Special Report: Emerging concepts for energy storage
During the last decade, our society has witnessed the emergence of innovative industrial applications in a wide range of technological fields such as biomedicine, consumer micro-electronics or aeronautics. More recently, the advent of commercial miniaturised electronic devices, such as biomedical implants and autonomous (wireless) sensors or smart cards, has triggered a great revolution in the classical energy storage concept.
Nanostructured electrodes for the energy storage devices of the future: a) Hybrid materials composed of electroactive conducting polymer-coated SiNWs; and b) Ternary systems composed of SiNWs/Crystalline Nanodiamond/electroactive conducting polymer
Presently, the disadvantages of low energy, power density and high fabrication cost of conventional supercapacitors/batteries are identified as the major challenge in the field of energy storage science. Within this context, the use of on-chip energy storage units based on micro-supercapacitors and micro-batteries have awakened a great interest due to their excellent performance in terms of high power and energy densities, long lifespan and fast response. Thereby, over the past years tremendous efforts have been devoted to the development of ultra-high performance batteries and supercapacitors for their integration into such systems and use in our daily lives.
Currently, several strategies have been proposed in order to achieve this commitment. Among them, the research of new 1D or 2D nanostructured material architectures, innovative electrolytes and the design of creative device architectures will play a key role in the field of energy storage (Fig.1 ). From this perspective, in recent years an intensive investigation has been focused on the research and synthesis of electrode materials based on nanostructured silicon (e.g. silicon nanowires – SiNWs) and carbon (e.g. onion-like and nanoporous carbon, graphene or carbon nanotubes), which make them potential candidates due to their large specific surface and high compatibility with the microelectronics industry.
Additionally, these materials have demonstrated a great capacity to deliver high power density values in short periods of time as well as a long cycling stability (e.g. millions of galvanostatic cycles in the case of SiNWs). In this direction, another important strategy based on the functionalisation of electrodes by using pseudocapacitive materials has also attracted great attention owing to their excellent charge transfer by means of faradaic reactions. Thus, the research of new electroactive conducting polymers, transition metal oxides or metallic hydroxides will aim at improving the electrochemical performance of these electrodes (anodes) in the near future. In this regard, the energy density of supercapacitors can be also enhanced by increasing the voltage, which is directly related to the electrolyte.
Nowadays, several important approaches have been addressed to the synthesis of ionic liquid-based chemical structures, which are able to provide large electrochemical windows, high thermal stabilities, low volatility and excellent environmental stability. These characteristics are of vital importance for the design of energy storage units. Moreover, the development of new architectures comprising planar (stacked), interdigitated and 3D configurations will allow for a better comprehension of the device optimisation.
Despite the impressive progress reached in this domain, the need of reliable energy storage micro-devices is still a big challenge, especially for enhancing their energy and power density and reducing the cost at the same time. Thus, the synergy of elements involved in a battery or supercapacitor (electrodes, electrolyte and device configuration) will require the fundamental and in-depth understanding of the associated energy storage mechanisms. Furthermore, improvements of the properties of electrode materials, electrolytes and device configurations for their encapsulation and integration will be primordial.
CEA-INAC in Grenoble (France) has defined its roadmap in the field of energy storage devices as follows. Among its primordial objectives, the exploitation of SiNWs for battery devices, the comprehension of charge storage mechanism (e.g. formation of the solid-electrolyte-interface/SEI layer during the charge-discharge cycles in a battery) through the use of large scale facilities (e.g. ILL, ESRF), as well as the development of new 2D nanostructured materials will play a crucial role in the research on emerging energy storage concepts. These activities will be complemented through the newly set-up Hybrid-EN platform, which is equipped for the preparation and characterisation of electrodes and the testing of the electrochemical performance of battery and supercapacitor devices. This scenario reflects the relevance of this activity at the core of CEA-INAC for its consolidation and projection in the field of energy storage devices in the next years.
David Aradilla
CEA Grenoble
INAC (France)
+33 (0)4 38 78 29 66
