High-energy Lithium-sulfur Research Articles

Bimetallic Coupling Strategy Modulating Electronic Construction to Accelerate Sulfur Redox Reaction Kinetics for High-Energy Flexible Li-S Batteries.

Lithium-sulfur (Li-S) batteries are considered the most promising energy storage battery due to their low cost and high theoretical energy density. However, the low utilization rate of sulfur and slow redox kinetics have seriously limited the development of Li-S batteries. Herein, the electronic state modulation of metal selenides induced by the bi-metallic coupling strategy is reported to enhance the redox reaction kinetics and sulfur utilization, thereby improving the electrochemical performance of Li-S batteries. Theoretical calculations reveal that the electronic structure can be modulated by Ni-Co coupling, thus lowering the conversion barrier of lithium polysulfides (LiPSs)and Li+, and the synergistic interaction between NiCoSe nanoparticles and nitrogen-doped porous carbon (NPC) is facilitating to enhance electron transport and ion transfer kinetics of the NiCoSe@NPC-S electrodes. As a result, the assembled Li-S batteries based on NiCoSe@NPC-S exhibit high capacities (1020mAhg-1 at 1C) and stable cycle performance (80.37% capacity retention after 500 cycles). The special structural design and bimetallic coupling strategy promote the batteries working even under lean electrolyte (7.2µLmg-1) with a high sulfur loading (6.5mgcm-2). The proposed bimetallic coupling strategy modulating electronic construction with N-doping porous carbon has jointly contributed the good redox reaction kinetics and high sulfur utilization.

High-Density, Low-Tortuosity Sulfur Electrodes for High Energy Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries have attracted significant attention due to their promising theoretical energy and cost-effectiveness.[1] While recently studies have predominantly focused on increasing sulfur mass loading and utilization rate for high specific energy, there remains a noticeable gap in addressing the intrinsic challenge of improving volumetric energy density.[2] This challenge arises as many Li-S investigations rely on highly porous electrodes.[3] Here, we employ a shear-rolling approach to prepare free-standing electrodes characterized by high density (porosity<15%), low tortuosity, and substantial S content (>70%). The incorporation of a vascular-like porous network, facilitated by a pore soft template, plays a pivotal role in achieving high sulfur utilization (>1000 mAh g-1) in high-loading electrodes (>4 mg cm-2) under lean electrolyte condition (E/S 4 mL g-1). This approach results in an extraordinarily high volumetric energy density (668 Wh L-1 of dry cell) when applied to practical Li–S pouch cells. Our study underscores that realizing high volumetric energy in Li–S cell can be achieved by rationalizing the dense electrode architecture. Furthermore, the shear-rolling approach holds broad applicability for fabricating high-energy electrodes using porous or nanoparticle materials with desirable structures. Details of the progress will be discussed at the conference.

Nitrogen-Doped TiO2- x(B)/MXene Heterostructures for Expediting Sulfur Redox Kinetics and Suppressing Lithium Dendrites.

Practical application of lithium-sulfur (Li-S) batteries is severely impeded by the random shuttling of soluble lithium polysulfides (LiPSs), sluggish sulfur redox kinetics, and uncontrollable growth of lithium dendrites, particularly under high sulfur loading and lean electrolyte conditions. Here, nitrogen-doped bronze-phase TiO2(B) nanosheets with oxygen vacancies (OVs) grown in situ on MXenes layers (N-TiO2- x(B)-MXenes) as multifunctional interlayers are designed. The N-TiO2- x(B)-MXenes show reduced bandgap of 1.10eV and high LiPSs adsorption-conversion-nucleation-decomposition efficiency, leading to remarkably enhanced sulfur redox kinetics. Moreover, they also have lithiophilic nature that can effectively suppress dendrites growth. The cell based on the N-TiO2- x(B)-MXenes interlayer under sulfur loading of 2.5mg cm-2 delivers superior cycling performance with a high specific capacity of 690.7 mAh g-1 over 600 cycles at 1.0 C. It still has a notable areal capacity of 6.15 mAh cm-2 after 50 cycles even under a high sulfur loading of 7.2mg cm-2 and a low electrolyte-to-sulfur (E/S) ratio of 6.4 µL mg-1. The Li-symmetrical battery with the N-TiO2- x(B)-MXenes interlayer showcases a low over-potential fluctuation with 21.0mV throughout continuous lithium plating/stripping for 1000h. This work offers valuable insights into the manipulation of defects and heterostructures to achieve high-energy Li-S batteries.

