Electrochemical Performance Of Lithium-sulfur Batteries Research Articles

Effect of activated Ketjen black and nano-size sulfur particles on electrochemical performance of lithium-sulfur battery

The sulfur-activated Ketjen black nanostructure (S@KB), as the cathode in lithium-sulfur (Li-S) battery, was synthesized using the sulfur-amine chemistry technique. The nano-sized sulfur particles expedite the electrical conductivity, and strengthen the sulfur utilization. Moreover, the sulfur nanoparticles compensate for its massive volume expansion driven by the lithiation process. The activation of KB can cultivate the electrochemical properties of the cathodic composition for protracted cycling by intensifying the available surface area. The sulfur mass loading was about 1 mg cm−2. The premier specific capacity was acquired 1190.63 mAh g−1 at 0.1 C, which was stabilized to 671.32 mAh g−1 after 200 cycles. The accomplished characterizations substantiate the suitable incorporation of sulfur into the activated KB (AKB) structure and the splendid interaction between them. It was educed that the S@KB cathode can relieve the penetration of polysulfides toward the anode and, as a result subdue the shuttle effect. It was determined a notable reversible capacity of 1002.81 mAh g−1 after 40 cycles at varied current rates.

Modulation of Potential-Limiting Steps in Lithium-Sulfur Batteries by Catalyst Synergy.

Electrocatalysis is considered to be an effective method to solve the sluggish kinetics of lithium-sulfur batteries. However, a single catalyst cannot simultaneously catalyze multi-step sulfur reductions. And once the catalyst surface is covered by the initially deposited solid products, the subsequent catalytic activity will significantly deteriorate. Here, microporous ZIF-67 and its derivative nano-metallic Co0 are used as dual-catalyst aiming to address these drawbacks. The dual catalytic center effectively cooperates the adsorption and electron transfer for multi-steps of sulfur reductions, transforming the potential-limited step (Li2S4→Li2S2/Li2S) into a thermodynamic spontaneous reaction. ZIF-67 first adsorbs soluble Li2S4 to form a coordination structure of ZIF-Li2S4. Then nano-metallic Co0 attracts uncoordinated S atoms in ZIF-Li2S4 and facilitates the breaking of S-S bonds to form transient reductive ZIF-Li2S2 and Co-S2 via. spontaneous electron transfer. These intermediates facilitate continuous conversion to Li2S with reduced formation energy, which is beneficial to the regeneration of the catalyst. As a result, the cathode with ZIF@CNTs/Co@CNFs synergetic catalyst achieves initial areal capacity of 4.7mAhcm-2 and maintains 3.5mAhcm-2 at low electrolyte/sulfur ratio (E/S) of 5µLmg-1. This study provides valuable guidance for improving the electrochemical performance of lithium-sulfur batteries through catalyst synergistic strategies for multi-step reactions.

Cherry blossom derived micron carbon sheets loaded with Co based particles served as sulfur host for lithium sulfur batteries

In order to effectively alleviate the shuttle effect in lithium-sulfur batteries (LSBs), cherry blossom-derived micron carbon sheets loaded with a small amount of Co-based nano-particles are synthesized in this work. After the thermal decomposition of ZIF-67, the composite shows a high specific surface area (2768.2 m² g−1) and pore volume (1.63 cm³ g−1), which can enhance the physical adsorption of polysulfides. Moreover, the Co-N and Co nano-particles obtained by ZIF-67 have strong catalytic and polar adsorption abilities. Not only can they accelerate the electrochemical reaction, but also effectively inhibit the shuttle effect of polysulfides, which in turn improves the electrochemical performance of lithium-sulfur batteries. Thus, the initial discharge capacity of the Co-PB@S electrodes reached 933 mAh g−1, with a remaining capacity of 550 mAh g−1 after 500 cycles at 0.5 C. This work may provide a practical way for the application of LSBs and the field of electrocatalysis.

