Isometric Thionated Naphthalene Diimides As Organic Cathodes for High Capacity Lithium Batteries

Although naphthalene diimide (NDI)
and its derivatives have been
widely used for organic Li-ion batteries (OLIBs), they are limited
by a low lithium uptake capacity and ambiguous lithiation mechanism.
Herein, we report two isometric thionated-NDI cathodes (cis-2S and trans-2S) obtained by replacing O with S in the
imide groups which improves the battery performance compared with
parent NDI (P-NDI). Remarkably, the position of S atoms
plays an important role as the potential plateau of cis-2S was 100 mV higher than trans-2S, 256 mV higher than P-NDI, and the capacity of cis-2S was twice than that of trans-2S, four times as P-NDI after
400 cycles. The in situ Raman, X-ray
photoelectron spectroscopy (XPS), and DFT calculations revealed that
the lithiation process occurs on the less electronegative S atoms.
For cis-2S, the electron
density on the lithiation sites is lower than trans-2S because of a stronger electron inductive
effect. This in turn enhances the redox potential and cycling stability
of cis-2S. This contribution
provides an additional molecular engineering strategy to develop novel
organic cathode materials for high performance OLIBs.