Bodio, Switzerland


Bodio, Switzerland
Time filter
Source Type

Goers D.,TIMCAL SA | Spahr M.E.,TIMCAL SA | Leone A.,TIMCAL SA | Markle W.,Paul Scherrer Institute | Novak P.,Paul Scherrer Institute
Electrochimica Acta | Year: 2011

The local current density related to the exfoliation process of graphite negative electrodes in mixed ethylene carbonate/propylene carbonate electrolytes was controlled by a variation of the current applied to lithium half-cells containing either single type graphite electrodes or electrodes consisting of mixtures of an exfoliating and a non-exfoliating graphite. The partial local current density attributed to graphite passivation and its distribution within the volume of the electrode was found to be a key parameter to explain differences in the exfoliation behaviour observed for graphite electrodes. The local current density is related with a local overpotential which may suppress one of several possible electrochemical processes. In a negative electrode consisting of a mixture of a non-exfoliating and an exfoliating graphite component, the exfoliation of the exfoliation-sensitive graphite component can be completely suppressed when increasing the partial local current density attributed to the graphite exfoliation process above a certain threshold, by either decreasing the amount of exfoliating graphite particles in the electrode or by increasing the total current density, i.e., the specific current. The consideration of the local current density distribution for the electrochemical processes throughout the electrode leads to a more general concept for the graphite passivation behaviour during the first lithium insertion in lithium-ion batteries. © 2011 Elsevier Ltd. All rights reserved.

Weingarth D.,Paul Scherrer Institute | Weingarth D.,Leibniz Institute for New Materials | Cericola D.,TIMCAL SA | Mornaghini F.C.F.,TIMCAL SA | And 2 more authors.
Journal of Power Sources | Year: 2014

Electrochemical double layer capacitors (EDLCs) are inherently high power devices when compared to rechargeable batteries. While capacitance and energy storage ability are mainly increased by optimizing the electrode active material or the electrolyte, the power capability could be improved by including conductive additives in the electrode formulations. This publication deals with the use of four different carbon additives - two carbon blacks and two graphites - in standard activated carbon based EDLC electrodes. The investigations include: (i) physical characterization of carbon powder mixtures such as surface area, press density, and electrical resistivity measurements, and (ii), electrochemical characterization via impedance spectroscopy and cyclic voltammetry of full cells made with electrodes containing 5 wt.% of carbon additive and compared to cells made with pure activated carbon electrodes in organic electrolyte. Improved cell performance was observed in both impedance and cyclic voltammetry responses. The results are discussed considering the main characteristics of the different carbon additives, and important considerations about electrode structure and processability are drawn. © 2014 Elsevier B.V. All rights reserved.

Doberdo I.,University of Munster | Doberdo I.,Polytechnic University of Turin | Loffler N.,University of Munster | Laszczynski N.,University of Munster | And 5 more authors.
Journal of Power Sources | Year: 2014

In this manuscript a novel approach to enable aqueous binders for lithium ion battery (LIB) cathodes is reported. Producing LiNi1/3Mn 1/3Co1/3O2 (NMC) electrodes using sodium-carboxymethylcellulose (CMC) as a binder and water as a solvent, in fact, results in serious aluminum corrosion during electrode manufacturing due to the high pH of the slurry. In order to prevent the direct contact of the corrosive slurry with aluminum foil, the latter is first coated with a thin carbon layer. The CMC-based electrodes formed on carbon coated aluminum foil show enhanced performance than those made using unprotected aluminum instead. In particular, electrodes using protected aluminum foil are able to deliver a capacity of 126 mAh g-1 at 1C rate, which is rather close to that delivered by polyvinylidene-di-fluoride (PVdF)-based electrode having the same composition. © 2013 Published by Elsevier B.V.

