A High Voltage Mg-ion Battery Cathode via a Solid Solution Cr-Mn Spinel Oxide

(a) EDS mapping of MgCrMnO4, (b) solid-state NMR spectra of MgCr2O4 (black), MgCrMnO4 (red), and MgMn2O4 (blue), (c) representative potential versus capacity profile of MgCrMnO4 measured in a coin cell at 95 oC, (d) synchrotron XRD patterns of the corresponding different states of charges, (e) Mn K-edge spectra of MgCrMnO4 with different states of charges, (f) schematic description of Mg2+ intercalation and (g) representative potential versus capacity of MgCrMnO4 paired with a carbon counter electrode at 60 oC.

Scientific Achievement

The capability of the tailored MgCrMnO4 spinel to (de)intercalate Mg2+ electrochemically at high potentials was evaluated by the theoretical and experimental approaches. High Mg2+ activity was observed in bulk, with a remarkable degree of lattice breathing and reversibility.

Significance and Impact

Lattice Mg2+ in a tailored solid solution spinel, MgCrMnO4, is electrochemically utilized at high Mn-redox potentials in a non-aqueous electrolyte. Possible cyclability at moderate temperature (60 ℃) was observed along with a ~180 Wh/Kg of energy density delivered at the first discharge reaction. This study redefines lattice design via chemical and structural composition of functional spinel oxides utilized by Mg2+ intercalation at high potentials. Our findings uncover a new subclass of cathode material for rechargeable Mg-ion batteries.

Research Details

The intrinsic design weaknesses in a single B site Cr- or Mn-spinel for a Mg-ion cathode are alleviated by building a solid-solution MgCrMnO4 where the mixed transition metal lattice provides mobility via Mg2+ bound by Cr3+ and suitable high redox potential via Mg2+ bound by Mn3+ for (de)intercalation.

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DOI: 10.1021/acs.chemmater.0c01988

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