This paper reports on electroanalytical studies of the intercalation-deintercalation of lithium into lithiated transition metal oxides which are used as cathodes for Li ion batteries. These include LixCoO2 LixNiO2 and LixMn2O4 spinel. The basic electroanalytical response of these systems in LiAsF6 1M/EC-DMC solutions was obtained from the simultaneous use of slow and fast scan cyclic voltammetry (SSCV), potentiostatic intermittent titration (PITT) (from which D vs. E was calculated), and impedance spectroscopy (EIS). Surface sensitive FTIR spectroscopy and XRD were also used for surface and 3D characterization, respectively. A large and important denominator was found in the electrochemical behavior of lithium intercalation-deintercalation into these transition metal oxides and graphite. The use of the electroanalytical response of these systems as a tool for the study of stabilization and failure mechanisms of these materials as cathodes in rechargeable Li batteries is demonstrated and discussed.

The technology of lithium ion batteries has been developed so that these systems can be used to power portable electronic devices. The next step is to increase the size of the batteries so that they power larger systems such as electric vehicles. However, before such a step can be taken the thermal stability of any materials placed in such a battery must be determined. Although the thermal properties of the materials are important for the small systems, which can reach high temperatures when abused, they become even more important in large systems where heat dissipation is more difficult because of the physical size of the system. This paper will discuss our approach, which uses an Accelerated Rate Calorimeter, to the study of the thermal behaviour of lithium ion battery electrode materials.

The effect of hydrofluoric acid (HF) concentration in conventional LiPF6/EC+DEC electrolyte on the properties of solid electrolyte interphase (SEI) films formed on synthetic graphite electrode and the electrochemical performance were studied using x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), elemental analysis and electrochemical measurement. The morphology and composition of SEI are affected by a small amount of HF in the electrolyte. Higher F content in the SEI was observed when high HF electrolyte were used, although the irreversible capacities used for formation of SEI were nearly the same value. The cycleability of the synthetic graphite electrode was greatly improved when surface film contains larger amount of LiF.

Electrochemistry of a nickel electrode in propylene carbonate [PC] containing LiClO4, LiCF3SO3, LiPF6 was studied through a micro electrode (φ =25 μ m) techniques in the wide potential range between +4.5 and -0.2 V vs. Li/Li+. Common pronounced peaks were observed in the potential range positive to lithium electrodeposition on nickel in all electrolyte solutions examined. Thus, these peaks can be attributed to reactions related to Li+ or commonly contained contaminants such as water and acids. In particular, the peak which appeared at the most negative potential seemed to be underpotential deposition (UPD) of lithium.

To prove this hypothesis a nickel electrode in highly dried PC (water content : 3 – 8 ppm) intentionally contaminated with a small amount of water and CF3COOH was examined via cyclic voltammetry. Changing the content of water and acid (and its ratio) in PC resulted in a variety of voltammograms and one of them was identical to the one observed in PC containing lithium electrolytes. These facts preclude the existence of UPD of lithium on nickel in the electrolyte solutions. Instead, the existence of NiOH on nickel and its redox reaction mechanism have been postulated. The mechanism is consistent with the experimental facts : a nickel electrode passivates in PC with a small amount of water, and a small amount of acid, CF3COOH, can prevent passivation. The vicinity of the electrode surface may be exposed to an alkaline atmosphere owing to the reduction product of water. This seems to be the cause of troubles we run into with the electrodes at cathodic potentials

The initial irreversible capacity loss in lithium-ion cells has been attributed to passive-film formation on the carbon and graphite anodes during the first intercalation. We have examined the nature of these passive films on select metal substrates. We studied film formation on Cu, 304 stainless steel, and Mo cycled in a 1M LiPF6/ethylene carbonate (EC)-dimethyl carbonate (DMC) solution (1:1 v/v) over a potential range of 3 V to below 0 V. Film formation occurs readily on each of the metals and involves both solvent and salt species. The composition, thickness, and distribution of the films depends strongly on the substrate. The redox processes that occur during film formation and the potential for Li plating are highly dependent on the substrate composition.

