Bio: Werner Weppner is an academic researcher from University of Kiel. The author has contributed to research in topics: Lithium & Ionic conductivity. The author has an hindex of 45, co-authored 193 publications receiving 12168 citations. Previous affiliations of Werner Weppner include Max Planck Society & Stanford University.
Papers published on a yearly basis
TL;DR: In this paper, an electrochemical galvanostatic intermittent titration technique (GITT) is described which combines both transient and steady-state measurements to obtain kinetic properties of solid mixed-conducting electrodes, as well as thermodynamic data.
Abstract: An electrochemical galvanostatic intermittent titration technique (GITT) is described which combines both transient and steady‐state measurements to obtain kinetic properties of solid mixed‐conducting electrodes, as well as thermodynamic data. The derivation of quantities such as the chemical and component diffusion coefficients, the partial conductivity, the mobility, the thermodynamic enhancement factor, and the parabolic rate constant as a function of stoichiometry is presented. A description of the factors governing the equilibration of composition gradients in such phases is included. The technique is applied to the determination of the kinetic parameters of the compound which has a narrow composition range. For the chemical diffusion coefficient is at 360°C. This value is quite high, due to a large thermodynamic enhancement factor of . The lithium component diffusion coefficient is comparatively small at this composition, . The partial conductivity and electrical mobility of lithium are and , respectively, at the same stoichiometry and temperature. Because of the very large values of the chemical diffusion coefficient and the fact that 3 moles of lithium can react per mole of antimony, this system may be of interest for use in new types of secondary batteries.
TL;DR: In this paper, compositional variations of the thermodynamic and mass transport properties of the β phase in the lithium-aluminum system have been investigated over the temperature range from 415° to 600°C.
Abstract: The compositional variations of the thermodynamic and mass transport properties of the β phase in the lithium‐aluminum system have been investigated over the temperature range from 415° to 600°C. At 415°C, the emf of the single phase lies between 300 and 70 mV relative to pure Li and this corresponds to a Li activity increasing from 0.0063 to 0.31 over the phase stability range from 46.8 to 55.0 atomic percent Li. At the ideal stoichiometry, the standard Gibbs free energy of formation of is −29.2 kJ/mole at 415°C and the corresponding enthalpy and entropy are −43.3 kJ/mole and −20.6 J/mole °K, respectively. Two different electrochemical transient techniques have been used to measure the chemical diffusion coefficient in as a function of the stoichiometry; the experimental results obtained are in good agreement. On the lithium deficit side of the ideal stoichiometry, the chemical diffusion coefficient increases with decreasing Li concentration, becoming about 10−4 cm2/sec near the phase boundary. On the other hand, it is composition independent on the Li excess side of varying with temperature from at 415°C to at 600°C.
TL;DR: In this paper, Li3xLa(2/3)-x□(1/3)2xTiO3 (0 < x < 0.16) and its related structure materials, the x ≈ 0.1 member exhibits conductivity of 1 × 10-3 S/cm at room temperature with an activation energy of 0.40 eV.
Abstract: To date, the highest bulk lithium ion-conducting solid electrolyte is the perovskite (ABO3)-type lithium lanthanum titanate (LLT) Li3xLa(2/3)-x□(1/3)-2xTiO3 (0 < x < 0.16) and its related structure materials. The x ≈ 0.1 member exhibits conductivity of 1 × 10-3 S/cm at room temperature with an activation energy of 0.40 eV. The conductivity is comparable to that of commonly used polymer/liquid electrolytes. The ionic conductivity of LLT mainly depends on the size of the A-site ion cation (e.g., La or rare earth, alkali or alkaline earth), lithium and vacancy concentration, and the nature of the B−O bond. For example, replacement of La by other rare earth elements with smaller ionic radii than that of La decreases the lithium ion conductivity, while partial substitution of La by Sr (larger ionic radii than that of La) slightly increases the lithium ion conductivity. The high lithium ion conductivity of LLT is considered to be due to the large concentration of A-site vacancies, and the motion of lithium by a...
TL;DR: Titanium dioxide is the most investigated single-crystalline system in the surface science of metal oxides, and the literature on rutile (1.1) and anatase surfaces is reviewed in this paper.
