Practical Lithium-sulfur Batteries Research Articles

A Volcano Correlation between Catalytic Activity for Sulfur Reduction Reaction and Fe Atom Count in Metal Center.

Sulfur reduction reaction (SRR) facilitates up to 16 electrons, which endows lithium-sulfur (Li-S) batteries with a high energy density that is twice that of typical Li-ion batteries. However, its sluggish reaction kinetics render batteries with only a low capacity and cycling life, thus remaining the main challenge to practical Li-S batteries, which require efficient electrocatalysts of balanced atom utilization and site-specific requirements toward highly efficient SRR, calling for an in-depth understanding of the atomic structural sensitivity for the catalytic active sites. Herein, we manipulated the number of Fe atoms in iron assemblies, ranging from single Fe atom to diatomic and triatomic Fe atom groupings, all embedded within a carbon matrix. This led to the revelation of a "volcano peak" correlation between SRR catalytic activity and the count of Fe atoms at the active sites. Utilizing operando X-ray absorption and X-ray diffraction spectroscopies, we observed that polysulfide adsorption-desorption and electrochemical conversion kinetics varied up and down with the incremental addition of even a single iron atom to the catalyst's metal center. Our results demonstrate that the metal center with exactly two iron atoms represents the optimal configuration, maximizing atom utility and adeptly handling the conversion of varied intermediate sulfur species, rendering the Li-S battery with a high areal capacity of 23.8 mAh cm-2 at a high sulfur loading of 21.8 mg cm-2. Our results illuminate the pivotal balance between atom utilization and site-specific requirements for optimal electrocatalytic performance in SRR and diverse electrocatalytic reactions.

Tuning the solubility of polysulfides for constructing practical lithium-sulfur battery

Li-S batteries are regarded as one of the most promising candidates for next-generation battery systems with high energy density and low cost. However, the dissolution-precipitation reaction mechanism of the sulfur (S) cathode enhances the kinetics of the redox processes of the insulating sulfur, which also arouses the notorious shuttle effect, leading to serious loss of S species and corrosion of Li anode. To get a balance between the shuttle restraining and the kinetic property, a combined strategy of electrolyte regulation and cathode modification is proposed via introducing 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoroprpyl ether (HFE) instead of 1,2-dimethoxyethane (DME), and SeS7 instead of S8. The introduction of HFE tunes the solvation structure of the LiTFSI and the dissolution of intermediate polysulfides with Se doping (LiPSSes), and optimize the interface stability of the Li anode simultaneously. The minor Se substitution compensates the decrease in kinetic due to the decreased solubility of LiPSs. In this way, the Li-SeS7 batteries deliver a reversible capacity of 1062 and 1037 mAh g−1 with 2.0 and 5.5 mg SeS7 cm−2 loading condition, respectively. Besides, an electrolyte–electrode loading model is established to explain the relationship between the optimal electrolyte and cathode loading. It makes more sense to guide the electrolyte design for practical Li-S batteries.

Constructing honeycomb-structured LaCoO3 as an efficient polysulfide converter on the separator to achieve practical lithium-sulfur batteries

Owing to its remarkable energy density and specific capacity, lithium-sulfur (Li-S) battery has emerged as one of the most promising energy storage devices. Nevertheless, the shuttle effect and the sluggish conversion of polysulfides significantly impede the practical application of Li-S batteries. Hence, a LaCoO3 functional material with a unique honeycomb structure was designed as an efficient polysulfide converter. The honeycomb-structured LaCoO3 not only exhibits strong bonding energy towards polysulfides but also possesses abundant adsorption sites on its surface. The LaCoO3 material also shows excellent catalytic properties to quickly convert the adsorbed and aggregated polysulfides, effectively suppressing the shuttle effect. Moreover, the honeycomb structure of LaCoO3 can facilitate the rapid wetting and infiltration of the electrolyte. Consequently, the Li-S cell with LaCoO3 functionalized separator provides an areal specific capacity of 3.10 mAh cm−2 after 150 cycles under high sulfur loading of 6.52 mg cm−2. Moreover, under practical conditions where the electrolyte content is as low as 7 μL mg−1 and the sulfur loading is 7.96 mg cm−2, the Li-S battery equipped with LaCoO3-separator can still provide an areal specific capacity of 5.93 mAh cm−2 after 50 cycles.

