Rechargeable Lithium-sulfur Batteries Research Articles

Defect-Rich, Mesoporous Cobalt Sulfide Hexagonal Nanosheets as Superior Sulfur Hosts for High-Rate, Long-Cycle Rechargeable Lithium–Sulfur Batteries

The performance of lithium–sulfur (Li–S) batteries is strongly limited by the sluggish lithium polysulfides (LiPSs) conversion kinetics and LiPSs shuttling. Herein, mesoporous Co3S4 hexagonal nanos...

Evaluation of the Surface Film Formed on Cu in Li[N(CF3SO2)2]-Tetraglyme Solvate Ionic Liquids

Rechargeable lithium-sulfur batteries have been investigated as a next generation battery due to low cost and abundant resources. Li-S batteries using conventional organic electrolytes have been realized by addition of some additives forming some protecting films on the Li anode in order to avoid self-discharge due to dissolution of lithium polysulfides in the electrolytes. On the other hand, it has been known that the solubility of lithium polysulfides is very low in the ionic liquids composed of [N(CF3SO2)2]– (bis(trifluoromethylsulfonyl)amide, TFSA–) because of its weak coordinating ability. The equimolar mixture of LiTFSA and tetraglyme (G4) has been known to give a liquid composed of [Li(G4)]+ and TFSA– at room-temperature. This liquid is called a solvate ionic liquid (SIL). LiTFSA-G4 SILs have such favorable properties as high lithium ion concentration and low solubility of lithium polysulfides. Therefore, the LiTFSA-G4 SILs have been studied as the promising electrolytes for rechargeable Li-S batteries. In order to realize Li-S batteries using the LiTFSA-G4 SILs, it is necessary to evaluate the performance of the Li anode in the SILs. We have already reported that the coulombic efficiency of deposition and dissolution of lithium on a Cu substrate was improved by the formation of the surface film (solid-electrolyte interphase) on the Cu substrate at the potential of Li(I)/Li[1]. In the present study, the surface film formed in LiTFSA-G4 SILs with and without a diluent, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether (HFE), has been characterized using electrochemical impedance spectroscopy (EIS), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS) without exposing the samples to air. LiTFSA-G4 SILs were prepared by mixing LiTFSA and G4 at the specified molar ratios (50.0 : 50.0 and 54.5 : 45.5). EIS was conducted using an air-tight three electrode cell. A Cu disk electrode (3 mm in diameter) was used as the working electrode. Li foil was used as the counter and reference electrode. The surface film was prepared on the Cu electrode by keeping the potential at 0 V vs. Li/Li(I). The EIS spectra were taken at 0 V vs. Li/Li(I) with an amplitude of 5 mV in the frequency range from 1 Hz to 20 kHz. TEM grids made of Cu and Cu foils in contact with Li foil were immersed in the SILs with different compositions for three days. The samples were washed with monoglyme (G1) and dried under dry Ar atmosphere. The samples were installed into TEM equipped with EDX using a transfer holder. XPS spectra were obtained by focused Al Kα radiation with Ar+ and Ar gas cluster ion beam (GCiB) etching guns. The impedance spectra assignable to the surface films formed on the Cu electrodes at 0 V vs. Li/Li(I) were observed in the SILs with and without addition of HFE. The resistance of the surface film in 54.5-45.5 mol% LiTFSA-G4 SIL was larger than that in 50.0-50.0 mol% one, suggesting the ionic conductivity of the surface film reflect the concentration of Li(I) in the electrolyte. The resistance of the surface film increased with addition of HFE probably due to a decrease in the concentration of Li(I). The formation of the surface films with the thickness of 20-100 nm was confirmed by TEM. The shrinkage of the films was observed during TEM observation, indicating the decomposition of organic substances and/or elevation of temperature occurred by electron irradiation. Although no spot was observed in the electron diffraction diagram at the beginning of the observation, the spots assignable to LiF and Li2S appeared after the shrinkage of the film by electron irradiation, indicating LiF was not formed electrochemically at 0 V vs. Li/Li(I) in the SILs. In addition, no peak assignable to LiF was not observed in the XPS spectra of the surface films with Ar GCiB etching gun. Therefore, the surface films formed in the SIL were considered to composed of the organic substances derived from reductive decomposition of G4 and the ions existing in the SIL.Reference[1] Y. Katayama, N. Tachikawa, and N. Serizawa, 235th ECS meeting, A02-0265, Dallas, (2019).

