Kinetic and Electrochemical Reaction Mechanism Investigations of Rodlike CoMoO4 Anode Material for Sodium-Ion Batteries

Reshaping carbon-coated Mn2Mo3O8 nanotubes and enhanced sodium storage performance

Mn2Mo3O8/C nanotubes are successfully reshaped from micron-sized MnMoO4 blocks using a simple microwave-combined calcination method with dopamine as both scissors and carbon source. The synthesized Mn2Mo3O8/C nanotube (MMOC-2) exhibits enhanced sodium storage performance as anodes for half-cell (217 mA h g-1 with ca. 99% coulombic efficiency after 500 cycles) and full-cell (capacity retention of 75% after 100 cycles), which is attributed to the uniquely reshaped nanostructures with abundant active sites, short ion diffusion path and fast charge transfer.

Defects enriched cobalt molybdate induced by carbon dots for a high rate Li-ion battery anode

A defects-enriched CoMoO₄/carbon dot (CD) with CoMoO₄around 37 nm is achieved via hydrothermal reaction by introducing CDs to buffer large volume changes of CoMoO₄during lithiation-delithiation and enhance rate performance. The phase, morphology, microstructure, as well as the interface of the CoMoO₄/CD composites were investigated by x-ray diffraction, scanning electron microscopy, transmission electron microscopy and x-ray photoelectron spectroscopy. When employed as Li-ion battery anode, the CoMoO₄/CD exhibits a reversible capacity of ∼531 mAh g^-1after 400 cycles at a current density of 2.0 A g^-1. Under the scan rate at 2 mV s^-1, the CoMoO₄/CD shows accounts for 81.1% pseudocapacitance. It may attribute to the CoMoO₄with surface defects given more reaction sites to facilitate electrons and lithium ions transfer at high current densities. Through galvanostatic intermittent titration technique, the average lithium ion diffusion coefficient calculated is an order of magnitude larger than that of bulk CoMoO₄, indicating that the CoMoO₄/CD possesses promising electrons and lithium ions transportation performance as anode material.

Calcination-Free Synthesis of Well-Dispersed and Sub-10 nm Spinel Ferrite Nanoparticles as High-Performance Anode Materials for Lithium-Ion Batteries: A Case Study of CoFe2 O4

Spinel ferrites are promising anode materials for lithium-ion batteries (LIBs) owing to their high theoretical specific capacities. However, their practical application is impeded by inherent low conductivity and severe volume expansion, which can be surpassed by increasing the surface-to-volume ratio of nanoparticles. Currently, most methods produce spinel ferrite nanoparticles with large size and severe aggregation, degrading their electrochemical performance. In this study, a low-temperature aminolytic route was designed to synthesize sub-10 nm CoFe₂ O₄ nanoparticles with good dispersion through carefully exploiting the reaction of acetates and oleylamine. The performance of CoFe₂ O₄ nanoparticles obtained by a traditional co-precipitation method was also investigated for comparison. This work demonstrates that CoFe₂ O₄ nanoparticles synthesized by the aminolytic route are promising as anode materials for LIBs. Besides, this method can be extended to design other spinel ferrites for energy storage devices with superior performance by simply changing the starting material, such as MnFe₂ O₄ , MgFe₂ O₄ , ZnFe₂ O₄ , and so on.

Selenizing CoMoO4 nanoparticles within electrospun carbon nanofibers towards enhanced sodium storage performance

Transition metal oxides/selenides as anodes for sodium-ion batteries (SIBs) suffer from the insufficient conductivity and large volumetric expansion, which leads to the poor electrochemical performance. To address these issues, we herein demonstrate a facile selenization method to enhance the sodium storage capability of CoMoO₄ nanoparticles which are encapsulated into the electrospun carbon nanofibers (CMO@carbon for short). The partially and fully selenized CoMoO₄ within carbon nanofibers (denote as CMOS@carbon and CMS@carbon, respectively) can be readily obtained by controlling the annealing temperature (at 400 and 600 °C, correspondingly). When examined as anode materials for SIBs, the CMOS@carbon nanofibers display an outstanding electrochemical performance with a higher reversible capacity of 396 mA h g^-1 after 200 cycles at 0.2 A g^-1 and a high-rate capacity of 365 mA h g^-1 at 2 A g^-1, as compared with the CMO@carbon and CMS@carbon counterparts. The enhanced sodium storage performance of the CMOS@carbon can be owing to the partial selenization of the CoMoO₄ nanoparticles which are rooted into the porous electrospun carbon nanofibers, thus endowing them with superior ionic/electronic charge transfer efficiencies and a cushion against the electrode pulverization during cycling. Moreover, this work proposed a useful strategy to enhance the sodium storage performance of metal oxides via controlled selenization, which is promising for exploiting the advanced anode materials for SIBs.