Abstract: Titanium dioxide is the most investigated single-crystalline system in the surface science of metal oxides, and the literature on rutile (1 1 0), (1 0 0), (0 0 1), and anatase surfaces is reviewed This paper starts with a summary of the wide variety of technical fields where TiO 2 is of importance The bulk structure and bulk defects (as far as relevant to the surface properties) are briefly reviewed Rules to predict stable oxide surfaces are exemplified on rutile (1 1 0) The surface structure of rutile (1 1 0) is discussed in some detail Theoretically predicted and experimentally determined relaxations of surface geometries are compared, and defects (step edge orientations, point and line defects, impurities, surface manifestations of crystallographic shear planes—CSPs) are discussed, as well as the image contrast in scanning tunneling microscopy (STM) The controversy about the correct model for the (1×2) reconstruction appears to be settled Different surface preparation methods, such as reoxidation of reduced crystals, can cause a drastic effect on surface geometries and morphology, and recommendations for preparing different TiO 2 (1 1 0) surfaces are given The structure of the TiO 2 (1 0 0)-(1×1) surface is discussed and the proposed models for the (1×3) reconstruction are critically reviewed Very recent results on anatase (1 0 0) and (1 0 1) surfaces are included The electronic structure of stoichiometric TiO 2 surfaces is now well understood Surface defects can be detected with a variety of surface spectroscopies The vibrational structure is dominated by strong Fuchs–Kliewer phonons, and high-resolution electron energy loss spectra often need to be deconvoluted in order to render useful information about adsorbed molecules The growth of metals (Li, Na, K, Cs, Ca, Al, Ti, V, Nb, Cr, Mo, Mn, Fe, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au) as well as some metal oxides on TiO 2 is reviewed The tendency to ‘wet’ the overlayer, the growth morphology, the epitaxial relationship, and the strength of the interfacial oxidation/reduction reaction all follow clear trends across the periodic table, with the reactivity of the overlayer metal towards oxygen being the most decisive factor Alkali atoms form ordered superstructures at low coverages Recent progress in understanding the surface structure of metals in the ‘strong-metal support interaction’ (SMSI) state is summarized Literature is reviewed on the adsorption and reaction of a wide variety of inorganic molecules (H 2 , O 2 , H 2 O, CO, CO 2 , N 2 , NH 3 , NO x , sulfur- and halogen-containing molecules, rare gases) as well as organic molecules (carboxylic acids, alcohols, aldehydes and ketones, alkynes, pyridine and its derivates, silanes, methyl halides) The application of TiO 2 -based systems in photo-active devices is discussed, and the results on UHV-based photocatalytic studies are summarized The review ends with a brief conclusion and outlook of TiO 2 -based surface science for the future
TL;DR: The theoretical charge capacity for silicon nanowire battery electrodes is achieved and maintained a discharge capacity close to 75% of this maximum, with little fading during cycling.
Abstract: There is great interest in developing rechargeable lithium batteries with higher energy capacity and longer cycle life for applications in portable electronic devices, electric vehicles and implantable medical devices. Silicon is an attractive anode material for lithium batteries because it has a low discharge potential and the highest known theoretical charge capacity (4,200 mAh g(-1); ref. 2). Although this is more than ten times higher than existing graphite anodes and much larger than various nitride and oxide materials, silicon anodes have limited applications because silicon's volume changes by 400% upon insertion and extraction of lithium which results in pulverization and capacity fading. Here, we show that silicon nanowire battery electrodes circumvent these issues as they can accommodate large strain without pulverization, provide good electronic contact and conduction, and display short lithium insertion distances. We achieved the theoretical charge capacity for silicon anodes and maintained a discharge capacity close to 75% of this maximum, with little fading during cycling.
