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The development of high‐energy and long‐lifespan NASICON‐type cathode materials for sodium‐ion batteries has always been a research hotspot but a daunting challenge. Although Na4MnCr(PO4)3 has emerged as one of the most promising high‐energy‐density cathode materials owing to its three‐electron reactions, it still suffers from serious structural distortion upon repetitive charge/discharge processes caused by the Jahn‐Teller active Mn3+. Herein, the selective substitution of Cr by Zr in Na4MnCr(PO4)3 was explored to enhance the structural stability, due to the pinning effect of Zr ions and the ≈2.9‐electron reactions, as‐prepared Na3.9MnCr0.9Zr0.1(PO4)3/C delivers a high capacity retention of 85.94% over 500 cycles at 5 C and an ultrahigh capacity of 156.4 mAh g−1 at 0.1 C, enabling the stable energy output as high as 555.2 Wh kg−1. Moreover, during the whole charge/discharge process, a small volume change of only 6.7% was verified by in situ X‐ray diffraction, and the reversible reactions of Cr3+/Cr4+, Mn3+/Mn4+, and Mn2+/Mn3+ redox couples were identified via ex situ X‐ray photoelectron spectroscopy analyses. Galvanostatic intermittent titration technique tests and density functional theory calculations further demonstrated the fast reaction kinetics of the Na3.9MnCr0.9Zr0.1(PO4)3/C electrode. This work offers new opportunities for designing high‐energy and high‐stability NASICON cathodes by ion doping. [ABSTRACT FROM AUTHOR]

Oxygen vacancies (Vo) as a common structural defect play a critical and fascinating role in regulating the physico‐chemical properties of metal oxides. For the layered transitional‐metal oxides (LTMOs) used as the popular cathodes for lithium/sodium‐ion batteries (LIBs or SIBs), Vo can modulate their intrinsic multi‐scale structural properties, thereby significantly affecting the final electrochemical performance. In this concept article, we summarize the fundamental structural regulation mechanisms of Vo in lithium/sodium‐based LTMOs in terms of ligand, local, and crystal structures. Finally, the current challenges and outlooks of Vo engineering are highlighted for future development of high‐performance layered oxide cathode materials. [ABSTRACT FROM AUTHOR]

Anionic redox chemistry has aroused increasing attention in sodium‐ion batteries (SIBs) by virtue of the appealing additional capacity. However, up to now, anionic redox reaction has not been reported in the mainstream phosphate cathodes for SIBs. Herein, the ultrathin VOPO4 nanosheets are fabricated as promising cathodes for SIBs, where the oxygen redox reaction is first activated accompanied by reversible ClO4− (from the electrolyte) insertion/extraction. As a result, the VOPO4 cathode harvests a record‐high capacity (168 mAh g−1 at 0.1 C) among its counterparts ever reported. Moreover, the ClO4− insertion efficiently expands the interlayer spacing of VOPO4 and accelerates the ion diffusion, enabling an unprecedentedly high rate performance (69 mAh g−1 at 30 C). Via systematic ex situ characterizations and theoretical computations, the anionic redox chemistry and charge storage mechanism upon cycling are thoroughly elucidated. This study opens up a new avenue toward high‐energy phosphate cathodes for SIBs by triggering anionic redox reactions. [ABSTRACT FROM AUTHOR]

Layered V2O5 is a star cathode material of rechargeable aqueous zinc‐based batteries (RAZBs) owing to the rich redox chemistry of vanadium, which commonly exhibits the 2D ion‐diffusion mechanism through Zn2+ (de)intercalation at edge sites but is plagued by the inert basal planes. Here, hierarchically porous V2O5 nanosheets vertically grown on carbon cloth (V2O5/C) are innovatively prepared, where the porous structure with lattice defects successfully unlocks the V2O5 basal plane to provide additional ion‐diffusion channels and abundant active sites. Thus, highly efficient and ultrafast 3D Li+/Zn2+ co‐insertion/extraction behaviors along both the c‐axis and ab plane of V2O5 are realized for the first time in the formulated 15 m LiTFSI + 1 m Zn(CF3SO3)2 aqueous electrolyte, as elucidated by systematic ex situ analyses, multiple electrochemical measurements, and theoretical computations. As a result, the porous V2O5/C electrode delivers an exceptional high‐rate capability (up to 100 A g−1) and an ultralong cycling durability (15 000 cycles) in RAZBs. Finally, quasi‐solid‐state wearable rechargeable zinc batteries employing the porous V2O5/C cathode demonstrate respectable performance even under severe deformations and low temperatures. This work achieves a conceptual breakthrough represented by an upgrading of the traditional 2D ion transportation in layered cathodes to the more facile 3D diffusion for designing high‐performance battery electrochemistry. [ABSTRACT FROM AUTHOR]

