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Polymer electrolytes, problems, prospects, and promises

Description: Ionically conducting polymer electrolytes have generated, in recent years, wide-spread interest as candidate materials for a number of applications including high energy density and power lithium batteries. In the early 70s the first measurements of ionic conductivity in polyethylene oxide (PEO)-salt complexes were carried out. However, Armand was the first one to realize potential of these complexes (polymer-salt complexes) as practical ionically conducting materials for use as electrolytes in lithium batteries. Subsequent research efforts identified the limitations and constraints of the polymer electrolytes. These limitations include poor ionic conductivity at RT (< 10{sup {minus}8} S/cm), low cation transport number (<0.2) etc. Several different approaches have been made to improving the ionic conductivity of the polymer electrolytes while retaining the flexibility, processibility, ease of handling and relatively low impact on the environment that polymers inherently possess. This paper- reviews evolution of polymer electrolytes from conventional PEO-LiX slat complexes to the more conducting polyphosphazene and copolymers, gelled electrolytes etc. We also review the various chemical approaches including modifying PEO to synthesizing complicated polymer architecture. In addition, we discuss effect of various lithium salts on the conductivity of PEO-based polymers. Charge/discharge and cycle life data of polymer cells containing oxide and chalcogenide cathodes and lithium (Li) anode are reviewed. Finally, future research directions to improve the electrolyte properties are discussed.
Date: July 1, 1995
Creator: Nagasubramanian, G. & Boone, D.
Partner: UNT Libraries Government Documents Department

Linear air-fuel sensor development

Description: The electrochemical zirconia solid electrolyte oxygen sensor, is extensively used for monitoring oxygen concentrations in various fields. They are currently utilized in automobiles to monitor the exhaust gas composition and control the air-to-fuel ratio, thus reducing harmful emission components and improving fuel economy. Zirconia oxygen sensors, are divided into two classes of devices: (1) potentiometric or logarithmic air/fuel sensors; and (2) amperometric or linear air/fuel sensors. The potentiometric sensors are ideally suited to monitor the air-to-fuel ratio close to the complete combustion stoichiometry; a value of about 14.8 to 1 parts by volume. This occurs because the oxygen concentration changes by many orders of magnitude as the air/fuel ratio is varied through the stoichiometric value. However, the potentiometric sensor is not very sensitive to changes in oxygen partial pressure away from the stoichiometric point due to the logarithmic dependence of the output voltage signal on the oxygen partial pressure. It is often advantageous to operate gasoline power piston engines with excess combustion air; this improves fuel economy and reduces hydrocarbon emissions. To maintain stable combustion away from stoichiometry, and enable engines to operate in the excess oxygen (lean burn) region several limiting-current amperometric sensors have been reported. These sensors are based on the electrochemical oxygen ion pumping of a zirconia electrolyte. They typically show reproducible limiting current plateaus with an applied voltage caused by the gas diffusion overpotential at the cathode.
Date: December 14, 1996
Creator: Garzon, F. & Miller, C.
Partner: UNT Libraries Government Documents Department

An investigation of the impedance rise and power fade in high-power, Li-ion cells.

Description: Two different cell chemistries, Gen 1 and Gen 2, were subjected to accelerated aging experiments. In Gen 1 calendar life experiments, useful cell life was strongly affected by temperature and time. Higher temperature accelerated cell performance degradation. The rates of impedance 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 Gen 1 calendar life increase and power fade data follow (time){sup 1/2} kinetics. This may be due to solid electrolyte interface (SEI) layer growth. From the cycle life experiments, the impedance increase data follow (time){sup 1/2} kinetics also, there is an apparent change in overall power fade mechanism, from 3% to 6% {Delta}SOC. Here, the power of time changes to a value less than 0.5 indicating that the power fade mechanism is due to factors more complex than just SEI layer growth. The Gen 2 calendar and cycle life experiments show the effect of cell chemistry on kinetics. The calendar life impedance data follow either ''linear'' or (time){sup 1/2} plus linear kinetics, depending on time and temperature.
Date: July 18, 2002
Creator: Bloom, I.; Jones, S. A.; Battaglia, V. S.; Polzin, E. G.; Henriksen, G. L.; Motloch, C. G. et al.
Partner: UNT Libraries Government Documents Department

Electrical and Electrochemical Performance Characteristics of Small Commercial Li-Ion Cells