04 Apr 2005
Abstract: Preface. Preface to the First Edition. Contributors. Contributors to the First Edition. Chapter 1. Fundamentals of Impedance Spectroscopy (J.Ross Macdonald and William B. Johnson). 1.1. Background, Basic Definitions, and History. 1.1.1 The Importance of Interfaces. 1.1.2 The Basic Impedance Spectroscopy Experiment. 1.1.3 Response to a Small-Signal Stimulus in the Frequency Domain. 1.1.4 Impedance-Related Functions. 1.1.5 Early History. 1.2. Advantages and Limitations. 1.2.1 Differences Between Solid State and Aqueous Electrochemistry. 1.3. Elementary Analysis of Impedance Spectra. 1.3.1 Physical Models for Equivalent Circuit Elements. 1.3.2 Simple RC Circuits. 1.3.3 Analysis of Single Impedance Arcs. 1.4. Selected Applications of IS. Chapter 2. Theory (Ian D. Raistrick, Donald R. Franceschetti, and J. Ross Macdonald). 2.1. The Electrical Analogs of Physical and Chemical Processes. 2.1.1 Introduction. 2.1.2 The Electrical Properties of Bulk Homogeneous Phases. 22.214.171.124 Introduction. 126.96.36.199 Dielectric Relaxation in Materials with a Single Time Constant. 188.8.131.52 Distributions of Relaxation Times. 184.108.40.206 Conductivity and Diffusion in Electrolytes. 220.127.116.11 Conductivity and Diffusion-a Statistical Description. 18.104.22.168 Migration in the Absence of Concentration Gradients. 22.214.171.124 Transport in Disordered Media. 2.1.3 Mass and Charge Transport in the Presence of Concentration Gradients. 126.96.36.199 Diffusion. 188.8.131.52 Mixed Electronic-Ionic Conductors. 184.108.40.206 Concentration Polarization. 2.1.4 Interfaces and Boundary Conditions. 220.127.116.11 Reversible and Irreversible Interfaces. 18.104.22.168 Polarizable Electrodes. 22.214.171.124 Adsorption at the Electrode-Electrolyte Interface. 126.96.36.199 Charge Transfer at the Electrode-Electrolyte Interface. 2.1.5 Grain Boundary Effects. 2.1.6 Current Distribution, Porous and Rough Electrodes- the Effect of Geometry. 188.8.131.52 Current Distribution Problems. 184.108.40.206 Rough and Porous Electrodes. 2.2. Physical and Electrochemical Models. 2.2.1 The Modeling of Electrochemical Systems. 2.2.2 Equivalent Circuits. 220.127.116.11 Unification of Immitance Responses. 18.104.22.168 Distributed Circuit Elements. 22.214.171.124 Ambiguous Circuits. 2.2.3 Modeling Results. 126.96.36.199 Introduction. 188.8.131.52 Supported Situations. 184.108.40.206 Unsupported Situations: Theoretical Models. 220.127.116.11 Unsupported Situations: Equivalent Network Models. 18.104.22.168 Unsupported Situations: Empirical and Semiempirical Models. Chapter 3. Measuring Techniques and Data Analysis. 3.1. Impedance Measurement Techniques (Michael C. H. McKubre and Digby D. Macdonald). 3.1.1 Introduction. 3.1.2 Frequency Domain Methods. 22.214.171.124 Audio Frequency Bridges. 126.96.36.199 Transformer Ratio Arm Bridges. 188.8.131.52 Berberian-Cole Bridge. 184.108.40.206 Considerations of Potentiostatic Control. 220.127.116.11 Oscilloscopic Methods for Direct Measurement. 18.104.22.168 Phase-Sensitive Detection for Direct Measurement. 22.214.171.124 Automated Frequency Response Analysis. 126.96.36.199 Automated Impedance Analyzers. 188.8.131.52 The Use of Kramers-Kronig Transforms. 184.108.40.206 Spectrum Analyzers. 3.1.3 Time Domain Methods. 220.127.116.11 Introduction. 18.104.22.168 Analog-to-Digital (A/D) Conversion. 22.214.171.124 Computer Interfacing. 126.96.36.199 Digital Signal Processing. 3.1.4 Conclusions. 3.2. Commercially Available Impedance Measurement Systems (Brian Sayers). 3.2.1 Electrochemical Impedance Measurement Systems. 188.8.131.52 System Configuration. 184.108.40.206 Why Use a Potentiostat? 220.127.116.11 Measurements Using 2, 3 or 4-Terminal Techniques. 18.104.22.168 Measurement Resolution and Accuracy. 