Sulfur-infiltrated micro- and mesoporous silicon carbide-derived carbon cathode for high-performance lithium sulfur batteries

Insights into the solvation chemistry in liquid electrolytes for lithium-based rechargeable batteries

Lithium-based rechargeable batteries have dominated the energy storage field and attracted considerable research interest due to their excellent electrochemical performance. As indispensable and ubiquitous components, electrolytes play a pivotal role in not only transporting lithium ions, but also expanding the electrochemical stable potential window, suppressing the side reactions, and manipulating the redox mechanism, all of which are closely associated with the behavior of solvation chemistry in electrolytes. Thus, comprehensively understanding the solvation chemistry in electrolytes is of significant importance. Here we critically reviewed the development of electrolytes in various lithium-based rechargeable batteries including lithium-metal batteries (LMBs), nonaqueous lithium-ion batteries (LIBs), lithium-sulfur batteries (LSBs), lithium-oxygen batteries (LOBs), and aqueous lithium-ion batteries (ALIBs), and emphasized the effects of interactions between cations, anions, and solvents on solvation chemistry, and functions of solvation chemistry in different types of electrolytes (strong solvating electrolytes, moderate solvating electrolytes, and weak solvating electrolytes) on the electrochemical performance and redox mechanism in the abovementioned rechargeable batteries. Specifically, the significant effects of solvation chemistry on the stability of electrode-electrolyte interphases, suppression of lithium dendrites in LMBs, inhibition of the co-intercalation of solvents in LIBs, improvement of anodic stability at high cut-off voltages in LMBs, LIBs and ALIBs, regulation of redox pathways in LSBs and LOBs, and inhibition of hydrogen/oxygen evolution reactions in LOBs are thoroughly summarized. Finally, the review concludes with a prospective outlook, where practical issues of electrolytes, advanced in situ/operando techniques to illustrate the mechanism of solvation chemistry, and advanced theoretical calculation and simulation techniques such as "material knowledge informed machine learning" and "artificial intelligence (AI) + big data" driven strategies for high-performance electrolytes have been proposed.

CoO embedded porous biomass-derived carbon as dual-functional host material for lithium-sulfur batteries

A new strategy is developed to fabricate sulfur electrode by infusing sulfur into a conductive biochar decorated with highly dispersed CoO nanoparticles. The loading of the CoO nanoparticles, as the active sites for reactions, is efficiently increased by using the microwave-assisted diffusion method. It is demonstrated that biochar can serve as an excellent conductive framework to effectively activate sulfur. Simultaneously, the CoO nanoparticles possessing excellent capability to adsorb polysulfides can remarkably alleviate the dissolution of polysulfides, and greatly enhance the conversion kinetics between the polysulfides and Li₂S₂/Li₂S in the charge/discharge processes. The sulfur electrode dual-functionalized with biochar and CoO nanoparticles exhibits excellent electrochemical performance, including high initial discharge specific capacity of 930.5 mAh g^-1 and low capacity decay rate of 0.069 % per cycle during 800 cycles at 1C rate. It is particularly interesting that the CoO nanoparticles distinctively enhance the Li⁺ diffusion during the charge process, endowing the material with excellent high-rate charging performance. This could be beneficial for the development of Li-S batteries with fast charging feature.

Rational Design of Silicon Nanodots/Carbon Anodes by Partial Oxidization Strategy with High-Performance Lithium-Ion Storage

Silicon (Si) is considered a promising anode material for rechargeable lithium-ion batteries (LIBs) due to its high theoretical capacity, low working potential, and safety features. However, the practical use of Si-based anodes is hampered by their huge volume expansion during the process of lithiation/delithiation, and they have relatively low intrinsic electronic conductivity, therefore seriously restricting their application in energy storage. Here, we propose a facile approach to directly transform siliceous biomass (bamboo leaves) into a porous carbon skeleton-wrapped Si nanodot architecture through a partial oxidization strategy and magnesium thermal reaction to obtain a high Si nanodot component composite (denoted as Si/C-O). With the synergistic effect of the porous carbon skeleton structure and uniformly dispersed Si nanodots, the Si/C-O composite anode with a stable structure that can avoid pulverization and accommodate volume expansion during cycling is fabricated. As expected, the biomass-converted Si/C-O anode not only presents a high Si component (59.7 wt %) by TGA but also exhibits an excellent capacity of 1013 mAh g^-1 at 0.5 A g^-1 and robust cycling stability with a capacity retention of 526 mAh g^-1 after 650 cycles. Moreover, the Si/C-O anode demonstrates considerable performance in practical LIBs when assembled with a commercial LiNi_0.8Co_0.1Mn_0.1O₂ cathode. This work provides an effective strategy and long-term insights into the utilization of porous Si-based materials converted by biomass to design and synthesize high-performance LIB materials.

