Practical Lithium-sulfur Batteries Research Articles

A Permselective Coating Protects Lithium Anode toward a Practical Lithium-Sulfur Battery.

Lithium metal is a desirable anode for high-energy density lithium-sulfur (Li-S) batteries. However, its reliability is severely limited by dendrite growth and side reactions with polysulfides, which are yet challenging to solve simultaneously. Herein, we report a protective layer that works the same way as the ion-permselective cell membrane, yielding a corrosion-resistant and dendrite-free Li metal anode specially for Li-S batteries. A self-limited assembly of octadecylamine together with Al3+ ions on a Li metal anode surface produces a dense, stable yet thin layer with ionic conductive Al-Li alloy uniformly embedded in it, which prevents the passage of polysulfides but regulates the penetrated Li ion flux for uniform Li deposition. As a result, the assembled batteries show excellent cycling stability even with a high sulfur-loaded cathode, suggesting a straightforward but promising strategy to stabilize highly active anodes for practical applications.

Progress and Prospect of Practical Lithium-Sulfur Batteries Based on Solid-Phase Conversion

Lithium–sulfur (Li–S) batteries hold great promise in the field of power and energy storage due to their high theoretical capacity and energy density. However, the “shuttle effect” that originates from the dissolution of intermediate lithium polysulfides (LiPSs) during the charging and discharging process is prone to causing continuous irreversible capacity loss, which restricts the practical development. Beyond the traditional Li–S batteries based on the dissolution-diffusion mechanism, novel Li–S batteries based on solid-phase conversion exhibit superior cycling stability owing to the absolute prevention of polysulfides shuttling. Radically eliminating the formation of polysulfides in cathodes or cutting off their diffusion in electrolytes are the two main ways to achieve solid-phase conversion. Generally, direct transformation of sulfur to final Li2S without polysulfides participation tends to occur in short-chain sulfur polymers or special molecular forms of sulfur substances, while specific regulations of liquid electrolytes with solvating structure or solid-state electrolytes can effectively suppressing the polysulfides dissolution. In this review, we systematically organized and summarized the structures and approaches to achieve solid-phase conversion, introduce their preparation methods, discuss their advantages and disadvantages, and analyze the factors and effects of different structures on battery performances. Finally, the problems demanding a prompt solution for the practical development of solid-phase conversion-based Li–S batteries, as well as their future development direction, are suggested.

A triple-functional carbon molecular sieve (CMS) that addresses the performance trilemma in practical lithium sulfur batteries

Lithium-sulfur batteries offer an attractive energy storage alternative independent of critical minerals such as cobalt or nickel. However, their inadequate stability under long term cycling, and storage capacity on a volumetric basis hampers their uptake. These limitations can be addressed by seeking to control the formation and crossover of polysulfides, oligomers generated through reaction of solvated sulfur moieties with the lithium anode, and by seeking to restrict the consumption of active materials. Here, we report the development of a triple-functional carbon molecular sieve (CMS) interlayer. The microporous, polar, and conductive structure of the CMS provides physisorption, chemisorption, and reactivation capabilities concurrently. Therefore, the soluble polysulfides can be trapped, suppressed from shuttling, and reutilized to not only improve the kinetics of the redox reaction but also hinder the loss of active materials. As a result, our CMS-based Li–S batteries deliver combined exceptional gravimetric (1282 mAh g−1) and areal (7.05 mAh cm−2) capacities at 0.1 C rate as well as cycling stability up to 1000 cycles at 0.2 C rate over 9 months.

