An article by K.M. Abraham (@lithiumabraham) of Northeastern University and E-KEM Sciences.

UPDATE (12/16/2016): We checked back in with Dr. Abraham to see if anything has changed since the publication of this article. According to Abraham, hoverboard manufacturers have improved the safety of the devices since wide-spread instances of explosion in 2015. This has been brought about by a certification program by the Underwriters Laboratory (UL). The UL, which is a safety consulting and certification company, has introduced their NATIONAL STANDARD UL 2272 Certification for Personal e-Mobility. Any hoverboard that is marked with the UL certification can be expected to be much safer than previous generations. Several companies, including Sharper Image, now sell UL certified hoverboards. “As with any manufactured product — and especially devices powered by very energy rich Li-ion batteries — there is a potential for safety hazard,” Abraham says. “But we can expect hoverboards to be significantly safer if UL certified.”

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(Feb. 2016) Recent reports of hoverboards burning on the streets of America have created a great deal of concern about the safety of lithium-ion (Li-ion) batteries that power them (1) .

This is notwithstanding the fact that that Li-ion batteries have contributed immensely to shape the modern world by being the indispensable power source of choice for portable data and voice communication devices such as smartphones, laptop computers, tablets and music players.

With very high energy densities and long discharge/charge cycle life they are the driving force behind the increasing acceptance of battery powered family cars including Tesla Model S, Nissan Leaf, Chevrolet Volt and others.

Li-ion batteries are also being developed for large scale energy storage in electric utilities, telephone and cable TV exchanges and as auxiliary power systems in airplanes such as Boeing 787 Airliners, and military fighter aircraft. The energy density of Li-ion batteries of about 300 Wh/kg or 750 Wh/l that has placed them in the enviable position of the power source of choice for wide-spread applications, from small cells to large battery packs, has also made them susceptible to safety hazards (2,3) .

What’s going on?

YouTube videos of fires on conference tables, smoke and fire shooting out of cellphones and laptops, Li-ion batteries burning in the storage bins of cargo planes leading to the downing of aircrafts, smoke spewing out of the auxiliary power units in Boeing 787 airliners parked on airport tarmacs, and a large number of recent fires in hoverboards while being ridden on public roads or on charging (Figure 1), have given Li-ion batteries notoriety as a power source to be handled with utmost care and safety concern.

What is going on? It is safe to say that these well-publicized hazardous events are rooted in the uncontrolled release of the large amount of energy stored in Li-ion batteries as a result of manufacturing defects, inferior active and inactive materials used to build cells and battery packs, substandard manufacturing and quality control practices by a small fraction of cell manufacturers, and user abuses of overcharge and over-discharge, short-circuit, external thermal shocks and violent mechanical impacts. All of these mistreatments can lead Li-ion batteries to thermal runaway reactions accompanied by the release of hot combustible organic solvents which catch fire upon contact with oxygen in the atmosphere.

Safety hazards of Li-ion batteries occur when the fundamental principle of controlled release of energy on which battery technology is based is compromised by materials and manufacturing defects and operational abuses. The recent occurrence of fires and personal injuries from popular hoverboards have brought home the concerns of Li-ion battery safety while recognizing that these batteries are used uneventfully every day by billions of consumers worldwide in cellphones, tablets, music players and laptops.

Anatomy of Li-ion cells

The potential safety hazards of Li-ion batteries are understood from knowledge of the chemistry of Li-ion cells and the amount of energy stored in a commercial cell like the 18650 cylindrical cell, the building block of laptop computer power packs. A typical Li-ion cell is composed of a graphite anode (represented as C 6 ) (negative electrode) and a lithium transition metal oxide cathode (positive electrode), usually lithium cobalt dioxide (LiCoO 2 ) or a related layered transition metal oxide, with the two electrodes electrically separated from direct contact with each other by a 16-25 micron thick micro-porous polymer membrane separator (typically polyethylene) as depicted in Figure 2.