Enhancing the supercapacitive performance of a carbon-based electrode through a balanced strategy for porous structure, graphitization degree and N,B co-doping.

Regarding carbon-based electrodes, simultaneously establishing a well-defined meso-porous architecture, introducing abundant hetero-atoms and improving the graphitization degree can effectively enhance their capacitive performance. However, it remains a significant challenge to achieve a good balance between defects and graphitization degree. In this study, the porous structure and composition of carbon materials are co-optimised through a 'dual-function' strategy. Briefly, K3Fe(C2O4)3 and H3BO3 were hybridised with a gelatin aqueous solution to form a homogeneous composite hydrogel, followed by lyophilisation and carbonisation. Owing to the dual functionality of raw materials, the graphitization, activation and hetero-atom doping processes can occur simultaneously during a one-step high-temperature treatment. The resultant carbon material exhibits a high graphitization degree (ID/IG = 0.9 ± 0.1), high hetero-atom content (N: 9.0 ± 0.3 at.%, B: 6.9 ± 0.5 at.%) and a large specific area (1754 ± 58 m2/g). The as-prepared electrode demonstrates a superior capacitance of 383 ± 1F g-1 at 1 A/g. Interestingly, the cyclic voltammetry (CV) curves exhibit a distinctive pair of broad redox peaks, which is uncommon in KOH electrolyte. Experiment data and density functional theory (DFT) simulation verify that N-5, B co-doping enhances the activity of the faradic reaction of carbon electrodes in KOH electrolyte. Furthermore, the fabricated Zn-ion hybrid supercapacitor (ZHSC) based on this carbon electrode delivers a high-energy density of 140.7 W h kg-1 at a power density of 840 W kg-1.

K3 v2 (Po4 )3 /C as a New High-Voltage Cathode Material for Calcium-Ion Batteries with a Water-In-Salt Electrolyte.

Aqueous Ca-ion batteries (ACIBs) attract immense attention due to its high safety and the high abundance of calcium. However, the development of ACIBs is hindered by the lack of high voltage cathode materials to host the large radius and divalent Ca2+ . Herein, polyanionic phosphate K3 V2 (PO4 )3 /C (KVP/C) is provided as a new cathode material for ACIBs. Due to the robust structure of polyanion material and the wide electrochemical window of water-in-salt electrolyte, KVP/C delivers a high working voltage of 3.74 V versus Ca2+ /Ca with a specific capacity of 102.4 mAh g-1 and a long-life of 6000 cycles at 500 mA g-1 . Furthermore, the calcium storage mechanism of KVP/C is shown to be the coexistence of solid solution and two-phase reaction by in situ X-ray diffraction, ex situ transmission electron microscope, and X-ray photoelectron spectroscopy. Finally, an aqueous calcium-ion full cell, based on an organic compound as anode and KVP/C as cathode, is constructed and it shows good stability for 200 cycles and a specific capacity of 80.2 mAh g-1 . This work demonstrates that vanadium-based phosphate materials are promising high-voltage cathode materials for ACIBs and renew the prospects for ACIBs.

Mg2+ Ion Pre-Insertion Boosting Reaction Kinetics and Structural Stability of Ammonium Vanadates for High-Performance Aqueous Zinc-Ion Batteries.

Aqueous zinc-ion batteries (AZIBs) attract much attention owing to their high safety, environmentally friendliness and low cost. However, the unsatisfactory performance of cathode materials is one of the unsolved important factors for their widespread application. Herein, we report NH4 V4 O10 nanorods with Mg2+ ion preinsertion (Mg-NHVO) as a high-performance cathode material for AZIBs. The preinserted Mg2+ ions effectively improve the reaction kinetics and structural stability of NH4 V4 O10 (NHVO), which are confirmed by electrochemical analysis and density functional theory calculations. Compared with pristine NHVO, the intrinsic conductivity of Mg-NHVO is improved by 5 times based on the test results of a single nanorod device. Besides, Mg-NHVO could maintain a high specific capacity of 152.3 mAh g-1 after 6000 cycles at the current density of 5 A g-1 , which is larger than that of NHVO (only exhibits a low specific capacity of 30.5 mAh g-1 at the same condition). Moreover, the two-phase crystal structure evolution process of Mg-NHVO in AZIBs is revealed. This work provides a simple and efficient method to improve the electrochemical performance of ammonium vanadates and enhances the understanding about the reaction mechanism of layered vanadium-based materials in AZIBs.

