Addressing the Flammability of Lithium Batteries Using Polystyrene Ionogels.

My son just finished his first semester, very successfully, in Engineering School; I'm a happy and proud dad.

One of the pleasures of having him home is to watch Air Disasters on the Smithsonian Channel, which is a wonderful show to watch with a budding engineer, particularly a budding materials science engineer, since many aircraft failures turn out to be problems in materials science.

The job of engineers is to make the lives of human beings safer and more sustainable, and one of the most important tasks in this enterprise is failure analysis, which is what "Air Disasters" is all about, failure analysis.

(There is good television, if you look.)

A recent episode, which I had to watch alone, concerned the crash of UPS 6, a cargo plane that crashed in Dubai in 2010 despite a heroic effort by its two crew members to land the plane after it has caught fire spontaneously.

The cause of the fire was determined to be spontaneous combustion of lithium batteries. Lithium batteries, of course, are widely used in computers, cell phones (including the Samsung Galaxy 7), and stupid electric cars, and, as Dubai is an air cargo transportation hub for shipping electrical components, it was hauling a few tons of highly flammable lithium batteries.

It was thus with interest that I came across a paper in the scientific literature which is about research into a means to address this problem - the flammability of lithium batteries is tied to the organic solvents utilized as electrolytes, generally organic carbonates, both symmetric and asymmetric. The paper is here: Syndiotactic Polystyrene-Based Ionogel Membranes for High Temperature Electrochemical Applications (Jana, et al (ACS Appl. Mater. Interfaces, 2017, 9 (36), pp 30933–30942)

Some excerpts from the introduction to the paper:

A new generation of high-temperature materials for energy storage applications is the need of time owing to the rise of usage of high-power electric vehicles, aircraft, and pulsed power systems that require energy storage devices for their functions often at elevated temperatures.(1) Lithium-ion batteries (LIBs) present the most suitable storage technology for electric vehicles (EVs) due to their high energy density and better cycling performance over other battery chemistries.(2)...

...Current LIB technologies show thermal stability up to 50 °C; at higher temperatures, LIBs lead to hazards like thermal runaway, gas evolution, and ultimately fire; the primary responsible factors are the volatile liquids used as the electrolytes.(3) The battery packs of hybrid electric vehicles (HEVs) and electric vehicles (EVs) are cooled to ambient temperature to prevent the hazards.(1, 4) The most common cooling agent is air, while more effective liquid-based cooling systems are incorporated to keep up with the increasing demand of higher power in cars that use big battery packs. It is reported that these liquid coolants can be conductive when hot and can, in turn, cause the short circuit of the cells.(5) In this context, a high temperature Li-ion battery (HT-LIB) that is stable and produces higher power density can potentially reduce or even eliminate the energy requirements to cool the battery packs and to allow an overall simplified vehicle cooling system.(4)

Traditionally, the cathode and the anode of the LIBs are highly researched areas, while the electrolytes and separators receive much less attention.(6, 7) A major source of hazards in LIBs originates from the use of highly volatile organic liquids as the electrolytes.(7-9) The carbonate-based liquids are often limited to usage temperatures below 50 °C due to their high volatility and flammability that often lead to such risks as fire and explosions. Ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) are the most commonly used carbonate-type liquids used in LIBs.

In general, although there is much pop rhetoric to the contrary by people who consider themselves to be environmentalists without actually appreciating the cold hard facts associated with environmental issues, a battery is not a device that increases energy efficiency. Quite the opposite is true. The second law of thermodynamics, which cannot be repealed, dictates that a battery is a device that always wastes energy. It follows that an electric car is also a device that wastes energy, a matter of high environmental relevance in the case where electricity is generated using dangerous fossil fuels, which overwhelmingly, is how most electricity is generated.

This paper adds another point, which is that cooling batteries - anything that needs to be cooled is dumping energy into the environment where it cannot be recovered - can and often does even waste more energy to run the cooling device.

