Na 2.32 Co 1.84 (SO 4 ) 3 as a new member of the alluaudite family of high-voltage sodium battery cathodes

• Published in: Dalton transactions : an international journal of inorganic chemistry 2017, Vol.46 (1), p.55-63
• Main Authors: Dwibedi, Debasmita, Gond, Ritambhara, Dayamani, Allumolu, Araujo, Rafael B., Chakraborty, Sudip, Ahuja, Rajeev, Barpanda, Prabeer
• Format: Article
• Language: English
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/C6DT03767D

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 (Na 2 Fe 2 (SO 4 ) 3 ) has been reported, with the highest Fe 3+ /Fe 2+ 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 Na 2+2x Co 2−x (SO 4 ) 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 C 2/ c symmetry, which undergoes antiferromagnetic ordering below 10.2 K. Isotypical to the Fe-homologue, it forms a complete family of solid-solution Na 2+2x (Fe 1−y Co y ) 2−x (SO 4 ) 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, Na 2+2x Co 2−x (SO 4 ) 3 can work as a cathode material (∼5 V) for sodium-ion batteries.