Amount Of Sulfur Loading Research Articles

Novel pentagonal carbon-based materials as multifunctional electrodes in lithium-sulfur batteries, a theoretical study

The commercialization process of lithium-sulfur batteries (LISBs) is hindered by several problems, including low electroconductivity, the dissolution of lithium polysulfides (LiPSs) and sluggish charging-discharging kinetics. Recently, two-dimensional (2D) penta-furrow structures have emerged as a distinct family of 2D structures with low mass densities, which are predicted to accelerate redox kinetics and enable sulfur conversion. Here, several novel pentagonal carbon-based substrates, including penta-graphene (penta-G) and penta-B2C (C2N, C2P, C2Si, and N2C), were first investigated in LISBs based on density functional theory (DFT) calculations. It is found that the penta-G, penta-C2P and penta-C2Si have excellent anchoring ability and can greatly improve conductivity during the whole S8/LiPSs insertion, which can effectively suppress the shuttle effect. More importantly, penta-G, penta-C2P and penta-C2Si can reduce the free energy of sulfur reduction reactions to 0.63–0.68 eV and lower the energy barriers of electrochemical conversions to 0.82–1.57 eV (Li2S dissociation) and 0.05–0.14 eV (Li-ion diffusion), thereby enhancing catalytic conversion efficiency in the discharging/charging processes. In addition, penta-G showed a much smaller volume expansion (34 %) than the 80 % value for elemental sulfur and a considerable sulfur loading amount (53.78 wt%). Our findings demonstrate that metallic pentagonal carbon-based materials could be a potential LISBs cathode material with high performance.

Two-Dimensional Conductive Metal-Organic Frameworks as Highly Efficient Electrocatalysts for Lithium-Sulfur Batteries.

Lithium-sulfur batteries (LiSBs) which are expected to fulfill the increasing demands of high-density energy storage have been under intensive investigation. However, the development of LiSBs is facing many obstacles, such as the poor electronic conductivity of sulfur, shuttling effects of lithium polysulfides (LiPSs), sluggish Li2S decomposition, and low discharging/charging efficiency. Suitable electrocatalysts that can solve the above problems are promising in the development of LiSBs. Herein, 13 two-dimensional (2D) metal-organic frameworks (MOFs) of nitrogen-, sulfur-, and oxygen-coordinated transition-metal (TM) atoms (Co, Ni, Cu, and Zn) are selected and constructed to reveal the structure-activity relationship of 2D MOFs in terms of the electrocatalytic performance. Among all the 2D MOFs investigated, Cu3(HITP)2, Zn3(HITP)2, and Cu3(C18H9O3N3)2 offer moderate binding strength to LiPSs, which effectively suppresses Li2Sn dissolution and shuttling. Cu3(HITP)2 exhibits good electrical conductivity, a low Gibbs free energy barrier, effective electrocatalytic ability for Li2S decomposition, and a high sulfur loading amount. A descriptor φ is proposed to correlate the binding energies of the 2D MOFs to the coordination environment and the electronegativity of the TM atoms in the LiPSs via an implicit volcano plot. These findings are helpful for understanding the electrocatalytic effect of 2D MOFs in LiSBs and represent a promising approach for the development of future LiSBs.

300Wh/Kg Class High-Energy Li-S Laminated Batteries Using High-Sulfur Loading Cathode on 3D Mesh Structured Aluminum Foam

