Glenn G. Amatucci

An Asymmetric Hybrid Nonaqueous Energy Storage Cell

A nonaqueous asymmetric electrochemical cell technology is presented where the positive electrode stores charge through a reversible nonfaradaic or pseudocapacitive reaction of anions on the surface of an activated carbon positive electrode. The negative electrode is a crystalline intercalation compound which supports the fast reversible intercalation of lithium ions. Using a positive electrode material of activated carbon and newly developed negative electrode material of nanostructured Li 4 Ti 5 O 12 we obtain a cell which exhibits a sloping voltage profile from 3 to 1.5 V, 90% capacity utilization at 10C charge/discharge rates, and 10-15% capacity loss after 5000 cycles. Electrolyte oxidation on the activated carbon positive electrode was characterized in a Li metal asymmetric hybrid cell by cyclic voltammetry. Oxidation during the anodic scan was found to decrease significantly after surface passivation at high voltage and elevated temperatures. We also introduce the asymmetric hybrid technology in a bonded flat plate plastic cell configuration where packaged energy densities were calculated to be in excess of 20 Wh/kg. In addition, a practical method for three-electrode analysis of Li cells by use of a Ag quasi-reference electrode wire is discussed.

CoO[sub 2], The End Member of the Li[sub x]CoO[sub 2] Solid Solution

While has been widely studied in the past 15 years as a promising positive electrode material in lithium‐ion batteries, suprisingly, many questions are still unanswered concerning the electrochemical characteristics of the lithium intercalation material. Among these is the existence of an end member phase on complete lithium deintercalation. The use of dry plastic lithium‐ion battery technology has allowed the construction of an in situ x‐ray diffraction cell which allows structural characterization of at x values at and close to 0 for the first time. Instead of the expected destruction of the core structure of by a drastic increase in structural disorder, an increase in crystallographic quality occurred as x approached 0. For the first time, the end member phase was isolated. This phase is a hexagonal single‐layered phase (O1) believed to be isostructural with and has lattice parameters of a = 2.822 A and c = 4.29 A. The phase converted immediately back to a three‐layer (O3) delithiated type phase on lithium reinsertion. Electrochemical studies show that 95% of lithium can be reinserted back into the structure on complete delithiation and reversible cycling properties are maintained when cycled back to 4.2 V.

Self-discharge of LiMn2O4/C Li-ion cells in their discharged state: Understanding by means of three-electrode measurements

The potential distribution through plastic Li-ion cells during electrochemical testing was monitored by means of three- or four-electrode measurements in order to determine the origin of the poor electrochemical performance (namely, premature cell failure, poor storage performance in the discharged state) of LiMn{sub 2}O{sub 4}/C Li-ion cells encountered at 55 C. Several approaches to insert reliably one or two reference electrodes that can be either metallic lithium or an insertion compound such as Li{sub 4}Ti{sub 5}O{sub 12} into plastic Li-ion batteries are reported. Using a reference electrode, information regarding the evolution of (1) the state of charge of each electrode within a Li-ion cell, (2) their polarization, and (3) their rate capability can be obtained. From these three-electrode electrochemical measurements, coupled with chemical analyses, X-ray diffraction, and microscopy studies, one unambiguously concludes that the poor 55 C performance is mainly due to the instability of the LiMn{sub 2}O{sub 4} phase toward Mn dissolution in LiPF{sub 6}-type electrolytes. A mechanism, based on Mn dissolution, is proposed to account for the poor storage performance of LiMn{sub 2}O{sub 4}/C Li-ion cells.

A comparative study of Li-ion battery, supercapacitor and nonaqueous asymmetric hybrid devices for automotive applications

Abstract The specific energy, specific power, fast-charge capability, low temperature operation, cycle-life and self-discharge of five energy storage devices was compared. The group included a conventional carbon–carbon supercapacitor, Li-ion battery and three types of asymmetric hybrid supercapacitors. Asymmetric hybrid supercapacitors use a nanostructured Li 4 Ti 5 O 12 anode, and an acetonitrile electrolyte containing a lithium salt. Their cathode was activated carbon, LiCoO 2, or LiMn 2 O 4 . All devices were built using common plastic Li-ion technology developed by Telcordia Technologies.

Carbon-Metal Fluoride Nanocomposites Structure and Electrochemistry of FeF 3 : C

The practical electroactivity of electrically insulating iron fluoride was enabled through the use of carbon-metal fluoride nanocomposites (CMFNCs). The nanocomposites were fabricated through the use of high energy mechanical milling and resulted in nanodomains of FeF, on the order of 1-20 nm encompassed in a matrix of carbon as characterized by transmission electron microscopy and X-ray diffraction (XRD) Electrochemical characterization of CMFNCs composed of 85/15 wt % FeF 3 /C resulted in a nanocomposite specific capacity as high as 200 mAh/g (235 mAh/(g of FeF 3 ) with the electrochemical activity associated with the Fe 3+ → Fe 2+ occurring in the region of 2.8-3.5 V. The CMFNCs revealed encouraging rate capability and cycle life with <10% fade after 50 cycles. Structural evolution during the first lithiation reaction was investigated with the use of ex situ and in situ XRD. Initial results suggest that x from 0 to 0.5 in Li x FeF 3 proceeds in a two-phase reaction resulting in a phase with significant redistribution of the Fe atoms within a structure very similar to the base FeF 3 . FeF 3 -based CMFNCs also exhibited a very high specific capacity of 600 mAh/g at 70°C due to a reversible reaction at approximately 2 V.

