By Kyle Proffitt
April 2, 2025 | Researchers from the Massachusetts Institute of Technology have identified a redox-active organic cathode material that excels in sodium-ion batteries, enabling energy density comparable to lithium-ion technologies, high power, and stable performance projected to last over 13,000 cycles. “It can actually compete with the state of the art lithium-ion technology—not just sodium-ion, but with lithium-ion— as well as having a very stable cycling performance and rate performance… it has very high power,” lead author Tianyang Chen said. The research appeared February in the Journal of the American Chemical Society (DOI: 10.1021/jacs.4c17713).
While lithium-ion batteries continue to push limits with solid-state, silicon anode, lithium-sulfur, and additional designs and tweaks, they typically rely on contentious metals including cobalt, nickel, and manganese, and underneath it all, a limited supply of lithium. Sodium-ion batteries are increasingly seen as a worthy contender to help meet the demands of increased electrification, but they have not really come of age yet. Compared to lithium, sodium is plentiful and cheap, but a combination of materials that allow sufficient energy density, charge/discharge speed, and overall stability has not materialized. Battery Power Online spoke with Chen to learn about the discoveries that are changing this.
Organic Molecules As Cathode
The first fundamental discovery is the material used as cathode for these batteries. This material is bis-tetraaminobenzoquinone (TAQ), a planar, 3-ring aromatic molecule containing redox-active carbonyl (C=O) groups. The group of Mircea Dincǎ, principal investigator on the sodium-ion story, now at Princeton University, first reported this molecule for use in pseudocapacitive energy storage in a 2023 Joule publication. They showed that hydrogen bonding between molecules results in the formation of effectively 2-dimensional sheets of the material, almost like extended polymers. Those layers also stack neatly, leaving room for ion diffusion between layers—3.14 angstroms of distance to be exact, which Chen says is superior to layered oxide materials with typical interlayer distance of 2.8 to 2.9 angstroms. Of course, using organic materials (carbon, hydrogen, nitrogen, oxygen) for the cathode avoids metals such as cobalt, and TAQ is easy to come by. “The starting material for TAQ is a really widely produced industrial material for the dye industry,” Chen said.
A report last year from Dincǎ’s group, also with Chen as first author, saw TAQ used in lithium-ion batteries, where it outperformed lithium iron phosphate (LFP) and most nickel-manganese-cobalt (NMC) cathodes in terms of gravimetric (weight-based) energy density and rate performance. Getting TAQ to work with sodium required just a few additional tweaks.
Unique Sodium-Ion Battery Issues
That interlayer distance becomes especially important with sodium, because although it is in the same chemical group and behaves similarly as lithium, sodium ions are much larger, meaning they “cause a lot more structural distortion and volume change during storage,” Chen explained. For their sodium-ion batteries, the researchers paired TAQ cathode with either sodium metal anode or hard carbon pre-loaded with sodium, and they landed on NaPF6 in DME/diglyme for the electrolyte.
Sodium cycling in these TAQ batteries shows some unique characteristics. One molecule of TAQ can accept 4 sodium ions and 4 electrons, which means that four individual reduction events occur during discharge, appearing in a voltage discharge curve as two primary steps, each containing two smaller plateaus. The pattern occurs because the redox events are discrete, unlike the gradual intercalation of lithium into an NMC cathode and its associated gradual discharge curve. The voltage window is also lower for sodium, with an average discharge voltage of 2 V. Chen says the unique voltage curve may actually be a benefit. “This just simply means that there is one kind of quite stable intermediate during the discharge… you can keep that voltage for a long time.”
The layers of TAQ have good electronic conductivity. “Within each layer, electrons can transport very efficiently, because the material has very good extended conjugation, which is facilitated by its flat and pi-conjugated molecular structure as well as hydrogen bonding between different molecules,” Chen said. Finally, the hydrogen bonding between molecules and interactions between layers help prevent solubility in electrolyte, a problem with many other organic electrode materials that would limit battery longevity.
