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.

A zero-strain layered metal oxide as the negative electrode for long-life sodium-ion batteries

“…Recently, several layered Na x MO 2 (M: 3d transition metals, TMs) compounds have been proposed as positive electrode materials for sodium-ion batteries [42][43][44][45][46][47][48][49][50][51][52] . It has also been demonstrated that P2-type materials show better storage performance than that of O3-type materials (Note that the notations of P2 and O3 were defined by Delmas et al 53 , they refer to different ways of the stacking of the oxygen layer, for example, ABBA for P2, ABCABC for O3 and so on) 46 .…”

Utilizing Co2+/Co3+ Redox Couple in P2‐Layered Na0.66Co0.22Mn0.44Ti0.34O2 Cathode for Sodium‐Ion Batteries

“…By comparing with the spectra of the standard transition metal oxide compounds, it is revealed that the average valence states of the Co, Mn, and Ti ions in the as‐synthesized NCMT‐2 are 2+, 3.7+, and 4+. It is very surprising that Co ions can be stabilized at 2+ in the P2‐type layer‐structured compounds, since the valence state of Co ions in most layer‐structured cathode materials is 3+ 12, 23, 39. In addition, the valence state of Mn ions in NCMT‐2 is 3.7+, which is higher than Mn 3+ in tunnel‐structured Na 0.66 Mn 0.66 Ti 0.34 O 2 18.…”

“…Over the past years, various cathode materials have been investigated, including layered oxides,9, 10, 11, 12, 13, 14, 15 tunnel‐structured oxides,16, 17, 18 polyanion compounds,19, 20 and organic compounds 21. Among them, layered oxides are promising cathode materials with a general formula of Na x TMO 2 (TM = transition metals, such as Co, Ni, Mn, Cr, Fe, and Cu),9, 12, 22, 23, 24 which can be categorized into two main groups: P2‐type and O3‐type. P2 and O3 are defined according to the oxygen stacking sequence and coordination environment of the alkali ions 25, 26.…”

“…To address these issues, using other transition metals, such as cobalt, nickel to substitute the Mn ions in layered Na x MnO 2 , has been investigated 29, 30, 31. It was found that P2‐type Na 2/3 Co 2/3 Mn 1/3 O 2 displays a reversible 0.5 Na + intercalation between 1.5 and 4.0 V. The good reversibility is attributed to the fact that the introduced low‐spin Co 3+ ions can stabilize Mn ions at a valence state of 4+ 23, 34. Li et al reported that Ni and Co substitution in Na 0.7 Mn 0.7 Ni 0.3− x Co x O 2 could enhance sodium diffusion coefficient and high‐rate capability by shortening the bond lengths of TM—O and O—O 12.…”

“…In a large number of P2‐type layered oxides,12, 22, 23, 24, 36, 37, 38 transition metal ordering is mainly determined by the difference between the ionic radii of M1 and M2, in which small difference (usually less than 15%) favors to form disordered arrangement if M1 and M2 content is close to a rational rate, while a larger difference (greater than 15%) favors an ordered arrangement. In the case of charge ordering, it is determined by the redox potential of M1 and M2.…”