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High-entropy oxides (HEOs) have been considered revolutionary electrode materials due to their stable crystal structure and robust lithium storage properties. Here, we synthesize a spinel (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)Fe2O4 HEO in several seconds. This simple and effective method enhances the preparation efficiency by four orders of magnitude compared to that of the common sintering methods. As an anode material for Li-ion storage, to our knowledge, for the first time, the as-prepared HEO obtained a high reversible capacity of ∼812 mA h g−1 at 50 mA g−1 in the first cycle and an astonishing cycling stability over 650 cycles at 1 A g−1. Moreover, conversion and alloying reaction kinetics are identified during the lithiation and de-lithiation processes. Another interesting finding is that the spinel structure disappears after lithiation but recovers in the following de-lithiation stage, suggesting a homogeneous conversion reaction for the charge–discharge cycle. [ABSTRACT FROM AUTHOR]

Zinc (Zn) metal anodes of aqueous zinc‐ion batteries (AZIBs) have attracted significant attention due to their high theoretical capacities, low redox potentials, and low cost. However, uncontrollable dendrite formation and side reactions can result in limited reversible cycling and quick failure of the batteries. Herein, a polyvinylidene fluoride (PVDF)‐based protection layer (PVDF‐MXene) with high β‐phase content is built by the 3D printing method. The synergistic effect attributed to the 3D printing approach and MXene nanosheets contributes to phase transition of the PVDF polymer chains from α‐phase to β‐phase, improving the ferroelectric properties of the printed PVDF films. Such a protection layer can manipulate the concentration distribution of zinc ions and enable the uniform growth of zinc plates. As a result, symmetrical zinc batteries using such anodes (PVDF‐MXene‐Zn) exhibit reversible Zn plating/stripping with low voltage hysteresis at 1.0 mA cm−2, 1.0 mAh cm−2 for over 4200 h, and a high‐rate capability up to 10 mA cm−2. When assembled with MnO2 and activated carbon, the resulting Zn‐MnO2 battery and zinc‐ion capacitor exhibited significantly enhanced cycling stability. The proposed strategy in this study provides a novel strategy for the protection of the zinc anode, thus promoting the practical application of ZIBs. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) printing offers a unique approach to fabricating free-standing and complex structured electrodes for high-performance micro-supercapacitors (MSCs). Among the different 3D-printing techniques, fused deposition modeling (FDM) is a promising technique for upscaling due to its low price and maturity in industry. Herein, a conductive carbon black-based 3D-printable filament is designed to be used as a free-standing electrode after FDM printing, solvent activation, and MXene coating. The MXene layers could provide higher capacitances due to the pseudocapacitive charge storage mechanism and high metallic conductivity. In a three-electrode test system, the MXene decorated 3D-printed electrode (MXene@PTC-12 h) shows a capacitance of 30.2 mF cm−2 at a current density of 0.1 mA cm−2. With polyvinyl alcohol (PVA)/H2SO4 gel electrolyte, the MSCs based on the 3D printed electrodes provide a specific capacitance of 20.8 mF cm−2 at a current density of 0.1 mA cm−2 and a stable cycle life with 95% capacitance retention after 10 000 cycles. The method in this work offers a new way to prepare customized free-standing electrodes for high-performance energy storage devices. [ABSTRACT FROM AUTHOR]

Manganese dioxide (MnO2), as a cathode material for multivalent ion (such as Mg2+ and Al3+) storage, is investigated due to its high initial capacity. However, during multivalent ion insertion/extraction, the crystal structure of MnO2 partially collapses, leading to fast capacity decay in few charge/discharge cycles. Here, through pre-intercalating potassium-ion (K+) into δ-MnO2, we synthesize a potassium ion pre-intercalated MnO2, K0.21MnO2·0.31H2O (KMO), as a reliable cathode material for multivalent ion batteries. The as-prepared KMO exhibits a high reversible capacity of 185 mAh/g at 1 A/g, with considerable rate performance and improved cycling stability in 1 mol/L MgSO4 electrolyte. In addition, we observe that aluminum-ion (Al3+) can also insert into a KMO cathode. This work provides a valid method for modification of manganese-based oxides for aqueous multivalent ion batteries. [ABSTRACT FROM AUTHOR]

Vanadium‐based oxides with high theoretical specific capacities and open crystal structures are promising cathodes for aqueous zinc‐ion batteries (AZIBs). In this work, the confined synthesis can insert metal ions into the interlayer spacing of layered vanadium oxide nanobelts without changing the original morphology. Furthermore, we obtain a series of nanomaterials based on metal‐confined nanobelts, and describe the effect of interlayer spacing on the electrochemical performance. The electrochemical properties of the obtained Al2.65V6O13 ⋅ 2.07H2O as cathodes for AZIBs are remarkably improved with a high initial capacity of 571.7 mAh ⋅ g−1 at 1.0 A g−1. Even at a high current density of 5.0 A g−1, the initial capacity can still reach 205.7 mAh g−1, with a high capacity retention of 89.2 % after 2000 cycles. This study demonstrates that nanobelts confined with metal ions can significantly improve energy storage applications, revealing new avenues for enhancing the electrochemical performance of AZIBs. [ABSTRACT FROM AUTHOR]

Compared to the commonly applied metallic ion charge carriers (e.g., Li+ and Na+), batteries using nonmetallic charge carriers (e.g., H+ and NH4+) generally have much faster kinetics and high‐rate capability thanks to the small hydrated ionic sizes and nondiffusion control topochemistry. However, the hosts for nonmetallic charge carriers are still limited. In this work, it is suggested that mixed ionic–electronic conductors can serve as a promising host for NH4+ storage. Using hexagonal tungsten oxide (h‐WO3) as an example, it is shown that the existence of ionic conductive tunnels greatly promotes the high‐rate NH4+ storage. Specifically, a much higher capacity of 82 mAh g–1 at 1 A g–1 is achieved on h‐WO3, in sharp contrast to 14 mAh g–1 of monoclinic tungsten oxide (m‐WO3). In addition, unlike layered materials, the insertion and desertion of NH4+ ions are confined within the tunnels of the h‐WO3, which minimizes the damage to the crystal structure. This leads to outstanding stability of up to 200 000 cycles with 68% capacity retention at a high current of 20 A g–1. [ABSTRACT FROM AUTHOR]

Zinc‐ion batteries (ZIBs) have been regarded as one of the most promising aqueous energy storage devices due to their low‐cost, high capacity, and intrinsic safety. However, the relatively low Coulombic efficiency caused by the dendrite formation and side reactions greatly hinders the rejuvenation of ZIBs. Here, an utterly simple approach by pencil drawing is employed to improve the poor performance of normal Zn anode and hinders the formation of passivated byproduct as well as serious dendrite growth. Significantly, the functional graphite layer can not only act as ions buffer, but also guide the uniform nucleation of Zn2+ in graphite voids. With such synergy effect, the graphite‐coated Zn anode (Zn–G) displays low overpotential, high reversibility, and dendrite‐free durability compared with the pristine Zn. Consequently, a low voltage hysteresis of ≈28 mV can be achieved and maintained over 200 h. Furthermore, the Zn–G anode is paired with a V2O5·xH2O cathode to construct a rechargeable ZIB. As‐assembled device can output high energy/power density of 324.3 Wh kg−1/3269.8 W kg−1 (based on the active mass loading in cathode) together with a capacity retention of ≈84% over 1500 cycles at a current density of 5 A g−1. [ABSTRACT FROM AUTHOR]