A Novel All-Solid-State Thin-Film-Type Lithium-Ion Battery with In-Situ Prepared Electrode Active Materials

Abstract

All-solid-state thin-film rechargeable lithium batteries have received much attention as a power source for micro devices. Especially, in recent years, thin-film batteries using lithium phosphorus oxynitride glass electrolyte (LiPON) discovered by Wang and co-workers (Wang et al., 1996) have been extensively investigated. In the fabrication process of these film batteries, thin films of electrodes, solid electrolyte, and current collectors are sequentially piled-up on a substrate using different kinds of vapor deposition techniques such as pulsed laser deposition, r.f. magnetron sputtering, and vacuum evaporation. For the practical application of thin-film batteries, the fabrication process is desirable to be simplified as much as possible. One of the effective methods to overcome the above problem will be the use of ‘‘in-situ formed’’ material in the battery system. Using this in situ formed material, fabrication of at least one of the material in a battery will not be necessary, leading to both the simplification and cost reduction for its fabrication process. The use of ‘‘in situ formed’’ solid electrolyte have been already shown in a primary battery system of Li/poly2-vinylpyridide (P2VP)•I2 (Greatbatch et al., 1971), which was commercialized as power sources of cardiac pacemakers. In this battery system, solid electrolyte of LiI was prepared at the negative electrode/positive electrode interface through the reaction of these electrodes. Neudecker et al. have proposed ‘‘Lithium-free’’ thin-film rechargeable lithium battery using LiPON, where electrochemically plated Li was used as an in situ formed anode material (Neudecker et al., 2000). Because of high reactivity of Li, the battery system required an overlayer to prevent side reactions with the Li anode. Lee et al. proposed a reversed structural configuration of the lithium-free battery so that the overlayer was not required. Although the use of in situ formed Li anode is very attractive to simplify the fabrication process, this battery system relies on specific stability of LiPON against lithium metal. Most of oxide-based solid electrolyte dose not obtain such stability against lithium metal and then this technique will not be used to these solid electrolytes. It is well known that there are so many oxide-based solid electrolytes containing transition metal ions. It should be noted that some of these solid electrolytes can act as an electrode material when the electrode potential exceed their voltage windows. For example, Li3xLa(2/3)-xTiO3(0.04 < x < 0.16) (LLT) with ABO3-perovskite structure can be an insertion electrode material after 4