S C

IE N

T IF

IC H

IG H

LI G

H T

S X

-R A

Y N

A N

O P

R O

B E

8 5 I H I G H L I G H T S 2 0 2 1

were used as the initial conditions for the Kuramoto analysis, which was used to simulate the evolution of the nacreous ultrastructure. Specifically, the topography, the phase field and the elastic energy landscape at the growth front of nacre were analysed (Figure 67). The topography and the phase field clearly demonstrate smoothing of the growing tissue and synchronisation of the periodic structure, which are driven by the decreasing elastic energy stored in the system. The areas around dislocation cores carry the highest amount of energy, which is gradually reduced during growth as a result of defect motion and annihilation. The numerical model reproduced the overall defect dynamics, the spatial coupling between dislocation pairs and the synchronisation that is observed in the biologically formed nacre.

Topological defects in nacre link the physico-chemical process that underlies the formation of the layered pattern and the geometric constraints throughout tissue morphogenesis. This work demonstrates that defects propagate through the growth front and move to reduce the elastic energy stored in the system, which determines the driving force for the morphogenesis of new nacre layers and thus, directs the evolution of the nacreous ultrastructure. This process is accompanied by a gradual increase in periodicity and coherence of the entire tissue structural synchronisation.

PRINCIPAL PUBLICATION AND AUTHORS

Dynamics of topological defects and structural synchronization in a forming periodic tissue, M. Beliaev (a), D. Zöllner (a), A. Pacureanu (b), P. Zaslansky (c), I. Zlotnikov (a), Nat. Phys. 17, 410-415 (2021); https:/doi.org/10.1038/s41567-020-01069-z (a) B CUBE Center for Molecular Bioengineering, Technische Universität Dresden (Germany) (b) ESRF (c) Department for Operative and Preventive Dentistry, Centrum für Zahn-, Mund- und Kieferheilkunde Charité Universitätsmedizin Berlin (Germany)

REFERENCES

[1] V. Schoeppler et al., Adv. Mater. 30, 1803855 (2018). [2] M. Beliaev et al., J. Struct. Biol. 209, 107432 (2019). [3] Y. Kuramoto, Int. Symp. Math. Probl. Theor. Phys. (1975).

Revealing the complexity of the battery electrode architecture

X-ray phase-contrast nanotomography provided remarkable insight into how the electrode microstructure of the lithium-ion battery can be improved for better performance. The data suggest how the carbon binder domain (CBD) should be optimised in future electrode architecture.

The microstructure of the porous composite electrode is well known to play an important role in the performance of lithium-ion (Li-ion) batteries. One of the main problems is that their micro-architecture is regulated by a trial- and-error approach, using basic adjustment of the ratio of different compounds. This work presents an evidence-based method to better determine the complex microstructure of 3D electrodes with a clear distinction of the light polymer phase and electrochemical active materials.

The electrodes of Li-ion batteries are made up of three components: the active material, lithium nickel manganese cobalt oxide (NMC); the carbon binder domain (CBD), in which the carbon promotes the electrical connectivity of a polymer binder; and finally, a network of pores, which are filled with a liquid electrolyte.

The technique X-ray phase-contrast nanotomography, available at beamline ID16B, allows a low-absorbing object to be imaged in 3D with high spatial resolution (50 nm), making it possible to clearly image light elements, such as the CBD, with enhanced contrast (Figure 68). This holotomography technique still provides a persistent and high-throughput workflow to capture other microstructural details, such as NMC secondary particles. As a result, a comprehensive quantitative 3D analysis of the microstructures of three high-energy density NMC electrodes, including the characterisation of each phase separately as well as the statistical quantification of their inter-connectivity at particle scale, was performed using a set of 500 individual NMC particles. The microstructural heterogeneities were quantified and compared to different electrodes.

The results of the 3D image processing indicate the reasons for the negative impacts of the excess CBD on the electrode performance at high C-rates. The unexpected degradation of the electrochemical properties is due to the reduction of the electrochemical active surface area. It was shown that with higher CBD content, CBD provides a higher interfacial area with the NMC phase, providing good electronic conductivity. However, electrode performance deteriorates at high C-rates when comparing two electrodes with lower CBD content.