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Anion Activity and Metastable Phase Formation in Li1- FePO4 Investigated Using Soft-to-Hard X-ray Absorption and
Abiram Krishnan1, Doyoub Kim1, Cherno Jaye2
1School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States.
Abstract:
We systematically investigate the intricate roles of cations as well as anions during phase transformation, specifically, the formation of a metastable phase in phospho-olivine, LiFePO4 (LFP). The cation- and anion-specific electronic structures are studied using a combination of high-resolution soft-to-hard X-ray absorption and emission spectroscopy. Our findings reveal that the formation of the metastable phase at higher states-of-charge (SoC) is associated with a decreased oxidation state of iron, assisted by oxygen release. Additionally, we find that phosphorus is active in the charge process, exhibiting reduction, resulting from an electron density redistribution between oxygen and its neighboring iron and phosphorus atoms. Furthermore, the phase transformation process in LFP impacts its magnetic properties, with iron retaining its high-spin configuration along with an increased average spin during its transformation into FePO4 (FP).
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Ions as Acids and Bases
Salts are ionic compounds composed of cations and anions, either of which may be capable of undergoing an acid or base ionization reaction with water. Aqueous salt solutions, therefore, may be acidic, basic, or neutral, depending on the relative acid-base strengths of the salt’s constituent ions. For example, dissolving the ammonium chloride in water results in its dissociation, as described by the equation:
Alkali Metals
Table 1: Properties of the alkali metals

