Episode 3: Linas Vilčiauskas
Sodium-ion (Na-ion) batteries have gained increasing attention. One of the reasons is the greater abundance and lower cost of sodium as compared to lithium. What are the main differences and advantages of Na-ion compared to Li-ion batteries?
Na-ion batteries are a type of rechargeable battery that uses sodium ions as the charge carrier instead of lithium ions, in the more commonly known lithium-ion (Li-ion) batteries. The main advantages of Li-ion batteries are the higher energy density and mature manufacturing technology. However, there are also several main differences and advantages of Na-ion batteries compared to Li-ion batteries. Sodium is about three orders of magnitude more abundant than lithium in our environment. Another difference is the use of cobalt in the cathode. Cobalt is relatively rare, expensive and, unfortunately, concentrated in geopolitically unstable regions of the planet. Many high energy Li-ion batteries still typically use cobalt containing oxides in the cathode. In contrast, majority of the current Na-ion technology typically use cobalt free alternative materials such as sodium manganese and nickel oxides or phosphates which are more abundant and much cheaper. The third difference is the ability to use aluminum current collectors in Na-ion batteries in both electrodes due to sodium’s inability to alloy with aluminum at low potentials. This makes Na-ion batteries not only lower cost but also allows them to be stored at fully discharged state (the so-called zero-volt state). The main advantage of the latter is the easier storage and transportation. All of this makes Na-ion batteries a promising alternative to the current generation of Li-ion batteries in terms of cost and performance.
Na-ion batteries can use aqueous and non-aqueous electrolytes. Namperus LT, startup for which you serve as the CEO, develops aqueous sodium-ion battery materials and cells. What are the reasons behind the choice for aqueous electrolytes?
We work on the development of aqueous battery technology in general, and are somewhat agnostic towards the choice of charge carrier whether it be sodium, zinc, lithium or any combination of them. As the name implies, aqueous electrolytes are based on salts dissolved in water. Recently this definition was expanded to also include hybrid electrolytes i.e. those containing a mixture of water and some other solvent and something called the water-in-salt electrolytes which contain mixtures of salts and water where salt has a higher concentration than water. There are many advantages of the use of aqueous electrolytes in batteries. One of them is their inflammability and safety in comparison to the more common organic electrolytes. The second is that they have a significantly higher electrical conductivity and can transport ions more efficiently. This can lead to better performance especially in power applications. Finally, aqueous electrolytes based on simple salts are much cheaper, easier to produce and purify. This makes such batteries easier to maintain, dispose and recycle.
Which are suitable application scenarios for this innovative battery technology?
The main limitation of any aqueous battery technology is their lower energy density compared to the non-aqueous counterparts. At this stage of technology development, this limits their application exclusively to the field of stationary energy storage. In stationary solutions, the weight and size of a battery is usually not the primary concern, and the advantages related to the improved safety and sustainability are usually more important. It could well be that, the upcoming regulations such as the EU Battery Directive will further strengthen the position of alternative battery technologies in certain applications as well.
Which are some of the major limitations and research directions to be addressed to reach readiness level of aqueous sodium-ion batteries?
In my opinion, this field requires a very holistic approach which is not only limited to the development of electrode materials or novel electrolytes but should also encompass such things as the redevelopment of cell components (carbonaceous current collectors, ultra-thick electrodes, dry electrode coating technologies etc.), completely new cell designs (balanced cells, bipolar stacks) or even adoption of novel system architectures such as cell-to-structure.
What is the present stage of Namperus LT? What are your goals and ambitions by a five-year period?
We are currently still mostly working at the battery material level. The selection and bill of materials is probably still the main limitation basis for the development and adoption of any novel battery technology. We firmly believe into the diversification of battery technologies in the coming 5 to 10 years depending on the target application. It could well be that the batteries we will see in standard EV applications will be completely different from those in stationary battery parks not only in terms of materials (e.g. LFP vs. NMC) but also in terms of cell-to-pack-to-structure design. Our hope is to contribute to the development and become a relevant player in the latter field.