Electrochemical Performance of Carbon-Rich Silicon Carbonitride Ceramic as Support for Sulfur Cathode in Lithium Sulfur Battery

As a promising matrix material for anchoring sulfur in the cathode for lithium-sulfur (Li-S) batteries, porous conducting supports have gained much attention. In this work, sulfur-containing C-rich SiCN composites are processed from silicon carbonitride (SiCN) ceramics, synthesized at temperatures from 800 to 1100 °C. To embed sulfur in the porous SiCN matrix, an easy and scalable procedure, denoted as melting-diffusion method, is applied. Accordingly, sulfur is infiltrated under solvothermal conditions at 155 °C into pores of carbon-rich silicon carbonitride (C-rich SiCN). The impact of the initial porosity and microstructure of the SiCN ceramics on the electrochemical performance of the synthesized SiCN-sulfur (SiCN-S) composites is analysed and discussed. A combination of the mesoporous character of SiCN and presence of a disordered free carbon phase makes the electrochemical performance of the SiCN matrix obtained at 900 °C superior to that of SiCN synthesized at lower and higher temperatures. A capacity value of more than 195 mAh/g over 50 cycles at a high sulfur content of 66 wt.% is achieved.

The Functional Chameleon of Materials Chemistry-Combining Carbon Structures into All-Carbon Hybrid Nanomaterials with Intrinsic Porosity to Overcome the "Functionality-Conductivity-Dilemma" in Electrochemical Energy Storage and Electrocatalysis

Nanoporous carbon materials can cover a remarkably wide range of physicochemical properties. They are widely applied in electrochemical energy storage and electrocatalysis. As a matter of fact, all these applications combine a chemical process at the electrode-electrolyte interface with the transport (and possibly the transfer) of electrons. This leads to multiple requirements which can hardly be fulfilled by one and the same material. This "functionality-conductivity-dilemma" can be minimized when multiple carbon-based compounds are combined into porous all-carbon hybrid nanomaterials. This article is giving a broad and general perspective on this approach from the viewpoint of materials chemists. The problem and existing solutions are first summarized. This is followed by an overview of the most important design principles for such porous materials, a chapter discussing recent examples from different fields where the formation of comparable structures has already been successfully applied, and an outlook over the future development of this field that is foreseen.

Graphene Nanosphere as Advanced Electrode Material to Promote High Performance Symmetrical Supercapacitor

To get carbon electrode with both excellent gravimetric and volumetric capacitances at high mass loadings is critical to supercapacitors. Herein, cracked defective graphene nanospheres (GNS) well meet above requirements. The morphology and structure of the GNS are controlled by polystyrene sphere template/glucose ratio, microwave heating time, and Fe content. The typical GNS with specific surface area of 2794 m² g^-1 , pore volume of 1.48 cm³ g^-1 , and packing density of 0.74 g cm^-3 performs high gravimetric and volumetric capacitances of 529 F g^-1 and 392 F cm^-3 at 1A g^-1 with a capacitance retention of 62.5% at 100 A g^-1 in a three-electrode system in 6 mol L^-1 KOH aqueous electrolyte. In a two-electrode system, the GNS possesses energy density of 18.6 Wh kg^-1 (13.8 Wh L^-1 ) at the power density of 504 W kg^-1 , which is higher than all reported pure carbon materials in gravimetric energy density and higher than all reported heteroatom-doped carbon materials in volumetric energy density, in aqueous solution, as far as it is known. A structural feature of carbon materials that possess both high energy density and high power density is pointed out here.

Trifunctional Electrolyte Additive Hexadecyltrioctylammonium Iodide for Lithium-Sulfur Batteries with Extended Cycle Life

Lithium-sulfur (Li-S) battery with a very high theoretical energy density (∼2500 Wh kg^-1) is a very promising alternative to the commercial lithium-ion battery as the next-generation energy storage device. However, the Li-S battery suffers from shuttle effect and Li dendrites growth due to the solubility of polysulfides in the electrolyte system and the inhomogeneous deposition of Li, resulting in short cycling life span, which is the major obstacle in its practical application. Herein, we report an additive, hexadecyltrioctylammonium iodide (HTOA-I), in the conventional electrolyte system, which shows trifunctional effect on extending Li-S battery cycle life. It can not only help us to form a protective solid-electrolyte interface (SEI) on the surface of Li anode so as to reduce the contact of polysulfides with Li but also hinder the shuttling of polysulfides to the Li anode due to the strong combination of large-sized HTOA⁺ with polysulfide anions (S_n^2-), which retard the migration of S_n^2- and cause homogeneous Li deposition owing to the large size and stronger trend of HTOA⁺ to be absorbed on Li anode as well. A new method of phosphorescence analysis for direct observation of polysulfides shuttling has been put forward for the first time, which can be further developed in future studies. The cell with the HTOA-I-added electrolyte system shows high cycling stability, retaining 83.4% of the initial capacity after 200 cycles at 1 A g^-1 and achieving 689 mAh g^-1 even after 1000 cycles. This cost-effective and facile approach will not increase the complexity of the battery manufacturing process. Compared to other electrolyte additives, the additive in our work, HTOA-I, has better positive effects on extending cycle life. This trifunctional electrolyte additive will inspire the design of other new additives and further promote the development of Li-S batteries.