[Introduction] In recent years, lithium-sulfur batteries can be expected as a promising candidate for next generation energy storage devices because of its high energy density. Generally, the cathode is fabricated by infiltration of sulfur into Ketjen black (KB) with aluminum foil current collector. However, it is not easy to increase the sulfur loading amounts and maintain the rate performances for electric vehicles which are required more than 3C rate, due to the lack of Li ion and electron paths. To solve this issue, we have reported the new type sulfur electrode prepared using 3D mesh structured Al foam, resulting in increased sulfur loading amounts which are 5 - 10 times or more compared to conventional sulfur cathode fabricated using 2D structured aluminum foil current collector [1], [2], [3]. In this study, we optimized the fabrication method of sulfur cathode for high sulfur loading on 3D mesh structured Al foam for a high energy density Li-S laminated battery.[Experimental] S/KB composite was obtained by mixing sulfur and KB with weight ratio of 6:4, by heating at 155 °C for 12 h under N2 atmosphere. Afterward obtained S/KB composite was dispersed by ball milling for 12h. S/KB cathode was fabricated by S/KB slurry (weight ratio of S/KB (6/4) : Binder = 96.5 : 3.5). The high sulfur loaded cathode (15.3 mg/cm2) was obtained using 3D mesh structured Al foam (1mm in thickness). To assemble the cell, the cathode was pressed (0.4 mm in thickness). 5 Ah class laminated cell (70 x 70 mm) was prepared using the S/KB cathodes (6 stacked), Li anodes (7 stacked), separators (7 stacked), and the electrolyte (LiTFSI: G1(monoglyme)/G3(triglyme): HFE(hydrofluoroether)= 1: 1: 4 (molar ratio)). Electrochemical performances were tested with voltage range between 1.0 V – 3.3 V after activation process.In addition, coin cells were prepared using above materials to evaluate the ionic conductivity by DC polarization method.[Results and Discussion] To design a high energy density cell such as laminated type cell, it is important to optimize the ratio between using amount of electrolyte and solid materials in electrode. Fig. 1 shows the relationship between the calculated E/S ratio (electrolyte amount (µℓ)/sulfur loading amounts (mg)), porosity filling rate of electrolyte (%), and the gravimetric energy density (Wh/kg). It was possible to reduce the electrolyte filling rate to 100% which is corresponding to E/S = 1.7, achieving the 340 Wh/kg theoretically. It is important to secure an ion path in whole electrode to optimize utilization of E/S ratio. In our previous report, we fabricated the S/KB cathode using 3D mesh structured Al foam regardless of the porosity, implying that it has bad ion conductivity. To improve the ion conductivity of S/KB cathode which has high sulfur loading amounts, we prepared a cathode that loaded S/KB very uniformly and retained the high porosity of the 3D mesh structured Al foam.As a result, we confirmed that the S/KB cathode/3D Al mesh which has good porosity shows improved ionic conductivity than control sample fabricated by conventional method.Fig. 2 shows the charge/discharge curve of Li-S laminated battery prepared by a new method with optimized E/S ratio of 2.3 (conventional method requires high E/S ratio of 3.6 or more). High capacity of 5.2 Ah, and energy density (301 Wh/kg and 435 Wh/ℓ, excluding laminate and tab) was achieved with high sulfur loaded laminated cell (sulfur loading amount of 15.4 mg/cm2, 1156 mAh/g-S).

Reduced graphene oxide wrapped sulfur nanocomposite as cathode material for lithium sulfur battery

Sulfur has been investigated as an active electrode material for secondary batteries due to theoretically specific capacity compared to the lithium-ion battery. In the present study, reduced graphene oxide (RGO) sheets wrapped Sulfur nanocomposite (S-RGO) synthesized by hydrothermal method and confirmed the wrapping of RGO sheets on Sulfur nanoparticles by various analytical techniques. The synthesized S-RGO nanocomposite demonstrated improved interaction of sulfur nanoparticles with RGO which is confirmed through XPS analysis. The synthesized S-RGO resulted in significantly improved reversible specific capacity and higher rate capability (823 mAh/g at 0.1C, 400 mAh/g at 1C) with 77 wt% of sulfur loading amount on the cathode of the Li–S battery. Therefore, the present study opens up new insights into sustainable development in the field of Li–S battery energy storage applications.

