David Ingersoll

An accelerated calendar and cycle life study of Li-ion cells

Abstract The accelerated calendar and cycle life of lithium-ion cells was studied. Useful cell life was strongly affected by temperature, time, state-of-charge (SOC) and change in state-of-charge (ΔSOC). In calendar life experiments, useful cell life was strongly affected by temperature and time. Temperature accelerated cell performance degradation. The rates of area specific impedance (ASI) increase and power fade followed simple laws based on a power of time and Arrhenius kinetics. The data have been modeled using these two concepts and the calculated data agree well with the experimental values. The calendar life ASI increase and power fade data follow (time) 1/2 kinetics. This behavior may be due to solid electrolyte interface layer growth. From the cycle life experiments, the ASI increase data follow (time) 1/2 kinetics also, but there is an apparent change in overall power fade mechanism when going from 3 to 6% ΔSOC. Here, the power of time drops to below 1/2, which indicates that the power fade mechanism is more complex than layer growth.

Synthesis of an ionic liquid with an iron coordination cation

An iron-based ionic liquid, Fe((OHCH(2)CH(2))(2)NH)(6)(CF(3)SO(3))(3), is synthesized in a single-step complexation reaction. Infrared and Raman data suggest NH(CH(2)CH(2)OH)(2) primarily coordinates to Fe(iii) through alcohol groups. The compound has T(g) and T(d) values of -64 degrees C and 260 degrees C, respectively. Cyclic voltammetry reveals quasi-reversible Fe(iii)/Fe(ii) reduction waves.

Simultaneous in situ-neutron diffraction studies of the anode and cathode in a lithium-ion cell

In situ neutron diffraction analysis was employed to study the behavior of the cathode and anode materials in a commercial Li-ion cell (Saehan Enertech, Inc) using the exact configuration of the commercial product. Accurate lattice parameters were refined for the LiCoO 2 type cathode based on measurements collected as a function of the state of charge. Simultaneous structural characterization was possible on the graphitic anode as well. The simultaneous direct correlation of structural information for both the anode and cathode with the electrochemical data provided a highly detailed picture of the behavior of the active cell materials that ultimately underlie the cell performance.

In situ analysis of LiFePO4 batteries: Signal extraction by multivariate analysis

Electrochemical reaction behavior of a commercial Li-ion battery (LiFePO4-based cathode, graphite-based anode) has been measured via in-situ neutron diffraction. Multivariate analysis was successfully applied to the neutron diffraction dataset facilitating in the determination of Li bearing phases participating in the electrochemical reaction in both the anode and cathode as a function of state-of-charge (SOC). Analysis resulted in quantified phase fraction values for LiFePO4 and FePO4 cathode compounds as well as identification of staging behavior of Li6 ,L i12, Li24 and graphite phases in the anode. An additional Li-graphite phase has also been tentatively identified during electrochemical cycling as LiC48 at conditions of ~5 to 15% SOC.

Artificial neural network simulation of battery performance

Although they appear deceptively simple, batteries embody a complex set of interacting physical and chemical processes. While the discrete engineering characteristics of a battery, such as the physical dimensions of the individual components, are relatively straightforward to define explicitly, their myriad chemical and physical processes, including interactions, are much more difficult to accurately represent. For this reason, development of analytical models that can consistently predict the performance of a battery has only been partially successful, even though significant resources have been applied to this problem. As an alternative approach, we have begun development of non-phenomenological models for battery systems based on artificial neural networks. The paper describes initial feasibility studies as well as current models and makes comparisons between predicted and actual performance.