Description: Advanced rechargeable lithium-ion batteries are presently being developed and commercialized worldwide for use in consumer electronics, military and space applications. At Sandia National Laboratories we have used different electrochemical techniques such as impedance and charge/discharge at ambient and subambient temperatures to probe the various electrochemical processes that are occurring in Li-ion cell. The purpose of this study is to identify the component that reduces the cell performance at subambient temperatures. Our impedance data suggest that while the variation in the electrolyte resistance between room temperature and {minus}20 C is negligible the anode electrolyte interfacial resistance increases by an order of magnitude in the same temperature regime. We believe that the solid electrolyte interface (SEI) layer on the carbon anode may be responsible for the increase in cell impedance. We have also evaluated the cells in hybrid mode with capacitors. High-current operation in the hybrid mode allowed fill usage of the Li-ion cell capacity at 25 C and showed a factor of 5 improvement in delivered capacity at {minus}20 C.
Date: December 22, 1998
Creator: Ingersoll, D.; Nagasubramanian, G. & Roth, E.P.
Partner: UNT Libraries Government Documents Department

Magnetic resonance and X-ray absorption studies of materials for advanced batteries. Semiannual report, October 15, 1996 - March 15, 1997

Description: Although only 5 months have elapsed since the official award date for this new grant, there is progress to report, including work on Li{sub x}V{sub 6}O{sub 13}, Li{sub x}FeS{sub 2}, polymer electrolytes, and lithiated carbon.
Date: March 1, 1997
Creator: DenBoer, M. L. & Greenbaum, S. G.
Partner: UNT Libraries Government Documents Department

Utilization of sensitivity coefficients to guide the design of a thermal battery

Description: Equations are presented to describe the sensitivity of the temperature field in a heat-conducting body to changes in the volumetric heat source and volumetric heat capacity. These sensitivity equations, along with others not presented, are applied to a thermal battery problem to compute the sensitivity of the temperature field to 19 model input parameters. Sensitivity coefficients, along with assumed standard deviation in these parameters, are used to estimate the uncertainty in the temperature prediction. From the 19 parameters investigated, the battery cell heat source and volumetric heat capacity were clearly identified as being the major contributors to the overall uncertainty in the temperature predictions. The operational life of the thermal battery was shown to be very sensitive to uncertainty in these parameters.
Date: August 1, 1998
Creator: Blackwell, B.F.; Dowding, K.J.; Cochran, R.J. & Dobranich, D.
Partner: UNT Libraries Government Documents Department

Characterization of lithium phosphorous oxynitride thin films

Description: Electrical and electrochemical properties of an amorphous thin-film lithium electrolyte, lithium phosphorous oxynitride (Lipon), have been studied with emphasis on the stability window vs Li metal and the behavior of the Li/Lipon interface. Ion conductivity of Lipon exhibits Arrhenius behavior at {minus}26 to +140 C, with a conductivity of 1.7 {times} 10{sup {minus}6}S/cm at 25 C and an activity energy of 0.50 {plus_minus} 0.01 eV. A stability window of 5.5 V was observed with respect to a Li{sup +}/Li reference, and no detectable reaction or degradation was evident at the Li/Lipon interface upon lithium cycling.
Date: January 1, 1996
Creator: Yu, Xiaohua; Bates, J. B. & Jellison, G. E., Jr.
Partner: UNT Libraries Government Documents Department

PREPARATION AND CHARACTERIZATION OF SOLID ELECTROLYTES: FUEL CELL APPLICATIONS

Description: The intent of this project with Federal Energy Technology Center (FETC)/Morgantown Energy Technology Center (METC) is to develop research infrastructure conductive to Fuel Cell research at Southern University and A and M College, Baton Route. A state of the art research laboratory (James Hall No.123 and No.114) for energy conversion and storage devices was developed during this project duration. The Solid State Ionics laboratory is now fully equipped with materials research instruments: Arbin Battery Cycling and testing (8 channel) unit, Electrochemical Analyzer (EG and G PAR Model 273 and Solartron AC impedance analyzer), Fuel Cell test station (Globe Tech), Differential Scanning Calorimeter (DSC-10), Thermogravimetric Analyzer (TGA), Scanning Tunneling Microscope (STM), UV-VIS-NIR Absorption Spectrometer, Fluorescence Spectrometer, FT-IR Spectrometer, Extended X-ray Absorption Fine Structure (EXAFS) measurement capability at Center for Advanced Microstructure and Devices (CAMD- a multimillion dollar DOE facility), Glove Box, gas hood chamber, high temperature furnaces, hydraulic press and several high performance computers. IN particular, a high temperature furnace (Thermodyne 6000 furnace) and a high temperature oven were acquired through this project funds. The PI Dr. R Bobba has acquired additional funds from federal agencies include NSF-Academic Research Infrastructure program and other DOE sites. They have extensively used the multimillion dollar DOE facility ''Center'' for Advanced Microstructures and Devices (CAMD) for electrochemical research. The students were heavily involved in the experimental EXAFS measurements and made use of their DCM beamline for EXAFS research. The primary objective was to provide hands on experience to the selected African American undergraduate and graduate students in experimental energy research.The goal was to develop research skills and involve them in the Preparation and Characterization of Solid Electrolytes. Ionically conducting solid electrolytes are successfully used for battery, fuel cell and sensor applications.
Date: December 31, 1997
Creator: Bobba, Rambabu; Hormes, Josef; Wang, T.; Baker, Jaymes A.; Prier, Donald G.; Rockwood, Tommy et al.
Partner: UNT Libraries Government Documents Department