Emergent electrochemical functions and future opportunities of hierarchically constructed metal-organic frameworks and covalent organic frameworks

Designing spatial and architectural features across from the molecular to bulk scale is one of the most important topics in materials science which has received a lot of attention in recent years. Looking back to the past research, findings on the influences of spatial features denoted as porous structures on the applications related to mass transport phenomena have been widely studied in traditional inorganic materials, such as ceramics over the past two decades. However, due to the difficulties in precise control of the porous structures at the molecular level in this class of materials, the mechanistic understanding of the effects of spatial and architectural features across from the molecular level to meso-/macroscopic scale is still lacking, especially in electrochemical reactions. Further understanding of fundamental electrochemical functions in well-defined architectures is indispensable for the further advancement of key next-generation energy devices. Furthermore, creating periodic porosity in reticular structures is starting to be recognized as an emerging approach to control the electronic structure of materials. In this review, we focus on the investigations on preparing well-defined molecular-level crystalline porous materials known as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) into hierarchically constructed architectures from molecular structures lower than the reticular frameworks to meso-/macroscopic scale structures. By connecting well-defined nanosized porous structures in MOFs/COFs and additional length-scale space or shapes, emergent electrochemical functions towards emerging devices, such as beyond Li-ion batteries including all-solid-state rechargeable batteries, are expected to be obtained. By summarizing recent advancements in synthetic strategies of hierarchically constructed MOF/COF based materials and fundamental investigation of their structural effect in a wide spectrum of electrochemical applications, we highlight the importance and future direction of this developing field of hierarchically constructed MOFs/COFs, while emphasizing the required chemical stability of the MOFs/COFs which meet the use in the game-changing electrochemical devices.

Boosting High-Performance in Lithium-Sulfur Batteries via Dilute Electrolyte

Polysulfide shuttle effects, active material losses, formation of resistive surface layers, and continuous electrolyte consumption create a major barrier for the lightweight and low-cost lithium-sulfur (Li-S) battery adoption. Tuning electrolyte composition by using additives and most importantly by substantially increasing electrolyte molarity was previously shown to be one of the most effective strategies. Contrarily, little attention has been paid to dilute and super-diluted LiTFSI/DME/DOL/LiNO₃ based-electrolytes, which have been thought to aggravate the polysulfide dissolution and shuttle effects. Here we challenge this conventional wisdom and demonstrate outstanding capabilities of a dilute (0.1 mol L^-1 of LiTFSI in DME/DOL with 1 wt. % LiNO₃) electrolyte to enable better electrode wetting, greatly improved high-rate capability, and stable cycle performance for high sulfur loading cathodes and low electrolyte/sulfur ratio in Li-S cells. Overall, the presented study shines light on the extraordinary ability of such electrolyte systems to suppress short-chain polysulfide dissolution and polysulfide shuttle effects.

Enhanced Multiple Anchoring and Catalytic Conversion of Polysulfides by Amorphous MoS3 Nanoboxes for High-Performance Li-S Batteries

The practical implementation of lithium-sulfur batteries is obstructed by poor conductivity, sluggish redox kinetics, the shuttle effect, large volume variation, and low areal loading of sulfur electrodes. Now, amorphous N-doped carbon/MoS₃ (NC/MoS₃ ) nanoboxes with hollow porous architectures have been meticulously designed as an advanced sulfur host. Benefiting from the enhanced conductivity by the N-doped carbon, reduced shuttle effect by the strong chemical interaction between unsaturated Mo and lithium polysulfides, improved redox reaction kinetics by the catalytic effect of MoS₃ , great tolerance of volume variation and high sulfur loading arising from flexible amorphous materials with hollow-porous structures, the amorphous NC/MoS₃ nanoboxes enabled sulfur electrodes to deliver a high areal capacity with superior rate capacity and decent cycling stability. The synthetic strategy can be generalized to fabricate other amorphous metal sulfide nanoboxes.

Aminomethyl-Functionalized Carbon Nanotubes as a Host of Small Sulfur Clusters for High-Performance Lithium-Sulfur Batteries

Here we propose an effective strategy to stabilize small sulfur species by using aminomethyl-functionalized carbon nanotubes (AM-CNT) without impairing the conductive channel of the carbon nanotube (CNT) cathode. The linear S_n clusters can be anchored strongly to the AM-CNT for the favorable size of n=5 and the maximum size of n=6 in the production of the cathode, which depresses the mass loss of active sulfur effectively and eliminates the formation of high-order polysulfides completely during the discharge process. The most stable 3 D cross-linked Inter-S₅ -AM-CNT network shows a fast electron transfer redox reaction through the CNT skeleton that possesses a theoretical capacity of 1337 mA h g^-1 (based on sulfur) or 592 mA h g^-1 (based on the cathode). The discharge products of the linear S₅ cluster tend to form a hyperbranched tight structure through N⋅⋅⋅S⋅⋅⋅Li bridges that are fully impregnated in the AM-CNT bundles, and thus stabilize the entire system. Importantly, this study provides vital guidance into how to design cathodes based on small sulfur clusters for Li-S batteries to depress the shuttle effect intrinsically during charge-discharge cycles, which can be extended to the other small-sulfur-cluster-based batteries.