Mimicking a cell plasma membrane to regulate dynamic polysulfide chemistry for a practical lithium-sulfur battery

Mimicking a cell plasma membrane to regulate dynamic polysulfide chemistry for a practical lithium-sulfur battery

High-entropy perovskite oxide nanofibers as efficient bidirectional electrocatalyst of liquid-solid conversion processes in lithium-sulfur batteries

Transition metal oxides are a class of promising host materials of sulfur for lithium-sulfur (Li-S) batteries due to their robust polysulfide adsorption, and catalytic effect on sulfur redox reaction. It is proven that the adsorption-catalysis property can benefit a lot from incorporating multiple metal elements, and high-entropy oxides (HEOs) show good competitive potential for durable Li-S batteries. Herein, HEO nanofibers are designed as bidirectional catalytic host of sulfur to promote both the reduction of soluble intermediates and the re-oxidation of insoluble products. Specifically, the high-entropy perovskite oxide La0.8Sr0.2(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 (HE-LSMO) nanofibers prepared via an electrospinning-calcination method show a unique porous fibrous structure for incorporation with sulfur. The introduced multiple metal elements can effectively modulate the binding strength of soluble polysulfides, and HE-LSMO nanofibers act as bidirectional electrocatalyst for the liquid-solid conversion processes between soluble polysulfides and insoluble Li2S, which is enabled by the high entropic contribution. As a result, the S/HE-LSMO cathode with a sulfur loading of 8.4 mg cm−2 shows a high areal capacity of 6.6 mAh cm−2 at low electrolyte/sulfur ratio of 5.3 μL mg−1, as well as good cycle stability. This work provides a foundation understanding of the bidirectional catalytic role of HEOs toward practical Li-S batteries.

Modulating Electron Conducting Properties at Lithium Anode Interfaces for Durable Lithium-Sulfur Batteries.

The lithium (Li) ion and electron diffusion behaviors across the actual solid electrolyte interphase (SEI) play a critical role in regulating the Li nucleation and growth and improving the performance of lithium-sulfur (Li-S) batteries. To date, a number of researchers have pursued an SEI with high Li-ion conductivity while ignoring the Li dendrite growth caused by electron tunneling in the SEI. Herein, an artificial anti-electron tunneling layer with enriched lithium fluoride (LiF) and sodium fluoride (NaF) nanocrystals is constructed using a facile solution-soaking method. As evidenced theoretically and experimentally, the LiF/NaF artificial SEI exhibits an outstanding electron-blocking capability that can reduce electron tunneling, resulting in dendrite-free and dense Li deposition beneath the SEI, even with an ultrahigh areal capacity. In addition, the artificial anti-electron tunneling layer exhibits improved ionic conductivity and mechanical strength, compared to those of routine SEI. The symmetric cells with protected Li electrodes achieve a stable cycling of 1500 h. The LiF/NaF artificial SEI endows the Li-S full cells with long-term cyclability under conditions of high sulfur loading, lean electrolyte, and limited Li excess. This study provides a perspective on the design of the SEI for highly safe and practical Li-S batteries.

Mott-Schottky electrocatalyst selectively mediates the sulfur species conversion in lithium-sulfur batteries

The lithium sulfur (Li-S) battery is an active research area in the field of energy storage systems, but the shuttle effect is a serious obstacle hindering its application. Herein, a CoSe2/CoO Mott-Schottky catalyst is blended with carbon nanotubes (CNTs) and subsequently coated onto a commercial separator as a modifier, whereby the synergy between the high electrocatalytic activity of the CoSe2/CoO heterostructure and high conductivity of the CNTs selectively mediate the conversion of sulfur species. As a result, a cell with a CoSe2/CoO-CNTs modified separator displays a high initial discharge capacity of 1573 and 910 mAh/g at 0.1 and 2C, respectively. Furthermore, a low decay rate of 0.070% per cycle can be obtained over 500 cycles at 2C. The results of this study suggest that the as-prepared CoSe2/CoO-CNTs is an effective modifier that can improve the performance of Li-S batteries for use in next-generation energy storage systems. This study provides fundamental insights into the rational design of Mott-Schottky catalysts for practical high-performance Li-S batteries.

