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June 1, 2018

Lithium-ion Battery Thermal Runaway: What’s the Risk?

Man standing in the bed of a truck shoveling a mound of white powder. Truck is surrounded by mounds of white powder.
Large fire at recycling facility in Rocky View County (Source: Global News)
Lithium-ion batteries have become an essential part of our everyday lives and continue to enable the trend towards electrified transport. However, from exploding train cars to waste facilities burning down, it is becoming increasingly evident that there needs to be better awareness, controls, and behaviors to address the safety risks associated with lithium-ion batteries.
​Since 1991, 206 separate incidents occurred involving the combustion of lithium batteries on airlines. Thermal runaway, which is a term for an uncontrollable exothermic reaction that emits large amounts of heat, can occur in lithium-ion batteries when damaged or short circuited. Disasters from uncontrolled thermal runaway can be devastating, even when caused by portable/small format lithium-ion batteries. For example, Rumpke’s recycling facility in Cincinnati (a general materials recovery facility/MRF) experienced 6 fires in 2016 alone due to consumers disposing of their batteries improperly. The image below provides an example of one of these fires from 2016.​
Lithium-ion battery and thermal runaway fundamentals
When considering the dangers of a lithium-ion battery cell, its fundamentals must be understood. A lithium-ion battery cell consists of the following:
  • Cathode: the positive terminal of the battery – typically a form of lithium metal oxide or similar
  • Anode: the negative terminal of the battery – typically graphite
  • Separator: a thin permeable polymer or similar that separates the cathode and anode
  • Electrolyte: a solvent (typically alkyl carbonate based) containing conductive salts that permit the flow of ionic charge

To produce electricity, an oxidation reaction at the anode, releasing electrons. Simultaneously, a reduction reaction occurs at the cathode, allowing the cathode to receive the electrons released by the anode, forming an electrical circuit.

The anode and the cathode are isolated from each other via the separator, but over time, separators have the potential to wear down. Breaching of the separator causes high amounts of current to flow directly between the anode and cathode, short-circuiting the cell and producing tremendous amounts of trapped thermal energy.

At the onset of thermal runaway, the battery heats in seconds from room temperature to approximately 700°C. As a result, the electrolyte breaks down into constituents such as methane, ethane, and ethene, as well as flammable and toxic gases such as carbon dioxide, carbon monoxide, and hydrogen gas. The cathode then begins to decompose, releasing oxygen, further accelerating the thermal runaway process. When the flammable electrolyte gases react with oxygen in the presence of heat, combustion occurs. The risk for explosion increases as the pressure in the cell builds.

Lithium-ion batteries have a dual chemical and electrical hazard, including the chemical hazards listed in the table below.

Mechanical damage of lithium-ion batteries such as accidental rupture or puncturing can result in the release of the electrolyte leading to the exposure of possibly toxic, corrosive, and flammable chemicals.

There are numerous factors that can cause thermal runaway:

  • Overcharging: increases internal temperatures, leading to thermal runaway. A faulty charger can contribute to overcharging
  • External factors: extreme temperatures will degrade battery components. Leaving batteries near a heat source will greatly increase the risk of a battery undergoing thermal runaway
  • Manufacturing defects: in 2016, Samsung had to recall the Samsung Galaxy Note 7 due to thermal runaway typically occurring during charging, as shown by the example below

Comparison of lithium-ion battery safety relative to other energy storage mediums

Although it is important to be aware of the specific safety risks associated with lithium-ion batteries, technology cannot be assessed in a vacuum. The graph below puts the relative energy density between example energy storage mediums into perspective. Evidently, lithium-ion batteries have a much lower energy release potential compared to gasoline, the fossil fuel that powers most of the internal combustion engines that society interacts with.

Lithium-ion battery safety – now and into the future

The majority of lithium-ion batteries have historically been manufactured for portable uses (e.g. personal electronic devices such as laptops, mobile phones). Given the inherently limited calendar lives of portable lithium-ion batteries, and their broad use globally, spent lithium-ion battery volumes have been rapidly increasing in recent years. As this has occurred, spent lithium-ion batteries have increasingly made their way to unsuitable supply chains (e.g. general material recovery facilities/MRFs). Safety concerns are now growing even more with the emergence of large format batteries such as battery electric vehicle batteries and grid scale energy storage solutions.

Emerging solid-state battery technology aims to address a key driver of the historical safety issues in lithium-ion batteries – the low flash point electrolyte solvent that essentially acts as a ‘fuel’. Solid state batteries use solid electrolytes and electrodes, eliminating the fire hazard present with current liquid electrolytes. However, this new technology is still in its nascent phase with years ahead until commercialization.

Nonetheless, there is an impending ‘tsunami’ of spent lithium-ion batteries that will enter the market, in addition to the existing robust base of spent batteries. As a result, there is a serious need to continue to develop safe and effective means of handling, transporting, and storing lithium-ion batteries.

What can consumers and manufacturers do to ensure safe lithium-ion battery practices?

At a consumer level, most lithium-ion battery incidents occur due to over-charging, mechanical abuse of the electronic equipment in which the battery is enclosed, and disposal of lithium-ion batteries into the wrong waste streams. Consumers should always follow the manufacturer’s specified charge times and the voltage at which the battery should be recharged. Thus, it is recommended that lithium-ion batteries should be recharged using the original charger that came with the product or one that meets the manufacturer’s charging specifications.

In addition, lithium-ion batteries and electronics should never be placed in the garbage or regular household recycling bins. In typical material recycling facilities, materials get crushed, punctured, and dropped – all conditions that will likely cause thermal runaway in a lithium-ion battery. Consumers need to do their part to contact their local battery or electronic waste collection service provider to dispose of their batteries and/or electronics properly.

At an industrial level, manufacturers, recyclers, and other key entities involved in the lithium-ion battery supply chain should aim to mitigate the risks of lithium-ion battery incidents by strictly complying to and exceeding all applicable standards and regulations.
​Li-Cycle™ estimates that the world will be faced with an estimated 11 million tonnes of spent lithium-ion batteries between 2018 and 2030. Stockpiling lithium-ion batteries could reportedly cause a fire epidemic within the waste industry. Li-Cycle Technology™ is a key part of the solution to this problem. Our technology is uniquely positioned to provide a safe, environmentally friendly, and low cost/high value recycling solution. Moreover, Li-Cycle™ continues to engage with partners across the lithium-ion battery supply chain to ensure world-class safety standards as Li-Cycle™ and the industry continues to scale rapidly.