22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Nanoparticles jet deposition of silicon, silicon-carbon and titania hierarchical
nano-structures for energy applications
G. Nava1,2, F. Fumagalli2 and F. Di Fonzo2
1
2
Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133, Milan, Italy
Center for Nano Science and Technology @PoliMI Istituto Italiano di Tecnologia, Via Giovanni Pascoli 70/3, 20133
Milan, Italy
Abstract: A novel high rate and large area plasma based physical vapour deposition
technique is presented for the fabrication of silicon, silicon-carbon and titania
nanostructures for application in next generation lithium ion batteries and solar cells. The
process, named Nanoparticles Jet Deposition (Nano-JeD), exploits the combination of a
dusty non thermal plasma stage environment, providing ultra-high throughput, and a
supersonic inseminated jet.
Keywords: PECVD, supersonic nanoparticle inseminated jet, high rate, large area
1. General
In the last decade the fields of energy production via
renewable energy sources and effective energy storage
represent very active areas of research.
In the former field, dye sensitized solar cells (DSC) and
nanocrystalline silicon thin films solar cells have been
widely studied as promising and economical PV
technology. In the first case, as proved by several
experimental studies, enhanced performances compatible
with commercial applications are achieved with the use of
nanostructured materials, increasing the specific surface
available for photoelectrochemical reactions, charge
collection and charge transport, whereas for
nanocrystalline silicon solar cells the lack of high rate
production technique represent the main issue hindering a
technological breakthrough [1, 2].
In the field of energy storage lithium-ion batteries are
widely considered the most mature technology (long
cycle life, high gravimetric and volumetric density),
though still insufficient to fulfil the requirements for
demanding applications, such as Pure Electic or Hybryd
vehicles [3]. In the last few years intense research efforts
have thus been invested in the development of new high
capacity anode materials in order to boost the
performances of this technology. Silicon – low cost and
earthly abundant – has the highest theoretical capacity
(4200 mAh/g) among the studied materials and represents
the most appealing alternative to the commercially
widespread graphite anodes (372 mAh/g) [4].
In
particular the use of silicon nanostructures, composed by
aggregates below the critical size for crack propagation
(300 nm) and with an optimized system of voids to
withstand the volume change upon lithiation (up to
300%), combined with carbon coatings that increase the
stability of the solid electrolyte interface (SEI) has been
proved by several works to be a suitable strategy to obtain
superior cyclability and storage capacity [4-6]. The
production of these optimized anode structures usually
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relies on complex multistep and low yield (45 mg/h)
chemical synthesis methods, not suitable for large scale
applications [7].
In the present work a novel large area (100 cm2), high
yield (up to 200 mg/h) plasma-based deposition technique
– named Nanoparticles Jet Deposition (NANO JeD) – is
presented for single process fabrication of silicon,
composite silicon-carbon and titania nanostructured
materials, for application in lithiuim ion batteries anodes
and dye sensitized solar cells phoanodes respectively.
Gas phase self-assembled nanostructured films are
obtained by coupling PECVD technique and nanoparticles
inseminated sonic jet technique in a single reactor design.
This novel process is based on the segmentation of the gas
phase material synthesis in two separate steps: (i)
precursor dissociation chemistry control in a non-thermal
dusty plasma environment, allowing low temperature
crystallization (mainly controlling over hydrogen dilution
and coupled radiofrequency power in the discharge) and
narrow size distribution synthesis of nanoclusters
(controlled by the gas residence time in the discharge) [8];
(ii) nanoparticles nucleation and aggregation control by
means of a sonic jet. The morphological properties of
synthetized films range from aerogels through ordered
dendritic nanostructures to compact films by controlling
plasma process parameters and aerosol gas dynamic of the
sonic jet flow field.
Dense nanocrystalline silicon films are fabricated at
high troughtput, exploiting the low temperature
crystallization crystallization process preoviuosly
discussed. Results concerning the control over silicon
crystalline fraction and nanocrystals size tuning are
presented.
A nano-composite lithium ion battery anode (see Fig. 1.
left), is fabricated, comprising of a bottom layer of
hydrogenated carbon to improve the electrical contact and
adhesion to the copper collector, an intermediate layer of
hydrogenated amorphous silicon with a tree-like
1
nanostructured morphology for optimal volume
adjustment upon swelling, and a top layer of
hydrogenated carbon for the SEI stabilization. The
nanocomposite anode is synthetized by alternating the use
of acetylene (C 2 H 2 ) as the carbon precursor and silane
(SiH 4 ) as the silicon precursor, all performed in an argon
plasma. Preliminary characterizations of the above
described design are presented.
TiO 2 photoanodes (see Fig. 1 right) consisting of
anatase single crystals assembled in quasi 1-D arrays of
high aspect ratio hierarchical mesostructures are
fabricated onto the F-doped SnO covered glass surfaces
by self-assembly from the gas phase. Structural and
morphological characteristics of TiO 2 nanostructured
photoanodes can be optimized to achieve simultaneously
high specific surface area for optimal dye uptake and
broadband light scattering. As an example of the efficacy
of the new process, we present the results of the first
functional tests on DSC.
[2]
[2]
[3]
[4]
[5]
[6]
Fig. 1. Left: Composite carbon-silicon-carbon material
for application in lithium ion batteries anodes. Right:
Nanostructured titania photoanode for application in dye
sensitized solar cells.
2. References
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