Blog Post

Cheap Lithium-ion Batteries in Hoverboards Raise the Spectre of Thermal Runaway Again

Over the holiday season Hoverboards emerged as the year’s “must-have” gift for consumers. This fad frenzy spurred cheap knock-offs with defective batteries that started fires in nine states, even bursting into flames under rider’s feet. Airlines moved quickly into action and banned the devices on their flights.


While media reports place the blame on lower cost knockoffs or improper charging that allows the batteries to overheat, we are willing to say this year’s hottest gift (literally) became persona non grata not only because of its faulty lithium-ion (LI) batteries, but because of one element commonly used within the chemistry of LI battery cells – cobalt. Cobalt is found in the majority of lithium-ion battery chemistries, except for Lithium Ferrous Phosphate (LFP), also known as Lithium iron phosphate, the chemistry utilized by SimpliPhi Power.

Cobalt cathodes used in LI batteries commonly heat up to very high temperatures and are prone to creating chemical fires. Called thermal runaway, this is a kind of uncontrolled feedback in which heat build-up breaks down a battery’s chemistry, releasing oxides that can make a fire burn out of control. Perhaps most significantly, due to the extreme temperature at which the cobalt oxide burns, as well as the chemical composition itself, there is no known flame retardant that can extinguish the fires once they ignite, so they must be controlled and allowed to burn until they self-extinguish.

Hoverboards are the latest in a long line of thermal runaway instances, including battery fires on the Boeing Dreamliner fleet and at least two Tesla all-electric vehicles, not to mention laptops, cell phones, etc. These fires have resulted in hundreds of recalls of batteries and the FAA considering a ban on all commercial shipments of lithium-ion batteries, regardless if they contain cobalt or not. By contrast, at SimpliPhi Power, we utilize the lithium ferro phosphate chemistry and, combined with proprietary architecture and power electronics, have demonstrated to the U.S Army and Marine Corps that our batteries are safe to transport worldwide. This is due to the fact that they do not contain cobalt or generate excessive heat. As a result, SimpliPhi obtained “Special Permissions Approval” from the FAA & US Department of Transportation to transport our OES3.9 kWh batteries for critical military installations both domestically and abroad.

Managing Thermal Runaway

Thermal runaway is an intrinsic risk of lithium-ion batteries that use cobalt oxide cathodes. In any size, from small formats in laptops, to large residential and commercial energy storage systems, thermal runaway can take place regardless of internal precautionary battery management (BMS), ventilation or cooling. In addition to monitoring and controlling the internal thermal profile of a li-on with cobalt battery, the environmental and ambient temperatures where the batteries are housed must also be monitored and controlled. This adds to the complexity and costs associated with Li-on with cobalt battery installations and applications.

Li-on with cobalt batteries cells also generate much more heat at high rates of charge and discharge. Therefore, mitigating the likelihood of thermal runaway and heat buildup in an Li-on with cobalt battery not only requires sophisticated internal cooling and ventilation, but also balancing hardware/software, shallow discharging and longer charge and discharge cycles. These mitigation factors can ultimately contribute significantly to the actual cost, weight and size per kWh. Cooling equipment increases the weight and footprint required for the battery or overall installation and also increases the amount of energy that must be dedicated to maintaining the appropriate ambient temperature. The result is less energy available to run the actual electrical loads of the home or business.

Additionally, precautionary equipment and installation guidelines to safeguard against heat buildup and consequent vulnerabilities of the overall battery system must be adhered to for the safe maintenance of Li-on with cobalt batteries.

Removing the Risks of Thermal Runaway

The attraction of Li-on with cobalt batteries is that the chemistry itself is more energy dense, and therefore can store more energy per pound/kg. However, with the proper architecture, battery management system (BMS) and design, a lithium ferrous phosphate battery can store just as much energy and deliver more power per cubic inch as one containing cobalt. This is especially true when the extensive ancillary equipment (cooling and monitoring) that must be built into the lithium cobalt battery is taken into consideration.

Yet, even with the LFP category of batteries, some manufacturers must still ventilate and cool their batteries for optimum performance. This is due to a variety of factors, including the choice of LFP cells used, the proprietary BMS, circuitry and internal architecture. In concert, these factors can conspire to create greater electrical impedance during the charge and discharge cycles and prevent electrons from flowing efficiently. This impedance generates heat and just like the Li-on with cobalt batteries, cooling and ventilation is required.

By contrast, the energy storage technology developed by SimpliPhi Power does not require ventilation or cooling. It has a charge and discharge efficiency rate of 98+%, can withstand 100% depth of discharge and peak charge and discharge rates. Having developed the technology in very strenuous environments typical of on-location shoots for the entertainment industry, we have perfected a combination of LFP cell selection, power electronics, manufacturing techniques and a BMS that effectively minimize electrical impedance such that our energy storage technology does not require cooling or ventilation and offers an extended operating temperature range of -4 to 140 degrees F. Additionally, we have never had an instance of thermal runaway in our 14 years of selling products, even though we began designing systems with the earlier lithium-ion cobalt based chemistry back in 2002. The end result is a modular battery that scales easily and has a small, lightweight and safe performance profile that is installed directly inside homes and or businesses, both on the grid and off.

In sum, the power electronics (BMS) and internal architecture of a battery can have as much to do with the overall performance, levelized cost of energy and safety as the fundamental chemistry itself. Buyers should inquire about the use of cobalt and heat mitigation requirements of a technology before making purchasing decisions, particularly when it comes to the issue of cost, efficiency and safety over the lifetime of the battery.