Lithium-ion versus challenge: sodium-ion batteries

Which is more sustainable: Li-ion or Na-ion batteries? That’s a complex and dynamic question without a simple answer. The electrification of everything is expected to lead to post-lithium-ion battery (LIB) technologies, such as potassium-ion batteries (PIBs), sodium-ion batteries (SIBs), and possibly more exotic chemistries. In the near term, the dominance of LIBs will be almost unassailable. The key word is “almost.”

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Among the keys to replacing LIBs will be the ability of the contenders to o er improved sustainability in addition to matching the performance capabilities of LIBs. There is no single agreed-upon international definition of sustainability. That makes any discussion or analysis of sustainability problematic. Sustainability is often described in three dimensions related to environmental, economic, and social factors. E ective recycling can be an important environmental consideration related to sustainability. For example, the materials in lead-acid batteries (PbAs) are about 96% recycled, making them a highly sustainable technology. Looking at challengers to LIBs’ dominance, SIBs are already being commercialized, while PIBs are mostly a work in progress.

Rechargeable batteries are a key technology supporting sustainable systems such as electric vehicles and grid-scale energy storage. LIBs will continue to improve. But they are a mature technology, and it’s expected that the improvement rate for competitive chemistries, such as SIBs, will be faster and eventually close the gap with LIBs. It’s not clear how rapidly any transition away from LIBs will occur. If it occurs, sustainability must compete with economic and technical performance considerations.

Japan is one of the leaders in maximizing the sustainability of LIBs and has developed multiple streams for using old LIBs, especially LIB battery packs in EVs. Even when EV battery packs no longer deliver the needed range, they can still have significant capacity. Sometimes, the battery packs can be refurbished for less demanding transportation applications, used in di erent applications such as stationary energy storage, or recycled.

Recycling is well-established for PbAs but is not generally available for LIBs. Materials such as plastic cases and metals are first separated when batteries are commercially recycled. With LIBs, the next step is to separate

Battery recycling is a four-step process that can help increase the sustainability of rechargeable batteries.

| courtesy of EPRI Journal the cathode materials, such as lithium and cobalt — both are in very limited supply. Today’s challenge is that the cost of separating lithium and cobalt is too high compared to the cost of new materials. That’s one factor that makes it uneconomic to recycle LIBs.

Standardized and simplified

Among the challenges to effectively recycling LIBs are the wide variety of package styles and chemistries. PbAs have a much more limited range of package sizes and are mostly packaged in specific types of plastics. In addition, the lead grids are relatively easy to melt down and recycle. In contrast, many sizes and package materials are used for LIBs and a range of LIB chemistries, which significantly complicates any recycling processes. While there is also a wide range of SIB chemistries, including sodium manganese magnesium oxide (NaMMO), sodium nickel manganese magnesium titanate (NaNMMT), sodium and ironbased Prussian blue analogs (NaPBA), and others, SIBs are generally easier to recycle compared with LIBs. But the materials’ low economic value limits the commercial recycling prospects.

SIBs are an emerging technology, and there’s an opportunity for the SIB industry to develop a limited range of package styles modeled after PbAs, reducing the cost of recycling SIBs and improving the economic equation of recyclability. The performance of NaPBAs is getting close to or even better than that of their LIB counterparts. As SIB performance rivals that of LIBs, sustainability may take a more central role in choosing between the technologies. Battery recycling can be envisioned as a four-step process:

• Collection

• Disassembly

• Material recovery

• Material reuse

LCA for rechargeable batteries includes the production of the batteries, their integration into systems such as EVs, and the impact of their lifetime use and recycling. | courtesy of Advanced Energy Materials.

E ective LIB and SIB battery recycling technologies are still a work in progress. They will need to process “secondary” materials, such as graphite, polymers, electrolytes, solvents, and salts, and recover any higher-value materials. Several options are available, including removing organics and electrolytes using thermal processes and recovering other elements using pyrometallurgical or hydrometallurgical processes. Work under the European Battery Directive has identified hydrometallurgical processes as the most promising for recovering battery materials with the quality levels needed to support battery production and a circular battery economy.

Battery recycling processes must also be developed with sustainability and minimizing environmental impacts as key considerations. It does not necessarily increase sustainability if the recycling process results in large amounts of environmental damage. A comprehensive strategy for battery recycling requires that both the batteries and recycling processes be simultaneously optimized. This process is called “design for recycling,” which extends from the physical design and assembly of batteries to simplify

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