Free-Standing and Flexible Carbon Membrane for Lithium-Sulphur Batteries

Graphene oxide; Sulfur/carbon composite; Graphene nanoscroll; Metal oxides nanowires; Interlayer; Li−S batteries Nowadays, the growing grievous environmental problems together with the exhaustion of energy resources put urgent demands for developing high energy density devices, whereas traditional lithium-ion batteries (LIBs) are getting close to their energy density. Consideration of the factors including capacity, resource and environment, lithium sulfur (Li-S) batteries are the most potential lithium secondary batteries.[1] However, many drawbacks need to be overcome before its industrial application, such as low electronic conductivity of sulfur, serious shuttling effects of dissolution polysulfides, volume change of electrode during charging-discharging process and problems such as lithium dendrites, passivation and corrosion of lithium anode. This work aims to improve the properties of Li-S batteries by preparation of sulfur/carbon composite cathode materials and building high-efficiency interlayer .[2-4] Firstly, a modified lyophilization approach is developed and used for highly efficient transformation of 2D graphene oxide sheet into 1D graphene nanoscroll (GNS) with high topological transforming efficiency (94%). Because of the unique open tubular structure and large specific surface area (545 m2 g−1), GNS is utilized for the first time as a porous cathode scaffold for encapsulating sulfur with a high loading (81 wt%). The interlayer space and pores of obtained GNS provide large sites for sulfur loading, and this unique structure can accommodate volume expansion and prevent the dissolution of polysulfides. As a result, the composite deliver good rate performance and cycling stability (the capacity decay is only 0.04% per cycle after 400 cylces at 2C).[5] Furthermore, a flexible self-standing hybrid interlayer is engineered by intertwining one-dimensional (1D) metal oxides nanowires (NWs) with GNS into a robust interconnected 3D network to be used as both an upper current collector and physical/chemical polysulfide-trapper. Combining GNS with MnO2, V2O5 and MoO3 respectively, free-standing membranes are obtained to serve as interlayers for Li-S battery (namely, GNSMn, GNSV and GNSMo). The highly conductive and open GNS framework provides bicontinuous transfer channels for rapid electron and ion transport across the cathode/separator interface. Meanwhile, the metal oxides nanowires act as ideal redox mediators to dynamically block polysulfide dissolution and facilitate their conversion into sulfides via formation of active intermediate polythionate complexes. Even though GNSV is used as an interlayer for lithium sulfur battery with bare sulfur as cathodethese cells with 70 wt% sulfur content in the whole cathode have significantly improved performance with a long cycling life (1000 cycles), low capacity decay (0.041% per cycle), and considerable areal capacity (>4 mA h cm- 2), even at a high sulfur loading of 5.5 mg cm- 2. This novel interlayer design strategy has great potential for promoting the practical use of Li–S batteries.[6] In summary, the work described here shows a potential of GNS as a promising functional carbon material to realize high sulfur loading and electrochemically stable electrode configuration aimed toward developing high-performance Li−S batteries. Figure 1 (a) SEM images and (b) TEM images of GNS, (c) schematic illustration on the advantages in entrapping polysulfides of the S@GNS (insert: typical colors of the cycled S@GNS and Gs-S cathodes after soaking in a mixture of DOL/DME for 24 h), (d) schematic model of the cell (insert: photos of the free-standing and flexible GNSM interlayer).