Milder operating parameters for one‐step conversion of fructose to levulinic acid over sulfonated H‐β zeolite in aqueous media

AbstractThe sulfonated H‐β zeolite was successfully prepared and used for the synthesis of levulinic acid (LA) from D‐fructose. The catalyst was characterized by powder X‐ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscope, N2 physisorption, NH3‐temperature programmed desorption and carbon–hydrogen–nitrogen–sulfur analysis. The total acid amount is increased with increase in sulfur loading, confirmed that the sulfonic acid group (SO3‐H) is successfully grafted onto zeolite structure. The various parameters such as different amount of sulfur loading, reaction temperature, time, catalyst loading was studied for selective production of LA. The catalytic activity of sulfonated H‐β (S‐β) zeolite was found to be efficient for synthesis of LA from D‐fructose in aqueous media. Maximum LA yield of 43.5 mol%, low HMF yield (<1%) with 98.15% fructose conversion was obtained with 3% S‐β catalyst at 160°C for 7 hr. The catalyst was reusable for minimum three times by H2O2 regeneration. This study provides the new zeolitic catalyst for the efficient production of LA at shorter reaction time (7 hr) and low catalyst to substrate ratio (0.7:1).

Effects of structural feature of biomass raw materials on carbon products as matrix in cathode of Li-S battery and its electrochemical performance

In this study, three types of biomass with different structures were selected to synthesize carbon matrix in a cathode of Li-S battery. The influence of the structure of raw biomass on microstructure, sulfur-loading amount, and electrochemical performance was investigated in detail. The results demonstrated that the catkin-derived porous carbon (CPC) inherited the 1D-structured morphology and exhibited the highest specific surface area (2033.09 m2/g), the largest sulfur loading (53.72%), and the highest initial discharge specific capacity (1369.52 mA h g−1) under 0.1 C. Comparatively speaking, the wrinkled cloth-like sakura petal–derived porous carbon showed a better capacity (1218.14 mA h g−1) but poor cycling performance. And the 3D network structure of bamboo-derived porous carbon (BPC) exhibited a relatively high capacity retention. These results demonstrated that the structural feature of biomass raw materials plays an important role in the microstructure and electrochemical performance of the carbon products.

Synergy between Interconnected Porous Carbon-Sulfur Cathode and Metallic MgB2 Interlayer as a Lithium Polysulfide Immobilizer for High-Performance Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are the potential candidates for developing high-energy-density electric vehicles. However, poor electrical conductivity of sulfur/discharged products, low active material utilization, shuttle mechanism, and poor cycle life remain the major challenges for the development of Li-S batteries. Herein, we report the nitrogen-doped highly porous carbon (NC) with interconnected pores as the sulfur host (NC-S), which is synthesized by a facile one-step process without using any template and activation agents. The highly interconnected porous structure of NC can accommodate a high amount of sulfur loading and provide space for sulfur volume expansion during redox reactions. Besides, to mitigate the lithium polysulfide dissolution and shuttle mechanism, metallic and polar magnesium diboride (MgB2) is used as an interlayer. Consequently, the NC-S/MgB2 cathode delivers higher specific capacity, rate capability, and excellent cyclic stability than the NC-S cathode and bulk sulfur cathode with MgB2 interlayer. The lithium polysulfide (LPS) adsorption test shows that MgB2 has strong chemisorption toward lithium polysulfides, which can inhibit the dissolution of LPS into the electrolyte and minimizes the shuttle effect. The dynamic electrochemical impedance spectroscopy analysis investigates the electrochemical reaction kinetics of the NC-S/MgB2 cathode during the charging and discharging processes. Overall, this work demonstrates that the synergy between the nitrogen-doped porous carbon-sulfur host and polar metallic MgB2 improves the performance of the Li-S battery, which is beneficial for the development of high-energy-density batteries for the future.

