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The elaboration of nanostructures including both functional materials and functional morphology is a crucial scientific and technological challenge. In this work diatom frustule replicas mainly consisting of magnesium silicon nitride and nanocrystalline silicon have been obtained by simultaneous metallothermic reduction and nitriding of silica diatom frustules at 800 °C. The frustule replicas retained most of the complex nanoporous structures from the original frustules in the conversion. The optical scattering, transmittance and luminescence properties of the replicas have been investigated. Luminescence was observed and attributed to the presence of silicon nanocrystals. Wavelength dependent diffraction of light was observed in bio-silica frustules but not in frustule replicas, this was attributed to surface coarsening of the replicas during reaction. Light transmittance was found to be lower in frustule replicas and was consistent with absorption of light by Si nanocrystals.

Layered Li[Ni0.8Co0.1Mn0.1]O2 cathode materials have been prepared by sol–gel and co-precipitation methods. The structural, morphological and electrochemical properties of the materials were compared. The XRD patterns show that both the sol–gel and the co-precipitation method formed single phase materials with good layered characteristics. Rietveld refinement reveals some differences in cation disorder between the two materials, where the sample synthesized by the sol–gel method shows lower Li/Ni cation disorder. SEM and BET measurements show that the sol–gel sample consists of relatively less aggregated particles giving larger BET surface area compared to the co-precipitation sample. Electrochemical tests indicate that the material prepared by the sol–gel method has slightly better electrochemical properties, with an initial discharge capacity of 200 mAh·g− 1 and capacity retention of 82.2% after 50 cycles at a cycling rate of 0.5 C, as well as better capability at 5 C. The improved performances of the sol–gel synthesized material may be attributed to the low Li/Ni disorder combined with high surface area, the latter increasing the interfacial contact area between the electrolyte and the active material. Effects of calcination conditions on the structure and electrochemical performance of the materials were also investigated. The electrochemical performance was improved by either increasing the O2 concentration in the calcination atmosphere, or by increasing the flow rate of air, showing the potential of developing low-cost synthesis routes for high-quality cathode materials.

The physio-chemical stability of the oxygen carrier material during chemical looping combustion (CLC) operation is crucial. In the present paper we discuss the challenges connected to operating a metal oxide base material in a cyclic manner between oxidizing and reducing atmospheres. Especially, focus has been put on the phase changes occurring within the oxygen carrier particles leading to changes in particle volume during operation and consequently, with time, also particle disintegration. Particle sintering may also occur for some oxygen carrier materials in their reduced form. These challenges have been exemplified through lab-scale CLC experiments carried out both in fixed bed and fluidized bed reactors. © 2013 The Author.

The crystal structure, anisotropic thermal expansion and structural phase transition of the perovskite LaFeO3 has been studied by high-temperature X-ray diffraction from room temperature to 1533 K. The structural evolution of the orthorhombic phase with space group Pbnm and the rhombohedral phase with R 3 ¯ c structure of LaFeO3 is reported in terms of lattice parameters, thermal expansion coefficients, atomic positions, octahedral rotations and polyhedral volumes. Non-linear lattice expansion across the antiferromagnetic to paramagnetic transition of LaFeO3 at TN=735 K was compared to the corresponding behavior of the ferroelectric antiferromagnet BiFeO3 to gain insight to the magnetoelectric coupling in BiFeO3, which is also multiferroic. The first order phase transition of LaFeO3 from Pbnm to R 3 ¯ c was observed at 1228±9 K, and a subsequent transition to P m 3 ¯ m was extrapolated to occur at 2140±30 K. The stability of the Pbnm and R 3 ¯ c polymorphs of LaFeO3 is discussed in terms of the competing enthalpy and entropy of the two crystal polymorphs and the thermal evolution of the polyhedral volume ratio VA/VB.

One important challenge, among several others, in using silicon nanostructures as anodes in lithium ion batteries concerns finding cost effective fabrication routes for their connection to a suitable current collector. Here we present synthesis and characterization of silicon nanostructures by plasma enhanced chemical vapor deposition and template assisted electrodeposition on conducting substrates. The two methods give materials with different morphologies. Silicon nanowires were grown by chemical vapor deposition utilizing the gold catalyzed vapor-liquid-solid growth mechanism. A decrease in the nucleation time for silicon wire growth on stainless steel and aluminum substrates was observed with increasing growth temperature and SiH4 pressure. The utilization of plasma enhancement resulted in the formation of silicon thin films. Copper substrates, without diffusion barrier, were found to be unsuitable for gold catalyzed vapor-liquid-solid growth. Silicon films and dots were deposited on copper and copper/gold substrates by template assisted electrochemical deposition in ionic liquids.