Spahr M.E.,TIMCAL SA | Goers D.,TIMCAL SA | Markle W.,Paul Scherrer Institute | Dentzer J.,CNRS Mulhouse Institute of Materials Science | And 6 more authors.
Electrochimica Acta | Year: 2010

The first electrochemical lithium insertion was characterized for several graphite materials with high degree of crystallinity, different particle size distributions and surface morphologies in an ethylene carbonate (EC)/propylene carbonate (PC) electrolyte. For coarser graphite materials and graphites with a low superficial defect concentration, an irreversible process was observed which correlated with the electrochemical exfoliation of graphite. Different natural and synthetic graphites with similar particle size distribution and active surface area showed differences in the passivation behavior during the first electrochemical reduction. The fraction of graphite particles exfoliating during the first galvanostatic lithium insertion linearly increased with length of the irreversible plateau, which concomitantly moved to more positive potentials. This behavior can be rationalized when considering, besides the surface structure, local overpotentials for the solid electrolyte interphase formation process, and especially the overpotential distribution through the graphite electrode. These overpotentials cause a distribution of the local current density attributed to the passivation process. Optimizing the particle contacts in the electrode by applying mechanical pressure or by selecting the proper binder decreased the overpotentials and suppressed the graphite exfoliation in the EC/PC electrolyte. Therefore, both graphite surface structure and electrode engineering aspects have to be considered for successful passivation against exfoliation. © 2010 Elsevier Ltd All rights reserved.

Bernardo P.,CNRS Mulhouse Institute of Materials Science | Bernardo P.,Paul Scherrer Institute | Dentzer J.,CNRS Mulhouse Institute of Materials Science | Gadiou R.,CNRS Mulhouse Institute of Materials Science | And 6 more authors.
Carbon | Year: 2011

The electrochemical insertion of lithium ions into graphite materials having different surface chemistry and defect concentration was studied during the first cycle in half-cell containing 1 M LiPF6 in an electrolytic solvent mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC). The graphite surface properties were varied by thermal treatments in either hydrogen, oxygen, or nitrogen oxide or chemical treatment in boiling nitric acid. The influence of the surface modifications on the course of the first electrolyte reduction was investigated. The surface group chemistry was analyzed by temperature-programmed desorption coupled with mass spectrometry. The surface defect concentration was determined in terms of the active surface area (ASA) measured by oxygen chemisorption and a subsequent temperature-programmed desorption. The experimental results showed that the ASA parameter governs the exfoliation tendency of the graphite negative electrode material with the existence of a critical value below which the graphite systematically exfoliates. The specific charge loss during the first electrochemical insertion of lithium and the exfoliation behavior of the graphite negative electrode material are not influenced by the type and amount of oxygen surface groups. But hydrogen present on the graphite surface increased the graphite exfoliation tendency even for graphite materials with an ASA above the critical value. © 2011 Elsevier Ltd. All rights reserved.

Spahr M.,TIMCAL AG | Nesper R.,ETH Zurich | Ensling J.,Johannes Gutenberg University Mainz | Gutlich P.,Johannes Gutenberg University Mainz | And 4 more authors.
Zeitschrift fur Anorganische und Allgemeine Chemie | Year: 2011

We have investigated the magnetic ordering and spin dynamics of the solid solution series Ba1-xEuxSi with 0 < x ≤ 1 applying X-ray diffraction, electric conductivity measurements, Mo;die&ssbauer spectroscopy, muon spin depolarization, and neutron diffraction. Our results suggest a spin glass-like behavior of Ba;bsubesubbsubesub&Si for concentrations close to x = 0.3 exist. Different spin ordering phenomena are found, which are dependent on the relative europium concentrations. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The present disclosure relates to ground expanded graphite agglomerate compositions, methods for making such agglomerates, their use as conductive additive, and conductive composites including such ground expanded graphite agglomerates. The disclosure also pertains to methods for making such composites and the use of such composites in preparing thermally conductive materials. The agglomerates may be characterized by a certain softness allowing the agglomerates to dissolve, e.g., through shear forces applied during compounding, thereby leading to an improved feedability and a highly homogenous distribution of the expanded graphite material in the composite matrix.

Timcal S.A. | Date: 2010-02-03

A non-exfoliated graphite powder comprises highly oriented grain aggregates (HOGA) having a new morphology and surface chemistry. Methods for the production of such graphite powders as well as products comprising such novel graphite particles is also disclosed.

Loading TIMCAL SA collaborators
Loading TIMCAL SA collaborators