3D MXene architectures as sulfur hosts for high-performance lithium-sulfur batteries

Lithium-sulfur batteries(LSBs)are one of the most promising energy storage devices because of their high theoretical energy density;however,inherent issues including poor electrical conductivity and severe dissolution of S and its discharged products hinder their practical applications.MXenes have metallic conductivity,ultra-thin two-dimensional(2D)structures,rich surface functional groups,and macrostructural adjustability and have been widely used to design advanced sulfur hosts.3D network structures assembled by 2D MXene nanosheets have shown superior performance for improving reaction kinetics,accommodating and dispersing sulfur at the micro-/nanoscale,and capturing polysulfides due to their porous interconnected structure.Herein,the applications of MXene architectures related to 2D layered structures,3D multilayered structures,and 3D spherical structures as sulfur hosts are reviewed.The structure-performance relationship,challenges for current designs,and opportunities for future 3D architectures for LSBs are also analyzed.

Bio-derived N-doped porous carbon as sulfur hosts for high performance lithium sulfur batteries

Shuttle effect,poor conductivity and large volume expansion are the main factors that hinder the practical application of sulfur cathodes.Currently,rational structure designing of carbon-based sulfur hosts is the most effective strategy to address the above issues.However,the preparation process of carbon-based sulfur hosts is usually complex and costly.Therefore,it is necessary to develop an efficient and cost-effective method to fabricate carbon hosts for high-performance sulfur cathodes.Herein,we reported the fabrication of a bio-derived nitrogen doped porous carbon materials(BNPC)via a molten-salt method for high performance sulfur cathodes.The long-range-ordered honeycomb structure of BNPC is favorable for the trapping of polysulfide(PS)species and accommodates the volumetric variation of sulfur during cycling,while the high graphitization degree of BNPC favors the redox kinetics of sulfur cathodes.Moreover,the nitrogen doping content not only enhances the electrical conductivity of BNPC,but also provides ample anchoring sites for the immobilization of PS,which plays a key role in suppressing the shuttle effect.As a result,the S@BNPC cathode exhibits a high initial specific capacity of 1189.4 mA·h/g at 0.2C.After 300 cycles,S@BNPC still maintains a capacity of 703.2 mA·h/g which corresponds to a fading rate of 0.13%per cycle after the second cycle.This work offers vast opportunities for the large-scale application of high performance carbon-based sulfur hosts.

Mesoporous Mn-Sn bimetallic oxide nanocubes as long cycle life anodes for Li-ion half/full cells and sulfur hosts for Li-S batteries

Mesoporous Mn-Sn bimetallic oxide （BO） nanocubes with sizes of 15-30 run show outstanding stable and reversible capacities in lithium ion batteries CLIBs）, reaching 856.8 mAh.g-1 after 400 cycles at 500 mA·g^-1 and 506 mAh·g^-1 after 850 cycles at 1,000 mA·g^-1. The prelimLnary investigation of the reaction mechanism, based on X-ray diffraction measurements, indicates the occurrence of both conversion and alloying-dealloying reactions in the Mn-Sn bimetallic oxide electrode. Moreover, Mn-Sn BO//LiCoO2 Li-ion full cells were successfully assembled for the first time, and found to deliver a relatively high energy density of 176.25 Wh·kg^-1 at 16.35 W·kg^-1 （based on the total weight of anode and cathode materials）. The superior long-term stability of these materials might be attributed to their nanoscale size and unique mesoporous nanocubic structure, which provide short Li^＋ diffusion pathways and a high contact area between electrolyte and active material. In addition, the Mn-Sn BOs could be used as advanced sulfur hosts for lithium-sulfur batteries, owing to their adequate mesoporous structure and relatively strong chemisorption of lithium polysulfide. The present results thus highlight the promising potential of mesoporous Mn-Sn bimetallic oxides for application in Li-ion and Li-S batteries.

Simultaneous realization of high sulfur utilization and lithium dendrite-free via dual-effect kinetic regulation strategy toward lithium-sulfur batteries