Improving Rate Performance of Encapsulating Lithium‐Polysulfide Electrolytes for Practical Lithium−Sulfur Batteries

AbstractThe cycle life of high‐energy‐density lithium−sulfur (Li−S) batteries is severely plagued by the incessant parasitic reactions between Li metal anodes and reactive Li polysulfides (LiPSs). Encapsulating Li‐polysulfide electrolyte (EPSE) emerges as an effective electrolyte design to mitigate the parasitic reactions kinetically. Nevertheless, the rate performance of Li−S batteries with EPSE is synchronously suppressed. Herein, the sacrifice in rate performance by EPSE is circumvented while mitigating parasitic reactions by employing hexyl methyl ether (HME) as a co‐solvent. The specific capacity of Li−S batteries with HME‐based EPSE is nearly not decreased at 0.1 C compared with conventional ether electrolytes. With an ultrathin Li metal anode (50 μm) and a high‐areal‐loading sulfur cathode (4.4 mgS cm−2), a longer cycle life of 113 cycles was achieved in HME‐based EPSE compared with that of 65 cycles in conventional ether electrolytes at 0.1 C. Furthermore, both high energy density of 387 Wh kg−1 and stable cycle life of 27 cycles were achieved in a Li−S pouch cell (2.7 Ah). This work inspires the feasibility of regulating the solvation structure of LiPSs in EPSE for Li−S batteries with balanced performance.

Improving Rate Performance of Encapsulating Lithium-Polysulfide Electrolytes for Practical Lithium-Sulfur Batteries.

The cycle life of high-energy-density lithium-sulfur (Li-S) batteries is severely plagued by the incessant parasitic reactions between Li metal anodes and reactive Li polysulfides (LiPSs). Encapsulating Li-polysulfide electrolyte (EPSE) emerges as an effective electrolyte design to mitigate the parasitic reactions kinetically. Nevertheless, the rate performance of Li-S batteries with EPSE is synchronously suppressed. Herein, the sacrifice in rate performance by EPSE is circumvented while mitigating parasitic reactions by employing hexyl methyl ether (HME) as a co-solvent. The specific capacity of Li-S batteries with HME-based EPSE is nearly not decreased at 0.1 C compared with conventional ether electrolytes. With an ultrathin Li metal anode (50 μm) and a high-areal-loading sulfur cathode (4.4 mgS cm-2 ), a longer cycle life of 113 cycles was achieved in HME-based EPSE compared with that of 65 cycles in conventional ether electrolytes at 0.1 C. Furthermore, both high energy density of 387 Wh kg-1 and stable cycle life of 27 cycles were achieved in a Li-S pouch cell (2.7 Ah). This work inspires the feasibility of regulating the solvation structure of LiPSs in EPSE for Li-S batteries with balanced performance.

First-row transition metal carbide nanosheets as high-performance cathode materials for lithium-sulfur batteries.

Despite the prodigious potential of lithium-sulfur (Li-S) batteries as future rechargeable electrochemical systems, their commercial implementation is hindered by several vital issues, including the shuttle effect and sluggish migration of lithium-polysulfides leading to rapid capacity fading. Here, we systematically investigate the potential of first-row two-dimensional transition metal carbides (TMCs) as sulfur cathodes for Li-S batteries. The adsorption strength of lithium-polysulfides on TMCs is induced by the amount of charge transfer from the former to the latter and the proposed periodic relationship between sulfur in Li2S and 3d-transition metals. Our findings show that the VC nanosheet possesses immense anchoring potential and exhibits a comparatively low migration energy barrier for lithium-ion and Li2S molecules. Additionally, we report ab initio molecular dynamics simulations for lithiated polysulfide species anchored on a TMC-based model with a liquid-electrolyte medium. The microscopic reaction mechanism, revealed by the evolution of the reaction voltage during lithiation, demonstrates that the dissolution of high-order lithium-polysulfides in the electrolytes can be prevented due to their robust interaction with TMC-based cathode materials. These appealing features suggest that TMCs present colossal performance improvements for anchoring lithium-polysulfides, stimulating the active design of sulfur cathodes for practical Li-S batteries.

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.

Molecular-Level Anion and Li+ Co-Regulation by Amphoteric Polymer Separator for High-Rate Stable Lithium Metal Anode.

Regulating ion transport is a prevailing strategy to suppress lithium dendrite growth, in which the distribution of ion regulatory sites plays an important role. Here a hyperbranched polyamidoamine (HBPA) grafted polyethylene (PE) composite separator (HBPA-g-PE) is reported. The densely and uniformly distributed positive -NH2 and negative -CHNO- groups efficiently restrict the anion migration and promote Li+ transport at the surface of the lithium metal anode. The obtained Li foil symmetric cell delivers a stable cycle performance with a low-voltage hysteresis of 130 mV for over 1500 h (3000 cycles) at an ultrahigh current density of 20 mA cm-2 and a practical areal capacity of 5 mAh cm-2. Moreover, HBPA-g-PE separator enables a practical lithium-sulfur battery to achieve over 200-cycle stable performance with initial and retained capacity of 700 and 455 mAh g-1, at a high sulfur loading of 4 mg cm-2 and a low electrolyte content/sulfur loading ratio of 8 μL mg-1.

