Sulfur Cathode Research Articles

Three-dimensional Ti3C2 structure design and in-situ growth of nano-TiO2 crystals to realize high performance lithium-sulfur battery

Lithium–sulfur (Li–S) batteries represent a promising energy storage system with the potential to replace traditional lithium-ion batteries. Recent research has explored the practical applications of Li–S batteries. However, due to the insulation properties of the sulfur components and the shuttle effect of polysulfides, the practical application of Li–S batteries is hindered by poor cycle stability and short life. In this study, we developed a controllable three-dimensional Ti3C2 structure design process, and through in situ growth of TiO2 nanocrystals, we prepared three-dimensional porous materials with TiO2@Ti3C2 heterostructures. These materials constructed using two-dimensional lamellar Ti3C2 function as a conductive skeleton to improve the conductivity of the sulfur cathodes, and through the in-situ growth of nano-TiO2 to introduce more binding sites and provide more chemisorption sites to limit the dissolution and shuttle of polysulfides. In addition, the TiO2@Ti3C2 heterointerface generated in situ on the surface of the lamellar structure can induce an internal electric field and increase active reaction sites, which promotes reaction kinetics, accelerates charge diffusion/transport, and promotes LiPS transformation. The materials designed in this study can effectively restrain the shuttle effect by realising the association process of adsorption, capture, and transformation of polysulfides. Thus, when applied as the sulfur cathode frame, it shows a high specific capacity of 1261.41 mAh g−1 at a rate of 0.1 C. In addition, a specific capacity of 66.5 % is maintained over 500 cycles at a rate of 1 C. This strategy supports the development of Li–S batteries with extraordinary performance and opens up a promising way to design next-generation electrochemical energy storage devices.

Metal-organic-framework derived NiS2/C hollow structures for enhanced polysulfide redox kinetics in lithium-sulfur batteries.

To cope with the shuttling of soluble lithium polysulfides in lithium-sulfur batteries, confinement tactics, such as trapping of sulfur within porous carbon structures, have been extensively studied. Although performance has improved a bit, the slow polysulfide conversion inducing fast capacity decay remains a big challenge. Herein, a NiS2/carbon (NiS2/C) composite with NiS2 nanoparticles embedded in a thin layer of carbon over the surface of micro-sized hollow structures has been prepared from Ni-metal-organic frameworks. These unique structures can physically entrap sulfur species and also influence their redox conversion kinetics. By improving the reaction kinetics of polysulfides, the NiS2/carbon@sulfur (NiS2/C@S) composite cathode with a suppressed shuttle effect shows a high columbic efficiency and decent rate performance. An initial capacity of 900 mAh g-1 at the rate of 1 C (1 C = 1675 mA g-1) and a low-capacity decline rate of 0.132% per cycle after 500 cycles are obtained, suggesting that this work provides a rational design of a sulfur cathode.

Bifunctional separator with nest-like MnOOH network via facile in situ synthesis for highly stable and “Li-dendrite free” lithium-sulfur batteries

The slow redox kinetics in the sulfur cathode and lithium (Li)-dendrite growth on the lithium anode leads to significant capacity degradation and serious safety incidents for lithium-sulfur (Li–S) batteries. Herein, a bifunctional polypropylene separator with nest-like MnOOH network synergistic carbon layer (MnOOH/C/PP) via facile in situ synthesis method was designed as an effective host for both sulfur cathode and lithium anode. A series of electrochemical tests and non–in situ scanning electron microscope characterization confirmed that the as-prepared MnOOH/C layer has good physical/chemical adsorption and catalytic activity of polysulfides. Furthermore, the Li||Li symmetric batteries exhibited inhibited dendrite growth even after undergoing cycling for more than 2200 h at 1 mA/cm2. Consequently, the Li–S battery based on a functional MnOOH/C/PP separator shows high discharge capacity (1358 mAh/g at 0.1 C), good rate capability (755 mAh/g at 3 C) and stable cyclability (0.049 % decay per cycle over 700 cycles). Particularly, an areal capacity can reach 3.55 mAh/cm2 even at a high sulfur loading of 7.02 mg/cm2 and a high-capacity retention rate of 90.2 % remained over 200 cycles, demonstrating the viability of this simple and efficient strategy for creating highly stable and safe Li–S batteries.

