High-Energy, High-Power Sodium-Ion Batteries from a Layered Organic Cathode

Sodium-ion batteries (SIBs) attract
significant attention due to
their potential as an alternative energy storage solution, yet challenges
persist due to the limited energy density of existing cathode materials.
In principle, redox-active organic materials can tackle this challenge
because of their high theoretical energy densities. However, electrode-level
energy densities of organic electrodes are compromised due to their
poor electron/ion transport and severe dissolution. Here, we report
the use of a low-bandgap, conductive, and highly insoluble layered
metal-free cathode material for SIBs. It exhibits a high theoretical
capacity of 355 mAh g–1 per formula unit, enabled
by a four-electron redox process, and achieves an electrode-level
energy density of 606 Wh kg–1electrode (90 wt % active material) along with excellent cycling stability.
It allows for facile two-dimensional Na+ diffusion, which
enables a high intrinsic rate capability. Growth of the active cathode
material in the presence of as little as 2 wt % carboxyl-functionalized
carbon nanotubes improves charge transport and charge transfer kinetics
and further enhances the power performance. Altogether, these allow
the construction of SIB cells built from an affordable, sustainable
organic small molecule, which provide a cathode energy density of
472 Wh kg–1electrode when charging/discharging
in 90 s and a top specific power of 31.6 kW kg–1electrode.