Nitrogen-vacancy-regulated Mo2N quantum dots electrocatalyst enables fast polysulfides redox for high-energy-density lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have great promise in the next generation higher-energy-density storage devices, however, the shuttle effect and sluggish conversion kinetics severely hindered their development. Herein, facile spray drying strategy is selected to construct nitrogen-vacancy-regulated Mo2N quantum dots embedded in mesoporous carbon matrix (QMo2N-V) as functional electrocatalyst. The double effect of quantum dots and vacancy engineering in Li-S chemistry is carefully studied. The Mo2N quantum dots provide abundant active sites for the chemisorption and conversion of polysulfides. Moreover, the nitrogen vacancies reinforce the affinity towards polysulfides and further accelerate their redox conversion due to the regulated local electron structure. Additionally, QMo2N-V presents hollow spherical structure with excellent conductivity, which works like microreactor to effectively capture the diffused polysulfides and facilitate the in situ fast reaction. Therefore, Li-S batteries with QMo2N-V separator has a reversible capacity of 510 mAh g−1 after 400 cycles even at 4.0 C, indicating that possess excellent cycling stability. An areal capacity up to 6.6 mAh cm−2 was achieved with a high sulfur loading of 8.1 mg cm−2 under lean electrolyte condition (E/S = 5.0 μL mg−1). Overall, this work proposes a combination strategy of quantum dots and vacancy engineering towards fast polysulfides conversion and durable cycling stability, showing great potential in the practical Li-S batteries.

Weakening the Solvating Power of Solvents to Encapsulate Lithium Polysulfides Enables Long-Cycling Lithium-Sulfur Batteries.

Long cycling lifespan is a prerequisite for practical lithium-sulfur batteries yet is restricted by side reactions between soluble polysulfides and the lithium-metal anode. The regulation on solvation structure of polysulfides renders encapsulating polysulfides electrolytes (EPSE) as a promising solution to suppress the parasitic reactions. The solvating power of the solvents in the outer solvent shell of lithium polysulfides is critical for the encapsulation effect of EPSE. Herein, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether(HFE) is demonstrated as a superior outer-shell solvent to construct EPSE. Based on thelarge steric hindrance of the fluorohydrocarbon chains, the electron-withdrawing perfluoro segment (CF2  further endows HFE with prominently weak solvating power. The HFE-EPSE improves the lifespan from 54 to 135 cycles for lithium-sulfur batteries with an ultrathin lithium-metal anode (50µm) and high-areal-loading sulfur cathode (4.4mg cm-2 ). Furthermore, a 334Wh kg-1 lithium-sulfur pouch cell (2.4 Ah level) with HFE-EPSE stably undergoes 25 cycles. This work demonstrates the role of weakening solvating power of outer-shell solvents to construct superior EPSE and inspires the significance of the solvation chemistry of polysulfides to achieve practical lithium-sulfur batteries.

Constructing lithium oxysulfide-rich solid electrolyte interphase to shield polysulfides in practical lithium–sulfur batteries

Long-cycling practical lithium–sulfur batteries are hindered by the parasitic reactions between lithium polysulfide (LiPS) intermediates and lithium metal anodes. Solid electrolyte interphase (SEI) on lithium metal anodes plays a crucial role in shielding the parasitic reactions of LiPSs. Herein, a lithium oxysulfide-rich SEI is demonstrated to shield polysulfides for stabilizing lithium metal anodes in working lithium–sulfur batteries. Li2SO4 is sustainably released as an additive to introduce abundant lithium oxysulfide components, such as sulfates, sulfites, and other Li2SxOy in SEI. The lithium oxysulfide-rich SEI effectively shields the parasitic reactions of LiPSs and the lifespan of lithium–sulfur batteries increases by 60% under demanding conditions of ultrathin Li anodes (50 μm) and high-loading S cathodes (4.0 mg cm−2). Furthermore, a practical 2.59 Ah lithium–sulfur pouch cell with the lithium oxysulfide-rich SEI delivers 25 cycles with an initial specific energy of 352 Wh kg−1. This work provokes insights into the role of lithium oxysulfide in SEI and inspires rational regulation of SEI to stabilize lithium–sulfur batteries.

Ionic-Liquid-Assisted Synthesis of FeSe-MnSe Heterointerfaces with Abundant Se Vacancies Embedded in N,B Co-Doped Hollow Carbon Microspheres for Accelerating the Sulfur Reduction Reaction.

