2D carbon nanomaterials such as graphene and its derivatives, have gained tremendous research interests in energy storage because of their high capacitance and chemical stability. However, scalable synthesis of ultrathin carbon nanosheets with well-defined pore architectures remains a great challenge. Herein, the first synthesis of 2D hierarchical porous carbon nanosheets (2D-HPCs) with rich nitrogen dopants is reported, which is prepared with high scalability through a rapid polymerization of a nitrogen-containing thermoset and a subsequent one-step pyrolysis and activation into 2D porous nanosheets. 2D-HPCs, which are typically 1.5 nm thick and 1-3 µm wide, show a high surface area (2406 m g ) and with hierarchical micro-, meso-, and macropores. This 2D and hierarchical porous structure leads to robust flexibility and good energy-storage capability, being 139 Wh kg for a symmetric supercapacitor. Flexible supercapacitor devices fabricated by these 2D-HPCs also present an ultrahigh volumetric energy density of 8.4 mWh cm at a power density of 24.9 mW cm , which is retained at 80% even when the power density is increased by 20-fold. The devices show very high electrochemical life (96% retention after 10000 charge/discharge cycles) and excellent mechanical flexibility.

Owing to the high theoretical specific capacity (1166 mAh g), lithium sulfide (LiS) has been considered as a promising cathode material for Li-S batteries. However, the polysulfide dissolution and low electronic conductivity of LiS limit its further application in next-generation Li-S batteries. In this report, a nanoporous LiS@C-Co-N cathode is synthesized by liquid infiltration-evaporation of ultrafine LiS nanoparticles into graphitic carbon co-doped with cobalt and nitrogen (C-Co-N) derived from metal-organic frameworks. The obtained LiS@C-Co-N architecture remarkably immobilizes LiS within the cathode structure through physical and chemical molecular interactions. Owing to the synergistic interactions between C-Co-N and LiS nanoparticles, the LiS@C-Co-N composite delivers a reversible capacity of 1155.3 (99.1% of theoretical value) at the initial cycle and 929.6 mAh g after 300 cycles, with nearly 100% Coulombic efficiency and a capacity fading of 0.06% per cycle. It exhibits excellent rate capacities of 950.6, 898.8, and 604.1 mAh g at 1C, 2C, and 4C, respectively. Such a cathode structure is promising for practical applications in high-performance Li-S batteries.

Nickel nanomaterials with a wide range of morphologies and sizes, such as superfine nanoparticles, urchinlike chains, smooth chains, rings, and hexagonal Ni/Ni(OH)2 heterogeneous structure plates, are synthesized in a single reaction system by simply adjusting the reaction conditions. The morphology transformation mechanism is systematically investigated. Magnetic measurement of urchinlike chains, smooth chains, and rings shows that the saturation magnetization (M s) decreases with reduced sample size, and remanent magnetization (M r) decreases with increasing reaction temperature. Additionally, coercivity (H c) of urchinlike chains which is apparently larger than that of bulk nickel depends more on size than on shape anisotropy according to spherical chain reversal magnetization model. Enhanced microwave absorption of Ni/Ni(OH)2 hexagonal plates compared with smooth chains and rings is due to the synergistic effect of magnetic loss and dielectric loss. Particularly, the urchinlike nickel chains exhibit a best absorption property in contrast with other as-synthesized samples and other reported nickel structures, which can be attributed to the geometrical effect, high initial permeability, point discharge effect, and multiple absorption. The prepared nickel nanomaterials can be applied as promising absorbing materials.

Three-dimensional aerogel with ultrathin tellurium nanowires (TeNWs) wrapped homogeneously by reduced graphene oxide (rGO) is realized via a facile hydrothermal method. Featured with high conductivity and large flexibility, the rGO constructs a conductive three-dimensional (3D) backbone with rich porosity and leads to a free-standing, binder-free cathode for lithium-tellurium (Li-Te) batteries with excellent electrochemical performances. The cathode shows a high initial capacity of 2611 mAh cm(-3) at 0.2 C, a high retention of 88% after 200 cycles, and a high-rate capacity of 1083 mAh cm(-3) at 10 C. In particular, the 3D aerogel cathode delivers a capacity of 1685 mAh cm(-3) at 1 C after 500 cycles, showing pronounced long-cycle performance at high current density. The performances are attributed to the well-defined flexible 3D architecture with high porosity and conductivity network, which offers highly efficient channels for electron transfer and ionic diffusion while compromising volume expansion of Te in charge/discharge. Owing to such advantageous properties, the reported 3D rGO/tellurium nanowire (3DGT) aerogel presents promising application potentials as a high-performance cathode for Li-Te batteries.

Three-dimensional (3D) CNT/graphene-Li2S (3DCG–Li2S) cathodes with 81.4 wt % record Li2S loading have been realized through solvothermal reaction and a subsequent liquid-infiltration-evaporation coating method. The highly flexible, conductive 3D mesoporous interconnected network based on two-dimensional (2D) graphene nanosheets and one-dimensional (1D) carbon nanotubes (CNTs) provides highly efficient channels for electron transfer and ionic diffusion, and leads to a low solubility of polysulfides in electrolytes in charges/discharges. Without polymeric binders or conductive additives, the freestanding 3DCG–Li2S cathode exhibits record electrochemical performances including reversible discharge capacities of 1123.6 mAh g–1 and 914.6 mAh g–1, 0.02% long-term capacity decay per cycle and a high-rate capacity of 514 mAh g–1 at 4 C. The reported 3DCG–Li2S aerogel with ultrahigh Li2S content presents promising application potentials in high-performance Li–S batteries.