Li-S batteries are among the most promising candidates for the next generation rechargeable batteries due to their high energy density, low raw material cost and environmental friendliness [1]. Despite this great potential, the complicated electrochemical process introduces many challenges for Li-S batteries, including low conductivity of both elemental sulfur and end discharge product Li2S, large volume expansion of 80% upon discharge, and unfavorable redox shuttle effect due to soluble nature of intermediate lithium polysulfide LiPS [2,3]. Although Li-S batteries possess a high theoretical cathode specific capacity of 1,672 mAh g-1, the energy density of practical Li-S batteries is much smaller and depends on electrolyte/sulfur (E/S in mL g-1) ratio. From previous works, successful operation of Li-S batteries under lean electrolyte conditions can be challenging, especially in the case when the solubility of LiPS sets an upper bound for polysulfide dissolution. Very recently, we have demonstrated that the E/S ratio of Li-S cells has a significant effect on both performance and theoretical energy density of Li-S batteries. Since the lower-bound for E/S ratio is restricted by the solubility of LiPS in the organic electrolyte, the theoretical energy density of Li-S batteries is significantly reduced. Experimentally, it was approved that when the LiPS concentration reached to the solubility limitation in the electrolyte, the reaction rate of reducing sulfur to LiPS in the cathode will reduce significantly [4]. In this talk, we will discuss the relationship between theoretical specific energy and the solubility of LiPS in the electrolyte. The theoretical specific energy of a Li-S battery can be expressed as: e=CLVcell/(MC+MA+Mele) (1) where, CL is the lower capacity in amount of cathode and anode, Vcell is the cell voltage (e.g. 2.1 V), MC, MA, Mele are weights of sulfur (cathode), lithium (anode), and electrolyte, respectively. In an ideal case, capacities of cathode and anode are equal and to be MA=2×6.94MC/32.065, the atomic weights of lithium and sulfur are 6.94 and 32.065 g/mol, respectively, the capacity is CL=cSMC where cS=1,672 mAh/g is the theoretical specific capacity of sulfur. The minimum weight ratio of electrolyte to sulfur is: Mele/MC=rele/32.065S (2) where, rele is the mass density of electrolyte (e.g. 1.2 g/cm3) and S is the solubility of LiPS in unit of M[S]/L; therefore, the theoretical specific energy for a Li-S battery is: e=3511/(1.4327+37.42/S[M/L])[Wh/kg] (3) Fig. 1 shows the theoretical specific energy of Li-S batteries when the LiPS solubility is considered as an intrinsic limitation for Li-S battery capacity. Here only the weight of active electrode material, such as sulfur and lithium, as well as electrolyte weight is included in calculation. From Fig. 1, it can be seen that for commonly used electrolytes with LiPS solubility less than 8 M[S]/L, the theoretical energy is less than 575 Wh/g. Fig. 2 further presents a series of specific energy calculation for Li-S battery with different E/S ratios. From Fig. 2(a), it can be seen that the electrolyte weight would dominate in a Li-S battery even in relatively low E/S conditions. Fig. 2(b) plots the effective theoretical specific capacity of a Li-S battery. Fig. 2(c) that the reduced effective specific capacity introduced by LiPS solubility limit would offset electrolyte weight loss under low E/S conditions, making the theoretical specific energy curve relatively flat under low E/S region, while without considering LiPS solubility the specific energy will increase sharply when E/S ratio is decreased. The above results imply that reducing E/S ratio would become pointless when LiPS solubility is reached. For further boosting capacity of Li-S batteries, electrolyte with even higher LiPS solubility is favorable. Fig. 2(d) plots the specific energy of an ideal Li-S cell under different LiPS solubility. Reference: [1] A. Manthiram, Y. Fu, S. Chung, C. Zu, Y. Su, Rechargeable Lithium–Sulfur Batteries, Chem. Rev. 114 (2014) 11751–11787. [2] Z.W. Seh, Y. Sun, Q. Zhang, Y. Cui, Designing high-energy lithium–sulfur batteries, Chem. Soc. Rev. (2016). [3] W. Kang, N. Deng, J. Ju, Q. Li, D. Wu, X. Ma, et al., A review of recent developments in rechargeable lithium-sulfur batteries, Nanoscale. 1 (2016) 16541–16588. [4] C. Shen, J. Xie, M. Zhang, J.P. Zheng, M. Hendrickson, and E.J. Plichta, J. Electrochem. Soc., 164 (2017) A1220-A1222. Figure 1

