The development of manganese dioxide as the cathode for aqueous Zn-ion battery (ZIB) is limited by the rapid capacity fading and material dissolution. Here, a highly reversible aqueous ZIB using graphene scroll-coated α-MnO as the cathode is proposed. The graphene scroll is uniformly coated on the MnO nanowire with an average width of 5 nm, which increases the electrical conductivity of the MnO nanowire and relieves the dissolution of the cathode material during cycling. An energy density of 406.6 Wh kg (382.2 mA h g ) at 0.3 A g can be reached, which is the highest specific energy value among all the cathode materials for aqueous Zn-ion battery so far, and good long-term cycling stability with 94% capacity retention after 3000 cycles at 3 A g are achieved. Meanwhile, a two-step intercalation mechanism that Zn ions first insert into the layers and then the tunnels of MnO framework is proved by in situ X-ray diffraction, galvanostatic intermittent titration technique, and X-ray photoelectron spectroscopy characterizations. The graphene scroll-coated metallic oxide strategy can also bring intensive interests for other energy storage systems.

The aqueous zinc ion batteries (ZIBs) composed of inexpensive zinc anode and nontoxic aqueous electrolyte are attractive candidates for large-scale energy storage applications. However, their development is limited by cathode materials, which often deliver inferior rate capability and restricted cycle life. Herein, the VO 2 nanorods show significant electrochemical performance when used as an intercalation cathode for aqueous ZIBs. Specifically, the VO 2 nanorods display high initial capacity of 325.6 mAh g −1 at 0.05 A g −1 , good rate capability, and excellent cycling stability of 5000 cycles at 3.0 A g −1 . Furthermore, the VO 2 unit cell expands in a, b, and c directions sequentially during the discharge process and contracts back reversibly during the charge process, and the zinc storage mechanism is revealed to be a highly reversible single-phase reaction by operando techniques and corresponding qualitative analyses. Our work not only opens a new door to the practical application of VO 2 in ZIB systems but also broadens the horizon in understanding the electrochemical behavior of rechargeable ZIBs.

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NASICON-type materials are one of the most promising cathodes for sodium-ion batteries (SIBs) due to their stable structure and the three-dimensional framework for the migration of Na+. During the usage of SIBs, they should hold the ability to endure sudden changes in temperature and current density, which have a profound impact on battery life. However, little research focused on the reaction mechanism under the above situations. Here, the phase transformation processes of NASICON-type material, Na3V2(PO4)3, are investigated by applying high-resolution in situ X-ray diffraction and Raman coupled with electrochemical tests under different temperatures (273 and 293 K) and scan rates (0.5, 2, and 5 mV s–1). The results demonstrate that the phase evolution process is one-phase solid solution during the desodiation process rather than the traditionally two-phase reaction at a high scan rate or low temperature. An electrochemical phase diagram is also drawn based on thein situ results, which can be used to explain the asymmetric result. This work can help with understanding the phase evolution process of NASICON-type cathodes, as well as guiding the application of SIBs in various working conditions.

As cathode materials in lithium-ion batteries, layered vanadium oxides have been extensively studied and used in many aspects varying from industrial production to our daily life, due to their excellent physical property and gorgeous lithium storage performance. During lithiation/delithiation, layered vanadium oxides such as V 2 O 5 xerogel (with a bilayer structure), undergoes "lattice breathing" which leads to the deactivation of electrode materials and fast capacity fading, which limits its large-scale application. In this work, VO x is used as the cathode material of lithium-ion batteries to study the "lattice breathing" phenomenon. The phase evolution has been observed and studied via in situ method. The X-ray diffraction (XRD) patterns show typical (001) diffraction peaks characteristic of vanadium oxide xerogel structure and also confirm the good crystallinity. This compound with crystal parameters of a＝4.56 Å, b＝14.87 Å, c＝12.38 Å, α＝117.26°, β＝96.02°, γ＝ 81.86°, forms a triclinic structure. Results of scanning electron microscope (SEM) and transmission electron microscope (TEM) further verify the layered structure of VO x . The thermo gravimetric analysis (TGA) at air and nitrogen atmosphere shows that the carbon content of the sample is about 2.4 wt% and the water content is about 2.1%. As lithium-ion battery cathode the initial discharge capacity of the compound is about 136 mA•h/g at a current density of 100 mA/g, with a capacity retention of 92.6% after 50 cycles. To study the lithium storage mechanism of VO x , electrochemical discharge/charge processes are further investigated by in situ XRD. It is found that the lattice plane diffraction displays three different stages linked during the insertion and deinsertion of lithium ions, indicating three solid solution reactions. During discharge process, the three diffraction changes show continuous shifts to higher diffraction angles, demonstrating three different continuous contraction processes with the insertion of lithium ions. Nevertheless, the evolution of the (001) peak is swift during the beginning and the end of discharge, in contrast to the slow deviation of the intermediate process. In the whole process, the diffraction pattern displays periodic changes, confirming the reversibility of the reaction process. The corresponding calculations of d 001 during the discharge/charge process prove the notable discontinuity between these three stages. In addition, cycling experiments conducted at the higher and the lower temperature indicate that the electrochemical performance of this compound is highly sensitive to temperature.

Irreversible phase transition caused capacity fading has been considered as an obstacle for rechargeable batteries. An in-depth investigation of the irreversible phase transition is critical for understanding the reaction mechanism and developing advanced batteries. In this work, taking vanadium oxide and its alkali ion-stabilized intercalation compounds (A-V-O, A = Li, Na, K) as prototypes, utilizing operando characterizations, we discovered coupled discontinuous (interlayer)–continuous (intralayer) transitions in the stabilized multielectron intercalation cathodes. The highly ordered crystal of vanadium pentoxide irreversibly transfers to a disordered/amorphous structure after the first cycle, whereas A-V-O enables reversible discontinuous lattice transitions at the interlayer pathway for facilitating lithium diffusion. Among the A-V-O family, K-V-O, with the highest capacity retention, shows a coupled discontinuous–continuous transition, which exhibits a continuous transition and the minimum volume change at the V-O intralayer during lithium intercalation/deintercalation. These coupled discontinuous–continuous lattice transitions were captured for the first time in cathode materials. It implies that the suitable ion intercalation induced continuous intralayer transition inhibits the irreversible ion intercalation and phase transition.