The electrolytic conductivity, the lithium cycling efficiency of lithium electrode and the energy density for Li/V2O5(2025) coin-type cell were examined in ternary solvent electrolytes containing LiPF6 and LiClO4 with ethylene carbonate(EC) – 1,2-dimethoxyethane(DME) equimolar binary mixture at 25°C. The solvents applied to EC – DME mixture are dimethyl carbonate(DMC), ethyl methyl carbonate(EMC), diethyl carbonate(DEC), 1,3-dioxolane(DOL), 2,2-bis(trifluoromethyl)-1,3-dioxolane(TFMDOL), 1,3-dimethy1–2-imidazolidinone(DMI) and 1-methyl-2-pyrrolidinone(NMP). The order of decrease of the molar conductivities in ternary solvents electrolytes except DMI and NMP systems is agreement with that of increase in viscosities of the solvents applied to EC – DME binary mixture. The molar conductivities in ternary solvent electrolytes containing DMI and NMP are mainly affected by the dielectric constants rather than viscosities of mixed solvents. The energy density of Li/V2O5(2025) coin-type cell in LiPF6/EC – DME – DOL electrolyte with the highest molar conductivity was 500 Wh kg−1, which is the highest value in every ternary electrolyte. The lithium cycling efficiency(charge - discharge coulombic cycling efficiency of lithium electrode) in EC – DME – EMC, EC – DME – DMI and EC – DME – TFMDOL electrolytes containing LiPF6 is more than 75% at 40 cycle numbers. The lithium electrodeposition on the Ni(working) electrode surface in ternary solvent electrolytes by cyclic voltammetry was observed by atomic force microscopy(AFM) and scanning electron microscope(SEM).

Copolymers of pyrrole with a polyether-substituted pyrrole were tested as cathodes for lithium batteries. The charge and discharge characteristics showed that anion transport was much faster in the copolymer than in polypyrrole. As a result these electrodes store and release much more charge at higher current densities but are similar to polypyrrole at low currents. Pulse and relaxation measurements of the ion diffusion showed that this difference was due to a ten-fold increase in the anion diffusion coefficient.

The electrochemical permeation method was applied to the determination of the diffusion coefficient of Li+ ion (DLi+) in a glassy carbon (GC) plate. The cell was composed of two compartments, which were separated by the GC plate. Li+ ions were inserted electrochemically from one face, and extracted from the other. The flux of the permeated Li+ ions was monitored as an oxidation current at the latter face. The diffusion coefficient was determined by fitting the transient current curve with a theoretical one derived from Fick's law. When the potential was stepped between two potentials in the range of 0 to 0.5 V, transient curves were well fitted with the theoretical one, which gave DLi+ values on the order of 10−8 cm2 s−1. In contrast, when the potential was stepped between two potentials across 0.5 V, significant deviation was observed. The deviation indicated the presence of trap sites as well as diffusion sites for Li+ ions, the former of which is the origin of the irreversible capacity of GC.

The adaptable layer structure of molybdenum trioxide was exploited to insert the amino derivative form of the conductive polymer poly(para-phenylene) (PPPNH2) within the van der Waals gap. Two polymer insertion routes were designed that yield novel PPPNH2-MoO3 materials of different composition. Characterization of these materials using powder XRD, thermal analysis, and FTIR spectroscopy shows insertion of the polymer has occurred. The properties of the nanocomposites for low potential electrochemical lithium insertion were compared to those of the sodium molybdenum bronze using the materials as cathodes in conventional lithium cells. Initial results indicate the specific charge capacity and irreversibility during the first charge are effected by polymer content whereas polarization is not.

