based on the plethora of investigations done in the literature on electrolyte instabilities. In addition, approaches like AIRSS (ab initio random structure searching) could be explored to predict new electrolytes with structures that go beyond those currently known. One cannot truly begin to explore the electrolyte frontier until one knows, documents, and understands the past.

There is a critical need to evaluate lithium-sulfur (Li-S) batteries with practically relevant high sulfur loadings and minimal electrolyte. Under such conditions, the concentration of soluble polysulfide intermediates in the electrolyte drastically increases, which can alter the fundamental nature of the solution-mediated discharge and thereby the total sulfur utilization. In this work, we present an investigation into various high donor number (DN) electrolytes that allow for increased polysulfide dissolution, and demonstrate how this property may in fact be necessary for increasing sulfur utilization at low electrolyte and high loading conditions. The solvents dimethylacetamide, dimethyl sulfoxide, and 1-methylimidazole are holistically evaluated against dimethoxyethane as electrolyte co-solvents in Li-S cells, and they are used to investigate chemical and electrochemical properties of polysulfide species at both dilute and practically relevant conditions. The nature of speciation exhibited by lithium polysulfides is found to vary significantly between these concentrations, particularly in regards to the S 3 •− species. Furthermore, the extent of the instability in conventional electrolyte solvents and high DN solvents with both lithium metal and polysulfides is thoroughly investigated. These studies establish a basis for future efforts into rationally designing an optimal electrolyte for a lean electrolyte, high energy density Li-S battery.

An organotrisulfide (RSSSR, R is an organic group) has three sulfur atoms which could be involved in multi-electron reduction reactions; therefore it is a promising electrode material for batteries. Herein, we use dimethyl trisulfide (DMTS) as a model compound to study its redox reactions in rechargeable lithium batteries. With the aid of XRD, XPS, and GC-MS analysis, we confirm DMTS could undergo almost a 4 e(-) reduction process in a complete discharge to 1.0 V. The discharge products are primarily LiSCH3 and Li2 S. The lithium cell with DMTS catholyte delivers an initial specific capacity of 720 mAh g(-1) DMTS and retains 82 % of the capacity over 50 cycles at C/10 rate. When the electrolyte/DMTS ratio is 3:1 mL g(-1) , the reversible specific energy for the cell including electrolyte can be 229 Wh kg(-1) . This study shows organotrisulfide is a promising high-capacity cathode material for high-energy rechargeable lithium batteries.

owing to their weak affinity toward LiPSs. [15] To compete with the state-of-theart lithium-ion batteries, an areal capacity of 4 mA h cm −2 is required, which means a higher sulfur loading of >4 mg cm −2 is crucial. [15] To meet such a requirement, various polar metal compounds including metal oxides, metal sulfides, and metal nitrides have been developed as LiPS absorbents and catalysts to further improve the sulfur loading in electrodes and enhance the LiPS redox kinetics. [16-19] However, for sulfur cathodes, such issues are far from settled: i) most of the polar compounds have poor electronic conductivity (e.g., SiO 2 and TiO 2) and the trapped active materials cannot be fully utilized; ii) the poor electrocatalytic activity (e.g., Ti 4 O 7) for LiPS redox process results in sluggish kinetics during the conversion reactions. [20-23] Molybdenum-based materials, such as molybdenum disulfides, molybdenum carbides, and molybdenum phosphides, have been reported as good catalysts for improving the LiPS redox kinetics, indicating the great potential of molybdenum-based materials in Li-S batteries. [24-27] Molybdenum borides (MoBs) are similarly attractive but have garnered little attention due to the notorious difficulty of their synthesis. [28,29] In addition, due to the growing interest and applications of borides in battery applications, boride materials, such as Co 2 B/carbon nanotube and Ni n+1 ZnB n , have been investigated in different Li-based battery systems, which further motivated us to employ molybdenum borides as a catalyst in Li-S batteries. [30,31] Furthermore, the fabrication of Li-S pouch cells with high-performance is a prerequisite for realizing the commercialization of Li-S batteries; however, there have been very few studies or discussions focused on modified sulfur cathodes at the pouch-cell level under realistic conditions. Herein, for the first time, MoB is prepared via a facile solidstate reaction and employed as a catalyst in Li-S batteries to improve LiPS conversion. When MoB is employed as a catalyst, it shows several unique advantages in contrast to the noncatalytic electrode, as shown in Figure 1. First, MoB has both good conductivity (1.7 × 10 5 S m −1) and rich catalytically active sites, derived from the significant electron deficiency of boron atoms, [32,33] resulting in highly efficient electrocatalytic LiPS conversion activity. Second, the nanosized MoB can greatly maximize the catalytic surface for LiPS redox. Third, the hydrophilic nature and good wettability toward electrolyte of MoB (Figure S1, Supporting Information) can facilitate electrolyte penetration