The net effect is some impressive stats. TAQ has a theoretical specific capacity of 355 mAh/g, and the researchers were able to experimentally achieve 606 Wh/kg at the electrode level. This value falls short of typical NMC811 lithium-ion energy density (up to about 750 Wh/kg) but outperforms LFP (~450 Wh/kg). The energy density is better than other sodium-ion cathodes, including layered oxides (up to about 600 Wh/kg) and Prussian blue analogues (up to around 450 Wh/kg; this is the technology Natron Energy uses in their batteries). It surpasses all other organic cathodes. Because its electronic conductivity is very high among organic electrode materials, the researchers could load the cathode with 90% of this active material and accomplish this high gravimetric energy density. The volumetric energy density may still be an impediment, as the researchers report 723 Wh/L at the electrode for TAQ with sodium, whereas LFP values are about 50% higher. In other words, a TAQ sodium-ion battery would be lighter but larger than an equivalent LFP battery using lithium.
The researchers cycled a hard carbon anode cell 5,000 times with energy density of 336 Wh/kg at the cathode, losing only 7.4% of peak capacity for this rate of cycling, slightly higher than 2C. They extrapolate from this measurement to suggest that the cell would retain 80% capacity after 13,500 cycles, if the degradation rate remains consistent.
Faster with Nanotubes
The researchers decided to push these batteries even further, based on an understanding that the electronic conductivity still created a bottleneck against faster rate performance. To this end, they “wrap carbon nanotubes” around TAQ using an in situ growth method. They used carboxyl-functionalized single-walled carbon nanotubes (cSWCNTs), and the researchers improved cathode performance by adding just 2% cSWCNTs. “Each particle is wrapped by carbon nanotube, and each particle is connected with adjacent particles through carbon nanotubes,” Chen said. “We use a very small amount of carbon nanotubes to grab all of these particles together to facilitate electron transport.”
With this modification, the rate performance took off. Performing 90-second charge/discharge cycles, they demonstrated 472 Wh/kg. Pushing even faster, they were able to cycle cells with current density as high as 20 A/g (less than 30 second charge/discharge), giving a top specific power of 31.6 kW/kg at the electrode level. The difference between the TAQ with cWSCNTs and other sodium-ion cathodes becomes quite pronounced at these higher energy densities; at 10 A/g, the electrode-level energy density for the TAQ is still 472 Wh/kg, whereas the next nearest cathode material is about 200 Wh/kg.
What’s Next
Sodium-ion technology is most likely a complement to other chemistries. Even with the developments outlined here, it’s unlikely that sodium-ion will be able to compete with NMC-based lithium-ion technology, especially on a volumetric energy density basis. However, it can outperform LFP even on this metric. “This technology might be able to in the future replace LFP technology,” Chen said. This is especially relevant for stationary energy storage, everything from individual home backup systems to renewable energy grid deployments, data centers, etc., where weight and size are not major drawbacks. Stability, reliable power, and low cost become the key parameters there. Additionally, as vehicle manufacturers increasingly use LFP for medium-range trims, a TAQ-based sodium-ion battery could be used in the same application. Chen estimates that TAQ is one half to one third the cost of NMC and one half the cost of LFP, providing a financial incentive. Additionally, nearly all LFP production transits China, whereas TAQ could be produced anywhere.
This work was supported by Lamborghini, and it stands to reason that they will appreciate these developments because of the power performance (providing rapid acceleration) of TAQ-sodium-ion batteries. TAQ has also led to one spin-off company, Daqus energy, founded by co-author Harish Banda and Dincǎ. Daqus is currently focused on the lithium-variant TAQ batteries, and they are scaling up production to create the kinds of cells that might go into an EV. Again, lithium-ion TAQ outperformed NMC811 on a weight-based energy density and outcompeted LFP in both gravimetric and volumetric energy density, giving it the opportunity to compete with state-of-the-art EV batteries.