A multifunctional SnO2-nanowires/carbon composite interlayer for high-performance lithium-sulfur batteries

Recently, lithium–sulfur (Li–S) batteries have been demonstrated as promising next-generation energy-storage devices. However, their practical application is hindered by poor cycling performance and rate capability. In this study, we prepared a multifunctional interlayer composed of SnO2 nanowires (NWs) and conductive carbon paper (CP) to enhance the electrochemical performance of Li–S batteries. This SnO2 NWs@CP interlayer could efficiently adsorb lithium polysulfides and provide electron-conductive pathways to the sulfur electrode, leading to suppression of the polysulfide shuttle effect and enhancement of the electrochemical reaction kinetics for cycling performance and rate capability. A lithium-sulfur cell fabricated with SnO2 NWs@CP interlayer at a high sulfur loading amount (ca. 4.0 mg cm−2) could deliver a high specific capacity of 815 mAh g−1 (based on sulfur) even after 100 cycles at 0.2 C with a high coulombic efficiency of 98.2%. These results demonstrate that the introduction of multifunctional SnO2 NWs@CP interlayers should be a promising new strategy for the development of high-energy-density Li–S batteries.

Synergy between partially exfoliated carbon nanotubes-sulfur cathode and nitrogen rich dual function interlayer for high performance lithium sulfur battery

Confinement of lithium polysulfides (LPS) within the cathode is one of the major challenges of LithiumSulfur Batteries (LiS), which hinders its practical application. Herein, a simple strategy is demonstrated to reduce the dissolution of LPS by graphitic carbon nitride nanosheets (GCN) supported by a gas diffusion layer (GDL), which consists of high nitrogen content, acts as polar sites for LPS adsorption. The partially exfoliated multi-walled carbon nanotube is used as a sulfur host (PECNT/S), which accommodates the high amount of sulfur loading due to its high specific surface area and pore volume. PECNT/S/GCN-GDL cathode remarkably exhibits excellent cyclic stability at 1C with 92.2% of initial capacity retention even after 500 cycles due to the strong trapping of LPS by chemisorption on GCN while the electrically conducting GDL ropes the electron conduction as well as electrolyte and Li+ ion diffusion. Dynamic electrochemical impedance spectroscopy technique further provides the understanding of confinement of LPS on the resultant PECNT/S/GCN-GDL electrode during charge-discharge processes. In addition, the importance of the upper potential limits has been studied in this work. Our study thus addresses many challenges of the LiS batteries by the use of carbon-based nanomaterials.

High electrical conductivity of 3D mesporous carbon nanocage as an efficient polysulfide buffer layer for high sulfur utilization in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries display a high theoretical energy density compared with commercial lithium-ion batteries (LIBs). However, there are several major challenges including the poor conductivity and large volumetric expansion of sulfur, and the shuttle effect and uncontrollable deposition of lithium polysulfides, which lead to the low sulfur utilization and poor cycle life in practical applications. The fabrication of state-of-the-art separator based on high electrical conductivity of 3D porous carbon is believed to restrain the shuttle effect of lithium polysulfides and control the deposition of lithium sulfide. Herein, we report a kind of 3D mesporous carbon nanocage (PCN) with a high electrical conductivity as an efficient polysulfide buffer layer on PP separator in Li-S batteries for high sulfur utilization. The extraordinary electrical conductivity of the 3D PCN can promote the transformation reaction of Li2S/sulfur-to-lithium polysulfides between PCN separators and sulfur cathode. During charge/discharge, PCN serves as a buffer layer to redistribute the shuttling back of LiPSs owing to its abundant mesoporous structure. Thereby, Li-S batteries using PCN separator shows an extraordinary initial discharge capacity of 1044 mAh g−1 which still remains 652 mAh g−1 after 200 cycles at 1C. This is a significantly boost for sulfur utilization compared with that in Li-S batteries using PP separator. In addition, the advanced Li-S batteries with PCN separators reveal a superior areal capacity (2.5 mAh cm−2) at a high sulfur loading amount of 7.34 mg cm−2, showing the potential in practical application.