Sodium insertion/extraction investigations into zinc ferrite nanospheres as a high performance anode material

Electrode materials with high fast charging and high capacity are urgently required for the realization of sodium-ion batteries (SIBs). In this work, zinc ferrite (ZnFe₂O₄) nanospheres have been prepared by the simple hydrothermal route and the structural analysis of ZnFe₂O₄ was evaluated by using X-ray diffraction. The morphology and microstructural characterizations are obtained using scanning electron microscopy and transmission electron microscopy. The results indicate that a single phase material was obtained with uniform sphere-like morphology and high crystallinity. The Brunauer–Emmett–Teller method was employed to determine the specific surface area of the ZnFe₂O₄ nanospheres which has been calculated to be 32 m² g⁻¹. The electrochemical results indicate that the composite possesses high sodium storage capability (478 mA h g⁻¹), and good cycling stability (284 mA h g⁻¹ at 100^th cycle) and rate capability (78 mA h g⁻¹ at 2 A g⁻¹). The high sodium storage performance of the ZnFe₂O₄ electrode is ascribed to the mesoporous nature of the ZnFe₂O₄ nanospheres. Further, sodium kinetics and the reaction mechanism in ZnFe₂O₄ nanospheres have been elucidated using electrochemical impedance spectroscopy, galvanostatic intermittent titration technique, ex situ TEM, and XAS. The acquired results indicate sluggish kinetics, reversibility of the material, and the stable structure of ZnFe₂O₄. Therefore, such a structure can be considered to be an attractive contender as a low cost anode for SIBs.

Electrode materials with high fast charging and high capacity are urgently required for the realization of sodium-ion batteries (SIBs).

Promoting Ge Alloying Reaction via Heterostructure Engineering for High Efficient and Ultra-Stable Sodium-Ion Storage

Germanium (Ge)-based materials have been considered as potential anode materials for sodium-ion batteries owing to their high theoretical specific capacity. However, the poor conductivity and Na+ diffusivity of Ge-based materials result in retardant ion/electron transportation and insufficient sodium storage efficiency, leading to sluggish reaction kinetics. To intrinsically maximize the sodium storage capability of Ge, the nitrogen doped carbon-coated Cu3Ge/Ge heterostructure material (Cu3Ge/Ge@N-C) is developed for enhanced sodium storage. The pod-like structure of Cu3Ge/Ge@N-C exposes numerous active surface to shorten ion transportation pathway while the uniform encapsulation of carbon shell improves the electron transportation, leading to enhanced reaction kinetics. Theoretical calculation reveals that Cu3Ge/Ge heterostructure can offer decent electron conduction and lower the Na+ diffusion barrier, which further promotes Ge alloying reaction and improves its sodium storage capability close to its theoretical value. In addition, the uniform encapsulation of nitrogen-doped carbon on Cu3Ge/Ge heterostructure material efficiently alleviates its volume expansion and prevents its decomposition, further ensuring its structural integrity upon cycling. Attributed to these unique superiorities, the as-prepared Cu3Ge/Ge@N-C electrode demonstrates admirable discharge capacity, outstanding rate capability and prolonged cycle lifespan (178 mAh g-1 at 4.0 A g-1 after 4000 cycles).

MnSe embedded in carbon nanofibers as advanced anode material for sodium ion batteries

MnSe with high theoretical capacity and reversibility is considered as a promising material for the anode of sodium ion batteries. In this study, MnSe nanoparticles embedded in 1D carbon nanofibers (MnSe-NC) are successfully prepared via facile electrospinning and subsequent selenization. A carbon framework can effectively protect MnSe dispersed in it from agglomeration and can accommodate volume variation in the conversion reaction between MnSe and Na⁺ to guarantee cycling stability. The 1D fiber structure can increase the area of contact between electrode and electrolyte to shorten the diffusion path of Na⁺ and facilitate its transfer. According to the kinetic analysis, the storage process of sodium by MnSe-NC is a surface pseudocapacitive-controlled process with promising rate capability. Impressively, An MnSe-NC anode in sodium ion full cells is investigated by pairing with an Na₃V₂(PO₄)₂@rGO cathode, which exhibits a reversible capacity of 195 mA h g^-1 at 0.1 A g^-1.

N-doped carbon encapsulated CoMoO4 nanorods as long-cycle life anode for sodium-ion batteries

Volume expansion and poor conductivity result in poor cyclability and low rate capability, which are the major challenges of transition-metal oxide as anode materials for sodium-ion batteries (SIBs). Herein, N-doped carbon encapsulated CoMoO₄ (CoMoO₄@NC) nanorods are developed as excellent anode materials for SIBs with long-cycle life. The N-doped carbon shells serve as buffer to accommodate severe volume changes during sodiation/desodiation, and at the same time improve electronic conductivity and activate surface sites of CoMoO₄. The optimized composite presents rapid reaction kinetics and excellent cycle stability. Even at a high current density of 1 A g^-1, it still shows long-cycle life and maintains specific capacity of 190 mAh g^-1 after 3200 cycles. Furthermore, CoMoO₄@NC anode is applied to match with Na₃V₂(PO₄)₃ cathode to assemble full-cells, in which it accomplishes reversible capacity of 152 mAh g^-1 after 100 cycles, with capacity retention of 75% at a current density of 1 A g^-1, highlighting the practical application for SIBs.

A soft chemistry approach to preparing (de)sodiated transition-metal hydroxy molybdates

Polymorphic transformations were investigated for (de)sodiated Ni and Zn hydroxy molybdates prepared under mild hydrothermal conditions.