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.     

Galvanic Corrosion of Lithium‐Powder‐Based Electrodes

Lithium metal is considered to be the most promising anode for the next generation of batteries if the issues related to safety and low coulombic efficiency can be overcome. It is known that the initial morphology of the lithium metal anode has a great influence on the cycling characteristics of a lithium metal battery (LMB). Lithium‐powder‐based electrodes (Li_p‐electrodes) are reported to diminish the occurrence of high surface area lithium deposits. Usually, ultra‐thin lithium foils (<50 µm) and Li_p‐electrodes are prepared on a copper substrate, thus a metal–metal contact area is generated. The combination of these two metals in the presence of an electrolyte, however, can lead to galvanic corrosion. Herein, the corrosion behavior of Li_p‐electrodes is studied. The porosity of such electrodes leads to a high amount of accessible Cu surface in contact with electrolyte. As a consequence, Li_p‐electrodes aged for 1 week in the electrolyte show spontaneous lithium dissolution near the junction to copper and void formation on the lithium‐powder particles. This corrosion process affects the delivered capacity of Li_p‐electrodes and increases the overvoltage of the lithium electrodissolution process. The occurrence of corrosion at the Cu|Li_p interface raises concerns about the practicality of multi‐metallic component systems for LMBs.     

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.     

From Lithium‐Oxygen to Lithium‐Air Batteries: Challenges and Opportunities

Lithium ‐ air batteries have become a focus of research on future battery technologies. Technical issues associated with lithium‐air batteries, however, are rather complex. Apart from the sluggish oxygen reaction kinetics which demand efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts, issues are also inherited from the nature of an open battery system and the use of reactive metal lithium as anode. Lithium‐air batteries, which exchange oxygen directly with ambient air, face more challenges due to the additional oxidative agents of moisture, carbon dioxide, etc. which degrade the metal lithium anode, deteriorating the performance of the batteries. In order to improve the cycling performance one must hold a full picture of lithium‐oxygen electrochemistry in the presence of carbon dioxide and/or moisture and fully understand the fundamentals of chemistry reactions therein. Recent advances in the exploration of the effect of moisture and CO₂ contaminants on Li‐O₂ batteries are reviewed, and the mechanistic understanding of discharge/charge process in O₂ at controlled level of moisture and/or CO₂ are illustrated. Prospects for development opportunities of Li‐air batteries, insight into future research directions, and guidelines for the further development of rechargeable Li‐air batteries are also given.     

Graphene‐Containing Nanomaterials for Lithium‐Ion Batteries

Graphene‐containing nanomaterials have emerged as important candidates for electrode materials in lithium‐ion batteries (LIBs) due to their unique physical properties. In this review, a brief introduction to recent developments in graphene‐containing nanocomposite electrodes and their derivatives is provided. Subsequently, synthetic routes to nanoparticle/graphene composites and their electrochemical performance in LIBs are highlighted, and the current state‐of‐the‐art and most recent advances in the area of graphene‐containing nanocomposite electrode materials are summarized. The limitations of graphene‐containing materials for energy storage applications are also discussed, with an emphasis on anode and cathode materials. Potential research directions for the future development of graphene‐containing nanocomposites are also presented, with an emphasis placed on practicality and scale‐up considerations for taking such materials from benchtop curiosities to commercial products.     

Countersolvent Electrolytes for Lithium‐Metal Batteries

Development of electrolytes that simultaneously have high ionic conductivity, wide electrochemical window, and lithium dendrite suppression ability is urgently required for high‐energy lithium‐metal batteries (LMBs). Herein, an electrolyte is designed by adding a countersolvent into LiFSI/DMC (lithium bis(fluorosulfonyl)amide/dimethyl carbonate) electrolytes, forming countersolvent electrolytes, in which the countersolvent is immiscible with the salt but miscible with the carbonate solvents. The solvation structure and unique properties of the countersolvent electrolyte are investigated by combining electroanalytical technology with a Molecular Dynamics simulation. Introducing the countersolvent alters the coordination shell of Li⁺ cations and enhances the interaction between Li⁺ cations and FSI^? anions, which leads to the formation of a LiF‐rich solid electrolyte interphase, arising from the preferential reduction of FSI^? anions. Notably, the countersolvent electrolyte suppresses Li dendrites and enables stable cycling performance of a Li||NCM622 battery at a high cut‐off voltage of 4.6 V at both 25 and 60 °C. This study provides an avenue to understand and design electrolytes for high‐energy LMBs in the future.     