Currently, extensive research efforts are being devoted to suppressing the shuttle effect of polysulfides. The uncontrollable deposition of insulating Li2 S onto the surface of sulfur host materials dramatically inhibits the continuous reduction of polysulfides in lithium-sulfur (Li-S) batteries. Herein, N,B co-doped hollow carbon microspheres embedded with dense FeSe-MnSe heterostructures and abundant Se vacancies (FeSe-MnSe/NBC) are rationally designed and synthesized via a facile hydrothermal reaction using ionic liquids as dopants. The introduction of abundant heterostructures subtly guides Li2 S nucleation and deposition in 3D frameworks, thus avoiding the formation of the Li2 S passivation layer and allowing for continuous Li+ diffusion and subsequent nucleation of Li2 S. Owing to these beneficial features, Li-S batteries comprising an FeSe-MnSe/NBC electrode exhibit significantly improved performance, including a high initial capacity of 1334 mAh g-1 at 0.2 C and ultralong cycle stability with a low capacity fading rate of 0.029% cycle-1 over 1000 cycles at 1.0 C. Remarkably, the FeSe-MnSe/NBC pouch cell delivers a considerable areal capacity of 3.6 mAh cm-2 at 0.1 C. This study provides valuable insight into heterostructures and Se vacancies for developing practical Li-S batteries.

Rationalizing nitrogen-doped secondary carbon particles for practical lithium-sulfur batteries

Nanostructured carbon host materials are widely used to improve both sulfur utilization rate and reaction kinetics in lithium-sulfur (Li-S) batteries. However, high complexity/cost of materials synthesis and difficulty in processing nano-materials into high-mass-loading electrodes are still significant barriers to the development of low-cost and high-energy Li-S batteries. In this study, we reported a generic and scalable synthesis approach to prepare nitrogen-doped secondary carbon particles. By using nitrogen-containing precursor as an integration reagent, the nanosized Ketjen Black particles were integrated into micron-size secondary ones and nitrogen-doped (NKB) simultaneously through a one-step heat treatment. With NKB as an example material, the effects of particle integration degree on the secondary particles’ structures, pore volume and connectivity, sulfur loading capability, and cell performance were studied and discussed. At an optimal integration condition, the NKB particles had significantly improved particle dimensions with well-maintained high specific surface area and pore volume. Contributed by the micron size and high pore volume, the NKB/S were successfully used for high-sulfur-loading cathode coating (4–7 mgs cm−2) and were able to deliver a specific capacity of ∼1100 mAh g−1 at a practical low-porosity (50 %) and lean-electrolyte conditions (E/S =4 µL mg−1). Feasibility of the materials for practical use was validated through scaling up synthesis (40 g/batch), large-area electrode coating, and practical pouch cell (1.6 Ah) assembly and test.

Emerging catalytic materials for practical lithium-sulfur batteries

High-energy lithium-sulfur batteries (LSBs) have experienced relentless development over the past decade with discernible improvements in electrochemical performance. However, a scrutinization of the cell operation conditions reveals a huge gap between the demands for practical batteries and those in the literature. Low sulfur loading, a high electrolyte/sulfur (E/S) ratio and excess anodes for lab-scale LSBs significantly offset their high-energy merit. To approach practical LSBs, high loading and lean electrolyte parameters are needed, which involve budding challenges of slow charge transfer, polysulfide precipitation and severe shuttle effects. To track these obstacles, the exploration of electrocatalysts to immobilize polysulfides and accelerate Li-S redox kinetics has been widely reported. Herein, this review aims to survey state-of-the-art catalytic materials for practical LSBs with emphasis on elucidating the correlation among catalyst design strategies, material structures and electrochemical performance. We also statistically evaluate the state-of-the-art catalyst-modified LSBs to identify the remaining discrepancy between the current advancements and the real-world requirements. In closing, we put forward our proposal for a catalytic material study to help realize practical LSBs.

