Exploration of materials electrochemistry in rechargeable batteries using advanced in situ/operando x-ray absorption spectroscopy

Abstract

Rechargeable batteries (Li-ion batteries and beyond) have received extensive attention as powerful boosters for the development of human society. The rapid progress achieved in this research area largely relies on the in-depth efforts on the improvement of battery electrode materials and decrease of the cost. However, the application of rechargeable batteries is still hindered by low energy density, serious voltage hysteresis, and long-term degradation. Therefore, it is of great importance for understanding the underlying redox reaction and capacity fading mechanisms to circumvent these problems and improve the overall battery performance. Advanced characterization techniques, especially synchrotron-based x-ray absorption spectroscopy (XAS), have been widely applied to the mechanistic understanding of rechargeable batteries. Particularly, in situ/operando XAS allows the characterization of practical working mechanisms by measuring the electronic structure evolution of the electrode materials under real operation conditions, which is an imperative prerequisite for the further optimization of the battery performance. Herein, the recent progress in the understanding of the operating principles of several common rechargeable batteries (including lithium-ion batteries, sodium-ion batteries, and lithium–sulfur batteries) based on in situ/operando XAS technique is reviewed and summarized. We aim to provide a comprehensive treatise on in situ/operando characterization of rechargeable batteries using XAS, which could provide guidance for further improvement of battery performance.

Crystallography of Active Particles Defining Battery Electrochemistry

“…XPS analysis was able to show the enrichment of Ni 2+ from 12.2% to 16.6% in surface rock salt phases of NMC cathodes [33] and the disproportionation of manganese ions of a lithium manganese oxide (LMO) cathode as the Mn 3+ :Mn 4+ ratio changed from 60:40 to 25:75 during cycling. [34] In addition to XPS, X-ray absorption spectroscopy (XAS), as well as X-ray absorption near edge spectroscopy (XANES) experiments are repeatedly used for high resolution in situ and in-operando measurements, when using synchrotron x-ray sources, [35][36][37] as shown in Figure 2b, to detect changes in elements and their oxidation state at the bulk electrode scale. [38] Less common techniques shown in Figure 2b are Raman spectroscopy, effective in measuring M-O bond shortening and MO 6 octahedra distortion [28] and nuclear magnetic resonance (NMR) for determining the change in chemical environment for 7 Li atoms for detecting lithium-ion trajectory and storage during cycling.…”

Theoretical and experimental insight into nano-optoelectronics

“…The experimental contributions are dominated by photoelectron spectroscopy, which is not surprising as 'photoelectrons know everything about how the electrons inside the material behave' [19] and UPS and XPS are, thus, the most important techniques of electronic structure research. Another seminal technique, which also allows insight in the unoccupied density of states, was covered in another focus issue of Electronic Structure: 'X-ray Absorption Spectroscopy of Energy Materials' [20]. Half of the contributions to our focus issue are from America, which seems to be a bit unbalanced, but two of them are from Brazil [15,16] (and the two others from the USA [17] and from Canada [11]).…”