Morphological, A.C. conductivity and dielectric properties of LiCoO2 cathode films grown by RF magnetron sputtering (original) (raw)
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Structural and AC impedance analysis of rf sputtered Ti doped LiCoO 2 thin films
2014
Lithium transition metal oxides such as LiMO 2 (where M= Co, Ni, Mn etc.) are commonly used cathode material for micro-battery applications. Am ong these, LiCoO 2 is one of the most promising cathode materials because of its high energy density, high discharge capacity and good reversibility during th e oxidation and reduction process. In the present investigatio n, the influence of Ti doping on the structural and electrical properties of LiCoO 2 thin films were studied. Ti doped LiCoO 2 thin films were deposited by rf-sputtering at moderate substrate temperature of 523K with subsequent annealing at 923K. The structural analysis was carried out using X-ray diffraction (XRD) and atomic force microscopy (AFM). Electrical and dielectric propert ies of deposited films were studied at different temperatu res over a frequency range of 1Hz - 1MHz. The electrical conductivity of the films was observed to be increa sed with increasing temperature. The dielectric pro perties were analyzed in ...
Journal of Electroanalytical Chemistry, 2018
LiCoO 2 thin film cathodes have been well established in Li-ion rechargeable batteries, however, its useful capacity hardly exceeds 50% of the theoretical value. Irreversible structural changes will occur upon exchange of Li ions i.e. >0.5 per unit formula limit, during intercalation/deintercalation reactions. Reportedly, lattice doping phenomenon has noticed an improvement in cyclability of LiCoO 2. In this work, the influence of Zr doping on microstructural and electrochemical properties of RF magnetron sputtered LiCoO 2 thin film cathodes have been presented. A series of LiZr x Co 1−x O 2 thin films have been deposited on Au/Ti/SiO 2 /Si (100) substrates using a Zr-LiCoO 2 mosaic target. All the films were deposited at optimized processing conditions. XRD and Raman spectroscopy measurements confirmed the hexagonal layered structure with R m symmetry for Zr doped LiCoO 2 film cathodes. The AFM reveals the estimated average grain size is around 50 nm. The cyclic voltammetry studies for these cathodes exhibit narrow potential peak separation of 24 mV and resulting highest diffusion coefficient (Li) of about 1.8 × 10-11 cm 2 s-1 , respectively. These films exhibited a highest initial discharge capacity of 64.4 µA h cm-2 µm-1 with a capacity retention of 98.5% even after 25 cycles. In non-aqueous region, the cell exhibited an initial discharge capacity of about 65 µA h cm-2 µm-1 with good cycling stability even after 80 cycles, and is observed to be the more promising cathode candidate than the pristine LiCoO 2 films.
Advanced Materials - TechConnect Briefs 2017, 2017
Li 4 Ti 5 O 12 (LTO) thin films were deposited at ambient temperature on Ti/silicon (Si) (100) substrate by using RF magnetron sputtering method. All the deposited thin-films were annealed at three different temperatures 400, 500 and 600 o C under an oxygen atmosphere to enhance the crystallinity. X-ray diffraction patterns showed the formation of cubic spinel structure phase of LTO thin film annealed at 600 o C. AFM micrographs for LTO thin films reveal the surface morphology and roughness modifications. The ac conductivity, dielectric constant (ε′) and electric modulus (M'') for the as-deposited and postannealed LTO thin films were evaluated by analyzing the measured impedance data as a function temperature in the frequency range of 100 Hz to 10 MHz.
Ionics, 2012
Films of LiCoO 2 are prepared on metallized silicon substrates using RF-magnetron sputtering technique. The microstructural properties of the films are investigated by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. The films deposited at a substrate temperature of 250°C with subsequent annealing at 650°C exhibited hexagonal layered structure with R3m symmetry. The kinetics of lithium ions in LiCoO 2 film cathode host matrix and its cycleability are studied in aqueous Pt//LiCoO 2 and nonaqueous Li// LiCoO 2 cell. Both the electrochemical cells at same current density of 50 μA cm −2 delivered the same initial discharge capacity of about 60 μA hcm −2 μm −1 with a chemical diffusion coefficient of ca. 10 −11 cm 2 s −1 for Li + ions. The capacity fade rates for the Pt//LiCoO 2 and Li//LiCoO 2 cells, in average are 3.0 and 0.15 % per cycle, respectively, for the first 20 cycles. The Pt//LiCoO 2 cell is found to be advantageous for small number of cycles and is cost effective than the Li//LiCoO 2 cell.
