Performance Of Lithium-sulfur Batteries Research Articles

Mesoporous N-rich Carbon with Single-Ni Atoms as a Multifunctional Sulfur Host for Li-S Batteries.

Physicochemical confinement and catalytic conversion of lithium polysulfides (LiPSs) are crucial to suppress the shuttle effect and enhance the redox kinetics of lithium-sulfur (Li-S) batteries. In this study, a NH4 Cl-assisted pyrolysis strategy is developed to fabricate highly mesoporous N-rich carbon (designed as NC(p)) featuring thin outer shells and porous inner networks, on which single-Ni atoms are anchored to form an excellent sulfur host (designed as Ni-NC(p)) for Li-S batteries. During pyrolysis, the pyrolytic HCl from confined NH4 Cl within ZIF-8 will in situ etch ZIF-8 to produce rich mesoporous in the carbonized product NC(p). The mesoporous Ni-NC(p) enables favorable electron/ion transfer, high sulfur loading, and effective confinement of LiPSs, while the catalytic effect of single-Ni species enhances the redox kinetics of LiPSs. As a result, the sulfur cathode based on the Ni-NC(p) host delivers obviously improved Li-S battery performance with high specific capacity, good rate capability, and cycling stability.

An overlooked parameter in Li-S batteries: The impact of electrolyte-to-sulfur ratio on capacity fading

The Lithium-Sulfur (Li-S) system has gained a lot of interest as a promising next-generation rechargeable battery due to the high theoretical energy density, high theoretical capacity and abundance of sulfur. Many parameters of Li-S batteries such as sulfur loading, electrolyte-to-sulfur (E/S) ratio, type of the conductive network, electrode design, etc. have a profound impact on the capacity, energy density and cycling performance. But the effect of E/S ratio on the electrochemical performance of Li-S batteries is often neglected, although it is one of the most important parameters. A high electrolyte amount in the cells could decrease the energy density and increase the cost, therefore it could limit the practical use of Li-S batteries. In this work, we first presented a statistical study on the sulfur loading and electrolyte quantity in Li-S cells by reviewing 240 selected papers from the state-of-the-art Li-S research. This analysis revealed that the electrolyte quantity was not reported as often as the sulfur loading in the literature, and the reported E/S values differ by a fair amount from each other. Second, in order to explore the effect of different E/S ratios on the performance of Li-S cells, batteries with 5:1, 10:1, 20:1 and 30:1 E/S ratios were prepared. Galvanostatic cycling with potential limitation (GCPL), electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) were used to analyze the effect of E/S ratio on the capacity fade, impedance, internal resistance and ion diffusivity in Li-S batteries. The effects of different electrolyte penetration conditions on the electrochemical performance of cells with the same E/S ratios were also studied by preparing cells with different resting times. It was shown that E/S ratio has a strong influence on the electrochemical performance of Li-S batteries, and an optimal E/S ratio should be achieved, which is low enough to minimize the free migration of active materials between the electrodes, and at the same time high enough in order to have a sufficient electrolyte wetting of the active material. It is suggested that capacity decay in batteries with low E/S ratios could be originating from electrolyte depletion, whereas the capacity decay in batteries with high E/S ratios could be due to the dissolved lithium polysulfide species in the liquid electrolyte and their diffusion to the lithium anode surface.

Modulating the d-p orbital coupling of manganese chalcogenides for efficient polysulfides conversion in lithium–sulfur batteries

The commercialization of lithium-sulfur battery (LSB) is seriously limited by the shuttling effect and sluggish reaction kinetics. Metal chalcogenides have been widely used as catalysts to enhance electrochemical performance, but the modulation essence of these non-metal anions is unclear. Herein, cubic manganese chalcogenides (MnO, MnS, MnSe) with fixed cation (Mn) and various anions (O, S, Se) are synthesized, and the anion effect on the performance of LSBs is systematically investigated. Based on the complementary experimental characterization and advanced theoretical calculations, it is clear that the interfacial redox reaction dynamics are governed by the catalytic activity of manganese chalcogenides, while the catalytic activity is modulated by the gap between the d-band of cation and p-band of anion (Δd-p). Among these manganese chalcogenides, Se has the largest atom radius and lowest electronegativity, which makes the p-band center of Se move to the Fermi level, thus increasing the electron's energy to react. Consequently, the LSBs based on MnSe catalyst exhibit the best rate (613.5 mAh g−1 at 4C) and cyclic performance (847.5 mAh g−1 after 250 cycles at 0.2C). This comparative study may encourage more effort and provide a new paradigm for developing highly effective catalysts for high-performance LSBs.

