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The development of electronic equipment and electric vehicles fields has brought enormous challenges to the energy storage sector. Electrode cost has become the biggest problem for large‐scale applications of lithium‐ion batteries. Herein, we use carbonized hemp rods as a current collector instead of expensive copper foil. Meanwhile, the three‐dimensional (3D) structure of carbonized hemp stalk (C‐hemp) has a large number of hollow channels, in which a large amount of Co3O4 nanowires are grown, providing an area specific capacity of 10 mAh/cm2. The battery exhibits a good cycle performance and keeps a stable capacity during 50 charge‐discharge cycles. At the same time, the carbon matrix provides an excellent 3D conductive network that combines with metal oxide nanorods to show an excellent rate performance. [ABSTRACT FROM AUTHOR]

Porous FeVO4 is prepared by hydrothermal method and further modified by coating with carbon to obtain FeVO4/C with a hierarchical pore structure. FeVO4/C is used as an anodic electrode in aqueous rechargeable magnesium-ion batteries. The FeVO4/C material not only has improved electrical conductivity as a result of the carbon coating layer, but also has an increased specific surface area as a result of the hierarchical pore structure, which is beneficial for magnesium-ion insertion/deinsertion. Therefore, an aqueous rechargeable magnesium-ion full battery is successfully constructed with FeVO4/C as the anode, Mg-OMS-1 (OMS=octahedral molecular sieves) as the cathode, and 1.0 mol L−1 MgSO4 as the electrolyte. The discharge capacity of the Mg-OMS-1//FeVO4/C aqueous battery is 58.9 mAh g−1 at a current density of 100 mA g−1; this value is obtained by calculating the total mass of two electrodes and the capacity retention rate of this device is 97.7 % after 100 cycles, with almost 100 % coulombic efficiency, which indicates that the system has a good electrochemical reversibility. Additionally, this system can achieve a high energy density of 70.4 Wh kg−1, which provides powerful evidence that an aqueous magnesium-ion battery is possible. [ABSTRACT FROM AUTHOR]

For the first time, hierarchically porous carbon materials with a sandwich-like structure are synthesized through a facile and efficient tri-template approach. The hierarchically porous microstructures consist of abundant macropores and numerous micropores embedded into the crosslinked mesoporous walls. As a result, the obtained carbon material with a unique sandwich-like structure has a relatively high specific surface (1235 m2 g−1), large pore volume (1.30 cm3 g−1), and appropriate pore size distribution. These merits lead to a comparably high specific capacitance of 274.8 F g−1 at 0.2 A g−1 and satisfying rate performance (87.7 % retention from 1 to 20 A g−1). More importantly, the symmetric supercapacitor with two identical as-prepared carbon samples shows a superior energy density of 18.47 Wh kg−1 at a power density of 179.9 W kg−1. The asymmetric supercapacitor based on as-obtained carbon sample and its composite with manganese dioxide (MnO2) can reach up to an energy density of 25.93 Wh kg−1 at a power density of 199.9 W kg−1. Therefore, these unique carbon material open a promising prospect for future development and utilization in the field of energy storage. [ABSTRACT FROM AUTHOR]

Developing advanced supercapacitors with both high areal and volumetric energy densities remains challenging. In this work, self‐supported, compact carbon composite electrodes are designed with tunable thickness using 3D printing technology for high‐energy‐density supercapacitors. The 3D carbon composite electrodes are composed of the closely stacked and aligned active carbon/carbon nanotube/reduced graphene oxide (AC/CNT/rGO) composite filaments. The AC microparticles are uniformly embedded in the wrinkled CNT/rGO conductive networks without using polymer binders, which contributes to the formation of abundant open and hierarchical pores. The 3D‐printed ultrathick AC/CNT/rGO composite electrode (ten layers) features high areal and volumetric mass loadings of 56.9 mg cm−2 and 256.3 mg cm−3, respectively. The symmetric cell assembled with the 3D‐printed thin GO separator and ultrathick AC/CNT/rGO electrodes can possess both high areal and volumetric capacitances of 4.56 F cm−2 and 10.28 F cm−3, respectively. Correspondingly, the assembled ultrathick and compact symmetric cell achieves high areal and volumetric energy densities of 0.63 mWh cm−2 and 1.43 mWh cm−3, respectively. The all‐component extrusion‐based 3D printing offers a promising strategy for the fabrication of multiscale and multidimensional structures of various high‐energy‐density electrochemical energy storage devices. The all‐graphene‐oxide (GO)‐based symmetric supercapacitor is assembled with a thin GO separator and compact active carbon/carbon nanotube/reduced graphene oxide composite electrodes with tunable thickness, which are fabricated using the advanced extrusion‐based 3D printing technology. The 3D‐printed ultrathick and compact symmetric supercapacitor with a high mass loading can achieve both high areal and volumetric energy densities. [ABSTRACT FROM AUTHOR]