(689d) A Facile and Highly Efficient Method for the Construction of Mg Intercalated 1T Phase MoS2 Materials As Anode of Li Ion Battery

The advancement of energy storage technologies, especially lithium-ion batteries, plays a crucial role in the shift towards renewable energy sources and the expansion of electric vehicles. Nonetheless, the search for materials that deliver higher energy densities, improved charging times, and extended durability is a constant endeavor. Transition metal dichalcogenides (TMDs), characterized by their layered structures, are significant in the domains of energy conversion and storage. Among them, molybdenum disulfide (MoS₂) stands out due to its distinct physical and chemical attributes, making it a highly promising candidate for lithium-ion battery anodes. MoS₂, through conversion reactions, possesses a theoretical capacity of 690 mAh g^-1, markedly surpassing the capacity of conventional graphite materials at 372 mAh g^-1. However, challenges such as limited conductivity and volume expansion during battery cycling impede its performance and practical application. The semiconducting nature of MoS₂ restricts charge and lithium-ion flow, leading to suboptimal utilization and slow reaction speeds. Efforts to mitigate these issues include the integration of MoS₂ with carbon or other metal oxides/sulfides to create composite materials. These heterostructures enhance local conductivity and add active sites for lithium-ion migration, although the added components may deplete electrolytes and undergo expansion, diminishing efficiency, and cycling stability.

MoS₂ exhibits polymorphism with three phases: trigonal prismatic (2H), octahedral (1T), and rhombohedral (3R), each distinguished by crystal symmetry. The 2H phase is stable but suffers from poor conductivity due to a 1.9 eV direct bandgap, whereas the 1T phase, owing to octahedral coordination of Mo and S atoms, exhibits significantly higher conductivity and metallic characteristics. Through phase engineering, the electrochemical performance of the 1T phase can be harnessed to improve MoS₂ conductivity. Nevertheless, the 1T phase's metastable nature poses challenges for its production, highlighting the importance of refining synthesis techniques. Intercalation has proven effective for creating high-purity 1T-phase MoS₂, utilizing alkaline and transition metals to stabilize the 1T phase, enhance conductivity, and expand interlayer distances. Traditional methods for synthesizing intercalated 1T-phase MoS₂, such as insertion via molten alkaline metal and exfoliation, involve complex, high-risk procedures not suited for large-scale production.

Herein, magnesium (Mg) intercalated 1T phase MoS₂ is designed and synthesized by a hydrothermal method, using regulated MBs as the precursor for the first time. The novel method can efficiently synthesize homogeneous Mg-intercalated 1 T MoS₂ with 1 T-phase purity of 90.5 % while avoiding harsh experimental conditions.

Results:

The Mg-intercalated MoS₂ demonstrated a remarkable transition to a stable 1T phase, exhibiting an enhanced surface area and providing additional active sites for lithium-ion storage. Electrochemical tests revealed a significant improvement in lithium storage capacity, achieving a higher charge storage capacity compared to conventional 2H-phase MoS₂. Moreover, the Mg-intercalated 1T-phase MoS₂ displayed superior rate capability and cycling stability, sustaining minimal capacity loss over hundreds of charge-discharge cycles.

Discussion:

The enhanced performance of Mg-intercalated 1T-phase MoS₂ is attributed to several key factors. The metallic 1T phase facilitates faster electron transfer, reducing the charge transfer resistance and enabling higher rate capabilities. Additionally, the Mg intercalation process contributes to an increased interlayer spacing, promoting faster lithium ion diffusion. This structural optimization, combined with the inherent stability of the 1T phase, underpins the outstanding electrochemical performance observed.

Conclusion:

In summary, a facile and highly efficient method for the construction of Mg intercalated high 1T phase purity MoS₂ materials is reported, using a hydrothermal method to synthesize Mg-intercalated 1T MoS₂ for the first time. Utilizing organized nanostructure MB as the precursor, the as-prepared Mg-intercalated 1T MoS₂ possesses a well-defined morphology without agglomeration and exhibits a high 1T phase purity of 90.5 %. The intercalated Mg forms an octahedral coordination with adjacent S, as shown by XPS measurement. The increased interlayer spacing created by the intercalated Mg atoms enhances the electron conductivity and electrochemical activity of the MoS₂ material. The novel Mg-intercalated 1 T MoS₂ possesses outstanding cycling and rate performance