Potassium ion pre-intercalated MnO2 for aqueous multivalent ion batteries.

Manganese dioxide (MnO2), as a cathode material for multivalent ion (such as Mg2+ and Al3+) storage, is investigated due to its high initial capacity. However, during multivalent ion insertion/extraction, the crystal structure of MnO2 partially collapses, leading to fast capacity decay in few charge/discharge cycles. Here, through pre-intercalating potassium-ion (K+) into δ-MnO2, we synthesize a potassium ion pre-intercalated MnO2, K0.21MnO2·0.31H2O (KMO), as a reliable cathode material for multivalent ion batteries. The as-prepared KMO exhibits a high reversible capacity of 185 mAh/g at 1 A/g, with considerable rate performance and improved cycling stability in 1 mol/L MgSO4 electrolyte. In addition, we observe that aluminum-ion (Al3+) can also insert into a KMO cathode. This work provides a valid method for modification of manganese-based oxides for aqueous multivalent ion batteries.

Flexible Ammonium-Ion Pouch Cells Based on a Tunneled Manganese Dioxide Cathode.

Aqueous ammonium-ion (NH4+) batteries are becoming the competitive energy storage candidate on account of their safety, affordability, sustainability, and intrinsically peculiar properties. Herein, an aqueous NH4+-ion pouch cell is investigated based on a tunneled manganese dioxide (α-MnO2) cathode and a 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) anode. The MnO2 electrode possesses a high specific capacity of ∼190 mA h g-1 at 0.1 A g-1 and displays excellent long cycling performance after 50,000 cycles in 1 M (NH4)2SO4, which outperforms the most reported ammonium-ion host materials. Besides, a solid-solution behavior is revealed about the migration of NH4+ in the tunnel-like α-MnO2. The battery displays a splendid rate capacity of 83.2 mA h g-1 even at 10 A g-1. It also exhibits a high energy density of ∼78 W h kg-1 as well as a high power density of ∼8212 W kg-1 (based on the mass of MnO2). What is more, the flexible MnO2//PTCDA pouch cell based on the hydrogel electrolyte shows excellent flexibility and good electrochemical properties. The topochemistry results of MnO2//PTCDA point to the potential practicability of ammonium-ion energy storage.

Ethanol-Induced Ni2+ -Intercalated Cobalt Organic Frameworks on Vanadium Pentoxide for Synergistically Enhancing the Performance of 3D-Printed Micro-Supercapacitors.

The synthesis of metal-organic framework (MOF) nanocomposites with high energy density and excellent mechanical strength is limited by the degree of lattice matching and crystal surface structure. In this study, dodecahedral ZIF-67 is synthesized uniformly on vanadium pentoxide nanowires. The influence of the coordination mode on the surface of ZIF-67 in ethanol is also investigated. Benefitting from the different coordination abilities of Ni2+ , Co2+ , and N atoms, spatially separated surface-active sites are created through metal-ion exchange. Furthermore, the incompatibility between the d8 electronic configuration of Ni2+ and the three-dimensional (3D) structure of ZIF-67 afforded the synthesis of hollow structures by controlling the amount of Ni doping. The formation of NiCo-MOF@CoOOH@V2 O5 nanocomposites is confirmed using X-ray absorption fine structure analysis. The high performance of the obtained composite is illustrated by fabricating a 3D-printed micro-supercapacitor, exhibiting a high area specific capacitance of 585 mF cm-2 and energy density of 159.23 µWh cm-2 (at power density = 0.34 mW cm-2 ). The solvent/coordination tuning strategy demonstrated in this study provides a new direction for the synthesis of high-performance nanomaterials for electrochemical energy storage applications.

Co-Intercalation of Dual Charge Carriers in Metal-Ion-Confining Layered Vanadium Oxide Nanobelts for Aqueous Zinc-Ion Batteries.

