Per Vullum - Academia.edu (original) (raw)

Papers by Per Vullum

ACS Nano, Mar 14, 2018

A rechargeable Mg battery where the capacity mainly originates from reversible reactions occurrin... more A rechargeable Mg battery where the capacity mainly originates from reversible reactions occurring at the electrode/electrolyte interface efficiently avoids the challenge of sluggish Mg intercalation encountered in conventional Mg batteries. The interfacial reactions in a cell based on microwave exfoliated graphite oxide (MEGO) as the cathode, and all phenyl complex (APC) as electrolyte, are by quantitative kinetics analysis identified as a combination of diffusioncontrolled reactions involving ether solvents (esols) and capacitive processes. During magnesiation, esols in APC electrolytes can significantly affect the electrochemical reactions and charge transfer resistances at the electrode/electrolyte interface, and thus govern the charge storage properties of the MEGO cathode. In APC-tetrahydrofuran (THF) electrolyte, MEGO exhibits a reversible capacity of ~220 mAh g-1 at 10 mA g-1 , while a reversible capacity of ~750 mAh g-1 at 10 mA g-1 was obtained in APC-1,2-dimethoxyethane (DME) electrolyte. The high capacity improvement not only points to the important role of the esols in the APC electrolytes, but also presents a Mg battery with high interfacial charge storage capability as a very promising and viable competitor to the conventional intercalation-based batteries.

Metallurgical and Materials Transactions, May 10, 2023

Hybrid metal extrusion & bonding (HYB) is a solid-state welding method where an aluminum (Al) fil... more Hybrid metal extrusion & bonding (HYB) is a solid-state welding method where an aluminum (Al) filler wire is continuously extruded into the weld groove between the metal parts to be joined by the use of a rotating steel tool that provides friction and plastic deformation. Although the HYB method was originally invented for Al joining, the process has shown great potential also for multi-material joining. This potential is explored through characterization of a unique Al-copper-steel-titanium (Al-Cu-steel-Ti) butt joint made in one pass. Each of the three dissimilar metal interface regions are characterized in terms of microstructure and tensile properties. Scanning and transmission electron microscopy reveals that bonding is achieved through a combination of nanoscale intermetallic phase formation and microscale mechanical interlocking. Electron diffraction is used to identify the main intermetallic phases present in the interfacial layers. Machining of miniature specimens enables tensile testing of each interface region. Overall, the presented characterization demonstrates the great potential for multi-material joining by HYB and provides fundamental insight into solid-state welding involving bonding of Al to Ti, steel, and Cu.

$Research paper thumbnail of Dynamic observation of dislocation evolution and interaction with twin boundaries in silicon crystal growth using in – situ synchrotron X-ray diffraction imaging$

Acta Materialia, May 1, 2021

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

ACS applied nano materials, Jul 21, 2023

Nano Energy, Jun 1, 2018

Mg batteries are one of several new battery technologies expected to partially substitute lithium... more Mg batteries are one of several new battery technologies expected to partially substitute lithium-based batteries in the future due to the lower cost and higher safety. However, the development of Mg batteries has been greatly hindered by the sluggish Mg migration kinetics in the solid state. Here, we exploit a high performance cathode for Mg battery based on a tailored nanocomposite, synthesized by in-situ growth of nanocrystalline Mn3O4 on graphene substrates, which provides high reversible capacities (~220 mAh g-1 at 15.4 mA g-1 and ~80 mAh g-1 at 1.54 A g-1), good rate performance (high reversibility at various current rates), and excellent cycling stability (no capacity decay after 700 hundred cycles). The magnesiation mechanism in our cell system has been identified as a combination of capacitive processes and diffusion-controlled reactions involving electrolyte solvents. Characterization is performed by ex-situ transmission electron microscopy (TEM)/scanning TEM (STEM), energy dispersive spectroscopy (EDS), electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS) in addition to quantitative kinetics analysis. Exploiting the highperformance capacitive-type electrodes, where the specific capacity is limited by the kinetics of surface processes and not by bulk Mg ion diffusion governing the properties of conventional intercalation-type electrodes, could reveal a new approach to developing commercially viable Mg batteries.

