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Rechargeable aqueous zinc-ion batteries hold great prospects in grid-level energy storage due to their virtues of good safety, low cost and eco-friendliness. However, the sluggish intercalation kinetics of divalent Zn2+ makes the exploration of a suitable Zn2+-host cathode being a formidable challenge. In this work, we unveil the crucial role of crystal water on boosting the Zn2+ intercalation kinetics of layered MoS2 host. The crystal water molecules could function as structural pillars to enlarge the interlayer distance of MoS2 and improve the surface hydrophilicity. Notably, a substantially-enhanced Zn2+ intercalation kinetics is realized by accelerating the charge-transfer transportation and Zn2+ diffusivity. Consequently, the hydrated MoS2 nanosheets enable efficacious Zn2+ insertion/extraction to achieve a high specific capacity of 182 mAh g−1 at 0.1 A g−1 and superior rate/cycling performance. The present study will enlighten the water implantation strategy to engineering hydrated cathode materials toward high-performance aqueous batteries.

Hierarchically two-dimensional (2D) heteroarchitecture with ultrafine MoS2 nanosheets vertically patterned on graphene is developed by using a facile solvothermal method. It is revealed that the strong interfacial interaction between acidic Mo precursors and graphene oxides allows for uniform and tight alignment of edge-oriented MoS2 nanosheets on planar graphene. The unique sheet-on-sheet architecture is of grand advantage in synergistically utilizing the highly conductive graphene and the electroactive MoS2, thus rendering boosted reaction kinetics and robust structural integrity for energy storage. Consequently, the heterostructured MoS2@graphene exhibits impressive Li/Na-ion storage properties, including high-capacity delivery and superior rate/cycling capability. The present study will provide a positive impetus on rational design of 2D metal sulfide/graphene composites as advanced electrode materials for high-efficient alkali–metal ion storage.

Rechargeable zinc-ion batteries based on Zn/MnO2 in neutral aqueous electrolytes are promising for grid-scale energy storage applications owing to their favorable merits of high safety, low cost and environmental benignity. However, MnO2 cathodes are subjected to the challenging issues of poor cyclability and low rate capability. Herein, we report a facile chemical method for the preparation of mesoporous MnO2 flower-like nanospheres with the layered framework stabilized by hydrated Zn2+ pillars. The MnO2 cathode could deliver a reversible specific capacity of 358 mA h g−1 at 0.3 A g−1 after 100 cycles, a high rate capacity of 124 mA h g−1 at 3.0 A g−1, and excellent operating stability over 2000 cycles. Structural and morphological investigations demonstrate an energy storage mechanism of co-insertion/extraction of H+ and Zn2+ accompanied by deposition/dissolution of zinc sulfate hydroxide hydrate flakes on the electrode surface. The superior electrochemical performance makes the zinc ion stabilized MnO2 promising for high capacity and long lifespan zinc-ion batteries.

Electrode materials with high tap density are important for their practical application to achieve high volumetric energy density Li-ion batteries. In this work, large-scale fabrication of microsized carbon/MnOx/carbon nanotube composites by a low-cost spray-drying method is reported. The carbon/MnOx/carbon nanotube is characteristic of microspherical morphology consisting of interconnected carbon nanotubes and nano-MnOx with an exterior carbon coating. The micropacking enables the composite to exhibit a tap density as high as 2.54 g cm−3. When evaluated as anode materials for Li-ion batteries, the high-tap-density carbon/MnOx/carbon nanotube electrode delivers a specific capacity of 927 mAh g−1 after 100 cycles, corresponding to an ultrahigh volumetric capacity of 2355 mAh cm−3. The carbon network also has dual-functions of excellent electrical conductivity and good mechanical elasticity for the MnOx to sustain superior rate and cycling properties. The scale-up production method provides a reliable practical avenue of fabricating high-tap-density metal-oxide materials for high-performance Li-ion batteries.

