Tuning the phase fraction of multiphase Na 0.9 Fe 0.5 Mn 0.5 O 2 cathode by biotemplating for Na-ion Batteries Rebecca Huang and Rebecca Boston University of Sheffield, UK Sodium ion batteries (SIBs) are considered to be promising alternatives to lithium ion batteries for energy grid- scale applications. [1] Layered structures have been extensively studied as cathode materials for SIBs due to their relatively high specific capacity and straightforward synthesis route. [2] One such material, Na y Fe x Mn 1-x O 2 is environmentally benign, composed of low cost and earth-abundant raw materials, making this a good candidate for future batteries. Different polymorphs of this material exist, and although single-phase P2 and O3 are the most common for Na y Fe x Mn 1-x O 2 , [3] research recently has been more interested in investigating the synergetic effect of multiphase materials. [4] To date, however, there has been little control of the phase fraction during synthesis, and some synthesis processes consume vast amounts of energy by calcining at high temperatures for long periods of time. Here we report a systematic study of phase fraction with different calcination temperatures for Na 0.9 Fe 0.5 Mn 0.5 O 2 .Using a biotemplating synthesis method, layered structures with O3 and P3 biphase (ca. 1:1) were produced at 600 °C for 2 hours, while the P2 phase was present at 620 °C and higher. When increasing the calcination temperature, the O3 phase became dominant in the crystal structure and the P3 phase fully converted at 900 °C. A reversible transition between the P3 and O3 phase was detected after a second heat treatment at 500 °C for 2 hours. The best electrochemical results exhibit high specific discharge capacity, almost 140 mAh/g and still remain 82% of capacity after 50 cycles. References 1. N. Yabuuchi, K. Kubota, M. Dahbi, and S. Komaba, “Research development on sodium-ion batteries,” Chem. Rev ., 114, 11636-11682, 2014 . DOI: 10.1021/cr500192f 2. P.-F. Wang, Y. You, Y.-X. Yin, and Y.-G. Guo, “Layered oxide cathodes for sodium-ion batteries: phase transition, air stability, and performance,” Adv. Energy Mater. , 8, 1701912, 2018 . DOI: 10.1002/aenm.201701912 3. Yabuuchi, N., Kajiyama, M., Iwatate, J. et al. P2-type Nax[Fe1/2Mn1/2]O2 made from earth-abundant elements for rechargeable Na batteries. Nature Mater., 11, 512–517, 2012 . DOI: 10.1038/nmat3309 4. Q. Wang, S. Chu, and S. Guo, “Progress on multiphase layered transition metal oxide cathodes of sodium ion batteries,” Chinese Chem. Lett., 31, 2167-2178, 2020 . DOI: 10.1016/j.cclet.2019.12.008
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