Facile synthesis of sulfurized polyacrylonitrile composite as cathode for high-rate lithium-sulfur batteries

Sulfurized polyacrylonitrile(SPAN)as a promising cathode material for lithium sulfur(Li-S)batteries has drawn increasing attention for its improved electrochemical performance in carbonate-based electrolyte.However,the relatively poor electronic and ionic conductivities of SPAN limit its high-rate and lowtemperature performances.In this work,a novel one-dimensional nanofiber SPAN(SFPAN)composite is developed as the cathode material for Li-S batteries.Benefitting from its one-dimensional nanostructure,the SFPAN composite cathode provides fast channels for the migration of ions and electronics,thus effectively improving its electrochemical performance at high rates and low temperature.As a result,the SFPAN maintains a high reversible specific capacity^1200 mAh g−1 after 400 cycles at 0.3 A g−1 and can deliver a high capacity of^850 mAh g−1 even at a high current density of 12.5 A g−1.What is more,the SFPAN can achieve a capacity of^800 mAh g−1 at 0℃and^1550 mAh g−1 at 60℃,thus providing a wider temperature range of applications.This work provides new perspectives on the cathode design for high-rate lithium-sulfur batteries.

Cobalt coordination with pyridines in sulfurized polyacrylonitrile cathodes to form conductive pathways and catalytic M-N4S sites for accelerated Li-S kinetics

Sulfurized polyacrylonitrile(SPAN)represents a unique class of cathode material for lithium sulfur(Li-S)batteries as it eradicates the polysulfides shuttling issue in carbonate-based electrolyte.However,due to the essential chemical S-linking and organic nature of SPAN,the active mass percentage and rate capability are two bottleneck issues preventing its ultimate deployment outside of laboratories.In the current work,aiming to endow both the charge conductivity and catalytic activity to SPAN for maximizing the redox kinetics of S conversion,a freestanding nanofibrous SPAN cathode embedding conductive CNTs and atomically dispersed Co centers is fabricated via multivariate electrospinning.While the CNTs enable dramatically enhancing the fiber conductivity and generating mesoscopic porosity for facilitating charge and mass transportation,the cross-linking of SPAN by Co-N_(4) S motifs creates extra charge conduction pathways and further serves as the catalytic active sites for expediting redox S conversion.As a result,an extraordinary Li-SPAN performance is achieved with a high specific capacity up to 1856 mAh g^(-1)@0.2 C,a superb rate capability up to 10 C,and an ultra-long battery life up to 1500 cycles@1 C.Consequently,our study here provides insights into the adoption of coordination chemistry to maximize the sulfur utilization by ensuring a more complete redox conversion from SPAN to Li2 S,and vice versa.

SnS_(2)nanoparticles embedded in sulfurized polyacrylonitrile composite fibers for high-performance potassium-ion batteries

Potassium-ion batteries(PIBs)have garnered significant attention as a promising alternative to commercial lithium-ion batteries(LIBs)due to abundant and cost-efficient potassium reserves.However,the large size of potassium ions and the resulting sluggish reaction kinetics present major obstacles to the widespread use of PIBs.Herein,we present a simple method to ingeniously encapsulate SnS_(2)nanoparticles within sulfurized polyacrylonitrile(SPAN)fibers(SnS_(2)@SPAN)for serving as a high-performance PIB anode.The large interlayer spacing of SnS_(2)provides a fast transport channel for potassium ions during charge–discharge cycles,while the one-dimensional SPAN skeleton offers massive binding sites and shortens the diffusion path for potassium ions,facilitating faster reaction kinetics.Additionally,the excellent ductility of SPAN can effectively accommodate the large volume changes that occur in SnS_(2)upon potassium-ion insertion,thereby enhancing the cyclic stability of SnS_(2).Benefiting from the above advantages,the SnS_(2)@SPAN composites exhibit impressive cyclability over 500 cycles at 4 A g−1,with a capacity retention rate close to 100%.This study provides an effective approach for stabilizing high-capacity PIB anode materials with large volume variations.