Two-Dimensional MoS2 for Li-S Batteries: Structural Design and Electronic Modulation

Two-dimensional molybdenum disulfide (MoS₂ ) nanosheets attract great interest for applications in lithium-sulfur (Li-S) batteries, due to their unique physical and chemical properties, which originate from diverse chemical compositions and unique electronic structures. In recent years, many efforts have been devoted to employing MoS₂ as a polysulfide immobilizer and catalyst, functional separator, and Li-metal protection for Li-S batteries through structural design and electronic modulation. A fundamental understanding of the interplay between structural features, electronic properties, and advanced electrochemical performance is crucial for providing valuable insights for the development of Li-S batteries. In this regard, recent advances in Li-S batteries with 2D MoS₂ materials are summarized from the perspective of structural design and electronic modulation. Finally, future prospects and remaining challenges of MoS₂ for Li-S batteries are highlighted.

Straightforward synthesis of Sulfur/N,S-codoped carbon cathodes for Lithium-Sulfur batteries

An upgrade of the scalable fabrication of high-performance sulfur-carbon cathodes is essential for the widespread commercialization of this technology. Herein we present a simple, cost-effective and scalable approach for the fabrication of cathodes comprising sulfur and high-surface area, N,S-codoped carbons. The method involves the use of a sulfur salt, i.e. sodium thiosulfate, as activating agent, sulfur precursor and S-dopant, and polypyrrole as carbon precursor and N-dopant. In this way, the production of the porous host and the incorporation of sulfur are combined in the same procedure. The porous hosts thus produced have BET surface areas in excess of 2000 m² g⁻¹, a micro-mesoporous structure, as well as sulfur and nitrogen contents of 5–6 wt% and ~2 wt%, respectively. The elemental sulfur content in the composites can be precisely modulated in the range of 24 to ca. 90 wt% by controlling the amount of sodium thiosulfate used. Remarkably, these porous carbons are able to accommodate up to 80 wt% sulfur exclusively within their porosity. When analyzed in lithium-sulfur batteries, these sulfur-carbon composites show high specific capacities of 1100 mAh g⁻¹ at a low C-rate of 0.1 C and above 500 mAh g⁻¹ at a high rate of 2 C for sulfur contents in the range of 50–80 wt%. Remarkably, the composites with 51–65 wt% S can still provide above 400 mAh g⁻¹ at an ultra-fast rate of 4 C (where a charge and discharge cycle takes only ten minutes). The good rate capability and sulfur utilization was additionally assessed for cathodes with a high sulfur content (65–74%) and a high sulfur loading (>5 mg cm⁻²). In addition, cathodes of 4 mg cm⁻² successfully cycled for 260 cycles at 0.2 C showed only a low loss of 0.12%/cycle.

Hierarchically Porous SnO2 Nanoparticle-Anchored Polypyrrole Nanotubes as a High-Efficient Sulfur/Polysulfide Trap for High-Performance Lithium-Sulfur Batteries

Conductive supports could improve the electrical conductivity of the electrode in lithium-sulfur (Li-S) batteries but suffer from the shuttle effect originated from the polysulfide dissolution, while the hydrophilic metal oxides could avoid the shuttle effect but with poor conductivity. Herein, a facile approach was developed to fabricate hierarchically porous tin oxide (SnO₂) nanoparticle-anchored tubular polypyrrole (T-PPy) as a sulfur host, in order to integrate the advantages of conductive supports and metal oxides but overcome their shortcomings. In the unique structure, the T-PPy nanotubes acted as a conductive network to not only improve the electrical conductivity of cathodes but also accommodate the volume expansion of the sulfur cathode during cycling as well as relatively confine the polysulfide diffusion, while the SnO₂ nanoparticles served as a high-efficient polysulfide trap to mitigate the shuttle effect due to the chemical bond between SnO₂ and polysulfides. Moreover, the hierarchically porous structure and therefore large surface area of the proposed S/(T-PPy)@SnO₂ cathode were favorable for the accommodation of sulfur and lithium sulfides. Consequently, S/(T-PPy)@SnO₂ with 64.7% sulfur mass content exhibited excellent cyclic stability with a decay rate of only 0.05% per cycle along with 500 cycles at 1 C, rate capability of 383.7 mA h/g at 5 C, and Coulombic efficiency above 90%, outstanding among most of the reported PPy-based sulfur cathodes and PPy-based ternary sulfur cathodes.

Guidelines and trends for next-generation rechargeable lithium and lithium-ion batteries

This review article summarizes the current trends and provides guidelines towards next-generation rechargeable lithium and lithium-ion battery chemistries.

Recent advances in cathode materials for rechargeable lithium-sulfur batteries

Lithium-sulfur batteries (Li-S) are regarded as a promising candidate for next-generation energy storage systems due to their high specific capacity (1675 mA h g^-1) and energy density (2600 W h kg^-1) as well as the abundance, safety and low cost of sulfur materials. However, many disadvantages hinder the further development of Li-S batteries, such as the insulating nature of the active materials, the dissolution of intermediate products, large volume expansion and safety concerns related to metal lithium anodes. During the past decade, tremendous efforts have been made in the design and synthesis of electrode materials. In this review, we briefly discuss the electrochemical mechanism of Li-S batteries and their practical problems. Then, we systematically summarize the current strategies for designing cathode materials with stable and long cycling performance, including sulfur cathodes and Li₂S cathodes; subsequently, the current development of solid-state electrolytes and protective strategies for lithium metal anodes are briefly discussed. Finally, the current challenges and future perspectives of Li-S batteries are presented.

