首页|Reversible Mn2+/Mn4+ double-electron redox in P3-type layer-structured sodium-ion cathode
Reversible Mn2+/Mn4+ double-electron redox in P3-type layer-structured sodium-ion cathode
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The balance between cationic redox and oxygen redox in layer-structured cathode materials is an impor-tant issue for sodium batteries to obtain high energy density and considerable cycle stability.Oxygen redox can contribute extra capacity to increase energy density,but results in lattice instability and capac-ity fading caused by lattice oxygen gliding and oxygen release.In this work,reversible Mn2+/Mn4+ redox is realized in a P3-Na0.65Li0.2Co0.05Mn0.75O2 cathode material with high specific capacity and structure stability via Co substitution.The contribution of oxygen redox is suppressed significantly by reversible Mn2+/Mn4+ redox without sacrificing capacity,thus reducing lattice oxygen release and improving the structure stability.Synchrotron X-ray techniques reveal that P3 phase is well maintained in a wide volt-age window of 1.5-4.5 V vs.Na+/Na even at 10 C and after long-term cycling.It is disclosed that charge compensation from Co/Mn-ions contributes to the voltage region below 4.2 V and O-ions contribute to the whole voltage range.The synergistic contributions of Mn2+/Mn4+,Co2+/Co3+,and O2-/(On)2-redox in P3-Na0.65Li0.2Co0.05Mn0.75O2 lead to a high reversible capacity of 215.0 mA h g-1 at 0.1 C with consid-erable cycle stability.The strategy opens up new opportunities for the design of high capacity cathode materials for rechargeable batteries.
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