(Invited) New Electrode and Electrolyte Approaches for Rechargeable Li-S Battery

A strong demand for low-cost and high-energy-density rechargeable batteries has spurred lithium-sulfur (Li-S) rechargeable battery research. First, sulfur is an abundant and low-cost material. Second, the Gibbs energy of the lithium (Li) and sulfur reaction is approximately 2,600 Wh/kg, assuming the complete reaction of Li with sulfur to form Li2S, more than five times the theoretical energy of transition metal oxide cathode materials and graphite coupling. With these advantages, Li-S batteries could be both high energy density and low cost, satisfying demand in energy storage for transportation application. The major obstacle is the loss of sulfur cathode material as a result of polysulfide dissolution into common electrolytes, which causes a shuttle effect and significant capacity fade. The polysulfide shuttle effect leads to poor sulfur utilization and fast-capacity fade, which have hindered widespread use of rechargeable Li-S batteries. Here, we present a body of work on both electrode materials design and synthesis, electrode fabrication and novel electrolyte materials for Li-S rechargeable batteries. We report the development of new electrode materials, electrolytes and additives for Li-S battery. The properties of the combined electrode and electrolyte stabilized polysulfides, and promoting the polysulfide affiliation with the electrode substrate to prevent polysulfide dissolution.

Development of a High Energy Density, Long Cycle Life and Safety Enhanced Li-S Battery

Rechargeable lithium-sulfur (Li-S) batteries are widely considered the most promising “Beyond Li-ion” candidates, notably for their high theoretical energy density. The low and moderate atomic weight of Li and S, respectively, translates to a battery chemistry pairing that is lightweight. Since each S atom can ultimately host two lithium ions (Li+), compared with 0.5–0.7 Li+ per host atom in Li-ion batteries [1], the Li-S battery chemistry offers a much higher Li storage capacity potential. Assuming a complete redox couple reaction, S8 + 16Li+ + 16e- ↔ 8Li2S, the S cathode can have a high theoretical specific capacity of 1672 mAh/g with an average discharge voltage of ~2.1V (vs. Li/Li+), which leads to a theoretical specific energy of ~2500 Wh/kg based on the active material weight of a Li-S cell [2]. Other compelling attributes of Li-S batteries include high S natural abundance, low cost of S materials and safety characteristics owing to an intrinsic tolerance to overcharge [3]. In addition, the primary constituents of Li-S batteries are non-toxic and environmentally friendly [4].However, currently no commercial Li-S battery exists due to some significant technical challenges that have thus far prevented the realization of the tremendous energy density and performance potentials of Li-S batteries. These technical challenges include: low practical specific energy or energy density yield, significant capacity loss with cycling, high self-discharge rates, low Coulombic efficiency and safety concerns due to the use of Li metal anode [5].We will present our efforts in the development of a high energy density, long cycle life, safe and economically scalable Li-S battery technology via a holistic approach to nanoengineer/functionalize cell components including active components (i.e., S cathode, Li metal anode) and inactive components (e.g., separator, electrolyte), to address the Li-S battery cycle life degradation challenges and safety concerns. We will show that our comprehensive approaches afforded high discharge specific capacity, Coulombic efficiency (CE) and stable cycle life of the resultant Li-S cells (Figure 1).Our study demonstrates that the holistic approach of nanoengineering/functionalizing the active and inactive cell components represent a very promising strategy to develop a high energy density, long cycle life and safety enhanced Li-S battery technology.

Micro-/mesoporous nature of carbon nanofiber/silica matrix as an effective sulfur host for rechargeable lithium–sulfur batteries

Lithium–sulfur batteries are considered as promising candidate for next-generation electric vehicles due to their high-energy density and cyclability behaviour. However, the poor conductivity, large volumetric expansion of sulfur and dissolution of the intermediate polysulfides result in poor cyclic stability. Herein, sulfur–silica–carbon nanofiber (S–SiO2–CNF) based ternary composite cathode materials are prepared via simple heat treatment for lithium–sulfur batteries. The prepared materials are physically subjected to x-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, surface area and porosity analyses. The prepared S–SiO2–CNF cathode material exhibits an initial discharge capacity of 801 mAh g−1 at 0.2 C with a decay rate of 0.18% per cycle up to 300 cycles. The significantly enhanced electrochemical performance of the S–SiO2–CNF cathode is ascribed to the micro and mesoporous nature of prepared material and binding nature of silica, which restricting the volume changes of active material and limits the polysulfide dissolution.

