Oxygen-participated electrochemistry of new lithium-rich layered oxides Li3MRuO5 (M = Mn, Fe)

We describe the synthesis, crystal structure and lithium deinsertion-insertion electrochemistry of two new lithium-rich layered oxides, Li 3 MRuO 5 (M = Mn, Fe), related to rock salt based Li 2 MnO 3 and LiCoO 2 . The Li 3 MnRuO 5 oxide adopts a structure related to Li 2 MnO 3 ( C 2/ m ) where Li an...

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Published in:Physical chemistry chemical physics : PCCP 2015-02, Vol.17 (5), p.3749-376
Main Authors: Laha, S, Natarajan, S, Gopalakrishnan, J, Morán, E, Sáez-Puche, R, Alario-Franco, M. Á, Dos Santos-Garcia, A. J, Pérez-Flores, J. C, Kuhn, A, García-Alvarado, F
Format: Article
Language:English
Subjects:
Electrochemical Techniques
Ions - chemistry
Iron - chemistry
Lithium - chemistry
Magnetics
Manganese - chemistry
Oxidation-Reduction
Oxides - chemistry
Oxygen - chemistry
Photoelectron Spectroscopy
Ruthenium Compounds - chemistry
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Summary:We describe the synthesis, crystal structure and lithium deinsertion-insertion electrochemistry of two new lithium-rich layered oxides, Li 3 MRuO 5 (M = Mn, Fe), related to rock salt based Li 2 MnO 3 and LiCoO 2 . The Li 3 MnRuO 5 oxide adopts a structure related to Li 2 MnO 3 ( C 2/ m ) where Li and (Li 0.2 Mn 0.4 Ru 0.4 ) layers alternate along the c -axis, while the Li 3 FeRuO 5 oxide adopts a near-perfect LiCoO 2 ( R 3&cmb.macr; m ) structure where Li and (Li 0.2 Fe 0.4 Ru 0.4 ) layers are stacked alternately. Magnetic measurements indicate for Li 3 MnRuO 5 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 ( ) 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 Li 3 MnRuO 5 and Li 3 FeRuO 5 , 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 Li 3 MRuO 5 reveals that in the Li 3 MnRuO 5 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 Li 3 FeRuO 5 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. Synthesis, crystal structure and lithium electrochemistry of two new lithium-rich layered oxides, Li 3 MRuO 5 (M = Mn, Fe), are described.
ISSN:1463-9076
1463-9084
DOI:10.1039/c4cp05052e