Rational nanostructured FeSe2 wrapped in nitrogen-doped carbon shell for high-rate capability and long cycling sodium-ion storage

Enhanced redox kinetics in hierarchical tubular FeSe2 by incorporating Se quantum dots towards high-performance sodium-ion batteries

Metal selenides have emerged as promising Na-storage anode materials owing to their substantial theoretical capacity and high cost-effectiveness. However, the application of metal selenides is hindered by inferior electronic conductivity, huge volume variation, and sluggish kinetics of ionic migration. In response to these challenges, herein, a hierarchical hollow tube consisting of FeSe2 nanosheets and Se quantum dots anchored within a carbon skeleton (HT-FeSe2/Se/C) is strategically engineered and synthesized. The most remarkable feature of HT-FeSe2/Se/C is the introduction of Se quantum dots, which could lead to high electron density near the Fermi level and significantly enhance the overall charge transfer capability of the electrode. Moreover, the distinctive hollow tubular structure enveloped by the carbon skeleton endows the HT-FeSe2/Se/C anode with robust structural stability and fast surface-controlled Na-storage kinetics. Consequently, the as-synthesized HT-FeSe2/Se/C demonstrates a reversible capacity of 253.5 mAh/g at a current density of 5 A/g and a high specific capacity of 343.9 mAh/g at 1 A/g after 100 cycles in sodium-ion batteries (SIBs). Furthermore, a full cell is assembled with HT-FeSe2/Se/C as the anode, and a vanadium-based cathode (Na3V2(PO4)2O2F), showcasing a high specific capacity of 118.1 mAh/g at 2 A/g. The excellent performance of HT-FeSe2/Se/C may hint at future material design strategies and advance the development and application of SIBs.

Multifunctional Fe-S bonds assist poly(3,4-ethylenedioxythiophene) to enhance iron diselenide for ultra-long sodium storage lifetime

Transition metal selenides (TMS) have been used to prepare hundreds of electrode materials for ion batteries due to their superior theoretical capacity, but have been repeatedly limited by the sluggish reaction kinetics and the enormous volume change during the repeated charge/discharge process. Here, we report a facile strategy to fabricate organic-inorganic composites by engineering a unique chemical bonding interface between TMS and conductive polymers. For the first time, poly(3,4-ethylenedioxythiophene) (PEDOT) is utilized to encapsulate iron diselenide (FeSe2) nanoparticles by in situ polymerization, and the Fe-S bonds are meanwhile formed at the interface of FeSe2 and PEDOT. The experimental analysis demonstrates the stability of Fe-S bonds during the sodiation/desodiation process and after long cycling, which can serve as a "bridge" for fast charge transfer and also serve as a "rivet" to stabilize the composite structure. When used for sodium ion storage, the composite offers an exceptionally long lifetime of up to 17,000 loops at 10 A/g without capacity degradation. In addition, it delivers a high specific capacity of 490.4 mAh/g and retains 60 % when the current density is amplified 150 times. The assembled full cell also exhibits excellent cycling stability. This work will provide a feasible way to improve the metal oxide/sulfide/selenides for long-life ion batteries.

Metal Selenides Find Plenty of Space in Architecting Advanced Sodium/Potassium Ion Batteries

The rapid evolution of smart grid system urges researchers on exploiting systems with properties of high-energy, low-cost, and eco-friendly beyond lithium-ion batteries. Under the circumstances, sodium- and potassium-ion batteries with the semblable work mechanism to commercial lithium-ion batteries, hold the merits of cost-effective and earth-abundant. As a result, it is deemed a promising candidate for large-scale energy storage devices. Exploiting appropriate active electrode materials is in the center of the spotlight for the development of batteries. Metal selenides with special structures and relatively high theoretical capacity have aroused broad interest and achieved great achievements. To push the smooth development of metal selenides and enhancement of the electrochemical performance of sodium- and potassium-ion batteries, it is vital to grasp the inherent properties and electrochemical mechanisms of these materials. Herein, the state-of-the-art development and challenges of metal selenides are summarized and discussed. Meanwhile, the corresponding electrochemical mechanism and future development directions are also highlighted.

