(March 2007) Lithium-ion batteries...Unsafe at Any Altitude ?
by Donald Georgi
Lithium-ion battery use continues to rise as do the number of smoke and fire related recalls of the chemistry and the number of incidents on aircraft. Fires on airborne aircraft are not only frightening but also deadly. In 1996, ValueJet flight 592 and SwissAir Flight 111 in 1998 crashed due to onboard fires. All passengers and crew on both planes were killed. Neither fire was due to Lithium-ion batteries. But there are many cases of in-flight and on-ground Lithium-ion fires. On March 22, 2007 the U. S. Department of Transportation’s Pipeline and Hazardous Materials Safety Administration reported that on February 10th, 2007 a fire broke out in the overhead baggage compartment of a JetBlue flight, and on March 18th, 2007 a battery overheated or ignited on board an American Airlines aircraft flying from Argentina. Fires were contained and both aircraft landed safely. By 2005, there were nine fires involving lithium batteries either on the ground or in flight. A Chicago Lufthansa jet about to leave developed Lithium-ion smoke in the overhead bin, and in 2006 a Philadelphia bound UPS jet was destroyed by fire with charred laptops near the center of the fire.
To complicate the situation, in-flight fires which are not readily extinguishable go to the top of the list of fears. Lithium metal and ion battery fires are difficult, if not impossible, to put out with standard fire extinguishers. In 1999, after flying from Japan to LAX, a palet of Lithium-ion batteries caught fire and upon dousing with water reentered a burning mode. Unfortunately, as we have seen from the current laptop fires, Lithium-ion does fall into the difficult-to-impossible category to extinguish in the air.
Anything which restricts the flying public’s access to convenience is considered a restriction of freedom. Failing that argument, the public can always replace it with a limp ‘restriction of privacy.’ Is the flying public lucky or will the grim reaper of aircraft Lithium-ion catastrophe catch up with statistical averages? Additional Lithium-ion safety is being addressed by the U. S. Department of Transportation (DOT), the Federal Aviation Agency and many regulatory organizations.
As noted in BD Portals, the IEEE is revisiting Lithium-ion standards. Underwriters Laboratories, a voluntary force in battery safety testing, is in the process of increasing testing regimen standards for Lithium-ion batteries in 2007. The Public and Hazardous Materials Safety Administration of the DOT are investigating new restrictions for checked baggage but not for carry on luggage. Both the National Transportation Safety Board and the United Nations have improved regulations and recommendations addressing lithium batteries transported by aircraft, but years will be required for implementation. Meanwhile, the Airline Pilots Association wants bulk shipments of lithium metal batteries banned from cargo flights and the National Association of State fire Marshals recommends that bulk shipments of Lithium-ion batteries should be restricted.
Critics of tightening regulations regarding the transportation of Lithium-ion in the air point to the uncontrolled manufacture of renegade cells by low-quality, knock-off, counterfeit manufacturers, but that argument presently carries little weight since the recall problem has principally been with industry-standard, top-quality Sony batteries. These problems snuck by the best of safety investigators at high-tech market leaders - Apple, HP and Dell.
System wide Lithium-ion safety
If the cell were intrinsically safe, there would be no more problem than with any other popular battery chemistry. But the very nature of Lithium-ion electrochemistry allows poorly manufactured, physically damaged, overcharged or mismanaged cells to thermally run away. In this respect, the quality of thermal or mechanical damage response, charging methods and safety devices such as chargers, regulators, shutdown separators, pressure relief valves, temperature sensors plus positive temperature coefficient (PTC) resistors share in adding to, or removing, safe performance. To make a total improvement, short of an intrinsically safe chemistry, the cell, its system design and all safety related components must share the responsibility for improving safety.
(June 2006) Altair Nanotechnologies, Inc. successfully competes safety testing cycle for its Lithium Titanium Oxide negative electrode (nLTO) material. Nanotechnologies reported, “To put nLTO to the test, Altairnano performed the ‘hot box” exercises on its batteries at temperatures up to 2400 C -- which is more than 1000 C above the temperature at which graphite-based batteries can explode -- with zero explosions or safety concerns. The Company also performed high-rate overcharge, puncture, crush, drop and other comparative tests with nLTO and had no malfunctions.
