E.M. Kelder

Size Effects in the Li4+xTi5O12 Spinel

The nanosized Li(4+x)Ti(5)O(12) spinel is investigated by electrochemical (dis)charging and neutron diffraction. The near-surface environment of the nanosized particles allows higher Li ion occupancies, leading to a larger storage capacity. However, too high surface lithium storage leads to irreversible capacity loss, most likely due to surface reconstruction or mechanical failure. A mechanism where the large near-surface capacity ultimately leads to surface reconstruction rationalizes the existence of an optimal particle size. Recent literature attributes the curved voltage profiles, leading to a reduced length of the voltage plateau, of nanosized electrode particles to strain and interface energy from the coexisting end members. However, the unique zero-strain property of the Li(4+x)Ti(5)O(12) spinel implies a different origin of the curved voltage profiles observed for its nanosized crystallites. It is proposed to be the consequence of different structural environments in the near-surface region, depending on the distance from the surface and surface orientation, leading to a distribution of redox potentials in the near-surface area. This phenomenon may be expected to play a significant role in all nanoinsertion materials displaying the typical curved voltage curves with reduced length of the constant-voltage plateau.

Lithium Storage in Amorphous TiO2 Nanoparticles

Amorphous titanium oxide nanoparticles were prepared from titanium isopropoxide. In situ measurements reveal an extraordinary high capacity of 810 mAh/g on the first discharge. Upon cycling at a charge/discharge rate of 33.5 mA/g, this capacity gradually decreases to 200 mAh/g after 50 cycles. The origin of this fading was investigated using X-ray absorption spectroscopy and solid-state nuclear magnetic resonance. These measurements reveal that a large fraction of the total amount of the consumed Li atoms is due to the reaction of H2O/OH species adsorbed at the surface to Li2O, explaining the irreversible capacity loss. The reversible capacity of the bulk, leading to the Li0.5TiO2 composition, does not explain the relatively large reversible capacity, implying that part of Li2O at the TiO2 surface may be reversible. The high reversible capacity, also at large (dis)charge rates up to 3.35 A/g (10C), makes this amorphous titanium oxide material suitable as a low cost electrode material in a high power battery.

ELECTROSTATIC SOL–SPRAY DEPOSITION OF NANOSTRUCTURED CERAMIC THIN FILMS

Abstract Electrospraying has been developed into an electrostatic spray deposition technique for the deposition of ceramic thin films. The cone-jet spraying mode appears to be the most preferable for this purpose, and the domain where the cone-jet mode exists was found to depend strongly on the nozzle design. A nozzle with a large diameter and a tilted outlet widens the windows for both the applied high DC voltage and the flow rates of a precursor liquid keeping the cone-jet mode intact. The results of three nozzle designs are compared, one of which has been selected for feeding two different precursor liquids simultaneously. With three relevant sols as precursor liquids, nanostructured thin films of ZnO, ZrO 2 , and Al 2 O 3 have been deposited. Their morphologies are dependent on the preparation of the precursor sols and the deposition temperature. Highly porous films were obtained by using a high deposition temperature and a sol prepared from a metal alkoxide or a metal acetate.

Electrostatic sol-spray deposition (ESSD) and characterisation of nanostructured TiO2 thin films

Abstract A novel film fabrication technique, i.e. electrostatic sol-spray deposition (ESSD), has been used in this study to prepare TiO 2 thin films of various surface morphologies and crystalline structures. Scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and UV/Vis absorption spectroscopy were employed to characterize the as-deposited and annealed TiO 2 thin films. It has been found that silicon dopant can increase the anatase-to-rutile phase transformation temperature up to about 1050°C. Two possible mechanisms are proposed to explain the phase stabilisation effect, i.e. reduction of the oxygen vacancy concentration by dissolution of SiO 2 in the TiO 2 lattice and segregation of a SiO 2 second phase. The energy bandgap of amorphous SiO 2 doped TiO 2 films decreases with increasing annealing temperature.

Fabrication of LiCoO2 thin film cathodes for rechargeable lithium battery by electrostatic spray pyrolysis

Abstract LiCoO 2 thin films for cathodes in rechargeable lithium batteries were prepared by the electrostatic spray pyrolysis technique. The surface morphology may be either dense or porous, depending on the process conditions. Low temperature (280 °C) results in amorphous films. Deposition at a temperature higher than 340 °C results in the hexagonal phase of LiCoO 2 . The lithium chemical diffusion coefficients of these films range between 10 −13 and 10 −12 cm 2 /s.

