Building nanoparticle-stacking MoO2-CDs via in-situ carbon dots reduction as high-performance anode material for lithium ion and sodium ion batteries

Biomass-Derived Carbon Dots: Sustainable Solutions for Advanced Energy Storage Applications

The growing energy demand has underscored the importance of sustainable energy storage devices. Biomass-derived carbon dots (B-Cdots) have gained significant attention for their potential to address this challenge. Utilizing greener routes for the large-scale synthesis of B-Cdots is not only eco-friendly and cost-effective but also promotes sustainability. This review highlights various synthesis methods for B-Cdots, including microwave-assisted, hydrothermal, and pyrolysis-based carbonization processes. It also explores their electrochemical applications in supercapacitors, lithium-ion batteries, sodium-ion batteries, and other energy storage devices, along with recent advancements in the field. The fabrication of electrodes using B-Cdots offers several advantages, such as tunable chemical and physical properties, porous structures, efficient heteroatom doping, and excellent electrical conductivity. These attributes make B-Cdots highly attractive for energy storage applications. Overall, this review emphasizes the critical role of sustainable materials in shaping the future of energy storage technologies.

Electron-rich hybrid matrix to enhance molybdenum oxide-based anode performance for Lithium-Ion batteries

Although MoO₂-based electrodes have been intensively studied as potential candidate anodes for lithium-ion batteries (LIBs) based on their high theoretical capacity (840 mAh g^-1 and 5447 mAh cm^-3), common issues such as severe volume variation, electrical conductivity loss, and low ionic conductivity, are prevalent. In this study, we demonstrate enhanced Li-ion kinetics and electrical conductivity of MoO₂-based anodes with ternary MoO₂-Cu-C composite materials. The MoO₂-Cu-C was synthesized via two-step high energy ball milling where Mo and CuO are milled, followed by the secondary milling with C. With the introduction of the Cu-C hybrid matrix in MoO₂ nanoparticles via the element transfer method using mechanochemical reactions, the sluggish Li-ion diffusion and unstable cycling behavior were significantly improved. The inactive Cu-C matrix contributes to the increase in electrical and ionic conductivity and mechanical stability of active MoO₂ during cycling, as characterized by various electrochemical analyses and ex situ analysis techniques. Hence, the MoO₂-Cu-C anode delivered promising cycling performance (674 mAh g^-1 (at 0.1 A g^-1) and 520 mAh g^-1 (at 0.5 A g^-1), respectively, after 100 cycles) and high-rate property (73% retention at 5 A g^-1 as comparison with the specific capacity at 0.1 A g^-1). The MoO₂-Cu-C electrode is a propitious next-generation anode for LIBs.

Construction of a ternary MoO2/Ni/C hybrid towards lithium-ion batteries as a high-performance electrode

The high lithium storage performance of 3D flower-like MoO2/Ni/C through a temperature annealing strategy is benefitted from the high capacitive contribution, high electrical conductivity, and good structural stability.

Carbon dot/inorganic nanomaterial composites

The preparation methods, formation mechanism, properties and applications of carbon dot/inorganic nanohybrid materials are reported.

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.

Nanocomposite of ultra-small MoO2 embedded in nitrogen-doped carbon: In situ derivation from an organic molybdenum complex and its superior Li-Ion storage performance

MoO₂ is a promising anode material for lithium-ion batteries, however, the lithiation of bulk MoO₂ is usually limited to addition-type reaction at room temperature, and the conversion reaction is hindered because of the sluggish kinetics. Herein, a nanocomposite of MoO₂ embedded in nitrogen-doped carbon (MoO₂/NC) is synthesized through the in situ thermolysis of an organic molybdenum complex MoO₂(acac)(phen) (acac = acetylacetone, phen = 1,10-Phenanthroline). Owing to the fact that [MoO₂]²⁺ can be strongly chelated by phen, the molybdenum source in the MoO₂(acac)(phen) precursor is highly dispersed, leading to the formation of ultra-small MoO₂ nanoparticles in the nanocomposite, which can facilitate the conversion reaction. Moreover, the NC matrix can guarantee a high electrical conductivity and effectively accommodate the volume changes triggered by the conversion reaction. Consequently, the MoO₂/NC nanocomposite exhibits outstanding electrochemical properties, including large reversible capacity of 950 mA h g^-1 at 0.1 A g^-1, high-rate capability of 605 mA h g^-1 at 2 A g^-1, and excellent cycling stability over 500 cycles as an anode material for lithium-ion batteries.

