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Samsung Galaxy Note 7 – chemicals and materials now on fire!
Posted on October 18th, 2016 by Dr. Sina Ebnesajjad in New Materials & Applications
In October 2016 the auto-ignition and explosion of Samsung Galaxy Note 7 smart phones came to a head. The Korean company walked away from the Note 7 at the cost of billions of dollars, but well worth preservation of the long-term reputation of Samsung Corp. Here is a brief recount of the story. Throughout 2016 phantom fires and explosions of the Note 7 were reported. Some of the accidents were quite serious including a vehicle burning down and people waking up in bedrooms filled with smoke. The company issued a recall and began to replace the errant Galaxy Note 7 devices with new phones.
Out of concern for a midair disaster the civilian aerospace industry asked passengers not to pack Note 7 phones in the checked luggage or turn them on during flights. Samsung began to replace the Note 7 rapidly even though the company claimed they had no idea about the cause of the phones self-igniting. It is virtually impossible to solve a problem without knowing its root cause. Samsung assumed a problem with the supplier of the batteries and replaced the “old” Note 7’s with with batteries supplied by a different company.
Samsung hoped the replacement of the phones would alleviate the problem but those also caught fire! For example, a Southwest Airlines flight from Louisville, Kentucky to Baltimore, Maryland was canceled after a passenger’s replacement Note 7 phone caught fire on board. He noticed smoke billowing from his pocket where the replacement phone was. He took the phone out and threw in the isle. Fortunately the aircraft was still on the ground mitigating the risk of a catastrophic fire during flight. Burning replacement Note 7’s were also reported in Korea, China and the US, clearly indicating the problem had not been solved. Reports indicate the phones caught fire while being charged or in use. One report said the batteries discharged rapidly resulting in the overheating of the phone.
Everyone agrees this much: the cause of the fire resides in the batteries of the Galaxy Note 7. Samsung engineers were not able to replicate the fire and explosion under their tight deadline. There is, however, past research to help explain the cause of the fire (Sources: E. P. Roth, C. J. Orendorff, The Electrochemical Society, Interface, Summer 2012 and B. Scrosati, J. Garcche, J. of Power Sources 195, pp 2419–30, 2010 and Science Shorts Lynn Yarris, http://newscenter.lbl.gov/2013/12/17/roots-of-the-lithium-battery, Dec 17, 2013)
We pick up the story at its origins.
Attempts to develop rechargeable lithium metal batteries began in the 1980’s because metallic lithium offered very high energy density. Why lithium? Because it is the lightest metal and yields the most surface of any metal per unit weight. Originally, metallic lithium looked promising but inherent instabilities of lithium metal meant the cell had the potential of a thermal run-away. Temperature would quickly rise to above the melting point of the metallic lithium and cause a violent reaction. After numerous accidents and a large recall of lithium metal batteries in 1991 the market shifted to a non-metallic lithium battery based on lithium ions. The trade-off was slightly lower energy density for a relatively safer lithium-ion system.
How does a lithium ion battery work? A battery cell (Figure 1) has three components: a positive electrode (cathode), a negative electrode (anode), a separator and an electrolyte in between them. The cathode is made from a chemical compound called lithium-cobalt oxide (LiCoO2) or in the newer batteries from lithium iron phosphate (LiFePO4). The anode is generally made from carbon (graphite). There are different electrolytes depending on the type of battery but they are universally based on combinations of linear and cyclic alkyl carbonates all of which are flammable.
The choice of electrolyte can have a significant impact on the safety, thermal stability, and abuse tolerance of the cell. Typically, the electrolyte consists of a solution of a lithium salt (commonly LiPF6) in a mixed organic solvent such as ethylene carbonate and dimethyl carbonate. Some salts that have superior performance properties, such as LiAsF6, cannot be used because of high toxicity. Certain solvent species, such as propylene carbonate (PC), are limited in concentration because they cause disruption of the anode graphite grains (Source: B. Scrosati, J. Garcche, J. of Power Sources 195, pp 2419–30, 2010).
The separator is a micro porous polymeric membrane that allows lithium ions to pass through it (Figure 1). It is usually made from a plastic such as polyethylene or polypropylene. The separator’s critical function is to keep apart the two electrodes. It must be resistant to penetration otherwise the battery would short. The result of a short in the battery is generation of heat leading to runaway reactions, igniting of the flammable of electrolyte and melting of lithium. The outcome is fire and or explosion. The separator layer has had to be thinned down after the batteries were constructed as small cells (Figure 2). As the thickness of the separator membrane becomes thinner the probability of its penetration thus failure increases.
Miniaturization of smart phones requires fitting numerous components in a small space. Pressure is applied to the battery during installation, which can be an aggravating factor for failure. One possible mechanism of failure is formation of dendrites in the electrolyte that itself contains a lithium compound. Dendrite refers to a string of small particles of lithium metal formed during use as seen in Figure 3.
Scientists at the Department of Energy’s Oak Ridge National Laboratory have captured the first real-time nano scale images of lithium dendrite structures known to degrade lithium-ion batteries. The Oak Ridge electron microscopy team have also captured a real-time video of dendrite formation and growth (See at: www.youtube.com/watch?v=rpPUTM_u_PM). Dendrites form when metallic lithium takes root on a battery’s anode and begin growing haphazardly. If the dendrites grow too large, they can puncture the separator between the electrodes and short-circuit the cell, resulting in catastrophic battery failure, fire and explosion (Source: R. L. Sacci, J. M. Black et al, Nano Letters, 15 (3), pp 2011–18, 2015). This is the most plausible explanation of lithium ion battery fiasco.
Smart phones have become ubiquitous devices in the 21st century used by children and adults everywhere. Let’s hope battery problems are solved permanently and soon to avoid future bodily and property damage by smart phones and other battery-powered devices.
On October 14, the United States Federal Aviation Administration (FAA) banned Samsung Galaxy Note 7 from all US passenger airplanes. That action by FAA was promptly followed by enactment of the same ban by the similar regulatory agencies and airlines around the world.
All opinions shared in this post are the author’s own.
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Dr. Sina Ebnesajjad
President at FluoroConsultants Group, LLC
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