Structure and reactions mechanism of sulfurized polyacrylonitrile as cathodes for rechargeable Li-S batteries

Sulfurized polyacrylonitrile(S@pPAN)composite provides a conductive pathway for sulfur active material at the molecular level and has already become one of the most promising cathode materials in lithium-sulfur batteries because of its outstanding electrochemical performances via novel solid-solid conversion mechanism.Although there are a great number of researches on the S@pPAN composite material,the accurate structure of S@pPAN and its redox reaction mechanism during the charge-discharge process still have not been determined.The previous research and inferences about the structure of S@pPAN and its electrochemical reaction mechanism were summarized in this review,providing a reference for the future study of lithiumsulfur batteries.

Flexible,solid-state,fiber-network-reinforced composite solid electrolyte for long lifespan solid lithium-sulfurized polyacrylonitrile battery

Solid lithium-sulfur batteries(SLSBs)show potential for practical application due to their possibility for high energy density.However,SLSBs still face tough challenges such as the large interface impedance and lithium dendrite formation.Herein,a highperformance SLSB is demonstrated by using a fiber network reinforced Li_(6.75)La_(3)Zr_(1.75)Ta_(0.25)O_(12)(LLZTO)based composite solid electrolyte(CSE)in combination with sulfurized polyacrylonitrile(SPAN)cathode.The CSE consisting of an electrospun polyimide(PI)film,LLZTO ionically conducting filler and polyacrylonitrile(PAN)matrix,which is named as PI-PAN/LLZTO CSE,possesses high room-temperature ionic conductivity(2.75×10^(-4)S/cm),high Li^(+)migration number(tLi+)of 0.67 and good interfacial wettability.SPAN is utilized due to its unique electrochemical properties:reasonable electronic conductivity and no polysulfides shuttle effect.The CSE enables a highly stable Li plating/stripping cycle for over 600 h and good rate performance.Moreover,the assembled SLSB exhibits good cycle performance of accomplishing 120 cycles at 0.2 C with the capacity retention of 474 mAh/g,good rate properties and excellent long-term cycling stability with a high capacity retention of 86.49%from 15^(th)to 1,000^(th)cycles at 1.0 C.This work rationalizes our design concept and may guide the future development of SLSBs.

Te0.045S0.955PAN composite with high average discharge voltage for Li–S battery

As a sulfur-containing cathode material,sulfide polyacrylonitrile(SPAN)is expected to be used for longlife lithium-sulfur battery because there is no shuttle effect occurred in its charge process.However,its specific capacity and discharge potential need to be further improved to satisfy the urgent demands for high-performance batteries.In this paper,Te0.045S0.955PAN composite was synthesized by co-heating TexS1-x and PAN,and the superior electrochemical performance to that of SPAN was obtained because of doping Te with high conductivity.The as-prepared Te0.045S0.955PAN composite possessed the specific capacity of 675 mAh g^-1 after 100 cycles at the current density of 0.1 A g^-1 with high capacity retention of96.6%compared to the second cycle.Especially,during cycling,Te0.045S0.955PAN showed average discharge voltages of 1.88-1.91 V,which were higher than 1.85-1.88 V for SPAN at the same current density.Thus doping Te provides a new strategy for increasing the energy density of SPAN.

A Mixed Ether Electrolyte for Lithium Metal Anode Protection in Working Lithium-Sulfur Batteries

Lithium-sulfur(Li-S) battery is considered as a promising energy storage system to realize high energy density.Nevertheless,unstable lithium metal anode emerges as the bottleneck toward practical applications,especially with limited anode excess required in a working full cell.In this contribution,a mixed diisopropyl ether-based(mixed-DIPE) electrolyte was proposed to effectively protect lithium metal anode in Li-S batteries with sulfurized polyacrylonitrile(SPAN) cathodes.The mixed-DIPE electrolyte improves the compatibility to lithium metal and suppresses the dissolution of lithium polysulfides,rendering significantly improved cycling stability.Concretely,Li | Cu half-cells with the mixed-DIPE electrolyte cycled stably for 120 cycles,which is nearly five times longer than that with routine carbonate-based electrolyte.Moreover,the mixedDIPE electrolyte contributed to a doubled life span of 156 cycles at 0.5 C in Li | SPAN full cells with ultrathin 50 μm Li metal anodes compared with the routine electrolyte.This contribution affords an effective electrolyte formula for Li metal anode protection and is expected to propel the practical applications of high-energy-density Li-S batteries.

