Randolph A. Leising

Silver vanadium oxides and related battery applications

Abstract This review contains references from journals, proceedings volumes, and patents involving the preparation, characterization, reactivity, and battery applications of materials containing silver, vanadium, and oxygen, hereafter referred to as silver vanadium oxide (SVO). SVO has been a subject of regular study for a number of years, with earlier reports involving the synthesis and characterization of the various phases of SVO. However, with the relatively recent discovery of SVO as an important electrode material in batteries, the number of publications and patents involving the preparation, structure, reactivity and related battery applications of SVO has increased markedly. In light of this recent increase in research activity involving SVO and its related battery applications, this review is a timely examination of this exciting and growing area of research.

Abuse testing of lithium-ion batteries: Characterization of the overcharge reaction of LiCoO2/Graphite cells

The short-circuit and overcharge behavior of prismatic lithium-ion batteries containing LiCoO 2 cathodes and graphite anodes were studied in detail. Internal thermocouples were used to characterize the thermal profiles of the cells under abusive conditions. Differences between the internal and surface temperatures of the cells during the safety tests highlighted the importance of the internal measurement for obtaining more meaningful data. Under short-circuit conditions the cells remained hermetically sealed, reached an internal temperature of 132°C (the shutdown temperature of the separator), and then slowly cooled to ambient temperature. However, on extreme overcharge testing different results were obtained depending on the current used to charge the battery. At low currents (≤C/5) the cells remained hermetic, but swelled significantly. When higher currents were used, the cells ruptured during overcharge. Experimental cells were constructed with a systematic variation in cell balance and the point of cell rupture tracked to the amount of cathode in the cell, independent of the amount of anode material. The internal de resistance of the cell was also measured during the overcharge reaction and remained low throughout most of the test, although a large increase was observed at the end of the test due to the melting of the shutdown separator. The cells overcharged with high currents all reached high temperatures (≥ 195°C) immediately prior to rupturing, which suggests that the melting of lithium is a key underlying factor leading to the rupture of the cells. To test this proposal, cells were assembled with lithium removed from the LiCoO 2 cathode, so that lithium metal would not plate on the anode during the overcharge test. These cells reached a significantly higher temperature (∼280°C) prior to rupture.

Batteries, 1977 to 2002

Battery systems have undergone significant improvements over the past 25 years. Older systems have been updated with new materials and constructions. New lithium and nickel systems have been introduced, especially in the rechargeable segment, and have undergone tremendous growth and reached maturity. The technology and applications of the various battery systems are reviewed here, and the status of commercial aqueous and nonaqueous systems updated. NEC first introduced electrochemical capacitors in August 1978 under the trade name Supercapacitor. Electrochemical capacitor technology has evolved from first generation products with low energy density for memory protection applications through several generations of designs to create megajoule-size capacitors for transportation and power quality applications.

A study of the overcharge reaction of lithium-ion batteries

The overcharge behavior of prismatic lithium ion batteries was studied under abusive conditions. Experimental cells were constructed with a systematic variation in cell balance and overcharge tested to the point of failure. This test demonstrated that the point of cell rupture tracked the amount of cathode in the cell, independent of the amount of anode material. The rate of charge was found to be an important parameter, as cells overcharged at low charge rates remained hermetic while high charge rates (C/2 and above) resulted in cell rupture. The internal temperature of the cells monitored during overcharge was found to be as high as 199°C, which was 93°C higher than the external skin temperature of the cell. Coin cell tests identified the cathode as the source of heat produced in the cell, and Rdc measurements identified a large increase in cell resistance past the full delithiation point of LixCoO2.

Anode Passivation and Electrolyte Solvent Disproportionation: Mechanism of Ester Exchange Reaction in Lithium‐Ion Batteries

Carbonate-based electrolytes used in lithium-ion electrochemical cells were found to undergo ester exchange reactions, where the use of dimethyl carbonate and diethyl carbonate resulted in the in situ formation of ethyl methyl carbonate. The reaction was found to be reversible and occurs during the first charge cycle of the LiCoO 2 /petroleum coke lithium-ion system. Mechanistic studies were carried out and determined that the ester exchange reaction is reductively initiated at the carbon anode. A mechanism has been deduced, with an intermediate alkoxide species responsible for the ester exchange reaction. Electrode passivation was found to limit the extent of the reaction during subsequent cycles, with the choice of electrolyte solvent impacting the passivation of the electrode.

Advanced lithium batteries for implantable medical devices: mechanistic study of SVO cathode synthesis

Abstract Silver vanadium oxide (SVO, Ag 2 V 4 O 11 ) was synthesized in solid-state reactions from silver carbonate and silver metal powder starting materials with vanadium oxide (V 2 O 5 ) as the vanadium source. These powders were prepared as primary cathode materials for lithium batteries. Thermal analyses of stoichiometric mixtures of V 2 O 5 and silver sources were used to elucidate the mechanism of Ag 2 V 4 O 11 formation. V 2 O 5 reacts with Ag 2 CO 3 in a two step decomposition/combination (DC) reaction. Weight gain measured by TGA during the reaction of Ag(0)+V 2 O 5 in O 2 indicated the formation of Ag 2 V 4 O 11 . XRD analysis of the synthesis products of the Ag(0)+V 2 O 5 reaction indicated the formation of AgV 2 O 5 under inert atmosphere and Ag 2 V 4 O 11 under oxidizing (air or O 2 ) conditions. The surface area and morphology of the materials were strongly influenced by the synthesis method, linked to the parameters of time, temperature, and reaction atmosphere. The electrochemical performance of the SVO cathode material also depended on the synthesis method, where SVO prepared from the DC reaction mechanism yielded improved long-term performance.

