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Zinc-ion batteries (ZIBs) have garnered substantial attention as a potential alternative to Li-ion batteries (LIBs) because of their low cost and high safety. However, commercialization challenges persist for ZIBs, which are primarily attributed to the absence of electrode materials with sufficient energy density. In this study, we initiate the exploration of β-LiVOPO4 as a high-energy and high-power ZIB cathode due to its robust 3D structural framework and elevated operating potential. Specifically, we achieved a high working voltage of 1.61 V vs. Zn/Zn2+ for β-LiVOPO4. The cathode delivered a discharge capacity of 114.1 mA h g−1 at a current density of 100 mA g−1 with considerable cyclability and rate performance. We explored the storage mechanism of the β-LiVOPO4 cathode using various characterization techniques, including in situ synchrotron X-ray diffraction (XRD), ex situ X-ray absorption spectroscopy, ex situ XRD, and theoretical calculations. During cycling, a reversible and stable phase transition through capacitive-based surface reactions and repeated Li+/Zn2+ (de)insertion were maintained. This contributed to the high electrochemical performance of β-LiVOPO4 when used as a ZIB cathode. [ABSTRACT FROM AUTHOR]

In this study, we present a Prussian white (Na2MnFe(CN)6)–carbon nanotube (PW–CNT) composite material with a carbon conductive network as a promising high energy cathode for sodium-ion batteries (SIBs). This cathode, which is prepared by a chelating-agent-assisted precipitation method to regulate defect crystallization, is showcased as a promising solution to the bottlenecks of high lattice defects, irreversible phase transitions, the resulting structural instability and hence unstable cycling usually present in the PW cathode for SIBs. Precisely, the PW–CNT composite formation highlights the effectively controlled moisture content achieved through the strategic integration of CNTs and a chelating agent during the material synthesis. Moreover, the electrochemical behavior and performance of PW–CNT composites, particularly in sodium-ion batteries, are explored within the context of controlled moisture environments. The intricate interplay between PW, CNTs, and the chelating agent, as well as their synergistic influence on moisture management and subsequent electrochemical performance, is thoroughly examined. At an extreme rate of 10C, the PW–CNT composite cathode exhibited a high reversible capacity of 133 mA h g−1, very close to the theoretical value (∼140 mA h g−1), and almost 30% higher than that of the PW (∼103 mA h g−1) and 1.2 times greater than that of a conventional Prussian blue (PB) cathode (∼58 mA h g−1), respectively. A coin-type full-cell configuration with a hard carbon (HC) anode exhibited ∼58% capacity retention after 1500 cycles at 1C thereby underscoring the potential of the PW–CNT composite cathode to advance the real-time applications for energy storage applications including SIBs. [ABSTRACT FROM AUTHOR]

Sodium-ion batteries (SIBs) display the essential properties required of a reliable energy-storage device, such as vast availability, good voltage output, and cost-effectiveness. Although initial SIB cathodes delivered a significantly lower capacity than their lithium-ion battery counterparts, new high-capacity cathode materials for SIBs continue to be developed today. This study employed a combined machine-learning (ML), ab initio density functional theory (DFT), and experimental approach to develop low-cost and high-energy cathode materials, i.e. Na3.5MnV0.5Ti0.5(PO4)3 (NMVTP), Na3.5MnV0.5Fe0.5(PO4)3 (NMVFP), and Na3.5MnV0.5Al0.5(PO4)3 (NMVAP). Among these materials, the carbon-coated Na3.5MnV0.5Ti0.5(PO4)3 (NMVTP/C) with the most stable formation energy (−1.99 eV) registered an exceedingly high specific capacity of 133.14 mA h g−1, a satisfactory Na+ (de)insertion voltage of 3.42 V, and a superior energy output of 455 W h kg−1 in the half-cell configuration. NMVTP/C also exhibits a rapid sodium storage capability for 8000 cycles with a capacity retention of 75% at a considerably high current rate of 14C and an impressive rate proficiency of 59.2 mA h g−1 at 17.5C. [ABSTRACT FROM AUTHOR]

