Fabrication of three-dimensional hollow C@CoO@graphene composite anode for long-life Li-ion batteries

Graphene-wrapped yolk-shell of silica-cobalt oxide as high-performing anode for lithium-ion batteries

Silica (SiO2) shows promise as anode material for lithium-ion batteries due to its low cost, comparable lithium storage discharge potential and high theoretical capacity (approximately 1961 mA h g-1). However, it is plagued by issues of low electrochemical activity, low conductivity and severe volume expansion. To address these challenges, we initially coat SiO2 with CoO, followed by introducing SiO2@CoO into graphene sheets to fabricate an anode composite material (SiO2@CoO/GS) with uniformly dispersed particles and a 3D graphene wrapped yolk-shell structure. The coating of CoO on SiO2 converted the negative surface charge of SiO2 to positive, enabling effective electrostatic interactions between SiO2@CoO and graphene oxide sheets, which provided essential prerequisites for synthesizing composite materials with uniformly dispersed particles and good coating effects. Furthermore, the Co-metal formed during the charge-discharge process can act as a catalyst and electron transfer medium, activating the lithium storage activity of SiO2 and enhancing the conductivity of the electrode, conclusively achieving a higher lithium storage capacity. Ultimately, due to the activation of SiO2 by Co-metal during cycling and the excellent synergistic effect between SiO2@CoO and graphene, SiO2@CoO/GS delivers a high reversible capacity of 738 mA h g-1 after 500 cycles at 200 mA g-1. The product also demonstrates excellent rate performance with a reversible capacity of 206 mA h g-1 at a high specific current of 12.8 A g-1. The outstanding rate performance of SiO2@CoO/GS may be ascribed to the pseudo-capacitive contribution at high specific current upon cycling.

Consecutive engineering of anodic graphene supported cobalt monoxide composite and cathodic nanosized lithium cobalt oxide materials with improved lithium-ion storage performances

Downsizing the electrochemically active materials in both cathodic and anodic electrodes commonly brings about enhanced lithium-ion storage performances. It is particularly meaningful to explore simplified and effective strategies for exploiting nanosized electrode materials in the advanced lithium-ion batteries. In this work, the spontaneous reaction between few-layered graphene oxide (GO) and metallic cobalt (Co) foils in mild hydrothermal condition is for the first time employed to synthesize a reduced graphene oxide (RGO) supported nanosized cobalt monoxide (CoO) anode material (CoO@RGO). Furthermore, the CoO@RGO sample is converted to nanosized lithium cobalt oxide cathode material (LiCoO2, LCO) by taking the advantages of the self-templated effect. As a result, both the CoO@RGO anode and the LCO cathode exhibit inspiring lithium-ion storage properties. In half-cells, the CoO@RGO sample maintains a reversible capacity of 740.6 mAh·g-1 after 300 cycles at the current density of 1000 mA·g-1 while the LCO sample delivers a reversible capacity of 109.1 mAh·g-1 after 100 cycles at the current density of 100 mA·g-1. In the CoO@RGO//LCO full-cells, the CoO@RGO sample delivers a reversible capacity of 553.9 mAh·g-1 after 50 cycles at the current density of 200 mA·g-1. The reasons for superior electrochemical behaviors of the samples have been revealed, and the strategy in this work can be considered to be straightforward and effective for engineering both anode and cathode materials for lithium-ion batteries.

Hierarchical porous Co-CoO@NC hollow microspheres with capacity growth by reactivation of solid-electrolyte interface films

Transition metal oxide (TMO)-based electrodes exhibit increased capacities, yet the mechanism behind the true cause of capacity in such materials remains unclear. Herein, hierarchical porous and hollow Co-CoO@NC spheres assembled by nanorods with refined nanoparticles and amorphous carbon have been synthesized by a two-step annealing approach. A temperature gradient-driven mechanism is revealed for the evolution of the hollow structure. Compared with the solid CoO@NC spheres, the novel hierarchical of Co-CoO@NC can fully utilize the interior active material by exposing both ends of each nanorod into electrolyte. The hollow interior provides extra space for the volume variation, leading to an up-trend capacity of 919.3 mAh g^-1 at 200 mA g^-1 over 200 cycles. Differential capacity curves disclose that solid electrolyte interface (SEI) films reactivation partly contributes to increasing reversible capacity. The introduction of nanosized Co particles benefits the process by participating in the transformation of SEI components. This study provides a guide for constructing anodic material with exceptional electrochemical performance.

