Peter H. L. Notten

Yttrium and lanthanum hydride films with switchable optical properties

Abstract We discovered that yttrium-, lanthanum- and rare earth-hydride films exhibit remarkable optical properties near their metal–insulator transition: the dihydrides are metallic and shiny while the trihydrides are semiconducting and transparent. The transition between the shiny and transparent state is reversible and can simply be induced by changing the H 2 gas pressure or the voltage in an electrolytic cell. No deterioration of the films is detected if they are protected by a thin palladium caplayer. The optical switching is also observed in hydrides of alloys of Y and La. Several theoretical models leading to an insulating and transparent trihydride state are discussed.

Modeling Battery Behavior for Accurate State-of-Charge Indication

Li-ion is the most commonly used battery chemistry in portable applications nowadays. Accurate state-of-charge (SOC) and remaining run-time indication for portable devices is important for the users convenience and to prolong the lifetime of batteries. A new SOC indication system, combining the electromotive force (EMF) measurement during equilibrium and current measurement and integration during charge and discharge, has been developed and implemented in a laboratory setup. During discharge, apart from simple Coulomb counting, the effect of the overpotential is also considered. Mathematical models describing the EMF and the overpotential functions for a Li-ion battery have been developed. These models include a variety of parameters whose values depend on the determination method and experimental conditions. In this paper the battery measurement and modeling efforts are described. The method of implementing the battery model in an SOC indication system is also described. The aim is an SOC determination within 1% inaccuracy or better under all realistic user conditions, including a wide variety of load currents and a wide temperature range. The achieved results show the effectiveness of our novel approach for improving the accuracy of the SOC indication.

Influence of diffusion plane orientation on electrochemical properties of thin film LiCoO2 electrodes

Submicrometer LiCoO2 films have been prepared on silicon substrates with RF sputtering and pulsed laser deposition (PLD). The electrochemical activity of both types of thin film electrodes is compared using scanning cyclic voltammetry, galvanostatic and potentiostatic intermittent titration, and electrochemical impedance spectroscopy. The RF films exhibit a axis orientation and have an accessible diffusion plane alignment, unlike the c axis oriented PLD films. The preferential orientation of the host crystal lattice toward the electrolyte solution is critical for the intercalation rate and cycling efficiency. The RF films show superior electrochemical performance and faster relaxation characteristics than the PLD films. Based on the analysis of the time and frequency domain measurements a model for the electrode response is proposed. Apparently, the intercalation rate of the RF films is not diffusion-limited, but hindered by the large charge-transfer resistance, the phase boundary movement, and the hindrance by the solid electrolyte interface.

Battery management systems

This chapter gives general information on Battery Management Systems (BMS) required as a background in later chapters. Section 2.1 starts with the factors that determine the complexity of a BMS and shows a general block diagram. The function of each part in a BMS is discussed in more detail in section 2.2 and examples of adding BMS intelligence are given. The BMS aspects of two types of portable devices are discussed in section 2.3. This serves to illustrate the theory presented in sections 2.1 and 2.2.

Structure and stability of high pressure synthesized Mg–TM hydrides (TM = Ti, Zr, Hf, V, Nb and Ta) as possible new hydrogen rich hydrides for hydrogen storage

A series of hydrogen rich Mg6–7TMH14–16 (TM = Ti, Zr, Hf, V, Nb and Ta) hydrides have been synthesized at 600 °C in a high pressure anvil cell above 4 GPa. All have structures based on a fluorite type metal atom subcell lattice with a ≈ 4.8 A. The TM atom arrangements are, however, more ordered and can best be described by a superstructure where the 4.8 A FCC unit cell axis is doubled. The full metal atom structure corresponds to the Ca7Ge type structure. This superstructure was also observed from electron diffraction patterns. The hydrogen atoms were found from powder X-ray diffraction using synchrotron radiation to be located in the two possible tetrahedral sites. One coordinates three Mg atoms and one TM atom and another coordinates four Mg atoms. These types of new hydrogen rich hydrides based on immiscible metals were initially considered as metastable but have been observed to be reversible if not fully dehydrogenated. In this work, DFT calculations suggest a mechanism whereby this can be explained: with H more strongly bonded to the TM, it is in principle possible to stepwise dehydrogenate the hydride. The remaining hydrogen in the tetrahedral site coordinating the TM would then act to prevent the metals from separating, thus making the system partially reversible.

