I would feel so much safer on my next flight from Phoenix to Silicon Valley if I knew that there were safeguards in place inside passengers’ smartphones that could prevent fire and explosion from such design decisions like a company packing 10 pounds of Lithium-ion battery into a 5 pound compartment or a smartphone owner buying a lower cost, after-market battery replacing the original battery in their phone from some country and supplier of which I had never heard.

This article will serve as a technical and thought-provoking effort to stir some ideas that will render the Lithium-ion battery safe under any conditions of manufacturing defect or mechanical damage to the battery; hopefully in an expedient manner before catastrophe strikes.

The problem is not just smartphone batteries, but laptops and other battery-operated electronics with Lithium-ion batteries. However, since the Samsung case is so recent and widespread, I wanted to focus mostly upon the smartphone in this article.

Typically, Lithium-ion batteries are safe and reliable. Just think about the $28B market they had in 2013 with a relatively small amount of fires and explosions. But every fire and explosion incident has the potential to cause a loss of life or serious personal injury (Not to mention the collateral material damage and cost). For those of us who fly often, an immediate solution would be nice. The Federal Aviation Administration’s strong warning against using the Samsung Galaxy Note 7 aboard planes is necessary but not sufficient.

Let’s look at seven possible solutions based on solid technical research, which will build upon my recent initial article touching on this subject.

1. Using liquid coolant around the battery

Earlier this year, when Samsung released its Galaxy S7, a tech blog revealed a teardown that took a good look at the liquid cooling system which was employed by Samsung designers. The system used a very small amount of water that would continuously evaporate into steam and travel away from the processor (or, even better, the battery) to keep the temperature down on the graphics processing unit (GPU) and central processing unit (CPU), which will be running at high speed as they perform such tasks as fast Internet browsing or HD video playback. The steam later condenses back into water and evenly spreads the heat around. See this PhoneArena article for more information.

Little did they know at that time that the Lithium-ion battery would be the main culprit seemingly because it was squeezed too tightly in its under-sized enclosure (the cause still to be determined in my mind). Obviously, the cooling system was not able to prevent the fire and explosion during thermal runaway of the battery. Maybe an improvement in the cooling design might help prevent future fires like this in the event of mechanical damage or battery construction defects. Everyone was looking at cooling the processors (which is necessary), but not the battery as a primary cause of heat and ultimately fire. Designers will now need to take that into account in a better cooling system design that addresses the battery as well.

Nonetheless, Samsung had created a heat-conducting flat copper tubing inside the handset much like Sony smartphones have used. This solution equally distributes the extra heat in the GPU for faster dissipation. The system prevents the smartphone from either freezing or overheating. This improves the reliability and lifetime of internal components (Figure 1 ).

Figure 1 The Sony Xperia Z5 dual heat pipe solution helps control heat in the smartphone. (Image courtesy of Xperia blog)

There is also a 2009 patent for a battery system cooled via coolant and a 2013 patent on a little larger scale than that of a handset, but the concept can be extrapolated to a smartphone with some ingenuity.

Check out the following 2014 video for more insights into cooling, before the use of this technology in the Sony Xperia Z2 smartphone. By the way, NEC apparently was the first to use this technology in the industry.

2. Maybe coolant is not enough: Adding fire-retardant thermal insulation surrounding the battery

Suppressing a Lithium-ion battery fire is critical when applying a coolant does not lower the battery temperature enough, especially during thermal runaway. The added step in safety might be to employ a form of cargo foam which airlines use to both cool and prevent a fire from progressing and spreading. Ventura Aerospace has an excellent aircraft fire suppression system used in Class E compartments which can also be creatively adapted by smartphone and laptop designers to be contained inside the battery enclosure.

With the use of cargo foam, a fire can be suppressed in two ways:

Cargo foam is an argon-generated foam that is totally inert. Argon does not react chemically like other gases such as Nitrogen or CO 2 . This inerting property prevents materials such as cardboard packaging from continuing to burn by displacing oxygen completely. The method is not a simple reduction of oxygen concentration but a complete displacement. Cargo foam also has a cooling effect on Lithium-ion and other batteries. By cooling the batteries which are already burning and also the ones which have not yet ignited, the fire progression rate is reduced and eventually is stopped. The Ventura Aerospace fire suppression system is not only capable of suppressing the FAA standard cardboard and paper fire but, more importantly with regards to this article, a real fire consisting of electronic devices such as in smartphones or laptops, particularly those with Lithium-ion batteries.

Designers may find a way to implement such a system in conjunction with a liquid coolant if deemed necessary (and I think it is necessary). Tests will need to be performed by a recognized independent agency or agencies such as the National Fire Protection Association (NFPA) and/or other international agencies to ensure a viable, proven solution.

3. Efforts to minimize thermal runaway: Improved cathode materials3

This paper on thermal safety with various cathode materials (Reference 3 ) has some excellent references of its own regarding battery safety in the areas of air and liquid cooling, heat pipes, phase change material, as well as positive temperature coefficient (PTC) devices, reaction-temperature sensing control (RTC) safety vent, and current interrupt devices (CIDs). It may be an investment to purchase this article and/or become a member of ResearchGate.

In essence, thermal runaway in a Lithium-ion battery begins when heat rises in the battery, leading to a protective layer breakdown, which causes the electrolyte in turn to break down into a flammable gas. The electrolyte separator then melts and can usually cause a short circuit between the anode and the cathode and finally the cathode breaks down and generates oxygen; this feeds a fire very well. Sandia Labs has a very good article on thermal runaway energetics (Reference 4 ) as does Exponent, Inc. (Reference 5 ).

