title: Oxygen-participated electrochemistry of new lithium-rich layered oxides Li3MRuO5 (M = Mn, Fe).
abstract: We describe the synthesis, crystal structure and lithium deinsertion-insertion electrochemistry of two new lithium-rich layered oxides, Li3MRuO5 (M = Mn, Fe), related to rock salt based Li2MnO3 and LiCoO2. The Li3MnRuO5 oxide adopts a structure related to Li2MnO3 (C2/m) where Li and (Li0.2Mn0.4Ru0.4) layers alternate along the c-axis, while the Li3FeRuO5 oxide adopts a near-perfect LiCoO2 (R3[combining macron]m) structure where Li and (Li0.2Fe0.4Ru0.4) layers are stacked alternately. Magnetic measurements indicate for Li3MnRuO5 the presence of Mn(3+) and low spin configuration for Ru(4+) where the itinerant electrons occupy a π*-band. The onset of a net maximum in the χ vs. T plot at 9.5 K and the negative value of the Weiss constant (θ) of -31.4 K indicate the presence of antiferromagnetic superexchange interactions according to different pathways. Lithium electrochemistry shows a similar behaviour for both oxides and related to the typical behaviour of Li-rich layered oxides where participation of oxide ions in the electrochemical processes is usually found. A long first charge process with capacities of 240 mA h g(-1) (2.3 Li per f.u.) and 144 mA h g(-1) (1.38 Li per f.u.) is observed for Li3MnRuO5 and Li3FeRuO5, respectively. An initial sloping region (OCV to ca. 4.1 V) is followed by a long plateau (ca. 4.3 V). Further discharge-charge cycling points to partial reversibility (ca. 160 mA h g(-1) and 45 mA h g(-1) for Mn and Fe, respectively). Nevertheless, just after a few cycles, cell failure is observed. X-ray photoelectron spectroscopy (XPS) characterisation of both pristine and electrochemically oxidized Li3MRuO5 reveals that in the Li3MnRuO5 oxide, Mn(3+) and Ru(4+) are partially oxidized to Mn(4+) and Ru(5+) in the sloping region at low voltage, while in the long plateau, O(2-) is also oxidized. Oxygen release likely occurs which may be the cause for failure of cells upon cycling. Interestingly, some other Li-rich layered oxides have been reported to cycle acceptably even with the participation of the O(2-) ligand in the reversible redox processes. In the Li3FeRuO5 oxide, the oxidation process appears to affect only Ru (4+ to 5+ in the sloping region) and O(2-) (plateau) while Fe seems to retain its 3+ state.
authors.affiliation: Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, India. gopal@sscu.iisc.ernet.in.
authors.forename: S
authors.initials: S
authors.lastname: Laha
authors.forename: S
authors.initials: S
authors.lastname: Natarajan
authors.forename: J
authors.initials: J
authors.lastname: Gopalakrishnan
authors.forename: E
authors.initials: E
authors.lastname: Morán
authors.forename: R
authors.initials: R
authors.lastname: Sáez-Puche
authors.forename: M Á
authors.initials: MÁ
authors.lastname: Alario-Franco
authors.forename: A J
authors.initials: AJ
authors.lastname: Dos Santos-Garcia
authors.forename: J C
authors.initials: JC
authors.lastname: Pérez-Flores
authors.forename: A
authors.initials: A
authors.lastname: Kuhn
authors.forename: F
authors.initials: F
authors.lastname: García-Alvarado
mesh_terms: D055664:Electrochemical Techniques; D007477:Ions / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D008094:Lithium / Q000737:chemistry*; D008280:Magnetics; D008345:Manganese / Q000737:chemistry*; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry*; D056951:Photoelectron Spectroscopy; D017975:Ruthenium Compounds / Q000737:chemistry*
chemical_list: D007477:Ions; D010087:Oxides; D017975:Ruthenium Compounds; D008345:Manganese; D008094:Lithium; D007501:Iron; D010100:Oxygen