Polysulfide‐Shuttle Control in Lithium‐Sulfur Batteries with a Chemically/Electrochemically Compatible NaSICON‐Type Solid Electrolyte

A NaSICON‐type Li⁺‐ion conductive membrane with a formula of Li_{1+ x} Y _x Zr_{2? x} (PO₄)₃ (LYZP) (x = 0–0.15) has been explored as a solid‐electrolyte/separator to suppress polysulfide‐crossover in lithium‐sulfur (Li‐S) batteries. The LYZP membrane with a reasonable Li⁺‐ion conductivity shows both favorable chemical compatibility with the lithium polysulfide species and exhibits good electrochemical stability under the operating conditions of the Li‐S batteries. Through an integration of the LYZP solid electrolyte with the liquid electrolyte, the hybrid Li‐S batteries show greatly enhanced cyclability in contrast to the conventional Li‐S batteries with the porous polymer (e.g., Celgard) separator. At a rate of C/5, the hybrid Li ||LYZP|| Li₂S₆ batteries developed in this study (with a Li‐metal anode, a liquid/LYZP hybrid electrolyte, and a dissolved lithium polysulfide cathode) delivers an initial discharge capacity of ≈1000 mA h g^?1 (based on the active sulfur material) and retains ≈90% of the initial capacity after 150 cycles with a low capacity fade‐rate of <0.07% per cycle.     

Tungsten Disulfide Catalysts Supported on a Carbon Cloth Interlayer for High Performance Li–S Battery

The capacity limitations of insertion‐compound cathodes has motivated interest in a sulfur cathode for a rechargeable battery cell with a metallic‐lithium anode; but irreversible capacity loss owing to solubility of intermediate Li₂S_x (x = 2–8) polysulfides in the organic‐liquid electrolytes used has prevented practical application. A dual‐function cathode structure consisting of layered tungsten disulfide (WS₂) supported both on the cathode current collector and on a carbon cloth interlayer (CCl) gives excellent performance in a lithium half‐cell by providing strong adsorption of the soluble Li₂S_x on the WS₂ with fast access to electrons from the current collector via a blocking carbon cloth interlayer.     

High‐Performance Aqueous Rechargeable Li‐Ni Battery Based on Ni(OH)2/NiOOH Redox Couple with High Voltage

New energy storage and conversion systems require large‐scale, cost‐effective, good safety, high reliability, and high energy density. This study demonstrates a low‐cost and safe aqueous rechargeable lithium‐nickel (Li‐Ni) battery with solid state Ni(OH)₂/NiOOH redox couple as cathode and hybrid electrolytes separated by a Li‐ion‐conductive solid electrolyte layer. The proposed aqueous rechargeable Li‐Ni battery exhibits an approximately open‐circuit potential of 3.5 V, outperforming the theoretic stable window of water 1.23 V, and its energy density can be 912.6 W h kg^‐1, which is much higher than that of state‐of‐the‐art lithium ion batteries. The use of a solid‐state redox couple as cathode with a metallic lithium anode provides another postlithium chemistry for practical energy storage and conversion.     

Hybrid Lithium‐Sulfur Batteries with an Advanced Gel Cathode and Stabilized Lithium‐Metal Anode

The insulating nature of sulfur, polysulfide shuttle effect, and lithium‐metal deterioration cause a decrease in practical energy density and fast capacity fade in lithium‐sulfur (Li‐S) batteries. This study presents an integrated strategy for the development of hybrid Li‐S batteries based on a gel sulfur cathode, a solid electrolyte, and a protective anolyte composed of a highly concentrated salt electrolyte containing mixed additives. The dense solid electrolyte completely blocks polysulfide diffusion, and also makes it possible to investigate the cathode and anode independently. This gel cathode effectively traps the polysulfide active material while maintaining a low electrolyte to sulfur ratio of 5.2 mL g^?1. The anolyte effectively protects the Li metal and suppresses the consumption of liquid electrolyte, enabling stable long‐term cycling for over 700 h in Li symmetric cells. This advanced design can simultaneously suppress the polysulfide shuttle, protect Li metal, and reduce the liquid electrolyte usage. The assembled hybrid batteries exhibit remarkably stable cycling performance over 300 cycles with high capacity. Finally, surface‐sensitive techniques are carried out to directly visualize and probe the interphase formed on the surface of the Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) pellet, which may help stabilize the solid–liquid interface.     

