Sodium-Ion Batteries: The Sustainable Alternative to Lithium-Ion?

The rechargeable batteries powering everything from smartphones to electric vehicles are, for the most part, lithium-ion (Li-ion) batteries. Since their introduction in the early 1990s, Li-ion technology has become dominant due to its high energy density, lightweight construction, and ability to deliver substantial voltage. But a new contender is emerging that could, in specific applications, begin to displace Li-ion: the sodium-ion (Na-ion) battery. These batteries store energy using sodium ions instead of lithium ions.

A Matter of Abundance: Why Sodium?

The core appeal of Na-ion batteries lies in the sheer availability of sodium. While lithium is found in limited deposits around the globe, sodium is far more abundant – the sixth most common element on Earth, with a natural abundance of 2,360 mg/L, compared to lithium’s 20 mg/L according to research. This difference in availability has significant implications for cost, supply chain resilience, and sustainability.

“Particularly, sodium is cheaper, more abundant and less geographically concentrated than lithium,” explains Dustin Bauer, an associate at intellectual property firm Reddie & Grose with expertise in both Na-ion and Li-ion battery technology. The past decade has underscored the vulnerabilities of relying on geographically concentrated supply chains for critical minerals, and the demand for scalable solutions to meet the growing demand for electrified grids and transportation.

Beyond Supply Chains: Safety and Simplicity

The benefits of Na-ion batteries extend beyond just resource availability. They also offer inherent safety advantages, particularly for large-scale, stationary energy storage systems. Thermal runaway – a dangerous chain reaction that can lead to battery fires – is less likely to occur in Na-ion batteries due to the larger size of sodium ions. These larger ions experience greater “friction” within the battery, slowing down the rate at which they flow to a potential impact point and reducing the risk of rapid overheating and ignition. Lithium ions, in contrast, flow more quickly, increasing the likelihood of thermal runaway.

the chemistry of Na-ion batteries can simplify manufacturing processes and reduce costs. For example, Li-ion batteries require copper for the negative current collector, a relatively expensive and heavy material. Na-ion batteries can utilize aluminum instead, a more affordable and lighter alternative. Carmen M. López, principal scientist in the electrochemistry group at the National Physical Laboratory (NPL), highlights this advantage: “Because of the operating voltage of the batteries, Li-ion requires the leverage of copper for the negative current collector, but copper is more expensive and weighs more than aluminum.”

There’s also potential to replace the organic electrolytes used in Li-ion batteries – the conducting medium for ions – with aqueous electrolytes in Na-ion batteries. This would further enhance sustainability and reduce production costs.

Na-ion Batteries and Electric Vehicles: A Complex Equation

While the lower cost and increased safety of Na-ion batteries make them attractive for various applications, their suitability for electric vehicles (EVs) is more nuanced. The primary challenge lies in their lower energy density compared to Li-ion batteries. This is a direct consequence of the larger size of sodium ions, which limits the amount of energy that can be stored within a given volume or weight.

Currently, CATL, the world’s largest battery manufacturer, has begun commercial production of Na-ion batteries, initially targeting heavy vehicles. Their first-generation Na-ion batteries achieve an energy density of 160 Wh/kg, significantly lower than the 100-300 Wh/kg range typical of Li-ion batteries.

This lower energy density translates to a shorter driving range for EVs using Na-ion batteries, making them less competitive for mainstream passenger vehicles. Bauer describes energy density as the “main and possibly decisive” drawback for Na-ion batteries in this context. Though, Na-ion batteries could find a niche in specific EV applications where weight and size are less critical, such as short-range urban vehicles or low-speed electric buses.

Grid-Scale Storage: A Sweet Spot for Na-ion

The most promising near-term application for Na-ion batteries appears to be grid-scale energy storage. As the world transitions to renewable energy sources like solar and wind, the need for large-scale energy storage solutions to stabilize the grid and ensure a reliable power supply is growing rapidly. Battery energy storage systems (BESS) are playing an increasingly important role in this transition.

Na-ion batteries offer several advantages for grid storage. Their lower cost and improved safety profile are particularly appealing. The risk of thermal runaway, a concern with Li-ion batteries in large-scale deployments, is reduced with Na-ion technology. Recent incidents of BESS fires in the UK, linked to thermal runaway, have highlighted the importance of safety considerations as noted by the UK Parliament.

While Na-ion batteries currently have lower energy density than Li-ion for grid storage as well – BYD’s MC Cube-SIB ESS delivers 2.3 MWh in a 20-foot configuration, compared to 6.4 MWh for their Li-ion equivalent – the cost savings and safety benefits may outweigh this disadvantage in many applications.

Commercial Availability and Future Outlook

Na-ion battery technology is no longer confined to the laboratory. Commercial production is underway, with companies like CATL leading the charge. However, further research and development are needed to improve energy density and optimize battery performance.

López cautions that more real-world safety testing is crucial before widespread deployment. “For example, will it be more desirable and practicable to deploy these batteries in urban vs remote environments? How do we adapt them to existing electricity infrastructure?” she asks.

Despite these challenges, the future of Na-ion batteries looks bright. Their abundance, lower cost, and improved safety profile position them as a viable alternative to Li-ion batteries, particularly in applications where energy density is not the primary concern. As production scales up and technology matures, Na-ion batteries are poised to play an increasingly important role in the global energy landscape.

The development of Na-ion batteries represents a significant step towards a more sustainable and resilient energy future. Ongoing research and investment will be key to unlocking their full potential and accelerating their adoption across a range of applications.