A team of scientists from Stanford University has developed a system that notifies users when lithium ion batteries are overheating or are a few degrees from burning a hole in one's pocket.

"Our goal is to create an early-warning system that saves lives and property," said Yi Cui, associate professor of materials science and engineering at Stanford. "The system can detect problems that occur during the normal operation of a battery, but it does not apply to batteries damaged in a collision or other accident."

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A lithium ion battery is composed of two electrodes, a lithium metal-oxide cathode and a carbon anode, packed tightly side-by-side. The two electrodes are separated by a thin layer of polymer. Batteries that have a damaged polymer film would let its two electrodes meet, possibly leading to overheating, short-circuiting or an explosion.

The layer of polymer, which is composed of the same material that make up plastic bottles, is also porous enough to let the flow of lithium ions between the electrons through a flammable electrolyte solution. The polymer is designed to behave as such, but any problems during its manufacturing stage could be potentially dangerous.

Overcharging is another hazard. It results in the aggregation of lithium ions, creating dendrites that are capable of breaching the separator. If the dendrites reach the cathode, it may cause the battery to short.

The system developed by Cui and his team involves adding a thin layer of copper on one side of the plastic separator, making an extra layer, which is described by the team as the third electrode.

"The copper layer acts like a sensor that allows you to measure the voltage difference between the anode and the separator," said co-lead author and graduate student Denys Zhuo. "When the dendrites grow long enough to reach the copper coating, the voltage drops to zero."

The zero voltage of the battery is the indicator of that the dendrites have already grown halfway across the battery. I serves as a notification that the battery should be taken out, before the dendrites get to the cathode, closing the circuit.

TagsSmart Battery, Stanford University, Lithium ion batteries, Laptop, Tablet, Overheating battery, Short circuit