Enhanced Electrochemical Performance of MWCNT-Intercalated Silica/Sulfur Composite Cathode for Rechargeable Lithium-Sulfur Batteries

Sulfur (S)/silicon dioxide (SiO2)/multiwalled carbon nanotube (MWCNT) ternary composites with potential application in high-performance lithium-sulfur (Li-S) batteries have been prepared by a heat treatment method. The S/SiO2/MWCNT composite with MWCNT content of 20 wt.% exhibited efficient electrochemical performance for use as a cathode in Li-S batteries, with initial discharge capacity of 926 mAh g−1 and coulombic efficiency of 99% at 0.2 C rate. A discharge capacity of 501 mAh g−1 was observed after 300 cycles with a decay rate of 0.15% per cycle. The average capacity retention was found to be 81.7% and 54.1% after 100 cycles and 300 cycles, respectively. These results demonstrate that a high content of MWCNT improved the electronic conductivity while the SiO2/MWCNT matrix represents a strong physical and chemical host for the polysulfides and active material. This study determines the combined effect of silica and MWCNT to improve the performance of the sulfur cathode.

Hollow MnO2 spheres/porous reduced graphene oxide as a cathode host for high-performance lithium-sulfur batteries

Rechargeable lithium-sulfur (Li-S) batteries, with a theoretical specific energy (2600 ​Wh kg-1) and theoretical specific capacity (1675 ​mAh g-1), are superior to current commercial lithium ion batteries. However, severe capacity fading due to volume breath and polysulfide dissolution greatly hinders the commercialization of Li-S battery. As an attempt to solve the problem, a hollow MnO2 spheres/porous reduced graphene oxide/S (MnO2/RGO/S) composite was synthesized by an one-step hydrothermal method, of which the hollow MnO2 spheres can effectively restrains the volume expansion/contraction of S8 and the dissolution of polysulfides during the charge-discharge processes. Furthermore, 3D RGO with high electronic conductivity can facilitates a fast electronic transfer. The initial specific capacity of the MnO2/RGO/S composite is 1202.0 ​mAh g-1 and remains 577.0 ​mAh g-1 with the coulombic efficiency of 93.2% at 0.2C after 200 cycles, and the capacity retention remains higher than 61.4% of the initial capacity after 100 cycles at 1C, indicating a synergistic effect of hollow MnO2 spheres and conductive 3D RGO.

Electrochemical Behaviors of Sulfurized-Polyacrylonitrile with Synthesized Polyacrylonitrile Precursors Based on the Radical Polymerization Through Monomer Acrylonitrile

Polyacrylonitrile (PAN) precursors have been polymerized at different radical polymerization temperatures for preparing sulfurized-polyacrylonitrile (S-PAN) composite cathodes in rechargeable lithium sulfur battery. The physical properties of these composites have been investigated using X-ray diffraction, Fourier transform infrared spectrometry, Raman spectroscopy, Brunner-Emmet-Teller measurement and Gel permeation chromatography analysis. The electrochemical performance of the S-PAN composite cathodes made from the PAN precursor was investigated. The results showed that the molecular weight distribution of the PAN precursors affected the electrochemical performance of the S-PAN made from the PAN precursor. S-PAN composites derived from PAN with a narrower molecular weight distribution at 65 °C were exhibit the best electrochemical performance in lithium-sulfur battery.

