High-performance Li-S Batteries Research Articles

High-performance Li-S battery cathode enabled by immobilizing sulfur in hybrid Janus host with hierarchical structure

A facile and effective strategy is proposed to fabricate high-performance Li-S battery cathodes with a hierarchically structural Janus host composed of multiwall carbon nanotubes (MWCNTs) and polyethyleneimine (PEI). The MWCNTs act as conductive skeleton for physical confinement of S and the PEI can chemically immobilize the S/lithium polysulfides. Benefiting from synergistic effects of the multifunctional host, the cathode can load with high S and simultaneously achieves excellent reversible capacity and outstanding rate performance. For instance, the capacity remains around 500 mAh g−1 even after 350 cycles at 0.2 A g−1 with a capacity decay of only 0.12% per cycle. Even at a higher rate current of 1 A g−1, the per cycle capacity decay is only 0.1% within 160 cycles.

Triple-Layered Carbon-SiO2 Composite Membrane for High Energy Density and Long Cycling Li–S Batteries

Here we report a highly scalable yet flexible triple-layer structured porous C/SiO2 membrane via a facile phase inversion method for advancing Li-sulfur battery technology. As a multifunctional current-collector-free cathode, the conductive dense layer of the C/SiO2 membrane offers hierarchical macropores as an ideal sulfur host to alleviate the volume expansion of sulfur species and facilitate ion/electrolyte transport for fast kinetics, as well as spongelike pores to enable high sulfur loading. The triple-layer structured membrane cathode enables the filling of most sulfur species in the macropores and additional loading of a thin sulfur slurry on the membrane surface, which facilitates ion/electrolyte transport with faster kinetics than the conventional S/C slurry-based cathode. Furthermore, density functional theory simulations and visual adsorption measurements confirm the critical role of the doped SiO2 nanoparticles (∼10 nm) in the asymmetric C membrane in suppressing the shuttle effect of polysulfides via chemisorption and electrocatalysis. The rationally designed C/SiO2 membrane cathodes demonstrate long-term cycling stability of 300 cycles at a high sulfur loading of 2.8 mg cm-2 with a sulfur content of ∼75%. This scalable yet flexible self-supporting cathode design presents a useful strategy for realizing practical applications of high-performance Li-S batteries.

Advanced Co3O4 interlayer as an efficient polysulfide barrier for high-performance Li-S batteries

Advanced Co3O4 interlayer as an efficient polysulfide barrier for high-performance Li-S batteries

Promoting polythionate intermediates formation by oxygen-deficient manganese oxide hollow nanospheres for high performance lithium-sulfur batteries

Mediating polysulfides redox by forming surface-bound insoluble intermediates on metal oxides is an efficient strategy to curtail polysulfides shuttling. Herein, the formation of surface-bound insoluble intermediates is further promoted by surface engineering of manganese oxide host via introducing oxygen vacancies. Hollow MnO2 nanospheres are first synthesized via a facial hard-template method, which provide a huge void for sulfur immobilization and volumetric expansion. Surface oxygen vacancies are then introduced by heating the products in a reduction atmosphere. These oxygen vacancies are proposed to accelerate the formation of polythionate intermediates, and which can adsorb polysulfides species more strongly than normal oxide sites and assist in their dissociation to lithium sulfide. The cathode based on oxygen-deficient manganese oxide hollow nanospheres achieves high initial discharge capacity of 1053 mAh g−1 at 0.5 C and high reversible capacity of 551 mAh g−1 at 2 C over 400 cycles, while only initial discharge capacity of 918 mAh g−1 and reversible capacity of 410 mAh g−1 are obtained for pristine MnO2. This work provides a novel strategy to establish cathode with engineered surface chemistry of metal oxides for high performance Li-S batteries.

