JTSB rules out overcharging in ANA battery incident

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The All Nippon Airways Boeing 787 involved in an emergency landing on 16 January did not have an over-charged battery when the lithium-ion unit experienced an in-flight malfunction, Japanese investigators said today according to local reports.

The update means the Japan Transportation Safety Board probe of the ANA incident aligns now with the US National Transportation Safety Board investigation of a battery failure and fire aboard a parked Japan Airlines 787 in Boston on 7 January.

NTSB investigators said on 20 January that the JAL 787 was not over-charged before the auxiliary power unit battery failed. Two days before, Japanese investigators had told reporters that the ANA 787 main battery may have been over-charged when it failed, but now that theory appears to have been ruled out.

Separately, Boeing has confirmed the 787 uses a lithium cobalt oxide chemistry for the 787's batteries.

It is a chemistry used widely in consumer electronics, but eschewed by the majority of the automotive industry's electric- and hybrid-electric-powered vehicles.

An automotive battery supplier called American Manganese has publicly rebuked Boeing for using the lithium cobalt oxide chemistry, as it is considered more flammable than other lithium ion-based chemistries, such as lithium manganese oxide.

Cosmin Laslau, an automotive analyst for Lux Research, also criticised Boeing for using what he describes as the most potentially flammable lithium-ion chemistry on the market. Lithium cobalt oxide erupts into flames if the battery temperature exceeds about 170°C (338°F), he says. Lithium manganese oxide is safe until it reaches temperatures above about 310°C, he adds.

The trade-off is that safer chemstries of lithium-ion batteries tend to provide 20-30% less energy density than lithium cobalt oxide, Laslau says, meaning that more battery cells would be required to produce the same amount of energy.

Boeing supplier GS Yuasa's web site advertises the volumetric energy density of the 787's eight-cell, 32V lithium ion battery as 232wh/l.