Fabrication of SnO2-P2O5-B2O3 for anode of thin film battery by Aerosol Flame Deposition

Abstract

Rechargeable thin film battery has various applications to electronic devices such as micro-electro-mechanical system, smart card, medical appliances, and so on. To realize the thin film battery, each parts of battery cell must be developed to the practical level of performance. Among the components of thin film battery, the anode is less developed compared to the cathode and electrolyte. Several materials are discussed as candidates of anode. Due to the intense reactivity in air, Li metal is unlikely to become popular anode material. Also, graphite is impractical as thin film anode since the proper deposition method is not available. The practical materials for thin film anode seem to be limited to the metallic alloy of Si, amorphous oxides containing SnO2, and some oxynitrides. However, these material systems also have their own limitations and problems. Among these material systems, SnO2 system was selected as an anode in this study since it is compatible to the thin film oxide glass electrolyte of which our research group is studying. In this study, we employed the completely new method to synthesize the oxide glass films, which is called "Aerosol Flame Deposition (AFD)" method. In the deposition process, single or multi-component amorphous oxide nano particles (soot) are synthesized by supplying metal halide sources such as chloride in the form of gas into oxy-hydrogen flame. The deposited film composed of synthesized nano particles is subsequently consolidated into solid film by high temperature heat treatment. Tin oxide is very useful for many applications, notably in Taguchi-type gas sensors as an active sensor material. Recently, Fuji Film Celtech Co. used a tin-based oxide as the anode material in lithium-ion batteries. Recently, it has been pointed out that electrodes composed of nano-crystalline particles exhibit high capacity and better cyclability.[1,2] For instance, a nano-structured SnO2-based electrode can deliver very high capacity(~700mAhg-1 at a rate of 8C)and still retain the ability to be discharged and recharged for 800 cycles.[3] Besides tin oxides (MO, where M is Co, Ni, Fe or Cu)have been reported by Tarascon and co-workers.[4] These electrodes exhibited electrochemical capacities as high as 700mAhg-1 with a 100% capacity retention up to 100 cycles. In this research, the aerosol flame deposition was applied to fabricate anodes film of SnO2. The aqueous precursor solution of the Tin(Ⅳ)chloride(99%, Aldrich) and Ethanol was first atomized with an ultrasonic vibrator (1.7MHz). SnO2 were formed by oxy-hydrogen flame.. SnCl4 mixed ethanol and gases of POCl3 and BCl3 produced by Ar bubbling under controlled temperature were delivered to an oxy-hydrogen torch and hydrolyzed to form porous soot film on Si substrates were hydrolyzed in an oxy-hydrogen flame and converted into oxide or hydroxide by the hydrolysis reaction and subsequent Brownian coagulation. To make uniform thin film, SnO2 soot was first deposited on substrate placed in rotating stage, which was kept at 150°C to eliminate H2O produced during hydrolysis. The whole processes are carried out under normal air atmosphere with only optional control for moisture. Their properties were investigated by scanning electron microscopy(SEM) and X-ray diffraction(XRD) showed that the prepared films are of nano-crystalline structure with the average particle size ＜100nm. The Aerosol Flame Deposition (AFD) preparation technique is a cheap and easy technique to synthesize ultrafine metal-oxide powders. According to our report, the present electrochemical measurements show better anodic characteristics of this composite material is a good anode candidate for application in a Lithium-ion battery.