Sulfur-based Cathode Research Articles

S@FeS2 Core-Shell Cathode Nanomaterial for Preventing Polysulfides Shuttling and Forming Solid Electrolyte Interphase in High-Rate Li-S Batteries.

Lithium-sulfur (Li-S) battery is a potential next-generation energy storage technology over lithium-ion batteries for high capacity, cost-effective, and environmentally friendly solutions. However, several issues including polysulfides shuttle, low conductivity and limited rate-capability have hampered its practical application. Herein, a new class of cathode active material with perfect core-shell structure is reported, in which sulfur is fully encapsulated by conductivity-enhancing FeS2 (named as S@FeS2), for high-rate application. Surface-stabilized S@FeS2 cathode exhibits a stable cycling performance under 2 - 20 times higher rates (1-2 C, charged in 30-60min) than standard rates (e.g., 0.1-0.5C, charged in 2-10h), without polysulfides shuttle event. Surface analysis results reveal the unprecedented formation of a stable solid electrolyte interphase (SEI) layer on S@FeS2 cathode, which is distinguished from other sulfur-based cathodes that are not able to form the SEI layer. The data suggest that the prevention of polysulfides shuttling is owing to the surface protection effect of FeS2 shell and the SEI layer formation overlying core-shell S@FeS2. This unique and potential material concept proposed in the present study will give insight into designing a prospective fast charging Li-S battery.

Fluorinated ester additive to regulate nucleation behavior and interfacial chemistry of room temperature sodium-sulfur batteries

Room temperature sodium-sulfur (RT Na-S) batteries are considered as advanced energy storage technology due to their low cost and high theoretical energy density. However, challenges such as the growth of sodium dendrite and dissolution of sodium polysulfides significantly hinder the electrochemical performance. Herein, we developed a propylene carbonate (PC)-based electrolyte with Methyl 2-Fluoroisobutyrate (MFB) as an additive. The ester group in the MFB additive is capable of participating in and reconfiguring the coordination of their Na+ solvated structures, thereby lowering the desolvation barrier and regulating the Na anode’s interfacial reaction and nucleation behavior. The polar C−F bond at the other end helps to reduce the lowest unoccupied molecular orbital (LUMO) energy of the MFB additive, enabling the preferential decomposition of MFB to form the F-rich inorganic phase strong polar solid electrolyte interphase (SEI), contributing to the inhibition of Na dendrite growth, the accumulation of dead Na. In addition, NaF-riched cathode electrolyte interphase (CEI) was also observed on sulfur-based cathode, which can effectively inhibited the shuttle effect. Consequently, the developed RT Na-S battery exhibit excellent electrochemical performance.

Developing Cathode Films for Practical All-Solid-State Lithium-Sulfur Batteries.

The development of all-solid-state lithium-sulfur batteries (ASSLSBs) toward large-scale electrochemical energy storage is driven by the higher specific energies and lower cost in comparison with the state-of-the-art Li-ion batteries. Yet, insufficient mechanistic understanding and quantitative parameters of the key components in sulfur-based cathode hinders the advancement of the ASSLSB technologies. This review offers a comprehensive analysis of electrode parameters, including specific capacity, voltage, S mass loading and S content toward establishing the specific energy (Wh kg-1) and energy density (Wh L-1) of the ASSLSBs. Additionally, this work critically evaluates the progress in enhancing lithium ion and electron percolation and mitigating electrochemical-mechanical degradation in sulfur-based cathodes. Last, a critical outlook on potential future research directions is provided to guide the rational design of high-performance sulfur-based cathodes toward practical ASSLSBs.

Design of Coatings for Sulfur-Based Cathode Materials in Lithium-Sulfur Batteries: A review.

