Ivan Exnar

High efficiency dye-sensitized nanocrystalline solar cells based on ionic liquid polymer gel electrolyte

An ionic liquid polymer gel containing 1-methyl-3-propylimidazolium iodide (MPII) and poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) has been employed as quasi-solid-state electrolyte in dye-sensitized nanocrystalline TiO2 solar cells with an overall conversion efficiency of 5.3% at AM 1.5 illumination.

Rocking Chair Lithium Battery Based on Nanocrystalline TiO2 (Anatase)

Reference LPI-ARTICLE-1995-007View record in Web of Science Record created on 2006-02-21, modified on 2017-05-12

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

Enhanced Electrochemical Performance of Mesoparticulate LiMnPO4 for Lithium Ion Batteries

LiMnPO 4 was synthesized using a sol-gel method and tested as a cathode material for lithium ion batteries. After calcination at temperatures between 520 and 570°C particle sizes in the range of 140 to 160 nm were achieved. Subsequent dry ballmilling reduced the diameter to 130 ± 10 nm. Reversible capacities of 156 mAh/g at C/100 and 134 mAh/g at C/10 were measured. At 92 and 79% of the theoretical values, respectively, these are the highest values reported to data for this material. At faster charging rates, the electrochemical performance was found to be improved when smaller particles were used.

Improving the Electrochemical Activity of LiMnPO4 Via Mn-Site Substitution

HPL SA report the modification of the electrochemical performance of lithium manganese phosphate (LiMnPO4) via Mn-site bivalent substitution. Manganese (10%) is substituted with iron, nickel, magnesium, or zinc. These substituents are shown via an X-ray to form solid solutions. The choice of substituent is demonstrated to have a strong influence on the electrochemical performance. The optimum performance improvement was achieved when 10% of Fe is substituted. This is ascribed to a smaller crystallite and a higher electronic conductivity observed in this material: Presumably Fe plays a role in hindering the crystallite growth and in increasing the carriers transportation. Electronic structures were calculated by density function theory to understand the different influences of substitute cations.

Novel 2 V rocking-chair lithium battery based on nano-crystalline titanium dioxide

A novel type of 2 V rocking-chair lithium batteries with nano-crystalline TiO2 (anatase) as the negative and LiNi0.5Co0.5O2 as the positive electrode with LiN(CF3SO2)2 + ethylene carbonate/dimethoxyethane electrolyte has been studied. The closed R921 button cells showed excellent cycling performance and a charge density of about 50 mAh/g. The advantages of the specific porous morphology of nano-crystalline insertion materials for Li insertion and release are discussed.

On the Thermal Stability of Olivine Cathode Materials for Lithium-Ion Batteries

The thermal stability of pristine and electrochemically delithiated LiMPO4 (Carbon coated-LiMnPO4, Carbon coated-LiMn0.8Fe0.2PO4, and Carbon coated-LiFePO4), LiCoO2 and LiNi0.8Co0.15Al0.05O2 (NCA) composite electrodes with LiPF6 solutions in ethylene carbonate (EC)/dimethyl carbonate (DMC) and EC/propylene carbonate (PC), was investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis, coupled with mass spectrometry. The thermal reactions products were measured by XRD and electron microscopy. The LiFePO4 and LiMnPO4 cathode materials were found to have comparable thermal stability in their pristine and fully delithiated states. The onset temperatures of the thermal reactions are lower in EC/DMC than in EC/PC solutions but the specific heat evolution of all the thermal reactions are higher with EC-PC solutions. No evidence was found that delithiated LiMnPO4 or Li[MnFe]PO4 have lower thermal stability than delithiated LiFePO4. The thermal reactivity of the layered LiCoO2 and LiNi0.8Co0.15Al0.05O2 cathode materials was found to be comparable to that of the LiMPO4 materials. Oxygen release was detected from the layered compounds upon their heating around 200°C.

In situ neutron radiography of lithium-ion batteries during charge/discharge cycling

Commercial, prismatic lithium-ion cells, type ICP-340848 (Renata AG, Switzerland), were investigated using neutron radiography. The measurements revealed that an excess of electrolyte initially present in the cell was consumed after first cell charging and solid electrolyte interphase formation. In situ neutron radiography of the lithium-ion cells during the first charge/discharge cycles showed a displacement of such excess electrolyte owing to volume changes of the electrode assembly as well as to an evolution of gases in the first charging cycle.

Li4Ti5O12/LiMnPO4 Lithium-Ion Battery Systems for Load Leveling Application

A new type of lithium-ion cell based on the combination of spinel Li4Ti5O12 anode with a high voltage olivine LiMnPO4 cathode, which can be promising for load leveling applications, is demonstrated for the first time. The power and safety characteristics of this battery system were found to meet the requirement for this application. The structure, surface morphology, and the performance were characterized by X-ray diffraction (XRD), high-resolution scanning electron microscopy (HRSEM) and standard electrochemical techniques. A stable reversible capacity up to 125 mAh g � 1 of the cathode in full cell could be measured at discharge potentials >2.5 V with a reasonable capacity retention during prolonged charge/discharge cycling. The thermal stability of pristine and electrochemically delithiated LiMnPO4-Li4Ti5O12 composite cathodes and anodes in contact with the electrolyte solution was investigated by differential scanning calorimetry (DSC). The electrodes were also studied by thermogravimetric analysis, coupled with mass spectrometry. We did not found appreciable changes in the thermal stability of the electrodes in their pristine and charged states, in contact with LiPF6 solution in mixtures of ethylene carbonate (EC) and dimethyl carbonate (DMC).