Phl Peter Notten

State-of-the-art of battery state-of-charge determination

From the early days of its discovery, humanity has depended on electricity, a phenomenon without which our technological advancements would not have been possible. With the increased need for mobility, people moved to portable power storage—first for wheeled applications, then for portable and finally nowadays wearable use. Several types of rechargeable battery systems, including those of lead–acid, nickel–cadmium, nickel–metal hydride, lithium ion and lithium-ion polymer exist in the market. The most important of them will be discussed in this review. Almost as long as rechargeable batteries have existed, systems able to give an indication about the state-of-charge (SoC) of a battery have been around. Several methods, including those of direct measurements, book-keeping and adaptive systems (Bergveld et al 2002 Battery Management Systems, Design by Modelling (Philips Research Book Series) vol 1 (Boston: Kluwer)) are known in the art for determining the SoC of a cell or battery of cells. An accurate SoC determination method and an understandable and reliable SoC display to the user will improve the performance and reliability, and will ultimately lengthen the lifetime of the battery. However, many examples of poor accuracy and reliability can be found in practice (Bergveld et al 2002, cited above). This review presents an overview on battery technology and the state-of-the-art of SoC methods. The goal of all the presented SoC indication methods is to design an SoC indication system capable of providing an accurate SoC indication under all realistic user conditions, including those of spread—in both battery and user behaviour, a large temperature and current range and ageing of the battery.

In situ Scanning Electron Microscopy (SEM) observation of interfaces within plastic lithium batteries

Abstract Cross-sections of plastic rechargeable Li-cells were observed in a quasi in situ mode by means of a scanning electron microscope. All cells were composed of a composite cathode, containing LiMn 2 O 4 as active material, and of a hybrid polymer electrolyte consisting of a polymer matrix embedded with a solution of lithium salt. At the negative side, three kinds of anodes (Li, Cu and graphite) were successively used. The influence of the current density on the morphology of the lithium deposit was studied from these three different configurations. Scanning Electron Microscopy (SEM) evidences for (1) the accumulation of mossy lithium, and (2) the Li-dendrites growth at the interface between Li and electrolyte are given, and correlated to the poor cell cyclability. This deterioration of the interface was confirmed by AC-impedance measurements.

Lithium-Ion (De)Insertion Reaction of Germanium Thin-Film Electrodes: An Electrochemical and In Situ XRD Study

Germanium is a promising negative electrode candidate for lithium-ion thin-film batteries because of its very high theoretical storage capacity. When assuming full conversion of the material into the room-temperature equilibrium lithium saturated germanium phase Li 22 Ge 5 , a theoretical capacity of 1625 mAh g -1 or 8643 mAh cm -3 of germanium starting material is expected. However, the lithium-ion (de)insertion reaction of pure germanium thin films and the resulting electrochemical thermodynamic and kinetic properties are not yet fully understood. To address some of these questions, a combined electrochemical and in situ X-ray diffraction (XRD) study is presented. Results on the crystallographic phase transitions, occurring upon Li-(de)insertion of evaporated and sputtered germanium thin films are discussed. Moreover, the difference in reaction between evaporated and sputtered films is addressed. In addition, a detailed electrochemical investigation (cyclic voltammetry, galvanostatic intermittent titration technique, and electrochemical impedance spectroscopy) of evaporated germanium is conducted. The results reveal that evaporated and sputtered germanium crystallizes into Li 15 Ge 4 when fully inserted with Li ions. This composition corresponds to a maximum storage capacity of 1385 mAh g -1 or 7366 mAh cm -3 of germanium starting material.

Optical Switching of Y‐Hydride Thin Film Electrodes A Remarkable Electrochromic Phenomenon

The optical appearance of yttrium thin film electrodes can be electrochemically switched from mirrorlike to highly transparent by making use of the hydride-forming properties of Y. A strong alkaline solution is a suitable electrolytic environment for obtaining stable electrochromic electrodes. The presence of a thin Pd layer covering the Y electrode is essential in providing a sufficiently high electrocatalytic activity for the electrochemical charge-transfer reaction. Hydrogen is irreversibly bound in Y-dihydride and reversibly bound in Y-trihydride. The optical changes are reversible and are induced within a narrow hydrogen concentration range, making this typical electrode material interesting for application in a new type of electrochromic devices.