Norwegian industrial tailings and by-products, as well as naturally occurring minerals and ores have been surveyed with the purpose of identifying candidate oxygen carrier materials for use in a chemical looping combustion process. Nine materials, based on manganese and/or iron oxide, were selected for an initial screening test; six were deemed promising and were hence investigated further. Thermogravimetric experiments were performed to investigate the oxygen capacity, the reaction kinetics and reversibility of the oxygen absorption reaction. A manganese ore with a reversible capacity of 4.9 wt% oxygen at 1000 °C was selected as the most promising for chemical looping combustion applications. This material was modified by addition of calcia to explore the possibility of enhancing the kinetic, catalytic and mechanical properties. The addition of excess calcium relative to manganese resulted in formation of calcium manganite and related phases. The oxygen capacity of the modified material was 4.5 wt% at 1000 °C, but it has potential advantages in terms of kinetics and chemical and mechanical stability relative to the pure ore.

Contrary to interstitial metal hydrides, where the thermodynamic stability of the metal hydride can be tuned by substitutions on the metal lattice, few examples of such substitutions have been reported for complex hydrides. The present paper shows a new and alternative approach to affect the stability of complex hydrides by substitution on the anion lattice. A mixed hydride−flouride has been prepared from NaF, Al, and H2. The resulting complex hydride Na3AlH6-xFx is less stable than Na3AlH6. Pressure composition isotherms indicate a plateau pressure of about 25 bar for dehydrogenation at 120 °C. The crystal structure has been determined by combined neutron diffraction and synchrotron X-ray diffraction to be isostructural with Na3AlF6 and Na3AlD6. The space group is P21/n, and x was determined to be approximately 4. No ordering of D and F was observed.

Oxygen permeation measurements were performed on dense symmetric samples of Ca0.5Sr0.5Ti0.6Fe0.15Mn0.25O3−δ and compared to CaTi0.6Fe0.15Mn0.25O3−δ in order to assess the influence of the perovskite lattice volume on oxygen permeation. Oxygen flux measurements were performed in the temperature range 700–1000 °C and as function of feed side pO2 from 10−2 to 1 bar, and at high pressures up to 4 bar with a pO2 of 3.36 bar. The O2 permeability of the Sr-doped sample was significantly lower than that of the Sr-free sample, amounting to 3.9×10−3 mL min−1 cm−1 at 900 °C for a feed side pO2 of 0.21 bar. The O2 permeability of CaTi0.6Fe0.15Mn0.25O3−δ shows little variation with increased feed side pressures and reaches 1.5×10−2 mL min−1 cm−1 at 900 °C for a feed side pO2 of 3.36 bar. This is approximately 1.5 times higher than the O2 permeability with a feed side pO2 of 0.21 bar. Furthermore, in order to assess the applicability of CaTi0.6Fe0.15Mn0.25O3−δ as an oxygen membrane material, creep tests were performed under compressive loads of 30 and 63 MPa, respectively, in air in the temperature range 700–1000 °C; the results indicate a high creep resistance for this class of materials. The measured O2 permeabilities and creep rates are compared with other state-of-the-art membrane materials and their performance for relevant applications is discussed in terms of chemical and mechanical stability.

The A-site cation diffusion in LaFeO3 has been examined by inter-diffusion experiments between LaFeO3 and NdFeO3. Dense, polycrystalline bodies were annealed in contact at temperatures between 1100° and 1300°C in ambient air. The bulk- and grain-boundary inter-diffusion coefficients were calculated from concentration profiles determined by electron probe micro analysis of cross sections. The bulk- and grain-boundary inter-diffusion coefficients showed Arrhenius-type behavior with activation energies 610±30 and 600±100 kJ/mol, respectively. Based on the assumption of 1 nm thick grain boundaries the grain-boundary inter-diffusion coefficient was ∼4 orders of magnitude higher than the bulk inter-diffusion coefficient.

The phase relations in the pseudo-ternary system La 2 O 3 -SrO-Fe 2 O 3 have been investigated in air. Isothermal sections at 1100 and 1300 C are presented based on X-ray diffraction and thermal analysis of annealed samples.Extended solid solubility was observed for the compounds Sr n + 1 - v La v Fe n O 3 n + 1 - δ (n = 1, 2, 3, and x) and Sr 1 - x La x Fe 1 2 O 1 9 , while only limited solubility of La in Sr 4 - z La z Fe 6 O 1 3 ′ δ was observed. At high Fe 2 O 3 content, a liquid with low La 2 O 3 content was stable at 1300 C.

