Lithium cobalt oxide cathode film prepared by rf sputtering

Thin films of LiCoO₂ prepared by radio frequency magnetron sputtering on Pt-coated silicon are investigated under various deposited parameters such as working pressure, gas flow rate of Ar to O₂, and heat-treatment temperature. The as-deposited film was a nanocrystalline structure with (1 0 4) preferred orientation. After annealing at 500–700 °C, single-phase LiCoO₂ is obtained when the film is originally deposited under an oxygen partial pressure (P_O2) from 5 to 10 mTorr. When the sputtering process is performed outside these P_O2 values, a second phase of Co₃O₄ is formed in addition to the HT-LiCoO₂ phase. The degree of crystallization of the LiCoO₂ films is strongly affected by the annealing temperature; a higher temperature enhances the crystallization of the deposited LiCoO₂ film. The grain sizes of LiCoO₂ films annealed at 500, 600 and 700 °C are about 60, 95, and 125 nm, respectively. Cyclic voltammograms display well-defined redox peaks. LiCoO₂ films deposited by rf sputtering are electrochemically active. The first discharge capacity of thin LiCoO₂ films annealed at 500, 600 and 700 °C is about 41.77, 50.62 and 61.16 μAh/(cm² μm), respectively. The corresponding 50th discharge capacities are 58.1, 72.2 and 74.9% of the first discharge capacity.     

Synthesis and electrochemical properties of LiNi0.80(Co0.20−xAlx)O2 (x = 0.0 and 0.05) cathodes for Li ion rechargeable batteries

The effect of simultaneous cobalt as well as aluminum doping was studied to understand their effect on the phase formation behavior and electrochemical properties of solution derived lithium nickel oxide cathode materials for rechargeable batteries. The discharge capacities of LiNi_0.80Co_0.20O₂ and LiNi_0.80Co_0.15Al_0.05O₂ cathodes, measured at constant current densities of 0.45 mA cm⁻² in the cut-off voltage range of 4.3–3.2 V, were 100 and 136 mAh g⁻¹, respectively. LiNi_0.80Co_0.15Al_0.05O₂ had better cycleability than the LiNi_0.80Co_0.20O₂ cathodes. The retention of undesirable Li₂CO₃ phase both in LiNi_0.80Co_0.20O₂ and LiNi_0.80Co_0.15Al_0.05O₂ cathodes was argued to be responsible for the relatively lower discharge capacity of these materials.     

Rapid thermal annealing effect on surface of LiNi1−xCoxO2 cathode film for thin-film microbattery

The effect of rapid thermal annealing (RTA) on the surface of a LiNi_1−xCo_xO₂ cathode film is examined by means of scanning electron microscopy (SEM), atomic force microscopy (AFM) and auger electron spectroscopy (AES). It is found that the as-deposited LiNi_1−xCo_xO₂ film undergoes a surface reaction with oxygen in the air, due to the high activity of lithium in the film. AES spectra indicate that the surface layer consists of lithium and oxygen atoms. The RTA process at 500 °C eliminates the surface layer to some extent. An increase in annealing temperature to 700 °C results in complete elimination of the surface layer. The surface evolution of the LiNi_1−xCo_xO₂ film with increasing annealing time at 700 °C is examined by means of AFM examination. It is found that the surface layer, which is initially present in the form of an amorphous like-film, becomes agglomerated and then vaporizes after 5 min of annealing. A thin-film microbattery (TFB), fabricated by using the LiNi_1−xCo_xO₂ film without a surface layer, exhibits more stable cycliability and a higher specific discharge capacity of 60.2 μAh cm⁻² μm than a TFB with an unannealed LiNi_1−xCo_xO₂ film. Therefore, it is important to completely eliminate the surface layer in order to achieve high performance from all solid-state thin-film microbatteries.     

