High sulfur loading and shuttle inhibition of advanced sulfur cathode enabled by graphene network skin and N,P,F-doped mesoporous carbon interfaces for ultra-stable lithium sulfur battery

Achieving high loading of active sulfur yet rational regulating the shuttle effect of lithium polysulfide(LiPS)is of great significance in pursuit of high-performance lithium-sulfur(Li-S)battery.Herein,we develop a free-standing graphene nitrogen(N),phosphorus(P)and fluorine(F)co-doped mesoporous carbon-sulfur(G-NPFMC-S)film,which was used as a binder-free cathode in Li-S battery.The developed mesoporous carbon(MC)achieved a high specific surface area of 921 m^(2)·g^(-1)with a uniform pore size distribution of 15 nm.The inserted graphene network inside G-NPFMC-S cathode can effectively improve its electrical conductivity and simultaneously restrict the shuttle of LiPS.A high sulfur loading of 86%was achieved due to the excellent porous structures of graphene-NPFMC(G-NPFMC)composite.When implemented as a freestanding cathode in Li-S battery,this G-NPFMC-S achieved a high specific capacity(1,356 mAh·g^(-1)),favorable rate capability,and long-term cycling stability up to 500 cycles with a minimum capacity fading rate of 0.025%per cycle,outperforming the corresponding performances of NPFMC-sulfur(NPFMC-S)and MC-sulfur(MC-S).These promising results can be ascribed to the featured structures that formed inside G-NPFMC-S film,as that highly porous NPFMC can provide sufficient storage space for the loading of sulfur,while,the N,P,F-doped carbonic interface and the inserted graphene network help hinder the shuttle of LiPS via chemical adsorption and physical barrier effect.This proposed unique structure can provide a bright prospect in that high mass loading of active sulfur and restriction the shuttle of LiPS can be simultaneously achieved for Li-S battery.

Construction of strong built-in electric field in binary metal sulfide heterojunction to propel high-loading lithium-sulfur batteries

The practical application of lithium-sulfur(Li-S)batteries is greatly hindered by soluble polysulfides shuttling and sluggish sulfur redox kinetics.Rational design of multifunctional hybrid materials with superior electronic conductivity and high electrocatalytic activity,e.g.,heterostructures,is a promising strategy to solve the above obstacles.Herein,a binary metal sulfide MnS-MoS_(2) heterojunction electrocatalyst is first designed for the construction of high-sulfur-loaded and durable Li-S batteries.The MnS-MoS_(2) p-n heterojunction shows a unique structure of MoS_(2) nanosheets decorated with ample MnS nanodots,which contributes to the formation of a strong built-in electric field at the two-phase interface.The MnS-MoS_(2) hybrid host shows strong soluble polysulfide affinity,enhanced electronic conductivity,and exceptional catalytic effect on sulfur reduction.Benefiting from the synergistic effect,the as-derived S/MnS-MoS_(2) cathode delivers a superb rate capability(643 m A h g^(-1)at 6 C)and a durable cyclability(0.048%decay per cycle over 1000 cycles).More impressively,an areal capacity of 9.9 m A h cm^(-2)can be achieved even under an extremely high sulfur loading of 14.7 mg cm^(-2)and a low electrolyte to sulfur ratio of 2.9μL mg^(-1).This work provides an in-depth understanding of the interfacial catalytic effect of binary metal compound heterojunctions on sulfur reaction kinetics.

