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Augustyn V.,University of California at Los Angeles | Simon P.,University Paul Sabatier | Simon P.,CNRS RS2E | Dunn B.,University of California at Los Angeles
Energy and Environmental Science | Year: 2014

Electrochemical energy storage technology is based on devices capable of exhibiting high energy density (batteries) or high power density (electrochemical capacitors). There is a growing need, for current and near-future applications, where both high energy and high power densities are required in the same material. Pseudocapacitance, a faradaic process involving surface or near surface redox reactions, offers a means of achieving high energy density at high charge-discharge rates. Here, we focus on the pseudocapacitive properties of transition metal oxides. First, we introduce pseudocapacitance and describe its electrochemical features. Then, we review the most relevant pseudocapacitive materials in aqueous and non-aqueous electrolytes. The major challenges for pseudocapacitive materials along with a future outlook are detailed at the end. This journal is © 2014 the Partner Organisations. Source


Simon P.,University Paul Sabatier | Simon P.,CNRS RS2E | Gogotsi Y.,Drexel University
Accounts of Chemical Research | Year: 2013

Securing our energy future is the most important problem that humanity faces in this century. Burning fossil fuels is not sustainable, and wide use of renewable energy sources will require a drastically increased ability to store electrical energy. In the move toward an electrical economy, chemical (batteries) and capacitive energy storage (electrochemical capacitors or supercapacitors) devices are expected to play an important role. This Account summarizes research in the field of electrochemical capacitors conducted over the past decade.Overall, the combination of the right electrode materials with a proper electrolyte can successfully increase both the energy stored by the device and its power, but no perfect active material exists and no electrolyte suits every material and every performance goal. However, today, many materials are available, including porous activated, carbide-derived, and templated carbons with high surface areas and porosities that range from subnanometer to just a few nanometers. If the pore size is matched with the electrolyte ion size, those materials can provide high energy density. Exohedral nanoparticles, such as carbon nanotubes and onion-like carbon, can provide high power due to fast ion sorption/desorption on their outer surfaces. Because of its higher charge-discharge rates compared with activated carbons, graphene has attracted increasing attention, but graphene had not yet shown a higher volumetric capacitance than porous carbons.Although aqueous electrolytes, such as sodium sulfate, are the safest and least expensive, they have a limited voltage window. Organic electrolytes, such as solutions of [N(C2H5) 4]BF4 in acetonitrile or propylene carbonate, are the most common in commercial devices. Researchers are increasingly interested in nonflammable ionic liquids. These liquids have low vapor pressures, which allow them to be used safely over a temperature range from -50 C to at least 100 C and over a larger voltage window, which results in a higher energy density than other electrolytes.In situ characterization techniques, such as nuclear magnetic resonance (NMR), small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS), and electrochemical quartz crystal microbalance (EQCM) have improved our understanding of the electrical double layer in confinement and desolvation of ions in narrow pores. Atomisitic and continuum modeling have verified and guided these experimental studies. The further development of materials and better understanding of charged solid-electrolyte interfaces should lead to wider use of capacitive energy storage at scales ranging from microelectronics to transportation and the electrical grid. Even with the many exciting results obtained using newer materials, such as graphene and nanotubes, the promising properties reported for new electrode materials do not directly extrapolate to improved device performance. Although thin films of nanoparticles may show a very high gravimetric power density and discharge rate, those characteristics will not scale up linearly with the thickness of the electrode. © 2012 American Chemical Society. Source


Franco A.A.,CNRS Laboratory of Chemistry and Reactivity of Solids | Franco A.A.,CNRS RS2E
RSC Advances | Year: 2013

This review focuses on the role of physical theory and computational electrochemistry for fundamental understanding, diagnostics and design of new electrochemical materials and operation conditions for energy storage through rechargeable Li ion batteries (LIBs). More particularly, deep insight based on multiscale physical modelling techniques, spanning scales from few atoms to the device level, can advise about the materials behaviour and aging and how components with optimal specifications could be made and how they can be integrated into operating devices. Concepts and different existing multiscale modelling methodologies are presented and some of the ongoing efforts within the community to understand from physical multiscale modelling and numerical simulation electrochemical mechanisms and degradation processes in LIBs are discussed. Finally, major challenges and perspectives in multiscale modelling for battery applications are highlighted. © 2013 The Royal Society of Chemistry. Source


Masquelier C.,CNRS Laboratory of Chemistry and Reactivity of Solids | Masquelier C.,French National Center for Scientific Research | Masquelier C.,CNRS RS2E | Croguennec L.,CNRS Laboratory of Condensed Matter Chemistry, Bordeaux | And 2 more authors.
Chemical Reviews | Year: 2013

The concept of investigating three-dimensional frameworks based on the NASICON structure as hosts for reversible insertion/extraction of alkali cations (electrodes) arose in the mid 1980s mostly from concerns about possible stability or reactivity versus metallic Na (or Li) when used as solid electrolytes. The NASICON framework was used by Goodenough in the late 1980s as a very demonstrative example of the possibility for the chemist to elaborate electrode materials functioning at controlled operating voltages. Noticeably, these structures have been recently investigated by three independent groups as model compounds for the understanding of complex Li NMR signals in paramagnetic compounds, and useful insights into the activation energies for hopping between the lithium sites were provided. Source


Brousse T.,University of Nantes | Brousse T.,CNRS RS2E | Belanger D.,University of Quebec at Montreal | Long J.W.,U.S. Navy
Journal of the Electrochemical Society | Year: 2015

There are an increasing number of studies regarding active electrode materials that undergo faradaic reactions but are used for electrochemical capacitor applications. Unfortunately, some of these materials are described as "pseudocapacitive" materials despite the fact that their electrochemical signature (e.g., cyclic voltammogram and charge/discharge curve) is analogous to that of a "battery"material, as commonly observed for Ni(OH)2 and cobalt oxides in KOH electrolyte. Conversely, true pseudocapacitive electrode materials such as MnO2 display electrochemical behavior typical of that observed for a capacitive carbon electrode. The difference between these two classes of materials will be explained, and we demonstrate why it is inappropriate to describe nickel oxide or hydroxide and cobalt oxide/hydroxide as pseudocapacitive electrode materials. © The Author(s) 2015. Published by ECS. Source

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