Current Status and Future Prospects of Metal-Sulfur Batteries

Lithium-sulfur batteries are a major focus of academic and industrial energy-storage research due to their high theoretical energy density and the use of low-cost materials. The high energy density results from the conversion mechanism that lithium-sulfur cells utilize. The sulfur cathode, being naturally abundant and environmentally friendly, makes lithium-sulfur batteries a potential next-generation energy-storage technology. The current state of the research indicates that lithium-sulfur cells are now at the point of transitioning from laboratory-scale devices to a more practical energy-storage application. Based on similar electrochemical conversion reactions, the low-cost sulfur cathode can be coupled with a wide range of metallic anodes, such as sodium, potassium, magnesium, calcium, and aluminum. These new "metal-sulfur" systems exhibit great potential in either lowering the production cost or producing high energy density. Inspired by the rapid development of lithium-sulfur batteries and the prospect of metal-sulfur cells, here, over 450 research articles are summarized to analyze the research progress and explore the electrochemical characteristics, cell-assembly parameters, cell-testing conditions, and materials design. In addition to highlighting the current research progress, the possible future areas of research which are needed to bring conversion-type lithium-sulfur and other metal-sulfur batteries into the market are also discussed.

Impact of the Mechanical Properties of a Functionalized Cross-Linked Binder on the Longevity of Li-S Batteries

One of the very challenging aspects of Li-S battery development is the fabrication of a sulfur electrode with high areal loading using conventional Li-ion binders. Herein, we report a new multifunctional polymeric binder, synthesized by the free-radical cross-linking polymerization of [2-(acryloyloxy)ethyl]trimethylammonium chloride (AETMAC) and ethylene glycol diacrylate (EGDA) to form poly(AETMAC- co-EGDA), that not only helps to confine the soluble polysulfide species but also has the desired mechanical properties to allow stable cycling of high-sulfur loading cathodes. Through a combination of spectroscopic and electrochemical studies, we elucidate the chemical interactions that inhibit polysulfide shuttling. We also show that extensive cross-linkage enables this polymeric binder to exhibit a low degree of swelling as well as high tensile modulus and toughness. These attributes are essential to maintain the architectural integrity of the sulfur cathode during extended cycling. Using this material, Li-S cells with a high-sulfur loading (6.0 mg cm^-2) and a low-intermediate electrolyte/sulfur ratio (7 μL:1 mg) achieve an areal capacity of 5.4 mA h cm^-2 and can be (dis)charged for 300 cycles with stable reversible redox behavior after the initial cycles.

Enhanced Cycling Performance for Lithium-Sulfur Batteries by a Laminated 2D g-C3 N4 /Graphene Cathode Interlayer

Decay in electrochemical performance resulting from the "shuttle effect" of dissolved lithium polysulfides is one of the biggest obstacles for the realization of practical applications of lithium-sulfur (Li-S) batteries. To meet this challenge, a 2D g-C₃ N₄ /graphene sheet composite (g-C₃ N₄ /GS) was fabricated as an interlayer for a sulfur/carbon (S/KB) cathode. It forms a laminated structure of channels to trap polysulfides by physical and chemical interactions. The thin g-C₃ N₄ /GS interlayer significantly suppresses diffusion of the dissolved polysulfide species (Li₂ S_x ; 2<x≤8) from the cathode to the anode, as proven by using an H-type glass cell divided by a g-C₃ N₄ /GS-coated separator. The S/KB cathode with the g-C₃ N₄ /GS interlayer (S/KB@C₃ N₄ /GS) delivers a discharge capacity of 1191.7 mAh g^-1 at 0.1 C after 100 cycles, an increase of more than 90 % compared with an S/KB cathode alone (625.8 mAh g^-1 ). The S/KB@C₃ N₄ /GS cathode shows good cycling life, delivering a discharge capacity as high as 612.4 mAh g^-1 for 1 C after 1000 cycles. According to XPS results, the anchoring of the g-C₃ N₄ /GS interlayer to Li₂ S_x can be attributed to a coefficient chemical binding effect of g-C₃ N₄ and graphene on long-chain polysulfides. Generally, the improvement in electrochemical performance originates from a coefficient of the enhanced Li⁺ diffusion coefficient, increased charge transfer, and the weakening of the shuttle effect of the dissolved Li₂ S_x as a result of the g-C₃ N₄ /GS interlayer.

