Rechargeable organic batteries using chloro-substituted naphthazarin derivatives as positive electrode materials

The use of redox active organic compounds as an alternative positive electrode material of rechargeable lithium batteries can be a solution for the resource issues of the current battery system. To satisfy both the high capacity and long cycle life of the batteries using organic active materials, naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) derivatives, which potentially exhibit a four-electron transfer redox reaction, were investigated. While the unsubstituted naphthazarin lithium salt (1), having a high theoretical capacity of up to about 550 mAh g−1, showed only half the expected capacity and a short cycle life as a positive electrode active material, the chloro-substituted ones (1-Cl 2 , 1-Cl 4 ) exhibited improved properties in both their initial capacity utilization and cycle life. In addition, the high stability of a chloro-substituted naphthazarin salt (1-Cl 4 ) was supported by a reversible electrochromic behavior during the redox reaction. The substituent effect of the naphthazarin derivatives on the cycle stability was discussed with respect to the battery performance and electrochromic behavior. Also, a guide for designing a new organic active material which shows a high capacity and long cycle life is suggested.