Modification of cobalt-containing MOF-derived mesoporous carbon as an effective sulfur-loading host for rechargeable lithium-sulfur batteries

Cobalt-containing metal-organic frameworks (MOF) are synthesized, then carbonized and then acid etched to obtain mesoporous carbon for its potential application as lithium-sulfur (Li-S) battery cathode scaffolds. Before etching the resulting mesoporous carbon acquires a specific surface area of 206.5 m2 g−1 and a pore volume of 0.29 cm3 g−1, and in its sulfur-loading composite-1 the S-content is ∼45.2 wt%. After etching the modified mesoporous carbon exhibits a great improvement in porosity (Surface area ∼650.2 m2 g−1 and pore volume ∼ 0.77 cm3 g−1) and/or in sulfur-loading amount (i.e., the S-content of composite-2 ∼ 50.0 wt%). At 0.5 C (1 C = 1675 mA g−1), a composite-2 cathode delivers a high discharge capacity of 925.1 mAh g−1 in 2nd cycle and maintains a specific value of 781.1 mAh g−1 in the 140th cycle, much higher than those of composite-1 cathode. Both of the two composite electrodes display a slight increase of electrolyte-solution resistance and surface-film resistance and an obvious decrease of charge-transfer resistance. By comparison, these resistances of composite-2 are smaller than those of composite-1. This, together with the acid-modified structural parameters reasonably account for the enhanced electrochemical properties of composite-2.

Electrocatalytic Activity of Carbon in N-Doped Graphene to Achieve High-Energy Density Li–S Batteries

High-energy and cost-effective lithium–sulfur battery (LSB) technology has been regarded as a promising alternative to current rechargeable lithium-ion batteries. However, the utilization of LSB suffered from the gap between the theoretical expectation and practical observation. Here, we propose the mechanistic origin of the electrocatalytic role of carbon in the N-doped graphene (NDG) layer placed on the entire cathode. We understand that the carbon in NDG acts as an electrocatalyst by interactions with polysulfide, leading to efficient electrochemical charge and discharge behaviors. A sufficient sulfur loading amount (ca. 5.75 mg cm–2) is successfully achieved, and the developed cell in this work enables remarkable energy density (200 W h kgtotal cell–1) and high areal capacity (4 mA h cm–2).

CoO/Co-Activated Porous Carbon Cloth Cathode for High Performance Li-S Batteries.

Li-S batteries are one of the most promising candidates for the next generation of batteries because of their high theoretical specific capacity of 1675 mA h g-1 . However, the dissolution of polysulfide causes severe capacity fading during cycling. Herein, a 3 D CoO/Co-activated free-standing porous carbon fiber cloth (CoO/Co@PCF) is designed to suppress polysulfide diffusion from the cathode. The metallic Co and polar CoO can anchor polysulfide through Co-S ionic bonding and the pores of the carbon cloth can provide abundant active sites for electrochemical reactions. Specifically, sulfur in the cathode is loaded by sulfur vapor deposition, which is scalable for fabrication and adjustable to the sulfur-loading amount. The CoO/Co@PCF cathode with sulfur loading of 3 mg cm-2 displays high discharge capacities of 1214.2 and 684.3 mA h g-1 at 0.1 and 2 C, respectively. When the sulfur loading is increased to 5.4 mg cm-2 , low capacity fading of 0.075 % per cycle over 100 cycles at 0.5 C is still observed.

Lithium-Sulfur Batteries: The Effect of High Sulfur Loading on the Electrochemical Performance

It is no secret that sulfur as a cathode material is a promising candidate for next generation Li metal-based batteries. However, the intrinsic limitations associated with low conductivity of sulfur and instability of sulfur based composite prevents the commercialization of lithium sulfur batteries. For the past years of Li-S batteries research, many research has been carried out on the cathode design to improve the electrochemical performance. However, it has been mathematically determined that even with high sulfur loading amount and effective sulfur utilization, the true value of energy density cannot outperform the currently available LIBs. That is, other inactive materials must be utilized to address the inherent sulfur issues which would only add more weight. Thus, we propose a novel and facile synthesis of binder-free three-dimensional carbon nanotubes (3D CNTs)/sulfur (S) hybrid composite as an electrode material, where 3D CNTs provide a high conduction path and short diffusion length for Li-ions, while providing ample amount of space for higher sulfur loading. In addition to sulfur loading, the amount of electrolyte also determines the electrochemical performance of Li-S cell in terms of sulfur utilization and cycling stability. However, the statistical analysis shows that more than 90% of reported publications have neglected this E/S ratio. This is important parameter for determining sulfur utilization and energy density of the cell. Here, we report the performance of three-dimensional carbon nanotubes/sulfur hybrid composite with different sulfur loading amounts from 1 to 9 mg/cm2 while tuning the electrolyte/sulfur (E/S) ratio from 12 to 1. The results have demonstrated the E/S ratio of 7 (60 µL electrolyte to 8.5 mg cm-2 sulfur) with reversible specific capacity of ~1068 mAh g-1 at 0.1C rate (~1.4mA cm-2) for up to 150 cycles.