Single-Nanostructured Electrochemical Detection for Intrinsic Mechanism of Energy Storage: Progress and Prospect

Energy storage appliances are active by means of accompanying components for renewable energy resources that play a significant role in the advanced world. To further improve the electrochemical properties of the lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and lithium-sulfur (Li-S) batteries, the electrochemical detection of the intrinsic mechanisms and dynamics of electrodes in batteries is required to guide the rational design of electrodes. Thus, several researches have conducted in situ investigations and real-time observations of electrode evolution, ion diffusion pathways, and side reactions during battery operation at the nanoscale, which are proven to be extremely insightful. However, the in situ cells are required to be compatible for electrochemical tests and are therefore often challenging to operate. In the past few years, tremendous progresses have been made with novel and more advanced in situ electrochemical detection methods for mechanism studies, especially single-nanostructured electrodes. Herein, a comprehensive review of in situ techniques based on single-nanostructured electrodes for studying electrodes changes in LIBs, SIBs, and Li-S batteries, including structure evolution, phase transition, interface formation, and the ion diffusion pathway is provided, which is instructive and meaningful for the optimization of battery systems.

Novel Non-Carbon Sulfur Hosts Based on Strong Chemisorption for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are considered as promising candidates for energy storage systems owing to their high theoretical capacity and high energy density. The application of Li-S batteries is hindered by several obstacles, however, including the shuttle effect, poor electrical conductivity, and the severe volume expansion of sulfur. The traditional method is to integrate sulfur with carbon materials. But the interaction between polysulfide intermediates and carbon is only weak physical adsorption, which easily leads to the escape of species from the framework (shuttle effect) of the material causing capacity loss. Recently, however, there has been a trend for the introduction of novel non-carbon materials as sulfur hosts based on the strong chemisorption. This review highlights recent research progress on novel non-carbon sulfur hosts based on strong chemisorption, in Li-S batteries. In comparison with carbon-based sulfur hosts, most non-carbon sulfur hosts have been demonstrated to be polar host materials that could efficiently adsorb polysulfide via strong chemisorption, mitigating their dissolution. The intrinsic mechanism associated with the role of non-carbon-based host materials in improving the performance of Li-S batteries is discussed.

Rational Design of Low Cost and High Energy Lithium Batteries through Tailored Fluorine-free Electrolyte and Nanostructured S/C Composite

We report a new Li-S cell concept based on an optimized F-free catholyte solution and a high loading nanostructured C/S composite cathode. The Li₂ S₈ present in the electrolyte ensures both buffering against active material dissolution and Li⁺ conduction. The high S loading is obtained by confining elemental S (≈80 %) in the pores of a highly ordered mesopores carbon (CMK3). With this concept we demonstrate stabilization of a high energy density and excellent cycling performance over 500 cycles. This Li-S cell has a specific capacity that reaches over 1000 mA h g^-1 , with an overall S loading of 3.6 mg cm^-2 and low electrolyte volume (i.e., 10 μL cm^-2 ), resulting in a practical energy density of 365 Wh kg^-1 . The Li-S system proposed thus meets the requirements for large scale energy storage systems and is expected to be environmentally friendly and have lower cost compared with the commercial Li-ion battery thanks to the removal of both Co and F from the overall formulation.

Almond Shell as a Microporous Carbon Source for Sustainable Cathodes in Lithium⁻Sulfur Batteries

A microporous carbon derived from biomass (almond shells) and activated with phosphoric acid was analysed as a cathodic matrix in Li⁻S batteries. By studying the parameters of the carbonization process of this biomass residue, certain conditions were determined to obtain a high surface area of carbon (967 m² g^-1) and high porosity (0.49 cm³ g^-1). This carbon was capable of accommodating up to 60% by weight of sulfur, infiltrated by the disulphide method. The C⁻S composite released an initial specific capacity of 915 mAh g^-1 in the Li⁻S cell at a current density of 100 mA g^-1 with a high retention capacity of 760 mAh g^-1 after 100 cycles and a coulombic efficiency close to 100%. The good performance of the composite was also observed under higher current rates (up to 1000 mA g^-1). The overall electrochemical behaviour of this microporous carbon acting as a sulfur host reinforces the possibility of using biomass residues as sustainable sources of materials for energy storage.

An Ultrahigh Capacity Graphite/Li2S Battery with Holey-Li2S Nanoarchitectures

The pairing of high-capacity Li2S cathode (1166 mAh g-1) and lithium-free anode (LFA) provides an unparalleled potential in developing safe and energy-dense next-generation secondary batteries. However, the low utilization of the Li2S cathode and the lack of electrolytes compatible to both electrodes are impeding the development. Here, a novel graphite/Li2S battery system, which features a self-assembled, holey-Li2S nanoarchitecture and a stable solid electrolyte interface (SEI) on the graphite electrode, is reported. The holey structure on Li2S is beneficial in decomposing Li2S at the first charging process due to the enhanced Li ion extraction and transfer from the Li2S to the electrolyte. In addition, the concentrated dioxolane (DOL)-rich electrolyte designed lowers the irreversible capacity loss for SEI formation. By using the combined strategies, the graphite/holey-Li2S battery delivers an ultrahigh discharge capacity of 810 mAh g-1 at 0.1 C (based on the mass of Li2S) and of 714 mAh g-1 at 0.2 C. Moreover, it exhibits a reversible capacity of 300 mAh g-1 after a record lifecycle of 600 cycles at 1 C. These results suggest the great potential of the designed LFA/holey-Li2S batteries for practical use.

