out in the most critical metric: performance.
LIBs can operate longer, cover more distance, provide more energy, and charge quicker, all with a smaller surface area than SIBs of similar power. There’s also still room for further development of LIBs, even as the more mature technology of the two.
Lithium-ion’s mass market commercialization across private road-use vehicles and off-highway industry applications means a wealth of data to assess when improving this battery type. Sodium-ion is far from this, so it’s unlikely ever to become a mainstream e-mobility market player. However, that’s not to say it can’t carve out its own niche.
Cost-effectiveness and increased safety make SIBs ideal for energy storage systems (ESS) since they’re static applications. Another option would be vehicles that don’t need to cover great distances or reach high speeds and have the space to house the larger battery without redesigning the vehicle structure. That could be last-mile delivery vans, open-pit mine vehicles, and the like.
There’s certainly room for expansion though, especially with more tests lined up for sodium-ion batteries, so this prediction may have to be revisited in the future. Also, by providing a functioning alternative to lithium, sodium batteries could be one of the catalysts for bringing down lithium-ion production costs.
Time to go electric
In summary, lithium-ion batteries will remain the go-to technology for vehicle electrification for the foreseeable future. Would you like to know how lithium-ion can help you power the change in your industry? Head to our online catalogue to see whether we’ve got a battery to suit your needs or reach out to us in person.
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