CoS-interposed and Ketjen black-embedded carbon nanofiber framework as a separator modulation for high performance Li-S batteries

Lithium sulfur batteries are regarded as the promising energy storage device for its high energy density (theoretical: ∼2600 Wh kg−1). In addition, the low cost of sulfur and its small impacts on the environment also arise tremendous interests of industries and governments. However, lithium sulfur batteries are still severely plagued by the free migration of intermediary polysulfides, which are the roots of lithium sulfur batteries' challenges. Besides various cathode design, carbon-based modification layers on the separator are also developed to enhance the electrochemical performance of the lithium sulfur batteries. In this study, carbon nanofiber/CoS/Ketjen black is successfully integrated on the commercial separator as an effective polysulfide blocker. It is demonstrated that the cell with a carbon nanofiber/CoS/Ketjen black-modified separator and high sulfur content (70 wt%) cathode can exhibit excellent stability with a capacity decay of 0.076% per cycle for more than 700 cycles under 1.0 C current density. Especially, the robust and flexible coating strategy can greatly expand the range of materials available to be integrated on the commercial separator.

Cobalt-embedded carbon nanofiber as electrocatalyst for polysulfide redox reaction in lithium sulfur batteries

Efficient redox conversions between polysulfides and sulfur or lithium sulfide have a significant impact on the electrochemical performance of lithium-sulfur batteries especially with high sulfur loading. Herein, a readily available cobalt-embedded carbon nanofiber (Co-CNF) is designed as the current collector for sulfur cathodes. It is shown that the Co-CNF promotes electron and Li-ion transfer, thus leading to fast redox conversion, which mitigates the dissolution and shuttling of polysulfides. Furthermore, the embedded cobalt metal facilitates the uniform nucleation of lithium sulfide on the surface of the carbon nanofiber, which reduces the polarization and leads to high specific capacity. The Co-CNF with 4.6 mg cm−2 sulfur loading delivers 970 mA h g−1 (4.5 mA h cm−2) at 0.1 C and 670 mA h g−1 at 1 C. Even when sulfur loading reaches as high as 9.6 mg cm−2, the reversible capacity of 730 mA h g−1 (7 mA h cm−2) is obtained. The Co-CNF/Li2S6 cathode shows a degradation rate at 0.06% per cycle over 300 cycles. This work demonstrates the effect of cobalt metal catalysis and a simple but useful sulfur cathode design for high performance Li-S batteries.

Physical activation of graphene: An effective, simple and clean procedure for obtaining microporous graphene for high-performance Li/S batteries

Graphene nanosheets are a promising scaffold to accommodate S for achieving high performance Li/S battery. Nanosheet activation is used as a viable strategy to induce a micropore system and further improve the battery performance. Accordingly, chemical activation methods dominate despite the need of multiple stages, which slow down the process in addition to making them tiresome. Here, a three-dimensional (3D) N-doped graphene specimen was physically activated with CO2, a clean and single step process, and used for the preparation of a sulfur composite (A-3DNG/S). The A-3DNG/S composite exhibited outstanding electrochemical properties such as an excellent rate capability (1,000 mAh·g−1 at 2C), high reversible capacity and cycling stability (average capacity ~ 800 mAh·g−1 at 1C after 200 cycles), values which exceed those measured in chemically activated graphene. Therefore, these results support the use of physical activation as a simple and efficient alternative to improve the performance of carbons as an S host for high-performance Li-S batteries.

A Pt decorated polypropylene separator for high performance Li-S battery

Retarding the shuttling of soluble polysulfide is a key issue for enhancing the performance of a lithium-sulfur battery. Modification of the battery separator with an active component that could facilitate the conversion of soluble polysulfide effectively suppress the shuttling effect by timely consumption of soluble polysulfide. Herein, a novel Pt decorated polypropylene separator is developed and its excellent performance in lithium sulfur battery is demonstrated. The excellent performance of the Pt decorated PP separator is resulted from its enhanced electrolyte affinity as well as its ability to catalyze polysulfide conversion.