Materials' effects on the elevated and room temperature performance of CLiMn2O4 Li-ion batteries

Li-ion rechargeable batteries based on LiMn2O4 suffer from relatively poor storage and cycling performance at elevated temperatures. In order to address this issue, a structural and electrochemical study of LiMn2O4-based systems at room and elevated temperatures were undertaken. Some of the spinel material characteristics such as morphology, defects, surface area, structural instability, single-versus two-phase lithium-insertion processes, cation and oxygen stoichiometry, and manganese solubility were investigated. We found that the sample surface area, which also influences the manganese dissolution and electrolyte oxidation, is one of the most critical parameters in controlling the rate of irreversible self-discharge, with the lowest irreversible self-discharge being observed for samples with the lowest surface area. These results are discussed in terms of active surface centers and the possibility of surface treatments to rectify this problem. The elevated temperature storage and room temperature cycling performance was found to be the best for those Li4Mn2O4+δ samples having a low surface area (0.5–1 m2/g), Li in excess (x > 1.00), show no evidence of Jahn-Teller distortion down to −50 °C, and for which the Li-extraction mechanism occurs over a single-phase reaction at room temperature.

Mechanism for limited 55 C storage performance of Li{sub 1.05}Mn{sub 1.95}O{sub 4} electrodes

A survey of the chemical stability of high-surface area LiMn{sub 2}O{sub 4} in various Li-based electrolytes was performed as a function of temperature. The evidence for an acidic-induced Mn dissolution was confirmed, but more importantly the authors identified, by means of combined infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction measurements, the growth, upon storage of LiMn{sub 2}O{sub 4} in the electrolyte at 100 C, of a protonated {lambda}-MnO{sub 2} phase partially inactive with respect to lithium intercalation. This results sheds light on how the mechanism of high temperature irreversible capacity loss proceeds. Mn dissolution first occurs, leading to a deficient spinel having all the Mn in the +4 oxidation state. Once this composition is reached, Mn cannot be oxidized further, and a protonic ion-exchange reaction takes place at the expense of the delithiation reaction. The resulting protonated {lambda}-Mn{sub 2{minus}y}O{sub 4} phase has a reduced capacity with respect to lithium, thereby accounting for some of the irreversible capacity loss experienced at 55 C for such a material.

Differential Scanning Calorimetry Study of the Reactivity of Carbon Anodes in Plastic Li‐Ion Batteries

Chemical reactions taking place at elevated temperatures in a polymer-bonded lithiated carbon anode were studied by differential scanning calorimetry. The influences of parameters such as degree of intercalation, number of cycles, specific surface area, and chemical nature of the binder were elucidated. It was clearly established that the first reaction taking place at ca. 120-140 °C was the transformation of the passivation layer products into lithium carbonate, and that lithiated carbon reacted with the molten binder via dehydrofluorination only at T > 300 °C. Both reactions strongly depend on the specific surface area of the electrodes and the degree of lithiation.

The elevated temperature performance of the LiMn2O4/C system: Failure and solutions

This paper reviews various chemical approaches that have participated in the improvement of the high temperature performance of the LiMn2O4/C Li-ion system. These approaches range from chemical surface and bulk modification of the spinel to the improvement of electrolyte stability towards acidification, and to the stabilization of the SEI chemistry of the carbon anode. More specifically, we describe the advantages of (1) modifying the surface chemistry of the spinel in order to obtain encapsulated particles or (2) modifying the crystal chemistry of the spinel through dual cationic and anionic substitutions by improving its stability towards Mn dissolution. The role of the carbon negative electrode towards the high temperature issue, namely through the formation/dissolution of the SEI layer is discussed, and a way of controlling such an SEI layer through a pre-conditioning of the cell is presented. The benefit of adding zeolites to the Li-ion cell to trap some of the species (H+, or others) generated during cell functioning as the result of the electrolyte decomposition or SEI layer is presented. Finally, from a compilation of other reports on that topic together with the present work, our present understanding of the failure mechanism in the LiMn2O4/C system is elucidated.

Surface treatments of Li1+xMn2−xO4 spinels for improved elevated temperature performance

Abstract In this paper, we introduce the use of surface treatments to improve the elevated temperature storage characteristics of the Li 1+ x Mn 2− x O 4 spinel in Li-ion batteries. Two approaches are introduced, the first consists of the application of an inorganic lithium borate glass composition to the surface, the second utilizes an acetylacetone complexing agent. All surface treatments were found to improve the elevated temperature performance of the Li 1+ x Mn 2− x O 4 spinel to some degree. Results are discussed with respect to the active failure mechanisms.