The fracture strength, fracture toughness and apparent Young’s modulus of LaFeO3 ceramics in the temperature region 25–800 °C are reported. The fracture strength of the material was observed to increase from 202 ± 18 MPa at room temperature to 235 ± 38 MPa at 800 °C. The room temperature fracture toughness was 2.5 ± 0.1 MPa m1/2. The fracture toughness decreased to 2.1 ± 0.1 MPa m1/2 at 600 °C, followed by an increase to 3.1 ± 0.3 MPa m1/2 at 800 °C. The temperature dependence of the fracture toughness correlates well with the crystallographic strain, |(a−c)|/(a+c), and ferroelastic toughening of LaFeO3 materials is inferred. Non-elastic stress–strain behaviour of the LaFeO3 materials due to ferroelasticity was confirmed by cyclic compression experiments, and residual strain was observed in the material after unloading.

Crystal structure and thermal properties of La 1-x Sr x FeO 3-δ (x = 0, 0.1, 0.3, 0.4, 0.5, and 0.75) have been studied by high-temperature X-ray diffraction and thermal analysis in air and nitrogen (p(O 2 ) 10 -3 atm) atmosphere. The first-order phase transition from orthorhombic-to-rhombohedral La 1-x -Sr x FeO 3-δ (x = 0, 0.1) was strongly shifted to lower temperatures with increasing Sr content. The phase-transition temperature was observed significantly lower in polycrystalline ceramics compared with fine powders. The temperature depression of the phase transition in the ceramics was qualitatively explained by stresses induced both by the anisotropic thermal expansion of LaFeO3 and the observed volume contraction of the phase transition. Rhombohedral La 1-x Sr x -FeO 3-δ (x = 0.3, 0.4, 0.5) were observed to transform to the cubic perovskite structure during heating. The second-order phase-transition temperature decreased with increasing Sr content and decreasing partial pressure of oxygen. On the basis of the present findings, a pseudobinary phase diagram of the LaFeO 3 -SrFeO 3-δ system is presented. Finally, a severely nonlinear thermal expansion was observed for the Sr-rich materials at high temperature. The high thermal expansion in this region is due to a chemical expansion resulting from a reduction of the valence state of Fe.

The phase relations in the pseudo-binary system SrO–Fe2O3 have been investigated in air up to 1150°C by means of powder X-ray diffraction and thermal analysis. Sr3Fe2O7−δ, SrFeO3−δ and SrFe12O19 are stable phases in the entire investigated temperature region, whereas Sr2FeO4−δ and Sr4Fe3O10−δ decompose above 930±10°C and 850±25°C, respectively. Sr4Fe6O13±δ is entropy-stabilized relative to SrFeO3−δ and SrFe12O19 above 775±25°C. Extended solid-solution Sr1±xFeO3−δ was demonstrated. On the Fe-deficient side, the extent of solid solubility appeared to decrease gradually with temperature, whereas an abrupt decrease due to formation of Sr4Fe6O13±δ was observed above 775°C on the Sr-deficient side.

The densification, microstructure and phase evolution of Sr4Fe6−xCoxO13 (0≤x≤4) materials have been investigated by powder X-ray diffraction, electron microscopy and thermal analysis. Powders were prepared by the solid state reaction method or by the EDTA precursor method. Pure Sr4Fe6O13 is stable above 775±25°C in air until it melts peritectically at 1220±5°C. Below 775°C, Sr4Fe6O13 is unstable with respect to the formation of Sr1−xFeO3−δ and SrFe12O19. Co substituted Sr4Fe6O13 is only stable in a narrow temperature region near 900°C. At higher or lower temperature, the Co-content is reduced due to formation of the perovskite SrFe1−zCozO3−δ and the solid solutions Co3−yFeyO4 (below 900°C) or Co1−yFeyO (above 900°C). A plate-like morphology of Sr4Fe6−xCoxO13 grains was observed both in calcined powders and in sintered ceramics. Ball milling of the calcined powders was necessary prior to the sintering in order to achieve dense materials in the temperature region 1120–1170°C. Only pure Sr4Fe6O13 appeared as a single-phase material after sintering. Increasing amounts of the phases SrFe1−zCozO3−δ and Co1−yFeyO were observed with increasing sintering temperature and increasing Co-content due to the limited solubility of Co in Sr4Fe6−xCoxO13. The thermal expansion coefficient of the materials deviates from linear behavior due to the decreasing oxidation state of iron with increasing temperature. The present investigation demonstrates that Sr4Fe4Co2O13 materials with high oxygen permeability are not single-phase materials when sintered at high temperature.