Dual Enhancement of Sodium Storage Induced through Both S-Compositing and Co-Doping Strategies

As a promising alternative to lithium-ion batteries (LIBs), rechargeable sodium-ion batteries (SIBs) are attracting enormous attention due to the abundance of sodium. However, the lack of high-performance sodium anode materials limits the commercialization of SIBs. In this work, the dual enhancement of SnS₂/graphene anodes in sodium storage is achieved through S-compositing and Co doping via an innovative one-step hydrothermal reaction at a relatively low temperature of 120 °C. The as-prepared 7% Co-SnS₂/S@r-G composite consisting of 15.4 wt % S and 1.49 atom % Co shows both superior cycling stability (over 1000 cycles) and rate capability, giving high reversible specific capacities of 878, 608, and 470 mAh g^-1 at 0.2, 5, and 10 A g^-1, respectively. More encouragingly, the full-cell also exhibits an outstanding long-term cycling performance under 0.5 A g^-1, which delivers a reversible capacity of 500 mAh g^-1 over 200 cycles and still retains a high reversible capacity of 432 mAh g^-1 over 400 cycles. The enhancement mechanism is attributed to the favorable three-dimensional structure of the composite, Co doping, and S-composition, which can induce a synergistic effect.

High lithium storage performance of CoO with a distinctive dual-carbon-confined nanoarchitecture

Herein, a distinctive dual-carbon-confined nanoarchitecture, composed of an inner highly conductive, robust carbon nanotube (CNT) support and outer well-designed porous carbon (PC) coating, was demonstrated to efficiently improve the electrochemical properties of CoO nanoparticles for the first time, and the CoO nanoparticles were confined between the CNTs and porous carbon. The well-designed porous carbon coating showed significant superiority compared to common non-porous carbon coatings, due to its distinctive characteristics such as high flexibility, rich free space and open tunnel-like structure. Therefore, the synergistic effects of the CNT core and the porous carbon sheath endowed the CoO-based composite (CNTs@CoO@PC) with improved electrochemical reaction kinetics, large pseudocapacitive contribution and superior structural stability. As a result, the CNTs@CoO@PC showed outstanding performance with 1090, 571 and 242 mA h g^-1 at 200, 1000 and 5000 mA g^-1 after 300, 600 and 1000 cycles, respectively. Furthermore, this strategy may be used to improve other metal oxide anode materials for lithium storage.

Redox Dual-Cocatalyst-Modified CdS Double-Heterojunction Photocatalysts for Efficient Hydrogen Production

Cadmium sulfide (CdS) as one of the most common visible-light-responsive photocatalysts has been widely investigated for hydrogen generation. However, its low solar-hydrogen conversion efficiency caused by fast carrier recombination and poor catalytic activity hinders its practical applications. To address this issue, we develop a novel and highly efficient nickel-cobalt phosphide and phosphate cocatalyst-modified CdS (NiCoP/CdS/NiCoPi) photocatalyst for hydrogen evolution. The dual-cocatalysts were simultaneously deposited on CdS during one phosphating step by using sodium hypophosphate as the phosphorus source. After the loading of the dual-cocatalysts, the photocurrent of CdS significantly increased, while its electrical impedance and photoluminescence emission dramatically decreased, which indicates the enhancement of charge carrier separation. It was proposed that the NiCoP cocatalyst accepts electrons and promotes hydrogen evolution, while the NiCoPi cocatalyst donates electrons and accelerates the oxidation of sacrificial agents (e.g., lactic acid). Consequently, the visible-light-driven hydrogen evolution of this composite photocatalyst greatly improved. The dual-cocatalyst-modified CdS with a loading content of 5 mol % showed a high hydrogen evolution rate of 80.8 mmol·g^-1·h^-1, which was 202 times higher than that of bare CdS (0.4 mmol·g^-1·h^-1). This is the highest enhancement factor for metal phosphide-modified CdS photocatalysts. It also exhibited remarkable stability in a continuous photocatalytic test with a total reaction time of 24 h.

Insight into the Superior Lithium Storage Properties of Ultrafine CoO Nanoparticles Confined in a 3 D Bimodal Ordered Mesoporous Carbon CMK-9 Anode

Ultrafine CoO particles immobilized into the mesopores of three-dimensional cubic bimodal ordered mesoporous carbon CMK-9 is successfully prepared by using a combination of nanocasting and wet-impregnation methods. It is found that the cubic bimodal interconnected mesoporous framework of CMK-9 plays a crucial role in achieving the excellent electrochemical performances by assisting the rapid mass and charge transfer. Among the prepared nanocomposites, CoO(10)@CMK-9 delivers a discharge capacity of 830 mAh g^-1 after 200 cycles at a current density of 100 mA g^-1 in lithium-ion batteries. At a higher current density of 1000 mA g^-1 , the anode presents an outstanding discharge capacity of 636 mAh g^-1 after 200 cycles. In sodium-ion batteries, the anode provides a discharge capacity of 296 mAh g^-1 after 250 cycles at a current density of 100 mA g^-1 . The remarkable performances of CoO(10)@CMK-9 demonstrate the promising potentials of the nanocomposite as the anode for rechargeable batteries.

