Researchers at MIT have developed a layered organic electrode material with high electrical conductivity, high storage capacity, and complete insolubility to enable reversible intercalation of Li⁺ ions that allow it to compete at the electrode level, in all relevant metrics, with inorganic-based lithium-ion battery cathodes.

In an open-access paper in the journal ACS Central Science, they report that the optimized cathode stores 306 mAh g^–1_cathode, delivers an energy density of 765 Wh kg^–1_cathode—higher than most cobalt-based cathodes—and can charge–discharge in as little as 6 min.

These results demonstrate the operational competitiveness of sustainable organic electrode materials in practical batteries.

—Chen et al.

Organic materials so far have mostly not been able to match the conductivity, storage capacity, and lifetime of cobalt-containing batteries. Because of their low conductivity, such organic materials typically need to be mixed with binders such as polymers, which help maintain a conductive network. These binders, which make up at least 50% of the overall material, bring down the battery’s storage capacity.

About six years ago, the lab of Mircea Dincă, the W.M. Keck Professor of Energy at MIT and senior author on the paper, began working on a project, funded by Lamborghini, to develop an organic battery that could be used to power electric cars. While working on porous materials that were partly organic and partly inorganic, Dincă and his students realized that a fully organic material they had made appeared that it might be a strong conductor.

This material consists of many layers of TAQ (bis-tetraaminobenzoquinone)—an organic small molecule that contains three fused hexagonal rings. These layers can extend outward in every direction, forming a structure similar to graphite. Within the molecules are chemical groups called quinones, which are the electron reservoirs, and amines, which help the material to form strong hydrogen bonds.

Common organic cathodes with low active material content and TAQ-based cathodes with high and practical-relevant active material content. Chen et al.

Those hydrogen bonds make the material highly stable and also very insoluble. That insolubility is important because it prevents the material from dissolving into the battery electrolyte, as some organic battery materials do, thereby extending its lifetime.

A 2D layer of TAQ molecules formed by intermolecular hydrogen bonding (dashed lines). Chen et al.

One of the main methods of degradation for organic materials is that they simply dissolve into the battery electrolyte and cross over to the other side of the battery, essentially creating a short circuit. If you make the material completely insoluble, that process doesn’t happen, so we can go to over 2,000 charge cycles with minimal degradation.

—Mircea Dincă

Tests of this material showed that its conductivity and storage capacity were comparable to that of traditional cobalt-containing batteries. Also, batteries with a TAQ cathode can be charged and discharged faster than existing batteries, which could speed up the charging rate for electric vehicles.

To stabilize the organic material and increase its ability to adhere to the battery’s current collector, which is made of copper or aluminum, the researchers added filler materials such as cellulose and rubber. These fillers make up less than one-tenth of the overall cathode composite, so they don’t significantly reduce the battery’s storage capacity.

These fillers also extend the lifetime of the battery cathode by preventing it from cracking when lithium ions flow into the cathode as the battery charges.

The primary materials needed to manufacture this type of cathode are a quinone precursor and an amine precursor, which are already commercially available and produced in large quantities as commodity chemicals. The researchers estimate that the material cost of assembling these organic batteries could be about one-third to one-half the cost of cobalt batteries.

Lamborghini has licensed the patent on the technology. Dincă’s lab plans to continue developing alternative battery materials and is exploring possible replacement of lithium with sodium or magnesium, which are cheaper and more abundant than lithium.

Resources

• Tianyang Chen, Harish Banda, Jiande Wang, Julius J. Oppenheim, Alessandro Franceschi, and Mircea Dincǎ (2024) “A Layered Organic Cathode for High-Energy, Fast-Charging, and Long-Lasting Li-Ion Batteries” ACS Central Science doi: 10.1021/acscentsci.3c01478