Formation of 2D Amorphous Lithium Sulfide Enabled by Mo2C Clusters Loaded Carbon Scaffold for High-Performance Lithium Sulfur Batteries

Lithium-sulfur (Li-S) batteries, operated through the interconversion between sulfur and solid-state lithium sulfide, are regarded as next-generation energy storage systems. However, the sluggish kinetics of lithium sulfide deposition/dissolution, caused by its insoluble and insulated nature, hampers the practical use of Li-S batteries. Herein, leaf-like carbon scaffold (LCS) with the modification of Mo2C clusters (Mo2C@LCS) is reported as host material of sulfur powder. During cycles, the dissociative Mo ions at the Mo2C@LCS/electrolyte interface are detected to exhibit competitive binding energy with Li ions for lithium sulfide anions, which disrupts the deposition behavior of crystalline lithium sulfide and trends a shift in the configuration of lithium sulfide toward an amorphous structure. Combining the related electrochemical study and first-principle calculation, it is revealed that the formation of amorphous lithium sulfides shows significantly improved kinetics for lithium sulfide deposition and decomposition. As a result, the obtained Mo2C@LCS/S cathode shows an ultralow capacity decay rate of 0.015% per cycle at a high mass loading of 9.5 mg cm-2 after 700 cycles. More strikingly, an ultrahigh sulfur loading of 61.2 mg cm-2 can also be achieved. This work defines an efficacious strategy to advance the commercialization of Mo2C@LCS host for Li-S batteries.

Effects of Lithium Halides on Electrode-Electrolyte Bifunctional Materials for High-Capacity All-Solid-State Batteries

All-solid-state batteries have attracted attention because of their high energy density, safety, and long cycle life. Sulfide active materials exhibit high capacities and enable an enhanced energy density in all-solid-state batteries. In this study, we synthesized electrode-electrolyte bifunctional materials in the system Li2S-V2S3-LiX (X = F, Cl, Br, or I) through a mechanochemical process. In addition, the effects of the addition of lithium halides on the electrochemical properties were investigated. All-solid-state batteries with the Li2S-V2S3-LiI electrode showed the highest capacity of 400 mAh g-1 among all the cells, even though their electronic and ionic conductivities were the same. From the point of view of the ionic conductivity and structure of the electrodes during cycling, it was clarified that a high reversible capacity was achieved not only by high ionic and electronic conductivities before cycling but also by maintaining the ionic conductivity even at the deep state of charge. Furthermore, high-loading all-solid-state cells were fabricated using the Li2S-V2S3-LiI materials with a mass loading of 37.3 mg cm-2, exhibiting a high areal capacity of approximately 11.5 mAh cm-2 at 60 °C and good cycle performance.

High Capacity Li2 S-Li2 O-LiI Positive Electrodes with Nanoscale Ion-Conduction Pathways for All-Solid-State Li/S Batteries

All-solid-state lithium-sulfur (Li/S) batteries are promising next-generation energy-storage devices owing to their high capacities and long cycle lives. The Li2 S active material used in the positive electrode has a high theoretical capacity; consequently, nanocomposites composed of Li2 S, solid electrolytes, and conductive carbon can be used to fabricate high-energy-density batteries. Moreover, the active material should be constructed with both micro- and nanoscale ion-conduction pathways to ensure high power. Herein, a Li2 S-Li2 O-LiI positive electrode is developed in which the active material is dispersed in an amorphous matrix. Li2 S-Li2 O-LiI exhibits high charge-discharge capacities and a high specific capacity of 998 mAh g-1 at a 2 C rate and 25 °C. X-ray photoelectron spectroscopy, X-ray diffractometry, and transmission electron microscopy observation suggest that Li2 O-LiI provides nanoscale ion-conduction pathways during cycling that activate Li2 S and deliver large capacities; it also exhibits an appropriate onset oxidation voltage for high capacity. Furthermore, a cell with a high areal capacity of 10.6 mAh cm-2 is demonstrated to successfully operate at 25 °C using a Li2 S-Li2 O-LiI positive electrode. This study represents a major step toward the commercialization of all-solid-state Li/S batteries.