Rechargeable lithium-sulfur (Li-S) batteries have emerged as the most promising electrochemical energy storage systems due to their high energy density, wide range of temperature operation, cost effectiveness, and eco-friendly in nature. Nevertheless, the drawbacks associated with the Li-S batteries such as insulating nature of sulfur species, corrosive nature of predeposited polysulfides at electrodes during discharge-charge processes, and formation of thick SEI layer still need to be circumvented. One of the promising ways to alleviate these problems is to use highly porous, conductive, and active species which can improve the kinetics of polysulfide conversion reactions and diffusion processes. In this context, we have investigated electronically conductive species incorporated graphene, specifically Metal/graphene hybrids (metal = Pt, Ni, and Co) as cathode in Li-S batteries and performed systematic studies to understand the electrochemical behavior of polysulfides during discharge-charge processes. Metal/graphene hybrids were prepared through wet chemical routes and employed them as electrodes for the conversion of polysulfides in Li-S batteries. Structural and morphological techniques depicted phase purity of the materials and well-dispersed metallic nanocrystallites with an average size of 5 nm on the graphene sheets. Electrochemical studies were carried out by assembling Li/sulfur cells inside glove box using a porous metal/graphene as electrodes cathode, 0.6M Li2S8-1M LiTFSI in TEGDME as electrolyte, and metallic lithium as anode. Galvanostatic discharge-charge tests indicated a two-fold increment in the Li-S battery performance with metal/graphene compared to pure graphene. A high discharge capacity of 750 mAh/g at C-rates of C/10 has been observed with Pt/graphene. The studies on metal/graphene based Li-S battery revealed pivotal role of metallic nanoparticles in enhancing the polysulfide conversion processes. # - Corresponding Author - leela.arava@wayne.edu

Water-based phytic acid-crosslinked supramolecular binders for lithium-sulfur batteries

The sluggish kinetics of lithium-sulfur (Li-S) batteries severely impedes the application in extreme conditions. Bridging the sulfur cathode and lithium anode, the electrolyte plays a crucial role in regulating kinetic behaviors of Li-S batteries. Herein, we report a multifunctional electrolyte additive of phenyl selenium bromide (PhSeBr) to simultaneously exert positive influences on both electrodes and the electrolyte. For the cathode, an ideal conversion routine with lower energy barrier can be attained by the redox mediator and homogeneous catalyst derived from PhSeBr, thus improving the reaction kinetics and utilization of sulfur. Meanwhile, the presence of Se-Br bond helps to reconstruct a loose solvation sheath of lithium ions and a robust bilayer SEI with excellent ionic conductivity, which contributes to reducing the de-solvation energy and simultaneously enhancing the interfacial kinetics. The Li-S battery with PhSeBr displays superior long cycling stability with a reversible capacity of 1164.7 mAh g-1 after 300 cycles at 0.5 C rate. And the pouch cell exhibits a maximum capacity of 845.3 mAh and a capacity retention of 94.8 % after 50 cycles. Excellent electrochemical properties are also obtained in extreme conditions of high sulfur loadings and low temperature of -20 °C. This work demonstrates the versatility and practicability of the special additive, striking out an efficient but simple method to design advanced Li-S batteries.

Lithium-sulfur (Li-S) batteries have been intensively investigated as a next-generation rechargeable battery due to their high energy density of 2600 W·h kg(-1) and low cost. However, the systemic issues of Li-S batteries, such as the polysulfide shuttling effect and low Coulombic efficiency, hinder the practical use in commercial rechargeable batteries. The introduction of a conductive interlayer between the sulfur cathode and separator is a promising approach that has shown the dramatic improvements in Li-S batteries. The previous interlayer work mainly focused on the physical confinement of polysulfides within the cathode part, without considering the further entrapment of the dissolved polysulfides. Here, we designed an ultrathin poly(acrylic acid) coated single-walled carbon nanotube (PAA-SWNT) film as a synergic functional interlayer to address the issues mentioned above. The designed interlayer not only lowers the charge transfer resistance by the support of the upper current collector but also localizes the dissolved polysulfides within the cathode part by the aid of a physical blocking and chemical bonding. With the synergic combination of PAA and SWNT, the sulfur cathode with a PAA-SWNT interlayer maintained higher capacity retention over 200 cycles and achieved better rate retention than the sulfur cathode with a SWNT interlayer. The proposed approach of combining a functional polymer and conductive support material can provide an optimiztic strategy to overcome the fundamental challenges underlying in Li-S batteries.

Many problems associated with Li-S and Na-S batteries essentially root in the generation of their soluble polysulfide intermediates. While conventional wisdom mainly focuses on trapping polysulfides at the cathode using various functional materials, few strategies are available at present to fully resolve or circumvent this long-standing issue. In this study, we propose the concept of sulfur-equivalent cathode materials, and demonstrate the great potential of amorphous MoS3 as such a material for room-temperature Li-S and Na-S batteries. In Li-S batteries, MoS3 exhibits sulfur-like behavior with large reversible specific capacity, excellent cycle life, and the possibility to achieve high areal capacity. Most remarkably, it is also fully cyclable in the carbonate electrolyte under a relatively high temperature of 55 °C. MoS3 can also be used as the cathode material of even more challenging Na-S batteries to enable decent capacity and good cycle life. Operando X-ray absorption spectroscopy (XAS) experiments are carried out to track the structural evolution of MoS3 It largely preserves its chain-like structure during repetitive battery cycling without generating any free polysulfide intermediates.