Unraveling the lithium iodide-mediated interfacial process in lithium-sulfur batteries: An in situ AFM study

Among various energy storage devices, lithium-sulfur batteries have attracted widespread attention due to their high theoretical energy density and specific capacity. To improve the performance and realize practical applications of lithium-sulfur batteries, it is crucial to unravel the dynamic evolution and reaction mechanism at the electrode/electrolyte interfaces during cycling. Nevertheless, the details are still not well known despite generous efforts, which need more in situ and non-destructive imaging characterizations. Herein, we have combined AFM with an electrochemical workstation to dynamically visualize the morphological evolution and structural changes of the interfacial process, which reveals the lithium iodide-mediated interfacial reactions in lithium-sulfur batteries. In situ measurements showed that the electrode surface was coated by a reticular layer consists of elemental iodine and polyether with lithium iodide additive during charging, which could effectively prevent insolube sulfides from gathering on the surface and improve the cycling performances of lithium-sulfur batteries. These findings shed new light on the interfacial mechanism and establish design ideas for the future development of better electrolytes for lithium-sulfur batteries.

Improvement of Sulfur Cathode Reversibility by Specific Chemical Lithium Pre-doping Method

1.IntoroductionRecently, lithium-ion batteries (LIBs) have been required in terms of a high energy density for large-scale applications such as power supplies for electric vehicles. Lithium-sulfur (Li-S) batteries are, therefore, expected as next generation batteries because of their high energy density.Sulfur is utilized as cathode material for Li-S batteries because of a high specific capacity. However, sulfur has a low electric conductivity and a risk of dissolution into an electrolyte during a charge-discharge process [1]. L. Nazar et al. applied activated carbon as substrate for sulfur to help electric conduction and prevent dissolution of sulfur [2]. The activated carbon allows Li-S batteries to show high specific capacity with high reversibility. Even if these problems are solved, however, Li-S batteries have a further problem of excessive initial irreversible capacity during the first discharge process. Li pre-doping is a useful technique to cancel the large irreversible capacity in actual LIBs. Abe et al. reported a chemical lithium pre-doping method for a graphite using lithium naphthalenide [3]. Studies have been reported on the use of such pre-doping to improve the performance of Li-S batteries, for instance, with a sulfur-Ketjenblack composite cathode [4]. In our previous study, we have applied that method to a sulfur cathode composed of microporous activated carbon and sulfur before cell assembly and developed a Li2S cathode that suppressed the initial irreversible capacity during the first discharge process. However, the Li2S cathode showed an unignorable initial irreversible capacity and poor cycle life [5].This work attempts to improve the reversible capacity of the Li2S cathode by a specialized chemical lithium pre-doping method. Our report would lead to the proposal of novel cathode and anode options in Li-S batteries. Method 2-1. Fabrication of lithium naphthalenide solutionAs Li metal and Li2S are both sensitive to moisture in air, all the following synthesis processes were carried out in an Ar-filled glove box. Lithium naphthalenide, a dark green solution was prepared by mixing an equal mol amount of Li metal with naphthalene in a cyclic ether solvent.2-2. Fabrication of Li2S-AC cathodesEach sulfur cathode was prepared by mixing the S-AC (a composite of microporous activated carbon and sulfur), acetylene black, carboxymethyl cellulose, and styrene butadiene rubber at a respective weight ratio of 93: 3: 2: 2 and coating the resulting aqueous slurry on a carbon paper.The 1M lithium naphthalenide solution was dropped on the sulfur cathode. After 20 min reaction, the cathode was rinsed several times with 2–dimethoxyethane (DME) to remove the residues of reagents. The cathode was then dried under reduced pressure for 12 h. After that, the resulting Li2S cathode was impregnated with a mixture of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) (VC: FEC = 1: 1 by weight). After 20 min impregnation, the cathode was dried under reduced pressure for 12 h.2-3. Assembling of cellsCells were assembled with the Li2S electrode and Li metal foil as an anode. Lithium bis(trifluorosulfonyl)imide (LiTFSI): tetraglyme (G4): 1,1,2,2–tetrafluoroethyl–2,2,3,3–tetrafluoropropyl ether (D2) at a respective ratio of 10: 8: 40 (by mol) was used as the electrolyte.3.Major results and discussionThe Li2S cathode without the VC/FEC impregnation showed an initial charge capacity of 1791 mAh g-1 and an initial discharge capacity of 1298 mAh g-1, indicating a large irreversible capacity. In contrast, the Li2S cathode with the VC/FEC impregnation showed 1446 mAh g-1 and 1422 mAh g-1, respectively. Thus, the impregnation with VC/FEC reduced the initial irreversible capacity and improved the initial charge capacity. According to these results, Li remaining in the sulfur cathode would be partially consumed to form a film by the impregnation with VC/FEC. In addition, the capacity retention of the Li2S cathode with and without the VC/FEC impregnation was 73 % and 64 % at the 30th cycle, respectively. This suggests that the Li2S cathode with the film leads to better cycle performance than that without the film.We will also report the results of surface composition analysis of the Li2S cathode with and without the VC/FEC impregnation by Hard X-ray Photoelectron Spectroscopy (HAXPES).