Synthesis of Deliquescent Lithium Sulfide in Air

In the field of lithium-sulfur batteries (LSBs) and all-solid-state batteries, lithium sulfide (Li2S) is a critical raw material. However, its practical application is greatly hindered by its high price due to its deliquescent property and production at high temperatures (above 700 °C) with carbon emission. Hereby, we report a new method of preparing Li2S, in air and at low temperatures (∼200 °C), which presents enriched and surprising chemistry. The synthesis relies on the solid-state reaction between inexpensive and air-stable raw materials of lithium hydroxide (LiOH) and sulfur (S), where lithium sulfite (Li2SO3), lithium thiosulfate (Li2S2O3), and water are three major byproducts. About 57% of lithium from LiOH is converted into Li2S, corresponding to a material cost of ∼$64.9/kg_Li2S, less than 10% of the commercial price. The success of conducting this water-producing reaction in air lies in three-fold: (1) Li2S is stable with oxygen below 220 °C; (2) the use of excess S can prevent Li2S from water attack, by forming lithium polysulfides (Li2Sn); and (3) the byproduct water can be expelled out of the reaction system by the carrier gas and also absorbed by LiOH to form LiOH·H2O. Two interesting and beneficial phenomena, i.e., the anti-hydrolysis of Li2Sn and the decomposition of Li2S2O3 to recover Li2S, are explained with density functional theory computations. Furthermore, our homemade Li2S (h-Li2S) is at least comparable with the commercial Li2S (c-Li2S), when being tested as cathode materials for LSBs.

Green Synthesis for Battery Materials: A Case Study of Making Lithium Sulfide via Metathetic Precipitation

For some future clean-energy technologies (such as advanced batteries), the concept of green chemistry has not been exercised enough for their material synthesis. Herein, we report a waste-free method of synthesizing lithium sulfide (Li₂S), a critical material for both lithium-sulfur batteries and sulfide-electrolyte-based all-solid-state lithium batteries. The key novelty lies in directly precipitating crystalline Li₂S out of an organic solution after the metathetic reaction between a lithium salt and sodium sulfide. Compared with conventional methods, this method is advantageous in operating at ambient temperatures, releasing no hazardous wastes, and being economically more competitive. To collect the valuable byproduct out of the liquid phases, a "solventing-out crystallization" technique is employed by adding an antisolvent (AS) of low boiling point. The subsequent distillation of the new solution under vacuum evaporates off the AS rather than the high-boiling-point reaction solvent (RS), saving a lot of energy. Consequently, the separated AS and RS containing the unreacted lithium salt can be directly reused. For industrial production, the entire process may be operated continuously in a closed loop without discharging any wastes. Moreover, Li₂S cathodes and sulfide-electrolyte Li₆PS₅Cl derived from the synthesized Li₂S show impressive battery performance, displaying the great potential of this method for practical applications.

Lithium Sulfide: Magnesothermal Synthesis and Battery Applications

As a critical material for emerging lithium-sulfur batteries and sulfide-electrolyte-based all-solid-state batteries, lithium sulfide (Li₂S) has great application prospects in the field of energy storage and conversion. However, commercial Li₂S is expensive and is produced via a carbon-emissive and time-consuming method of reducing lithium sulfate with carbon materials at high temperatures. Herein we report a novel method of synthesizing Li₂S by thermally reducing lithium sulfate with the first non-carbon-based reductant Mg. Compared with the commercial carbothermal method, our magnesothermal technique has multiple advantages, such as completion in minutes, operation at lower temperatures, emission of zero amount of greenhouse-gases, and a valuable byproduct MgO. Moreover, the prepared Li₂S product demonstrates excellent cathode performance in lithium-sulfur batteries, in terms of cycling stability, activation voltage, and rate capability. Thus, this innovative method opens a new direction for the research of Li₂S and has great potential for practical applications.

"First-Cycle Effect" of Trace Li2S in a High-Performance Sulfur Cathode

Lithium-sulfur battery is one of the most promising choices for next-generation batteries due to its high theoretical energy density and natural abundance. However, the sulfur cathode undergoes a stepwise reduction process and generates multiple soluble polysulfide intermediates; for the further conversion from the dissolved intermediates to the final solid product (Li₂S), the surface nucleation barrier limits the speed of the electrochemical precipitation, resulting in serious polysulfide diffusion loss and low sulfur utilization. Herein, the trace Li₂S (tLi₂S) is modified on the carbon fiber (CF) skeleton as preloaded crystal nuclei to boost the electrokinetics of Li₂S deposition in the initial cycle. The trace Li₂S decreases the nucleation barrier on the modified electrode (tLi₂S@CF), resulting in a high initial capacity of 1423 mAh g^-1 for the Li₂S₆ catholyte (0.2 C), which corresponds to a nearly 100% utilization of Li₂S₆. Furthermore, the trace Li₂S nuclei induce a uniform distribution of the redeposited active materials, and the uniform distribution persists in the following cycles, which benefits the cycle life significantly. The sulfur cathode based on the tLi₂S@CF matrix maintains a capacity of 1106 mAh g^-1 at 1 C rate after 100 cycles. The strategy can provide a new avenue for the rational design of the sulfur cathode.

