Despite high-energy density and low cost of the lithium–sulfur (Li–S) batteries, their commercial success is greatly impeded by their severe capacity decay during long-term cycling caused by polysulfide shuttling. Herein, a new phase engineering strategy is demonstrated for making MXene/1T-2H MoS2-C nanohybrids for boosting the performance of Li–S batteries in terms of capacity, rate ability, and stability. It is found that the plentiful positively charged S-vacancy defects created on MXene/1T-2H MoS2-C, proved by high-resolution transmission electron microscopy and electron paramagnetic resonance, can serve as strong adsorption and activation sites for polar polysulfide intermediates, accelerate redox reactions, and prevent the dissolution of polysulfides. As a consequence, the novel MXene/1T-2H MoS2-C-S cathode delivers a high initial capacity of 1194.7 mAh g−1 at 0.1 C, a high level of capacity retention of 799.3 mAh g−1 after 300 cycles at 0.5 C, and reliable operation in soft-package batteries. The present MXene/1T-2H MoS2-C becomes among the best cathode materials for Li–S batteries.

Rational Design of MXene/1T-2H MoS2-C Nanohybrids for High-Performance Lithium–Sulfur Batteries

Recent Development of Metallic (1T) Phase of Molybdenum Disulfide for Energy Conversion and Storage

The rapid development of electrochemical energy storage (EES) systems requires novel electrode materials with high performance. A typical 2D nanomaterial, layered transition metal dichalcogenides (TMDs) are regarded as promising materials used for EES systems due to their large specific surface areas and layer structures benefiting fast ion transport. The typical methods for the preparation of TMDs and TMD-based nanohybrids are first summarized. Then, in order to improve the electrochemical performance of various kinds of rechargeable batteries, such as lithium-ion batteries, lithium-sulfur batteries, sodium-ion batteries, and other types of emerging batteries, the strategies for the design and fabrication of layered TMD-based electrode materials are discussed. Furthermore, the applications of layered TMD-based nanomaterials in supercapacitors, especially in untraditional supercapacitors, are presented. Finally, the existing challenges and promising future research directions in this field are proposed.

Layered Transition Metal Dichalcogenide-Based Nanomaterials for Electrochemical Energy Storage.

In the past few decades, great effort has been made toward the preparation and development of advanced transition metal dichalcogenide (TMD) materials for anodes of alkali metal ion batteries (AMIBs). However, their electrochemical performance is still severely impaired by structural aggregation and fracture during the conversion reaction. To address these issues, various methodologies for the fabrication of hierarchical and hybrid nanostructures, with optimization of materials and electrodes, have been fully investigated and reviewed. As regards tuning the TMD-based materials, extensive efforts have been undertaken toward optimization of their intrinsic structure at the atomic level, including surface defects, interlayer spacing expansion, phase control, alloying, and heteroatom doping. However, the design strategies and methods to manipulate the intrinsic structures and electrochemical mechanisms in AMIBs have not been fully summarized. This review provides a well-timed and critical appraisal of recent advances in the engineering of TMDs at the atomic level for AMIBs, by combining computational and experimental approaches. The correlation between these strategies and electrochemical performance is highlighted. The challenges and opportunities in this research field are also outlined. We expect that this review would be beneficial for improving the overall knowledge on the charge storage mechanisms in TMDs and for pointing out the importance of intrinsic structure engineering for enhancing the performance of TMDs in energy storage.

Transition metal dichalcogenides for alkali metal ion batteries: engineering strategies at the atomic level

1T MoS2 is metallic octahedral type molybdenum disulfide (MoS2). Compared to the most stable and widely existing triangle prismatic (2H) phase of MoS2, 1T MoS2 possesses distinct electrochemical and electronic properties, such as a high conductivity, abundant active sites both at the edges and on the basal plane for electrochemical catalysis, and enlarged interlayer distance. Due to these merits, the last few years have witnessed a growing amount of interest in both synthesis and application of this unique material. So far, a series of methods have been developed to obtain 1T rich or 1T containing MoS2 and the applications of 1T MoS2 have covered a wide range of areas from electrochemical reactions, photoelectrocatalysis and photodetectors to photothermal agents, energy storage devices, and biosensors. In this article, to obtain a hint of the key reasons for the formation of 1T structured MoS2 and instruct the exploration of more desirable new approaches, the means for fabricating 1T MoS2 that have been reported are carefully classified and compared with a focus on the detailed procedures and the underlying mechanisms. Meanwhile, a full image of the explored applications with 1T MoS2 is provided with an emphasis on the relationship between the properties of 1T MoS2 and the performance and a hope to inspire the development of other potential applications for 1T MoS2. Additionally, the stabilization issue of 1T MoS2 is discussed with a review of the current efforts. The content will be not only helpful for researchers currently working in the related areas but also instructive for the ones new to this field.