Photoluminescence properties and energy level locations of RE3+ (RE = Pr, Sm, Tb, Tb/Ce) in CaAlSiN3 phosphors

RE3+ (RE = Pr, Sm, Tb, Tb/Ce)-activated CaAlSiN3 samples were prepared by a solid-state reaction method at high temperature, and their photoluminescence properties were investigated. An interesting observation is that the 5d bands of Pr3+ and Tb3+ are at rather low energy in CaAlSiN3 compared to oxides. Pr3+-doped CaAlSiN3 shows strong 4f15d1 → 4f2 emission bands (334–480 nm) as well as typical 4f2 → 4f2 emission lines (480–800 nm) of Pr3+ under 4f2 → 4f15d1 excitation. Sm3+-doped CaAlSiN3 exhibits bright red emission originating from 4G5/2 → 6HJ (J = 5/2, 7/2 and 9/2) transitions, and the charge transfer band of Sm3+ was observed at an unusually low energy of 3.91 eV. In Tb3+-doped samples, the direct Tb3+ 4f8 → 4f75d1 excitation leads to 5D3 → 7FJ (J = 6, 5, 4, 3, 2, 1) (blue) and 5D4 → 7FJ (J = 6, 5, 4, 3) (green) line emissions. The bands at about 252 nm in the excitation spectra are attributed to the host lattice absorption. It is observed that there is energy transfer from the host lattice to the luminescent activators (Pr3+, Sm3+, Tb3+). In Tb3+/Ce3+-codoped CaAlSiN3, an effective energy transfer process exists from Tb3+ to Ce3+. A detailed energy level diagram that contains the position of the 4f and 5d levels of all divalent and trivalent lanthanide ions with respect to the valence and conduction bands of CaAlSiN3 has been constructed and explained.

Structural Analysis of Submicrometer LiCoO2 Films

Submicrometer LiCoO2 films were prepared with pulsed laser deposition (PLD) and rf sputtering using stoichiometric targets. The influences of both substrate material and annealing procedure on the polycrystalline microstructure of the LiCoO2 films were investigated. XRD analysis revealed strong preferential orientation: annealed films deposited with PLD had their (00l) planes parallel to the surface, while rf sputtered films had their (110) planes in this orientation. The rf-film also developed the (003) reflection typical of PLD-films, but only after prolonged annealing at 600°C. The degree of preferential orientation is influenced significantly by the annealing procedure and only little by the substrate material and the thickness of the deposited film. Pulsed laser deposition on an rf-sputtered seed layer revealed the PLD-film reflections. Extinction of the otherwise dominating (003) reflection indicated a random cationic distribution in LiCoO2 with an NaCl-type structure.

Photoluminescence properties of Yb2+ in CaAlSiN3 as a novel red-emitting phosphor for white LEDs

This paper reports on the diffuse reflection spectra, photoluminescence spectra and chromaticity of ytterbium in CaAlSiN3 at room temperature. It can be excited efficiently over a broad spectral range between 280 and 580 nm and exhibits a single intense red emission at 629 nm with a full width at half maximum of 75 nm due to the electronic transitions from the excited state of 4f135d to the ground state 4f14 of Yb2+. The low energy of Yb2+ emission in CaAlSiN3 can be attributed to the large nephelauxetic effect and crystal field splitting due to the coordination of Yb2+ by nitrogen. This novel developed CaAlSiN3:Yb2+, which is the first Yb2+-activated nitride red-emitting phosphor, has potential applications in spectral conversion materials for warm-white LEDs. The width of the emission band, Stokes shift and thermal quenching mechanism of Yb2+ in CaAlSiN3 and (oxy)nitride-based phosphors are discussed and compared with those of Eu2+.

3D negative electrode stacks for integrated all-solid-state lithium-ion microbatteries

The deposition feasibility and electrochemical evaluation of highly structured negative electrode stacks for 3D-integrated batteries is demonstrated. The stacks comprise a TiN thin film, serving as both current collector and Li-barrier layer, covered by a polycrystalline Si (poly-Si) thin film as electrode material. In comparison with planar films, these poly-Si films present a storage capacity increase of about 5× for the highest pore aspect ratio electrodes. The step coverage of poly-Si can be considerably improved by growing TiN and poly-Si into wide trenches. This results in much smoother poly-Si films and significantly improved step coverage. Further optimization of the trench dimensions should result in poly-Si films with a Li-storage capacity increase of more than one order of magnitude with respect to planar films.

Battery aging and its influence on the electromotive force

Li-ion is currently the most commonly used battery chemistry in portable applications. Accurate state-of-charge (SOC) and remaining run-time indication for portable devices is important for user convenience and to prolong the lifetime of batteries. The actual SOC algorithms, which the main companies use in practice, make use of the so-called electromotive force (emf). In these SOC systems it is assumed that the emf of an Li-ion battery only depends on aging to a limited extent. In this paper, novel emf measurement and modeling efforts are presented as a function of battery aging. As will be shown, a better understanding of this dependence is useful for improving SOC accuracy.