Volatile Single-Source Molecular Precursor for the Lithium Ion Battery Cathode

The first single-source molecular precursor for a lithium–manganese cathode material is reported. Heterometallic β-diketonate LiMn₂(thd)₅ (<b>1</b>, thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) was obtained in high yield by simple one-step solid-state reactions employing commercially available reagents. Substantial scale-up preparation of <b>1</b> was achieved using a solution approach. The crystal structure of the precursor contains discrete Li:Mn = 1:2 trinuclear molecules held together by bridging diketonate ligands. The complex is relatively stable in open air, highly volatile, and soluble in all common solvents. It was confirmed to retain its heterometallic structure in solutions of non-coordinating solvents. The heterometallic diketonate <b>1</b> was shown to exhibit clean, low-temperature decomposition in air/oxygen that results in nanosized particles of spinel-type oxide LiMn₂O₄, one of the leading cathode materials for lithium ion batteries

Volatile Single-Source Molecular Precursor for the Lithium Ion Battery Cathode

The first single-source molecular precursor for a lithium–manganese cathode material is reported. Heterometallic β-diketonate LiMn₂(thd)₅ (<b>1</b>, thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) was obtained in high yield by simple one-step solid-state reactions employing commercially available reagents. Substantial scale-up preparation of <b>1</b> was achieved using a solution approach. The crystal structure of the precursor contains discrete Li:Mn = 1:2 trinuclear molecules held together by bridging diketonate ligands. The complex is relatively stable in open air, highly volatile, and soluble in all common solvents. It was confirmed to retain its heterometallic structure in solutions of non-coordinating solvents. The heterometallic diketonate <b>1</b> was shown to exhibit clean, low-temperature decomposition in air/oxygen that results in nanosized particles of spinel-type oxide LiMn₂O₄, one of the leading cathode materials for lithium ion batteries

Molecular Mechanisms for the Lithiation of Ruthenium Oxide Nanoplates as Lithium-Ion Battery Anode Materials: An Experimentally Motivated Computational Study

First-principles computational studies were used to calculate discharge curves for lithium in RuO₂ and to understand the molecular mechanism of lithium sorption into crystalline bulk RuO₂. These studies were complemented by experiments to provide new insights into the molecular mechanisms for the first and subsequent discharges of RuO₂ anodes in lithium ion batteries. RuO₂ nanoplates show slow fading of capacity over multiple cycles, retaining 76% of their original capacity after 20 cycles. The calculated discharge curves for lithium in RuO₂ lattice show qualitative agreement with experimental discharge curves for RuO₂ nanoplates. The molecular level analysis shows that an intercalation mechanism is operational until a 1:1 Li:Ru ratio is reached, which is followed by a conversion mechanism into Ru metal and Li₂O. Furthermore, in agreement with experiment, the computations predict superstoichiometric capacity of RuO₂, i.e., accommodation of lithium well beyond the stoichiometric limit of 4:1 Li:Ru ratio, and show that the additional lithium atoms reside at the interface of the Ru metal and Li₂O. This shows that the extra capacity can be explained without invoking electrolyte or solvent–electrolyte interface effects

Mixed-Ligand Approach to Design of Heterometallic Single-Source Precursors with Discrete Molecular Structure

Heterometallic single-source precursors for the Pb/Fe = 1:1 oxide materials, PbFe­(β-dik)₄ (β-dik = hexafluoroacetylacetonate (hfac, <b>1</b>), acetylacetonate (acac, <b>2</b>), and trifluoroacetylacetonate (tfac, <b>4</b>)), have been isolated by three different solid-state synthetic methods. The crystal structures of heterometallic diketonates <b>1</b>, <b>2</b>, and <b>4</b> were found to contain polymeric chains built on alternating [Fe­(β-dik)₂] and [Pb­(β-dik)₂] units that are held together by bridging M–O interactions. Heterometallic precursors are highly volatile, but soluble only in coordinating solvents, in which they dissociate into solvated homometallic fragments. In order to design the heterometallic precursor with a proper metal/metal ratio and with a discrete molecular structure, we used a combination of two different diketonate ligands. Heteroleptic complex Pb₂Fe₂­(hfac)₆­(acac)₂ (<b>5</b>) has been obtained by optimized stoichiometric reaction of an addition of homo-Fe­(acac)₂ to heterometallic Pb₂Fe­(hfac)₆ (<b>3</b>) diketonate that can be run in solution on a high scale. The combination of two ligands with electron-withdrawing and electron-donating groups allows changing the connectivity pattern within the heterometallic assembly and yields the precursor with a discrete tetranuclear structure. In accord with its molecular structure, heteroleptic complex <b>5</b> is soluble even in noncoordinating solvents and was found to retain its heterometallic structure in solution. Thermal decomposition of heterometallic precursors in air at 750 °C resulted in the target Pb₂­Fe₂O₅ oxide, a prospective multiferroic material. Prolonging the annealing time or increasing the decomposition temperature leads to another phase-pure lead–iron oxide Pb­Fe₁₂O₁₉ that is a representative of the important family of magnetic hexaferrites