In situ assembly of MnO2 nanosheets on sulfur-embedded multichannel carbon nanofiber composites as cathodes for lithium-sulfur batteries

Rechargeable lithium-sulfur batteries have been regarded as the promising next generation energy storage system due to their overwhelming advantages in energy density. However, their practical implementations are hindered by severe capacity fading and low sulfur utilization, which are caused by polysulfide shuttling and the insulating nature of sulfur. Herein, sulfur-embedded porous multichannel carbon nanofibers coated with MnO2 nanosheets (CNFs@S/MnO2) are rationally designed and fabricated as cathode for lithium-sulfur battery. The high conductivity of porous multichannel carbon nanofibers facilitates the kinetics of electron and ion transport in the electrodes, and the porous structure encapsulates and sequesters sulfur in its interior void space to physically retard the dissolution of high-order polysulfides. Moreover, the MnO2 shell exhibits a combination of physical and chemical adsorption for high-order polysulfides, which could sequester polysulfides leaked from the carbon matrix after long-time charge/discharge cycles, resulting in enhanced cyclic stability. As a result, the electrode delivers a specific capacity of 1286 mA h g−1 at 0.1 C and 728 mA h g−1 at 3 C. And the capacity could remain 774 mA h g−1 after 600 cycles at 1 C.

Theoretical and Experimental Strategies for New Heterostructures with Improved Stability for Rechargeable Lithium Sulfur Batteries

The prowess of Li4SiO4, a known Li-ion conductor for effectively trapping solvents while enabling Li-ion migration contributing to Li-S battery stability was previously demonstrated. Herein Li-ion conductivity enhancement of Li4SiO4 was investigated using first principles calculations and correspondingly, Ca, Mg and F ion substituted Li4SiO4 were shown to yield ∼3–4 order improvement in room temperature Li+ ion conductivities with reduced activation barriers via vacancy mechanism favoring easy diffusion. To demonstrate effects on Li-S battery performance, high sulfur loading cathodes (∼3.8 mg S cm−2) were generated by coating substituted silicates onto sulfur infiltrated copper bipyridine complex framework material (S-Cu-bpy-CFM) electrodes. These ions substituted Li4SiO4 coated sulfur electrodes demonstrated high areal capacities (∼2.21–2.67 mAh cm−2), good capacity retention (∼0.19%–0.33%/cycle) and rate capabilities (∼800 mAh g−1−700 mAh g−1 @100 mA g−1, 600 mAh g−1− 500 mAh g−1 @300 mA g−1, 400 mAh g−1−300 mAh g−1 @ 500 mA g−1 and ∼250 mAh g−1–190 mAh g−1 @1000 mA g−1) contrasted with unsubstituted Li4SiO4. Post cycle electrochemical impedance spectroscopy analysis of the batteries also shows that the difference in charge-transfer resistance (Rct) between the 1st and the 100th cycle is 49.7Ω for the pristine Li4SiO4 coated electrodes while only 2.14Ω is observed for the calcium substituted Li4SiO4 coated cathodes justifying the cycling performance improvements using the ion-substituted Li4SiO4 coating.

Enhanced Chemical Immobilization and Catalytic Conversion of Polysulfide Intermediates Using Metallic Mo Nanoclusters for High-Performance Li-S Batteries.

Rechargeable lithium-sulfur batteries have attracted tremendous scientific attention owing to their high energy density. However, their practical application is greatly hindered by the notorious shuttling of soluble lithium polysulfide (LPS) intermediates with sluggish redox reactions and uncontrolled precipitation behavior. Herein, we report a semiliquid cathode composed of an active LPS solution/carbon nanofiber (CNF) composite layer, capped with a carbon nanotube (CNT) thin film decorated with metallic Mo nanoclusters that regulate the electrochemical redox reactions of LPS. The trace amount (0.05 mg cm-2) of metallic Mo on the CNT film provides sufficient capturing centers for the chemical immobilization of LPS. Together with physical blocking of LPS by the compact CNT film, free diffusion of LPS is significantly restrained and the self-discharge behavior of the Li-S cell is thus effectively suppressed. Importantly, the metallic Mo nanoclusters enable fast catalytic conversion of LPS and regular deposition of lithium sulfide. As a result, the engineered cathode exhibits a high active sulfur utilization (1401 mAh g-1 at 0.1 C), stable cycling (500 cycles at 1 C with 0.06% decay per cycle), high rate performance (694 mAh g-1 at 5 C), and low self-discharge rate (3% after 72 h of rest). Moreover, a high reversible areal capacity of 4.75 mAh cm-2 is maintained after 100 cycles at 0.2 C for a cathode with a high sulfur loading of 7.64 mg cm-2. This work provides significant insight into the structural and materials design of an advanced sulfur-based cathode that effectively regulates the electrochemical reactions of sulfur species in high-energy Li-S batteries.