Dual-additives enable stable electrode-electrolyte interfaces for long life Li-SPAN batteries

Sulfurized polyacrylonitrile(SPAN)is proposed as a promising cathode material for lithium sulfur batteries.However,the continuous side reactions at the electrolyte-electrode interfaces as well as the slow redox kinetics of SPAN cathode deteriorate the electrochemical performance.In this study,an electrolyte with dual-additives comprising 2-fluoropyridine(2-FP)and lithium difluorobis(oxalato)phosphate(LiDFBOP)was used to improve the performance of Li||SPAN cells.2-FP has a lower lowest occupied molecular orbital energy than that of the solvents in the electrolyte,leading to its prior reduction.A LiF-rich film can be formed on the electrode,effectively improving the stability of the electrolyte-electrode interfaces and prolonging the life.Simultaneously,LiDFBOP could form an electrolyte-electrode interface film containing a large amount of Li_(x)PO_(y)F_(z) species,compensating for the kinetic deterioration caused by the lower ionic conductive of LiF formed at the electrolyte-electrode interface.Hence,an electrode-interface film with good chemical stability and high Li^(+) transport was established by LiF and Li_(x)PO_(y)F_(z)-rich species.The Li||SPAN cell with the electrolyte containing dual-additives demonstrates an excellent capacity retention of 97.5%after 200 cycles at 1.0 C,25℃,comparing to 56.2%capacity retention without additives.Moreover,the rate capacities of cells with dual-additives can reach 1128.1 mAh/g at 5 C,comparing to only 813.5 mAh/g using electrolyte without additives.Our results shown that the dual-additives in electrolyte provide a promising strategy for practical application of lithium sulfur batteries with SPAN cathodes.

Sulfurization accelerator coupled Fe_(1-x)S electrocatalyst boosting SPAN cathode performance

Sulfurized polyacrylonitrile(SPAN)cathode exhibits improved cycling stability in carbonate electrolytes due to the existent of-S_(x)^(2-)-(2≤n≤4)units.However,it is still challenging for SPAN to achieve higher sulfur content,superior conductivity,and faster polysulfide conversion kinetics in ether electrolytes.Herein,polyacrylonitrile(PAN),2-morpholinothiobenzothiazole(MBS),and FeCl_(3)coated reduced graphene oxide(rGO)were used to fabricate advanced sulfur cathode through electrospinning technology to address these problems.During PAN sulfuration reactions,the MBS with abundant unsaturated bonds served as the vulcanization accelerator to facilitate the formation of longer chain sulfur species(-S_(3)-/-S_(4)-)and increase the sulfur content in the SPAN electrode system.Meanwhile,Fe_(1-x)S is in situ converted from FeCl_(3),which acts as the electrocatalyst to promote Li_(2)S nucleation and decomposition reactions.As a result,the Fe_(1-x)S/SPAN/rGO electrode with high sulfur loading of 2.0 mg·cm^(-2)delivers a reversible capacity of 1122 mAh·g^(-1)at 0.1 A·g^(-1).Notably,at a large current density of 5.0 A·g^(-1),the Fe_(1-x)S/SPAN/rGO electrode still displays a high specific capacity of 924 mAh·g^(-1)with an ultra-stable cycling life over 2000 cycles.The present work provides new insights into designing of high-performance electrode materials for long-lasting Li-S batteries.

Flexible and stable 3D lithium metal anodes based on self-standing MXene/COF frameworks for high-performance lithium-sulfur batteries

Lithium metal(Li)is believed to be the ultimate anode for lithium-ion batteries(LIBs)owing to the advantages of high theoretical capacity,the lowest electrochemical potential,and light weight.Nevertheless,issues such as uncontrollable growth of Li dendrites,large volume changes,high chemical reactivity,and unstable solid electrolyte interphase(SEI)hinder its rapid development and practical application.Herein a stable and dendrite-free Li-metal anode is obtained by designing a flexible and freestanding MXene/COF framework for metallic Li.COF-LZU1 microspheres are distributed among the MXene film framework.Lithiophilic COF-LZU1 microspheres as nucleation seeds can promote uniform Li nucleation by homogenizing the Li^(+)flux and lowering the nucleation barrier,finally resulting in dense and dendrite-free Li deposition.Under the regulation of the COF-LZU1 seeds,the Coulombic efficiency of the MXene/COF-LZU1 framework and electrochemical stability of corresponding symmetric cells are obviously enhanced.Li-S full cells with the modified Li-metal anode and sulfurized polyacrylonitrile(S@PAN)cathode also exhibited a superior electrochemical performance.