Journal of power sources advances, Mar 1, 2023

The use of orthophosphoric acid to stabilize aqueous processing of high nickel NMC622 electrodes ... more The use of orthophosphoric acid to stabilize aqueous processing of high nickel NMC622 electrodes was assessed under rapid processing conditions, in which the active material powder was in suspension for less than 1 hour. It was found, as previously reported, that corrosion of the aluminum current-collector was suppressed, and capacity retention greatly improved relative to aqueous-processed material without orthophosphoric acid addition. The rapid processing conditions led to incomplete reaction of the orthophosphoric acid with the surface of the electrode active material however, with concomitant formation of orthophosphate precipitates upon drying. Reaction of these with organic carbonate electrolytes resulted in rapid cell death typically occurring between 50 and 100 cycles, characterized by formation of a thick degradation film on the NMC622 cathode. Washing with ethanol was found to remove the components responsible for the degradation process, yielding an electrode that demonstrated almost 400 cycles with 78% capacity retention. It is concluded that whilst the addition of orthophosphoric acid aids aqueous processing of NMC materials, close attention must be paid to the quantities and reaction times used. Sustainability spotlight Aqueous Li-ion cathode production is aligned with: SDG7. Affordable and clean energy-LIBs can mitigate issues associated with the intermittency of energy harvesting (e.g., solar cells and wind turbines). Aqueous processing can further decrease the price of cathode processing and hence of LIBs. By replacing the uorinated cathode binder with a biopolymer, the price and environmental footprint will be further improved. SDG13. Climate actionaqueous cathode processing will mitigate the use and recovery of the harmful organic pyrrolidone solvent used in the LIB industry. Lower energy consuming and more environmentally friendly battery production will contribute to improving our climate.

Nanotechnology, Sep 27, 2013

3D aligned-carbon-nanotubes (ACNTs)@Li2FeSiO4 nanocomposite arrays on Al foil were developed as c... more 3D aligned-carbon-nanotubes (ACNTs)@Li2FeSiO4 nanocomposite arrays on Al foil were developed as cathode materials for Li-ion batteries. The ACNTs were grown directly on an Al foil by a chemical vapor deposition method to achieve a 3D current collector structure for direct charge transport. Li2FeSiO4 nanoparticles were deposited on the surface of the ACNTs by a polyvinylalcohol (PVA)-assisted sol-gel method. The 3D samples showed a high degree of alignment of nanotubes with a favorable pore morphology before and after cycling. According to electrochemical measurements, the 3D sample with optimized mass ratio of ACNTs and Li2FeSiO4 (2:1) showed excellent rate capability and capacity retention, delivering a discharge specific capacity of 142 mAh g(-1) at a rate of 0.5 C (C = 160 mAg(-1)) and maintaining 99% of the initial discharge capacity after 50 cycles at 24 ° C. Up to 20 C, the delivered charge/discharge capacity was 94 mAh g(-1) after 172 cycles, which is 54% of the value obtained at C/20 (175 mAh g(-1)). In comparison, carbon coated nanoporous Li2FeSiO4 obtained under analogous conditions by a PVA-assisted sol-gel method can only deliver a capacity of 80 mAh g(-1) and showed poor rate capability. In addition, despite amorphization, dissolution and chemical composition changes occurring in the 3D samples upon extended cycling, the 3D samples showed good long-term cycling stability at a high current density (5 C), maintaining ~80% of the initial discharge capacity after 1000 cycles and ~70% after 2000 cycles.

Journal of Physical Chemistry C, May 24, 2016

Vanadium substitution is an interesting approach to manipulate the properties of the poor electro... more Vanadium substitution is an interesting approach to manipulate the properties of the poor electronic and ionic conducting lithium transition metal orthosilicates. Especially, if incorporated on the Si-site it could alter the highly insulating character of the SiO 4 framework. This study addresses the feasibility and limitations of V substitution in Li 2 MnSiO 4. Nominal compositions of Li 2 Mn 1-x V x SiO 4 (0 ≤ x ≤ 0.2) and Li 2 MnSi 1-x V x O 4 (0 ≤ x ≤ 0.3) were synthesized by a sol-gel method, and the structural evolution was analyzed by X-ray diffraction and transmission electron microscopy (TEM) coupled with electron energy loss spectroscopy (EELS). While the solid solubility of V on tetrahedral Mn-sites was shown to be limited, substantial amounts of V entered the structure when intended to substitute Si. Elemental mapping by TEM showed that V was highly inhomogeneously distributed and high energy resolution EELS demonstrated that the