Synergistic improvements on capacity and Coulombic efficiency of lithium-sulfur batteries with NiSe-Ni2P/C modification on PP separators

Lithium-sulfur batteries (LSBs) emerge as promising energy storage devices due to their high theoretical energy density. So far, there are constrained issues that need to be urgently addressed, such as the shuttle effect of lithium polysulfides (LiPS) and the sluggish kinetics of redox reactions. Herein, NiSe-Ni2P/C composite was synthesized and casted on the cathode side of polypropylene (PP) separator. This investigation reveals that the adsorption-catalysis synergistic effect of NiSe-Ni2P/C composite, accelerates the reduction of LiPS to lithium sulfide (Li2S) as well as the oxidation of Li2S. The synergistic effect effectively mitigates the shuttle effect of LiPS, reduces concentration polarization, and improves Coulombic efficiency (CE) throughout the entire lifespan. At a current density of 0.05 C, LSBs with NiSe-Ni2P/C modified PP separators exhibit a remarkable high initial CE of 97.0% and a substantial discharge specific capacity of 1205.4 mAh gs−1. Even under conditions of a high sulfur loading (4.3 mg cm−2) and a limited electrolyte dosage (10 μL mgs−1), the LSBs maintained a reversible specific capacity of 804 mAh gs−1, a CE of 94%, and an energy density of 1232.1 Wh kgs−1 after 720 h of continuous cycling at 0.05 C. This work provides a solution for achieving long-time, high-capacity, and high-CE electrochemical performance in LSBs with a high sulfur loading and a limited electrolyte dosage.

Carbon nanotubes integrated with multiphasic molybdenum diselenide nanosheets as hybrid membrane accomplish highly efficient electrocatalysts for lithium-sulfur batteries

Lithium sulfur (Li-S) batteries are considered a promising application device due to their high theoretical capacity and energy density. However, the commercialization of Li-S batteries is hindered by the rapid capacity fading caused by the shuttle effect of lithium polysulfide (LiPSs) and the sluggish redox reaction of sulfur cathodes. To address these issues, the hybrid membrane with combination of multiphasic molybdenum diselenide nanosheets (MMS) modified carbon nanotubes (MMS@CNTs) and utilized Li2S6 catholyte for Li-S batteries. The conductivity CNTs facilitate fast electronic/ionic transport, while the polarity of MMS has a strong affinity for LiPSs, effectively anchoring them, facilitating the redox conversion of lithium polysulfides, and effectively diminishing reaction barriers. The cell with MMS@CNTs displays an initial discharge capacity of 1036.2 mAh g−1 and maintains 810.5 mAh g−1 after 300 cycles at 0.2 C with 5.4 mg sulfur loading. Remarkably, even at 10.8 mg sulfur loading, the MMS@CNTs membrane displays high capacity of 8.1 mAh and maintains 6.7 mAh over 100 cycles. The results show that the efficient chemical anchoring polysulfides and catalyzing redox reaction by multifunctional MMS@CNTs hybrid composites is promising for assembling with a high sulfur loading electrode, which exhibits a superior electrochemical performance in Li-S batteries.

Synergistic Effect of CNT-TiO2 Catalyst and 3D Electrode Architecture for Electrochemical Performance in Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are a potential electrochemical storage system for the future with high capacity (1675 mAh g−1) and energy density (∼2600 Wh kg−1). The poor conductivity of sulfur, polysulfide shuttle effect, and volume expansion of the sulfur cathode are the main hurdles to their commercialization. To mitigate these issues, this work represents a rational composite of hybrid multiwalled carbon nanotubes (MWCNT) -TiO2 high surface area carbon-sulfur composite (CTHS) onto a 3D carbon fiber (CF) based free-standing electrode (CTHS@CF) architecture. TiO2 can effectively anchor the polysulfides by chemical bonding and improve cyclability. MWCNTs and CFs are the effective electron transport materials that accelerate the redox kinetics of polysulfides. The electrochemistry of CTHS@CF reveals an excellent discharge capacity of 910 mAh g−1 (1st cycle) at 100 mA g−1 compared to the conventional aluminum-coated (CTHS@Al) of 532 mAh g−1. The CTHS@CF (at 300 mA g−1) displays 514 mAh g−1 (initial discharge) capacity with 83% capacity retention up to 100 cycles, whereas CTHS@Al shows 394 mAh g−1 with 44% capacity retention. Combining 3D electrode architecture with the metal oxide (TiO2) plays a vital role in the electrochemistry of LSBs by improving the stability of the battery’s cycle life and overall energy density.

