Lithium-copolymerized polyimide cathodes for stable and fast lithium-ion storage

Organic materials as cathodes have attracted a lot of attention for lithium-ion batteries due to their structural designability and high theoretical capacity. However, most organic polymer cathode materials, such as π-conjugated polymers, have slow diffusion of lithium ions due to closely packed structures, resulting in inferior properties. Herein, we have synthesized lithium modified polyimides by condensation polymerization between 3,4,9,10-perylenetetracarboxylic acid dianhydride and 1,2-ethylenediamine in the presence of N-(2-aminoethyl)glycine lithium salt. The lithium-copolymerized polyimides exhibit lamellar structure and have increased specific surface area and therefore lead to enhanced lithium-ion diffusion coefficient and electronic conductivity. Lithium metal half cells employing lithium modified polyimide cathodes have a high discharge capacity of 138.3 mAh g−1 at a current density of 30 mA g−1 and good cycling stability with 71 % capacity retention at a current density of 1000 mA g−1 after 5000 cycles, which are much better than those employing general polyimides.