Carbon paper with attached hollow mesoporous nickel oxide microspheres as a sulfur-hosting material for rechargeable lithium-sulfur batteries

Hollow nickel hydroxide microspheres built of nanosheets could be obtained by hydrothermal synthesis in the presence of glycine. After heating to 400 °C in air, the hexagonal β-Ni(OH)2 was converted into cubic NiO which showed better electrical conductivity and greater surface area compared with other annealing temperatures. The surface morphology remained almost unchanged, while the Ni(OH)2 nanosheets with solid interior were changed into NiO nanosheets composed of interconnected nanoparticles and mesopores after annealing at 400 °C. The sulfur-filled hollow mesoporous NiO microspheres obtained after annealing at 400 °C was loaded into the carbon paper as cathode (NiO/S) for lithium-sulfur batteries. The NiO/S cathode could deliver a large specific capacity of 1300 mAh g−1 at 0.2C (335 mA g−1), much greater than bare sulfur loaded into the carbon paper (1000 mAh g−1). Moreover, the NiO/S cathode showed superior capacity recovery after C-rate test and coulombic efficiency during cycling test than S cathode. The improved performance for NiO/S could be attributed to the conductive NiO microspheres with mesoporous nanosheets that provided intimate electrical contact for boosting the charge-transfer reaction between lithium ions and sulfur materials, limited the polysulfide shuttle, and buffered volumetric expansion/contraction during charging and discharging.

Separator coatings as efficient physical and chemical hosts of polysulfides for high-sulfur-loaded rechargeable lithium–sulfur batteries

Abstract Lithium–sulfur batteries (LSBs) are promising alternative energy storage devices to the commercial lithium-ion batteries. However, the LSBs have several limitations including the low electronic conductivity of sulfur (5 × 10−30 S cm−1), associated lithium polysulfides (PSs), and their migration from the cathode to the anode. In this study, a separator coated with a Ketjen black (KB)/Nafion composite was used in an LSB with a sulfur loading up to 7.88 mg cm−2 to mitigate the PS migration. A minimum specific capacity (Cs) loss of 0.06% was obtained at 0.2 C-rate at a high sulfur loading of 4.39 mg cm−2. Furthermore, an initial areal capacity up to 6.70 mA h cm−2 was obtained at a sulfur loading of 7.88 mg cm−2. The low Cs loss and high areal capacity associated with the high sulfur loading are attributed to the large surface area of the KB and sulfonate group (SO3−) of Nafion, respectively, which could physically and chemically trap the PSs.

AlF3 coating as sulfur immobilizers in cathode material for high performance lithium-sulfur batteries

Although the rechargeable lithium-sulfur battery is an advanced energy storage system, their practical implementation has been impeded by many issues, in particular the ‘shuttle effect’ causing rapid capacity fade and low coulombic efficiency. Herein, the AlF3 coating, prepared via a facile solution-based method, is used as sulfur immobilizers in cathodes for Li–S batteries for the first time. The physical confinement, chemical anchoring and catalysis conversion for polysulfide are achieved simultaneously through the existence of the AlF3 coating, which is confirmed by experimental results. Meanwhile, the CNTs improved the electrical conductivity of composite materials significantly, and a suitable three-dimensional conductive framework was formed to accommodate sulfur. Due to these merits, the as-designed composite materials of carbon nanotubes-sulfur coating by aluminum fluoride (CNTs-S@AlF3) cathode exhibited excellent electrochemical properties and stable capacity retention. The initial discharge capacity reaches 1144.1 mAh g−1 and after 250 cycles is 783 mAh g−1 at 1 C, which is much higher than the composite materials of without AlF3 coating. Moreover, the CNTs-S@AlF3 cathode presents excellent long-term capacity stability with a capacity decay of 0.062% per cycle during 1000 cycles at 0.5 C, offering a potentiality for use in high energy Li–S batteries.

Enhanced Electrochemical Performance of Simple Electrospun Non-Woven Nickel/Carbon Nanofibers as a Functional Interlayer for Lithium-Sulfur Batteries.

