Search

Iron-based oxides are a class of attractive anode materials for lithium-ion batteries by virtue of their high theoretical capacity, abundant resource, and low cost. Nevertheless, their practical applications in energy storage are seriously hampered by their inherent large volume expansion, poor conductivity, and sluggish reaction kinetics. Herein, we design a unique bone-like Fe3O4@N-doped carbon (B-Fe3O4@C) composite via a facile Sn2+-induced hydrothermal route. Taking advantage of a unique morphology, a thin carbon layer coating of about 5 nm, and in situ nitrogen doping, the as-prepared B-Fe3O4@C anode material demonstrates excellent lithium storage capability. It delivers a high first discharge capacity (1480.3 mA h g-1 at 0.1 A g-1), superior cycling stability (a capacity fading of only 0.026% per cycle for 100 cycles at 0.1 A g-1), and good rate capability (480.8 mA h g-1 at 2 A g-1). The theoretical analysis results indicate that the enhanced electrochemical performance mainly comes from the increased Li+ adsorption energy on the Sn-doped Fe3O4 surface. The present synthetic study also paves a way for the facile design of advanced electrode materials for next-generation energy storage and conversion.

Owing to excellent conductivity and abundant surface terminals, MXene-based heterostructures have been intensively investigated as energy storage materials. However, elaborate design of the structure and composition of MXene-based hybrids towards superior electrochemical performance is still challenging. Herein, we present an ingenious leaf-inspired design for preparing a unique Sb2S3/nitrogen-doped Ti3C2Tx MXene (L-Sb2S3/Ti3C2) hybrid. In-situ TEM observations reveal that the leaflike Sb2S3 nanoparticles with numerous mesopores can well relieve the large volume changes via an inward pore filling mechanism with only 20% outward expansion, whereas highly conductive N-doped Ti3C2Tx nanosheets can serve as the robust mechanical support to reinforce the structural integrity of the hybrid. Benefiting from the structural and constituent merits, the L-Sb2S3/Ti3C2 anode fabricated exhibits a fast sodium storage behavior in terms of outstanding rate capability (339.5 mA h g−1 at 2,000 mA g−1) and high reversible capacity at high current density (358.2 mA h g−1 at 1,000 mA g−1 after 100 cycles). Electrochemical kinetic tests and theoretical simulation further manifest that the boosted electrochemical performance mainly arises from such a unique leaf-like Sb2S3 mesoporous nanostructure with abundant active sites, and enhanced Na+ adsorption energy on the heterojunction formed between Sb2S3 nanoparticles and Ti3C2 matrix. [Figure not available: see fulltext.].

Transition-metal dichalcogenides with a lamellar structure have been recognized as a class of attractive host materials for Na+ insertion, and intensively investigated as anodes for sodium-ion batteries. However, large-scale applications are severely restricted by their intrinsic inferior conductivity and large volume expansion during deep cycles. Herein, a unique 0D/2D heterostructure of SnS2 quantum dots (QDs) with N-doped Ti3C2Tx MXene (namely, SnS2 QDs/Ti3C2) has been successfully designed via an ingenious solvent spatial confinement growth strategy. During the hydrothermal process, the nucleation and growth of SnS2 nanoparticles can be effectively regulated by N-methyl pyrrolidone, which results in the uniform growth of SnS2 QDs of about 3 nm onto the Ti3C2Tx MXene matrix. Meanwhile, in situ N-doping of Ti3C2Tx MXene can also be realized because of the NH3 released from the decomposition of the sulfur precursor, which greatly enhances the interfacial Na+ transport. Such a rational design endows the newly developed SnS2 QDs/Ti3C2 electrode with fascinating sodium storage properties including a high specific capacity of 763.2 mA h g-1 at 100 mA g-1 and ultrastable cycling stability (345.3 mA h g-1 at 100 mA g-1 after 600 cycles). The experimental and theoretical simulation results demonstrate that the ultrafine SnS2 QDs with abundantly active sites on the interface and stronger Na+ adsorption energy on the heterojunction formed between N-doped Ti3C2 MXenes contribute to the superior sodium storage capability.

