Michael Holzapfel | Fraunhofer - Academia.edu (original) (raw)
Papers by Michael Holzapfel
Journal of Electroanalytical Chemistry, 2003
In this study graphite has been characterised by electrochemical impedance spectroscopy (EIS) usi... more In this study graphite has been characterised by electrochemical impedance spectroscopy (EIS) using a three electrode coin cell. The initial lithiation shows that lithium insertion can be modelled using the Langmuir insertion isotherm as well as the Frumkin insertion isotherm for very low insertion levels. A description of the equivalent circuits used to fit the high frequency (HF) part of
Journal of the Electrochemical Society, 2008
ABSTRACT Three lithium vanadate materials with the nominal composition Li1.1V3O8 have been prepar... more ABSTRACT Three lithium vanadate materials with the nominal composition Li1.1V3O8 have been prepared by a spray-drying technique with subsequent heat-treatment (A) at 320 degrees C, (B) at 585 degrees C, and (C) at 585 degrees C with carbon. They have been analyzed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, electronic conductivity, Brunauer-Emmett-Teller surface-area characterization, and electrochemical charge-discharge tests in lithium cells. The best material had a spherical aggregate morphology and exhibited, at 25 degrees C in a narrow potential range of 2.0-3.3 V vs Li/Li+, at 116 mA/g (C/3) a high discharge capacity of 260 mAh/g in the 2nd cycle and 220 mAh/g in the 60th cycle, respectively, which is to the best of our knowledge the best electrochemical performance reported so far for Li1.1V3O8. The rate capability of these positive-electrode materials was found to be limited mainly by the lithium diffusion length in the primary particles. (c) 2008 The Electrochemical Society.
Structural changes occurring upon electrochemical delithiation in Li x Co 1− y Fe y O 2 solid sol... more Structural changes occurring upon electrochemical delithiation in Li x Co 1− y Fe y O 2 solid solutions have been examined using in-situ electrochemical X-ray diffraction on plastic batteries, for y= 0.1, 0.2, 0.4 and 0.7. Two key points are emphasised in this study:(i) the ...
Solid State Ionics, 2010
Cubic Li2TiO3 samples (space group Fm-3m) were synthesized by hydrothermal reactions at 180°C for... more Cubic Li2TiO3 samples (space group Fm-3m) were synthesized by hydrothermal reactions at 180°C for 18h, using titania powder and lithium hydroxide in de-ionized water. The samples were found to be unstable under atmospheric conditions as Li2CO3 could be detected by X-ray powder diffraction (XRPD) on their surface. Therefore, the stability of cubic Li2TiO3 when exposed to water was investigated. In water-flushing and bathing experiments the interaction of water with the samples could be demonstrated. The observed lithium loss was analyzed by atomic absorption spectroscopy and its influence on the structural properties of cubic Li2TiO3 was determined by conventional XRPD and multi-temperature synchrotron XRPD.
Zeitschrift für Kristallographie, 2011
Page 1. Temperature-dependent structural transformations of hydrothermally synthesized cubic Li2T... more Page 1. Temperature-dependent structural transformations of hydrothermally synthesized cubic Li2TiO3 studied by in-situ neutron diffraction Andreas Laumann*, I, Karl Thomas FehrI, Hans BoysenII, Markus HoelzelIII, 1 and Michael HolzapfelIV ...
Journal of Solid State Chemistry, 2000
ABSTRACT
Journal of Power Sources, 2004
In situ neutron radiography (NR) was used to study the gas evolution on graphite electrodes in li... more In situ neutron radiography (NR) was used to study the gas evolution on graphite electrodes in lithium-ion cells containing different PVDF-based gel-type electrolytes. The amount of gas bubbles and channels was calculated by image analysis. Gas production was extremely high in the case of the electrolyte containing ethylene carbonate (EC) and propylene carbonate (PC) (2:3, w/w), 1 M LiClO 4 . About 60% of the electrode surface consisted of the gas phase which resulted in an inhomogeneous local current distribution. In contrast, the electrolyte containing EC and ␥-butyrolactone (GBL) (1:1, w/w), 1 M LiBF 4 only showed a small increase of the gas volume between the electrodes of about 3%. In situ NR also revealed the displacement of the electrolyte due to gas evolution and volume changes of the electrodes.
Journal of Materials Chemistry, 2004
Structural changes occurring upon electrochemical delithiation in Li x Co 1− y Fe y O 2 solid sol... more Structural changes occurring upon electrochemical delithiation in Li x Co 1− y Fe y O 2 solid solutions have been examined using in-situ electrochemical X-ray diffraction on plastic batteries, for y= 0.1, 0.2, 0.4 and 0.7. Two key points are emphasised in this study:(i) the ...
