Non-toxic substitute for lithium batteries found

RESEARCHERS have found an alternative to lithium ion batteries made from carbon nanotubes and coated in combustible materials that produce similar current outputs.

A team at the Massachusetts Institute of Technology (MIT), US, has developed an electricity generation system which can harness heat and contains no toxic metals. Lithium batteries have a limited global supply, gradually lose power if left shelved for a long period of time, and are difficult to dispose of after use, prompting the need for an alternative.

The approach involves a wire made from carbon nanotubes that produces an electrical current when it is progressively heated from one end to the other. Coating the wire with combustible accelerants and lighting one end will burn the wire like a fuse.

The pulse of heat known as a thermopower wave causes a phenomenon in which the electrons are pushed through a bundle of carbon nanotubes in a wave, producing a current of electricity. Sometimes the current splits, creating two waves of current. When the two waves are synchronised, they can amplify one another. If they are not synchronised, they cancel each other out, eliminating the voltage.

The team have been working on improving the efficiency by amplifying the voltage for the last five years, and have improved their process a thousand-fold. The devices made by the team can produce a current that is, for its size, comparable to lithium batteries, and can power a smart device for similar lengths of time.

The team’s initial experiments had used potentially explosive materials to generate the pulse of heat that drives the reaction. The team now use a more benign fuel such as sucrose to achieve power generation.

Michael Strano, professor in chemical engineering at MIT, said: “Unlike other technologies that are specific to a particular chemical formulation, the carbon nanotube-based power system works just on heat, so as better heat sources are developed they could simply be swapped into a system to improve its performance.”

The team report that the device is around 1% efficient in converting heat into electrical energy, however this is still 10,000 times more efficient than the original discovery in 2010. Since the process involves combustion, the team hope to improve the efficiency of the heat conversion further in order to develop a device safe for commercial use.

Potential uses beyond smartphone, laptop and electric car batteries include small wearable devices. The process can be scaled down to power very small devices, as the wires themselves can shrink down the scale of the nanotubes themselves. The technology also has an indefinite shelf-life, unlike conventional lithium ion batteries which lose power over time, meaning they can be used in deep space probes where they would remain dormant for many years until the probe reaches its distant destination.

The team say it will take several years before this method will become commercially viable. However, they have already developed a device powerful enough that can power simple electronic devices such as an LED light.

Energy & Environmental Science, DOI: 10.1039/C5EE03651H