Aqueous zinc-ion hybrid supercapacitors (ZHSCs) represent a promising avenue for safe and efficient energy storage. However, their practical application has been limited by the low energy densities resulting from the inferior capacitance of carbon cathodes. To address this challenge, we introduce a nanoconfined carbonization approach to porous carbons with a well-balanced porosity and density, thereby achieving superior gravimetric and volumetric zinc-ion storage capabilities. The nanoconfined carbonization effectively inhibits the expansion of carbonaceous char and leads to dense porous carbon. By adjusting the silica amount, the density and pore structure of the resultant carbon materials can be facilely tuned. When used as cathodes in ZHSCs, the typical high-density porous carbon exhibits an exceptional combination of high gravimetric capacitance (452 F g-1) and volumetric capacitance (353 F cm-3), along with remarkable rate capability and cycling stability, surpassing conventional porous carbons and commercial microporous carbons. Insights into the zinc-ion storage behavior reveal that pores with diameters in the range of 1.2-5.5 nm are identified as the main sites for zinc ion storage, while pores above 5.5 nm are crucial for fast ion diffusion, contributing to high rate performance. This study highlights the potential of nanoconfined carbonization to engineer carbon cathodes for high-energy-density ZHSCs.
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