Rechargeable aqueous Zn-ion batteries have shown considerable potential for stationary grid-scale energy storage systems owing to their characteristics of low cost and non-pollution. Nevertheless, the development of high-performance cathode materials is still a formidable challenge. In this work, for the first time, we report a superior silver vanadate (β-AgVO3) cathode for Zn-ion batteries, and demonstrate the fundamental Zn2+ storage mechanism in detail. In sharp contrast to the previously-reported layered vandium-based materials, the β-AgVO3 cathode experiences an initial phase transition to form a layered Zn3V2O7(OH)2·2H2O through a displacement/reduction reaction of Zn2+/Ag+ in the first discharge process. The in situ generated Ag0 along with the residual Ag+ and structural water within the framework afford high electronic/ionic conductivity, thus enabling enhanced Zn2+ intercalation/deintercalation kinetics in the layered phase. As a consequence, the cathode can deliver remarkable rate performance (103 mAh g-1 at 5000 mA g-1) and long-term cycling stability (95 mAh g-1 after 1000 cycles at 2000 mA g-1). The present study offers a totally new insight into the exploration of non-layered-structured vandium-based cathodes for high performance Zn-ion batteries.

The rod-like manganese dioxide (MnO2)/acid-treated carbon nanotube (a-CNT) nanocomposites have been synthesized by a simple co-precipitation method. The MnO2 nanorod with the diameter of about 10 nm and length of 50∼120 nm is in-situ deposited on the surface of acid-treated CNT through the redox reaction of KMnO4 and Mn(CH3COO)2·4H2O. Results show that the electron transfer efficiency of the MnO2/a-CNT nanocomposites is greatly enhanced and results in a high electrical conductivity. The energy storage mechanism of as-prepared MnO2/a-CNT in mild aqueous electrolyte (ZnSO4 and MnSO4) is associated with the insertion/extraction of zinc ion into/from the tunnels of crystalline α-MnO2. The composites display both excellent storage properties with zinc ions (∼400 mAh·g−1 at 1 A·g−1) and reversibility at various current rates (∼100% coulombic efficiency after 500 charge/discharge cycles). The MnO2/a-CNT nanocomposites are rather promising cathode material for high performance rechargeable zinc ion batteries.

Manganese oxides represent a class of promising cathode materials for rechargeable aqueous zinc-ion batteries (ZIBs) due to their high energy density, safety, low cost, eco-friendliness and non-toxicity. However, manganese monooxide (MnO) is considered to be inactive for Zn2+ energy storage. Herein, for the first time, we demonstrate the possible application of commercial MnO microsized particles as cathodes for high performance ZIBs. It is interesting to note that electrochemical activation (or oxidation) is observed during the initial charging process, which leads to the formation of porous layered-type MnO2 nanosheets surrounding the MnO surface. As a result, the activated cathode could deliver a maximum specific capacity of 330 mAh g−1 in ZnSO4 aqueous electrolyte at a current density of 0.1 A g−1. In addition, the underlying energy storage mechanism is systematically investigated. The present work provides a new insight into the electrochemical activation strategy for developing advanced cathodes for high-performance zinc-ion batteries.

Formation and conversion mechanisms between single-crystal gamma-MnOOH and manganese oxides had investigated systematically. Without extra surfactant or template, α-MnO2 nanorods and prismatic single crystalline γ-MnOOH rods had been synthesized under hydrothermal treatment in this study. The formation and conversion mechanisms of prismatic γ-MnOOH rod were investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that the formation process includes three evolution stages: (1) formation of α-MnO2 nanorods whiskers; (2) transformation from α-MnO2 nanorods to prismatic γ-MnOOH rods by a dissolution-growth-recrystallization process; and (3) preferred growth on ( 1 1 1 ¯ ) crystal plane. In addition, β-MnO2, Mn2O3 or Mn3O4 rods could be obtained by calcination of the γ-MnOOH rods at different temperatures, which indicated that γ-MnOOH is an important precursor for preparing manganese oxides. The morphology and dimension of γ-MnOOH rods remained unchanged after converted to β-MnO2, Mn2O3 and Mn3O4.