Lithium-sulfur (Li-S) batteries are considered as one of the most potential next-generation rechargeable batteries due to their high theoretical energy density. However, some critical issues, such as low capacity, poor cycling stability, and safety concerns, must be solved before Li-S batteries can be used practically. During the past decade, tremendous efforts have been devoted to the design and synthesis of electrode materials. Benefiting from their tunable structural parameters, hollow porous carbon materials (HPCM) remarkably enhance the performances of both sulfur cathodes and lithium anodes, promoting the development of high-performance Li-S batteries. Here, together with the templated synthesis of HPCM, recent progresses of Li-S batteries based on HPCM are reviewed. Several important issues in Li-S batteries, including sulfur loading, polysulfide entrapping, and Li metal protection, are discussed, followed by a summary on recent research on HPCM-based sulfur cathodes, modified separators, and lithium anodes. After the discussion on emerging technical obstacles toward high-energy Li-S batteries, prospects for the future directions of HPCM research in the field of Li-S batteries are also proposed.

As a secondary Li-ion battery with high energy density, lithium-sulfur (Li-S) batteries possess high potential development prospects. One of the important ingredients to improve the safety and energy density in Li-S batteries is the solid-state electrolyte. However, the poor ionic conductivity largely limits its application for the commercial market. At present, the gel electrolyte prepared by combining the electrolyte or ionic liquid with the all-solid electrolyte is an effective method to solve the low ion conductivity of the solid electrolyte. We present a cross-linked gel polymer electrolyte with fluoroethylene carbonate (FEC) as a solid electrolyte interface (SEI) film formed for Li-S quasi-solid-state batteries, which can be simply synthesized without initiators. This gel polymer electrolyte with FEC as an additive (GPE@FEC) possesses high ionic conductivity (0.830 × 10-3 S/cm at 25 °C and 1.577 × 10-3 S/cm at 85 °C) and extremely high Li-ion transference number (tLi+ = 0.674). In addition, the strong ability toward anchoring polysulfides resulting in the high electrochemical performance of Li-S batteries was confirmed in GPE@FEC by the diffusion experiment, X-ray photoelectron spectroscopy analysis (XPS), and scanning electron microscopy (SEM) mapping of the S element. Such a high ion conductivity (IC) gel polymer electrolyte enables a competitive specific capacity of 940 mAh/g at 0.2C and supreme cycling performance for 180 cycles at 0.5C, which is far beyond that of conventional poly(ethylene oxide)-based quasi-solid-state Li-S batteries.