The main challenge for developing transition metal oxides (TMOs) as anode materials for sodium-ion batteries (SIBs) is to rationally design and synthesize TMO-based hybrid structures and precisely control the transport of ions and electrons. Herein, we propose a facile in situ interfacial growth strategy to achieve a novel sandwich structured P-SnO2/Ti3C2 composite, where SnO2 nanocrystals modified with an ulthathin polypyrrole (PPy) layer of about 3 nm are strongly coupled with Ti3C2Tx Mxene nanosheets through Sn-O-Ti chemical bonds. Uniformly dispersed SnO2 nanocrystals confined in PPy and Ti3C2Tx nanosheets provide abundant acitve sites, while the conductive polymer PPy and Ti3C2Tx serve as robust protective layers alleviating the volume expansion and fast channels for Na ions and electron transport. Thanks to the advantages of structure and composition, the resulting P-SnO2/Ti3C2 anode demonstrates excellent sodium storage properties in terms of long cycle life (325.6 mA h g-1 at 100 mA g-1 after 100 cycles) and outstanding rate performance (204.4 mA h g-1 at 1000 mA g-1). The density functional theory calculations further prove that the P-SnO2/Ti3C2 heterostructure can balance the adsorption and release of Na atoms on the interface, thus boosting the performance of SIBs. This approach developed can also provide valuable guidance for the constuction of more functional TMO-based composites.

© 2020 American Chemical Society. A new two-dimensional material (MXene) has been compounded lately with silicon as anodes for lithium-ion batteries to achieve excellent lithium storage performances on account of its unique properties, such as high electrical conductivities, low ion diffusion barrier, and large surface area. However, the exposed silicon particles may lead to fast capacity decaying upon direct contact with the electrolyte. To solve this issue, the porous silicon and SiOx are introduced into Ti3C2Tx to construct a conductive network, and then Ti3C2@Si/SiOx are covered with amorphous TiO2 to make a sandwiched Ti3C2@Si/SiOx@TiO2 composite. Owing to the cooperation of the Ti3C2 matrix, Si/SiOx interlayer, and amorphous TiO2 layer, the reversible capacity of the Ti3C2@Si/SiOx@TiO2 composite with a sandwiched structure can be maintained at 939 mA h g-1 after 100 cycles and enhanced capacity retention capabilities in the initial 10 cycles can be came ture. The combination of these four components also makes the Ti3C2@Si/SiOx@TiO2 composite material a promising application prospect in lithium-ion batteries.

Due to the abundant potassium resource on the Earth's crust, researchers now have become interested in exploring high-performance potassium-ion batteries (KIBs). However, the large size of K+ would hinder the diffusion of K ions into electrode materials, thus leading to poor energy/power density and cycling performance during the depotassiation/potassiation process. So, few-layered V5S8 nanosheets wrapping a hollow carbon sphere fabricated via a facile hollow carbon template induced method could reversibly accommodate K storage and maintain the structure stability. Hence, the as-obtained V5S8@C electrode enables rapid and reversible storage of K+ with a high specific capacity of 645 mAh/g at 50 mA/g, a high rate capability, and long cycling stability, with 360 and 190 mAh/g achieved after 500 and 1000 cycles at 500 and 2000 mA/g, respectively. The excellent electrochemical performance is superior to the most existing electrode materials. The DFT calculations reveal that V5S8 nanosheets have high electrical conductivity and low energy barriers for K+ intercalation. Furthermore, the reaction mechanism of the V5S8@C electrode in KIBs is probed via the in operando synchrotron X-ray diffraction technique, and it indicates that the V5S8@C electrode undergoes a sequential intercalation (KV5S8) and conversion reactions (K2S3) reversibly during the potassiation process.

The application of high-performance silicon-based anodes, which are among the most prominent anode materials, is hampered by their poor conductivity and large volume expansion. Coupling of silicon-based anodes with carbonaceous materials is a promising approach to address these issues. However, the distribution of carbon in reported hybrids is normally inhomogeneous and above the nanoscale, which leads to decay of coulombic efficiency during deep galvanostatic cycling. Herein, we report a porous silicon-based nanocomposite anode derived from phenylene-bridged mesoporous organosilicas (PBMOs) through a facile sol-gel method and subsequent pyrolysis. PBMOs show molecularly organic-inorganic hybrid character, and the resulting hybrid anode can inherit this unique structure, with carbon distributed homogeneously in the Si-O-Si framework at the atomic scale. This uniformly dispersed carbon network divides the silicon oxide matrix into numerous sub-nanodomains with outstanding structural integrity and cycling stability.