Unique porous LiCoO2 thin layers prepared by electrostatic spray deposition

Electrostatic spray deposition (ESD) technique was used to fabricate thin LiCoO2 layers on a metal substrate. A unique, highly porous structure with a narrow pore-size distribution around 1 μm was obtained at 230 °C using acetates as precursors and a mixture of ethanol (15 vol %) and butyl carbitol (85 vol %) as solvent. The pores were three-dimensionally interconnected. This structure was thermally stable at temperatures up to 600 °C. At small flow rates of the precursor solution, a nearly linear relation was found between pore size and flow rate. At deposition temperatures above 230 °C the porous structure disappeared. A possible formation mechanism for the porous structure has been proposed.

Electrostatic spray deposition of thin layers of cathode materials for lithium battery.

Abstract A novel fabrication technique, namely electrostatic spray deposition (ESD), has been developed in order to prepare thin layers of solid electrolytes and cathode materials for lithium batteries. In this study, the 4-volt cathode material LiCoO 2 was chosen, and prepared by spraying alcohol solutions of nitrates and acetates of cobalt. ESD set-ups, with either horizontal or vertical configurations, were used. Depending on the precursor and process deposition conditions, the morphology of the layers can be relatively dense, fractal-like porous, or unique 3-D cross-linked porous structures with a high porosity and a narrow pore size distribution. For low deposition temperatures, LiCoO 2 layers are XRD amorphous. Upon annealing, crystallized layers are obtained. The lithium chemical diffusion coefficient of the LiCoO 2 layers has been measured with Galvanostatic Intermittent Titration Technique (GITT), values range from 10 −14 to 10 −12 cm 2 /s, depending on the lithium content and the annealing temperatures. Cyclic voltammograms of a test cell reveal that both lithium insertion and extraction are one-step processes.

A practical circuit-based model for Li-ion battery cells in electric vehicle applications

This paper proposes a practical circuit-based model for Li-ion cells, which can be directly connected to a model of a complete electric vehicle (EV) system. The goal of this paper is to provide EV system designers with a tool in simulation programs such as Matlab/Simulink to model the behaviour of Li-ion cells under various operating conditions in EV or other applications. The current direction, state of charge (SoC), temperature and C-rate dependency are represented by empirical equations obtained from measurements on LiFePO4 cells. Tradeoffs between model complexity and accuracy have been made based on practical considerations in EV applications. Depending on the required accuracy and operating conditions, the EV system designer can choose the influences to be included in the system simulation.

High-voltage LiMgδNi0.5−δMn1.5O4 spinels for Li-ion batteries

New high-voltage cathode materials for lithium and Li-ion batteries, with the general formula LiMgδNi0.5−δMn1.5O4 (δ=0.00, 0.05 and 0.10), have been synthesized and characterized. The crystal structure of these cubic spinel materials has been refined with space group P4332 with the following site occupation: Li+ on 8c, Mg2+ on 4b, Ni2+ on 4b/12d, Mn4+ on 12d/4b and O2− on 24e and 8c. Refinement with space group Fd3m was not possible. As a function of the Mg content, it was found that: (I) the cubic lattice constant increases from 8.1685 A (δ=0.00) and 8.1703 A (δ=0.05) to 8.1733 A (δ=0.10); (II) the flat potential profile at 4.7 V vs. Li/Li+ (δ=0.00) changes to a slightly sloping profile with an increased average potential of 4.75 V (δ=0.10); (III) the cyclability and the conductivity of the materials improve. It is concluded that LiMgδNi0.50−δMn1.5O4 (δ<0.10) are promising cathode materials that, when combined with a low-voltage anode material like LiCrTiO4, can result in ∼3.25 V rechargeable Li-ion battery with spinel electrodes.

Electrochemical characterization of commercial lithium manganese oxide powders

Abstract Five commercial lithium manganese oxide powders have been studied. The XRD spectra showed all samples to exhibit the spinel structure. The composition and morphology were analyzed by Jaeger–Vetter titration and scanning electron microscopy. The lithium intercalation/de-intercalation characteristics and the cycleability have been studied using state-of-the-art cells. The morphology of the particles and crystallites, as well as the defect structure of the spinel, were found to play an important role in the capacity retention during electrochemical cycling. The capacity corresponding to the 4.1 V phase transformation process faded faster than that of the 4.0 V single-phase transition during cycling, which enhanced lower plateau capacity fading and higher voltage polarization. The cycleability at the 3.0 V region has also been studied and indicated that the typical spinel lithium manganese oxide is not suitable to be cycled in the 3.0 V region. Therefore, it will be deleterious to overdischarge the spinel materials.