Tailoring Oxygen Reduction Reaction Kinetics on Perovskite Oxides via Oxygen Vacancies for Low-Temperature and Knittable Zinc-Air Batteries.

High kinetics oxygen reduction reaction (ORR) electrocatalysts under low temperature are critical and highly desired for temperature-tolerant energy conversion and storage devices, but remain insufficiently investigated. Herein, oxygen vacancy-rich porous perovskite oxide (CaMnO3 ) nanofibers coated with reduced graphene oxide coating (V-CMO/rGO) are developed as the air electrode catalyst for low-temperature and knittable Zn-air batteries. V-CMO/rGO exhibits top-level ORR activity among perovskite oxides and shows impressive kinetics under low temperature. Experimental and theoretical calculation results reveal that the synergistic effect between metal atoms and oxygen vacancies, as well as the accelerated kinetics and enhanced electric conductivity and mass transfer over the rGO coated nanofiber 3D network contribute to the enhanced catalytic activity. The desorption of ORR intermediate is promoted by the regulated electron filling. The V-CMO/rGO drives knittable and flexible Zn-air batteries under a low temperature of -40 °C with high peak power density of 56 mW cm-2 and long cycle life of over 80 h. This study provides insight of kinetically active catalyst and facilitates the ZABs application in harsh environment.

MOF derived double-carbon layers boosted the lithium/sodium storage performance of SnO2nanoparticles.

Tin oxide (SnO2) was considered as a promising alternative to commonly used graphite anode in energy storage devices thanks to its superior specific capacity. However, its electrochemical property was severely limited due to the inherent poor conductivity and drastic volume variation during the charging/discharging process. To overcome this disadvantage, we grew Sn-MOF directly on graphene oxide (GO) layers to synthesize a double carbon conductive network-encapsulated SnO2nanoparticles (SnO2/C/rGO) via a facile solvothermal method. During the process, Sn-MOF skeleton transformed into porous carbon shells, in which nanosized SnO2particles (~8nm) were embedded, while GO template was reduced to highly conductive rGO layer tightly wrapping the SnO2/C particles. This double-carbon structure endowed SnO2/C/rGO anode with enhanced specific capacity and rate property both in lithium ion batteries (LIB) and sodium ion batteries (SIB). The SnO2/C/rGO anode showed a highly reversible specific capacity of 1038.3 mAh g-1at 100 mA g-1, and maintained a stable capacity of 720.2 mAh g-1(70.1%) under 500 mA g-1after 150 cycles in LIBs. Similarly, highly reversible capacity of 350.7 mAh g-1(81.1%) under 100 mA g-1after 150 cycles was also achieved in SIBs. This work provided a promising strategy in improving the electrochemical properties of SnO2nanoparticles (NPs), as well as other potential anode materials suffering from huge volume change and poor conductivity.

MOF-derived porous carbon nanofibers wrapping Sn nanoparticles as flexible anodes for lithium/sodium ion batteries.

Facile synthesis of flexible electrodes with high reversible capacity plays a key role in meeting the ever-increasing demand for flexible batteries. Herein, we incorporated Sn-based metal-organic framework (Sn-MOF) templates into crosslinked one-dimensional carbon nanofibers (CNFs) using an electrospinning strategy and obtained a hierarchical porous film (Sn@C@CNF) after a carbothermal reduction reaction. Merits of this modification strategy and its mechanism in improving the electrochemical performance of Sn nanoparticles (NPs) were revealed. Electrospun CNFs substrate ensured a highly conductive skeleton and excellent mechanical toughness, making Sn@C@CNF a self-supported binder-free electrode. Serving as a self-sacrificing template, Sn-MOF provided Sn NPs and derived into porous structures on CNFs after pyrolysis. The hierarchical porous structure of the carbon substrate was beneficial to enhancing the Li+/Na+ storage of the active materials, and the carbon wrappings derived from polyacrylonitrile (PAN) nanofibers and the MOF skeleton could jointly accommodate the violent volume variation during cycling, enabling Sn@C@CNF to have excellent cycle stability. The Sn@C@CNF anode exhibited a stable discharge specific capacity of 610.8 mAh g-1 under 200 mA g-1 for 180 cycles in lithium ion batteries (LIBs) and 360.5 mAh g-1 under 100 mA g-1 after 100 cycles in sodium ion batteries (SIBs). As a flexible electrode, Sn@C@CNF demonstrated a stable electromechanical response to repeated 'bending-releasing' cycles and excellent electrochemical performance when assembled in a soft-pack half-LIB. This strategy provided promising candidates of active materials and fabrication methods for advanced flexible batteries.

