Excitonic Effects in X-ray Absorption Spectra of Fluoride Salts and Their Surfaces
[1];
[3];
[3];
[4];
[3];
[1]
- Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Joint Center for Energy Storage Research (JCESR); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Molecular Foundry
- Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Molecular Foundry
- Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Joint Center for Energy Storage Research (JCESR); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
- Joint Center for Energy Storage Research, Lemont, Il (United States); ; Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States). Material, Physical and Chemical Sciences Center
Given their natural abundance and thermodynamic stability, fluoride salts may appear as evolving components of electrochemical interfaces in Li-ion batteries and emergent multivalent ion cells. This is due to the practice of employing electrolytes with fluorine-containing species (salt, solvent, or additives) that electrochemically decompose and deposit on the electrodes. Operando X-ray absorption spectroscopy (XAS) can probe the electrode–electrolyte interface with a single-digit nanometer depth resolution and offers a wealth of insights into the evolution and Coulombic efficiency or degradation of prototype cells, provided that the spectra can be reliably interpreted in terms of local oxidation state, atomic coordination, and electronic structure about the excited atoms. Here we explore fluorine K-edge XAS of mono- (Li, Na, and K) and di-valent (Mg, Ca, and Zn) fluoride salts from a theoretical standpoint and discover a surprising level of detailed electronic structure information about these materials despite the relatively predictable oxidation state and ionicity of the fluoride anion and the metal cation. Utilizing a recently developed many-body approach based on the ΔSCF method, we calculate the XAS using density functional theory and experimental spectral profiles are well reproduced despite some experimental discrepancies in energy alignment within the literature, which we can correct for in our simulations. We outline a general methodology to explain shifts in the main XAS peak energies in terms of a simple exciton model and explain line-shape differences resulting from the mixing of core-excited states with metal d character (for K and Ca specifically). Given ultimate applications to evolving interfaces, some understanding of the role of surfaces and their terminations in defining new spectral features is provided to indicate the sensitivity of such measurements to changes in interfacial chemistry.
- Research Organization:
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- NA0003525; AC02-05CH11231
- OSTI ID:
- 1894614
- Report Number(s):
- SAND2022-14016J; 710804
- Journal Information:
- Chemistry of Materials, Vol. 34, Issue 20; ISSN 0897-4756
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Similar Records
Study of C-coated LiFe{sub 0.33}Mn{sub 0.67}PO{sub 4} as positive electrode material for Li-ion batteries
Degradation of Lithium Iron Phosphate Sulfide Solid-State Batteries by Conductive Interfaces