The voltage limit for aqueous asymmetric supercapacitors is usually 2 V, which impedes further improvement in energy density. Here, high Na content Birnessite Na MnO nanosheet assembled nanowall arrays are in situ formed on carbon cloth via electrochemical oxidation. It is interesting to find that the electrode potential window for Na MnO nanowall arrays can be extended to 0-1.3 V (vs Ag/AgCl) with significantly increased specific capacitance up to 366 F g . The extended potential window for the Na MnO electrode provides the opportunity to further increase the cell voltage of aqueous asymmetric supercapacitors beyond 2 V. To construct the asymmetric supercapacitor, carbon-coated Fe O nanorod arrays are synthesized as the anode and can stably work in a negative potential window of -1.3 to 0 V (vs Ag/AgCl). For the first time, a 2.6 V aqueous asymmetric supercapacitor is demonstrated by using Na MnO nanowall arrays as the cathode and carbon-coated Fe O nanorod arrays as the anode. In particular, the 2.6 V Na MnO //Fe O @C asymmetric supercapacitor exhibits a large energy density of up to 81 Wh kg as well as excellent rate capability and cycle performance, outperforming previously reported MnO -based supercapacitors. This work provides new opportunities for developing high-voltage aqueous asymmetric supercapacitors with further increased energy density.

A surface-modified Co O ultrathin nanosheet (denoted as PCO) is reported via controllable phosphate ion functionalization for pseudocapacitors. An energy density of 71.6 W h kg (at 1500 W kg ) is achieved by the PCO-based pseudocapacitor. The unique porous nanosheet morphology, high surface reactivity, and fast electrode kinetics of PCO are found to be responsible for the enhanced pseudocapacitive performance.

High energy density at high power density is still a challenge for the current Li‐ion capacitors (LICs) due to the mismatch of charge‐storage capacity and electrode kinetics between capacitor‐type cathode and battery‐type anode. In this work, B and N dual‐doped 3D porous carbon nanofibers are prepared through a facile method as both capacitor‐type cathode and battery‐type anode for LICs. The B and N dual doping has profound effect in tuning the porosity, functional groups, and electrical conductivity for the porous carbon nanofibers. With rational design, the developed B and N dual‐doped carbon nanofibers (BNC) exhibit greatly improved electrochemical performance as both cathode and anode for LICs, which greatly alleviates the mismatch between the two electrodes. For the first time, a 4.5 V “dual carbon” BNC//BNC LIC device is constructed and demonstrated, exhibiting outstanding energy density and power capability compared to previously reported LICs with other configurations. In specific, the present BNC//BNC LIC device can deliver a large energy density of 220 W h kg−1 and a high power density of 22.5 kW kg−1 (at 104 W h kg−1) with reasonably good cycling stability (≈81% retention after 5000 cycles).

Metal sulfides are promising anode materials for sodium-ion batteries due to their large specific capacities. The practical applications of metal sulfides in sodium-ion batteries, however, are still limited due to their large volume expansion, poor cycling stability, and sluggish electrode kinetics. In this work, a two-dimensional heterostructure of CoS (CoS and CoS) quantum dots embedded N/S-doped carbon nanosheets (CoS@NSC) is prepared by a sol-gel method. The CoS quantum dots are in situ formed within ultrafine carbon nanosheets without further sulfidation, thus resulting in ultrafine CoS particle size and embedded heterostructure. Meanwhile, enriched N and S codoping in the carbon nanosheets greatly enhances the electrical conductivity for the conductive matrix and creates more active sites for sodium storage. As a result, the hybrid CoS@NSC electrode shows excellent rate capability (600 mAh g at 0.2 A g and 500 mAh g at 10 A g) and outstanding cycling stability (87% capacity retention after 200 cycles at 1 A g), making it promising as an anode material for high-performance sodium-ion batteries. A CoS@NSC//NaMnO full cell is demonstrated, and it can deliver a specific capacity of 414 mAh g (based on the mass of CoS@NSC) at a current density of 0.2 A g.

Two-dimensional materials with intrinsic magnetism have recently drawn intense interest for both the fundamental studies and potential technological applications. However, the studies to date have been largely limited to mechanically exfoliated materials. Herein, an atmospheric pressure chemical vapor deposition route to ultrathin group VB metal telluride MTe (M = V, Nb, Ta) nanoplates with thickness as thin as 3 nm is reported. It is shown that the resulting nanoplates can be systematically evolved from mostly thicker hexagonal domains to thinner triangular domains with an increasing flow rate of the carrier gas. X-ray diffraction and transmission electron microscopy studies reveal MTe (M = V, Nb, Ta) nanoplates are high-quality single crystals. High-resolution scanning transmission electron microscope imaging reveals the VTe and NbTe nanoplates adopt the hexagonal 1T phase and the TaTe nanoplates show a monoclinic distorted 1T phase. Electronic transport studies show that MTe single crystals exhibit metallic behavior. Magnetic measurements show that VTe and NbTe exhibit ferromagnetism and TaTe shows paramagnetic behavior. The preparation of ultrathin few-layered MTe nanoplates will open up exciting opportunities for the burgeoning field of spintronics, sensors, and magneto-optoelectronics.