Synthesis,structural and electrochemical properties of pulsed laser deposited Li(Ni,Co)O2 films

We report the epitaxial growth of the LiNi_1−yM_yO₂ films (M = Co, Co–Al) on heated nickel foil using pulsed laser deposition in oxygen environment from lithium-rich targets. The structure and morphology was characterized by X-ray diffractometry, electron scanning microscopy and Raman spectroscopy. Data reveal that the formation of oriented films is dependent on two important parameters: the substrate temperature and the gas pressure during ablation. The charge–discharge process conducted in Li-microcells demonstrates that effective high specific capacities can be obtained with films 1.35 μm thick. Stable capacities of 83 and 92 μAh cm⁻² μm are available in the potential range 4.2–2.5 V for LiNi_0.8Co_0.2O₂ and LiNi_0.8Co_0.15Al_0.05O₂ films, respectively. The self-diffusion coefficient of Li ions determined from galvanostatic intermittent titration experiments is found to be 4 × 10⁻¹² cm² s⁻¹.     

Stannum doping of layered LiNi3/8Co2/8Mn3/8O2 cathode materials with high rate capability for Li-ion batteries

Sn doped lithium nickel cobalt manganese composite oxide of LiNi_3/8Co_2/8Mn_3/8−xSn_xO₂ (0 ≤ x ≤ 0.10) was synthesized by stannum substitute of manganese to enhance its rate capability at first time. Its structure and electrochemical properties were characterized by X-ray diffraction (XRD), SEM, cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT) and charge/discharge tests. LiNi_3/8Co_2/8Mn_3/8−xSn_xO₂ had stable layered structure with α-NaFeO₂ type as x up to 0.05, meanwhile, its chemical diffusion coefficient D_Li of Li-ion was enhanced by almost one order of magnitude, leading to notable improvement of the rate capability of LiNi_3/8Co_2/8Mn_3/8O₂. The compound of x = 0.10 showed the best rate capability among Sn doped samples, but its discharge capacity reduced markedly due to secondary phase Li₂SnO₃ and increase of cation-disorder. The compound with x = 0.05 showed high rate capability with initial discharge capacity in excess of 156 mAh g⁻¹. It is a promising alternative cathode material for EV application of Li-ion batteries.     

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.     

Effect of organic acids and nano-sized ceramic doping on PEO-based solid polymer electrolytes

Composite solid polymer electrolytes (CSPEs) consisting of polyethyleneoxide (PEO), LiClO₄, organic acids (malonic, maleic, and carboxylic acids), and/or Al₂O₃ were prepared in acetonitrile. CSPEs were characterized by Brewster Angle Microscopy (BAM), thermal analysis, ac impedance, cyclic voltammetry, and tested for charge–discharge capacity with the Li or LiNi_0.5Co_0.5O₂ electrodes coated on stainless steel (SS). The morphologies of the CSPE films were homogeneous and porous. The differential scanning calorimetric (DSC) results suggested that performance of the CSPE film was highly enhanced by the acid and inorganic additives. The composite membrane doped with organic acids and ceramic showed good conductivity and thermal stability. The ac impedance data, processed by non-linear least square (NLLS) fitting, showed good conducting properties of the composite films. The ionic conductivity of the film consisting of (PEO)₈LiClO₄:citric acid (99.95:0.05, w/w%) was 3.25 × 10⁻⁴ S cm⁻¹ and 1.81 × 10⁻⁴ S cm⁻¹ at 30 °C. The conductivity has further improved to 3.81 × 10⁻⁴ S cm⁻¹ at 20 °C by adding 20 w/w% Al₂O₃ filler to the (PEO)₈LiClO₄ + 0.05% carboxylic acid composite. The experimental data for the full cell showed an upper limit voltage window of 4.7 V versus Li/Li⁺ for CSPE at room temperature.     

Anode-supported solid oxide fuel cell with yttria-stabilized zirconia/gadolinia-doped ceria bilalyer electrolyte prepared by wet ceramic co-sintering process

To protect the ceria electrolyte from reduction at the anode side, a thin film of yttria-stabilized zirconia (YSZ) is introduced as an electronic blocking layer to anode-supported gadolinia-doped ceria (GDC) electrolyte solid oxide fuel cells (SOFCs). Thin films of YSZ/GDC bilayer electrolyte are deposited onto anode substrates using a simple and cost-effective wet ceramic co-sintering process. A single cell, consisting of a YSZ (∼3 μm)/GDC (∼7 μm) bilayer electrolyte, a La_0.8Sr_0.2Co_0.2Fe_0.8O₃–GDC composite cathode and a Ni–YSZ cermet anode is tested in humidified hydrogen and air. The cell exhibited an open-circuit voltage (OCV) of 1.05 V at 800 °C, compared with 0.59 V for a single cell with a 10-μm GDC film but without a YSZ film. This indicates that the electronic conduction through the GDC electrolyte is successfully blocked by the deposited YSZ film. In spite of the desirable OCVs, the present YSZ/GDC bilayer electrolyte cell achieved a relatively low peak power density of 678 mW cm⁻² at 800 °C. This is attributed to severe mass transport limitations in the thick and low-porosity anode substrate at high current densities.     

