<p></p><p>Porous
carbon has attracted extensive attentions as the electrode material for various
energy storage devices considering its advantages like high theoretical
capacitance/capacity, high conductivity, low cost and earth abundant inherence.
However, there still exists some disadvantages limiting its further
applications, such as the tedious fabrication process, limited metal-ion
transport kinetics and undesired structure deformation at harsh electrochemical
conditions. Herein, we report a facile strategy, with calcium gluconate firstly
reported as the carbon source, to fabricate ultrathin porous carbon nanosheets.
<a>The as-prepared Ca-900 electrode delivers excellent K-ion
storage performance including high reversible capacity (430.7 mAh g<sup>-1</sup>),
superior rate capability (154.8 mAh g<sup>-1</sup> at an ultrahigh current
density of 5.0 A g<sup>-1</sup>) and ultra-stable long-term cycling stability
(a high capacity retention ratio of ~81.2% after 4000 cycles at 1.0 A g<sup>-1</sup>).
</a>Similarly, when being applied in Zn-ion capacitors, the Ca-900 electrode
also exhibits an ultra-stable cycling performance with ~90.9% capacity retention
after 4000 cycles at 1.0 A g<sup>-1</sup>, illuminating the applicable potentials.
Moreover, the origin of the fast and smooth metal-ion storage is also revealed
by carefully designed consecutive CV measurements. Overall, considering the
facile preparation strategy, unique structure, application flexibility and
in-depth mechanism investigations, this work will deepen the fundamental
understandings and boost the commercialization of high-efficient energy storage
devices like potassium-ion/sodium-ion batteries, zinc-ion batteries/capacitors and
aluminum-ion batteries.</p><br><p></p>