Controllably tailoring alloying anode materials to achieve fast charging and enhanced structural stability is crucial for sodium‐ion batteries with high rate and high capacity performance, yet remains a significant challenge owing to the huge volume change and sluggish sodiation kinetics. Here, a chemical tailoring tool is proposed and developed by atomically dispersing high‐capacity Ge metal into the rigid and conductive sulfide framework for controllable reconstruction of GeS bonds to synergistically realize high capacity and high rate performance for sodium storage. The integrated GeTiS3 material with stable Ti–S framework and weak GeS bonding delivers high specific capacities of 678 mA h g−1 at 0.3 C over 100 cycles and 209 mA h g−1 at 32 C over 10 000 cycles, outperforming most of the reported alloying type anode materials for sodium storage. Interestingly, in situ Raman, X‐ray diffraction (XRD), and ex situ transmission electron microscopy (TEM) characterizations reveal the formation of well‐dispersed NaxGe confined in the rigid Ti–S matrix with suppressed volume change after discharge. The synergistically coupled alloying‐conversion and surface‐dominated redox reactions with enhanced capacitive contribution and high reaction reversibility by a binding‐energy‐driven atomic scissors method would break new ground on designing a high‐rate and high‐capacity sodium‐ion batteries.
Strong intermolecular interactions in 2D organic molecular crystals arising from π–π stacking have been widely explored to achieve high thermal stability, high carrier mobility, and novel physical properties, which have already produced phenomenal progress. However, strong intermolecular interactions in 2D inorganic molecular crystals (2DIMCs) have rarely been investigated, severely limiting both the fundamental research in molecular physics and the potential applications of 2DIMCs for optoelectronics. Here, the effect of strong intermolecular interactions induced by unique short intermolecular Se–Se and P–Se contacts in 2D α-P4Se3 nanoflakes is reported. On the basis of theoretical calculations of the charge density distribution and an analysis of the thermal expansion and plastic–crystal transition, the physical picture of strong intermolecular interactions can be elucidated as a higher charge density between adjacent P4Se3 molecules, arising from an orderly and close packing of P4Se3 molecules. More importantly, encouraged by the strong intermolecular coupling, the in-plane mobility of α-P4Se3 nanoflakes is first calculated with a quantum nuclear tunneling model, and a competitive hole mobility of 0.4 cm2 V–1 s–1 is obtained. Our work sheds new light on the intermolecular interactions in 2D inorganic molecular crystals and is highly significant for promoting the development of molecular physics and optoelectronics.
Alloying-type metal sulfides with high theoretical capacities are promising anodes for sodium-ion batteries, but suffer from sluggish sodiation kinetics and huge volume expansion. Introducing intercalative motifs into alloyingtype metal sulfides is an efficient strategy to solve the above issues. Herein, robust intercalative InS motifs are grafted to high-capacity layered Bi 2 S 3 to form a cation-disordered (BiIn) 2 S 3 , synergistically realizing high-rate and large-capacity sodium storage. The InS motif with strong bonding serves as a space-confinement unit to buffer the volume expansion, maintaining superior structural stability. Moreover, the grafted high-metallicity Indium increases the bonding covalency of BiS, realizing controllable reconstruction of BiS bond during cycling to effectively prevent the migration and aggregation of atomic Bi. The novel (BiIn) 2 S 3 anode delivers a high capacity of 537 mAh g −1 at 0.4 C and a superior high-rate stability of 247 mAh g −1 at 40 C over 10000 cycles. Further in situ and ex situ characterizations reveal the in-depth reaction mechanism and the breakage and formation of reversible BiS bonds. The proposed space confinement and bonding covalency enhancement strategy via grafting intercalative motifs can be conducive to developing novel high-rate and large-capacity anodes.
Alloying‐type metals with high theoretical capacity are promising anode materials for sodium ion batteries, but suffer from large volume expansion and sluggish reaction kinetics. Dispersing alloying‐type metal into a buffer matrix with interfacial anionic covalent bonding is an effective method to solve the above issues. Here, this bifunctional structural unit is designed by incorporating high‐capacity Sb metal into a rigid CrSe framework for fast‐charging applications. The high‐capacity and high‐rate sodium storage can be synergistically realized in the bifunctional SbCrSe system, where the rigid CrSe framework endows the SbCrSe3 anodes with superior structural stability and improved intercalative redox pseudocapacitance. Moreover, the volume expansion of Sb during discharge can be buffered by the CrSe chain‐like matrix. The novel SbCrSe3 anode delivers a high charge capacity of 472 mAh g−1 at a current density of 0.4 C and retains ≈100% capacity at 60 C over 10 000 cycles. Further in situ and ex situ characterization reveal the multistep reaction mechanism, and the breakage and formation of reversible SbSe bonds during (dis)charge. The proposed bifunctional structural unit that combines alloying type anodes and intercalative anodes is expected to pave a new road for the development of high capacity and high rate anode materials.
