Electrochemical behavior of Sn/SnO2 mixtures for use as anode in lithium rechargeable batteries

Anodes derived from oxides of tin have, of late, been of considerable interest because, in principle, they can store over twice as much lithium as graphite. A nanometric matrix of Li₂O generated in situ by the electrochemical reduction of SnO₂ can provide a facile environment for the reversible alloying of lithium with tin to a maximum stoichiometry of Li_4.4Sn. However, the generation of the matrix leads to a high first-cycle irreversible capacity. With a view to increasing the reversible capacity as well as to reduce the irreversible capacity and capacity fade upon cycling, tin–tin oxide mixtures were investigated. SnO₂, synthesized by a chemical precipitation method, was mixed with tin powder at two compositions, viz., 1:2 and 2:1, ball-milled and subjected to cycling studies. A mixture of composition Sn:SnO₂ = 1:2 exhibited a specific capacity of 549 mAh g⁻¹ (13% higher than that for SnO₂) with an irreversible capacity, which was 7% lower than that for SnO₂ and a capacity fade of 1.4 mAh g⁻¹ cycle⁻¹. Electrodes with this composition also exhibited a coulombic efficiency of 99% in the 40 cycles. It appears that a matrix in which tin can be distributed without aggregation is essential for realizing tin oxide anodes with high cyclability.     

Nanocrystalline tin oxides and nickel oxide film anodes for Li-ion batteries

Tin oxides and nickel oxide thin film anodes have been fabricated for the first time by vacuum thermal evaporation of metallic tin or nickel, and subsequent thermal oxidation in air or oxygen ambient. X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements showed that the prepared films are of nanocrystalline structure with the average particle size <100 nm. The electrochemical properties of these film electrodes were examined by galvanostatic cycling measurements and cyclic voltammetry. The composition and electrochemical properties of SnO_x (1<x<2) films strongly depend on the oxidation temperature. The reversible capacities of SnO and SnO₂ films electrodes reached 825 and 760 mAh g⁻¹, respectively, at the current density of 10 μA cm⁻² between 0.10 and 1.30 V. The SnO_x film fabricated at an oxidation temperature of 600 °C exhibited better electrochemical performance than SnO or SnO₂ film electrode. Nanocrystalline NiO thin film prepared at a temperature of 600 °C can deliver a reversible capacity of 680 mAh g⁻¹ at 10 μA cm⁻² in the voltage range 0.01–3.0 V and good cyclability up to 100 cycles.     

SnO2-carbon composites for lithium-ion battery anodes

A SnO₂-carbon composite prepared by heat treating a mixture of colloidal SnO₂ and sucrose demonstrated a reversible lithium storage capacity of 680 mA h/g on the 1st cycle. The discharge curve of the composite did not exhibit the 1.0 V plateau characteristic of SnO₂. The high reversible capacity of the composite suggests that lithium is stored in both tin and carbon. The composite demonstrated reduced capacity fade over SnO₂ as well as SnO:graphite and Sn:graphite composites.     

In situ polyol-assisted synthesis of nano-SnO2/carbon composite materials as anodes for lithium-ion batteries

Nano-SnO₂/carbon composite materials were synthesized in situ using the polyol method by oxidizing SnCl₂·2H₂O in the presence of a carbon matrix. All the as-synthesized composites consisted of SnO₂ nanoparticles (5–10 nm) uniformly embedded into the carbon matrix as evidenced by TEM. XRD confirmed the presence of nano-sized SnO₂ particles that are crystallized in a rutile structure and XPS revealed a tin oxidation state of +4. Cyclic voltammetry of the composites showed an irreversible peak at 1.4 V in the first cycle and a typical alloying/de-alloying process at 0.1–0.5 V. The best composite (“composite I”, 15 wt% SnO₂) showed an improved lithium storage capacity of 370 mAh g^?1 at 200 mA g^?1 (～C/2) which correspond to 32% improvement and lower capacity fade compared to commercial SnO₂ (50 nm). We have also investigated the effect of the heating method and we found that the use of a microwave was beneficial in not only shortening reaction time but also in producing smaller SnO₂ particles that are also better dispersed within the carbon matrix which also resulted in higher lithium storage capacity.     