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.     

Exploiting Lithium–Ether Co‐Intercalation in Graphite for High‐Power Lithium‐Ion Batteries

The intercalation of lithium ions into graphite electrode is the key underlying mechanism of modern lithium‐ion batteries. However, co‐intercalation of lithium‐ions and solvent into graphite is considered undesirable because it can trigger the exfoliation of graphene layers and destroy the graphite crystal, resulting in poor cycle life. Here, it is demonstrated that the [lithium–solvent]⁺ intercalation does not necessarily cause exfoliation of the graphite electrode and can be remarkably reversible with appropriate solvent selection. First‐principles calculations suggest that the chemical compatibility of the graphite host and [lithium–solvent]⁺ complex ion strongly affects the reversibility of the co‐intercalation, and comparative experiments confirm this phenomenon. Moreover, it is revealed that [lithium–ether]⁺ co‐intercalation of natural graphite electrode enables much higher power capability than normal lithium intercalation, without the risk of lithium metal plating, with retention of ≈87% of the theoretical capacity at current density of 1 A g^?1. This unusual high rate capability of the co‐intercalation is attributed to the (i) absence of the desolvation step, (ii) negligible formation of the solid–electrolyte interphase on graphite surface, and (iii) fast charge‐transfer kinetics. This work constitutes the first step toward the utilization of fast and reversible [lithium–solvent]⁺ complex ion intercalation chemistry in graphite for rechargeable battery technology.     

Introducing Highly Redox‐Active Atomic Centers into Insertion‐Type Electrodes for Lithium‐Ion Batteries

The development of alternative anode materials with higher volumetric and gravimetric capacity allowing for fast delithiation and, even more important, lithiation is crucial for next‐generation lithium‐ion batteries. Herein, the development of a completely new active material is reported, which follows an insertion‐type lithiation mechanism, metal‐doped CeO₂. Remarkably, the introduction of carefully selected dopants, herein exemplified for iron, results in an increase of the achievable capacity by more than 200%, originating from the reduction of the dopant to the metallic state and additional space for the lithium ion insertion due to a significant off‐centering of the dopant atoms in the crystal structure, away from the original Ce site. In addition to the outstanding performance of such materials in high‐power lithium‐ion full‐cells, the selective reduction of the iron dopant under preservation of the crystal structure of the host material is expected to open up a new field of research.     

Lithium‐ and Manganese‐Rich Oxide Cathode Materials for High‐Energy Lithium Ion Batteries

Layered lithium‐ and manganese‐rich oxides (LMROs), described as xLi₂MnO₃·(1–x)LiMO₂ or Li_1+yM_1–yO₂ (M = Mn, Ni, Co, etc., 0 < x <1, 0 < y ≤ 0.33), have attracted much attention as cathode materials for lithium ion batteries in recent years. They exhibit very promising capacities, up to above 300 mA h g^?1, due to transition metal redox reactions and unconventional oxygen anion redox reaction. However, they suffer from structural degradation and severe voltage fade (i.e., decreasing energy storage) upon cycling, which are plaguing their practical application. Thus, this review will aim to describe the pristine structure, high‐capacity mechanisms and structure evolutions of LMROs. Also, recent progress associated with understanding and mitigating the voltage decay of LMROs will be discussed. Several approaches to solve this problem, such as adjusting cycling voltage window and chemical composition, optimizing synthesis strategy, controlling morphology, doping, surface modification, constructing core‐shell and layered‐spinel hetero structures, are described in detail.     

