A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription.For more information, please contact eprints@nottingham.ac.uk Journal NameThis journal is © The Royal Society of Chemistry 20xxJ. Name., 2013, 00, 1-3 | 1 Electrolyte is a key component of electrochemical energy storage (EES) devices and its properties greatly affect the energy capacity, rate performance, cyclability and safety of all EES devices. This article offers a critical review of recent progresses and challenges in electrolyte research and development particularly for supercapacitors and supercapatteries, recharegable batteries (such as lithium-ion and sodium-ion batteries), and redox flow batteries (including fuel cells in a broad sense). The review will focus on liquid electrolytes, particularly aqueous and organic electrolytes, ionic liquids and molten salts. Influences of electrolyte properties on the performances of different EES devices are discussed in detail.

Redox electrode materials, including transition metal oxides and electronically conducting polymers, are capable of faradaic charge transfer reactions, and play important roles in most electrochemical energy storage devices, such as supercapacitor, battery and supercapattery. Batteries are often based on redox materials with low power capability and safety concerns in some cases. Supercapacitors, particularly those based on redox inactive materials, e.g. activated carbon, can offer high power output, but have relatively low energy capacity. Combining the merits of supercapacitor and battery into a hybrid, the supercapattery can possess energy as much as the battery and output a power almost as high as the supercapacitor. Redox electrode materials are essential in the supercapattery design. However, it is hard to utilise these materials easily because of their intrinsic characteristics, such as the low conductivity of metal oxides and the poor mechanical strength of conducting polymers. This article offers a brief introduction of redox electrode materials, the basics of supercapattery and its relationship with pseudocapacitors, and reviews selectively some recent progresses in the relevant research and development.

9This article aims to offer a critical overview of selected literature on capacitive and non-10 capacitive faradaic charge storage. It is particularly relevant to the concept of 11 pseudocapacitance that is generally described as a result of fast surface faradaic processes. In 25 This is the accepted manuscript which differs slightly from the finally published version. http://dx

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