Cryptands and crown ethers along with the lithium salt, LiCF3SO2N(CH2)3OCH3 (LiMPSA) were employed to produce a new type of amorphous electrolyte. The key to producing an amorphous phase was the mismatch between the cavity size of the macrocycle and the diameter of the cation. The addition of poly(bis-(2(2-methoxyethoxy)ethoxy)phosphazene) (MEEP) to the amorphous complex, LiMPSA/2.2.2 Cryptand, imparts improved electrochemical and viscoelastic properties. Conversely, when poly(sodium-4-styrenesulfonate) (PS4SS) is added to the amorphous complex, LiMPSA/2.2.2 Cryptand, the product crystallizes. The ionic conductivity of the MEEP rubbery electrolyte is a full order of magnitude higher when compared to the analogous PS4SS doped electrolyte (3.8×10−5 S cm−1 (MEEP), 1.7×10−6 S cm1 (PS4SS) both at 30°K).

The synthesis, characteristics and properties of a PEO-based, dry composite electrolyte are presented and discussed. The major feature of this electrolyte is the high stability towards the lithium metal electrode. This unique property makes the electrolyte quite promising for the development of rechargeable polymer lithium batteries.

The state of the art (SOA) Li-ion cells utilize carbon anodes. However, to improve specific energy, energy density, and safety of cells using carbon anodes, alternative anodes must be developed. Recently, Fuji Film Inc. has suggested the use of tin oxide based anodes in Li-ion cells. It is believed mat cells containing tin oxide based anodes have the potential to meet the need for NASA's future missions. As a result, we conducted an analysis to compare the performance of cells containing carbon anodes and cells containing tin oxide anodes. The comparison between these cells involved the following: 1) reaction mechanisms between Li and carbon and reaction mechanisms between Li and tin oxide, 2) half-cell and full-cell performance characteristics, 3) interactions between the anode materials and electrolyte types and compositions, and 4) the optimization of binder composition.

Electron spin resonance (ESR), magnetic susceptibility, and transport measurements were recently performed on a set of heat-treated polyparaphenylene (PPP)-based carbon samples, which are of significant interest as novel carbon-based anode electrodes in Li-ion batteries. Attention is focused on the evolution of the carbonaceous structures formed at low heat-treatment temperatures (THT) in the regime of 600° C ≤ THT ≤ 800° C, where percolative transport behavior is observed. At the percolation threshold, the coexistence of two spin centers with peak-to-peak Lorentzian linewidths of ΔHpp(300K) = 0.5 and 5.0 G is observed. The relatively high ratio of hydrogen. carbon (H/C) near is believed to influence the ESR results through an unresolved hyperfine interaction. Curie-Weiss temperaures are found from measurements of [Ipp(ΔHpp)2]–1, where Ipp is the peak-to-peak lineheight, yielding results that are in agreement with static susceptibility, χ(T), measurements. At low THT, PPP-based materials exhibit a large amount of disorder and this is evidenced by the high density of localized spins, Nc, which is obtained from a Curie-Weiss fit to χ(T) assuming a spin quantum number of S = ½. A model explaining the microstructure and high electrochemical doping capacity of PPP samples heat-treated to 700° C can be related to Li-ion battery performance.

Disordered polymethacrylonitrile (PMAN) carbon monoliths have been studied as potential tailored electrodes for lithium ion batteries. A combination of electrochemical and surface spectroscopie probes have been used to investigate irreversible loss mechanisms. Voltammetric measurements show that Li intercalates readily into the carbon at potentials IV positive of the reversible Li potential. The coulometric efficiency rises rapidly from 50% for the first potential cycle to greater than 85% for the third cycle, indicating that solvent decomposition is a self-limiting process. Surface film composition and thickness, as measured by x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS), does not vary substantially when compared to more ordered carbon surfaces. Li+ profiles are particularly useful in discriminating between the bound states of Li at the surface of solution permeable PMAN carbons.