Exploiting Lithium‐Depleted Cathode Materials for Solid‐State Li Metal Batteries

Solid‐state lithium metal batteries (SSLMBs) may become one of the high‐energy density storage devices for the next generation of electric vehicles. High safety and energy density can be achieved by utilizing solid electrolytes and Li metal anodes. Therefore, developing cathode materials which can match with Li metal anode efficiently is indispensable. In SSLMBs, Li metal anodes can afford the majority of active lithium ions, then lithium‐depleted cathode materials can be a competitive candidate to achieve high gravimetric energy density as well as save lithium resources. Li_0.33MnO₂ lithium‐depleted material is chosen, which also has the advantages of low synthesis temperature and low cost (cobalt‐free). Notably, solid‐state electrolyte can greatly alleviate the problem of manganese dissolution in the electrolyte, which is beneficial to improve the cycling stability of the battery. Thus, SSLMBs enable practical applications of lithium‐depleted cathode materials.     

A Lithium–Sulfur Cell Based on Reversible Lithium Deposition from a Li2S Cathode Host onto a Hostless‐Anode Substrate

The development of lithium–sulfur batteries necessitates a thorough understanding of the lithium‐deposition process. A novel full‐cell configuration comprising an Li₂S cathode and a bare copper foil on the anode side is presented here. The absence of excess lithium allows for the realization of a truly lithium‐limited Li–S battery, which operates by reversible plating and stripping of lithium on the hostless‐anode substrate (copper foil). Its performance is closely tied to the efficiency of lithium deposition, generating valuable insights on the role and dynamic behavior of lithium anode. The Li₂S full cell shows reasonable capacity retention with a Coulombic efficiency of 96% over 100 cycles, which is a tremendous improvement over that of a similar lithium‐plating‐based full cell with LiFePO₄ cathodes. The exceptional robustness of the Li₂S system is attributed to an intrinsic stabilization of the lithium‐deposition process, which is mediated by polysulfide intermediates that form protective Li₂S and Li₂S₂ regions on the deposited lithium. Combined with the large improvements in energy density and safety by the elimination of a metallic lithium anode, the stability and electrochemical performance of the lithium‐plating‐based Li₂S full cell establish it as an important trajectory for Li–S battery research, focusing on practical realization of reversible lithium anodes.     

Toward a Reversible Calcium‐Sulfur Battery with a Lithium‐Ion Mediation Approach

Calcium represents a promising anode for the development of high‐energy‐density, low‐cost batteries. However, a lack of suitable electrolytes has restricted the development of rechargeable batteries with a Ca anode. Furthermore, to achieve a high energy density system, sulfur would be an ideal cathode to couple with the Ca anode. Unfortunately, a reversible calcium‐sulfur (Ca‐S) battery has not yet been reported. Herein, a basic study of a reversible nonaqueous room‐temperature Ca‐S battery is presented. The reversibility of the Ca‐S chemistry and high utilization of the sulfur cathode are enabled by employing a Li⁺‐ion‐mediated calcium‐based electrolyte. Mechanistic insights pursued by spectroscopic, electrochemical, microscopic, and theoretical simulation (density functional theory) investigations imply that the Li⁺‐ions in the Ca‐electrolyte stimulate the reactivation of polysulfide/sulfide species. The coordination of lithium to sulfur reduces the formation of sturdy Ca‐S ionic bonds, thus boosting the reversibility of the Ca‐S chemistry. In addition, the presence of Li⁺‐ions facilitates the ionic charge transfer both in the electrolyte and across the solid electrolyte interphase layer, consequently reducing the interfacial and bulk impedance of Ca‐S batteries. As a result, both the utilization of active sulfur in the cathode and the discharge voltage of Ca‐S batteries are significantly improved.     

