Redox-active polyimide–polyether block copolymers as electrode materials for lithium batteries

Abstract

Redox-active polyimide–polyether multi-block copolymers were synthesized by polycondensation reaction of aromatic dianhydrides with α-ω-diamino poly(ethylene oxide). Polyimide-b-polyether block copolymers showed microphase separation between a hard-polyimide domain and a soft-polyether domain as observed by Atomic Force Microscopy. The block copolymers were investigated as cathodes for polymer/lithium metal batteries. Polymer cathodes were formulated where the block copolymer had a dual role as active material and binder, with a small amount of carbon black (15 wt%). Naphthalene polyimides showed higher discharge voltages, higher specific capacities as well as better cycling performance, compared to pyromellitic polyimides. The longest PEO blocks resulted in a better performance as electrodes. The best performing naphthalene polyimide-b-PEO2000 presented an excellent value of discharge capacity of 170 mA h g⁻¹, stable after 100 cycles at a current density of 1Li⁺/5 h and considering the polyimide as the active material. The average discharge plateaus were 2.51 V and 2.37 V vs. Li⁺/Li.