Airbus and supplier Saft have confirmed several key details of the A350-900’s rechargeable lithium-ion batteries which are soon to become the production standard.
Though incomplete, the details show Airbus and Saft designed the batteries with more conservative power output and energy levels than found on the 787 batteries that caused a four-month grounding in 2013.
The grounding was lifted in May 2013 only after Boeing revised the installation design, although the architecture of the GS Yuasa-designed system remained the same. The 787 uses two rechargeable lithium-ion batteries to start the auxiliary power unit and provide temporary, back-up power to the avionics, with each battery consisting of eight cells storing 72Ah of electrical power and running at 3.7V.
Though much heavier than the Boeing design, the Airbus approach is more cautious. Instead of the 787’s two batteries, Airbus will install four Saft-made lithium-ion batteries in each A350-900. Each of the Saft batteries consists of 14 cells storing a combined 45Ah of energy and running at 3.6V.
One of the four batteries is dedicated to starting the APU, and the three others will provide power to other components in the A350 electrical system, Airbus says.
Details of the A350’s lithium-ion batteries have been a closely held secret since Saft was identified as the supplier six years ago. As the 787 entered the battery-induced grounding, Airbus said the A350 would first be certificated with more traditional nickel-cadmium batteries, which produce significantly less power for the same weight as a lithium-ion battery. In early October, however, Airbus said the nickel-cadmium batteries would be replaced by the Saft lithium-ion batteries by early next year.
Unlike GS Yuasa, which has released a specification sheet on the 787 batteries, Saft had never revealed the technical characteristics of the A350-900 battery until recently to Flightglobal.
The company displayed a mock-up of the A350-900’s lithium-ion batteries at the NBAA convention in Orlando on 21 October. The unit’s power levels were displayed on the box.
Airbus and Saft then confirmed the number of cells inside the battery and the voltage of each cell after being contacted by Flightglobal with pictures of the battery mock-up. Despite repeated requests, however, both companies have refused to identify the chemistry of the positive electrode, or cathode, in the A350 battery.
The chemistry is a significant feature in the design. The 787 battery, says GS Yuasa, uses a lithium cobalt oxide chemistry – which is considered the most reactive and inherently volatile electrolytes in lithium ion-based systems.
The voltage of the A350 battery appears to rule out lithium iron phosphate, which is the least volatile lithium-based chemistry, says Cosmin Laslau, a battery industry analyst for Lux Research. But Airbus could still be using other chemistries considered safer than lithium cobalt oxide, such as lithium nickel manganese oxide.
Boeing’s original installation for the 787 batteries consisted of densely packed cells with no thermal shielding planked into an aluminium box. The redesigned installation added ceramic tiles for thermal shielding between the cells, a stainless steel box and new ductwork to vent fumes and smoke directly off board the aircraft in case a battery caught fire. The new installation worked as designed when a single cell vented in a Japan Airlines 787 parked on the ground last January.
The A350 installation always included an “overboard venting system”, Airbus says. That system is now being reviewed by the European Aviation Safety Agency and the US Federal Aviation Administration.
“We are progressing well with EASA and FAA – also considering recommendations from the US National Transportation Safety Board – to certify the li-ion main batteries in order to offer them to our customers at a later stage,” Airbus says.
Source: Cirium Dashboard