Study of multicomponent diffusion and transport phenomena. Technical report, July 1, 1984--June 30, 1995

Description: This progress report summarizes a project to treat the diffusion and transport phenomena in multicomponent systems from an atomistic point of view mainly by means of a kinetic method based on the Cluster Variation Method (CVM)-Path Probability Method (PPM) formalism. As is well known, the CVM has established itself as one of the most systematic methods of statistical thermodynamics, and macroscopic phenomena treated by thermodynamics can thus be investigated atomistically in great detail. The author describes work in a number of different applications, summarized here by the section titles: percolation threshold in electronic conduction {beta}-alumina type solid electrolytes; mixed alkali effect; chemical diffusion problem; soft lattice gas model and rigid lattice gas model; diffusion in semiconductors; diffusion in ordered alloys; kinetics of relaxation process of hopping ionic conduction.
Date: September 1, 1995
Creator: Sato, Hiroshi
Partner: UNT Libraries Government Documents Department

FIRST PRINCIPLES MODELING OF YTTRIUM-DOPED BAZRO3 SOLID ELECTROLYTE

Description: Ab initio Quantum mechanics calculations of the equation of states for BaZrO{sub 3} have been performed and the bulk modulus has been obtained. The value of the modulus is in good agreement with reported experimental values. Equilibrium proton positions in Y-doped BaZrO{sub 3} with dopant concentrations from 12.5 to 50% were investigated. Initial rough estimates of the transition barriers have been made. Our results suggest that the proton migration pathway may involve secondary minima with two maxima (symmetric with respect to the center of the path). In the next phase of this project the results of our quantum mechanical calculations will be used to develop a new Reactive Force Field (ReaxFF) based on first principles. This Reactive Force Field will be used for much molecular dynamics simulations or much larger systems to investigate proton migration in bulk and surface regions of fuel cells.
Date: April 30, 2003
Creator: Dorso, Claudio O.; Merinov, Boris V. & III, William A. Goddard
Partner: UNT Libraries Government Documents Department

Electric field-induced deformation of polyelectrolyte gels

Description: Water-swollen polyelectrolyte gels deform in an electric field. We observed that the sign and magnitude of the deformation is dependent on the nature of the salt bath in which the gel is immersed and electrocuted. These results are compatible with a deformation mechanism based upon creation of ion density gradients by the field which, in turn, creates osmotic pressure gradients within the gel. A consistent interpretation results only if gel mobility is allowed as well as free ion diffusion and migration.
Date: August 1, 1995
Creator: Adolf, D. & Hance, B.G.
Partner: UNT Libraries Government Documents Department

Solid Electrolyte/Electrode Interfaces: Atomistic Behavior Analyzed Via UHV-AFM, Surface Spectroscopies, and Computer Simulations Computational and Experimental Studies of the Cathode/Electrolyte Interface in Oxide Thin Film Batteries

Description: The goals of the research were to understand the structural, dynamic, and chemical properties of solid electrolyte surfaces and the cathode/electrolyte interface at an atomistic and nanometer level using both computational and experimental techniques.
Date: March 21, 2012
Creator: Garofalini, Stephen H.
Partner: UNT Libraries Government Documents Department

Characterization of the SEI on a carbon film electrode by combinedEQCM and spectroscopic ellipsometry