Lithium-sulfur batteries (LSBs) are considered next-generation energy storage and conversion solutions owing to their high theoretical specific capacity and the high abundance/low-cost of sulfur-based cathode materials. However, LSBs still encounter significant challenges, including the low conductivities of sulfur-based materials, severe volumetric expansion of sulfur during the discharge process, and the persistent "shuttle effect" of polysulfides. In recent years, a tremendous amount of research has been conducted to address the above challenges by developing coating and compositing materials and corresponding fabrication strategies for sulfur-based cathode materials. In this study, the surface coating, compositing materials, and fabrication methodologies of LSB cathodes are comprehensively reviewed in terms of advanced materials, structure/component characterization, functional mechanisms, and performance validation. Some technical challenges are analyzed in detail, and possible future research directions are proposed to overcome the challenges toward practical applications of lithium-sulfur batteries.

Green biomass-derived hierarchically porous non-activated carbon from carob waste for high-performance lithium-sulfur batteries

To expedite the development of lithium-sulfur (Li–S) battery technology, it is necessary to address the inherent technological hurdles surrounding sulfur-based cathodes, including mitigating the shuttle effect and enhancing the electrical conductivity of sulfur. The use of biomass-derived carbonaceous materials offers a promising avenue to alleviate these challenges and help reduce the carbon footprint associated with battery technologies. Herein, we report the green synthesis of carob-derived carbonaceous material without additional physical/chemical activation steps, making the process sustainable, affordable, and eco-friendly. The obtained carob-derived carbon (CC) offers a hierarchical micro/meso/macroporous structure with a high surface area of 633 m2 g−1. The electrochemical performance with a sulfur content of 70% (CC@S70) in the composite and a sulfur mass loading of 1 mg cm−2 delivers an initial discharge capacity of 1405 mAh g−1, reducing to 798 mAh g−1 after 260 cycles. Increasing the sulfur content to 90% in the cathode (CC@S90) yields a high capacity in Li–S cells, reaching a discharge capacity of 937 mAh g−1 with a sulfur loading of 2 mg cm−2 at 0.3C (1C = 1675 mA g−1) after 100 cycles. The improved performance can be attributed to the well-preserved interconnected pores within the carbon material, serving as an efficient framework to accommodate high sulfur content.

One-pot Synthesis of High-capacity Sulfur Cathodes via In-situ Polymerization of a Porous Imine-based Polymer.

Lithium-ion batteries, essential for electronics and electric vehicles, predominantly use cathodes made from critical materials like cobalt. Sulfur-based cathodes, offering a high theoretical capacity of 1675mAhg-1 and environmental advantages due to sulfur's abundance and lower toxicity, present a more sustainable alternative. However, state-of-the-art sulfur-based electrodes do not reach the theoretical capacities, mainly because conventional electrode production relies on mixing of components into weakly coordinated slurries. Consequently, sulfur's mobility leads to battery degradation - an effect known as the "sulfur-shuttle". This study introduces a solution by developing a microporous, covalently-bonded, imine-based polymer network grown in-situ around sulfur particles on the current collector. The polymer network (i) enables selective transport of electrolyte and Li-ions through pores of defined size, and (ii) acts as a robust host to retain the active component of the electrode (sulfur species). The resulting cathode has superior rate performance from 0.1C (1360mAhg-1) to 3C (807mAhg-1). Demonstrating a high-performance, sustainable sulfur cathode produced via a simple one-pot process, our research underlines the potential of microporous polymers in addressing sulfur diffusion issues, paving the way for sulfur electrodes as viable alternatives to traditional metal-based cathodes.

Ultralight Electrolyte with Protective Encapsulation Solvation Structure Enables Hybrid Sulfur-Based Primary Batteries Exceeding 660 Wh/kg.

An electrochemical couple of lithium and sulfur possesses the highest theoretical energy density (>2600 Wh/kg) at the material level. However, disappointingly, it is out of place in primary batteries due to its low accessible energy density at the cell level (≤500 Wh/kg) and poor storage performance. Herein, a low-density methyl tert-butyl ether was tailored for an ultralight electrolyte (0.837 g/mL) with a protective encapsulation solvation structure which reduced electrolyte weight (23.1%), increased the utilization of capacity (38.1%), and simultaneously forfended self-discharge. Furthermore, active fluorinated graphite partially replaced inactive carbon to construct a hybrid sulfur-based cathode to bring the potential energy density into full play. Our demonstrated pouch cell achieved an incredible energy density of 661 Wh/kg with a negligible self-discharge rate based on the above innovations. Our work is anticipated to provide a new direction to realize the practicality of lithium-sulfur primary batteries.

