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We have successfully synthesized Reduced graphene oxide (rGO) sheets by modified Hummer’s method without additional reducing procedures, such as chemical and thermal treatment, by using appropriate drying temperatures under ambient atmosphere. The rGO sample dried at the optimum temperature of 250 has the most increased specific surface area and porosity as evidenced by SEM and BET analysis, leading to improved lithium-ion, sodium-ion and potassium-ion storage properties. We confirmed the use of a moderate drying temperature led to electrodes’ enhanced cyclability and good electrochemical performance at high current densities. The dimensions of the sheets ranged from nanometers to micrometres and these were entangled with each other to form aggregates. These morphological features of rGO facilitates the movement of guest ions larger than Li-ions, however there were slight instability during repeated cycling. To improve the electrochemical properties, we adopted simple chemical strategies using surfactant/solvent-assisted ultrasonication or mechanical or thermal methods. Our results will be useful for improving the full cell characteristics, and especially for preventing potential drop in sodium-ion batteries and potassium-ion batteries, which are expected to replace the lithium-ion battery system.

Research attention in aqueous rechargeable zinc-ion batteries (ARZIBs) is growing immensely because of their low-cost and eco-friendly cell components. However, its challenging to find new cathode materials towards practical application of ARZIBs. In this contribution, ground-breaking work on the potassium-pillared V2O5.nH2O (K0.5V2O5.nH2O) nanorod with exposed layer structure as high-performance cathode for ARZIB is presented. The storage mechanism of the K0.5V2O5.nH2O cathode in ARZIB is systematically elucidated using a combined of in situ synchrotron X-ray diffraction, ex situ synchrotron X-ray absorption spectroscopy, ex situ TEM analyses, and first-principle calculations. The K0.5V2O5. nH2O cathode displays a notable discharge capacity of 439 mAh g−1 at a current density of 50 mA g−1. Furthermore, it recovers 96% of the capacity after 1500 cycles at 8000 mA g−1. Impressively, the Zn/K0.5V2O5.nH2O battery offers a specific energy of 121 Wh kg−1 at a high specific power of 6480 W kg−1. The superior performance of the cathode is attributed to its unique exposed layer structure with high surface energy, high conductivity, and low migration barrier. The zinc (Zn) insertion pathway into K0.5V2O5.nH2O was studied using density function theory (DFT). This study provides an insight for designing high-performance cathode materials for ARZIBs and other electrochemical systems.

In this work, we studied about Br-doped Li4Ti5O12-xBrx (“x”= 0, 0.1, 0.3, 0.5 and 0.7) anode materials, which were synthesized by a conventional solid-state reaction using precursors of Li2CO3, TiO2 and LiBr, and we found that their electrochemical properties were related to the doping behavior Most of the Br ions are situated on the surfaces/interfaces of agglomerated particles rather than in the bulk lattice after quantitative instrumental analysis. This lead to the formation of Narrow conduction paths of electron and Li-ion on their surfaces/interfaces. The presence of these narrow surface electrical conduits increased the rate-capability of the LTOBr samples during charging/discharging process. Highly Br-doped sample (LTOBr0.7) showed a slight reduction in capacity. The LTOBr0.5 sample, by the mean time, showed the highest capacity of 125 mAh/g at 1C compared to 115 mAh/g for pure LTO. This was explained with the formation of fine precipitations (Br-containing second phase) on the surfaces of the LTO particles due to high Br addition. The formation of fine precipitations (Br-containing second phase) on the surfaces of the LTO particles due to high Br addition could be the explanation of this.

In this study, anatase-type titanium dioxide (TiO2) anodes were prepared by a polyol-assisted pyro-synthetic process followed by mild annealing in the range of 300 to 600 °C. The XRD studies confirmed the formation of anatase-type TiO2 and the Scherrer formula aided in establishing the average crystallite size to be less than 50 nm for all of the prepared samples. Electron microscopy studies revealed the average particle-size to be in the range between 5 and 50 nm whereas the adsorption studies demonstrated the mesoporous characteristics of all the prepared samples and the 500 °C electrode, in particular, exhibited tri-porosity. This unique tri-porous feature in combination with the sufficiently high particle crystallinity appears to contribute to the impressive electrochemical lithium storage (154.7 and 116.4 mAh g-1 at 3.2 and 6.4 C, respectively) in the 500 °C electrode. Furthermore, the pyro-synthetic strategy aids in developing nanostructured battery electrodes with porous morphologies and appears promising to be developed as an energy saving process for large-scale applications.

