title: Na2.32Co1.84(SO4)3as a new member of the alluaudite family of high-voltage sodium battery cathodes.
abstract: Electrochemical energy storage has recently seen tremendous emphasis being placed on the large-scale (power) grid storage. Sodium-ion batteries are capable of achieving this goal with economic viability. In a recent breakthrough in sodium-ion battery research, the alluaudite framework (Na2Fe2(SO4)3) has been reported, with the highest Fe3+/Fe2+redox potential (ca. 3.8 V, Barpanda, et al., Nat. Commun., 2014, 5, 4358). Exploring this high-voltage sodium insertion system, we report the discovery of Na2+2xCo2-x(SO4)3(x = 0.16) as a new member of the alluaudite class of cathode. Stabilized by low-temperature solid-state synthesis (T ≤ 350 °C), this novel Co-based compound assumes a monoclinic structure with C2/c symmetry, which undergoes antiferromagnetic ordering below 10.2 K. Isotypical to the Fe-homologue, it forms a complete family of solid-solution Na2+2x(Fe1-yCoy)2-x(SO4)3[y = 0-1]. Ab initio DFT analysis hints at potential high voltage operation at 4.76-5.76 V (vs. Na), depending on the degree of desodiation involving a strong participation of the oxygen sub-lattice. With the development of safe organic electrolytes, Na2+2xCo2-x(SO4)3can work as a cathode material (∼5 V) for sodium-ion batteries.
authors.affiliation: Faraday Materials Laboratory, Materials Research Center, Indian Institute of Science, C. V. Raman Avenue, Bangalore, 560012, India. prabeer@mrc.iisc.ernet.in.
authors.forename: Debasmita
authors.initials: D
authors.lastname: Dwibedi
authors.affiliation: Faraday Materials Laboratory, Materials Research Center, Indian Institute of Science, C. V. Raman Avenue, Bangalore, 560012, India. prabeer@mrc.iisc.ernet.in.
authors.forename: Ritambhara
authors.initials: R
authors.lastname: Gond
authors.affiliation: Faraday Materials Laboratory, Materials Research Center, Indian Institute of Science, C. V. Raman Avenue, Bangalore, 560012, India. prabeer@mrc.iisc.ernet.in.
authors.forename: Allumolu
authors.initials: A
authors.lastname: Dayamani
authors.affiliation: Condensed Matter Theory Group, Department of Physics and Astronomy, Box 516, Uppsala University, S-75120 Uppsala, Sweden.
authors.forename: Rafael B
authors.initials: RB
authors.lastname: Araujo
authors.affiliation: Condensed Matter Theory Group, Department of Physics and Astronomy, Box 516, Uppsala University, S-75120 Uppsala, Sweden.
authors.forename: Sudip
authors.initials: S
authors.lastname: Chakraborty
authors.affiliation: Condensed Matter Theory Group, Department of Physics and Astronomy, Box 516, Uppsala University, S-75120 Uppsala, Sweden.
authors.forename: Rajeev
authors.initials: R
authors.lastname: Ahuja
authors.affiliation: Faraday Materials Laboratory, Materials Research Center, Indian Institute of Science, C. V. Raman Avenue, Bangalore, 560012, India. prabeer@mrc.iisc.ernet.in.
authors.forename: Prabeer
authors.initials: P
authors.lastname: Barpanda