Vanadium-based oxides with high theoretical specific capacities and open crystal structures are promising cathodes for aqueous zinc-ion batteries (AZIBs). In this work, the confined synthesis can insert metal ions into the interlayer spacing of layered vanadium oxide nanobelts without changing the original morphology. Furthermore, we obtain a series of nanomaterials based on metal-confined nanobelts, and describe the effect of interlayer spacing on the electrochemical performance. The electrochemical properties of the obtained Al2.65 V6 O13 ⋅ 2.07H2 O as cathodes for AZIBs are remarkably improved with a high initial capacity of 571.7 mAh ⋅ g-1 at 1.0 A g-1 . Even at a high current density of 5.0 A g-1 , the initial capacity can still reach 205.7 mAh g-1 , with a high capacity retention of 89.2 % after 2000 cycles. This study demonstrates that nanobelts confined with metal ions can significantly improve energy storage applications, revealing new avenues for enhancing the electrochemical performance of AZIBs.

Unlocking the High Capacity Ammonium-Ion Storage in Defective Vanadium Dioxide.

Aqueous ammonium-ion storage has been considered a promising energy storage competitor to meet the requirements of safety, affordability, and sustainability. However, ammonium-ion storage is still in its infancy in the absence of reliable electrode materials. Here, defective VO2 (d-VO) is employed as an anode material for ammonium-ion batteries with a moderate transport pathway and high reversible capacity of ≈200 mAh g-1 . Notably, an anisotropic or anisotropic behavior of structural change of d-VO between c-axis and ab planes depends on the state of charge (SOC). Compared with potassium-ion storage, ammonium-ion storage delivers a higher diffusion coefficient and better electrochemical performance. A full cell is further fabricated by d-VO anode and MnO2 cathode, which delivers a high energy density of 96 Wh kg-1 (based on the mass of VO2 ), and a peak energy density of 3254 W kg-1 . In addition, capacity retention of 70% can be obtained after 10 000 cycles at a current density of 1 A g-1 . What's more, the resultant quasi-solid-state MnO2 //d-VO full cell based on hydrogel electrolyte also delivers high safety and decent electrochemical performance. This work will broaden the potential applications of the ammonium-ion battery for sustainable energy storage.

Ionically Conductive Tunnels in h-WO3 Enable High-Rate NH4 + Storage.

Compared to the commonly applied metallic ion charge carriers (e.g., Li+ and Na+ ), batteries using nonmetallic charge carriers (e.g., H+ and NH4 + ) generally have much faster kinetics and high-rate capability thanks to the small hydrated ionic sizes and nondiffusion control topochemistry. However, the hosts for nonmetallic charge carriers are still limited. In this work, it is suggested that mixed ionic-electronic conductors can serve as a promising host for NH4 + storage. Using hexagonal tungsten oxide (h-WO3 ) as an example, it is shown that the existence of ionic conductive tunnels greatly promotes the high-rate NH4 + storage. Specifically, a much higher capacity of 82 mAh g-1 at 1 A g-1 is achieved on h-WO3 , in sharp contrast to 14 mAh g-1 of monoclinic tungsten oxide (m-WO3 ). In addition, unlike layered materials, the insertion and desertion of NH4 + ions are confined within the tunnels of the h-WO3 , which minimizes the damage to the crystal structure. This leads to outstanding stability of up to 200 000 cycles with 68% capacity retention at a high current of 20 A g-1 .

Niobium Tungsten Oxide in a Green Water-in-Salt Electrolyte Enables Ultra-Stable Aqueous Lithium-Ion Capacitors.

Aqueous hybrid supercapacitors are attracting increasing attention due to their potential low cost, high safety and eco-friendliness. However, the narrow operating potential window of aqueous electrolyte and the lack of suitable negative electrode materials seriously hinder its future applications. Here, we explore high concentrated lithium acetate with high ionic conductivity of 65.5 mS cm-1 as a green "water-in-salt" electrolyte, providing wide voltage window up to 2.8 V. It facilitates the reversible function of niobium tungsten oxide, Nb18W16O93, that otherwise only operations in organic electrolytes previously. The Nb18W16O93 with lithium-ion intercalation pseudocapacitive behavior exhibits excellent rate performance, high areal capacity, and ultra-long cycling stability. An aqueous lithium-ion hybrid capacitor is developed by using Nb18W16O93 as negative electrode combined with graphene as positive electrode in lithium acetate-based "water-in-salt" electrolyte, delivering a high energy density of 41.9 W kg-1, high power density of 20,000 W kg-1 and unexceptionable stability of 50,000 cycles.

