Plasma-assisted Thermal Evaporation Research Articles

Self-Relaxant Superelastic Matrix Derived from C60 Incorporated Sn Nanoparticles for Ultra-High-Performance Li-Ion Batteries.

Homogeneously dispersed Sn nanoparticles approximately ⩽10 nm in a polymerized C60 (PC60) matrix, employed as the anode of a Li-ion battery, are prepared using plasma-assisted thermal evaporation coupled by chemical vapor deposition. The self-relaxant superelastic characteristics of the PC60 possess the ability to absorb the stress-strain generated by the Sn nanoparticles and can thus alleviate the problem of their extreme volume changes. Meanwhile, well-dispersed dot-like Sn nanoparticles, which are surrounded by a thin SnO2 layer, have suitable interparticle spacing and multilayer structures for alleviating the aggregation of Sn nanoparticles during repeated cycles. The Ohmic characteristic and the built-in electric field formed in the interparticle junction play important roles in enhancing the diffusion and transport rate of Li ions. SPC-50, a Sn-PC60 anode consisting of 50 wt % Sn and 50 wt % PC60, as confirmed by energy-dispersive X-ray spectroscopy analysis, exhibited the highest electrochemical performance. The resulting SPC-50 anode, in a half-cell configuration, exhibited an excellent capacity retention of 97.18%, even after 5000 cycles at a current density of 1000 mA g-1 with a discharge capacity of 834.25 mAh g-1. In addition, the rate-capability performance of this SPC-50 half-cell exhibited a discharge capacity of 544.33 mAh g-1 at a high current density of 10 000 mA g-1, even after the current density was increased 100-fold. Moreover, a very high discharge capacity of 1040.09 mAh g-1 was achieved with a capacity retention of 98.67% after 50 cycles at a current density of 100 mA g-1. Futhermore, a SPC-50 full-cell containing the LiCoO2 cathode exhibited a discharge capacity of 801.04 mAh g-1 and an areal capacity of 1.57 mAh cm-2 with a capacity retention of 95.27% after 350 cycles at a current density of 1000 mA g-1.

Fast and convenient growth of vertically aligned ZnO nanorods via microwave plasma-assisted thermal evaporation

A new approach to grow vertically aligned ZnO nanorods on glass substrates under ambient pressure was developed using microwave plasma-assisted thermal evaporation (MPATE). The results revealed that ZnO nanorods grew preferentially along their (002) plane on glass substrates without using catalysts/seed layers. Interestingly, the ZnO nanorods were completely formed within 7 min, which was much faster than other methods. The optical band gap of ZnO nanorods was 3.22 eV, indicating the photoresponse at UV region (<400 nm). Moreover, room-temperature photoluminescence of the ZnO nanorods, excited by 325 nm light, showed a dominance of green-light emission and a small UV emission.

Protecting and preserving clear barrier layers for flexible packaging materials In-line thermal evaporation of organic topcoat layer

The end market for transparent flexible barrier films is larger than for metallized films. Presently, the market is still dominated by polymeric barrier layers but the used chemicals may be harmful for the environment. An alternative would be transparent thin layers deposited by vacuum deposition techniques using reactive processes. Ceramic materials like silicon oxide or aluminum oxide are used having a film thickness of just ∼10 nm, a coating uniformity of +/−5% across and along the film at a barrier performance below 2.0 sccm/m2d for oxygen transmission rate (OTR) and below 1.0 g/m2d for water vapor transmission rate (WVTR) on PET substrates. In this paper, details will be provided about the deposition processes for these barrier layers using thermal evaporation, plasma-assisted thermal evaporation as well as deposition by electron beam evaporation. An important factor for these high barrier transparent coatings is also to withstand the downstream processes in the whole packaging stream like slitting, lamination, printing etc. One solution is to protect the barrier layers by a Topcoat. For example, off-line deposition of lacquers is used in field but the market penetration is low due to high process and material costs. An in-situ Topcoat deposition is a smart solution to overcome this issue saving time and costs. Such an approach will be also described in the presentation and the impact on the performance of the final package will be discussed.

