Main content area

Sodium deficient nickel–manganese oxides as intercalation electrodes in lithium ion batteries

Kalapsazova, M., Stoyanova, R., Zhecheva, E., Tyuliev, G., Nihtianova, D.
Journal of materials chemistry A 2014 v.2 no.45 pp. 19383-19395
X-ray diffraction, X-ray photoelectron spectroscopy, acetates, electrochemistry, electrodes, electron paramagnetic resonance spectroscopy, freeze drying, ions, lithium, lithium batteries, manganese, models, nanoparticles, nickel, oxidation, oxides, sodium, solubility, transmission electron microscopy
Sodium deficient nickel–manganese oxides NaₓNi₀.₅Mn₀.₅O₂ with a layered structure are of interest since they are capable of participating in reactions of intercalation of Li⁺ and exchange of Na⁺ with Li⁺. Taking into account the intercalation properties of these oxides, we provide new data on the direct use of NaₓNi₀.₅Mn₀.₅O₂ as low-cost electrode materials in lithium ion batteries instead of lithium analogues. Sodium deficient nickel–manganese oxides NaₓNi₀.₅Mn₀.₅O₂ are prepared at 700 °C from freeze-dried acetate precursors. The structure of NaₓNi₀.₅Mn₀.₅O₂ is analyzed by means of powder X-ray diffraction, SAED and HRTEM. The oxidation states of nickel and manganese ions are determined by X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectroscopy (EPR). Model lithium cells are used to monitor the lithium intercalation into NaₓNi₀.₅Mn₀.₅O₂. The surface and composition stability of NaₓNi₀.₅Mn₀.₅O₂ during the electrochemical reaction is monitored by using ex situ XPS and LA-ICPMS. Layered oxides NaₓNi₀.₅Mn₀.₅O₂ exhibit a P3-type of structure, in which the solubility of sodium is limited between 0.5 and 0.75. At 700 °C, NaₓNi₀.₅Mn₀.₅O₂ consists of thin well-crystallized nanoparticles; some of the particles have sizes higher than 100 nm, displaying a trigonal superstructure. For all oxides, manganese ions occur in the oxidation state of +4, while the oxidation state of nickel ions is higher than +2 and depends on the sodium content. The electrochemical reaction occurs within two potential ranges at 3.1 and 3.8 V due to the redox manganese and nickel couples, respectively. During the first discharge, Li⁺ intercalation and Li⁺/Na⁺ exchange reactions take place, while the consecutive charge process includes mainly Li⁺ and Na⁺ deintercalation. As a result, all oxides manifest a reversible capacity of about 120–130 mA h g⁻¹, corresponding to 0.5–0.6 moles of Li⁺. The formation of surface layers in the course of the electrochemical reaction is also discussed.