Description: The electrochemical quartz crystal microbalance (EQCM) andcyclic voltammetry have been applied simultaneously to characterizeelectron-beam deposited carbon film electrodes in LiClO4 orLiPF6-containing mixed electrolytes of ethylene carbonate (EC) anddimethyl carbonate (DMC). The structure of the carbon electrode was foundto be amorphous/disordered using Raman spectroscopy. Cyclic voltammetryin LiClO4 / EC+DMC demonstrated features typical of Liintercalation/deintercalation into/from the disordered carbon electrode,and EQCM showed a corresponding mass increase/decrease. Contrary to thecase of LiClO4 / EC+DMC electrolyte, LiPF6/EC+DMC electrolyte showed noLi deintercalation out of the thin-film carbon electrode. Combined EQCMand spectroscopic ellipsometry data were compared, and the solidelectrolyte interphase density after the first cycle in LiClO4 /EC+DMCwas estimated to be 1.3 g/cm3.
Date: January 1, 2002
Creator: Kwon, Kyungjung; Kong, Fanping; McLarnon, Frank & Evans, James W.
Partner: UNT Libraries Government Documents Department

Electrochemical storage cell containing a substituted anisole or di-anisole redox shuttle additive for overcharge protection and suitable for use in liquid organic and solid polymer electrolytes

Description: A electrochemical cell is described comprising an anode, a cathode, a solid polymer electrolyte; and a redox shuttle additive to protect the cell against overcharging and a redox shuttle additive to protect the cell against overcharging selected from the group consisting of: (a) a substituted anisole having the general formula shown in a figure (in an uncharged state): where R{sub 1} is selected from the group consisting of H, 0CH{sub 3}, OCH{sub 2}CH{sub 3}, and OCH{sub 2}phenyl, and R{sub 2} is selected from the group consisting of OCH{sub 3}, OCH{sub 2}CH{sub 3}, OCH{sub 2} phenyl, and O{sup {minus}}Li{sup +}; and (b) a di-anisole compound having the general formula shown in a second figure (in an uncharged state): where R is selected from the group consisting of -OCH{sup 3} and -CH{sub 3}, m is either 1 or 0, n is either 1 or 0, and X is selected from the group consisting of -OCH{sub 3} (methoxy) or its lithium salt -O{sup {minus}}Li{sup +}. The lithium salt of the di-anisole is the preferred form of the redox shuttle additive because the shuttle anion will then initially have a single negative charge, it loses two electrons when it is oxidized at the cathode, and then moves toward the anode as a single positively charged species where it is then reduced to a single negatively charged species by gaining back two electrons.
Date: March 1998
Creator: Kerr, John B. & Tian, Minmin
Partner: UNT Libraries Government Documents Department

Plasma Synthesis of Lithium Based Intercalation Powders for Solid Polymer Electrolyte Batteries

Description: The invention relates to a process for preparing lithium intercalation compounds by plasma reaction comprising the steps of: forming a feed solution by mixing lithium nitrate or lithium hydroxide or lithium oxide and the required metal nitrate or metal hydroxide or metal oxide and between 10-50% alcohol by weight; mixing the feed solution with O2 gas wherein the O2 gas atomizes the feed solution into fine reactant droplets, inserting the atomized feed solution into a plasma reactor to form an intercalation powder; and if desired, heating the resulting powder to form a very pure single phase product.
Date: January 4, 2005
Creator: Kong, Peter C.; Pink, Robert J. & Nelson, Lee O.
Partner: UNT Libraries Government Documents Department

Rechargeable thin-film lithium batteries

Description: Rechargeable thin-film batteries consisting of lithium metal anodes, an amorphous inorganic electrolyte, and cathodes of lithium intercalation compounds have recently been developed. The batteries, which are typically less than 6-{mu}m thick, can be fabricated to any specified size, large or small, onto a variety of substrates including ceramics, semiconductors, and plastics. The cells that have been investigated include Li-TiS{sub 2}, Li-V{sub 2}O{sub 5}, and Li-Li{sub x}Mn{sub 2}O{sub 4}, with open circuit voltages at full charge of about 2.5, 3.6, and 4.2, respectively. The development of these batteries would not have been possible without the discovery of a new thin-film lithium electrolyte, lithium phosphorus oxynitride, that is stable in contact with metallic lithium at these potentials. Deposited by rf magnetron sputtering of Li{sub 3}PO{sub 4} in N{sub 2}, this material has a typical composition of Li{sub 2.9}PO{sub 3.3}N{sub 0.46} and a conductivity at 25{degrees}C of 2 {mu}S/cm. The maximum practical current density obtained from the thin-film cells is limited to about 100 {mu}A/cm{sup 2} due to a low diffusivity of Li{sup +} ions in the cathodes. In this work, the authors present a short review of their work on rechargeable thin-film lithium batteries.
Date: August 1, 1993
Creator: Bates, J. B.; Gruzalski, G. R.; Dudney, N. J.; Luck, C. F. & Yu, Xiaohua
Partner: UNT Libraries Government Documents Department

