C-P/C=O bonds assisted desolvation effect in ultra-micropores carbon for boosting Zn-ion storage capability

Aqueous zinc-ion hybrid capacitors (ZIHCs) are a promising new type of energy storage device, but there is a plight that the unsatisfactory Zn2+ storage capability of carbonaceous cathodes limits further application. To address this issue, desolvation strategy is employed to tailor the solvation sheath of Zn2+ in the ultra-micropores (0.59 nm) nanospheres, where H3PO4 acts as phosphorus source for forming C-P bonds and enhancing C=O bonds to further reduce the desolvation energy barrier. In practical application, a quasi-solid-state flexible ZIHC is constructed, which provides a battery-level energy density (293.4 Wh kg−1) at a power density (180 W kg−1) and a remarkable capacity retention of 93.4 % after 10 000 cycles. Electrochemical analyses, DFT calculations and structural characterization reveal that ultra-microporous is proved to be a prerequisite for C-P/C=O that are expected to further deplete solvent molecules within a Zn2+ solvation sheath. Also, the coupling effect between the strong adsorption of Zn2+ by C-P/C=O and the hydrophobic effect of C-P play an important role in facilitating desolvation process. This work creates a precedent for the application of ultra-microporous carbon materials in ZHICs and provides a brand-new approach for breaking the bottleneck of the low energy density and poor lifespan of ZHICs.