Electrical,optical, and structural characterization of arsenic–tin oxidized transparent conducting films

A comprehensive structural, optical, electrical, and optoelectronic study of arsenic-doped SnO₂ was conducted. Several arsenic-doped SnO₂ thin films with different arsenic content have been prepared on glass and silicon substrates by a vacuum thermal evaporation technique. The structural, electrical and optical study show that some of As⁵⁺ ions occupied locations in interstitial positions of SnO₂ lattice. The prepared oxidized pure tin film is found to be consisting of orthorhombic and tetragonal SnO₂ structure. The optical properties show that arsenic-doped SnO₂ films are good transparent oxides. The bandgap of arsenic-doped SnO₂ varies with arsenic content following the Moss–Burstein rule. The electrical behaviors show that the prepared arsenic-doped SnO₂ films are degenerate semiconductors and might transform into insulators with increasing arsenic doping level. The electrical properties (resistivity, mobility, and carrier concentration) vary depending on the arsenic doping level. The SnO₂ film doped with wt. 0.6% arsenic shows utmost dc electrical conductivity parameters: resistivity of 4.6 × 10^?2 Ω cm, mobility of 6.0 cm²/V s, and carrier concentration of 2.25 × 10¹⁹ cm^?3. From transparent-conducting-oxide (TCO) point of view, low arsenic concentration (less that 1%) is effective for SnO₂ donor doping but not emulate doping with other dopant like Sb.     

Preparation of carbon-coated Sn powders and their loading onto graphite flakes for lithium ion secondary battery

Carbon-coated Sn powders were prepared from the powder mixtures of thermoplastic precursor PVA, SnO₂ and MgO. The characterization of composite powders synthesized was carried out by XRD, TG, TEM, SEM and anodic performance measurement. SnO₂ was reduced to metallic Sn by heating with PVA, and its particle size in carbon shell was around 30–100 nm. MgO existence hindered the agglomeration of molten metallic Sn and made the dispersion of metallic Sn as fine particles possible. They showed high anodic performance in lithium ion batteries; high charge capacity as 500 mAh g⁻¹ even after tenth cycle and stable cyclic performance. The spaces left in carbon shell by MgO after its dissolution were supposed to absorb a large volume expansion of Sn metal particle by Li alloying during discharging. When carbon-coated Sn loaded onto graphite flakes, metallic tin contributed to the increase in capacity.     

Study of NiO cathode modified by ZnO additive for MCFC

The preparation and subsequent oxidation of nickel cathodes modified by impregnation with zinc oxide (ZnO) were evaluated by surface and bulk analysis. The electrochemical behaviors of ZnO impregnated NiO cathodes was also evaluated in a molten 62 mol% Li₂CO₃ + 38 mol% K₂CO₃ eutectic at 650 °C by electrochemical impedance spectroscopy (EIS) as a function of ZnO content and immersion time. The ZnO impregnated nickel cathodes showed the similar porosity, pore size distribution and morphology to the reference nickel cathode. The stability tests of ZnO impregnated NiO cathodes showed that the ZnO additive could dramatically reduce the solubility of NiO in a eutectic carbonate mixture under the standard cathode gas condition. The impedance spectra for cathode materials show important variations during the 100 h of immersion. The incorporation of lithium in its structure and the low dissolution of nickel oxide and zinc oxide are responsible of these changes. After that, the structure reaches a stable state. The cathode material having 2 mol% of ZnO showed a very low dissolution and a good catalytic efficiency close to the NiO value. We thought that 2 mol% ZnO/NiO materials would be able to adapt as alternative cathode materials for MCFCs.     