Sulfonic group modified carbon nanotubes: the decorative strategy for enhancing the performance of lithium-sulfur batteries

Sulfonic group-modified thin-walled porous CNTs are successfully designed by reacting with sulfuric acid, and enhance the electrochemical performance of lithium-sulfur batteries by dispersing sulfur and adsorbing polysulfides.

A gel polymer electrolyte functionalized separator for high-performance lithium-sulfur batteries.

Lithium-sulfur (Li-S) batteries, featuring ultrahigh specific theoretical energy density with low-cost raw materials, have been deemed one of the most promising candidates for next-generation energy storage and conversion devices. However, the shuttle effect of soluble Li polysulfides (LiPSs) has seriously hindered their practical deployment. Herein, we report that tris(pentafluorophenyl)borane (TPFPB) is used to modify the separator (TPFPB/Al2O3) for suppressing the shuttle effect of LiPSs. In detail, the introduction of TPFPB induces 1,3-dioxolane solvent ring-opening polymerization to form a gel layer between the S cathode and separator for suppressing the shuttle effect of Li polysulfides, effectively improving the electrochemical performance of Li-S batteries. The Li-S batteries using the TPFPB/Al2O3 separator demonstrate outstanding cycling stability and high capacity retention rates. This work provides a useful guideline for separator modification using a functional interface layer to design high-performance Li-S batteries.

CoFe2O4 nanoparticles modified amidation of N-doped carbon nanofibers hybrid catalysts to accelerate electrochemical kinetics of Li-S batteries with high sulfur loading

Lithium-sulfur battery have been considered as promising energy storage devices because of its superiority in energy density. However, the low active material utilization, low sulfur loading, shuttle effect and torpid kinetics of polysulfides, and poor cycling stability limit its commercial applications. Herein, the functionalized nitrogen doped carbon nanofibers containing amide groups were designed by electrospun and polyamidoamine dendrimer (PAMAM) solution impregnation techniques. The obtained amide groups modified nitrogen-doped carbon nanofibers (ANF) were combined with spinel CoFe2O4 (CFO) nanoparticles (CFOANF) via hydrothermal method to design as membrane electrode containing Li2S6 catholyte for lithium-sulfur batteries. The introduction of nitrogen doped and amide groups modified ANF can increase fibers polarity, which have chemical adsorption capability toward lithium polysulfides. CFO nanoparticles can further absorb the soluble polysulfides by strong chemical interaction due to its intrinsic polarity and also serve as a catalyst to promote the redox kinetics of polysulfides conversion. Benefiting from the synergism of the physical confinement, polar chemical adsorption, and catalytic conversion, the as-prepared CFOANF delivers excellent electrochemical performances at high sulfur loading. The as-prepared CFOANF membrane with 6.3 mg cm−2 sulfur loading delivers a high initial capacity of 940 mAh g−1 and excellent long-term cycling stability up to 450 cycles with a low decay rate 0.059 % per cycle at 0.2C. Remarkably, even at 12.6 mg cm−2 and 16.4 mg cm−2 sulfur loading, the CFOANF membrane electrodes show high capacity of 9.7 mAh cm−2 and 11.8 mAh cm−2, respectively. The results show that the chemically anchoring polysulfides and catalyzing redox reaction by multifunctional CFOANF hybrid composite is promising for assembling with a high sulfur loading electrode, which exhibits a superior electrochemical performance in lithium-sulfur batteries.

