Judith Grinblat

LiMnPO4 as an Advanced Cathode Material for Rechargeable Lithium Batteries

LiMnPO4 nanoparticles synthesized by the polyol method were examined as a cathode material for advanced Li-ion batteries. The structure, surface morphology, and performance were characterized by X-ray diffraction, high resolution scanning electron microscopy, high resolution transmission electron microscopy, Raman, Fourier transform IR, and photoelectron spectroscopies, and standard electrochemical techniques. A stable reversible capacity up to 145 mAh g(-1) could be measured at discharge potentials > 4 V vs Li/Li+, with a reasonable capacity retention during prolonged charge/discharge cycling. The rate capability of the LiMnPO4 electrodes studied herein was higher than that of LiNi0.5Mn0.5O2 and LiNi0.8Co0.15Al0.05O2 (NCA) in similar experiments and measurements. The active mass studied herein seems to be the least surface reactive in alkyl carbonate/LiPF6 solutions. We attribute the low surface activity of this material, compared to the lithiated transition-metal oxides that are examined and used as cathode materials for Li-ion batteries, to the relatively low basicity and nucleophilicity of the oxygen atoms in the olivine compounds. The thermal stability of the LiMnPO4 material in solutions (measured by differential scanning calorimetry) is much higher compared to that of transition-metal oxide cathodes. This is demonstrated herein by a comparison with NCA electrodes

LiMn0.8Fe0.2PO4: An Advanced Cathode Material for Rechargeable Lithium Batteries†

Keywords: cathode materials ; lithium batteries ; nanoparticles ; surface chemistry ; thermal stability ; Performance ; Electrodes Reference EPFL-ARTICLE-159236doi:10.1002/anie.200903587View record in Web of Science Record created on 2010-11-30, modified on 2017-05-12

Morphological and Structural Studies of Composite Sulfur Electrodes upon Cycling by HRTEM, AFM and Raman Spectroscopy

In this work, structural and morphological changes in composite sulfur electrodes were studied due to their cycling in rechargeable Li-S cells produced by Sion Power Inc. Composite sulfur cathodes, comprising initially elemental sulfur and carbon, undergo pronounced structural and morphological changes during discharge-charge cycles due to the complicated redox behavior of sulfur in nonaqueous electrolyte solutions that contain Li ions. Nevertheless, Li―S cells can demonstrate prolonged cycling. To advance this technology, it is highly important to understand the evolution of the structure and morphology of sulfur cathodes as cycling proceeds. High resolution scanning and tunneling microscopy, scanning probe microscopy, and Raman spectroscopy were used in conjunction with the electrochemical measurements. A special methodology for slicing composite sulfur electrodes and their cross sectioning and depth profiling was developed. The gradual changes in the structure of sulfur cathodes due to cycling is described and discussed herein. Important phenomena include changes in the surface electrical conductivity of sulfur electrodes and pronounced morphological changes due to the irreversibility of the sulfur redox reactions. Based on the observations presented in this work, it may be possible to outline guidelines for improving Li-S battery technology and extending its cycle life.

A One‐Step Process for the Antimicrobial Finishing of Textiles with Crystalline TiO2 Nanoparticles

Titanium oxide (TiO(2)) nanoparticles (NPs) in their two forms, anatase and rutile, were synthesized and deposited onto the surface of cotton fabrics by using ultrasonic irradiation. The structure and morphology of the nanoparticles were analyzed by using characterization methods such as XRD, TEM, STEM, and EDS. The antimicrobial activities of the TiO(2)-cotton composites were tested against Escherichia coli (gram-negative) and Staphylococcus aureus (gram-positive) strains, as well as against Candida albicans. Significant antimicrobial effect was observed, mainly against Staphylococcus aureus. In addition, the combination of visible light and TiO(2) NPs showed enhanced antimicrobial activity.