Introduction Electrochemical storage units such as batteries and capacitors are used to store electrical energy for a wide range of applications. Different battery chemistries can be selected depending on their applications. The last decades, Li ion batteries have been widely introduced in e.g. hybrid and electrical vehicles. In the Li ion battery, the active electrode materials typically consist of metal oxide as the cathode and graphite as the anode where both have the ability to intercalate Li ions. For a more widespread use of Li ion batteries, either price has to decrease or the performance must be enhanced. Capacity can be increased by different means, such as replacing graphite with silicon by different methods and/or by changing the cathode materials. However, more effort should be focused on the cathode electrode chemistry, since this electrode has higher cost, use less environmentally benign materials and have a lower capacity compared to the anode. The introduction of LiFePO4has partly solved this problem, by removing the expensive, toxic and less abundant metals. However, this cathode material has challenges related to poor electronic conductivity and introduction of carbon and the importance of nanosized particles make the process more complex and expensive. The orthosilicates Li2(Fe, Mn, Co)SiO4 have been proposed as a promising family of cathode materials with possible additional benefits compared to LiFePO4 such as two available Li ions per formula unit for charge transport and better stability due to the SiO4 group. However, the orthosilicates with the even lower conductivity compared to LiFePO4and challenges related to the existence of several stable crystallographic polymorphs must be solved. Preferably this should be accomplished using inexpensive processing routes and precursors. Here, we present possible ways to accomplish this by using raw materials readily available in Norway, combined with conventional processing routes. The cathode materials are compared with similar materials synthesized by other complex routes. Experimental Li2Fe1-xMnxSiO4/C composites where prepared by mixing Li2CO3, iron and/or manganese source, silica source and carbon source. The different sources were Fe3O4 submicron powders and Fe-oxalate Mn-oxide based dust / Mn-oxide chemical grade. Fused silica and silica waste from Si production Sucrose and glucose. The pressed pellets were heat treated in an argon atmosphere at optimized temperature and time to form as phase pure active cathode material as possible. The composites were examined for phase purity (XRD) and morphology (SEM and TEM). The electrochemical performance Li2Fe1-xMnxSiO4 cathode materials was studied using a CR2016 coin cell consisting of a Li foil anode, Celgard 2320 separator and 1.0M LiPF6in 3:7 EC:DEC electrolyte. Charge/discharge behavior was studied by galvanostatic cycling to evaluate the charge capacity and stability while the insertion and extraction reactions were studied by cyclic voltammetry. The electrochemical characteristics of the different batteries are discussed and related to the synthesis techniques and different precursors of the cathodes. Acknowledgement Financial support is gratefully acknowledged from the Research Council of Norway RENERGI program, grant number 216469/E20.

Rechargeable Li-ion batteries are already widely used, and the dominating solution for automotive as well as portable, high-power applications due to the superior power density. However, several challenges of Li-ion battery technology are yet to be overcome, e.g. with respect to cost, resource availability, safety issues related to risk of thermal runaway of batteries and the limited temperature window of Li-ion batteries due to electrolyte deterioration at low temperatures. Although expected to dominate the portable battery market in the foreseeable future, the above mentioned drawbacks of Li-based batteries mean they have limited suitability in several markets, including stationary energy storage systems and auxiliary power applications where low cost and high reliability under a wide temperature range are more important than low weight and high power density. There is therefore a need for development of new battery types, specifically aimed at low cost markets. Batteries based on magnesium and other divalent metal ions, with the option of transferring two electrons, compared to the one electron transferred in Li-ion batteries, were introduced around 2000 by Aurbach et al.[1] and represent a promising solution for future low cost, high energy density batteries. Rechargeable Mg-batteries are not yet commercially available, but have a theoretical energy density in the range of 100 Wh/kg[2] for Chevrel-phase cathodes and up to 500 Wh/kg for MgMnSiO4 cathodes[3]. Still, fundamental research is needed in order to produce high-performance batteries which are also stable and recyclable. In this aspect, an interdisciplinary approach covering modeling, innovative material synthesis routes and advanced experimental characterization techniques is a powerful combination which is herein proposed for the development of low cost novel Mg-ion batteries. Such developments will be beneficial for a wide range of applications, mainly stationary, that require use of batteries, such as for storage of renewable energy from intermittent energy sources (solar, wind and wave), stand-alone power systems, telecommunication base stations, auxiliary power, etc. In this work, selected (Mg,M)2SiO4 (M=Mn or Co) materials are synthesized through an advanced sol-gel route as well as flame spray pyrolysis, aiming to obtain enhanced electrical conductivity. The developed cathode materials are characterized electrochemically by using Mg alloys as the anode and a state-of-the art electrolyte. In-situ X-ray diffraction (XRD) is used to characterize phase evolution in the materials during cycling. The effect of different synthesis methods on morphology, phase purity, crystal structure and electrochemical properties will be presented. [1] D. Aurbach, Lu, Z., Schechter, A., Gofer, Y., Gizbar, H., Turgeman, R., Cohen, Y., Moshkovich, M., Levi, E., Nature 2000, 407, 724-727. [2] D. Aurbach, Y. Gofer, Z. Lu, A. Schechter, O. Chusid, H. Gizbar, Y. Cohen, V. Ashkenazi, M. Moshkovich, R. Turgeman, E. Levi, Journal of Power Sources 2001, 97-98, 28-32. [3] Z. Z. Feng, J. Yang, Y. Nuli, J. L. Wang, X. J. Wang, Z. X. Wang, Electrochemistry Communications 2008, 10, 1291-1294. Acknowledgements Financial support is gratefully acknowledged from the Research Council of Norway, grant number 221785/F20.

