Abstract
The application of Li‐S batteries is hindered by low sulfur utilization and rapid capacity decay originating from slow electrochemical kinetics of polysulfide transformation to Li
2
S at the ...second discharge plateau around 2.1 V and harsh shuttling effects for high‐S‐loading cathodes. Herein, a cobalt‐doped SnS
2
anchored on N‐doped carbon nanotube (NCNT@Co‐SnS
2
) substrate is rationally designed as both a polysulfide shield to mitigate the shuttling effects and an electrocatalyst to improve the interconversion kinetics from polysulfides to Li
2
S. As a result, high‐S‐loading cathodes are demonstrated to achieve good cycling stability with high sulfur utilization. It is shown that Co‐doping plays an important role in realizing high initial capacity and good capacity retention for Li‐S batteries. The S/NCNT@Co‐SnS
2
cell (3 mg cm
−2
sulfur loading) delivers a high initial specific capacity of 1337.1 mA h g
−1
(excluding the Co‐SnS
2
capacity contribution) and 1004.3 mA h g
−1
after 100 cycles at a current density of 1.3 mA cm
−2
, while the counterpart cell (S/NCNT@SnS
2
) only shows an initial capacity of 1074.7 and 843 mA h g
−1
at the 100th cycle. The synergy effect of polysulfide confinement and catalyzed polysulfide conversion provides an effective strategy in improving the electrochemical performance for high‐sulfur‐loading Li‐S batteries.
The development and commercialization of Li ion batteries during recent decades is one of the great successes of modern electrochemistry. The increasing reliability of Li ion batteries makes them ...natural candidates as power sources for electric vehicles. However, their current energy density, which can reach an average of 200 Wh kg−1 on the single cell level, limits the possible driving range of electric cars propelled by Li‐ion batteries. Thereby, there is a strong driving force to develop power sources technologies beyond Li‐ion batteries that will mark breakthroughs in energy density capabilities. Li‐sulfur batteries have high theoretical energy density that can revolutionize electrochemical propulsion capability. Consequently, in recent years there has been much work throughout the world related to these systems. The scope of work on this topic justifies frequent publications of review articles that summarize recent extensive work and provide guidelines and direction for focused future work. Here, a comprehensive, systematic work related to Li‐sulfur battery systems is described, beginning with the Li anode challenges, carbon‐encapsulated sulfur cathodes, and various kinds of relevant electrolyte solutions. Based on the work described and parallel recent studies by other groups, important and comprehensive guidelines for further research and development efforts in this field are provided.
Lithium sulfur batteries are very promising due to the very high theoretical capacity of sulfur electrodes, 1675 mAh g−1. However, the complicated conversion reaction of elemental sulfur to LixSy moieties and the incompatibility of Li metal in rechargeable batteries make development of these systems a great challenge. As described, intensive work in the field has resulted in impressive progress.
Despite their potential advantages over currently widespread lithium‐ion batteries, lithium–sulfur (Li–S) batteries are not yet in practical use. Here, for the first time bipolar all‐solid‐state Li–S ...batteries (ASSLSBs) are demonstrated that exhibit exceptional safety, flexibility, and aesthetics. The bipolar ASSLSBs are fabricated through a solvent‐drying‐free, ultraviolet curing‐assisted stepwise printing process at ambient conditions, without (high‐temperature/high‐pressure) sintering steps that are required for inorganic electrolyte‐based all‐solid‐state batteries. Two thermodynamically immiscible and nonflammable gel electrolytes based on ethyl methyl sulfone (EMS) and tetraethylene glycol dimethyl ether (TEGDME) are used to address longstanding concerns regarding the grain boundary resistance of conventional inorganic solid electrolytes, as well as the polysulfide shuttle effect in Li–S batteries. The EMS gel electrolytes embedded in the sulfur cathodes facilitate sulfur utilization, while the TEGDME gel composite electrolytes serve as polysulfide‐repelling separator membranes. Benefiting from the well‐designed cell components and printing‐driven facile processability, the resulting bipolar ASSLSBs exhibit unforeseen advancements in bipolar cell configuration, safety, foldability, and form factors, which lie far beyond those achievable with conventional Li–S battery technologies.
Bipolar all‐solid‐state Li–S batteries (ASSLSBs) are fabricated via solvent‐drying‐free, ultraviolet curing‐assisted stepwise printing under ambient conditions without high‐temperature or high‐pressure sintering steps commonly used for inorganic solid electrolyte‐based ASSLSBs. Instead of conventional inorganic solid electrolytes, two thermodynamically immiscible and nonflammable gel electrolytes are used. The bipolar ASSLSBs show exceptional improvements in bipolar configuration, safety, flexibility, and aesthetic diversity.
