The search for highly performing cathode materials for sodium batteries is a fascinating topic. Unfortunately, Na0.44MnO2 (NMO), the well-known cathode material with good electrochemical performances, su ers from structural degradation due to reduction of Mn4+ to the Jahn–Teller Mn3+ ion, limiting the long-term cyclability. The cation substitution can be a useful way to mitigate the problem, thanks to the possible stabilization of mixtures of di erent polymorphs. In this paper, NMO was rst substituted with Fe ions, obtaining Na0.44Mn0.5Fe0.5O2, with layered structure, then Al, Si and Cu (10% atom) were substituted on both Mn and Fe ions. Mixtures of P3 type phases, in di erent amount depending on dopant, were obtained and quanti ed by Rietveld re nements, and relationships between chemical composition, polymorph type and morphology were proposed. Cyclic voltammetry showed broad peaks, due to the complex structural transitions consequent to the intercalation/deintercalation of sodium. Charge discharge cycles disclosed the superior performances of Cu doped sample, which also bene ts from improved air stability, a well-known issue of layered compounds. Discharge capacity values of about 63 mAh/g were detected at 1C, obtained, with a capacity retention of 86%.

From tunnel NMO to layered polymorphs oxides for sodium ion batteries

Nuti, Michele;Spada, Daniele;Quinzeni, Irene;Albini, Benedetta;Galinetto, Pietro;Bini, Marcella
2020

Abstract

The search for highly performing cathode materials for sodium batteries is a fascinating topic. Unfortunately, Na0.44MnO2 (NMO), the well-known cathode material with good electrochemical performances, su ers from structural degradation due to reduction of Mn4+ to the Jahn–Teller Mn3+ ion, limiting the long-term cyclability. The cation substitution can be a useful way to mitigate the problem, thanks to the possible stabilization of mixtures of di erent polymorphs. In this paper, NMO was rst substituted with Fe ions, obtaining Na0.44Mn0.5Fe0.5O2, with layered structure, then Al, Si and Cu (10% atom) were substituted on both Mn and Fe ions. Mixtures of P3 type phases, in di erent amount depending on dopant, were obtained and quanti ed by Rietveld re nements, and relationships between chemical composition, polymorph type and morphology were proposed. Cyclic voltammetry showed broad peaks, due to the complex structural transitions consequent to the intercalation/deintercalation of sodium. Charge discharge cycles disclosed the superior performances of Cu doped sample, which also bene ts from improved air stability, a well-known issue of layered compounds. Discharge capacity values of about 63 mAh/g were detected at 1C, obtained, with a capacity retention of 86%.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11571/1351314
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