Electrochemical characterization of blend polymer electrolytes based on poly(oligo[oxyethylene]oxyterephthaloyl) for rechargeable lithium metal polymer batteries

Solid polymer electrolytes composed of poly(ethylene oxide)(PEO), poly(oligo[oxyethylene]oxyterephthaloyl) and lithium perchlorate have been prepared and characterized. Addition of poly(oligo[oxyethylene]oxyterephthaloyl) to PEO/LiClO₄ reduced the degree of crystallinity and improved the ambient temperature ionic conductivity. The blend polymer electrolyte containing 40 wt.% of poly(oligo[oxyethylene]oxyterephthaloyl) showed an ionic conductivity of 2.0 × 10⁻⁵ S cm⁻¹ at room temperature and a sufficient electrochemical stability to allow application in the lithium batteries. By using the blend polymer electrolytes, the lithium metal polymer cells composed of lithium anode and LiCoO₂ cathode were assembled and their cycling performances were evaluated at 40 °C.     

Carbon anode for dry-polymer electrolyte lithium batteries

A spherical carbon material of meso-carbon microbead (MCMB) was examined as an anode in a polyethylene oxide (PEO) based polymer electrolyte lithium battery. The electrochemical performance of the carbon electrode with the polymer electrolyte depended on the electrode thickness and the particle size of MCMB. The 30 μm-thick electrode of MCMB with the particle size of 20–30 μm showed a reversible capacity comparable with that in a liquid electrolyte, but the 100 μm-thick electrode showed a half of the 30 μm-thick electrode. The smaller particle size of 5–8 μm exhibited a high irreversible capacity at the first charge–discharge cycle. The reaction heat between MCMB and the polymer electrolyte was 0.5 J mAh^?1, which was much lower compared to those between lithium metal and the polymer electrolyte, 1.2 J mAh^?1, and MCMB and conventional liquid electrolyte, 4.3 J mAh^?1.     

Effect of metal ion concentration on synthesis and properties of La0.84Sr0.16MnO3 cathode material

A reactive powder of La_0.84Sr_0.16MnO₃ is synthesized as a cathode material for solid oxide fuel cells by a citrate–nitrate auto-ignition process and characterized by thermal analysis, X-ray diffraction and electrical conductivity measurements. The effect of starting metal ion concentration in the precursor solution on the properties of the final oxide is studied and correlated through particle size analyses, sintering studies and microstructural examination. Sintered La_0.84Sr_0.16MnO₃ ceramics of relative density around 93% can be fabricated by preferably keeping the metal ion concentration in the precursor to less than 0.8 M, whereas to make porous ceramics (relative densities of 75–80%) a higher metal ion concentration is preferred. At 1000 °C, the 93% dense ceramics exhibit electrical conductivities of around 168–169 S cm⁻¹ and the porous ceramics of around 136–146 S cm⁻¹.     

Sintered porous heat sink for cooling of high-powered microprocessors for server applications

This paper experimentally investigates the sintered porous heat sink for the cooling of the high-powered compact microprocessors for server applications. Heat sink cold plate consisted of rectangular channel with sintered porous copper insert of 40% porosity and 1.44 × 10^?11 m² permeability. Forced convection heat transfer and pressure drop through the porous structure were studied at Re ? 408 with water as the coolant medium. In the study, heat fluxes of up to 2.9 MW/m² were successfully removed at the source with the coolant pressure drop of 34 kPa across the porous sample while maintaining the heater junction temperature below the permissible limit of 100 ± 5 °C for chipsets. The minimum value of 0.48 °C/W for cold plate thermal resistance (R_cp) was achieved at maximum flow rate of 4.2 cm³/s in the experiment. For the designed heat sink, different components of the cold plate thermal resistance (R_cp) from the thermal footprint of source to the coolant were identified and it was found that contact resistance at the interface of source and cold plate makes up 44% of R_cp and proved to be the main component. Convection resistance from heated channel wall with porous insert to coolant accounts for 37% of the R_cp. With forced convection of water at Re = 408 through porous copper media, maximum values of 20 kW/m² K for heat transfer coefficient and 126 for Nusselt number were recorded. The measured effective thermal conductivity of the water saturated porous copper was as high as 32 W/m K that supported the superior heat augmentation characteristics of the copper–water based sintered porous heat sink. The present investigation helps to classify the sintered porous heat sink as a potential thermal management device for high-end microprocessors.     

