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

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2014-01, Vol.2 (45), p.19383-19395
• Main Authors: Kalapsazova, M., Stoyanova, R., Zhecheva, E., Tyuliev, G., Nihtianova, D.
• Format: Article
• Language: English
• Subjects: Intercalation; Ion exchangers; Lithium; Lithium batteries; Nickel; Oxides; Sodium; Valence
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/C4TA04094E

Sodium deficient nickel–manganese oxides Na x Ni 0.5 Mn 0.5 O 2 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 Na x Ni 0.5 Mn 0.5 O 2 as low-cost electrode materials in lithium ion batteries instead of lithium analogues. Sodium deficient nickel–manganese oxides Na x Ni 0.5 Mn 0.5 O 2 are prepared at 700 °C from freeze-dried acetate precursors. The structure of Na x Ni 0.5 Mn 0.5 O 2 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 Na x Ni 0.5 Mn 0.5 O 2 . The surface and composition stability of Na x Ni 0.5 Mn 0.5 O 2 during the electrochemical reaction is monitored by using ex situ XPS and LA-ICPMS. Layered oxides Na x Ni 0.5 Mn 0.5 O 2 exhibit a P3-type of structure, in which the solubility of sodium is limited between 0.5 and 0.75. At 700 °C, Na x Ni 0.5 Mn 0.5 O 2 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.