Needle-like CoO nanowire composites with NiO nanosheets on carbon cloth for hybrid flexible supercapacitors and overall water splitting electrodes

A nanoscale core–shell NiO@CoO composite is prepared on flexible carbon cloth for electrodes in supercapacitors and overall water splitting. The needle-like CoO nanowires with NiO nanosheets as the active materials improve the elemental constituents as well as surface area. The NiO@CoO electrode boasts a capacity of 2.87 F cm⁻² (1024.05 F g⁻¹) at 1 A g⁻¹ current density, and even at a large current density of 20 A g⁻¹ the retention ratio is 80.9% after 5000 cycles. The excellent specific capacity with high rate capability can be ascribed to the unique structure which increases the area of the liquid–solid interface and facilitates electron and ion transport, improving the utilization efficiency of active materials. The asymmetric hybrid supercapacitor prepared with the core–shell electrode shows the energy output of 40.3 W h kg⁻¹ at 750 W kg⁻¹ with a better retention (71.7%) of specific capacitance after 15 000 cycles. In addition, linear sweep voltammetry is performed to assess the performance of the electrode in water splitting and the electrode shows excellent activity in the OER as manifested by a Tafel slope of 88.04 mV dec⁻¹. Our results show that the bifunctional structure and design strategy have large potential in energy applications.

A nanoscale core–shell NiO@CoO composite is prepared on flexible carbon cloth for electrodes in supercapacitors and overall water splitting.

Hollow Boron-Doped Si/SiOx Nanospheres Embedded in the Vanadium Nitride/Nanopore-Assisted Carbon Conductive Network for Superior Lithium Storage

SiO_x-based anode materials with high capacity and outstanding cycling performance have gained numerous attentions. Nevertheless, the poor electrical conductivity and non-negligible volume change hinder their further application in Li-ion batteries. Herein, we propose a new strategy to construct a hollow nanosphere with boron-doped Si/SiO_x decorated with vanadium nitride (VN) nanoparticles and embedded in a nitrogen-doped, porous, and partial graphitization carbon layer (B-Si/SiO_x@VN/PC). Benefiting from such structural and compositional features, the B-Si/SiO_x@VN/PC electrode exhibits a stable cycling capacity of 1237.1 mA h g^-1 at a current density of 0.5 A g^-1 with an appealing capacity retention of 87.0% after 300 cycles. Additionally, it delivers high-rate capabilities of 1139.4, 940.7, and 653.4 mA h g^-1 at current densities of 2, 5, and 10 A g^-1, respectively, and ranks among the best SiO_x-based anode materials. The outstanding electrochemical performance can be ascribed to the following reasons: (1) its hollow structure makes the Li⁺ transportation length decreased. (2) The existing nanopores facilitate the Li⁺ insertion/desertion and accommodate the volume variation. (3) The nitrogen-doped partial graphitization carbon enhances the electrical conductivity and promotes the formation of stable solid electrolyte interface layers during the repetitive Li⁺ intercalation/extraction process.

A New Aspect for Band Gap Energy of Graphene-Mg2CuSnCoO6-Gallic Acid as a Counter Electrode for Enhancing Dye-Sensitized Solar Cell Performance

To develop counter electrodes (CEs) for dye-sensitized solar cells (DSSCs), band gap energy of quaternary semiconductor materials is of great interest. In the present study, a novel graphene sheet based on Mg₂CuSnCoO₆-Gallic acid nanomaterials (G/MCS@Gallic) was modified with a new Joule heating method, and a laser was applied for measuring band gap energy. Synergistic effect between graphene and Mg₂CuSnCoO₆-Gallic ensured excellent electron transport through the electrode and low band gap energy. The large surface area of the hybrid graphene materials rivaled the catalytic capability for iodide reduction. DSSCs achieved a maximum photoelectric conversion efficiency of 13.30% based on the 10% G/MCS@Gallic CE, which was higher than the platinum conversion efficiency. Thus, G/MCS@Gallic provides a novel, inexpensive, high-performance, and flexible cathode for solar cell applications.

Dandelion-like Mn/Ni Co-doped CoO/C Hollow Microspheres with Oxygen Vacancies for Advanced Lithium Storage

Hollow structures have attracted great attention based on the advantage to accommodate volume expansion. However, template removal usually results in structure destruction. Herein, dandelion-like Mn/Ni co-doped CoO/C hollow microspheres (CMNC-10h) are synthesized via an Ostwald ripening process without templates. The high-angle annular dark field mapping images at the atomic level indicate the successful doping of Mn and Ni into CoO. Via an annular bright field image, oxygen vacancies induced by doping can be clearly observed. The residual two electrons in the oxygen vacancy site are highly delocalized, as confirmed by density functional theory calculations, effectively improving electrical conductivity. According to electron holography analysis, the dielectric polarization field in superficial regions of primary nanoparticles can facilitate insertion of Li⁺ ions into nanoparticles and thus enhance electrochemical kinetics. Combining those advantages, CMNC-10h demonstrates a high capacity of 1126 mAh g^-1 at 1 A g^-1 after 1000 cycles as anode material for a lithium-ion battery. Additionally, based on the strong adsorption toward polysulfide, the porous structure to accommodate sulfer/polysulfide, and the effects of oxygen vacancies to immobilize and catalyze polysulfide, CMNC-10h-S as cathode material for a lithium-sulfur battery also displays a high capacity of 642 mAh g^-1 after 500 cycles at 1 C.