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Exploiting Zn metal-free anode materials would be an effective strategy to resolve the problems of Zn metal dendrites that severely hinder the development of Zn ion batteries (ZIBs). However, the study of Zn metalfree anode materials is still in their infancy, and more importantly, the low energy density severely limits their practical implementations. Herein, a novel (NH 4 ) 2 V 10 O 25 • 8H 2 O@Ti 3 C 2 T x (NHVO@Ti 3 C 2 T x ) film anode is proposed and investigated for constructing "rocking-chair" ZIBs. The NHVO@Ti 3 C 2 T x electrode shows a capacity of 514.7 mAh g −1 and presents low potential which is 0.59 V (vs Zn 2+ /Zn) at 0.1 A g −1 . The introduction of Ti 3 C 2 T x not only affords an interconnected conductive network, but also stabilizes the NHVO nanobelts structure for a long cycle life (84.2% retention at 5.0 A g −1 over 6000 cycles). As a proof-of-concept, a zinc metal-free full battery is successfully demonstrated, which delivers the highest capacity of 131.7 mAh g −1 (mass containing anodic and cathodic) and energy density of 97.1 Wh kg −1 compared to all reported aqueous "rocking-chair" ZIBs. Furthermore, a long cycling span of 6000 cycles is obtained with capacity retention reaching up to 92.1%, which is impressive. This work is expected to provide new moment toward V-based materials for "rocking-chair" ZIBs.

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Owing to several advantages of metallic sodium (Na), such as a relatively high theoretical capacity, low redox potential, wide availability, and low cost, Na metal batteries are being extensively studied, which are expected to play a major role in the fields of electric vehicles and grid-scale energy storage. Although considerable efforts have been devoted to utilizing MXene-based materials for suppressing Na dendrites, achieving a stable cycling of Na metal anodes remains extremely challenging due to, for example, the low Coulombic efficiency (CE) caused by the severe side reactions. Herein, a g-C3N4 layer was attached in situ on the Ti3C2 MXene surface, inducing a surface state reconstruction and thus forming a stable hetero-interphase with excellent sodiophilicity between the MXene and g-C3N4 to inhibit side reactions and guide uniform Na ion flux. The 3D construction can not only lower the local current density to facilitate uniform Na plating/stripping but also mitigate volume change to stabilize the electrolyte/electrode interphase. Thus, the 3D Ti3C2 MXene@g-C3N4 nanocomposite enables much enhanced average CEs (99.9% at 1 mA h cm–2, 0.5 mA cm–2) in asymmetric half cells, long-term stability (up to 700 h) for symmetric cells, and stable cycling (up to 800 cycles at 2 C), together with outstanding rate capability (up to 20 C), of full cells. The present study demonstrates an approach in developing practically high performance for Na metal anodes.

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