Controllable synthesis of few-layer ammoniated 1T'-phase WS2 as an anode material for lithium-ion batteries

Robust Growth of 2D Transition Metal Dichalcogenide Vertical Heterostructures via Ammonium-Assisted CVD Strategy

Two dimension (2D) transition metal dichalcogenides (TMD) heterostructures have opened unparalleled prospects for next-generation electronic and optoelectronic applications due to their atomic-scale thickness and distinct physical properties. The chemical vapor deposition (CVD) method is the most feasible approach to prepare 2D TMD heterostructures. However, the synthesis of 2D vertical heterostructures faces competition between in-plane and out-of-plane growth, which makes it difficult to precisely control the growth of vertical heterostructures. Here, a universal and controllable strategy is reported to grow various 2D TMD vertical heterostructures through an ammonium-assisted CVD process. The ammonium-assisted strategy shows excellent controllability and operational simplicity to prevent interlayer diffusion/alloying and thermal decomposition of the existed TMD templates. Ab initio simulations demonstrate that the reaction between NH4Cl and MoS2 leads to the formation of MoS3 clusters, promoting the nucleation and growth of 2D MoS2 on existed 2D WS2 layer, thereby leading to the growth of vertical heterostructure. The resulting 2D WSe2/WS2 vertical heterostructure photodetectors demonstrate an outstanding optoelectronic performance, which are comparable to the performances of photodetectors fabricated from mechanically exfoliated and stacked vertical heterostructures. The ammonium-assisted strategy for robust growth of high-quality vertical van der Waals heterostructures will facilitate fundamental physics investigations and device applications in electronics and optoelectronics.

Construction of WS2/NC@C nanoflake composites as performance-enhanced anodes for sodium-ion batteries

The development of layered metal sulfides with stable structure and accessible active sites is of great importance for sodium-ion batteries (SIBs). Herein, a simple liquid-mixing method is elaborately designed to immobilize WS2 nanoflakes on N-doped carbon (NC), then further coat carbon to produce WS2/NC@C. In the formation process of this composite, the presence of NC not only avoids the overlap and improves the dispersion of WS2 nanoflakes, but also creates a connection network for charge transfer, where the wrapped carbon provides a stable chemical and electrochemical reaction interface. Thus, the composite of WS2/NC@C exhibits the desired Na+ storage capacity as anticipated. The reversible capacity reaches the high value of 369.8 mA h g-1 at 0.2 A g-1 after 200 cycles, while excellent rate performances and cycle life are also acquired in that capacity values of 256.7 and 219.6 mA h g-1 at 1 and 5 A g-1 are preserved after 1000 cycles, respectively. In addition, the assembled sodium-ion hybrid capacitors (SIHCs, AC//WS2/NC@C) exhibit an energy/power density of 68 W h kg-1 at 64 W kg-1, and capacity retention of 82.9% at 1 A g-1 after 2000 cycles. The study provides insight into developing layered metal sulfides with eminent performance of Na+ storage.

NiFe-LDH/MXene nano-array hybrid architecture for exceptional capacitive lithium storage

Layered double hydroxides (LDHs) have great advantages in the domain of energy storage because of their exchangeable anions and large specific surface area. Nevertheless, the shortcomings of their poor electrical conductivity, easy stacking of nanosheets, and large volume variation in the cycling processes lead to unsatisfactory cycling stability and rate performance, which severely limits their further application. Therefore, we generated homogeneous nanoarrays of NiFe-LDH on the surface of Ti₃C₂T_x-MXene by a refluxing process. The resulting NiFe-LDH/MXene-500 hybrid material was applied as an anode of a lithium-ion battery (LIB) and exhibited a discharge capacity of 894.8 mA h g^-1 at 200 mA g^-1 (over 300 cycles) and could maintain a reversible capacity of 547.1 mA h g^-1 even at 1 A g^-1. With the addition of MXene, the volume increases of the NiFe-LDH/MXene hybrid materials were also significantly alleviated. The thickness of the NiFe-LDH/MXene-500 electrode only increased by 31% after 50 cycles, which was far better than the prepared NiFe-LDH electrode. On the hand, the synergistic interaction of NiFe-LDH and MXene could stabilize the structure, reduce the activation barrier of ion/electron diffusion, and promote electron transfer in the electrode. MXene with high conductivity can be used as electrical and ionic conductance media to promote the transformation reaction of NiFe-LDH. According to the detailed kinetic analysis, the capacitance control behavior is the main electrochemical reaction of NiFe-LDH/MXene electrodes.