Effect of fullerene coating on silicon thin film anodes for lithium rechargeable batteries

To improve the electrochemical performances of Si thin film anodes for lithium rechargeable batteries, fullerene thin films are prepared by plasma-assisted evaporation methods to be used as coating materials. Analyses via Raman and X-ray photoelectron spectroscopy indicate that amorphous polymeric films originated from fullerene are formed on the surface of the silicon thin film. The electrochemical performance of these fullerene-coated silicon thin film as an anode material for rechargeable lithium batteries has been investigated by cyclic voltammetry, charge/discharge tests, and electrochemical impedance spectroscopy. The fullerene-coated Si thin films demonstrated a high specific capacity of above 3,000 mAh g⁻¹ as well as good capacity retention for 40 cycles. In comparison with bare silicon anodes, the fullerene-coated silicon thin film showed superior and stable cycle performance which can be attributed to the fullerene coating layer which enhances the Li-ion kinetic property at the electrode/electrolyte interface.     

Structural studies of the new carbon-coated silicon anode materials using synchrotron-based in situ XRD

The structural changes of graphite-mixed and carbon-coated silicon, used as lithium intercalation materials, have been studied during discharge–charge using synchrotron-based in situ X-ray diffraction. The lithium intercalation (de-intercalation) takes place in the graphite first during discharge (charge), and then in the silicon. This graphite–lithium buffer combined with the uniformly distributed carbon coating greatly improve the quality and morphology of the Li–Si alloys formed at the surface of silicon powders. Therefore, the superior specific capacity and cycling performance are obtained for the graphite-mixed and carbon-coated silicon materials.     

Corrosion and wear resistance properties of multilayered diamond‐like carbon nanocomposite coating

Multilayered diamond‐like carbon (DLC) nanocomposite coating has been deposited on silicon and stainless steel substrates by combination of cathodic arc evaporation and magnetron sputtering. In order to make DLC coating adhered to metal substrate, a chromium interlayer has been deposited with constant bias voltage of −150 V applied to the substrate. Dense multilayered coating consists of metallic or nonmetallic and tetrahedral carbon (ta‐C) layers with total thickness of 1.44 μm. The coating has been studied for composition, morphology, surface nature, nanohardness, corrosion resistance, and tribological properties. The composition of the coating has been estimated by energy‐dispersive spectroscopy. Field‐emission scanning electron microscopy and atomic force microscopy have been used to study the surface morphology and topography. I_D/I_G ratio of ta‐C:N layer obtained from Raman spectroscopy is 1.2, indicating the disorder in the layer. X‐ray photoelectron spectroscopy studies of individual ta‐C:N, CrN, and Cr‐doped DLC layers confirm the presence of sp²C, sp³C, CrN, Cr₂N, and carbidic carbon, and sp²C, sp³C, and Cr carbide. Nanohardness studies show the maximum penetration depth of 70 to 85 nm. Average nanohardness of the multilayered DLC coating is found to be 35 ± 2.8 GPa, and Young's modulus is 270 GPa. The coating demonstrates superior corrosion resistance with better passivation behavior in 3.5% NaCl solution, and corrosion potential is observed to move towards nobler (more positive) values. A low coefficient of friction (0.11) at different loads is observed from reciprocating wear studies. Wear volume is lower at all loads on the multilayered DLC nanocomposite coating compared to the substrate.     

The influence of Ti plasma etching pre-treatment on mechanical properties of DLC film on cemented carbide

The pre-treatment of substrate surface had been a key part of DLC film preparation to improve mechanical and tribological properties. Ti plasma etching pre-treatment was investigated in this paper as a new effective surface pre-treatment method to substitute transition layer. This pre-treatment used high-energy Ti plasma to impact substrate surface. Ti plasma etched the substrate to a depth of 407 nm and increased the roughness from 1.36 to 40.39 nm. A trace layer of substrate, together with cobalt, oxides, and other impurities, was removed. Ti plasma broke some top WC crystals and combined with the free carbon ions separating from the substrate. A DLC film was deposited on the etched surface. Compared with DLC films deposited on the untreated substrate and Ti transition layer, the DLC film on the Ti plasma etched substrate had best adhesion strength of 34.14 N. The three DLC films had the same sp³ bonding carbon content, but Ti plasma etching treatment could promote the formation of sp³ bonds on the interface of substrate and DLC film. This DLC film had low friction coefficient of 0.12 and low wear rate of 5.11 × 10⁻⁷ mm³/m·N. In summary, Ti plasma etching pre-treatment could significantly improve the adhesion of DLC film and keep its excellent tribological properties.     