Journal of Power Sources, Feb 1, 2019

This work investigates the impact of electrochemical reactions and products on discharge capacity... more This work investigates the impact of electrochemical reactions and products on discharge capacity and cycling stability with electrolytes based on two common solvents-tetraethylene glycol dimethyl ether (TEGDME) and dimethyl sulfoxide (DMSO). Although the DMSO-based electrolyte exhibits better initial electrochemical properties compared to that based on TEGDME, e.g., higher discharge capacity and potential, the use of TEGDME results in a significantly better cycling stability. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) investigations of the gas diffusion electrodes (GDE) after first discharge reveal a considerable difference in discharge product morphology. With DMSO as solvent one high-potential reduction process leads to the formation of crystalline lithium peroxide (Li2O2) particles on the cathode surface area. SEM imaging of GDE cross-sections depicts that the (non-crystalline) product film formation at lower potentials during discharge with the TEGDME-based electrolyte results in a GDE pore clogging close to the O2 inlet, so that gas transport is hindered and the discharge ends at an earlier point. The higher cycling stability with LiTFSI/TEGDME, however, is attributed to (i) the apparently complete recovery of the GDE active surface by recharge and (ii) different parasitic reactions resulting in the formation of side product particles rather than films.

Journal of Alloys and Compounds, 2011

Possibilities and limitations in using transmission electron microscopy to characterize pure NaAl... more Possibilities and limitations in using transmission electron microscopy to characterize pure NaAlH4 and transition metal enhanced NaAlH4 have been investigated in detail. NaAlH4 is extremely sensitive to O2 and H2O and must be handled under inert atmosphere at all times. Furthermore, it is highly unstable under the electron beam and only basic techniques such as diffraction contrast imaging and selected

Chemistry of Materials, Dec 21, 2022

arXiv (Cornell University), Nov 27, 2016

Geometric phase analysis has been applied to high resolution aberration corrected (scanning) tran... more Geometric phase analysis has been applied to high resolution aberration corrected (scanning) transmission electron microscopy images of InAs/GaAs quantum dot (QD) materials. We show quantitatively how the lattice mismatch induced strain varies on the atomic scale and tetragonally distorts the lattice in a wide region that extends several nm into the GaAs spacer layer below and above the QDs. Finally, we show how V-shaped dislocations originating at the QD/GaAs interface efficiently remove most of the lattice mismatch induced tetragonal distortions in and around the QD.

Inorganic Chemistry, Sep 22, 2022

The crystal structure of tetragonal tungsten bronzes, with the general formula A12A24C4B12B28O30,... more The crystal structure of tetragonal tungsten bronzes, with the general formula A12A24C4B12B28O30, is flexible both from a chemical and structural viewpoint, resulting in a multitude of compositions. The A1 and A2 lattice sites, with different coordination environments, are usually regarded to be occupied by two different cations such as in Ba4Na2Nb10O30 with Na+ and Ba2+ occupying the A1 and A2 sites, respectively. Here, we report on a systematic study of the lattice site occupancy on the A1 and A2 sites in the series Ba4M2Nb10O30 (M = Na, K, and Rb). The three compounds were synthesized by a two-step solid-state method. The site occupancy on the A1 and A2 sites were investigated by a combination of Rietveld refinement of X-ray diffraction patterns and scanning transmission electron microscopy with simultaneous energy-dispersive spectroscopy. The two methods demonstrated consistent site occupancy of the cations on the A1 and A2 sites, rationalized by the variation in the size of the alkali cations. The cation order–disorder phenomenology in the tungsten bronzes reported is discussed using a thermodynamic model of O’Neill and Navrotsky, originally developed for cation interchange in spinels.

Ultramicroscopy, Dec 1, 2021

Nitrogen (N) is a common element added to GaAs for band gap engineering and strain compensation. ... more Nitrogen (N) is a common element added to GaAs for band gap engineering and strain compensation. However, detection of small amounts of N is difficult for electron microscopy as well as for other chemical analysis techniques. In this work, N in GaAs is examined by using different transmission electron microscopy (TEM) techniques. While both dark-field TEM imaging using the composition sensitive (002) reflections and selected area diffraction reveal a significant difference between the doped thin-film and the GaAs substrate, spectroscopy techniques such as electron energy loss and energy dispersive X-ray spectroscopy are not able to detect N. To quantify the N content, quantitative convergent beam electron diffraction (QCBED) is used, which gives a direct evidence of N substitution and As vacancies. The measurements are enabled by the electron energy-filtered scanning CBED technique. These results demonstrate a sensitive method for composition analysis based on quantitative electron diffraction.