Ultrathin Two-Dimensional Ordered Porous Carbon Host with Atomically Dispersed Electrocatalytic Sites toward High Volumetric Energy Lithium-Sulfur Battery

Despite multimodal approaches to increase the gravimetric capacity of lithium-sulfur (Li-S) batteries over the years, strategies on achieving high volumetric capacity (Qv) at close to practical cell operating conditions with high areal sulfur loading and low electrolyte-to-sulfur (E/S) ratio are still lacking. Here, we report that a synergistic effect of a carbonaceous framework with precisely-controlled porous structure/dimension and highly-active, surface-mediated electrocatalysis by a ruthenium (Ru) single-atom electrocatalyst (SAC) composed of N2RuCl2 achieves high Qv in Li-S batteries. Two-dimensional (2D) and hierarchically ordered porous structures of polymer interfacial self-assembly derived N-doped carbon nanosheets (NCNS) realize a highly-packed sulfur cathode with outstanding Li+ ion diffusivity and electrode stability, which have been considered as main impediments to achieving high Qv in a dense sulfur cathode. Moreover, homogeneous incorporation of N2RuCl2 SAC which has novel Ru coordination environment with two N and Cl atoms on the surface of NCNS remarkably accelerated the reaction kinetics of Li-S electrochemistry and achieved high Qv even at high sulfur loading (5.0 mg cm−2), extremely low E/S ratio (4.5 μL mg−1), and low electrode porosity (50 %).

Interfacial synergy of nanoengineered PANI/MnO2 for strong anchoring and fast conversion of polysulfides in Li-S batteries

The shuttle of polysulfides and slow sulfur redox kinetics are the two main issues in the practical application of lithium sulfur (Li-S) batteries. The interface-induced electric fields produced in MnO2-based conductive composites are proposed to solve the above obstacles. Herein, a novel hybrid structure of birnessite-MnO2 nanosheets in situ formed inside polyaniline nanotubes (NSs-MnO2@PANI) is prepared and applied as a catalytic host in Li-S batteries. The DFT calculation combined with experiments reveal the interface-induced electric field with a direction pointing from PANI to birnessite-MnO2 is created, which would induce interface charge redistribution and result in electron-rich MnO2 region and electron-deficient PANI region, optimizing the strong anchoring of polysulfides and their fast catalytic conversions. Owing to the interfacial synergy, the NSs-MnO2@PANI/S cathode delivers higher capacity than PANI/S at rates from 0.1 C (1473.7 vs. 467.5 mAh g−1) to 5 C (513.2 vs. 38.1 mAh g−1), with a low decay rate of 0.054% during 500 cycles at 0.2 C. Further, at an extremely high sulfur loading of 15.9 mg cm−2, the areal capacity achieves a high level of 10.2 mAh cm−2 at 0.05 C, with stable cycling at 1 C. Our work provides new insights for attaining high-energy and stable Li-S batteries.

Flexible and binder free electrode with d-p band center manipulated MoTe2 nanosheets towards high energy Lithium–Sulfur batteries

The practical usage of lithium sulfur (Li–S) batteries has been hampered by the severely sluggish conversion kinetics of lithium polysulfides (LiPSs) and the overused of binders and electrolyte, resulting in energy density decreased dramatically. In this work, as a catalyst for LiPSs conversion of great potential, the poor catalytic performance of MoTe2 is revealed to be the wide gap of d-p band center, which hinders the electron exchange of interfacial redox dynamics. Accordingly, the binder-free cathodes are fabricated by recrystallizing sulfur on phosphorus-doped MoTe2 decorated carbon cloth (P-MoTe2/CC) to boost Li–S battery performance. The electron deficient P in MoTe2 lifts the d-band center of P-MoTe2 to Fermi level and narrows the gap of d-p band center when it interacts with LiPSs, which significantly increases the catalytic activity of MoTe2 towards both LiPSs oxidation and reduction. With these features, the P-MoTe2/CC cathodes therefore offers a high initial discharge capacity of 1480.55 mAh g−1 and a low capacity decay of 0.42 % per cycle. Even at high sulfur loading and lean electrolyte of 4.3 (E/S ratio), the Li–S pouch cell can also perform an outstanding cycling stability and reach a high energy density of about 400 Wh kg−1.