Investigation of the corrosion behavior influence of carbon interlayer on aluminum collector in lithium-sulfur battery system

Due to the shuttle effect brought by polysulfides, the commercialization of lithium-sulfur batteries still faces significant difficulties. Carbon interlayer is introduced to enhance the electrochemical performance of lithium-sulfur batteries, while the drawback that the interlayer will reversely affect the performance of the current collector was ignored. The current collector has a significant influence and contribution to the cycle stability of lithium-sulfur batteries. In this study, we looked into the electrochemical stability and corrosion situation of standard aluminum foil collectors in lithium-sulfur batteries with carbon interlayer. The results show that the introduction of carbon interlayer into the lithium-sulfur batteries will make aluminum foil and carbon paper form an electronic conduction path and galvanic corrosion occurs, accelerating the corrosion of aluminum foil. Therefore, we propose a new corrosion model. During the cycle, the surface of the aluminum collector becomes a non-dense passivation film and lithium polysulfide terminal (ST−1). Then, under the action of the carbon interlayer, the passivation film peels off and the oxide film is attacked by the electrolyte, thiosulfate and polythionate, resulting in pitting holes and ultimately accelerating the corrosion of the aluminum foil collector. This research has some guiding significance for the commercial application of lithium-sulfur batteries.

A bifunctional electrolyte additive ammonium hexafluorophosphate for long cycle life lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are regarded as the next-generation battery systems for their high theoretical specific capacity andenvironmental friendliness. However, some hard knots such as the “shuttle effect” and lithium dendrite growth impede the engineering application. Here, a bifunctional electrolyte additive (ammonium hexafluorophosphate (AFP)) was chosen to improve the electrochemical performance of Li-S batteries. The addition of AFP has been proved to facilitate the dissolution of Li2S, which reduces the decay of battery capacity and improves the electrochemical kinetics. Meanwhile, AFP induces the formation of “F-rich” SEI, which protects the anode. This work provides a bifunctional AFP electrolyte additive to enhance the performance of Li-S batteries.

Uniform loading of ultrathin MoS2 nanosheets on hollow carbon spheres with mesoporous walls as efficient sulfur hosts for promising lithium-sulfur batteries

The electrochemical performance of lithium-sulfur batteries (LSBs) can be improved by combining rational structural design with the high-efficient catalyst to construct sulfur host materials. The PVP-assisted hydrothermal method was used to synthesize a composite (HCSM@uMoS2) with ultrathin MoS2 nanosheets uniformly loaded on hollow carbon spheres with mesoporous walls (HCSM). The ultrathin MoS2 nanosheets containing 1T metal phase (uMoS2) improved the electrical conductivity of the material while exposing more active sites, enhanced the adsorption to polysulfide and improved the redox reaction kinetics for polysulfide, thus fully suppressing the shuttle effect. Together with the advantages of HCSM, the mesoporous walls and internal cavity can offer enough sulfur storage room and significantly buffer the volume expansion of sulfur species; the high specific surface area and abundant porosity favor electron/ion transfers. As a result, the HCSM@uMoS2-S electrode exhibited outstanding electrochemical performance (675.4 mAh g−1 retention capacity at 0.5 C for 500 cycles) even under the conditions of high areal sulfur loading (5.6 mg cm−2) and less electrolyte (E/S = 10 μL mg−1). This study provides a reference for building sulfur hosts for high-capacity, long-life, and practical LSBs.