Batteries using potassium metal (K‐metal) anode are considered a new type of low‐cost and high‐energy storage device. However, the thermodynamic instability of the K‐metal anode in organic electrolyte solutions causes uncontrolled dendritic growth and parasitic reactions, leading to rapid capacity loss and low Coulombic efficiency of K‐metal batteries. Herein, an advanced electrolyte comprising 1 M potassium bis(fluorosulfonyl)imide (KFSI) + 0.05 M potassium hexafluorophosphate (KPF6) dissolved in dimethoxyethane (DME) is introduced as a simple and effective strategy of regulated solvation chemistry, showing an enhanced interfacial stability of the K‐metal anode. Incorporating 0.05 M KPF6 into the 1 M KFSI in DME electrolyte solution decreases the number of solvent molecules surrounding the K ion and simultaneously leads to facile K+ de‐solvation. During the electrodeposition process, these unique features can lower the exchange current density between the electrolyte and K‐metal anode, thereby improving the uniformity of K electrodeposition, as well as potentially suppressing dendritic growth. Even under a high current density of 4 mA cm−2, the K‐metal anode in 0.05 M KPF6‐containing electrolyte ensures high areal capacity and an unprecedented lifespan with stable Coulombic efficiency in both symmetrical half‐cells and full‐cells employing a sulfurized polyacrylonitrile cathode. [ABSTRACT FROM AUTHOR]

Owing to high natural abundance and relatively low redox potential of potassium (K), the K-ion battery (KIB) is a compelling substitute technology for the currently used lithium-ion battery (LIB). In this study, we propose a natural eco-friendly nitrogen (N)-doped porous carbon matrix from waste coffee grounds, which are abundantly available as biomass for KIB anode application. High electrical conduction and effective doping of active N atoms with lone electron pairs can be achieved through simple carbonization. Heteroatom N exists in multiple forms, such as graphitic N, pyridinic N, and pyrrolic N, all of which have lone pair electrons. The NCcoff-800 is optimized mesoporous structure with a good balance of graphitic N and coexistence of amorphous and graphitic carbon, allowing the highly reversible K storage properties to be preserved. To ensure practical utilization of NCcoff-800 as an anode, we assembled K-ion full-cells using a high-voltage Prussian blue/graphene (PB/G) composite as the cathode, which exhibited a high specific capacity of 90 mA h g−1 at 0.1C and long-term cycling stability over 1000 cycles at 0.5C. This study suggests that an affordable, eco-friendly, high-performance practical KIB, providing excellent electrochemical properties, could be developed using an inexpensive anode derived from used coffee grounds together with a PB/G cathode. [ABSTRACT FROM AUTHOR]

Manganese (Mn)‐based cathode materials have garnered huge research interest for rechargeable aqueous zinc‐ion batteries (AZIBs) due to the abundance and low cost of manganese and the plentiful advantages of manganese oxides including their different structures, wide range of phases, and various stoichiometries. A novel in situ generated Mn‐deficient ZnMn2O4@C (Mn‐d‐ZMO@C) nanoarchitecture cathode material from self‐assembly of ZnO‐MnO@C for rechargeable AZIBs is reported. Analytical techniques confirm the porous and crystalline structure of ZnO‐MnO@C and the in situ growth of Mn deficient ZnMn2O4@C. The Zn/Mn‐d‐ZMO@C cell displays a promising capacity of 194 mAh g−1 at a current density of 100 mA g−1 with 84% of capacity retained after 2000 cycles (at 3000 mA g−1 rate). The improved performance of this cathode originates from in situ orientation, porosity, and carbon coating. Additionally, first‐principles calculations confirm the high electronic conductivity of Mn‐d‐ZMO@C cathode. Importantly, a good capacity retention (86%) is obtained with a year‐old cell (after 150 cycles) at 100 mA g−1 current density. This study, therefore, indicates that the in situ grown Mn‐d‐ZMO@C nanoarchitecture cathode is a promising material to prepare a durable AZIB. [ABSTRACT FROM AUTHOR]