Enabling High-Areal Capacity and Long-Term Stability of Layered Oxide Cathodes in All Solid State Batteries

The stability of electrode/electrolyte interfaces play a key role in the performance-determination of solid state batteries[1]. Such interfacial stability including not only the chemical/electrochemical stability such as side reactions, but also physical or electrochemo-stabilitry such as stable physical contact between solid electrode and solid electrolytes which may not a big issue in liquid-type Li-ion batteries[2]. In this presentation, we will present some newest research[3-6] in the comprehensive characterization and undersstanding of the effects of interfacial behaviour on the electrochemical performance of the oxide-type or sulfide-type solid state batteries with high capacity cathodes such as Ni-rich and Sulfur-based cathodes. In addition, operando-NMR results reveal the failure processes of Li metal anode in all-solid-state Li battery(ASSLB)[7] will be also presented. It is also shown that Ni-rich cathode is able to deliver a high areal capacity (~13mAh/cm2) but with promising long-term stability in ASSLB. [8] Reference s : Y. Yang, Solid State Electrochemistry; First Edition, Chem. Indus. Press, Beijing, 2017Y. X. Xiang, et al; Materials Today; 2020 ，36，139-157J. P. Zhu, et al; Chem. Mater.; 2020, 32，4998-5003X. S.Liu, et al; Advanced Energy Materials; 2021，11, 2003583Z.R.Chen, et al; ACS Energy Lett.; 2022, 7(8), 2761Y. Q. Wu et al; Energy Environmental Science; 2022, 15, 3470Z. T.Liang, et al; Nature Commun., 2023, 14, 259Z.T.Liang et al; submitted

Inorganic Polysulfide Chemistries for Better Energy Storage Systems.

ConspectusSulfur-based cathode materials have become a research hot spot as one of the most promising candidates for next-generation, high-energy lithium batteries. However, the insulating nature of elemental sulfur or organosulfides has become the biggest challenge that leads to dramatic degradation and hinders their practical application. The disadvantage is more obvious for all-solid-state battery systems, which require both high electronic and ionic migration at the same sites to realize a complete electrochemical reaction. In addition to adding conductive components into the cathode composites, another effective way to realize high-reversibility sulfur-based cathodes is by optimizing the inherent nature of sulfur-based materials to make them "conductive". Inorganic polysulfide materials including polysulfide molecules, selenium-sulfur solid solutions, and (lithium) metal polysulfides are promising, as they have different structures that can make them intrinsically conductive or becoming conductive during lithiation. They all contain at least one -S-S- bridged bond, which is the intrinsic structural characteristic and the source of the chemical properties of these polysulfide compounds. For example, by balancing the conductivity and reversible capacity, researchers in the US National Aeronautics and Space Administration (NASA) have shown that 500 Wh/kg solid-state Li-Se/S batteries can power cars and even electric aircraft.We have long been focusing on the inorganic polysulfide component, reported the selenium-sulfur solid solutions, the first sulfur-rich phosphorus polysulfide molecules, and followed the research of metal polysulfide components. The proposed Account summarizes our current knowledge of the fundamental aspects of inorganic polysulfides in energy storage systems based on state-of-the-art publications on this topic. Both fast electron and ion migrations within the electrode materials are vital to achieving high-energy batteries. We begin by illustrating effective approaches to enhance the electronic/ionic conductivity of sulfur-based electrode materials. We then present some basic observations and properties (especially the intrinsic high conductivities) of the inorganic polysulfide electrode materials. The key chemical and structural factors dictating their conductive and electrochemical behaviors will be discussed. Finally, we show the advantages and broad applications of inorganic polysulfides in energy storage areas. The proposed Account will provide an insightful perspective on the current knowledge of inorganic polysulfide materials, as well as their future research directions and development potential, serving as a keynote reference for researchers in the field of energy storage.