Lithium storage in perovskite lithium lanthanum titanate

Perovskite lithium lanthanum titanate (LLTO) was synthesized using sol–gel method. It shows a reversible capacity of 145 mA h g^− 1 and moderate cycling performance between 0.01 and 2.00 V. Cyclic voltammetry and X-ray diffraction results demonstrate a two-step solid–solution reaction behavior in the voltage range of 0.00–3.00 V upon lithium insertion/extraction. A stable solid electrolyte interphase (SEI) layer is formed on the surface of LLTO after the initial discharge. Carbon coating by chemical vapor deposition improves its cycling performance significantly.     

Atomic layer coating to mitigate capacity fading associated with manganese dissolution in lithium ion batteries

Ultrathin surface coatings (< 5 nm) on electrodes have been developed to mitigate the capacity decay induced by manganese (Mn) dissolution, a limiting factor for Mn-based oxide electrode materials in lithium ion batteries. We demonstrated that the capacity decay was attributed to the Mn deposited on the graphite electrode accelerating the electrolyte decomposition. While the Al₂O₃ coating on the positive electrode suppressed the Mn dissolution, we found that the Al₂O₃ coating on the negative electrode was counter-intuitively more beneficial and efficient in preventing the Mn deposition and achieving excellent capacity retention in lithium ion batteries.     

High-performance thin-film Li4Ti5O12 electrodes fabricated by using ink-jet printing technique and their electrochemical properties

Li₄Ti₅O₁₂ thin-film anode with high discharge capacity and excellent cycle stability for rechargeable lithium ion batteries was prepared successfully by using ink-jet printing technique. The prepared Li₄Ti₅O₁₂ thin film were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, cyclic voltammograms, and galvanostatic charge–discharge measurements. It was found that the average thickness of 10-layer Li₄Ti₅O₁₂ film was about 1.7~1.8 μm and the active material Li₄Ti₅O₁₂ in the thin film was nano-sized about 50–300 nm. It was also found that the prepared Li₄Ti₅O₁₂ thin film exhibited a high discharge capacity of about 174 mAh/g and the discharge capacity in the 300th cycle retained 88% of the largest discharge capacity at a current density of 10.4 μA/cm² in the potential range of 1.0–2.0 V.     

InP as new anode material for lithium ion batteries

InP thin film has been successfully fabricated by pulsed laser deposition (PLD) and was investigated for its electrochemistry with lithium for the first time. InP thin film presented a large reversible discharge capacity around 620 mAh g^?1. The reversibility of the crystalline structure and electrochemical reaction of InP with lithium were revealed by using ex situ XRD and XPS measurements. The high reversible capacity and stable cycle of InP thin film electrode with low overpotential made it one of the promise energy storage materials for future rechargeable lithium batteries.     

Enhanced electron field emission from ZnO nanoparticles-embedded DLC films prepared by electrochemical deposition

ZnO nanoparticles-embedded diamond-like amorphous (DLC) carbon films have been prepared by electrochemical deposition. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) results confirm that the embedded ZnO nanoparticles are in the wurtzite structure with diameters of around 4 nm. Based on Raman measurements and atomic force microscope (AFM) results, it has been found that ZnO nanoparticles embedding could enhance both graphitization and surface roughness of DLC matrix. Also, the field electron emission (FEE) properties of the ZnO nanoparticles-embedded DLC film were improved by both lowering the turn-on field and increasing the current density. The enhancement of the FEE properties of the ZnO-embedded DLC film has been analyzed in the context of microstructure and chemical composition.     

High-capacity LiV3O8 thin-film cathode with a mixed amorphous–nanocrystalline microstructure prepared by RF magnetron sputtering

LiV₃O₈ thin films with a mixed amorphous–nanocrystalline microstructure were deposited on stainless steel substrates using radio-frequency (RF) magnetron sputtering for the first time. The films exhibited good performance as a cathode material for lithium ion batteries. Results indicate that the film electrodes had a smooth surface and consisted mainly of an amorphous structure containing nanocrystalline zones dispersed within it. Depending on its microstructure, the films delivered an initial discharge capacity as high as 382 mAh/g and exhibited good capacity retention, with discharge capacity of 301 mAh/g after 100 cycles representing a loss rate of 0.21% per cycle.     

