Project description:Background: Gradient temperature Raman spectroscopy (GTRS) applies the continuous temperature gradients utilized in differential scanning calorimetry (DSC) to Raman spectroscopy, providing a new means for rapid high throughput material identification and quality control. Methods: Using 20 Mb three-dimensional data arrays with 0.2 °C increments and first/second derivatives allows complete assignment of solid, liquid and transition state vibrational modes. The entire set or any subset of the any of the contour plots, first derivatives or second derivatives can be utilized to create a graphical standard to quickly authenticate a given source. In addition, a temperature range can be specified that maximizes information content. Results: We compared GTRS and DSC data for five commercial fish oils that are excellent sources of docosahexaenoic acid (DHA; 22:6n-3) and eicosapentaenoic acid (EPA; 20:5n-3). Each product has a unique, distinctive response to the thermal gradient, which graphically and spectroscopically differentiates them. We also present detailed Raman data and full vibrational mode assignments for EPA and DHA. Conclusion: Complex lipids with a variety of fatty acids and isomers have three dimensional structures based mainly on how structurally similar sites pack. Any localized non-uniformity in packing results in discrete "fingerprint" molecular sites due to increased elasticity and decreased torsion.
Project description:In situ formation of a stable interphase layer on zinc surface is an effective solution to suppress dendrite growth. However, the fast transport of bivalent Zn-ions within the solid interlayer remains very challenging. Herein, we engineer the SEI components and enable superior kinetics of Zn metal batteries under harsh conditions through regulating the sequence of interfacial chemical reaction. With the differences in chemical reactivity of trimethyl phosphate co-solvent and trifluoromethanesulfonate anions in the Zn2+-solvation shell, Zn3(PO4)2 and ZnF2 are successively generated on Zn metal surface to form a gradient ZnF2-Zn3(PO4)2 interphase. Mechanistic studies reveal the outer ZnF2 facilitates Zn2+ desolvation and inner Zn3(PO4)2 serves as channels for fast Zn2+ transport, contributing to long-term cycling at subzero temperatures. Impressively, the gradient SEI enables a high lifespan over 7000 hours in Zn symmetric cell and a capacity retention of 86.1% after 12000 cycles in Zn-KVOH full cell at -50 °C.
Project description:Knowledge of electrolyte transport and thermodynamic properties in Li-ion and beyond Li-ion technologies is vital for their continued development and success. Here, we present a method for fully characterising electrolyte systems. By measuring the electrolyte concentration gradient over time via operando Raman microspectroscopy, in tandem with potentiostatic electrochemical impedance spectroscopy, the Fickian "apparent" diffusion coefficient, transference number, thermodynamic factor, ionic conductivity and resistance of charge-transfer were quantified within a single experimental setup. Using lithium bis(fluorosulfonyl)imide (LiFSI) in tetraglyme (G4) as a model system, our study provides a visualisation of the electrolyte concentration gradient; a method for determining key electrolyte properties, and a necessary technique for correlating bulk intermolecular electrolyte structure with the described transport and thermodynamic properties.
Project description:To harness all of the benefits of solid-state battery (SSB) architectures in terms of energy density, their negative electrode should be an alkali metal. However, the high chemical potential of alkali metals makes them prone to reduce most solid electrolytes (SE), resulting in a decomposition layer called an interphase at the metal|SE interface. Quantitative information about the interphase chemical composition and rate of formation is challenging to obtain because the reaction occurs at a buried interface. In this study, a thin layer of Na metal (Na0) is plated on the surface of an SE of the NaSICON family (Na3.4Zr2Si2.4P0.6O12 or NZSP) inside a commercial X-ray photoelectron spectroscopy (XPS) system while continuously analyzing the composition of the interphase operando. We identify the existence of a solid electrolyte interphase at the Na0|NZSP interface, and more importantly, we demonstrate for the first time that this protocol can be used to study the kinetics of interphase formation. A second important outcome of this article is that the surface chemistry of NZSP samples can be tuned to improve their stability against Na0. It is demonstrated by XPS and time-resolved electrochemical impedance spectroscopy (EIS) that a native Na x PO y layer present on the surface of as-sintered NZSP samples protects their surface against decomposition.
Project description:Understanding the interfacial dynamics of batteries is crucial to control degradation and increase electrochemical performance and cycling life. If the chemical potential of a negative electrode material lies outside of the stability window of an electrolyte (either solid or liquid), a decomposition layer (interphase) will form at the interface. To better understand and control degradation at interfaces in batteries, theoretical models describing the rate of formation of these interphases are required. This study focuses on the growth kinetics of the interphase forming between solid electrolytes and metallic negative electrodes in solid-state batteries. More specifically, we demonstrate that the rate of interphase formation and metal plating during charge can be accurately described by adapting the theory of coupled ion-electron transfer (CIET). The model is validated by fitting experimental data presented in the first part of this study. The data was collected operando as a Na metal layer was plated on top of a NaSICON solid electrolyte (Na3.4Zr2Si2.4P0.6O12 or NZSP) inside an XPS chamber. This study highlights the depth of information which can be extracted from this single operando experiment and is widely applicable to other solid-state electrolyte systems.