Journal of Magnetism and Magnetic Materials, 2001
ABSTRACT
Journal of Magnetism and Magnetic Materials, 2002
ABSTRACT
Journal of The Electrochemical Society, 2012
Li 4 Ti 5 O 12 , which is a high performance anode material for rechargeable Li-ion batteries, is... more Li 4 Ti 5 O 12 , which is a high performance anode material for rechargeable Li-ion batteries, is crystallized directly via a novel continuous flow hydrothermal method using lithium ethoxide and titanium isopropoxide as reactants. Crystalline nanoparticles are obtained in a single step and in less than one minute, by mixing the reactants with superheated water in a continuous flow reactor at nearand supercritical conditions. The Li 4 Ti 5 O 12 nanoparticles have an average crystallite size of 4.5 nm with a specific surface area of ≥230 m 2 /g. In-situ synchrotron powder X-ray diffraction measurements upon annealing of the nanocrystalline Li 4 Ti 5 O 12 were performed in order to investigate the structural and microstructural changes from room temperature to 727 • C. The as-prepared crystalline nanoparticles show significant crystallographic strain, which is found to relax upon annealing above 500 • C, concurrent with crystallite growth. Electrochemical tests of the as-prepared Li 4 Ti 5 O 12 and a sample annealed at 600 • C reveal that heat-treatment results in a significant improvement of the performance in terms of the specific capacity and the rate capability, and overall the annealed nanoparticles have excellent electrochemical properties. The origin of the crystallographic strain is discussed, and further optimization of this rapid, green and scalable synthesis approach is suggested.
Journal of Applied Crystallography, 2008
ABSTRACT
European Journal of Inorganic Chemistry, 2011
... In-situ Synchrotron X-ray Diffraction Study of the Formation of Cubic Li 2 TiO 3 Under Hydrot... more ... In-situ Synchrotron X-ray Diffraction Study of the Formation of Cubic Li 2 TiO 3 Under Hydrothermal Conditions. Andreas Laumann 1 ,; Kirsten Marie ??rnsbjerg Jensen 2 ,; Christoffer Tyrsted 2 ,; Martin Bremholm 3 ,; Karl Thomas Fehr 1 ,; Michael Holzapfel 4 ,; ... Mulder , J. Am. Chem ...
Chemistry of Materials, 2011
The structure of the anode material Li4Ti5O12 has been investigated by neutron powder diffraction... more The structure of the anode material Li4Ti5O12 has been investigated by neutron powder diffraction up to 1100° C. At 900° C, lithium migration to 32e sites around the 16c positions takes part, leading to a new long-range three-dimensional diffusion path in all⟨ 110⟩ ...
Chemical Communications, 2004
1-Ethyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide (EMI-TFSI) has been shown to revers... more 1-Ethyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide (EMI-TFSI) has been shown to reversibly permit lithium intercalation into standard graphite when vinylene carbonate is used in small amounts as an additive.
Journal of Power Sources, 2011
This manuscript presents the work carried out within the European project ILLIBATT, which was ded... more This manuscript presents the work carried out within the European project ILLIBATT, which was dedicated to the development of green, safe and high performance ionic liquids-based lithium batteries. Different types of ionic liquids-based electrolytes were developed in the project, based on different ionic liquids and polymers. Using these electrolytes, the performance of several anodic and cathodic materials has been tested and promising results have been obtained. Also, electrodes were formulated using water soluble binders. Using these innovative components, lithium-ion and lithium-metal battery prototypes (0.7–0.8Ah) have been assembled and cycled between 100% and 0% SOC. The results of these tests showed that such ionic liquids-based prototypes are able to display high capacity, high coulombic efficiency and high cycle life. Moreover, safety tests showed that the introduction of these alternative electrolytes positively contribute to the safety of the batteries.
Journal of Power Sources, 2005
Several TIMREX ® synthetic and natural graphite negative electrode materials with different parti... more Several TIMREX ® synthetic and natural graphite negative electrode materials with different particle size distributions were tested with regard to their compatibility with propylene carbonate used as electrolyte component in lithium-ion cells. The first lithium insertion properties of these graphite materials were characterised in electrochemical lithium half-cells containing 1 M LiPF 6 in ethylene carbonate/propylene carbonate as electrolyte system. Post mortem scanning electron microscopy was applied to study the exfoliation process observed for some of these graphite materials especially with coarser particle sizes. X-ray diffraction, Raman spectroscopy and nitrogen gas adsorption were used to characterise and correlate the material bulk and surface properties of the graphite materials with their electrochemical performance. Differential electrochemical mass spectrometry was applied to study the passivation process of the graphite material surface during the first electrochemical reduction. Non-exfoliating graphite materials indicate the formation of an efficient solid electrolyte interphase, which seems to be kinetically controlled by intrinsic properties of the graphite material bulk and surface.
