Reactivity and Potential Profile across the Electrochemical LiCoO2-Li3PS4 Interface Probed by Operando X-ray Photoelectron Spectroscopy

Spatio-Chemical Deconvolution of the LiNi0.6Co0.2Mn0.2O2/Li6PS5Cl Interphase Layer in All-Solid-State Batteries Using Combined X-ray Spectroscopic Methods

The (electro)chemical degradation at the interface between Li6PS5Cl (LPSC) and LiNi0.6Co0.2Mn0.2O2 (NCM622) is systematically investigated using nondestructive synchrotron X-ray absorption spectroscopy and X-ray photoemission electron microscopy. These measurements were surface chemical depth profiling (from 2 to several hundred nanometers) and high-resolution elemental imaging of both LPSC and NCM622 particles. This analysis was complemented by galvanostatic cycling, impedance spectroscopy, and operando cell pressure characterization. Several correlations between interphase evolution and cell electrochemical performance are clarified, while some inconsistencies are rationalized and discussed. First, the intrinsic LPSC electrochemical oxidation mechanisms were studied using an LPSC:C65 working electrode (WE). The results showed that increased cell resistance during the first charge stemmed from polysulfide byproducts and particle contact loss due to LPSC volume shrinkage at the interface. Second, when using an NCM622:LPSC WE, species, such as SO32-, SO42-, and PO43-, were detected on both LPSC and NCM622 particles, while electrochemically inactive reduced transition metals were observed only at NCM622 surfaces. These species, initially present at open-circuit potential, increased after the first charge due to the chemical reactions between LPSC and NCM622 surface lattice oxygen. The estimated interphase thickness on the LPSC and NCM622 surfaces over the cycling remains below ∼3 nm. Our findings highlight that the formation of an electrochemically inactive NCM622 surface is a primary cause of impedance rise during the first charge, along with the formation of LPSC byproducts and contact loss. However, the continuous increase in cell resistance could not be attributed to further interphase growth after the first charge. We hypothesize that this may result from slow and progressive LPSC polymerization reactions (e.g., Li2P2S6 and P2S5) and structural changes at the NCM622 surface.

Formation Processes of a Solid Electrolyte Interphase at a Silicon/Sulfide Electrolyte Interface in a Model All-Solid-State Li-Ion Battery

Understanding the electrochemical reactions at the interface between a Si anode and a solid sulfide electrolyte is essential in improving the cycle stabilities of Si anodes in all-solid-state batteries (ASSBs). Highly dense Si films with very low roughnesses of <1 nm were fabricated at room temperature via cathodic arc plasma deposition, which led to the formation of a Si/sulfide electrolyte model interface. Li (de)alloying through the model interface hardly occurred during the first cycle, whereas it proceeded stably in subsequent cycles. Hard X-ray photoelectron spectroscopy and neutron reflectometry directly revealed that the reduction or oxidation of the interfacial component or Li3PS4 electrolyte occurred during the first cycle. Consequently, an interfacial layer with a thickness of 13 nm and primarily composed of Li2S, SiS2, and P2S5 glasses was formed during the first cycle. The interfacial layer acted as a Li-conductive, electron-insulating solid electrolyte interphase (SEI) that provided reversible (de)lithiation. Our model interface directly demonstrates the electrochemical reaction processes at the Si/Li3PS4 interface and provides insights into the structures and electrochemical properties of SEIs to activate the (de)lithiation of Si anodes using a sulfide electrolyte.