Non-woven nickel/carbon nanofibers (NW(Ni/C)NFs) are developed using a facile one-pot electrospinning method as a functional interlayer for rechargeable lithium-sulfur (Li-S) batteries. The functional interlayer of NW(Ni/C)NFs is sandwiched between a sulfur cathode and the separator and acts as a shuttle inhibitor to sulfur and polysulfides. Because of the sandwiched structure and the nickel additive, the Li-S cell shows better performance in terms of capacity utilization and reversibility. When the NW(Ni/C)NFs were calcined at 900 °C with 1 g of nickel salt additive, the discharge capacity of the cells was the best, and the initial discharge capacity was 1062 mAh g-1. With 200 charge-discharge cycles at 1 C, the discharge capacity of the cells remained above 910 mAh g-1, which is about 85.7% of its initial capacity. The improvement to the cells' electrochemical performance is attributed to the 3D architecture of the NW(Ni/C)NFs as a functional interlayer and to the appropriate amount of nickel addition. This provides a good conductive network with structural stability and the migrating polysulfide reduces the "shuttling phenomenon" during the charge-discharge processes.

Performance Enhancement of Rechargeable Lithium-Sulfur Battery Utilizing High Mass-Loading Cathodes of Azulmic Carbon Composite

A sulfur (S) cathode has a high theoretical capacity (1,672 mAh g-1). However, a major problem is the behavior of Li polysulfide (Li2Sn) intermediates, which may dissolve into an electrolyte. If dissolution of Li2Sn occurs, this should lead to a rapid capacity decay. We have investigated microporous activated carbon as matrix stabilizing S and realized stable cycling performance.1-2 However, the S content (ca.30 wt.%) and S loading were relatively low, which remains to be improved. To enhance them, in this study we applied azulmic carbon(AZC)3 with a large pore volume and also a porous 3-D Al current collector. Using these materials together with our fluorinated electrolyte, we have successfully realized stable and high capacity of the S-based cathode. Methods: azulmic carbon (AZC) used in this study was an alkaline-activated type with basically micropores with some meso pores more than 2 nm in diameter. The AZC-S composite was prepared by mixing AZC with S at a weight ratio of AZC: S = 45:55, and then applying heat treatment: 155°C for 5 h, then 300°C for 2 h. The AZC-S composite cathode was prepared by mixing the AZC-S composite, acetylene black, and alginate binder at a respective weight ratio of 90:5:5 and loading the resulting slurry into a 3-D Al current collector, “celmet (Sumitomo Electric Industries)”. The electrolyte was 1.0 mol dm-3 LiTFSI/FEC:HFE(1:1) +VC [9+1] (by vol.). All the cell components were installed into a pouch cell with a Li anode. A typical charge-discharge cycling test was carried out at 167.2 mA g-1 (0.1 C) with cutoff voltages of 3.0 and 1.0 V at 25°C. Major results and conclusion: we carried out the thermogravimetric analysis of elemental S and the AZC. The weight loss of AZC-S corresponds to the S content: 55 wt.%. The resulting S mass loading into the 3-D collector was 8.2 mg cm-2. We also investigated the discharge capacities in 1.0 mol dm-3 /FEC: HEF+VC (vinylene carbonate) electrolyte and also 2.0 mol dm-3/EC: DMC+VC electrolyte during cycling. The present fluorinated electrolyte contributed to stable discharge capacity showing 505 mAh (g-S)-1 at the 300th cycle. We found that there was a reduction at the surface of the sulfur at the first discharge, and excellent SEI was formed. It protected from direct contact with the electrolyte. The fluorinated electrolyte is, therefore, applicable to AZC even including the meso pores more than 2 nm as pore size. On the other hand, the carbonate electrolyte system showed two plateaus in the discharge curve at the first cycle. The carbonate electrolyte penetrated into the meso pores and the dissolution of Li2Sn occurred. As a result, the discharge capacity showed only 317 mAh (g-S)-1 at the 170th cycle. Thus, using the fluorinated electrolyte enabled the present activated carbon to cycle, as the meso porous carbon containing a large amount of sulfur. We will also report other results in the improvement of discharge capacity by ball-milling and heat treatment for AZC. This work was supported by “Advanced Low Carbon Technology Research and Development Program, Specially Promoted Research for Innovative Next Generation Batteries (ALCA-SPRING)” from JST.[1] T. Takahashi et al., Prog. Nat. Sci., 25 (2015) 612. [2] S. Okabe et al., Electrochemistry, 85 (2017) 671.[3] S. Usuki et al., Electrochemistry, 85 (2017) 650. Figure 1

Rational Design of Highly Packed, Crack-Free Sulfur Electrodes by Scaffold-Supported Drying for Ultrahigh-Sulfur-Loaded Lithium-Sulfur Batteries.

