Power/Performance Bits: Oct. 14

Safety first
A technology designed for conventional lithium-ion batteries by Stanford University researchers warns the user before it overheats and bursts into flames.

The goal was to create an early-warning system to saves lives and property, by detecting problems that occur during the normal operation of a battery, the researchers said. The technology does not apply to batteries damaged in a collision or other accident.

The ultrathin copper sensor is deposited atop a conventional battery separator (white square) as part of an early warning system to alert users that a lithium-ion battery is overheating. (Source: Stanford University)

A typical lithium-ion battery contains two tightly-packed electrodes: a carbon anode and a lithium metal-oxide cathode, with an ultrathin polymer separator in between. The separator keeps the electrodes apart and if it’s damaged, the battery could short-circuit and ignite the flammable electrolyte solution that shuttles lithium ions back and forth.

The separator was manufactured out of the same material used in plastic bottles, and is porous so that lithium ions can flow between the electrodes as the battery charges and discharges.

While most lithium-ion batteries are used in small electronic devices, the bigger the battery pack, the more important this becomes, especially considering that some electric cars today are equipped with thousands of lithium-ion battery cells. If one battery explodes, the whole pack can potentially explode.

Electrically conductive plastics
Thanks to engineers at Purdue University, an emerging class of electrically conductive plastics called “radical polymers” may allow low-cost, transparent solar cells, flexible and lightweight batteries, and ultrathin antistatic coatings to be implemented in consumer electronics and aircraft.

The researchers have established the solid-state electrical properties of one such polymer, called PTMA, which is about 10 times more electrically conductive than common semiconducting polymers. The polymer is a glass that conducts charge, which seems like a contradiction because glasses are usually insulators, and is easy to manufacture, resembling Plexiglas.Unlike Plexiglas, it conducts electricity.

The researchers noted that PTMA is in a class of electrically active polymers that could allow inexpensive transparent solar cells; antistatic and antiglare coatings for cellphone displays; antistatic coverings for aircraft to protect against lightning strikes; flexible flash drives; and thermoelectric devices, which generate electricity from heat.

The polymers have seen commercial use in new types of batteries. However, finding widespread practical applications for the polymers will require increasing the conductivity another 100 to 1,000 times, they added.

An emerging class of electrically conductive plastics are called “radical polymers.” The graphic at left depicts the structure of a polymer. At right, transparent polymer overlays the Purdue logo. (Source: Purdue University)