Emily Daniels put together a workshop for kids that teaches them how to make a salt water + paper based battery, which can power an LED. She writes:
In front of a room of 25 astonished faces I dipped my finger into the brine and dabbed the last of the water onto the flower, the LED popping on and cries of “But but…where’s the battery?” echoing amid “Wait…what?”
This workshop focused on understanding how a battery works by taking the traditional model of a voltaic cell and crafting homemade batteries out of paper and wire with 9 to 11 year olds through the ongoing LCRC-Artengine Awesome Indies after school program.
I devised two designs that utilized the absorbency of paper to act as the salt bridge between two dissimilar wires. Wiring together 6 cells produced enough current to light an LED for 2 hours. I had an additional challenge of making the design solder less to accomodate the size of the class and the technical challenges of not having hot irons in the room we were in. In preparation for the class I cut out bases and laid out the rows of holes in the paper ahead of time so that the kids could just focus on weaving the wires and decorating the paper.
All of the materials are common household items- salt, water, paper (the more absorbant the longer the LED stays lit), cardboard, the wire is easily purchased at a hardware store and the LEDs you can get at an electronics store. I’ve posted instructions on how to assemble them here. While testing the design the lights went through 6 uses of 2 hours each and it still seems to be going strong. After a while the metal will oxidize to the point of non-use, and then you can just recycle the parts or make something else with them!
I’d also suggest you follow her on Twitter — she’s always doing something rad.