Enhanced performance of SnO2 xerogel electrochemical capacitor prepared by novel crystallization process

The performance of both blank and RuO₂-impregnated SnO₂ (Sb-6 mol%) xerogel electrodes are enhanced significantly by improved crystallinity via a novel crystallization process, which effectively suppresses grain coarsening and hence allows the xerogel to be crystallized at high temperatures while maintaining a high surface area. The improved SnO₂ electrodes show maximum specific capacitances which exceed 10 F g⁻¹ in 1 M KOH_aq at 200 mV s⁻¹ after firing at 800 °C. The enhancement becomes increasingly pronounced with increasing charge–discharge rate due to improved oxide conductivity.     

Synthesis and electrochemical properties of lithium cobalt oxides prepared by molten-salt synthesis using the eutectic mixture of LiCl–Li2CO3

Lithium cobalt oxide powders have been successfully prepared by a molten-salt synthesis (MSS) method using a eutectic mixture of LiCl and Li₂CO₃ salts. The physico-chemical properties of the lithium cobalt oxide powders are investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), particle-size analysis and charge–discharge cycling. A lower temperature and a shorter time (∼700°C and 1 h) in the Li:Co=7 system are sufficient to prepare single-phase HT-LiCoO₂ powders by the MSS method, compared with the solid-state reaction method. Charge–discharge tests show that the lithium cobalt oxide prepared at 800°C has an initial discharge capacity as high as 140 mA h g⁻¹, and 100 mA h g⁻¹ after 40 cycles. The dependence of the synthetic conditions of HT-LiCoO₂ on the reaction temperature, time and amount of flux with respect to starting oxides is extensively investigated.     

Electrochemical properties of LiM1/6Mn11/6O4 (M = Mn,Co, Al and Ni) as cathode materials for Li-ion batteries prepared by ultrasonic spray pyrolysis method

Spinel lithium manganese oxide LiMn₂O₄ and its substituted forms LiM_1/6Mn_11/6O₄ (M=Co, Al and Ni) were prepared by ultrasonic spray pyrolysis method. As-prepared particles showed a spherical morphology and a densely congested interior structure. The geometric mean diameter was between 0.76 and 0.93 μm, and the geometric standard deviation was approximately 1.33. The crystallite size was approximately 30 nm, and the specific surface area of the particles ranges from 5.7 to 12.7 m²/g. As-prepared particles were used as cathode active materials for lithium secondary battery and their charge/discharge properties have been investigated. As a result, it could be seen that ultrasonic spray pyrolysis is an effective method to prepare lithium manganese oxide (LiMn₂O₄) and its substituted forms within very short production time, which is only 4.8 min in the present work.     

Effects of addition of TiO2 nanoparticles on mechanical properties and ionic conductivity of solvent-free polymer electrolytes based on porous P(VdF-HFP)/P(EO-EC) membranes

To enhance the performance (i.e., mechanical properties and ionic conductivity) of pore-filling polymer electrolytes, titanium dioxide (TiO₂) nanoparticles are added to both a porous membrane and its included viscous electrolyte, poly(ethylene oxide-co-ethylene carbonate) copolymer (P(EO-EC)). A porous membrane with 10 wt.% TiO₂ shows better performance (e.g., homogeneous distribution, high uptake, and good mechanical properties) than the others studied and is therefore chosen as the matrix to prepare polymer electrolytes. A maximum conductivity of 5.1 × 10⁻⁵ S cm⁻¹ at 25 °C is obtained for a polymer electrolyte containing 1.5 wt.% TiO₂ in a viscous electrolyte, compared with 3.2 × 10⁻⁵ S cm⁻¹ for a polymer electrolyte without TiO₂. The glass transition temperature, T_g is lowered by the addition of TiO₂ (up to 1.5 wt.% in a viscous electrolyte) due to interaction between P(EO-EC) and TiO₂, which weakens the interaction between oxide groups of the P(EO-EC) and lithium cations. The overall results indicate that the sample prepared with 10 wt.% TiO₂ for a porous membrane and 1.5 wt.% TiO₂ for a viscous electrolyte is a promising polymer electrolyte for rechargeable lithium batteries.     