Two-birds with one stone: Improving both cathode and anode electrochemical performances via two-dimensional Te-CoTe2/rGO ultrathin nanosheets as sulfur hosts in lithium-sulfur batteries

A Te-doped CoTe2 film could be grown in situ on reduced graphene oxide (rGO) to develop a Te-CoTe2/rGO composite with an ultrathin layered structure, which has multiple protective effects on both the sulfur positive electrode and lithium negative electrode in lithium sulfur (Li-S) batteries. The Te-CoTe2/rGO composite as a sulfur host not only shows a strong adsorbing ability for lithium polysulfides (LiPSs) but can also accelerate the conversion reaction of active material sulfur during the charging/discharging process. More importantly, this host can turn the shuttle effect from an unfavorable factor to a favorable factor, which could improve the electrochemical performance of the lithium anode with uniform lithium plating/stripping resulting from the intermediate polytellurosulfide species (Li2TexSy), which could be generated on the cathode surface via Te reacting with soluble Li2Sn (4 ≤ n ≤ 8). As a result, the S@Te-CoTe2/rGO cathode shows a discharge capacity of 970.0 mA h g−1 in the first cycle at 1 C and retains a high capacity of 545.5 mA h g−1 after 1000 cycles, corresponding to a low capacity decay rate of only 0.043% per cycle. In addition, in situ X-ray diffraction (XRD) and in situ Raman were used to explore the sulfur conversion process. This study not only demonstrates that a two-dimensional (2D) ultrathin Te-CoTe2/rGO composite is successfully developed with multiple effects on Li-S batteries but also opens a new pathway for designing unique sulfur hosts to promote the electrochemical performance of Li-S batteries.

Construction of MoS2@reduced graphene oxide/carbon nanotubes three-dimensional network structure and its application in lithium-sulfur batteries

In order to enhance the electrochemical performance of lithium-sulfur batteries, reduced graphene oxide (rGO), and carbon nanotubes (CNTs) were used to construct a conductive and mechanical skeleton of the overall electrode composite. And molybdenum disulfide (MoS2) grew on the skeleton in situ. Thus, a composite MoS2@rGO/CNTs with a three-dimensional (3D) network structure was constructed. A series of corresponding structural characterizations and electrochemical performance tests were carried out. And the results showed that the 3D porous skeleton composed of rGO and CNTs could act as a 3D conductive network, which not only significantly improved the conductivity and structural stability of the cathode material for lithium-sulfur batteries but also provided a large number of active sites for the active substance S. MoS2 had a strong chemisorption effect on lithium polysulfides, which could effectively hinder their shuttle behavior. So, the MoS2@/CNTs/rGO/S cathode material showed good electrochemical performance. Its first discharge specific capacity was up to 1417.8 mAh/g at 0.1 C. After 200 cycles at 0.5 C, its capacity decay rate per cycle was only 0.09%. Its discharge capacity could still maintain at 803.2 mAh/g at 3 C, showing a good application prospect.

B/N co-doping rGO/BNNSs heterostructure with synergistic adsorption-electrocatalysis function enabling enhanced electrochemical performance of lithium-sulfur batteries

The practical applications of lithium-sulfur (Li-S) batteries are obstructed by low sulfur utilization and poor cycling stability caused by notorious shuttle effect of soluble lithium polysulfide (LiPSs) and sluggish redox reaction kinetics. Herein, a creative B/N co-doping reduced graphene oxide/boron nitride nanosheets (B/N co-doping rGO/BNNSs) heterostructure prepared by a facile in-situ pyrolysis reaction strategy, is rationally designed as a multifunctional coating for high-performance Li-S batteries. The modified separator with B/N co-doping rGO/BNNSs displays excellent flexibility, thermal conductivity and electrolyte wettability. The superior shielding effect to LiPSs provided by the high density of B-N, B-C and C-N polar bonds and hierarchical pore structures, not only enhance the utilization of sulfur but also prevent the Li-anode from corrosion by LiPSs. Meanwhile, the improved electrochemical kinetics resulting from B/N co-doping sites and rGO/BNNSs heterostructure, effectively promote Li-ions diffusion and catalyze the redox kinetics of Li2S and LiPSs. Encouraged by the synergistic effect, the Li-S battery with B/N co-doping rGO/BNNSs coating shows a reversible capacity of 966.6 mAh g−1 at 1C. Upon increased current density of 4C, a desirable initial discharge capacity of 741.5 mAh g-1can be acquired with ultralow capacity decay of 0.015% per cycle after 500 cycles. Even under high sulfur areal loading configuration, the cell still has remarkable cycling stability. The fundamental explorations on inhibiting LiPSs shuttle and promoting various sulfur species conversion demonstrate the great potential of B/N co-doping rGO/BNNSs in practical Li-S batteries.

