Today we’re revisiting our research on sodium-ion batteries (SiBs) & sharing some interesting findings from our ongoing research into several commercially available cells. Come along as we expand upon our 1st research report about this new technology poised to compete with lithium-ion as an alternative in advanced energy storage solutions!
Contact: Betsy Barry
Acculon’s research and development endeavors center around our expandable battery system architecture, which is designed to accommodate a range of cell form factors and chemistries, including sodium-ion cells. As such, we have been engaged in exploratory research on several commercially available sodium-ion batteries that are entering the market so that we have as much information as possible to create modules and packs with these cells to fit any low or high-voltage application for our OEM customers.
There are two significant areas of inquiry that we will be exploring today with respect to SiBs that will include broad comparisons to lithium cells: capacity and degradation. Understanding the concepts of capacity and degradation is paramount as these factors play a pivotal role in determining the overall performance and longevity of energy storage systems. Capacity, denoting the amount of electric charge a battery can store, is a fundamental metric influencing the duration a device can operate before requiring a recharge. It directly correlates with the usability and efficiency of batteries across various applications. On the other hand, degradation refers to the gradual loss of a battery’s capacity over time, impacting a battery’s lifespan, which is also key in determining if a battery technology is a viable one for the application at hand.
So where do sodium-ion cells stand on these two fundamental aspects of energy storage?
We sourced and tested several types of commercially available sodium-ion cells to get insight into their performance to de-risk future battery programs using said cells. The initial volumetric and gravimetric capacities of all available cells in the market are quite similar, which indicates the current level of technology. This similarity is due to the fact that the cathode and anode materials of the sourced cells are based on the oxide-based and amorphous carbon materials, respectively. Therefore, a good correlation was observed in the both volumetric and gravimetric energy density of these cells. Averaged energy density values for the four different tested form factors are 120kWh/kg and 250 Wh/l.
We have noticed a significant difference in the rate of capacity degradation among cells that were obtained from the market, despite the consistent cycling protocol, which includes a 0.5 CCCV charge and a 0.5C CC discharge at 100% DoD at room temperature. One of the cell types tested degrades extremely quickly, to as low as 80% capacity after only 30 cycles. This is an unacceptable degradation rate and suggests that some manufacturers are struggling with technology transfer.
Based on ongoing research conducted here at Acculon Energy, we believe
sodium-ion batteries are a competitive alternative to lithium batteries due to their comparable energy density
& capacity degradation, along with being safer & more sustainable.
Therefore, careful cell selection is crucial. All other testing cell types show a reasonably good degradation rate, and the linear approximation predicts a range of 1600 to 6500 cycles to reach 80% capacity, depending on the cell type. Although linear approximation may not be the best method to predict the actual long-term performance, it is still a legitimate metric to compare the results until better statistics are available and a full capacity retention test is done.
How do sodium cells compare to their lithium counterparts?
Acculon’s research indicates that sodium-ion batteries are almost on par with LFP lithium-ion chemistry in terms of gravimetric energy density and just slightly beyond in terms of volumetric energy density. So while many demanding mobility applications may exceed the capabilities of sodium-ion batteries, other industrial applications, including stationary energy storage and non-demanding mobility products, may opt for sodium-ion batteries if other metrics beyond energy density are aligned.
The rate at which batteries degrade is greatly influenced by the conditions in which they are used. Therefore, specific tests must be conducted for each application to accurately predict battery performance. However, initial testing at room temperature and a rate of 0.5C is generally a good representation for a wide range of applications. In such cases, it is worth comparing the performance of sodium-ion batteries with that of lithium-ion ones at these conditions. Lithium-ion battery degradation is well-known. Under moderate conditions, LFP batteries are expected to last for 2000-8000 cycles, while energy-dense NCA or NMC batteries are expected to last for 1000-4000 cycles. Therefore, sodium-ion is already comparable with lithium-ion in terms of capacity degradation.
What about safety and sustainability?
Sodium-ion batteries are considered safer than lithium-ion batteries due to their lower energy density. Sodium-ion batteries also can be safely transported in a truly fully discharged state (0V), which is impossible for Li-Ion batteries. Additionally, safety standards like UL 2271 have been updated to include sodium batteries under the purview that lithium batteries fall under.
Another bright spot for sodium-ion batteries is sustainability, which is a concept that is at the heart of the electrification movement. The abundance of sodium creates a context for a variety of sourcing options while also reducing the need for critical materials. Even so, we are a ways out from the establishment of reliable supply chains for this technology.
For a diverse range of applications, we believe that sodium-ion batteries are a competitive alternative to lithium batteries and are poised to accelerate the energy transition, which pushes global markets toward significant sustainability strides.