On the Performance of LiNi1 / 3Mn1 / 3Co1 / 3O2 Nanoparticles as a Cathode Material for Lithium-Ion Batteries

We report on the behavior of nanometric LiMn 1/3 Ni 1/3 CO 1/3 O 2 (LiMNC) as a cathode material for Li-ion batteries in comparison with the same material with submicrometric particles. The LiMNC material was produced by a self-combustion reaction, and the particle size was controlled by the temperature and duration of the follow-up calcination step. X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared, Raman spectroscopy, electron paramagnetic resonance, inductively coupled plasma, and atomic force microscopy were used in conjunction with standard electrochemical techniques (cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy) for characterizing the electrode materials. The effect of cycling and aging at 60°C was also explored. Nanomaterials are much more reactive in standard electrolyte solutions than LiMNC with a submicrometric particle. They develop surface films that impede their electrochemical response, while their bulk structure remains stable during aging and cycling at elevated temperatures. The use of nanomaterials in Li-ion batteries is discussed.

Study of electrolytic cobalt sulfide Co9S8 as an electrode material in lithium accumulator prototypes

With the purpose to obtain a sulfide material for lithium and lithium-ionic thin-film batteries, cobalt sulfide Co9S8 was synthesized on an aluminum foil or stainless steel by electrolysis of aqueous solutions containing cobalt sulfate, sodium thiosulfate and sodium sulfide. The surface morphology of electrolytic Co9S8 is characterized by close packing of ball-like particles 8–12 μm in diameter, consisting of submicrometer structures 300–400 nm in size. It was found that e-Co9S8 electrodes exhibit stable behavior during 100 lithiation-delithiation cycles in a voltage range of 2.8–1.1 V, providing a discharge capacity of ∼200 mAh/g. In a lithium cell with ethylene carbonate (EC)-dimethyl carbonate (DMC)-1M LiClO4 electrolyte, a discharge capacity of the e-Co9S8-electrode was 250–450 mAh/g in a voltage range of 2.80–0.2 V. It was found that higher discharge capacities can be achieved for e-Co9S8-electrodes with a smaller active material mass.

Stabilizing nickel-rich layered cathode materials by a high-charge cation doping strategy: zirconium-doped LiNi0.6Co0.2Mn0.2O2

Ni-rich layered lithiated transition metal oxides Li[NixCoyMnz]O2 (x + y + z = 1) are the most promising materials for positive electrodes for advanced Li-ion batteries. However, one of the drawbacks of these materials is their low intrinsic stability during prolonged cycling. In this work, we present lattice doping as a strategy to improve the structural stability and voltage fade on prolonged cycling of LiNi0.6Co0.2Mn0.2O2 (NCM-622) doped with zirconium (+4). It was found that LiNi0.56Zr0.04Co0.2Mn0.2O2 is stable upon galvanostatic cycling, in contrast to the undoped material, which undergoes partial structural layered-to-spinel transformation during cycling. The current study provides sub-nanoscale insight into the role of Zr4+ doping on such a transformation in Ni-rich Li[NixCoyMnz]O2 materials by adopting a combined experimental and first-principles theory approach. A possible mechanism for a Ni-mediated layered-to-spinel transformation in Ni-rich NCMs is also proposed.

Studies of nanosized LiNi0.5Mn0.5O2-layered compounds produced by self-combustion reaction as cathodes for lithium-ion batteries

We report here on the synthesis of layered nanosized LiNi 0.5 Mn 0.5 O 2 compound by a modified self-combustion reaction and the studies of its electrochemical behavior as a cathode material for Li cells. Capacities up to 180-200 mAh/g could be reached during cycling of these electrodes even at 60°C in LiPF 6 /alkyl-carbonate solutions. The nano-LiNi 0.5 Mn 0.5 O 2 material exhibits remarkable stability during prolonged aging and cycling at elevated temperatures. Surface films developed on the nano-LiNi 0.5 Mn 0.5 O 2 particles in the course of cycling/aging contain polycarbonates, LiF, nickel and manganese oxides, and fluorides, and lead to efficient passivation and stabilization of the electrodes.

