K.H. Prasad, R. Arumugam, E.S. Srinadhu, N. Satyanarayana
Keywords: RF magnetron sputtering, nanocrystalline Li4Ti5O12 thin films, XRD, AFM, impedance, DC & AC conductivities
Summary:All-solid-state rechargeable batteries with high energy density are the most promising energy storage devices for electric vehicles and other portable electronic devices. Among the available energy sources, lithium-ion (Li-ion) batteries are more suitable, since these not only exhibit high power and high energy density but also miniaturization of battery technology is possible. Li-ion micro-batteries can be utilized in various microsystems applications such as micro-sensors, micro-mechanics, microelectronics, etc. In order to realize such micro-batteries, developing thin-film technology is very important. Spinel Li4Ti5O12, (LTO) is found to be a potential candidate as an anode material for rechargeable Li-ion batteries because of the following properties. Good Li-ion intercalation and de-intercalation reversibility, exhibits no structural change during charge-discharge cycling, zero-strain effect, good safety characteristics, thermal stability, etc. Hence, in the present investigation, structural and electrical conductivity studies of Li4Ti5O12 thin films grown by rf magnetron sputtering were studied to find out its suitability for developing all-solid-state thin-film Li-ion micro-batteries. Li4Ti5O12 thin films were grown on Ti/Si (100) substrate at ambient temperature by RF magnetron sputtering. All the prepared thin films were annealed at 400 oC, 500 oC, and 600 oC under an oxygen atmosphere to enhance the crystallinity. Table 1 gives the summary of sputtering parameters for the grown LTO thin films. Fig.1 shows the X-ray diffraction patterns of as-deposited and post-annealed at various temperatures of LTO thin films along with the standard JCPDS data. Fig. 2, shows the 3-dimensional AFM surface micro graphs of the LTO thin films of [a] as-deposited, and post-annealed at [b] 400 oC, [c] 500 oC, and [d] 600 oC. Fig. 3, shows the AC conductivity versus frequency plots obtained at room temperature of LTO thin films as-deposited and post-annealed at different temperatures. The conductivity results indicated that the LTO electrode thin films deposited in an argon atmosphere and post-annealed at 600 oC show the high electronic conductivity of 5.47×10−6 S cm−1. Detailed results will be presented and discussed.