Fabrication And Characterization Of Inorganic Electrolyte Thin Films For All-solid-state Lithium Battery

The miniaturization of electronic devices has resulted in micro-power sources requirements. Specially, with the development of micro-electronic mechanical system (MEMS), micro-batteries have received great attention. Presently, several micro-batteries have been studied such as Zn-Ni micro-battery, all-solid-state lithium micro-battery, solar micro-cell, micro thermoelectric battery and fuel micro-battery. Among these, all-solid-state lithium micro-battery may be one of the promising power sources because lithium is the lightest metal and has a low potential to provide high energy density. This kind of battery can be used in many fields such as micro-satellites MEMS and portable electronic devices. Many thin film electrode materials for all-solid-state lithium batteries have been reported previously, however, the progress of electrolyte thin films is not as notable as that of electrode materials, which has delayed the development of all-solid-state thin film lithium batteries and limited these batteries to be commercialized. Accordingly, the fabrication of high-performance and low-cost electrolyte thin films plays an important role to develop all-solid-state thin film lithium batteries.In this thesis we selected two kinds of remarkable electrolyte thin films LiPON and Li-V-Si-O as major subjects investigated. To our knowledge, this is the first time to fabricate LiPON and Li-V-Si-O electrolyte thin films by pulsed laser deposition (PLD) method. Their electrochemical and structural characteristics dependence of deposition conditions were examined by electrochemical and other testing methods. Three all-solid-state lithium thin film batteries were preliminarily fabricated using LiPON and Li3PO4 as electrolyte. The new results in this thesis are summarized as follows:(1). Reactive pulsed laser deposition was employed to prepare the lithiumelectrolyte LiPON films under 355-nm laser irradiation for the first time. Increasing the ambient N2 gas pressure is beneficial improve the ionic conductivity of LiPON thin films. However, high ambient N2 gas pressure will result in the contraction of the plume region and decrease the deposition rate. A dense, smooth and uniform LiPON thin film without pinholes and cracks was obtained by pulsed laser ablating a Li3PO4 target at the ambient N2 gas pressure of 200 mTorr, a laser fluence of 15 J/cm2, a target-substrate distance of 5 cm, substrate temperature of 25 oC and deposition time of 1.0 h. The dependence of ionic conductivity of LiPON thin film prepared by PLD on the temperature obeys an Arrhenius equation and activation energy and room temperature ionic conductivity were estimated to be 0.58 eV and 1.6×10-6 S/cm, respectively. The characteristics of LiPON thin films prepared by PLD were examined by XRD, SEM, EDX, FTIR and XPS. The deposited LiPON thin films have an amorphous structure which is beneficial for lithium ion mobility. The incorporation of N into Li3PO4 substituting O in the P-O-P structure and bonding with P to form the triply coordinated P-N