Manganese‐rich layered oxide cathodes of sodium‐ion batteries (SIBs) are extremely promising for large‐scale energy storage owing to their high capacities and cost effectiveness, while the Jahn–Teller (J–T) distortion and low operating potential of Mn redox largely hinder their practical applications. Herein, we reveal that annealing in argon rather than conventional air is a universal strategy to comprehensively upgrade the Na‐storage performance of Mn‐based oxide cathodes. Bulk oxygen vacancies are introduced via this method, leading to reduced Mn valence, lowered Mn 3d‐orbital energy level, and formation of the new‐concept Mn domains. As a result, the energy density of the model P2‐Na0.75Mg0.25Mn0.75O2 cathode increases by ≈50 % benefiting from the improved specific capacity and operating potential of Mn redox. The Mn domains can disrupt the cooperative J–T distortion, greatly promoting the cycling stability. This exciting finding opens a new avenue towards high‐performance Mn‐based oxide cathodes for SIBs. [ABSTRACT FROM AUTHOR]

Initiating anionic redox chemistry in layered sodium oxide cathodes is a prevalent method to break the capacity limit set by traditional transition metal redox. However, realizing the "win‐win" scenario of high capacity and high cycling stability is still challenging due to the high‐voltage structural distortion and irreversible oxygen loss. Herein, a Mn activation mechanism is unveiled in a novel P2‐Na0.80Li0.08Ni0.22Mn0.67O2 cathode. By elevating the charge cut‐off voltage to 4.3 V, anionic redox is successfully triggered and partial oxygen loss enables the reduction of Mn upon discharge, thus activating more Mn3+/Mn4+ redox reactions in the following cycles and maintaining the total capacity almost unchanged. In situ X‐ray diffraction reveals a complete solid‐solution reaction with an ultralow volume change of 1.04% upon cycling. Consequently, the P2‐Na0.80Li0.08Ni0.22Mn0.67O2 cathode simultaneously accomplishes a high discharge capacity (134.8 mAh g−1 at 0.1 C) and an unexpectedly long cycling life (capacity retention of 91.5% and 85.2% after 500 and 1000 cycles at 10 C, respectively). Via systematic ex situ characterizations and theoretical computations, the charge compensation mechanism upon Na+ insertion/extraction is elucidated. This work broadens the horizons of current oxygen redox chemistry and provides a new path to design high‐performance layered oxide cathode materials for sodium‐ion batteries. [ABSTRACT FROM AUTHOR]

Aqueous Zn‐ion batteries (AZIBs) are considered as promising large‐scale energy storage devices due to their high safety and low cost. Transition metal dichalcogenides (TMDs) as the potential aqueous Zn‐storage cathode materials are under the research spotlight because of their facile 2D ion‐transport channels and weak electrostatic interactions with Zn2+. In this concept article, we summarize the intrinsic structural features and aqueous Zn‐storage mechanisms of the TMDs‐based electrodes. More significantly, the latest design concepts of TMDs materials for high‐performance AZIBs are discussed in detail from three aspects of interlayer expansion engineering, phase transition engineering, and structure defects engineering. Finally, the current challenges facing TMDs cathodes and possible remedies are outlined for future developments towards efficient, rapid, and stable aqueous Zn‐ion storage. [ABSTRACT FROM AUTHOR]

