Evaluation of commercial lithium-ion cells based on composite positive electrode for plug-in hybrid electric vehicle applications. Part I: Initial characterizations

Evaluating commercial Li-ion batteries presents some unique benefits. One of them is to use cells made from established fabrication process and form factor, such as those offered by the 18650 cylindrical configuration, to provide a common platform to investigate and understand performance deficiency and aging mechanism of target chemistry. Such an approach shall afford us to derive relevant information without influence from processing or form factor variability that may skew our understanding on cell-level issues. A series of 1.9 Ah 18650 lithium ion cells developed by a commercial source using a composite positive electrode comprising {LiMn_1/3Ni_1/3Co_1/3O₂ + LiMn₂O₄} is being used as a platform for the investigation of certain key issues, particularly path-dependent aging and degradation in future plug-in hybrid electric vehicle (PHEV) applications, under the US Department of Energy's Applied Battery Research (ABR) program. Here we report in Part I the initial characterizations of the cell performance and Part II some aspects of cell degradation in 2C cycle aging. The initial characterizations, including cell-to-cell variability, are essential for life cycle performance characterization in the second part of the report when cell-aging phenomena are discussed. Due to the composite nature of the positive electrode, the features (or signature) derived from the incremental capacity (IC) of the cell appear rather complex. In this work, the method to index the observed IC peaks is discussed. Being able to index the IC signature in details is critical for analyzing and identifying degradation mechanism later in the cycle aging study.     

Metallic glasses: Gaining plasticity for microsystems

Since the 1960s, metallic glasses (MGs) have attracted tremendous re-search interest in materials science and engineering, given their unique cornbination of mechanical properties. How-ever, the industrial applications of MGs have been hindered due to their lack of ductility in bulk form at room temperature. In contrast, it was observed that MGs could exhibit excellent plasticity at the small size scale. In this article, we summarize the related experimental findings having been reported so far together with the possible origins of such a size effect in MGs. The enhanced plasticity of MGs in small volumes, together with their high mechanical strengths and remarkable thermoplastic formability, strongly implies that MGs are the promising materials for fabricating the next generation of micro- and nano-devices.     

Thin film metallic glasses: Preparations,properties, and applications

With unique properties such as high strength, amorphous alloys in the bulk form have been a focus for many studies in recent years. Yet, the amorphous alloys (metallic glass) in the thin film form have not received much attention. In this paper, we will review and report some important and interesting results obtained from these thin film metallic glasses in which unique physical and mechanical properties can be enhanced by changing their compositions and by the precipitation of nanoscale particles.     

Calculation of impurity diffusivities in α-Fe using first-principles methods

Self- and impurity diffusivities in body-centered-cubic (bcc) iron have been calculated within the formalisms of harmonic transition-state theory and the Le Claire nine-frequency model for vacancy-mediated diffusion. The approach combines first-principles calculations of vacancy formation, migration, and solute-binding enthalpies and entropies in the ferromagnetic phase, with an empirical relationship for the effect of magnetic disorder on diffusion activation energies. Calculated Fe self-diffusion and Mo and W impurity-diffusion coefficients are shown to agree within a factor of five with the most recent experimental measurements in both the ferromagnetic and paramagnetic phases. Calculated diffusion coefficients for Mo and W impurities are comparable to or larger than that for Fe self-diffusion at all temperatures below the α–γ phase transition. Calculated activation energies for Ta and Hf impurities suggest that these solutes should also display impurity-diffusion coefficients larger than that for self-diffusion in body-centered cubic Fe.     

Fatigue and Fracture Behavior of a Ca-Based Bulk-Metallic Glass

The compression and fatigue behavior of a Ca₆₅Mg₁₅Zn₂₀ bulk-metallic glass (BMG) was studied in air at room temperature. During the preparation of cubical samples of the Ca₆₅Mg₁₅Zn₂₀ for compression and fatigue investigations, small spherical cavities were found. Under both monotonic and cyclic compression loadings of the samples, fractures initiated at these cavities and propagated in a direction generally parallel to the loading axis. Finite-element analysis (FEA) was used to model the fracture behavior. The FEA of a centrally located spherical void showed that under compression loading, large tensile stresses evolved in the cavities. The orientation of the maximum principal stress (P1) was found to be normal to the direction of crack propagation, which is consistent with the experimental finding. Stresses in deeply embedded adjacent voids and those in superficial voids were also studied. The influence of the void location in the cubical sample on the fracture behavior was quantitatively discussed.     

