Liquid Batteries Without Metals: New Polymer Inspired by Cells Discovered

A team of scientists from Northwestern University has synthesized a liquid material capable of charging like a battery and altering its physical structure based on the energy accumulated. The researchers have combined the processes of energy collection, storage, and utilization into a single supramolecular system, a step that allows for the elimination of heavy metals or plastics in storage systems.

The research group, led by Samuel I. Stupp, drew inspiration from the cellular cytoskeleton. This biological scaffold continuously assembles and disassembles to allow the cell to maintain its shape, move, and divide. The scientists replicated this dynamic behavior on a synthetic scale, with the compound using electrons gathered from sunlight, electricity, chemical sources, or X-rays to trigger the phase transition.

How the Northwestern University Liquid Battery Works

The fluid, initially a yellow solution of globular aggregates, absorbs energy transforming into a conductive black hydrogel. The study, published in the journal Chem, details the molecular functioning of this system that operates under anaerobic conditions. The molecular building blocks assemble through stacking forces and radical polymerization, trapping electrons within the polymeric network. The main co-authors, Tyler Jaynes and Luka Dordevic, worked on validating the mechanism.

The customized molecule, named ANI-MV, combines a light-sensitive aromatic unit of amino-naphthalene (ANI) with a fraction of methyl-viologen (MV), tasked with electron accumulation. When the ANI section captures energy, it donates electrons to the MV portion. Nearby molecules exhibit a strong mutual attraction, forming stable molecular pairings called pimers. These organize into nanometric semiconductors where electrons move freely.

This lattice retains charge for months in the absence of air. Restoring the initial liquid state simply requires exposure to atmospheric oxygen, while oxygen dissolves the hydrogel, reverting the material to small isolated clusters suspended in the yellow liquid. During the reverse transition, the accumulated electrons are transferred to the oxygen, generating reactive species used to drive oxidation reactions of organic substrates.

The team demonstrated the feasibility of this reaction by carrying out chemical processes in complete darkness: since light stimulation can selectively activate gelation, the researchers printed microscopic conductive circuits destined to fade with the oxygenation of the medium. Stupp estimated that a single gram of this substance has the capacity to store enough energy to power a common smartwatch, with the entire system operating stably in water and suitable for applications in soft electronics and programmable materials.

The research received funding from the Center for Bio-inspired Energy Science of the U.S. Department of Energy.