Highly Dispersed Cobalt Clusters in Nitrogen‐Doped Porous Carbon Enable Multiple Effects for High‐Performance Li–S Battery

The lithium–sulfur (Li–S) battery is considered a promising candidate for the next generation of energy storage system due to its high specific energy density and low cost of raw materials. However, the practical application of Li–S batteries is severely limited by several weaknesses such as the shuttle effect of polysulfides and the insulation of the electrochemical products of sulfur and Li₂S/Li₂S₂. Here, by doping nitrogen and integrating highly dispersed cobalt catalysts, a porous carbon nanocage derived from glucose adsorbed metal–organic framework is developed as the host for a sulfur cathode. This host structure combines the reported positive effects, including high conductivity, high sulfur loading, effective stress release, fast lithium‐ion kinetics, fast interface charge transport, fast redox of Li₂S_n, and strong physical/chemical absorption, achieving a long cycle life (86% of capacity retention at 1C within 500 cycles) and high rate performance (600 mAh g^?1 at 5C) for a Li–S battery. By combining experiments and density functional theoretical calculations, it is demonstrated that the well‐dispersed cobalt clusters play an important role in greatly improving the diffusion dynamics of lithium, and enhance the absorption and conversion capability of polysulfides in the host structure.     

Unraveling the Dual Functionality of High‐Donor‐Number Anion in Lean‐Electrolyte Lithium‐Sulfur Batteries

Minimizing electrolyte use is essential to achieve high practical energy density of lithium–sulfur (Li–S) batteries. However, the sulfur cathode is more readily passivated under a lean electrolyte condition, resulting in low sulfur utilization. In addition, continuous electrolyte decomposition on the Li metal anode aggravates the problem, provoking rapid capacity decay. In this work, the dual functionalities of NO₃^? as a high‐donor‐number (DN) salt anion is presented, which improves the sulfur utilization and cycling stability of lean‐electrolyte Li–S batteries. The NO₃^? anion elevates the solubility of the sulfur species based on its high electron donating ability, achieving a high sulfur utilization of above 1200 mA h g^?1. Furthermore, the anion suppresses electrolyte decomposition on the Li metal by regulating the lithium ion (Li⁺) solvation sheath, enhancing the cycle performance of the lean electrolyte cell. By understanding the anionic effects, this work demonstrates the potential of the high‐DN electrolyte, which is beneficial for both the cathode and anode of Li–S batteries.     

A Li2S‐TiS2‐Electrolyte Composite for Stable Li2S‐Based Lithium–Sulfur Batteries

Li₂S is a fully lithiated sulfur‐based cathode with a high theoretical capacity of 1166 mAh g^?1 that can be coupled with lithium‐free anodes to develop high‐energy‐density lithium–sulfur batteries. Although various approaches have been pursued to obtain a high‐performance Li₂S cathode, there are still formidable challenges with it (e.g., low conductivity, high overpotential, and irreversible polysulfide diffusion) and associated fabrication processes (e.g., insufficient Li₂S, excess electrolyte, and low reversible capacity), which have prevented the realization of high electrochemical utilization and stability. Here, a new cathode design composed of a homogeneous Li₂S‐TiS₂‐electrolyte composite that is prepared by a simple two‐step dry/wet‐mixing process is demonstrated, allowing the liquid electrolyte to wet the powder mixture consisting of insulating Li₂S and conductive TiS₂. The close‐contact, three‐phase boundary of this system improves the Li₂S‐activation efficiency and provides fast redox‐reaction kinetics, enabling the Li₂S‐TiS₂‐electrolyte cathode to attain stable cyclability at C/7 to C/3 rates, superior long‐term cyclability over 500 cycles, and promising high‐rate performance up to 1C rate. More importantly, this improved performance results from a cell design attaining a high Li₂S loading of 6 mg cm^?2, a high Li₂S content of 75 wt%, and a low electrolyte/Li₂S ratio of 6.     