Toward High-Performance Lithium-Sulfur Batteries: Upcycling of LDPE Plastic into Sulfonated Carbon Scaffold via Microwave-Promoted Sulfonation

Lithium-sulfur batteries were intensively explored during the last few decades as next-generation batteries owing to their high energy density (2600 Wh kg^-1) and effective cost benefit. However, systemic challenges, mainly associated with polysulfide shuttling effect and low Coulombic efficiency, plague the practical utilization of sulfur cathode electrodes in the battery market. To address the aforementioned issues, many approaches have been investigated by tailoring the surface characteristics and porosities of carbon scaffold. In this study, we first present an effective strategy of preparing porous sulfonated carbon (PSC) from low-density polyethylene (LDPE) plastic via microwave-promoted sulfonation. Microwave process not only boosts the sulfonation reaction of LDPE but also induces huge amounts of pores within the sulfonated LDPE plastic. When a PSC layer was utilized as an interlayer in lithium-sulfur batteries, the sulfur cathode delivered an improved capacity of 776 mAh g^-1 at 0.5C and an excellent cycle retention of 79% over 200 cycles. These are mainly attributed to two materialistic benefits of PSC: (a) porous structure with high surface area and (b) negatively charged conductive scaffold. These two characteristics not only facilitate the improved electrochemical kinetics but also effectively block the diffusion of polysulfides via Coulomb interaction.

Functional Differentiation of Three Pores for Effective Sulfur Confinement in Li-S Battery

Shuttle effect of the dissolved intermediates is regarded as the primary cause that leads to fast capacity degradation of Li-S battery. Herein, a microporous carbon-coated sulfur composite with novel rambutan shape (R-S@MPC) is synthesized from microporous carbon-coated rambutan-like zinc sulfide (R-ZnS@MPC), via an in situ oxidation process. The R-ZnS is employed as both template and sulfur precursor. The carbon frame of R-S@MPC composite possesses three kinds of pores that are distinctly separated from each other in space and are endowed with the exclusive functions. The central macropore serves as buffer pool to accommodate the dissolved lithium polysulfides (LPSs) and volumetric variation during cycling. The marginal straight-through mesoporous, connected with the central macropore, takes the responsibility of sulfur storage. The micropores, evenly distributed in the outer carbon shell of the as-synthesized R-S@MPC, enable the blockage of LPSs. These pores are expected to perform their respective single function, and collaborate synergistically to suppress the sulfur loss. Therefore, it delivers an outstanding cycling stability, decay rate of 0.013% cycle^-1 after 500 cycles at 1 C, when the sulfur loading is kept at 4 mg cm^-2 .

A Sulfur-Limonene-Based Electrode for Lithium-Sulfur Batteries: High-Performance by Self-Protection

The lithium-sulfur battery is considered as one of the most promising energy storage systems and has received enormous attentions due to its high energy density and low cost. However, polysulfide dissolution and the resulting shuttle effects hinder its practical application unless very costly solutions are considered. Herein, a sulfur-rich polymer termed sulfur-limonene polysulfide is proposed as powerful electroactive material that uniquely combines decisive advantages and leads out of this dilemma. It is amenable to a large-scale synthesis by the abundant, inexpensive, and environmentally benign raw materials sulfur and limonene (from orange and lemon peels). Moreover, owing to self-protection and confinement of lithium sulfide and sulfur, detrimental dissolution and shuttle effects are successfully avoided. The sulfur-limonene-based electrodes (without elaborate synthesis or surface modification) exhibit excellent electrochemical performances characterized by high discharge capacities (≈1000 mA h g^-1 at C/2) and remarkable cycle stability (average fading rate as low as 0.008% per cycle during 300 cycles).

Three dimensional porous SiC for lithium polysulfide trapping

A series of 3D porous SiC materials with active sp² hybridized Si atoms have been designed for lithium polysulfide retention in Li–S batteries. The shuttle effect can be effectively depressed by the strong Si⋯S interaction between Li₂S_n and the 3D porous SiC hosts.

Clustered-Microcapsule-Shaped Microporous Carbon-Coated Sulfur Composite Synthesized via in Situ Oxidation

Hollow materials as sulfur hosts have been intensively investigated to address the poor cycling stabilities of Li-S batteries. Herein, we report an enhanced hollow framework to improve the applicability of the sulfur confinement. A clustered-microcapsule-shaped microporous carbon coated sulfur (CM-S@MPC) composite is prepared from the clustered zinc sulfide precursor, through an in situ oxidation process. The high specific surface area and the in situ preparation guarantee the uniform distribution of sulfur inside the carbon microcapsule, even under a higher sulfur content of 83 wt %. In addition, the interconnected frame constructed by the stacking of carbon microcapsules also mitigates the lithium polysulfide loss by setting interlayered hurdles on their pathway along the outward diffusion. Hence, these enable a full demonstration of excellent cycling stability, compared to the control sample obtained via physical sulfur infiltration. The outstanding decay rate of 0.039% per cycle is achieved during 700 cycles at 1 C, even under high sulfur loading.

