Electrochimica Acta 53 (2007) 549–554 Electrochemical performances of lithium ion battery using alkoxides of group 13 as electrolyte solvent Fuminari Kaneko, Yuki Masuda, Masanobu Nakayama, Masataka Wakihara ∗ Department of Applied Chemistry, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152-8552, Japan Received 13 April 2007; accepted 7 July 2007 Available online 12 July 2007 Abstract Tris(methoxy polyethylenglycol) borate ester (B-PEG) and aluminum tris(polyethylenglycoxide) (Al-PEG) were used as electrolyte solvent for lithium ion battery, and the electrochemical property of these electrolytes were investigated. These electrolytes, especially B-PEG, showed poor electrochemical stability, leading to insufficient discharge capacity and rapid degradation with cycling. These observations would be ascribed to the decomposition of electrolyte, causing formation of unstable passive layer on the surface of electrode in lithium ion battery at high voltage. However, significant improvement was observed by the addition of aluminum phosphate (AlPO 4 ) powder into electrolyte solvent. AC impedance technique revealed that the increase of interfacial resistance of electrode/electrolyte during cycling was suppressed by adding AlPO 4 , and this suppression could enhance the cell capabilities. We infer that dissolved AlPO 4 components formed electrochemically stable layer on the surface of electrode. © 2007 Elsevier Ltd. All rights reserved. Keywords: Lithium ion battery; Lithium polymer battery; Plasticizer; AlPO 4 dispersion; LiFePO 4 1. Introduction The present commercial lithium ion battery contains organic solutions, for example ethylene carbonate (EC) and diethyl car- bonate (DEC), as electrolyte. Because of flammability of these solutions, the risk of ignition is unavoidable for battery. Many efforts have been carried out, and one of the conclusion is the utilization of all-solid-state lithium polymer battery (LPB). The LPBs use the lithium ion conductive polymer instead of organic solutions. This polymer electrolyte is not flammable unlike the organic solutions. Moreover, polymer electrolyte causes no electrolyte-leakage and is superior to organic solution or inor- ganic solid electrolytes in handing and formability. However, polymer electrolyte has poor ionic conductivity beside organic solutions [1], preventing the practical use of LPB. Therefore, intensive R&D of polymer electrolyte has been carried out mainly to improve the ionic conductivity [2,3]. We have reported that the addition of 13 group alkoxides into matrix polymer as plasticizers increased the ionic con- ∗ Corresponding author. E-mail address: mwakihar@o.cc.titech.ac.jp (M. Wakihara). ductivity [4–9]. Although many investigations have reported about polymer electrolyte itself, there exist limited numbers of examinations on the battery performance in the form of practical LPB style. This would be due to the technical dif- ficulty to make desirable solid–solid (electrode–electrolyte) connection. Thus, the effect of adding plasticizer for the prac- tical battery usage is still uncertain despite increase in ionic conductivity. In present paper, we constructed more simple and conven- tional battery form, or Li|liquid electrolyte|cathode material where the 13 group alkoxides was used as liquid electrolyte instead of assembling LPBs, and investigated their electro- chemical property. Through the study on the electrochemical behavior of above cell, the practical and potential problems that could occur in LPB using the plasticizers would be clarified. 2. Experimental B-PEG and Al-PEG were synthesized as shown in Fig. 1 by using methoxy poly(ethyleneglycol) (n = 3, 9) and boric acid or aluminum isopropoxide, respectively [5,9]. LiClO 4 (Soekawa chemicals) was dissolved into B-PEG and Al-PEG to 0013-4686/$ – see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2007.07.005