Towards full demonstration of high areal loading sulfur cathode in lithium–sulfur batteries

Lithium–sulfur(Li–S)batteries have been recognized as promising substitutes for current energy-storage technologies owing to their exceptional advantages in very high-energy density and excellent material sustainability.The cathode with high sulfur areal loading is vital for the practical applications of Li–S batteries with very high energy density.However,the high sulfur loading in an electrode results in poor rate and cycling performances of batteries in most cases.Herein,we used diameters of 5.0(D5)and 13.0(D13)mm to probe the effect of electrodes with different sizes on the rate and cycling performances under a high sulfur loading(4.5 mg cm^-2).The cell with D5 sulfur cathode exhibits better rate and cycling performances comparing with a large(D13)cathode.Both the high concentration of lithium polysulfides and corrosion of lithium metal anode impede rapid kinetics of sulfur redox reactions,which results in inferior battery performance of the Li–S cell with large diameter cathode.This work highlights the importance of rational matching of the large sulfur cathode with a high areal sulfur loading,carbon modified separators,organic electrolyte,and Li metal anode in a pouch cell,wherein the sulfur redox kinetics and lithium metal protection should be carefully considered under the flooded lithium polysulfide conditions in a working Li–S battery.

Comprehensive Design of the High-Sulfur-Loading Li–S Battery Based on MXene Nanosheets

The lithium-sulfur battery is the subject of much recent attention due to the high theoretical energy density,but practical applications are challenged by fast decay owing to polysulfide shuttle and electrode architecture degradation.A comprehensive study of the sulfur host microstructure design and the cell architecture construction based on the MXene phase(Ti3C2Tx nanosheets) is performed,aiming at realize stable cycling performance of Li-S battery with high sulfur areal loading.The interwoven KB@Ti3C2Tx composite formed by self-assembly of MXene and Ktej en black,not only provides superior conductivity and maintains the electrode integrality bearing the volume expansion/shrinkage when used as the sulfur host,but also functions as an interlayer on separator to further retard the polysulfide cross-diffusion that possibly escaped from the cathode.The KB@Ti3C2Tx interlayer is only 0.28 mg cm-2 in areal loading and 3 μm in thickness,which accounts a little contribution to the thick sulfur electrode;thus,the impacts on the energy density is minimal.By coupling the robust KB@Ti3C2Tx cathode and the effective KB@Ti3C2Tx modified separator,a stable Li-S battery with high sulfur areal loading(5.6 mg cm-2) and high areal capacity(6.4 mAh cm-2) at relatively lean electrolyte is achieved.

A strategy to achieve high loading and high energy density Li-S batteries

Lithium-sulfur(Li-S) batteries are one of the most promising rechargeable storage devices due to the high theoretical energy density.However,the low areal sulfur loading impedes their commercial development.Herein,a 3 D free-standing sulfur cathode scaffold is rationally designed and fabricated by coaxially coating polar Ti_3 C_2 T_x flakes on sulfur-impregnated carbon cloth(Ti_3 C_2 T_x@S/CC) to achieve high loading and high energy density Li-S batteries,in which,the flexible CC substrate with highly porous structure can accommodate large amounts of sulfur and ensure fast electron transfer,while the outer-coated Ti_3 C_2 T_x can serve as a polar and conductive protective layer to further promote the conductivity of the whole electrode,achieve physical blocking and chemical anchoring of lithium-polysulfides as well as catalyze their conversion.Due to these advantages,at a sulfur loading of 4 mg cm^(-2),Li-S cells with Ti_3 C_2 T_x@S/CC cathodes can deliver outstanding cycling stability(746.1 mAh g^(-1) after 200 cycles at1 C),superb rate performance(866.8 mAh g^(-1) up to 2 C) and a high specific energy density(564.2 Wh kg^(-1) after 100 cycles at 0.5 C).More significantly,they also show the commercial potential that can compete with current lithium-ion batteries due to the high areal capacity of 6.7 mAh cm^(-2) at the increased loading of 8 mg cm^(-2).