A Binder Free and High Sulfur Loaded Three-Dimensional Carbon Nanotubes Electrode for High Performance Li-S Batteries

Rechargeable Li-S batteries represent advanced battery system offering high energy density with low cost cathode material compared to currently available Li-ion batteries. The critical limitations are mainly associated with the insulating nature of sulfur (5 x 10-30 S/m), and shuttle effect involving polysulfides (Li2Sx; 2<x<8) during charge/discharge process resulting in capacity fading and low cycling stability. Most of the previous strategies suggest entrapment of these polysulfides considering the areal density of the sulfur in the cathode to be less than 2mg/cm2. However, to compete with the electrochemical performance of available state-of-the art Li-ion batteries, the sulfur loading amount must be incremented substantially (>6mg/cm2). Here, we develop a simple and facile binder free approach to increase the sulfur loading amount from ~3mg/cm2 (~40wt.% S) to ~9mg/cm2 (~60wt.%S) in three-dimensional carbon nanotubes (3D CNTs). The parameters influencing cathode performance were investigated and provide a detail electrochemical analysis for improving the performance of Li-S batteries.

Flexible sulfur film from inverse vulcanization technique

Flexible, freestanding polysulfide films with high sulfur content (50–90% sulfur) were prepared via inverse vulcanization technique by reacting sulfur and diallyl disulfide; a naturally occurring diene. The prepared films are partially transparent depending on the amount of sulfur loading. SEM images showed a smooth and uniform surface of the film. XRD and DSC results confirmed the conversion of crystalline sulfur into an amorphous co-polymer. Low Young modulus and high tensile extension at break confirmed the flexible and elastic nature of the films. The flexibility of the films could be due to the presence of freely rotating low aliphatic carbon chains, which leads to low glass transition temperature (Tg=−13°C to −4°C) of these films.

A Binder Free and High Sulfur Loaded Three-Dimensional Carbon Nanotubes Electrode for High Performance Li-S Batteries

Rechargeable Li-S batteries represent advanced battery system offering high energy density with low cost and environmentally benign electrochemical energy storage compared to currently available Li-ion batteries. The critical limitations are mainly associated with the insulating nature of sulfur (5 x 10-30 S/m), and formation and dissolution of intermediate polysulfides (Li2Sx; 2<x<8) into the electrolyte during charge/discharge processes resulting in capacity fading and low cycling stability. Most of the previous strategies reported in literature suggested for entrapment of polysulfides considered the areal density of the sulfur in the cathode to be less than 2mg/cm2. However, in order to obtain superior electrochemical performance (high volumetric and gravimetric energy density) compared to currently available state-of-the art Li-ion batteries, the sulfur loading amount has to be incremented substantially, increasing the sulfur weight percentage in the cathode electrode, and optimize with the electrolyte (µL)/sulfur (mg) ratio for maximum electrochemical performance. Here in, we develop a simple and facile binder free approach without the use of any complex chemical routes (use of carbon black, PVDF, and NMP) to impregnate different S loading amount into micro-channeled conducting framework of three dimensional carbon nanotubes (3D CNTs). It also provides effective utilization of sulfur particles, high electrolyte absorbability facilitating well-localized polysulfides within the electrode structure, and maintaining good structural integrity during volume expansion. The proposed strategy delivered a specific capacity of ~1285mAh/g at 0.5C rate (1.55mA/cm2) and excellent rate capability for all different loading amounts. Furthermore, in this presentation the detailed synthesis for higher loading amount of sulfur and their superior electrochemical performance with unique physical and electrochemical properties will be discussed in detail.