Nanofiber-based electrode current collector for high-energy Li-S batteries towards practical application for energy storage

The slow sulfur electrochemical reactions are one of the key factors hindering the practical use of lithium-sulfur (Li-S) batteries. However, the polysulfide shuttling and the sluggish redox kinetics, which emerge simultaneously in sulfur cathode, hinder the commercial application of Li-S batteries. Herein, we employ a design to solve the above-mentioned problems via building nitrogen-doping carbon nanofibers with twinborn nickel sulfide nanoparticles (NiS2/Ni3S4@NCNF) as self-supporting current collector for Li-S batteries. Experimental results and theoretical calculations show that the three-dimensional cross-linked carbon structure promotes Li-ion/electron transfer and physically offers wide internal space for sulfur accommodation. Meanwhile, powerful capability of chemical anchoring of the polysulfides endowed by NiS2 mitigates the shuttle effect. Notably, the surface of mixed-valence Ni3S4 has more active sites, which can effectively reduce the energy barrier due to its high catalytic activity and fast sulfur conversion from solid Li2S/Li2S2 to soluble polysulfides. Based on these merits, the Li-S battery with NiS2/Ni3S4@NCNF shows stable sulfur electrochemistry including a highly reversible capacity of 1212.8 mAh g−1 at 0.2C with capacity retention rate of 75.3 % after 100 cycle, and an excellent cycle stability of pouch battery. This work provides a promising strategy to build advanced sulfur current collectors for practical Li-S battery.

Lithium-Ion Battery Electrolyte Miscibility Studied By Spectroscopy

Interfaces, interphases, and surfaces are of immense interest to the battery research community since the key reactions and much of the kinetics that determine the performance of the cell occur there. While solid/liquid and solid/solid interfaces have been thoroughly studied, liquid/liquid interfaces have attracted much less attention.Here we target the liquid/liquid interfaces between two liquid electrolytes, employed to create dual electrolyte batteries. The grand idea is that based on two either chemically or mechanically immiscible electrolytes we can expand the overall electrochemical stability window to achieve both high electrolyte oxidation stability on the positive electrode and efficient and stable solid electrolyte interphase (SEI) formation on the negative electrode [1][2].To understand the dual electrolyte systems created we study diffusion across the liquid/liquid interfaces, the formation of any emulsion layers, and if there are chemical reactions occurring. We use confocal Raman spectroscopy focusing on the interface between two porous separators soaked with two different electrolytes as well as in situ Raman depth profiling with micrometer resolution, including the role of pressure to the stack of separators (both glass fibre and polymer based).The observations of for example diffusion and mixing are subsequently correlated with the physicochemical properties of the two electrolytes in order to pave the way for rational design of a dual electrolyte cell.[1] S. He, S. Huang, Y. Zhao, H. Qin, Y. Shan and X. Hou. “Design of a Dual-Electrolyte Battery System Based on a High-Energy NCM811-Si/C Full Battery Electrode-Compatible Electrolyte”. ACS Applied Materials & Interfaces 2021 13 (45), 54069-54078. DOI: 10.1021/acsami.1c17841[2] Ren, Y., Manthiram, A., “A Dual-Phase Electrolyte for High-Energy Lithium–Sulfur Batteries. Adv. Energy Mater”. 2022, 12, 2202566. https://doi.org/10.1002/aenm.202202566

Applications, prospects and challenges of metal borides in lithium sulfur batteries

Although the lithium-sulfur (Li-S) battery has a theoretical capacity of up to 1675 mA h g−1, its practical application is limited owing to some problems, such as the shuttle effect of soluble lithium polysulfides (LiPSs) and the growth of Li dendrites. It has been verified that some transition metal compounds exhibit strong polarity, good chemical adsorption and high electrocatalytic activities, which are beneficial for the rapid conversion of intermediate product in order to effectively inhibit the “shuttle effect”. Remarkably, being different from other metal compounds, it is a significant characteristic that both metal and boron atoms of transition metal borides (TMBs) can bind to LiPSs, which have shown great potential in recent years. Here, for the first time, almost all existing studies on TMBs employed in Li-S cells are comprehensively summarized. We firstly clarify special structures and electronic features of metal borides to show their great potential, and then existing strategies to improve the electrochemical properties of TMBs are summarized and discussed in the focus sections, such as carbon-matrix construction, morphology control, heteroatomic doping, heterostructure formation, phase engineering, preparation techniques. Finally, the remaining challenges and perspectives are proposed to point out a direction for realizing high-energy and long-life Li-S batteries.