LaCoO3 and LaFeO3 based perovskites have been studied as model materials for oxygen permeable membranes. To avoid gas leakages it is of crucial importance to obtain dense membranes, hence the densification behavior in terms of temperature, stoichiometry (AB-ratio), presence of secondary phases and substituents (Ca and Sr) have been investigated. Only a narrow temperature window for the sintering is available and it is important to avoid the formation of secondary phases. The upper temperature to obtain high density materials is limited by a severe swelling. Mechanical properties such as bending strength and fracture toughness have been determined both at ambient- and elevated temperatures. Non elastic behaviour due to ferroelasticity is reported for pure LaFeO3, LaCoO3 and La0.8Ca0.2CoO3. The ferroelasticity is found to influence the behavior of the fracture toughness and fracture strength as a function of temperature. The electrical conductivity of pure LaFeO3 at 1000°C is determined in terms of partial pressure of oxygen. Cation diffusion is found to be rate controlling for the establishment of a time independent conductivity in the p-conductivity regime.

Alternatives to Li-ion batteries are of increasing interest, mainly due to the ever increasing need for good and reliable rechargeable batteries for energy storage and delivery in a wide variety of applications, while recognizing that Li is a very limited resource. Mg ions are considered promising alternative charge carrier candidates in novel ion batteries due to the high theoretical volumetric capacity of Mg, its high abundance in the earth crust, and its stability for handling and electrode preparation processes despite high potential reactivity. However, replacing Li with Mg in conventional ion batteries is not straight forward, particularly due to the switch from monovalent to divalent ions. Changing the charge carrying ion imposes large changes on the chemical environment, thus providing the scientific community with a huge challenge in finding good anode and cathode materials, as well as electrolytes and container materials that all work together. The present work focuses on olivine-structured materials as potential cathodes, studied by theoretical methods. The work is carried out in close collaboration with experimental studies. Atomic scale calculations of the olivine structure, MgTMSiO4, with varying transition metals (TM), were performed with the Vienna ab initio simulation package (VASP). This is a density functional theory (DFT) code and the PBE generalized gradient approximation (GGA) was chosen. The unit cell was allowed to relax during ionic optimisations, and single point energy calculations on the final structure were performed for the final electronic relaxation. Hybrid calculations with 25% Hartree-Fock exchange were performed as benchmark single point calculations for some structures, as well as Hubbard GGA+U calculations to investigate the effect of localized strongly correlated d electrons. We will present results on a number of TMs in order to screen promising candidates from a thermodynamic and kinetic point of view. Some preliminary results are shown in Figure 1. Figure 1a shows that for MgTMSiO4 with TM = V, Mn and Fe, the formation of an intermediary MgxTMSiO4, x=0.25, 0.5 or 0.75, is stable with respect to the extremes with full or no magnesiation. Unit cell expansion during the uptake and release of Mg may be of crucial importance for long term stability of the final cathode. Figure 1b) shows that the maximum unit cell expansion from TMSiO4 to MgTMSiO4 is much more prominent for TM= Mn than TM = V or Fe. Nudged elastic band (NEB) calculations for the diffusion of Mg between different sites in MgMnSiO4 are shown in Figure 1c and d. Figure 1c shows that moving Mg from to a neighbouring (empty) Mg site has a 1 eV barrier. It should be noted that although the unit cell contains 4 formula units, removing either of the four Mg atoms gives 4 equivalent Mg0.75MnSiO4. This is reflected in Figure 1c where the start and end points of the NEB path are at the same energy level. In the perfect MgMnSiO4 crystal Mg occupies sites denoted 4a, and Mn the sites denoted 4c. However, scrambling is possible, and Figure 1d shows the NEB path for Mg diffusing to an empty Mn (4c) site in the case of MgMn0.75SiO4. The 0.8 eV energy difference between end and start point indicates that empty 4c sites are thermodynamically unfavourable for MgMnSiO4 and that defects arising from Mn vacancies are easily reoccupied by Mg. Figure 1 Preliminary results of calculations on MgTMSiO4 olivine materials as potential candidates for cathodes in Mg-ion batteries. (a) Reaction energies for x MgTMSiO4 + (1-x) TMSiO4 → MgxTMSiO4. (b) Maximum unit cell expansion during magnesiation. NEB-path with diffusion energies when Mg diffuses from (c) one 4a to a neighbouring 4a position in Mg0.75MnSiO4 (d) from a 4a to a 4c site in MgMn0.75SiO4.

