133HIGHLIGHTS 2020

Spatial dynamics of lithiation and lithium plating during high-rate operation of graphite electrodes, D.P. Finegan (a), A. Quinn (a), D. Wragg (b), A. Colclasure (a), X. Lu (c), C. Tan (c), T.M. Heenan (c), R. Jervis (c), D. Brett (c), S. Das (d), T. Gao (d),

D. Cogswell (d), M. Bazant (d), M. Di Michiel (e), S. Checchia (e), P.R. Shearing (c) and K. Smith (a), Energy Environ. Sci. 13, 2570-2584 (2020); https://doi.org/10.1039/D0EE01191F. (a) National Renewable Energy Laboratory,

Golden (USA) (b) University of Oslo, Oslo (Norway) (c) University College London, London (UK) (d) Massachusetts Institute of Technology, Cambridge (USA) (e) ESRF

LUCY HAD AN APE-LIKE BRAIN, BUT PROLONGED BRAIN GROWTH LIKE HUMANS

Three-million-year-old brain imprints in fossil skulls of the species Australopithecus afarensis have shed new light on the evolution of brain growth and organisation. Lucy s species had an ape-like brain. Protracted brain growth, however, suggests that infants may have had a long dependence on caregivers.

PRINCIPAL PUBLICATION AND AUTHORS

The high free-energy barrier for transition between lithiation states was observed to have influenced the lithiation behaviour of the electrode during charging. When the electrode near the separator reached a certain lithiation state, further local lithiation slowed, and the lithiation front progressed to deeper regions, bringing those regions to a similar lithiation state before lithiation of the frontal regions resumed. In addition to quantifying the physical state of the system with time, the rate of change of the system with respect to the rates of change of the distinct lithiation stages of graphite was quantified, establishing a direct link between Li plating and local physical and dynamic state of the graphite. Phase co- existence was observed within single depths during operation and after the electrode was fully delithiated at regions where Li plating

was present. Li plating was shown to affect the equilibrium state of particles, which has raised questions for how the performance of graphite particles will be influenced by Li plating; for example, whether the plating hinders or improves further (de)lithiation, and how the transport properties of graphite are affected by the presence of plating.

This work has provided a detailed experimental description of the response of a graphite electrode to fast-charging and discharging conditions as well as a description of the onset of Li plating and stripping. This work sheds new light on the limitations of high energy density electrodes to charge quickly (in 10 minutes) and is expected to help guide the design of next- generation electrode materials with higher rate and energy density capabilities.

The brains of modern humans are not only much larger than those of our closest living ape relatives, they are also organised differently, and take longer to grow and mature. For example, compared with chimpanzees, modern human infants learn longer at the expense of being entirely dependent on parental care for longer periods of time. Together, these characteristics are important for human cognition and social behaviour, but their evolutionary origins remain unclear.

Brains do not fossilise, but as the brain grows and expands before and after birth, the tissues surrounding its outer layer leave an imprint in the bony braincase. Such endocranial imprints point to evolutionary changes in both brain size and brain organisation within the hominin lineage. A comprehensive re-evaluation of brain growth and organisation in Australopithecus afarensis was undertaken by combining data on

endocranial imprints and virtual dental histology [1]. This species, famous for the partial skeletons Lucy and the Dikika child [2], occupies a key position in hominin phylogeny, as it is widely accepted to be ancestral to all later hominins, including the Homo lineage. The Dikika cranium and mandible were first imaged on beamline ID17. The procedure involved single-distance propagation phase-contrast X-ray synchrotron microtomography, using a specific absorption control protocol to improve data quality when scanning large fossils with a monochromatic beam [3]. For more detailed studies on dental development, the Dikika infant was also scanned on the ID19 beamline.

Several years of painstaking fossil reconstruction, and counting of dental growth lines, yielded an exceptionally preserved brain imprint of the Dikika child (Figure 116), a precise age at death, new endocranial volume estimates, and