Mechanism of Improved Lithium-Sulfur Battery Performance by Oxidation Treatment to Microporous Carbon as Sulfur Matrix

1. IntroductionLithium-sulfur (Li-S) batteries are rechargeable devices assembled with a sulfur cathode and a lithium metal anode. Li-S batteries have twice the volumetric energy density and 5 times the gravimetric energy density of lithium-ion batteries (LIB). Hence, Li-S batteries are expected to be applied to stationary power sources and EV vehicles [1]. However, Li-S batteries have the following issues:・Sulfur and the final discharge product (Li2S) are insulators.・In the discharge process, sulfur expands up to 1.8 times, so the structure of batteries is unstable.・Intermediate products (Li2Sx (x = 4 – 8)) dissolve in an electrolyte; Li2Sx (x = 4 – 8) diffused to an anode to provide an insulating layer at the anode surface.・In the charge process, Li2Sx (x = 4 – 8) causes redox shuttling.As a result, Li-S batteries cannot charge and discharge stably. In order to deal with this problem, Nazar et al. reported the method that sulfur is confined in porous carbon [2]. This approach provides a cathode realizing good electronic conductivity, restriction of sulfur expansion, and suppression of Li2Sx (x = 4 – 8) dissolution. Although these improved characteristics allow Li-S batteries to operate, The discharge capacity of Li-S batteries is still not high enough and this needs to be addressed.In our previous study, we reported that oxidation treatment to microporous carbon (MC) with HNO3 improves Li-S batteries' discharge capacity [3]. Moreover, we clarified that the discharge capacity of Li-S batteries has an approximate proportional relation with the amount of oxygen-containing functional groups on the MC surface [4].This work attempts to elucidate the mechanism of improved Li-S battery performance by oxidation treatment to MC. Our report would lead to the proposal of a novel strategy to improve the performance of Li-S batteries.2. Method2.1 Preparation of Oxidized MC-Sulfur composite (Ox MC-S)MC was added into 69 wt.% HNO3 and refluxed at 120ºC for 2 h. By vacuum filtration and washing with deionized water, Ox MC was obtained. Ox MC dried in vacuum at 80ºC overnight was mixed with sulfur at a weight ratio of Ox MC: S = 48: 52. The mixture was thermally annealed at 155ºC for 5 h (Ox MC-S). Untreated MC was also composited with sulfur by the same method (MC-S).2.2 Assembling of CellsEach MC-S cathode was prepared by mixing the MC-S, acetylene black, carboxymethyl cellulose, and styrene butadiene rubber at a respective weight ratio of 89: 5: 3: 3 and coating the resulting aqueous slurry on an Al foil current collector. The cells with the MC-S electrode and Li metal foil as an anode were assembled in a glove box filled with Ar. Lithium bis(trifluorosulfonyl)imide (LiTFSI): tetraglyme (G4): hydrofluoroether (HFE) = 10: 8: 40 (by mol) was used as the electrolyte.2.3 Electrochemical Impedance Spectroscopy (EIS)To elucidate the effect of oxidation treatment on the internal resistance of Li-S batteries, EIS was carried out at various potentials (Discharge 2.0 – 1.0 V and Charge 1.0 – 3.0 V). The obtained Nyquist plots were used for the evaluation of solid electrolyte interphase (SEI) resistance (Rsei), charge-transfer resistance (Rct), and Warburg impedance (Rw). Rw was investigated with the calculation of Warburg coefficient (σ).3. Major results and conclusionSince oxidation treatment to MC significantly increased the discharge capacity of Li-S batteries [3][4], it was expected that oxidation treatment would lower the internal resistance of Li-S batteries. EIS of MC-S and Ox MC-S at various potentials showed that oxidation treatment reduced Rsei by an average of 12.2 Ω. This indicates that the SEI thickness was reduced, or the SEI was composed of highly ion-conductive components by the oxidation treatment. Rct decreased only at lower potentials, and the Warburg coefficient decreased except at the end of charge and discharge potential. These results suggest that the oxidation treatment decreases overall resistance, but especially SEI resistance and Warburg impedance, which may improve the discharge capacity of Li-S batteries.We will also report the activation energy of Rsei and Rct and mechanism analysis of decreasing Rsei by oxidation to MC. This work was supported by “Advanced Low Carbon Technology Research and Development Program, Specially Promoted Research for Innovative Next Generation Batteries (ALCA-SPRING [JPMJAL1301])” from JST.[1] Y. Guo et al., Angew. Chem. Int. Ed., 52 (2013) 13186.[2] X. Ji et al., Nat. Mater., 8 (2009) 500.[3] S. Okabe et al., Electrochemistry, 85 (2017) 671.[4] L. Yoshida et al., ECS 238th PRiME Meeting s (2020).

