Supercapacitors

Materials, Systems, and Applications

Francois Beguin, Elzbieta Frackowiak, Francois Beguin, Elzbieta Frackowiak, Max Lu

• Publisher: Wiley-VCH
• Year: 2013
• Print ISBN: 9783527328833
• eBook ISBN: 9783527646685
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Supercapacitors are a relatively new energy storage system that provides higher energy density than dielectric capacitors and higher power density than batteries. They are particularly suited to applications that require energy pulses during short periods of time, e.g., seconds or tens of seconds. They are recommended for automobiles, tramways, buses, cranes, fork-lifts, wind turbines, electricity load leveling in stationary and transportation systems, etc. Despite the technological maturity of supercapacitors, there is a lack of comprehensive literature on the topic. Many high performance materials have been developed and new scientific concepts have been introduced. Taking into account the commercial interest in these systems and the new scientific and technological developments now is the ideal time to publish this book, capturing all this new knowledge. The book starts by giving an introduction to the general principles of electrochemistry, the properties of electrochemical capacitors, and electrochemical characterization techniques. Electrical double layer capacitors and pseudocapacitors are then discussed, followed by the various electrolyte systems. Modelling, manufacture of industrial capacitors, constraints, testing, and reliability as well as applications are also covered. 'Supercapacitors - Materials, Systems, and Applications' is part of the series on Materials for
Sustainable Energy and Development edited by Prof. G.Q. Max Lu. The series covers advances in materials science and innovation for renewable energy, clean use of fossil energy, and greenhouse gas mitigation and associated environmental technologies.

1

General Principles of Electrochemistry

Scott W. Donne

1.1 Equilibrium Electrochemistry

1.1.1 Spontaneous Chemical Reactions

Chemical reactions move toward a dynamic equilibrium in which both reactants and products are present but have no further tendency to undergo net change. In some cases, the concentration of products in the equilibrium mixture is so much greater than the concentration of the unchanged reactants that for all practical purposes the reaction is complete. However, in many important cases, the equilibrium mixture has significant concentrations of both reactants and products.

1.1.2 The Gibbs Energy Minimum

The equilibrium composition of a reaction mixture can be calculated from the Gibbs energy by identifying the composition that corresponds to a minimum in the Gibbs energy. To elaborate further, consider the simple chemical equilibrium:

1.1

Suppose now that an infinitesimal amount dξ of A turns into B, then the change in the amount of A present is dn_A = −dξ and the change in the amount of B present is dn_B = + dξ. The quantity ξ is called the extent of reaction.

The reaction Gibbs energy (ΔG_r) is defined as

1.2

where μ represents the chemical potential or molar Gibbs energy for each species.

Because the chemical potentials vary with composition, the Gibbs energy will change as the reaction proceeds. Moreover, because the reaction runs in the direction of decreasing G, it means that the reaction A → B is spontaneous when μ_A > μ_B, whereas the reverse reaction is spontaneous when μ_B > μ_A. When the derivative in Eq. (1.2) is zero, the reaction is spontaneous in neither direction, and so

1.3

which occurs when μ_A = μ_B. It follows that if the composition of the reaction mixture can be identified such that μ_A = μ_B, then we can identify the composition of the reaction mixture at equilibrium.

To generalize these concepts, consider the more generic chemical reaction:

1.4

When the reaction advances by dξ, the amounts of reactants and products change by

1.5

and in general dn_J = ν_Jdξ where ν_J is the stoichiometric number of J in the chemical equilibrium. The resulting infinitesimal change in the Gibbs energy at constant temperature and pressure is therefore

1.6

The general form of this expression is

1.7

It follows that

1.8

To progress further, we note that the chemical potential of a species J is related to its activity (a_J) by

1.9

Substituting an equivalent expression to Eq. (1.9) for each species into Eq. (1.8) gives rise to

1.10

where Q is the...

Table of contents

• Cover
• Related Titles
• Title Page
• Copyright
• Editorial Board
• Series Editor Preface
• Preface
• About the Series Editor
• About the Volume Editors
• List of Contributors
• Chapter 1: General Principles of Electrochemistry
• Chapter 2: eneral Properties of Electrochemical Capacitors
• Chapter 3: Electrochemical Techniques
• Chapter 4: Electrical Double-Layer Capacitors and Carbons for EDLCs
• Chapter 5: Modern Theories of Carbon-Based Electrochemical Capacitors
• Chapter 6: Electrode Materials with Pseudocapacitive Properties
• Chapter 7: Li-Ion-Based Hybrid Supercapacitors in Organic Medium
• Chapter 8: Asymmetric and Hybrid Devices in Aqueous Electrolytes
• Chapter 9: EDLCs Based on Solvent-Free Ionic Liquids
• Chapter 10: Manufacturing of Industrial Supercapacitors
• Chapter 11: Supercapacitor Module Sizing and Heat Management under Electric, Thermal, and Aging Constraints
• Chapter 12: Testing of Electrochemical Capacitors
• Chapter 13: Reliability of Electrochemical Capacitors
• Chapter 14: Market and Applications of Electrochemical Capacitors
• Index