Potassium, the third alkali element after sodium on the periodic table, provides several advantages over lithium and sodium as a charge carrier in rechargeable batteries. Pertaining to its natural features, potassium has a lower standard redox potential than other metallic elements (−2.93 V vs. the standard hydrogen electrode (SHE)) and is highly abundant in the Earth's crust. For these reasons, to date, the development of rechargeable potassium batteries has attracted considerable attention in the search for high-energy and cost-effective energy storage systems. In the development of rechargeable potassium batteries, K metal anodes are the key material and act as the counter electrode to evaluate electrochemical electrode materials in the half-cell configuration. Moreover, they are also an essential component of full-cell potassium–sulfur and potassium–oxygen systems. However, the main hurdle in the widespread acceptance of K metal as an anode in rechargeable potassium batteries lies in identifying fundamental problems and developing suitable solutions. Here, we initially investigate and evaluate potassium metal as an anode for rechargeable potassium batteries and detail the major challenges for K metal systems, that at this time, limit the feasibility of rechargeable potassium batteries, particularly, dendritic growth for liquid systems, poor coulombic efficiency, and the unstable interface between the K metal and electrolyte. In addition, we also highlight the key developments and recent achievements in the stabilization of K metal anodes and their application. This will be helpful in reducing trial and error in studies pertaining to the development of rechargeable potassium batteries and provide crucial insights for potential scientific and industrial applications. [ABSTRACT FROM AUTHOR]

α-MnO2 is considered as an attractive cathode material for lithium, sodium and magnesium-ion battery applications because of its relatively large [2 × 2] tunnel, high discharge capacity, environmental benignity and low cost. Therefore, understanding the electrochemical properties of α-MnO2 for eco-friendly trivalent aluminum-ion battery is of great research interest. Herein, we presented a theoretical study of Al insertion into α-MnO2 using first principles calculations based on the density functional theory. We found that Al insertion into α-MnO2 proceeded through 4 insertion stages. The average calculated voltage was found to be 1.55 V. Moreover, our calculations suggested the structural distortion of α-MnO2 upon Al insertion even in the dilute limit of insertion. In addition, the electronic properties of the Al-inserted phases and the effect of the metal doping strategy in α-MnO2 for performance improvement were also discussed. Our study may provide an insight and pave the way for further applications of α-MnO2 as an electrode material and potential insertion host for aluminum-ion batteries. [ABSTRACT FROM AUTHOR]

Aqueous rechargeable zinc-ion batteries (ARZIBs) have drawn enormous attention because of their low-cost and eco-friendly cell components. However, designing high-performance cathode materials towards practical application of ARZIBs remains a major challenge. Therefore, in this contribution, a comprehensive study on K+ intercalated V2O5 (KVO) nanorods with exposed facets as a high-performance cathode for ARZIBs is presented. The KVO cathode exhibits remarkable discharge capacities of 439 and 286 mAh g−1 at current densities of 50 and 3000 mA g−1, respectively. Furthermore, it recovers 96% of the capacity after 1500 cycles at 8000 mA g−1. Impressively, the Zn/KVO battery offers a specific energy of 121 W h kg−1 at high specific power of 6480 W kg−1. The storage mechanism of the KVO cathode in an ARZIB is systematically elucidated using in operando synchrotron X-ray diffraction, ex situ synchrotron X-ray absorption spectroscopy, ex situ TEM analyses and first-principles calculations. The superior performance of the cathode is attributed to its unique exposed layer structure with high surface energy, high conductivity and low migration barrier for Zn2+ migration. This study provides insight into designing high-performance cathode materials for ARZIBs and other electrochemical systems. [ABSTRACT FROM AUTHOR]

We explore NaV6O15 (NVO) nanorod cathodes prepared by a sol–gel method for aqueous rechargeable zinc-ion battery applications for the first time. The NVO cathode delivers a high capacity of 427 mA h g−1 at 50 mA g−1 current density. Furthermore, based on the mass of the active materials, it exhibits a high energy density of 337 W h kg−1. [ABSTRACT FROM AUTHOR]