Electrochemical lithium insertion into amorphous MoO3·2H2O

Following the route of synthesis of β-MoO₃ through soft chemistry methods a new amorphous material with composition MoO₃·2H₂O has been detected. The hydrated molybdenum oxide showed the capacity for electrochemical lithium insertion. The maximum amount of lithium incorporated in this material (∼3.3 Li/Mo) leads to a specific capacity of 490 Ah kg⁻¹. The charge–discharge curve showed a good reversibility in the potential range from 3.2 to 1.1 V versus Li⁺/Li⁰ where the cell voltage decreased monotonously as a function of the degree of lithium inserted. The electrochemical features of amorphous MoO₃·2H₂O suggest that it can be considered as a possible cathode candidate in rechargeable lithium batteries.     

LiFePO4/carbon cathode materials prepared by ultrasonic spray pyrolysis

Small crystallites LiFePO₄ powder with conducting carbon coating can be synthesized by ultrasonic spray pyrolysis. Cheaper trivalent iron ion is used as the precursor. The pure olivine phase can be prepared with the duplex process of spray pyrolysis (synthesized at 450, 550 or 650 °C) and subsequent heat-treatment (at 650 °C for 4 h). The results indicate that the pyrolysis temperature of 450 °C is appropriate for best results. The carbon coating on the LiFePO₄ surface is critical to the electrochemical performance of LiFePO₄ cathode materials of the lithium secondary battery, since the carbon coating does not only increase the electronic conductivity via carbon on the surface of particles, but also enhance the ion mobility of lithium ion due to prohibiting the grain growth during post-heat-treatment. The carbon of 15 wt.% evenly distributed on the final LiFePO₄ powders can get the highest initial discharge capacity of 150 mA h g⁻¹ at C/10 and 50 °C.     

Preparation of LiMn2O4 at the low temperature of 250 °C using eutectic self-mixing method

Spinel LiMn₂O₄ as a cathode material for lithium rechargeable batteries is prepared at the low temperature of 250 °C without any artificial mixing procedures of reactants. The phase transitions of lithium manganese oxide are found three times on heating at 250 °C. The prepared material exhibits the initial discharge capacity of 85.5 mAh g⁻¹ and the discharge capacity retention of 91.5% after 50 cycles.     

Interface properties between a lithium metal electrode and a poly(ethylene oxide) based composite polymer electrolyte

The interface resistance between a lithium metal electrode and a polymer electrolyte has been measured for composite polymer electrolytes using various ceramic fillers with poly(ethylene oxide) (PEO) and lithium salts (LiX). The interface resistance depended on the properties of added fillers and lithium salts. The PEO with LiClO₄ electrolyte contacted with lithium metal showed the high interfacial resistance of 1000 Ω cm² at 70°C for 25 days. In contrast, the interface resistance between lithium metal and PEO with Li(CF₃SO₂)₂N was as low as 67 Ω cm² after contacting at 80°C for 30 days. The interface stability and the lithium ion conductivity were improved by addition of a small amount of ferroelectric BaTiO₃ as the filler into the PEO–LiX electrolyte.     

Lead–samarium alloys for positive grids of valve-regulated lead–acid batteries

The influence of the rare earth metal, samarium, as an alloying additive on the electrochemical behaviour of pure lead is studied by means of X-ray diffraction, self-depassivation, linear sweep voltammetry and a.c. impedance spectroscopy in 4.87 M H₂SO₄ at 25 °C. Studies on Pb–Sm alloys (Sm = 0.02, 0.04, and 0.12 wt.%) indicate that the oxide film formed on the alloy surface at 0.9 V is thicker than that on pure lead when the alloy contained less than 0.1 wt.% Sm. In addition, samarium exercises little influence on the conversion of PbSO₄ to PbO₂ in the oxide film during charging. The electrochemical impedance of the oxide film is much larger than that of the oxide formed on pure lead. With the addition of more than 0.1% Sm, however, the oxide film on the alloy surface is thinner and samarium obviously promotes the conversion of passive PbSO₄ in oxide film to conductive PbO₂. The a.c. impedance data show that a high content of samarium greatly inhibits the growth of the passivation layer and decreases the electrochemical impedance of the film.