Reversible sodium storage behavior of aromatic diimide disodium carboxylates

The synthesis, characterization and electrochemical sodiation/desodiation performance of two novel disodium diimide carboxylates, disodium salt of N,N'-bis (glycinyl) pyromellitic diimide (Na2-BPDI) and disodium salt of N,N'-bis (glycinyl) naphthalene diimide (Na2-BNDI) were reported for the first time. The Na2-BNDI electrode material delivers a reversible capacity of 122 mAh g-1 in the first cycle and retains a reasonable capacity of 92 mAh g-1 after 50 cycles at a current density of 50 mA g-1, whereas a rapid capacity fading is observed in the case of Na2-BPDI electrode material in subsequent cycles. Ex-situ NMR and FT-IR studies confirmed that the decomposition of Na2-BPDI electrode material upon continuous electrochemical sodiation/desodiation process. These results demonstrate that the importance of extended conjugation, as in Na2-BNDI, for efficient electrochemical sodium storage in the redox active aromatic compound.