Advanced Characterisation of Energy Materials
Wednesday 21st April 2021
The Advanced Characterisation of Energy Materials is co-hosted by FutureCat and the Henry Royce Institute at the University of Sheffield and follows on from our successful events held in Sheffield over the past two years.
The event will showcase Advanced Characterisation facilities and expertise, and spark new collaborations as a result of the event.
‘Imaging Nanoscale Battery Materials and Processes by Atomic Resolution and Operando Scanning Transmission Electron Microscopy’
D. Browning1,2,3, M. Bahri1, W. Li1, D. Nicholls1, A. Robinson1, I. Siachos1, F. Schnaider-Tontini1, J. O. M. Wells1, B. L Mehdi1,2
1Mechanical, Materials & Aerospace Engineering, University of Liverpool, Liverpool, L69 3GH
2Pacific Northwest National Laboratory, Richland, WA 99352, USA
3Sivananthan Laboratories, 590 Territorial Drive, Bolingbrook, IL 60440, USA
Reactions at the interfaces between the main components of a battery play a dominant role in determining the overall energy density and coulombic efficiency of the system as a whole. In many of the new chemistries being developed, the systems that show the most promise for individual components run into severe problems when they are combined together to form a full operating cell. Side reactions at interfaces can cause electrolyte breakdown, passivation or corrosion in addition to the formation of a solid-electrolyte-interphase (SEI) layer. Furthermore, deposition of an excess of metal ions during charging can lead to the formation of dendrites during cycling. Each of these effects is extremely sensitive to the local chemistry/field at the electrode/electrolyte interface and a full understanding of the materials parameters that can lead to better batteries requires the ability to observe all of the dynamic processes taking place at these interfaces during battery operation. It is precisely these kinetics that can be studied using operando electrochemical stages in the (Scanning) Transmission Electron Microscope. In this presentation, examples of the use of operando (S)TEM methods for battery materials will be discussed and how the dynamics that are observed can be linked directly to extensive ex-situ atomic resolution STEM images/spectra from the pristine and cycled components.
‘Orientation Glass Formation and its role in Photo-Induced Halide Segregation in CH3NH3Pb(ClxBr1-x)3’
Bandgap tuning of hybrid metal-halide perovskite semiconductors by halide substitution holds promise for tailored light emission in LEDs and absorption for tandem solar cells. However, the impact of halide substitution on the crystal structure and the fundamental mechanism of photo-induced halide segregation remain open questions. In this talk I will show how using a combination of temperature-dependent X-ray diffraction and calorimetry measurements, we find the emergence of a disorder- and frustration-driven orientational glass for a wide range of compositions in CH3NH3Pb(ClxBr1-x)3 and discuss how this is related to local strain and photo-induced halide segregation. Evidence for the absence of glassy behaviour in CsPb(ClxBr1-x)3 will be presented, highlighting the importance of the A cation on the structural and magnetic properties. I will then present first-principles calculations which identify the local preferential alignment of the organic cations driving the glass formation mechanism. Using these results I will then discuss how these can be used to generate guidelines for stabilising hybrid-photovoltaics.
3D Batteries – Challenges of through the length-scales microscopy and analysis
In seeking the holy grail of the high-performing, everlasting, cheap, non-toxic battery, batteries are now engineered from the nano-to-macroscopic scale. It is a significant challenge quantify battery performance and evolution at size and time-scales that are representative to the mechanisms operating. Here we will examine progression in in-situ and in-operando microscopy methodologies relevant to the battery field, using 3D electron, ion and X-ray techniques, with focus on the data achievable and environments used.
Shining (Synchrotron) Light on Oxygen in Li-Rich Battery Cathodes: What can RIXS and HAXPES tell us?
Commercial high-capacity lithium-ion batteries employ Ni-rich layered oxides (derived from LiCoO2) as cathodes with practical capacities of ~190 mAh/g. To ultimately achieve energy density targets for the automotive industry of 500 Wh/Kg, cathodes with practical capacities > 250 mAh/g are required i.e., go beyond the limits of conventional metal redox. Lithium-rich NMC (LR-NMC) compounds exhibit high capacities beyond the traditional redox, but it remains unclear whether the anomalous charge compensation mechanism is due to oxidized lattice oxygen (holes or peroxides) or migration-assisted Mn oxidation facilitating trapped molecular O2. Here, I will discuss the recent application of local probes sensitive to the oxygen environment for studying charge compensation mechanism within lithium excess cathodes i.e. hard x-ray photoemission spectroscopy (HAXPES) and O K-edge resonant inelastic x-ray scattering (RIXS). The former is found to be best suited for studying metal densification associated with surface oxygen loss at high voltages, whereas O K-edge RIXS is determined to be a reliable probe of bulk lattice oxygen redox. Surprisingly, signatures of oxygen redox absent for Li2MnO3, are observed in classical layered materials at the highest states of delithiation. Reconciling these observations may prove critical for a complete description of oxygen activity (gas evolution and reversible redox) in this class of cathodes.
‘Research on NMC cathodes’
C.Bock, L. Gaburici, C. Yim, S. Niketic, National Research Council of Canada
Nickel Manganese Cobalt (NMC) oxide powders are the preferred material for Li-ion battery cathodes. There is a trend to increase the Nickel content of the NMC materials to lower the Cobalt content (due to Cobalt’s high toxicity and price) and to access the theoretically high capacities of Nickel-rich NMCs by extending the potential range.
However, the advantage of the higher voltage of the Nickel-rich Li-ion cathode materials is accompanied by a capacity fade. It is likely that multiple degradation mechanism contribute to the capacity fade and correspondingly, many factors and mechanism are proposed in the literature. For example, it has been proposed that Ni4+ located at the Li-ion cathode surface interacts with the electrolyte, while recent, detailed evidence suggests a chemical reaction of the electrolyte with lattice oxygen. Similarly, rock salt formed on the cathode surface can contribute to the capacity fade or be of benefit depending on the thickness of the rock salt layer. Recent literature also emphasizes that more factors and contributions from Co and Ni surface species could also play a role.
Practically relevant NMC cathode materials are spherical, dense particles and are in the micro-meter size range. They are synthesized through a two-step reaction, which consists of the formation of the NMC-hydroxide through a precipitation reaction, followed by a solid state reaction to form the lithiated NMC-oxide at higher temperatures. It is evident that many factors in both synthesis steps not only affect the bulk of the resulting NMC powders but also the surface properties. In this presentation, we examine the synthesis parameters and its resulting effects on the chemical, structural and physicochemical properties of NMC-hydroxide and NMC-oxides. The charging-discharging behaviour of the oxides will also be discussed. Efforts on using machine learning to identify suitable ad-metals to allow access to higher delithiated states and reduce the capacity fade are also presented.