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TheGrid BMWopts into series hydrogen BMW has started series production of electric powertrains based on hydrogen fuel cells, in a major step forward for the technology (writes Nick Flaherty). Previous production had been for prototype and test vehicles, using fuel cell technology developed in-house. BMW’s hydrogen powertrain will now be used in the company’s iX5 Hydrogen, which will be built in a small series next year and used worldwide for test and demonstration purposes. The powertrain provides 125 kW/ 170 bhp from the fuel cell, and is combined with an electric engine from the fifth generation of BMW eDrive technology and a high-performance battery developed specially for this vehicle, providing a total power of 275 kW/374 bhp. The development team integrated two hydrogen tanks, the fuel cell and the electric engine into the architecture of a BMW X5. Consistent supply of air and hydrogen to the membrane in the fuel cell is crucial to ensuring high drive efficiency, so alongside existing technology for charge- air coolers, air filters, control devices and sensors, the team developed special hydrogen components. These include a high-speed compressor with turbine and a high-voltage coolant pump. “We have managed to more than double the fuel cell’s continuous output in the second-generation fuel cell in the iX5 Hydrogen, while weight and size have both decreased drastically,” said Frank Weber, member of the board of management of BMW for development. FUEL CELLS Modi ied anodes boost cell cycling Researchers in South Korea have developed a new method of modifying conventional anodes to improve the cycling performance of a battery cell (writes Nick Flaherty). The team, at the Gwangju Institute of Science and Technology, used a layer of graphene oxide – a single atomic layer of carbon – on a silicon anode to prevent irreversible volume change in the anode during the charge-discharge cycle. During charging, lithium ions move from the cathode and combine with the nanoparticles in the anode. During discharging, the ions move back to the cathode. Over time, the nanoparticles in the anode crack and cluster together at the electrode-electrolyte interface. That causes an electrical disconnection, reducing the amount of charge the anode can store or transport. The method developed by the researchers strengthens the anode by encapsulating the nanoparticles in an elastic web-like structure. While the researchers used a silicon anode, the method is applicable to other anode materials, such as tin, antimony, aluminium and magnesium. The anodes can also be modified regardless of how they were manufactured, making it a universally applicable method for improving battery life. The researchers used an anode containing silicon nanoparticles held together by a polyvinylidene fluoride polymer binder. They removed the binder by heating the anode using an annealing process and replaced it with a reduced graphene oxide (rGO) solution, which dries to form a web that holds the silicon nanoparticles together and prevents them from cracking. The web also provides a conductive pathway for the electrons, allowing the nanoparticles to bind with lithium. The rGO coating serves as a seed layer for the deposition of a protective layer consisting of zinc oxide with magnesium and gallium metal oxides (MGZO) added to it. The MGZO layer provides structural stability to the anode. Upon testing, the modified anode could retain most of its charge, even after several charge-discharge cycles. The structure retained a high storage capacity of 1566 mAh/g after 500 cycles and showed a 91% coulombic efficiency, a measure of battery life. BATTERIES The fuel cell in BMW’s iX5 Hydrogen delivers 125 kW to the powertrain 8 Winter 2022 | E-Mobility Engineering