22.214.171.124 Single Sine and FFT Measurement Techniques. 126.96.36.199 Multielectrode Techniques. 188.8.131.52 Effects of Connections and Input Impedance. 184.108.40.206 Verification of Measurement Performance. 220.127.116.11 Floating Measurement Techniques. 18.104.22.168 Multichannel Techniques. 3.2.2 Materials Impedance Measurement Systems. 22.214.171.124 System Configuration. 126.96.36.199 Measurement of Low Impedance Materials. 188.8.131.52 Measurement of High Impedance Materials. 184.108.40.206 Reference Techniques. 220.127.116.11 Normalization Techniques. 18.104.22.168 High Voltage Measurement Techniques. 22.214.171.124 Temperature Control. 126.96.36.199 Sample Holder Considerations. 3.3. Data Analysis (J. Ross Macdonald). 3.3.1 Data Presentation and Adjustment. 188.8.131.52 Previous Approaches. 184.108.40.206 Three-Dimensional Perspective Plotting. 220.127.116.11 Treatment of Anomalies. 3.3.2 Data Analysis Methods. 18.104.22.168 Simple Methods. 22.214.171.124 Complex Nonlinear Least Squares. 126.96.36.199 Weighting. 188.8.131.52 Which Impedance-Related Function to Fit? 184.108.40.206 The Question of "What to Fit" Revisited. 220.127.116.11 Deconvolution Approaches. 18.104.22.168 Examples of CNLS Fitting. 22.214.171.124 Summary and Simple Characterization Example. Chapter 4. Applications of Impedance Spectroscopy. 4.1. Characterization of Materials (N. Bonanos, B. C. H. Steele, and E. P. Butler). 4.1.1 Microstructural Models for Impedance Spectra of Materials. 126.96.36.199 Introduction. 188.8.131.52 Layer Models. 184.108.40.206 Effective Medium Models. 220.127.116.11 Modeling of Composite Electrodes. 4.1.2 Experimental Techniques. 18.104.22.168 Introduction. 22.214.171.124 Measurement Systems. 126.96.36.199 Sample Preparation-Electrodes. 188.8.131.52 Problems Associated With the Measurement of Electrode Properties. 4.1.3 Interpretation of the Impedance Spectra of Ionic Conductors and Interfaces. 184.108.40.206 Introduction. 220.127.116.11 Characterization of Grain Boundaries by IS. 18.104.22.168 Characterization of Two-Phase Dispersions by IS. 22.214.171.124 Impedance Spectra of Unusual Two-phase Systems. 126.96.36.199 Impedance Spectra of Composite Electrodes. 188.8.131.52 Closing Remarks. 4.2. Characterization of the Electrical Response of High Resistivity Ionic and Dielectric Solid Materials by Immittance Spectroscopy (J. Ross Macdonald). 4.2.1 Introduction. 4.2.2 Types of Dispersive Response Models: Strengths and Weaknesses. 184.108.40.206 Overview. 220.127.116.11 Variable-slope Models. 18.104.22.168 Composite Models. 4.2.3 Illustration of Typical Data Fitting Results for an Ionic Conductor. 4.3. Solid State Devices (William B. Johnson and Wayne L. Worrell). 4.3.1 Electrolyte-Insulator-Semiconductor (EIS) Sensors. 4.3.2 Solid Electrolyte Chemical Sensors. 4.3.3 Photoelectrochemical Solar Cells. 4.3.4 Impedance Response of Electrochromic Materials and Devices (Gunnar A. Niklasson, Anna Karin Johsson, and Maria Stromme). 22.214.171.124 Introduction. 126.96.36.199 Materials. 188.8.131.52 Experimental Techniques. 184.108.40.206 Experimental Results on Single Materials. 220.127.116.11 Experimental Results on Electrochromic Devices. 18.104.22.168 Conclusions and Outlook. 4.3.5 Time-Resolved Photocurrent Generation (Albert Goossens). 22.214.171.124 Introduction-Semiconductors. 126.96.36.199 Steady-State Photocurrents. 188.8.131.52 Time-of-Flight. 184.108.40.206 Intensity-Modulated Photocurrent Spectroscopy. 220.127.116.11 Final Remarks. 4.4. Corrosion of Materials (Digby D. Macdonald and Michael C. H. McKubre). 4.4.1 Introduction. 4.4.2 Fundamentals. 4.4.3 Measurement of Corrosion Rate. 4.4.4 Harmonic Analysis. 4.4.5 Kramer-Kronig Transforms. 4.4.6 Corrosion Mechanisms. 18.104.22.168 Active Dissolution. 22.214.171.124 Active-Passive Transition. 126.96.36.199 The Passive State. 4.4.7 Point Defect Model of the Passive State (Digby D. Macdonald). 188.8.131.52 Introduction. 184.108.40.206 Point Defect Model. 220.127.116.11 Electrochemical Impedance Spectroscopy. 18.104.22.168 Bilayer Passive Films. 4.4.8 Equivalent Circuit Analysis (Digby D. Macdonald and Michael C. H. McKubre). 22.214.171.124 Coatings. 4.4.9 Other Impedance Techniques. 126.96.36.199 Electrochemical Hydrodynamic Impedance (EHI). 188.8.131.52 Fracture Transfer Function (FTF). 184.108.40.206 Electrochemical Mechanical Impedance. 4.5. Electrochemical Power Sources. 4.5.1 Special Aspects of Impedance Modeling of Power Sources (Evgenij Barsoukov). 220.127.116.11 Intrinsic Relation Between Impedance Properties and Power Sources Performance. 18.104.22.168 Linear Time-Domain Modeling Based on Impedance Models, Laplace Transform. 22.214.171.124 Expressing Model Parameters in Electrical Terms, Limiting Resistances and Capacitances of Distributed Elements. 126.96.36.199 Discretization of Distributed Elements, Augmenting Equivalent Circuits. 188.8.131.52 Nonlinear Time-Domain Modeling of Power Sources Based on Impedance Models. 184.108.40.206 Special Kinds of Impedance Measurement Possible with Power Sources-Passive Load Excitation and Load Interrupt. 4.5.2 Batteries (Evgenij Barsoukov). 220.127.116.11 Generic Approach to Battery Impedance Modeling. 18.104.22.168 Lead Acid Batteries. 22.214.171.124 Nickel Cadmium Batteries. 126.96.36.199 Nickel Metal-hydride Batteries. 188.8.131.52 Li-ion Batteries. 4.5.3 Impedance Behavior of Electrochemical Supercapacitors and Porous Electrodes (Brian E. Conway). 184.108.40.206 Introduction. 220.127.116.11 The Time Factor in Capacitance Charge or Discharge. 18.104.22.168 Nyquist (or Argand) Complex-Plane Plots for Representation of Impedance Behavior. 22.214.171.124 Bode Plots of Impedance Parameters for Capacitors. 126.96.36.199 Hierarchy of Equivalent Circuits and Representation of Electrochemical Capacitor Behavior. 188.8.131.52 Impedance and Voltammetry Behavior of Brush Electrode Models of Porous Electrodes. 184.108.40.206 Impedance Behavior of Supercapacitors Based on Pseudocapacitance. 220.127.116.11 Deviations of Double-layer Capacitance from Ideal Behavior: Representation by a Constant-phase Element (CPE). 4.5.4 Fuel Cells (Norbert Wagner). 18.104.22.168 Introduction. 22.214.171.124 Alkaline Fuel Cells (AFC). 126.96.36.199 Polymer Electrolyte Fuel Cells (PEFC). 188.8.131.52 Solid Oxide Fuel Cells (SOFC). Appendix. Abbreviations and Definitions of Models. References. Index.
TL;DR: In this article, a review of the key technological developments and scientific challenges for a broad range of Li-ion battery electrodes is presented, and the potential/capacity plots are used to compare many families of suitable materials.
Abstract: This review covers key technological developments and scientific challenges for a broad range of Li-ion battery electrodes. Periodic table and potential/capacity plots are used to compare many families of suitable materials. Performance characteristics, current limitations, and recent breakthroughs in the development of commercial intercalation materials such as lithium cobalt oxide (LCO), lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), lithium iron phosphate (LFP), lithium titanium oxide (LTO) and others are contrasted with that of conversion materials, such as alloying anodes (Si, Ge, Sn, etc.), chalcogenides (S, Se, Te), and metal halides (F, Cl, Br, I). New polyanion cathode materials are also discussed. The cost, abundance, safety, Li and electron transport, volumetric expansion, material dissolution, and surface reactions for each type of electrode materials are described. Both general and specific strategies to overcome the current challenges are covered and categorized.