Unveiling the catalytic potential of two-dimensional boron nitride in lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries, renowned for their potential high energy density, have attracted attention due to their use of earth-abundant elements. However, a significant challenge lies in developing suitable materials for both lithium-based anodes, which are less prone to lithium dendrite formation, and sulfur-based cathodes. This obstacle has hindered their widespread commercial viability. In this study, we present a novel sulfur host material in the form of a two-dimensional semiconductor boron nitride framework, specifically the 2D orthorhombic diboron dinitride (o-B2N2). The inherent conductivity of o-B2N2 mitigates the insulating nature often observed in sulfur-based electrodes. Notably, the o-B2N2 surface demonstrates a high binding affinity for long-chain Li-polysulfides, leading to a significant reduction in their dissolution into the DME/DOL electrolytes. Furthermore, the preferential deposition of Li2S on the o-B2N2 surface expedites the kinetics of the lithium polysulfide redox reactions. Additionally, our investigations have revealed a catalytic mechanism on the o-B2N2 surface, significantly reducing the free energy barriers for various sulfur reduction reactions. Consequently, the integration of o-B2N2 as a host cathode material for Li–S batteries holds great promise in suppressing the shuttle effect of lithium polysulfides and ultimately enhancing the overall battery performance. This represents a practical advancement for the application of Li–S batteries.

Beaded CoSe2-C Nanofibers for High-Performance Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are regarded as highly promising energy storage devices due to their high theoretical specific capacity and high energy density. Nevertheless, the commercial application of Li-S batteries is still restricted by poor electrochemical performance. Herein, beaded nanofibers (BNFs) consisting of carbon and CoSe2 nanoparticles (CoSe2/C BNFs) were prepared by electrospinning combined with carbonization and selenization. Benefitting from the synergistic effect of physical adsorption and chemical catalysis, the CoSe2/C BNFs can effectively inhibit the shuttle effect of lithium polysulfides and improve the rate performance and cycle stability of Li-S batteries. The three-dimensional conductive network provides a fast electron and ion transport pathway as well as sufficient space for alleviating the volume change. CoSe2 can not only effectively adsorb the lithium polysulfides but also accelerate their conversion reaction. The CoSe2/C BNFs-S cathode has a high reversible discharge specific capacity of 919.2 mAh g-1 at 0.1 C and presents excellent cycle stability with a low-capacity decay rate of 0.05% per cycle for 600 cycles at 1 C. The combination of the beaded carbon nanofibers and polar metal selenides sheds light on designing high-performance sulfur-based cathodes.

Design of Size-Controlled Sulfur Nanoparticle Cathodes for Lithium-Sulfur Aviation Batteries.

Lithium-sulfur (Li-S) battery has been considered as a strong contender for commercial aerospace battery, but the commercialization requires Ah-level pouch cells with both efficient discharge at high rates and ultra-high energy density. In this paper, the application of lithium-sulfur batteries for powering drones by using the cathode of highly dispersed sulfur nanoparticles with well-controlled particle sizes have been realized. The sulfur nanoparticles are prepared by a precipitation method in an eco-friendly and efficient way, and loaded on graphene oxide-cetyltrimethylammonium bromide by molecular grafting to realize a large-scale fabrication of sulfur-based cathodes with superior electrochemical performance. A button cell based on the cathode exhibits an excellent discharge capacity of 62.8 mAh cm-2 at a high sulfur loading of 60mg cm-2 (i.e., 1046.7 mAh g-1 ). The assembled miniature pouch cell (PCmini) shows a discharge capacity of 130 mAh g-1 , while the formed Ah-level pouch cell (PCAh) achieves energy density of 307Wh kg-1 at 0.3C and 92Wh kg-1 at 4C. Especially, a four-axis propeller drone powered by the PC has successfully completed a long flight (>3 min) at high altitudes, demonstrating the practical applicability as aviation batteries.

