Molecular Photothermal Effects on Time-Resolved IR Spectroscopy: Solute-Solvent Intermolecular Energy Transfer

Molecular Photothermal Effect on the 2D-IR Spectroscopy of Acetonitrile-Based Li-Ion Battery Electrolytes

Advancements in Li-ion battery (LIB) technology hinge on an understanding of Li-ion solvation and charge transport dynamics. Ultrafast two-dimensional infrared (2D-IR) spectroscopy has been used to investigate these dynamics in electrolytes by probing chemical exchange processes through time-dependent cross-peak analysis. However, accurate interpretation is complicated by factors such as vibrational energy transfer and molecular photothermal effect (MPTE), affecting cross-peak evolution. Pinpointing the precise origin of these cross-peaks has posed a significant challenge in time-resolved IR spectroscopic studies of LIB electrolytes. Here, we trace the origin of 2D-IR cross-peaks of LIB electrolytes utilizing acetonitrile as a solvent. Time-dependent analysis of LiSCN and CH3SCN mixtures in CD3CN revealed distinctive MPTE features. Furthermore, direct observation of intermolecular MPTE through two-color IR pump-probe spectroscopy lends support to the findings. Our results emphasize the non-negligible artifacts induced by MPTE and the necessity of considering these effects to accurately observe the ultrafast dynamics within LIB electrolytes.

Understanding the bio-crystallization: An insight to therapeutic relevance

In the realm of biomedical engineering and materials science, the synthesis of biomaterials plays a pivotal role in advancing therapeutic strategies for regeneration of tissues. The deliberate control of crystallization processes in biomaterial synthesis has emerged as a key avenue for tailoring the properties of these materials, enabling the design of innovative solutions for a wide array of medical applications. This review delves into the interplay between controlled crystallization and biomaterial synthesis, exploring its multifaceted applications in the therapeutic domains. The investigation encompasses a wide spectrum of matrices, ranging from small molecules to large biomolecules, highlighting their unique contributions in modulating crystallization processes. Furthermore, the review critically assesses the analytical techniques and methodologies employed to probe and characterize the depths of crystallization dynamics. Advanced imaging, spectroscopic, and computational tools are discussed in the context of unraveling the intricate mechanisms governing nucleation and crystallization processes within the organic matrix. Finally we delve in the applications of such advance material in therapeutics of hard and soft tissues.

Water-Ion Interaction Determines the Mobility of Ions in Highly Concentrated Aqueous Electrolytes

Solvation engineering plays a critical role in tailoring the performance of batteries, particularly through the use of highly concentrated electrolytes, which offer heterogeneous solvation structures of mobile ions with distinct electrochemical properties. In this study, we employed spectroscopic techniques and molecular dynamics simulations to investigate mixed-cation (Li+/K+) acetate aqueous electrolytes. Our research unravels the pivotal role of water in facilitating ion transport within a highly viscous medium. Notably, Li+ cations primarily form ion aggregates, predominantly interacting with acetate anions, while K+ cations emerge as the principal charge carriers, which is attributed to their strong interaction with water molecules. Intriguingly, even at a concentration as high as 40 m, a substantial amount of water molecules persistently engages in hydrogen bonding with one another, creating mobile regions rich in K+ ions. Our observations of a redshift of the OH stretching band of water suggest that the strength of the hydrogen bond alone cannot account for the expansion of the electrochemical stability window. These findings offer valuable insights into the cation transfer mechanism, shedding light on the contribution of water-bound cations to both the ion conductivity and the electrochemical stability window of aqueous electrolytes for rechargeable batteries. Our comprehensive molecular-level understanding of the interplay between cations and water provides a foundation for future advances in solvation engineering, leading to the development of high-performance batteries with improved energy storage and safety profiles.

Revisiting Ultrafast Dynamics in Carbonate-Based Electrolytes for Li-Ion Batteries: Clarifying 2D-IR Cross-Peak Interpretation

Understanding chemical exchange in carbonate-based electrolytes employed in Li-ion batteries (LIBs) is crucial for elucidating ion transport mechanisms. Ultrafast two-dimensional (2D) IR spectroscopy has been widely used to investigate the solvation structure and dynamics of Li-ions in organic carbonate-based electrolytes. However, the interpretation of cross-peaks observed in picosecond carbonyl stretch 2D-IR spectra has remained contentious. These cross-peaks could arise from various phenomena, including vibrational couplings between neighboring carbonyl groups in the first solvation shell around Li-ions, vibrational excitation transfers between carbonyl groups in distinct solvation environments, and local heating effects. Therefore, it is imperative to resolve the interpretation of 2D-IR cross-peaks to avoid misinterpretations regarding ultrafast dynamics found in LIB carbonate-based electrolytes. In this study, we have taken a comprehensive investigation of carbonate-based electrolytes utilizing 2D-IR spectroscopy and molecular dynamics (MD) simulations. Through meticulous analyses and interpretations, we have identified that the cross-peaks observed in the picosecond 2D-IR spectra of LIB electrolytes predominantly arise from intermolecular vibrational excitation transfer processes between the carbonyl groups of Li-bound and free carbonate molecules. We further discuss the limitations of employing a picosecond 2D-IR spectroscopic technique to study chemical exchange and intermolecular vibrational excitation transfer processes, particularly when the effects of the molecular photothermal process cannot be ignored. Our findings shed light on the dynamics of LIB electrolytes and resolve the controversy related to 2D-IR cross-peaks. By discerning the origin of these features, we could provide valuable insights for the design and optimization of next-generation Li-ion batteries.