Materials Science and Engineering: B, 2016
In an attempt to enhance the microstructural and electrochemical properties, LiCoO 2 thin films were doped with titanium or zirconium. RF magnetron sputtering technique has been employed for the deposition of films on Au/Ti/SiO 2 /Si substrates from lithium-rich LiCoO 2 target with mosaic configuration. The as-deposited and Ti-and Zr-doped LiCoO 2 thin films at lower doping concentration exhibited the ␣-NaFeO 2 structure with R3m symmetry as confirmed from X-ray diffraction and Raman studies. The cyclic voltammogram of micro-electrodes in aqueous electrolyte exhibited perfect redox peaks with good reversibility. The chronopotentiometry studies revealed that the discharge capacity of pure LiCoO 2 was 64 Ah cm −2 m −1 , while 2% Ti-and Zr-doped films showed enhanced capacities 69 and 68 Ah cm −2 m −1 (248 mC cm −2 m −1 , 245 mC cm −2 m −1) respectively. The Zr-doped films exhibited good structural stability even after 25 cycles with the capacity retention of 95%.
Advanced Materials - TechConnect Briefs 2017, 2017
Spinel LiMn 2 O 4 (LMO) thin films were deposited on Ti/silicon (Si) (100) substrate at ambient temperature by RF magnetron sputtering method. All the grown thin films were post-annealed up to 500 o C, in the presence of oxygen to enrich the crystallinity of the thin film. XRD and Raman results showed the formation of the cubic spinel structured LMO thin film annealed at 500 o C. AFM micrographs of LMO thin films reveal the surface morphology and roughness modifications. The ac conductivity, dielectric constant (ε′), and electric modulus (M′′) for the as-deposited and post-annealed LMO thin films were evaluated by analyzing measured impedance data as a function temperature in the frequency range of 100 Hz to 10 MHz.
LiCoO 2 thin film cathodes grown by sol–gel method
Journal of Electroceramics, 2009
Lithiated layered transitional metal oxide materials of the LiMO2 type and especially LiCoO2 presents interesting specific properties as high energy density, long cycle life and constant discharging properties in a wide range of working conditions as well as a good safety. These properties made these materials excellent candidates as active compounds for high capacity cathode materials for rechargeable lithium batteries. LiCoO2 is the most common lithium storage material for lithium rechargeable batteries, used widely to power portable electronic devices. Operation of lithium rechargeable batteries is dependent on reversible lithium insertion and extraction processes into and from the host materials of lithium storage. In this study, LiCoO2 thin films were prepared by the sol–gel spin coating technique using metal acetate and citric acid as starting materials. Citric acid acts as a chelating agent, which promotes the preliminary reaction between lithium and cobalt and suppresses the precipitation of acetates. The sol–gel method is well known as one of promising thin-film preparation methods, which has good advantages such as low fabrication cost, relatively easy stoichiometry control, high deposition rate and also known as a low-temperature synthesis method for various ceramics. In addition, the crystal phases involved in the thin film can also be controlled by changing the chemical compositions of the sol. The crystallinity, microstructure and electrochemical properties of final films are also studied by XRD, SEM, AFM and galvanostatic charge/discharge cycling test. Films heat-treated under appropriate conditions exhibit high capacity and good crystallinity so those films are considered to be candidates as cathodes for thin-film micro batteries.
TechConnect Briefs 2018 - Advanced Materials, 2018
Li1.3Al0.3Ti1.7 (PO4)3 (LATP) electrolyte thin films were deposited on aluminum oxide (Al2O3) substrate at ambient temperature by RF magnetron sputtering method. The asgrown LATP thin film was post-annealed up to 500 o C in the presence of oxygen to enrich the crystallinity of the thin film. XRD results confirm the formation of the crystalline phase of the LATP thin film annealed at 500 o C. AFM micrographs of LATP thin films revealed the surface morphology and roughness properties. The ac conductivity, dielectric constant (ε′), and electric modulus (M′′) for the as-deposited and post-annealed LATP thin films were evaluated by analyzing measured impedance data as a function temperature in the frequency range of 100 Hz to 10 MHz.
La0.5Sr0.5CoO3 thin films were prepared by rf magnetron sputtering from stoichiometric La0.5Sr0.5CoO3 powder target. The rf power and the post deposition annealing conditions have been optimized to obtain conducting La0.5Sr0.5CoO3 thin films. The dependence of conductivity, optical and structural properties of the thin films on the deposition and the post deposition annealing conditions has been investigated. The crystallinity of the films was found to improve with increase of rf power and annealing temperature. The variation in resistivity and band gap with rf power and annealing conditions are correlated.
Sputtered LiCoO2 Cathode Materials for All-solid-state Thin-film Lithium Microbatteries
Materials
This review article presents the literature survey on radio frequency (RF)-magnetron sputtered LiCoO2 thin films used as cathode materials in all-solid-state rechargeable lithium microbatteries. As the process parameters lead to a variety of texture and preferential orientation, the influence of the sputtering conditions on the deposition of LiCoO2 thin films are considered. The electrochemical performance is examined as a function of composition of the sputter Ar/O2 gas mixture, gas flow rate, pressure, nature of substrate, substrate temperature, deposition rate, and annealing temperature. The state-of-the-art of lithium microbatteries fabricated by the rf-sputtering method is also reported.