Material Optimization Engineering toward xLiFePO4·yLi3V2(PO4)3 Composites in Application-Oriented Li-Ion Batteries.

The development of LiFePO4 (LFP) in high-power energy storage devices is hampered by its slow Li-ion diffusion kinetics. Constructing the composite electrode materials with vanadium substitution is a scientific endeavor to boost LFP's power capacity. Herein, a series of xLiFePO4·yLi3V2(PO4)3 (xLFP·yLVP) composites were fabricated using a simple spray-drying approach. We propose that 5LFP·LVP is the optimal choice for Li-ion battery promotion, owning to its excellent Li-ion storage capacity (material energy density of 413.6 W·h·kg-1), strong machining capability (compacted density of 1.82 g·cm-3) and lower raw material cost consumption. Furthermore, the 5LFP·LVP||LTO Li-ion pouch cell also presents prominent energy storage capability. After 300 cycles of a constant current test at 400 mA, 75% of the initial capacity (379.1 mA·h) is achieved, with around 100% of Coulombic efficiency. A capacity retention of 60.3% is displayed for the 300th cycle when discharging at 1200 mA, with the capacity fading by 0.15% per cycle. This prototype provides a valid and scientific attempt to accelerate the development of xLFP·yLVP composites in application-oriented Li-ion batteries.

CNTs/LiV3O8/Y2O3 Composites with Enhanced Electrochemical Performances as Cathode Materials for Rechargeable Solid-State Lithium Metal Batteries.

Solid-state lithium metal battery (SSLMB) is regarded as a safer energy storage system compared to the liquid one. The performance of the SSLMB depends on the cathode performance and the side reactions derived from the interface of the cathode and the electrolyte, which becomes much severe at high temperatures. Herein, we carried out a facile spray-drying route to prepare a CNTs/LiV3O8/Y2O3 (M-LVO-Y) composite. The synthesized cathode material exhibits an outstanding Li+ storage performance with a high reversible capacity of 279.9 mA h g-1 at 0.05 A g-1, excellent power capability (182.5 mA h g-1 at 2 A g-1), and a long cycle lifespan of 500 cycles with a capacity retention of 66.5% at a current density of 1 A g-1. The fabricated rechargeable solid-state Li/M-LVO-Y-2 lithium metal battery (LMB) with a poly(ethylene oxide) (PEO)-based solid polymer electrolyte (SPE) achieves a high discharge capacity of 302.1 mA h g-1 at 0.05 A g-1 and a stable cycling performance with the highest capacity of 72.1% after 100 cycles at 0.2 A g-1 and 80 °C. The above battery performance demonstrates that SSLMBs with the CNTs/LiV3O8/Y2O3 cathode and the PEO-based SPE film can provide high energy density and are suitable for applying in a high-temperature environment.

Methanol-derived high-performance Na3V2(PO4)3/C: from kilogram-scale synthesis to pouch cell safety detection.

