Rechargeable lithium-metal batteries (LMBs) are regarded as the "holy grail" of energy-storage systems, but the electrolytes that are highly stable with both a lithium-metal anode and high-voltage cathodes still remain a great challenge. Here a novel "localized high-concentration electrolyte" (HCE; 1.2 m lithium bis(fluorosulfonyl)imide in a mixture of dimethyl carbonate/bis(2,2,2-trifluoroethyl) ether (1:2 by mol)) is reported that enables dendrite-free cycling of lithium-metal anodes with high Coulombic efficiency (99.5%) and excellent capacity retention (>80% after 700 cycles) of Li||LiNi Mn Co O batteries. Unlike the HCEs reported before, the electrolyte reported in this work exhibits low concentration, low cost, low viscosity, improved conductivity, and good wettability that make LMBs closer to practical applications. The fundamental concept of "localized HCEs" developed in this work can also be applied to other battery systems, sensors, supercapacitors, and other electrochemical systems.

High-voltage batteries with Li-metal anodes can offer desirable high energy densities. Despite their excellent oxidative stability, sulfones have various limitations to be useful in Li-metal batteries, in particular their instability with Li metal. Here, we achieved a high Li Coulombic efficiency of nearly 99% in a sulfonebased localized high-concentration electrolyte (LHCE) with the addition of a nonsolvating co-solvent. In addition, this co-solvent is highly beneficial for realizing stable battery cycling up to 4.9 V.

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Despite the high theoretical capacity of lithium-sulfur batteries, their practical applications are severely hindered by a fast capacity decay, stemming from the dissolution and diffusion of lithium polysulfides in the electrolyte. A novel functional carbon composite (carbon-nanotube-interpenetrated mesoporous nitrogen-doped carbon spheres, MNCS/CNT), which can strongly adsorb lithium polysulfides, is now reported to act as a sulfur host. The nitrogen functional groups of this composite enable the effective trapping of lithium polysulfides on electroactive sites within the cathode, leading to a much improved electrochemical performance (1200 mAh g(-1) after 200 cycles). The enhancement in adsorption can be attributed to the chemical bonding of lithium ions by nitrogen functional groups in the MNCS/CNT framework. Furthermore, the micrometer-sized spherical structure of the material yields a high areal capacity (ca. 6 mAh cm(-2)) with a high sulfur loading of approximately 5 mg cm(-2), which is ideal for practical applications of the lithium-sulfur batteries.

Rechargeable lithium metal batteries are regarded as the ''holy grail'' of energy storage systems, but their practical applications have long been hindered by poor cyclability and severe safety concerns. In this work, we report a fire-retardant localized high-concentration electrolyte consisting of 1.2 M lithium bis(fluorosulfonyl)imide in a mixture of flame-retardant triethyl phosphate/bis(2,2,2-trifluoroethyl) ether (1:3 by mol) for 4-V class lithium metal batteries. This electrolyte enables stable, dendrite-free cycling of lithium metal anodes with high Coulombic efficiency of up to 99.2%. Moreover, it exhibits excellent anodic stability even up to 5.0 V and greatly enhances the cycling performance of lithium metal batteries. A LijjLiNi 0.6 Mn 0.2 Co 0.2 O 2 battery using this electrolyte can retain >97% capacity after 600 cycles at 1 C rate (ca. 1.6 mA cm À2 ), corresponding to a negligible capacity decay of <0.005% per cycle. Therefore, this new electrolyte can enable safe operation of high-energy lithium metal batteries for practical applications.

Lithium (Li)-metal batteries have regained broad interest in the battery research community. Although many studies on Li anode have been published in recent years, it is difficult to evaluate and compare these advances for practical applications. A key challenge is a gap between materials and component properties and the achievable large-format cell-level performance. In this paper, we investigate the critical experimental parameters that determine the cycle number of coin cells to understand the performance variations reported in the literature. To define the range of cell parameters, we exemplify a representative Li-metal pouch cell with specific energy of 300 Wh/kg to provide an effective validation of electrode materials and accurate cell performance evaluations. Based on the pouch-cell-level requirements, we propose a set of coin-cell parameters and testing conditions to expedite the discovery of new materials and their full integration into realistic battery systems.

Sodium (Na) metal is a promising anode for Na-ion batteries. However, the high reactivity of Na metal with electrolytes and the low Na metal cycling efficiency have limited its practical application in rechargeable Na metal batteries. High-concentration electrolytes (HCE, ≥4 M) consisting of sodium bis(fluorosulfonyl)imide (NaFSI) and ether solvent could ensure the stable cycling of Na metal with high Coulombic efficiency but at the cost of high viscosity, poor wettability, and high salt cost. Here, we report that the salt concentration could be significantly reduced (≤1.5 M) by a hydrofluoroether as an "inert" diluent, which maintains the solvation structures of HCE, thereby forming a localized high-concentration electrolyte (LHCE). A LHCE [2.1 M NaFSI/1,2-dimethoxyethane (DME)−bis(2,2,2-trifluoroethyl) ether (BTFE) (solvent molar ratio 1:2)] enables dendrite-free Na deposition with a high Coulombic efficiency of >99%, fast charging (20C), and stable cycling (90.8% retention after 40 000 cycles) of Na∥Na 3 V 2 (PO 4 ) 3 batteries.

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