Roles of In-Situ Forming Hard Particles in a Zr-Based Bulk-Metallic Glass during Monotonic and Cyclic Loading

Zr₆₇Ni₂₀Cu₅Al₈ (in at. pct) is a bulk-metallic glass (BMG) with in-situ forming hard particles. Some crystalline particles can be observed in the polished beam samples under optical microscopy (OM). The hardness measurements show that these crystalline particles are harder than the matrix of Zr₆₇Ni₂₀Cu₅Al₈. The energy-dispersive spectroscopy (EDS) analyses demonstrate that there is little difference in the compositions between the crystalline particles and the matrix. The Zr₆₇Ni₂₀Cu₅Al₈ BMG under compressive loading exhibits yield strength of 1580 MPa with an up to 7.7 pct fracture strain. The fatigue behavior of Zr₆₇Ni₂₀Cu₅Al₈ is investigated under four-point-bending loading. The fatigue results show that the fatigue limit of Zr₆₇Ni₂₀Cu₅Al₈ is approximately 361 MPa, based on the stress range. It is generally found that the fatigue cracks initiate from the hard particles. The influence of the hard inclusions on the fracture and fatigue behavior of Zr-based BMGs is discussed.     

Glass-Forming Ability and Competitive Crystalline Phases for Lightweight Ti-Be–Based Alloys

The glass-forming ability (GFA) for the Ti-Be–based alloys in the Ti-Be-Zr ternary system is systematically studied. It was found that the best GFA obtained at a composition of Ti₄₁Be₃₄Zr₂₅ (at. pct) in the Ti-Be-Zr ternary system, and the bulk-metallic-glass (BMG) rod samples with a diameter of 5 mm were fabricated by Cu-mold casting. The competitive crystalline phases around the composition of the best GFA materials were determined by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The GFA of the ternary alloys was further improved by an addition of 4 at. pct vanadium (V). The largest supercooled liquid region, ΔT _x (ΔT _x  = T _x − T _g , T _g is the glass-transition temperature, and T _x the crystallization temperature), in the ternary alloy system reaches about 110 K (110 °C) for the Ti₃₅Be₃₂Zr₃₃ alloy.     

Air-Oxidation Behavior of a [(Co50Cr15Mo14C15B6)97.5Er2.5]93Fe7 Bulk-Metallic Glass at 873?K to 973?K (600?°C to 700?°C)

The oxidation behavior of a [(Co₅₀Cr₁₅Mo₁₄C₁₅B₆)_97.5Er_2.5]₉₃Fe₇ bulk-metallic glass (Co7-BMG) was studied over the temperature range of 873?K to 973?K (600?°C to 700?°C) in dry air. The oxidation kinetics of the Co7-BMG generally followed the parabolic-rate law, as its oxidation rates increased with temperature. The scaling rate of the Co7-BMG was significantly lower than that of pure Co, which indicates a better oxidation resistance for the amorphous alloy. The scales formed on the Co7-BMG consisted mostly of CoMoO₄ and Co₃O₄, as well as minor amounts of CoO, Cr₂O₃, and uncorroded Co₃B. The formation of CoMoO₄ and Cr₂O₃ is responsible for the lower oxidation rates of the glassy alloy with respect to those of pure Co. In addition, the presence of Co₃B further indicated that the crystallization of the amorphous substrate during the oxidation was taken place.     

Synthesis of 4‐link function generating mechanisms for optimum transmission angle

Abstract

A combined equation of the expression of optimum transmission angle μ and the loop displacement equation is presented for the synthesis of plane 4‐link function generating mechanisms with the highest minimum (or optimum) μ. The expression of optimum μ is derived via the sensitivity of a function generator, and covers various types of equal deviations of μ between |90 deg‐μ_min | and |90 deg‐|μ_max |. A numerical example is given.