Anode‐Free Lithium–Sulfur Cells Enabled by Rationally Tuning Lithium Polysulfide Molecules

AbstractThe two major barriers of practical lithium–sulfur batteries are the poor reversibility of lithium‐metal anode and sluggish kinetics of sulfur cathode. Here, we report a simple yet cogent, molecular tailoring approach for lithium polysulfides, enabling a synergistic enhancement of anode reversibility and cathode kinetics. We show that SnI4coordinates with lithium polysulfides to form soluble complexes, resulting in a Li2SnS3‐rich anode interphase layer. As Li2SnS3is stable against parasitic reactions and has a lower ionic resistance over cycling, the Li plating/stripping efficiency is greatly improved. In addition, the formation of soluble complexes between SnI4and lithium polysulfides play a non‐negligible role in suppressing the clustering behavior of lithium polysulfide molecules, resulting in a significant enhancement in sulfur conversion kinetics under lean electrolyte conditions. The synergistic improvement is validated in anode‐free, lean‐electrolyte pouch cells with a Li2S cathode that displays capacity retention of 78 % after 100 cycles.

Anode‐Free Lithium–Sulfur Cells Enabled by Rationally Tuning Lithium Polysulfide Molecules

The two major barriers of practical lithium-sulfur batteries are the poor reversibility of lithium-metal anode and sluggish kinetics of sulfur cathode. Here, we report a simple yet cogent, molecular tailoring approach for lithium polysulfides, enabling a synergistic enhancement of anode reversibility and cathode kinetics. We show that SnI4 coordinates with lithium polysulfides to form soluble complexes, resulting in a Li2 SnS3 -rich anode interphase layer. As Li2 SnS3 is stable against parasitic reactions and has a lower ionic resistance over cycling, the Li plating/stripping efficiency is greatly improved. In addition, the formation of soluble complexes between SnI4 and lithium polysulfides play a non-negligible role in suppressing the clustering behavior of lithium polysulfide molecules, resulting in a significant enhancement in sulfur conversion kinetics under lean electrolyte conditions. The synergistic improvement is validated in anode-free, lean-electrolyte pouch cells with a Li2 S cathode that displays capacity retention of 78 % after 100 cycles.

Regulating Lithium Salt to Inhibit Surface Gelation on an Electrocatalyst for High-Energy-Density Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries have great potential as high-energy-density energy storage devices. Electrocatalysts are widely adopted to accelerate the cathodic sulfur redox kinetics. The interactions among the electrocatalysts, solvents, and lithium salts significantly determine the actual performance of working Li-S batteries. Herein, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), a commonly used lithium salt, is identified to aggravate surface gelation on the MoS2 electrocatalyst. In detail, the trifluoromethanesulfonyl group in LiTFSI interacts with the Lewis acidic sites on the MoS2 electrocatalyst to generate an electron-deficient center. The electron-deficient center with high Lewis acidity triggers cationic polymerization of the 1,3-dioxolane solvent and generates a surface gel layer that reduces the electrocatalytic activity. To address the above issue, Lewis basic salt lithium iodide (LiI) is introduced to block the interaction between LiTFSI and MoS2 and inhibit the surface gelation. Consequently, the Li-S batteries with the MoS2 electrocatalyst and the LiI additive realize an ultrahigh actual energy density of 416 W h kg-1 at the pouch cell level. This work affords an effective lithium salt to boost the electrocatalytic activity in practical working Li-S batteries and deepens the fundamental understanding of the interactions among electrocatalysts, solvents, and salts in energy storage systems.

A Nafion protective layer for stabilizing lithium metal anodes in working lithium–sulfur batteries

AbstractLithium–sulfur batteries are promising next‐generation energy storage devices due to their ultrahigh theoretical energy density. However, the parasitic reactions between lithium polysulfides and lithium metal anodes render lithium anodes extremely unstable during cycling and result in limited lifespan of working lithium–sulfur batteries. Herein, a Nafion protective layer is fabricated for stabilizing lithium metal anodes in working lithium–sulfur batteries. The Nafion protective layer eliminates the parasitic reactions between lithium polysulfides and lithium metal anodes. Accordingly, the cycling lifespan of lithium–sulfur batteries is doubled to 92 cycles with the Nafion protective layer using high‐sulfur‐loading cathodes and ultrathin lithium metal anodes. This study describes an effective Nafion protective layer for stabilizing lithium metal anodes and provides a possible avenue for further protective layer design for achieving long‐cycling practical lithium–sulfur batteries.