Synergistic effect of double Schottky potential well and oxygen vacancy for enhanced plasmonic photocatalytic U(VI) reduction

Plasmonic photocatalysis is an effective strategy to solve radioactive uranium hazards in wastewater. A plasmonic photocatalyst Bi/Bi₂O_3-x@COFs was synthesized by in-situ growth of covalent organic frameworks (COFs) on Bi/Bi₂O_3-x surface for the U(VI) adsorption and plasmonic photoreduction in rare earth tailings wastewater. The presence of oxygen vacancy in Bi/Bi₂O_3-x and Schottky potential well formed by Bi and Bi₂O_3-x interface increased the number of free electrons, which induced localized surface plasmon resonance (LSPR) and enhanced the light absorption performance of composites. In addition, oxygen vacancy improved the Fermi level of Bi/Bi₂O_3-x, leading to another potential well between Bi₂O_3-x and COFs interface. The electron transport direction was reversed, thus increasing the electron density of COFs layer. COFs was an N-type semiconductor with specific binding U(VI) groups and suitable band structure, which could be used as an active reaction site. Bi/Bi₂O_3-x@COFs had 1411.5 mg g^-1 removal capacity and high separation coefficient for U(VI) due to the synergistic action of photogenerated electrons and hot electrons. Moreover, the removal rate of uranium from rare earth tailings wastewater by regenerated Bi/Bi₂O_3-x@COFs was over 93.9%. The scheme of introducing LSPR and Schottky potential well provides another way to improve the photocatalytic effect.

Numerical Recognition System and Ultrasensitive Fluorescence Sensing Platform for Al3+ and UO22+ Based on Ln (III)-Functionalized MOF-808 via Thiodiglycolic Acid Intermediates

Continuous accumulation of Al³⁺ in the human body and unintended leakage of UO₂²⁺ have posed a great threat to human health and the global environment; thus searching an efficient probe for the detection of Al³⁺ and UO₂²⁺ is of great importance. Herein, we designed and synthesized two hydrolytically stable Eu³⁺- and Tb³⁺-functionalized MOF materials Eu@MOF-808-TDA and Tb@MOF-808-TDA via thiodiglycolic acid (TDA) intermediates by the postsynthetic modification method. Among them, Tb@MOF-808-TDA was applied to construct numerical recognition systems of multiples of three and four by the combination of fluorescent signals, hierarchical cluster analysis, and logical gates. In addition, Tb@MOF-808-TDA exhibits good selectivity and sensitivity for the detection of Al³⁺ and UO₂²⁺. The detection limit is calculated to be 0.085 ppm for Al³⁺ and 0.082 ppm for UO₂²⁺ in aqueous solutions, which is lower than or close to that of latest reported Ln-MOFs. Moreover, the probe shows excellent hydrolytic stability and luminescence stability in the pH range of 4-11, further providing solid evidence for the practical application of Tb@MOF-808-TDA. More importantly, a mixed matrix hydrogel PVA-Tb@MOF-808-TDA was prepared to achieve the visual detection of Al³⁺, which broadens the potential in real-world sensing applications.

Li-ion solvation in TFSI and FSI -based ionic liquid electrolytes probed by X-ray photoelectron spectroscopy

For Li-ion batteries, the Li-ion solvation in liquid electrolytes is a crucial parameter affecting directly the electrochemical cycling performance. X-ray photoelectron spectroscopy (XPS) can play an essential role for investigating the cation and anion electronic structure and monitoring the Li-ion solvation into various solvent and salt environments. In this contribution, we demonstrate the capability of conventional laboratory XPS using Al Kα X-ray source to determine the anions solvation shell of Li+ cation within the low vapour pressure and vacuum compatible ionic liquid electrolytes. 1M of LiTFSI and 1M of LiFSI salts dissolved in (EMIM+-FSI-) and (EMIM+-TFSI-) ionic liquids respectively are investigated by acquiring the F1s, N1s, C1s, S2p and Li1s core levels. The binding energy difference between the N1s component originating from the EMIM+ cation and the N1s component originating from TFSI- or FSIanions solvating the Li+ confirms that both TFSI- and FSIcontribute simultaneously to the Li+ solvation. Additionally, the stability of the TFSI and FSI -based ionic liquid electrolytes is carefully discussed for long X-ray exposure times.