Controlled synthesis of hollow C@TiO2@MoS2 hierarchical nanospheres for high-performance lithium-ion batteries

Band engineering enhances the electrochemical properties by constructing TiO2 NRs-MoS2 NSFs flexible electrode

Research and development of flexible electrodes with high performance are crucial to largely determine the performance of flexible lithium-ion batteries (FLIBs) to a large extent. In this work, a flexible anode (TiO2 NRs-MoS2 NSFs/CC) is rationally designed and successfully constructed, in which TiO2 nanorods arrays (NRs) vertically grown on CC as a supporting backbone for MoS2 nanosheets flowers (NSFs) to form a TiO2 NRs-MoS2 NSFs heterostructure. The backbone can not only serve as a mechanical support MoS2 and improve its electronic conductivity, but also limit the dissolution of polysulfides issue during cycling. The density functional theory (DFT) analysis manifests that the obvious interaction between O and S at the interface for the TiO2 NRs-MoS2 NSFs heterostructure changes the electronic structure and reduces the band gap of TiO2 NRs-MoS2 NSFs. The small band gap and high electron state at the Fermi level are both beneficial to the transport of electrons, enhancing the kinetics, and giving the long cycling stability at high density and excellent rate capacity. Furthermore, the assembled TiO2 NRs-MoS2 NSFs/CC//NCM622 full cell delivers superior rate capacity and good cycling stability. Meanwhile, the soft-packed cell shows good mechanical flexibility, which can be lighted up successfully and keep brightness when folding with different angles. This result illustrates that it is a highly potential strategy for constructing flexible electrodes with the controlled electronic structure through band engineering to not only improve the electrochemical performance, but also possibly meet the requirements of high-performance FLIBs.

Hierarchical core/shell titanium dioxide/molybdenum disulfide nanosheets coupled with carbon architecture for superior lithium/sodium ion storage

The peculiar core/shell structure with abundant interfaces is favorable for Li⁺/Na⁺ storage, which can elevate the efficiency of energy storage and conversion. Herein, a unique core/shell structure composite with diverse interfaces was successfully designed and fabricated via a facile coordination reaction combined with thermal treatment. Specially, well-crystallized TiO₂ nanoparticles were encapsulated and embedded in carbon nanospheres wrapped with MoS₂ nanosheets, leading to abundant interfacial structure and boundaries. Benefitting from the synergistic effect between numerous interfaces and distinctive hierarchal core/shell structure, such a hybrid material possesses fascinating features including ultrafast ion diffusion, plentiful storage active sites and prominent electric conductivity. As a proof of concept, as-prepared samples demonstrated superior reversible lithium storage capacity and hybrid lithium-ion capacitor. What is more, when the material was acted as anode material for SIBs, the discharge capacity maintained at a high capacity of 267.2 mA h g^-1 after 1000 cycles at 2.0 A g^-1. This work highlights a convenient strategy to synthesize other hybrid materials for electrode materials of energy storage and conversion applications.

In-situ fabrication of few-layered MoS2 wrapped on TiO2-decorated MXene as anode material for durable lithium-ion storage

Rational construction of hybrid materials integrating the collective virtues of individual building blocks has spurred significant interest in electrode materials for energy storage. Herein, a smart hybrid was fabricated via in-situ assembling of the few-layered MoS₂ (f-MoS₂) coated on the multi-layered Ti₃C₂ MXene decorated with the TiO₂ nanoparticles by the scalable hydrothermal and annealing approaches. In the unique architecture, the multi-layered Ti₃C₂ with the expanded interspaces as the conductive backbone can facilitate the electron transport, provide adequate space to facilitate the infiltration of organic electrolyte into the interior of electrode, and inhibit the aggregation of MoS₂ nanosheets, while the f-MoS₂ with enlarged interlayer can be beneficial for the lithium-ion diffusion and prevent the multi-layered Ti₃C₂from restacking. Moreover, the TiO₂ decorated on the Ti₃C₂ can effectively inhibit the instability of long-chain lithium polysulfides dissolved in organic electrolyte to improve the cycling stability. Thanks to the synergistic effect of the building blocks, the Ti₃C₂/TiO₂@f-MoS₂ hybrid employed as lithium storage anode delivers an extraordinary endurable ability with a high storage capacity of 403.1 mA h g^-1 after 1200 cycles at 2 A g^-1. Importantly, the smart hybridization strategy in this work paves an efficient way to explore the high-performance MXene-based hybrid materials in energy storage fields.