A Li2S-Based Catholyte/Solid-State-Electrolyte Composite for Electrochemically Stable Lithium-Sulfur Batteries

Li₂S, which features a high theoretical capacity of 1,166 mA·h g^-1, is an attractive cathode material for developing high-energy-density lithium-sulfur batteries. However, pristine Li₂S requires a high activation voltage of 4.0 V, which degrades both the electrolyte and electrode, leading to poor cycling performance. In an effort to reduce the activation overpotential, in this study, we investigate the use of P₂S₅ in an advanced Li₂S-P₂S₅ catholyte and demonstrate a new synthetic approach that enables facile and low-temperature processing. Our findings show the P₂S₅ additive generates two thiophosphates with high ionic conductivities in the catholyte, which improve the activation efficiency and the electrochemical utilization. To further improve this advanced catholyte design, we also investigate two modified Li₂S-P₂S₅ catholytes based on carbon black (to strengthen the conductivity) and dilute polysulfide (Li₂S₆; to amplify the reaction activity). Our analysis indicates that the optimal Li₂S-P₂S₅-Li₂S₆ catholyte attains high ionic conductivity and strong reaction kinetics, achieving a high charge-storage capacity of 700 mA·h g^-1 with a long-term cyclability of 200 cycles.

Stable Electrode/Electrolyte Interface for High-Voltage NCM 523 Cathode Constructed by Synergistic Positive and Passive Approaches

Increasing the working voltage of lithium-ion batteries (LIBs) is an efficient way to increase energy density. However, high voltage triggers excessive electrolyte decomposition at the electrode-electrolyte interfaces, where the electrochemical performance such as cyclic stability and rate capability is seriously deteriorated. A new synergistic positive and passive approach is proposed in this work to construct a stable electrode-electrolyte interface at high voltage. As a positive approach, inorganic lithium sulfide salt (Li₂S) is used as an electrolyte additive to build a stable cathode electrolyte interface (CEI) at the LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) cathode surface. In a passive way, acetonitrile (AN) is applied as a solvent additive to suppress oxidative decomposition of a carbonate electrolyte via preferential solvation with a lithium ion. Because of the synergistic interaction between the positive and passive approaches, the cyclic stabilities of NCM523/Li cells improved with a tiny amount of Li₂S (0.01 mg mL^-1) and AN (0.5 vol %). The capacity retention increased to 80.74% after 200 cycles compared to the cells with the blank electrolyte (67.98%) and AN-containing electrolyte (75.8%). What is more, the capacity retention of the NCM523/graphite full cell is increased from 65 to 81% with the addition of the same amount of Li₂S and AN after 180 cycles. The mechanism is revealed on the basis of the theoretical calculations and various characterizations. The products derived from the preferential adsorption and oxidation of Li₂S on the surface of NCM523 effectively increase the content of inorganic ingredients. However, the presence of AN prevents oxidation of the solvent. This study provides new principle guiding studies on a high-voltage lithium-ion battery with excellent electrochemical performance.

Atomically Dispersed and O, N-Coordinated Mn-Based Catalyst for Promoting the Conversion of Polysulfides in Li2S-Based Li-S Battery

Nowadays, Li-S batteries are facing many thorny challenges like volume expansion and lithium dendrites on the road to commercialization. Due to the peculiarity of complete lithiation and the capability to match non-lithium anodes, Li₂S-based Li-S batteries have attracted more and more attention. Nevertheless, the same notorious shuttle effect of polysulfides as in traditional Li-S batteries and the poor conductivity of Li₂S lead to sluggish conversion reaction kinetics, poor Coulombic efficiency, and cycling performance. Herein, we propose the interconnected porous carbon skeleton as the host, which is modified by an atomically dispersed Mn catalyst as well as O, N atoms (named as ON-MnPC) via the melt salt method, and introduce the Li₂S nanosheet into the carbon host with poly(vinyl pyrrolidone) ethanol solution. It has been found that the introduction of O, N to bind with Mn atoms can endow the nonpolar carbon surface with ample unsaturated coordination active sites, restrain the shuttle effect, and enhance the diffusion of Li⁺ and accelerate the conversion reaction kinetics. Besides, due to the ultra-high catalyst activity of atomically dispersed Mn catalysts, the Li₂S/ON-MnPC cathode shows good electrochemical performance, e.g., an initial capacity of 534 mAh g^-1, a capacity of 514.18 mAh g^-1 after 100 cycles, a high retention rate of 96.23%, and a decay rate of 0.04% per cycle. Hence, use of atomically dispersed Mn catalysts to catalyze the chemical conversion reactions of polysulfides from multiple dimensions is a significant exploration, and it can provide a brand-new train of thought for the development and commercialization of the economical, high-performance Li₂S-based Li-S batteries.