Biomass-Derived Carbon for High-Performance Lithium-Sulfur Batteries

With the advantages of high conductivity and low cost, porous carbons have been considered as the most attractive materials as hosts of sulfur cathode in lithium-sulfur batteries (LSBs). However, LSBs always suffer short cycle life due to the “shuttle effect” of lithium polysulfide species (polysulfides), which are intermediate products during the charge/discharge processes. The weak interaction between carbon and polysulfides results in the dissolution of polysulfides from the cathodes, loss of active material and eventually fast capacity fading. To overcome these drawbacks, we employed a biomass-derived carbon as the host material in sulfur cathodes. Results from X-ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen sorption reveals that this biomass-derived product is amorphous carbon and is composed of both large (>10 nm) and small (<5 nm) pores. Using as hosts of cathodes in LSBs, the biomass-derived carbons could deliver a high reversible capacity of > 800 mAh/g and retain >80% of initial capacity after 200 cycles. Especially, the activated carbons exhibited 80% capacity retention after 400 cycles. The promising LSB performance could be ascribed to the unique porous architecture of biomass-derived carbons. The meso/micropores in biomass-derived carbons could provide more sites to anchor sulfur and polysulfides, while macropores provide channels for fast transport of ions. This was corroborated by the results from the electrochemical impedance spectroscopy (EIS), the thermogravimetric analysis (TGA) and absorption measurements.

Effect of CeO2-x-CNT/S cathode on the electrochemical performance of lithium-sulfur batteries

Despite extensive research into cerium oxide as a cathode for lithium-sulfur batteries, there are still problems with low specific capacity and high decay rate. This paper used a simple gas reduction method to prepare CeO2-x nanoparticles with more oxygen vacancies. It has been demonstrated experimentally that the presence of oxygen defects increases the electrochemical reaction rate. Using CeO2-x-CNT/S as cathode for lithium-sulfur battery not only improves the conductivity of cathode, but also restricts the movement of polysulfide. The CeO2-x-CNT/S cathode exhibits good electrochemical properties. The first discharge specific capacity of CeO2-x-CNT/S cathode is 1556.8 mAh g -1 at 0.1C. The initial discharge specific capacity is 1233.9 mAh g -1 at 0.5C, and has a small capacity decay rate after 600 cycles. It provides a new answer to the problems in lithium-sulfur batteries.

