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Renewable and environmentally friendly biomass‐based carbon electrode materials naturally possess fast ion transport, high adsorption, and excellent chemical stability for high‐performance energy‐storage devices. However, intelligently building the effectively biomass‐transferred carbon materials for the requirement of high energy density is still a big challenge to date. Here, a hierarchically divacancy defect building platform is reported for effectively biomass‐transferred and highly interconnected 3D dual‐activated porous carbon fibers (DACFs) based on the internal−external dual‐activation function of the pre‐embedded KOH and CO2 molecular. This uniquely interconnected frameworks not only fully provide the abundant active sites for ion interaction, but also efficiently guarantee the substantial accommodation for ion storage. Based on this, the as‐prepared DACFs‐based supercapacitors deliver a high energy density of 61.3 Wh kg−1 at a power density of 875 W kg−1 in the EMIMBF4 ionic liquid. This work not only provides a simple and efficient technique to enhance the energy density of carbon materials, but also probably promotes its additional application in environmental remediation. [ABSTRACT FROM AUTHOR]

The O-N-S co-doped hierarchical porous carbons are prepared by direct pyrolysis of kraft lignin which is the byproduct from papermaking black liquor. The proposed preparation method is extremely facile, green-environmental, and low-cost without any additional activating agents, additives or templates. The kraft lignin-derived carbon materials possess large specific surface areas (338−1307 m2 g−1), hierarchical porous structures and abundant multi-heteroatoms co-doping (9.84–19.91 wt%). Benefiting from above synergistic advantages, the as-fabricated symmetric supercapacitor in aqueous electrolyte delivers a high specific capacitance of 244.5 F g−1 at 0.2 A g−1, excellent rate-capability (81.8% retention of initial capacitance at 40.0 A g−1), and outstanding cycling stability (91.6% retention over 10000 cycles). Importantly, this device in aqueous electrolyte delivers an energy density of 8.5 W h kg−1 at a power density of 100 W kg−1. Furthermore, a remarkable energy density of 66.8 W h kg−1 at a power density of 1.75 kW kg−1 has been achieved and 32.2 W h kg−1 is still maintained even at an ultrahigh power density of 40.0 kW kg−1 when ionic liquid serves as electrolyte. This study demonstrates the successful conversion of low-valued natural biomass derivative into sustainable high-performance supercapacitor electrode materials with a simple, low-cost, and green-environmental production process. Image 1 [ABSTRACT FROM AUTHOR]

Highly microporous carbon material with nitrogen doping has been synthesized via a facile one-step approach by employing natural biowaste miscellaneous wood fibers derived hydrochar as precursor and melamine as nitrogen source respectively. The added melamine not only results in the incorporation of some nitrogen into the carbon framework but also increases the specific surface area of carbon material. Such resultant N -doped microporous carbon possesses the functionalized nitrogen doping (1.75 at. %), a large specific surface area (∼1807 m2 g−1) and abundant highly interconnected micropores. Benefiting from the synergistic effect of high specific surface area, well-developed pore size distribution and functionalized groups, this carbon material delivers a high specific capacitance of 345 F g−1 at 0.5 A g−1, an excellent capacitance retention with 270 F g−1 at up to 30 A g−1, and a remarkable cycle ability with 91.3% retention after 10,000 cycles at 5.0 A g−1. Based on it, the as-developed flexible symmetric solid-state supercapacitor delivers a high energy density of 7.92 W h kg−1 at the power density of 250 W kg−1. Evidently, this work provides a facile and cost-effective route for functionalized natural biowaste-based carbon materials and further opens up a way for highly value-added recycling of biowaste-like materials. [ABSTRACT FROM AUTHOR]

Supercapacitors with ionic liquid (IL) electrolytes can reach high work voltage and accompanied high energy density, which are the critical parameters for supercapacitors’ rapid development. However, supercapacitors with IL electrolytes usually suffer from low power density due to low conductivity, large ionic size and high viscosity of the electrolytes. Herein we reported hierarchically porous sheet-like nanocarbons (HPSNCs) prepared by direct activation of graphene oxide and polytetrafluoroethylene (PTFE) polymer are promising electrode materials for high power supercapacitors with also high energy density. During the activation process, the PTFE particles as a spacer that can effectively hinder the restack of graphene oxide and simultaneously transformed into sheet-like nanocarbons at high temperatures. As a result, the as-prepared samples exhibit highest surface area of ∼2000 m 2 g −1 and largest pore volume of 1.90 cm 3 g −1 . Benefit from hierarchically porous structure from micro-to-macro-pores, which largely shorten the diffusion distance of electrolyte ions, the HPSNC electrodes show a high energy density of 51.7 Wh kg −1 at a power density of 35 kW kg −1 in symmetric supercapacitors with IL electrolyte. In addition, the HPSNC-based supercapacitors also possess an excellent cycling stability with 88% capacitance retention after 5000 cycles. Unambiguously, this work demonstrated the potential of HPSNCs for high power supercapacitors with high energy density and application in integrated energy management electronics. [ABSTRACT FROM AUTHOR]