Metal-organic framework (MOF) based synthesis of battery electrodes has presently become a hot topic of significant research interest. Considering the complications to prepare Co3V2O8 due to the criticality of its stoichiometric composition, we report here by a simple MOF formation by solvothermal technique followed by air annealing to synthesize Co3V2O8 for use as potential anodes for lithium battery applications. Structrual investigations by X-ray diffraction, X-ray photoelectron spectroscopy, high resolution electron microscopy, and surface area studies revealed that the phase pure Co3V2O8 nanoparticles are inter connected to form a sponge-like morphology with porous properties. Electrochemical measurements exposed the excellent lithium storage (~ 1000 mAhg-1 at 200 mAg-1) and retention properties (500 mAhg-1 at 1000 mAg-1 after 700 cycles) of the prepared Co3V2O8 electrode. A notable rate performance of 430 mAhg-1 at 3200 mAg-1 was also observed and ex-situ analysis confirmed the morphological and structural stability of this material after long cycles performance. These results validate that the unique nanostructured morphology arising from the use of the ordered array of MOF networks is favorable for improving the cyclability and rate capability in battery electrodes. The synthetic strategy presented herein may provide solutions to develop phase pure mixed metal oxides for high performance electrodes for useful energy storage applications. Figure 1

Nowadays, extensive researches to overcome the world energy crisis has emphasized the urgent necessity of developing sustainable energy storage systems. The rechargeable lithium-ion battery (LIB) dominates today's battery market for portable device applications. Nonetheless, the crucial issues concerning its safety, eco-friendliness, and cost-effectiveness, as well as the controversies associated with the availability of lithium resources, have led to the continuous exploration of new battery chemistries. Sodium-ion, potassium-ion, and aluminum-ion batteries are promising alternative since these devices are based on relatively abundant and cheap sodium, potassium, and aluminum elements, respectively. However, these battery systems also suffer from complicated issues of safety, processing costs, and environmental concerns. Earlier efforts for developing a rechargeable aqueous zinc-ion battery (ZIB), which facilitates energy storage application via zinc-ion insertion/extraction, has opened the way for the realization of safe, environmentally benign and cost-effective next generation energy storage system. ZIB is still in the stage of early phase of development, therefore, fundamental studies concentrating on the zinc-ion insertion mechanism is an attractive goal to pursue. In this work, we used nanorod alpha-type manganese dioxide cathode for ZIB application. Alpha-type manganese deioxide was prepared by a simple hydrothermal synthesis. SEM and TEM studies showed rod-type sample with approximately 20 and 200 nm of width and length, respectively. The nanorod cathode exhibited an initial discharge capacity of 176.8 mAh g-1 at a current density of 83 mA g-1 and demonstrated nearly 100% Coulombic efficiencies under prolonged cycling when tested for zinc storage properties. Rate performance measurements revealed that specific capacities of 43.33 and 31.48 mAh g-1 were registered at current densities as high as 1333 and 1666 mA g-1. A combination of ex-situ synchrotron XRD and XAS studies confirmed the reversibility of electrochemical zinc-ion insertion into [2x2] tunnels of the alpha-type manganese dioxide host structure. The host exhibits structural stability by accommodating an unit cell volume expansion of approximately 3.12% during Zn-insertion. The present study hence paves the way for further development of rechargeable aqueous ZIB as an alternative ideal energy storage system due to its excellent safety and reliability. Figure 1

Earlier efforts to develop an aqueous zinc-ion battery (ZIB), which facilitates energy storage/conversion via Zn-ion intercalation/de-intercalation, has paved the way not only to realizing safe and environmentally benign energy devices, but also to reducing the processing costs of next generation batteries. [1,2] From the viewpoint of developing low-cost and environmentally safe rechargeable batteries that can be easily scaled up for large-scale production, the present study reports on a high surface area mesoporous tunnel-type γ-MnO2 cathode obtained by a simple template-free ambient temperature strategy and subsequent annealing at low temperatures for ZIB applications. An in-depth study on the structural transformation in a mesoporous γ-MnO2 cathode during electrochemical reaction in a zinc-ion battery (ZIB) has been conducted. A combination analyses of in-situ synchrotron XANES and XRD reveal that the tunnel-type parent γ-MnO2 experiences a structural transformation to spinel-type Mn(III) phase (ZnMn2O4) and two new intermediary Mn(II) phases namely, tunnel-type γ-ZnxMnO2 and layered-type L-ZnyMnO2 and that these phases with multioxidation states co-exist after complete electrochemical Zn-intercalation. On sequential Zn-de-intercalation, a majority of these phases with multi-oxidation states was observed to revert back to the parent γ-MnO2 phase. The mesoporous γ-MnO2 cathode exhibits an initial discharge capacity of 285 mAh g-1 at 0.05 mA cm-2 with a defined plateau at around 1.25 V vs. Zn/Zn2+. Further, ex-situ HR-TEM studies of the discharged electrode aided to identify the lattice fringe widths corresponding to the Mn(III) and Mn(II) phases and the stoichiometric composition estimated by ICP appear to be in agreement with the in-situ findings. References C. Xu, B. Li, H. Du, F. Kang, Angew. Chem. Int. Ed., 51, 933, (2012). C. Yuan, Y. Zhang, Y. Pan, X. Liu, G. Wang, D. Cao, Electrochim. Acta, 116, 404 (2014).