“Ship-In-a-Bottle” Strategy to Construct Polymeric Sulfur Inside Mesoporous Carbon for High-Performance Lithium–Sulfur Batteries

Polymeric sulfur was synthesized via an interfacial polycondensation reaction and incorporated inside the mesopores of the mesoporous carbons through the “ship-in-a-bottle” strategy for lithium–sulfur batteries. Based on the excellent physical properties of the carbon host and the C–S bonds in the polymer, the polymeric sulfur composite cathode exhibited a strong confined effect on polysulfides, thus inhibiting the shuttle effect and delivering a reversible discharge capacity of 846 mA h g–1 at 0.5 C over 200 cycles and of 813 mA h g–1 at 1 C for 200 cycles with a capacity decay rate of 0.04% per cycle. Even at a rate of 2 C, the obtained polymeric sulfur-based cathode also maintained a capacity of 535 mA h g–1 after 600 cycles with a decay rate of only 0.04% per cycle.

Advances in sulfide-based all-solid-state lithium-sulfur battery: Materials, composite electrodes and electrochemo-mechanical effects

Sulfide-based all-solid-state lithium-sulfur batteries (ASSLSBs) have recently attracted great attention. The “shuttle effect” caused by the migration of polysulfides in conventional liquid lithium-sulfur batteries could be eliminated. Therefore, the utilization of active materials and cycling stability, as well as battery safety, can be significantly improved. Impressive progress has been made in the research of materials for sulfide-based ASSLSBs, including sulfide solid-state electrolytes (SSEs), sulfur-based cathode materials, and anode materials. However, challenges such as scalable fabrication of large-scale, high-areal capacity composite electrodes and robust, high-conductivity thin SSE films, as well as the serious electrochemo-mechanical issues in sulfur-based electrodes, still hinder the practical application and development of sulfide-based ASSLSBs. In this review, recent research progress on sulfide-based ASSLSBs materials is summarized and discussed. In addition, the challenges in the practical application of sulfide-based ASSLSBs, such as scalable composite electrodes/SSE membranes fabrication and complicated electrochemo-mechanical coupling effects, are also systematically overviewed.

Hierarchical Porous and Three-Dimensional MXene/SiO2 Hybrid Aerogel through a Sol-Gel Approach for Lithium–Sulfur Batteries

A unique porous material, namely, MXene/SiO2 hybrid aerogel, with a high surface area, was prepared via sol-gel and freeze-drying methods. The hierarchical porous hybrid aerogel possesses a three-dimensional integrated network structure of SiO2 cross-link with two-dimensional MXene; it is used not only as a scaffold to prepare sulfur-based cathode material, but also as an efficient functional separator to block the polysulfides shuttle. MXene/SiO2 hybrid aerogel as sulfur carrier exhibits good electrochemical performance, such as high discharge capacities (1007 mAh g–1 at 0.1 C) and stable cycling performance (823 mA h g–1 over 200 cycles at 0.5 C). Furthermore, the battery assembled with hybrid aerogel-modified separator remains at 623 mA h g–1 over 200 cycles at 0.5 C based on the conductive porous framework and abundant functional groups in hybrid aerogel. This work might provide further impetus to explore other applications of MXene-based composite aerogel.

Quasi-Solid-State Lithium-Sulfur Batteries Consist of Super P – Sulfur Composite Cathode