Thin Nano Cages with Limited Hollow Space for Ultrahigh Sulfur Loading Lithium-Sulfur Batteries.

Owning to its various advantages, the lithium-sulfur battery is one of the research hot spots for new energy storage systems. Diverse hollow structures with specific morphologies have been used as the sulfur host materials to adsorb or/and catalyze the polysulfides, and can in particular concurrently inhibit the volume expansion during electrochemical processes in lithium-sulfur batteries. However, hollow space with a large volume will restrict the performance of the cell under high sulfur area loading, which is a very important indicator for the practical applications of the lithium-sulfur battery. Here, we report a nano thin cage cobalt acid zinc (ZnCo2O4) with limited hollow space as the cathode catalyst for lithium-sulfur batteries, which greatly reduces the electrode volume occupied by the hollow structure. The hollow volume of these thin cages is much smaller than those of the normally reported hollow materials in the literatue. The electrochemical performance of lithium-sulfur batteries with ZnCo2O4 thin cages could greatly improve due to the unique structure and the synergistic adsorption/catalytic effect of Zn/Co sites, especially at an ultrahigh S area load. Under a high S loading of 8 mg cm-2, the cell could keep a reversible capacity of 600 mAh g-1 after 500 cycles. Even at a sulfur loading of 10 mg cm-2, the cell still releases a discharge capacity of 1000 mAh g-1 which is equivalent of an area capacity of 10 mAh cm-2. This work provides a feasible way to develop lithium sulfur batteries with a high area sulfur load. This idea provides a possible solution to develop a Li-S battery at high area S loading and move one step closer to the practical applications.

Construction of nanoporous Mo2C shell/MoO3 core composite by converting MoO3 and its superior performance in lithium sulfur battery

• Mo 2 C/MoO 3 prepared by the combination of synthesis of MoO 3 particle and its surface conversion (reduction and carbonization) to Mo 2 C. • Mo 2 C/MoO 3 -modified separator. • Wasted CFRP acts as the carbon source for Mo 2 C, and CF is simultaneously reclaimed. • The core–shell structured Mo 2 C/MoO 3 has high capability to anchor LiPS and prompt the electrochemistry of S. • The Li-S battery with Mo 2 C/MoO 3 -modified separator owns excellent electrochemical performance. The lithium-sulfur (Li-S) battery is a promising energy storage device in the future. However, its performance is strongly affected by the shuttle effect and inherent sluggish kinetics. Herein, Mo 2 C/MoO 3 -modified separator is constructed, in which MoO 3 particles are derived by the decomposition of Mo source and simultaneously their surfaces are converted (reduced and carbonized) into Mo 2 C, i.e., Mo 2 C shell/MoO 3 core. In addition, the resin matrix of the waste CFRP (Carbon fiber reinforced polymer) acts as the carbon source for the change from MoO 3 to Mo 2 C, while CF is claimed from CFRP. The synergistic effect of conductive Mo 2 C-shell and polar MoO 3 -core anchors lithium polysulfide to promote the conversion of sulfur. Benefited from block effect on the soluble lithium polysulfide (LiPS) and catalytic effect on sulfur, Li-S battery with Mo 2 C/MoO 3 -modified separator owns excellent electrochemical performance: A high initial discharge specific capacity of 1288 mAh g −1 at 0.2C and an initial capacity of 670 mAh g −1 at 4C, as well as the average decay rate per cycle of 0.039% over 250 times.