A Powerful One-Step Puffing Carbonization Method for Construction of Versatile Carbon Composites with High-Efficiency Energy Storage

Carbon materials play a critical role in the advancement of electrochemical energy storage and conversion. Currently, it is still a great challenge to fabricate versatile carbon-based composites with controlled morphology, adjustable dimension, and tunable composition by a one-step synthesis process. In this work, a powerful one-step maltose-based puffing carbonization technology is reported to construct multiscale carbon-based composites on large scale. A quantity of composite examples (e.g., carbon/metal oxides, carbon/metal nitrides, carbon/metal carbides, carbon/metal sulfides, carbon/metals, metal/semiconductors, carbon/carbons) are prepared and demonstrated with required properties. These well-designed composites show advantages of large porosity, hierarchical porous structure, high conductivity, tunable components, and proportion. The formation mechanism of versatile carbon composites is attributed to the puffing-carbonization of maltose plus in situ carbothermal reaction between maltose and precursors. As a representative example, Li₂ S is in situ implanted into a hierarchical porous cross-linked puffed carbon (CPC) matrix to verify its application in lithium-sulfur batteries. The designed S-doped CPC/Li₂ S cathode shows superior electrochemical performance with higher rate capacity (621 mAh g^-1 at 2 C), smaller polarization and enhanced long-term cycles as compared to other counterparts. The research provides a general way for the construction of multifunctional component-adjustable carbon composites for advanced energy storage and conversion.

Consolidating Lithiothermic-Ready Transition Metals for Li2 S-Based Cathodes

Li₂ S holds a promising role as a high-capacity Li-containing cathode, circumventing use of metallic lithium in constructing next-generation batteries to replace current Li-ion batteries. However, progress of Li₂ S cathode has been plagued by its intrinsic drawbacks, including high activation potentials, poor rate performance, and rapid capacity fading during long cycling. Herein, a series of Li₂ S/transition metal (TM) nanocomposites are synthesized via a lithiothermic reduction reaction, and it is realized that the presence of TMs in Li₂ S matrix can transform electrochemical behaviors of Li₂ S. On the one hand, the incorporation of W, Mo, or Ti greatly increases electronic and ionic conductivity of Li₂ S composites and inhibits the polysulfide dissolution via the TMS bond, effectively addressing the drawbacks of Li₂ S cathodes. In particular, Li₂ S/W and Li₂ S/Mo exhibit the highest ionic conductivity of solid-phase Li-ion conductors ever-reported: 5.44 × 10^-2 and 3.62 × 10^-2 S m^-1 , respectively. On the other hand, integrating Co, Mn, and Zn turns Li₂ S into a prelithiation agent, forming metal sulfides rather than S₈ after the full charge. These interesting findings may shed light on the design of Li₂ S-based cathode materials.

Effect of Aging-Induced Dioxolane Polymerization on the Electrochemistry of Carbon-Coated Lithium Sulfide

Lithium sulfide-based materials have been considered as potential positive electrodes for the next generation batteries. Lithium sulfide is the fully lithiated form of sulfur, i.e., they share the same high theoretical capacity. However, it has the benefit of already containing lithium, which allows making cells with lithium-free negative electrodes. Lithium sulfide, however, shares with sulfur the polysulfide dissolution drawback upon cycling. One possible solution to this problem is to envelop the active material particles with carbonaceous materials. In this work, we investigate the effect of a nitrogen-rich carbon coating on lithium sulfide particles. The effect of such coating on the surface properties and electrochemistry of lithium sulfide cathodes is investigated in details, in particular, regarding its interaction with fresh vs. aged electrolyte. The polymerization of dioxalane (DOL) due to aging is found to affect the electrochemistry of lithium sulfide and, interestingly, to improve the cycling performance.

Lithium Sulfide-Carbon Composites via Aerosol Spray Pyrolysis as Cathode Materials for Lithium-Sulfur Batteries

We demonstrate a new technique to produce lithium sulfide-carbon composite (Li₂S-C) cathodes for lithium-sulfur batteries via aerosol spray pyrolysis (ASP) followed by sulfurization. Specifically, lithium carbonate-carbon (Li₂CO₃-C) composite nanoparticles are first synthesized via ASP from aqueous solutions of sucrose and lithium salts including nitrate (LiNO₃), acetate (CH₃COOLi), and Li₂CO₃, respectively. The obtained Li₂CO₃-C composites are subsequently converted to Li₂S-C through sulfurization by reaction to H₂S. Electrochemical characterizations show excellent overall capacity and cycle stability of the Li₂S-C composites with relatively high areal loading of Li₂S and low electrolyte/Li₂S ratio. The Li₂S-C nanocomposites also demonstrate clear structure-property relationships.