Synthesis of magnetic iron and iron oxide micrometre-sized composite particles of narrow size distribution by annealing iron salts entrapped within uniform porous poly(divinylbenzene) microspheres

This article describes a new simple approach to produce poly(divinylbenzene) and carbon micrometre-sized magnetic composite particles of narrow size distribution. For this purpose, uniform porous poly(divinylbenzene) microspheres were prepared by a single-step swelling of uniform polystyrene microspheres with divinylbenzene and benzoyl peroxide, followed by polymerization of the divinylbenzene within the swollen polystyrene particles. Uniform porous poly(divinylbenzene) microspheres were then formed by dissolution of the polystyrene part of the polystyrene–poly(divinylbenzene) composite particles. Iron salts, e.g., FeCl2·4H2O, dissolved in an organic continuous phase were then entrapped by vacuum within the pores of the cross-linked poly(divinylbenzene) microspheres. The obtained microspheres containing the iron salts were then annealed at 250 °C under ambient atmosphere. The formed magnetic microspheres were then annealed at 500 and 800 °C, respectively, under inert atmosphere. The annealing temperature allowed for control of the composition, crystallinity, size and size distribution and the magnetic properties of the obtained microspheres. Magnetic PDVB–α-Fe2O3 microspheres were obtained at 250 °C, while annealing of these microspheres at 500 and 800 °C under inert atmosphere leads to carbonization of the particles, and thereby the formation of C–Fe3O4 and air stable C–Fe microspheres, respectively. The magnetic moment of the C–Fe microspheres is notably high, 106.5 emu g−1. HR-TEM combined with STEM for elemental Fe mapping and imaging illustrated that by increasing the annealing temperature the size of the composite particles significantly decreased, while at the same time the size of the magnetic grains entrapped within the particles increased. Characterization of the various microspheres was also accomplished by other routine methods such as XRD, EDS, TGA, DSC, SQUID and Mossbauer spectroscopy.

Improved capacity and stability of integrated Li and Mn rich layered-spinel Li1.17Ni0.25Mn1.08O3 cathodes for Li-ion batteries

A Li-rich layered-spinel material with a target composition Li1.17Ni0.25Mn1.08O3 (xLi[Li1/3Mn2/3]O2.(1 − x)LiNi0.5Mn1.5O4, (x = 0.5)) was synthesized by a self-combustion reaction (SCR), characterized by XRD, SEM, TEM, Raman spectroscopy and was studied as a cathode material for Li-ion batteries. The Rietveld refinement results indicated the presence of monoclinic (Li[Li1/3Mn2/3]O2) (52%), spinel (LiNi0.5Mn1.5O4) (39%) and rhombohedral LiNiO2 (9%). The electrochemical performance of this Li-rich integrated cathode material was tested at 30 °C and compared to that of high voltage LiNi0.5Mn1.5O4 spinel cathodes. Interestingly, the layered-spinel integrated cathode material exhibits a high specific capacity of about 200 mA h g−1 at C/10 rate as compared to 180 mA h g−1 for LiNi0.5Mn1.5O4 in the potential range of 2.4–4.9 V vs. Li anodes in half cells. The layered-spinel integrated cathodes exhibited 92% capacity retention as compared to 82% for LiNi0.5Mn1.5O4 spinel after 80 cycles at 30 °C. Also, the integrated cathode material can exhibit 105 mA h g−1 at 2 C rate as compared to 78 mA h g−1 for LiNi0.5Mn1.5O4. Thus, the presence of the monoclinic phase in the composite structure helps to stabilize the spinel structure when high specific capacity is required and the electrodes have to work within a wide potential window. Consequently, the Li1.17Ni0.25Mn1.08O3 composite material described herein can be considered as a promising cathode material for Li ion batteries.