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Orthorhombic crystal structure of the V₃O₇·H₂O material has large interlayer spacing with an open tunnel, making it promising as an intercalation-based cathode for aqueous zinc-ion batteries. However, structural degradation and dissolution cause quick capacity fading for V₃O₇·H₂O. We addressed this issue via a dual modification of the V₃O₇·H₂O material by pre-intercalation with Ag(I) inside the layers (henceforth will be mentioned as AgₓV₃O₇·H₂O) and simultaneous in situ composite formation with reduced graphene oxide (rGO). Computationally, we showed that Ag(I) pre-intercalation in V₃O₇ facilitates the Zn²⁺ intercalation process by thermodynamically stabilizing the material with an intercalation energy of −34.3 eV. The AgₓV₃O₇·H₂O cathode showed ∼1.44-fold improved capacity (270 mA h g–¹) with much improved rate capability, over the pristine V₃O₇·H₂O. The specific capacity and cycle stability was further significantly improved in the graphene constructed conductive flexible architecture with hydrothermally assisted self-assembled packing of several intertwined AgₓV₃O₇·H₂O microbelt mats with rGO core (AgₓV₃O₇·H₂O@rGO). The AgₓV₃O₇·H₂O@rGO cathode enabled a reversible Zn²⁺ insertion/de-insertion process during charge/discharge (as observed in ex situ XRD study) and a significantly decreased (>27 times) charge transfer resistance over pristine V₃O₇·H₂O to promote high specific capacity of 437 and 170 mA h g–¹ at both low (100 mA g–¹) and high (2000 mA g–¹) current, respectively. The morphological analysis of the AgₓV₃O₇·H₂O@rGO before and after 1000 cycles reveals that, although the structural breakdown of the AgₓV₃O₇·H₂O is inevitable during repetitive cycling, the rGO support provides strong interaction with the AgₓV₃O₇·H₂O mat and buffers the structural strain, prevents the agglomeration of the active material, and slows down the structural dissolution at the interface. The synergistic interaction enabled ∼2.3-fold improved cycle stability over the pristine V₃O₇·H₂O with only 0.028% capacity loss per cycle over 1000 cycles.

Meeting the increasing global energy demand has pushed the energy storage research towards developing energy dense and safer electrochemical energy storage devices following sustainable and economic approach. In this regard, past few years have witnessed a rising interest in aqueous electrolyte-based energy storage systems. However, the narrow voltage window of the aqueous electrolyte (1.23 V) limits the choice of electrodes as well as the energy density of traditional aqueous batteries. To overcome this challenge, there is a quest to improve the energy density of aqueous electrolytes by extending the electrochemical stability window. In this regard, a major breakthrough was recorded by switching from conventional ‘salt-in-water’ to ‘water-in-salt’ electrolyte. In “water-in-salt” (WiS) electrolytes, dissolved salts far outnumber water molecules (salt/solvent ratio > 1) by volume or weight. Unlike the conventional aqueous electrolyte (∼1.0 m), in the ‘water-in-salt’ (WiS) system, the interionic interaction becomes dominant over the solvent–ion interaction and the solvation sheath of the metal-ion charge carrier is dominated by contact ion pairs. Such systems with a suitable anion in the contact ion pair could form stable solid electrolyte interfaces at the anode and the reduced water activity expands the electrochemical stability window (ESW) to allow the coupling of a high voltage cathode with a low voltage anode to uplift the energy density. In addition, WiS as the electrolyte offers high safety, good ionic conductivity, high chemical compatibility, and thermal stability, which are crucial to compete with non-aqueous based electrolytes. In recent years, continuous research and development have found an application of this concept in ‘water-in-bisalt’, water-in-ionomer, hybrid aqueous/non-aqueous, and hydrate-melt electrolytes, pushing ESWs up to 4.1 V. In this review, we consolidate recent developments in aforementioned aqueous electrolytes with expanded ESWs for rechargeable batteries (metal-ion, metal–sulfur, and metal–air). The formulation of electrolytes, their physicochemical properties, and electrochemical performance in the different chemistries of batteries has been discussed. This review also addresses scientific and technical issues along with insights to boost the electrochemical performance of future aqueous electrolytes.

In this article, we have reported a one-step scalable synthesis of MgCo2O4 nanostructures as efficient anode material for Li-ion batteries and investigated the role of post-synthesis calcination temperature (400, 600 and 800 °C) on its physiochemical properties and electrochemical performances. The XRD pattern of the calcinated sample at 400 °C (MC 400) indicates a pure phase of MgCo2O4. However, on increasing the calcination temperature to 600 °C (MC 600), an additional phase corresponding to MgO was detected and the corresponding XRD peak intensity further increased on increasing the calcination temperature to 800 °C (MC 800 °C). This was accompanied by a morphological transformation from flake and rod-like nanostructures, to an agglomerated dense flake-like morphology. Electrochemical studies revealed that the calcination temperature plays an important role in determining the electrochemical performance of the MgCo2O4 as anode material. In a half cell, the MC 600 showed the best electrochemical performance with high discharge capacity of 980 mA h g−1 (2nd discharge at 60 mA g−1) and a reversible discharge capacity of 886 mA h g−1 at the end of 50 cycles with high coulombic efficiency of 98%. Long term stability was carried out at 0.5C which showed a capacity retention of 358 mA h g−1 at the end of 500 cycles. The superior electrochemical performance of the MC600 can be attributed to the presence of the small amount of MgO, which is believed to provide the anode materials better structural stability during cycling. The claim was further supported by ex-situ TEM analysis of the anode material of a cycled cell (50 cycles).

