Heterointerface effects in the electro-intercalation of van der Waals heterostructures (1711.03465v3)

Abstract: Molecular-scale manipulation of electronic/ionic charge accumulation in materials is a preeminent challenge, particularly in electrochemical energy storage. Layered van der Waals (vdW) crystals exemplify a diverse family of materials that permit ions to reversibly associate with a host atomic lattice by intercalation into interlamellar gaps. Motivated principally by the search for high-capacity battery anodes, ion intercalation in composite materials is a subject of intense study. Yet the precise role and ability of heterolayers to modify intercalation reactions remains elusive. Previous studies of vdW hybrids represented ensemble measurements at macroscopic films/powders, which do not permit the isolation and investigation of the chemistry at individual 2-dimensional (2D) interfaces. Here, we demonstrate the intercalation of lithium at the level of individual atomic interfaces of dissimilar vdW layers. Electrochemical devices based on vdW heterostructures comprised of deterministically stacked hexagonal boron nitride, graphene (G) and molybdenum dichalcogenide (MoX2; X = S, Se) layers are fabricated, enabling the direct resolution of intermediate stages in the intercalation of discrete heterointerfaces and the extent of charge transfer to individual layers. Operando magnetoresistance and optical spectroscopy coupled with low-temperature quantum magneto-oscillation measurements show that the creation of intimate vdW heterointerfaces between G and MoX2 engenders over 10-fold accumulation of charge in MoX2 compared to MoX2/MoX2 homointerfaces, while enforcing a more negative intercalation potential than that of bulk MoX2 by at least 0.5 V. Beyond energy storage, our new combined experimental and computational methodology to manipulate and characterize the electrochemical behavior of layered systems opens up new pathways to control the charge density in 2D (opto)electronic devices.

The Impact of Heterointerfaces on Electro-Intercalation Dynamics in vdW Heterostructures

This paper explores the intricate dynamics of electro-intercalation in van der Waals (vdW) heterostructures, focusing on the precise contribution of heterointerfaces in ion intercalation processes. By employing a multitude of techniques, such as in situ magnetoresistance, optical spectroscopy, and low-temperature quantum transport measurements, the authors provide a nuanced understanding of charge transfer and ionic interactions at individual atomic interfaces in these complex systems.

Key Findings and Methodology

The paper revolves around vdW heterostructures constructed from hexagonal boron nitride (hBN), graphene (G), and molybdenum dichalcogenides (MoX, where X = S, Se). These fabricated heterostructures allow for the direct observation of lithium intercalation at specific heterointerfaces, significantly deviating from traditional bulk or macroscopic measurements that average responses over larger domains. The experimental strategy is reinforced by transmission electron microscopy and ab initio calculations, offering a comprehensive portrayal of the electrochemical behavior at mesoscopic scales.

The pivotal discovery is the pronounced role of intimate graphene–molybdenum dichalcogenide interfaces in facilitating charge accumulation. Specifically, when G/MoX heterointerfaces are established, they elicit an increase in charge density by over an order of magnitude compared to MoX homointerfaces. Furthermore, these interfaces promote lithium intercalation at more negative potentials, enhancing the thermodynamic landscape for energy storage applications.

Implications and Future Directions

This research underscores the potential of engineering vdW heterointerfaces to optimize electrochemical performance, particularly in energy storage devices. By leveraging the unique properties of different 2D materials and their heterointerfaces, it becomes possible to tailor charge density profiles and intercalation kinetics with exceptional precision. The findings could revolutionize the design of high-capacity battery electrodes, facilitating the development of materials with improved storage capabilities and efficiency.

Beyond practical applications in energy storage, the insights gained from this paper open avenues for the fine-tuning of interfacial properties in 2D electronic and optoelectronic devices. The ability to manipulate intercalation energetics and structural transitions at the atomic scale could also find relevance in fields such as ion separations and desalination, where selective ion transport is crucial.

In the broader context of material science and electrochemistry, the techniques developed for in situ characterization of vdW heterostructures present a blueprint for further exploration of ultrathin layered systems. As such, there is a compelling case for extending this methodology to other material combinations and exploring the effects of heterointerfaces under various environmental and electrochemical conditions.

Conclusion

The exploration of heterointerface effects in electro-intercalation provides a new lens through which the behavior of vdW heterostructures can be understood and harnessed. This paper not only elucidates the intricate role of interface engineering in enhancing charge storage but also sets the stage for future explorations into the rapidly evolving landscape of 2D materials and their applications spanning energy, electronics, and beyond.