Enabling high electrochemical activity of a hollow SiO2 anode by decorating it with ultrafine cobalt nanoparticles and a carbon matrix for long-lifespan lithium ion batteries

Diatom Frustules Decorated with Co Nanoparticles for the Advanced Anode of Li-Ion Batteries

Silica is regarded as a promising anode material for lithium-ion batteries (LIBs) because of its high theoretical capacity. However, large volume variation and poor electrical conductivity are limiting factors for the development of SiO₂ anode materials. To solve this problem, combining SiO₂ with a conductive phase and designing hollow porous structures are effective ways. In this work, The Co(II)-EDTA chelate on the surface of diatom biosilica (DBS) frustules and obtained DBS@C-Co composites decorated with Co nanoparticles by calcination without a reducing atmosphere is first precipitated. The unique three-dimensional structure of diatom frustules provides enough space for the volume change of silica during lithiation/delithiation. Co nanoparticles effectively improve the electrical conductivity and electrochemical activity of silica. Through the synergistic effect of the hollow porous structure, carbon layer and Co nanoparticles, the DBS@C-Co-60 composite delivers a high reversible capacity of >620 mAh g^-1 at 100 mA g^-1 after 270 cycles. This study provides a new method for the synthesis of metal/silica composites and an opportunity for the development of natural resources as advanced active materials for LIBs.

Preparation of a SiO2 @Carbon Sphere/SiO2 -CNF Multilayer Self-standing Anode Prepared via an Alternate Electrospraying - Electrospinning Technique

The development of flexible lithium-ion batteries (FLIBs) is restrained by traditional rigidity anodes. Carbon nanofiber (CNF) is a promising anode material owing to its high specific surface and superior ion transportation capability. However, the low amount of active material loaded on the CNFs and the poor stability during long cycling restrain their applications. Herein, a SiO₂ @carbon sphere/SiO₂ -CNF self-standing anode was prepared via alternate electrospraying-electrospinning. The SiO₂ content of the anode was increased through the electrospraying SiO₂ @carbon spheres layers, and the electrospun SiO₂ -CNFs as robust layers enhanced the stability of the anode. The self-standing anode exhibited 633 mA h g^-1 in the initial cycle and maintained a 70% Coulomb efficiency for 1000 cycles at a current density of 100 mA g^-1 , which could be applied in FLIB and other electrochemical storage devices.

Carbon Yarn-Ball-Entangled SiO2 Anode with Excellent Electrochemical Performance for Lithium-Ion Batteries

Various nanoscale SiO₂ and their composites have demonstrated superior electrochemical performance as anodes for lithium-ion batteries. However, both the battery production and real applications require the integration of nanoscale SiO₂ into micrometer-sized secondary particles while preserving their excellent stability and conductivity, which remains a great challenge. In this work, a unique carbon yarn-ball structure is successfully synthesized that entangles nanoscale SiO₂ together to build a micrometer-sized secondary particle. The hook-like carbon wires closely adhere to individual SiO₂ nanoparticles, which constitute the basic unit of the yarn-ball structure. The entangled carbon wires create a network of electron conduction highways for SiO₂ , and the yarn-ball structure provides a resilient 3D matrix that can effectively buffer the anisotropic volume changes of SiO₂ during Li ion insertion/extraction. Under 0.1 A g^-1 , the carbon yarn-ball-entangled SiO₂ can deliver a 1297 mAh g^-1 discharge capacity with a small irreversible capacity of 82 mAh g^-1 . The entangled carbon yarn ball firmly maintains its structural integrity during high-rate cycling (1 A g^-1 ), which gives rise to a large accessible capacity (709 mAh g^-1 , 90.7% retention for 500 cycles), superior coulombic efficiency (>99.9%), and excellent structural stability.

A binary carbon@silica@carbon hydrophobic nanoreactor for highly efficient selective oxidation of aromatic alkanes

Nanoreactors with a delimited void space and a large number of mesoporous structures have attracted great attention as potential heterogeneous catalysts. In this work, a cobalt and nitrogen co-doped binary carbon@silica@carbon hydrophobic nanoreactor was synthesized by an in situ synthesis method. Cobalt porphyrin was used as an active component to construct Co-N_x sites, and the purpose of the double carbon layer coating was to enhance the hydrophobicity of the surface of the nanoreactor. The optimal nanoreactor could achieve 96.9% ethylbenzene conversion and 99.1% acetophenone selectivity and showed outstanding universality to many other aromatic alkanes. The superior performance was mainly due to the presence of double carbon layers and the high content of Co-N_x sites. The double hydrophobic carbon layer coating could not only promote the adsorption of organic molecules, but also implant Co-N_x active sites on both the inner and outer surfaces of the nanoreactor. This work proposed a meaningful strategy to obtain a highly efficient nanoreactor for C-H bond oxidation.

