Casting amorphorized SnO2/MoO3 hybrid into foam-like carbon nanoflakes towards high-performance pseudocapacitive lithium storage

A Brief Review of MoO3 and MoO3-Based Materials and Recent Technological Applications in Gas Sensors, Lithium-Ion Batteries, Adsorption, and Photocatalysis

Molybdenum trioxide is an abundant natural, low-cost, and environmentally friendly material that has gained considerable attention from many researchers in a variety of high-impact applications. It is an attractive inorganic oxide that has been widely studied because of its layered structure, which results in intercalation ability through tetrahedral/octahedral holes and extension channels and leads to superior charge transfer. Shape-related properties such as high specific capacities, the presence of exposed active sites on the oxygen-rich structure, and its natural tendency to oxygen vacancy that leads to a high ionic conductivity are also attractive to technological applications. Due to its chemistry with multiple valence states, high thermal and chemical stability, high reduction potential, and electrochemical activity, many studies have focused on the development of molybdenum oxide-based systems in the last few years. Thus, this article aims to briefly review the latest advances in technological applications of MoO3 and MoO3-based materials in gas sensors, lithium-ion batteries, and water pollution treatment using adsorption and photocatalysis techniques, presenting the most relevant and new information on heterostructures, metal doping, and non-stoichiometric MoO3-x.

Fe2O3/MoO3@NG Heterostructure Enables High Pseudocapacitance and Fast Electrochemical Reaction Kinetics for Lithium-Ion Batteries

Transition metal oxides (TMOs) hold great potential for lithium-ion batteries (LIBs) on account of the high theoretical capacity. Unfortunately, the unfavorable volume expansion and low intrinsic electronic conductivity of TMOs lead to irreversible structural degradation, disordered particle agglomeration, and sluggish electrochemical reaction kinetics, which result in perishing rate capability and long-term stability. This work reports an Fe₂O₃/MoO₃@NG heterostructure composite for LIBs through the uniform growth of Fe₂O₃/MoO₃ heterostructure quantum dots (HQDs) on the N-doped rGO (NG). Due to the synergistic effects of the "couple tree"-type heterostructures constructed by Fe₂O₃ and MoO₃ with NG, Fe₂O₃/MoO₃@NG delivers a prominent rate performance (322 mA h g^-1 at 20 A g^-1, 5.0 times higher than that of Fe₂O₃@NG) and long-term cycle stability (433.5 mA h g^-1 after 1700 cycles at 10 A g^-1). Theoretical calculations elucidate that the strong covalent Fe-O-Mo, Mo-N, and Fe-N bonds weaken the diffusion energy barrier and promote the Li⁺-ion reaction to Fe₂O₃/MoO₃@NG, thereby facilitating the structural stability, pseudocapacitance contribution, and electrochemical reaction kinetics. This work may provide a feasible strategy to promote the practical application of TMO-based LIBs.

Porous nanotube networks of SnO2/MoO3@Graphene as anodes for rechargeable lithium-ion batteries

We successfully fabricated composite porous nanotube networks of SnO₂/MoO₃@Graphene through electrospinning and used it as lithium-ion battery anodes. When the ratio of SnO₂ to MoO₃ is 1:1, the composite of SnO₂/MoO₃ delivers a high capacity of 560 mAh g^-1 at 1 A g^-1 after 300 cycles. The excellent electrochemical performance was attributed to the unique 3D porous nanotube network structure which could provide more transmission channels for Li⁺ ions and electrons, and provide more electrochemical reaction sites. The hybrid nanostructure can also weaken local stress and relieve volume expansion which contributes to the attractive cycling stability. Moreover, we added a small amount of graphene in the composite to improve the electrical conductivity, and the SnO₂/MoO₃@Graphene composite showed favorable electrochemical performance (798 mAh g^-1 at 1 A g^-1 after 300 cycles). Finally, electrospinning technology is a simple and efficient synthesis strategy, which can promote the preparation of different types of metal oxide composite materials and has good application prospects.

Embedding amorphous lithium vanadate into carbon nanofibers by electrospinning as a high-performance anode material for lithium-ion batteries

We design and fabricate a novel hybrid with amorphous lithium vanadate (LiV₃O_x, LVO for short) uniformly encapsulated into carbon nanofibers (denoted as LVO@CNFs) via an easy electrospinning strategy followed by proper postannealing. When examined for use as anode materials for lithium-ion batteries (LIBs), the optimized LVO@CNFs present a high discharge capacity of 603 mAh g^-1 with a capacity retention as high as 90% after 200 cycles at 0.5 A g^-1 and a high rate capacity of 326 mAh g^-1 after 400 cycles even at a high rate of 5 A g^-1. The superior electrochemical performance with excellent cycling stability and rate capability is attributed to the full encapsulation of the amorphous LVO into the conductive carbon nanofibers, which hold enlarged electrochemically active sites for lithium storage, facilitate the charge transfer, and efficiently alleviate the volume changes upon lithium insertion/extraction. More importantly, the current synthesis can be a general strategy to fabricate various alkaline earth metal vanadates, which is promising for developing advanced electrochemical energy storage devices.

Molybdenum-doped tin oxide nanoflake arrays anchored on carbon foam as flexible anodes for sodium-ion batteries

Tin oxide (SnO₂) has been widely used as an anode material for sodium-ion storage because of its high theoretical capacity. However, it suffers from large volume expansion and poor conductivity. To overcome these limitations, in this study, we have designed and prepared Mo-doped SnO₂ nanoflake arrays anchored on carbon foam (Mo-SnO₂@C-foam with 38.41 wt% SnO₂ and 3.7 wt% Mo content) by a facile hydrothermal method. The carbon foam serves as a three-dimensional conductive network and a buffer skeleton, contributing to improved rate performance and cycling stability. In addition, Mo doping enhances the kinetics of sodium-ion transfer, and the interlaced SnO₂ nanoflake arrays is beneficial to promote the conversion reactions during the charge/discharge process. The as-prepared composite with a unique structure demonstrate a high initial capacity of 1017.1 mAh g^-1 at 0.1 A g^-1, with a capacity retention over three times higher than that of the control sample (SnO₂@C-foam) at 1 A g^-1, indicating a remarkable rate performance.

Porous N-doped carbon nanoflakes supported hybridized SnO2/Co3O4 nanocomposites as high-performance anode for lithium-ion batteries

Alloy-/conversion-type metal oxides usually exhibit high theoretical lithium storage capacities but suffer from the large volume change induced electrode pulverization and the poor electric conductivity, which limit their practical applications. Hybrid/mixed metal oxides with different working mechanisms/potentials can display advantageous synergistic enhancement effect if delicate structure engineering is performed. Herein, atomically hybridized SnO₂/Co₃O₄ nanocomposites with amorphous nature are successfully cast onto the porous N-doped carbon (denoted as NC) nanoflakes through facile pyrolysis of the tin (II) 2-ethylhexanoate (C₁₆H₃₀O₄Sn) and cobalt (II) 2-ethylhexanoate (C₁₆H₃₀O₄Co) mixture within NC nanoflakes in air at 300 °C for 1 h. The Sn/Co atomic ratio and the loading amount of SnO₂/Co₃O₄ can be readily controlled, whose effect on lithium storage are investigated as anodes for lithium ion batteries (LIBs). Notably, SnO₂/Co₃O₄@NC (R_Sn/Co = 1.25) nanoflakes exhibit the most excellent lithium storage properties, delivering a reversible capacity of 1450.3 mA h g^-1 after 300 cycles at 200 mA g^-1, which is much higher than that of the single metal oxide SnO₂@NC and Co₃O₄@NC electrodes.