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

Abstract

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, NH 2–(CH 2) n –NH 2 (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-III) were performed. The results indicated that the polyamides were electroactive in the organic electrolyte solution (propylene carbonate (PC)-1,2-dimethoxyethane (DME), 1:1 by volume containing lithium salt, such as LiClO 4). 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 LiClO 4/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×average cell voltage (2.10 V)). Performance of the cell with linear polyamide containing disulfide bond (–CO–(CH 2) 2–S–S–(CH 2) 2–CONH–(CH 2) 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×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.