High-Rate and Long-Term Cycle Stability of Li-S Batteries Enabled by Li2S/TiO2-Impregnated Hollow Carbon Nanofiber Cathodes

The high theoretical energy density of lithium-sulfur (Li-S) batteries makes them an alternative battery technology to lithium ion batteries. However, Li-S batteries suffer from low sulfur loading, poor charge transport, and dissolution of lithium polysulfide. In our study, we use the lithiated S, Li₂S, as the cathode material, coupled with electrospun TiO₂-impregnated hollow carbon nanofibers (TiO₂-HCFs), which serve as the conductive agent and protective barrier for Li₂S in Li-S batteries. TiO₂-HCFs provide much improved electron/ionic conductivity and serve as a physical barrier, which prevents the dissolution of lithium polysulfides. The Li₂S/TiO₂-HCF composite delivers a discharge capacity of 851 mA h g_Li2S^-1 at 0.1C and the bilayer TiO₂-HCFs/Li₂S/TiO₂-HCF composite delivers a high specific capacity of 400 mA h g_Li2S^-1 at 5C.

In Situ Electrochemically Derived Amorphous-Li2 S for High Performance Li2 S/Graphite Full Cell

High-capacity Li₂ S cathode (1166 mAh g^-1 ) is regarded as a promising candidate for the next-generation lithium ion batteries. However, its high potential barrier upon the initial activation process leads to a low utilization of Li₂ S. In this work, a Li₂ S/graphite full cell with the zero activation potential barrier is achieved through an in situ electrochemical conversion of Li₂ S₈ catholyte into the amorphous Li₂ S. Theoretical calculations indicate that the zero activation potential for amorphous Li₂ S can be ascribed to its lower Li extraction energy than that of the crystalline Li₂ S. The constructed Li₂ S/graphite full cell delivers a high discharge capacity of 1006 mAh g^-1 , indicating a high utilization of the amorphous Li₂ S as a cathode. Moreover, a long cycle life with 500 cycles for this Li₂ S/graphite full cell is realized. This in situ electrochemical conversion strategy designed here is inspired for developing high energy Li₂ S-based full cells in future.

Revealing the Electrochemical Charging Mechanism of Nanosized Li2S by in Situ and Operando X-ray Absorption Spectroscopy

Lithium sulfide (Li₂S) is a promising cathode material for lithium-sulfur (Li/S) cells due to its high theoretical specific capacity (1166 mAh g^-1) and ability to pair with nonmetallic lithium anodes to avoid potential safety issues. However, when used as the cathode, a high charging voltage (∼4 V versus Li⁺/Li) is always necessary to activate Li₂S in the first charge process, and the voltage profile becomes similar to that of a common sulfur electrode in the following charge processes. In this report, we have prepared an electrode of nanosphere Li₂S particles and investigated its charging mechanism of the initial two charge processes by in situ and operando X-ray absorption spectroscopy. The results indicate that Li₂S is directly converted to elemental sulfur through a two-phase transformation in the first charge process, while it is oxidized first to polysulfides and then to sulfur in the second charge process. The origin of the different charging mechanisms and corresponding charge-voltage profiles of the first and second charge processes is found to be related to the remaining polysulfides at the end of the first discharge process: they can not only facilitate the charge-transfer process at the Li₂S/electrolyte interface but also chemically react with Li₂S and act as the polysulfide facilitator for the electrochemical oxidation of Li₂S in the following charge processes. Our present study provides a new fundamental understanding of the charging mechanism of the Li₂S electrode, which should be of help for the further development of high-performance Li/S cells.

Ammonium Additives to Dissolve Lithium Sulfide through Hydrogen Binding for High-Energy Lithium-Sulfur Batteries

In rechargeable Li-S batteries, the uncontrollable passivation of electrodes by highly insulating Li₂S limits sulfur utilization, increases polarization, and decreases cycling stability. Dissolving Li₂S in organic electrolyte is a facile solution to maintain the active reaction interface between electrolyte and sulfur cathode, and thus address the above issues. Herein, ammonium salts are demonstrated as effective additives to promote the dissolution of Li₂S to 1.25 M in DMSO solvent at room temperature. NMR measurements show that the strong hydrogen binding effect of N-H groups plays a critical role in dissolving Li₂S by forming complex ligands with S^2- anions coupled with the solvent's solvating surrounding. Ammonium additives in electrolyte can also significantly improve the oxidation kinetics of Li₂S, and therefore enable the direct use of Li₂S as cathode material in Li-S battery system in the future. This provides a new approach to manage the solubility of lithium sulfides through cation coordination with sulfide anion.