Lithium-Sulfur (Li-S) batteries stand out to be one of the most promising candidates to meet the current energy storage requirement, with its natural abundance of materials, high theoretical capacity of 1672 mAhg-1, high energy density of 2600 Whkg-1, and low cost and lower environmental impact. Sulfur itself (S8), Li2S2 and Li2S formed during the discharge process, are electrical insulators and hence reduce the active material utilization and the electronic conductivity of the cathode affecting the battery performance. Combining of Carbon Super P (SP) with sulfur in cathode formulation is used to overcome these issues. In Liquid electrolyte batteries, polysulfides formed while charging and discharging, easily dissolve in liquid electrolyte and the resulting polysulfide shuttling leads to poor coulombic efficiency and cyclability. Liquid electrolytes used in the conventional Li-S batteries are easy to flow and become flammable. Further, Lithium dendrites piercing through separator causing short circuit paths leads to safety concerns. Replacement of the liquid electrolyte by a solid-state electrolyte (SSE) proves to be a strategy to overcome above mentioned issues. Sulfide based solid electrolytes have received greater attention due to their higher ionic conductivity, compatible interface with sulfur-based cathodes, and lower grain boundary resistance. Novel Li6PS5F0.5Cl0.5 due to its remarkable ionic conductivity of 3.5 x 10-4 S cm-1 makes it an excellent candidate for use in a Li-S solid state battery. However, the interface between SSEs and cathodes has become a challenge to be addressed in all solid-state Li-S batteries due to the rigidity of the participating surfaces. A hybrid electrolyte containing of SSE coupled with a small amount of ionic liquid at the interface, has been employed to improve the interface contact of the SSE with the electrodes.Cathode formulation consisting of sulfur as the active material, Super P as the conductive carbon black, acetylene carbon black as conductive carbon additive, with water based carboxymethyl cellulose (CMC) solution and Styrene butadiene rubber (SBR) as the binder was successfully developed. Thermo gravimetric analysis (TGA) studies of the cathode were carried out by the thermo gravimetric analyzer TA 2050 under N2 gas flow of 100 ml/min. Cathode surface morphology was characterized using the Field emission gun scanning electron microscope (FEI), TESCAN scanning electron microscope with energy dispersive X-ray spectroscopy (EDAX). Using a solvent-based process, Li6PS5F0.5Cl0.5 and Li6PS5F0.5Cl2 SSE were synthesized via the introduction of LiF into the argyrodite crystal structure, which enhances both the ionic conductivity and interface-stabilizing properties of the SSE. Relevant Ionic Liquids (IL) were prepared using Lithium bis(trifluoromethyl sulfonyl)imide (LiTFSI) as salt, with premixed pyrrolidinium bis(trifluoromethyl sulfonyl)imide (PYR) as solvent and 1,3-dioxolane (DOL) as diluent.SP-S cathode with 0.70 mgcm-2 sulfur loading was punched into disks of 2.0 cm2. SSE was pressed into 150 mg pellets using a stainless-steel tank. During the assembly, SSE was wetted with total of 40 μl of IL (LiTFSI dissolved in PYR and DOL solution) from both ends using a micropipette. 2032 type coin cells of Quasi-solid-state Li-S batteries (QSSLSB) consisting of SP-S based composite cathodes, Li anodes and novel Li6PS5F0.5Cl0.5 SSE were tested with an ionic liquid wetting both electrode-SSE interfaces. All the QSSLSB were cycled at 30 °C between 1.0 V and 2.8 V using an 8 channel Arbin battery testing system.Effect of IL dilution, co-solvent amount, LiTFSI concentration and C rate at which the batteries are tested, were systematically studied and optimized to develop a QSSLSB with higher capacity retention and cyclability. Optimum batteries had initial discharge capacity >1100 mAh/g and discharge capacity >400 mAh/g after 100 cycles at the C rate of C/10 with a significant coulombic efficiency. 40 μl of LiTFSI (2M) dissolved in PYR:DOL(1:1) IL was found to be optimum for high performance QSSEBs with low sulfur loading of 0.7 mg/cm2. From the C rate performance study QSSEBs have shown improved stability with the higher current rates. Next, cathodes with higher sulfur loading were studied and for sulfur loading > 4 mgcm-2, initial discharge capacity >950 mAh/g and 400 mAh/g after 60 cycles at C/20 rate were achieved with 40 μl of IL consisting of LiTFSI (3M) dissolved in PYR:DOL(1:3) for the SSE Li6PS5F0.5Cl2. Further testing is underway to improve the performance at high C rate for higher loading by incorporating SSE in the cathode to realize QSSLSB with higher capacity with improved cycle retention.

