LiNi₀.₅Mn₁.₅O₄ thin films have been grown by pulsed laser deposition (PLD) on stainless steel (SS) substrates. The crystallinity and structure of thin films were investigated by X-ray diffraction (XRD). Microstructure and surface morphology of the thin films were examined using a field-emission scanning electron microscope (FESEM). The electrochemical properties of the thin films were studied with cyclic voltammetry (CV) and galvanostatic charge-discharge in the potential range between 3.0 and 4.9 V. The electrochemical behavior of LiNi₀.₅Mn₁.₅O₄ thin films showed reversible capacity above 4.7 V and good cycle performance up to 50 cycles. / Singapore-MIT Alliance (SMA)

The magnificent development of on-board solutions for electronics has resulted in the race towards scaling down of autonomous micro-power sources. In order to maintain the reliability of miniaturized devices and to reduce the power dissipation in high density memories like CMOS RAM, localized power for such systems is highly desirable. Therefore these micro-power sources need to be integrated in to the electronic chip level, which paved the way for the research and development of rechargeable thin film batteries (TFB). A Thin film battery is defined as a solid-state electrochemical source fabricated on the same scale as and using the same type of processing techniques used in microelectronics. Various aspects of deposition and characterization of LiCoO2/LiPON/Sn thin film battery are investigated in this thesis. Prior to the fabrication of thin film battery, individual thin film layers of cathode-LiCoO2, electrolyte-LiPON and anode-Sn were optimized separately for their best electrochemical performance. Studies performed on cathode layer include theoretical and experimental aspects of deposition of electrochemically active LiCoO2 thin films. Mathematical simulation and experimental validation of process kinetics involved in sputtering of a LiCoO2 compound target have been performed to analyze the effect of process kinetics on film stoichiometry. Studies on the conditioning of a new LiCoO2 sputtering target for various durations of pre-sputtering time were performed with the help of real time monitoring of glow discharge plasma by OES and also by analysing surface composition, and morphology of the deposited films. Films deposited from a conditioned target, under suitable deposition conditions were electrochemically tested for CV and charge/discharge, which showed an initial discharge capacity of 64 µAh/cm2/µm. Studies done on the deposition and characterization of solid electrolyte layer-LiPON have shown that, sputtering from powder target can be useful for certain compounds like Li3PO4 in which breaking of ceramic target and loss of material are severe problems. An ionic conductivity of 1.1 x10-6 S/cm was obtained for an Nt/Nd ratio of 1.42 for a RF power density of 3 W/cm2 and N2 flow of 30 sccm. Also the reasons for reduction in ionic conductivity of LiPON thin films on exposure to air have been analyzed by means of change in surface morphology and surface chemistry. Ionic conductivity of 2.8 x10-6 S/cm for the freshly deposited film has dropped down to 9.9 x10-10 S/cm due to the reaction with moisture, oxygen and carbon content of exposed air. Interest towards a Li-free thin film battery has prompted to choose Sn as the anode layer due to its relatively good electrochemical capacity compared with other metallic thin films and ease of processing. By controlling the rate of deposition of Sn, thin films of different surface morphology, roughness and crystallinity can be obtained with different electrochemical performance. The reasons for excessive volume changes during lithiation/delithiation of a porous Sn thin film have been analyzed with the aid of physicochemical characterization techniques. The results suggest that the films become progressively pulverized resulting in increased roughness with an increase in lithiation. Electrochemical impedance data suggest that the kinetics of charging becomes sluggish with an increase in the quantity of Li in Sn-Li alloy. Thin film batteries with configuraion LiCoO2/LiPON/Sn were fabricated by sequential sputter deposition on to Pt/Si substartes. Pt/Cu strips were used as the current collector leads with a polymer packaging. Electrochemical charge/discharge studies revealed discharge capacities in the range 6-15 µAh/cm2/µm with hundreds of repeated cycles. TFB with a higher capacity of 35 µAh/cm2/µm suffered capacity fade out after 7 cycles, for which reasons were analyzed. The surface and cross-sectional micrographs of cycled TFB showed formation of bubble like features on anode layer reducing integrity of electrolyte-anode interface. The irreversible Li insertion along with apparent surface morphology changes are most likely the main reasons for the capacity fade of the LiCoO2/LiPON/Sn TFB.