Sputter-Coated Li Electrodes for High Performance Li-S Batteries

Li-S technology stands out as a potential alternative for Li-ion batteries due to the improved energy density, particularly in applications where the specific energy density is important [1,2]. OXIS Energy is currently developing Li-S batteries that outperform other battery technologies available in the market nowadays. Among the different challenges to obtain a high-performance Li-S battery, the issues related to metallic Li electrode are a limiting factor [3]. Among others, the continuous degradation reactions on Li surface and dendrite formation result in poor cycle life and arise safety hazards. Different approaches have been proposed to overcome these effects, such as the use of additives on the electrolyte, the development of structured composite Li anode or the formation of an artificial solid electrolyte interphase (SEI) [3,4]. Direct deposition of protective coatings on the surface of Li electrodes by means of Magnetron Sputtering is an easy and potentially scalable method to successfully produce thin and homogeneous layers with upgraded properties as an artificial SEI [5]. In this work current research activities in sputter deposited coatings being developed at OXIS Energy will be described, focusing both on the deposition process of coating materials and the electrochemical response of coated electrodes. [1] Manthiram, Arumugam, et al. "Rechargeable lithium–sulfur batteries." Chemical reviews 114.23 (2014): 11751-11787. [2] Fotouhi, Abbas, et al. "Lithium-Sulfur Battery Technology Readiness and Applications—A Review." Energies 10.12 (2017): 1937. [3] Cheng, Xin-Bing, Jia-Qi Huang, and Qiang Zhang. "Li metal anode in working lithium-sulfur batteries." Journal of The Electrochemical Society 165.1 (2018): A6058-A6072. [4] Cheng, Xin‐Bing, et al. "A review of solid electrolyte interphases on lithium metal anode." Advanced Science 3.3 (2016): 1500213. [5] Li, Juchuan, et al. "An artificial solid electrolyte interphase enables the use of a LiNi0. 5 Mn1. 5 O4 5 V cathode with conventional electrolytes." Advanced Energy Materials 3.10 (2013): 1275-1278.

Plasma Treatment for Nitrogen-Doped 3D Graphene Framework by a Conductive Matrix with Sulfur for High-Performance Li-S Batteries.

Carbon materials have received considerable attention as host cathode materials for sulfur in lithium-sulfur batteries; N-doped carbon materials show particularly high electrocatalytic activity. Efforts are made to synthesize N-doped carbon materials by introducing nitrogen-rich sources followed by sintering or hydrothermal processes. In the present work, an in situ hollow cathode discharge plasma treatment method is used to prepare 3D porous frameworks based on N-doped graphene as a potential conductive matrix material. The resulting N-doped graphene is used to prepare a 3D porous framework with a S content of 90 wt% as a cathode in lithium-sulfur cells, which delivers a specific discharge capacity of 1186 mAh g-1 at 0.1 C, a coulombic efficiency of 96% after 200 cycles, and a capacity retention of 578 mAh g-1 at 1.0 C after 1000 cycles. The performance is attributed to the flexible 3D structure and clustering of pyridinic N-dopants in graphene. The N-doped graphene shows high electrochemical performance and the flexible 3D porous stable structure accommodates the considerable volume change of the active material during lithium insertion and extraction processes, improving the long-term electrochemical performance.

A hybrid shell material with mixed ion/electron conductivity used for high-performance Li-S batteries.

A hybrid shell material of hollow Nb2O5 microspheres has been engineered as an effective sulfur host for use in Li-S batteries. Of particular note is that the selected Nb2O5 not only exhibits ultrafast Li+ motion properties due to its unique room-and-pillar NbO6/NbO7 framework structure, but also demonstrates moderate polar affinities to the lithium polysulfides based on theoretical calculations.

Freestanding sulfur-graphene oxide/carbon composite paper as a stable cathode for high performance lithium-sulfur batteries

The structural design and synthesis of sulfur-carbon composite materials with high performance is still a major challenge for rechargeable lithium-sulfur batteries. Interconnected three-dimensional frameworks comprising multi-walled carbon nanotubes, graphene, or carbon particles offer a combination of constituent advantages and can thus be used to achieve superior energy conversion and storage properties. Herein, we designed and prepared free-standing three-dimensional sulfur papers containing interconnected highly conductive carbon materials, which enable to be flexible binder-free cathodes for Li-S batteries. The resultant sulfur-carbon composite paper cathode exhibited high reversible specific capacity of 1386 mAhg−1, good rate capability up to 5C, and excellent cycling performance (a capacity retention 68% after 400 cycles), all of which are significantly improved from those of bare sulfur cathode or sulfur-GO composite only. Rational design of cathode composition, structure, and a simple fabrication process can give insight into the development of various advanced cathode materials for high-performance Li-S batteries.