Pseudocapacitance-boosted ultrafast and stable Na-storage in NiTe2 coupled with N-doped carbon nanosheets for advanced sodium-ion half/full batteries

Developing high-rate and durable anode materials for sodium-ion batteries (SIBs) is still a challenge because of the larger ion radius of sodium compared with the lithium ion during charge-discharge processes. Herein, NiTe₂ coupled with N-doped carbon (NiTe₂/NC) hexagonal nanosheets has been fabricated through a solvothermal and subsequent carbonisation strategy. This unique hexagonal nanosheet structure offers abundant active sites and contact area to the electrolyte, which could shorten the Na⁺ diffusion path. The heterostructured N-doping carbon improves the electrochemical conductivity and accelerates the kinetics of Na⁺ transportation. Electrochemical analysis shows that the charge-discharge process is controlled by the pseudocapacitive behavior thus leading to high-rate capability and long lifespan in half batteries. As expected, high capacities of 311 mA h g^-1 to 217 mA h g^-1 at 5 A g^-1 to 10 A g^-1 are maintained after 800 and 1200 cycles, respectively. Furthermore, a full battery equipped with a Na₃V₂(PO₄)₂O₂F cathode and a NiTe₂/NC anode offers a maximum energy density of 104 W h kg^-1 and a maximum power density of 9116 W kg^-1. The results clearly show that the NiTe₂/NC hexagonal nanosheet with superior Na storage properties is an advanced new material for energy storage systems.

Dual carbon-confined Sb2Se3 nanoparticles with pseudocapacitive properties for high-performance lithium-ion half/full batteries

Transition metal selenides have attracted enormous research attention as anodes for lithium-ion batteries (LIBs) due to their high theoretical specific capacities. Nevertheless, the low electronic conductivity and dramatic volume variation in electrochemical reaction processes result in rapid capacity fading and poor rate capability. Herein, a metal-organic framework is used as a template to in situ synthesize Sb₂Se₃ nanoparticles encapsulated in N-doped carbon nanotubes (N-CNTs) grafted on reduced graphene oxide (rGO) nanosheets. The synergistic effects of N-doped carbon nanotubes and reduced graphene oxide nanosheets are beneficial for providing good electrical conductivity and maintaining the structural stability of electrode materials, leading to stable cycling performance and superior rate performance. Kinetic analysis suggests that the electrochemical reaction kinetics is dominated by pseudocapacitive contribution. Notably, a high discharge capacity of 451.1 mA h g^-1 at a current density of 2.0 A g^-1 is delivered after 450 cycles. Even at a high current density of 10.0 A g^-1, a discharge capacity of 192.6 mA h g^-1 is maintained after 10 000 cycles. When coupled with a commercial LiFePO₄ cathode, the full batteries show an excellent discharge specific capacity of 534.5 mA h g^-1 at 0.2 A g^-1. This work provides an effective strategy for constructing high-performance anodes for Li⁺ storage.