Synthesis and characterization of spherical morphology [Ni0.4Co0.2Mn0.4]3O4 materials for lithium secondary batteries

Spherical morphology [Ni_0.4Co_0.2Mn_0.4]₃O₄ materials have been synthesized by ultrasonic spray pyrolysis. The Li[Ni_0.4Co_0.2Mn_0.4]O₂ powders were prepared at various pyrolysis temperatures between 500 and 900 °C. The Li[Ni_0.4Co_0.2Mn_0.4]O₂ material prepared at a pyrolysis temperature of 600 °C samples are exhibited excellent electrochemical cycling performance and delivered the highest discharge capacity at over 180 mAh g⁻¹ between 2.8 and 4.4 V. The structural, electrochemical, morphological property and thermal stability of the powders were characterized by X-ray diffraction (XRD), galvanostatic charge/discharge testing, scanning electron microscopy (SEM), and differential scanning calorimeter (DSC), respectively.     

Synthesis and characterization of high tap-density layered Li[Ni1/3Co1/3Mn1/3]O2 cathode material via hydroxide co-precipitation

Li[Ni_1/3Co_1/3Mn_1/3]O₂ was prepared by mixing uniform co-precipitated spherical metal hydroxide (Ni_1/3Co_1/3Mn_1/3)(OH)₂ with 7% excess LiOH followed by heat-treatment. The tap-density of the powder obtained was 2.38 g cm⁻³, and it was characterized using X-ray diffraction (XRD), particle size distribution measurement, scanning electron microscope-energy dispersive spectrometry (SEM-EDS) and galvanostatic charge–discharge tests. The XRD studies showed that the material had a well-ordered layered structure with small amount of cation mixing. It can be seen from the EDS results that the transition metals (Ni, Co and Mn) in Li[Ni_1/3Co_1/3Mn_1/3]O₂ are uniformly distributed. Initial charge and discharge capacity of 185.08 and 166.99 mAh g⁻¹ was obtained between 3 and 4.3 V at a current density of 16 mA g⁻¹, and the capacity of 154.14 mAh g⁻¹ was retained at the end of 30 charge–discharge cycles with the capacity retention of 93%.     

Effect of annealing temperature on electrochemical performance of thin-film LiMn2O4 cathode

Spinel LiMn₂O₄ thin-film cathodes were obtained by spin-coating the chitosan-containing precursor solution on a Pt-coated silicon substrate followed by a two-stage heat-treatment procedure. The LiMn₂O₄ film calcined at 700 °C for 1 h showed the highest Li-ion diffusion coefficient, 1.55 × 10⁻¹² cm² s⁻¹ (PSCA measurement) among all calcined films. It is attributed to the larger interstitial space and better crystal perfection of LiMn₂O₄ film calcined at 700 °C for 1 h. Consequently, the 700 °C-calcined LiMn₂O₄ film exhibited the best rate performance in comparison with the ones calcined at other temperatures.     

Effect of components in electrodes on sintering characteristics of Ce0.9Gd0.1O1.95 electrolyte in intermediate-temperature solid oxide fuel cells during fabrication

The effects of anode and cathode components on solid-state reaction and sintering characteristics of Ce_0.9Gd_0.1O_1.95 (CGO) electrolyte were investigated in the temperature range from 900 to 1200 °C. The solubility limit of components in the anode was <4 mol% for 1/2Fe₂O₃, <1 mol% for NiO, and <3 mol% for CuO. The solubility limit of components in the cathode was <4 mol% for 1/2La₂O₃, <4 mol% for SrO, and <1 mol% for 1/3Co₃O₄. A small amount of addition of Fe₂O₃, Co₃O₄ or CuO remarkably enhanced the sintering characteristics of the CGO nanopowder. NiO, La₂O₃ or SrO addition lowered. In the case of the mixture of the CGO and La_0.6Sr_0.4CoO₃, enhancement of sintering characteristics of the CGO and no reaction products were observed. From scanning electron microscopy observation, the sintered CGO samples with Fe₂O₃ showed the feature by solid-state sintering mechanism. For the CGO with CuO, the samples showed the trace of liquid-phase sintering. The samples of CGO with Co₃O₄ included large grains, which seem to relate to cobalt vapor from the cobalt oxide particles.     