Enhanced performance of sulfur-infiltrated bimodal mesoporous carbon foam by chemical solution deposition as cathode materials for lithium sulfur batteries

The porous carbon matrix is widely recognized to be a promising sulfur reservoir to improve the cycle life by suppressing the polysulfide dissolution in lithium sulfur batteries (LSB). Herein, we synthesized mesocellular carbon foam (MSUF-C) with bimodal mesopore (4 and 30 nm) and large pore volume (1.72 cm2/g) using MSUF silica as a template and employed it as both the sulfur reservoir and the conductive agent in the sulfur cathode. Sulfur was uniformly infiltrated into MSUF-C pores by a chemical solution deposition method (MSUF-C/S CSD) and the amount of sulfur loading was achieved as high as 73% thanks to the large pore volume with the CSD approach. MSUF-C/S CSD showed a high capacity (889 mAh/g after 100 cycles at 0.2 C), an improved rate capability (879 mAh/g at 1C and 420 mAh/g at 2C), and a good capacity retention with a fade rate of 0.16% per cycle over 100 cycles.

High-Energy Laminated-Type Li-S Batteries Using High-Sulfur Loading Positive Electrode on Aluminum Foam

[Introduction]Interesting in Li-S batteries has been accelerated because it is expected to realize Li ion batteries delivering high energy density. Moreover, its poor cycle stability caused by severe dissolution of sulfur active material in organic carbonate electrolyte has been much improved by introducing novel materials such as Li ion selective separators [1] and Li salt solvate ionic liquid as insoluble electrolyte [2]. Hence, many researches have recently performed to enhance specific energy density. Although, Al foil, in general, has been widely used as a cathode current collector so far, it has not easy with increase in the loading amount of active material, in particularly S/KB composite. When the S/KB loading amount increases on the conventional Al foil, the cathode is suffered from difficulty in Li ion path into bulk active material and large internal resistance with reduced electrical conductivity. To solve such drawbacks, 3D mesh structured metallic foams have been researched and used as a current collector, which reported stable cycle performances with even 10 times larger sulfur loading amount than conventional Al foil [3]. In this report, we enlarged sulfur loading amount by introducing the 3D mesh structured Al foam as a current collector of cathode. Furthermore, optimization of the solvate ionic liquid was also investigated. Herein, it is suggested development on high energy density laminated Li-S battery delivering 200 wh kg-1. [Experimental]S/KB composite was obtained by mixing sulfur and KB in the weight ratio of 5:5, followed by heating at 155 degree C for 12 hours under N2 atmosphere. Cathode slurry was prepared in the weight ratio of S/KB (1/1) : KB : PVdF = 60 : 30 : 10. The sulfur amount of 1 – 12 mg cm-2 was loaded on 3D mesh structured Al foam (1mm in thickness). Laminated cells with 70 x 70 mm in size were prepared by assembling the prepared S/KB cathode, Li metal anode, separator (UPORE) and solvate ionic liquid (either G3 : LiTFSI : HFE = 1 : 1 : 4 or G1 + G3 : LiTFSI : HFE = 1 : 1 : 4). Cycle performances were tested between 1.5 V – 3.3 V with 16.7 mA g-1-S after 2 cycles of activation process. [Results and discussion]Both areal and specific discharge capacity of the laminated Li-S batteries are shown in Fig. 1a dependent for sulfur loading amount on 3D mesh structured Al foam, i.e., 1.3, 6.2 and 8.6 mg cm-2. Same values of specific discharge capacity delivering ca. 1400 mAh g-1-S were obtained from the different three samples. It revealed that sulfur was efficiently utilized compared to the previous report. This result assumed that loading S/KB on the 3D mesh structured Al foam enhanced Li ion and electron path in comparison to the conventional Al foil. Moreover, since the areal discharge capacity increased linearly with increase in sulfur loading amount, it is considered that stable Li ion and electron path would be maintained within this sulfur loading range.The laminated Li-S battery containing 11.5 mg cm-2 of sulfur loading was successfully prepared (see its picture in Fig.1b) and cycled with solvate ionic liquid (G1 + G3 : LiTFSI : HFE = 1 : 1 : 4). Fig.2 shows its charge-discharge potential profile. It attained specific discharge capacity delivering 1400 mA h g-1-S and areal discharge capacity delivering 15 mAh cm-2. Furthermore, the laminated Li-S battery achieved 735 mA h of cell capacity with a pair of electrode 70 x 70 mm in size. [Conclusion]We developed Li-S batteries composed of S/KB cathode with 3D mesh structured Al foam current collector, Li metal anode and Li salt solvate ionic liquid as electrolyte. The Li-S battery containing 11.5 mg cm-2 of sulfur achieved high specific and areal discharge capacity delivering 1400 mA h g-1-S and 15 mA cm-2, respectively. These results suppose that laminated batteries with high energy density delivering 200 Wh kg-1would be realized by efficiently laminating the electrode material and optimizing Li anode. [Acknowledgement] This work is supported by Advanced Low Carbon Technology Research and Development Program (JST-ALCA) Special Priority Research Area "Next-generation Rechargeable Battery". [References] [1]N. Nakamura, Y. Wu, T. Yokoshima, H. Nara, T. Momma, T. Osaka, J.Electrochem. Soc., 163, A683 (2016). [2]K. Yoshida, M. Nakamura, Y. Kazue, N. Tachikawa, S. Tsuzuki, S. Seki, K.Dokko, and M. Watanabe, J. Am. Chem. Soc., 133, 13121 (2011). [3]G. Zhou et al., Nano Energy(2015) 11, 356–365. Figure 1

