“…As shown in Figure S2 (Supporting Information), “ a ” decreases and “ c ” increases with increasing Li content in the structure. The contraction of the “ a ” parameter is associated with a decrease in the TM─O bond length and an increment in TM oxidation states, which was further confirmed by XPS [ 41–43 ] (Figures S3–S5, Supporting Information). ; The average oxidation states in Na 1 Li 0 are Ni 2.0+ , Mn 2.0+ , and Fe 2.11+ .…”
Na‐ion batteries have recently emerged as a promising alternative to Li‐based batteries, driven by an ever‐growing demand for electricity storage systems. In the present work, we propose a cobalt‐free high‐capacity cathode for Na‐ion batteries, synthesized using a high‐entropy approach. The high‐entropy approach entails mixing more than five elements in a single phase; hence, obtaining the desired properties is a challenge since this involves the interplay between different elements. Here, instead of oxide, oxyfluoride is chosen to suppress oxygen loss during long‐term cycling. Supplement to this, Li was introduced in the composition to obtain high configurational entropy and Na vacant sites, thus stabilizing the crystal structure, accelerating the kinetics of intercalation/deintercalation, and improving the air stability of the material. With the optimization of the cathode composition, a reversible capacity of 109 mAh g−1 (2‐4 V) and 144 mAh g−1 (2‐4.3 V) is observed in the first few cycles, along with a significant improvement in stability during prolonged cycling. Furthermore, in‐situ and ex‐situ diffraction studies during charging/discharging reveal that the high‐entropy strategy is successful in suppressing the complex phase transition. The impressive outcomes of the present work strongly motivate the pursuit of the high‐entropy approach to develop efficient cathodes for Na‐ion batteries.This article is protected by copyright. All rights reserved
“…As shown in Figure S2 (Supporting Information), “ a ” decreases and “ c ” increases with increasing Li content in the structure. The contraction of the “ a ” parameter is associated with a decrease in the TM─O bond length and an increment in TM oxidation states, which was further confirmed by XPS [ 41–43 ] (Figures S3–S5, Supporting Information). ; The average oxidation states in Na 1 Li 0 are Ni 2.0+ , Mn 2.0+ , and Fe 2.11+ .…”
Na‐ion batteries have recently emerged as a promising alternative to Li‐based batteries, driven by an ever‐growing demand for electricity storage systems. In the present work, we propose a cobalt‐free high‐capacity cathode for Na‐ion batteries, synthesized using a high‐entropy approach. The high‐entropy approach entails mixing more than five elements in a single phase; hence, obtaining the desired properties is a challenge since this involves the interplay between different elements. Here, instead of oxide, oxyfluoride is chosen to suppress oxygen loss during long‐term cycling. Supplement to this, Li was introduced in the composition to obtain high configurational entropy and Na vacant sites, thus stabilizing the crystal structure, accelerating the kinetics of intercalation/deintercalation, and improving the air stability of the material. With the optimization of the cathode composition, a reversible capacity of 109 mAh g−1 (2‐4 V) and 144 mAh g−1 (2‐4.3 V) is observed in the first few cycles, along with a significant improvement in stability during prolonged cycling. Furthermore, in‐situ and ex‐situ diffraction studies during charging/discharging reveal that the high‐entropy strategy is successful in suppressing the complex phase transition. The impressive outcomes of the present work strongly motivate the pursuit of the high‐entropy approach to develop efficient cathodes for Na‐ion batteries.This article is protected by copyright. All rights reserved
“…These indicate the harmful effects of ester electrolytes on the electrochemical performance of NiSe. Compared to ester-based electrolytes, the use of ether-based electrolytes can significantly limit the side reactions during the operation of the electrodes. , Moreover, the strong interfacial adhesion between the NiSe-850°C-4 h electrode and the electrolyte also improves the electrochemical properties (Figure S8).…”
Ni-based selenide has flourished as one of the most competitive anode materials for sodium-ion batteries due to its low cost, wide source, and high theoretical specific capacity. As one of the members, NiSe microparticles with the sizes of 2.0−10.6 μm are synthesized with disused nickel foam fragments by a facile and rapid one-step selenization method, possessing a prominent rate capability of 304.3 mAh g −1 at 15 A g −1 and a remarkable lifespan with 291.7 mAh g −1 after 1600 cycles at 2 A g −1 . A Na 3 V 2 (PO 4 ) 2 F 3 @reduced graphene oxide//NiSe full cell also exhibits excellent sodium storage behavior and potential utility, achieving the largest power density of 1919.0 W Kg −1 , the highest energy density of 146.0 Wh kg −1 , and a capacity of 119.7 mAh g −1 after 600 cycles at 1 A g −1 accompanied by impressive Coulombic efficiency (>95%, except for the first two cycles). The reversible phase transition, proper use of the ether electrolyte, low electrochemical impedance, and favorable structural stability all synergistically contribute to the satisfactory electrochemical property of NiSe. This work effectively improves the preparation efficiency of NiSe, tendering a new synthetic route for the anode materials.
“…It is worth mentioning that the insertion capacity of most conversion-type TMC anodes is irreversible in the high-voltage region. ,− To investigate the origin of the reversible insertion capacity in FeSe-NS, density functional theory (DFT) calculations were performed. First, the Na + insertion site is optimized in the Fe 36 Se 36 supercell (3 × 3 × 2).…”
Section: Synthesis Physical Properties and Electrochemistrymentioning
confidence: 99%
“…As displayed in Figure 3d, the deconvoluted Fe 2p XPS spectra of FeSe-NS discharged to 0.5 and 0.01 V are almost identical, which means that Fe 2+ ↔ Fe 0 is inactive in the S14, where Fe nanoclusters are observed in the TEM images discharged to 0.5 and 0.01 V, and FeSe is not observed. 37,38 The ex situ XPS and TEM results reveal that the moment variation of FeSe-NS in the low-voltage region is independent of Fe 2+ ↔ Fe 0 . It is worth mentioning that the insertion capacity of most conversion-type TMC anodes is irreversible in the high-voltage region.…”
Transition-metal chalcogenides (TMCs) are recognized
as promising
sodium-ion battery anodes for their high theoretical specific capacity
and low sodium metal plating risk. Nevertheless, their unsatisfactory
rate capability along with unstable cyclability are bottlenecks to
their implementation, especially for fast-charging applications. Herein,
we report two-dimensional FeSe nanosheets (FeSe-NS) and monitor the
fast-charging degradation mechanism of FeSe-NS with in situ magnetometry
as the central role. Specifically, first, combining in situ XRD and
in situ magnetometry with theoretical calculations, we reshape the
sodium storage mechanism of FeSe-NS, namely, the “insertion–conversion–space
charge” sodium storage mechanism. Then, with the aid of in
situ magnetometry and ex situ characterizations, we reveal that the
sluggish kinetics and inferior reversibility of the conversion reaction
(Fe2+ ↔ Fe0) in the medium-voltage region
are barriers to the fast-charging performance of FeSe-NS. Therefore,
we propose that enhancing the kinetics and reversibility of the conversion
reaction is the key point for constructing a fast-charging TMC anode.
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