Unraveling the Coupling Effect between Cathode and Anode toward Practical Lithium-Sulfur Batteries.

The localized reaction heterogeneity of the sulfur cathode and the uneven Li deposition on the Li anode are intractable issues for lithium-sulfur (Li-S) batteries under practical operation. Despite impressive progress in separately optimizing the sulfur cathode or Li anode, a comprehensive understanding of the highly coupled relationship between the cathode and anode is still lacking. In this work, inspired by the Butler-Volmer equation, a binary descriptor (IBD ) assisting the rational structural design of sulfur cathode by simultaneously considering the mass-transport index (Imass ) and the charge-transfer index (Icharge ) is identified, and subsequently the relationship between IBD and the morphological evolution of Li anode is established. Guided by the IBD , a scalable electrode providing interpenetrated flow channels for efficient mass/charge transfer, full utilization of active sulfur, and mechanically elastic support for aggressive electrochemical reactions under practical conditions is reported. These characteristics induce a homogenous distribution of local current densities and reduced reaction heterogeneity on both sides of the cathode and anode. Impressive energy density of 318Wh kg-1 and 473Wh L-1 in an Ah-level pouch cell can be achieved by the design concept. This work offers a promising paradigm for unlocking the interaction between cathode and anode and designing high-energy practical Li-S batteries.

Multifunctional Interlayer Engineering for Silkworm Excrement-Derived Porous Carbon Enabling High-Energy Lithium Sulfur Batteries.

Lithium-sulfur (Li-S) batteries show advantage of high theoretical capacity. However, the shuttle effect of polysulfides and sluggish sulfur redox kinetics seriously reduce their service life. Inspired by the porous structural features of biomass materials, herein, a functional interlayer is fabricated by silkworm excrement-derived three-dimensional porous carbon accommodating nano sized CoS2 particles (SC@CoS2 ). The porous carbon delivers a high specific surface area, which provides adequate adsorption sites, being responsible for suppressing the shuttle effect of polysulfides. Meanwhile, the porous carbon is favorable for hindering the aggregation of CoS2 and maintaining its high activity during extended cycles, which effectively accelerates the polysulfides conversion kinetics. Moreover, the SC@CoS2 functional interlayer effectively limits the formation of Li dendrites and promotes the uniform deposition of Li on the Li electrode surface. As a result, the CMK-3/S cathode achieves a high initial capacity of 1599.1 mAh g-1 at 0.2 C rate assisted by the polypropylene separator coated with the functional interlayer and 1208.3 mAh g-1 is maintained after the long cycling test. This work provides an insight into the designing of long-lasting catalysts for stable functional interlayer, which encourages the application of biomass-derived porous carbon in high-energy Li-S batteries.

Strategy for High-Energy Li-S Battery Coupling with a Li Metal Anode and a Sulfurized Polyacrylonitrile Cathode.

Among lithium-sulfur (Li-S) battery materials, sulfurized polyacrylonitrile (SPAN) has attracted substantial attention as a cathode material owing to its potential to bypass the problematic polysulfide formation and shuttling effect. Carbonate-based electrolytes have been eschewed compared with ether-based electrolytes because of their poor compatibility with Li metal anodes. In this work, we design and study an electrolyte comprising 0.8 M of lithium bis(trifluoromethanesulfonyl)imide, 0.2 M of lithium difluoro(oxalate)borate, and 0.05 M of lithium hexafluorophosphate in ethyl methyl carbonate/fluoroethylene carbonate = 3:1 v/v solution in the Li-S battery coupled with a Li metal anode and SPAN cathode. The well-designed carbonate-based electrolyte effectively stabilizes both electrodes, delivering high Coulombic efficiencies with stable cyclability. Studies using operando optical microscopy and atomic force microscopy demonstrate that dense, uniform Li deposition is promoted to suppress dendrite growth even at a high current density. Operando Raman spectroscopy reveals a reversible Li+ storage behavior in the SPAN structure through the cleavage of disulfide bonds and their redimerization during lithiation and delithiation. As a result, the proposed Li-S battery delivers an overall capacity retention of 73.5% over 1000 cycles, with high Coulombic efficiencies over 99.9%.

