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(Hutchinson and Poznan University of Technology). In this way,

INAC has recently inaugurated a new technological platform

(Hybrid-EN) which contains state-of-the-art facilities, enabling

electrode elaboration, device fabrication, electrochemical cell

testing and cycling for electrochemical energy storage devices.

Within this context, the Hybrid-EN platform envisages

important progress for the integration and validation of energy

storage micro-units in a great variety of industrial technological

applications, e.g. biomedical implants (biosensors),

microelectronics or aerospace fields (satellites).

SiNTr-based micro-supercapacitor devices demonstrate

extraordinary properties in terms of high power densities

(225mW cm

-2

), excellent cycling stability (millions of

galvanostatic charge-discharge cycles) and ultra-fast high

frequency response (a few milliseconds) in the presence of ionic

liquid electrolytes. The results obtained in this project

demonstrate the importance of this research activity for the

technological progress of our modern society in the near future.

In this regard, INAC has recently been exploring other challenges

and possibilities in the frame of a national project (ISICAP,

In

situ

nanostructured SI-based superCAPacitors). This project, co-

ordinated by Professor Saïd Sadki (INAC), mainly envisages the

elaboration of novel architectures based on SiNTr-interdigitated

devices as well as design of advanced electrolytes using

ionogels (gelled ionic liquids), in collaboration with leading

technological centres (IMN Nantes). Thus, both the NEST and

ISICAP projects are directly related to the possibility of

integrating miniaturised micro-supercapacitors into real devices

with excellent performances.

On the other hand, many sectors exist where much higher

electrical energy storage capacities are required. One example is

electric vehicles: the cruising range of electric cars still falls far

behind that of cars equipped with combustion engines, retarding

their broader market penetration. Another example is the

necessity of storing huge amounts of energy coming from

intermittent sustainable power sources such as solar panels or

wind turbines. Existing battery technologies are reaching their limit

and new disruptive approaches are required.

Future objectives

For the coming years INAC has defined its roadmap in the field

of energy storage devices as follows. Among its primary

objectives is the exploitation of SiNWs in battery devices. Silicon

gives the possibility for enhancing the storage capacity of Li-ion

batteries by one order of magnitude when used as the anode

material instead of the established graphite. However, as the

charge and discharge cycles of the battery imply large volume

changes of the anode material, bulk silicon presents low cycling

stability. Nanostructuration is once again a way to circumvent

this shortcoming.

Silicon nanostructures can ‘breathe’ during lithium insertion and

release owing to the reduced lattice strain at such small

dimensions. Furthermore, owing to their one-dimensional

morphology, Si nanowires provide ‘highways’ for electronic

conduction. Considering the huge amount of electrode material

required for the fabrication of Li-ion batteries, INAC recently

developed a proprietary technology for the large scale production

of SiNWs. It relies on the use of low cost, air-stable precursors and

gives access to Si nanowires of small diameter and controlled

doping level, produced on a scale of at least four orders of

magnitude larger than with CVD growth. Carbon/silicon nanowire

composite materials can be obtained with the same process.

EnWires, a spin-off company of INAC, is developing and

commercialising these materials

(www.enwires.com).

Another research challenge concerns the better

comprehension of the charge storage mechanisms at play in

batteries. INAC progresses in this direction through the study

of the solid-electrolyte interface layer formed during the

charge-discharge cycles in a battery using large scale facilities

such as the European Synchrotron Radiation Facility and

Institut Laue-Langevin.

Finally, research on new two-dimensional nanostructured

materials, as well as organic and ‘post-lithium’ batteries (e.g. Mg,

Al), will play a crucial role in the emerging energy storage

concepts explored at INAC.

Dr DavidAradilla

CEA Grenoble INAC

tel :

+33 04 38 78 29 66

david.aradilla@cea.fr http://inac.cea.fr/en/index.php http://www.project-nest.eu/ www.horizon2020projects.com

H O R I Z O N 2 0 2 0 P R O J E C T S : P O R TA L

I S S U E S E V E N

51

P R O F I L E

S P E C I A L F E AT U R E : M AT E R I A L S

Fig. 2 Electrochemical performance of a SiNW-based symmetric micro-

supercapacitor. a) Galvanostatic charge-discharge cycles at a current

density of 1mA cm

-2

using a cell voltage of 4V; b) Cycling stability

performed using 500,000 complete galvanostatic charge-discharge

cycles using the same conditions as in a)