Metal-free two-dimensional phosphorene-based electrocatalyst with covalent P-N heterointerfacial reconstruction for electrolyte-lean lithium-sulfur batteries

The use of lithium-sulfur batteries under high sulfur loading and low electrolyte concentrations is severely restricted by the detrimental shuttling behavior of polysulfides and the sluggish kinetics in redox processes.Two-dimensional(2D)few layered black phosphorus with fully exposed atoms and high sulfur affinity can be potential lithium-sulfur battery electrocatalysts,which,however,have limitations of restricted catalytic activity and poor electrochemical/chemical stability.To resolve these issues,we developed a multifunctional metal-free catalyst by covalently bonding few layered black phosphorus nanosheets with nitrogen-doped carbon-coated multiwalled carbon nanotubes(denoted c-FBP-NC).The experimental characterizations and theoretical calculations show that the formed polarized P-N covalent bonds in c-FBP-NC can efficiently regulate electron transfer from NC to FBP and significantly promote the capture and catalysis of lithium polysulfides,thus alleviating the shuttle effect.Meanwhile,the robust 1D-2D interwoven structure with large surface area and high porosity allows strong physical confinement and fast mass transfer.Impressively,with c-FBP-NC as the sulfur host,the battery shows a high areal capacity of 7.69 mAh cm^(−2) under high sulfur loading of 8.74 mg cm^(−2) and a low electrolyte/sulfur ratio of 5.7μL mg^(−1).Moreover,the assembled pouch cell with sulfur loading of 4 mg cm^(−2) and an electrolyte/sulfur ratio of 3.5μL mg^(−1) shows good rate capability and outstanding cyclability.This work proposes an interfacial and electronic structure engineering strategy for fast and durable sulfur electrochemistry,demonstrating great potential in lithium-sulfur batteries.

In situ sulfur-doped graphene nanofiber network as efficient metal-free electrocatalyst for polysulfides redox reactions in lithium–sulfur batteries

The major challenge for realistic application of Li-S batteries lies in the great difficulty in breaking through the obstacles of the sluggish kinetics and polysulfides shuttle of the sulfur cathode at high sulfur loading for continuously high sulfur utilization during prolonged charge-discharge cycles.Here we demonstrate that large percentage of sulfur can be effectively incorporated within a three-dimensional(3D)nanofiber network of high quality graphene from chemical vapor deposition(CVD),through a simple ball-milling process.While high quality graphene network provided continuous and durable channels to enable efficient transport of lithium ions and electrons,the in-situ sulfur doping from the alloying effect of ball milling facilitated desirable affinity with entire sulfur species to prevent sulfur loss and highly active sites to propel sulfur redox reactions over cycling.This resulted in remarkable rate-performance and excellent cycling stability,together with large areal capacity at very high sulfur mass loading(Specific capacity over 666 mAh g-1after 300 cycles at 0.5 C,and areal capacity above 5.2 mAh cm-2at 0.2C at sulfur loading of 8.0 mg cm-2 and electrolyte/sulfur(E/S)ratio of 8μL mg-1;and high reversible areal capacities of 13.1 m Ah cm-2 at a sulfur load of 15 mg cm-2 and E/S of 5μL mg-1).

Emerging catalytic materials for practical lithium-sulfur batteries

High-energy lithium-sulfur batteries(LSBs)have experienced relentless development over the past decade with discernible improvements in electrochemical performance.However,a scrutinization of the cell operation conditions reveals a huge gap between the demands for practical batteries and those in the literature.Low sulfur loading,a high electrolyte/sulfur(E/S)ratio and excess anodes for lab-scale LSBs significantly offset their high-energy merit.To approach practical LSBs,high loading and lean electrolyte parameters are needed,which involve budding challenges of slow charge transfer,polysulfide precipitation and severe shuttle effects.To track these obstacles,the exploration of electrocatalysts to immobilize polysulfides and accelerate Li-S redox kinetics has been widely reported.Herein,this review aims to survey state-of-the-art catalytic materials for practical LSBs with emphasis on elucidating the correlation among catalyst design strategies,material structures and electrochemical performance.We also statistically evaluate the state-of-the-art catalyst-modified LSBs to identify the remaining discrepancy between the current advancements and the real-world requirements.In closing,we put forward our proposal for a catalytic material study to help realize practical LSBs.

