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Composites Structural Supercapacitors for Power Storage

Project overview

The focus of this research is developing a multifunctional composite material that can simultaneously carry mechanical loads and at the same time storing (and delivering) electrical energy. Conventional approaches to energy storage include batteries, capacitors and supercapacitors. Batteries have a high energy density, but low power density, due to high internal resistance at high discharge rates associated with the kinetics of the redox process; capacitors offer a limited energy density with a high power density, since the energy is only stored as charge on the electrodes. The focuses of our research are supercapacitors, which have a higher specific power than most of the batteries, and specific energy which is significantly higher than conventional capacitor (typical energy and power densities of 1-10 Wh/kg and 0.2-5 kW/kg respectively). This combination (energy and power density) allows supercapacitor to occupy he position between batteries and conventional capacitors. Moreover, supercapacitors have much longer cycle live compare to batteries. The electrical performance of supercapacitors makes them desirable as short term storage media and high power density energy sources in applications in which fast bursts of energy are inherent. These components are particularly useful for the load-levelling applications; when used in combination with a battery they provide for peak power demands (for example, during rapid acceleration of a vehicle) that cannot be supplied efficiently by the battery, giving substantial improvements in battery life. The most common form of electrochemical double layer supercapacitor consists of two electrodes, a separator, and an electrolyte. The two electrodes (made of activated carbon fibre in this project), provide a high surface area, and are separated by a layer that is ionically-conducting but electrically insulating. The energy is stored in an electrochemical double layer (Helmholtz Layer) formed at a solid/electrolyte interface. The amount of stored energy is a function of the available electrode surface, the size of the ions, and the electrolyte stability (usually about 3V). Our subsequent research is developing a proof-of-concept multifunctional structural power storage material. We have investigated development of a carbon fibre reinforced polymer composite which can act as a supercapacitor and show good mechanical properties (Young’s Modulus, Shear stiffness, compression strength, and peel and shear toughness). To this end we have investigated multifunctional composites derived from carbon fibres and their activation as mechanically robust electrode materials, polymer gel electrolytes as the ion conducting phase, glass fibres as the insulator layers and sol-gel derived porous silica as further structural reinforcement. We have developed a treatment for structural carbon fibres with an activated surface, allowing them to act both as a reinforcement and an electrode. 50-fold increase in surface area with negligible loss in mechanical properties has been achieved. The composite with the specific capacitance 20 mF/g and specific energy about 0.011Wh/kg has been formed.

Researcher

Dr. Natasha Shirshova
Post-doctoral Research Associate

Supervisors:
Prof. Alexander Bismarck
Prof. Milo Shaffer
Dr. Emile Greenhalgh
Dr. Joachim Steinke 

Sponsor:
EU FP7

 

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