Three-Dimensional Interconnected Spherical Graphene Framework/SnS Nanocomposite for Anode Material with Superior Lithium Storage Performance: Complete Reversibility of Li2S

Three-dimensional (3D) interconnected spherical graphene framework-decorated SnS nanoparticles (3D SnS@SG) is synthesized by self-assembly of graphene oxide nanosheets and positively charged polystyrene/SnO₂ nanospheres, followed by a controllable in situ sulfidation reaction during calcination. The SnS nanoparticles with diameters of ∼10-30 nm are anchored to the surface of the spherical graphene wall tightly and uniformly. Benefiting from the 3D interconnected spherical graphene framework and subtle SnS nanoparticles, the generated Li₂S could keep in close contact with Sn to make possible the in situ conversion reaction SnS + 2Li⁺ + 2e^- ↔ Sn + Li₂S. As a result, the 3D SnS@SG as the anode material for lithium ion batteries shows a high initial Coulombic efficiency of 75.3%. Apart from the irreversible capacity loss of 3D spherical graphene, the initial Coulombic efficiency of SnS in the 3D SnS@SG composite is as high as 99.7%, demonstrating the almost complete reversibility of Li₂S in this system. Furthermore, it also exhibits an excellent reversible capacity (800 mAh g^-1 after 100 cycles at 0.1 C and 527.1 mAh g^-1 after 300 cycles at 1 °C) and outstanding rate capability (380 mAh g^-1 at 5 °C).

From Metal-Organic Framework to Li2S@C-Co-N Nanoporous Architecture: A High-Capacity Cathode for Lithium-Sulfur Batteries

Owing to the high theoretical specific capacity (1166 mAh g^-1), lithium sulfide (Li₂S) has been considered as a promising cathode material for Li-S batteries. However, the polysulfide dissolution and low electronic conductivity of Li₂S limit its further application in next-generation Li-S batteries. In this report, a nanoporous Li₂S@C-Co-N cathode is synthesized by liquid infiltration-evaporation of ultrafine Li₂S nanoparticles into graphitic carbon co-doped with cobalt and nitrogen (C-Co-N) derived from metal-organic frameworks. The obtained Li₂S@C-Co-N architecture remarkably immobilizes Li₂S within the cathode structure through physical and chemical molecular interactions. Owing to the synergistic interactions between C-Co-N and Li₂S nanoparticles, the Li₂S@C-Co-N composite delivers a reversible capacity of 1155.3 (99.1% of theoretical value) at the initial cycle and 929.6 mAh g^-1 after 300 cycles, with nearly 100% Coulombic efficiency and a capacity fading of 0.06% per cycle. It exhibits excellent rate capacities of 950.6, 898.8, and 604.1 mAh g^-1 at 1C, 2C, and 4C, respectively. Such a cathode structure is promising for practical applications in high-performance Li-S batteries.

Infiltrated Porous Polymer Sheets as Free-Standing Flexible Lithium-Sulfur Battery Electrodes

Free-standing, high-capacity Li2 S electrodes with capacity loadings in the range from 1.5 to 3.8 mA h cm(-2) are produced by using infiltration of active materials into porous carbonized biomass sheets. The proposed electrode design can be effectively utilized for the low-cost fabrication of flexible lithium batteries with high specific energy.

Promising Cell Configuration for Next-Generation Energy Storage: Li2S/Graphite Battery Enabled by a Solvate Ionic Liquid Electrolyte

Lithium-ion sulfur batteries with a [graphite|solvate ionic liquid electrolyte|lithium sulfide (Li2S)] structure are developed to realize high performance batteries without the issue of lithium anode. Li2S has recently emerged as a promising cathode material, due to its high theoretical specific capacity of 1166 mAh/g and its great potential in the development of lithium-ion sulfur batteries with a lithium-free anode such as graphite. Unfortunately, the electrochemical Li(+) intercalation/deintercalation in graphite is highly electrolyte-selective: whereas the process works well in the carbonate electrolytes inherited from Li-ion batteries, it cannot take place in the ether electrolytes commonly used for Li-S batteries, because the cointercalation of the solvent destroys the crystalline structure of graphite. Thus, only very few studies have focused on graphite-based Li-S full cells. In this work, simple graphite-based Li-S full cells were fabricated employing electrolytes beyond the conventional carbonates, in combination with highly loaded Li2S/graphene composite cathodes (Li2S loading: 2.2 mg/cm(2)). In particular, solvate ionic liquids can act as a single-phase electrolyte simultaneously compatible with both the Li2S cathode and the graphite anode and can further improve the battery performance by suppressing the shuttle effect. Consequently, these lithium-ion sulfur batteries show a stable and reversible charge-discharge behavior, along with a very high Coulombic efficiency.