Tuning Redox Behavior of Sulfur Cathodes Via Ternary-Coordinated Single Fe Atom in Lithium-Sulfur Batteries.

Modulating the coordination configuration of single Fe atom has been an efficient strategy to strengthen the redox dynamics for lithium-sulfur batteries (LSBs) but remains challenging. Herein, the single Fe atom is functioned with nitrogen and carbon atoms in the first shell, and simultaneously, oxidized sulfur (─SOx) in the second shell, which presents a lower antibonding state and well address the redox activity of sulfur cathodes. In the ternary-coordinated single Fe atom catalyst (FeN2C2-SOx-NC), the binary structure of FeN2C2 provides a lower Fe-S bonding strength and d-p orbital hybridization, which obviously optimizes the adsorption and desorption behavior of sulfur species during the reduction and oxidation reaction processes. Simultaneously, the ─SOx redistributes the electron density of the coordinating nitrogen atoms, which possesses high electron-withdrawing ability and develops electrocatalytic activity. As a result, the sulfur cathodes with FeN2C2-SOx-NC present an excellent high-rate cyclic performance, accompanied by a capacity decay rate of 0.08% per cycle for 500 cycles at 4.0 C. This study provides new insights for optimizing the redox dynamics of sulfur cathodes in LSBs at the atomic level.

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.

Achievements, challenges, and perspectives in the design of polymer binders for advanced lithium-ion batteries

The design of binders for lithium-ion batteries is highlighted, with an emphasis on key parameters affecting device performance and failure mechanisms. These issues are discussed in detail using the example of a silicon anode and a sulfur cathode.

A solid-state electrolyte for electrochemical lithium-sulfur cells.

Post-lithium-ion batteries are designed to achieve high energy density and high safety by modifying their active material and cell configuration. In terms of the active material, lithium-sulfur batteries have the highest charge-storage capacity and high active-material utilization because of the use of a conversion-type sulfur cathode, which involves conversion between solid-state sulfur, liquid-state polysulfides, and solid-state sulfides. In terms of the configuration, solid-state batteries ensure high safety by using a solid-state electrolyte in between the two electrodes. Herein, we use a lithium lanthanum titanate (LLTO) solid-state electrolyte in the lithium-sulfur cell with a polysulfide catholyte electrode. The LLTO, which replaces the conventional liquid electrolyte, is a solid-state electrolyte that offers smooth lithium-ion diffusion and prevents the loss of polysulfides, while the highly active polysulfide electrode, which replaces the solid-state sulfur cathode, improves the reaction kinetics and the active-material utilization. The material and electrochemical analyses confirm the stabilized electrodes exhibit long-lasting lithium stripping/plating stability and limited polysulfide diffusion. Moreover, the morphologically and electrochemically smooth interface between the solid-state electrolyte and catholyte enables fast charge transfer in the cell, which demonstrates a high charge-storage capacity of 1429 mA h g-1, high rate performance, and high electrochemical efficiency.

Interface engineering toward stable lithium–sulfur batteries

The interfaces, interfacial issues, and their impact on lithium–sulfur electrochemistry are overviewed for both coin cells and practical lithium–sulfur batteries.

Synergistic design of a semi-hollow core-shell structure and a metal-organic framework-derived Co/Zn selenide coated with MXene for high-performance lithium-sulfur batteries.

Lithium-sulfur batteries have garnered significant interest as potential energy storage systems for the future, owing to their remarkable theoretical specific capacity (1675 mA h g-1) and energy density (2600 W h kg-1). However, their development has been severely impeded by several challenges, including the low intrinsic conductivity of sulfur, volume expansion issues, and the polysulfide shuttle effect. To address these issues, polar metal compounds with nanostructures featuring hollow shells and catalytic functions have emerged as promising materials for designing advanced lithium-sulfur batteries. In this study, bimetallic selenides with varying degrees of hollowness are synthesized using a tannic acid etching and selenization strategy. By comparing the electrochemical characteristics of composite electrodes with different degrees of hollowness, an optimal semi-hollow core-shell structure is identified, implying that reasonable structural designing of metal compounds carries immense importance in improving electrochemical reactions. Moreover, the appropriate degree of hollowness effectively mitigates volume expansion issues associated with the sulfur cathode. Consequently, bimetallic selenides with a hollow core-shell structure coated with conductive MXene material exhibit superior electrochemical performance. The synergistic effect achieved through the judicious design of the hollow core-shell structure and the utilization of polar metal compounds has proved instrumental in enhancing the redox kinetics of lithium-sulfur batteries. As such, this research presents a novel avenue for the development of high-performance lithium-sulfur batteries.

