Local structures in mixed Li{sub x}Fe{sub 1−y}M{sub y}PO{sub 4} (M=Co, Ni) electrode materials

Journal Article · Thu Oct 15 04:00:00 EDT 2015 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/J.JSSC.2015.07.025· OSTI ID:22486829

Jalkanen, K. ^[1]; Lindén, J. ^[2]

---

1. Department of Chemistry, Aalto University, FI-00076 Espoo (Finland)
2. Department of Physics, Åbo Akademi, FI-20500 Turku (Finland)

We employ {sup 57}Fe Mössbauer spectroscopy as a local tool to probe electrical environments of Fe{sup 2+} and Fe{sup 3+} at different lithiation (x) and cation-substitution (y) levels in Li{sub x}Fe{sub 1−y}M{sub y}PO{sub 4}/C (M=Co, Ni) Li-ion battery electrode materials. Upon delithiation the local environment of Fe{sup 3+} remains unaffected for the parent y=0 system due to the LiFePO{sub 4}/FePO{sub 4} phase separation, whereas for y>0 changes in the electrical environment are seen for Fe{sup 3+}. When the Fe{sup 2+}/Fe{sup 3+} redox couple is partially-delithiated, a decreasing quadrupole splitting value is observed for Fe{sup 3+} with increasing y, implying a more symmetric electrical environment. The increasing concentration of the Co{sup 2+}/Ni{sup 2+} substituent introduces increasing amounts of Li atoms in the Fe{sup 3+}-containing phase, and these nearest-neighbor Li atoms are suspected to cause the changes seen in the local environment of Fe{sup 3+}. - Graphical abstract: Local environment of iron in Li{sub x}Fe{sub 1−y}(Co/Ni){sub y}PO{sub 4} is studied by {sup 57}Fe Mössbauer spectroscopy at different lithiation (x) and cation-substitution (y) levels. - Highlights: • Local Fe environment in Li{sub x}Fe{sub 1−y}(Co/Ni){sub y}PO{sub 4} is studied by {sup 57}Fe Mössbauer spectroscopy. • Co/Ni-for-Fe substitution results in a more symmetric electrical environment for Fe{sup 3+}. • Due to presence of Co{sup 2+}/Ni{sup 2+}, Li atoms are introduced into the Fe{sup 3+}-containing phase. • These nearest-neighbor Li atoms are suggested to change the local Fe{sup 3+} environment.

• OSTI ID: 22486829
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Vol. 230; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
CATIONS
COBALT IONS
COBALT PHOSPHATES
CONCENTRATION RATIO
ELECTRODES
IRON 57
IRON IONS
IRON PHOSPHATES
LITHIUM ION BATTERIES
LITHIUM PHOSPHATES
NICKEL IONS
NICKELATES