Abstract: Rechargeable hybrid aqueous batteries (ReHABs) have emerged as promising sustainable energy‐storage devices because all components are environmentally benign and abundant. In this study, a carbon‐wrapped sponge‐like Na3V2(PO4)3 nanoparticle (NVP@C) cathode is prepared by a simple pyrosynthesis for use in the ReHAB system with impressive rate capability and high cyclability. A high‐resolution X‐ray diffraction study confirmed the formation of pure Na ion superionic conductor (NASICON) NVP with rhombohedral structure. When tested in the ReHAB system, the NVP@C demonstrated high rate capability (66 mAh g−1 at 32 C) and remarkable cyclability over 1000 cycles (about 72 % of the initial capacity is retained at 30 C). Structural transformation and oxidation change studies of the electrode evaluated by using in situ synchrotron X‐ray diffraction and ex situ X‐ray photoelectron spectroscopy, respectively, confirmed the high reversibility of the NVP@C electrode in the ReHAB system through a two‐phase reaction. The combined strategy of nanosizing and carbon‐wrapping in the NVP particles is responsible for the remarkable electrochemical properties. The pyrosynthesis technique appears to be a promising and feasible approach to prepare a high‐performance electrode for safe and low‐cost ReHAB systems as nextgeneration large‐scale energy storage devices. [ABSTRACT FROM AUTHOR]

Aqueous Zn-ion batteries (ZIBs) have emerged as promising and eco-friendly next-generation energy storage systems to substitute lithium-ion batteries. Therefore, discovering new electrode materials for ZIBs with high performance and unraveling their electrochemical reactions during Zn-ion insertion/extraction are of great interest. Here, we present, for the first time, tunnel-type β-MnO2 nanorods with exposed (101) planes, prepared via a facile microwave-assisted hydrothermal synthesis within only 10 min, for use as a high performance cathode for ZIBs. In contrast to its bulk counterpart, which showed no electrochemical reactivity, the present β-MnO2 nanorod electrode exhibited a high discharge capacity of 270 mA h g−1 at 100 mA g−1, high rate capability (123 and 86 mA h g−1 at 528 and 1056 mA g−1, respectively), and long cycling stability (75% capacity retention with 100% coulombic efficiency at 200 mA g−1) over 200 cycles. The Zn-ion storage mechanism of the cathode was also unraveled using in situ synchrotron, ex situ X-ray diffraction, ex situ X-ray photoelectron spectroscopy, and ex situ X-ray absorption spectroscopy. Our present study indicates that Zn intercalation occurred via a combination of solid solution and conversion reactions. During initial cycles, the β-MnO2 cathode was able to maintain its structure; however, after prolonged cycles, it transformed into a spinel structure. The present results challenge the common views on the β-MnO2 electrode and pave the way for the further development of ZIBs as cost-effective and environmentally friendly next-generation energy storage systems. [ABSTRACT FROM AUTHOR]

A porous TiN/N-doped carbon composite electrode prepared via a metal–organic framework strategy exhibited high reversible lithium specific capacity (561 mA h g−1 at 50 mA g−1), excellent rate capability (281 mA h g−1 at 2 A g−1), and good cycle stability (310 mA h g−1 at 2 A g−1 for 400 cycles). [ABSTRACT FROM AUTHOR]

A nanostructured Mn3O4/C electrode was prepared by a one-step polyol-assisted pyro-synthesis without any post-heat treatments. The as-prepared Mn3O4/C revealed nanostructured morphology comprised of secondary aggregates formed from carbon-coated primary particles of average diameters ranging between 20 and 40 nm, as evidenced from the electron microscopy studies. The N2 adsorption studies reveal a hierarchical porous feature in the nanostructured electrode. The nanostructured morphology appears to be related to the present rapid combustion strategy. The nanostructured porous Mn3O4/C electrode demonstrated impressive electrode properties with reversible capacities of 666 mAh g−1 at a current density of 33 mA g−1, good capacity retentions (1141 mAh g−1 with 100 % Coulombic efficiencies at the 100th cycle), and rate capabilities (307 and 202 mAh g−1 at 528 and 1056 mA g−1, respectively) when tested as an anode for lithium-ion battery applications. [ABSTRACT FROM AUTHOR]