Biomass-derived self-supporting sulfur host with NiS/C composite for high-loading Li-S battery cathode

High sulfur loading is a practical way to realize the advantages of high energy density lithium-sulfur(Li-S)batteries.Herein,we report a biomass-derived flexible self-supporting carbon(SSC)coupled with Ni S/C used as a sulfur host for high-efficiency sulfur storage.A high areal sulfur loading of 5.3 mg cm-2can be achieved in the as-prepared composite host,and physical/chemical dual blocking effects for polysulfides are implemented in the SSC-Ni S/C electrode.The 3D SSC with an interwoven structure offers a large surface area and wide internal space for sulfur accommodation.Moreover,the powerful capability of physical immobilization/chemical anchoring of the polysulfides endowed by SSC and Ni S mitigates the shuttle effect.We compared electrodes with different current collectors,and the SSC-Ni S/C-1200 electrode material showed outstanding electrochemical performance,exhibiting a first specific capacity of 1268.36 m A h g-1at a high sulfur loading of 5.3 mg cm-2.Additionally,the SSC-Ni S/C-1200 electrode exhibited a good remaining capacity of 555.15 m A h g-1at a current density of0.5 A g-1with a high sulfur loading of 3.3 mg cm-2after 300 cycles.In addition,the active material loaded in the traditional way easily falls off when the conventional current collector is folded with increasing sulfur loading,but the flexible self-supporting carbon current collector can solve this problem.This study prepared a flexible free-standing 3D interconnected carbon current collector.Via the introduction of amorphous carbon-coated Ni S,the self-supporting cathode SSC-Ni S/C-1200 achieved high sulfur loading that results in excellent electrochemical performance,providing a reference for future research on high sulfur loading in lithium-sulfur batteries.

A high-loading and cycle-stable solid-phase conversion sulfur cathode using edible fungus slag-derived microporous carbon as sulfur host

Developing a high sulfur(S)-loading cathode with high capacity utilization and long term cyclability is a key challenge for commercial implementation of Li-S battery technology.To overcome this challenge,we propose a solid-phase conversion sulfur cathode by using an edible fungus slag-derived porous carbon(CFS)as sulfur host to fabricate the S/CFS composite and meanwhile,utilizing the vinyl carbonate(VC)as co-solvent of the ether-based electrolyte to in-situ form a protective layer on the S/CFS composite surface through its nucleophilic reaction with the freshly generated lithium polysulfides(LiPSs)at the very beginning of initial discharge,thus isolating the interior sulfur from the outer electrolyte and inhibiting the further generation of soluble LiPSs.Benefitting from the ultrahigh specific surface area of>3,000 m^(2)·g^(−1),ideal pore size of<4 nm,and large pore volume of>2.0 cm^(3)·g^(−1)of the CFS host matrix,the S/CFS cathode even with a high S-loading of 80 wt.%(based on the weight of S/CFS composite)can still operate in a solid-phase conversion manner in the VC-ether co-solvent electrolyte to exhibit a high reversible capacity of 1,557 mAh·g^(−1),a high rate capability with 50%remaining capacity at 2 A·g^(−1)and a high cycling efficiency of 99.9%over 500 cycles.The results presented in this work suggest that a combined action of solid-phase conversion electrochemistry and nanoarchitectured host structure may provide a new path for the design and development of practical lithium-sulfur batteries.

High loading cotton cellulose-based aerogel self-standing electrode for Li-S batteries

Lithium-sulfur(Li-S) batteries have attracted considerable attention due to their high energy density(2600 Wh kg-1). However, its commercialization is hindered seriously by the low loading and utilization rate of sulfur cathodes. Herein, we designed the cellulose-based graphene carbon composite aerogel(CCA) self-standing electrode to enhance the performance of Li-S batteries. The CCA contributes to the mass loading and utilization efficiency of sulfur, because of its unique physical structure: low density(0.018 g cm-3), large specific surface area(657.85 m2 g-1), high porosity(96%), and remarkable electrolyte adsorption(42.25 times). Compared to Al(about 49%), the CCA displayed excellent sulfur use efficiency(86%) and could reach to high area capacity of 8.60 mAh cm-2 with 9.11 mgS loading. Meanwhile,the CCA exhibits the excellent potential for pulse sensing applications due to its flexibility and superior sensitivity to electrical response signals.