Li-ion thin film battery technology has attracted much attention in recent years due to its highest need in portable electronic devices. Development of new materials for lithium ion battery (LIB) is very crucial for enhancement of the performance. LIB can supply higher energy density because Lithium is the most electropositive (-3.04V vs. standard hydrogen electrode) and lightest metal (M=6.94 g/mole). LIBs show many advantages over other kind of batteries such as, high energy density, high power density, long cycle life, no memory effect etc. The major work presented in this thesis is on the development of nanostructured materials for anode of Li-ion battery. It involves the synthesis and analysis of grapheme nanosheet (GNS) and its performance as anode material in Li ion battery. We studied the synthesis of GNS over different substrates and performed the anode studies. The morphology of GNS has great impact on Li storage capacity. Tin and Tin oxide nanostructures have been embedded in the GNS matrix and their electrochemical performance has been studied. Chapter 1 gives the brief introduction about the Li ion batteries (LIBs), working and background. Also the relative advantages and characterization of different electrode materials used in LIBs are discussed. Chapter 2 discusses various experimental techniques that are used to synthesize the electrode materials and characterize them. Chapter3 presents the detailed synthesis of graphene nanosheet (GNS) through electron cyclotron resonance (ECR) microwave plasma enhanced chemical vapor deposition (ECR PECVD) method. Various substrates such as metallic (copper, Ni and Pt coated copper) and insulating (Si, amorphous SiC and Quartz) were used for deposition of GNS. Morphology, structure and chemical bonding were analyzed using SEM, TEM, Raman, XRD and XPS techniques. GNS is a unique allotrope of carbon, which forms highly porous and vertically aligned graphene sheets, which consist of many layers of graphene. The morphology of GNS varies with substrate. Chapter 4 deals with the electrochemical studies of GNS films. The anode studies of GNS over various substrates for Li thin film batteries provides better discharge capacity. Conventional Li-ion batteries that rely on a graphite anode have a limitation in the capacity (372 mAh/g). We could show that the morphology of GNS has great effect in the electrochemical performance and exceeds the capacity limitation of graphite. Among the electrodes PtGNS shown as high discharge capacity of ~730 mAh/g compare to CuGNS (590 mAh/g) and NiGNS (508 mAh/g) for the first cycle at a current density of 23 µA/cm2. Electrochemical impedance spectroscopy provides the various cell parameters of the electrodes. Chapter 5 gives the anodic studies of Tin (Sn) nanoparticles decorated over GNS matrix. Sn nanoparticles of 20 to 100nm in size uniformly distributed over the GNS matrix provides a discharge capacity of ~1500 mAh/g mAh/g for as deposited and ~950 mAh/g for annealed Sn@GNS composites, respectively. The cyclic voltammogram (CV) also shows the lithiation and delithiation process on GNS and Sn particles. Chapter 6 discusses the synthesis of Tinoxide@GNS composite and the details of characterization of the electrode. SnO and SnO2 phases of Tin oxide nanostructures differing in morphologies were embedded in the GNS matrix. The anode studies of the electrode shows a discharge capacity of ~1400 mAh/g for SnO phase (platelet morphology) and ~950 mAh/g for SnO2 phase (nanoparticle morphology). The SnO phase also exhibits a good coulumbic efficiency of ~95%. Chapter 7 describes the use of SnO2 nanowire attached to the side walls of the GNS matrix. A discharge capacity of ~1340 mAh/g was obtained. The one dimensional wire attached to the side walls of GNS film and increases the surface area of active material for Li diffusion. Discharge capacity obtained was about 1335 mAhg-1 and the columbic efficiency of ~86% after the 50th cycle. The research work carried out as part of this thesis, and the results have summarized in chapter 8.