Utilizing Co2+/Co3+ Redox Couple in P2‐Layered Na0.66Co0.22Mn0.44Ti0.34O2 Cathode for Sodium‐Ion Batteries. Issue 11 (6th July 2017)

• Record Type: Journal Article
• Authors: Wang, Qin‐Chao; Hu, Enyuan; Pan, Yang; Xiao, Na; Hong, Fan; Fu, Zheng‐Wen; Wu, Xiao‐Jing; Bak, Seong‐Min; Yang, Xiao‐Qing; Zhou, Yong‐Ning
• Is Part Of: Advanced science. Volume 4:Issue 11(2017)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2017-07-06
• Subjects: cathode materials -- layered structures -- sodium‐ion batteries -- X‐ray absorption spectroscopy; Science -- Periodicals; 505
• DOI: 10.1002/advs.201700219
• Languages: English
• ISSNs: 2198-3844

Abstract

Abstract: Developing sodium‐ion batteries for large‐scale energy storage applications is facing big challenges of the lack of high‐performance cathode materials. Here, a series of new cathode materials Na0.66 Co x Mn0.66– x Ti0.34 O2 for sodium‐ion batteries are designed and synthesized aiming to reduce transition metal‐ion ordering, charge ordering, as well as Na + and vacancy ordering. An interesting structure change of Na0.66 Co x Mn0.66– x Ti0.34 O2 from orthorhombic to hexagonal is revealed when Co content increases from x = 0 to 0.33. In particular, Na0.66 Co0.22 Mn0.44 Ti0.34 O2 with a P2‐type layered structure delivers a reversible capacity of 120 mAh g −1 at 0.1 C. When the current density increases to 10 C, a reversible capacity of 63.2 mAh g −1 can still be obtained, indicating a promising rate capability. The low valence Co 2+ substitution results in the formation of average Mn 3.7+ valence state in Na0.66 Co0.22 Mn0.44 Ti0.34 O2, effectively suppressing the Mn 3+ ‐induced Jahn–Teller distortion, and in turn stabilizing the layered structure. X‐ray absorption spectroscopy results suggest that the charge compensation of Na0.66 Co0.22 Mn0.44 Ti0.34 O2 during charge/discharge is contributed by Co 2.2+ /Co 3+ and Mn 3.3+ /Mn 4+ redox couples. This is the first time that the highly reversible Co 2+ /Co 3+ redox couple is observed in P2‐layered cathodes for sodium‐ion batteries. This finding may open new approaches to design advanced intercalation‐type cathode materials. Abstract : Na0.66 Co x Mn0.66‐ x Ti0.34 O2 (0 ≤ x ≤ 0.33) for new cathode materials of sodium‐ion batteries are designed and synthesized aiming to reduce transition metal ordering, charge ordering, as well as Na + and vacancy ordering. The Co 2+ /Co 3+ redox couple is revealed for the first time experimentally in the P2‐layered cathodes, enabling a high rate capability with the help of Ti substitution.