Ž . Journal of Power Sources 90 2000 27–32 www.elsevier.comrlocaterjpowsour Characteristics of the electrolyte with fluoro organic lithium salts Fusaji Kita a, ) , Hideo Sakata a , Sayaka Sinomoto a , Akira Kawakami a , Haruki Kamizori a , Takaaki Sonoda b , Hideo Nagashima b , Jin Nie c , Natalya V. Pavlenko d , Yurii L. Yagupolskii d a Hitachi Maxell Ltd. Battery R & D Laboratory, 1-1-88, Ushitora, Ibaraki, Osaka 567-8567, Japan b Institute of AdÕanced Material Study, Kyushu UniÕersity, Kasuga, Fukuoka 816-8580, Japan c Department of Chemistry Huazhong UniÕersity of Science and Technology, Wuham, Hubei 430074, People’s Republic of China d Institute of Organic Chemistry Ukrainian Academy of Science, Dom 5, Murmanskaya, KieÕ-94, 253660, Ukraine Received 14 November 1999; received in revised form 25 January 2000; accepted 10 February 2000 Abstract Some fluoro organic lithium salts have attractive features as organic electrolyte such as solubility, conductivity, and oxidation potentials. The fluoro organic lithium salts with SO groups show higher conductivities than those with CO groups. Methide 2 Ž . Ž . CF SO CLi and imide RfSO NLi salts show higher conductivities than oxide salts RfSO OLi with only one RfSO group. The 3 23 22 2 2 lithium salts with long fluoroalkyl groups and two or more RfSO groups show high oxidation potentials and high aluminum corrosion 2 Ž . Ž .Ž . potentials over 4.3 V. The battery performances of modified imide salts such as C F SO NLi, C F SO CF SO NLi, and 2 5 22 4 9 2 3 2 ŽŽ . . CF CHOSO NLi are satisfactory. The cycle characteristics of the imide salt cells are better than those of the LiPF cell. Especially, 32 22 6 ŽŽ . . the CF CHOSO NLi shows the best cycle characteristics. In XPS analysis the anode surfaces of the imide cells are covered with 32 22 imide salt components. q 2000 Elsevier Science S.A. All rights reserved. Keywords: Fluoro organic lithium salt; Conductivity; Oxidation potential; Aluminum corrosion potential; Cycle characteristics 1. Introduction Ž . Many types of organic lithium salts such as LiB C H , 6 54 Li C O , LiSO C F SO Li, CF SO Li, CF CO Li, C F - 2 4 4 3 2 4 3 3 3 3 2 4 9 Ž . Ž . Ž . SO Li, CF SO NLi, CF CO NLi, CF SO - 3 3 2 2 3 2 3 2 3 Ž . Ž . Ž . CLi, CF SO CFLi, C F SO NLi, LiB C H O , 3 2 2 2 5 2 2 6 4 2 2 Ž . and LiB COC H O have been reported as lithium 6 4 2 w x battery electrolyte 1–9 . Among them CF SO Li, 3 3 Ž . C F SO Li, and CF SO NLi have been used or were 4 9 3 3 2 2 used as lithium battery electrolytes. The following features are required for lithium salts as electrolytes. 1. Good conductivity Ž 2. Good electrochemical and thermal stability high oxida- . tion potential 3. Safety and nontoxicity 4. Low cost ) Corresponding author. Tel.: q 81-726-23-8140; fax: q 81-726-23- 9231. Ž . E-mail address: fusaji-kita@maxell.co.jp F. Kita . The most advantageous features of organic lithium salts are their characteristics to be improved by structural modi- fication. We report here the structural effects of fluoro organic lithium salts on the conductivity, electrochemical stability, aluminum corrosion at high voltage, and cell performance 2. Experimental 2.1. HOMO calculation The energy levels for the highest occupied molecular Ž . orbital HOMO of different kinds of geometry-optimized electrolyte anions were calculated with MNDO, PM3, HFr3-21G ) , and B3LYPr6-31G ) I HFr3-21G ) meth- ods by SPARTAN V 5.0. 2.2. ConductiÕity The conductivities of several kinds of electrolyte solu- Ž . tions 0.1 molrl lithium salts in 1r2vrv PCrDME were 0378-7753r00r$ - see front matter q 2000 Elsevier Science S.A. All rights reserved. Ž . PII: S0378-7753 00 00443-2