Formation of Solid–Electrolyte Interfaces in Aqueous Electrolytes by Altering Cation‐Solvation Shell Structure

Aqueous lithium/sodium‐ion batteries (AIBs) have received increasing attention because of their intrinsic safety. However, the narrow electrochemical stability window (1.23 V) of the aqueous electrolyte significantly hinders the development of AIBs, especially the choice of electrode materials. Here, an aqueous electrolyte composed of LiClO₄, urea, and H₂O, which allows the electrochemical stability window to be expanded to 3.0 V, is developed. Novel [Li (H₂O)_x(organic)_y]⁺ primary solvation sheath structures are developed in this aqueous electrolyte, which contribute to the formation of solid–electrolyte interface layers on the surfaces of both the cathode and anode. The expanded electrochemical stability window enables the construction of full aqueous Li‐ion batteries with LiMn₂O₄ cathodes and Mo₆S₈ anodes, demonstrating an operating voltage of 2.1 V and stability over 2000 cycles. Furthermore, a symmetric aqueous Na‐ion battery using Na₃V₂(PO₄)₃ as both the cathode and anode exhibits operating voltage of 1.7 V and stability over 1000 cycles at a rate of 5 C.     

Regulating the Hidden Solvation‐Ion‐Exchange in Concentrated Electrolytes for Stable and Safe Lithium Metal Batteries

Lithium–sulfur batteries are attractive for automobile and grid applications due to their high theoretical energy density and the abundance of sulfur. Despite the significant progress in cathode development, lithium metal degradation and the polysulfide shuttle remain two critical challenges in the practical application of Li–S batteries. Development of advanced electrolytes has become a promising strategy to simultaneously suppress lithium dendrite formation and prevent polysulfide dissolution. Here, a new class of concentrated siloxane‐based electrolytes, demonstrating significantly improved performance over the widely investigated ether‐based electrolytes are reported in terms of stabilizing the sulfur cathode and Li metal anode as well as minimizing flammability. Through a combination of experimental and computational investigation, it is found that siloxane solvents can effectively regulate a hidden solvation‐ion‐exchange process in the concentrated electrolytes that results from the interactions between cations/anions (e.g., Li⁺, TFSI^?, and S^2?) and solvents. As a result, it could invoke a quasi‐solid‐solid lithiation and enable reversible Li plating/stripping and robust solid‐electrolyte interphase chemistries. The solvation‐ion‐exchange process in the concentrated electrolytes is a key factor in understanding and designing electrolytes for other high‐energy lithium metal batteries.     

MoN Supported on Graphene as a Bifunctional Interlayer for Advanced Li‐S Batteries

Rational design of effective polysulfide barriers is highly important for high‐performance lithium‐sulfur (Li‐S) batteries. A variety of adsorbents have been applied as interlayers to alleviate the shuttle effect. Nevertheless, the unsuccessful oxidation of Li₂S on interlayers leads to loss of active materials and blocks Li ion transport. In this work, a MoN‐based interlayer sandwiched between the C‐S cathode and the separator is developed. Such an interlayer not only strongly binds lithium polysulfides via Mo‐S bonding but also efficiently accelerates the decomposition of Li₂S. The acceleration mechanism toward Li₂S decomposition is determined to be a combination of contributions of catalytic cleavage of Li‐S bond in Li₂S based on the proposed covalence‐activation mechanism and rapid migration of the produced Li ions. As a result, the C–S cathodes with the as‐developed interlayer manifest a negligible charging potential barrier and outstanding cycling stability with a very low capacity fading rate of 0.023% per cycle during 1500 cycles at 1 C. High areal capacity of 6.02 mAh cm^?2 is achieved for high sulfur loading of 7.0 mg cm^?2 after cycling at 0.1 C. The material and strategy demonstrated in this work can open the door toward developing shuttle suppression interlayers without impairing cathode performance.     

Hybrid and Aqueous Lithium‐Air Batteries

Lithium‐air (Li‐air) batteries have become attractive because of their extremely high theoretical energy density. However, conventional Li‐air cells operating with non‐aqueous electrolytes suffer from poor cycle life and low practical energy density due to the clogging of the porous air cathode by insoluble discharge products, contamination of the organic electrolyte and lithium metal anode by moist air, and decomposition of the electrolyte during cycling. These difficulties may be overcome by adopting a cell configuration that consists of a lithium‐metal anode protected from air by a Li⁺‐ion solid electrolyte and an air electrode in an aqueous catholyte. In this type of configuration, a Li⁺‐ion conducting “buffer” layer between the lithium‐metal anode and the solid electrolyte is often necessary due to the instability of many solid electrolytes in contact with lithium metal. Based on the type of buffer layer, two different battery configurations are possible: “hybrid” Li‐air batteries and “aqueous” Li‐air batteries. The hybrid and aqueous Li‐air batteries utilize the same battery chemistry and face similar challenges that limit the cell performance. Here, an overview of recent developments in hybrid and aqueous Li‐air batteries is provided and the factors that influence their performance and impede their practical applications, followed by future directions are discussed.     