With the high theoretical specific capacity and energy density,lithium-sulfur batteries(LSBs)have been intensively studied as promising candidates for energy storage devices.However,LSBs are largely hindered by inferior sulfur utilization and uncontrollable dendritic growth.Herein,a hierarchical functionalization strategy of stepwise catalytic-adsorption-conversion for sulfur species via the synergetic of the efficiently catalytic host cathode and light multifunctional interlayer has been proposed to concurrently address the issues arising on the dual sides of the LSBs.The multi-layer SnS_(2) micro-flowers embedded into the natural three-dimensional(3D)interconnected carbonized bacterial cellulose(CBC)nanofibers are fabricated as the sulfur host that provides numerous catalytic sites for the rapid catalytic conversion of sulfur species.Moreover,the distinctive CBC-based SnO_(2)-SnS_(2) heterostructure network accompanied high conductive carbon nanofibers as the multifunctional interlayer promotes the rapid anchoringdiffusion-conversion of lithium polysulfides,Li^(+)flux redistribution,and uniform Li deposition.LSBs equipped with our strategy exhibit a high reversible capacity of 1361.5 m A h g^(-1)at 0.2 C and superior cycling stability with an ultra-low capacity fading of 0.031%per cycle in 1000 cycles at 1.5 C and 0.046%at 3 C.A favorable specific capacity of 859.5 m A h g^(-1)at 0.3 C is achieved with a high sulfur mass loading of 5.2 mg cm^(-2),highlighting the potential of practical application.The rational design in this work can provide a feasible solution for high-performance LSBs and promote the development of advanced energy storage devices.

Hierarchically porous, ultrathin N–doped carbon nanosheets embedded with highly dispersed cobalt nanoparticles as efficient sulfur host for stable lithium–sulfur batteries

The sluggish redox kinetics and shuttle effect of soluble polysulfides intermediate primarily restrict the electrochemical performance of lithium–sulfur(Li–S) batteries. To address this issue, rational design of high–efficiency sulfur host is increasingly demanded to accelerate the polysulfides conversion during charge/discharge process. Herein, we propose a macro–mesoporous sulfur host(Co@NC), which comprises highly dispersed cobalt nanoparticles embedding in N–doped ultrathin carbon nanosheets. Co@NC is simply synthesized via a carbon nitride–derived pyrolysis approach. Owing to the highly conductive graphene–like matrix and well defined porous structure, the designed multifunctional Co@NC host enables rapid electron/ion transport, electrolyte penetration and effective sulfur trapping. More significantly,N heteroatoms and homogeneous Co nanocatalysts in the graphitic carbon nanosheets could serve as chemisorption sites as well as electrocatalytic centers for sulfur species. These Co–N active sites can synergistically facilitate the redox conversion kinetics and mitigate the shuttling of polysulfides, thus leading to improved electrochemical cycling performance of Li–S batteries. As a consequence, the S/Co@NC cathode demonstrates high initial specific capacity(1505 mA h g-1 at 0.1 C) and excellent cycling stability at 1 C over 300 cycles, giving rise to a capacity retention of 91.7% and an average capacity decline of 0.03%cycle-1.

Incorporation of layered tin(Ⅳ) phosphate in graphene framework for high performance lithium-sulfur batteries

To anchor the polysulfide and enhance the conversion kinetics of polysulfide to disulfide/sulfide is critical for improving the performance of lithium-sulfur battery.For this purpose,the graphene-supported tin(Ⅳ) phosphate(Sn(HPO_4)_2·H_2 O,SnP) composites(SnP-G) are employed as the novel sulfur hosts in this work.When compared to the graphene-sulfur and carbon-sulfur composites,the SnP-G-sulfur composites exhibit much better cycling performance at 1.0 C over 800 cycles.Meanwhile,the pouch cell fabricated with the SnP-G-sulfur cathodes also exhibits excellent performance with an initial capacity of1266.6 mAh g^(-1)(S) and capacity retention of 76.9% after 100 cycles at 0.1 C.The adsorption tests,density functional theory(DFT) calculations in combination with physical cha racterizations and electrochemical measurements provide insights into the mechanism of capture-accelerated conversion mechanism of polysulfide at the surface of SnP.DFT calculations indicate that the Li-O bond formed between Li atom(from Li_2 S_n,n=1,2,4,6,8) and O atom(from PO_3-OH in SnP) is the main reason for the strong interactions between Li_2 S_n and SnP.As a result,SnP can effectively restrain the shuttle effect and improving the cycling performance of Li-S cell.In addition,by employing the climbing-image nudged elastic band(ciNEB) methods,the energy barrier for lithium sulfide decomposition(charging reaction) on SnP is proved to decrease significantly compared to that on graphene.It can be concluded that SnP is an effective sulfur hosts acting as dual-functional accelerators for the conversion reactions of polysulfude to sulfide(discharging reaction) as well as polysulfide to sulfur(charging reaction).