Low-Tortuous and Dense Electrode for High-Energy Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries feature a high theoretical capacity of 1675 mAh/g and hence is considered as a promising alternative to lithium-ion batteries. However, deployment of Li-S batteries has been hindered by the low practical energy and limited cycle life.1, 2 Reducing cathode porosity is essential to balancing the electrolyte distribution in Li-S cell, conserving more pore-filling electrolyte to extend cell cycle life.3-5 However, low-porosity electrodes built with nanosized sulfur/carbon (S/C) materials suffer from high tortuosity that significantly deteriorates electrode wetting and hence sulfur utilization. Enabling operation of high-loading sulfur electrodes under both low-porosity and lean-electrolyte conditions is still a challenge and is seldom discussed. In this study,6 we demonstrated a novel and facile strategy for constructing low-tortuosity through-pores across both vertical and planar directions of electrodes by casting large particles into single-particle-layer electrodes. Through multi-scale characterizations and simulations, correlations between material/electrode structures, electrolyte permeability, polysulfide migration, and sulfur reactions were elucidated. The high-loading and dense sulfur cathode fabricated by this method delivers a high specific capacity (>1000 mAh g-1) at a very low electrolyte/sulfur (E/S) ratio of 4 μL mg-1. This study provides a novel approach to reducing the tortuosity of dense sulfur electrodes by manipulating the porosity distribution, which would be also applicable to improving the rate capability of other high-energy electrodes. More details of the progress will be discussed at the meeting.Reference. Dörfler, S.; Althues, H.; Härtel, P.; Abendroth, T.; Schumm, B.; Kaskel, S., Challenges and Key Parameters of Lithium-Sulfur Batteries on Pouch Cell Level. Joule 2020, 4 (3), 539-554.Xue, W.; Miao, L.; Qie, L.; Wang, C.; Li, S.; Wang, J.; Li, J., Gravimetric and volumetric energy densities of lithium-sulfur batteries. Current Opinion in Electrochemistry 2017, 6 (1), 92-99.Lu, D.; Li, Q.; Liu, J.; Zheng, J.; Wang, Y.; Ferrara, S.; Xiao, J.; Zhang, J. G.; Liu, J., Enabling High-Energy-Density Cathode for Lithium-Sulfur Batteries. ACS Appl Mater Interfaces 2018, 10 (27), 23094-23102.Kang, N.; Lin, Y.; Yang, L.; Lu, D.; Xiao, J.; Qi, Y.; Cai, M., Cathode porosity is a missing key parameter to optimize lithium-sulfur battery energy density. Nat Commun 2019, 10 (1), 4597.Feng, S.; Liu, J.; Zhang, X.; Shi, L.; Anderson, C.; Lin, Y.; Song, M.-K.; Liu, J.; Xiao, J.; Lu, D., Rationalizing nitrogen-doped secondary carbon particles for practical lithium-sulfur batteries. Nano Energy 2022, 103.Feng, S.; Singh, R. K.; Fu, Y.; Li, Z.; Wang, Y.; Bao, J.; Xu, Z.; Li, G.; Anderson, C.; Shi, L.; Lin, Y.; Khalifah, P. G.; Wang, W.; Liu, J.; Xiao, J.; Lu, D., Low-tortuous and dense single-particle-layer electrode for high-energy lithium-sulfur batteries. Energy & Environ. Sci. 2022.

Cooperative catalytic platinum species accelerating polysulfide redox reactions for Li-S batteries

