K. Hari Prasad, P. Muralidharan, E.S. Srinadhu, N. Satyanarayana
Keywords: nanocrystalline Li4Ti5O12 thin films, radio-frequency magnetron sputtering, impedance, electrical conductivity, dielectric properties
Summary:There is a great demand for developing miniaturized energy sources for the medical implantable micro devices, portable electronic devices, self powered direct and remote sensing portable devices used in naval, defense, space applications, etc. Among the available energy sources, lithium batteries are more suitable, since these not only exhibit high energy density but also miniaturization of battery technology is possible. Spinel Li4Ti5O12, (LTO) as an anode material, has attracted great attention for rechargeable lithium batteries because of the following attributes like zero-strain effect, flat Li-insertion voltage, excellent reversibility during charge-discharge cycling process, good safety characteristics, etc. Hence, in the present investigation, the influence of annealing on the a.c. conductivity, dielectric and electric modulus properties of Li4Ti5O12 thin films grown by rf magnetron sputtering were studied to find out its suitability for developing all solid state thin film lithium ion micro batteries. Table-1 gives the summery of the sputtering parameters for the grown LTO thin films. Fig. 1, shows the X-ray diffraction (XRD)patterns of as deposited and annealed at various temperatures of LTO thin films along with the standard JCPDS data. From fig. 1, the observed XRD peaks of the deposited LTO thin film annealed at 600 oC are compared with the JCPDS (card no. 49-0207) data and confirmed the formation of crystalline cubic spinel Li4Ti5O12 structure. Fig. 2. [a, b, c, d] show the three-dimensional (3D) AFM micrographs of the as-grown as well as post-annealed (at 400, 500, and 600 oC) LTO thin films. From fig. 2. [a, b, c, d], the AFM micrographs clearly showed that the grain size of the LTO thin film increases with post-annealing temperature. XRD and AFM results confirm the formation of nanocrystalline cubic spinel LTO thin films. Fig. 3, shows the σac vs. log (ω) plots obtained as grown as well as post annealed (at 400, 500, and 600 oC) LTO thin films. Fig. 4, shows the real part of dielectric permittivity (ε') vs. Log (ω) obtained as-grown as well as post annealed (at 400, 500, and 600 oC) LTO thin films. Fig. 5 shows the imaginary part of electric modulus (M'') versus log(ω) plots obtained at room temperature of LTO thin films as deposited and post annealed at different temperatures. Electrical and dielectric properties results confirm the suitability of the prepared Li4Ti5O12 anode thin films for developing all solid state thin film lithium ion micro batteries. Detailed results will be presented and discussed.