Operando Lithium Dynamics in the Li‐Rich Layered Oxide Cathode Material via Neutron Diffraction

Neutron diffraction under operando battery cycling is used to study the lithium and oxygen dynamics of high Li‐rich Li(Li_x/3Ni_(3/8‐3x/8)Co_(1/4‐x/4)Mn_(3/8+7x/24)O₂ (x = 0.6, HLR) and low Li‐rich Li(Li_x/3Ni_(1/3‐x/3)Co_(1/3‐x/3)Mn_(1/3+x/3)O₂ (x = 0.24, LLR) compounds that exhibit different degrees of oxygen activation at high voltage. The measured lattice parameter changes and oxygen position show largely contrasting changes for the two cathodes where the LLR exhibits larger movement of oxygen and lattice contractions in comparison to the HLR that maintains relatively constant lattice parameters and oxygen position during the high voltage plateau until the end of charge. Density functional theory calculations show the presence of oxygen vacancy during the high voltage plateau; changes in the lattice parameters and oxygen position are consistent with experimental observations. Lithium migration kinetics for the Li‐rich material is observed under operando conditions for the first time to reveal the rate of lithium extraction from the lithium layer, and transition metal layer is related to the different charge and discharge characteristics. At the beginning of charging, the lithium extraction predominately occurs within the lithium layer. Once the high voltage plateau is reached, the lithium extraction from the lithium layer slows down and extraction from the transition metal layer evolves at a faster rate.     

Optimized Bicompartment Two Solution Cells for Effective and Stable Operation of Li–O2 Batteries

Lithium–oxygen batteries are in fact the only rechargeable batteries that can rival internal combustion engines, in terms of high energy density. However, they are still under development due to low‐efficiency and short lifetime issues. There are problems of side reactions on the cathode side, high reactivity of the Li anode with solution species, and consumption of redox mediators via reactions with metallic lithium. Therefore, efforts are made to protect/block the lithium metal anode in these cells, in order to mitigate side reactions. However, new approach is required in order to solve the problems mentioned above, especially the irreversible reactions of the redox mediators which are mandatory to these systems with the Li anode. Here, optimized bicompartment two solution cells are proposed, in which detrimental crossover between the cathode and anode is completely avoided. The Li metal anode is cycled in electrolyte solution containing fluorinated ethylene carbonate, in which its cycling efficiency is excellent. The cathode compartment contains ethereal solution with redox mediator that enables oxidation of Li₂O₂ at low potentials. The electrodes are separated by a solid electrolyte membrane, allowing free transport of Li ions. This approach increases cycle life of lithium oxygen cells and their energy efficiency.     

Atomic Structure of Li2MnO3 after Partial Delithiation and Re‐Lithiation

Li₂MnO₃ is the parent compound of the well‐studied Li‐rich Mn‐based cathode materials xLi₂MnO₃·(1‐x)LiMO₂ for high‐energy‐density Li‐ion batteries. Li₂MnO₃ has a very high theoretical capacity of 458 mA h g^?1 for extracting 2 Li. However, the delithiation and lithiation behaviors and the corresponding structure evolution mechanism in both Li₂MnO₃ and Li‐rich Mn‐based cathode materials are still not very clear. In this research, the atomic structures of Li₂MnO₃ before and after partial delithiation and re‐lithiation are observed with spherical aberration‐corrected scanning transmission electron microscopy (STEM). All atoms in Li₂MnO₃ can be visualized directly in annular bright‐field images. It is confirmed accordingly that the lithium can be extracted from the LiMn₂ planes and some manganese atoms can migrate into the Li layer after electrochemical delithiation. In addition, the manganese atoms can move reversibly in the (001) plane when ca. 18.6% lithium is extracted and 12.4% lithium is re‐inserted. LiMnO₂ domains are also observed in some areas in Li_1.63MnO₃ at the first cycle. As for the position and occupancy of oxygen, no significant difference is found between Li_1.63MnO₃ and Li₂MnO₃.     

