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As the Note 7 incidents illustrate, Li-ion batteries are still prone to catching fire and endangering their owners. The reason behind this is the fact that flammable liquids are used as electrolytes. A number of additives are mixed with these electrolytes to act as flame retardants, but the truth remains that—under the right conditions—thermal runaway is still an issue, and even the best BMS (battery management systems) cannot fully prevent accidental fires from happening.

As a matter of fact, combustion in Li-ion batteries can be triggered hours, if not weeks, after a battery pack has been irreversibly damaged, but the reaction time of the BMS might be too slow to block thermal runaway once it is detected, since heat propagates at an exponential rate in these cases. The consumers' hunger for fast-charging smartphones also does not help, since in order to achieve this, batteries have to be charged at constant voltage. This might trigger the lithium plating phenomenon on graphite anodes, a preamble to the growth of so-called dendrites, which are lithium metal whiskers that can puncture the separator, create a short circuit, and offer a local source of overheating that is sufficiently strong to set the whole device on fire.

The solution lies in the quest for inherently safe batteries that do not contain flammable electrolytes. E-bus company Microvas showcased a non-flammable liquid electrolyte for their Li-ion batteries that can potentially revolutionise the sector, although it is yet to be seen if it can deliver the power capabilities needed by products other than buses (e.g., smartphones, laptops and electric cars).

Ionic liquids have long been heralded as a viable solution due to their extremely high flashpoint; however, an industrial production that can bring their cost down has not yet been put into place. Inorganic and polymer electrolytes also have the potential to make batteries safer. This year, an article on the peer-reviewed journal Nature Energy reported a sulphur-chlorine-based solid conductor that conducts lithium ions faster than state-of-the-art liquid electrolytes; companies like Toyota, Samsung SDI, and LGChem are already looking into its potential.

Using non-flammable electrolytes also has the added benefit of increasing a battery's energy density at pack level, because they can make thermal management systems redundant and reduce the amount and weight of ancillary components. Solid Power, a Colorado-based start-up, will be presenting its take on safe, solid-state, sulphur-based batteries for electric vehicles by showcasing its 350Wh/kg (750Wh/L) energy storage technology for mobility applications at the IDTechEx Santa Clara conference.

Editor's Note: Lithium-ion batteries have acquired quite a reputation. Not too long ago, they were implicated in the Dreamliner fires. And Sony faced a bit of a crisis just a decade ago when millions of battery packs were affected with recalls taking place from 2006 through 2007. Click on a few links below to get a sense of the scope of that recall.