Layered oxide cathodes for sodium‐ion batteries (SIBs) have drawn increasing attention owing to their fascinating additional capacity contributed by oxygen‐redox chemistry. Unfortunately, excessive oxygen redox incurs an irreversible oxygen release, deteriorating the cyclic stability and compromising the advantage of additional capacity. Significant efforts have been made so far to stabilize lattice oxygen, but the potential advantages associated with oxygen loss have been ignored. Herein, a complementary Mn and O redox mechanism is first revealed in a novel P2‐Na0.75Ca0.04[Li0.1Ni0.2Mn0.67]O2 cathode. The partial oxygen release activates more Mn3+/Mn4+ redox capacities upon cycling, which effectively compensate the capacity loss from O2‐/On‐ redox and thus enable an ultra‐stable cycling performance (capacity retentions of 102.1% and 95.2% over 100 and 200 cycles at 5 C, respectively). The fast Na+ diffusion kinetics of the cathode also ensure an exceptional rate capability (133.1 and 68.8 mAh g‐1 at 0.1 and 20 C, respectively). The electrode crystal/electronic structure evolution and charge compensation mechanism upon sodiation/desodiation have been elucidated via systematic operando measurements and theoretical computations. The complementary chemistry is a universal principle that stabilizes the Na‐storage behaviors of Mn‐based oxide cathodes, providing new opportunities for anionic redox to boost the energy density and cycling life of SIBs simultaneously. [ABSTRACT FROM AUTHOR]

Layered VS2 holds great potential as a cathode material for aqueous Zn‐ion batteries owing to its large interlayer spacing, high electrical conductivity, and the rich redox chemistry of vanadium. Nevertheless, structural instability during charge/discharge severely hinders the further development of VS2 cathodes. Herein, distinctive hierarchitectures of 1T‐VS2 nanospheres assembled by nanosheets, which feature abundant active sites, superior electron/ion transport property, and robust structure, are developed. More intriguingly, Zn2+ "pillars" residing in VS2 interlayers, achieved by controlling the charge cut‐off voltage are first proven to reinforce the layered structure of VS2 upon repeated Zn2+ insertion/extraction, redefining the commonly perceived "dead Zn2+". Hence, exceptional rate performance (212.9 and 102.1 mA h g−1 at 0.1 and 5 A g−1, respectively) and ultralong cycling life (86.7% capacity retention over 2000 cycles at 2 A g−1) are obtained. The rapid and highly reversible Zn‐ion (de) intercalation behavior within the VS2 nanospheres is verified by first‐principles computations and multiple ex‐situ characterizations. Finally, the flexible quasi‐solid‐state rechargeable Zn battery employing the tailored VS2 cathode demonstrates great application prospects in wearable devices. This work provides new perspectives for prolonging the lifespan of layered Zn‐storage materials by simply modulating the charge/discharge processes. [ABSTRACT FROM AUTHOR]

Triggering the anionic redox chemistry in layered oxide cathodes has emerged as a paradigmatic approach to efficaciously boost the energy density of sodium‐ion batteries. However, their practical applications are still plagued by irreversible lattice oxygen release and deleterious structure distortion. Herein, a novel P2‐Na0.76Ca0.05[Ni0.23□0.08Mn0.69]O2 cathode material featuring joint cationic and anionic redox activities, where native vacancies are produced in the transition‐metal (TM) layers and Ca ions are riveted in the Na layers, is developed. Random vacancies in the TM sites induce the emergence of nonbonding O 2p orbitals to activate anionic redox, which is confirmed by systematic electrochemical measurements, ex situ X‐ray photoelectron spectroscopy, in situ X‐ray diffraction, and density functional theory computations. Benefiting from the pinned Ca ions in the Na sites, a robust layered structure with the suppressed P2‐O2 phase transition and enhanced anionic redox reversibility upon charge/discharge is achieved. Therefore, the electrode displays exceptional rate capability (153.9 mA h g−1 at 0.1 C with 74.6 mA h g−1 at 20 C) and improved cycling life (87.1% capacity retention at 0.1 C after 50 cycles). This study provides new opportunities for designing high‐energy‐density and high‐stability layered sodium oxide cathodes by tuning local chemical environments. [ABSTRACT FROM AUTHOR]