Stereoassembled V2O5@FeOOH Hollow Architectures with Lithiation Volumetric Strain Self-Reconstruction for Lithium-Ion Storage.

Vanadium oxides have recently attracted widespread attention due to their unique advantages and have demonstrated promising chemical and physical properties for energy storage. This work develops a mild and efficient method to stereoassemble hollow V2O5@FeOOH heterostructured nanoflowers with thin nanosheets. These dual-phased architectures possess multiple lithiation voltage plateau and well-defined heterointerfaces facilitating efficient charge transfer, mass diffusion, and self-reconstruction with volumetric strain. As a proof of concept, the resulting V2O5@FeOOH hollow nanoflowers as an anode material for lithium-ion batteries (LIBs) realize high-specific capacities, long lifespans, and superior rate capabilities, e.g., maintaining a specific capacity as high as 985 mAh g-1 at 200 mA g-1 with good cyclability.

Selective Solid-Liquid Interface Sulfidation Growth of Hierarchical Copper Sulfide and Its Hybrid Nanoflakes for Superior Lithium-Ion Storage.

Two-dimensional metal sulfides and their hybrids are emerging as promising candidates in various areas. Yet, it remains challenging to synthesize high-quality 2D metal sulfides and their hybrids, especially iso-component hybrids, in a simple and controllable way. In this work, a low-temperature selective solid-liquid sulfidation growth method has been developed for the synthesis of CuS nanoflakes and their hybrids. CuS nanoflakes of about 20 nm thickness and co-component hybrids CuOx /CuS with variable composition ratios derived from different sulfidation time are obtained after the residual sulfur removal. Besides, benefiting from the mild low-temperature sulfidation conditions, selective sulfidation is realized between Cu and Fe to yield iso-component FeOx /CuS 2D nanoflakes of about 10-20 nm thickness, whose composition ratio is readily tunable by controlling the precursor. The as-synthesized FeOx /CuS nanoflakes demonstrate superior lithium storage performance (i. e., 707 mAh g-1 at 500 mA g-1 and 627 mAh g-1 at 1000 mA g-1 after 450 cycles) when tested as anode materials in LIBs owing to the advantages of the ultrathin 2D nanostructure as well as the lithiation volumetric strain self-reconstruction effect of the co-existing two phases during charging/discharging processes.

General Approach to Single and Hybrid Metal Oxide Fiber Structures for High-Performance Lithium-Ion Batteries.

Owing to the high specific capacity and energy density, metal oxides have become very promising electrodes for lithium-ion batteries (LIBs). However, poor electrical conductivity accompanied with inferior cycling stability resulting from large volume changes are the main obstacles to achieve a high reversible capacity and stable cyclability. Herein, a facile and general approach to fabricate SnO2 , Fe2 O3 and Fe2 O3 /SnO2 fibers is proposed. The appealing structural features are favorable for offering a shortened lithium-ion diffusion length, easy access for the electrolyte and reduced volume variation when used as anodes in LIBs. As a consequence, both single and hybrid oxides show satisfactory reversible capacities (1206 mAh g-1 for Fe2 O3 and 1481 mAh g-1 for Fe2 O3 /SnO2 after 200 cycles at 200 mA g-1 ) and long lifespans.