The shuttle effect derived from diffusion of lithium polysulfides (LiPSs) and sluggish redox kinetic bring about poor cycling stability and low utilization of sulfur, which have always been the key challenging issues for the commercial application of lithium-sulfur (Li-S) batteries. Rational design of cathode materials to catalyze Li2S dissociation/nucleation processes is an appealing and valid strategy to develop high-energy practical Li-S batteries. Herein, considering the synergistic effect of bidirectional catalysis on LiPSs conversion and enhanced chemical immobilization for LiPSs by heteroatom doping, Pt nanoparticles loaded on nitrogen-doped carbon spheres (Pt/NCS composites) were constructed as cathode materials. According to the dynamic evolution of Pt catalysts and sulfur species, Pt0 and Pt2+ species were identified as active species for the accelerated dissociation and nucleation of Li2S, respectively. Meanwhile, in-situ Raman results demonstrated the expedited conversion of sulfur species resulted from bidirectional catalysis of active Pt species, corresponding to boosted redox kinetics. Consequently, Pt/NCS cathode exhibited improved long-term cyclability with high initial capacity, along with enhanced rate capability. This work provides a facile approach to construct cathode materials with bidirectional catalysis on Li2S dissociation/nucleation, and sheds light on a more global understanding of the catalytic mechanism of metal catalysts during LiPSs conversion.

An in situ fabricated multifunctional gel electrolyte for lithium–sulfur batteries

Despite the high-energy lithium–sulfur (Li–S) batteries being a promising secondary batteries system, their commercialization is seriously hindered by the polysulfides shuttle, unstable lithium anode and safety hazards in the traditional liquid electrolytes. Herein, a multifunctional gel polymer electrolyte (ANPD-GPE) is fabricated, which is composed of Nafion-coated Al2O3 nanofibers and in-situ polymerized 1,3-dioxolane (DOL). Lewis-acidic Al2O3 has a strong effect on the Lewis base of bis(trifluoromethanesulphony)imide anions, facilitating the transport of Li+ and resulting in a reduced Li+ concentration gradient. In addition, the replacement of a flammable polyolefin separator by the inorganic Al2O3 robust nanofibers skeleton can effectively promote the structural and thermal stability of electrolytes. The introduction of Nafion effectively inhibits the shuttle effect vis polymerization of DOL and the electrostatic repulsion of its anions. The in-situ polymerized elastic poly-DOL (PDOL) can stabilize the lithium anode because of its accommodation for the fluctuating interface during cycling. Consequently, Li–S cells with ANPD-GPE present improved electrochemical performance in terms of cathode cyclability and lithium anode stability.

Integrated host configuration of flexibly fibrous skeleton towards efficient polysulfide conversion and dendrite-free behavior in stable lithium-sulfur pouch cells

The commercialization of lithium-sulfur (Li-S) batteries is obstructed by the sluggish sulfur electrochemical reaction, severe polysulfide shuttling effect, and damaging dendritic lithium growth. Herein, a three-dimensional (3D) conductive carbon nanofibers skeleton-based bifunctional electrode host material is fabricated, which consists of a two-dimensional (2D) ultra-thin NiSe2-CoSe2 heterostructured nanosheet built on one-dimensional (1D) carbon nanofibers (NiSe2-CoSe2@CNF). When serving as cathodic host, the heterostructured NiSe2-CoSe2@CNF offers a synergistic function of polysulfide confinement and catalysis conversion. The S/NiSe2-CoSe2@CNF cathode shows outstanding cycling stability of 0.03% capacity decay rate per cycle over 500 cycles at 1 C. As anodic host, the NiSe2-CoSe2@CNF with high-flux Li+ diffusion property and good lithiophilic capability realizes dendrite-free Li plating/stripping behavior. Benefiting from these synergistically merits, the Li-S full cell with S/NiSe2-CoSe2@CNF|Li/NiSe2-CoSe2@CNF electrodes exhibits excellent electrochemical performance including a high specific capacity of 1021 mA h g−1 over 100 cycles at 0.2 C and reversible areal capacity of 3.05 mA h cm−2 under a high sulfur loading of 4.33 mg cm−2 at 0.1 C. The pouch cell also delivers ultra-stable Li/S electrochemistry. This study demonstrates a rational and universal electrode construction strategy for developing practical and high-energy Li-S batteries.

Inhibiting polysulfide shuttling with a flexible “skin” for highly stable Lithium-Sulfur batteries

Ion electrokinetic regulation on separator is crucial for reducing polysulfide shuttling in lithium-sulfur (Li-S) batteries. Inspired by the electrostatic shielding effect, we implant a flexible “skin” composed of organic molecules (PDDA/PSS) with different charges anchored on carbon nanotubes (CNT), which act as a functional interlayer to prevent the shuttling of polysulfides. Systematic experiments and advanced theoretical calculations show that PDDA@CNT with positively charged amino groups not only provides adequate surface affinity to capture polysulfide anions, but also the highly conductive and high specific surface area CNT enables fast electron/ion migration and physical barrier. Consequently, the cell with PDDA@CNT/PP exhibits a high discharge capacity of 706 mAh g−1 and a favorable cycle stability of 1054 mAh g−1 after 250 cycles at 1C with high coulombic efficiency of 97%. This proof-of-concept work offers new perspectives on how to tailor the ionic behaviors of separators for high-energy Li-S batteries.