Electrochemical and Solid-State Letters, 2005
Post mortem scanning electron microscopy was used to study the surface film formation on differen... more Post mortem scanning electron microscopy was used to study the surface film formation on different cathode materials for lithium-ion batteries. The effect of the kind of oxide, the type of solvent and conducting salt, as well as the influence of additives on this process was investigated. In the case of an electrolyte containing ethylene carbonate ͑EC͒ and propylene carbonate ͑PC͒ ͑1:1, w/w͒ with 1 M LiPF 6 , film formation was observed on LiCoO 2 , LiMn 2 O 4 , and especially pronounced on LiNiO 2 oxide materials. In contrast, with EC, dimethyl carbonate ͑1:1, w/w͒ 1 M LiPF 6 containing electrolyte, no solid electrolyte interface formation was detected. The substitution of LiClO 4 for LiPF 6 with PC-based electrolytes leads to a less prominent layer. If 2% vinylene carbonate was added to the PC-based electrolyte a pronounced film, presumably consisting of polymerization products of this additive, was created.
Journal of Power Sources, 2006
Graphite and nano-silicon-based negative electrodes in lithium-ion batteries with low binder cont... more Graphite and nano-silicon-based negative electrodes in lithium-ion batteries with low binder content were evaluated. The effectiveness of styrene butadiene rubber (SBR) and various types of cellulose containing electrodes were compared to standard electrodes containing PVdF as binder. The cycling performance of lithium-based half cells in EC:DMC (1:1), 1 M LiPF 6 shows that styrene butadiene rubber (SBR), sodium carboxymethyl cellulose (Na-CMC), or both combined have a similar bonding ability as conventional poly(vinylidene fluoride) (PVdF). However, using Na-CMC the irreversible charge capacity in the first cycle decreased in comparison with electrodes containing PVdF binder. Nano-Si electrode containing 1% SBR/1% Na-CMC as binder show the same cycle stability as an identical electrode containing 10% PVdF binder.
Journal of Electroanalytical Chemistry, 2003
In this study graphite has been characterised by electrochemical impedance spectroscopy (EIS) usi... more In this study graphite has been characterised by electrochemical impedance spectroscopy (EIS) using a three electrode coin cell. The initial lithiation shows that lithium insertion can be modelled using the Langmuir insertion isotherm as well as the Frumkin insertion isotherm for very low insertion levels. A description of the equivalent circuits used to fit the high frequency (HF) part of
Journal of the Electrochemical Society, 2008
ABSTRACT Three lithium vanadate materials with the nominal composition Li1.1V3O8 have been prepar... more ABSTRACT Three lithium vanadate materials with the nominal composition Li1.1V3O8 have been prepared by a spray-drying technique with subsequent heat-treatment (A) at 320 degrees C, (B) at 585 degrees C, and (C) at 585 degrees C with carbon. They have been analyzed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, electronic conductivity, Brunauer-Emmett-Teller surface-area characterization, and electrochemical charge-discharge tests in lithium cells. The best material had a spherical aggregate morphology and exhibited, at 25 degrees C in a narrow potential range of 2.0-3.3 V vs Li/Li+, at 116 mA/g (C/3) a high discharge capacity of 260 mAh/g in the 2nd cycle and 220 mAh/g in the 60th cycle, respectively, which is to the best of our knowledge the best electrochemical performance reported so far for Li1.1V3O8. The rate capability of these positive-electrode materials was found to be limited mainly by the lithium diffusion length in the primary particles. (c) 2008 The Electrochemical Society.
Structural changes occurring upon electrochemical delithiation in Li x Co 1− y Fe y O 2 solid sol... more Structural changes occurring upon electrochemical delithiation in Li x Co 1− y Fe y O 2 solid solutions have been examined using in-situ electrochemical X-ray diffraction on plastic batteries, for y= 0.1, 0.2, 0.4 and 0.7. Two key points are emphasised in this study:(i) the ...
