The capability of high‐rate cycling and environmental benignity at less expensive defines the ingress of upcoming energy storage system. The urge of such system comes into the picture because today, the state‐of‐the‐art lithium technology is ineffectual to improve its rapid‐charging ability beyond a certain limit, in commercial scale. Here, we introduce reversible electrochemistry of Ca‐ion full cell in conjunction with inexpensive aqueous electrolyte, 1M aq. Ca(ClO4)2. In the full cell, carbon cloth, barium hexacyanoferrate (BaHCF) and meso‐carbon microbeads (MCMB) have been explored as the current collector, cathode and anode material, respectively. The full cell provides 40 mAh g‐1 capacity at 5C rate till 100 cycles. We believe, the investigation of this simple full cell at the early stage of Ca‐ion battery will pave a fast transition in the forthcoming energy storage systems.

The narrow electrochemical stability window (1.23 V) of an aqueous electrolyte hinders the practical realization of calcium-ion chemistries of high-energy-density and long-cycle-life batteries. Furthermore, developing an aqueous electrolyte that is low cost, is environmentally friendly, and has a wide voltage window is essential to designing safe, high-energy-density, and sustainable calcium-ion batteries. A calcium-based water-insalt (WISE) aqueous electrolyte surpasses the narrow stability window by offering a 2.12 V wide window by suppressing the hydrogen evolution at the anode and minimizing the overall water activity at the cathode. A comprehensive theoretical study predicts the preferential reduction of salt aggregates over water to form a passivation layer at the electrode−electrolyte interface and enhance the electrolyte stability window. Additionally, Raman spectroscopy reveals that the calcium ion coordination number, which is the number of nitrate ions surrounding the calcium ions in the aqueous electrolyte, gradually increases with an increase in the electrolyte concentration, leading to a gradual decrease in the hydration number of the calcium ions. A full cell in WISE was demonstrated to exhibit an excellent rate capability and cycling stability with negligible capacity loss (0.01 per cycle), maintaining 80% capacity retention over 1800 cycles with ∼99.99% Coulombic efficiency. The full cell provides an energy density of 232 Wh kg −1 at a power density of 69 W kg −1 and a current rate of 0.15 A g −1 . Even at a higher current rate of 5 A g −1 , the battery delivers an energy density of 182 Wh kg −1 (based on the active mass of the anode). This is one of the best performances to date of all previously reported full-cell aqueous calcium-ion batteries. A fundamental understanding of the storage mechanism and a electrode degradation study was achieved. This work suggests and expands new avenues for the practical realization of low-cost, safe, eco-friendly, and high-performance aqueous calcium-ion batteries for future large storage applications.

Direct Utilization of commercial sulfur as a cathode material is ideal for the bulk production of high-energy-density lithium−sulfur (Li−S) batteries. However, due to large ion-diffusion length, commercial sulfur suffers from low practical capacity. To achieve adequate capacity with long-term cyclability using the commercial sulfur-based cathodes, we introduce ultrathin lithium aluminate (LiAlO 2 ) nanoflakes as polysulfide immobilizers with excellent Li + ion conductivity. The ultrathin LiAlO 2 nanoflake-inlaid sulfur cathode exhibits high areal capacity with extremely stable cycling performance. At a current rate of 0.2C, our cathode delivered a high areal capacity of 4.86 mA h cm −2 during the first cycle and retains 4.75 mA h cm −2 after 100 cycles. At a high current rate of 3C, the cathode retains the areal capacity of 2.52 mA h cm −2 after 500 cycles, with an extremely low capacity decay rate of 0.02% per cycle. In situ Raman spectroscopy studies coupled with the chronoamperometry technique reveal that LiAlO 2 nanoflakes catalyze the redox kinetics in the Li−S batteries. This work shows a promising strategy to directly utilize commercial sulfur powder in practical Li−S batteries.

More than three times higher bulk density, easy to handle in air, and high abundance on earth crust make magnesium metal a desirable element in battery application. Several efforts have been attempted to construct the rechargeable magnesium‐ion battery, unfortunately none of them are successful to a limit. Here, a new generation of vanadium oxide linked with ammonium ions is considered an active cathode for magnesium ion insertion. The Zr doped‐NH4V4O10 (Zr‐NVO) nanorod exhibits an initial discharge capacity of 328 mAh g−1 at 40 mA g−1 current density with negligible capacity fading till 150 cycles. The estimated Mg2+ diffusivity in such cathode is found to be in the range of 10−11 to 10−12 cm2 s−1, demonstrating a pronounced Mg‐ion mobility in Zr‐NVO cathode. In addition, a detailed mechanistic study is performed at different states of charge using XRD, XPS and in‐situ XANES analysis. In conclusion, to achieve the ultimate goal of such study, a full‐cell is assembled and evaluated by coupling tin anode with magnesiated Zr‐NVO cathode. The cell has been cycled for a limited number of cycles and the reason behind the limited cycling behaviour is discussed and offers us a pathway to a resolution of the problem for rechargeable magnesium‐ion battery development in the near future.

Despite higher conductivity and larger d‐spacing (0.65 nm) of MoSe2 compare to its analogous MoS2 and higher theoretical capacity (∼422 mA h g−1) compare to commercially available graphite, it experiences high volume expansion, sheets agglomeration during cycling, which limits their capacities and high rate application. Herein, we have shown interest in MoSe2 materials as analogous to MoS2 anode and grown MoSe2 nanosheets on the nitrogen‐doped carbon followed by covered with reduced graphene oxides sheets (NC@MoSe2@rGO) composite through a simple solvothermal synthesis followed by annealing treatment. The porous NC compound could bring several advantages like, it can reserve a sufficient amount of electrolyte for easy access of Na‐ion diffusion. Increasing the conductivity by introducing the doping of nitrogen on the NC structure and simultaneously rGO can reduce the volume expansion of MoSe2 during the cyclic performance. Ex‐situ XANES and XPS technique explored the sodiation mechanism of the NC@MoSe2@rGO composite. It has been found the irreversible conversion of MoSe2 after 1st cycle by converting the discharged products of Mo and Na2Se. The NC@MoSe2@rGO anode is connected with electrolyte and a high potential Na3V2O2(PO4)2F (NVOPF) to acquire potential applications′ approval cathode material. The full‐cell delivers a voltage of operation at 2.1 V with high specific capacity of ∼176 mA h g−1 (current rate of 0.05 A g−1) with an energy density of ∼369.6 W h/kg anode at 20 °C.