Aqueous Zn‐storage behaviors of MoS2‐based cathodes mainly rely on the ion‐(de)intercalation at edge sites but are limited by the inactive basal plane. Herein, an in‐situ molecular engineering strategy in terms of structure defects manufacturing and O‐doping is proposed for MoS2 (designated as D‐MoS2‐O) to unlock the inert basal plane, expand the interlayer spacing (from 6.2 to 9.6 Å), and produce abundant 1T‐phase. The tailored D‐MoS2‐O with excellent hydrophilicity and high conductivity allows the 3D Zn2+ transport along both the ab plane and c‐axis, thus achieving the exceptional high rate capability. Zn2+ diffusion through the basal plane is verified by DFT computations. As a proof of concept, the wearable quasi‐solid‐state rechargeable Zn battery employing the D‐MoS2‐O cathode operates stably even under severe bending conditions, showing great application prospects. This work opens a new window for designing high‐performance layered cathode materials for aqueous Zn‐ion batteries. [ABSTRACT FROM AUTHOR]

We demonstrate that the capacity decay and voltage drop issues of the Li3V2(PO4)3 cathode are significantly addressed by using a concentrated aqueous electrolyte based on Zn and Li salts. The resultant aqueous Zn//Li3V2(PO4)3 battery achieves a high output voltage of 1.75 V and a long lifespan with 82.3% capacity retention over 2000 cycles. Joint structural and spectroscopic characterizations reveal that this battery operates through Li+ (de)intercalation into the cathode along with Zn2+ plating/stripping at the anode. [ABSTRACT FROM AUTHOR]

Layered transition metal oxides (TMOs) are appealing cathode candidates for sodium‐ion batteries (SIBs) by virtue of their facile 2D Na+ diffusion paths and high theoretical capacities but suffer from poor cycling stability. Herein, taking P2‐type Na2/3Ni1/3Mn2/3O2 as an example, it is demonstrated that the hierarchical engineering of porous nanofibers assembled by nanoparticles can effectively boost the reaction kinetics and stabilize the structure. The P2‐Na2/3Ni1/3Mn2/3O2 nanofibers exhibit exceptional rate capability (166.7 mA h g−1 at 0.1 C with 73.4 mA h g−1 at 20 C) and significantly improved cycle life (≈81% capacity retention after 500 cycles) as cathode materials for SIBs. The highly reversible structure evolution and Ni/Mn valence change during sodium insertion/extraction are verified by in operando X‐ray diffraction and ex situ X‐ray photoelectron spectroscopy, respectively. The facilitated electrode process kinetics are demonstrated by an additional study using the electrochemical measurements and density functional theory computations. More impressively, the prototype Na‐ion full battery built with a Na2/3Ni1/3Mn2/3O2 nanofibers cathode and hard carbon anode delivers a promising energy density of 212.5 Wh kg−1. The concept of designing a fibrous framework composed of small nanograins offers a new and generally applicable strategy for enhancing the Na‐storage performance of layered TMO cathode materials. [ABSTRACT FROM AUTHOR]