Solid State Ionics, 2010
Cubic Li2TiO3 samples (space group Fm-3m) were synthesized by hydrothermal reactions at 180°C for... more Cubic Li2TiO3 samples (space group Fm-3m) were synthesized by hydrothermal reactions at 180°C for 18h, using titania powder and lithium hydroxide in de-ionized water. The samples were found to be unstable under atmospheric conditions as Li2CO3 could be detected by X-ray powder diffraction (XRPD) on their surface. Therefore, the stability of cubic Li2TiO3 when exposed to water was investigated. In water-flushing and bathing experiments the interaction of water with the samples could be demonstrated. The observed lithium loss was analyzed by atomic absorption spectroscopy and its influence on the structural properties of cubic Li2TiO3 was determined by conventional XRPD and multi-temperature synchrotron XRPD.
Zeitschrift für Kristallographie, 2011
Page 1. Temperature-dependent structural transformations of hydrothermally synthesized cubic Li2T... more Page 1. Temperature-dependent structural transformations of hydrothermally synthesized cubic Li2TiO3 studied by in-situ neutron diffraction Andreas Laumann*, I, Karl Thomas FehrI, Hans BoysenII, Markus HoelzelIII, 1 and Michael HolzapfelIV ...
Journal of Solid State Chemistry, 2000
ABSTRACT
Journal of Power Sources, 2004
In situ neutron radiography (NR) was used to study the gas evolution on graphite electrodes in li... more In situ neutron radiography (NR) was used to study the gas evolution on graphite electrodes in lithium-ion cells containing different PVDF-based gel-type electrolytes. The amount of gas bubbles and channels was calculated by image analysis. Gas production was extremely high in the case of the electrolyte containing ethylene carbonate (EC) and propylene carbonate (PC) (2:3, w/w), 1 M LiClO 4 . About 60% of the electrode surface consisted of the gas phase which resulted in an inhomogeneous local current distribution. In contrast, the electrolyte containing EC and ␥-butyrolactone (GBL) (1:1, w/w), 1 M LiBF 4 only showed a small increase of the gas volume between the electrodes of about 3%. In situ NR also revealed the displacement of the electrolyte due to gas evolution and volume changes of the electrodes.
Journal of Materials Chemistry, 2004
Structural changes occurring upon electrochemical delithiation in Li x Co 1− y Fe y O 2 solid sol... more Structural changes occurring upon electrochemical delithiation in Li x Co 1− y Fe y O 2 solid solutions have been examined using in-situ electrochemical X-ray diffraction on plastic batteries, for y= 0.1, 0.2, 0.4 and 0.7. Two key points are emphasised in this study:(i) the ...
Journal of Magnetism and Magnetic Materials, 2001
ABSTRACT
Journal of Magnetism and Magnetic Materials, 2002
ABSTRACT
Journal of The Electrochemical Society, 2012
Li 4 Ti 5 O 12 , which is a high performance anode material for rechargeable Li-ion batteries, is... more Li 4 Ti 5 O 12 , which is a high performance anode material for rechargeable Li-ion batteries, is crystallized directly via a novel continuous flow hydrothermal method using lithium ethoxide and titanium isopropoxide as reactants. Crystalline nanoparticles are obtained in a single step and in less than one minute, by mixing the reactants with superheated water in a continuous flow reactor at nearand supercritical conditions. The Li 4 Ti 5 O 12 nanoparticles have an average crystallite size of 4.5 nm with a specific surface area of ≥230 m 2 /g. In-situ synchrotron powder X-ray diffraction measurements upon annealing of the nanocrystalline Li 4 Ti 5 O 12 were performed in order to investigate the structural and microstructural changes from room temperature to 727 • C. The as-prepared crystalline nanoparticles show significant crystallographic strain, which is found to relax upon annealing above 500 • C, concurrent with crystallite growth. Electrochemical tests of the as-prepared Li 4 Ti 5 O 12 and a sample annealed at 600 • C reveal that heat-treatment results in a significant improvement of the performance in terms of the specific capacity and the rate capability, and overall the annealed nanoparticles have excellent electrochemical properties. The origin of the crystallographic strain is discussed, and further optimization of this rapid, green and scalable synthesis approach is suggested.
Journal of Applied Crystallography, 2008
ABSTRACT
European Journal of Inorganic Chemistry, 2011
... In-situ Synchrotron X-ray Diffraction Study of the Formation of Cubic Li 2 TiO 3 Under Hydrot... more ... In-situ Synchrotron X-ray Diffraction Study of the Formation of Cubic Li 2 TiO 3 Under Hydrothermal Conditions. Andreas Laumann 1 ,; Kirsten Marie ??rnsbjerg Jensen 2 ,; Christoffer Tyrsted 2 ,; Martin Bremholm 3 ,; Karl Thomas Fehr 1 ,; Michael Holzapfel 4 ,; ... Mulder , J. Am. Chem ...
