May_June_2022_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A Y / J U N E 2 0 2 2 2 4 in both the battery systems are largely convergent. These families are said to be “ordered” which means that the lithium ions and transition metal ions sit in specific sites within them (Slide 1). Lithium iron phosphate has the lowest voltage and the lowest energy density, but is the safest. Lithium manganese spinel has a higher voltage but mediumenergy density. Layered cathodes—so named because of their distinct layered structure—have the highest energy density. As the nickel content in these materials increases, they become less safe. However, they have emerged as a global leader because of their high energy density and because of the perception that safety can be engineered on the pack level of storage. The safety concern for the layered family can be understood through the example of lithium cobalt oxide. The structure typically consists of alternating layers of cobalt and lithium interleaved with oxygen. As more and more lithium is pulled out during charging and discharging, the material becomes unstable—like a jenga tower—and finally collapses. Increasing the cobalt, nickel, and manganese content causes structural instabilities so that the cathode cannot be charged more than 70 or 80%. They also release oxygen at high charge, leading to porosity and cracking of the electrodes. Yet, we can essentially only make layeredmaterials with nickel and cobalt as active redox elements. All other transition metals will migrate upon delithiation, resulting in lower voltage and shutting down lithiummigration. This has a significant impact on the future of electric storage. Estimates of the electric storage capacity needed for 2022 range from 2 to 20 terawatt hours. Two terawatt hours is equivalent to approximately two million tons of nickel and cobalt, and 10 terawatt hours is correspondingly 10million tons of nickel and cobalt. As the diagram in Slide 2 shows, the cobalt production today is almost an order of magnitude less than needed. Therefore, new materials that perhaps use disorder to their advantage by keeping lithium diffusion pathways open need to be actively explored. IRYNA V. ZENYUK: PRESENTER Professor, Department of Chemical and Biomolecular Engineering, University of California, Irvine Associate Director, National Fuel Cell Research Center Fuel Cell Electric Vehicles: Materials Needs for Deployment at Scale Hydrogen can be a competitive energy source for this industry as it has a similar range to internal combustion engines, has quick refueling time, and produces zero emissions if extracted from clean sources. The gravimetric density of hydrogen is three times that of diesel, producing between 100 and 120 MJ/kg. The U.S. produces more than 10 million metric tons of hydrogen, but unfortunately, 99% of this is from fossil fuels with 95% generated through steammethane reforming. This emits carbon dioxide and is harmful to the environment. If compressed hydrogen is used instead of diesel, there is no substantial reduction in the payload capacity of heavy duty trucks. However, a hydrogen fuel cell based system would take up significant space, reducing the available payload capacity from 50,000 to 35,850 lbs. Compressed hydrogen also takes 15 minutes for refueling, while a diesel truck only takes 5 minutes. Despite this, hydrogen is very suitable for heavy duty transportation as it enables Zenyuk Slide 2 Slide 1

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