Graphene-Li2S-Carbon Nanocomposite for Lithium-Sulfur Batteries

Lithium sulfide (Li2S) with a high theoretical specific capacity of 1166mAh g(-1) is a promising cathode material for next-generation Li-S batteries with high specific energy. However, low conductivity of Li2S and polysulfide dissolution during cycling are known to limit the rate performance and cycle life of these batteries. Here, we report on the successful development and application of a nanocomposite cathode comprising graphene covered by Li2S nanoparticles and protected from undesirable interactions with electrolytes. We used a modification of our previously reported low cost, scalable, and high-throughput solution-based method to deposit Li2S on graphene. A dropwise infiltration allowed us to keep the size of the heterogeneously nucleated Li2S particles smaller and more uniform than what we previously achieved. This, in turn, increased capacity utilization and contributed to improved rate performance and stability. The use of a highly conductive graphene backbone further increased cell rate performance. A synergetic combination of a protective layer vapor-deposited on the material during synthesis and in situ formed protective surface layer allowed us to retain ∼97% of the initial capacity of ∼1040 mAh gs(-1) at C/2 after over 700 cycles in the assembled cells. The achieved combination of high rate performance and ultrahigh stability is very promising.

Three-Dimensional Growth of Li2S in Lithium-Sulfur Batteries Promoted by a Redox Mediator

During the discharge of a lithium-sulfur (Li-S) battery, an electronically insulating 2D layer of Li2S is electrodeposited onto the current collector. Once the current collector is enveloped, the overpotential of the cell increases, and its discharge is arrested, often before reaching the full capacity of the active material. Guided by a new computational platform known as the Electrolyte Genome, we advance and apply benzo[ghi]peryleneimide (BPI) as a redox mediator for the reduction of dissolved polysulfides to Li2S. With BPI present, we show that it is now possible to electrodeposit Li2S as porous, 3D deposits onto carbon current collectors during cell discharge. As a result, sulfur utilization improved 220% due to a 6-fold increase in Li2S formation. To understand the growth mechanism, electrodeposition of Li2S was carried out under both galvanostatic and potentiostatic control. The observed kinetics under potentiostatic control were modeled using modified Avrami phase transformation kinetics, which showed that BPI slows the impingement of insulating Li2S islands on carbon. Conceptually, the pairing of conductive carbons with BPI can be viewed as a vascular approach to the design of current collectors for energy storage devices: here, conductive carbon "arteries" dominate long-range electron transport, while BPI "capillaries" mediate short-range transport and electron transfer between the storage materials and the carbon electrode.

Facile Synthesis of Lithium Sulfide Nanocrystals for Use in Advanced Rechargeable Batteries

This work reports a new method of synthesizing anhydrous lithium sulfide (Li2S) nanocrystals and demonstrates their potential as cathode materials for advanced rechargeable batteries. Li2S is synthesized by reacting hydrogen sulfide (H2S) with lithium naphthalenide (Li-NAP), a thermodynamically spontaneous reaction that proceeds to completion rapidly at ambient temperature and pressure. The process completely removes H2S, a major industrial waste, while cogenerating 1,4-dihydronaphthalene, itself a value-added chemical that can be used as liquid fuel. The phase purity, morphology, and homogeneity of the resulting nanopowders were confirmed by X-ray diffraction and scanning electron microscopy. The synthesized Li2S nanoparticles (100 nm) were assembled into cathodes, and their performance was compared to that of cathodes fabricated using commercial Li2S micropowders (1-5 μm). Electrochemical analyses demonstrated that the synthesized Li2S were superior in terms of (dis)charge capacity, cycling stability, output voltage, and voltage efficiency.

PVP-Assisted Synthesis of Uniform Carbon Coated Li2S/CB for High-Performance Lithium-Sulfur Batteries

The lithium-sulfur (Li-S) battery is a great alternative to the state-of-the-art lithium ion batteries due to its high energy density. However, low utilization of active materials, the insulating nature of sulfur or lithium sulfide (Li2S), and polysulfide dissolution in organic liquid electrolyte lead to low initial capacity and fast performance degradation. Herein, we propose a facile and viable approach to address these issues. This new approach entails synthesis of Li2S/carbon black (Li2S/CB) cores encapsulated by a nitrogen-doped carbon shell with polyvinylpyrrolidone (PVP) assistance. Combining energy-filtered transmission electron microscopy (EFTEM) elemental mappings, XPS and FTIR measurements, it is confirmed that the as-synthesized material has a structure of a Li2S/CB core with a nitrogen-doped carbon shell (denoted as Li2S/CB@NC). The Li2S/CB@NC cathode yields an exceptionally high initial capacity of 1020 mAh/g based on Li2S mass at 0.1 C with stable Coulombic efficiency of 99.7% over 200 cycles. Also, cycling performance shows the capacity decay per cycle as small as 0.17%. Most importantly, to further understand the materials for battery applications, field emission transmission electron microscopy (FETEM) and elemental mapping tests without exposure to air for Li2S samples in cycled cells are reported. Along with the first ever FETEM and field emission scanning electron microscopy (FESEM) investigations of cycled batteries, Li2S/CB@NC cathode demonstrates the capability of robust core-shell nanostructures for different rates and improved capacity retention, revealing Li2S/CB@NC designed here as an outstanding system for high-performance lithium-sulfur batteries.