Designing metal sulfide-based cathodes and separators for suppressing polysulfide shuttling in lithium-sulfur batteries

Lithium-sulfur(Li-S)batteries,known for their high energy density,are attracting extensive research interest as a promising next-generation energy storage technology.However,their widespread use has been hampered by certain issues,including the dissolution and migration of polysulfides,along with sluggish redox kinetics.Metal sulfides present a promising solution to these obstacles regarding their high electrical conductivity,strong chemical adsorption with polysulfides,and remarkable electrocatalytic capabilities for polysulfide conversion.In this review,the recent progress on the utilization of metal sulfide for suppressing polysulfide shuttling in Li-S batteries is systematically summarized,with a special focus on sulfur hosts and functional separators.The critical roles of metal sulfides in realizing high-performing Li-S batteries have been comprehensively discussed by correlating the materials’structure and electrochemical performances.Moreover,the remaining issues/challenges and future perspectives are highlighted.By offering a detailed understanding of the crucial roles of metal sulfides,this review dedicates to contributing valuable knowledge for the pursuit of high-efficiency Li-S batteries based on metal sulfides.

A flexible design strategy to modify Ti3C2Tx MXene surface terminations via nucleophilic substitution for long-life Li-S batteries

MXene-based materials have gained considerable attention for lithium-sulfur(Li-S)batteries cathode materials due to their superior electric conductivity and high affinitive to polysulfides.However,there are still challenges in modifying the surface functional groups of MXene to further improve the electrochemical performance and increase the structure variety for MXene-based sulfur host.Herein,we report an efficient and flexible nucleophilic substitution(S_(N))strategy to modify the Ti_(3)C_(2)T_(x) surface terminations and purposefully designed Magnolol-modified Ti_(3)C_(2)T_(x)(M-Ti_(3)C_(2)T_(x))as powerful cathode host materials.Benefiting from more C-Ti-O bonds forming and diallyl groups terminations reducing after the dehalogenation and nucleophilic addition reactions,the given M-Ti_(3)C_(2)T_(x) electrode could effectively suppress the lithium polysulfides shuttling via chemisorption and C—S covalent bond formation.Besides,the Magnolol-modified Ti_(3)C_(2)T_(x) significantly accelerates polysulfide redox reaction and reduces the activation energy of Li_(2) S decomposition.As a result,the as-prepared M-Ti_(3)C_(2)T_(x) electrode displays an excellent rate capability and a high reversible capacity of 7.68 mAh cm^(-2)even under 7.2 mg cm^(-2)S-loaded with a low decay rate of 0.07%(from 2 nd cycle).This flexible surface-modified strategy for MXene terminations is expected to be extended to other diverse MXene applications.

Hierarchical and lamellar porous carbon as interconnected sulfur host and polysulfide-proof interlayer for Li–S batteries

A robust three-dimensional(3D)interconnected sulfur host and a polysulfide-proof interlayer are key components in high-performance Li–S batteries.Herein,cellulose-based 3D hierarchical porous carbon(HPC)and two-dimensional(2D)lamellar porous carbon(LPC)are employed as the sulfur host and polysulfide-proof inter-layer,respectively,for a Li–S battery.The 3D HPC displays a cross-linked macroporous structure,which allows high sulfur loading and restriction capability and provides unobstructed electrolyte diffusion channels.With a stackable carbon sheet of 2D LPC that has a large plane view size and is ultrathin and porous,the LPC-coated separator effectively inhibits polysulfides.An optimized combination of the HPC and LPC yields an electrode structure that effectively protects the lithium anode against corrosion by polysulfides,giving the cell a high ca-pacity of 1339.4 mAh g^(-1) and high stability,with a capacity decay rate of 0.021% per cycle at 0.2C.This work provides a new understanding of biomaterials and offers a novel strategy to improve the performance of Li–S batteries for practical applications.

Vapor deposition of aluminium oxide into N-rich mesoporous carbon framework as a reversible sulfur host for lithium-sulfur battery cathode

Restraining the shuttle effects of lithium polysulfides is the key to improve the cycling reversibility and stability of lithium-sulfur(Li-S)batteries for which design of robust sulfur hosts has been regarded as the most effective strategy.In this work,we report a new type of hybrid sulfur host which is composed of Al_(2)O_(3) homogenously decorated in nitrogen-rich mesoporous carbon framework(NMC-Al_(2)O_(3)).The NMC-Al_(2)O_(3) hybrid host features a poly-dispersed spherical morphology and a mesoporous configuration with high surface area and large pore volume that can accommodate a high sulfur content up to 73.5 wt.%.As a result,the fabricated NMC-Al_(2)O_(3)-S cathode exhibits all-round improvements in electrochemical properties in term of capacities(1,212 mAh·g^(-1)at 0.2 C;755 mAh·g^(-1)at 2 C),cycling charge-discharge reversibility(sustainably 100%efficiencies)and stability(1,000 cycles with only 0.023%capacity decay per cycle at 0.5 C).By contrast,the Al_(2)O_(3)-free NMC-S cathode shows both decreased capacities and rapidly descending Coulombic efficiencies during cycling.Density functional theory(DFH")calculations further reveal that the implanted Al_(2)O_(3) can greatly enhance the chemical adsorption and catalytic conversion for various lithium polysulfides and thereby effectively prevent the polysulfide shuttling and significantly improve the utilizability,reversibility and stability of sulfur cathode.