Designing a Stable Solid Electrolyte Interphase on Lithium Metal Anodes by Tailoring a Mg Atom Center and the Inner Helmholtz Plane for Lithium–Sulfur Batteries

Arising from the extraordinary theoretical energy density, rechargeable lithium-sulfur (Li-S) batteries have been reputed as one of the most appealing options for next-generation high-performance energy storage and conversion devices. Unfortunately, their industrial implementation has been strongly governed by the formation of Li dendrites caused by the unstable solid electrolyte interphase (SEI) film. Herein, we report a novel electrolyte by introducing the Mg(NO3)2 additive to suppress the growth of Li dendrites, further improving the cycling lifetime of Li-S batteries. On the one hand, Mg2+ can rapidly react with Li atoms to generate Mg atoms, replacing the Li atoms on the top surface of Li metal and forming the Mg center simultaneously. On the other hand, NO3- can be adsorbed in the inner Helmholtz plane and reduced as an inorganic-rich SEI film for stabilizing the Li metal anode when the electrolyte comes in contact with Li metal, effectively mitigating the formation of Li dendrites. Combining the experimental results and theoretical calculations, we confirm that the Mg atom center and the inorganic-rich SEI film are both beneficial for enhancing the electrochemical performance of Li-S batteries. This work provides a new insight into the electrolyte additive and a possible alternative for the design of high-performance Li-S batteries beyond the LiNO3 additive.

Co-Ni Bimetallic Sulfides Functionalized Interlayer with Efficient Catalytic Conversion for Li-S Batteries

Tardive practical development of lithium-sulfur (Li-S) batteries faces two fatal nuisances, the grievous shuttle effect of sulfur electrodes as well as rock-ribbed Li dendrites, which results in undesired cycling lifespan and the potential safety hazard. Diversified electrocatalytic materials are employed to enhance polysulfides conversion kinetics and subsequently restrain shuttle effect. Here, pyrite-type cation regulation strategy is applied to motivate the electrochemical catalysis capability of bimetallic sulfide by regulating the cation ratio of Co and Ni ions. The reformative bimetallic sulfide with Co to Ni ratio near 2:1 shows stronger chemical adsorption capability towards lithium polysulfides in contrast to pristine NiS₂, which resulted from the strong contribution of metal oxide layer. The comparable electrochemical kinetics and electrochemical performances of Li-S batteries with CNS-2/CP interlayer show in the aspects of low polarization voltage, high lithium ion diffusion rate, high discharge capacity, as well as better rate performances. These results demonstrate cation regulation could be an efficient strategy for material design to optimize the surface physicochemical properties of iron pyrite for boosting the cycle durability of Li-S batteries.

Selenium defects of 2D VSe2/CNTs composite as an efficient sulfur host for high-performance Li-S batteries