Despite the notable progress in the development of rechargeable lithium-sulfur batteries over the last decade, achieving high performance with high-sulfur-loaded sulfur cathodes remains a key challenge on the path to the commercialization of practical lithium-sulfur batteries. This paper presents a novel method by which to fabricate a crack-free sulfur electrode with anultrahigh sulfur loading (16 mg cm-2) and a high sulfur content (64%). By introducing a porous scaffold on the top of a cast of sulfur cathode slurry, the formation of cracks during the drying of the cast can be prevented due to the lower volume shrinkage of the skin. The scaffold-supported sulfur cathode delivers anotably high capacities of 10.3 mAh cm-2 and 473 mAh cm-3 after a prolonged cycle, demonstrating that the crack-free structure renders more uniform redox reactions at such high sulfur loading. The highly packed, crack-free feature of the sulfur cathode is advantageous, given that it reduces the electrolyte uptake to as low as an E/S ratio of 4 μL mg-1, which additionally contributes to the high energy density. Therefore, the scaffold-supported drying fabrication method as presented here provides an effective route by which to design practically viable, energy-dense lithium-sulfur batteries.

Novel Tailored 3D Carbon Nanotube Cathodes for Effective Trapping of Polysulfides in Lithium Sulfur Batteries

Lithium-sulfur batteries are one of the most promising Li-Ion batteries. Sulfur, with the highest gravimetric capacity of all cathode materials, allows a theoretical energy density that is five times higher than state of the art rechargeable batteries. Furthermore, sulfur is a cheap and earth abundant material, which makes it possible to be used in large-scale applications. Hereby, progress in the field of mobile energy storage can be achieved.[1]However, rechargeable lithium-sulfur batteries still suffer from the intrinsic problems of sulfur in the battery environment. The insulating character, the expansion of sulfur during cycling as well as the well-known polysulfide shuttle effect are still a challenge and are studied with great effort. The phenomena described lead to lowered sulfur utilization and loss of active material during cycling, resulting in an overall reduced energy density and a continuous fading of the battery capacity, unsuitable for practical applications. The shuttle effect, characterized by the dissolution of sulfur into the electrolyte during cycling, is still a major concern, but can be reduced by using for example nanomaterials.[2][3]Much of the research is done on the electrolyte or electrode composition, but the structural design of the cathode plays major role. The use of nanomaterials based on carbon, such as graphene, graphene oxide or carbon nanotubes, have shown already huge potential in the use as a cathode scaffold material.³ However, these materials need to be arranged into a macroscopic 3D structure to make use of their extraordinary electrical and mechanical properties. The approach presented here is based on the fabrication process established in a previous work[4], for the preparation of an open porous 3D self-organized hierarchical carbon nanotube tube network, used to minimize the shuttle effect. A highly porous 3D network based on tetrapodal zinc oxide[5] is coated with carbon nanotubes using wet chemical techniques. The tetrapodal zinc oxide is used as a removable scaffold material, giving the cathode a defined 3D structure. After zinc oxide removal, a conductive, mechanically stable, 3D scaffold of carbon nanotubes remains possessing a hierarchical porous structure. The structure has a large pore to volume ratio and therefore a large reachable surface inside the cathode material. By employing these open porous network structures in combination with sulfur vapour deposition methods, the sulfur is homogenously distributed throughout the structure, improving the sulphur utilization and improving the overall contact to the highly conductive carbon host scaffold. In addition the structure of the network acts as a trap for polysulfide due to tailorable micro and macro pores, reducing capacity fading of the battery from the shuttle effect. The performance of these sulphur cathodes was shown to be almost constant from the 5th to the 50th cycle with a capacity of 950mAh/g and sulfur loadings up to 50wt.%. This novel electrode design is able to counteract the polysulfide-shuttle effect, withstand the expansion of sulfur during cycling, and offers promising results in the battery performance. [1] Manthiram, Arumugam; Fu, Yongzhu; Chung, Sheng-Heng; Zu, Chenxi; Su, Yu-Sheng (2014): Rechargeable lithium-sulfur batteries. In: Chemical reviews 114 (23), S. 11751–11787. DOI: 10.1021/cr500062v. [2] Liquid electrolyte lithium/sulfur battery. Fundamental chemistry, problems, and solutions (2013). In: Journal of Power Sources 231, S. 153–162. [3] Wang, Hailiang; Yang, Yuan; Liang, Yongye; Robinson, Joshua Tucker; Li, Yanguang; Jackson, Ariel et al. (2011): Graphene-Wrapped Sulfur Particles as a Rechargeable Lithium–Sulfur Battery Cathode Material with High Capacity and Cycling Stability. American Chemical Society [4]Schütt, Fabian; Signetti, Stefano; Krüger, Helge; Röder, Sarah; Smazna, Daria; Kaps, Sören et al. (2017): Hierarchical self-entangled carbon nanotube tube networks. In: Nature Communications 8 (1), S. 1215. DOI: 10.1038/s41467-017-01324-7. [5] Mishra, Yogendra Kumar; Adelung, Rainer (2018): ZnO tetrapod materials for functional applications. In: Materials Today 21 (6), S. 631–651. DOI: 10.1016/j.mattod.2017.11.003.