Template-free fabrication of 1D core-shell MoO2@MoS2/nitrogen-doped carbon nanorods for enhanced lithium/sodium-ion storage

A universal anode material of 1D core-shell MoO₂@MoS₂/nitrogen-doped carbon (MoO₂@MoS₂/NC) nanorods has been elaborately synthesized via a facile fabrication route for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), in which MoO₂ core not only acts as a conductive backbone for efficient electron transport, but creates structural disorders in MoS₂ nanosheets to prevent aggregation and expose more active sites for alkali-ions. Meanwhile, the MoO₂ core is tightly encapsulated by the parallelly aligned MoS₂ nanosheets to constrain the size of crystals, which greatly shortens the ionic diffusion path and accelerates diffusion rate, thus ensuring fast reaction kinetics. Additionally, the resilient and conductive N-doped carbon matrix in the hybrid could maintain the structural integrity and enhance the electrical conductivity of the electrodes, improving the rate capability and life span. The flexible 1D nanorods could contract freely during the charge/discharge process, further assuring the structural stability of the electrodes. Benefiting from the above-mentioned advantages, the MoO₂@MoS₂/NC electrodes still remains a specific capacity of 583.5 mA h g^-1 after 1500 cycles at a high current density up to 10 A g^-1 in LIBs, and a capacity of 419.8 mA h g^-1 is steadily kept over 800 cycles at 2 A g^-1 in SIBs.

Surface chemical functionality of carbon dots: influence on the structure and energy storage performance of the layered double hydroxide

As a kind of zero-dimensional material, carbon dots (CDs) have become a kind of promising novel material due to their incomparable unique physical and chemical properties. Despite the optical properties of CDs being widely studied, their surface chemical functions are rarely reported. Here we propose an interesting insight into the important role of surface chemical properties of CDs in adjusting the structure of the layered double hydroxide (LDH) and its energy storage performance. It was demonstrated that CDs with positive charge (p-CDs) not only reduce the size of the flower-like LDH through affecting the growth of LDH sheets, but also act as a structure stabilizer. After calcination, the layered double oxide (LDO) maintained the morphology of the LDH and prevented the stacking of layers. And the superiority of the composite in lithium-ion batteries (LIBs) was demonstrated. When used as an anode of LIBs, composites possess outstanding specific capacity, cycle stability and rate performance. It presents the discharge capacity of 1182 mA h g-1 and capacity retention of 94% at the current density of 100 mA g-1 after 100 cycles. Our work demonstrates the important chemical functions of CDs and expands their future applications.

Comparative Studies on Two-Dimensional (2D) Rectangular and Hexagonal Molybdenum Dioxide Nanosheets with Different Thickness

Molybdenum dioxide (MoO₂) a kind of semi-metal material shows many unique properties, such as high melting point, good thermal stability, large surface area-to-volume ratio, high-density surface unsaturated atoms, and excellent conductivity. There is a strong connection between structural type and optoelectronic properties of 2D nanosheet. Herein, the rectangular and hexagonal types of thin and thick MoO₂ 2D nanosheets were successfully prepared from MoO₃ powder using two-zone chemical vapor deposition (CVD) with changing the experimental parameters, and these fabricated nanosheets displayed different colors under bright-field microscope, possess margins and smooth surface. The thickness of the blue hexagonal and rectangular MoO₂ nanosheets are ~ 25 nm and ~ 30 nm, respectively, while typical thickness of orange-colored nanosheet is around ~ 100 nm. Comparative analysis and investigations were carried out, and mix-crystal phases were indentified in thick MoO₂ as main matrix through Raman spectroscopy. For the first time, the emission bands obtained in thick MoO₂ nanosheets via a Cathodoluminescence (CL) system exhibiting special properties of semi-metallic and semi-conductors; however, no CL emission detected in case of thin nanosheets. The electrical properties of thin MoO₂ nanosheets with different morphologies were compared, and both of them demonstrated varying metallic properties. The resistance of thin rectangular nanosheet was ~ 25 Ω at ± 0.05 V while 64 Ω at ± 0.05 V was reported for hexagonal nanosheet, and observed lesser resistance by rectangular nanosheet than hexagonal nanosheet.

Highly uniform nitrogen-doped carbon decorated MoO2 nanopopcorns as anode for high-performance lithium/sodium-ion storage

Molybdenum dioxides (MoO₂) featuring low cost and high theoretical capacity endow them competitive anode materials for lithium-ion batteries (LIBs)/sodium-ion batteries (SIBs). However, the low electrical conductivity and severe volume expansion occurring during the ion insertion/extraction process hamper their practical application. Herein, a novel dual-annealing design has been developed for the synthesis of highly uniform MoO₂ nanopopcorns decorated with nitrogen-doped carbon shell (MoO₂/NC). Owing to the unique structural characteristics and vital amorphous NC component, the MoO₂/NC nanopopcorn hybrid composite exhibits stabilized charge storage capacity of 1073 mAh g^-1 after 200 cycles for LIBs, while 301 mAh g^-1 after 500 cycles for SIBs at 0.5 A g^-1. Furthermore, when the current density increases to 5 A g^-1, the specific capacity could still maintain 630 mAh g^-1 and 174 mAh g^-1 for LIBs and SIBs, respectively, which disclose the outstanding rate capability of MoO₂/NC nanopopcorn anode.