A Computational Study on Halogen/Halide Redox Mediators and Their Role in 1O2 Release in Aprotic Li–O2 Batteries

We present a computational study on the redox reactions of small clusters of Li superoxide and peroxide in the presence of halogen/halide redox mediators. The study is based on DFT calculations with a double hybrid functional and an implicit solvent model. It shows that iodine is less effective than bromine in the oxidation of Li2O2 to oxygen. On the basis of our thermodynamic data, in solvents with a low dielectric constant, iodine does not spontaneously promote either the oxidation of Li2O2 or the release of singlet oxygen, while bromine could spontaneously trigger both events. When a solvent with a large dielectric constant is used, both halogens appear to be able, at least on the basis of thermodynamics, to react spontaneously with the oxides, and the ensuing reaction sequence turned out to be strongly exoergic, thereby providing a route for the release of significant amounts of singlet oxygen. The role of spin–orbit coupling in providing a mechanism for singlet–triplet intersystem crossing has also been assessed

Outstanding compatibility of hard-carbon anodes for sodium-ion batteries in ionic liquid electrolytes

: Hard carbons (HC) from natural bio-waste have been investigated as anodes for sodium-ion batteries in electrolytes based on the 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIFSI) and N-trimethyl-N-butylammonium bis(fluorosulfonyl)imide (N1114FSI) ionic liquids. The Na+ intercalation process has been analyzed by cyclic voltammetry tests, performed at different scan rates for hundreds of cycles, in combination with impedance spectroscopy measurements to decouple bulk and interfacial resistances of the cells. The Na+ diffusion coefficient in the HC host has been also evaluated via the Randles-Sevcik equation. Battery performance of HC anodes in the ionic liquid electrolytes has been evaluated in galvanostatic charge/discharge cycles at room temperature. The evolution of the SEI (Solid Electrochemical Interface) layer grown on the HC surface has been carried out by Raman spectroscopy. Overall the sodiation process of the HC host is highly reversible and reproducible. In particular, a capacity retention exceeding 98 % of the initial value has been recorded in N1114FSI electrolytes after more than 1500 cycles with a coulombic efficiency above 99 %, largely beyond standard carbonate-based electrolytes. Raman, transport properties and impedance confirms that ILs disclose the formation of SEI layers with superior ability to support the reversible Na+ intercalation with the possible minor contributions from the EMI+ cation

Stable cycling of sodium metal anodes enabled by a sodium/silica‐gel host

Sodium metal batteries (SMBs) are innovative and promising energy storage systems. SMBs are a competitive technological paradigm compared to the state-of-the-art lithium-ion batteries thanks to the high specific capacity of sodium metal, i. e., 1166 mAhg1, and the Na+/Na0 low redox potential of 2.71 V vs. standard hydrogen electrode. Unstable solid electrolyte interface (SEI), uncontrolled overpotentials and dendrite growth of sodium are the main drawbacks that hinder the development of SMBs. Herein, we propose a functionalized silica gel material with extended porosity (NaSGII) as an active host material in order to obtain stable cycling of sodium metal anodes. NaSGII was incorporated in composite electrodes using a conductive carbon additive and polymeric binders and the functional properties in SMBs cells demonstrated by galvanostatic tests. A Butler-Volmer analysis demonstrated an improvement of electrokinetic parameters induced by NaSGII

Insights into the LiI Redox Mediation in Aprotic Li–O2 Batteries: Solvation Effects and Singlet Oxygen Evolution

Lithium−oxygen aprotic batteries (aLOBs) are highly promising next-generation secondary batteries due to their high theoretical energy density. However, the practical implementation of these batteries is hindered by parasitic reactions that negatively impact their reversibility and cycle life. One of the challenges lies in the oxidation of Li2O2, which requires large overpotentials if not catalyzed. To address this issue, redox mediators (RMs) have been proposed to reduce the oxygen evolution reaction (OER) over- potentials. In this study, we focus on a lithium iodide RM and investigate its role on the degradation chemistry and the release of singlet oxygen in aLOBs, in different solvent environments. Specifically, we compare the impact of a polar solvent, dimethyl sulfoxide (DMSO), and a low polarity solvent, tetraglyme (G4). We demonstrate a strong interplay between solvation, degradation, and redox mediation in OER by LiI in aLOBs. The results show that LiI in DMSO-based electrolytes leads to extensive degradation and to 1O2 release, affecting the cell performance, while in G4- based electrolytes, the release of 1O2 appears to be suppressed, resulting in better cyclability