For realizing practically viable lithium-sulfur (Li-S) batteries, it is imperative to stabilize Li deposition and improve cyclability while reducing excess Li and electrolyte. We have discovered that introducing tellurium (Te) into the Li-S system as a cathode additive significantly improves the reversibility of Li plating and stripping by forming a tellurized and sulfide-rich solid-electrolyte interphase (SEI) layer on the Li surface. A remarkable improvement in cyclability is demonstrated in anode-free full cells with limited Li inventory and large-area Li-S pouch cells under lean electrolyte conditions. Tellurium reacts with polysulfides to generate soluble polytellurosulfides that migrate to the anode side and form stabilizing lithium thiotellurate and lithium telluride in situ as SEI components. A significant reduction in electrolyte decomposition on the Li surface is also engendered. This work demonstrates Te inclusion as a viable strategy for stabilizing Li deposition and establishes a robust evaluation framework for preserving electrochemical performance under limited Li and limited electrolyte conditions.

The electrochemistry of lithium−sulfur (Li−S) batteries is heavily reliant on the structure and dynamics of lithium polysulfides, which dissolve into the liquid electrolyte and mediate the electrochemical conversion process during operation. This behavior is considerably distinct from the widely used lithium-ion batteries, necessitating new mechanistic insights to fully understand the electrochemical phenomena. Testing at low-temperature conditions presents a unique opportunity to glean new insights into the chemistry in kinetically constrained environments. Under such conditions, despite the low freezing point and favorable ionic conductivity of the glyme-based electrolyte, Li−S batteries exhibit counterintuitively poor performance. Here, we show that beyond just existing in singlemolecule conformations, lithium polysulfides tend to cluster and aggregate in solution, particularly at low-temperature conditions, which subsequently constrains the kinetics of electrochemical conversion. Energetics and coordination implications of this behavior are extended toward a new framework for understanding the solution coordination dynamics of dissolved lithium species. Based on this framework, a favorable strongly bound lithium salt is introduced in the Li−S electrolyte to disrupt polysulfide clustered networks, enabling substantially enhanced low-temperature electrochemical performance. More broadly, this mechanistic insight heightens our understanding of polysulfide chemistry irrespective of temperature, confirming the link between the solution conformation of active material and electrochemical behavior.

The practical viability of Li–S cells depends on achieving high electrochemical utilization of sulfur under realistic conditions, such as high sulfur loading and low electrolyte/sulfur (E/S) ratio. Here, metallic 2D 1T′‐ReS2 nanosheets in situ grown on 1D carbon nanotubes (ReS2@CNT) via a facile hydrothermal reaction are presented to efficiently suppress the “polysulfide shuttle” and promote lithium polysulfide (LiPS) redox reactions. The designed ReS2@CNT nanoarchitecture with high conductivity and rich nanoporosity not only facilitates electron transfer and ion diffusion, but also possesses abundant active sites providing high catalytic activity for efficient LiPS conversion. Li–S cells fabricated with ReS2@CNT exhibit high capacity with superior long‐term cyclability with a capacity retention of 71.7% over 1000 cycles even at a high current density of 1C (1675 mA g−1). Also, pouch cells fabricated with the ReS2@CNT/S cathode maintain a low capacity fade rate of 0.22% per cycle. Furthermore, the electrocatalysis mechanism is revealed based on electrochemical studies, theoretical calculations, and in situ Raman spectroscopy.

Sulfur-based cathodes are promising to enable high-energy-density lithium-sulfur batteries; however, elemental sulfur as active material faces several challenges, including undesirable volume change (∼80%) when completely reduced and high dependence on liquid electrolyte wherein an electrolyte/sulfur ratio >10 μL mg is required for high material utilization. These limit the attainable energy densities of these batteries. Herein, we introduce a new class of phenyl polysulfides CHS CH (4 ≤ x ≤ 6) as liquid cathode materials synthesized in a facile and scalable route to mitigate these setbacks. These polysulfides possess sufficiently high theoretical specific capacities, specific energies, and energy densities. Spectroscopic techniques verify their chemical composition and computation shows that the volume change when reduced is about 37%. Lithium half-cell testing shows that phenyl hexasulfide (CHSCH) can provide a specific capacity of 650 mAh g and capacity retention of 80% through 500 cycles at 1 C rate along with superlative performance up to 10 C. Furthermore, 1302 Wh kg and 1720 Wh L are achievable at a low electrolyte/active material ratio, i.e., 3 μL mg. This work adds new members to the cathode family for Li-S batteries, reduces the gap between the theoretical and practical energy densities of batteries, and provides a new direction for the development of alternative high-capacity cathode materials.