This study reports the use of a layered-type birnessite δ-MnO 2 nano-flake cathode for eco-friendly zinc-ion battery (ZIB) applications. The present δ-MnO 2 was prepared via the simple low temperature thermal decomposition of KMnO 4 . The X-ray diffraction (XRD) pattern of the samples was well indexed to the δ-MnO 2 phase. Field emission SEM and TEM images of the δ-MnO 2 revealed flake-like morphologies with an average diameter of 200 nm. The electrochemical properties, investigated by cyclic voltammetry and constant current charge-discharge measurements, revealed that the nano-flake cathode exhibited first discharge capacity of 122 mAh g − 1 under a high current density of 83 mA g − 1 versus zinc. The discharge capacity thereafter increased until it reached 252 mAh g − 1 in the fourth cycle. On the hundredth cycle, the electrode registered a discharge capacity of 112 mAh g − 1 . Coulombic efficiencies of nearly 100% were maintained on prolonged cycling and thereby indicate the long cycle stability of the δ-MnO 2 . Besides, the realization of specific capacities of 92 and 30 mAh/g at high current densities of 666 and 1333 mA g −1 , respectively, clearly demonstrates the decent rate capabilities of δ-MnO 2 nano-flake cathode. These results may facilitate the utilization of layered-type birnessite δ-MnO 2 in ZIB applications. [ABSTRACT FROM AUTHOR]

In the present study, a nanorod-type α-MnO 2 cathode is prepared by a facile hydrothermal method for rechargeable aqueous zinc-ion battery (ZIB) applications. Electron microscopy studies reveal rod shaped particles with approximately 20 nm of width and 200 nm of length. When tested for aqueous ZIBs, the α-MnO 2 nanorod cathode exhibits an initial discharge capacity of 233 mA h/g at a current density of 83 mA/g with nearly 100% Coulombic efficiencies under prolonged cycling. Besides, the prepared cathode demonstrates decent rate capabilities at higher current densities (43.33 and 31.48 mA h/g at 1333 and 1666 mA/g, respectively). Ex-situ synchrotron XAS investigations clearly establish the reversibility of electrochemical Zn-insertion into the α-MnO 2 nanorod cathode. The analyses also reveal that the host α-MnO 2 structure demonstrates considerable structural stability during Zn-insertion/extraction. Further, a combination of ex-situ synchrotron XRD studies, visualization and pattern-fitting software programs not only confirm electrochemical Zn-insertion into the host α-MnO 2 structure but also suggest that the unit cell volume of the [2×2] tunnels in the α-MnO 2 host expands by approximately 3.12% during Zn-insertion. The present study thus paves the way for further development of eco-friendly ZIB as an ideal energy storage system due to its excellent safety and reliability. [ABSTRACT FROM AUTHOR]

Hierarchical meso-/macroporous anatase TiO2 was synthesized by the hydrolysis of a titanium metal–organic framework precursor followed by calcination in air. This unique porous feature enables the superior rate capability and excellent cycling stability of anatase TiO2 as an anode for rechargeable lithium-ion batteries. [ABSTRACT FROM AUTHOR]

Anatase-type titanium dioxide (TiO2) anodes were prepared by a polyol-assisted pyro-synthetic process followed by mild annealing at temperatures in the range of 300 to 600°C for 3 h. The XRD studies clearly revealed the formation of anatase-type TiO2 for all of the prepared samples. The average crystallite size, calculated using the Scherrer formula, was determined to be less than 50 nm in all samples. Electron microscopy studies revealed that the particle-size in all samples ranged from 5 to 50 11m. N2 adsorption studies confirmed that the samples show mesoporous characteristics and in particular the TiO2 anode prepared at 500' C demonstrated a unique tri-porous feature that appears to benefit its electrochemical performances vs. lithium. Although there is no order of variation in the particle-size of the samples prepared at temperatures under 600°C, the tri-porous feature in combination with the sufficiently high particle crystallinity in the TiOi anode prepared at 500°C appears to contribute to its impressive electrochemical lithium storage properties among the prepared electrodes. The pyro-synthetic strategy aids in developing nanostructured battery electrodes with porous morphologies and appears to offer promise for being developed as an energy saving process for large-scale applications. [ABSTRACT FROM AUTHOR]

Lithium-sulfur (Li-S) batteries using Li 2 S and Li-free anodes have emerged as a potential high-energy and safe battery technology. Although the operation of Li-S full batteries based on Li 2 S has been demonstrated at room temperature, their effective use at a subzero temperature has not been realized due to the low electrochemical utilization of Li 2 S. Here, ammonium nitrate (NH 4 NO 3 ) is introduced as a functional additive that allows Li-S full batteries to operate at -10 °C. The polar N-H bonds in the additive alter the activation pathway of Li 2 S by inducing the dissolution of the Li 2 S surface. Then, Li 2 S with an amorphized surface layer undergoes the modified activation process, which consists of the disproportionation and direct conversion reaction, through which Li 2 S is efficiently converted into S 8 . The Li-S full battery using NH 4 NO 3 delivers a reversible capacity and cycling stability over 400 cycles at -10 °C.