Na3V2(PO4)3 (NVP) is regarded as a potential cathode material that can be applied in sodium ion batteries (SIBs) owing to its NASICON structure. However, most of the reported works have focused on the synthesis of materials and the improvement of their electrochemical properties, with little research on the design and safety of pouch cells. Herein, we implemented a cost-saving route to realize the industrial-scale synthesis of NVP cathode materials. The obtained NVP samples possess an impressive Na-ion storage capability with high reversible capacity (116.3 mA h g-1 at 0.2 C), superior power capability (97.9 mA h g-1 at 30 C), and long lifespan (71.6% capacity retention after 2500 cycles at 20 C). It was remarkable that industrial-scale NVP/hard carbon (HC) sodium-ion pouch cells could be designed with an 823 mA h discharge capacity at a current of 200 mA (about 0.25 C), and which possess a long life and high rate performance (1000 cycles with a little decay at a current of 4000 mA). Besides, the pouch cells also exhibit excellent thermal stability when demonstrated for application in unmanned aerial vehicles (UAVs), and puncturing experiment results can further prove the excellent safety performance of NVP-hard carbon pouch cells.

Three-Dimensional LiMnPO4·Li3V2(PO4)3/C Nanocomposite as a Bicontinuous Cathode for High-Rate and Long-Life Lithium-Ion Batteries.

Olivine-type LiMnPO4 has been extensively studied as a high-energy density cathode material for lithium-ion batteries. To improve both the ionic and electronic conductivities of LiMnPO4, a series of carbon-decorated LiMnPO4·Li3V2(PO4)3 nanocomposites are synthesized by a facile sol-gel method combined with the conventional solid-state method. The optimized composite presents a three-dimensional hierarchical structure with active nanoparticles well-embedded in a conductive carbon matrix. The combination of the nanoscale carbon coating and the microscale carbon network could provide a more active site for electrochemical reaction, as well as a highly conductive network for both electron and lithium-ion transportation. When cycled at 20 C, an initial specific capacity of 103 mA h g(-1) can be obtained and the capacity retention reaches 68% after 3000 cycles, corresponding to a capacity fading of 0.013% per cycle. The stable capacity and excellent rate capability make this carbon-decorated LiMnPO4·Li3V2(PO4)3 nanocomposite a promising cathode for lithium-ion batteries.

Substrate-assisted self-organization of radial ß-AgVO3 nanowire clusters for high rate rechargeable lithium batteries.

Rational assembly of unique complex nanostructures is one of the facile techniques to improve the electrochemical performance of electrode materials. Here, a substrate-assisted hydrothermal method was designed and applied in synthesizing moundlily like radial ß-AgVO(3) nanowire clusters. Gravitation and F(-) ions have been demonstrated to play important roles in the growth of ß-AgVO(3) nanowires (NWs) on substrates. The results of cyclic voltammetry (CV) measurement and X-ray diffraction (XRD) characterization proved the phase transformation from ß-AgVO(3) to Ag(1.92)V(4)O(11) during the redox reaction. Further electrochemical investigation showed that the moundlily like ß-AgVO(3) nanowire cathode has a high discharge capacity and excellent cycling performance, mainly due to the reduced self-aggregation. The capacity fading per cycle from 3rd to 51st is 0.17% under the current density of 500 mA/g, which is much better than 1.46% under that of 20 mA/g. This phenomenon may be related to the Li(+) diffusion and related kinetics of the electrode. This method is shown to be an effective and facile technique for improving the electrochemical performance for applications in rechargeable Li batteries or Li ion batteries.

Single beta-AgVO3 nanowire H2S sensor.

We report the electrical transport and H(2)S sensing properties of single beta-AgVO(3) nanowire device. beta-AgVO(3) nanowires were successfully prepared by ultrasonic treatment followed by hydrothermal reaction using V(2)O(5) sol. The individual beta-AgVO(3) nanowire exhibits a "threshold switching" phenomenon. High bias (i.e., 6 V for Au contacts) is required to initially switch the individual nanowire device from nonconductive to conductive, and it may be related to the formation of nanoscale metallic Ag when enough voltage is applied between the two electrodes. This novel nanomaterial shows good H(2)S sensing performances with short response and recovery time within 20 s, relatively low response concentration of 50 ppm, and good selectivity.