The P2-Na2/3Co2/3Mn1/3O2 phase: structure, physical properties and electrochemical behavior as positive electrode in sodium battery
ABSTRACT Manganese substituted sodium cobaltate, Na(2/3)Co(2/3)Mn(1/3)O(2), with a layered hexagonal structure (P2-type) was obtained by a co-precipitation method followed by a heat treatment at 950 °C. Powder X-ray diffraction analysis revealed that the phase is pure in the absence of long-range ordering of Co and Mn ions in the slab or Na(+) and vacancy in the interslab space. The oxidation states of the transition metal ions were studied by magnetic susceptibility measurements, electron paramagnetic resonance (ESR) and (23)Na magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The charge compensation is achieved by the stabilization of low-spin Co(3+) and Mn(4+) ions. The capability of Na(2/3)Co(2/3)Mn(1/3)O(2) to intercalate and deintercalate Na(+) reversibly was tested in electrochemical sodium cells. It appears that the P2 structure is maintained during cycling, the cell parameter evolution versus the sodium amount is given. From the features of the cycling curve the formation of an ordered phase for the Na(0.5)Co(2/3)Mn(1/3)O(2) composition is expected.
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ABSTRACT: Room-temperature stationary sodium-ion batteries have attracted great attention particularly in large-scale electric energy storage applications for renewable energy and smart grid because of the huge abundant sodium resources and low cost. In this article, a variety of electrode materials including cathodes and anodes as well as electrolytes for room-temperature stationary sodium-ion batteries are briefly reviewed. We compare the difference in storage behavior between Na and Li in their analogous electrodes and summarize the sodium storage mechanisms in the available electrode materials. This review also includes some new results from our group and our thoughts on developing new materials. Some perspectives and directions on designing better materials for practical applications are pointed out based on knowledge from the literature and our experience. Through this extensive literature review, the search for suitable electrode and electrolyte materials for stationary sodium-ion batteries is still challenging. However, after intensive research efforts, we believe that low-cost, long-life and room-temperature sodium-ion batteries would be promising for applications in large-scale energy storage system in the near future.Energy & Environmental Science 08/2013; 6(8-8):2338-2360. DOI:10.1039/c3ee40847g · 15.49 Impact Factor
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ABSTRACT: Fe containing Na-ion cathode materials are desirable due to their low cost and use of earth abundant raw materials. Here, the electrochemistry of layered NaxFex3+Ti1-x4+O2 is described. It was found that Mossbauer spectra can accurately detect Na vacancies in NaxFex3+Ti1-x4+O2 material from their effects on neighboring Fe3+ ions and this model can be used to analyse materials at different stages of charge or discharge. This Na vacancy model potentially has broader implications and may be useful as a probe for Na-vacancies in iron containing Na-ion cathode materials in general. The oxidation of Fe3+ to Fe4+ during electrochemical cycling is shown to be a major source of hysteresis and capacity fade, while the activation of the Fe2+/Fe3+ and Ti3+/Ti4+ redox couples results in stable cycling performance. Possible reasons for capacity fade and hysteresis are discussed in terms of ex-situ Mossbauer and XRD studies.Journal of The Electrochemical Society 08/2014; 161(12):A1801-A1805. DOI:10.1149/2.0291412jes · 2.86 Impact Factor
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ABSTRACT: A free-standing transparent film for sodium-ion conduction in PEO-based solid polymer electrolyte (additionally comprising NaClO4 and nano-sized TiO2) has been fabricated for use in Na-ion batteries by using a solution casting technique. The crystallinity of the solid polymer electrolyte and the interactions between PEO and the Na-ions is characterized by X-ray diffraction (XRD) and Fourier transformed infra-red (FTIR) spectra, which reveals the degree of Na+ ion solvation by PEO oxygen atoms (EO:Na). The ionic conductivities of the films are investigated by impedance analysis from 1 MHz to 1 Hz within the temperature range 303–363 K. A solid polymer electrolyte with anatomic ratio EO:Na = 20 exhibits a maximum ionic conductivity of 1.35 × 10−4 S cm−1, which increases to 2.62 × 10−4 S cm−1 by the addition of TiO2 (3.4 nm, 5 wt%) at temperature 60 °C. The performance of a Na2/3Co2/3Mn1/3O2 half cell with a polymer electrolyte is compared to a similar cell with a liquid electrolyte.Journal of Power Sources 03/2015; 278. DOI:10.1016/j.jpowsour.2014.11.047 · 5.21 Impact Factor