A simple one-pot polyol-assisted pyro-technique has been adopted to synthesize highly crystalline, carbon-coated LiMn 2 O 4 (LMO/C) nanoparticles for use as a cathode material in rechargeable Li-ion battery (LIB) applications. The phase purity, structure and stoichiometry of the prepared cathode was confirmed using X-ray techniques that included high-resolution powder X-ray diffraction and X-ray absorption fine structure spectroscopy. Electron microscopy studies established that the synthetic technique facilitated the production of nano-sized LMO particles with uniform carbon coating. The prepared LMO/C cathode demonstrates excellent electrochemical properties (cycling stabilities of 86% and 77.5% and high rate capabilities of 79% and 36% within the potential windows of 3.3-4.3 V and 2.5-4.3 V, respectively). The high electrochemical performance of the LMO/C cathode is attributed to the nano-size of the LiMn 2 O 4 particles enabling high surface area and hence greater lithium insertion and also the uniform amorphous carbon coating facilitating effective reduction in manganese dissolution and volume expansion during the lithium de-intercalation/intercalation reactions. In addition, cyclic voltametry and impedance characterization confirm the reversible Li-intercalation and the role of the solid electrolyte interface layer (SEI) in the stable electrochemical reaction of the LMO/C electrode. Furthermore, this study shows the efficacy of a simple and low-cost pyro-synthetic method to realize high performance nano-sized particle electrodes with uniform carbon coating for useful energy storage applications., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Reduced graphene oxide (rGO) sheets were synthesized by a modified Hummer's method without additional reducing procedures, such as chemical and thermal treatment, by appropriate drying of graphite oxide under ambient atmosphere. The use of a moderate drying temperature (250°C) led to mesoporous characteristics with enhanced electrochemical activity, as confirmed by electron microscopy and N 2 adsorption studies. The dimensions of the sheets ranged from nanometres to micrometres and these sheets were entangled with each other. These morphological features of rGO tend to facilitate the movement of guest ions larger than Li + . Impressive electrochemical properties were achieved with the rGO electrodes using various charge-transfer ions, such as Li + , Na + and K + , along with high porosity. Notably, the feasibility of this system as the carbonaceous anode material for sodium battery systems is demonstrated. Furthermore, the results also suggest that the high-rate capability of the present rGO electrode can pave the way for improving the full cell characteristics, especially for preventing the potential drop in sodium-ion batteries and potassium-ion batteries, which are expected to replace the lithium-ion battery system., Competing Interests: We declare that we have no competing interests.

Rechargeable hybrid aqueous batteries (ReHABs) have emerged as promising sustainable energy-storage devices because all components are environmentally benign and abundant. In this study, a carbon-wrapped sponge-like Na 3 V 2 (PO 4 ) 3 nanoparticle (NVP@C) cathode is prepared by a simple pyrosynthesis for use in the ReHAB system with impressive rate capability and high cyclability. A high-resolution X-ray diffraction study confirmed the formation of pure Na ion superionic conductor (NASICON) NVP with rhombohedral structure. When tested in the ReHAB system, the NVP@C demonstrated high rate capability (66 mAh g -1 at 32 C) and remarkable cyclability over 1000 cycles (about 72 % of the initial capacity is retained at 30 C). Structural transformation and oxidation change studies of the electrode evaluated by using in situ synchrotron X-ray diffraction and ex situ X-ray photoelectron spectroscopy, respectively, confirmed the high reversibility of the NVP@C electrode in the ReHAB system through a two-phase reaction. The combined strategy of nanosizing and carbon-wrapping in the NVP particles is responsible for the remarkable electrochemical properties. The pyrosynthesis technique appears to be a promising and feasible approach to prepare a high-performance electrode for safe and low-cost ReHAB systems as nextgeneration large-scale energy storage devices., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)