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Nitrogen‐doped hard carbon on Ni foam (NC/NF) with numerous active sites, expanded interlayer distance (0.49 nm), and highly ordered pseudo‐graphic structure is synthesized by a melamine‐assisted hydrothermal pretreatment and subsequent pyrolysis procedure. The high content configurations of pyrrolic‐nitrogen and pyridinic‐nitrogen in NC/NF could provide abundant active sites and defects for efficient Na+ adsorption/desorption and improved transport kinetics. The obvious flocculent structures on carbon surface, corresponding to the highly ordered pseudo‐graphic structure, could enhance the transport kinetics for electrons. The strong electrostatic repulsion of pyrrolic‐nitrogen could expand interlayer distance, facilitating Na+ insertion/extraction process. The balance between high nitrogen content and sufficient graphitization degree comes into strong carbon frameworks with enhanced structural stability and electronic conductivity. When served as free‐standing anodes for sodium‐ion batteries (SIBs), NC/NF presents high rate capability of 128.5 mAh g−1 at 10 A g−1, and excellent cycling stability of 225.4 mAh g−1 after 1000 cycles under high current density of 5 A g−1. These results demonstrate a new light to prepare advanced anodes for SIBs. [ABSTRACT FROM AUTHOR]

Developing 3 D self‐assembled nanoarchitectures with well‐defined crystal structures is an effective strategy to enhance the electrochemical performances of electrode materials. (1 1 0)‐oriented and bridged‐nanoblocks self‐assembled VS4 microspheres are controllably synthesized by a facile one‐step hydrothermal method. The (1 1 0)‐bridged structure sets up open pathways for Na+ diffusion among nanoblocks, and the (1 1 0)‐oriented structure provides unobstructed pathways for Na+ diffusion in the nanoblocks, which collectively constructs multidimensional Na+ transfer channels in the VS4 microspheres, promoting the electrochemical kinetics. As an anode for Na‐ion batteries (SIBs), this material exhibits pseudocapacitive Na+ storage and excellent rate capability, delivering high capacities of 339 and 270 mAh g−1 at rates of 0.1 and 2.0 A g−1, respectively, with a capacity retention of 79 % in the voltage window of 0.5–3.0 V. In particular, the reversible capacity reaches 575 mAh g−1 after 300 cycles even at 1.0 A g−1 in the voltage window of 0.05–3.0 V, outperforming those of the ever‐reported VS4‐based anode materials. This work presents an effective strategy to the exploration and design of high‐performance anodes for SIBs. [ABSTRACT FROM AUTHOR]

Cover Feature: Nitrogen-Doped Hard Carbon on Nickel Foam as Free-Standing Anodes for High-Performance Sodium-Ion Batteries (ChemElectroChem 3/2020) B The Cover Feature b illustrates a nitrogen-doped hard carbon on Ni foam as a free-standing anode for sodium-ion batteries. Nitrogen-doped carbon, free-standing anodes, sodium-ion batteries, high rate performance, long cycling life. [Extracted from the article]

Development of three-dimensional self-assembled hollow nanoarchitectures combining functional shells and inner voids is an important approach for realizing high-rate and long-life battery electrodes. As a potential high-performance anode for sodium-ion batteries (SIBs), (1 1 0)-bridged nanoblocks self-assembled VS 4 hollow microspheres (PNBH-VS 4) are controllably synthesized by a facile one-step hydrothermal method. The (1 1 0)-bridged structure constructs the Na+ conducting channels and e− transfer paths among nano-grains and nanoblocks, and the self-assembled hollow structure presents the double space physical entrapment effect for the excessive volume change of nanoblocks, which synergistically improve the Na+ storage kinetics and structure stability. When employed as an anode for SIBs, PNBH-VS 4 electrode exhibits the superior rate capability and long cycling life, outperforming those of the ever-reported VS 4 -based anode materials. At 0.2, 0.5, 1.0 and 2.0 A g−1, the capacity can reach 629, 564, 428 and 400 mAh g−1 after 250, 200, 350 and 700 cycles, respectively. Even at 5.0 A g−1, the capacity can still stabilize at 309 mAh g−1 after 1000 long cycles. In addition, it is revealed that PNBH-VS 4 electrode undertakes the insertion and conversion reaction in the potential range of 0.50–3.00 and 0.05–0.50 V, respectively, where the main capacity contribution originates from the insertion reaction. Meanwhile, PNBH-VS 4 electrode exhibits better insertion reversibility at lower current densities and conversion reversibility at higher current densities during cycling, respectively. [ABSTRACT FROM AUTHOR]

Porous carbon anodes are widely used for sodium-ion batteries storage, sodium-ion insertion/extraction in porous carbon anodes always accompanies with exfoliation/accumulation of carbon sheets. Whether exfoliation/accumulation of carbon sheets has influence on sodium storage is still unknown. We control alkali activation concentration to form porous carbon sheets with different etching degrees. Results show the etching degree is decided by exfoliation/accumulation rate of porous carbon sheets. When sodium ions insert into carbon sheets, carbon sheets with lower etching degree begin to exfoliate and carbon sheets with higher etching degree start to accumulate. As the current density increases, accumulation/exfoliation process alternates and repeats ceaselessly. The number of exposed inner defects near pores changes during electrochemical reaction process, which is caused by accumulating/exfoliating of carbon sheets. Some defects are hidden by sheets because of the move of carbon sheets, which reduces rate capacity. This paper reveals exposing inner defects of carbon sheets have essential influence on sodium-ion diffusion to achieve high rate performance. Unlabelled Image • The accumulation/exfoliation rate of carbon sheets is acquired by ID/IG value. • Stable rate performance is decided by exposed inner defects near pores. • The etching degree of carbon sheets is achieved by their thickness. [ABSTRACT FROM AUTHOR]