Alloying-type bismuth with high volumetric capacity has emerged as a promising anode for sodium-ion batteries but suffers from large volume expansion and continuous pulverization. Herein, a coordination constraint strategy is proposed, that is, chemically confining atomic Bi in an intercalation host framework via reconstruction-favorable linear coordination bonds, enabling a novel quasi-topological intercalation mechanism. Specifically, micron-sized Bi 0.67 NbS 2 is synthesized, in which the Bi atom is linearly coordinated with two S atoms in the interlayer of NbS 2 . The robust Nb−S host framework provides fast ion/electron diffusion channels and buffers the volume expansion of Na + insertion, endowing Bi 0.67 NbS 2 with a lower energy barrier (0.141 vs. 0.504 eV of Bi). In situ and ex situ characterizations reveal that Bi atom alloys with Na + via a solid-solution process and is constrained by the reconstructed Bi−S bonds after dealloying, realizing complete recovery of crystalline Bi 0.67 NbS 2 phase to avoid the migration and aggregation of atomic Bi. Accordingly, the Bi 0.67 NbS 2 anode delivers a reversible capacity of 325 mAh g −1 at 1 C and an extraordinary ultrahigh-rate stability of 226 mAh g −1 at 100 C over 25 000 cycles. The proposed quasi-topological intercalation mechanism induced by coordinated mode modulation is expected to be be conducive to the practical electrode design for fast-charging batteries.
The increasing demand for fast-charging batteries to expedite the widespread adoption of electric vehicles calls for continual improvements of the anode materials to confer high energy and power densities. However, the fundamental limitations of the mainstream graphite and Li-metal anodes for fast-charging applications include the capacity fading and safety issues mainly caused by the Li plating, as well as the sluggish transport kinetics at large current densities. Recently, great attention has been paid to the emergence of large-capacity anodes by tailoring the bonding covalency to modulate the electronic structure and alter the insertion voltage for boosting fast-charging ability and suppressing metal plating. Development of new fast-charging materials by tailoring anionic activity allows us to better understand the key aspects of the bond covalency and band positioning for cation/anion doping and interface/ surface engineering. This Review provides an overview of the recent advances in the development of fast-charging anodes around tuning the bonding covalency by bimetal modulation; alloying hard and soft anions to alter the electronic structure and metal plating voltage; constructing anion-derived interfacial films; and surface substituting the ordered terminal groups. Furthermore, we highlight the practical limits of capacity fading at large current densities and describe potential strategies of anionic redox in phosphides and interfacial energy storage of conversion-type anodes to offer additional capacities. We also discuss the prospects for the commercial adoption of high-performance anodes containing various elements to rival the prevalent graphite or Li anodes for fast-charging applications.
High‐capacity alloying‐type anodes suffer poor rate capability due to their great volume expansion, while high‐rate intercalation‐type anodes are troubled with low theoretical capacity. Herein, a novel mechanism of alloying in the intercalative frameworks is proposed to confer both high‐capacity and high‐rate performances on anodes. Taking the indium‐vanadium oxide (IVO) as a typical system, alloying‐typed In is dispersed in the stable intercalative V 2 O 3 to form a solid solution. The alloying‐typed In element provides high lithium storage capacity, while the robust, Li‐conductive V−O frameworks effectively alleviate the volume expansion and aggregation of In. Benefiting from the above merits, the anode exhibits a high specific capacity of 1364 mA h g −1 at 1 A g −1 and an extraordinary cyclic performance of 814 mA h g −1 at 10 A g −1 after 600 cycles (124.9 mA h g −1 after 10 000 cycles at 50 A g −1 ). The superior electrochemical rate capability of (In,V) 2 O 3 solid solution anode rivals that of the reported alloying anode materials. This strategy can be extended for fabricating other alloying/intercalation hybrid anodes, such as (Sn,V)O 2 and (Sn,Ti)O 2 , which demonstrates the universality of confining alloying motifs in intercalative frameworks for rapid and high‐capacity lithium storage.
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