N-doped carbon-coated hollow carbon nanofibers with interspersed TiO2 for integrated separator of Li-S batteries

Li-ion batteries have held a dominant position in the energy storage area for decades. However, due to the limitation of its chemistry, the energy density of Li-ion batteries is limited to ∼300 W h kg−1. In recent years, more attention has been paid to the Li-S batteries that are environmentally friendly, cost-effective and high energy density (theoretical value of cathode: ∼2600 W h kg−1). In this study, carbonized polydopamine (C-PDA)-coated hollow carbon nanofibers (CNFs) with TiO2 nanoparticles interspersed in the void space between the CNF skeleton and carbon coating layer were subtly designed. The C-PDA/TiO2/CNF composite (CTC) was integrated with the commercial separator as a polysulfide filter to achieve high-performance Li-S batteries. It is reveals that the CTC coating layer could effectively filter and reactivate the dissolved polysulfides to achieve a stabilized sulfur-based cathode. The Li-S battery assembled by this integrated separator and the regular cathode (sulfur/Ketjen black) with 72.7 wt% of sulfur achieved a high specific capacity and low decay rate (632.5 mAh g−1 at the first cycle and 0.06% per cycle) at 2.0C for 500 cycles. These good results indicate that the C-PDA/TiO2/CNF-modified separator could be a promising separator candidate for high performance Li-S batteries.

CNT-assembled dodecahedra core@nickel hydroxide nanosheet shell enabled sulfur cathode for high-performance lithium-sulfur batteries

Herein, we report the construction of three-dimensional hollow core@shell structure composed of N-doped CNT-assembled dodecahedra core derived from ZIF-67 and Ni(OH)2 nanosheet shell as the sulfur scaffold for Li-S batteries. The obtained sulfur cathode demonstrates outstanding electrochemical performance, including a high reversible capacity (1321 mAh g−1 at 0.1 C), excellent rate capability (1030 and 753 mAh g−1 at 1 and 3 C, respectively), and superior cycling stability (611 mAh g−1 after 1000 cycles at 3 C). The enhancement in electrochemical performance can be ascribed to the unique core@shell architecture: the interconnected CNT-assembled dodecahedra core provides rapid Li+/e- transport and sufficient free space for volume change; the Ni(OH)2 nanosheet shell not only acts as a durable physical barrier, but also serves as the polar material to restrain the dissolution of polysulfides with chemical interaction. In addition, in-situ nitrogen doping in CNTs introduces rich defects and active sites for polysulfides adsorption. This work provides a promising direction for high performance Li-S batteries by coating strong polar material on carbon materials.

Metal-N4/graphene as an efficient anchoring material for lithium-sulfur batteries: A computational study

Despite their high theoretical capacity, the practical commercialization of lithium-sulfur batteries have continued to face obstacles of low cycle stability and low efficiency, which stem from the dissolution and diffusion of lithium polysulfides intermediates in the electrolyte. Here, by means of comprehensive density functional theory computations, we exploited the potentials of the experimentally available metal-nitrogen/graphene as the anchoring material for high-performance Li-S batteries. Our results revealed that Cr-, Mn-, Fe-, Co-, and Cu-nitrogen/graphenes exhibit optimal interaction with soluble lithium polysulfides due to the synergistic effects between the metal and N atoms, which not only effectively traps the soluble lithium polysulfides to suppress the shuttle effects, but also well keeps their cyclic structures intact. Especially, the electronic properties of metal-nitrogen/graphenes are well preserved, and the computed voltages of discharge processes are larger than those of the well-established nitrogen-doped graphenes. Thus, the metal-nitrogen/graphene could present a kind of quite promising anchoring material for lithium sulfur battery cathodes to suppress the lithium polysulfides shuttle effect.