Systematic insight of the behavior of LiNO3 additive in Li[sbnd]S batteries with gradient S loading

Previous studies revealed that LiNO3 can enhance the cyclic stability of lithium‑sulfur (LiS) batteries by creating a solid electrolyte interface protecting the lithium electrode. However, this study investigated the effect of LiNO3 and concentration in the electrolyte, first studied under low and high sulfur loading. It is confirmed that adding a small amount of LiNO3 inhibits the shuttle effect phenomenon in LiS batteries, and the Coulombic efficiency was significantly improved. Appropriately increasing the concentration of LiNO3 to 2 % could prolong the cycle life. However, when LiNO3 is excessive, the rate and cycling performance decrease. The design of practical LiS batteries requires more research on the parameters of electrolyte additives under high‑sulfur-loading conditions. After gradient increasing the sulfur loading, the low concentration of LiNO3 cannot play the best performance of the battery, so it is necessary to improve the concentration of LiNO3 further. It is evident that adding LiNO3 in LiS batteries has certain benefits, and the optimal amount of additive is related to the value of sulfur loading.

Tandem Carbon Hollow Spheres with Tailored Inner Structure as Sulfur Immobilization for Superior Lithium–Sulfur Batteries

AbstractThe construction of lithium–sulfur battery cathode materials while simultaneously achieving high areal sulfur‐loading, adequate sulfur utilization, efficient polysulfides inhibition, rapid ion diffusion, etc. remains a major challenge. Herein, an internal regulatory strategy to fabricate the unique walnut‐like yolk–shell carbon flower@carbon nanospheres is presented (WSYCS) as sulfur hosts. The internal carbon flower, suitable cavity, and external carbon layer effectively disperse the insulate sulfur, accommodate volumetric expansion, and confine polysulfides, thus improving the performance of lithium–sulfur batteries. The finite element simulation method also deduces the enhanced Li+ diffusion and lithium–sulfur reaction kinetics. More importantly, WSYCS2 is grafted onto carbon fiber (CF) by electro‐spinning method to form a tandem WSYCS2@CF 3D film as a sulfur host for the free‐standing electrode. The corresponding battery exhibits an extremely high areal capacity of 15.5 mAh cm−2 with a sulfur loading of 13.4 mg cm−2. Particularly, the flexible lithium–sulfur pouch cell delivers a high capacity of 8.1 mAh cm−2 and excellent capacity retention of 65% over 800 cycles at a relatively high rate of 1C, corresponding to a calculated energy density of 539 Wh kg−1 and 591 Wh L−1. This work not only provides guidance for tailoring thick carbon/sulfur electrodes but also boosts the development of practical lithium–sulfur batteries.

Band Structure Engineering and Orbital Orientation Control Constructing Dual Active Sites for Efficient Sulfur Redox Reaction.

The kinetics difference among multistep electrochemical processes leads to the accumulation of soluble polysulfides and thus shuttle effect in lithium-sulfur (Li-S) batteries. While the interaction between catalysts and representative species has been reported, the root of the kinetics difference, interaction change among redox reactions, remains unclear, which significantly impedes the catalysts design for Li-S batteries. Here, this work deciphers the interaction change among electrocatalytic sulfur reactions, using tungsten disulfide (WS2 ) a model system to demonstrate the efficiency of modifying electrocatalytic selectivity via dual-coordination design. Band structure engineering and orbital orientation control are combined to guide the design of WS2 with boron dopants and sulfur vacancies (B-WS2- x ), accurately modulating interaction with lithium and sulfur sites in polysulfide species for relatively higher interaction with short-chain polysulfides. The modified interaction trend is experimentally confirmed by distinguishing the kinetics of each electrochemical reaction step, indicating the effectiveness of the designed strategy. An Ah-level pouch cell with B-WS2- x delivers a gravimetric energy density of up to 417.6 Wh kg-1 with a low electrolyte/sulfur ratio of 3.6µL mg-1 and negative/positive ratio of 1.2. This work presents a dual-coordination strategy for advancing evolutionarily catalytic activity, offering a rational strategy to develop effective catalysts for practical Li-S batteries.