N-doped CNTs wrapped sulfur-loaded hierarchical porous carbon cathode for Li-sulfur battery studies.

Lithium-sulfur (Li-S) batteries are considered promising next-generation energy storage devices due to their low cost and high energy density (2600 W h kg-1). However, the practical applicability of Li-S batteries is hindered by the insulating nature of sulfur cathodes, and the high solubility of polysulfides (Li2Sx, 3 < x ≤ 8) which are formed during the electrochemical process. Integrating sulfur into the carbon host is an effective way to enhance the conductivity of the electrode which hampers the shuttling effect of the polysulfides. Here in this study, hierarchical porous carbon structures (HPC) are prepared from spent coffee waste (SCW) by the KOH activation process and are encapsulated with sulfur (SHPC) which increases the interaction between sulfur and carbon and enhances both the electronic and ionic conductivities. Further wrapping of SHPC with N-doped multi-walled carbon nanotubes (NCNTs) gives a SHPC-NCNT composite, which alleviates the shuttling of polysulfides by trapping them and ensures the required conductivity to the sulfur cathode during the Li+ reactions. When studied as a cathode material for Li-S batteries, the prepared cathode showed 664 and 532 mA h g-1 specific capacities after 150 cycles at 0.2C and 0.5C, respectively. The stable cyclability and rate capability properties of SPHCNCNT suggest that the prepared sulfur composite is suitable as a cathode material for Li+ energy storage applications.

Dual-functional mediators of high-entropy Prussian blue analogues for lithiophilicity and sulfiphilicity in Li-S batteries.

Lithium-sulfur (Li-S) batteries are considered promising next-generation energy storage systems due to their high energy density (2600 W h kg-1) and cost-effectiveness. However, the shuttle effect of lithium polysulfides in sulfur cathodes and uncontrollable Li dendrite growth in Li metal anodes significantly impede the practical application of Li-S batteries. In this study, we address these challenges by employing a high-entropy Prussian blue analogue Mn0.4Co0.4Ni0.4Cu0.4Zn0.4[Fe(CN)6]2 (HE-PBA) composite containing multiple metal ions as a dual-functional mediator for Li-S batteries. Specifically, the HE-PBA composite provides abundant metal active sites that efficiently chemisorb lithium polysulfides (LiPSs) to facilitate fast redox conversion kinetics of LiPSs. In Li metal anodes, the exceptional lithiophilicity of the HE-PBA ensures a homogeneous Li ion flux, resulting in uniform Li deposition while mitigating the growth of Li dendrites. As a result, our work demonstrates outstanding long-term cycling performance with a decay rate of only 0.05% per cycle over 1000 cycles at 2.0 C. The HE-PBA@Cu/Li anode maintains a stable overpotential even after 600 h at 0.5 mA cm-2 under the total areal capacity of 1.0 mA h cm-2. This study showcases the application potential of the HE-PBA in Li-S batteries and encourages further exploration of prospective high-entropy materials used to engineer next-generation batteries.

Single-atom catalysts based on C2N for sulfur cathodes in Na-S batteries: a first-principles study.