Project description:We introduce a flexible microscale all-fiber-optic Raman probe which can be embedded into devices to enable operando in situ spectroscopy. The facile-constructed probe is composed of a nested antiresonant nodeless hollow-core fiber combined with an integrated high refractive index barium titanate microlens. Pump laser 785 nm excitation and near-infrared collection are independently characterized, demonstrating an excitation spot of full-width-half-maximum 1.1 μm. Since this is much smaller than the effective collection area, it has the greatest influence on the collected Raman scattering. Our characterization scheme provides a suitable protocol for testing the efficacy of these fiber probes using various combinations of fiber types and microspheres. Raman measurements on a surface-enhanced Raman spectroscopy sample and a copper battery electrode demonstrate the viability of the fiber probe as an alternative to bulk optic Raman microscopes, giving comparable collection to a 10 objective, thus paving the way for operando Raman studies in applications such as lithium battery monitoring.
Project description:The solid electrolyte interphase (SEI) remains a central challenge to lithium-ion battery durability, in part due to poor understanding of the basic chemistry responsible for its formation and evolution. In this study, the SEI on a non-intercalating tungsten anode is measured by operando neutron reflectometry and quartz crystal microbalance. A dual-layer SEI is observed, with a 3.7 nm thick inner layer and a 15.4 nm thick outer layer. Such structures have been proposed in the literature, but have not been definitively observed via neutron reflectometry. The SEI mass per area was 1207.2 ng/cm2, and QCM provides insight into the SEI formation dynamics during a negative-going voltage sweep and its evolution over multiple cycles. Monte Carlo simulations identify SEI chemical compositions consistent with the combined measurements. The results are consistent with a primarily inorganic, dense inner layer and a primarily organic, porous outer layer, directly confirming structures proposed in the literature. Further refinement of techniques presented herein, coupled with additional complementary measurements and simulations, can give quantitative insight into SEI formation and evolution as a function of battery materials and cycling conditions. This, in turn, will enable scientifically-guided design of durable, conductive SEI layers for Li-ion batteries for a range of applications.
Project description:The lithium-ion battery is currently the preferred power source for applications ranging from smart phones to electric vehicles. Imaging the chemical reactions governing its function as they happen, with nanoscale spatial resolution and chemical specificity, is a long-standing open problem. Here, we demonstrate operando spectrum imaging of a Li-ion battery anode over multiple charge-discharge cycles using electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). Using ultrathin Li-ion cells, we acquire reference EELS spectra for the various constituents of the solid-electrolyte interphase (SEI) layer and then apply these "chemical fingerprints" to high-resolution, real-space mapping of the corresponding physical structures. We observe the growth of Li and LiH dendrites in the SEI and fingerprint the SEI itself. High spatial- and spectral-resolution operando imaging of the air-sensitive liquid chemistries of the Li-ion cell opens a direct route to understanding the complex, dynamic mechanisms that affect battery safety, capacity, and lifetime.
Project description:Li-rich and catalytically active γ-LixV2O5 (x = 1.48) was investigated as a cathode for its heterogeneous charge transfer kinetics. Using a specially designed two-electrode system lithium half cell, Butler-Volmer analysis was performed, and Raman spectra were acquired in 18 mV intervals. A direct correlation was observed between the Raman shift of the active modes Ag,Bg, Au, and Bu, and the development of the Faraday current at the working electrode. The Raman intensity and the Raman shift were implemented to replace the current in a Tafel plot used for the analysis of Butler-Volmer kinetics. Striking similarities in the charge transfer proportionality constants α were found for current and Raman-based analysis. The potential of this new method of Raman-aided electrochemical detection at the diffraction limit is discussed.
Project description:Operando Raman spectroscopy is a powerful analytical tool to provide new insights in the working and deactivation principles of solid catalysts. Intense fluorescence can obscure Raman spectra to the extent that they become uninterpretable. Time-gated Raman spectroscopy, based on pulsed excitation and time-gated detection, suppresses background fluorescence based on its slower time dynamics compared to Raman scattering. In this work, we demonstrate and quantify the benefit of time gating for operando Raman spectroscopy, using the propane dehydrogenation reaction over Pt-Sn-based catalyst materials as a case study. Experimental time-gated Raman spectroscopy data are fitted to a time-trace model that is used to optimize time gating for the maximum signal-to-background-noise ratio. Time-gated Raman spectra of a spent propane dehydrogenation catalyst material show lower background fluorescence compared to the time-integrated Raman spectra counterparts. Simultaneous operando time-gated and time-integrated Raman spectroscopy experiments demonstrate the benefit of time gating to obtain more distinct Raman features, especially in the early coking stages where spectra are dominated by background fluorescence.