Dual Dopamine Derived Polydopamine Coated N-Doped Porous Carbon Spheres as a Sulfur Host for High-Performance Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are considered to be one of the most promising energy storage systems owing to their high energy density and low cost. However, their wide application is still limited by the rapid capacity fading. Herein, polydopamine (PDA)-coated N-doped hierarchical porous carbon spheres (NPC@PDA) are reported as sulfur hosts for high-performance Li-S batteries. The NPC core with abundant and interconnected pores provides fast electron/ion transport pathways and strong trapping ability towards lithium polysulfide intermediates. The PDA shell could further suppress the loss of lithium polysulfide intermediates through polar-polar interactions. Benefiting from the dual function design, the NPC/S@PDA composite cathode exhibits an initial capacity of 1331 mAh g-1 and remains at 720 mAh g-1 after 200 cycles at 0.5 C. At the pouch cell level with a high sulfur mass loading, the NPC/S@PDA composite cathode still exhibits a high capacity of 1062 mAh g-1 at a current density of 0.4 mA cm-2 .

Insights on the Proton Insertion Mechanism in the Electrode of Hexagonal Tungsten Oxide Hydrate.

This study reveals the transport behavior of lattice water during proton (de)insertion in the structure of the hexagonal WO3·0.6H2O electrode. By monitoring the mass evolution of this electrode material via electrochemical quartz crystal microbalance, we discovered (1) WO3·0.6H2O incorporates additional lattice water when immersing in the electrolyte at open circuit voltage and during initial cycling; (2) The reductive proton insertion in the WO3 hydrate is a three-tier process, where in the first stage 0.25 H+ is inserted per formula unit of WO3 while simultaneously 0.25 lattice water is expelled; then in the second stage 0.30 naked H+ is inserted, followed by the third stage with 0.17 H3O+ inserted per formula unit. Ex situ XRD reveals that protonation of the WO3 hydrate causes consecutive anisotropic structural changes: it first contracts along the c-axis but later expands along the ab planes. Furthermore, WO3·0.6H2O exhibits impressive cycle life over 20 000 cycles, together with appreciable capacity and promising rate performance.

Novel Potassium-Ion Hybrid Capacitor Based on an Anode of K2Ti6O13 Microscaffolds.

To fill the gap between batteries and supercapacitors requires integration of the following features in a single system: energy density well above that of supercapacitors, cycle life much longer than Li-ion batteries, and low cost. Along this line, we report a novel nonaqueous potassium-ion hybrid capacitor (KIC) that employs an anode of K2Ti6O13 (KTO) microscaffolds constructed by nanorods and a cathode of N-doped nanoporous graphenic carbon (NGC). K2Ti6O13 microscaffolds are studied for potential applications as the anode material in potassium-ion storage for the first time. This material exhibits an excellent capacity retention of 85% after 1000 cycles. In addition, the NGC//KTO KIC delivers a high energy density of 58.2 Wh kg-1 based on the active mass in both electrodes, high power density of 7200 W kg-1, and outstanding cycling stability over 5000 cycles. The usage of K ions as the anode charge carrier instead of Li ions and the amenable performance of this device suggest that hybrid capacitor devices may welcome a new era of beyond lithium.

High rate capability and superior cycle stability of a flower-like Sb2S3 anode for high-capacity sodium ion batteries.

Flower-like antimony sulfide structures were prepared by a simple and easy polyol reflux process. When tested as an anode for sodium ion batteries, the material delivered a high reversible capacity of 835.3 mA h g(-1) at 50 mA g(-1) after 50 cycles and maintained a capacity of 641.7 mA h g(-1) at 200 mA g(-1) after 100 cycles. Even up to 2000 mA g(-1), a capacity of 553.1 mA h g(-1) was obtained, indicating an excellent cycle performance and a superior rate capability. The mechanism of the formation of the micro-flowers was also investigated. The additive used facilitates the controlled release of the reactant to form uniform, shaped nanosheets and an optimum reaction time allows the nanosheets to self-assemble into micro-flowers.