Electrochemical hydrogen storage characteristics of thin film MgX (X = Sc, Ti, V, Cr) compounds

The hydrogen storage characteristics of thin film MgX (X=Sc, Ti, V, Cr) compounds were investigated electrochemically. The successful preparation of these metastable, crystalline single-phase, MgX compounds was achieved by means of electron-beam deposition at room temperature. The reversible hydrogen storage capacity of these compounds is excellent and up to six times higher than commercial AB5-type materials. The gravimetrical storage capacities of these new materials were determined to be 1790 mAh/g for Mg80Sc20, 1750 mAh/g for Mg80Ti20, 1700 mAh/g for Mg80V20, and 1325 mAh/g for Mg80Cr20, corresponding to 6.7, 6.5, 6.4, and 4.9 wt % H, respectively. The hydrogen absorption and desorption kinetics are profoundly influenced by the element X incorporated in the MgX compound. Galvanostatic measurements show that the rate capability of the Sc- and Ti-containing compounds is significantly better than that of the V- and Cr-containing compounds. Isotherms of these systems are obtained using galvanostatic intermittent titration technique, revealing that the equilibrium potential of the main charge/discharge plateau, apart from the Mg80Sc20 compound, only slightly depends on X in MgX. The electrochemical measurements show that low-cost Ti is an excellent substitute for the expensive Sc in MgSc, without introducing detrimental effects.

Remote Plasma ALD of Platinum and Platinum Oxide Films

Platinum and platinum oxide films were deposited by remote plasma atomic layer deposition (ALD) from the combination of (methylcyclopentadienyl)trimethylplatinum (MeCpPtMe 3 ) precursor and O 2 plasma. A short O 2 plasma exposure (0.5 s) resulted in low resistivity (15 μΩ cm), high density (21 g/cm 3 ), cubic Pt films, whereas a longer O 2 plasma exposure (5 s) resulted in semiconductive PtO 2 films. In situ spectroscopic ellipsometry studies revealed no significant nucleation delay, different from the thermal ALD process with O 2 gas which was used as a benchmark. A broad temperature window (100―300°C) for remote plasma ALD of Pt and PtO 2 was demonstrated.

Atomic layer deposition for nanostructured Li-ion batteries

Nanostructuring is targeted as a solution to achieve the improvements required for implementing Li-ion batteries in a wide range of applications. These applications range in size from electrical vehicles down to microsystems. Atomic layer deposition (ALD) could be an enabling technology for nanostructured Li-ion batteries as it is capable of depositing ultrathin films (1–100 nm) in complex structures with precise growth control. The potential of ALD is reviewed for three battery concepts that can be distinguished, i.e., particle-based electrodes, 3D-structured electrodes, and 3D all-solid-state microbatteries. It is discussed that a large range of materials can be deposited by ALD and recent demonstrations of battery improvements by ALD are used to exemplify its large potential.

Mg-Ti-H thin films for smart solar collectors

Mg–Ti–H thin films are found to have very attractive optical properties: they absorb 87% of the solar radiation in the hydrogenated state and only 32% in the metallic state. Furthermore, in the absorbing state Mg–Ti–H has a low emissivity; at 400K only 10% of blackbody radiation is emitted. The transition between both optical states is fast, robust, and reversible. The sum of these properties highlights the applicability of such materials as switchable smart coatings in solar collectors.

Photoelectrochemical Hydrogen Production on InP Nanowire Arrays with Molybdenum Sulfide Electrocatalysts

Semiconductor nanowire arrays are expected to be advantageous for photoelectrochemical energy conversion due to their reduced materials consumption. In addition, with the nanowire geometry the length scales for light absorption and carrier separation are decoupled, which should suppress bulk recombination. Here, we use vertically aligned p-type InP nanowire arrays, coated with noble-metal-free MoS3 nanoparticles, as the cathode for photoelectrochemical hydrogen production from water. We demonstrate a photocathode efficiency of 6.4% under Air Mass 1.5G illumination with only 3% of the surface area covered by nanowires.

In situ SEM study of the interfaces in plastic lithium cells

The interfaces of lithium cells were studied upon cycling within a scanning electron microscope (SEM). The LiMn2O4-cathode and the electrolyte consisted of a polymer matrix embedding a solution of LiPF6, while three types of anodes, Li, Cu and graphite, were tested and compared. For each configuration the morphology of the lithium deposit was correlated to the current density. Mossy lithium, at low current, and Li-dendrites, at high current, were observed at the Cu/electrolyte and Li/electrolyte interfaces, while no special morphology was noted at the graphite/electrolyte interface.