High‐Performance Lithium‐Sulfur Batteries with a Self‐Supported, 3D Li2S‐Doped Graphene Aerogel Cathodes

Lithium‐sulfur (Li‐S) batteries are being considered as the next‐generation high‐energy‐storage system due to their high theoretical energy density. However, the use of a lithium‐metal anode poses serious safety concerns due to lithium dendrite formation, which causes short‐circuiting, and possible explosions of the cell. One feasible way to address this issue is to pair a fully lithiated lithium sulfide (Li₂S) cathode with lithium metal‐free anodes. However, bulk Li₂S particles face the challenges of having a large activation barrier during the initial charge, low active‐material utilization, poor electrical conductivity, and fast capacity fade, preventing their practical utility. Here, the development of a self‐supported, high capacity, long‐life cathode material is presented for Li‐S batteries by coating Li₂S onto doped graphene aerogels via a simple liquid infiltration–evaporation coating method. The resultant cathodes are able to lower the initial charge voltage barrier and attain a high specific capacity, good rate capability, and excellent cycling stability. The improved performance can be attributed to the (i) cross‐linked, porous graphene network enabling fast electron/ion transfer, (ii) coated Li₂S on graphene with high utilization and a reduced energy barrier, and (iii) doped heteroatoms with a strong binding affinity toward Li₂S/lithium polysulfides with reduced polysulfide dissolution based on first‐principles calculations.     

Tailored Reaction Route by Micropore Confinement for Li–S Batteries Operating under Lean Electrolyte Conditions

Lithium‐sulfur (Li–S) batteries are one of the most promising alternative energy storage systems beyond Li‐ion batteries. However, the sluggish kinetics of the nucleation and growth of the solid discharge product of Li₂S/Li₂S₂ in the lower discharge plateau has been recently identified as a critical hurdle for attaining high specific capacity in Li–S batteries with high sulfur loadings under lean electrolyte conditions. Herein, a new strategy of breaking the charge‐transport bottleneck by successful generation of experimentally verified stable Li₂S₂ and a reservoir of quasi‐solid lithium polysulfides within the micropores of activated carbon fiber cloth as a high‐sulfur‐loading host is proposed. The developed Li–S cell is capable of delivering a highly sustainable areal capacity of 6.0 mAh cm^?2 under lower electrolyte to sulfur ratios (<3.0 mL_E g_S^?1). Micropore confinement leads to generation of solid Li₂S₂ that enables high utilization of the entire electroactive area by its inherent self‐healing capacity. This strategy opens a new avenue for rational material designs for Li–S batteries under lean electrolyte condition.     

Highly Stable Operation of Lithium Metal Batteries Enabled by the Formation of a Transient High‐Concentration Electrolyte Layer

Lithium (Li) metal has been extensively investigated as an anode for rechargeable battery applications due to its ultrahigh theoretical specific capacity and the lowest redox potential. However, significant challenges including dendrite growth and low Coulombic efficiency are still hindering the practical applications of rechargeable Li metal batteries. It is demonstrated that long‐term cycling of Li metal batteries can be realized by the formation of a transient high‐concentration electrolyte layer near the surface of Li metal anode during high rate discharge process. The highly concentrated Li⁺ ions in this transient layer will immediately be solvated by the available solvent molecules and facilitate the formation of a stable and flexible solid electrolyte interphase (SEI) layer composed of a poly(ethylene carbonate) framework integrated with other organic/inorganic lithium salts. This SEI layer largely suppresses the corrosion of Li metal anode attacked by free organic solvents and enables the long‐term operation of Li metal batteries. The fundamental findings in this work provide a new direction for the development of Li metal batteries that could be operated at high current densities for a wide range of applications.