Metal‐Halide Gelated MXene and Its Use as a Bifunctional Sulfur Host Stabilizing Both Cathode and Anode for Practical Lithium–Sulfur Batteries

AbstractThe gelation of MXene promises to assemble a 3D conductive and catalytic monolith for various applications. However, controllable assembly and function customization are still challenging. Here, with a “killing two birds with one stone” initiator (metal halide, typically ZnI2), the controllable gelation of MXene is enabled, which produces a sulfur host that stabilizes not only the cathode but also the lithium metal anode for lithium‐sulfur batteries. Zn2+ cations trigger the gelation and act as linkers between MXene nanosheets (NSs), while the iodine anions as spacers avoid the NSs restacking, forming a monolith with a well‐tunable 3D structure. As a sulfur host, the formed 3D monolith with adsorptive Zn─O sites and highly accessible surface greatly enhances the sulfur redox kinetics, effectively suppressing the shuttling and sulfur loss. At the same time, iodine anions are released into the electrolyte as additives eliminating dead Li for the anode in cycling. Thus, the assembled battery shows high Coulombic efficiency (∼above 99%, even under high sulfur loading: 6.6 mg cm−2) and long cycling stability. Under the practical condition (E/S ratio: 5 µL mgs−1, sulfur loading: 5 mg cm−2), high capacity retention of >70% for 200 cycles is achieved.

Biopolymer separators from polydopamine-functionalized bacterial cellulose for lithium-sulfur batteries

The advancement of the lithium-sulfur (Li-S) batteries is immensely impeded by two main challenges: polysulfide shuttling between the electrodes and Li dendrite formation associated with the Li-metal anode. To tackle these challenges, we synthesized a polydopamine coated bacterial cellulose (PDA@BC) separator in a way to create physical and chemical traps for the shuttling polysulfides and to control the Li+ flux. While nanocellulose offers its dense network as a physical trap, the presence of polydopamine in the separator offers polar functional groups which not only has a high binding energy towards the polysulfides but also helps in redistribution of the Li+ ions across it. The electrochemical and physiochemical results suggest that the synthesized separator can have practical applicability owing to its superior performance compared to a commercial separator. The Li-S batteries assembled with this separator showed a specific discharge capacity of 1449 mAh/g at 0.1C and 877 mAh/g at 1C, and a capacity fade of 0.03 % per cycle over 650 cycles at 1C. Using a PDA@BC separator, a practical Li-S battery cell with S loading of 7.5 mg cm−2 (and E/S ratio of 10 µLmg−1, 82 % S ratio) was also tested at 1C, which delivered a capacity of ∼ 6 mAh cm−2 for 500 cycles.

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.

Dual Functionalities of Rb Cation in Lean Electrolyte Lithium Sulfur Batteries

Achieving large discharge capacity and high cycling stability under high sulfur loading and lean electrolyte condition is critical for practical lithium sulfur batteries. However, it is impeded by the large overpotential for lithium sulfide (Li2S) nucleation at the cathode, caused by the sluggish reduction kinetics of lithium polysulfide and the short-circuit triggered by inhomogeneous Li electroplating at the anode. In this study, we report that adding rubidium cation to lean electrolyte in an additive level (0.05 M) can address the two challenges owing to the modifications of the cathode and anode surfaces by the formation of rubidium sulfide. At the sulfur cathode, the rubidium sulfide acts as a catalyst, accelerating the reduction of lithium polysulfides. At the Li metal anode, a rubidium sulfide-enriched inner SEI quickly passivates the surface, suppressing electrolyte decomposition and promoting uniform lithium deposition due to its lithiophilicity. The drop-in-solution leads to impressive results, delivering more than 3 mAh cm−2 over approximately 80 cycles at a sulfur loading of 3.8 mgsulfur cm−2 and an electrolyte to sulfur ratio of 3 μl mg−1.

Routes to Electrochemically Stable Sulfur Cathodes for Practical Li-S Batteries.

Lithium-sulfur (Li-S) batteries have been investigated intensively as a post-Li-ion technology in the past decade; however, their realizable energy density and cycling performance are still far from satisfaction for commercial development. Although many extremely high-capacity and cycle-stable S cathodes and Li anodes are reported in literature, their use for practical Li-S batteries remains challenging due to the huge gap between the laboratory research and industrial applications. The laboratory research is usually conducted by use of a thin-film electrode with a low sulfur loading and high electrolyte/sulfur (E/S) ratios, while the practical batteries require a thick/high sulfur loading cathode and a low E/S ratio to achieve a desired energy density. To make this clear, the inherent problems of dissolution/deposition mechanism of conventional sulfur cathodes are analyzed from the viewpoint of polarization theory of porous electrode after a brief overview of the recent research progress on sulfur cathodes of Li-S batteries, and the possible strategies for building an electrochemically stable sulfur cathode are discussed for practically viable Li-S batteries from the authors' own understandings.