Aerogel Constructed by Ultrasmall Mn-Doped Silica Nanoparticles for Superior Lithium-Ion Storage

The high internal stress during (de)lithiation, poor ionic/electronic conductivity, and relatively low specific capacity are the three critical issues for the applications of silica (SiO₂) anodes. Herein, a high-performance SiO₂ anode is designed from the microscale to the atomic scale, and for the first time, an aerogel constructed by the graphene and manganese atom (Mn)-doped ultrasmall SiO₂ nanoparticles (around 50 nm) is proposed to overcome the three issues. From the aspect of microscale, the ultrasmall SiO₂ nanoparticles and the porous feature of aerogel improve the structural stability during (de)lithiation and the lithium-ion diffusion kinetics. From the aspect of atomic scale, the doping of Mn introduces the impurity level, expands the coordination environment, and enhances the adsorption for Li⁺, boosting the ionic/electronic conductivity and the amount of the Li⁺ intercalation. Therefore, the anode ranks among the best SiO_x (0 < x ≤ 2) anodes. For example, the capacity is almost constant after 2000 cycles, and the specific capacities are around 1800, 1600, and 1300 mAh/g at 0.5, 1, and 3 A/g, respectively. Moreover, the reinforced reasons are revealed based on the density functional theory simulations and experiments.

A Low-Cost and Scalable Carbon Coated SiO-Based Anode Material for Lithium-Ion Batteries

Silicon monoxide (SiO) is considered as one of the most promising alternative anode materials thanks to its high theoretical capacity, satisfying operating voltage and low cost. However, huge volume change, poor electrical conductivity, and poor cycle performance of SiO dramatically hindered its commercial application. In this work, we report an affordable and simple way for manufacturing carbon-coated SiO-C composites with good electrochemical performance on kilogram scales. Industrial grade SiO was modified by carbon coating using cheap and environment friendly polyvinyl pyrrolidone (PVP) as carbon source. High-resolution transmission electron microscopy (HRTEM) and Raman spectra results show that there is an amorphous carbon coating layer with a thickness of about 40 nm on the surface of SiO. The synthesized SiO-C-650 composite shows great electrochemical performance with a high capacity of 1491 mAh.g-1 at 0.1 C rate and outstanding capacity retention of 67.2 % after 100 cycles. The material also displays an excellent performance with a capacity of 1100 mAh.g-1 at 0.5 C rate. Electrochemical impedance spectroscopy (EIS) results also prove that the carbon coating layer can effectively improve the conductivity of the composite and thus enhance the cycling stability of SiO electrode.

Nitrogen-doped carbon encapsulated hollow ZnSe/CoSe2 nanospheres as high performance anodes for lithium-ion batteries

Hierarchical nitrogen-doped carbon encapsulated hollow ZnSe/CoSe2 (ZnSe/CoSe2@N-C) nanospheres are fabricated by a convenient solvothermal and selenization approach, followed by a carbonization process. The as-obtained ZnSe/CoSe2@N-C possesses a multilevel nanoscale architecture composed of a thin carbon shell with a size of around 12 nm and hollow selenide nanoparticles as the core with tiny rough grains and rich voids as the subunits. The robust carbon protective shell and synergistic effect between double metal ions boost the electron and ion transportation as well as promote effective extraction and insertion of lithium ions. Hollow ZnSe/CoSe2@N-C spheres show high reversible capacity with 1153 mA h g-1 remaining over 100 cycles at 100 mA g-1. In particular, the hollow ZnSe/CoSe2@N-C spheres show an outstanding cycling stability at a high rate of 2000 mA g-1 with the reversible capacity of up to 966 mA h g-1 remaining after 500 cycles. As an advanced anode, ZnSe/CoSe2@N-C composite shows remarkable cycling stability and exceptional rate capability in the field of energy storage technologies.