A joint research team from Tohoku University and the University of California, Los Angeles (UCLA) has made a significant advancement towards high-voltage metal-free lithium-ion batteries that use a small organic molecule, croconic acid. The breakthrough moves us closer to realizing metal-free, high-energy, and inexpensive lithium-ion batteries.

An illustration of croconic acid and an image of a high-voltage environmentally friendly organic lithium-ion battery. Image Credit: ⒸYuto Katsuyama et al. Tohoku University. Click image for the largest view.

Organic, metal free, high-energy batteries may be a pathway to a greener future. Yet scientists have struggled to find ways to boost the voltage in organic lithium-ion batteries. Now, a study has proposed a small organic molecule known as croconic acid that can maintain a working voltage of around 4 Volts.

The team’s research paper, “Are Redox‐Active Organic Small Molecules Applicable for High‐Voltage (>4 V) Lithium‐Ion Battery Cathodes?” has been published in the journal Advanced Science.

Unlike conventional lithium-ion batteries, which depend on rare-earth materials such as cobalt and lithium, organic batteries exploit naturally abundant elements such as carbon, hydrogen, nitrogen, and oxygen. In addition, organic batteries have greater theoretical capacities than conventional lithium-ion batteries because their use of organic materials renders them lightweight.

Most reported organic batteries to date, however, possess a relatively low (1-3V) working voltage. Increasing organic batteries’ voltage will lead to higher energy density batteries.

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

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

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

Although the theoretical capacity was not achieved in this study, the researchers are optimistic capacity can be enhanced by the development of stable electrolytes at high-voltage and chemical modifications to croconic acid. Since most electrolytes cannot stand for such a strong working voltage of croconic acid, developing new electrolytes is vital. Additionally, the structures of small organic molecules, including croconic acid, can be easily modified. Appropriate structural modification can stabilize the molecule, leading to greater capacity and reversibility.


This looks like a breakthrough. Although in its’ infancy, this innovation is sure to trigger a rush of research and hopefully more innovation. Perhaps the field of organic batteries is in a new starting block, because we’re surely going to need them if the electrification effort keeps gaining power.

A side note. The lithium would be absent from the electrode replaced by croconic acid structure, thus saving the weight. There would likely still be lithium in the electrolyte, unless innovation comes up with something better. The demand for lithium would be reduced in a large way.


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