It almost sounds like one of the crazy, crappy products they try to sell you in home shopping programs or an April 1 joke, but in this case it’s true. Material scientists at Rice University in Texas have developed the first spray-on, paint-based batteries. The research team has successfully used this technique to turn objects such as a beer mug, bathroom tiles, and sheets of glass and stainless steel into lithium-ion batteries.
Every chemical battery is made out of multiple layers of different materials – charge collectors (the terminals on the top and bottom of an AA battery), the cathode and anode, and an electrolyte in the middle. In a cylindrical AA or laptop battery, these layers are rolled up; in a flat smart phone or tablet battery, the layers are just placed on top of each other, like a sandwich. Rice University’s spray-on battery is functionally identical to one of these flat batteries, but with layers made of paint, rather than sheets of aluminium, copper, graphite, and lithium compounds.
The key innovation behind Rice’s battery is the creation of charge collectors, electrodes, and an electrolyte that are liquid paints that adhere to plastic, metal, glass, and ceramic. Instead of an aluminium positive charge collector, which would be explosive in powdered aerosol form, the first (bottom) layer of the battery is made of single-walled carbon nano tubes (SWNT). The second layer, the cathode, is made from fairly standard lithium cobalt oxide dispersed in a polyvinylidine fluoride solution. The middle layer, the electrolyte/separator, is a mixture of resin and Perspex. The anode is lithium titanium oxide dispersed in a binder — and the final layer, the negative charge collector, is a commercially available conductive copper paint.
Before the battery can be used, it must be vacuum dried, soaked in an electrolyte (the polymer separate absorbs it), and then laminated with a polymer to seal it. The end result is a 200-micron-thick (the width of two human hairs) lithium-ion battery with surprisingly good characteristics, comparable to commercial layer/roll batteries: It provides a steady 2.4 volts, and 140 mAh per gram of lithium cobalt oxide, retaining 90% of its efficiency after 60 charge/discharge cycles. In the video at the bottom of the story, Rice demonstrates array of eight painted-battery ceramic tiles being charged by a photovoltaic cell, with the batteries then powering a bunch of LEDs for six hours.
Now, because of their thinness, there’s no getting around the fact that these batteries only store a tiny amount of power — each tile only stores around 30 mAh, while a laptop battery stores over 1500 mAh; a battery’s capacity is directly linked to the size of the cathode and anode. But… modern electronics don’t require a lot of power. If this process can be scaled up, it would mean that batteries could be printed on almost anything, from t-shirts to mugs to rolls of duct tape. We could put batteries, and thus sensors, computer chips, and wireless transmitters, everywhere.
This might develop into the ideal power source for field days, or the solution to the energy problems most ‘preppers‘ complain about. Give them a Baofeng UV-5R Camouflage, a can of Li-Ion Spray Paint and they will be happy bunnies.