Spectroelectrochemical Studies of Metallophthalocyanines Adsorbed on Electrode Surfaces

Co(II) and Fe(II)-phthalocyanines adsorbed on platinum and various carbon electrode surfaces have been studied by spectroelectrochemical techniques. The metallophthalocyanine (MPc) films were prepared on substrate electrodes by a drop-dry method after dissolving them in pyridine. While not much change in the spectroscopic properties is observed for MPcs adsorbed at the platinum electrode, both the Soret and Q bands were significantly broadened when adsorbed on the carbon electrodes. Also, the metal-ligand charge-transfer (MLCT) bands are observed from CoPc films adsorbed on carbon substrates even if they are not reduced. These observations lead to the conclusion that the MPc molecules not only undergo oligomerization but also interact strongly with carbon surfaces by perhaps sharing the {pi}-electrons of carbon. MPcs have been used as effective catalysts for oxygen reduction, which is used as a cathode reaction in fuel cells and metal-air batteries.

Direct Glucose Fuel Cell: Noble Metal Catalyst Anode Polymer Electrolyte Membrane Fuel Cell with Glucose Fuel

A 1 cm 2 constant flow glucose-oxygen fuel cell has been demonstrated using noble metal catalysis. The fuel cell is based on Pt―RuO 2 anode catalysts and Pt cathode. Operation of this cell under various concentrations of glucose has revealed the presence of a region of the polarization curve in which additional polarization leads to a decrease in current rather than the expected increase. We postulate that the appearance of this polarization loss is due to the adsorption of by-product lactones to the Pt―RuO 2 surface which is not desorbed under normal operating conditions, but instead decreases the number of catalytic sites over time, resulting in lower currents.

Electrochemical and surface spectroscopic investigation of copper(111) films on ruthenium(0001)

The direct coupling of electrochemical and ultrahigh vacuum surface spectroscopic probes has been employed to study Cu(111) films deposited in vacuum on an Ru(0001) substrate. A quantitative correlation was found for Cu coverage measurements made in vacuum and in solution using thermal desorption spectroscopy and linear sweep voltammetry. This quantitative correlation indicates that the Cu overlayer pseudomorphic structure generated in vacuum is retained or restored upon immersion in solution. Equivalent amounts of charge were measured for vacuum-deposited and electrodeposited Cu monolayer films, indicative of pseudomorphic initial growth of Cu films in solution. A disparity was found in the energetics of thermal desorption and anodic dissolution of Cu of ca. 8 kJ mol−1, indicative of a greater stability of monolayer versus bulk Cu in solution compared with vacuum.

An alternative lithium cathode material: Synthesis, characterization, and electrochemical analysis of Li{sub 8}(Ni{sub 5}Co{sub 2}Mn)O{sub 16}

The authors have previously reported a nonaqueous solution route to LiMn{sub 2}O{sub 4} and LiCoO{sub 2} materials that have demonstrated acceptable characteristics for use as lithium battery cathode materials. Due to the flexibility of processes, complex formulations of cathode materials can be easily generated and studied. Utilizing this flexibility, the authors have investigated a complex lithium transition metal oxide material, Li{sub 8}(Ni{sub 5}Co{sub 2}Mn)O{sub 16}, for use as an alternative cathode material. This material was analyzed by X-ray diffraction and scanning electron microscopy techniques which indicated it was phase pure. Electrochemical investigations revealed a high capacity ({approximately}150 mAh/g) with a fade rate of {approximately}0.41 mAh/g/cycle (0.27%/cycle).

Electrical and electrochemical performance characteristics of large capacity lithium-ion cells

Abstract We are currently evaluating large capacity (20–40 Ah) Bluestar (cylindrical) and Yardney (prismatic) lithium-ion cells for their electrical and electrochemical performance characteristics at different temperatures. The cell resistances were nearly constant from room temperature down to −20°C, but increased by over 10 times at −40°C. The specific energies and powers, as well as the energy densities and power densities are high and did not reach a plateau even at the highest discharge rates tested. For example, the prismatic lithium-ion cells gave close to 280 Wh dm−3 from a 4 A discharge and 249 Wh dm−3 at 20 A, both at room temperature. For the same current range the specific energy values were 102 Wh kg−1 and 91 Wh kg−1. Cycle life and other electrical and electrochemical properties of the cells will be presented.