MOFs derived ZnSe/N-doped carbon nanosheets as multifunctional interlayers for ultralong-Life lithium-sulfur batteries

• Zinc-based MOFs derived ZnSe/NC nanosheets were synthesized through a feasible process for improving the performance of Li-S batteries. • ZnSe/NC nanosheets have good conductivity and multiple adsorptive/catalytic sites. • The Li-S cells with the modified separator show an outstanding lifespan over 1500 cycles at 1 C with a low capacity decay of 0.046% per cycle. The shuttle effect and slow conversion rate of lithium polysulfides (LiPSs) have become the main obstructs to the development of lithium-sulfur (Li-S) batteries. Herein, the low cost metal-organic frameworks derived nitrogen-doped carbon nanosheets embedded with zinc selenide nanoparticles (ZnSe/NC nanosheets) were designed and synthesized for Li-S batteries. As the LiPSs trapping-layer, these nanocomposites provide some key benefits: (1) The nitrogen doping changes local electron distribution in the carbon nanosheets, thus the electrical conductivity is greatly improved for facilitating the transport of electrons/ions. (2) Nitrogen atoms and ZnSe nanoparticles play an important role in anchoring the LiPSs via chemical interactions. (3) The remarkable catalytic activity of ZnSe nanoparticles can accelerate the redox kinetics of LiPSs. As a result, the Li-S battery with the ZnSe/NC nanosheets modified separator exhibits ultralong lifespan over 1500 cycles with a small capacity loss of only 0.046% per cycle at 1 C, which is superior over those reported values. Furthermore, the Li-S battery with a high sulfur loading of 4.71 mg cm −2 can still maintain a high areal capacity of 4.28 mAh cm −2 after 50 cycles. This work provides a new route to the design of multifunctional low cost and high-performance separators for remarkably stable Li-S batteries.

A hollow Co0.12Ni1.88S2/NiO heterostructure that synergistically facilitates lithium polysulfide adsorption and conversion for lithium-sulfur batteries

• An ingenious Co 0.12 Ni 1.88 S 2 /NiO heterostructure with a hollow and semi-open architecture was engineered in situ , which synergistically enhanced lithium polysulfide adsorption and conversion for lithium-sulfur batteries. • The considerable electrochemical impedance variation was observed via in situ EIS measurements, which was proved to be related to the content of soluble LiPSs in the electrolyte. • The mechanisms of the strong affinities between Co 0.12 Ni 1.88 S 2 /NiO and lithium polysulfides, and the catalytic effect were further investigated by theoretical calculations. The significant capacity deterioration and inadequate cycling lifespan that are mainly caused by the undesirable “shuttle effect” and torpid redox kinetics have encumbered the development of practically applicable lithium-sulfur (Li-S) battery technology. Modifying sulfur cathodes with lithium polysulfide (LiPS) adsorptive and electrocatalytic host materials is a promising approach to resolving these issues. Herein, a Co 0.12 Ni 1.88 S 2 /NiO heterostructure, which has multiple merits, is designed and serves as a sulfur host to improve the electrochemical performance of Li-S batteries. Possessing strong LiPS adsorbability and excellent electrocatalytic activity, the heterostructural Co 0.12 Ni 1.88 S 2 /NiO exhibits favorable synergistic effects, which effectively facilitate the anchoring and converting of diffused LiPSs. As a result, the corresponding cell delivers rapid redox kinetics and higher sulfur utilization. An impressive initial discharge capacity of 1424.8 mAh g −1 and a reversible capacity near 1056.7 mAh g −1 at 1 C over 1000 cycles are achieved with an average Coulombic efficiency of 98.8%. Benefiting from the unique nanoarchitecture and superior catalytic efficiency, only a very small amount of Co 0.12 Ni 1.88 S 2 /NiO (∼7 wt% in the cathode) is used as the sulfur host. The rational design of Co 0.12 Ni 1.88 S 2 /NiO in this work will hopefully offer inspiration for exploring advanced heterostructure materials for Li-S batteries and other electrochemical devices. Heterostructural Co 0.12 Ni 1.88 S 2 /NiO was engineered as a sulfur host for lithium-sulfur batteries. The catalytic effect and strong LiPS adsorbability synergistically promoted redox kinetics and LiPS conversion, which significantly improved the sulfur utilization during the charging and discharging processes.

