Painting by Volts

by Paul McGoldrick

Conventional cylindrical batteries – the ubiquitous AA and AAA sizes, for example – are constructed in rolled-up layers. Although very convenient for dropping into consumer equipment, the technology does not produce the most efficient construction for the volume used. For the rechargeable Li-ion cell, the central layer is the cathode (more correctly the negative connection) – usually aluminum foil connected to a carbon electrode – with a soluble electrolyte and separator – a lithium salt in an organic solvent – and an anode (the positive connection) – a metal oxide with an outer copper foil for the electrical connection. The lithium ions travel to the positive connection during discharge and reverse during the charging process.

What is perhaps surprising is how relatively new Li-ion technology is. The chemistry was suggested in the 1970s but the first commercial cells were not produced until 1991, employed at that time by Sony.

Rice University, in Houston, has now published research (in Nature’s journal Scientific Reports) on a lithium-ion battery that can be painted onto virtually any surface and, intriguingly, can be combined with solar cells.

This is a dramatic improvement in form factor and opens the door to all sorts of possible designs for new technology using storage. With the possibility of bonding the five various paint layers – the two conductive layers together with the anode, cathode, and polymer separator – airbrushed on objects like ceramic tiles, glass, steel, and a beer mug, the researchers showed that virtually anything could be turned into a self-powered item. One of the cute tests they performed was using bathroom tiles, with the batteries painted on and connected in parallel, together with a solar cell and a series of forty LEDs powered up to spell out RICE. The batteries provided 2.4 V and the cells (charged with the solar cell illuminated by a laboratory light) powered the LEDs for six hours.

The batteries were also successfully cycled through sixty discharge/charge sequences with only a marginal drop in capacity.

The Rice researchers feel that the techniques they have developed – and the mélange of materials used in the paints – are scalable with an estimate that a few square feet of cells could eventually power a laptop, the painting being achieved with industrial spray techniques. One of the limitations with any materials containing lithium is to avoid moisture and any oxygen in their immediate environment.

The notion of perhaps having interlocked battery tiles, with enough of them to satisfy your particular charge capacity demands, is intelligent and very intriguing. The continuing use of lithium is, of course, a little disturbing to the future of the planet.