The quest to increase the energy density and improve the cycle life performance of lithium ion batteries (LIBs) and beyond has led to the development of various suitable and alternative materials for ...energy storage and conversion. The morphology and electrode architecture in advanced battery materials have been re-designed into nanofibers and composite nanofibers. Nanofiber-based separators and electrodes have demonstrated to improve the energy density and cycling performance of LIBs. The improvement in the structure and morphology of nanofibers in LIBs such as LiSi and LiSn, have once again ignited the interest in these Li:M alloy anodes as alternative anode and cathode materials. The major challenges that confront this new frontier have the lack of scalable method among the various techniques and designing nanofibers with good structure and morphology that could prevent dendrite penetrations. However, there seems to be a solution in sight with the advent of mass production techniques such as electrospinning and Forcespinning® that have recently been developed. In this paper, the use of nanofibers and composite nanofibers as electrode and separator materials for lithium ion, Li-O2 and Li-S batteries is reviewed. The discussion focuses on the performance characteristics of these nanostructured electrode and separator materials and methods used to improve their performances.
The application of Li‐S batteries is hindered by low sulfur utilization and rapid capacity decay originating from slow electrochemical kinetics of polysulfide transformation to Li2S at the second ...discharge plateau around 2.1 V and harsh shuttling effects for high‐S‐loading cathodes. Herein, a cobalt‐doped SnS2 anchored on N‐doped carbon nanotube (NCNT@Co‐SnS2) substrate is rationally designed as both a polysulfide shield to mitigate the shuttling effects and an electrocatalyst to improve the interconversion kinetics from polysulfides to Li2S. As a result, high‐S‐loading cathodes are demonstrated to achieve good cycling stability with high sulfur utilization. It is shown that Co‐doping plays an important role in realizing high initial capacity and good capacity retention for Li‐S batteries. The S/NCNT@Co‐SnS2 cell (3 mg cm−2 sulfur loading) delivers a high initial specific capacity of 1337.1 mA h g−1 (excluding the Co‐SnS2 capacity contribution) and 1004.3 mA h g−1 after 100 cycles at a current density of 1.3 mA cm−2, while the counterpart cell (S/NCNT@SnS2) only shows an initial capacity of 1074.7 and 843 mA h g−1 at the 100th cycle. The synergy effect of polysulfide confinement and catalyzed polysulfide conversion provides an effective strategy in improving the electrochemical performance for high‐sulfur‐loading Li‐S batteries.
The S/NCNT@Co‐SnS2 material acts as not only an effective shuttle‐suppressing shield for polysulfide but also an electrocatalyst in improving sulfur utilization and cycling stability for high‐sulfur‐loading lithium‐sulfur batteries. Therefore, it maintains 1004.3 mA h g−1 after 100 cycles at a current density of 1.3 mA cm−2.
Graphene‐based materials have been widely studied to overcome the hurdles of Li–S batteries, but suffer from low adsorptivity to polar polysulfide species, slow mass transport of Li+ ions, and severe ...irreversible agglomeration. Herein, via a one‐step scalable calcination process, a holey Fe, N codoped graphene (HFeNG) is successfully synthesized to address these problems. Diverging by the holey structures, the Fe atoms are anchored by four N atoms (Fe–N4 moiety) or two N atoms (Fe–N2 moiety) localized on the graphene sheets and edge of holes, respectively, which is confirmed by X‐ray absorption spectroscopy and density functional theory calculations. The unique holey structures not only promote the mass transport of lithium ions, but also prohibit the transportation of polysulfides across these additional channels via strong adsorption forces of Fe–N2 moiety at the edges. The as‐obtained HFeNG delivers a high rate capacity of 810 mAh g−1 at 5 C and a stable cycling performance with the capacity decay of 0.083% per cycle at 0.5 C. The concept of holey structure and introduction of polar moieties could be extended to other carbon and 2D nanostructures for energy storage and conversion devices such as supercapacitors, alkali‐ion batteries, metal–air batteries, and metal–halogen batteries.
A holey Fe, N codoped graphene (HFeNG) is developed via a scalable fabrication process that can “dig” holes onto the graphene and “modify” the edge of the holes with the Fe–N2 moiety. The HFeNG could not only accelerate Li+ transportation but also prohibit the transportation of polysulfides and therefore deliver high rate capacities and a stable cycling performance.
Li-Sulfur batteries (LSBs) have a wide application foreground for its high energy density and low-cost, however, the shuttle effect, volume fluctuation and irregular Li2S deposition on the cathode ...side often result in severe capacity decaying during its cycles. It is necessary to design and optimize the conversion route from sulfur (S8) to lithium sulfide (Li2S) to improve the reversibility of Li–S battery. Herein, novel MoO2–Mo2N binary nanobelts synthesized from α-MoO3 through an in situ topochemical nitridation process were employed as the highly efficient interlayer material for LSBs, which not only acted as a physical barrier to alleviate the shuttle effect but also regulated the conversion of lithium polysulfides (LiPSs) across the interface and optimized the nucleation of solid Li2S during cycling. Combining the polarity of MoO2 with the conductivity of Mo2N, such hybrid structure exhibited excellent cycling stability with a very low capacity decay of 0.028% per cycle up to 500 cycles at 1C. Even under the high areal sulfur loadings of 3.1 and 4 mg cm−2, the high discharge capacity and excellent capacity retention ratio can also be obtained. The concept of in-situ binary heterogeneous interfaces construction might also be used in the design and preparation of other electronic devices.