Unexpected assembly of a (μ-oxo)(μ-formato)diiron(III) complex from an aerobic methanolic solution of Fe(III) and the TPA ligand

Abstract Crystals of a (μ-oxo)(μ-formato)diiron(III) complex [Fe2(μ-O)(TPA)2(O2CH)](ClO4)3 (1) formed from a methanolic solution of Fe(ClO4)3 and the tetradentate tripodal ligand tris(2-pyridylmethyl)amine (TPA) in methanol when left standing for days under aerobic conditions, despite the fact that no formate ion had been added to the solution. Complex 1 was found to have UV—Vis and 1H NMR properties very similar to those of [Fe2(μ-O)(TPA)2(O2CCH3)](ClO4)3 (2), and its formula weight was corroborated by fast atom bombardment mass spectrometry. Complex 1 crystallized in the monoclinic space group P21 (No. 4) with a = 11.693(3), b = 10.414(4), c = 18.144(6) A, and β = 93.98(3)°. The structure was determined at −84°C from 4464 out of a total of 6753 reflections with R = 0.058 and Rw = 0.068. The crystal structure confirmed the presence of a (μ-oxo)(μ-carboxylato)diiron(III) unit with distinct iron sites as found for 2. The formate bridge was shown to derive from the aerobic oxidation of methanol: 1 was not formed in the absence of air, and 2 was formed from the reaction carried out in ethanol solvent. Manometric measurements showed that the amount of dioxygen consumed was approximately stoichiometric to the combined amounts of formate found in 1 (80%) and formaldehyde (20%) found in the reaction mixture.

Novel Impact of Short Term Aging on the Electrochemistry of CO 2 Treated Synthetic Graphite

A study was conducted of graphite prepared from heat-treatment of synthetic graphite LK-702 in flowing CO 2 . Samples were characterized by percent mass loss, X-ray powder diffraction, scanning electron microscopy imaging, thermogravimetric analysis, Brunauer-Emmett-Teller surface area, and methylene blue adsorption surface area measurements. Treated graphites were studied as possible electrode materials for Li-ion cells. Cycle tests demonstrated that the reversible capacity and percent capacity retained were relatively unaffected by CO 2 treatment, while the irreversible capacity was significantly influenced by CO 2 treatment. The change in irreversible capacity was strongly dependent upon the age of the treated samples, where samples freshly treated in CO 2 showed a decrease in irreversible capacity with treatment time, and treated samples aged for at least fourteen days (in a dry environment) showed an increase in irreversible capacity with treatment time. To our knowledge, this is the first report of the impact of short term aging on the electrochemistry of CO 2 treated graphite.

Synthesis, characterization and redox properties of mixed phosphine nitroruthenium(II) complexes. crystal structure of trans-[Ru(NO2)(terpy)-(PMe3)(PPh3)][ClO4]·H2O

The mixed phosphine complexes trans-[Ru(NO2)(terpy)(PMe3)(PR3)][ClO4](terpy = 2,2′ : 6′,2″-terpyridine; R = Et, Pr, Bz or Ph) were synthesized in high yields by a stepwise addition of each phosphine. These syntheses demonstrate the utility of ruthenium(II) in the preparation of mixed phosphine complexes. The stereochemistry of trans-[Ru(NO2)(terpy)(PMe3)(PPh3)][ClO4]·H2O was confirmed by a single-crystal X-ray diffraction study. This species crystallizes in the monoclinic space group P21/c with a= 11.0199(15), b= 18.3888(28), c= 19.3089(25)A, β= 112.845(9)° and Z= 4. The two phosphine ligands are mutually trans, with P–Ru–P 177.5(1)°. The relative redox stabilities of the mixed phosphine complexes and a related series of trans-[Ru(NO2)(terpy)(PR3)2][ClO4](R = Et, Pr, Bz or Ph) complexes were evaluated using cyclic voltammetric peak current ratios (ipc/ipa) for the ruthenium(III)–ruthenium(II) couples. The rate constants for nitroruthenium(III) decomposition were calculated from the ipc/ipa data and the contributions of electronic (E) and steric (S) factors to its rate of decomposition were determined using the relationship ln k=aE+bS+c. The average ratio of steric to electronic ligand effects on ln k is approximately 30 : 70.

Heat-Treatment of Synthetic Graphite under Argon and Effect on Li-Ion Electrochemistry

The novel use of heat-treatment in flowing Ar to systematically affect particle and crystallite dimensions of synthetic graphite LK-702 is reported. Samples were characterized by percent mass loss, X-ray powder diffraction, scanning electron microscopy, Brunauer-Emmett-Teller (BET) surface area, and methylene blue adsorption surface area measurements. The treated graphites were studied as possible electrode materials for Li-ion cells. The BET and methylene blue surface areas increased for treatment times up to 48 h, then remained constant. For times up to 48 h, Ar treatment was demonstrated to break apart larger graphite particles, narrowing the particle size distribution. The irreversible capacity of the graphite decreased substantially with increased Ar treatment time, while the reversible capacity remained unchanged.