Several major roadblocks, including the "shuttle effect" caused by the dissolved higher-order sodium polysulfides (NaPSs), extremely poor conductivity of sulfur cathodes, and sluggish conversion kinetics of charging-discharging reactions, have hindered the commercialization of sodium-sulfur batteries (NaSBs). In our study, representative C2N-based single-atom catalysts (SACs), TM@C2N (TM = Fe, Ni and V), are proposed to improve the comprehensive performance of NaSBs. Based on first-principles calculations, we first discuss in detail the anchoring behavior of all adsorption systems, TM@C2N/(S8 and NaPSs). The results indicate that compared to pristine C2N, TM@C2N substrates exhibit a stronger capability to capture S8/NaPSs clusters through physical/chemical binding, with V@C2N showing the most outstanding capability ranging from -2.37 to -5.03 eV. The density of states analysis reveals that metallic properties can be well maintained before and after adsorption of polysulfides. More importantly, TM@C2N configurations can greatly reduce the energy barriers of charging and discharging reactions, thereby accelerating the conversion efficiency of NaSBs. It is worth mentioning that V@C2N has lower charge-discharge energy barriers and Na ion migration rates, since the embedded TM atom weakens the strong binding of Na+ in the N6 cavity of C2N. The intrinsic mechanism analysis reveals that the interaction between the d orbitals of V and the p orbitals of S leads to the weakening of Na-S bonds, which can not only effectively inhibit the shuttle effect, but also promote the dissociation of Na2S. Overall, this work not only offers excellent catalytic materials, but also provides vital guidance for designing SACs in NaSBs.

Advances in nanoporous materials for next-generation battery applications.

In recent years, nanoporous materials, mainly represented by metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), have shown unparalleled potential in critical applications such as energy storage, gas separation and catalysis. The integration of MOFs/COFs into battery technology has garnered substantial research attention since it was found that such materials also play important roles in batteries. The highly controllable nanoporous features of MOFs/COFs enable the regulation of the solvation environment of lithium ions, thereby significantly improving the performance of lithium metal batteries. Moreover, the selective adsorption features of MOFs/COFs make them particularly useful for stabilising high nickel cathodes and sulfur cathodes. This review provides an overview of the application of MOFs/COFs in batteries, and explores potential future directions and challenges in this rapidly evolving interdisciplinary field.

MoS2 quantum dot-decorated CNT networks as a sulfur host for enhanced electrochemical kinetics in advanced lithium-sulfur batteries.

The slow redox kinetics and shuttle effect of polysulfides severely obstruct the further development of lithium-sulfur (Li-S) batteries. Constructing sulfur host materials with high conductivity and catalytic capability is well acknowledged as an effective strategy for promoting polysulfide conversion. Herein, a well-designed MoS2 QDs-CNTs/S@Ni(OH)2 (labeled as MoS2 QDs-CNTs/S@NH) cathode was synthesized via a hydrothermal process, in which conductive polar MoS2 quantum dot-decorated carbon nanotube (CNT) networks coated with an ultrathin Ni(OH)2 layer acted as an efficient electrocatalyst. MoS2 QD nanoparticles with a high conductivity and catalytic nature can enhance the kinetics of polysulfide conversion, expedite Li2S nucleation, and decrease the reaction energy barrier. The thin outer Ni(OH)2 layer physically confines active sulfur and meanwhile provides abundant sites for adsorption and conversion of polysulfides. Benefiting from these merits, a battery using MoS2 QDs-CNTs/S@NH as the sulfur host cathode exhibits excellent electrochemical performances with rate capabilities of 953.7 mA h g-1 at 0.1C and 606.6 mA h g-1 at 2.0C. A prominent cycling stability of a 0.052% decay rate per cycle after 800 cycles is achieved even at 2C.

First-principles study of the discharge electrochemical and catalytic performance of the sulfur cathode host Fe0.875M0.125S2 (M = Ti, V).