Counting d-Orbital Vacancies of Transition-Metal Catalysts for the Sulfur Reduction Reaction.

The electrocatalytic sulfur reduction reaction (SRR) would allow the production of renewable high-capacity rechargeable lithium-sulfur (Li-S) batteries using sustainable and nontoxic elemental sulfur as a cathode material, but its slow reaction rate causes a serious shuttle effect and dramatically reduces the capacity. We found that a catalyst composed of Pd nanoparticles supported by ordered mesoporous carbon (Pd/OMC) had a high reaction rate in the SRR, and a Li-S battery assembled with this catalyst had a low shuttle constant of 0.031 h-1 and a high-rate performance with a specific capacity of 1527 mAh g-1 at 0.1 C which is close to the theoretical value. The high activity of Pd/OMC with a d-orbital vacancy of 0.87 e was predicted from a volcano relationship between the d charge for the metal and the adsorption activation entropy and reaction rate for the SRR by examining Pd, Au, Pt, Rh, and Ru transition-metal nanocatalysts. The strategy of using a single electronic structure descriptor to design high-efficiency SRR catalysts has suggested a way to produce practical Li-S batteries.

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.

Conductive Metal Organic Framework as Trapping Cathode Additive for High Performance Lithium-Sulfur Batteries

Lithium-Sulfur (Li-S) batteries with high capacity and energy density have arisen as one of the most promising secondary batteries. However, higher order lithium polysulfide (LiPSs) shuttling and insulating nature of sulfur cathode results in capacity degradation and premature failure of the cell [1]. Here for the first time, we have implemented conductive Cu metal-based Metal organic framework (Cu-MOF) as a Li-S battery cathode material. Cu-MOF cathode catalyst not only reduce the LiPSs shuttle effect but also increase the conductivity of Li-S battery cathode [2].Here, Cu-MOF pore morphology will trap the polysulfides and further prevent LiPSs shuttling. In addition, the well-defined architecture of organic ligands of Cu-MOF also participate to explicate the involved surface-binding mechanisms of S and polysulfide products. Furthermore, Cu-MOF improve the diffusion rate of Li ions, shackling LiPSs, upsurging conduction of electrons/ions, and regulating the deposition of Li2S2/Li2S towards cathode side [3]. Furthermore, sulfur active material is well percolated inside the pores of conductive Cu-MOF which shows the long-cycling performance as shown in Figure 1.Benefiting from the unique fibrous, porous, interwoven structure, the conductive MOF@S-composite cathode demonstrates a high initial capacity of 1671 mAh g–1 at 0.05 C rate with a good coulombic efficiency of >95% and the outstanding capacity of 849 mAh g-1 cycles even after 200 cycles at the 0.5 C-rate with coulombic efficiency of 98.3%. It is believed that, the experimental findings and mechanistic understanding of Cu-MOF cathode in this work will open a new avenue for the further development of other conductive MOFs in the Li-S batteries. Figure 1: Cycling performance of S@Cu-MOF composite at 0.5 C-rate. References Mingyue Wang, Zhongchao Bai, Ting Yang, Chuanhao Nie, Xun Xu, Yunxiao Wang, Jian Yang, Shixue Dou, and Nana Wan."Advances in High Sulfur Loading Cathodes for Practical Lithium-Sulfur Batteries." Energy Mater, no.12 (2022): 2201585.Dan Luo, Chaojie Li, Yongguang Zhang, Qianyi Ma, Chuyin Ma, Yihang Nie, Matthew Li, Xuefei Weng, Rong Huang, Yan Zhao, Lingling Shui, Xin Wang, Zhongwei Chen. "Design of Quasi-MOF Nanospheres as a Dynamic Electrocatalyst toward Accelerated Sulfur Reduction Reaction for High-Performance Lithium–Sulfur Batteries." Mater, no.34 (2022): 210554. Jun Zhang, Ye Shi, Yu Ding, Lele Peng, Wenkui Zhang, Guihua Yu. "A Conductive Molecular Framework Derived Li2S/N,P-Codoped Carbon Cathode for Advanced Lithium–Sulfur Batteries." Energy Mater, no.7 (2017): 1602876. Figure 1

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.