High Rate Li-S Batteries: Hollow TiO2 Webbed Carbon Nanotubes with Dual Functional Porous Carbon-Paper

The Li–S batteries are becoming attractive due to the abundance of elemental sulfur and its environmental compatibility. In addition, sulfur undergoes a two-electron redox reaction with lithium and offers an extremely high theoretical specific capacity of 1675 mAh g−1 and a high energy density of 2600 Wh kg−1.1 Despite these advantages, several issues have hampered the practical use of Li–S batteries. For example, the insulating character of sulfur and lithium sulfide impede the full electrochemical utilization of sulfur. Moreover, the dissolution of lithium polysulfide inter-mediates in the electrolyte triggers undesirable shuttle reactions. Other issues such as low Coulombic efficiency, high self-discharge, and huge volume change remain unsolved. To overcome these drawbacks, several mitigation strategies have been explored by various research groups. One of the most followed routes deals with the mixing/impregnation/confinement of sulfur within highly conducting carbons. carbon nanotube-based composites have been used for high sulfur loading amount. Another approach is the use of metal oxides. In particular, TiO2 is a promising host for sulfur containment owing to its high absorption ability2. Further enhancement in the capacity and cycle life of Li–S batteries has been realized by Manthiram’s group by employing a free-standing interlayer (between the sulfur cathode and the separator) that plays the bifunctional role as a trap for mobile polysulfides and as an upper current collector for fast electron transport3.Herein, we synthesized and characterized (i) a S-HMT@CNT sulfur cathode comprised of hollow, spherical, nanostructured TiO2 and carbon nanotubes and (ii) DF-PCW interlayer comprised of highly porous carbon spheres and carbon nanotubes. The pores of TiO2 allowed for high sulfur loadings and accommodation of the volume expansion at the electrode level. The CNT component provided an overlap-ping network that improved both the electronic conductivity and mechanical strength of the S-HMT@CNT and DF-PCW. The pores in the carbon interlayer played the role of a medium that scavenged the dissolved lithium polysulfides, while improving Li-ion and electron transports. Owing to our cathode characteristics and cell design, the lithium–sulfur cell fabricated demonstrated good cycle life, high efficiency, and high rate capability. Of significance, the excellent cycling realized at the 2C and 5C rates is appealing for utilizing the lithium–sulfur batteries in high power applications