Tohoku, UCLA team promotes 4V class non-metallic organic Lithium batteries; crocodic acid cathode

A joint research team from Tohoku University and the University of California, Los Angeles (UCLA) has made a significant breakthrough toward high-voltage metal-free lithium-ion batteries by using a small organic molecule: croconic acid. . An open access article about their work is published in the journal Advanced Science.

Unlike conventional lithium-ion batteries, which rely on materials like cobalt and lithium, organic batteries exploit naturally abundant elements like carbon, hydrogen, nitrogen, and oxygen. Additionally, organic batteries have higher theoretical capacities than conventional lithium-ion batteries because the use of organic materials makes them lightweight.

Most of the organic batteries reported to date, however, have a relatively low working voltage (1-3V). Increasing the voltage of organic batteries could lead to higher energy density batteries.

Itaru Honma, professor of chemistry at Tohoku University’s Advanced Materials Multidisciplinary Research Institute, Hiroaki Kobayashi, assistant professor of chemistry at Tohoku University, and Yuto Katsuyama, a graduate student at UCLA, found that croconic acid, when used as lithium-ion battery cathode material, it maintains a strong working voltage of around 4V.

While organic batteries have drawn a lot of attention due to their high theoretical capacities, high-voltage active organic materials (>4 V vs Li/Li+) remain unexplored. Here, density functional theory calculations are combined with cyclic voltammetry measurements to investigate the electrochemistry of croconic acid (CA) for use as a lithium-ion battery cathode material in dimethyl sulfoxide and γ-butyrolactone electrolytes ( GBL).

DFT calculations show that the dilithium salt CA (CA–Li2) has two enolate groups that undergo redox reactions above 4.0 V and a material-level theoretical energy density of 1949 Wh kg–1 to store four lithium ions in GBL, exceeding the value of both known organic and conventional inorganic cathode materials.

Cyclic voltammetry measurements reveal a highly reversible redox reaction by the enolate group at ≈4 V in both electrolytes. AC battery performance tests as a lithium-ion battery cathode in GBL show two discharge voltage plateaus at 3.9 and 3.1 V, and a discharge capacity of 102.2 mAh g–1 without loss of capacity after five cycles. With the highest discharge voltages compared to known state-of-the-art organic small molecules, CA promises to be a leading cathode material candidate for future high-energy-density organic lithium-ion batteries.

Croconic acid has five carbon atoms bonded to each other in a pentagonal shape, and each of the carbons is bonded to oxygen. It also has a high theoretical capacity of 638.6mAh/g, which is much higher than conventional lithium-ion battery cathode materials (LiCoO2 ~ 140mAh/g).

We investigated the electrochemical behavior of croconic acid in the high voltage range above 3 V using theoretical calculations and electrochemical experiments. We found that croconic acid stores lithium ions at approximately 4 V, giving a very high theoretical energy density of 1949 Wh/kg, which is higher than most organic and inorganic lithium-ion batteries.

Conceptual illustration of work on croconic acid with multi-electron redox reaction at high voltage > 3.0 V. Katsuyama et al.

Although the theoretical capacity was not achieved in this study, the researchers are optimistic this can be improved by developing high-voltage stable electrolytes and chemical modifications to croconic acid.

Since most electrolytes cannot withstand such a strong working voltage of croconic acid, it is vital to develop new electrolytes. Furthermore, the structures of small organic molecules, including croconic acid, can be easily modified. A suitable structural modification can stabilize the molecule, leading to increased capacity and reversibility.

Yuto Katsuyama, Hiroaki Kobayashi, Kazuyuki Iwase, Yoshiyuki Gambe, Itaru Honma (2022) “Are Redox Active Small Organic Molecules Applicable to High Voltage (>4 V) Lithium-Ion Battery Cathodes?” Advanced Science doi: 10.1002/advs.202200187