Suppressing Li-Dendrite By the Structural Design of Li-Si Alloy-Anode in Sulfide Based All-Solid-State Batteries

All-solid-state batteries (ASSBs) were fabricated with alloy-anode composite (Li3.25-Si + Li2S-P2S5), sulfide-based glass electrolyte (Li2S-P2S5), and sulfur-based composite cathode (S + Li2S-P2S5 + C). When the anode was made of only lithium silicide, voltage noise occurred under 0.5-3.7 V cut-off condition, which is out of the electrochemical stability window of the solid electrolyte (SE). This result indicates that Li-dendrites were generated by irreversible Li-ion deposition at the limited interface between the anode and the SE due to oxidative decomposition of SE. We modified the anode to the composite structure consisting of lithium silicide + sulfide SE to increase the number of the alloying reaction site. The pyrolytic graphite sheet (PGS) was placed between the anode and the current collector to facilitate electron transport. As a result, the voltage noise did not occur under the 0.5-3.7 V cut-off condition. This study indicates that increasing the number of alloying reaction sites improves the structural stability of the full cell, thereby increasing the cycle life.

Dual-functional hosts derived from metal-organic frameworks reduce dissolution of polyselenides and inhibit dendrite growth in a sodium-selenium battery

Selenium-based cathodes for sodium-ion batteries have attracted considerable attention due to their high electronic conductivity and volumetric capacity compared to sulfur-based cathodes. However, the use of sodium-selenium batteries has been hindered due to the low selenium reaction activity towards sodium, rapid capacity fading caused by the shuttle effect of polyselenides, and the formation of sodium dendrites on the Na anodes. Herein, starting from the nitrogen and oxygen-containing ligands, two precursors of Ni&Zn-MOF and Zn-MOF were used to fabricate the cathode and anode, respectively. A N,O-codoped porous carbon host decorated with well-dispersed Ni single-atom catalyst was derived from the Ni&Zn-MOF for Se storage. When applied as a cathode in Na-Se batteries, this composite accelerated the reaction kinetics of Se and Na+, and at the same time weakened the Se-Se bond owing to its high adsorption to the Se8 ring, which resulted in a significant improvement of the cycle stability. Meanwhile, a dendrite-free anode was realized by using Zn-MOF derived N,O-codoped porous carbon host, which showed a strong sodiophilic ability for Na metal. As a result, the Na-Se battery employing these two composites as the cathode and anode showed an excellent cycle stability and improved safety.

Capturing Polysulfides with a Functional Anhydride Compound for Lithium–Sulfur Batteries

Lithium–sulfur batteries are the focus of the current development of high-energy storage devices. However, their practical application is hindered by the fast capacity decay caused by the “shuttle effect” of intermediate lithium polysulfides during cycling. In this study, we combine graphene (G) with the organic molecule 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) to form the G-PTCDA composite as the host material of sulfur cathodes. In particular, PTCDA with the conjugated benzene rings and the anhydride group is absorbed tightly on graphene through π–π stacking and thus enhances the polarity and conductivity of the G-PTCDA composite. Meanwhile, PTCDA can capture the otherwise dissolved intermediate polysulfides on the sulfur cathode by forming the Li–O bond with the oxygen atoms on the acid anhydride group in a collaborative manner. Thus, the “shuttle effect” can be effectively depressed, and the electrochemical performance is improved during discharge and charge cycling. We hope that the findings of this study can provide a deeper understanding of the design and preparation of the sulfur-based composite cathode material with functional organic molecules for lithium–sulfur batteries.

Regulating uniform nucleation of ZnS enables low-polarized and high stable aqueous Zn–S batteries

Sulfur-based cathode materials can greatly improve the overall energy density of the aqueous zinc ion batteries. However, it suffers from uneven accumulated discharge products of ZnS, which retard the conversion to S during charge process. Herein, we report a regulation strategy for uniform ZnS nucleation by introducing PEG-400 additive into 1 M Zn(CH3COO)2 electrolyte to form a modified solvation structure. Uniform and small ZnS with the average diameter of 180 nm can be formed, which is favorable for the conversion from ZnS to S. The S@CNTs cathode using such an aqueous electrolyte exhibits a lower voltage hysteresis of 0.47 V, high capacity of 1116 mAh/g at the current density of 0.1 A/g, and a good rate capacity of 774 mAh/g at 1 A/g. Furthermore, the addition of PEG can also improve the stability of Zn anode; as a result, we achieve a Zn–S full cell with a low overpotential performance and stable reversibility.