Recent studies have shown that disordered rock salt (DRS) oxyfluorides with Li excess are interesting candidates as cathode materials for Li-ion batteries. However, these materials have not been able to achieve the desired technological level yet owing to structure stability issues and the lack of direct evidence of the underlying Li+ (de)­insertion mechanism. In this work, we demonstrate how fluorine can increase the stability of the DRS structure and improve the lithium diffusion in a percolation network concomitant with accommodated structural Mn oxidation. Therefore, we synthesized four representative Mn-based DRS materials in the Li1+x Mn2/3Ti1/3O2F x (0 ≤ x ≤ 1) chemical system to clarify the effect of fluorine on the structural and electrochemical properties. All of the compositions have achieved higher than 210 mAh g–1 initial capacity and good cyclability, mainly for high F/Li ratios. The ex situ Raman spectroscopy analysis shed light on the lithium diffusion pathways inside the structure and on the effect of fluorine on the Li+ (de)­insertion during cycling. Thanks to the F-enrichment, the amount of Li+ trapped as LiO4 tetrahedral sites can be reduced, allowing more efficient lithium transport. The structure stability is reinforced by its MnIIO6 octahedral local ordering, resulting in better capacity retention. The study demonstrates the viability of the fluorination strategy toward developing cobalt-free cathode materials with enhanced performance.

Multivalent batteries show promising prospects for next‐generation sustainable energy storage applications. Herein, we report a polytriphenylamine (PTPAn) composite cathode capable of highly reversible storage of tetrakis(hexafluoroisopropyloxy) borate [B(hfip)4] anions in both Magnesium (Mg) and calcium (Ca) battery systems. Spectroscopic and computational studies reveal the redox reaction mechanism of the PTPAn cathode material. The Mg and Ca cells exhibit a cell voltage >3 V, a high‐power density of ∼∼3000 W kg−1 and a high‐energy density of ∼∼300 Wh kg−1, respectively. Moreover, the combination of the PTPAn cathode with a calcium‐tin (Ca−Sn) alloy anode could enable a long battery‐life of 3000 cycles with a capacity retention of 60 %. The anion storage chemistry associated with dual‐ion electrochemical concept demonstrates a new feasible pathway towards high‐performance divalent ion batteries.

We use a femtosecond pump-probe Z-scan technique to measure the thermal lens (TL) signal in a homologous series of primary alcohols. The trend in these experimentally measured TL signals deviates in a counterintuitive manner from the ones calculated using theoretical models that are only based on the macroscopic parameters. Introspection shows that the present TL theories are based on heat conduction for low absorbing samples without considering any convective mode of heat transfer. Our studies on highly absorbing samples indicate the importance of convective mode of heat transfer in TL studies.

Using the close-aperture Z-scan technique, the pure nonlinear refractive index (n₂) of carbon disulfide is measured with a 76 MHz repetition rate femtosecond laser. Strong interference of thermal effects exists with high-repetition-rate lasers that result in negative values of n₂. We remove the thermal effect completely by continuously increasing the sample flow rate (F) in a sample cell as indicated by the change in sign of n₂ from negative to positive. The positive value of n₂ is due to Kerr-type nonlinearity. At sufficiently high values of F of >25 ml/min, all thermal effects are removed, resulting in an n₂ value that matches low-repetition-rate experiments.

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