One of the biggest stumbling blocks to greater use of renewable energy, from regulating the grid to powering cars on solar electricity, is in the limitations of storage batteries. Though we've been storing electrical power as chemical energy since the first lead-acid battery was built in 1859, batteries are still too bulky, too expensive, and too slow to charge to do all the things we'd like them to do in the coming age of renewables.
But recent research at UC San Diego may result in lithium-ion batteries that are cheaper and faster-charging, all through adjusting the mathematical models we use to understand how batteries work.
Lithium-ion batteries are so-called because they store charge in the form of lithium ions, charged particles, which move from the battery's negative terminal -- its anode -- to its positive terminal when the battery is in use. When a lithium-ion battery is hooked up to a battery charger, the outside electrical power pushes those lithium ions back toward the anode, where the ions -- which are quite small even compared to other atoms -- lodge in "pores" in the anode's molecular structure, where they wait until the battery is connected to a closed electrical circuit.
Conventional battery chargers and regulators rely on voltage and current to measure how well a battery is charging or discharging, but that doesn't allow for inefficiencies in the lithium ion's movement inside the battery. In order to know how well the battery's functioning, you really need to know where the ions are distributed in the anode, which isn't easy.
"It's similar to having the person that collects tickets at the entrance to a movie theater try to estimate which of the seats the patrons are taking by watching the speed at which the line at the entrance is moving," says Scott Moura of the Department of Mechanical and Aerospace Engineering at UCSD's Jacobs School of Engineering. Moura, along with Professor Miroslav Krstic, is working to model the movement of lithium ions within the electrodes so that they can more accurately estimate where those ions are likely to be. This, according to Krstic, will allow batteries to be used more efficiently. "With advanced estimation algorithms that are based on mathematical models," says Krstic, "batteries can be charged faster and can run more powerful electric motors."
Moura and Krstic have received a Department of Energy grant of $460,000 to develop estimation algorithms for the lithium ion batteries used in electric cars. They're working on the project with auto products supplier Bosch and battery manufacturer Cobasys, and say that it's at least theoretically possible that the right estimation algorithm could provide a complete car battery charge in 15 minutes. That would go a long way to making electric cars more acceptable to the gasoline-accustomed public, and if batteries can also become lighter and cheaper as a result, then so much the better.