Lithium–sulfur (Li–S) batteries have the highest theoretical gravimetric energy density among sealed rechargeable batteries. S has, however, negligeable electronic conductivity and its reaction intermediates are easily eluted into an electrolyte, and these problems must be solved for aiming at practical Li-S batteries.1 We have confined S in a microporous carbon (C) material to allow electrons to enter and exit S and to stably retain S and its reaction intermediates.2 This strategy enabled stable charging and discharging of S with any electrolyte, but the percentage of S in the cathode was relatively poor: less than 50 wt.%. We have, therefore, utilized a specific nitrogen-containing C precursor as a porous C material, so we succeeded in loading as much as 75 wt.% of S in the cathode.3,4 We also worked on improving the porous C surface and found that surface oxidation treatment providing oxygen functionalities and polymer modification treatment.5 are effective in improving capacity as well as cycle stability. We also developed electrolytes suitable for such S-C composite cathodes. In this process, we designed electrolytes that do not leach S-reaction intermediates even when the cathode pore size is mesoporous.6 Furthermore, because the use of microporous C increases the degree of freedom in electrolyte design, we succeeded in developing excellent electrolytes that are compatible with both cathode and Li anode.7–10 It has become clear that the positive electrode reactions of sulfur in our research are all progressing as quasi-solid-state reactions, which enables stable charge-discharge cycle behavior and the use of small amounts of electrolyte.This presentation partly includes the results of JST ALCA-SPRING Project, grant number: JPMJAL1301, Japan as well as JST GteX Project: grant number: JPMJGX23S0, Japan. We would like to acknowledge the support from these projects. References M. Ishikawa et al., Part Ⅳ 32 in “Next generation batteries - Realization of high energy density rechargeable batteries” Springer (2021).T. Takahashi, M. Ishikawa et al., A sulfur–microporous carbon composite positive electrode for lithium/sulfur and silicon/sulfur rechargeble batteries, Prog. Nat. Sci. 25 (2015) 612.T. Tonoya, Y. Matsui, M. Ishikawa, Microporous activated carbon derived from azulmic acid precursor with high sulfur loading and its application to lithium-sulfur battery cathode, Electrochem. Commun. 140 (2022) 107333.T. Tonoya, Y. Matsui, M. Ishikawa et al., Capacity decay mechanism of lithium-sulfur batteries using a microporous activated carbon-sulfur composite as cathode material, J. Phys. Chem. C, 127 (2023) 10038.L. Yoshida, Y. Matsui, M. Ishikawa et al., Polyglycerol-functionalized microporous carbon/sulfur cathode for Li-S battery, Electrochim. Acta, 429 (2022) 141000.Y. Torii, Y. Matsui, M. Ishikawa et al., Preventing capacity fading in lithium–sulfur batteries using sulfur confinement in mesoporous carbon and fluorinated solvent-based electrolyte, J. Phys. Chem. C, 127 (2023) 15069.L. Yoshida, Y. Matsui, M. Watanabe, M. Ishikawa et al., Improvement of lithium-sulfur battery performance by porous carbon selection and LiFSI/DME electrolyte optimization, ACS Appl. Mater. Interfaces, 15 (2023) 37467.Y. Shimoda, Y. Matsui, M. Ishikawa et al., Potassium bis(fluorosulfonyl)imide is an effective additive for improving anode cyclability in sulfolane-based electrolytes for Li-S batteries, ACS Appl. Energy Mater. 6 (2023) 8909.T. Tonoya, Y. Matsui, M. Ishikawa, A tuned ether electrolyte for microporous carbon-based lithium-sulfur batteries enabling long cycle life and high specific capacity, Electrochemistry, 92 (2024) 77007.T. Hakari, M. Ishikawa et al, Fully carbonate-electrolyte-based high-energy-density Li–S batteries with solid-phase conversion, Carbon Energy, 6 (2024) e585.

Engineering rare earth metal Ce-N coordination as catalyst for high redox kinetics in lithium-sulfur batteries

Lithium-sulfur (Li-S) battery is a promising choice for the next generation of high-energy rechargeable batteries, but its application is impeded by the high dissolution of the polysulfides in commonly used organic electrolyte. Room temperature ionic liquids (RTILs) have been considered as appealing candidates for the electrolytes in Li-S batteries. We investigated the effect of cations in RTILs on the electrochemical performance for Li-S batteries. Ex situ investigation of lithium anode for Li-S batteries indicates that during the discharge/charge process the RTIL with N-methyl-N-propylpyrrolidine cations (P13) can effectively suppress the dissolution of the polysulfides, whereas the RTIL with 1-methyl-3-propyl imidazolium cation (PMIM) barely alleviates the shuttling problem. With 0.5 mol L−1 LiTFSI/P13TFSI as the electrolyte of Li-S battery, the ketjen black/sulfur cathode material exhibits high capacity and remarkable cycling stability, which promise the application of the P13-based RTILs in Li-S batteries.

Synergistic regulation of polysulfides immobilization and conversion by MOF-derived CoP-HNC nanocages for high-performance lithium-sulfur batteries