Synthesis, stabilization and applications of 2-dimensional 1T metallic MoS2

Novel Designed MnS-MoS2 Heterostructure for Fast and Stable Li/Na Storage:Insights into the Advanced Mechanism Attributed to Phase Engineering

As the most-studied III-nitride, theoretical researches have predicted the presence of gallium nitride (GaN) nanosheets (NSs). Herein, a facile synthesis approach is reported to prepare GaN NSs using graphene oxide (GO) as sacrificial template. As a new anode material of Li-ion battery (LIBs), GaN NSs anodes deliver the reversible discharge capacity above 600 mA h g–1 at 1.0 A g–1 after 1000 cycles, and excellent rate performance at current rates from 0.1 to 10 A g–1. These results not only extend the family of 2D materials but also facilitate their use in energy storage and other applications.

Graphene-Oxide-Assisted Synthesis of GaN Nanosheets as a New Anode Material for Lithium-Ion Battery.

Herein, we propose a practical way for direct preparation of gallium oxide nanosheets/reduced graphene oxide (Ga2O3 NSs/rGO) nanocomposites via oxygenic groups contained hydrophilic graphene oxide (GO) template with subsequent annealing treatment. Benefiting from the two-dimensional (2D) nanoarchitecture of Ga2O3 NSs and rGO, Ga2O3 NSs/rGO nanocomposites exhibit enhanced kinetics and improved cycling stability in Li-ion and Na-ion batteries (LIBs/SIBs). The pseudocapacitance performance is authenticated through kinetic analysis. Ex situ XRD and XPS measurements prove that the reversible Li-ion storage in Ga2O3 NSs/rGO electrodes is a conversion reaction and alloying mechanism. In addition, the full cells fabricated by coupling Ga2O3 NSs/rGO anode and LiFePO4/C or Na3V2(PO4)3/C cathodes exhibit outstanding electrochemical performances. In general, such a new approach, which is not specific to Ga2O3 NSs/rGO nanocomposites, offers great opportunities for 2D oxide nanomaterials or nanocomposites as high-perfo...

Graphene-Oxide-Assisted Synthesis of Ga2O3 Nanosheets/Reduced Graphene Oxide Nanocomposites Anodes for Advanced Alkali-Ion Batteries

Phase-transformation engineering in MoS 2 on carbon cloth as flexible binder-free anode for enhancing lithium storage

In this work, gallium nitride (GaN) nanowires (NWs) were synthesized by chemical vapor deposition (CVD) process. The hybrid electrode showed the capacity up to 486 mAh g–1 after 400 cycles at 0.1 A g–1. Even at 10 A g–1, the reversible capacity can stabilize at 75 mAh g–1 (after 1000 cycles). Pseudocapacitive capacity was defined by kinetics analysis. The dynamics analysis and electrochemical reaction mechanism of GaN with Li+ was also analyzed by ex situ XRD, HRTEM, and XPS results. These results not only cast new light on pseudocapacitance enhanced high-rate energy storage devices by self-assembled nanoengineering but also extend the application range of traditional binary III/V semiconductors.

Mingzhi Yang

Papers

Novel Designed MnS-MoS2 Heterostructure for Fast and Stable Li/Na Storage:Insights into the Advanced Mechanism Attributed to Phase Engineering

Graphene-Oxide-Assisted Synthesis of GaN Nanosheets as a New Anode Material for Lithium-Ion Battery.

Graphene-Oxide-Assisted Synthesis of Ga2O3 Nanosheets/Reduced Graphene Oxide Nanocomposites Anodes for Advanced Alkali-Ion Batteries

Phase-transformation engineering in MoS 2 on carbon cloth as flexible binder-free anode for enhancing lithium storage

Stable and Reversible Lithium Storage with High Pseudocapacitance in GaN Nanowires.