Sodium-ion batteries are a potentially low-cost and safe alternative to the prevailing lithium-ion battery technology. However, it is a great challenge to achieve fast charging and high power density for most sodium-ion electrodes because of the sluggish sodiation kinetics. Here we demonstrate a high-capacity and high-rate sodium-ion anode based on ultrathin layered tin(II) sulfide nanostructures, in which a maximized extrinsic pseudocapacitance contribution is identified and verified by kinetics analysis. The graphene foam supported tin(II) sulfide nanoarray anode delivers a high reversible capacity of ∼1,100 mAh g−1 at 30 mA g−1 and ∼420 mAh g−1 at 30 A g−1, which even outperforms its lithium-ion storage performance. The surface-dominated redox reaction rendered by our tailored ultrathin tin(II) sulfide nanostructures may also work in other layered materials for high-performance sodium-ion storage.

The abundant reserve and low cost of sodium have provoked tremendous evolution of Na-ion batteries (SIBs) in the past few years, but their performances are still limited by either the specific capacity or rate capability. Attempts to pursue high rate ability with maintained high capacity in a single electrode remains even more challenging. Here, an elaborate self-branched 2D SnS (B-SnS) nanoarray electrode is designed by a facile hot bath method for Na storage. This interesting electrode exhibits areal reversible capacity of ca. 3.7 mAh cm (900 mAh g) and rate capability of 1.6 mAh cm (400 mAh g) at 40 mA cm (10 A g). Improved extrinsic pseudocapacitive contribution is demonstrated as the origin of fast kinetics of an alloying-based SnS electrode. Sodiation dynamics analysis based on first-principles calculations, ex-situ HRTEM, in situ impedance, and in situ Raman technologies verify the S-edge effect on the fast Na migration and reversible and sensitive structure evolution during high-rate charge/discharge. The excellent alloying-based pseudocapacitance and unsaturated edge effect enabled by self-branched surface nanoengineering could be a promising strategy for promoting development of SIBs with both high capacity and high rate response.

For building high‐energy density asymmetric supercapacitors, developing anode materials with large specific capacitance remains a great challenge. Although Fe2O3 has been considered as a promising anode material for asymmetric supercapacitors, the specific capacitance of the Fe2O3‐based anodes is still low and cannot match that of cathodes in the full cells. In this work, a composite material with well dispersed Fe2O3 quantum dots (QDs, ≈2 nm) decorated on functionalized graphene‐sheets (FGS) is prepared by a facile and scalable method. The Fe2O3 QDs/FGS composites exhibit a large specific capacitance up to 347 F g−1 in 1 m Na2SO4 between –1 and 0 V versus Ag/AgCl. An asymmetric supercapacitor operating at 2 V is fabricated using Fe2O3/FGS as anode and MnO2/FGS as cathode in 1 m Na2SO4 aqueous electrolyte. The Fe2O3/FGS//MnO2/FGS asymmetric supercapacitor shows a high energy density of 50.7 Wh kg−1 at a power density of 100 W kg−1 as well as excellent cycling stability and power capability. The facile synthesis method and superior supercapacitive performance of the Fe2O3 QDs/FGS composites make them promising as anode materials for high‐performance asymmetric supercapacitors.

Although the theoretical capacitance of MnO is 1370 F g based on the Mn/Mn redox couple, most of the reported capacitances in literature are far below the theoretical value even when the material goes to nanoscale. To understand this discrepancy, in this work, the electrochemical behavior and charge storage mechanism of K-inserted α-MnO (or KMnO) nanorod arrays in broad potential windows are investigated. It is found that electrochemical behavior of KMnO is highly dependent on the potential window. During cyclic voltammetry cycling in a broad potential window, K ions can be replaced by Na ions, which determines the pseudocapacitance of the electrode. The K or Na ions cannot be fully extracted when the upper cutoff potential is less than 1 V vs Ag/AgCl, which retards the release of full capacitance. As the cyclic voltammetry potential window is extended to 0-1.2 V, enhanced specific capacitance can be obtained with the emerging of new redox peaks. In contrast, the K-free α-MnO nanorod arrays show no redox peaks in the same potential window together with much lower specific capacitance. This work provides new insights on understanding the charge storage mechanism of MnO and new strategy to further improve the specific capacitance of MnO-based electrodes.

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Self‐standing electrodes are the key to realize flexible Li‐ion batteries. However, fabrication of self‐standing cathodes is still a major challenge. In this work, porous LiCoO2 nanosheet arrays are grown on Au‐coated stainless steel (Au/SS) substrates via a facile “hydrothermal lithiation” method using Co3O4 nanosheet arrays as the template followed by quick annealing in air. The binder‐free and self‐standing LiCoO2 nanosheet arrays represent the 3D cathode and exhibit superior rate capability and cycling stability. In specific, the LiCoO2 nanosheet array electrode can deliver a high reversible capacity of 104.6 mA h g−1 at 10 C rate and achieve a capacity retention of 81.8% at 0.1 C rate after 1000 cycles. By coupling with Li4Ti5O12 nanosheet arrays as anode, an all‐nanosheet array based LiCoO2//Li4Ti5O12 flexible Li‐ion battery is constructed. Benefiting from the 3D nanoarchitectures for both cathode and anode, the flexible LiCoO2//Li4Ti5O12 battery can deliver large specific reversible capacities of 130.7 mA h g−1 at 0.1 C rate and 85.3 mA h g−1 at 10 C rate (based on the weight of cathode material). The full cell device also exhibits good cycling stability with 80.5% capacity retention after 1000 cycles at 0.1 C rate, making it promising for the application in flexible Li‐ion batteries.