Multifunctional α-MoO3 Nanobelt Interlayer with the Capacity Compensation Effect for High-Energy Lithium-Sulfur Batteries.

Spatial hindrance of lithium polysulfide (LiPS) diffusion by inserting a barrier interlayer has been deemed as an effective strategy to restrict the shuttle effect in lithium-sulfur batteries (LSBs). However, the extra interlayer without reversible capacity production inevitably reduces the actual energy density of the battery. Herein, a freestanding α-MoO3 nanobelt interlayer with the decoration of TiN nanoparticles and carbon nanotubes (denoted as MCT) is established. To investigate the capacity compensation effect of the MCT during cell operations, X-ray absorption near-edge spectrometry is conducted. It is revealed that MoO3 can sustain a reversible Li intercalation/deintercalation in a voltage range of 1.8-2.8 V, providing 180 mAh g-1 of extra capacity for compensating sulfur cathode. In addition, the adsorption of the lithiated α-MoO3 toward LiPSs is further evaluated. By matching a high-loading sulfur cathode (3.0 mg cm-2), a superior capacity of 713.3 mAh g-1 can be retained after 100 cycles under the MCT assistance.

MXene derivative Ta4C3-Ta2O5 heterostructure as bi-functional barrier for Li-S batteries

The shuttle effect of polysulfides during the charging and discharging of lithium-sulfur (Li-S) batteries and the growth of Li dendrites are crucial obstacles to hinder the commercialization of Li-S batteries. Heterostructure engineering is an effective strategy to accelerate catalytic conversion and suppress the dissolution of polysulfides. Herein, we report a Ta4C3-Ta2O5 heterostructure composite as a bi-functional modified separator that not only achieves effective protection for lithium metal but also accelerates the polysulfides redox kinetics process. This heterostructure possesses efficient chemical anchoring and abundant active sites to immobilize polysulfides by synergistic effect, which endows a stable long cycling performance for Li-S batteries. This corresponds to an initial high capacity of 801.9 mAh g–1 at 1 C with a decay rate of 0.086% for 500 cycles. Due to its high Young's modulus (up to 384 GPa), Ta4C3 contributes to forming a protective layer on the Li metal surface to inhibit the growth of Li dendrites. Accordingly, the symmetrical cell has a stable overpotential for 700 cycles at 20 mA cm–2/20 mAh cm–2. So, this “one stone two birds” design affords a novel perspective for high-energy Li-S battery storage system design and Li metal protection.

Bio-mass derived hierarchically porous and high surface area carbon as an efficient sulfur host for lithium-sulfur batteries

Lithium–sulfur (Li-S) batteries are attractive candidates for electric vehicles and grid storage applications due to their high energy density than Li-ion batteries. Development of high energy Li-S batteries employing eco-friendly, and bio-waste derived materials will further increase the sustainability of the energy storage devices. Herein, we utilize porous carbon derived from waste watermelon rind for Li-S battery application. The porous carbon with hierarchal architecture, and functional heteroatoms can efficiently infiltrate the sulfur cathode and overcomes the major challenges in the Li-S battery, namely (i) poor electronic conductivity of sulfur cathode, and (ii) dissolution of long-chain polysulfides. The Li-S cell with a sulfur-infiltrated porous carbon delivered a high initial discharge capacity of 1176 mAh g−1 at 0.5C rate with a low capacity fading rate of 0.057% over 500 cycles. The strong carbon framework can accommodate the volume changes during the sulfur conversion reaction, and the unoccupied pores in porous carbon can function as polysulfide reservoir to efficiently trap polysulfide migration to achieve a high stability. The highly inter-connected hierarchical pores further facilitated a faster electronic and ionic transport to achieve a high rate performance, higher than pristine sulfur cathode. These results demonstrate the potential to develop high-performance energy storage devices using eco-friendly and renewable materials for electric vehicles and other energy storage systems.