Application of Spinel MgMn2-X Al x O4 As Cathode for Mg Rechargeable Battery

Abstract

【Introduction】Lithium-ion battery (LIB) has mainly used in our life, but its high price due to Li and Co metals are crucial problem. Magnesium rechargeable battery (MRB) has been recently studied as a post LIB due to elemental abundant supply and superior theoretical volumetric energy density of magnesium. For cathode materials, spinel oxides is one of a candidate of MRB due to its high redox potential and three-dimensional diffusion paths.[1] Especially, MgMn2O4 is expected to perform high theoretical capacity because utilization of both Mn3+/Mn4+ and Mn2+/ Mn3+ redox is possible in the potential window of the common electrolyte.[2] But structural change from tetragonal to cubic occurs due to Jahn-Teller effect of Mn3+ ion during charge/discharge, which decreases reversibility. In this study, we tried to enhance reversibility of MgMn2O4 spinel by substituting Al for Mn to release its Jahn-Teller distortion, and the optimal substitution ratio and their electrochemical property were evaluated.【Experimental】MgMn2-xAlxO4 (x = 0, 0.1, 0.2, 0.5) were synthesized by Pechini method[3] with an annealing process of 400 ºC, 10 hour. Cathodes were prepared by mixing the obtained samples with acetylene black and polytetrafuluoroethylene at a weight ratio of 60/30/10 . Mg alloy (AZ31) was used for an anode. Galvanostatic charge/discharge profiles were obtained by using a coin cell with a 0.3 M Mg[B(HFIP)4]2/triglyme electrolyte at 25 ºC, 10 mA/g.【Results and discussion】According to X-ray diffraction(XRD) patterns, MgMn2-xAlxO4 (x = 0, 0.1, 0.2, 0.5) spinel were obtained and their crystallinity become lower by Al substitution. In MgMn1.5Al0.5O4, the crystal structure changed from tetragonal to cubic phase, suggesting that the Jahn-Teller effect is suppressed by the formation of the solid solution of tetragonal MgMn2O4 and cubic MgAl2O4. The Al-substituted MgMn2O4 exhibited higher discharge capacities compared with MgMn2O4 (64.0 mAh/g), and especially MgMn1.9Al0.1O4 showed the highest discharge capacity of 92.3 mAh/g. In the poster session, X-ray absorption spectroscopy (XAS) and cycle characteristics will be reported.【Acknowledgment】This work was supported by JST ALCA-SPRING Grant Number JPMJAL1301, Japan.【References】[1] S. Okamoto, T. Ichitsubo, T. Kawaguchi, Y. Kumagai, F. Oba, S. Yagi, K. Shimokawa, N. Goto, T. Doi and E. Matsubara, Adv. Sci., 2015, 2, 1500072[2] H. Kobayashi, K. Yamaguchi and I. Honma, RSC Adv., 2019, 9, 36434-36439.[3] J. Yin, A. B. Brady, E. S. Takeuchi, A. C. Marschilok and K. J. Takeuchi, Chem. Commun., 2017, 53, 3665-3668.