Polymer electrolytes for a rechargeable li-Ion battery

Description: Lithium-ion polymer electrolyte battery technology is attractive for many consumer and military applications. A Li{sub x}C/Li{sub y}Mn{sub 2}O{sub 4} battery system incorporating a polymer electrolyte separator base on novel Li-imide salts is being developed under sponsorship of US Army Research Laboratory (Fort Monmouth NJ). This paper reports on work currently in progress on synthesis of Li-imide salts, polymer electrolyte films incorporating these salts, and development of electrodes and cells. A number of Li salts have been synthesized and characterized. These salts appear to have good voltaic stability. PVDF polymer gel electrolytes based on these salts have exhibited conductivities in the range 10{sup -4} to 10{sub -3} S/cm.
Date: October 1, 1996
Creator: Argade, S.D.; Saraswat, A.K.; Rao, B.M.L.; Lee, H.S.; Xiang, C.L. & McBreen, J.
Partner: UNT Libraries Government Documents Department

Neutron and X-ray scattering experiments on lithium polymer electrolytes

Description: The authors are carrying out structural, dynamical and transport measurements of lithium polymer electrolytes, in order to provide information needed to improve the performance of secondary lithium battery systems. Microscopically, they behave as liquids under conditions of practical interest. Development of batteries based on these materials has focused on rechargeable systems with intercalation/insertion cathodes and lithium or lithium-containing materials as anodes. The electrolytes are generally composites of a polyethylene oxide (PEO) or another modified polyether and a salt such as LiClO{sub 4}, LiAsF{sub 6} or LiCF{sub 3}SO{sub 3}. Research on electrolyte materials for lithium batteries has focused on synthesis, characterization, and development of practical devices. Some characterization work has been carried out to determine the properties of the ion polymer and ion interactions, principally through spectroscopic, thermodynamic and transport measurements. It is generally believed that ionic conduction is a property of the amorphous phase of these materials. It is also believed that ion association, ion polymer interactions and local relaxations of the polymer strongly influence the ionic mobility. However, much about the nature of the charge carriers, the ion association processes, and the ion polymer interactions and the role that these play in the ionic conductivity of the electrolytes remains unknown. The authors have initiated a combined experimental and theoretical study of the structure and dynamics of lithium polymer electrolytes. They plan to investigate the effects of the polymer host on ion solvation and the attendant effects of ion pairing, which affect the ionic transport in these systems.
Date: September 1, 1997
Creator: Saboungi, M.L. & Price, D.L.
Partner: UNT Libraries Government Documents Department

Instability of Polyvinylidene Fluoride-Based Polymeric Binder in Lithium-Ion Cells: Final Report

Description: Thermal instabilities were identified in SONY-type lithium-ion cells and correlated with interactions of cell constituents and reaction products. Three temperature regions of interaction were identified and associated with the state of charge (degree of Li intercalation) of the cell. Anodes were shown to undergo exothermic reactions as low as 100 degree C involving the solid electrolyte interface (SEI) layer and the LiPF(6) salt in the electrolyte (EC-PC:DEC/IM LiPF(6)). These reactions could account for the thermal runaway observed in these cells beginning at 100 degree C. Exothermic reactions were also observed in the 200 degree C to 300 degree C region between the intercalated lithium anodes, the LiPF(6) salt, and the PVDF. These reactions were followed by a high-temperature reaction region, 300 degree C to 400 degree C, also involving the PVDF binder and the intercalated lithium anodes. The solvent was not directly involved in these reactions but served as a moderator and transport medium. Cathode exothermic reactions with the PVDF binder were observed above 200 degree C and increased with the state of charge (decreasing Li content). The stability of the PVDF binder as a function of electrochemical cycling was studied using FTIR. The infrared spectra from the extracts of both electrodes indicate that PVDF is chemically modified by exposure to the lithium cell electrolyte (as well as electrochemical cycling) in conjunction with NMP extraction. Preconditioning of PVDF to dehydrohalogenation, which may be occurring by reaction with LiPf(6), makes the PVDF susceptible to attack by a range of nucleophiles.
Date: May 1, 1999
Creator: Garcia, M.; Nagasubramanian, G.; Tallant, D.R. & Roth, E.P.
Partner: UNT Libraries Government Documents Department