Characterization of SEI layer formed on high performance Si–Cu anode in ionic liquid battery electrolyte

Formation of the SEI layer on Si–Cu film electrode in the ionic liquid electrolyte of 1 M lithium bis(trifluoromethylsulfonyl)imide/1-methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide (LiTFSI/MPP-TFSI) was investigated using ex-situ ATR FTIR and X-ray photoelectron spectroscopy. The SEI layer is found to be composed of organic and inorganic compounds that are the decomposition products of MPP cation and TFSI anion, and effectively passivate the electrode surface during initial cycling. Formation of a stable SEI layer leads to an excellent capacity retention 98% of the maximum discharge capacity, delivering discharge capacities of > 1620 mAhg^? 1 over 200 cycles. The data contribute to a basic understanding of SEI formation and composition responsible for the cycling performance of Si-based alloy anodes in ionic liquid electrolyte-based rechargeable lithium batteries.     

Cyclic voltammetry and galvanostatic cycling characteristics of LiNiVO4 thin films during lithium insertion and re/de-insertion

In this communication, we investigated the effects of LiNiVO₄ thin film electrodes composition, thickness, electrolytes, cycling temperature, crystallization of films, and substrates on the kinetics during lithium insertion/de-insertion behaviour, which were studied in detail by cyclic voltammetry. The stoichiometric and non-stoichiometric thin films were formed by using rf-sputtering by varying the partial pressure of oxygen, and the host films were characterized by a variety of methods like Nuclear techniques and surface science analytical methods. The galvanostatic studies give the lithium insertion amounts and the best electrochemical performance of 1300 mAh/g capacity has been obtained from the stoichiometric film deposited on a stainless steel substrate during the first discharge cycle. The lithium diffusion coefficients of the film during the first discharge–charge cycle were measured by using galvanostatic intermediate titration method. Overall, the voltammetric behaviours of LiNiVO₄ thin film electrodes are highly sensitive to the composition, thickness, cycling temperature, scan rate, substrates and crystal structure, and the above observed behaviours are discussed.     

Continuous supercritical hydrothermal synthesis: lithium secondary ion battery applications

Nanosized lithium iron phosphate (LiFePO₄) and transition metal oxide (MO, where M is Cu, Ni, Mn, Co, and Fe) particles are synthesized continuously in supercritical water at 25?C30?MPa and 400??C under various conditions for active material application in lithium secondary ion batteries. The properties of the nanoparticles, including crystallinity, particle size, surface area, and electrochemical performance, are characterized in detail. The discharge capacity of LiFePO₄ was enhanced up to 140?mAh/g using a simple carbon coating method. The LiFePO₄ particles prepared using supercritical hydrothermal synthesis (SHS) deliver the reversible and stable capacity at a current density of 0.1?C rate during ten cycles. The initial discharge capacity of the MO is in the range of 800?C1,100?mAh/g, values much higher than that of graphite. However, rapid capacity fading is observed after the first few cycles. The continuous SHS can be a promising method to produce nanosized cathode and anode materials.     

Synthesis and electrochemical properties of polypyrrole-coated poly(2,5-dimercapto-1,3,4-thiadiazole)

A new composite cathode active material, conductive polypyrrole (PPy)-coated poly(2,5-dimercapto-1,3,4-thiadiazole) (PDMcT) was prepared as a thin film via the surfactant template (TFST) technique. The formation of the uniform and well-connected film on the surface of PDMcT particles was confirmed by Fourier transform infrared spectra (FT-IR) and transmission electron micrographs (TEM). By cyclic voltammetry and galvanostatic charge–discharge tests, the coated composite showed a better electrochemical performance than PDMcT, such as enhanced redox processes and improved coulumbic efficiency, etc. The electrical conductivity of the material reached to 10⁻³ S cm⁻¹ and an initial discharge capacity of 250 mAhg⁻¹ was obtained. Moreover, it showed a slower fading of discharge capacity than PDMcT when used as cathode material in secondary lithium batteries with liquid electrolyte solution.     

Plasma Grooving System Using Atmospheric Pressure Surface Discharge Plasma

To fabricate narrow front contact grooves on a single crystalline silicon solar cell, we carried out etching of a silicon nitride film on a silicon substrate using the surface discharge plasma operated at atmospheric pressure. The control of groove width by changing the discharge voltage (V _d) and the length of a back electrode (l) used for formation of the surface discharge was examined. It was found that narrower electrode grooves could be obtained when l was short. For the case of l = 2 mm, the narrowest groove of 116 μm was obtained at V _d = 3.5 kV and the processing time (t _e) of 10 s.     