Na 0.44 MnO 2 has drawn great attention as a promising cathode material for sodium-ion batteries (SIBs) owing to its unique tunnel-type structure that allows facile Na+ insertion/extraction. We here report the controllable preparation of Na 0.44 MnO 2 nanowires (NMO NWs) through electrospinning and annealing processes and their SIB cathode application to boost the ionic diffusion dynamics and cyclic stability. The well-shaped NMO NWs with diameters of 50–200 nm effectively favour the easy access to electrolyte, facilitate the electrons/Na+ ions transportation, and retard the active materials fracture/pulverization upon prolonged cycling. Consequently, fascinating electrochemical performance in terms of high-rate capability (120.4 mAh g−1 at 0.1C; 31.7 mAh g−1 at 50C) and unprecedentedly long cycling life (89% capacity retention after 3300 cycles) is achieved. Furthermore, the underlying Na-ion storage mechanism and migration kinetics have been pioneeringly elucidated by a combination study of ex-situ structure/valence analyses and first-principles computations. The pseudocapacitive behaviour of NMO NWs electrode is also identified to benefit the high-rate performance. Finally, a pouch-type sodium-ion full battery assembled by the NMO NWs cathode and hard carbon nanofibers anode delivers an admirable energy density of 165.3 Wh kg−1 and an outstanding capacity retention of 88.57% over 200 cycles, showing great prospects. Well-shaped Na 0.44 MnO 2 nanowires featuring diameters in the range of 50–200 nm enable highly reversible Na+ insertion/extraction through the tunnel-type structure with low ionic diffusion energy barrier and proper pseudocapacitive contribution, demonstrating outstanding high-rate capability and unprecedentedly long cycling life as a cathode for sodium-ion batteries. Image 1 • Well-shaped Na 0.44 MnO 2 nanowires were prepared via a controllable and green electrospinning-annealing route. • Na 0.44 MnO 2 nanowires cathode enabled outstanding rate capability and unprecedented cycling stability in Na-ion batteries. • Highly reversible Na+ (de)insertion with low diffusion barrier and proper pseudocapacitive contribution was demonstrated. • A high-energy and long-life pouch-type Na-ion full battery was rationally constructed. [ABSTRACT FROM AUTHOR]

Abstract: Maricite NaFePO4 nanodots with minimized sizes (≈1.6 nm) uniformly embedded in porous N‐doped carbon nanofibers (designated as NaFePO4@C) are first prepared by electrospinning for maximized Na‐storage performance. The obtained flexible NaFePO4@C fiber membrane adherent on aluminum foil is directly used as binder‐free cathode for sodium‐ion batteries, revealing that the ultrasmall nanosize effect as well as a high‐potential desodiation process can transform the generally perceived electrochemically inactive maricite NaFePO4 into a highly active amorphous phase; meanwhile, remarkable electrochemical performance in terms of high reversible capacity (145 mA h g−1 at 0.2 C), high rate capability (61 mA h g−1 at 50 C), and unprecedentedly high cyclic stability (≈89% capacity retention over 6300 cycles) is achieved. Furthermore, the soft package Na‐ion full battery constructed by the NaFePO4@C nanofibers cathode and the pure carbon nanofibers anode displays a promising energy density of 168.1 Wh kg−1 and a notable capacity retention of 87% after 200 cycles. The distinctive 3D network structure of very fine NaFePO4 nanoparticles homogeneously encapsulated in interconnected porous N‐doped carbon nanofibers, can effectively improve the active materials' utilization rate, facilitate the electrons/Na+ ions transport, and strengthen the electrode stability upon prolonged cycling, leading to the fascinating Na‐storage performance. [ABSTRACT FROM AUTHOR]

NaVPO4F has received a great deal of attention as cathode material for Na-ion batteries due to its high theoretical capacity (143 mA h g−1), high voltage platform, and structural stability. Novel NaVPO4F/C nanofibers are successfully prepared via a feasible electrospinning method and subsequent heat treatment as self-standing cathode for Na-ion batteries. Based on the morphological and microstructural characterization, it can be seen that the NaVPO4F/C nanofibers are smooth and continuous with NaVPO4F nanoparticles (≈6 nm) embedded in porous carbon matrix. For Na-storage, this electrode exhibits extraordinary electrochemical performance: a high capacity (126.3 mA h g−1 at 1 C), a superior rate capability (61.2 mA h g−1 at 50 C), and ultralong cyclability (96.5% capacity retention after 1000 cycles at 2 C). 1D NaVPO4F/C nanofibers that interlink into 3D conductive network improve the conductivity of NaVPO4F, and effectively restrain the aggregation of NaVPO4F particles during charge/discharge process, leading to the high performance. [ABSTRACT FROM AUTHOR]