MoO2–Mo2N Binary Nanobelts were synthesized via a facile topochemical nitridation process and served as interlayer of Li-Sulfur battery. The in-situ constructed interface between monoclinic MoO2 and cubic γ-Mo2N is supposed to deliver a fast LiPSs conversion pathway includes ‘Capture-Diffusion-Precipitation’ process. The coin cells based on such heterostructure interlayer exhibited remarkable rate performance and cycling stability. Display omitted
•MoO2–Mo2N binary nanobelts were synthesized via a facile in-situ topochemical nitridation process.•Strong Mo–S, Li-X (X = O or N) interaction promoted the strong chemical confinement of polysulfides.•MoO2–Mo2N interfaces established a fast polysulfides redox conversion pathway from sulfur to Li2S through ‘Capture-Diffusion-Precipitation’ process.•Thus-derived interlayer coupled with carbon-sulfur cathode showed outstanding cycling stability and rate performance.
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Traditional carbon materials as sulfur hosts of Li-sulfur(Li-S) cathodes have slightly physical constraint for polysulfides, due to their no-polar property. Therefore, it is necessary ...to further enhance the affinity between sulfur hosts and polysulfides, and relieve the shuttle effects in the Li- S batteries. Herein, we report a novel vertical 2-dimensional (2D) p-SnS/n-SnS2 heterostructure sheets which grown on the surface of rGO. The excellent electrochemical properties of SnS-SnS2@rGO as Li-S cathode are ascribed to the stronger absorption effect of metal sulphides for polysulfides and the smooth trapping-diffusion-conversion effect of p-SnS/n-SnS2 heterostructure for polysulfides. As a conductive carrier for the growth of vertical 2D p-SnS/n-SnS2 heterostructure nanosheets, rGO can protect the steadiness and enhance the cycle stability of electrode, compared with heterostructure without rGO. In addition, the built-in electric field in the 2D p-SnS/n-SnS2 heterostructure during the discharge/charge processes can effectively accelerate charge transfer, and the charge transfer mechanism in SnS-SnS2 heterostructure during cycling has been investigated. At a rate capability of 2C, the designed SnS-SnS2@rGO as Li-S cathode delivers high specific capacities of 907 mAh g−1 and 571 mAh g−1 after the first cycle and 500 cycles, respectively, which shown excellent cycling ability.
We demonstrate the successful application of 3D printing (additive manufacturing) to construct high energy density and power density sulfur/carbon cathodes for Li-S batteries. A self-standing ...3D-printed sulfur/carbon cathode with high sulfur loading based on a low-cost commercial carbon black was fabricated via a facile robocasting 3D printing process. The 3D-printed sulfur/carbon cathode shows excellent electrochemical performance in terms of capacity, cycling stability, and rate retention by facilitating Li+/e- transport at the macro-, micro-, and nano-scale in Li-S batteries. Meanwhile, the areal loading of the sulfur/carbon cathode can be easily controlled by the number of stacking layers during 3D printing process. The Li-S batteries assembled with the 3D-printed sulfur/carbon cathodes with a sulfur-loading of 3 mg cm−2 deliver a stable capacity of 564 mA h g−1 within 200 cycles at 3 C. Moreover, cathodes with a sulfur-loading of 5.5 mg cm−2 show large initial specific discharge capacities of 1009 mA h g−1 and 912 mA h g−1, and high capacity retentions of 87% and 85% after 200 cycles at rates as high as 1 C and 2 C (equaling to high areal current densities of 9.2 mA cm−2 and 18.4 mA cm−2), respectively.
3DP-FDE applied in Li-S batteries with excellent Li+/e- transport in both micro- and nano-scale. Display omitted
•A self-standing S/C composites with high S-loading cathode is developed via 3D printing for high-energy-density Li-S batteries.•This 3D-printed cathode facilitates e-/Li+ transport at macro, micro and nano-scale.•This cathode delivers a stable specific capacities within 200 cycles at different current densities.
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Practical utilization of Li-sulfur batteries (LSBs) is still hindered by the sulfur cathode side due to its inferior electrical conductivity, huge volume expansion and adverse ...polysulfide shuttling effects. Though using polar catalysts coupled with mesoporous carbons may well surmount these barriers, such unsheltered catalysts rarely survive due to oversaturated polysulfide adsorption and extra sulfuration side reactions. To overcome above constrains, we herein propose to implant highly reactive nanocatalysts into carbon matrix with few nanometers insertion depth for mechanical protection. As a paradigm study, we have embedded La2O3-quantum dots (QDs) into carbon nanorods, which are then assembled into carbon microspheres (CMs). As evaluated, La2O3 QDs-CMs can help elevate the cathode redox reaction kinetics and sulfur utilization ratios, delivering a large capacity of 1392 mAh g−1 at 0.25C and high-capacity retention of 76% after total cycling. The thin carbon layers on La2O3 QDs exert a key role in impeding excess polysulfide accumulation on catalysts and thus prevent their deactivation/failure. Our strategy may guide a smart way to make catalysts-involved sulfur cathode systems with ultra-long working durability for LSBs applications.
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