No abstract

Rechargeable secondary batteries operating through fluoride-ion shuttling between the positive and negative electrodes, referred to as fluoride shuttle batteries (FSBs), offer a potentially promising solution to overcoming the energy-density limitations of current lithium-ion battery systems. However, there are many technical issues that need to be resolved to achieve high-quality fluoride-carrying electrolytes and ensure reversible transformations between a metal and its fluoride counterpart at both electrodes. Here, we introduce novel lactone-based liquid electrolytes consisting either of CsF or KF, which are prepared by a solvent substitution method. Although the maximum fluoride-ion concentration achieved by the method is approximately 0.05 M, these systems behave as strong electrolytes where CsF(KF) is almost fully dissociated into Cs+(K+) and F− ions to give a maximum ionic conductivity of 0.8 mS.cm−1. Hence, the solvent supports electrochemically active fluoride ions that can drive reversible metal/metal-fluoride transformations at room temperature for a wide range of metal electrodes. However, irreversible reductive reactions of the solvent, also promoted by the fluoride ions, limit currently the negative potential window to approximately −1.5 V vs the standard hydrogen electrode.

No abstract

The origin of the previously observed unusual photostability of 2,4,6-triisopropyl-4‘-(methoxycarbonyl)benzophenone (1-p-CO2Me) in the solid state was investigated. 1-p-CO2Me was found to photocyclize normally to produce the corresponding benzocyclobutenol 2-p-CO2Me when its solid-state photolysis was carried out either (a) after thorough grinding, (b) after solid−solid mixing with 2,4,6-triisopropyl-4‘-(ethoxycarbonyl)benzophenone (1-p-CO2Et), or (c) at elevated temperatures (an estimated energy barrier of 20 kcal/mol). Furthermore, when the photolysis was performed under more carefully deoxygenated conditions (closed argon atmosphere), formation of blue species that are persistent in the absence of oxygen was observed. On the basis of oxygen trapping and ESR experiments, the blue species are regarded as a mixture of a diradical intermediate DR and monoradicals derived thereof. The X-ray study of 1-p-CO2Me had revealed that the distances between the carbonyl oxygen and the o-i-Pr methine hydrogens are within the critical limit for hydrogen abstraction to occur, but a small reaction cavity or the compact crystal packing around both of the o-i-Pr groups is interfering with the photocyclization. The present results are consistent with this X-ray crystal structure; i.e., the photochemical hydrogen abstraction of 1-p-CO2Me to DR can take place, but DR reketonizes back to 1-p-CO2Me under the usual photolysis conditions because there is a high topochemical barrier to cyclization leading to 2-p-CO2Me.