Surface Anionization of Self-Assembled Iron Sulfide Hierarchitectures to Enhance Capacitive Storage for Alkaline-Metal-Ion Batteries.

Due to the ever-growing demand for cost-effective batteries toward greener and sustainable applications, continuous effort has been devoted to tailoring the interfacial kinetics of electrode materials. Herein, surface anionization has been introduced for the hierarchical assembly of iron sulfides on three-dimensional (3D) graphene foam (denoted FeS2@3DGF and FeS@3DGF). The surface-anchored sulfate species provide ideal electroactive sites, which is correlated with enhanced capacitive contribution and boosted energy storage. Consequently, remarkable rate capability and stable cyclability can be achieved in alkaline-metal-ion batteries. Specifically, FeS@3DGF displays superb cycling stability when evaluated as anodes for Li-ion batteries (a steady capacity of 1109 mAh g-1 after 200 cycles at 200 mA g-1). Moreover, superior rate capability can be achieved for Na-ion batteries (203 mAh g-1 at 10 000 mA g-1). These findings provide new insights into reinforcing interface kinetics during electrochemical processes and hold great promise for versatile applications in the future.

Rational Design of a Flexible CNTs@PDMS Film Patterned by Bio-Inspired Templates as a Strain Sensor and Supercapacitor.

Flexible devices integrated with sensing and energy storage functions are highly desirable due to their potential application in wearable electronics and human motion detection. Here, a flexible film is designed in a facile and low-cost leaf templating process, comprising wrinkled carbon nanotubes (CNTs) as the conductive layer and patterned polydimethylsiloxane (PDMS) with bio-inspired microstructure as a soft substrate. Assembled from wrinkled CNTs on patterned PDMS film, a strain sensor is realized to possess sensitive resistance response against various deformations, producing a resistance response of 0.34%, 0.14%, and 9.1% under bending, pressing, and 20% strain, respectively. Besides, the strain sensor can reach a resistance response of 3.01 when stretched to 44%. Furthermore, through the electro-deposition of polyaniline, the CNTs film is developed into a supercapacitor, which exhibits a specific capacitance of 176 F g-1 at 1 A g-1 and a capacitance retention of 88% after 10 000 cycles. In addition, the fabricated supercapacitor shows super flexibility, delivering a capacitance retention of 98% after 180° bending for 100 cycles, 95% after 45° twisting for 100 cycles, and 98% after 100% stretching for 400 cycles. The superior capacitance stability demonstrates that the design of wrinkled CNTs-based electrodes fixed by microstructures is beneficial to the excellent electrochemical performance.

Stereoselectively Assembled Metal-Organic Framework (MOF) Host for Catalytic Synthesis of Carbon Hybrids for Alkaline-Metal-Ion Batteries.

Cost-effective metal-based nanostructured hybrids have been widely dedicated to potential energy storage and conversion applications. Herein, we develop a facile methodology for the synthesis of precise carbon-confined hybrid nanostructures by stereoselective assembly accompanied by catalytic pyrolysis. Polyacrylonitrile fiber films favors not only metal-polymer coordination, but also oriented assembly to ensure the well-defined nanostructure of the carbon hybrids. During chemical vapor deposition (CVD), cobalt-nanoparticle-catalyzed growth of carbon-nanotube branches driven by organic molecules (e.g. melamine) delivers hierarchical carbon hybrids. The resulting carbon hybrids exhibit outstanding electrochemical performance for metal-ion batteries, for example, a high specific capacity of 680 mAh g-1 after 320 cycles (Li-storage) and 220 mAh g-1 after 500 cycles (Na-storage) without decay.

Topochemical pyrolytic synthesis of quasi-Mxene hybrids via ionic liquid-iron phthalocyanine as a self-template.

A quasi-Mxene architecture was synthesized by 1-ethyl-3-methylimidazolium dicyanamide-iron phthalocyanine via self-template pyrolysis. The unique quasi-Mxene structure results in a rich contact area and good electronic conductivity, showing excellent rate capacity and cycling stability for lithium storage.