Cathode Properties of Na3FePO4CO3 Prepared by the Mechanical Ball Milling Method for Na-ion Batteries

Baowei Xie; Ryo Sakamoto; Ayuko Kitajou; Kosuke Nakamoto; Liwei Zhao; Shigeto Okada; Yuki Fujita; Nobuto Oka; Tetsuaki Nishida; Wataru Kobayashi; Masaki Okada; Toshiya Takahara

doi:10.1038/s41598-020-60183-3

Cathode Properties of Na₃FePO₄CO₃ Prepared by the Mechanical Ball Milling Method for Na-ion Batteries

Sci Rep. 2020 Feb 24;10(1):3278. doi: 10.1038/s41598-020-60183-3.

Authors

Affiliations

¹ Interdisciplinary Graduate School of Engineering Science, Kyushu University, 6-1, Kasuga Koen, Kasuga, 816-8580, Japan.
² Organization for Research Initiatives, Yamaguchi University, 2-16-1 Tokiwadai, Ube, 755-8611, Japan.
³ Institute of Materials Chemistry and Engineering, Kyushu University, 6-1, Kasuga Koen, Kasuga, 816-8580, Japan.
⁴ Institute of Materials Chemistry and Engineering, Kyushu University, 6-1, Kasuga Koen, Kasuga, 816-8580, Japan. s-okada@cm.kyushu-u.ac.jp.
⁵ Department of Bioenvironmental Chemistry, Kindai University, Iizuka, Fukuoka, Japan.
⁶ Tosoh Corporation, 3-8-2, Shiba, Minato-Ku, 105-0014, Tokyo, Japan.

Abstract

The carbonophosphate Na₃FePO₄CO₃ was synthesized by the mechanical ball milling method for the first time. The composition of the obtained sample with a higher amount of Fe²⁺ was Na_2.66Fe²⁺_0.66Fe³⁺_0.34PO₄CO₃ as confirmed by Mössbauer analysis, owing to the good airtight properties of this method. The obtained samples in an organic electrolyte delivered an initial discharge capacity of 124 mAh/g at room temperature, and a larger discharge capacity of 159 mAh/g (1.66 Na⁺/mole) at 60 °C. With 17 m NaClO₄ aqueous electrolyte, a discharge capacity of 161 mAh/g (1.69 Na⁺/mole) was delivered because of the high ionic conductivity of the concentrated aqueous electrolyte. During the charge-discharge process, the formation of Fe⁴⁺ after charging up to 4.5 V and the return of Fe²⁺ after discharging down to 1.5 V were detected by ex-situ X-ray absorption near edge structure (XANES) analysis.