Atomic Sulfur Anchored on Silicene, Phosphorene, and Borophene for Excellent Cycle Performance of Li-S Batteries

Dissolution of intermediate lithium polysulfides (LiPS) is an inevitable obstacle for the solid sulfur-based cathode in Li-S batteries. For the first time, herein, atomic sulfur is incorporated into silicene, phosphorene, and borophene to intrinsically eliminate the dissolution of LiPS. The small molecular sulfur species are anchored on the silicene surface with stronger Si-S interaction than the P-S and B-S ones. Meanwhile, a high atomic sulfur coverage (63.1 wt %) is achieved in silicene and concomitantly stabilizes the silicene layer. For the S₃-covered silicene, a high theoretical capacity of 857 mA h g^-1 is achieved with slight dissolution of LiPS originated from the loss of interior S atoms that are not directly bound with silicene surface. By realizing the elemental S₂ coverage on silicene with large surface area, the Li⁺ ions can react fast with the S₂ species, leading to a high theoretical capacity of 891 mA h g^-1 without dissolution and migration of the intermediate LiPS. Most interestingly, the discharge products of atomic layer of lithium sulfides on silicene surface exhibit completely different behaviors from the traditional discharge products of solid Li₂S, which can function as effective adsorption and activation sites for the conversion of LiPS from long chain to short chain by accelerated redox reaction. The present study gains some key insights into how the atomic sulfur contributes to the intrinsic shuttle inhibition and offers a feasible way to design the atomic sulfur-based cathode materials of Li-S batteries with better electrochemical performance.

Liquid Structure with Nano-Heterogeneity Promotes Cationic Transport in Concentrated Electrolytes

Using molecular dynamics simulations, small-angle neutron scattering, and a variety of spectroscopic techniques, we evaluated the ion solvation and transport behaviors in aqueous electrolytes containing bis(trifluoromethanesulfonyl)imide. We discovered that, at high salt concentrations (from 10 to 21 mol/kg), a disproportion of cation solvation occurs, leading to a liquid structure of heterogeneous domains with a characteristic length scale of 1 to 2 nm. This unusual nano-heterogeneity effectively decouples cations from the Coulombic traps of anions and provides a 3D percolating lithium-water network, via which 40% of the lithium cations are liberated for fast ion transport even in concentration ranges traditionally considered too viscous. Due to such percolation networks, superconcentrated aqueous electrolytes are characterized by a high lithium-transference number (0.73), which is key to supporting an assortment of battery chemistries at high rate. The in-depth understanding of this transport mechanism establishes guiding principles to the tailored design of future superconcentrated electrolyte systems.

Dual Core-Shell-Structured S@C@MnO2 Nanocomposite for Highly Stable Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have currently excited worldwide academic and industrial interest as a next-generation high-power energy storage system (EES) because of their high energy density and low cost of sulfur. However, the commercialization application is being hindered by capacity decay, mainly attributed to the polysulfide shuttle and poor conductivity of sulfur. Here, we have designed a novel dual core-shell nanostructure of S@C@MnO₂ nanosphere hybrid as the sulfur host. The S@C@MnO₂ nanosphere is successfully prepared using mesoporous carbon hollow spheres (MCHS) as the template and then in situ MnO₂ growth on the surface of MCHS. In comparison with polar bare sulfur hosts materials, the as-prepared robust S@C@MnO₂ composite cathode delivers significantly improved electrochemical performances in terms of high specific capacity (1345 mAh g^-1 at 0.1 C), remarkable rate capability (465 mA h g^-1 at 5.0 C) and excellent cycling stability (capacity decay rate of 0.052% per cycle after 1000 cycles at 3.0 C). Such a structure as cathode in Li-S batteries can not only store sulfur via inner mesoporous carbon layer and outer MnO₂ shell, which physically/chemically confine the polysulfides shuttle effect, but also ensure overall good electrical conductivity. Therefore, these synergistic effects are achieved by unique structural characteristics of S@C@MnO₂ nanospheres.

Honeycomb-like Nitrogen and Sulfur Dual-Doped Hierarchical Porous Biomass-Derived Carbon for Lithium-Sulfur Batteries

Honeycomb-like nitrogen and sulfur dual-doped hierarchical porous biomass-derived carbon/sulfur composites (NSHPC/S) are successfully fabricated for high energy density lithium-sulfur batteries. The effects of nitrogen, sulfur dual-doping on the structures and properties of the NSHPC/S composites are investigated in detail by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and charge/discharge tests. The results show that N, S dual-doping not only introduces strong chemical adsorption and provides more active sites but also significantly enhances the electronic conductivity and hydrophilic properties of hierarchical porous biomass-derived carbon, thereby significantly enhancing the utilization of sulfur and immobilizing the notorious polysulfide shuttle effect. Especially, the as-synthesized NSHPC-7/S exhibits high initial discharge capacity of 1204 mA h g^-1 at 1.0 C and large reversible capacity of 952 mA h g^-1 after 300 cycles at 0.5 C with an ultralow capacity fading rate of 0.08 % per cycle even at high sulfur content (85 wt %) and high active material areal mass loading (2.8 mg cm^-2 ) for the application of high energy density Li-S batteries.