Chemistry of Materials, 2011
The structure of the anode material Li4Ti5O12 has been investigated by neutron powder diffraction... more The structure of the anode material Li4Ti5O12 has been investigated by neutron powder diffraction up to 1100° C. At 900° C, lithium migration to 32e sites around the 16c positions takes part, leading to a new long-range three-dimensional diffusion path in all⟨ 110⟩ ...
Chemical Communications, 2004
1-Ethyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide (EMI-TFSI) has been shown to revers... more 1-Ethyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide (EMI-TFSI) has been shown to reversibly permit lithium intercalation into standard graphite when vinylene carbonate is used in small amounts as an additive.
Journal of Power Sources, 2011
This manuscript presents the work carried out within the European project ILLIBATT, which was ded... more This manuscript presents the work carried out within the European project ILLIBATT, which was dedicated to the development of green, safe and high performance ionic liquids-based lithium batteries. Different types of ionic liquids-based electrolytes were developed in the project, based on different ionic liquids and polymers. Using these electrolytes, the performance of several anodic and cathodic materials has been tested and promising results have been obtained. Also, electrodes were formulated using water soluble binders. Using these innovative components, lithium-ion and lithium-metal battery prototypes (0.7–0.8Ah) have been assembled and cycled between 100% and 0% SOC. The results of these tests showed that such ionic liquids-based prototypes are able to display high capacity, high coulombic efficiency and high cycle life. Moreover, safety tests showed that the introduction of these alternative electrolytes positively contribute to the safety of the batteries.
Journal of Power Sources, 2005
Several TIMREX ® synthetic and natural graphite negative electrode materials with different parti... more Several TIMREX ® synthetic and natural graphite negative electrode materials with different particle size distributions were tested with regard to their compatibility with propylene carbonate used as electrolyte component in lithium-ion cells. The first lithium insertion properties of these graphite materials were characterised in electrochemical lithium half-cells containing 1 M LiPF 6 in ethylene carbonate/propylene carbonate as electrolyte system. Post mortem scanning electron microscopy was applied to study the exfoliation process observed for some of these graphite materials especially with coarser particle sizes. X-ray diffraction, Raman spectroscopy and nitrogen gas adsorption were used to characterise and correlate the material bulk and surface properties of the graphite materials with their electrochemical performance. Differential electrochemical mass spectrometry was applied to study the passivation process of the graphite material surface during the first electrochemical reduction. Non-exfoliating graphite materials indicate the formation of an efficient solid electrolyte interphase, which seems to be kinetically controlled by intrinsic properties of the graphite material bulk and surface.
Electrochemical and Solid-State Letters, 2005
Post mortem scanning electron microscopy was used to study the surface film formation on differen... more Post mortem scanning electron microscopy was used to study the surface film formation on different cathode materials for lithium-ion batteries. The effect of the kind of oxide, the type of solvent and conducting salt, as well as the influence of additives on this process was investigated. In the case of an electrolyte containing ethylene carbonate ͑EC͒ and propylene carbonate ͑PC͒ ͑1:1, w/w͒ with 1 M LiPF 6 , film formation was observed on LiCoO 2 , LiMn 2 O 4 , and especially pronounced on LiNiO 2 oxide materials. In contrast, with EC, dimethyl carbonate ͑1:1, w/w͒ 1 M LiPF 6 containing electrolyte, no solid electrolyte interface formation was detected. The substitution of LiClO 4 for LiPF 6 with PC-based electrolytes leads to a less prominent layer. If 2% vinylene carbonate was added to the PC-based electrolyte a pronounced film, presumably consisting of polymerization products of this additive, was created.
Journal of Power Sources, 2006
Graphite and nano-silicon-based negative electrodes in lithium-ion batteries with low binder cont... more Graphite and nano-silicon-based negative electrodes in lithium-ion batteries with low binder content were evaluated. The effectiveness of styrene butadiene rubber (SBR) and various types of cellulose containing electrodes were compared to standard electrodes containing PVdF as binder. The cycling performance of lithium-based half cells in EC:DMC (1:1), 1 M LiPF 6 shows that styrene butadiene rubber (SBR), sodium carboxymethyl cellulose (Na-CMC), or both combined have a similar bonding ability as conventional poly(vinylidene fluoride) (PVdF). However, using Na-CMC the irreversible charge capacity in the first cycle decreased in comparison with electrodes containing PVdF binder. Nano-Si electrode containing 1% SBR/1% Na-CMC as binder show the same cycle stability as an identical electrode containing 10% PVdF binder.