Understanding the formation of new clusters of alkali and alkaline Earth metals: a new synthetic approach, single-crystal structures, and theoretical calculations

Characteristics and properties of nano-LiCoO2 synthesized by pre-organized single source precursors: Li-ion diffusivity, electrochemistry and biological assessment

Background

LiCoO₂ is one of the most used cathode materials in Li-ion batteries. Its conventional synthesis requires high temperature (>800 °C) and long heating time (>24 h) to obtain the micronscale rhombohedral layered high-temperature phase of LiCoO₂ (HT-LCO). Nanoscale HT-LCO is of interest to improve the battery performance as the lithium (Li⁺) ion pathway is expected to be shorter in nanoparticles as compared to micron sized ones. Since batteries typically get recycled, the exposure to nanoparticles during this process needs to be evaluated.

Results

Several new single source precursors containing lithium (Li⁺) and cobalt (Co²⁺) ions, based on alkoxides and aryloxides have been structurally characterized and were thermally transformed into nanoscale HT-LCO at 450 °C within few hours. The size of the nanoparticles depends on the precursor, determining the electrochemical performance. The Li-ion diffusion coefficients of our LiCoO₂ nanoparticles improved at least by a factor of 10 compared to commercial one, while showing good reversibility upon charging and discharging. The hazard of occupational exposure to nanoparticles during battery recycling was investigated with an in vitro multicellular lung model.

Conclusions

Our heterobimetallic single source precursors allow to dramatically reduce the production temperature and time for HT-LCO. The obtained nanoparticles of LiCoO₂ have faster kinetics for Li⁺ insertion/extraction compared to microparticles. Overall, nano-sized LiCoO₂ particles indicate a lower cytotoxic and (pro-)inflammogenic potential in vitro compared to their micron-sized counterparts. However, nanoparticles aggregate in air and behave partially like microparticles.

Electronic supplementary material

The online version of this article (doi:10.1186/s12951-017-0292-3) contains supplementary material, which is available to authorized users.

Assembly of noncentrosymmetric coordination polymers by the integration of acentric Ba(ii)/Sr(ii) and Li(i) coordination polyhedra

Presented is a strategy to construct noncentrosymmetric CPs through the integration of acentric [LiO_xN_4−x] and [BaO_xN_y] coordination polyhedraviabridging organic ligands.

Analogy of the Coordination Chemistry of Alkaline Earth Metal and Lanthanide Ln2+ Ions: The Isostructural Zoo of Mixed Metal Cages [IM(OtBu)4{Li(thf)}4(OH)] (M=Ca, Sr, Ba, Eu), [MM′6(OPh)8(thf)6] (M=Ca, Sr, Ba, Sm, Eu, M′=Li, Na), and their Derivatives with 1,2-Dimethoxyethane

As previously shown, alkali and alkaline earth metal iodides in nonaqueous, aprotic solvents behave like transition metal halides, forming cis- and trans-dihalides with various neutral O-donor ligands. These compounds can be used as precursors for the synthesis of new mixed alkali/alkaline earth metal aggregates. We show here that Ln2+ ions form isostructural cluster compounds. Thus, with LiOtBu, 50% of the initial iodide can be replaced in MI2, M=Ca, Sr, Ba, Eu, to generate the mixed-metal alkoxide aggregates [IM(OtBu)4{Li(thf)}4(OH)], for which the M--OH contacts were investigated by theoretical methods. With M'OPh (M'=Li, Na), a new mixed-metal aryloxide cluster type [MM'6(OPh)8(thf)6] is obtained for M=Ca, Sr, Ba, Sm, Eu. Their stability versus DME (DME=1,2-dimethoxyethane) as bidentate ligand is studied.

From Monomers to Solids: Controlled Hydrolysis To Form Novel, Heteroleptic Hydroxide-Containing Complexes

Four novel alkaline earth metal tetranuclear aryloxide/pyrazolate hydroxides of the general formula M4(ligand)6(OH)2(donor)n have been prepared by either adding stoichiometric quantities of water to preformed alkaline earth metal aryloxides or in a direct metalation regime combining metal, ligand (alcohol, pyrazole), and donor with stoichiometric amounts of water. The compounds are considered as potential intermediates in the sol-gel process. A nonhydrolyzable magnesium aryloxide has also been obtained using the same reaction scheme. Unexpectedly, a dimeric strontium complex with further association of a second dimer via hydrogen bonding from the solvent of crystallization, ethylenediamine, has been isolated by the treatment of strontium metal with a mixture of alcohol and water. All compounds were characterized using X-ray crystallography, 1H and 13C NMR, and IR spectroscopy.

Syntheses, Crystal Structures, and Properties of Heterometallic Iodoplumbates: Bicubane, Ribbon, and Chain Configurations

Successful introduction of Cu/Ag cations into the Pb/I system has led to the formation of four unprecedented heterometallic iodoplumbates in which the common connection of PbI6 units has been remarkably altered. Also, interesting long-lived fluorescence properties have been found.

Recent advances in tailoring the aggregation of heavier alkaline earth metal halides, alkoxides and aryloxides from non-aqueous solvents

This overview on one of the subjects treated in our group deals with the synthesis and study of low-dimensional polymer and molecular solid state structures formed with alkaline earth metal ions in non-aqueous solvents. We have chosen several synthetic approaches in order to obtain such compounds. The first concept deals with the "cutting out" of structural fragments from a solid state structure of a binary compound, which will be explained with reference to BaI2. Depending on the size and concentration of oxygen donor ligands, used as chemical scissors on BaI2, three-, two-, one- and zero-dimensional derived adducts of BaI2 are obtained, comparable to a structural genealogy tree for BaI2. A second part deals with the supramolecular approach for the synthesis of low dimensional polymeric compounds based on alkaline earth metal iodides, obtained by the combination of metal ion coordination with hydrogen bonding between the cationic complexes and their anions. Certain circumstances allow rules to be established for the prediction of the dimensionality of a given compound, contributing to the fundamental problem of structure prediction in crystal engineering. A third section describes a synthetic approach for generating pure alkaline earth metal cage compounds as well as alkali and alkaline earth mixed metal clusters. A first step deals with different molecular solvated alkaline earth metal iodides which are investigated as a function of the ligand size in non-aqueous solvents. These are then reacted with some alkali metal compound in order to partially or totally eliminate alkali iodide and to form the targeted clusters. These unique structures of ligand stabilized metal halide, hydroxide and/or alkoxide and aryloxide aggregates are of interest as potential precursors for oxide materials and as catalysts. Approaches to two synthetic methods of the latter, sol-gel and (MO)CVD (metal-organic chemical vapour deposition), are investigated with some of our compounds. (D. C. Bradley, Chem. Rev., 1989, 89, 1317-22; K. G. Caulton and L. G. Hubert-Pfalzgraf, Chem. Rev., 1990, 90, 969-95; T. P. Hanusa, Coord. Chem. Rev., 2000, 210, 329-367; T. P. Hanusa, in Comprehensive Coordination Chemistry II, ed. J. A. McCleverty and T. J. Meyer, Elsevier, Amsterdam, 2004, vol. 3, 1-92). Finally, the physical properties of some of our compounds are described qualitatively in order to show the wide spectrum of possibilities and potential applications for chemistry in this field.