Sunday, January 27, 2013
Can The Dreamliner’s Nightmare Be Fixed? Probably not!
This comes to mind on reading a report of Japanese investigators in the wake of a Nippon Airways 787 emergency landing, after the 787’s lithium battery leaked (‘Leaking Lithium Batteries Central to 787’s Problems’, The Denver Post, Jan. 18, p. 16A. According to the article,
“An inspection of the Nippon Airways 787 that made an emergency landing in western Japan found that electrolytes, a flammable battery fluid, had leaked from the plane’s main lithium ion battery. Japan’s Kyodo News Agency quoted transport ministry investigator Hideyo Kosugi as saying the liquid leaked through the electrical room floor to the outside of the aircraft.”
The article cites another incident on Jan. 7 when it took firefighters 40 minutes to put out a blaze in an auxiliary power unit of another 787 used by Japan Airlines. Each incident resulted in the release of flammable electrolytes, as well as heat damage and smoke. The release of the battery fluid was particularly alarming given it’s extremely corrosive so can quickly damage electrical wiring and components. (787s rely far more on these Li batteries to power electronics rather than hydraulic or mechanical systems.)
As may be expected, Japan has halted all use of 787s. Meanwhile, the news emerged (reported from the Seattle Times) that in 2006 a devastating lab fire erupted in Arizona when a lithium ion battery blew up, showing how volatile the battery can be if the energy is not properly contained. (A single battery connected to prototype equipment exploded and the whole building housing the lab burned down.)
Let’s look at this energy issue and the construction of the battery in more detail.
Any first year General Physics student knows how an electrolytic cell is made. Usually, the student is first given a beaker of water into which two platinum electrodes are placed, connected to a source of emf –voltage. Hydrogen ions migrate to the negative electrode, pick up electrons and form hydrogen gas according to: 4H+ + 4(e-) -> 2H2
The hydroxide ions (-OH) that reach the positive electrode meanwhile give up their electrons to form oxygen gas and water:
4(OH-) -> 2 H2O + O2
This, of course, demonstrates electrolysis. The key aspect to note is the voltage is below 1.7V. Once the threshold voltage is exceeded the original electrolytic cell acts like a battery on charge. For example, in the decomposition of a kilomole (18g x 1000 = 18,000 g = 18 kg) of water, 69,000 kcal or 2.9 x 10^8 J of energy is released, or more accurately this amount of energy is converted to chemical energy (to drive the reaction H2O-> H2 + 1/2 O2.
Now, unlike the simple electrolytic cell above which can use water or dilute acid, the Li ion cell is made of thin sheet electrodes separated by micro-perforated plastic sheets. The positive electrodes are made of lithium cobalt, while the negative electrodes are made of carbon. The separator sheets allow Li ions to pass through while keeping positive and negative electrodes apart... or so one hopes. The Li ion battery itself is comprised of eight re-chargeable Li-ion cells connected in series. Each of the cells in turn is in a case within which the separator sheets are submerged in an organic solvent.
(+I ! I ! I ! I ! I ! I ! I ! I ! I+)
The configuration above gives an idea of the cell placed horizontally, with the outer positive electrode at far left then followed by a negative electrode, then positive and so on, alternating until reaching the final + electrode on the right. The outer brackets denote the shell casing. When one such cell charges, Li ions move through the electrolyte from (+) to (-) electrodes. On discharge they move back. This allows each cell to generate 3.7 V compared to only 1.5V for a normal alkaline cell.
So what’s the problem? The problem is the proximity of the electrodes to each other, with only thin plastic sheets acting as separators. If then even one separator fails, and the electrodes come into contact, the result is a short circuit which heats up the system. The cell then ‘vents’ the organic solvent. A spark can then cause a fire and the heat from one burning cell can cause others to ignite leading to a battery fire. If then the battery ruptures the corrosive fluid will have even further catastrophic consequences.
The very proximity of the separators, as well as electrodes in the cells, combined with the large emf generated in each cell amounts to what we call a potential “engineering catastrophe” (see e.g. ‘Catastrophe Theory’, Penguin Books, 1978, pp. 92-95). Catastrophe Theory shows that even one minor, but fatal flaw in a design, can translate into a systemic engineering failure. In the case of the 787 such a systemic failure would be a fire affecting the whole plane, likely of electrical origin, similar to what brought down a Swiss Air 111 jet (a McDonnell -Douglas MD-11) back in 1998, flying from NYC to Geneva and killing all 229 on board. Later inspections, examinations determined a probable short circuit, and electrical system overload causing a fire that affected the hydraulics.
Can the Li -ion battery problem be fixed and the 787s be airborne again? I don’t think so unless the design is changed. The Li ion batteries as they are now simply invite a major calamity. The electrode placement in a flammable solvent is way too dicey, unstable. Personally, I wouldn’t fly on one of those things even if they paid me, but that’s just me. If the Li ion batteries are retained, a supporting safety system needs to be installed on every Dreamliner, to enable any battery fire or explosion to be quickly contained. Of course this would add monumentally to the cost, but one must ask: What price safety?
The bottom line is the 787's battery suffers from a bad design! Moreover, the existing safety protocols are simply insufficient to contain the explosive energy that can be released by a Li ion battery with poor separators between electrodes which can too easily come into contact- say even from a rapid change in barometric pressure. As for Bill Maher’s question on his last Real Time: Do I need to worry about the lithium ion batteries in my laptop? Well, maybe. See: http://redtape.nbcnews.com/_news/2006/08/24/6346061-exploding-gadgets-its-not-just-laptops?lite