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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.

Raccichini R.,University of Munster | Raccichini R.,Helmholtz Institute Ulm | Raccichini R.,Karlsruhe Institute of Technology | Varzi A.,Helmholtz Institute Ulm | And 5 more authors.
Nature Materials | Year: 2015

Since its first isolation in 2004, graphene has become one of the hottest topics in the field of materials science, and its highly appealing properties have led to a plethora of scientific papers. Among the many affected areas of materials science, this 'graphene fever' has influenced particularly the world of electrochemical energy-storage devices. Despite widespread enthusiasm, it is not yet clear whether graphene could really lead to progress in the field. Here we discuss the most recent applications of graphene-both as an active material and as an inactive component-from lithium-ion batteries and electrochemical capacitors to emerging technologies such as metal-air and magnesium-ion batteries. By critically analysing state-of-the-art technologies, we aim to address the benefits and issues of graphene-based materials, as well as outline the most promising results and applications so far. © 2015 Macmillan Publishers Limited. All rights reserved.

News Article | March 7, 2016

Two new materials – a carbon-based active material produced from waste apples and a material of layered oxides – could help reduce the costs of future energy storage systems, as both are sustainable materials with excellent electrochemical properties. Developed by researchers at the Karlsruhe Institute of Technology (KIT)’s Helmholtz Institute Ulm in Germany, the materials could prove of use in sodium-ion batteries and are described in papers in ChemElectroChem and Advanced Energy Materials. Sodium-ion batteries are not only far more powerful than nickel-metal hydride or lead acid batteries, but also represent an alternative to lithium-ion batteries, as the initial materials needed are highly abundant, easily accessible and available at low cost. Hence, sodium-ion batteries are a very promising technology for stationary energy storage systems that can be used with renewable energy technologies such as wind and solar. Now, researchers from the Helmholtz Institute Ulm, led by Stefano Passerini and Daniel Buchholz, have made an important advance in the development of electrode materials for sodium-based energy storage systems. For the negative electrode, they have synthesized a carbon-based material from waste apples that possesses excellent electrochemical properties. So far, they have demonstrated more than 1000 charge and discharge cycles of high cyclic stability and high capacity. This discovery represents an important step towards the sustainable use and exploitation of resources such as organic waste. The material developed for the positive electrode consists of several layers of sodium oxides. Unlike the positive electrodes frequently used in commercial lithium-ion batteries, this material doesn’t contain cobalt, which is expensive and environmentally hazardous. Nevertheless, in laboratory tests, this material achieved the same efficiency, cyclic stability, capacity and voltage as materials containing cobalt. Both these materials mark an important step towards the development of inexpensive and environmentally friendly sodium-ion batteries. This story is adapted from material from Karlsruhe Institute of Technology, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

Su X.,Brown University | Wu Q.,Helmholtz Institute Ulm | Li J.,Oak Ridge National Laboratory | Xiao X.,General Motors | And 4 more authors.
Advanced Energy Materials | Year: 2014

There are growing concerns over the environmental, climate, and health impacts caused by using non-renewable fossil fuels. The utilization of green energy, including solar and wind power, is believed to be one of the most promising alternatives to support more sustainable economic growth. In this regard, lithium-ion batteries (LIBs) can play a critically important role. To further increase the energy and power densities of LIBs, silicon anodes have been intensively explored due to their high capacity, low operation potential, environmental friendliness, and high abundance. The main challenges for the practical implementation of silicon anodes, however, are the huge volume variation during lithiation and delithiation processes and the unstable solid-electrolyte interphase (SEI) films. Recently, significant breakthroughs have been achieved utilizing advanced nanotechnologies in terms of increasing cycle life and enhancing charging rate performance due partially to the excellent mechanical properties of nanomaterials, high surface area, and fast lithium and electron transportation. Here, the most recent advance in the applications of 0D (nanoparticles), 1D (nanowires and nanotubes), and 2D (thin film) silicon nanomaterials in LIBs are summarized. The synthetic routes and electrochemical performance of these Si nanomaterials, and the underlying reaction mechanisms are systematically described. The most recent advance in the applications of 0D (nanoparticles), 1D (nanowires and nanotubes), and 2D (thin film) silicon nanomaterials in lithium ion batteries (LIBs) are summarized. The synthetic routes, electrochemical performance, and underlying reaction mechanisms of these nanomaterials are described and the advantages and limitations using nanostructured silicon in LIBs are also discussed. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

Latz A.,Helmholtz Institute Ulm | Zausch J.,Fraunhofer Institute for Industrial Mathematics
Electrochimica Acta | Year: 2013

We present an exclusively thermodynamics based derivation of a Butler-Volmer expression for the intercalation exchange current in Li ion insertion batteries. In this first paper we restrict our investigations to the actual intercalation step without taking into account the desolvation of the Li ions in the electrolyte. The derivation is based on a generalized form of the law of mass action for non ideal systems (electrolyte and active particles). To obtain the Butler-Volmer expression in terms of overpotentials, it is necessary to approximate the activity coefficient of an assumed transition state as function of the activity coefficients of electrolyte and active particles. Specific considerations of surface states are not necessary, since intercalation is considered as a transition between two different chemical environments without surface reactions. Differences to other forms of the Butler-Volmer used in the literature [1,2] are discussed. It is especially shown, that our derivation leads to an amplitude of the exchange current which is free of singular terms which may lead to quantitative and qualitative problems in the simulation of overpotentials. This is demonstrated for the overpotential between electrolyte and active particles for a half cell configuration. © 2013 Elsevier Ltd. All rights reserved.

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.

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.

Bresser D.,University of Munster | Passerini S.,University of Munster | Scrosati B.,Helmholtz Institute Ulm
Chemical Communications | Year: 2013

This review is an attempt to report the latest development in lithium-sulfur batteries, namely the storage system that, due to its potential energy content, is presently attracting considerable attention both for automotive and stationary storage applications. We show here that consistent progress has been achieved, to the point that this battery is now considered to be near to industrial production. However, the performance of present lithium-sulfur batteries is still far from meeting their real energy density potentiality. Thus, the considerable breakthroughs so far achieved are outlined in this review as the basis for additional R&D, with related important results, which are expected to occur in the next few years. © 2013 The Royal Society of Chemistry.

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