From tunnel NMO to layered polymorphs oxides for sodium ion batteries
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From tunnel NMO to layered polymorphs oxides for sodium ion batteries Michele Nuti1 · Daniele Spada1 · Irene Quinzeni1 · Stefano Capelli2 · Benedetta Albini3 · Pietro Galinetto3 · Marcella Bini1 Received: 17 June 2020 / Accepted: 29 September 2020 © The Author(s) 2020 OPEN
Abstract The search for highly performing cathode materials for sodium batteries is a fascinating topic. Unfortunately, N a0.44MnO2 (NMO), the well-known cathode material with good electrochemical performances, suffers 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 different polymorphs. In this paper, NMO was first 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 different amount depending on dopant, were obtained and quantified by Rietveld refinements, 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 benefits from improved air stability, a well-known issue of layered compounds. Discharge capacity values of about 63 mAh/g were detected at 1C, and after 50 cycles at C/2, capacities of about 80 mAh/g are obtained, with a capacity retention of 86%. Keywords NMO · XRPD · Raman · CV · Charge–discharge
1 Introduction Lithium-ion rechargeable batteries (LIBs), the most successful power sources of the modern society for portable electric devices, cannot be employed for the large-scale energy storage due to many drawbacks mainly related to lithium element, such as its low abundance, high cost and nonuniform distribution on the earth crust. There is an urgent need to find an effective alternative. Very promising candidates for the future replacement of lithium technology seem the Na-ion batteries (NIBs) which
can work with the same ‘rocking chair’ storage mechanism of LIBs. Sodium based materials have many different interesting features: they are more abundant, environmental friendly and cheap if compared to lithium analogues [1–3]. Other advantages of sodium are represented by the globally equable distribution of its resources, its suitable redox potential [− 2.71 V and − 3.04 V for Na and Li versus standard hydrogen electrode (SHE)] and its lightness. In addition, sodium does not alloy with aluminium and therefore Al foil can be used as current collector for both cathode and anode materials, replacing the more
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s42452-020-03607-z) contains supplementary material, which is available to authorized users. * Marcella Bini, [email protected] | 1Chemistry Department,
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