Lithium-sulfur batteries (LSBs) are one of the most promising energy storage devices with high energy density. However, their application and commercialization are hampered by the slow Li-S redox chemistry. Fe0.875M0.125S2 (M = Ti, V), as the sulfur cathode host, enhances the Li-S redox chemistry. FeS2 with Pa3̄ is transformed into Li2FeS2 with P3̄m1 after discharge. The structure changes and physicochemical properties during Fe0.875M0.125S2 discharge process are further investigated to screen out the sulfur cathode host materials with the best comprehensive properties. The discharge structure of Fe0.875M0.125S2 is verified by the thermodynamic stability of Li-deficient phases, voltage and capacity based on Monte Carlo methods. Fe0.875M0.125S2 with Pa3̄ is transformed into Li2Fe0.875M0.125S2 with P3̄m1 after discharge. Using the first-principles calculations, the physicochemical properties of Li2Fe0.875M0.125S2 are systematically investigated, including the formation energy, voltage, theoretical capacity, electrical conductivity, Li+ diffusion, catalytic performance and Li2S oxidation decomposition. The average redox voltage of Li2Fe0.875V0.125S2 is higher than that of Li2Fe0.875Ti0.125S2. Li2Fe0.875M0.125S2 shows metallic properties. Li2Fe0.875V0.125S2 is more beneficial to the reduction reaction of Li2S2 and Li2S oxidation decomposition. Fe0.875V0.125S2 has more potential as the sulfur cathode host than Fe0.875Ti0.125S2 in LSBs. A new strategy for the selection of the sulfur cathode host material for LSBs is provided by this work.

Configuring a O,S-doped carbon substrate as sulfur anchor for Li–S batteries

Configuring a carbon substrate with low surface polarity seems very important and significant for accelerating the cathode electrochemical performances of the Lithium-sulfur batteries, which is widely regarded as one of the most promising candidates for the next-generation green energy suppliers. The corn starch-derived carbon with in-situ multi-elements doping, initially carbonized by 6 mol/L H2SO4 and then calcined in nitrogen atmosphere, is employed to configure sulfur cathode for Lithium–Sulfur batteries in this study. As-received carbon with randomly distributed graphical domains serves as charge carriers diffusion channels during discharging/charging cycles, thus endowing the cathode considerable excellent performances. Specifically, the loading amount of sulfur in cathode is around 60.31 wt% and the effective utilization efficiency of active reagent sulfur in cathode is up to 60 %. On activating the cathode at 0.114 A g−1 at 0, 25 and 40 °C, the initial discharge capacities of the Lithium–Sulfur batteries with corn starch-derived carbon-based composite cathode (with ∼1.3 mg cm−2 sulfur) are 278.6, 1023.7 and 976.1 mAh∙g−1, respectively. Accordingly, more uniform, and thinner solid electrolyte interphase membrane formed under room temperature activation, leaving in the dramatically diminished Rsur value, contributes to the comparable cycling stability and rate performances of as-designed carbon-based sulfur cathode for Lithium–Sulfur Batteries.

Effects of O, S, and P in transition-metal compounds on the adsorption and catalytic ability of sulfur cathodes in lithium–sulfur batteries

This work studies the effects of anionic species on the adsorption and catalytic abilities of sulfur cathodes. The results show that P-doped metal compounds are more beneficial for inhibiting the shuttle effect and improving reaction kinetics.

Core-shell oxygen-deficient Fe2O3 polyhedron serves as an efficient host for sulfur cathode.

Herein, an oxygen-defect-rich core-shell Fe2O3-x@C polyhedral sulfur host was prepared, which effectively promoted electrochemical conversion and further inhibited the "shuttle effect" in lithium-sulfur (Li-S) batteries. Fe2O3-x@C@S provided a high initial capacity of 1395 mA h g-1 and a low attenuation of ∼0.067% per cycle.

Thermal transport properties of graphene aerogel as an advanced carrier for enhanced energy storage.

Leveraging graphene aerogels as carriers offers innovative avenues for achieving enhanced energy density, thermal conductivity, and stability in energy storage materials due to their unique attributes. This study investigates the thermal transport properties of composite sulfur cathode materials and phase change materials based on graphene aerogels using molecular dynamics simulation. A graphene aerogel model is established, and the effects of sulfur and octadecane content on the thermal transport properties of graphene aerogels and graphene aerogel-based composites are examined. A theoretical model of heat transport is developed to analyze the contribution of fillers and graphene aerogels to the thermal conductivity of the composites. The results show that the theoretical analytical model shows strong agreement with the molecular dynamics results, especially at high filler content. This research provides valuable theoretical guidance for understanding the thermal transport properties of graphene aerogel-based composite sulfur cathode materials and phase change materials.

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.