Improved Low-Temperature Performance of Li-S Batteries via “Solid-Solid” Conversion of Sulfur

Lithium-sulfur (Li-S) batteries under the traditional “solid-liquid-solid” cathode process experience serious capacity degradation at low temperatures, because the intermediate polysulfides which dissolved into the electrolyte tend to cluster. Herein, a “solid-solid” conversion of sulfur is realized via an in situ formed protective layer on the cathode surface which separates the sulfur species from the electrolyte. So that the dissolution and agglomeration problem of the polysulfides is suppressed. As a result, the sulfur cathode via “solid-solid” conversion demonstrates a significantly improved low-temperature performance, even under lean electrolyte condition. This work provides a promising direction for developing available Li-S batteries under cryogenic conditions.

Carbon Coated Metal-Based Composite Electrode Materials for Lithium Sulfur Batteries: A Review.

Lithium-sulfur battery is one of the most promising secondary battery systems due to their high energy density and low material cost. During the past decade, great progress has been achieved in promoting the performances of Li-S batteries by addressing the challenges at the laboratory-level model systems. With growing attention paid to the application of Li-S batteries, new challenges at practical cell scales emerge as the bottleneck. However, challenges remain for the commercialization of lithium-sulfur batteries. The current review mainly focused on metal-based catalysts decorated-carbon materials for enhanced lithium sulfur battery performance. Firstly, the synthesis methods of various carbon-sulfur composites are discussed, as well as the influence of different material structures on the electrochemical performance. Secondly, a variety of catalysts, including metal atoms, metal oxides, sulfides, phosphides, nitrides, and carbide-decorated carbon nanomaterials, are systematically introduced to determine how lithium can be enhanced by suppressing polysulfides and promoting redox conversion reactions. Also, analyzed the multi-step electrochemical reaction mechanism of the battery during the charging and discharging process, and provide a feasible path for the practical application of high energy density lithium-sulfur batteries.

Review on recent advances in two‐dimensional nanomaterials‐based cathodes for lithium‐sulfur batteries

AbstractWith the advantages of superior energy density, lithium‐sulfur batteries (LSBs) have been considered as one of the promising next‐generation batteries. However, some key issues, such as the shuttle effect of the intermediate lithium polysulfides, poor conductivity of the sulfur, Li2S and Li2S2, and huge volume variation during charge/discharge process, have hindered its development. In this respect, a variety of nanomaterials have been used to overcome the above‐mentioned defects. Among them, two‐dimensional (2D) nanomaterials present unique merits for enhancing the electrochemical performance of LSBs owing to their unique structural properties. Nevertheless, the variation of 2D nanomaterials used in LSBs is rarely discussed. Herein, this work systematically reviews the state‐of‐the‐art progress in LSB cathode development through 2D materials such as graphene, MXenes, 2D compounds, and so forth. With a comprehensive analysis, the challenges and perspectives for 2D nanomaterials in LSBs application are proposed and discussed. image

Building polysulfides shuttle barrier with unblocked Li+ transit channels via in-situ grown FeOOH modified separator for Li-S batteries

The dissolution and shuttle of lithium polysulfides lead to unstable and unreliable cycling performances of commercial lithium sulfur batteries. Here, we present an in-situ grown FeOOH modified commercial polypropylene separator (FeOOH-PP) prepared by plasma surface pretreatment and one-step low-temperature hydrothermal method. The FeOOH, which has abundant active sites, builds polysulfides shuttle barrier with unblocked Li+ transit channels. FeOOH achieves a robust and effective chemisorption of lithium polysulfides (LiPSs) through Fe-S and Li-O bonds and enhances the redox reaction kinetics during charging and discharging. Accordingly, the FeOOH-PP achieves a stable long-term cycling of 500 cycles at 1C rate with a low decay rate of 0.039 % per cycle. It also shows an initial discharge capacity of up to 1149 mAh·g−1 at 0.2C rate. This work demonstrates tremendous potential for practical applications of Li-S batteries.