In fully-charged carbon materials, we tried to determine the nature of the interaction between Li species and carbon using variable temperature measurements of the Li Knight shift Only one interaction between the Li species and graphite carbon was observed from room temperature to -10°C. However, while only one average interaction between the Li species and the disordered carbon was observed at room temperature, three kinds of interactions were observed at low temperature. These results provide direct evidence for the model which explains why the discharge capacity of the carbon electrode with a disordered structure as an anode can exceed the theoretical capacity of a graphite anode in lithium ion rechargeable batteries.

In order to characterize the heat generation behavior of a lithium-ion cell during charge and discharge, calorimetry has been carried out. The influence of past treatments applied to the cell is examined based on heat generation. The test cell shows a voltage hysteresis during charge and discharge, and the heat generation behavior is related to this hysteresis. A hard carbon is used in the cell as the negative electrode material, and the hysteresis mechanism and heat generation are discussed based on the reactions in the hard carbon electrode.

Entire surfaces of the pitch-based well graphitized and poorly graphitized carbon fibers were covered with an evaporated metallic film of Au, Ag, Sn, or Zn, whose thickness was varied from 100 to 600 Å. Li dope and undope characteristics as the anode of Li-ion secondary battery were compared for the samples with and without evaporated film. Not only high rate charge/discharge characteristics but cycleability have been realized to be improved remarkably for the sample whose surface was covered with a thin metal film.

The local atomic structure of ball-milled carbons was investigated by radial distribution function (RDF) analysis using pulsed time-of-flight neutron diffraction. The results exhibit a gradual loss of long-range order as a function of milling time. Modeling of the elastic structure factors and of the differential correlation functions identified the structure of ball-milled carbons as finite-size graphene fragments whose size decreases continuously with milling time. The large increase in lithium reversible capacity after 20 hours of milling was correlated with the loss of interlayer correlation between graphite flakes, similar to the structure of hard carbons in the “House of Cards” model.

Mesophase pitch-based Carbon Fibers(MCF) have been investigated as anode materials for lithium secondary cells by examining their physical and electrochemical properties. Discharge capacity and initial charge-discharge efficiency of the materials were studied in relation to the heat treatment temperatures of MCF. MCF heat treated at about 3,000° C gave high discharge capacity over 310mAh/g, good efficiency (93 %) and superior current capability of 600mA/g (6mA/cm2). On the other hand, to improve the battery capacity, Boron was doped to the fiber about several % by adding B4C to the pre-carbonized milled fibers and then heat-treated up to 3000°C in Ar. Then heat treated at 2,500°C under vacuum condition to remove remained B 4 C. The structure of Boron-doped fibers was characterized and compared with that of non-doped standard fibers, and also Li ion battery performances are evaluated. The Boron-doped MCF indicated improvement in graphitization and increased discharge capacity as high as 360mAh/g. The voltammograms of both fibers are different from each other. The cell mechanism is discussed based on the unique structure of Boron-doping to the MCF is very effective for the battery performance.

Several types of carbonaceous materials from Superior Graphite Co. were investigated for lithium ion intercalation. These commercially available cokes, graphitized cokes and graphites have a wide range of physical and chemical properties. The coke materials were investigated in propylene carbonate based electrolytes and the graphitic materials were studied in ethylene carbonate / dimethyl solutions to prevent exfoliation. The reversible capacities of disordered cokes are below 230 mAh / g and those for many highly ordered synthetic (artificial) and natural graphites approached 372 mAh / g (LiC6). The irreversible capacity losses vary between 15 to as much as 200 % of reversible capacities for various types of carbon. Heat treated cokes with the average particle size of 10 microns showed marked improvements in reversible capacity for lithium intercalation. The electrochemical characteristics are correlated with data obtained from scanning electron microscopy (SEM), high resolution transmission electron microscopy (TAM), X - ray diffraction (XRD) and BET surface area analysis. The electrochemical performance, availability, cost and manufacturability of these commercial carbons will be discussed.