Recharging reverses the sequence: An applied current forces electrons to flow in the opposite direction, causing the sulfur electrode, or cathode, to give up electrons, converting Li 2S to Li 2S 2. At each step more energy is given up and passed to the load until at last the cell is depleted of energy. The process continues, stepping through further polysulfides, Li 2S 4 and Li 2S 2, to eventually become Li 2S. In the electrolyte, the newly produced Li 2S 8 immediately reacts with more lithium ions and more electrons to form a new polysulfide, Li 2S 6. At the anode, meanwhile, lithium molecules give up electrons to form positively charged lithium ions these freed electrons then move through the external circuit-the load-which takes them back to the cathode. When a cell discharges, lithium ions in the electrolyte migrate to the cathode, where they combine with sulfur and electrons to form a polysulfide, Li 2S 8. Lithium-sulfur batteries are unusual because they go through multiple stages as they discharge, each time forming a different, distinct molecular species of lithium and sulfur. For a large vehicle such as an airplane, scores of packs are connected to create a battery capable of providing tens or hundreds of amp-hours at several hundred volts.
#Lithium batteries on planes series
The cells are in turn connected together-both in series and in parallel-and packaged in a 20 ampere-hour, 2.15-volt battery pack.
These components are connected and packaged in foil as a pouch cell.
An electrolyte facilitates the electrochemical reaction by allowing the movement of ions between the two electrodes. The separator is bathed in an electrolyte containing lithium salts. A porous separator prevents the two electrodes from touching and causing a short circuit. The lithium, too, acts as a current collector, but it is also an active material, taking part in the electrochemical reaction. The negative electrode, or anode, releases electrons during discharge. There is also a small amount of binder added to ensure the carbon and sulfur hold together in the cathode. But it is an electrical insulator, so carbon, a conductor, delivers electrons to where they are needed. Sulfur is the active material that takes part in the electrochemical reactions. It is connected to an aluminum-foil current collector coated with a mixture of carbon and sulfur. The positive electrode, known as the cathode, absorbs electrons during discharge. The first set of flight trials have already been completed.įundamentally, a lithium-sulfur cell is composed of four components: The new technology has been a long time coming, but the wait is now over. After all, a plane can’t handle a sudden fire or some other calamity by simply pulling to the side of the road. Lithium sulfur is also capable of providing the required levels of power and durability needed for aviation, and, most important, it is safe enough. Our battery technology is extremely lightweight: Our most recent models are achieving more than twice the energy density typical of lithium-ion batteries. Since 2004 my company, Oxis Energy, in Oxfordshire, England, has been working on one of the leading contenders-lithium sulfur. It reached maturity years ago, with each new incremental improvement smaller than the last. Reducing battery weight would be an advantage not only for aviation, but for other electric vehicles, such as cars, trucks, buses, and boats, all of whose performance is also directly tied to the energy-to-weight ratio of their batteries.įor such applications, today’s battery of choice is lithium ion. Even for relatively small aircraft, such as two-seat trainers, the sheer weight of batteries limits the plane’s payload, curtails its range, and thus constrains where the aircraft can fly. But the technology has yet to take off, and for one reason: lack of a suitable battery.įor a large passenger aircraft to take off, cruise, and land hundreds of kilometers away would take batteries that weigh thousands of kilograms-far too heavy for the plane to be able to get into the air in the first place. Electric aircraft are all the rage, with prototypes in development in every size from delivery drones to passenger aircraft.
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