Energy storage with bulk liquid redox materials

The Problem

Electrifying transport and storing electricity from renewable intermittent sources is mandatory for a carbon neutral society. Best in class energy density helped Lithium-ion batteries (LIB) to now widespread use, giving a taste of the full promise of electrochemical energy storage (EES).

However, they rely on scarce elements with associated major cost and energy input for production. Hence, the required giant scale deployment makes no sense ecologically nor economically.

Alternative EES devices – supercapacitors and redox flow batteries – each alleviate some of the weaknesses of LIB such as power, used elements, and safety, but remain critically weak in energy per unit weight and mass. Overall, a carbon neutral society has critical demand for environmentally benign EES, which combines the best features of these technologies.

Challenges with LIBs

Success and troubles of LIBs stem from the used transition metal compounds (e.g., based on Cobalt). Being solid and dense, they allow for high energy, but processes are slow in solids, restricting power.

Further, transition metals are scarce, expensive, and energy hungry in production. Therefore, the ideal redox material was based on main group elements, liquid, and had solid-like redox density.

The Solution

In the ERC StG project OMICON, we discovered such a class of low molecular weight organic redox materials with exciting features:

1. They are liquid in pure form and dissolve salts, being active material and electrolyte at once.
2. They are reduced and oxidized with a significant voltage difference, hence can act as anode and cathode material.
3. They are mixed conducting, allowing for very high volume occupation in the electrode.
4. Being liquid, a redox flow battery with unmatched energy density is possible.
5. Consisting of mainly C, O, and H, the materials are accessible in cheap, scalable synthesis from bulk raw materials.