Adsorption‐Catalysis Design in the Lithium‐Sulfur Battery

Lithium‐sulfur (Li‐S) batteries are one of the most promising next‐generation energy‐storage systems. Nevertheless, the sluggish sulfur redox and shuttle effect in Li‐S batteries are the major obstacles to their commercial application. Previous investigations on adsorption for LiPSs have made great progress but cannot restrain the shuttle effect. Catalysts can enhance the reaction kinetics, and then alleviate the shuttle effect. The synergistic relationship between adsorption and catalysis has become the hotspot for research into suppressing the shuttle effect and improving battery performance. Herein, the adsorption‐catalysis synergy in Li‐S batteries is reviewed, the adsorption‐catalysis designs are divided into four categories: adsorption‐catalysis for LiPSs aggregation, polythionate or thiosulfate generation, and sulfur radical formation, as well as other adsorption‐catalysis. Then advanced strategies, future perspectives, and challenges are proposed to aim at long‐life and high‐efficiency Li‐S batteries.     

Coated Lithium Powder (CLiP) Electrodes for Lithium‐Metal Batteries

Safety issues caused by the metallic lithium inside a battery represent one of the main reasons for the lack of commercial availability of rechargeable lithium‐metal batteries. The advantage of anodes based on coated lithium powder (CLiP), compared to plain lithium foil, include the suppression of dendrite formation, as the local current density during stripping/plating is reduced due to the higher surface area. Another performance and safety advantage of lithium powder is the precisely controlled mass loading of the lithium anode during electrode preparation, giving the opportunity to avoid Li excess in the cell. As an additional benefit, the coating makes electrode manufacturing safer and eases handling. Here, electrodes based on coated lithium powder electrodes (CLiP) are introduced for application in lithium‐metal batteries. These electrodes are compared to lithium foil electrodes with respect to cycling stability, coulombic efficiency of lithium stripping/plating, overpotential, and morphology changes during cycling.     

Silicon‐Based Nanomaterials for Lithium‐Ion Batteries: A Review

There are growing concerns over the environmental, climate, and health impacts caused by using non‐renewable fossil fuels. The utilization of green energy, including solar and wind power, is believed to be one of the most promising alternatives to support more sustainable economic growth. In this regard, lithium‐ion batteries (LIBs) can play a critically important role. To further increase the energy and power densities of LIBs, silicon anodes have been intensively explored due to their high capacity, low operation potential, environmental friendliness, and high abundance. The main challenges for the practical implementation of silicon anodes, however, are the huge volume variation during lithiation and delithiation processes and the unstable solid‐electrolyte interphase (SEI) films. Recently, significant breakthroughs have been achieved utilizing advanced nanotechnologies in terms of increasing cycle life and enhancing charging rate performance due partially to the excellent mechanical properties of nanomaterials, high surface area, and fast lithium and electron transportation. Here, the most recent advance in the applications of 0D (nanoparticles), 1D (nanowires and nanotubes), and 2D (thin film) silicon nanomaterials in LIBs are summarized. The synthetic routes and electrochemical performance of these Si nanomaterials, and the underlying reaction mechanisms are systematically described.     

Lithium‐Pretreated Hard Carbon as High‐Performance Sodium‐Ion Battery Anodes

Hard carbon (HC) is the state‐of‐the‐art anode material for sodium‐ion batteries (SIBs). However, its performance has been plagued by the limited initial Coulombic efficiency (ICE) and mediocre rate performance. Here, experimental and theoretical studies are combined to demonstrate the application of lithium‐pretreated HC (LPHC) as high‐performance anode materials for SIBs by manipulating the solid electrolyte interphase in tetraglyme (TEGDME)‐based electrolyte. The LPHC in TEGDME can 1) deliver > 92% ICE and ≈220 mAh g^?1 specific capacity, twice of the capacity (≈100 mAh g^?1) in carbonate electrolyte; 2) achieve > 85% capacity retention over 1000 cycles at 1000 mA g^?1 current density (4 C rate, 1 C = 250 mA g^?1) with a specific capacity of ≈150 mAh g^?1, ≈15 times of the capacity (10 mAh g^?1) in carbonate. The full cell of Na₃V₂(PO₄)₃‐LPHC in TEGDME demonstrated close to theoretical specific capacity of ≈98 mAh g^?1 based on Na₃V₂(PO₄)₃ cathode, ≈2.5 times of the value (≈40 mAh g^?1) with nontreated HC. This work provides new perception on the anode development for SIBs.