Self-Supporting Carbon Nanofibers with Ni-Single-Atoms and Uniformly Dispersed Ni-Nanoparticles as Scalable Multifunctional Hosts for High Energy Density Lithium-Sulfur Batteries.

The energy density of lithium-sulfur batteries (LSBs) is currently hampered by modest sulfur loadings and high electrolyte/sulfur ratios (E/S). These limitations can potentially be overcome using easy-to-infiltrate sulfur hosts with high catalytic materials. However, catalytic materials in such hosts are very susceptible to agglomeration due to the lack of efficient confinement in easy-to-infiltrate structures. Herein, using carbon dots as an aggregation limiting agent, the successful fabrication of self-supporting carbon nanofibers (CNF) containing Ni-single-atoms (NiSA ) and uniformly dispersed Ni-nanoparticles (NiNP ) of small sizes as multifunctional sulfur hosts is reported. The NiSA sites coordinated by such NiNP offer outstanding catalytic activity for sulfur reactions and CNF is an easy-to-infiltrate sulfur host with a large-scale preparation method. Accordingly, such hosts that can be prepared on a large scale enable sulfur cathodes to exhibit high sulfur utilization (66.5 mAh cm-2 at ≈0.02 C) and cyclic stability (≈86.1% capacity retention after 100 cycles at ≈0.12 C) whilst operating at a high sulfur loading (50mg cm-2 ) and low E/S (5µL mg-1 ). This work provides a blueprint toward practical LSBs with high energy densities.

An ion sieving conjugated microporous thermoset ultrathin membrane for high-performance Li-S battery

Lithium-sulfur (Li-S) battery is an attractive candidate for next-generation energy storage devices due to its high theoretical energy density, but its practical applications are hindered by polysulfides shuttling and lithium dendrite growth. In this study, a solution-processable conjugated microporous thermoset (CMT) was used as an ultrathin ion sieving layer on a commercial PP separator. The CMT layer is as thin as ∼200 nm and possesses continuous sub-nanochannels. Molecular dynamic simulations show that the nanoporous polymeric network allows Li-ion passage while blocking polysulfides shuttling between the electrodes based on size-exclusive effects. In addition, the CMT layer acts as a buffer zone for the uniform distribution of Li ions on the surface of the Li anode to suppress the growth of lithium dendrites. As a result, Li-S battery employing the CMT-modified polypropylene separator achieves a high initial capacity of 849.6 mAh g−1 with an ultralow attenuation rate of 0.037% per cycle over 1000 cycles at 1 C, as well as a capacity of 619.0 mAh g−1 at an ultrahigh current density of 10 C. Remarkably, it exhibits a capacity of 727.8 mAh g−1 with ∼ 77% capacity retention over 500 cycles lifespan at a high current density of 5C, showing great potential for practical high-performance Li-S batteries.

Selective ion transport of catalytic hybrid aerofilm interlayer for long-stable Li-S batteries

Realistic prospects of high-energy and compact lithium-sulfur (Li-S) batteries promising as next-generation energy storages are hindered by their poor cycle life and severe self-discharge impelled through the polysulfide dissolution. Here, we report a feasible strategy to effectively suppress polysulfide and selectively control ions transport applying a new-type ultralight aerofilm membrane for practical Li-S batteries. Catalytic hybrid aerofilm interlayer (HAI) consisting of sulfonated tetrafluoroethylene and manganese dioxide nanowires suffices physical shield and sieve polysulfides through sulphophilicity polymer within the gaps of manganese dioxide layers, while also imparting chemical anchoring and catalysis of Mn-O. Such co-operative synergetic effects of the hybrid aerofilm interlayer for the Li-S cells enable the realization of a high discharge capacity of 1189 mAh g−1 at the end of the 500th cycle with a capacity retention of over 92.3 %, which is a 671 % improvement over sulfur battery with NO interlayer. Moreover, the aerofilm interlayer provides Li-dendritic growth inhibition and self-discharge prevention to retain the cycle life and safety of the device. This study presents a forward-looking strategy for developing an ultralight-compact and high-power Li-S battery.