The attainable specific energy of Li-S cells is largely affected by the electrolyteto-sulfur (E/S) ratio, with a low value [5] thereof being prerequisite to achieve a competitive energy density for a practical cell. However, the most commonly used electrolyte, a mixture of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) (i.e., v/v = 1:1), exhibits low Li 2 S 8 solubility of at most 0.7 m at room temperature. [6] This limited solubility constitutes an obstacle in the way of the full-depth utilization of sulfur under so-called lean electrolyte conditions. Although it could be overcome by using a large amount of electrolyte, this would severely impair the volumetric energy density. This notwithstanding, the DOL/DME system and its analogues served as standard electrolyte solvents in the early stages of investigation, because the stable environment they offer to Li metal anodes contributed greatly to enhancing the cycle life. Nevertheless, identifying electrolyte conditions that allow effective operation at low E/S ratios (i.e., below 2 μL electrolyte mg sulfur −1 in practice) is essential for practical cells. [7] Therefore, the development of alternative electrolyte solvents with high polysulfide solubility remains highly desirable. Electrolytes with a high Gutmann donor number, such as N,N-dimethyl acetamide (DMAc), [7a,8] dimethyl sulfoxide (DMSO), [6,7,9] N,N-dimethyl formamide (DMF), [10] and N-methyl-2-pyrrolidone (NMP) [9c] are good candidates for lean electrolyte conditions in Li-S batteries. High donicity affords an environment that promotes interaction with electrophilic cations, implying that the solvation of Li ions can facilitate the solubility of polysulfides. For example, high donor electrolytes were reported [6] to readily dissolve more than 1.6 m of Li 2 S 8. In the same line, the utilization of sulfur can be enhanced for the given amount of electrolyte introduced in the cell. Apart from the solvation capability, high donor electrolytes confer 3D morphology for the final discharging product, namely Li 2 S, contrary to low donor electrolytes that give rise to a 2D film-like morphology. The 3D morphology is beneficial in that it leaves the conductive electrode surface available for repeated dischargecharge over cycling without passivation. [11] In addition, high donor electrolytes activate reaction routes that involve S 3 •− species (Figure 1a), [8a,12] the availability of which represents diverse reaction pathways for discharge to further enhance the utilization of sulfur. Despite these remarkable advantages, high donor electrolytes are known to have a short cycle life mainly because of their catastrophic reactivity with the Li metal anode. [8a,11c] This problem was subsequently pinpointed by Gupta et al., [7a] who

Lithium–sulfur (Li–S) batteries continue to be considered promising post‐lithium‐ion batteries owing to their high theoretical energy density. In pursuit of a Li–S cell with long‐term cyclability, most studies thus far have relied on using ether‐based electrolytes. However, their limited ability to dissolve polysulfides requires a high electrolyte‐to‐sulfur ratio, which impairs the achievable specific energy. Recently, the battery community found high donor electrolytes to be a potential solution to this shortcoming because their high solubility toward polysulfides enables a cell to operate under lean electrolyte conditions. Despite the increasing number of promising outcomes with high donor electrolytes, a critical hurdle related to stability of the lithium‐metal counter electrode needs to be overcome. This review provides an overview of recent efforts pertaining to high donor electrolytes in Li–S batteries and is intended to raise interest from within the community. Furthermore, based on analogous efforts in the lithium‐air battery field, strategies for protecting the lithium metal electrode are proposed. It is predicted that high donor electrolytes will be elevated to a higher status in the field of Li–S batteries, with the hope that either existing or upcoming strategies will, to a fair extent, mitigate the degradation of the lithium–metal interface.

Extremely fast charging (i.e. 80% of storage capacity within 15 min) is a pressing requirement for current lithium-ion battery technology and also affects the planning of charging infrastructure. Accelerating lithium ion transport through the solid-electrolyte interphase (SEI) is a major obstacle in boosting charging rate; in turn, limited kinetics at the SEI layer negatively affect the cycle life and battery safety as a result of lithium metal plating on the electrode surface. Here, we report a γ-ray-driven SEI layer that allows a battery cell to be charged to 80% capacity in 10.8 min as determined for a graphite full-cell with a capacity of 2.6 mAh cm−2. This exceptional charging performance is attributed to the lithium fluoride-rich SEI induced by salt-dominant decomposition via γ-ray irradiation. This study highlights the potential of non-electrochemical approaches to adjust the SEI composition toward fast charging and long-term stability, two parameters that are difficult to improve simultaneously in typical electrochemical processes owing to the trade-off relation.

Regulating the morphology of lithium plating is the key to extending the cycle life of lithium metal batteries. Fatal dendritic growth is closely related to out-of-plane nucleation on the lithium metal surface. Herein, we report a nearly perfect lattice match between the lithium metal foil and lithium deposits by removing the native oxide layer using simple bromine-based acid-base chemistry. The naked lithium surface induces homo-epitaxial lithium plating with columnar morphologies and lower overpotentials. Using the naked lithium foil, the lithium-lithium symmetric cell maintains stable cycling at 10 mA cm−2 for more than 10,000 cycles, and the full-cell paired with LiFePO4 with high areal capacity of 3.3 mAh cm−2 and practical N/P ratio of 2.5 exhibits 86% capacity retention after 300 cycles. This study elucidates the usefulness of controlling the initial surface state to facilitate homo-epitaxial lithium plating for sustainable cycling of lithium metal batteries.

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