Harry D. Pratt

Polyoxometalate flow battery

A redox flow battery utilizing two, three-electron polyoxometalate redox couples (SiV3W9O40 7e/ SiV3W VI 9O40 10 and SiV3W9O40 10 /SiV3W3W6O40 13 ) was investigated for use in stationary storage in either aqueous or non-aqueous conditions. The aqueous battery had coulombic efficiencies greater than 95% with relatively low capacity fading over 100 cycles. Infrared studies showed there was no decomposition of the compound under these conditions. The non-aqueous analog had a higher operating voltage but at the expense of coulombic efficiency. The spontaneous formation of these clusters by selfassembly facilitates recovery of the battery after being subjected to reversed polarity. Polyoxometalates offer a new approach to stationary storage materials because they are capable of undergoing multielectron reactions and are stable over a wide range of pH values and temperatures. Published by Elsevier B.V.

Mixed addenda polyoxometalate “solutions” for stationary energy storage

A series of redox flow batteries utilizing mixed addenda (vanadium and tungsten), phosphorus-based polyoxometalates (A-α-PV3W9O40(6-), B-α-PV3W9O40(6-), and P2V3W15O62(9-)) were prepared and tested. Cyclic voltammetry and bulk electrolysis experiments on the Keggin compounds (A-α-PV3W9O40(6-) and B-α-PV3W9O40(6-)) established that the vanadium centers of these compounds could be used as the positive electrode (PV(IV)3W(VI)9O40(9-)/PV(V)3W(VI)9O40(6-)), and the tungsten centers could be used as the negative electrode (PV(IV)3W(VI)9O40(9-)/PV(IV)3W(V)3W(VI)6O40(12-)) since these electrochemical processes are separated by about 1 V. The results showed that A-α-PV3W9O40(6-) (where A indicates adjacent, corner-sharing vanadium atoms) had coulombic efficiencies (charge in divided by charge out) above 80%, while the coulombic efficiency of B-α-PV3W9O40(6-) (where B indicates adjacent edge-sharing vanadium atoms) fluctuated between 50% and 70% during cycling. The electrochemical yield, a measurement of the actual charge or discharge observed in comparison with the theoretical charge, was between 40% and 50% for A-α-PV3W9O40(6-), and (31)P NMR showed small amounts of PV2W10O40(5-) and PVW11O40(4-) formed with cycling. The electrochemical yield for B-α-PV3W9O40(6-) decreased from 90% to around 60% due to precipitation of the compound on the electrode, but there were no decomposition products detected in the solution by (31)P NMR, and infrared data on the electrode suggested that the cluster remained intact. Testing of P2V3W15O62(9-) (Wells-Dawson structure) suggested higher charge density clusters were not as suitable as the Keggin structures for a redox flow battery due to the poor stability and inaccessibility of the highly reduced materials.

Electrochemical activity of Fe-MIL-100 as a positive electrode for Na-ion batteries

Here we investigate the electrochemical activity of metal–organic frameworks (MOFs) as positive electrodes for Na-ion batteries in coin cell configurations. The performance of Fe-MIL-100 material is highly dependent on the choice of sodium salt source, and electrolyte system. The overall capacity fades over many cycles, however the high coulombic efficiency is maintained. This can be correlated with inaccessibility of active sites for Na intercalation, due to the increase of extra carbonaceous material inside the pores. Powder X-ray diffraction via synchrotron data and pair distribution function analyses of the as-made and cycled electrodes reveal the structure maintains the long-range order with progressive cycling. This finding suggests that careful consideration of all variables in battery components, and especially electrolyte selection can lead to greatly improved performances.

Screening for High Conductivity/Low Viscosity Ionic Liquids Using Product Descriptors

We seek to optimize Ionic liquids (ILs) for application to redox flow batteries. As part of this effort, we have developed a computational method for suggesting ILs with high conductivity and low viscosity. Since ILs consist of cation‐anion pairs, we consider a method for treating ILs as pairs using product descriptors for QSPRs, a concept borrowed from the prediction of protein‐protein interactions in bioinformatics. We demonstrate the method by predicting electrical conductivity, viscosity, and melting point on a dataset taken from the ILThermo database on June 18th, 2014. The dataset consists of 4,329 measurements taken from 165 ILs made up of 72 cations and 34 anions. We benchmark our QSPRs on the known values in the dataset then extend our predictions to screen all 2,448 possible cation‐anion pairs in the dataset.

Estimation of Transport and Kinetic Parameters of Vanadium Redox Batteries Using Static Cells

Mathematical models of Redox Flow Batteries (RFBs) can be used to analyze cell performance, optimize battery operation, and control the energy storage system efficiently. Among many other models, physics-based electrochemical models are capable of predicting internal states of the battery, such as temperature, state-of-charge, and state-of-health. In the models, estimating parameters is an important step that can study, analyze, and validate the models using experimental data. A common practice is to determine these parameters either through conducting experiments or based on the information available in the literature. However, it is not easy to investigate all proper parameters for the models through this way, and there are occasions when important information, such as diffusion coefficients and rate constants of ions, has not been studied. Also, the parameters needed for modeling charge-discharge are not always available. In this paper, an efficient way to estimate parameters of physics-based redox battery models will be proposed. This paper also demonstrates that the proposed approach can study and analyze aspects of capacity loss/fade, kinetics, and transport phenomena of the RFB system.

Organosilicon-based electrolytes for long-life lithium primary batteries

This report describes advances in electrolytes for lithium primary battery systems. Electrolytes were synthesized that utilize organosilane materials that include anion binding agent functionality. Numerous materials were synthesized and tested in lithium carbon monofluoride battery systems for conductivity, impedance, and capacity. Resulting electrolytes were shown to be completely non-flammable and showed promise as co-solvents for electrolyte systems, due to low dielectric strength.