Study of cobalt-doped lithium–nickel oxides as cathodes for MCFC

Cobalt substituted lithium–nickel oxides were synthesized by a solid-state reaction procedure using lithium nitrate, nickel hydroxide and cobalt oxalate precursor and were characterized as cathodes for molten carbonate fuel cell (MCFC). LiNi_0.8Co_0.2O₂ cathodes were prepared using non-aqueous tape casting technique followed by sintering in air. The X-ray diffraction (XRD) analysis of sintered LiNi_1−xCo_xO₂ indicated that lithium evaporation occurs during heating. The lithium loss decreases with an increase of the cobalt content in the mixed oxides. The stability studies showed that dissolution of nickel into the molten carbonate melt is smaller in the case of LiNi_1−xCo_xO₂ cathodes compared to the dissolution values reported in the literature for state-of-the-art NiO. Pore volume analysis of the sintered electrode indicated a mean pore size of 3 μm and a porosity of 40%. A current density of 160 mA/cm² was observed when LiNi_0.8Co_0.2O₂ cathodes were polarized at 140 mV. The electrochemical impedance spectroscopy (EIS) studies done on LiNi_0.8Co_0.2O₂ cathodes under different gas conditions indicated that the rate of the cathodic discharge reaction depends on the O₂ and CO₂ partial pressures.     

Sodium insertion into vanadium pentoxide in methanesulfonyl chloride–aluminum chloride ionic liquid

Methanesulfonyl chloride (MSC) forms a room temperature ionic liquid with AlCl₃. The electrochemical properties of vanadium pentoxide (V₂O₅) films prepared by the sol–gel route were studied in this electrolyte. As a potential cathode, sodium is reversibly intercalated into the V₂O₅ film up to a stoichiometry of 1.6 mole Na/mole V₂O₅ (−1 V versus Al(III)/Al<1.5 V) after the first discharge. The diffusion coefficient (D_Na⁺) in the V₂O₅ film was determined to be between 5E−14 and 9E−12 cm²/s using the potentiostatic intermittent-titration technique.     

Electrochemical characteristics and impedance spectroscopy studies of nano-cobalt silicate hydroxide for supercapacitor

Cobalt silicate hydroxide (Co₃[Si₂O₅]₂[OH]₂) was prepared by chemical method for use in electrochemical capacitors. X-ray diffraction (XRD) and transmission electron microscopy (TEM) tests indicate that the material was pure hexagonal phase with uniform nanometer size distribution. Cyclic voltammeter (CV) and galvanostatic charge/discharge measurements show that the cobalt silicate hydroxide-based electrode has stable electrochemical capacitor properties between potential range of 0.1–0.55 V with a maximum specific capacitance of 237 F g⁻¹ in alkaline solution and 95% of capacity efficiency was reached after 150 cycles. Electrochemical impedance spectra (EIS) investigation illustrates that the capacitance of the test electrode was mainly consisted of pseudo-capacitance, which was caused by underpotential deposition of H₃O⁺ at the electrode surface.     

Characterization and preparation of NiO-V2O5 composite film cathodes

NiO-V₂O₅ composite films have been fabricated by 355 nm pulsed laser reactive deposition using mixed metallic Ni and V targets with different molar ratios. The optimal deposition conditions of NiO-V₂O₅ composite films are found to be the substrate temperature of 300 °C and 100 mTorr O₂ ambient. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses showed that the crystallinity of the NiO-V₂O₅ composite films gradually decreased with increasing the amount of nickel oxide and transformed to amorphous phase as the molar ratio of NiO/V₂O₅ (x) approaches 0.5. The amorphous (NiO)_0.5V₂O₅ composite film electrode exhibited a specific capacity of 340 mAh/g at a discharge rate of 2 C upon cycling with no obvious fading up to 500 cycles. XRD and X-ray photo-electron spectroscopy (XPS) measurements of NiO-V₂O₅ composite film electrodes revealed that there exists two electrochemical processes upon cycling. During the first discharge, the Li ions insertion process is accompanied by the reduction of NiO into metallic Ni. Then, the reversible processes involving Li ions insertion/extraction in V₂O₅ matrix and oxidation/reduction of Ni and Li₂O take place upon the subsequent cycling.     