Ultrafast and ultrastable FeSe2embedded in nitrogen-doped carbon nanofibers anode for sodium-ion half/full batteries

Transition metal selenides are considered as promising anode materials for fast-charging sodium-ion batteries due to their high theoretical specific capacity. However, the low intrinsic conductivity, particle aggregation, and large volume expansion problems can severely inhibit the high-rate and long-cycle performance of the electrode. Herein, FeSe2nanoparticles embedded in nitrogen-doped carbon nanofibers (FeSe2@NCF) have been synthesized using the electrospinning and selenization process, which can alleviate the volume expansion and particle aggregation during the sodiation/desodiation and improve the electrical conductivity of the electrode. The FeSe2@NCF electrode delivers the outstanding specific capacity of 222.3 mAh g-1at a fast current density of 50 A g-1and 262.1 mAh g-1at 10 A g-1with the 87.8% capacity retention after 5000 cycles. Furthermore, the Na-ion full cells assembled with pre-sodiated FeSe2@NCF as anode and Na3V2(PO4)3/C as cathode exhibit the reversible specific capacity of 117.6 mAh g-1at 5 A g-1with the 84.3% capacity retention after 1000 cycles. This work provides a promising way for the conversion-based metal selenides for the applications as fast-charging sodium-ion battery anode.

A nanowire-assembled Co3S4/Cu2S@carbon binary metal sulfide hybrid as a sodium-ion battery anode displaying high capacity and recoverable rate-performance

A binary metal sulfide hybrid consisting of nanowire-assembled and polypyrrole-coated Co3S4/Cu2S spheres after nitrogen-doped carbon coating (Co3S4/Cu2S@NC) is developed as an anode, which displays a capacity exceeding 412.3 mA h g-1 after 550 cycles under 1.0 A g-1. Recoverable rate-performance and good temperature tolerance under 50 °C and -10 °C are achievable; a full cell delivers 339.5 mA h g-1, indicating promising potential for applications in various conditions.

In-situ synthesis of FeS/N, S co-doped carbon composite with electrolyte-electrode synergy for rapid sodium storage

Pyrrhotite (FeS) is extensively investigated as the anode for low-cost sodium-ion batteries (SIBs) due to their natural abundance and high theoretical capacity. However, it suffers from significant volume expansion and poor conductivity. These problems can be alleviated by promoting sodium-ion transport and introducing carbonaceous materials. Here, FeS decorated on N, S co-doped carbon (FeS/NC) is constructed through a facile and scalable strategy, which is the best of both worlds. Moreover, to give full play to the role of the optimized electrode, ether-based and ester-based electrolytes are used for matching. Reassuringly, the FeS/NC composite displays a reversible specific capacity of 387 mAh g^-1 after 1000 cycles at 5A g^-1 in dimethyl ether electrolyte. The even distribution of FeS nanoparticles on the ordered framework of carbon guarantees a fast electron/Na-ion transport channel, and the reaction kinetics can be further accelerated in the dimethyl ether (DME) electrolyte, ensuring the excellent rate capability and cycling performance of FeS/NC electrodes for sodium-ion storage. This finding not only provides a reference for the introduction of carbon via in-situ growth protocol, but also demonstrates the necessity for electrolyte-electrode synergy in realizing efficient sodium-ion storage.

In-situ fabrication of active interfaces towards FeSe as advanced performance anode for sodium-ion batteries

Transition metal selenides have gained enormous interest as anodes for sodium ion batteries (SIBs). Nonetheless, their large volume expansion causing poor rate and inferior cycle stability during Na⁺ insertion/extraction process hinders their further applications in SIBs. Herein, a confined-regulated interfacial engineering strategy towards the synthesis of FeSe microparticles coated by ultrathin nitrogen-doped carbon (NC) is demonstrated (FeSe@NC). The strong interfacial interaction between FeSeand NC endows FeSe@NC with fast electron/Na⁺ transport kinetics and outstanding structural stability, delivering unexceptionable rate capability (364 mAh/gat 10 A/g) and preeminent cycling durability (capacity retention of 100 % at 1 A/g over 1000 cycles). Furthermore, variousex situcharacterization techniques and density functional theory (DFT) calculations have been applied to demonstrate the Na⁺ storage mechanism of FeSe@NC. The assembled Na₃V₂(PO₄)₂F₃@rGO//FeSe@NC full cell also displays a high capacity of 241 mAh/gat 1 A/g with the capacity retention of nearly 100 % over 2000 cycles, and delivers a supreme energy density of 135 Wh kg^-1 and a topmost power density of 495 W kg^-1, manifesting the latent applications of FeSe@NC in the fast charging SIBs.