Altairnano notes that the life cycle of nLTP is unprecedented, having demonstrated more than 9,000 use cycles at charge/discharge rates which other battery types can’t function. Safe operating temperatures are listed as low as - 500 C and as high as 750 C.
Altairnano says the significance of these tests are especially significant for the advancement of the electric and hybrid electric vehicle market and will help speed the deployment of these powerful and efficient vehicles for mass usage.
(Feb 2006) Sandia National Laboratory researches Lithium-ion batteries for Freedom CAR program. . Sandia is researching ways to make Lithium-ion batteries work longer and safer for possible use in hybrid vehicles in the next five to ten years. Dan Doughty, manager of Sandia’s Advanced Power Sources Research and Development Department, said, “Batteries are a necessary part of hybrid electric-gasoline powered vehicles and someday, when the technology matures, will be part of hybrid electric-hydrogen fuel cell-powered vehicles.” He also noted that a safe Lithium-ion battery would be a better option for hybrids than Nickel-metal hydride because Lithium-ion has two to three times the energy density of Nickel-metal hydride and it has the potential to become one of the lowest-cost battery systems.
Sandia’s Freedom CAR program centers on the areas of battery abuse tolerance and accelerated lifetime prediction.
• Abuse tolerance - The technical goal is to comprehend mechanisms that lead to poor abuse tolerance, including heat-and gas- generating reactions. Understanding the chemical response to abuse can point the way to better battery materials. But, Doughty says, there is no “magic bullet” for completely stable Lithium-ion cells. “Fixing the problem will come from informed choices on improved cell materials, additives, and cell design, as well as good engineering practices.” Work in abuse tolerance is beginning to shed light on mechanisms that control cell response, including effects of the anode and cathode, electrolyte breakdown and battery additives.
Improved abuse test procedures developed at Sandia have led to Lithium-ion standards that the battery team has developed and recently published . Doughty anticipates that the Society of Automotive Engineers will soon adopt these test procedures as national standards, just as they adopted in 1999 the abuse test procedures Sandia developed for electric vehicle batteries.
• Accelerated life test - Sandia is working on developing a method to predict Lithium-ion battery life. “We have two approaches in our research - the empirical model and the mechanic model,” Doughty says. “The empirical model generates life prediction from accelerated degradation test data, while the mechanistic model relates life prediction to changes in battery materials. Our approach provides an independent measure of battery life so we don’t have to rely on what battery manufacturers tell us.”
Fijitsu-Siemens, Europe’s largest computer maker, recalls 250,000 notebook batteries in mid-June. Four reports have been received on batteries overheating. The company has not named the manufacturer of the batteries.( BD note: Why not?) For details on battery exchange see www.fujitsu-siemens.com/batteryexchange.
Safer Electrolytes for Lithium-ion Cells
Blending low flammability liquid oligomers and polymers with ethylene carbonate have been found to produce cells which are either nonflammable or self extinguishing. Their conductivity is about 2 mS/cm and will function down to temperatures of minus 5 degrees C. They are not suitable for high charge and discharge rates.
NASA Tech Briefs
June 2004, p. 52
Building safer LiIon batteries
An argument is made for considering replacement of the cobalt oxide cathode material with iron phosphate materials. One reason is that overcharge can lead to thermal runaway because 50 percent of the lithium remains in the fully discharged cobalt oxide cathode. Even construction with manganese oxide, while expanding the safety envelope, offers safety concerns. Secondary reasons include the availability of cobalt oxide and incomplete environmental impacts.
Replacing the cobalt oxide with a phosphate such as iron phosphate leads to greater stabilization. Extensive heating demands, greater than 800 degrees C, are required for decomposition.
Cobalt oxide cells experience swelling with discharge which inherently changes the structural integrity and safety of the cell. Conversely, the iron phosphate causes no structural modification in discharge such that a fully discharged cell retains both dimensional and structural integrity, again contributing to overall safety.
Lithium-ion iron phosphate cells constructed with polymer electrolyte technology would eliminate leakage, further expanding the safety characteristics.
August 2004, p. 16