Meeting abstracts, Sep 1, 2016

Silicon as anode material for Li-ion batteries is interesting due to its very high theoretical ca... more Silicon as anode material for Li-ion batteries is interesting due to its very high theoretical capacity. However, the positive ability to accommodate up to four lithium ions per silicon atom has a corresponding downside in the extreme changes occurring in the battery, usually leading to rapid degradation. A silicon-carbon composite made by a cost-effective and environmental-friendly production of the raw materials has been tested. The effect of silicon quality, as chemical composition and particle size as well as binder composition and electrolyte additives, have been examined. Post mortem studies were performed to understand the mechanisms. The tests showed more than 1200 cycles of a 600 mAh/g total anode.

Journal of physics, Aug 1, 2008

Transmission electron microscopy (TEM) has been used to characterize NaAlH 4, doped with Ti, afte... more Transmission electron microscopy (TEM) has been used to characterize NaAlH 4, doped with Ti, after H cycling. NaAlH 4 was shown to be highly unstable under the electron beam, and "knock on" damage lead to a decomposition of NaAlH 4 with Na and H evaporating from the sample. All Ti containing phases were stable under the electron beam. After H cycling, the Ti was present as a mixture of amorphous and crystalline Al 1-x Ti x .

Journal of Crystal Growth, Sep 1, 2020

Silicon carbide (SiC) micro bullets were grown on a bio-carbon based charcoal substrate, the morp... more Silicon carbide (SiC) micro bullets were grown on a bio-carbon based charcoal substrate, the morphology and crystal structure were analyzed. In order to collect the crystallographic details scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM/TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) were used. For this a thin lamella from the SiC micro bullet was extracted by focused ion beam (FIB). Electron microscopy revealed that the SiC micro bullets had a high density of stacking faults along their growth direction. However, the size and morphology of the micro bullets were relatively homogeneous, despite the high stacking fault density, i.e. the growth was quite robust at the synthesis temperature (1750°C). The findings open up to SiC ceramics from bio-carbon with anisotropic porosity for the development of novel light weight high temperature resistant materials.

Nanotechnology, Oct 30, 2018

We report on the self-assembled growth of high-density and vertically-oriented n-doped GaN nanoco... more We report on the self-assembled growth of high-density and vertically-oriented n-doped GaN nanocolumns on graphene by radio-frequency plasma-assisted molecular beam epitaxy. Graphene was transferred to silica glass, which was used as substrate carrier. Using a migration enhanced epitaxy grown AlN buffer layer for the nucleation is found to enable a high density of vertical GaN nanocolumns with c-axis growth orientation on graphene. Furthermore, micro-Raman spectroscopy indicates that the AlN buffer reduces damage on the graphene caused by impinging active N species generated by the radio-frequency plasma source during the initial growth stage and nucleation of GaN. In addition, the grown GaN nanocolumns on graphene are found to be virtually stress-free. Micro-photoluminescence measurements show near band-edge emission from wurtzite GaN, exhibiting higher GaN bandgap related photoluminescence intensity relative to a reference GaN bulk substrate and the absence of both yellow luminescence and excitonic defect emission. Transmission electron microscopy reveals the interface of GaN nanocolumns on graphene via thin AlN buffer layer. Even though the first few monolayers of AlN on top of graphene are strained due to in-plane lattice mismatch between AlN and graphene, the grown GaN nanocolumns have wurtzite crystal structure without observable defects. The results of this initial work pave the way towards realizing low-cost and high-performance electronic and optoelectronic devices based on III-N semiconductors grown on graphene.

Journal of Microscopy, Nov 3, 2016

Beryl in different varieties (emerald, aquamarine, heliodor etc.) displays a wide range of colour... more Beryl in different varieties (emerald, aquamarine, heliodor etc.) displays a wide range of colours that have fascinated humans throughout history. Beryl is a hexagonal cyclo-silicate (ringsilicate) with channels going through the crystal along the c-axis. The channels are about 0.5 nm in diameter and can be occupied by water and alkali ions. Pure beryl (Be 3 Al 2 Si 6 O 18) is colourless (variety goshenite). The characteristic colours are believed to be mainly generated through substitutions with metal atoms in the lattice. Which atoms that are substituted is still debated it has been proposed that metal ions may also be enclosed in the channels and that this can also contribute to the crystal colouring. So far spectroscopy studies have not been able to fully answer this. Here we present the first experiments using atomic resolution scanning transmission electron microscope imaging (STEM) to investigate the channel occupation in beryl. We present images of a natural beryl crystal (variety heliodor) from the Bin Thuan Province in Vietnam. The channel occupation can be visualized. Based on the image contrast in combination with ex situ element analysis we suggest that some or all of the atoms that are visible in the channels are Fe ions. Authors V. Arivazhagan and F. D. Schmitz contributed equally.