Three-Dimensional Graphene-Heteroatom-Doped Carbon Nanotubes Hierarchical Architecture As a Polysulfide Trap for Lithium-Sulfur Batteries

Recently, lithium–sulfur (Li–S) batteries have attracted tremendous attention as a strong candidate of replacing current lithium ion batteries due to the high theoretical capacity of 1675 mAh g−1, natural abundance, and low cost of sulfur cathode. However, the practical use of Li-S batteries is hindered by their low specific capacity, low coulombic efficiency, poor rate capability, and poor cycling stability caused by the low conductivity of sulfur, dissolution of polysulfides in the electrolyte and their redox shuttling/parasitic reactions and high volume expansion during discharge. Therefore, the structural design and synthesis of sulfur-carbon composite materials with high performance and long cycleability are a major challenge for rechargeable lithium-sulfur batteries. Interconnected three-dimensional frameworks comprising heteroatom-doped carbon nanotube and graphene oxide offer a combination of constituent advantages and can thus be used to achieve superior energy conversion and storage properties. Herein, we present an easily scalable, room-temperature/ambient-pressure chemical pathway for the synthesis of highly functioning cathode materials using electrostatically assembled, heteroatom-doped carbon nanotube materials. Moreover, we designed and prepared free-standing three-dimensional interlayer containing interconnected heteroatom-doped carbon nanotube. The interlayer provides a medium for scavenging the lithium polysulfides and suppressing them from diffusing to the anode side during charging/discharging. Lithium-sulfur batteries fabricated with the thus prepared sulfur/heteroatom-doped carbon nanotubes composite paper cathode and heteroatom-doped carbon nanotube interlayer exhibit high reversible capacity, stable cycling performance, and excellent rate capability. Thus, we expect the unique architecture of the above composite papers to provide a possible platform for high-performance Li-S batteries and facilitate their further development.

Porous honeycomb-like C3N4/rGO composite as host for high performance Li-S batteries

Lithium-sulfur (Li-S) batteries have attracted extensive attention along with the urgent increasing demand for energy storage owing to the high theoretical specific capacity and energy density, abundant reserves and low cost of sulfur. However, the practical application of Li-S batteries is still impeded due to the low utilization of sulfur and serious shuttle-effect of lithium polysulfides (LiPSs). Here, we fabricated the porous honeycomb-like C3N4 (PHCN) through a hard template method. As a polar material, graphitic C3N4 has abundant nitrogen content (∼58%), which can provide enough active sites to mitigate shuttle-effect, and then conductive reduced graphene oxide (rGO) was introduced to combine with PHCN to form PHCN/rGO composite in order to improve the utilization efficiency of sulfur. After sulfur loading, the PHCN/rGO/S cathode exhibited an initial discharge capacity of 1,061.1 mA h g−1 at 0.2 C and outstanding rate performance at high current density of 5 C (495.1 mA h g−1), and also retained 519 mA h g−1 after 400 cycles at 1 C. Even at high sulfur loading (4.3 mg cm−2), the capacity fade rate was only 0.16% per cycle at 0.5 C for 200 cycles. The above results de monstrate that the special design of PHCN/rGO composite as sulfur host has high potential application for Li-S rechargeable batteries.