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Interest has rekindled in reversible calcium plating and stripping, renewing hopes for the development of Ca-ion batteries. However, the development of an electrolyte that operates at room temperature and is stable to oxidation at practical potentials remains a significant barrier. Here we report the synthesis and crystal structure of a new fluorinated alkoxyborate Ca(B(Ohfip) 4 ) 2 •4DME salt. Reversible plating and the dissolution of calcium from pure solutions of this salt in dimethoxyethane are demonstrated at 25 °C with capacities of 1 mAh cm −2 at a rate of 0.5 mA cm −2 over 30−40 cycles, with an anodic stability of >4.1 V vs Ca/Ca 2+ (and up to 4.9 V in dimethyltriflamide). The dominant product is calcium, accompanied by CaF 2 that forms by the reduction of the fluorinated anion. Whereas the cathodic stability requires improvement, this work shows that facile calcium plating and stripping at room temperature can be achieved using bulk electrodes.

This article reports a low-cost and scalable approach that tackles the stabilization of Li metal electrodes by forming a single-ion-conducting and stable protective surface layer in vivo. This is achieved by using a rationally designed electrolyte additive complex that reacts with the Li surface to form the membrane, allowing stable Li plating/stripping at current densities over 4 mA cm À2 and long-term fullcell cycling with Li 4 Ti 5 O 12 electrodes at close to 99.99% coulombic efficiency.

A new disordered chlorospinel superionic conductor, Li2Sc2/3Cl4, enables high-voltage all solid state batteries up to 4.6 V vs. Li+/Li.

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Although Na-O2 batteries have a low overpotential and good capacity retention, degradation reactions of glyme-based electrolytes are the primary reason for inefficiency in cell performance. The discharge capacity is accounted for through analysis of the side-products. Although sodium superoxide is the primary product (90 % theoretical), quantitative and qualitative evaluation of the side-products (using (1) H NMR, iodometric titration, and on-line mass spectrometry) shows the presence of sodium acetate (∼3.5 %), and three-fold less sodium formate, methoxy (oxo)acetic anhydride, and sodium carbonate. Our reaction mechanism proposes two paths for their formation. Because the side-products are not fully removed during oxidation, they accumulate on the cathode upon cycling. Resting the cell at open circuit potential during discharge results in consumption of the superoxide through the reaction with diglyme, which greatly increases the fraction of side products, as also confirmed by ex situ reaction studies. These findings have implications in the search for more stable electrolytes.

The step-change in gravimetric energy density needed for electrochemical energy storage devices to power unmanned autonomous vehicles, electric vehicles, and enable low-cost clean grid storage is unlikely to be provided by conventional lithium ion batteries. Lithium-sulfur batteries comprising lightweight elements provide a promising alternative, but the associated polysulfide shuttle in typical ether-based electrolytes generates loss in capacity and low coulombic efficiency. The first new electrolyte based on a unique combination of a relatively hydrophobic sulfonamide solvent and a low ion-pairing salt, which inhibits the polysulfide shuttle, is presented. This system behaves as a sparingly solvating electrolyte at slightly elevated temperatures, where it sustains reversible capacities as high as 1200-1500 mAh g over a wide range of current density (2C-C/5, respectively) when paired with a lithium metal anode, with a coulombic efficiency of >99.7 % in the absence of LiNO additive.

We report on a family of lithium fast ion conductors, Li3+x [Si x P1–x ]­S4, that exhibit an entropically stabilized structure type in a solid solution regime (0.15 < x < 0.33) with superionic conductivity above 1 mS·cm–1. Exploration of the influence of aliovalent substitution in the thermodynamically unstable β-Li3PS4 lattice using a combination of single crystal X-ray and powder neutron diffraction, the maximum entropy method, and impedance spectroscopy reveals that substitution induces structural splitting of the localized Li sites, effectively stabilizing bulk β-Li3PS4 at room temperature and delocalizing lithium ion density. The optimal material, Li3.25[Si0.25P0.75]­S4, exhibits inherent entropic site disorder and a frustrated energy landscape, resulting in a high conductivity of 1.22 mS·cm–1 that represents an increase of three orders of magnitude compared to bulk β-Li3PS4 and one order of magnitude higher than the nanoporous form. The enhanced ion conduction and lowered activation barrier with increasing site disorder as a result of aliovalent “tuning” reveals an important strategy toward the design of fast ion conductors that are vital as solid state electrolytes.