Compact Carbon‐Based Ultra‐High‐Power Electrodes: A Sodium Alginate‐Induced Self‐Shrinkage and Densification Approach

The trade‐off between compact energy storage and high‐power performance presents a significant challenge in device development. While densifying carbon materials enhances volumetric energy density by optimizing the balance between porosity and packing density, it often disrupts electronic conductivity due to random physical contact between nanomodules, limiting the power performance. This work presents a sodium alginate (SA)‐induced self‐shrinkage densification strategy that overcomes this limitation by incorporating nanometer‐sized “spacers,” namely carbon quantum dots (CQDs), into graphene nanosheets and crosslinking them by carbonizing SA accompanying with the shrinkage. These CQDs and SA‐derived carbon enhance specific surface area, electronic conductivity, and ion transport rate due to the CQDs’ spacer function and the formation of welded junction between the reduced graphene oxide (rGO)/CQDs nanosheets. Subsequently, the rGO/CQDs/SA‐derived carbon film exhibits an extraordinary volumetric power density of 12307.7 W cm−3 in an aqueous electrolyte under a mass loading of 0.12 mg cm−2. Notably, the assembled aqueous supercapacitors achieve a high volumetric power density of 349.5 W cm−3 under a higher mass loading of 0.49 mg cm−2. This paves the way for developing compact, highly conductive carbon‐based electrodes without compromising high porosity, offering a significant advancement in ultra‐high‐power energy storage devices.