One of the major challenges in electrochemical energy storage (EES) is increasing the gravimetric capacity and energy density of the cathode material. Here we demonstrate how to increase the gravimetric energy density of electrical energy storage devices based on the use of organic materials through exploitation of the strong ionic coupling between a reduced carbonyl functionality and small cations such as lithium (Li(+)) and magnesium (Mg(2+)). Binding of the cation to the reduced carbonyl results in a positive shift of the formal reduction potential of the carbonyl couple. This has the effect of increasing the cell voltage which, in turn, results in an increase in the energy density. We show how this interaction can be used to dramatically increase, by up to a factor of 2, the energy density for a selected case study using 1,2-di(thiophen-2-yl)ethane-1,2-dione (DTED). We have carried out electrochemical and computational studies in order to understand the thermodynamic (positive shift of 250 mV and 1 V in the formal potential for the first and second reductions, respectively, of the carbonyl groups of DTED) and kinetic effects between small radii cations (Li(+) and Mg(2+)) and the reduced carbonyl functionality of carbonyl-based organic molecules (C-bOMs).

Organic compounds represent an attractive choice for cathode materials in rechargeable lithium batteries. Among all the organic functionalities, carbonyl-based organic molecules (C-bOMs) exhibit rapid and generally chemically reversible electrochemical behavior, and their reduced forms (enolates) can have strong ionic interactions with small radii cations (such as Li + ). Furthermore, a wide range of chemical variations/modifications can be performed on C-bOM structures via synthesis. We have systematically investigated how to modify their electrochemical behavior by shifting the formal potential, maximizing the interaction of the various redox forms with lithium ions, and maximizing the number of electrons transferred while minimizing the molecular weight of the compound, thus maximizing their gravimetric energy density. We have performed density-functional calculations to predict the formal potentials of the C-bOMs materials (E = 2.0−4.0 V) and identify the most promising candidates. We have determined how the addition of electron-withdrawing and -donating groups can be used to tune the formal potentials and lithium ion binding energies. Moreover, by using the LUMO energy levels and the aromaticity, which was calculated with nuclear independent chemical shift (NICS), it was possible to study the stability of these systems. Furthermore, we have been able to design and computationally characterize new C-bOMs molecules, which represent new potentially high gravimetric energy density cathode materials for electrical energy storage applications.

The full realization of a renewable energy strategy hinges upon electrical energy storage (EES). EES devices play a key role in storing energy from renewable sources (which are inherently intermittent), to efficient transmission (e.g., grid load-leveling), and finally into the electrification of transportation. Organic materials represent a promising class of electrode active materials for Li-ion and post-Li-ion batteries. Organics consist of low-cost, lightweight, widely available materials, and their properties can be rationally tuned using the well-established principles of organic chemistry. Within the class of organic EES materials, carboxylates distinguish themselves for Li-ion anode materials based on their observed thermal stability, rate capability, and high cyclability. Further, many of the carboxylates studied to date can be synthesized from renewable or waste feedstocks. This report begins with a preliminary molecular density-functional theory (DFT) study, in which the calculated molecular properties of a set of 12 known Li-ion electrode materials based on carboxylate and carbonyl redox couples are compared to literature data. Based on the agreement between theoretical and experimental data, an expanded study was undertaken to identify promising materials and establish design principles for anodes based on Li-carboxylate salts. Predictive computational studies represent an important step forward for the identification of organic anode materials.

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The reaction of 2,3-di(2-pyridyl)-5,6-diphenylpyrazine (dpdpz) with K(2)PtCl(4) in a mixture of acetonitrile and water afforded mono-Pt complex (dpdpz)PtCl(2)4 in good yield, with two lateral pyridine nitrogen atoms binding to the metal center. Two types of Ru(II)-Pt(II) heterodimetallic complexes bridged by dpdpz, namely, [(bpy)(2)Ru(dpdpz)Pt(C≡CC(6)H(4)R)](2+) (7-9, R = H, NMe(2), or Cl, respectively) and [(tpy)Ru(dpdpz)Pt(C≡CPh)] (+) (12), were then designed and prepared, where bpy = 2,2'-bipyridine and tpy = 2,2';6',2''-terpyridine. In both cases, the platinum atom binds to dpdpz with a C(∧)N(∧)N tridentate mode. However, the coordination of the ruthenium atom with dpdpz could either be noncyclometalated (N(∧)N bidentate) or cyclometalated (C(∧)N(∧)N tridentate). The electronic properties of these complexes were subsequently studied and compared by spectroscopic and electrochemical analyses and theoretical calculations. These complexes exhibit substantial absorption in the visible to NIR (near-infrared) region because of mixed MLCT (metal-to-ligand-charge-tranfer) transitions from both the ruthenium and the platinum centers. Complexes 7 and 9 were found to emit NIR light with higher quantum yields than those of the mono-Ru complex [(bpy)(2)Ru(dpdpz)](2+) (5) and bis-Ru complex [(bpy)(2)Ru(dpdpz)Ru(bpy)(2)](4+) (13). However, no emission was detected from complex 8 or 12 at room temperature in acetonitrile.