Ion-Conducting Polymer Films as Chemical Sensors

Description: Solid Polymer Electrolytes (SPE) are widely used in batteries and fuel cells because of the high ionic conductivity that can be achieved at room temperature. The ions are usually Li or protons, although other ions can be shown to conduct in these polymer films. There has been very little work on using these films as chemical sensors. We have found that thin films of polymers like polyethyleneoxide (PEO) are very sensitive to low concentrations of volatile organic compounds (VOCS) like common solvents. We will present impedance spectroscopy of PEO films in the frequency range 0.01 Hz to 1 MHz for different concentrations of VOCS. We find that the measurement frequency is important for distinguishing ionic conductivity from the double layer capacitance and parasitic capacitances.
Date: May 3, 1999
Creator: Hughes, R.C.; Patel, S.V.; Pfeifer, K.B. & Yelton, W.G.
Partner: UNT Libraries Government Documents Department

Characteristics and Mechanisms in Ion-Conducting Polymer Films as Chemical Sensors

Description: Solid Polymer Electrolytes (SPE) are widely used in batteries and fuel cells because of the high ionic conductivity that can be achieved at room temperature. The ions are usually Li or protons, although other ions can be shown to conduct in these polymer films. There has been very little published work on SPE films used as chemical sensors. The authors have found that thin films of polymers like polyethylene oxide (PEO) are very sensitive to low concentrations of volatile organic compounds (VOCs) such as common solvents. Evidence of a new sensing mechanism involving the percolation of ions through narrow channels of amorphous polymer is presented. They present impedance spectroscopy of PEO films in the frequency range 0.0001 Hz to 1 MHz for different concentrations of VOCs and relative humidity. They find that the measurement frequency is important for distinguishing ionic conductivity from the double layer capacitance and the parasitic capacitance.
Date: July 12, 2000
Creator: Hughes, Robert C.; Yelton, William G.; Pfeifer, Kent B. & Patel, Sanjay V.
Partner: UNT Libraries Government Documents Department

Application of ionic and electronic conducting ceramics in solid oxide fuel cells

Description: Solid oxide fuel cells (SOFCs) offer a pollution-free technology to electrochemically generate electricity at high efficiencies. These fuel cells consist of an oxygen ion conducting electrolyte, electronic or mixed electronic and ionic conducting electrodes, and an electronic conducting interconnection. This paper reviews the ceramic materials used for the different cell components, and discusses the performance of cells fabricated using these materials. The paper also discusses the materials and processing studies that are underway to reduce the cell cost, and summarizes the recently built power generation systems that employed state-of-the-art SOFCs.
Date: December 1, 1997
Creator: Singhal, S.C.
Partner: UNT Libraries Government Documents Department

Thermal stability of electrodes in Lithium-ion cells

Description: Differential scanning calorimetry (DSC) analysis was used to identify thermal reactions in Sony-type lithium-ion cells and to correlate these reactions with interactions of cell constituents and reaction products. An electrochemical half-cell was used to cycle the anode and cathode materials and to set the state-of-charge (SOC). Three temperature regions of interaction were identified and associated with the SOC (degree of Li intercalation) of the cell. Anodes were shown to undergo exothermic reactions as low as 80 C involving decomposition of the solid electrolyte interphase (SEI) layer. The LiPF{sub 6} salt in the electrolyte (EC:PC:DEC/1M LiPF{sub 6}) was seen to play an essential role in this reaction. DSC analysis of the anodes from disassembled Sony cells showed similar behavior to the half-cell anodes with a strong exotherm beginning in the 80 C--90 C range. Exothermic reactions were also observed in the 200 C--300 C region between the intercalated lithium anodes, the LiPF{sub 6} salt, and the PVDF binder. These reactions were followed by a high-temperature reaction region, 300 C--400 C, also involving the PVDF binder and the intercalated lithium anodes. Cathode exothermic reactions with the PVDF binder were observed above 200 C and increased with the SOC (decreasing Li content in the cathode). No thermal reactions were seen at lower temperatures suggesting that thermal runaway reactions in this type of cell are initiated at the anode. An Accelerating Rate Calorimeter (ARC) was used to perform measurements of thermal runaway on commercial Sony Li-ion cells as a function of SOC. The cells showed sustained thermal output as low as 80 C in agreement with the DSC observations of anode materials but the heating rate was strongly dependent on the SOC.
Date: February 7, 2000
Creator: ROTH,EMANUEL P. & NAGASUBRAMANIAN,GANESAN
Partner: UNT Libraries Government Documents Department