Elkem is one of the world’s leading companies for environment-friendly production of metals and materials. Among its principal products are metallurgical silicon, solar grade silicon, and different forms of carbon. For the coming generation of Li-ion batteries, silicon is a very attractive candidate to replace graphite as anodic material due to its remarkable energy density (3.6 Ah/g) and volumetric capacity (8.3 Ah/ccm). To tackle the massive cracking and degradation typically observed during electrochemical cycling of silicon anodes, we are developing composite nanostructured materials based on existing production of silicon and carbon at Elkem. The goal is to use silicon of optimum purity and doping w.r.t. production costs and performance mixed with carbon materials through milling techniques in a commercially viable way resulting in a product that can be used as anode material in Li-ion batteries. Results show that performance can be substantially improved by using appropriate milling methods. The current presentation focuses on silicon-carbon nanostructures obtained by high-energy ball-milling in argon atmosphere. Silicon-carbon composites showed improved cycle life-time with ball-milling time, though usually accompanied with a loss of initial capacity due to high-surface area and extensive SEI formation. More pronounced improvements were achieved by co-milling silicon with graphite. Further enhancements were obtained by using additives in the electrolyte and by controlling the delithiation step during cycling. The electrochemical performance was tested in half cells where typically the working electrode was made by mixing a silicon-carbon composite powder with an organic binder in an aqueous slurry and coated on a Cu-foil. Lithium metal was used as the counter electrode. Structural properties and degradation mechanisms were examined by electron microscopy (SEM, FIB-SEM, TEM) and XRD. Figure txt: A) Charge (delithiation) capacity retention for selected Si-C based materials. The electrodes were cycled with C/20 rate for the three first and the last cycle. Other cycles were performed at C/10 rate (C-rate was based on the mass of Si assuming full capacity of 3.6 Ah/gSi). The curves labeled 1 was for materials only treated by low-energy milling of Si. A rapid decrease in capacity is seen already from cycle one. This is in contrast to composite materials made by mixed milling of graphite and silicon by high-energy ball milling (curves labeled 2 represents material milled for 20 minutes at 800 rpm, curves labeled 3 were milled at 5 minutes) where a rapid degradation zone appears first after ca. 10 cycles. FIB-SEM cross-sectional images of the cycled electrodes (cycle 8 – just before rapid degradation sets in, cycle 15 – middle of rapid degradation zone, and “dead” electrode after 55 cycles) show that the electrodes gradually become clogged both by SEI formation and Si-intergrowth and lose porosity. This is accompanied with a thickness increase, most dramatically seen after the rapid degradation zone. B) Discharge-charge characteristics for a composite Si+C electrode restricting the charge capacity to 1200 mAh/gSi pr. cycle (material: 80wt.% Si and 20wt.% graphite ball-milled for 5 minutes at 800 rpm). All electrodes were tested as half-cells with a Li-counter electrode and consisted of 60wt.% silicon, 30wt.% graphite, 2 wt.% carbon black and 8wt.% CMC. Typical loading of the active material was 0.8-1.0 mg/cm2.

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