Introducing defects into two-dimensional materials can increase the ligand-unsaturated sites, thereby enhancing the redox catalysis of polysulphides. In this study, the selenium defects in the two-dimensional material VSe2 can effectively improve the electrochemical performance of lithium-sulfur batteries. Compared with VSe2, VSe2−x could strongly adsorb polysulfides, catalyze the conversion and accelerate the redox reactions of polysulfides. S/VSe2−x/CNTs cathode with an initial discharge specific capacity of 1457 mAh g−1 at 0.1 C current density and capacity decay rate per cycle of only 0.039% after 800 cycles at 0.5 C, showing excellent cycling stability. In addition, a high areal capacity of 4.35 mAh cm−2 and a reversible capacity of 4.106 mAh cm−2 after 100 cycles at 0.1 C can be achieved with the S/VSe2−x/CNTs cathode with a high areal sulfur loading of 4.5 mg cm−2. The results show that the shuttle effect is effectively suppressed by introducing defects in the two-dimensional transition metal dihalide compounds. Thus, the electrochemical performance of the sulfur electrode for lithium-sulfur batteries is improved. This work is expected to provide a new perspective for the rational design of sulfur host materials for high-performance lithium-sulfur batteries.

Deciphering the electrocatalysis essence of cobalt diselenide in lithium-sulfur electrochemistry from crystal-phase engineering

Polysulfide shuttle effect and sluggish sulfur reaction kinetics severely impede the cycling stability and sulfur utilization of lithium-sulfur (Li-S) batteries. Precisely designing effective electrocatalysts to accelerate sulfur conversion kinetics and suppress polysulfide migration is urgently needed. Generally, electrocatalytic activity is highly dependent on the electronic structures of catalysts, while the crystal phases play a pivotal role in governing the electronic structures. However, the “crystal phase - electronic structure - catalytic capability” relation chain of Li-S batteries catalysts usually lacks clear elucidation. Herein, crystal-phase engineering is reported by regulating phases of CoSe2 to enhance the electrochemical performance of Li-S batteries. Experimental investigations and atomic level analyses reveal that the orthorhombic CoSe2 can trap and accelerate the conversion of sulfur species more effectively than cubic one. Electronic structure analysis further demonstrates that the superior electrocatalytic activity is originated from the strong Jahn-Teller distortion. As a result, the Li-S batteries with orthorhombic CoSe2 modified separator exhibit a high initial capacity of 1390.7 mAh g−1 at 0.1C and outstanding rate performance with a specific capacity of 738.4 mAh g−1 at 3C. Moreover, even at a high sulfur loading of 10.09 mg cm−2, a favorable initial areal capacity of 12.0 mAh cm−2 is achieved at 0.05C, and the battery still maintains at 7.9 mAh cm−2 over 50 cycles under 0.1C. This work may provide a new strategy for effective catalyst design in Li-S batteries.

Nickel single atom overcoordinated active sites to accelerate the electrochemical reaction kinetics for Li-S cathode

Porous 2D N-doped carbon electrocatalyst consisting of atomically disperse Ni active centers with Ni-N 4 -O coordinated structure which act as efficient polysulfides traps and highly LiPSs conversion catalysts. Lithium-sulfur (Li-S) batteries with high theoretical energy density are promising advanced energy storage devices. However, shuttling of dissolute lithium polysulfide (LiPSs) and sluggish conversion kinetics impede their applications. Herein, single nickel (Ni) atoms on two-dimensional (2D) nitrogen(N)-doped carbon with Ni-N 4 -O overcoordinated structure (SANi-N 4 -O/NC) are prepared and firstly used as a sulfur host of Li-S batteries. Due to the efficient polysulfides traps and highly LiPSs conversion effect of SANi-N 4 -O/NC, the electrochemical performance of Li-S batteries obviously improved. The batteries can well operate even under high sulfur loading (5.8 mg·cm -2 ) and lean electrolyte (6.1 μL·mg -1 ) condition. Meanwhile, density functional theory (DFT) calculations demonstrate that Ni single atom’s active sites decrease the energy barriers of conversion reactions from Li 2 S 8 to Li 2 S due to the strong interaction between SANi-N 4 -O/NC and LiPSs. Thus, the kinetic conversion of LiPSs was accelerated and the shuttle effect is suppressed on SANi-N 4 -O/NC host. This study provides a new design strategy for a 2D structure with single-atom overcoordinated active sites to facilitate the fast kinetic conversion of LiPSs for Li-S cathode.