A Hierarchical Particle-Shell Architecture for Long-Term Cycle Stability of Li2S Cathodes

A hierarchical particle-shell architecture for long-term cycle stability of Li2S cathodes is described. Multiscale and multilevel protection prevents mechanical degradation and polysulfide dissolution in lithium-sulfur battery chemistries.

Li2S Nanocrystals Confined in Free-Standing Carbon Paper for High Performance Lithium-Sulfur Batteries

Lithium sulfide (Li2S) with a high theoretical capacity of 1166 mAh g(-1) is a promising cathode material for Li-S batteries as it allows for the use of lithium-free anodes. However, a large overpotential (~1 V) is usually needed to activate microsized Li2S particles due to their low electronic and ionic conductivities. Here, nano-Li2S/carbon paper electrodes are developed via a simple Li2S solution filtration method. Li2S nanocrystals with a size less than 10 nm are formed uniformly in the pores of carbon paper network. These electrodes show an unprecedented low potential difference (0.1 V) in the first and following charges, also show high discharge capacities, good rate capability, and excellent cycling performance. More specifically, the nano-Li2S/carbon nanotube paper electrodes show a reversible capacity of 634 mAh g(-1) with a capacity retention of 92.4% at 1C rate from the 4th to 100th cycle, corresponding to a low capacity fading rate of 0.078% per cycle. These results demonstrate a facile and scalable electrode fabrication process for making high performance nano-Li2S/carbon paper electrodes, and the superior performance makes them promising for use with lithium metal-free anodes in rechargeable Li-S batteries for practical applications.

Lithium Sulfide (Li2S)/Graphene Oxide Nanospheres with Conformal Carbon Coating as a High-Rate, Long-Life Cathode for Li/S Cells

In recent years, lithium/sulfur (Li/S) cells have attracted great attention as a candidate for the next generation of rechargeable batteries due to their high theoretical specific energy of 2600 W·h kg(-1), which is much higher than that of Li ion cells (400-600 W·h kg(-1)). However, problems of the S cathode such as highly soluble intermediate species (polysulfides Li2Sn, n = 4-8) and the insulating nature of S cause poor cycle life and low utilization of S, which prevents the practical use of Li/S cells. Here, a high-rate and long-life Li/S cell is proposed, which has a cathode material with a core-shell nanostructure comprising Li2S nanospheres with an embedded graphene oxide (GO) sheet as a core material and a conformal carbon layer as a shell. The conformal carbon coating is easily obtained by a unique CVD coating process using a lab-designed rotating furnace without any repetitive steps. The Li2S/GO@C cathode exhibits a high initial discharge capacity of 650 mA·h g(-1) of Li2S (corresponding to the 942 mA·h g(-1) of S) and very low capacity decay rate of only 0.046% per cycle with a high Coulombic efficiency of up to 99.7% for 1500 cycles when cycled at the 2 C discharge rate.

Lithium iodide as a promising electrolyte additive for lithium-sulfur batteries: mechanisms of performance enhancement

Lithium Iodide (LiI) is reported as a promising electrolyte additive for lithium-sulfur batteries. It induces formation of Li-ion-permeable protective coatings on both positive and negative electrodes, which prevent the dissolution of polysulfides on the cathode and reduction of polysulfides on the anode. In addition to enhancing the cell cycle stability, LiI addition also decreases the cell overpotential and voltage hysteresis.

Activated Li2S as a High-Performance Cathode for Rechargeable Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries with a high theoretical energy density of ∼2500 Wh kg(-1) are considered as one promising rechargeable battery chemistry for next-generation energy storage. However, lithium-metal anode degradation remains a persistent problem causing safety concerns for Li-S batteries, hindering their practical utility. One possible strategy to circumvent the aforementioned problems is to use alternative, high-capacity, lithium-free anodes (e.g., Si, Sn, carbon) and a Li2S cathode. However, a large potential barrier was identified on the initial charge of insulating bulk Li2S particles, limiting the cell performance. In this work, the bulk Li2S particles were effectively activated with an electrolyte containing P2S5, resulting in a lowered initial charging voltage plateau. This permits the direct use of commercially available bulk Li2S particles as a high-capacity cathode for room-temperature, rechargeable Li-S batteries, significantly lowering the manufacturing cost of Li-S cells.