There have been many studies regarding thermal stability of Lithium-ion cathode materials exploring the mechanism of thermal runaway and looking for more stable cathode materials. Reference 3 ranks the least safe cathode materials to the most safe materials and looks at the stability of the best materials.

The LiMN 2 O 4 cell showed the highest onset temperature (The temperature at which a cell starts to generate heat is commonly called the onset temperature of the thermal runaway phenomenon), which indicated the best thermal stability of five of the cathode materials tested. However, the heat generation rate of the LiFePO 4 proved much lower than the other cells tested, so this cell was deemed the safest cathode material with regard to thermal runaway risk in the test. The LiFePO 4 cell also was touted as being theoretically invulnerable to thermal runaway because it had a maximum temperature rise of 50o C in the oven abuse test3 . So improved cathode materials can greatly reduce the onset of thermal runaway.

4. A possible dual use mechanical protection: Smart multi-functional fluids2

Resistance to mechanical abuse and the external packaging of the battery will be covered in another section in this article, but here we will look at a seldom addressed opportunity for the electrolyte itself to protect the battery.

Smart multi-functional fluids exist which can have a two-fold effect to act as an excellent conductive battery electrolyte as well as a mechanical protection for the battery. Such fluids, known as shear thickening fluids (STFs), or a non-Newtonian fluid, have the property of a shear thickening effect under impact or pressure, thus creating a resistance to impact force, crushing, and I believe can be modified so that it can also prevent damage to the battery in the event of an enclosure that is too small (seemingly the Samsung issue recently), or a mechanical accident. By simply adding fumed silica to an electrolyte which is being used at present in Lithium-ion batteries, research efforts have shown that this may be a good possible solution for greatly improving battery safety (Reference 2 ).

The video below from the Boston University College of Engineering Block Party shows how a non-Newtonian fluid works.

This method was first targeted at EV and HEV automobiles in the event of a crash, but may be also adapted to smaller devices, even smartphones and laptops (Figure 2 ).

Figure 2 ( a) The discharge curve for a LiFePO 4 electrode in the STF electrolyte composed of a bare electrolyte of EC/DMC/LiPF 6 as well as a composite electrolyte of EC/DMC/LiPF 6 with 6.3 wt. % SiO 2 showing a shear thinning effect in the diagram. (b), (c) and (d) demonstrate the protective mechanism of the STF electrolyte under impact (or even pressure). (Image courtesy of Reference 2)

I firmly believe that this is one of the most promising methods of ensuring safety in Lithium-ion products and I am sure we will see much more development in this area.

5. Added protection: strengthening the mechanical battery enclosure

I really do not want to say much in this area because having a strong battery enclosure or surrounding case might be the last thing we really need for battery safety. I will only comment on the fact that some sort of mechanical enclosure needs to be used to possibly house the battery and any fire retardant material along with a connection to a possible cooling system. These are all mentioned in this article, so the actual case is secondary to all of the other suggestions mentioned, but nonetheless needed.

6. Better modeling in the design and manufacturing phase6

Pressure buildup/cell venting is deemed the most common response that is seen in Lithium-ion batteries that are subjected to abuse or poor design (Figure 3 ).

Figure 3 Mechanical damage due to a crush of short circuit is one of the many areas that can be simulated in the design and manufacturing phase with any changes tested before customers get the battery. (Image courtesy of Reference 6)

A good example of better modeling that may have helped the Samsung case (and I am a “Monday morning quarterback” here) would be better modeling in the area of venting of pouch cells, as can be seen in the National Renewable Energy Laboratory slideshow in 2013 (Reference 6 ). This tutorial integrated mathematical models for individual factors that could contribute to the swelling of Lithium-ion cells and related the pressures within those cells to the mechanical strength of the case. This modeling would lead to the identification of problems in the cell manufacturing process and proper sealing of the battery case.

The goal here was to create a single simulation tool, for battery designers and manufacturers that employ batteries in their products, that would help identify any material limitations as well as assess any design modifications in battery/cell fabrication.

7. Lower electrolyte flammability7

I wanted to mention this as a possibility for more research in the future. Present research studies have shown that the use of ionic fluids, gel polymer electrolytes, or solid-state electrolytes instead of volatile carbonates or additives can lower the flammability of the battery electrolyte. The drawback preventing their use is lower conductivity which leads to poorer battery performance in a time when the need for more efficient batteries is a must, as I mentioned at the beginning of this article. Consumers need better functionality in their smartphone, especially as we approach 5G. More research can be done in this area to improve upon the battery efficiency with better and less flammable electrolytes or additives which can significantly improve safety.

In closing, I have hopefully provided some solid tech ideas that will be insightful to engineers and product designers in the prevention of future fires and explosions in Lithium-ion battery operated products. Until then, I feel very strongly that the FAA needs to provide more than a ‘strong warning’ to passengers with devices that contain these batteries and freight companies that ship anything with a Lithium-ion battery to ensure the safety of air travel. The FAA or other government organizations (Canada has some really good guidelines) need to trace Lithium cells and batteries to their source and allow only trusted and reputable manufacturers’ batteries to be allowed on an aircraft. Authorities must demand that Lithium-ion cells and batteries be tested and certified by a reputable and recognized organization (The United Nations has some good suggestions).

EDN readers are a group of highly talented engineers and designers and can make a difference. Let me know what you think by sharing your comments below with our esteemed audience members so we can start a positive discussion that will lead to future improved safety results in Lithium-ion battery usage.

References

Also see: