Damian M. Cupid

Thermodynamic re-assessment of the Ti–Al–Nb system

Abstract A CALPHAD based re-assessment of the thermodynamic description of the Ti – Al – Nb system was performed to take into account experimental evidence of the extension of the primary crystallization of the -phase to higher Al contents. The adjustable parameters of the analytic expressions of the Gibbs free energy for the Liquid, β-, β0-, δ-, σ-, γ-, α-, and 2-phases were re-optimized using available experimental data from a critical assessment of the literature. The calculated primary crystallization of -phase is in better agreement with experiment although the extension of the single phase -field to higher Al compositions could not be calculated. Calculated isothermal sections are in good agreement with experiment in the temperature range 1923 K to 1273 K.

Thermodynamic aspects of liquid phase sintering of SiC using Al2O3 and Y2O3

Abstract A thermodynamic dataset for the Al – C – O – Si – Y system was used for calculations of multicomponent, multiphase reactions. Some aspects of the liquid phase sintering of silicon carbide using alumina and yttria sintering additives were analyzed. The phase relations in the SiC – Al2O3, SiC – Al2O3 – SiO2 and SiC – Y2O3 – SiO2 systems were calculated. Phase fraction diagrams, isopleths, isothermal sections, and potential phase diagrams are presented to illustrate the reactions between silicon carbide and sintering additives. The effect of Ar inert gas as an additional component and the related volume change of the gas phase were considered. In addition, the influence of surface silica on silicon carbide powder is taken into account.

Heat capacities and an updated thermodynamic model for the Li–Sn system

Phase-pure Li17Sn4 and Li7Sn3 intermetallic compounds were synthesized using defined heat treatment procedures in specially designed Ta crucibles. The products were characterized by inductively coupled plasma optical emission spectroscopy (ICP-OES) and powder X-ray diffraction (powder-XRD) techniques to determine their composition and phase purity. The heat capacities of the synthesized compounds were measured via the step method in sealed Ta crucibles using a Setaram C80 Tian-Calvet calorimeter. The experimentally determined heat capacities were then used to develop restricted Maier-Kelley models for each phase and to incorporate these data into the re-optimization of an existing thermodynamic description of the Li-Sn system. The new models for the intermetallic and liquid phases result in improved agreement between the calculated and experimental heat capacity, thermodynamic, electrochemical and phase diagram data. Since the re-optimized Gibbs free energy expressions are based on reliable heat capacity data, the models can now be used to predict emf values in the Li-Sn system at a variety of operation temperatures and active material compositions.

A thermodynamic investigation of the Li–Sb system

Many standard thermodynamic data in the binary system Li–Sb can be found in literature; however, they are often derived from electrochemical measurements taken at higher temperatures. The uncertainties associated with the extrapolation of these high-temperature data to room temperature are, however, inherently large. Therefore, a comprehensive investigation of the thermodynamic properties in the Li–Sb system was conducted in this work to generate more reliable data. Four different experimental techniques were used for the investigations. The heat capacities for both binary compounds, Li2Sb and Li3Sb, were measured for the very first time. In addition, the enthalpies of formation for both compounds were determined by drop solution and direct reaction calorimetry. Furthermore, Knudsen effusion mass spectrometry was performed to measure partial enthalpies and activities of Sb.

Phase diagram, thermodynamic investigations, and modelling of systems relevant to lithium-ion batteries

Abstract This article reports on two consecutive joint projects titled “Experimental Thermodynamics and Phase Relations of New Electrode Materials for Lithium-Ion Batteries”, which were performed in the framework of the WenDeLIB 1473 priority program “Materials with new Design for Lithium Ion Batteries”. Hundreds of samples were synthesized using experimental techniques specifically developed to deal with highly reactive lithium and lithium-containing compounds to generate electrochemical, phase diagram and crystal structure data in the Cu–Li, Li–Sn, Li–Sb, Cu–Li–Sn, Cu–Li–Sb and selected oxide systems. The thermochemical and phase diagram data were subsequently used to develop self-consistent thermodynamic descriptions of several binary systems. In the present contribution, the experimental techniques, working procedures, results and their relevance to the development of new electrode materials for lithium ion batteries are discussed and summarized. The collaboration between the three groups has resulted in more than fifteen (15) published articles during the six-year funding period.

Si- and Sn-containing SiOCN-based nanocomposites as anode materials for lithium ion batteries: synthesis, thermodynamic characterization and modeling

Abstract Novel nanocomposites consisting of silicon/tin nanoparticles (n-Si/n-Sn) embedded in silicon carbonitride (SiCN) or silicon oxycarbide (SiOC) ceramic matrices are investigated as possible anode materials for Li-ion batteries. The goal of our study is to exploit the large mass specific capacity of Si/Sn (3 579 mAh g−1/994 mAh g−1), while avoiding rapid capacity fading due to the large volume changes of Si/Sn during Li insertion. We show that a large amount (∼30–40 wt.%) of disordered carbon phase is dispersed within the SiOC/SiCN matrix and stabilizes the Si/Sn nanoparticles with respect to extended reversible lithium ion storage. Silicon nanocomposites are prepared by mixing of a polymeric precursor with commercial and “home-synthesized” crystalline and amorphous silicon. Tin nanocomposites, in contrast, are prepared using a single precursor approach, which allows the in-situ generation of Sn nanoparticles homogeneously dispersed within the SiOC host. The best electrochemical stability along with capacities of 600 – 700 mAh g−1 is obtained when amorphous/porous silicon is used. Mechanisms contributing to the increase of storage capacity and the cycle stability are clarified by analyzing elemental composition, local solid-state structures, intercalation hosts and Li-ion mobility. Our work is supplemented by first-principles based atomistic modeling and thermochemical measurements.

Enthalpies of formation of layered LiNixMnxCo1–2xO2 (0 ≤ x ≤ 0.5) compounds as lithium ion battery cathode materials

Abstract Layer-structured mixed transition metal oxides with the formula LiNixMnxCo1–2xO2 (0 ≤ x ≤ 0.5) are considered as important cathode materials for lithium-ion batteries. In an effort to evaluate the relative thermodynamic stabilities of individual compositions in this series, the enthalpies of formation of selected stoichiometries are determined by high temperature oxide melt drop solution calorimetry and verified by ab-initio calculations. The measured and calculated data are in good agreement with each other, and the results show that LiCoO2–LiNi0.5Mn0.5O2 solid solution approaches ideal behavior. By increasing x, i. e. by equimolar substitution of Mn4+ and Ni2+ for Co3+, the enthalpy of formation of LiNixMnxCo1–2xO2 from the elements becomes more exothermic, implying increased energetic stability. This conclusion is in agreement with the literature results showing improved structural stability and cycling performance of Ni/Mn-rich LiNixMnxCo1–2xO2 compounds cycled to higher cut-off voltages.

Coexistence of conversion and intercalation mechanisms in lithium ion batteries: Consequences for microstructure and interaction between the active material and electrolyte

Abstract Conversion-type lithium ion batteries experience severe and partly irreversible phase transitions during operation. Such phase transitions reduce the crystallite size and therefore enhance the exchange of the Li ions. Concurrently, the irreversible nature of the phase transitions may deteriorate the cycling stability and the long-term capacity of conversion-type batteries. In this contribution, the observed correlations between the crystal structures of compounds which are employed as anodes in conversion-type Li ion cells, the capacity and the long-term stability of these cells are discussed. The central characteristics affecting the performance of conversion-type Li ion cells seem to be the similarity of crystal structures of intermediately forming phases during the charge/discharge process, which facilitates strong local preferred orientation of nanocrystallites of neighboring phases and for the formation of local strain fields at partially coherent phase boundaries. The effect of the above-mentioned phenomena on capacity and cycle stability is argued from the point of view of a possibly impeded ion exchange. Equilibrium open circuit potentials are calculated using the CALPHAD method. However, it is shown that in order to better reproduce the experimentally determined plateau voltages, thermodynamic descriptions of the non-equilibrium intermediate phases have to be included. In addition, the stabilization of the conversion reaction by the electrolyte is pointed out.

Thermochemical stability of Li–Cu–O ternary compounds stable at room temperature analyzed by experimental and theoretical methods

Abstract Compounds in the Li–Cu–O system are of technological interest due to their electrochemical properties which make them attractive as electrode materials, i. e., in future lithium ion batteries. In order to select promising compositions for such applications reliable thermochemical data are a prerequisite. Although various groups have investigated individual ternary phases using different experimental setups, up to now, no systematic study of all relevant phases is available in the literature. In this study, we combine drop solution calorimetry with density function theory calculations to systematically investigate the thermodynamic properties of ternary Li–Cu–O phases. In particular, we present a consistently determined set of enthalpies of formation, Gibbs energies and heat capacities for LiCuO, Li2CuO2 and LiCu2O2 and compare our results with existing literature.

Interlaboratory study of the heat capacity of LiNi1/3Mn1/3Co1/3O2 (NMC111) with layered structure

Abstract An interlaboratory study was performed to determine the heat capacity of an active material for lithium-ion batteries with layered structure and nominal composition LiNi1/3 · Mn1/3Co1/3O2 (NMC111). The commercial sample, which was characterized using powder X-ray diffraction and inductively coupled plasma–optical emission spectroscopy, is single phase (α-NaFeO2 crystal structure) with a composition of Li1.02Ni0.32Mn0.31Co0.30O2. Heat capacity measurements of the homogeneous sample were performed at five laboratories using different operators, methods, devices, temperature ranges, gas atmospheres and crucible materials. The experimental procedures from each laboratory are presented and the results of the individual laboratories are analyzed. Based on a comprehensive evaluation of the data from each laboratory, the heat capacity of the NMC111 sample from 315 K to 1 020 K is obtained with an expanded reproducibility uncertainty of less than 1.22 %.