Interface Controls of Lithium-Ion Batteries Electrodes through a Polymerized C60 Surface Coating

The increasing demand on high-energy and high-power lithium-ion batteries (LIBs) especially for electric vehicles application has driven the search on the high-capacity anode and cathode materials. For this purpose, SnO2-based anode materials (theoretical capacity of 900 mAhg-1) and LiCoO2 (theoretical capacity of 274 mAhg-1) have been intensively studied. However, the commercialization of SnO2 anode is still hindered due to the alloying mechanism which leads to severe volume expansion and eventually contributes to disintegrated material. While LiCoO2 has been used as commercial cathode materials, only half of its theoretical capacity (~140 mAhg-1) can be extracted at a cut-off voltage of 3.0-4.2 V. Although increasing cut-off voltage to 4.5 V would significantly boost the specific capacity, however severe side reactions between electrode and electrolyte and a structural phase transition from hexagonal to monoclinic causing structural damages of the electrode are the common issues occurred during the electrochemical cycle. Moreover, unstable solid-electrolyte interphase (SEI) layer on the surface of anode and cathode materials may worsen the situation leading to rapid capacity fading. Surface coating is considered as an appropriate approach in order to overcome the above-mentioned problems owing to its function to enhance interfacial kinetics and protect the host material underneath. Some metal oxides- and carbonaceous-based materials has been used as the coating materials for both anode and cathode materials. In this study, the plasma-polymerized C60 coatings both on the anode and cathode thin film electrodes are presented. The C60 coatings prepared by a radio-frequency plasma-assisted thermal evaporation are carried out on the surface of fluorine-doped SnO2 (C60@SnO2:F) anode and three-dimensional LiCoO2 (C60@3D-LiCoO2) cathode. The samples are characterized by SEM, XRD, TEM, EDX, XPS, ToF-SIMS and assembled into pouch-type and coin cells for anodes and cathodes, respectively. The results demonstrate the improved electrochemical performance of both C60-coated anode and cathode materials. For example, the C60@3D-LiCoO2 electrode delivers an initial discharge capacity of 175 mAhg-1 and maintains the capacity retention of 80% after 50 cycles at 0.1 C even with a high-voltage regime (~ 4.5 V). The C60@SnO2:F exhibits a high initial discharge capacity of 1255 mAhg-1 at 0.15 mAcm-2 and increases Coulombic efficiency of 98%. The improved electrochemical performance for C60@3D-LiCoO2 and C60@SnO2:F is attributed to the facts that the unique plasma-polymerized C60 thin film could provide (1) a mechanical strength to the host materials during repeated cycles directing to the material integrity, (2) a stabilized solid-electrolyte interphase (SEI) layer through a minimized oxygen functional groups in the electrode surface and (3) an enhanced interfacial conductivity leading to a facile Li ion diffusivity. The proposed strategy may open a broad range of application, not only for the two-mentioned electrodes, but also for other anode and cathodes materials of LIBs having similar concerns.

A polymerized C60 coating enhancing interfacial stability at three-dimensional LiCoO2 in high-potential regime

The interfacial instabilities, including side reactions due to electrolyte decompositions and Cobalt (Co) dissolutions, are the main detrimental processes at LiCoO2 cathode when a high-voltage window (>4.2 V) is applied. Nevertheless, cycling the cathode with a voltage above 4.2 V would deliver an increased gravimetric capacity, which is desired for high power battery operation. To address these drawbacks, we demonstrate a synergistic approach by manufacturing the three-dimensional high-temperature LiCoO2 electrodes (3D HT-LCO) using laser-microstructuring, laser-annealing and subsequent coating with polymerized C60 thin films (C60@3D HT-LCO) by plasma-assisted thermal evaporation. The C60@3D HT-LCO cathode delivers higher initial discharge capacity compared to its theoretical value, i.e. 175 mA h g−1 at 0.1 C with cut-off voltage of 3.0–4.5 V. This cathode combines the advantages of the 3D electrode architecture and an advanced C60 coating/passivation concept leading to an improved electrochemical performance, due to an increased active surface area, a decreased charge transfer resistance, a prevented Co dissolution into the electrolyte and a suppressed side reaction and electrolyte decomposition. This work provides a novel solution for other cathode materials having similar concerns in high potential regimes for application in lithium-ion microbatteries.

