Li-on batteries feature in most of the mobile electronics we use because they pack far higher energy density than their competitors. But until now there have been a whole heap of problems with those same batteries overheating, and even catching fire.


One iPhone 4 burst into flames on a plane; another caught fire and burnt its user's hand while it was charging. Sony, Dell, and Apple have all had to recall laptops because their batteries got too hot and were considered dangerous.


All these battery problems are a result of something called thermal runaway: once a cell reaches a critical temperature, it can't cool down, so keeps getting hotter until something, umm, bad happens. Problem is, that can happen in seconds, not minutes or hours.

But now a team from the Johns Hopkins University Applied Physics Laboratory has developed an inexpensive sensor that can warn of impending catastrophic failure in lithium-ion batteries, reports The Engineer.

A simple electronic measurement can be used to measure the the temperature of the protective layers between the electrodes and the electrolyte of the battery during normal operation. Basically, a small alternating current is modified by the cell in a way that is directly related to the temperature of the interface between the electrodes and the electrolyte.

Because it's problems with those exact layers that cause thermal runaway, the sensor can spot the problem and shut the battery down before things get out of hand.


Rengaswamy Srinivasan, a chemist in APL's Research and Exploratory Development Department, said:

"Ultimately, the new sensor enables battery-management systems to more closely manage battery performance and, more importantly, detect unsafe thermal conditions at the critical moment when they occur and before the cell vents or sets itself and the battery on fire. By integrating this technology into their products, manufacturers of batteries and battery-management systems, and battery solution providers can increase both the safety and performance of their products."


Fortunately, it's also pretty cheap. Someone should tell Apple. [The Engineer; Image: rust.bucket]