While there’s no question that lithium-ion battery chemistry reigns supreme in manifold electronics, growing concerns over cost, safety, and production are casting doubt on the technology’s future. Sodium-ion (Na-ion) chemistry is nothing new, by comparison, yet has nudged its way into recent conversations as an alternative to Li-ion batteries.
Recent research developments (like those to increase sodium storage behavior via electron-rich element-doped amorphous carbon) are aiming to make Na-ion batteries a more affordable and sustainable replacement to Li-ion batteries.
Lithium-Ion Pros and Cons
Because lithium-ion (Li-ion) chemistry has unrivaled electro-positivity (or ability to produce energy) and charge density, it’s become wildly popular as the basis of batteries in today’s devices, ranging from personal electronics to automotive EVs. This means that manufacturers can produce more powerful batteries and keep packaging relatively compact.
During charging and discharging, lithium ions in a Li-ion battery move back and forth between the two electrodes. Image used courtesy of AZo Materials
Mainstream batteries—those filled with liquid electrolyte solution between cathode and anode—need a porous barrier to limit chemical activity. Temperature swings cause this liquid to expand, which can put stress on outer casings and make them more prone to cracking or puncture. Extreme heat readily causes combustion, although the overwhelming majority of batteries never operate under such conditions. Furthermore, leakage can corrode nearby components.
Internal electrolytes are converted to hydrofluoric acid (HF) after contacting ambient moisture. Short-term inhalation of HF is hazardous—often causing chronic lung disease and even death. This risk is elevated in exposed systems since the acid becomes gaseous at just 19°C. Consequently, EV giants like Tesla implement containment systems to combat this.
Thankfully, solid-state batteries now exist. These newer designs are notably safer. No separators are required, saving space and shrinking battery packs. Solid-state batteries also have a longer lifespan.
Comparison of the structure of Li-ion batteries vs. solid-state batteries. Image used courtesy of Samsung
However, more research is needed before this expensive battery-type is widely adopted.
Where Sodium-Ion Meets Lithium-Ion Challenges
Because billions of electronics rely on lithium-ion technology, there’s growing concern over long-term lithium shortages. Lithium is the 33rd most abundant element in the Earth’s crust.
Additionally, large amounts of cobalt—which are right above lithium in terms of abundance—are needed to form electrodes. In fact, four years ago, an MIT study found that cobalt demand could outpace global supply by 1.6 times.
Sixty percent of cobalt stores reside within the Democratic Republic of the Congo—where mining is linked to child labor. In addition to these ethical concerns, companies must also decide if cobalt’s $33,000-per-ton cost is a sustainable solution.
Sodium-ion (Na-ion) batteries don’t represent a massive departure from lithium-ion variants. The elemental structure of sodium is quite similar to lithium (being a Group 1 metal), and thus material testing processes are similar. Manufacturing processes are comparable, too.
Schematic of a Na-ion battery cell. Image used courtesy of ACS Energy Letters
Sodium is many magnitudes more abundant than lithium—ranked 6th overall. It’s found everywhere in the Earth’s crust and is harvestable from the ocean. Because Na-ion batteries don’t require cobalt electrodes, they are also considerably more affordable.
Research Makes Na-Ion an Attractive Li-ion Alternative
While Na-ion technology isn’t new by any means, certain chemical and manufacturing challenges have prevented it from being accepted as a Li-ion battery alternative. Researchers at various institutions in the past few months have aimed to overcome these barriers.
Modified Carbon Anodes
Korean researchers have already crafted new Na-ion designs using modified carbon anodes. This has yielded thermodynamic benefits and boosted capacity. Most Na-ion batteries still use graphite as an anode material—rendering them less performant. This move promises to offset the technology’s shortcomings. Scientists sought to do the following:
- Promote rapid electron transport from electrolyte to active material via a porous separator
- Make sodium ions more accessible to the active material across larger sites
- Enable structured co-intercalation (ion insertion) from surface to interior
- Maintain short diffusion paths and microstructures
- Increase the number of active sites
Basic diagram of how the researchers sought to improve Na-ion battery performance with carbon-based anodes. Image used courtesy of Korea Maritime and Ocean University
The researchers posit that when these conditions were met, Na-ion batteries could match or even outperform their cousins.
A Sodium-Oxide Cathode Alternative to Cobalt
Overall, however, sodium ions are larger than lithium ions; output improvements are essential in negating deficiencies in energy density. Sodium batteries aren’t quite viable (yet) for personal, portable electronics. They’re currently better suited for stationary applications.
Thankfully, Skoltech and its research partners have developed a new sodium oxide cathode material. While cobalt isn’t as integral to Na-ion batteries, sodium cobalt oxide (NaCoO2) remains a common cathode material. Any lessening of this material dependence is helpful.
Additionally, these experimental batteries retain capacity, resist moisture, and have little voltage fade. This phenomenon is common with prolonged LiB cycling. However, the researchers encountered voltage hysteresis, which may obstruct manganese migration within the battery.
Research May Be Key for Progressing Na-Ion Batteries
Na-ion technology certainly isn’t a fad. The research push reflects a need to overcome shortages and shortcomings with existing Li-ion technologies. Because the portfolio of LiB devices is so diverse, however, it could take quite some time before mainstream adoption.
Sodium-ion battery pack created by researchers at the Zhejiang University, Ningbo University, and Dongguan University of Technology. Image used courtesy of AIP Publishing
The industries that could most benefit from Na-ion batteries are often those that now rely on Li-ion batteries: namely, portable electronics and EVs.
Ironically, the similarities between both chemistries and production strategies are a boon for Na-ion. Sodium isn’t a complex, foreign material—it’s commonplace, and its weaknesses are well known. It may only be a matter of time before engineers and scientists work out the practical kinks and introduce this battery type to market.