Synthesis of nickel-porous carbon with controllable morphology and its electrochemical performance for lithium sulfur batteries

A series of nickel porous carbon (Ni-PC-x, x represents solvothermal temperature) materials with controllable morphology, which has the different catalytic effect of the metallic Ni catalyst derived from Ni-MOF and Li+ transfer efficiency, are designed and synthesized through the simple solvothermal method and pyrolysis. Among the composites, the S/Ni-PC-160 cathode exhibits excellent long-cycle stability (an average capacity fading rate of only 0.14% per cycle for 300 cycles at 1C), and wonderful rate performance with a capacity of 815.5 mAh·g−1 at 1C. The improved performance of S/Ni-PC-160 is attributed to the catalysis derived from Ni nanoparticles and rapid Li+ diffusion from a 3D honeycomb structure. This work provides an important reference value for the potential application of the relationship between morphology and electrochemical performance in LiS batteries.

Intrinsic Regularity of Catalytic Cobalt Chalcogenides in Lithium-Sulfur Battery: Theoretical Study Delivers New Insights.

Cobalt chalcogenides CoX2 (X=S, Se, Te) render great performance of lithium-sulfur batteries based on catalytic capacity to alleviate shuttle effect. Given that S/Se/Te belong to the same main group, the outstanding cycling stability delivered by CoTe2 aroused the curiosity about the uniqueness of CoTe2 and intrinsic laws of cobalt chalcogenide. Herein, comprehensive theoretical study delivers new insights into the intrinsic laws of CoX2 : the relative vertical distance of two X atomic layers (rather than atom electronegativity) mainly controls adsorption; CoX2 mainly regulates the charging process (rather than discharging process) thus contributes to great cycling stability. On this basis, the advantages of CoTe2 are three-fold: moderate polysulfide adsorption, facile ion transport capacity, and surprisingly great promotion of charging process. It is hope the results will facilitate the development of cobalt chalcogenides, especially tellurides as catalytic material in lithium sulfur batteries.

Tandem Co–O dual sites on halloysite with promoted reaction kinetics for sulfur reduction

Facilitating sulfur reduction reaction (SRR) is a promising pathway to tackle the polysulfide shuttle effect and enhance the electrochemical performance of lithium-sulfur (Li-S) batteries. Catalysts with a solo active site can reduce a reaction barrier of a certain transition-intermediate, but the linear scaling relationship between multi-intermediates still obstructs overall SRR. Herein, we construct tandem Co–O dual sites with accelerating SRR kinetics by loading highly dispersed cobalt sulfide clusters on halloysite. This catalyst features Co with upshifted d-orbital and O with downshifted p-orbital, which cooperatively adsorb long-chain polysulfide and dissociate an S–S bond, thus achieving both optimal adsorption–desorption strength and reduced conversion energy barrier of multi-intermediates in SRR. The Li-S coin batteries using the electrocatalyst endows a high specific capacity of 1224.3 mAh g−1 at 0.2 C after 200 cycles, and enhances cycling stability with a low-capacity decay rate of 0.03% per cycle at 1 C after 1000 cycles. Moreover, the strategy of the tandem Co–O dual sites is further verified in a practical Li-S pouch battery that realizes 1014.1 mAh g−1 for 100 cycles, which opens up a novel avenue for designing electrocatalysts to accelerate multi-step reactions.

Hierarchically porous carbon nanofiber binder-free electrode for high-performance lithium–sulfur batteries

It is still a challenge for lithium–sulfur (Li-S) batteries to possess high sulfur utilization and excellent electrochemical performances due to the low electrical conductivity and dissolution of polysulfides. To resolve these issues, a free-standing sulfur host composed of hierarchically porous carbon nanofibers (HPCNFs) has been synthesized via electrospinning technology. The HPCNFs with an interconnected and porous structure can facilitate electron transfer and electrolyte penetration. The mesopores in HPCNFs can provide high levels of sulfur loading, and the micropores can inhibit shuttle effects of the sulfur cathode during discharge and charge processes. After encapsulating a high mass of sulfur (76.4 wt%, HPCNFs@S), the electrode was directly applied as a cathode for the Li-S battery, which exhibited a high specific discharge capacity of 1,145 mA h g−1 at 0.1 C (1 C = 1,675 mA g−1) and maintained 787 mA h g−1 after 150 charge/discharge cycles. This work provides a new insight into optimizing the electrochemical performance of Li-S batteries.