Electrochemical behavior of polyamides with cyclic disulfide structure and their application to positive active material for lithium secondary battery

Polyamides (DTA-I, DTA-II, and DTA-III) containing cyclic disulfide structure were prepared by condensation between 1,2-dithiane-3,6-dicarboxylic acid (DTA) and alkyl diamine, NH2-(CH2)(n)-NH2 (DTA-I; n=4, DTA-II; n=6, DTA-III; n=8) and their application to positive active material for Lithium secondary batteries was investigated. Cyclic voltammetry (CV) measurements under slow sweep rate (0.5 mV s(-1)) with a carbon paste electrode containing the polyamide (DTA-I, DTA-II, or DTA-m) were performed. The results indicated that the polyamides were electroactive in the organic electrolyte solution (propylene carbonate (PC)-1,2-dimethoxyethane (DME), I:1 by volume containing Lithium salt, such as LiClO4). The responses based on the redox of the disulfide bonds in the polyamide were observed. Test cells, Li/PC-DME (1:1. by volume) with 1 mol dm(-3) LiClO4/the polyamide cathode, were constructed and their performance was tested under constant current charge/discharge condition. The average capacity of the test cells with the DTA-III cathode was 64.3 Ah kg(-1) of cathode (135 Wh kg(-1) of cathode, capacity (Ah kg(-1)) of the cathode x average cell voltage (2.10 V)). Performance of the cell with linear polyamide containing disulfide bond (-CO-(CH2)(2)S-S-(CH2)(2)-CONH-(CH2)(8)NH-, GTA-III) was also investigated and the average capacity was 56.8 Ah kg(-1) of cathode (100 Wh kg(-1) of cathode, capacity (Ah kg(-1)) of the cathode x average cell voltage (1.76 V)). Cycle efficiency of the test cell with the DTA-III cathode was higher than that with the GTA-III cathode. (C) 2001 Elsevier Science B.V. All rights reserved.