Electronic modulation of nickel selenide by copper doping and in situ carbon coating towards high-rate and high-energy density lithium ion half/full batteries

Over the past decades, metal selenides have drawn considerable attention due to their high theoretical specific capacity. However, huge volume changes and sluggish electrochemical transfer kinetics hinder their applications in energy storage and conversion. In this work, we demonstrate an efficient and ingenious synthesis strategy to regulate nickel selenide electrodes by the introduction of copper and in situ coating with carbon (Cu-NiSe2@C). When used as anodes for lithium-ion batteries, the as-synthesized Cu-NiSe2@C delivered a high capacity of 1630 mA h g-1 at 1.0 A g-1 after 200 cycles and excellent rate performance as well as long-term cycling stability with a high capacity of 489 mA h g-1 at 10 A g-1 after 20 000 cycles. When coupled with a commercial LiFePO4 cathode, the full cells showed a high capacity of 463 mA h g-1 at 0.2 A g-1. Their superior electrochemical performance can be attributed to the synergistic effect of the in situ carbon coating and copper doping, which can promote the electron/ion transfer kinetics, as well as alleviate the volume expansion during cycling. This work will open new opportunities for the development of high-performance anodes for lithium storage.

Controlled synthesis of N-doped carbon and TiO2 double-shelled nanospheres with encapsulated multi-layered MoO3 nanosheets as an anode for reversible lithium storage

α-Phase molybdenum trioxide (α-MoO₃) is one of the promising anode materials for lithium storage due to its high theoretical capacity and unique intercalation reaction mechanism. Herein, through an efficient step-by-step solvothermal synthesis strategy, multi-layered MoO₃ nanosheets are encapsulated by nitrogen-doped carbon (NC) and ultrathin TiO₂ double-shells to obtain hierarchical core-shell nanospheres (MoO₃@TiO₂@NC). The unique nanostructure enables shortening the Li⁺ diffusion distance, buffer the volume change during the intercalation/deintercalation process, and increase the active sites for the electrochemical reaction. Based on the hierarchical nanostructure and the synergistic effect of each component, the MoO₃@TiO₂@NC electrode exhibits a high Li⁺ storage capacity around 979.6 mA h g^-1 after 200 cycles at 0.2 A g^-1, a stable cycle performance of 800.3 mA h g^-1 at 1 A g^-1 after 700 cycles and an excellent rate capability of 418.0 mA h g^-1 at 5 A g^-1. Furthermore, the MoO₃@TiO₂@NC-based coin-type full cell with a commercial LiNi_1/3Mn_1/3Co_1/3O₂ cathode exhibited a good cycling stability at 0.2 A g^-1 for 100 cycles (∼190 mA h g^-1) and rate capability (134 mA h g^-1 at 5 A g^-1).

A MoS2@SnS heterostructure for sodium-ion storage with enhanced kinetics

Layered metal sulphides are promising anode materials for sodium-ion batteries (SIBs) and capacitors owing to their distinctive crystal structures and large interlayer spacings, which are suitable for Na⁺ insertion/extraction. However, low electronic conductivity, sluggish ion transfer and large volume variation of metal sulphides during sodiation/desodiation processes have hindered their practical application. In this work, we report the construction of a walnut-like core-shell MoS₂@SnS heterostructure composite as an anode for SIBs with high capacity, remarkable rate and superior cycling stability. Experimental observations and first-principles density functional theory (DFT) calculations reveal that the enhanced electrochemical performances can be mainly ascribed to the boosted charge transfer and ion diffusion capabilities at the heterostructure interface driven by a self-building internal electric field. Our findings herein may pave the way for the development of novel heterostructure composite materials for beyond lithium-ion batteries and capacitors.

MoS2 nanoflowers encapsulated into carbon nanofibers containing amorphous SnO2 as an anode for lithium-ion batteries

