Photoelectron Spectroscopy for Lithium Battery Interface Studies

Abstract

Photoelectron spectroscopy (PES) has become an important tool for investigating Li-ion battery materials, in particular for analyzing interfacial structures and reactions. Since the methodology was introduced in the battery research area, PES has undergone a dramatic development regarding photon sources, sample handling and electron energy analyzers. This includes the possibility to use synchrotron radiation with increased intensity and the possibility to vary the photon energy. The aim of the present paper is to describe how PES can be used to investigate battery interfaces and specifically highlight how synchrotron based PES has been implemented to address different questions useful for the development of the Li-ion batteries. We also present some recent developments of the techniques, which have the potential to further push the limits for the use of photoelectron spectroscopy in battery research. A classical Li-ion battery system is composed of a positive and a negative electrode able to reversibly host lithium. The electrodes are immersed in an electrolyte (lithium salt in an organic solvent) while a separator prohibits direct contact between the two electrodes, see Figure 1a. [1][2][3][4][5] Over the last decades, various electrodes materials have been investigated and an overview of the materials investigated as positive, negative electrode or electrolytes can be found in various recent reviews. [6][7][8] Further development of the battery chemistry requires understanding of the fundamental properties of the components and how it relates to their functionality in an operating device. Specifically, it is becoming more and more crucial to better understand the properties of the interface regions between the different battery components, since the interfacial chemistry is closely linked to battery behaviors such as self-discharge properties, safety and cycling stability.At the interface between the host material and the electrolyte side reactions occur and specifically at potentials outside the thermodynamic stability window of the electrolyte. For electrochemical potentials below about 0.8 V vs. Li + /Li, most organic solvents are thermodynamically unstable and a passivating SEI (Solid Electrolyte Interphase 9 ) layer is formed at the negative electrode/electrolyte boundary. Side products observed at the positive electrode/electrolyte interfaces are referred as to SPI (Solid Permeable Interphase) layer. 10The chemical compositions of the surface layers are different for the negative and the positive electrode materials and while thick SEI (∼30-100 Å) is formed on negative electrode materials, the SPI formed on the positive electrode materials is mostly much thinner (5-10 Å) as illustrated in Figure 1b. [11][12][13][14][15][16] Photoelectron spectroscopy (PES) displays several of the desirable features to investigate Li-ion battery interfacial chemistry. These features are foremost a controllable surface sensitivity, in the range of the interphase layer thicknesses, in combination with the composition sensit...

Selecting the Best Graphite for Long-Life, High-Energy Li-Ion Batteries

“…Moreover, new peaks at 686.2 eV in the F 1s spectra were also identified in all cycled anodes, which suggests the formation of inorganic SEI components likes LiF and PO y F z from LiPF 6 salt decomposition. 56,57 This was further confirmed from the slightly asymmetric Li 1s peak 58 and the presence of P. Of particular interest is that the SEI components were distinctly different in each cycled graphite anode, though no strong correlation was revealed with capacity retention. SLC 1520T, MAGE, and MAGE3 appeared to have more inorganic species like LiF and PO y F z than SCMG-BH, APS, or A12.…”

Fundamental interplay between anionic/cationic redox governing the kinetics and thermodynamics of lithium-rich cathodes

“…HAXPES characterization of anionic redox is repeatable, quantitative, and tunable from surface to bulk, which makes this technique indispensable for studying charge-compensation mechanisms, especially if operando mode is developed. 35 …”

“…The ability of HAXPES to systematically increase probe depths 35 allowed us to distinguish between surface and bulk effects. We consequently correlate these findings with detailed electrochemical measurements to reveal the interplay between anionic/cationic redox and electrochemical kinetics/thermodynamics of these electrodes.…”

Unreacted PbI2 as a Double-Edged Sword for Enhancing the Performance of Perovskite Solar Cells

“…The depth sensitivity in the PES measurements depends on the inelastic mean free path (IMFP) of the photoelectrons, which is related to their kinetic energy. Therefore, changing the photon energy will modify the depth sensitivity 11 . The depth sensitivity values reported in the present work were defined as three times the IMFP of the photoelectron, since 95% of the PES signal in a homogeneous material comes from a layer with this thickness.…”