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Title: Probing the effect of Mg doping on triclinic Na2Mn3O7 transition metal oxide as cathode material for sodium-ion batteries
Authors: Siriwardena, DP
Fernando, JFS
Wang, T
Firestein, KL
Zhang, C
Brand, HEA
Jones, MWM
Kewish, CM
Berntsen, P
Jenkins, T
Lewis, CEM
von Treifeldt, JE
Dubal, DP
Golberg, DV
Keywords: Sodium ions
Manganese oxides
Electric batteries
Issue Date: 20-Feb-2021
Publisher: Elsevier
Citation: Siriwardena, D. P., Fernando, J. F., Wang, T., Firestein, K. L., Zhang, C., Brand, H. E. A., Jones, W. M. W., Kewish, C. M., Berntsen, P., Jenkins, T., Lewis, C.-E. M., von Triefeldt, J. E., Dubal, D. P. & Golberg, D. V. (2021). Probing the effect of Mg doping on triclinic Na2Mn3O7 transition metal oxide as cathode material for sodium-ion batteries. Electrochimica Acta, 394, 139139. doi:10.1016/j.electacta.2021.139139
Abstract: Triclinic Na2Mn3O7 has been identified as a promising material for high-capacity sodium-ion batteries. However, the knowledge on the effect of doping of metal ions and structural transformations of Na2Mn3O7 during dis(charge) is limited. Integration of alkali metal-ions, specially Mg2+ can enhance the electrochemical properties in transition metal oxides. Herein, a series of Mg2+ doped triclinic Na2Mn3O7 cathode materials was explored for the first time. Electrochemical analysis revealed that Mg2+ improves specific capacities, and rate capabilities. Ex situ X-ray diffraction (XRD) and Galvanostatic charge discharge cycling (GCD) showed that the triclinic phase reversibly converts into two monoclinic phases at high Na+ insertion levels. Na+ extraction at high potentials is supported by another biphasic region which converts to a major triclinic phase at the end of the charge. GCD, cyclic voltammetry (CV) and ex situ X-ray absorption spectroscopy (XAS) documented that the capacity mainly evolved through a Mn4+/3+ redox couple and a reversible O2-/n− redox reaction. CV and Galvanostatic intermittent titration techniques (GITT) showed that Mg2+ reduces the Na+-vacancy ordering and improves the Na+ diffusion. The 2 mol.% Mg-doped material exhibited a high specific capacity of 143 mAh/g after 30 cycles and a rate capability of 93 mAh/g (at 500 mA/g). GCD analysis demonstrated that O2-/n− redox is remarkably stable up to at least 90 cycles. Full cells made using the 0.5 mol.% Mg-doped material displayed a promising discharge specific capacity of 80 mAh/g. The effects of cation doping into the complex crystal structures, phase transformations during Na+ de(intercalation) and the importance of O2-/n− redox for achieving high capacities were uncovered. The findings of this work will guide the design of novel cathode materials for sodium-ion batteries. ©2021 Elsevier Ltd.
ISSN: 0013-4686
Appears in Collections:Journal Articles

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