SnO₂ with high abundance, large theoretical capacity, and nontoxicity is considered to be a promising candidate for use as advanced electrodes. However, the poor electronic conductivity and large volume variations hinder the practical applications of SnO₂-based electrodes for use in lithium-ion batteries (LIBs). Herein, the MoS₂-SnO₂ heterostructures were encapsulated into carbon nanofibers (CNFs) via facile solvothermal and electrospinning methods. Remarkably, when the binder-free and robust MoS₂-SnO₂@CNF is employed as the anode for LIBs, such a clever structure yields a discharge capacity of 983 mA h g^-1 at a current density of 200 mA g^-1 after 100 cycles and a capacity of 710 mA h g^-1 after 800 cycles at a current density of 2000 mA g^-1. Moreover, full cells and flexible full cells were constructed, which exhibited high flexibility and delivered a high reversible capacity of 463 mA h g^-1 after 100 cycles at 500 mA g^-1. The exceptional performance of MoS₂-SnO₂@CNF could be attributed to the rational design of the electrode structure. On one hand, the robust structure of the amorphous SnO₂ and MoS₂ nanoflowers in the conductive carbon network not only provides direct current pathways, but also enhances electron transfer. On the other hand, the abundance of p-n heterogeneous interfaces considerably reduces the charge transfer resistance and enhances the surface reaction kinetics. This work proposes a feasible strategy to enhance the capacity and stability of SnO₂-based electrodes and opens up a new avenue for the potential applications of SnO₂ anode materials.

MOF-derived uniform Ni nanoparticles encapsulated in carbon nanotubes grafted on rGO nanosheets as bifunctional materials for lithium-ion batteries and hydrogen evolution reaction

The rational-design and synthesis of transition-metal compounds with outstanding electrochemical activity and durability for renewable energy systems have attracted tremendous research interest in recent years. Herein, we report a facile and unique strategy to synthesize N-doped carbon nanotube-encapsulated Ni nanoparticles on reduced graphene oxide (Ni@NC-rGO). The optimized nanostructure determines the synergetic effects among the Ni nanoparticles, N-doped CNTs and graphene nanosheets, thus resulting in extraordinary electrochemical performances. When applied as an anode for lithium-ion batteries (LIBs), the Ni@NC-rGO electrode displayed high reversible capacity, stable cycling performance and superior rate capability. Moreover, the resulting Ni@NC-rGO nanocomposites exhibited low overpotential and considerable durability for the hydrogen evolution reaction (HER). Our study may provide a feasible methodology for the preparation of high-performance nanostructured materials for practical energy storage and conversion applications.

A facile alkali metal hydroxide-assisted controlled and targeted synthesis of 1T MoS2 single-crystal nanosheets for lithium ion battery anodes

High-quality metallic 1T phase MoS2 single-crystal nanosheets were synthesized by a facile eco-friendly alkali metal hydroxide-assisted controlled and targeted approach via the calcination of lithium hydroxide and ammonium tetrathiomolybdate under argon atmosphere at 1000 °C. The 1T MoS2 single-crystal nanosheets were used as lithium-ion battery anodes, exhibiting superior electrochemical performances, including long cycle life and high capacities. The first charge and discharge capacities were up to 889.1 mA h g-1 and 892.5 mA h g-1, respectively, giving a first cycle coulombic efficiency of 98.0%, which exceeded 99.1% in the second cycle. In the 400th cycle, the charge and discharge capacities were 737.2 mA h g-1 and 738.0 mA h g-1, respectively, with 82.9% capacity retention ratio. This study not only provides a novel strategy for fabricating metallic 1T phase MoS2, which can be used as lithium ion battery anodes but also introduces a facile eco-friendly lithium hydroxide-assisted controlled and targeted approach for different phase MoS2 (1T and 2H). Moreover, it can be extended to other alkali metal hydroxide-assisted (NaOH and KOH) approaches for the MoS2 preparation.

A Facile Synthesis of MoS2/g-C3N4 Composite as an Anode Material with Improved Lithium Storage Capacity

The demand for well-designed nanostructured composites with enhanced electrochemical performance for lithium-ion batteries electrode materials has been emerging. In order to improve the electrochemical performance of MoS2-based anode materials, MoS2 nanosheets integrated with g-C3N4 (MoS2/g-C3N4 composite) was synthesized by a facile heating treatment from the precursors of thiourea and sodium molybdate at 550 °C under N2 gas flow. The structure and composition of MoS2/g-C3N4 were confirmed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis and elemental analysis. The lithium storage capability of the MoS2/g-C3N4 composite was evaluated, indicating high capacity and stable cycling performance at 1 C (A·g-1) with a reversible capacity of 1204 mA·h·g-1 for 200 cycles. This result is believed the role of g-C3N4 as a supporting material to accommodate the volume change and improve charge transport for nanostructured MoS2. Additionally, the contribution of the pseudocapacitive effect was also calculated to further clarify the enhancement in Li-ion storage performance of the composite.

