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Neu-Ulm, Germany

Matic A.,Chalmers University of Technology | Scrosati B.,Helmholtz Institute Ulm
MRS Bulletin | Year: 2013

There is an urgent need for new energy storage and conversion systems in order to tackle the environmental problems we face today and to make the transition to a fossil fuel-free society. New batteries, supercapacitors, and fuel cells have the potential to be key devices for large-scale energy storage systems for load leveling and electric vehicles. In many cases, the concepts are known, but the right materials solutions are lacking. Ionic liquids (ILs) have been highlighted as suitable materials to be included in new devices, most commonly as electrolytes. Attractive features of ILs such as high ionic conductivity, low vapor pressure, high thermal and electrochemical stability, large temperature range for the liquid phase, and flexibility in molecular design have drawn the attention of researchers from many different fields. In addition, there is the possibility of designing new materials and morphologies using electrochemical synthesis with ILs. In this article, we provide an introduction to ILs and their properties, serving as a base for the topical articles in this issue. © 2013 Materials Research Society.

Balducci A.,Helmholtz Institute Ulm
Journal of Power Sources | Year: 2016

The development of innovative electrolyte components is nowadays considered one of the most important aspects for the realization of high energy electrochemical double capacitors (EDLCs). Consequently, in the last years many investigations have been dedicated towards new solvents, new salts and ionic liquids able to replace the current electrolytes.This perspective article aims to supply a critical analysis about the results obtained so far on the development of new electrolytes for high energy EDLCs and to outline the advantages as well as the limits related to the use of these innovative components. Furthermore, this article aims to give indications about the strategies could be used in the future for a further development of advanced electrolytes. © 2016.

Petzl M.,Helmholtz Institute Ulm | Danzer M.A.,Center for Solar Energy and Hydrogen Research
IEEE Transactions on Energy Conversion | Year: 2013

Incremental open-circuit voltage (OCV) curves and low-current charge/discharge voltage profiles of a lithium-ion (Li-ion) battery are compared and evaluated for optimizing measurement time and resolution. Since these curves are often used for further analysis, minimizing kinetic contributions is crucial for approximating battery OCV behavior. In this context, an incremental OCV measurement is characterized by state of charge (SOC) intervals and relaxation times. Various constant low C-rates, SOC intervals, and relaxation times are tested for approximating OCV behavior. Differential capacity and voltage analysis is used to check whether the main electrode features can be resolved satisfactorily. An interpolation method yields additional data points for the differential analysis of incremental OCV curves. It is shown that incremental OCV measurements are suitable for an approximation of battery OCV behavior, rather than low current-voltage profiles. Furthermore, extrapolation of voltage relaxation enables the estimation of fully relaxed OCV. © 1986-2012 IEEE.

Landstorfer M.,University of Ulm | Jacob T.,University of Ulm | Jacob T.,Helmholtz Institute Ulm
Chemical Society Reviews | Year: 2013

Mathematical modeling of lithium ion batteries is a key feature for a profound understanding of the whole spectrum of phenomena occurring in such electrochemical systems. Due to their inherent multi-scale nature, batteries cannot be described with a single equation. It is necessary to couple the physical chemistry, reaction kinetics, ion flow, heat generation, et cetera, appropriately to obtain a coupled set of equations (a model) which has predictive efficiency. To adapt ideas and expertise obtained in the field of modeling to future type of batteries, new electrode or electrolyte materials or to improve the model reliability, a universal basis is desirable. In this sense, we carefully derive the commonly used set of equations based on the most general form of linear non-equilibrium thermodynamics. Due to chemical and physical assumptions the set of equations is reduced to facilitate numerical computations. Transport equations for a general electrolyte are derived and different electroneutrality assumptions are applied to obtain Poisson-Nernst-Planck-type equations or a generalized Ohmic law. Electrodes are described with single and many particle models, e.g. for phase separating materials, and the transition to porous electrode theory is given. A mathematical treatment of the intercalation reaction is finally presented, based on surface charge densities and electrode potentials. © 2013 The Royal Society of Chemistry.

Zeis R.,Helmholtz Institute Ulm
Beilstein Journal of Nanotechnology | Year: 2015

The performance of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFC) is critically dependent on the selection of materials and optimization of individual components. A conventional high-temperature membrane electrode assembly (HTMEA) primarily consists of a polybenzimidazole (PBI)-type membrane containing phosphoric acid and two gas diffusion electrodes (GDE), the anode and the cathode, attached to the two surfaces of the membrane. This review article provides a survey on the materials implemented in state-of-the-art HT-MEAs. These materials must meet extremely demanding requirements because of the severe operating conditions of HT-PEMFCs. They need to be electrochemically and thermally stable in highly acidic environment. The polymer membranes should exhibit high proton conductivity in low-hydration and even anhydrous states. Of special concern for phosphoric-acid-doped PBI-type membranes is the acid loss and management during operation. The slow oxygen reduction reaction in HT-PEMFCs remains a challenge. Phosphoric acid tends to adsorb onto the surface of the platinum catalyst and therefore hampers the reaction kinetics. Additionally, the binder material plays a key role in regulating the hydrophobicity and hydrophilicity of the catalyst layer. Subsequently, the binder controls the electrode-membrane interface that establishes the triple phase boundary between proton conductive electrolyte, electron conductive catalyst, and reactant gases. Moreover, the elevated operating temperatures promote carbon corrosion and therefore degrade the integrity of the catalyst support. These are only some examples how materials properties affect the stability and performance of HT-PEMFCs. For this reason, materials characterization techniques for HT-PEMFCs, either in situ or ex situ, are highly beneficial. Significant progress has recently been made in this field, which enables us to gain a better understanding of underlying processes occurring during fuel cell operation. Various novel tools for characterizing and diagnosing HT-PEMFCs and key components are presented in this review, including FTIR and Raman spectroscopy, confocal Raman microscopy, synchrotron X-ray imaging, X-ray microtomography, and atomic force microscopy. © 2015 Zeis; licensee Beilstein-Institut.

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