The authors note that the recall of the Samsung Galaxy 7 smart phone because of the spontaneous outbreak of fires originating in the battery was tied to this issue and give the motivation for the research is to address this very real problem:

...The root causes for battery failure were identified as inadequate volume to accommodate the negative electrode and the defects originating from welding.(11) The associated thermal run-away events causing explosion and fire were the products of high volatility of the organic liquids. This work provides an alternative to alleviate the concerns associated with the use of highly volatile liquids and thermal stability of the polyolefin membranes currently used in fabrication of LIBs...

Their work involves the synthesis and evaluation of a syndiotactic polymer impregnated with the salts of an ionic liquid, and ionic liquid being a low melting salt of one or two stable organic ions.

Here is their description, not a bad one, of the relevant points associated with ionic liquids, which is that they don't really have a vapor pressure - a tendency to evaporate - and they therefore are not generally flammable, except at extremely high temperatures, temperatures not found in batteries that are not on fire:

The ionic liquids have the potential to replace the hazardous carbonate-type liquids in LIBs due to their nonvolatile nature, nonflammability, and high ionic conductivity.(12, 13) Their properties can be tuned using several combinations of cations and anions. In this regard, pyrrolidinium-based ionic liquid, for example, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (PYR14TF2N) is suitable for high temperature applications as it is thermally stable up to 300 °C and provides ionic conductivity greater than 1 × 10–3 S/cm.(14-16) Pyrrolidinium cations offer broad electrochemical window in comparison to imidazolium cations when combined with the same TF2N anions in the IL molecular structure.(17) The presence of such ILs allows the use of anode materials with low electrode potential such as graphite. In this work, the ILs are introduced in LIBs in the form of ionogels where the meso- and macropores of a polymeric gel substrate with porosity greater than 90% are filled with the ILs

The authors go on to describe in considerable detail, the process by which they prepare their new electrolyte and then study it using instruments like DSC (differential scanning calorimetry) and TGA (thermogravimetric analysis) as well as evaluating its chemoelectronic properties as an electrolyte.

They compare the performance of their new material with the commercial product in use in lithium batteries today, a product called Celgard 3501.

Their conclusion:

This paper reported a simple two-step procedure for fabrication of sPS ionogel membrane, which was found to be stable for high temperature electrochemical operation, such in LIBs. The porosity of sPS ionogel membranes was significantly higher than that of Celgard-3501 ionogel membranes, which accounted for high IL to polymer weight ratio in the membranes and produced high room temperature conductivity of 6.33 × 10–4 S/cm. The contact angle data showed better wettability of sPS membrane with IL and EC/DEC electrolytes. The high porosity and better wettability of sPS by the electrolyte resulted in lower impedance for sPS ionogels compared to Celgard-3501 ionogel membranes at 25 and 100 °C. The impedance spectroscopy data indicated low bulk charge transfer resistance of sPS-ionogel attributed to better wettability and electrolyte retention of sPS-IL system. The LSV data show improved performance for sPS ionogel membrane over Celgard ionogel membrane at 25 °C. The sPS ionogel membrane also indicated stable electrochemical window up to 4.8 V at 100 °C. This electrochemical and thermal stability of sPS-ionogel allowed continuous operation of LIB cell at 100 °C.

Current lithium batteries can burst into flame at temperatures in excess of 50 °C.

I am not a big fan of storing energy in batteries, except as absolutely necessary. I think that the enthusiasm for them, particularly as macroscale storage devices is misplaced, and is based on the mistaken belief that so called "renewable energy" is sustainable and practical. It hasn't been; it isn't; and it won't be.

My own ideas about energy storage all involve thermal storage, usually in very high temperature materials like, say, supercritical fluids.

But it is very unlikely the need to utilize batteries, particularly in small personal electric devices will go away in the lifetime of anyone now living. Thus this is important research.

I note with less than concealed disgust that this research and all research like it is under threat because a cadre of short sighted and mindless officials holding our government hostage despise science.

I hope you will have a happy and prosperous New Year, and that the New Year will involve the restoration of sanity if not to the White House where fear and ignorance is highly prized, at least then to Congress, now controlled by awful, stupid and extremely ignorant men.

Work for the election of Democrats in 2018!