Preparation of mesocellular carbon foam and its application for lithium/oxygen battery

A mesocellular carbon foam (MCF-C) was prepared by nanocasting technology using mesocellular foam (MCF) silica hard template. The obtained carbon sample exhibits bimodal mesopores with narrow pore size distribution, centered at 4.3 and 30.4 nm. The MCF-C was evaluated as positive electrode in lithium/oxygen battery. It showed a higher discharge capacity, about 40% increased capacity compared to several commercial carbon black. The enhanced performance is probably ascribed to their large pore volumes and ultra-large mesoporous structures, which allow more lithium oxide deposit during discharge process.     

Electrochemical characterization of vertical arrays of tin nanowires grown on silicon substrates as anode materials for lithium rechargeable microbatteries

Vertical arrays of one-dimensional tin nanowires on silicon dioxide (SiO₂)/silicon (Si) substrates have been developed as anode materials for lithium rechargeable microbatteries. The process is complementary metal-oxide-semiconductor (CMOS) compatible for fabricating on-chip microbatteries. Nanoporous anodized aluminum oxide (AAO) templates integrated on SiO₂/Si substrates were employed for fabrication of tin nanowires resulting in high surface area of anodes. The microstructure of these nanowire arrays was investigated by scanning electron microscopy and X-ray diffraction. The electrochemical tests showed that the discharge capacity of about 400 mA h g⁻¹ could be maintained after 15 cycles at the high discharge/charge rate of 4200 mA g⁻¹.     

In vitro cytotoxicity evaluation of natural rubber latex film surface coated with PMMA nanoparticles

In order to increase surface roughness of the sulphur-prevulcanized natural rubber (SPNR) film and, hence, decrease the direct contact between the rubber and skin, the poly(methyl methacrylate) (PMMA) latex particles were deposited onto the SPNR film grafted with polyacrylamide (SPNR-g–PAAm). The surface coverage of PMMA particles on the SPNR-g–PAAm increased with increasing latex immersion time, particle size and concentration. Prior to the in vitro cytotoxicity evaluation on L-929 fibroblasts, the SPNR and SPNR-g–PAAm coated with PMMA particles were extracted by using the culture medium. Results showed that the cytotoxicity effect could be significantly reduced by coating PMMA particles onto the rubber film. At the extract concentrations of ≤12.5% for 24 h at 37 °C, no toxicity potential was detected. The study will be helpful for development of gloves designed for the hypersensitive person.     

The influence of anti‐wear additive ZDDP on doped and undoped diamond‐like carbon coatings

Diamond‐like carbon (DLC) coatings are recognised as a promising way to reduce friction and improve wear performance of automotive engine components. DLC coatings provide new possibilities in the improvement of the tribological performance of automotive components beyond what can be achieved with lubricant design alone. Lubricants are currently designed for metallic surfaces, the tribology of which is well defined and documented. DLC does not share this depth of tribological knowledge; thus, its practical implementation is stymied. In this work, three DLC coatings are tested: an amorphous hydrogenated DLC, a silicone‐doped amorphous hydrogenated DLC and a tungsten‐doped amorphous hydrogenated DLC. The three coatings are tested tribologically on a pin‐on‐reciprocating plate tribometer against a cast iron pin in a group III base oil, and a fully formulated oil that consists of a group III base oil and contains ZDDP, at 100 °C for 6 h and for 20 h in order to determine whether a phosphor‐based tribofilm is formed at the contact. The formation of a tribofilm is characterised using atomic force microscopy and X‐ray photoelectron spectroscopy techniques. The main findings of this study are the formation of a transfer film at the undoped, amorphous hydrogenated DLC surface, and also the tungsten amorphous hydrogenated DLC having a significant wear removal during the testing. The three coatings were found to have differing levels of wear, with the tungsten‐doped DLC showing the highest, the silicon‐doped DLC showing some coating removal and the amorphous hydrogenated DLC showing only minimal signs of wear. Copyright © 2015 John Wiley & Sons, Ltd.     

Nanocrystalline MnO thin film anode for lithium ion batteries with low overpotential

Nanocrystalline MnO thin film has been prepared by a pulsed laser deposition (PLD) method. The reversible lithium storage capacity of the MnO thin film electrodes at 0.125C is over 472 mAh g^?1 (3484 mAh cm^?3) and can be retained more than 90% after 25 cycles. At a rate of 6C, 55% value of the capacity at 0.125C rate can be obtained for both charge and discharge. As-prepared MnO thin film electrodes show the lowest values of overpotential for both charge and discharge among transition metal oxides. All these performances make MnO a promising high capacity anode material for Li-ion batteries.