Advanced energy-storage technologies are urgently needed to satisfy the energy demands of the society. Sulfur is an appealing candidate for high energy-density batteries, owing to its high theoretical capacity (1,675 mA h g-1), natural abundance, and low cost.1-3 However, the rapid capacity degradation, low Coulombic efficiency, and short cycle life originating from polysulfide dissolution and migration remain challenging for the practical application of lithium-sulfur (Li-S) batteries.4, 5 Our previous reports have demonstrated that configuring interlayers between the separator and the sulfur cathode is an effective and convenient strategy to alleviate the shuttle effect.6 However, most of those interlayers are fabricated by vacuum-filtration method, which makes those polar materials easily stack together and thus form a very thick interlayer. Therefore, on the one hand, the transport of lithium ions will be limited by the thick polar interlayers, which is not desirable for fast insertion/de-insertion of Li ions and high rate capacity. On the other hand, the stacked thick interlayers, as an inactive material, will decrease the overall cell energy density. To address such issues, we present here a novel Co9S8 nanowall array with vertical hollow naoarchitecture as an efficient barrier for lithium polysulfides (LiPS) in Li-S batteries.7 We present well-aligned, hollow Co9S8 arrays in-situ grown on a Celgard (Co9S8-Celgard) separator as an efficient polysulfide barrier for high-performance Li-S cells without any significant increase in the weight and volume (Fig. 1a). This novel concept/strategy of designing a multifunctional separator via in-situ grown polar and conductive materials (Co9S8 hollow arrays) on a commercial separator dramatically suppresses the shuttle effect of LiPSs and significantly improves the electrochemical performance of Li-S cells. Due to its well-designed structure, in-situ growth/transformation, and the polarity and high conductivity of Co9S8, the Li-S cell with the Co9S8-Celgard separator not only effectively blocks the LiPSs even with pure sulfur cathodes with a high sulfur loading (5.6 mg cm-2), but also delivers excellent specific capacity, outstanding rate capability, and remarkable cycling stability for an impressive number of 1,000 cycles (Fig. 1b - d). In essence, the novel design and in-situ growth of MOF-derived multifunctional Co9S8 layers are crucial to suppress the severe polysulfide diffusion and alleviate the shuttle effect of LiPSs. We believe that this approach would promote greatly the development of modified separators, particularly the design and synthesis of multifunctional separators. Fig. 1 (a) Schematic illustration of the synthesis process of Co9S8-Celgard. (b) Rate performances at various cycling rates with the Celgard, MOF-Celgard, and Co9S8-Celgard separators. (c) Cycling performances of Li-S cells with high sulfur-loading cathodes with Co9S8-Celgard separators. (d) Long-term cycling performances of the Li-S cells with the Co9S8-Celgard separators at 1C rate for 1,000 cycles. REFERENCES 1 J. He, Y. Chen, W. Lv, K. Wen, C. Xu, W. Zhang, Y. Li, W. Qin, W. He, ACS Nano 2016, 10, 10981. 2 J. He, L. Luo, Y. Chen, A. Manthiram, Adv. Mater. 2017, 29, 1702707. 3 F. Wu, J. T. Lee, N. Nitta, H. Kim, O. Borodin, G. Yushin, Adv. Mater. 2015, 27, 101. 4 G. Zhou, S. Pei, L. Li, D. Wang, S. Wang, K. Huang, L. Yin, F. Li, H. Cheng, Adv. Mater. 2014, 26, 625. 5 J. He, Y. Chen, P. Li, F. Fu, Z. Wang, W. Zhang, J. Mater. Chem. A 2015, 3, 18605. 6 Y. Su, A. Manthiram, Nat. Commun. 2012, 3, 1166. 7 J. He, Y. Chen, A. Manthiram, Energ. Environ. Sci. 2018, 11, 2560. Figure 1

The effects of polysulfide shuttle and volume expansion in lithium sulfur batteries limit their practical applications. In this work, a two-dimensional fabric with graphene cage interweaving was designed by the chemical vapor deposition method to resolve these issues. It has a large number of micropores, mesopores, and macropores. Sulfur was deposited in these pores by melting method to form sulfur/graphene complex. Polysulfides were confined within these pores, making them less likely to diffuse and shuttle. Graphene walls have strong flexibility and can alleviate the volume expansion effect during charge and discharge process. Sulfur/graphene complex as active materials were directly coated on aluminum foil by graphene oxide to build lithium-sulfur battery, where graphene oxide served not only as an adhesive but also as a conductive agent to improve the electrochemical performances of batteries. The lithium-sulfur battery had an initial capacity of 1400 mAh g-1 and high capacity retention (500 mAh g-1 after 200 cycles at 0.2 C rate). These results suggest that the reasonable design of material morphology for sulfur loading will effectively improve the performance of lithium sulfur batteries.