Silicon Nanowires Coated with C60 Layer As Anode Materials for Lithium-Ion Secondary Batteries

Silicon nanowires (Si NWs) with C60 coating layer as anode materials for lithium-ion batteries have been successfully synthesized by plasma enhanced chemical vapor deposition and plasma assisted thermal evaporation methods. The morphology, structure and electrochemical performance of C60 coated Si NWs are investigated in further. The results showed that the C60 coated Si NWs electrodes show an initial coulombic efficiency of 77% when cycling between 0 and 1.5 V (versus Li/Li+) at a current density of 100 μAcm-2 . The C60 coated Si NWs electrodes perform a capacity as high as 3377 mAhg−1 at the first cycle. Furthermore, they also demonstrate a good capacity retention compared with the un-coated ones due to the small interfacial resistance at the electrode/electrolyte interface.

Synthesis of Boron-Doped C60 Film Using Plasma-Assisted Thermal Evaporation Technique and its Electrochemical Characterizations

Boron doped C60 (B:C60) thin films were synthesized by a plasma-assisted thermal evaporation system. Scanning electron microscope (SEM), Raman spectroscopy, Fourier transform infra red (FTIR) and X-ray photo electron spectroscopy (XPS) were used to investigate the morphology and structural characteristics of the films, respectively. The electrochemical characterization of B:C60 films was then introduced as a coating layer for silicon film anodes in a lithium ion battery. Typical electrochemical measurements such as cyclic voltammetry (CV) and impedance spectroscopy were used to characterize the B:C60 coated silicon electrodes. CV profiles implied that B:C60 coating layer could act as a passive layer with respect to the insertion and extraction of lithium ions into the silicon film electrode. Moreover, impedance results showed that the coating layer contributed to the smaller charge transfer resistance at the electrode/electrolyte interface.

Estimation of Li-Ion Diffusion Coefficients in C&lt;sub&gt;60&lt;/sub&gt; Coated Si Thin Film Anodes Using Electrochemical Techniques

C60coated Si thin films were prepared sequentially by a plasma enhanced chemical vapor deposition and a plasma assisted thermal evaporation technique. The films were then utilized as anode materials for lithium ion batteries. The diffusion coefficients of Li-ions in the film electrodes were then estimated by typical electrochemical techniques such as cyclic voltammetry and electrochemical impedance spectroscopy. The diffusion coefficients determined by both methods were found to be consistent each other. The diffusion coefficient of coated samples was obviously higher than that of bare silicon thin films, indicated that the kinetic properties of lithium ion transport in silicon film electrodes were enhanced by the C60film coating on its surface.

Fullerene C&lt;SUB&gt;60&lt;/SUB&gt; Coated Silicon Nanowires as Anode Materials for Lithium Secondary Batteries

A Fullerene C60 film was introduced as a coating layer for silicon nanowires (Si NWs) by a plasma assisted thermal evaporation technique. The morphology and structural characteristics of the materials were studied by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). SEM observations showed that the shape of the nanowire structure was maintained after the C60 coating and the XPS analysis confirmed the presence of the carbon coating layer. The electrochemical characteristics of C60 coated Si NWs as anode materials were examined by charge-discharge tests and electrochemical impedance measurements. With the C60 film coating, Si NW electrodes exhibited a higher initial coulombic efficiency of 77% and a higher specific capacity of 2020 mA h g(-1) after the 30th cycle at a current density of 100 microA cm(-2) with cut-off voltage between 0-1.5 V. These improved electrochemical characteristics are attributed to the presence of the C60 coating layer which suppresses side reaction with the electrolyte and maintains the structural integrity of the Si NW electrodes during cycle tests.

