Hybrid Aqueous/Nonaqueous Water-in-Bisalt Electrolyte Enables Safe Dual Ion Batteries.

Dual ion batteries (DIBs) have recently attracted ever-increasing attention owing to the potential advantages of low material cost and good environmental friendliness. However, the potential safety hazards, cost, and environmental concerns mainly resulted from the commonly used nonaqueous organic solvents severely hinder the practical application of DIBs. Herein, a hybrid aqueous/nonaqueous water-in-bisalt electrolyte with both broad electrochemical stability window and excellent safety performance is developed. The lithium-based DIB assembled using KS6 graphite and niobium pentoxide as the active materials in the cathode and anode exhibits good comprehensive performance including capacity, cycling stability, rate performance, and medium discharge voltage. Initial capacities of ≈47.6 and 29.6 mAh g-1 retention after 300 cycles can be delivered with a medium discharge voltage of around 2.2 V in the voltage window of 0-3.2 V at the current density of 200 mA g-1 . Good rate performance for the battery can be indicated by 29.7 mAh g-1 discharge capacity retention at 400 mA g-1 . It is noteworthy that the coulombic efficiency of the battery can reach as high as 93.9%, which is comparable to that of the corresponding DIBs using nonaqueous organic electrolytes.

A Dual Carbon-Based Potassium Dual Ion Battery with Robust Comprehensive Performance.

Dual carbon-based potassium dual ion batteries (K-DCBs) have recently attracted ever-increasing attention owing to the potential advantages of high performance-to-cost ratio, good safety, and environmental friendliness. However, the reported K-DCBs still cannot simultaneously meet the requirements of high capacity, long cycling stability, and low cost, which are necessary for practical applications. In this study, a K-DCB with good comprehensive performance including capacity, cycling stability, medium discharge voltage, and energy density is developed by introducing the optimal cathode and anode materials, i.e., KS6 and natural graphite, respectively. An initial capacity of ≈54.6 mAh g-1 and 92.5% capacity retention after 400 cycles can be delivered in a wide voltage window of 2.4-5.4 V at the current density of 100 mA g-1 . A high medium discharge voltage around 4.2 V and an energy density up to 158.3 Wh kg-1 are meanwhile delivered by the K-DCB. In addition, the working mechanism of the devices is understood in detail. It is believed that valuable contributions to the electrochemical performance improvement of the related devices toward practical applications can be provided by this study.

Enhancement of zinc-ion storage capability by synergistic effects on dual-ion adsorption in hierarchical porous carbon for high-performance aqueous zinc-ion hybrid capacitors.

Aqueous zinc-ion capacitors (AZICs) are considered potential energy storage devices thanks to their ultrahigh power density, high safety, and extended cycling life. Carbon-based materials widely used as cathodes in AZICs face challenges, such as inappropriate pore sizes, poor electrolyte-electrode wettability, and insufficient vacancy defects and active sites. These limitations hinder efficient energy storage capacity and long-term stability. To address these issues, the B and F co-doped hierarchical porous carbon cathode materials (BFPC) are constructed through a facile annealing treatment process. The BFPC-2//Zn device exhibited high capacities of 222.4 and 118.3 mAh g-1 at current densities of 0.2 and 10 A g-1, respectively. Notably, the BFPC-2//Zn device demonstrated long-term cycling stability with a high capacity retention of 96.9 % after 20,000 cycles at 10 A g-1. Additionally, the assembled BFPC-2 based AZICs displayed a maximum energy density of 175.8 Wh kg-1 and an ultrahigh power density of 17.3 kW kg-1. Mechanism studies revealed that the exceptional energy storage ability and charge-transfer process of the BFPC cathode are attributed to the synergistic effect of B and F heteroatoms and the coupling effect between vacancy defects and pore size. This work presents a novel design strategy by incorporating B and F active sites into hierarchical porous carbon materials, providing enhanced energy storage capabilities for practical application in AZICs.

Pore-forming mechanisms and sodium-ion-storage performances in a porous Na3V2(PO4)3/C composite cathode.

Na3V2(PO4)3 (NVP) is regarded as one of the most promising cathode materials for sodium-ion batteries (SIBs). However, it suffers from a dense bulk structure and low intrinsic electronic conductivity, which lead to limited electrochemical performances. Herein, we propose a surfactant-assisted molding strategy to regulate the pore-forming process in NVP/C composite cathode materials. More precisely, the forming process of the pores in NVP could be easily controlled by utilizing the huge difference in critical micelle concentration of a surfactant (cetyltrimethylammonium bromide, CTAB) in water and ethanol. By reasonably modulating the ratio of water and ethanol in the solution, the as-synthesized NVP/C sample exhibited a three-dimensional interconnected structure with hierarchical micro/meso/macro-pores. Benefiting from these hierarchical porous structures in NVP/C, the structural stability, contact surface with the electrolyte, and electronic/ionic conductivity were improved simultaneously; whereby the optimized porous NVP/C sample exhibited an excellent high-rate performance (61.3 mA h g-1 at 10 C) and superior cycling stability (90.2% capacity retention after 500 cycles at 10 C).

Fabrication of dual heteroatom-doped graphitic carbon from waste sponge with "killing two birds with one stone" strategy for advanced aqueous zinc-ion hybrid capacitors.