α-Fe2 O3 Nanoparticles Decorated C@MoS2 Nanosheet Arrays with Expanded Spacing of (002) Plane for Ultrafast and High Li/Na-Ion Storage

MoS₂ nanosheets as a promising 2D nanomaterial have extensive applications in energy storage and conversion, but their electrochemical performance is still unsatisfactory as an anode for efficient Li⁺ /Na⁺ storage. In this work, the design and synthesis of vertically grown MoS₂ nanosheet arrays, decorated with graphite carbon and Fe₂ O₃ nanoparticles, on flexible carbon fiber cloth (denoted as Fe₂ O₃ @C@MoS₂ /CFC) is reported. When evaluated as an anode for lithium-ion batteries, the Fe₂ O₃ @C@MoS₂ /CFC electrode manifests an outstanding electrochemical performance with a high discharge capacity of 1541.2 mAh g^-1 at 0.1 A g^-1 and a good capacity retention of 80.1% at 1.0 A g^-1 after 500 cycles. As for sodium-ion batteries, it retains a high reversible capacity of 889.4 mAh g^-1 at 0.5 A g^-1 over 200 cycles. The superior electrochemical performance mainly results from the unique 3D ordered Fe₂ O₃ @C@MoS₂ array-type nanostructures and the synergistic effect between the C@MoS₂ nanosheet arrays and Fe₂ O₃ nanoparticles. The Fe₂ O₃ nanoparticles act as spacers to steady the structure, and the graphite carbon could be incorporated into MoS₂ nanosheets to improve the conductivity of the whole electrode and strengthen the integration of MoS₂ nanosheets and CFC by the adhesive role, together ensuring high conductivity and mechanical stability.

Fe3O4 nanoparticle decorated three-dimensional porous carbon/MoS2 composites as anodes for high performance lithium-ion batteries

Molybdenum disulfide (MoS2) is a promising anode material for lithium-ion batteries owing to its high theoretical capacity and low cost. However, it exhibits low electrical conductivity and volume expansion, resulting in poor electrochemical performance. In this work, three-dimensional porous carbon/MoS2 composites with Fe3O4 nanoparticles (C-MF) are synthesized via a mix-bake-wash method. The few-layered MoS2 in the porous carbon matrix provides improved electrical conductivity and facilitates lithium ion diffusion, so the composites exhibit a high specific capacity of 939.6 mA h g-1 on average at 0.1 A g-1 and a high rate capability (515.9 mA h g-1 at 5 A g-1). Moreover, the Fe3O4 nanoparticles in C-MF, which are anchored on the composites, improve the specific capacity and effectively mitigate diffusion of lithium polysulfides during cycling, resulting in remarkable cycling stability (590.1 mA h g-1 after 500 cycles at 2 A g-1). This work suggests that not only C-MF but also C@MoS2 with other metal oxides synthesized using this facile strategy have potential for energy-related applications.

Sn nanocrystals embedded in porous TiO2/C with improved capacity for sodium-ion batteries

A cylinder-like Sn/TiO₂/C composite was prepared by carbonization and exhibited improved specific capacity in SIBs due to the combination of a porous TiO₂/C structure and Sn nanocrystals.

Carbonization/oxidation-mediated synthesis of MOF-derived hollow nanocages of ZnO/N-doped carbon interwoven by carbon nanotubes for lithium-ion battery anodes

Partial carbonization/oxidation-mediated treatment of ZIF-8 precursors generates hollow nanocages of ZnO/N-doped carbon for high performance lithium-ion battery anodes.