Increased metal-insulator transition temperatures in epitaxial thin films of V2O3 prepared in reduced oxygen environments

Thin films of V2O3 were grown epitaxially on c-plane sapphire substrates by oxygen plasma-assisted thermal evaporation. Reducing the amount of oxygen supplied during growth led to a nearly 50 K increase in V2O3’s metal-insulator transition temperature to a temperature as high as 184 K. By systematically varying the oxygen pressure the transition temperature monotonically increased, which was accompanied by a concomitant increase in the room-temperature resistivity. These trends are consistent with a continuous change in the stoichiometry of V2O3.

P-Doped Fullerene Films as Coating Materials for Silicon Film Anodes of Lithium Secondary Batteries

Phosphorus doped fullerene C60 (P:C60) thin films were introduced as coating materials for silicon film anodes of lithium secondary batteries using a plasma assisted thermal evaporation technique. The P:C60 coated silicon films were then used as anode materials of lithium secondary batteries. The electrochemical characteristics of the coated electrodes were studied by charge-discharge tests, cyclic voltammetry and impedance spectroscopy. Electrochemical measurements revealed that the higher coulombic efficiency of 91% and lower irreversible capacity of 298 mAhg-1on the first cycle were observed for the P:C60 coated silicon electrodes in comparison with the bare silicon case. In addition, the stable cyclic property and high capacity retention after the 30th cycle were demonstrated. All above mentioned results were attributed to the improved conductivity due to the presence of C60 coating layer which might contribute to the faster transfer of Li-ions at the electrode/electrolyte interface.

Interfacial Properties of Fullerene Coated Silicon Film as an Anode Material for Lithium Secondary Batteries: Effect of Coating Layer Thickness

Silicon thin films with thickness of about 300 nm were coated by fullerene thin film with different thickness (50-200 nm) using plasma assisted thermal evaporation technique. The fullerene coated silicon films were then characterized as anode materials of lithium secondary batteries. The interfacial properties of the electrodes coated with fullerene film of different thicknesses have been studied using impedance spectroscopy and compared with those of uncoated silicon electrodes. An enhancement of the performances of the coated electrodes in terms of reduced solid electrolyte interface (SEI) and charge transfer resistances has been found. As the thickness of fullerene is increased, the coated electrodes demonstrated a smaller initial irreversible capacity and a more reduced charge transfer resistance. However, there was a thickness limit that gave a larger interfacial resistance than that of bare silicon film anodes.

Electrochemical Properties of Fullerene Coated Silicon Thick Film for Anode Material of Lithium Secondary Batteries

Silicon thick films were coated by fullerene thin film using plasma assisted thermal evaporation technique at plasma power of 50 and 100 W. The fullerene coated silicon films were then used as anode materials of lithium secondary batteries. The coated electrodes demonstrated a lower initial irreversible capacity and a better interfacial property, as shown by the cyclic voltammetry (CV) measurements and impedance analysis. It was attributed to the fullerene coating layer which could maintain the mechanical stability of electrodes by suppressing the side reaction with the electrolyte during the repeated charge-discharge tests.

In-situ formation of BSCCO thin films by plasma assisted thermal evaporation

Thin films of the superconductor Bi-Sr-Ca-Cu-O (BSCCO) have been prepared by thermal evaporation in an evaporator featuring an RF-excited oxygen plasma generator. Formation of the 2212 phase is obtained in situ, as confirmed by X-ray analysis. The films require postannealing, however, in order to exhibit a superconducting transition. Specifically, postanneals are required to obtain critical temperatures of up to 75 K; 1330 Pa is the minimum annealing pressure. The authors report the study of the superconducting properties as a function of oxygen annealing pressure as well as a characterization of the oxygen plasma. An investigation of the surface morphology was performed using a force microscopy (AFM) and a tunneling microscopy (STM). The latter clearly shows terraces and steps with a height of 1.5 nm, or multiples thereof, corresponding to one-half of the c-axis lattice constant of the 2212 compound. The AFM, on the other hand, shows a drastic difference between as-grown and annealed films, even when the former are sometimes insulating.