Emerging aqueous zinc-ion hybrid capacitors (AZICs) are considered a promising energy storage because of their superior electrochemical performance. The pore structure, suitable heteroatom content, and graphitization degree (GD) of carbon-based cathodes significantly influence the electrochemical performance of AZICs. The N, S dual-doped porous graphitic carbon materials (LC-750) with the combined characteristics of high GD (1.11) and large specific surface area (1678.38 m2 g-1) are successfully developed by a facile "killing two birds with one stone" strategy using K3Fe(C2O4)3·3H2O as the activating and graphitizing agent, and waste sponge (WS) and coal tar pitch (CTP) as the heteroatom and carbon resource, respectively. Results show that the LC-750 cathode displays high capacities of 185.3 and 95.2 mAh g-1 at 0.2 and 10 A g-1. Specifically, the assembled LC-750//Zn capacitor can offer a maximal energy density of 119.5 Wh kg-1, a power density of 20.3 kW kg-1, and a capacity retention of 87.8% after 15,000 cycles at 10 A g-1. Density functional theory simulations demonstrate that N and S dual-doping can promote the adsorption kinetics of Zn ions. This design strategy is a feasible and cost-effective method for the preparation of dual heteroatom-doped graphitic carbon electrodes, which enables recycling of WS and CTP into high-valued products.

Enhanced field emission performance of MXene-TiO2 composite films.

A facile method to produce an MXene-TiO2 composite is demonstrated for enhanced field emission display applications. The field emission performance of two-dimensional free-standing and linear-shaped field emitters has been systematically investigated and enhanced electron emission behaviors (e.g. emission current, stability and emission patterns) are achieved by compositing MXene and TiO2 nanowires. The relationship between the emission current density, electric field and anode-cathode gap distance is studied and the emitters, especially the cross-section of the composite film, show good performance. The emission current from the cross-section of the composite film can reach 289 mA cm-2, which is the best result of the state of the art compared to single MXene and TiO2 nanowires. We have also reported a triboelectric nanogenerator powered by free-standing MXene-TiO2 composite emitters, implying the feasibility of the self-powering field emission devices and possibly enlarging the applications of cold emitters in various fields.

Revealing the Impact of Oxygen Dissolved in Electrolytes on Aqueous Zinc-Ion Batteries.

Aqueous zinc-ion batteries (ZIBs) are promising low-cost and high-safety energy storage devices. However, their capacity decay especially at the initial cyclic stage is a serious issue. Herein, we reveal that the dissolved oxygen in aqueous electrolyte has significant impact on the electrochemistry of Zn anode and ZIBs. After removing oxygen, the symmetrical set-up of Zn/Zn is capable of reversible plating/stripping with a 20-fold lifetime enhancement compared with that in oxygen enrichment condition. Taking aqueous Zn-MnO2 battery as an example, although the presence of oxygen can contribute an extra capacity over 20% at the initial cycles due to the electrocatalytic activity of MnO2 with oxygen, the corrosion of Zn anode can be eliminated in the oxygen-free circumstance and thus offering a better reversible energy storage system. The impact of the dissolved oxygen on the cycling stability also exists in other ZIBs using vanadium-based compounds, Birnessite and Prussian blue analog cathodes.

Opening Magnesium Storage Capability of Two-Dimensional MXene by Intercalation of Cationic Surfactant.

Two-dimensional (2D) Ti3C2 MXene has attracted great attention in electrochemical energy storage devices (supercapacitors and lithium-ion and sodium-ion batteries) due to its excellent electrical conductivity as well as high volumetric capacity. Nevertheless, a previous study showed that multivalent Mg2+ ions cannot reversibly insert into MXene, resulting in a negligible capacity. Here, we demonstrate a simple strategy to achieve high magnesium storage capability for Ti3C2 MXene by preintercalating a cationic surfactant, cetyltrimethylammonium bromide (CTAB). Density functional theory simulations verify that intercalated CTA+ cations reduce the diffusion barrier of Mg2+ on the MXene surface, resulting in the significant improvement of the reversible insertion/deinsertion of Mg2+ ions between MXene layers. Consequently, the MXene electrode exhibits a desirable volumetric specific capacity of 300 mAh cm-3 at 50 mA g-1 as well as outstanding rate performance. This work endows MXene material with an application in electrochemical energy storage and, simultaneously, introduces magnesium battery materials as a member.

Silica-grafted ionic liquids for revealing the respective charging behaviors of cations and anions in supercapacitors.

Supercapacitors based on activated carbon electrodes and ionic liquids as electrolytes are capable of storing charge through the electrosorption of ions on porous carbons and represent important energy storage devices with high power delivery/uptake. Various computational and instrumental methods have been developed to understand the ion storage behavior, however, techniques that can probe various cations and anions of ionic liquids separately remain lacking. Here, we report an approach to monitoring cations and anions independently by using silica nanoparticle-grafted ionic liquids, in which ions attaching to silica nanoparticle cannot access activated carbon pores upon charging, whereas free counter-ions can. Aided by this strategy, conventional electrochemical characterizations allow the direct measurement of the respective capacitance contributions and acting potential windows of different ions. Moreover, coupled with electrochemical quartz crystal microbalance, this method can provide unprecedented insight into the underlying electrochemistry.