The SEINE project focused on developing and investigating two-dimensional (2D) heterostructures composed of graphene (Gr) and molybdenum disulfide (MoS2) as advanced anode materials for sodium-ion batteries (SIBs). Over the course of the project, significant technical and scientific progress was made across all key research objectives.
In the first phase of the project (RO1), single-layer graphene and MoS2 were successfully synthesized using chemical vapor deposition (CVD). These ultrathin films were then transferred to appropriate substrates and thoroughly characterized using Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) to confirm their quality, thickness, and chemical composition. These experiments established reliable protocols for producing high-quality 2D films with atomic-scale precision.
In the second phase (RO2), nitrogen-doped graphene (NGr) was prepared through plasma-based doping methods. Structural and compositional analyses confirmed successful incorporation of nitrogen in controlled configurations. While the original project plan also included nitrogen doping of MoS2 (NMoS2), further evaluation, supported by the fellow’s previous research, indicated that N-doped MoS2 suffers from instability under electrochemical operating conditions. In order to maintain experimental clarity, avoid introducing uncontrolled variables, and focus on the most scientifically robust systems, the decision was made to exclude NMoS2 from further development. This adjustment allowed for a more systematic and reproducible investigation of the role of doping in the performance of 2D heterostructures.
In the third phase (RO3), nine distinct three-layered 2D heterostructures were fabricated using combinations of pristine and nitrogen-doped graphene with MoS2. The stacking order and interface quality of these heterostructures were carefully controlled, and their physical properties were characterized using Raman spectroscopy, XPS, and transmission electron microscopy (TEM). This resulted in a unique dataset describing the structure-property relationships of engineered 2D materials at the atomic scale.
To evaluate their electrochemical behavior (RO4), coin-type sodium half-cells were assembled using the 2D heterostructures as anodes and metallic sodium as the counter/reference electrode. A combination of cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) tests were performed to study their rate capabilities, reversibility, and stability. The experimental results revealed unique CV features and peak shapes not typically observed in bulk analogues of these materials. These findings suggest the possibility of alternative intercalation and co-intercalation mechanisms that are likely suppressed or masked in thicker-layered structures. The reproducibility and distinctiveness of these results mark a key scientific achievement of the project.
Finally, in-situ Raman spectroscopy was employed to monitor the structural evolution of the heterostructures during electrochemical cycling (RO5). Clear correlations were observed between Raman intensity/peak shifts and specific electrochemical potentials, providing new insights into the redox behavior and ion interactions within the layered structures. Complementary operando optical microscopy and in-situ TEM investigations are ongoing to further elucidate dynamic changes at the nanoscale.
Overall, SEINE has successfully demonstrated the synthesis, integration, and electrochemical evaluation of tailored 2D heterostructures for sodium-ion storage. It has produced fundamental knowledge about structure-function relationships, highlighted the limitations of doping in certain 2D systems, and revealed novel electrochemical phenomena with implications for future battery technologies.