In this paper, we report the synthesis of graphene-like MoS 2 /graphene hybrid by a facile lithium-assisted sonication method and its cathode application for rechargeable Mg batteries. Instrumental analyses elucidate that the composite displays a three-dimensional (3D) porous architecture constructed by exfoliated single or few MoS 2 layers, and some graphene is intercalated in the MoS 2 gallery with an enlarged interlayer spacing from 0.62 to 0.98 nm. The obtained MoS 2 /graphene hybrid exhibits high electrochemical performance with a remarkable capacity (115.9 mA h g −1 ) and good cyclic stability (82.5 mA h g −1 after 50 cycles). This is owing to the synergistic effect between the graphene-like MoS 2 and the highly conductive graphene, which can effectively facilitate the Mg 2+ ions diffusion and electrons transfer, provide abundant active sites for Mg 2+ intercalation, and prevent structural collapse upon prolonged cycling. [ABSTRACT FROM AUTHOR]

In this paper, the synthesis of ultrasmall Na2FePO4F nanoparticles (≈3.8 nm) delicately embedded in porous N‐doped carbon nanofibers (denoted as Na2FePO4F@C) by electrospinning is reported. The as‐prepared Na2FePO4F@C fiber film tightly adherent on aluminum foil features great flexibility and is directly used as binder‐free cathode for sodium‐ion batteries, exhibiting admirable electrochemical performance with high reversible capacity (117.8 mAh g−1 at 0.1 C), outstanding rate capability (46.4 mAh g−1 at 20 C), and unprecedentedly high cyclic stability (85% capacity retention after 2000 cycles). The reaction kinetics and mechanism are explored by a combination study of cyclic voltammetry, ex situ structure/valence analyses, and first‐principles computations, revealing the highly reversible phase transformation of Na2FeIIPO4F ↔ NaFeIIIPO4F, the facilitated Na+ diffusion dynamics with low energy barriers, and the desirable pseudocapacitive behavior for fast charge storage. Pouch‐type Na‐ion full batteries are also assembled employing the Na2FePO4F@C nanofibers cathode and the carbon nanofibers anode, demonstrating a promising energy density of 135.8 Wh kg−1 and a high capacity retention of 84.5% over 200 cycles. The distinctive network architecture of ultrafine active materials encapsulated into interlinked carbon nanofibers offers an ideal platform for enhancing the electrochemical reactivity, electronic/ionic transmittability, and structural stability of Na‐storage electrodes. [ABSTRACT FROM AUTHOR]

Rechargeable aqueous zinc batteries have gained considerable attention for large‐scale energy storage systems because of their low cost and high safety, but they suffer from limitations in cycling stability and energy density with advanced cathode materials. Here, a high‐performance V5O12·6H2O (VOH) nanobelt cathode uniformly located on a stainless‐steel substrate via a facile electrodeposition technique is reported. We show that the hydrated layered VOH cathode enables highly reversible and ultrafast Zn2+ cation (de)intercalation processes, as confirmed by various electrochemical, X‐ray diffraction, X‐ray photoelectron spectroscopy, and transmission electron microscopy analyses. It is demonstrated that the binder‐free VOH cathode can deliver a discharge capacity of 354.8 mAh g−1 at 0.5 A g−1 with a high initial Coulombic efficiency of 99.5%, a high energy density of 194 Wh kg−1 at 2100 W kg−1, and a long cycle life with a capacity retention of 94% over 1000 cycles. In addition, a flexible quasi‐solid‐state Zn–VOH battery is constructed, achieving a reversible capacity of ≈300 mAh g−1 with a capacity retention of 96% after 50 cycles and displaying excellent electrochemical behaviors under different bending states. This work sheds light on the development of rechargeable aqueous zinc batteries for stationary grid storage applications or flexible energy storage devices. V5O12·6H2O nanobelts self‐supported on a stainless‐steel substrate are prepared by electrodeposition and applied as a binder‐free cathode for rechargeable aqueous zinc batteries. The V5O12·6H2O cathode with a large layered structure (≈1.18 nm) enables highly reversible Zn2+ (de)intercalation, and displays a high energy density (194 Wh kg‐1 at 2100 W kg‐1) and a long cycling life (94% retention after 1000 cycles). [ABSTRACT FROM AUTHOR]