ZIF-7@carbon composites as multifunctional interlayer for rapid and durable Li-S performance

The notorious"shuttle effect"of polysulfide during charge-discharge process induces grievous capacity fading,while the sluggish polysulfide conversion kinetics significantly hinders the development of practically viable lithium-sulfur(Li-S)batteries.In this study,a novel ZIF-7@carbon composite with ZIF-7 sheets vertically rooted on carbon cloth was developed as multifunctional interlayer to address these issues.The composite shows directional layered structure with outstanding compactness,and thus can provide massive active sites for accelerated redox reactions.The pore channels are perpendicular to the square surface,resulting in extremely high utilization of one-dimensional channels.Therefore,this structure can not only maintain the structural stability during the charge-discharge process by providing enough space for volume expansion,but also contribute to efficient exposure and utilization of active sites for the physical/chemical adsorption and catalytic conversion of polysulfide.As a result,Li-S batteries with the as-developed interlayer deliver a considerable areal capacity of 4.75 mAh cm^(-2) at an elevated sulfur loading of 5.5 mg cm^(-2),and an impressive cyclability with an extremely low capacity-fading rate of merely 0.04%per cycle over 500 cycles at 1 C.

Solution-based Preparation of High Sulfur Content Sulfur/Graphene Cathode Material for Li-S Battery

Practical Li-sulfur batteries require the high sulfur loading cathode to meet the large-capacity power demand of electrical equipment.However,the sulfur content in cathode materials is usually unsatisfactory due to the excessive use of carbon for improving the conductivity.Traditional cathode fabrication strategies can hardly realize both high sulfur content and homogeneous sulfur distribution without aggregation.Herein,we designed a cathode material with ultrahigh sulfur content of 88%(mass fraction)by uniformly distributing the water dispersible sulfur nanoparticles on three-dimensionally conductive graphene framework.The water processable fabrication can maximize the homogeneous contact between sulfur nanoparticles and graphene,improving the utilization of the interconnected conductive surface.The obtained cathode material showed a capacity of 500 mA·h/g after 500 cycles at 2.0 A/g with an areal loading of 2 mg/cm2.This strategy provides possibility for the mass production of high-performance electrode materials for high-capacity Li-S battery.

Regulating the Deposition of Insoluble Sulfur Species for Room Temperature Sodium-Sulfur Batteries

Room temperature sodium-sulfur(RT-Na-S) batteries are regarded as promising candidates for next-generation high-energy-density batteries. However, in addition to the severe shuttle effect, the inhomogeneous deposition of the insoluble sulfur species generated during the discharge/charge processes also contributes to the rapid capacity fade of RT-Na-S batteries. In this work, the deposition behavior of the insoluble sulfur species in the traditional slurry-coated sulfur cathodes is investigated using microporous carbon spheres as model sulfur host materials. To achieve uniform deposition of insoluble sulfur species, a self-supporting sulfur cathode fabricated by assembling microporous carbon spheres is designed. With homogeneous sulfur distribution and favorable electron transport pathway, the self-supporting cathode delivers remarkably enhanced rate capability(509 mA·h/g at 2.5 C, 1 C=1675 mA/g), cycling stability(718 mA·h/g after 480 cycles at 0.5 C) and areal capacity(4.98 mA·h/cm2 at 0.1 C), highlighting the great potential of manipulating insoluble sulfur species to fabricate high-performance RT-Na-S batteries.