Defect-rich porous tubular graphitic carbon nitride with strong adsorption towards lithium polysulfides for high-performance lithium-sulfur batteries

The commercialization of the lithium-sulfur(Li-S)batteries is severely hampered by the shuttle effect and sluggish kinetics of lithium polysulfides(Li PSs).In this study,porous tubular graphitic carbon nitride(PTCN)was synthesized as the sulfur host by hydrothermal treatment,thermal shock and etching methods.By etching technology,the hollow nanotube tentacles grow on the tube wall of PTCN,the mesoporous appears on the inner wall,and a large number of nitrogen defects are introduced.The verticallyrooted hollow nanotube tentacles on the PTCN surface facilitate electron conduction for sulfur redox reactions.The hollow and porous architecture exposes plentiful active interfaces for accelerated redox conversion of polysulfide.Furthermore,the nitrogen defects in PTCN enable more excellent intrinsic conductivity,higher adsorbability and conversion catalytic activity to Li PSs.Based on the above synergetic effect,the batteries with PTCN/S cathodes realize a high discharge capacity of 504 m Ah g^(-1) at 4 C and a stable cycling behavior over 500 cycles with a low capacity decay of 0.063%per cycle.The results indicate a promising approach todesigning a high performance electrode material for Li-S batteries.

Double role of CoOeCo_(4)N hetero-nanocages as sulfur host for lithiumsulfur batteries

Lithium-sulfur batteries(LiSBs)are widely deemed as the most promising energy storage devices to substitute for traditional Li-ion batteries.However,its wide application is impeded by the soluble lithium polysulfides(LiPSs),which is called the shuttle effect,and the irregular distribution of final product Li_(2)S.Herein,based on the interfaces engineering,CoO-Co_(4)N hetero-nanocages are used as the sulfur host for LiSBs.Taking advantage of the polarity of CoO with the conductivity of Co_(4)N,CoO-Co_(4)N nanocages not only can provide large void space for sulfur volume fluctuation,but also can adsorb polysulfides and simultaneously regulate the nucleation of solid Li_(2)S by the‘trapping-diffusion-conversion’mechanism,which significantly enhances the redox kinetic of LiSBs and the utilization of active materials.Eventually,LiSBs with CoO-Co_(4)N nanocages host exhibit higher rate capacity(737 mAh·g^(-1) at 2 C)and cycling stability(662 mAh·g^(-1) at^(-1) C after 350 cycles).Even when the areal sulfur loading is as high as 3.0 mg cm^(-2),a high capacity of 713 mAh·g^(-1) can still be achieved after 100 cycles at 0.2 C.This host with sufficient polar-conductive interfaces expands‘trapping-diffusion-conversion’concept for the design of fast kinetic and high performance LSBs.

Multilevel structured carbon film as cathode host for Li-S batteries with superhigh-areal-capacity

The commercialization of lithium-sulfur (Li-S) battery could be accelerated by designing advanced sulfur cathode with high sulfur utilization and stable cycle life at a high sulfur loading. To allow the energy density of Li-S batteries comparable to that of commercial Li-ion batteries, the areal capacity of sulfur cathode should be above 4 mA·h·cm−2. In general, a high sulfur loading often causes rapid capacity fading by slowing electron/ion transport kinetics, catastrophic shuttle effect and even cracking the electrodes. To address this issue, herein, a multilevel structured carbon film is built by covering highly conductive CNTs and hollow carbon nanofiber together with carbon layer via chemical vapor deposition. The self-standing carbon film exhibits well-interweaved conductive network, hollow fibrous structure and abundant N, O co-doped active sites, which combine the merits of high electronic conductivity (1200·S·m−1), high porosity and polar characteristic in one host. Benefiting from this attractive multilevel structure, the obtained sulfur cathode based on the carbon film host shows an ultra-high areal capacity of 8.9 mA·h·cm−2 at 0.2 C with outstanding cyclability over 60 cycles. This work shed light on designing advanced sulfur host for Li-S batteries with high areal capacity and high cycle stability, and might make a contribution to the commercialization of Li-S batteries.