We report a simple and scalable synthesis of MnCo2O4/MWCNT nanocomposite by a simple precipitation method and its application as a high capacity anode material for Li-ion batteries. X-ray diffraction analysis showed a pure phase of MnCo2O4 and morphological analysis revealed a uniform decoration of MnCo2O4 nanoparticles along MWCNT backbone. As an electrode material, MnCo2O4 showed a high initial discharge capacity of 1431 mA h g−1 with a capacity retention of 444 mA h g−1 at the end of 30 cycles. With a small addition of MWCNT to MnCo2O4, the stability of the composite increased with a reversible capacity of 871 mA h g−1 at the end of 30 cycles. The inclusion of MWCNT as a conductive matrix resulted in a significant improvement in rate capability and cyclic stability.

In this paper, we show that magnesium and cobalt doped SnO2 (Mg-SnO2 and Co-SnO2) nanostructures have profound influence on the discharge capacity and coulombic efficiency of lithium ion batteries (LIBs) employing pure SnO2 and zinc doped SnO2 (Zn-SnO2) as benchmark materials. The materials were synthesized via sol-gel technique. The structural, chemical and morphological characterization indicates that the Zn, Mg and Co dopants were effectively implanted into the SnO2 lattice and that Co doping significantly reduced the grain growth. The electrochemical performances of the nanoparticles were investigated using galvanostatic cycling, cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The Co-SnO2 electrode delivered a reversible capacity of around 575 mAh g−1 at the 50th cycle with capacity retention of ∼83% at 60 mA g−1current rate. A capacity of ∼415 mAh g−1 when cycling at 103 mA g−1and >60% improvement in coulombic efficiency compared to the pure compound clearly demonstrate the superiority of Co-SnO2 electrodes. The improved electrochemical properties are attributed to the reduction in particle size of the material up to a few nanometers, which efficiently reduced the distance of lithium diffusion pathway and reduction in the volume change by alleviating the structural strain caused during the Li+ intake/outtake process. The EIS analyses of the electrodes corroborated the difference in electrochemical performances of the electrodes: the Co-SnO2 electrode showed the lowest resistance at different voltages during cycling among other electrodes.

Metal sulfides, known as being analogous to metal oxides, have emerged as a new class of materials for energy conversion and/or storage applications due to their low cost and high electrochemical activity. They have shown fascinating properties such as excellent redox reversibility, conductivity, and capacitance. Further, binary metal sulfides have gained enormous attention due to their large redox reaction sites and high electrical conductivity compared to metal sulfides. Recently, use of binary metal sulfides as electrode materials for various applications such as lithium-ion batteries (LIBs), supercapacitors (SC), and solar cells has been extensively studied by various research groups and this review critically overviews the strategies and advances made towards attaining high performances from these sulfides in an effort to provide leads for scale-up and to find long term solutions for energy and environment crisis. Finally, challenges in achieving superior performances and the future scope of research for metal sulfide based energy materials have been outlined.

In this article, we report simple and scalable one-pot molten salt synthesis of CoFe2O4 as electrode material for Lithium ion batteries. X-ray diffraction studies along with Rietveld analysis showed a pure phase of CoFe2O4 with space group Fd-3m and crystallite size of 54 nm. As an anode material CoFe2O4 showed high initial discharge/charge capacity of 1556/1093 mA h g−1 and a reversible capacity of 926 mA h g−1 after 30 cycles with columbic efficiency of 99%. A relatively high reversible capacity of 594 mA h g−1 was observed at high current density of 1C (916 mA g−1) which shows the better reversibility of CoFe2O4 at high current density. As the current was reduced to 0.1C reversible capacity of 899 mA h g−1 was retained suggesting high rate performance of CoFe2O4. The long-term stability test, carried out using galvanostatic charge/discharge (GC) at a current density of 0.5C, showed a reversible capacity of 369 mA h g−1 at the end of 200th cycle. The structural and morphological evaluation of the sample after cycling, using ex-situ X-ray diffraction and ex-situ transmission electron microscopy, confirmed structural degradation and formation of metal nanoparticles, Li2O and amorphous nature of electrode material. The one-pot molten salt synthesis approach is quite simple and can be extended for large-scale production of electrode materials.

Precise control of micro-level objects for cell sorting, cell manipulation, targeted drug delivery etc., still remains a great challenge in the field of bio-medical engineering. Even though magnetic actuation has emerged as a harmless, high actuation speed, low cost alternative for micromanipulation of cells, the throughput of the system is still low because of the undesirable effects of flow fields and sensing noise. This paper reports a parametrized feedback policy to perform non-prehensile magnetic micromanipulation [9] to push the target cell to specified goal location under the influence of flow field, sensing noise, drag and magnetic forces. We report an optimization based parameter tuning approach to reduce the transport time using developed feedback policy. Flow field and image processing noise present in the system was experimentally measured and incorporated into the developed models and simulations. We have tuned the feedback policy parameter to reduce the travel time via simulation experiments.