Acceleration of bidirectional sulfur conversion kinetics and inhibition of lithium dendrites growth via a“ligand-induced”transformation strategy

The introduction of materials with dual-functionalities,i.e.,the catalytic(adsorption)features to inhibit shuttle effects at the cathode side,and the capability to facilitate homogenous Li-ion fluxes at the anode side,is a promising strategy to realize high performance lithium-sulfur batteries(LSBs).Herein,a facile and rational organic“ligand-induced”(trimesic acid(TMA))transformation tactic is proposed,which achieves the regulation of electronic performance and d-band center of bimetallic oxides(NiFe_(2)O_(4))to promote bidirectional sulfur conversion kinetics and stabilize the Li plating/striping during the charge/discharge process.The battery assembled with NiFe_(2)O_(4)-TMA modified separator exhibits a remarkable initial specific capacity of 1476.6 mAh·g^(-1)at 0.1 C,outstanding rate properties(661.1 mAh·g^(-1)at 8.0 C),and excellent cycling ability.The“ligand-induced”transformation tactic proposed in this work will open a whole new possibility for tuning the electronic structure and d-band center to enhance the performance of LSBs.

Interface-induced polymerization strategy for constructing titanium dioxide embedded carbon porous framework with enhanced chemical immobilization towards lithium polysulfides

The shuttle effect induced by soluble lithium polysulfides(LiPSs)is known as one of the crucial issues that limit the practical applications of lithium-sulfur(Li-S)batteries.Herein,a titanium dioxide nanoparticle embedded in nitrogen-doped porous carbon nanofiber(TiO_(2)@NCNF)composite is constructed via an interface-induced polymerization strategy to serve as an ideal sulfur host.Under the protection of the nanofiber walls,the uniformly dispersed TiO_(2) nanocrystalline can act as capturing centers to constantly immobilize LiPSs towards durable sulfur chemistry.Besides,the mesoporous microstructure in the fibrous framework endows the TiO_(2)@NCNF host with strong physical reservation for sulfur and LiPSs,sufficient pathways for electron/ion transfer,and excellent endurance for volume change.As expected,the sulfur-loaded TiO_(2)@NCNF composite electrode presents a fabulous rate performance and long cycle lifespan(capacity fading rate of 0.062%per cycle over 500 cycles)at 2.0 C.Furthermore,the assembled Li-S batteries harvest superb areal capacity and cycling stability even under high sulfur loading and lean electrolyte conditions.

Bio-inspired construction of electrocatalyst decorated hierarchical porous carbon nanoreactors with enhanced mass transfer ability towards rapid polysulfide redox reactions

Li-S batteries are considered as a highly promising candidate for the next-generation energy storage system, attributing to their tremendous energy density. However, the two-dimensional island nucleation-growth process of lithium sulfide leads to a thick insulating film covering the electrode, inducing slow electrons transfer and mass-transfer of ions and liquid sulfur species in working Li-S cells. Here, we demonstrate a bio-inspired strategy of constructing ant-nest-like hierarchical porous ultrathin carbon nanosheet networks with the implants of metallic nanoparticles electrocatalysts (HPC-MEC) as efficient nanoreactors enabling rapid mass transfer, via a simple and green NaCl template. Such nanoreactors with a large active surface area could effectively anchor polysulfides for mitigating the shuttle effect, facilitating uniformly thin Li2S film, and promoting the mass transfer for fast sulfur species conversions. This helps contribute to a continuously high sulfur utilization in Li-S batteries with the HPC-MEC reactors. As a typical exhibition, cobalt embedded hierarchical porous carbon (HPC-Co) could realize to deliver a remarkably high specific capacity of 1,540.6 mAh·g−1, an excellent rate performance of 878.8 mAh·g−1 at 2 C, and high area capacity of 11.6 mAh·cm−2 at a high sulfur load of 10 mg·cm−2 and low electrolyte/sulfur ratio of 5 µL·mg−1.