Lithium–Sulfur Batteries: Spiderweb‐Mimicking Anion‐Exchanging Separators for Li–S Batteries (Adv. Funct. Mater. 41/2018)

Spiderweb-mimicking anion-exchangeable separators are presented as a membrane-driven strategy for the development of high-performance Li-S batteries by Sang-Young Lee and co-workers in article number 1801422. The polyionic liquid (PVIm[TFSI])-based nanomat in the spider separator enables discharge voltage-dependent, reversible trap/release of polysulfides via an anion exchange reaction between TFSI− anions and polysulfides. The seperator's unique nanomat structure and chemical functionalities exceptionally improve the electrochemical performance of Li-S batteries.

Pitaya-Like Carbon Nanofiber Sulfur Composites as Promising Cathode Materials for High-Performance Li-S Batteries

Pitaya-Like Carbon Nanofiber Sulfur Composites as Promising Cathode Materials for High-Performance Li-S Batteries

Bifunctional Separator Coated with Hexachlorocyclotriphosphazene/Reduced Graphene Oxide for Enhanced Performance of Lithium-Sulfur Batteries.

Although extensive research has been performed in the field of Li-S rechargeable batteries, commercial applications are still hindered by the dissolution of the reaction intermediates of lithium polysulfides (LiPSs). Through the combination of experimental and theoretical results, a bifunctional separator has been designed by coating hexachlorocyclotriphosphazene (HCCP)-decorated reduced graphene oxide (rGO), which provides effective anchor sites for immobilizing the LiPSs. LiPSs can be adsorbed on the HCCP/rGO surface with moderate binding strength, and their structures and the electrical conductivity of HCCP/rGO are well maintained. The synergetic effect of the effective barrier and good electrical conductivity within the HCCP/rGO sheets efficiently anchors LiPSs and achieves enhanced electrochemical performance. More importantly, different substituents can be used to tune the immobilization of LiPSs by HCCP derivatives. Therefore, it is expected that HCCP and its derivatives can be utilized as a promising anchoring material for high-performance Li-S batteries.

Ion‐Selective Prussian‐Blue‐Modified Celgard Separator for High‐Performance Lithium–Sulfur Battery

Application of Li-S batteries has been restricted because of their major problem, that is, shuttling of soluble polysulfides between electrodes, which results in serious capacity fading. For the development of high-performance Li-S batteries, we first time utilize a simple growth method to introduce a Prussian blue (PB)-modified Celgard separator as an ion-selective membrane. The unique structure of PB could effectively suppress the shuttle of polysulfides but scarcely affect the transfer ability of lithium ions, which is beneficial to achieve high sulfur conversion efficiency and capacity retention. The Li-S battery with PB-modified Celgard separator has an average capacity decay of only 0.03 % per cycle at 1 C after 1000 cycles.

Ultrathin HfO2-modified carbon nanotube films as efficient polysulfide barriers for Li-S batteries

Ultrathin and cross-stacked carbon nanotube (CNT) films modified with hafnium oxide (HfO2) by atomic layer deposition are employed as efficient polysulfide barriers for high performance Li-S batteries. A HfO2/CNT interlayer has an ultrathin, flexible structure with a thickness of 1.5 μm and an areal density of 0.087 mg cm−2, along with excellent wettability to electrolyte. The highly conductive CNT network and the catalytic surface adsorption of polysulfide species by HfO2 significantly suppress the polysulfides shuttling phenomenon. With high sulfur loadings of up to 75 wt%, electrodes incorporating a HfO2/CNT interlayer show noticeable improvements in various electrochemical properties, including long-term cycling stability (721 mA h g−1 after 500 cycles at 1 C), high rate performance (800 mA h g−1 at 5 C), favorable anti-self-discharge capabilities, and suppression of Li anode corrosion. These results suggest a new and efficient polysulfide trapping material and a viable configuration for high-performance Li-S batteries.