Preparation of LaGaO3-based perovskite oxide film by a pulsed-laser ablation method and application as a solid oxide fuel cell electrolyte

LaGaO₃-based perovskite oxide films are deposited on a dense substrate consisting of NiO, Fe₃O₄, and Sm-doped CeO₂ (SDC). After in situ reduction, NiO and Fe₃O₄ are reduced to form an alloy and during reduction, the substrate becomes porous, and therefore can be used as a porous electrode substrate in a solid oxide fuel cell (SOFC). Since the reaction between NiO and LaGaO₃-based oxide is known, an interlayer of SDC is introduced between the LaGaO₃ film and the substrate. The LaGaO₃/SDC bilayer film exhibits electrical conductivity close to that of a bulk one. A single fuel cell using the LaGaO₃/SDC bilayer film shows an open-circuit potential of 1.1 V, which is close to the theoretical value. A quite large power density of 0.6 W cm⁻² is achieved at 773 K with a LaGaO₃ film of 5 μm in thickness. The effects of LaGaO₃ film thickness on power generation are further studied. Although the open-circuit potential increases, the maximum power density decreases with increasing thickness. On the other hand, the open-circuit potential becomes lower with thicknesess below 5 μm. This suggests that the reaction between NiO and the LaGaO₃ film occurs with an excessively thin film. Therefore, the largest power density is obtained with a film thickness of 5 μm. The effects of interlayer compound are also examined. The application of La(Sr)Ga(Fe)O₃ (LSGF) is also effective in obtaining high power density, but the maximum value is less than that achieved with a SDC interlayer. A two-cell stack is successfully demonstrated.     

Effects of synthesis conditions on the structural and electrochemical properties of layered Li[Ni1/3Co1/3Mn1/3]O2 cathode material via the hydroxide co-precipitation method LIB SCITECH

The uniform layered Li[Ni_1/3Co_1/3Mn_1/3]O₂ cathode material for lithium ion batteries was prepared by using (Ni_1/3Co_1/3Mn_1/3)(OH)₂ synthesized by a liquid phase co-precipitation method as precursor. The effects of calcination temperature and time on the structural and electrochemical properties of the Li[Ni_1/3Co_1/3Mn_1/3]O₂ were systemically studied. XRD results revealed that the optimal prepared conditions of the layered Li[Ni_1/3Co_1/3Mn_1/3]O₂ were 850 °C for 18 h. Electrochemical measurement showed that the sample prepared under the above conditions has the highest initial discharge capacity of 162.1 mAh g⁻¹ and the smallest irreversible capacity loss of 9.2% as well as stable cycling performance at a constant current density of 16 mA g⁻¹ between 3 and 4.3 V versus Li at room temperature.     

Thermal simulation of large-scale lithium secondary batteries using a graphite–coke hybrid carbon negative electrode and LiNi0.7Co0.3O2 positive electrode

Thermal simulation was applied to 2 Wh-class cells (diameter 14.2 mm, height 50 mm) using LiNi_0.7Co_0.3O₂ or LiCoO₂ as the positive electrode material, in order to clarify the thermal behavior of the cells during charge and discharge. The thermal simulation results for the 2 Wh-class cells showed a good agreement with measured temperature values. The heat generation of a cell using LiNi_0.7Co_0.3O₂ was found to be much less than that using LiCoO₂ during discharge. This difference was considered to be caused by the difference in the change of entropy. A 250 Wh-class cell (diameter 64 mm, height 296 mm) was also constructed using LiNi_0.7Co_0.3O₂ and thermal simulation was applied. We confirmed that the results of the thermal simulation agreed with measured values and that this simulation model is effective for analyzing the thermal behavior of large-scale lithium secondary batteries.     

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.