Study Of Intercalation Compounds Research Articles

Exploring Quasi-1D Oxides As Ca2+ Hosts for Calcium Battery Applications

The study of intercalation compounds [1] led to the identification of redox reactions in host transition metal compounds involving reversible (usually topotactic) insertion and deinsertion of Mn+ ions. Studies with Li+ turned out to be a cornerstone in the development of the Li-ion battery technology [2] that has synergistically boosted portable electronics, while intercalation of multivalent cations (n>1) remained an academic curiosity. Yet, the current energy needs for batteries require significant improvement in energy density, beyond the capabilities of the traditional Li-ion technology, and multivalent cation chemistries represent a thrilling alternative in terms of the amount of energy that can be delivered. Ca metal based batteries have been almost unexplored as reversible plating and stripping of Ca with conventional organic electrolytes at moderate temperature was reported only recently [3,4]. The alkylcarbonate based electrolytes used in this work offer a wide electrochemical stability window, thus inciting the exploration of possible high voltage cathode materials with reliable electrochemical set-ups [5]. Development of potential multivalent host structures is challenging and the choice of cathode materials extremely limited, as divalent cation insertion/extraction is associated with sluggish solid state diffusion kinetics and high activation energies for the charge transfer kinetics. Layered intercalation compounds, with expandable interlayer space like TiS2, V2O5, MoO3, etc., are typically the most studied, but fundamental understanding of the reaction mechanisms in these phases is limited [6,7]. In this work we have explored the possibility of using Ca3Co2O6 cobaltite as Ca-based battery cathode [8]. The pristine compound has a 1D structure of CoO6 octahedra and prisms alternating along chains. By means of ex-situ synchrotron X-ray powder diffraction we have realized that Ca can be extracted by electrochemical methods driving to an incommensurate structure of the type Can+2Con+1O3n+3 (or, equivalently Ca1+xCoO3), characterized by the alternation of n octahedra and one prism along the Co-chain. The reversibility of the redox process seems to be rather limited in the present experimental conditions, indicating some kinetic or thermodynamic issues. Structurally related phases have been also explored as strategy for identifying alternative Ca2+ hosts.

Study of intercalation compounds using ionic liquids into montmorillonite and their thermal stability

Abstract In the present study, we investigated the direct intercalation of three kinds of ionic liquids (ILs) of different salts (imidazolium and ammonium) and cation sizes into montmorillonite (M) clay, and successfully fabricated the IL intercalated montmorillonite (MIL) compounds. The peak shifts of the MIL intercalated compounds in comparison with dried montmorillonite powder as observed by XRD results showed that crystal swelling was significantly influenced by the cation sizes of the ILs. The intercalation behaviors of the MIL compounds were also compared by TEM and the results are in good agreement with the XRD. The TEM–EDS results further confirmed the intercalation of three types of ILs into the montmorillonite. Based on the cation exchange capacity as measured by ICP and mathematical calculations, the extent of the intercalation and arrangement of cations in the interlayers of the montmorillonite are proposed. The TG-DTA results showed an improved thermal stability of all three kinds of MIL intercalated compounds, and the XRD indicated that the remaining IL initiates a carbonization process with the montmorillonite at 1000 °C. Furthermore, the AC impedance results of the MIL compounds showed an ionic conductivity. These results suggest the possible application of the MIL intercalated compounds in electrical conductive films, solar cells, fuel cells, etc.