Poly(1,4-phenylene-1,2,4-dithiazol-3′,5′-yl):: the new redox system for lithium secondary batteries

A new redox system, poly(1,4-phenylene-1,2,4-dithiazol-3',5'-yl) (PPDTA), is presented as a cathode material for high-capacity lithium secondary batteries. This polymer, composed of 1,2,4-dithiazolium ring and benzene, is synthesized by a cyclooxidative reaction of aromatic thioamides with organic oxidizers. The advantages of this system are: (1)high theoretical charge density; (2) fast redox rate; and (3) electrical conductivity. The high capacity is realized by the successive redox reactions of an S-S bond and a 7-pi -electron unsaturated 1,2,4-dithiazolium ring. The fast redox rate is achieved by the pi -conjugation and by the SS bond in a 1,1,4-dithiazolium ring. MO calculation reveals that the S-S bond in a 1,2,4-dithiazolium ring of PPDTA causes a gap narrowing and a downshift of HOMO and LUMO levels, being consistent with the electrochemical experiment. A discharge test showed a capacity of 420 mA h g(-1), which is about 3-4 times higher than those of inorganic intercalation compounds and ordinary conducting polymers. (C) 2001 Elsevier Science Ltd. All rights reserved.