Laboratory operando Fe and Mn K-edges XANES and Mössbauer studies of the LiFe0.5Mn0.5PO4 cathode material

Revisited Ti2Nb2O9 as an Anode Material for Advanced Li-Ion Batteries

Ti₂Nb₂O₉ with a tunnel-type structure is considered as a perspective negative electrode material for Li-ion batteries (LIBs) with theoretical capacity of 252 mAh g^-1 corresponding to one-electron reduction/oxidation of Ti and Nb, but only ≈160 mAh g^-1 has been observed practically. In this work, highly reversible capacity of 200 mAh g^-1 with the average (de)lithiation potential of 1.5 V vs Li/Li⁺ is achieved for Ti₂Nb₂O₉ with pseudo-2D layered morphology obtained via thermal decomposition of the NH₄TiNbO₅ intermediate prepared by K⁺→ H⁺→ NH₄⁺ cation exchange from KTiNbO₅. Using operando synchrotron powder X-ray diffraction (SXPD), single-phase (de)lithiation mechanism with 4.8% unit cell volume change is observed. Operando X-ray absorption near-edge structure (XANES) experiment revealed simultaneous Ti⁴⁺/Ti³⁺ and Nb⁵⁺/Nb⁴⁺ reduction/oxidation within the whole voltage range. Li⁺ migration barriers for Ti₂Nb₂O₉ along [010] direction derived from density functional theory (DFT) calculations are within the 0.15-0.4 eV range depending on the Li content that is reflected in excellent C-rate capacity retention. Ti₂Nb₂O₉ synthesized via the ion-exchange route appears as a strong contender to widely commercialized Ti-based negative electrode material Li₄Ti₅O₁₂ in the next generation of high-performance LIBs.

Quantification of Redox Sites during Catalytic Propane Oxychlorination by Operando EPR Spectroscopy

Identification and quantification of redox-active centers at relevant conditions for catalysis is pivotal to understand reaction mechanisms and requires development of advanced operando methods. Herein, we demonstrate operando EPR spectroscopy as an important technique to quantify the oxidation state of representative CrPO₄ and EuOCl catalysts during propane oxychlorination, an attractive route for propylene production. In particular, we show that the space-time-yield of C₃ H₆ correlates with the amount of Cr²⁺ and Eu²⁺ ions generated over the catalysts during reaction. These results provide a powerful strategy to gather quantitative understanding of selective alkane oxidation, which could potentially be extrapolated to other functionalization approaches and operating conditions.

Laboratory Operando XAS Study of Sodium Iron Titanite Cathode in the Li-Ion Half-Cell

Electrochemical characterization of the novel sodium iron titanate Na_0.9Fe_0.45Ti_1.55O₄ was performed upon cycling in the Li-ion half-cell. The material exhibited stable cycling in the voltage range 2–4.5 V, and the number of alkali ions extracted per formula unit was approximately half of the Na stoichiometry value. Using laboratory X-ray absorption spectrometry, we measured operando Fe K-edge X-ray absorption spectra in the first 10 charge–discharge cycles and quantified the portion of charge associated with the transition metal redox reaction. Although 3d metals are commonly accepted redox-active centers in the intercalation process, we found that in all cycles the amount of oxidized and reduced Fe ions was almost 20% less than the total number of transferred electrons. Using density functional theory (DFT) simulations, we show that part of the reversible capacity is related to the redox reaction on oxygen ions.

One-pot coating of LiCoPO4/C by a UiO-66 metal-organic framework

LiCoPO4 (LCP) is a promising high voltage cathode material but suffers from low conductivity and poor electrochemical properties. These properties can be improved by coating with a conductive carbon layer. Ongoing research is focused on the protective layer with good adhesion and inhibition of electrolyte decomposition reactions. In the present work, we suggest a new robust one-pot procedure, featuring the introduction of UiO-66 metal-organic framework (MOF) nanoparticles during LCP synthesis to create a metal-carbon layer upon annealing. The LiCoPO4/C@UiO-66 was synthesized via the microwave-assisted solvothermal route, and 147 mA h g-1 discharge capacity was obtained in the first cycle. The MOF acts as a source of both carbon and metal atoms, which improves conductivity. Using operando X-ray absorption spectroscopy upon cycling, we identify two Co-related phases in the sample and exclude the olivine structure degradation as an explanation for a long-term capacity fade.